EXTREME ULTRAVIOLET LIGHT SOURCE

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to US Application No. 15/265,373, which was filed on

September 14, 2016, and which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The disclosed subject matter relates to a system and method tor measuring changes to aspects of a target along its trajectory in a laser produced plasma extreme ultraviolet light source.

BACKGROUND

Extreme ultraviolet (EUV) light; for example, electromagnetic radiation having wavelengths of around 50 ran or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13 nm, can be used in photolithography processes to produce extremely small features in substrates, for example, silicon wafers.

Methods to produce EU V light include, but are not necessarily limited to, convening a material that, has an element, for example, xenon, lithium, or tin, with an emission line in the EUV range in a plasma state. In one such method, often termed laser produced plasma ("LPP"), the required plasma can be produced by irradiating a target material, for example, in the form of a droplet, plate, tape, stream, or cluster of material, with an ampli fied light beam that can be referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, and .monitored using various types of metrology equipment.

SUMMARY

in some general aspects, a method is described for measuring a moving property of a target as it travels along its trajectory in a laser produced plasma extreme ultraviolet Sight source. The method includes: forming a remaining plasma that at least partially coincides with an extended target region, the remaining plasma being a plasma formed from an interaction between a prior target and a prior radiation pulse in a target space: releasing a current target along a trajectory toward the target space that is at least partly overlapping the extended target region, the current target including, a component, that emits extreme ultraviolet (EU V) light when con verted to plasma; determining one or more moving properties of the current target when the current target is within the extended target region and after a prior and adjacent target has interacted with a prior radiation pulse in the target space; and if any of the determined one or more mov ing properties of (he current target are outside an acceptable range, then adjusting one or more characteristics of a radiation puise directed toward the target space.

Implementations can include one or more of the following features. For example, the method cars a!so include interacting the radiation puise with a present target in the target space. The present target is either the current target that has entered the target space or another target that has entered the target space. The other target enters the target space at a time that follows the time when the current target enters the target space.

The adjustment to the one or more characteristics of the radiation pulse directed toward the target space can cause an adjustment in a relative position between the radiation pulse and tire present target.

The one or more moving properties of the current target can be determined by

determining one or more of a speed of the current target, a direction of the trajectory of the current target, and an acceleration of the current target.

The radiation pulse can deliver energy to the present target to modify a geometric distribution of the present target. The method can include, after directing the radiation pulse toward the present target, directing a main radiation pulse toward the present target to thereby convert at least part, of the present target into plasma that emits extreme ultraviolet light.

The method can include analyzing the determined one or more moving properties, wherein adjusting the one or more characteristics of the radiation pulse is based on the analysis of the determined one or more moving properties of the current target.

The one or more characteristics of the radiation pulse can be adjusted by adjusting one or more of a ti ming of a release of the radiation pulse and a direction at which the radiation pulse travels.

The one or more moving properties of the current target can be determined by: detecting a first interaction between a first diagnostic light beam and the current target at a first location within the extended target region; detecting a second interaction between a second diagnostic light beam and the current target at a second location within the extended target region, the second location being distinct from the first location; and deten.nin.ing the one or more moving properties based on the detections of the first and second interactions. The one or more moving properties of the current target can be determined by: directing the first diagnostic light beam toward the current target at. the .first location; and directing the second diagnostic light beam toward the current target at the second location.

The first diagnostic beam can be directed toward the current target at the first location by directing the first diagnostic beam along a first direction toward the current target; and the second diagnostic beam can be directed toward the current target at the second location by directing the second diagnostic beam a!ong a second direction toward the current target; the second direction is not parallel with the first direction.

The first interaction can be detected by detecting fight that is produced from the interaction between the current target and the first diagnostic beam at a first time. The second interaction can be detected by detecting light that is produced from the interaction between the current target and the second diagnostic beam at a second time that is distinct from the first time. The one or more moving properties of the current target can be determined based on an analysis of the detections of the light. The light, can he detected by detecting a one-dimensional aspect of the light and producing a one-dimensional signal.

The method can include detecting a third interaction between a third diagnostic light beam and the current target at a third location within the extended target region, the third location being distinct from the first and second locations.

In other general aspects, an apparatus includes a chamber that defines a target space, a first region, and a second region closer to the target space than the first region; a target delivery' system; a diagnostic system; and a control system. The target delivery system is configured to release a target along a trajectory toward the target space, the trajectory overlapping both the first region and the second region., the target comprising a material that emits extreme ultraviolet (EUV) light when converted to plasma and the target having a first moving property in the first region and a second moving property in the second region, the second moving property being different from the first moving property. The diagnostic system produces a diagnostic probe that interacts with the target in the second region and outputs data relating to the interaction. The control system is configured to: receive the data output from the diagnostic system; analyze the outputted data; and determine the second moving property of the target based on an analysis of the data. Implementations can include one or more of the following features. For example, the apparatus can include an optical source configured to produce a plurality of radiation pulses that are directed toward the target space. The second region can at least partially overlap an extended target region. The extended target region is defined by a region in which remaining plasma is formed from an interaction between a prior target and a prior radiation pulse from the plurality of radiation pulses.

The control system can be configured to control a relative position between a current radiation pulse and a present target based on the determined second moving property of the target. The apparatus can include an adjustment system coupled to the optical source and to the control system. The control system is configured to control a relative position between a current radiation pulse and the present target by sending a control signal to the adjustment system, the control signal causing the adjustment system to adjust one or more of a timing of a release of the current radiation pulse and a direction at winch the current radiation pulse travels.

The diagnostic system can include a light source that produces at least a fust diagnostic light beam and a second diagnostic Sight beam. The first diagnostic light beam can be directed toward the target to provide a first interaction between the first diagnostic light beam and the target at a first location within the second region; and the second diagnostic light beam can be directed toward the target to provide a second interaction between the second diagnostic light beam and the target at a second location within the second region. The diagnostic system can include a detection system that detects the first interaction and the second interaction, the detection system configured to output the data relating to the first and second interactions. The detection system can be configured to detect a light that is produced from the first interaction and to detect light that is produced from the second interaction.

The second moving property of the target can be one or more of a speed of the target, a direc tion of the target trajectory, and an acceleration of the target.

In other genera! aspects, a method is described for measuring a moving property of a target as it travels along a trajectory in a laser produced plasma extreme ultraviolet light source. The method includes: releasing a current target along a trajectory toward a target space, the current target including a component that emits extreme ultraviolet (EU ^' V) light when converted to plasma; directing a preliminary radiation pulse toward the target space to deliver energy to the current target to modify a geometric distribution of the current target; directing a main radiation pu!se toward the target space, an interaction between the main radiation poise and the current target converting at least part of the current target into plasma that emits extreme ultraviolet light: determining one or more moving properties of the current target before the current target enters the target space; and controlling one or more of a relative position between the main radiation pulse and a present target, and a relative position between the preliminary radiation pulse and a present target based on the determined one or more moving properties of the current target. The present target is either the current target that has entered the target space or another target that has entered the target space after the current target has interacted with the preliminary radiation pulse and the main radiation pulse.

Implementations can include one or more of the following features. For example, the one or more moving properties of the current target can be determined by measuring one or more of a speed of the current target; an acceleration of the current target, and a direction at which the current target moves.

The method can include detecting a ^' first interaction between a fust diagnostic light beam and the current target at a first location; and detecting a second interaction between a second diagnostic light beam and the current target at a second location that is distinct from the first location. The one or more -moving properties of the current target can be determined by analyzing the detections of the first and second interactions.

The method can include: directing the first diagnostic light beam toward the current target at the first location; and directing the second diagnostic light beam toward the current target at the second location. The first interaction can be detected by detecting light that is produced from the first interaction; and the second interaction can be detected by detecting light that is produced from the second interaction.

The method can include detecting a third interaction between a third diagnostic light beam and the current target at a third location that is distinct from the first and second locations.

The relative position between the preliminary radiation pulse and the present target can be controlled based on an analysis of the determined, moving property of the target. The relative position between the preliminary radiation pulse and the present target can be controlled by adjusting one or more of a timing of a release of the preliminary radiation pulse and a direction at which the preliminary radiation pulse travels. In other general aspects, a method is described for measuring a mo ving property of a target as it travels along a trajectory in a laser produced plasma extreme ultraviolet light source. The method includes releasing a target along its trajectory toward a target space, the target having a first moving property in a first region along the trajectory and having a second moving property in a second region along the trajectory, the second region being closer to the target space than the first region and the second moving property being different from the first moving property; and determining the second moving property of the target.

Implementations can include one or more of the following features. For example, the second moving property of the target can be determined by determi ning one or more of a second speed of the target; a second acceleration of the target; and a second direction at which the target moves. The target can emit extreme ultraviolet light when converted to a plasma.

The method can include directing a radiation pulse toward the target space, the radiation pulse converting at least part of the target into plasma that emits extreme ultraviolet light when the radiation pulse interacts with the target. The method can include, prior to directing the radiation pulse toward the target space, directing a preliminary radiation pulse toward the target in the target space to deliver energy to the target to modify a geometric distribution of the target.

The method can include controlling one or more of a relative position between the preliminary radiation pulse and the target and a relative position between the radiation pulse and the target based on the determined second mov ing property of the target. The method can include analyzing the determined second moving property, wherein controlling the relative position between the preliminary radiation pulse and the target or the relati ve position between the radiation pulse and the target is based on the analysis of the determined second moving property of the target.

The relative position between the preliminary radiation pulse and the target can be controlled by adjusting one or more of a timing of a release of the preliminary ntd.iat.ion pulse and a direction at which the preliminary radiation pulse travels; and the relative position between the radiation pulse and the target can be controlled by adjusting one or more of a timing of a release of the radiation pulse and a direction at which, the radiation pulse travels.

The second moving property of the target can be determined by: detecting a first interaction between a fu st diagnostic light beam and the target at a first location within the second region; detecting a second interaction between a second diagnostic light beam and the target at a second location within the second region, the second location being distinct from the first location; and determining the second moving property based on the detections of the first and second interactions.

The second moving property of the target can be determined by: directing the first diagnostic S ight beam toward the target at the first location within the second region; and directing the second diagnostic light beam toward the target at a second location within the second region. The first diagnostic beam can be directed toward the target at the first location within the second region by directing the first diagnostic beam along a first direction toward the target; and the second diagnostic beam can be directed toward the target at the second location within the second region by directing the second diagnostic beam along a second direction toward the target, the second direction is not parallel with the first direction.

The first interaction can be detected by detecting light that is produced from the first interaction; the second interaction can be detected by detecting light that is produced from the second interaction; and the second moving property caw be determined based on the detections of the light.

The method can also include detecting a third interaction between a third diagnostic Sight beam and the target at a third location within the second region, the third location being distinct from the first and second locations.

The second moving property of the target can be determined by determining the second moving property of the target along a first direction. The method can include determining a moving property of the target along a second direction that is perpendicular to the first direction. The second moving property of the target along the first direction can be determined by detecting a time stamp associated with an interaction between the target and the diagnostic light beam . DRAWING DESCRIPTION

Fig. 1 A is a block diagram of a laser produced plasma extreme ultraviolet light source including a diagnost ic system for detecting a moving property of a target tra veling in an extended target region toward a target space along the X direction;

Fig. I B is a schematic diagram showing a view of the light source of Fig. 1 A in which the X direction is coming out of the page and the target trajectory is into the page; Fig. 2 A is a schematic diagram showing a point in time just before a prior radiation pulse and a prior target interact with each other at a target location within a target space of the EUV light source of Fig. 1 ;

Fig. 2B is a schematic diagram showing a point in time just before a current radiation pu!se and a current target interact with each other at the target location within the target space of the EUV light source of Fig. 1 ;

Fig. 3 is a block diagram of an exemplary diagnostic system of the EUV light source of

Fig. I ;

Fig. 4 is a block diagram of an exemplary control system of the EUV light source of Fig. 1 ;

Fig. 5 is a block diagram of an exemplary diagnostic system of the EU V light, source of

Fig. 1 ;

Fig. 6 is a block diagram of an exemplary control system of the EUV light source of Fig. i ;

Fig. 7 is a block diagram of an exemplary diagnostic system of the EUV light source of

Fig. I ;

Fig. 8 is a block diagram of an exemplary control system of the EUV light source of Fig.

1 ;

Figs. 9A js a schematic diagram showing a close up of the interaction between a diagnostic radiation beam and a current target in which the diagnostic radiation beam axis is generally perpendicular to a trajectory of the current target and the current target trajectory is aligned with an X direction;

Figs. 9B is a schematic diagram showing a close up of the interaction between a diagnostic radiation beam and a current target in which the diagnostic radiation beam axis is generally perpendicular to a trajectory of the current target and the current target trajectory is offset from an X direction along a Y direction;

Figs. 9C is a schematic diagram showing a close up of the interaction between a diagnostic radiation beam and a current target in which the diagnostic radiation beam is directed at an angle along an axis that is in the XY plane and the current target trajectory is aligned with the X direction; Figs. 9D is a schematic diagram showing a close up of the interaction between a diagnostic radiation beam and a current target in which the diagnostic radiation beam is directed along an axis that is in the XY plane and the current target trajectory is offset from the X.

direction along the Y direction;

Fig. 10 is a block diagram of an exemplary diagnostic system of the HU V Sight source of

Fig. 1 ;

Fig. 1 1 is a schematic diagram showing a preliminary radiation pulse directed to a first target location and a main radiation pulse directed to a second target location for interaction with the current target of the EUV light source of Fig. I ;

Fig. 12 is a block diagram of an exemplary optical source for use in the EUV light source of Fig. 1 ;

Fig. 13 is a flow chart of an exemplary procedure performed by the EU V light source (under control of the control system) for determining a moving property of a current target in the extended target region;

Fig. 14A is a schematic diagram of an exemplary diagnostic system, extended target region, and target space as viewed along the Z. direction of the EUV light source of Fig. F showing a point in time just before a prior radiation pulse and a prior target interact with each other at a target location within a target space;

Fig. 14B is a schemat ic diagram of the exemplary diagnostic system, extended target region, and target space of Fig. 14A as viewed along the X direction, showing the same point in time as Fig. .14 A;

Fig. i 5 A is a schematic diagram of the exemplary diagnostic system, extended target region, and target space as viewed along the Z direction of the EUV Sight source of Fig. 1 , showing a point in time just after the prior radiation pulse and the prior target interact with each other at. the target location within the target space;

Fig. 1 5B is a schematic diagram of the exemplary diagnostic system, extended target region, and target space of Fig. 15A as viewed along the X direction, showing the same point in time as Fig. 15 A;

Fig. 16A is a schematic diagram of the exemplary diagnostic system, extended target region, and target space as viewed along the Z direction of the EUV light source of Fig. L sho wing a point in time when the current target interacts with a first diagnostic Sight beam of the diagnostic system within the extended target region;

Fig. 16B is a schematic diagram of the exemplary diagnostic system, extended target region, and target space of Fig. 16A as viewed along the X direction, showing the same point in time as Fig. 16A;

Fig. I 7A is a schematic diagram of the exemplary diagnostic system, extended target region, and target space as viewed along the Z direction of the EUV light source of Fig. I , showing a point in time when the current target interacts with a second diagnostic light beam of the diagnostic system within the extended target region;

Fig. 17B is a schematic diagram of the exemplary diagnostic system, extended target region, and target space of Fig. 17 A as viewed along the X direction, showing the same point in time as Fig. Γ7Α;

Fig. I SA is a schematic diagram of the exemplary diagnostic system, extended target region, and target space as viewed along the Z direction of the EUV light source of Fig. 1 , showing a point in time after the current target has interacted with the second diagnostic light beam in the extended target region and during which the current radiation pulse is being directed to the target space;

Fig. 18B is a schematic diagram of the exemplary diagnostic system, ex tended target region, and target space of Fig. 18A as viewed along the X direction, showing the same point in time as Fig. 18A;

Fig. 1 ' ⁾ A is a schematic diagram of the exemplary diagnostic system , extended target region, and target space of the EUV light source of Fig. I as viewed along the Z direction, showing a point in time during which the current target is interacting with the current radiation pulse in the target space;

Fig. 19B is a schematic diagram of the exemplary diagnostic system, extended target region, and target space of Fig. 19A as viewed along the X direction, showing the same point in time as Fig. Ί 9Α;

Fig. 19C is a schematic diagram of the exemplary diagnostic system, extended target region, and target space of the EU V light source of Fig. I , as viewed along the Z direction, showing a point in time during which the current target is interacting with a current main radiation pulse in the target space and producing EUV light; Fig. 1 9D is a schematic diagram of the exemplary diagnostic system, extended target region, and target space of Fig. 19C as viewed along the X direction, showing the same point in time as Fig. 1 9C;

Fig. 20A is a schematic diagram of an exemplary diagnostic system, extended target region, and target space as viewed along the Z direction of the EUV Sight source ofFig. 1 , showing a point in time after a current target has interacted with three diagnostic light beams of the diagnostic system in the extended target region and during which the current radiation pulse is being directed to the target space: and

Fig. 20B is a schematic d iagram of the exemplary diagnostic system, extended target region, and target space of Fig. 20Λ as viewed along the X direction, showing the same point in time as Fig. 20A .

DESCRIPTION

Referring to Figs. I A and I B, an extreme ultraviolet ( EUV ) light source 1 00 supplies EUV light 1 55 that has been produced by an interaction between a target and a radiation pulse to an output apparatus 1.60. The EUV light source 100 includes features or components that measure and analyze one or more moving properties (such as speed, velocity, and acceleration) of a current target 1 1 0 as the current target 1 1 0 travels in an extended target region 1 1 5. The current target 1 10 travels generally along a trajectory TR, the direction of which can be considered as a target (or axial) direction AT, toward a target space 120 that is defined within a chamber 1 75. The axial direction AT of the current target .1 10 lies in a three dimensional coordinate system, that is, the X, Y, Z coordinate system defined by the chamber 1 75. The axial direction AT of the current target 1 1 0 generally has a component that is parallel with the -X. direction of the coordinate system of the chamber 1 75. However, the axial direction AT of the current target 1 1 0 also can have components along one or more of the directions Y and Z that are perpendicular to the -X direction.

With reference to Figs. I B and 2B, the EUV light source 100 adjusts one or more characteristics of a radiation pulse 1 35 that is directed toward the target space 1 20 based on the analysis of the determined moving property of the current target 1 10. The adjustment to the one or more characteristics of the radiation pulse 1 35 improves a relative alignment between a present target 1 10' and the radiation pulse 135 at the target location 122 in the target space 120. The present target 1 10' is the target that has entered the target space 1 20 at the time that the radiation pulse 135 ( which has just been adjusted) arrives in the target space 1 20. Such adjustment to the one or more characteristics of the radiation pulse 135 improves the interaction between the present target 1 10 ^' and the radiation pulse 1 35 and increases the amount of EUV light 150 (such as shown in Fig. 1 A.) produced by such interaction .

In some implementations, the present target 1 10 ^' is the current target i 10. In these implementations, the adjustment to the one or more characteristics of the radiation pulse 135 happens in a relatively shorter time frame. A relatively shorter time frame means that the one or more characteristics of the radiation pulse 1 35 are adjusted during the time after the analysis of the moving properties of the current target 1 10 is completed to the t ime that the current target 1 10 enters the target space 120. Because the one or more characteristics of the radiation pulse 1 35 are able to be adjusted in the relatively shorter time frame, there is enough time to effect the interaction between the current target 1 10 (the moving properties of which have just been analyzed) and the radiation pulse .135.

In other implementations, the present target 1 1 (f is another target, that is, a target other than the current target 1 10, and following the current target 1 10 in time. In these

implementations, the adjustment to the one or more characteristics of the radiation pulse 135 happens in a relatively longer time frame such that it is not feasible to effect the interaction between the current target 1 1 0 (the moving properties of which have just been analyzed ) and the radiation pulse 135. On the other hand, it. is feasible to effect the interaction between the other (or later) target, and the radiation pulse .135. A. relatively longer time frame is a time frame that is greater than the time after the analysis of the moving properties of the current target 1 10 is completed to the time that the current target 1 10 enters the target space 120. Depending on the relatively longer time frame, the other target could be adjacent to the current target 1 10. Or, the other target could be adjacent to an intermediate target that is adjacent to the current target 1 10.

The EUV light source 100 is able to determine the moving property of the current target 1 S O and each target directed toward the target space 120, and also to adjust the characteristic (or characteristics) of the radiation pulse 135 in a short window of time. Specifically, the moving property of the current target 1 10 is determined after a prior and adjacent target 1 1 OP has interacted with a prior radiation pulse i 35 P (Fig. 2 A) but before the next target enters the extended target region 1 15. In this way, the moving property of every or nearly every target that is being directed io the target space 120 can be determined so that a specific adjustment to a particular radiation pulse can be tailored to the determined moving property of the target that the particular radiation pulse will interact with.

By measuring and analyzing the moving property of the current target 1 10 in this extended target region 1 1 5 and in the short window of time, it is possible determine the impact or effect of various forces and effects applied to the current target 1 10 as it travels toward the target space 120. For example, forces and effects that are applied to the current target 1 10 include plasma pushback forces 1 25 that are applied io the current target 1 1 0 due to the remaining plasma 1 30 that is formed from an interaction at the target location 1 22 within the target space 120 between the prior target 1 10P (shown in Fig. 2A > and the prior radiation pulse 1 35P ( shown in Fig. 2A) that is supplied by an optical source 1 40. Such plasma pushback forces 125 can become larger as the plasma power increases, and the plasma power depends on power of the prior radiation pulse 135P and the efficiency of the interaction between the prior radiation pulse 135P and the prior target 1 1 OP. Thus, it becomes important as these output powers are increased to account for and make adjustments to reduce the impact of the plasma pushback forces 125. Other forces and effects applied to the current target 1 1 0 include instabilities in the generation and transport of the current target 1 10 as it travels tow ard the target space 1 20 and disruptions to the target trajectory due to the current target 1 10 interacting with other gas (low (such as hydrogen gas) as it travels toward the target space 1 20.

The current target 1 1 0 {as well as the prior target 1 1 OP and targets released earlier and later than these targets) is produced by a target delivery system 1 45 and is directed toward the target space 120 along a trajectory or path TR and the current target 1 10 is directed along its own axial direction A j at each point along the trajectory TR. In some implementations, the axial direction AT of the current target 1 10 upon immediate release from the target delivery system 145, aligns or is parallel with the -X direction of the three dimensional coordinate system X, Y , Z. The current target 1 10 moves at a velocity and along its axial direction A c and such motion can be predicted based on the properties at the target delivery system 145. Each target released by the target delivery system 145 can have a slightly different actual trajectory and the trajectory depends on the physical properties of the target delivery system 145 at the time of release of the target as well as the environment within the chamber 1 75. However, as discussed above, various forces and effects (such as the plasma pushback forces 1 25 applied along the X direction as well the Y and Z directions) applied to the current target 1 10 can cause the motion of the current target 1 10 to divert or change from the predicted tnotion. For example, the plasma pushback forces 125 can slow the current target 1 10 (as well as the present target 1 10'} along the X direction or cause the current target 1 10 to move along the Y or Z directions in an unpredictable manner. Without taking into account the impact of these forces and effects (sue!) as the plasma pushback forces .1 25) on the movement of the present target 1 10' (which can be the current target 1 10), the radiation pulse 135 produced by the optical source 140 and directed toward the target location 1 22 within the target space 1 20 may miss the present target 1 1 0 ^' completely or may not efficiently interact with the present target 1 10' when the present target 1 10' reaches the target location 122. This inefficient interaction can lead to a reduction in the amount of EUV light 1 50 produced by the present target 1 10', and thus can lead to a reduction in the amount of EUV light 1 55 that is output from the light source 100 toward an output apparatus 160 such as a lithography exposure apparatus. Additionally, this inefficient interaction can produce excess debris from the material of the present target 1 10 ^" after it has interacted with the radiation pulse 135. This debris contaminates an interior of or optics within the chamber 1 75, and the contamination of the chamber interior and or optics within the chamber 1 75 can force stoppage of the EUV light source 100 in order to clean the interior and/or optics or to replace optics.

The current target 1 10 can experience plasma pushback forces 125 that change its velocity (an exemplary moving property), for example, on the order of 0. 1, to 10 m/s. To resolve such a change to the velocity of the current target 1 10, the EUV light source 100 should be able to detect changes in the velocity to within a level that can be less than or equal to about 0. .1 m/s (for example, less than or equal to about 0.04 m/s or 0.02 m/s) to ensure an acceptable accuracy in a relative position between the radiation pulse and the present target 1 10 ^' at the target location 122. for example, a relative position of less than 5 pm.

Referring again to Fig. 1 A, the extended target region 1 1 5 is that region in which the plasma pushback forces 125 affect the current target 1 10 and cause the motion of the current target 1 10 to deviate from a desired motion. By quantifying this deviation, it is possible to determine how to adjust the radiation pulse 135 to ensure that the radiation pulse 135 efficiently interacts with the present target 1 10' within the target space 120. If the present target 1 10' is a target other than the current target 1 10, then an assumption can be made that the effect of the various forces on the current target 1 10 is .similar to the effect of the various forces on the present target i 10' so that the analysis can be applied to adjust the radiation pulse 1 35 that interacts with the target other than the current target 1 10.

The extended target region i 1 5 therefore can include remaining plasma 130 formed from the i nteraction of the prior target 1 1 OP (as shown in f ig. 2A) and the prior radiation pu lse 135P (as shown in Fig. 2 A). A first region 165 between the extended target region i 15 and the target del ivery system 145 can be considered as a region in which the plasma pushback forces 125 have a much lower effect on the current target 1 10. Thus, it is expected that a moving property (such as a speed or direction) of the current target 1 1 0 in the extended target region 1 I 5 will be different from the moving property of the current target 1 10 in the first region 165. Such a difference may make it difficult to efficiently interact the radiation pulse 135 with the present target 1 10" when it reaches the target location 1 22 w ithin the target space 120 because the present target 1 10 ^* may arrive at a different location than planned within the target space 1 20 and thus the radiation pulse 135 may not fully or partly intercept the present target 1 10'.

In order to measure the moving property of the current target 1 10, the EUV light source 100 includes a diagnostic system 105 that provides one or more diagnostic probes 107 that interact with the current target 1 10 in the extended target region 1 1 5, as shown in Fig. I A.

Specifically, the one or more diagnostic probes 107 interact with the current target 1 10 in the extended target region 1 1 5 only after the prior and adjacent target i 10P has already interacted with the prior radiation pulse ! 35P in the target space 120. The one or more diagnostic probes 107 can be directed along a direction that is in a plane of the -X direction and the -Y direction, for example, along the -Y direction. Moreover, the one or more diagnostic probes 1 07 can be configured to interact with each and every target 1 10 that passes through the extended target region 1 15 so that the diagnostic system .105 analyzes information about each and every target 1 1 0.

The interaction between the current target 1 10 and the one or more diagnostic probes 107 releases information (such as light or photons) that can be detected by the diagnostic system. 105. The diagnostic system 105 outputs data based on the released information, and. that. data, can be used to determine the moving property of the current target 1 .10. The EUV S ight source 100 also includes a control system 170 that receives this data from the diagnostic system 105. The control system 170 analy zes this data and determines the movi ng property of the current target 1 10 based on this analysis.

The EUV light source 100 performs the measurement and analysis on the moving property of the current target 1 10 in the extended target region 1 15 and also makes a change to one or more characteristics of the radiation pu!se 135 that will interact with the present target 1 10' at the target location 122 within the target space 120 so that the present target 1 10" and the radiation pulse 1.35 efficiently interact with each other to produce EUV light 150. The radiation pulse 135 that interacts with the present target 1 10' at the target location 122 within the target space ! 20 may or may not be the very next radiation pulse that is produced by the optical source 140 after the production of the prior radiation pulse 1 35 P.

The time frame during which the EUV Sight source 100 performs the measurement and analysis as well as the adjustment or change to the radiation pulse 135 is constrained by one or more of the rate at which the target delivery system 145 generates and releases each target along the trajectory TR and a distance between the target delivery system 145 and the target space 120. For example, if the target delivery-' system 145 generates targets at a repetition rate of 50 kHz, and a velocity of a target is 70 meters per second (m/s) as it is released from the target delivery system 145, then each target in the trajectory TR is physically separated or spaced by about 1 .4 millimeters (mm) along the trajectory TR. Given these exemplary conditions, each target crosses the path of the diagnostic probe(s) 107 of the diagnostic system 105 every 20 microseconds (ps). In this example, the EUV light source 100 must perform the measurement and analysis on the current target 1 10 as well as affect the change to the radiation pulse 135 all within a time frame of 20 gs just, after the prior target 1 10P and the prior radiation pulse 135P interact, and also within distances that ate less than the spacing between the targets (which would be 1 .4 mm in this example),

The plasma pushback forces 125 extend out from the target space 120 and the size of the forces drop with the distance from the target space 120. For example, the plasma pushback forces 125 can drop with a linear multiple of the distance or with a square of the distance. For example, the plasma pushback forces 125 generated within the target space 120 can affect the current, target 1 10 as far out as 1.0 to 1 .5 mm or even up to 10 mm from the target space 120 along any of the directions, and for example, along the X direction. By contrast, the distance between the target space 120 and the target delivery system 145 is about 1 meter (m). The EUV light source .100 includes the chamber 175 that defines the target space 1.20, the first region 165, and the extended target region 1 15, which is closer to the target space 120 than the first region 165, ail within the three dimensional, coordinate system X, Y, Z. The target delivery system 145 is configured to release the current target 1 10 along the trajectory or path TR that overlaps both, five first region 165 and the extended target region 1 15. As discussed above, the target delivery system 145 releases a stream of targets at a particular rate, and the EUV light source 100 must take this rate into account when detenni.ni.ng the total amount of time needed to perform the measurement and analysis on the moving property (or properties) of the current target 1 10 as well as affecting a change to the radiation pulse 135 that interacts with the present target 1 10 ^' at the target location 122 within the target space 120.

The EUV light source 100 includes a light collector 180 that collects as much EUV fight 150 emitted from the plasma as possible and redirects that EUV light 150 as collected EUV light 155 toward the output apparatus 160.

The EUV light source .100 includes a beam delivery system 185 that directs the beam of radiation pulse or pulses 135P, 135 from the optica! source 140 to the target space 120 and generally along the Z direction (though the beam or beams 135, B5P can be at an angle relative to the Z direction)- The beam delivery system 185 can include optical steering components 185 A that change a direction or angle of the beam of radiation pulses 135, 135P and a focus assembly 185B that focuses the beam of radiation pulses 135, I35P to the target space 120. Exemplary optical steering components 185A include optical elements such as lenses and mirrors that steer or direct the beam of radiation pulses by refraction or reflection, as needed.. The beam delivery system 185 can also include an actuation system thai controls or moves the various features of the optica) components 1 85 A and the focus assembly 185B.

Each of the targets (such as the present target 1 10' the current target 1 10, the prior target 1 1 OP, and ail other targets produced by the target delivery system 145 } includes a materia! that emits EUV light when converted to plasma. Each target is converted at least partially or mostly to plasma through interaction with the radiation pulse 135 produced by the optica! source 140 at the target location 122 within the target space 120.

Each target (including the current, target Π 0 and the prior target 1 1 OP) produced by the target delivery system 145 is a target mixture that includes a target substance and optionally impurities such as non-target panicles. The target substance is the substance that is capable of being converted to a plasma state that has an emission line in the EUV range. The target substance can be, for example, a droplet of liquid or molten metal, a portion of a liquid stream, solid particles or clusters, solid particles contained within liquid droplets, a foam of target materia!, or solid panicles contained within a portion of a liquid stream. The target substance can include, for example, water, tin. lithium, xenon, or any material that, when converted to a plasma state, has an emission line in the EUV range. For example, the target substance can be the element tin, which can be used as pure tin (Sn); as a tin compound such as SnBr4, SnBr2, SnH4; as a tin alloy such as tin-gallium alloys, tin- indium alloys, tin-indium-galiium alloys, or any combination of these alloys. In the situation in which there are no impurities, then each target includes only the target substance. The discussion provided herein is an example in which each target is a droplet made of molten metal such as tin. However, each target produced by the target del ivery system 145 can take other forms.

The current target 1 10 can be provided to the target space 120 by passing molten target material through a nozzle of the target delivery system 145, and allowing the current target 1 1.0 to drift into the target space 1 20. in some implementations, die current target 1 10 can be directed to the target space 120 by force. The current target 1 10 can be a material that has already interacted with one or more radiation pulses 135 or the current target 1 .10 can be a material that has not yet interacted with one or more radiation pulses 1 35.

The optica! source 140 is configured to produce a plurality of radiation pulses that are directed toward the target space 120 by way of the beam deliver)' system 185. Each radiation pulse that interacts with a target, at the target location 1 22 within the target space .1 20 converts at least a part of that target into plasma that emits EUV light i 50.

The EUV light source 100 also includes an adjustment system 190 coupled to the optical source 140 and to the control system 170. The control system 1 70 is configured to control a relative position between a radiation pulse 1 35 and the present target 1 10 ^' by sending a control signal to the adjustment system 1 90. The control signal causes the adjustment system 190 to adjust one or more of a timing of a release of the radiation pulse 1 35 and a direction at which the radiation pulse 135 travels.

Referring to Fig. 3, an exemplary diagnostic system 305 is shown. The diagnostic system 305 includes a probe module 300 which can be an illumination module 300 that produces, under control of the control system 170 or control system 470 (discussed below), as the diagnostic probe 10? at least two diagnostic light beams 320, 330 that are directed toward the trajectory 1 ^" R of the current target i 1 0. As discussed above, the diagnostic probe 107 (in this case, the diagnostic tight beams 320, 330} interacts with the current target 1 10 in the extended target region 1 15. Accordingly, the diagnostic light beam 320 is directed to interact with the current target 1 1.0 at a location 322 and a time T320 in the extended target region 1 15, and the diagnostic light beam 330 is directed to interact with the current target 1 10 at a location 328 and at a time T330 in the extended target region 1 15. The time T330 is after the time Ty^. The diagnostic light beams 320. 330 form laser curtains through which the current target 1 10 traverses. In some implementations, such as shown in Fig. 3, the diagnostic light beams 320, 330 can be directed along a path that crosses the trajectory TR at a right angle ( an angle of approximately 90° ) to the X direction.

Moreover, the diagnostic light beams 320, 330 are separated from each other along the X direction by a known distance, for example, a value that can be referred to as Ad. For example, separation Ad can be less than the spacing between the targets and it can be determined or set based on the spacing between the targets to provide for greater precision in the measurements that are performed based on the interactions between the diagnostic light beams 320, 330 and the current target i 10. Up to a point and in general, the larger the separation Ad the higher the precision in the measurements that are performed. For example, the separation Ad can be between about 250 pm and 800 pm.

The interactions between the diagnostic light beams 320, 330 and the current target 1 10 enable the control system 170 or 470 to determine a moving property such as a velocity V of the current target 1 10 along the -X direction, ft is possible to determine trends in the velocity V or the changing velocity V over many targets. It is also possible to determine a change in a moving property of the current target 1 10 along the -X direction using only the diagnostic light beams 320, 330 if some assumptions about the motion of the current target 1 10 are made.

In some implementations, the illumination module 300 includes a single light source that produces a light beam that is split into two diagnostic light beams (such an exemplary design is shown in Fig. 5). For example, a single light source can be a solid-state laser such as a YAG laser, which can be a neodymiitm-doped YAG (Nd:YAG) laser operating at 1070 ran and at 50 W power, .In this example, the illumination module 300 also includes one or more optical elements (such as a beam splitter or .mirrors) that split the light beam from the YAG laser into two separate diagnostic l ight beams that are directed toward the trajectory TR of the target 1 10 as diagnostic light beams 320, 330. In other implementations, the illumination module 300 includes a pair of light sources such as two lasers, each producing its own diagnostic light beam 320, 330.

The diagnostic system 305 also includes a detection module 335. The detection module 335 is configured to detect the data that results from the interaction between the current target 1 10 and the respective diagnostic light beam 320, 330 within the extended target region 1 15, and then output the detected data to the control system 1 70 or 470. For example, the detection module 335 can detect each interaction by detecting a one-dimensional aspect or characteristic such as the intensity of the light 340, 350 that is reflected from the current target 1 10 as the respective diagnostic light beam 320, 330 strikes the target 1 10. Moreover, the control system 170 or 470 can analyze the data from the detection module 335 and, based on the analysis, detect the time at which the maximum intensity of the light 340, 350 that is reflected from the current target 1 10 reaches the detection module 335. The light 340, 350 that is reflected from the current target 1 10 can be a portion of the respective diagnostic light beam 320, 330 that is reflected from the current target 1 10. The accuracy with which the EUV light source 100 can detect the changes to the trajectory of the current target 1 10 is limited to the resolution of the detection module 335.

In some implementations, the detection module 335 includes a photo detector and one or more optical components such as reflective of refractive optics, filters, apertures to direct and modify the light 340, 350 prior to entering the photo detector.

The wavelength of the diagnostic probe (and the diagnostic light beams 320, 330) produced by the illumination module 300 should be distinct enough from the wavelength of the radiation pulses 135 produced by the optical source 140 so that the detection module 335 can distinguish between the light 340, 350 reflected from the current target 1 10 and stray light from the radiation pulses 135. In some implementations, the wavelength of the diagnostic light beams 320, 330 is 532 nm or 1550 n.m.

It is also possible that the diagnostic system 105, 305 includes an optic that changes a polarization state of one or more of the diagnostic light beams 320, 330.

In some implementations, the diagnostic light beams 320, 330 produced by a laser source are Gaussian beams, and thus the transverse profile of the optical intensity of each diagnostic light beam 320, 330 can be described with a Gaussian function. In such a function, the optical intensity correlates with the transverse distance from the axis of the light beam 320 ox 330. The transverse profile of the diagnostic Sight bean.) 320,, 330 also determines how the detection module 335 measures the light 340. 350 reflected from the current target 1 10 because the different transverse profiles of the diagnostic light beam 320, 330 can alter one or more aspects of the light 340. 350 detected by the detection module 335. The transverse profile of the diagnostic Sight beam 320 or 330 could be used to determine a moving, property of the current target 1 10 that has a component in the Y direction if the diagnostic light beam 320, 330 were to be directed along a path, that subtends a non-right angle with the trajectory TR of the current- target 110, such as shown in Fig. 7.

The control system 170 or 470 is configured to analyze the data output from the diagnostic system 105, 305 and control a relative position between the radiation pulse 135 and the present target 1 10' based on the analysis. To this end, and with reference to Fig. 4, an exemplary control system 470 includes a detection sub-controller 400 that receives the output from the diagnostic system 305. The detection sub-controller 400 analyzes the output from the detection module 335 of the diagnostic system 305, and determines one or more moving properties of the current target 1 10 based on this analysis. The detection sub-control ier 400 also determines whether an adjustment needs to be made to the radiation poise 135 output from the optical source 140 based on this determination; and if an adjustment is needed, the detection sub- controller 400 sends an appropriate signal to an optical source sub-controller 405, which interlaces with the optical source .140.

In some implementations, the detection module 335 of the diagnostic system 305 outputs a one-dimensional signal such as a voltage signal that is generated when photons of the light 340, 350 are detected. Thus, the detection module 335 detects a one-dimensional aspect (such as the photons) of the light 340, 350. The detection sub-controller 400 converts the output (such as the voltage signal) from the detection module 335 into a value associated with the light 340 produced from the interaction between the current target 1 10 and the diagnostic light beam 320, and a value associated with the light 350 produced from the interaction between the current target 1 10 and the diagnostic light, beam 330. These two valises can be used to determine the one or more moving properties of the target 1 10.

For example, the detection sub-controller 400 can convert the voltage signal from the detection module 335 into a first value that corresponds to a maximum intensity of the light 340 produced from the interaction between the current target i 10 and the diagnostic light beam 320, and a second value that corresponds to the maximum intensity of the Sight 350 produced from the interaction between the current target 1 10 and the diagnostic light beam 330. These two values of the maximum intensity can be digitally time stamped and then used to determine the one or more moving properties of the target i 10, as discussed below in greater detail.

The sub-controller 400 can include a field-programmable hardware circuit 400A. such as a field-programmable gate array (FPGA), which is an integrated circuit designed to be configured bv a customer or a desi ^g ner after mamrfeeturins. The circuit 400A can be dedicated hardware that receives the values of the time stamps from the detection module 335, performs a calculation on the received values, and uses one or more lookup tables to estimate a time of arrival of the present target 1 10' at the target location 122. In particular, the circuit 400A can be used to quickly perform a calculation to enable the adjustment to the one or more characteristics of the radiation pulse 135 in the relatively shorter time frame to enable the adjustment of the one or more characteristics of the radiation pulse 1 35 that interacts with the current target 1 10, the moving properties of which have just been analyzed by the circuit 400A.

For example, the circuit 400A can perform a subtraction step on the time stamps to determine the value of the difference ΛΤ. The circuit 400 A accesses the stored the values of the separation Ad, and the value of the distance DRB; between the crossing of the diagnostic light beam 330 with the trajectory TR of the current target i 10 and the target location 122 along the X direction. The circuit 400 A can therefore rapidly perform a calculation using a simple and fast technique that does not require the use of other software within the sub-controller 400 or within other components of the control system 470. For example, the circuit 400A can access a flight time lookup table that stores a set of velocities V for specific values of the difference AT given the value of the separation Ad, and a set of times of arrival to the target location 122 that, correlate with various values of D _RB ? divided by velocity V to quickly output the time of arrival to the sub-controller 400, for use by other components of the control system 470.

The control system 470 also includes a sub-controller 410 specifically configured to interface with the beam delivery system 185, a sub-controller 412 specifically configured to interface with the probe module 300. and a sub-controller 41 5 specifically configured to interface with the target delivery system 145. Moreover, the control system 470 can include other sub- controllers specifically configured to interface with other components of the light, source 100 not shown in Fig. 1, The control system 470 generally includes one or more of digital electronic circuitry, computei ^' hardware, firmware, arid software. The control system 470 can aiso include memory 450, which can he read-only memory and/or random access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including, by way of example, semiconductor memory devices, such as EPROM,

EE-PROM, and flash memory devices; magnetic disks such as interna! hard disks and removable disks, magneto-optical disks; and CD-ROM disks The control system 470 can also include one or more input devices 455 {such as a keyboard, touch screen, microphone, mouse, hand-held input device, etc.) and one or more output devices 460 (such as speakers and monitors).

The control system 470 includes one or more programmable processors 465, and one or more computer program products 467 tangibly embodied in a machine-readable storage device for execution by a programmable processor (such as the processors 465). Tire one or more programmable processors 465 can each execute a program of instructions to perform desired functions by operating on input data and generating appropriate output. Generally, the processor 465 receives instructions and data from memory 450. Any of the foregoing may be supplemented by, or incorporated in, specially designed ASICs (application-specific integrated circuits).

Moreover, any one or more of the sub-controllers 400, 405, 410, 412, 41 5 can include their own digital electronic circuitry, computer hardware, firmware, and software as well as dedicated memory, input and output devices, programmable processors, and computer program products. Likewise, any one or more of the sub-controllers 400, 405, 410, 412, 415 can access and use the memory 450, the input devices 455, the output devices 460, the programmable processors 465, and the computer program products 467.

Although, the control system 470 is shown as a separate and complete unit, it is possible for each of the components and sub-controllers 400, 405, 410, 412, 415 to be separate units within the light source 100.

Referring to Fig. 5„ an exemplary diagnostic system 505 is shown as having a probe module such as an illumination module 500 that includes a single light source 502 that produces, tinder control of the control system 170, 470, 670, a light beam 510, a set of optical components 515, 517, and a pair of diagnostic light, beams 520, 530 that serve as the diagnostic probe 107, The optical components 515, 51 7 of the set are configured and designed to split the light beam 510 into the two diagnostic light beams 520, 530 as well as direct the diagnostic light beams 520, 530 toward the trajectory TR of the current target 1 10. hi some examples, the optical component is a beam splitter 51 5 that splits the light beam 510 into diagnostic light beams 520, 530. For example, the beam splitter 515 can be a dielectric mirror; a beam splitter cube, or a polarizing beam splitter. One or more optical components 517 such as reflective optics can be placed to redirect either or both of the diagnostic light beams 520, 530 so that, both diagnostic light beams 520, 530 are directed toward the trajectory TR of the current target i 10. The set of optical components 515, 51? can include other optical components not. shown or in a different configuration from what is shown.

The diagnostic system 505 includes the detection module 535, which is configured to detect the light 540, 550 reflected from the current target 1 10 as the respective diagnostic light beam 520, 530 strikes the target 1 10. The detection module 535 can include a device such as a pholodkxie thai converts the light ( in the form of photons) into a current, and outputs a voltage that is related to the current. Thus, in this example, the output from the detection module 535 constitutes a one-dimensional voltage signal, which is output to the control system 670. The detection module 535 can also include optical filters, amplifiers, and built-in lenses, as needed. The photodiode generates the current when photons from the light 540, 550 are absorbed in the photodiode and outputs a voltage signal that corresponds to the generated current. The detection module 535 generates as the voltage signal an analog pulse 560 when the light 540 is detected and an analog pulse 570 when the light 550 is detected. These pulses 560, 570 are output from the detection module 535 to the control system 670 for further processing.

As shown, the detection module 535 includes a single device such as a photodiode detector that is able to detect both of the interactions (that is, both the light 540, 550). Such a design that uses a single device reduces complexity and also enables the data to be more efficiently analyzed. In other implementations, the detection module 535 includes one or more photo-transistors, light-dependent resistors, and photomultip!ier tubes. In other implementations, the detection module 535 includes one or more thermal detectors such as a pyroelectric detector, a bolometer, or a calibrated charged coupled device (CCD) or CMOS.

Referring to Fig. 6, an exemplary control system 670 is shown for processing the output from the diagnostic system 505 to determine a value of the velocity ( moving property) of the current target 1 10 along the X direction. The exemplary control system 670 includes a detection sub-controller 600 that receives tire pulses 560, 570 from the diagnostic system 505. The detection sub-controller 600 includes a discriminator module 605 that receives the pulses 560, 570 and filters this signal, amplifies tSiis signal and. differentiates it; as needed. At a zero- crossing of the derivative of ^" each current target 1 10 signal (generated from the pulses 560, 570), the discriminator module 605 generates a digital trigger pulse 610, 620. respectively. The discriminator module 605 can be an electrical circuit that includes a filter and a gain circuit as well as a peak predict circuit with differentiation capabilities.

The detection sub-controller 600 also includes a time module 625 that receives the di ^g ital trigger pulses 610, 620 and digitally time stamps each individual trigger pu!se 610, 620 as ! _¾ ø and TS.H). The difference between the time stamps and. Tj¾<> is given as ΛΤ. The detection sub-controller 600 includes a moving property module 635 to which the value of AT is input. Thus, the detection sub-controller 600 converts the signals associated with the respective light 540, 550 reflected from the current target 1 10 into respective single data values such as time stamps that can be used for further analysis.

The moving property module 635 also accesses the value of Ad from memory 450, which can be internal to or external to the moving property module 635. The moving property module 635 determines the value of the velocity of the current target 1 10 in the extended target, region 1 15. For example, the moving property module 635 could use the determined value of ΔΤ and the value of Ad, and compare those va lues to a set of pre-detemiined values stored in memory such as memory 450 to determine a value of the velocity of the current target 1 1.0. As another example, the moving property module 635 could calculate the average velocity V of the current target 1 .10 along the X direction as Ad/ΔΤ.

^' The moving property module 635 can also estimate or deten.ni.ne an acceleration of the current target 1 10 if assumptions are made about the motion of the current target i 10. It is possible to determine trends in the velocity V or the changing velocity V over many targets.

The moving property module 635 also determines the predicted time that the present target 1 10' ( which can be the current target 1 10} will be at the target location 122 within the target space 120. The moving property module 635 is able to determine the predicted time of arrival of the current target 1 10 at the target location 122 because the value of the velocity V of the current target 1 10 has been determined as well as other information about the current target 110 and the diagnostic radiation beam 530 relative to the target location 122, Specifically., the moving property module 635 knows the distance DRB? between the crossi ng of the diagnostic- light beam 530 with the trajectory TR of the current target 1 10 and the target location 122 along the X direction. The moving property module 635 also knows the time that the current target 1 10 passed through the path of the diagnostic light beam 530. Thus, it is possible to estimate or determine the arrival of the current target 1 10 at the target location 122 as being the distance DRB? divided by the velocity V (or DRB-'/V).

The output from the moving property module 635 is a control signal and is directed to the optical, source sub-controller 405, which interfaces with the adjustment system 190 coupled to the optical source 140. The control signal from the moving property .module 635 provides instructions that cause the adjustment system 190 to adjust, aspects of the optical source 140 to thereby adjust one or more of a timing of a release of the radiation pulse 135 and a direction at which the radiation pulse 135 travels.

Referring to Fig. 7, in other implementations, an exemplary diagnostic system 705 includes an illumination module 700 that produces as the diagnostic probe 107 three diagnostic light beams 720, 725, 730. The diagnostic light beams 720, 725, 730 are directed toward respective locations 722, 724, 728 along the trajectory TR of the current target 1 10 to interact with the current target 1 10 at respective times T???, T?^, T _? 2*. The respective interactions between the diagnostic light beams 720, 725, 730 and the current target 1 10 produce light 740, 745, 750. The diagnostic system 705 therefore includes the detection module 735, which is configured to detect the light 740. 745. 750 reflected from the current target 1 30 as the respective diagnostic light beam 720, 725, 730 interacts with the current target 1 10. The detection module 7.35 can include a device such, as a photodiode that converts the light into current. The diagnostic system 705 can be coupled to a control system 870, which is a specific implementation of the control system .170 and will, be discussed with reference to Fig. 8.

By including a third diagnostic light beam 725, it is possible to determine not only a moving property such as velocity V of the current target 1 10 along the -X direction, but also to determine a change in the moving property of the current target 1 10 along the -X direction. Thus, the use of the third diagnostic light beam 725 enables the control system 1 70 to determine both the velocity V and the acceleration A of the current target 1 10 along the -X direction.

Additionally, because the third diagnostic light beam 725 is directed toward the trajectory TR at a non-right angle relative to the trajectory TR, the control system 870 is able to determine one or more moving properties (such as the velocity or trajectory) of the current target 1 10 along a direction thai is perpendicular to the -X direction, for example along the Y direction, as discussed below.

The diagnostic light, beams 720, 730 are directed along a path that crosses the trajectory TR of the current target 1 10 at a right (90°) or approximately right angle relative to the -·Χ direction. The diagnostic light beam 725 is directed along a path that crosses the trajectory TR of the current target 1 10 at a non-right angle (for example, at an angle of approximately 45 ^;; ) relative to the -X direction. Thus, the diagnostic light beams 720, 730 generally travel along the -Y direction while the diagnostic light beam 725 travels along a direction in a plane defined by the X and Y (generally along Y and either -X or X directions).

As discussed above, the dia ^g nostic liaht beams 720, 725, 730 interact with the current target 1 10 as the current target 1 S O travels toward the target space 120 and while in the extended target region 1 15. The diagnostic light beams 720, 725, 730 are separated from each other along the X direction by known distances, as discussed below, and this known information can be used to determine one or more moving properties of the current target 1 10. for example, the velocity and acceleration of the current target 1 10 along the -X direction can be determined.

Additionally, information about a displacement or motion along the Y direction can also be determined.

Referring to Fig. 8, an exemplary detection sub-contro!!er 800 can be designed as a part of the control system 870 in order to analyze the data obtained from the interaction between the diagnostic system 705 and the current target 1 10. For example, the detection sub-controller 800 receives pulses 760, 765. 770 output from the diagnostic system 705. The pulses 760. 765, 770 correspond to the analog pulses produced by the detection module 735 when respective light 740, 745, 750 is detected.

The distance between the diag J-.'nostic li& 1,.'ht beams 720, - 730 alonu the X direction is known and can be denoted as Adl(X). In one example, the separation Ad i fX) is 100 gm. Thus, the diagnostic light beams 720, 730 can be used by the control system 870 to determine the velocity V 1 of the current target 1 10 along the X direction in the extended target region 1 1 5 using, for example, the method discussed above with respect to Figs, 5 and 6. Specifically, control system 170 determines time stamps Ί½ and Ί½ associated with the light 740, 750 produced from the interaction between the respective diagnostic light beams 720, 730 and the current target 1 10 at respective locations 722, 728 along the trajectory TR. The control system 870 calculates the difference between these time stamps Δ ^' Π(Χ). ^" Hie control system 870 determines the valise of the velocity V 1 of the curresit target 1 10 along the -X direction in the extended target region 1 15 based on the determined values of ΔΤΙ( ^' Χ) and Adl (X). For example, the control system 870 can calculate the velocity V I of the current target 1 10 along the X direction as Adl(X)/ATl(X).

Additionally, the control system 870 determines a time stamp T- ₂ 4 associated with the light 745 produced from the interaction between the diagnostic light beam 725 and the current target at the location 724 along the trajectory TR. The distance along the -X direction between the diagnostic light beams 720 and 725 at the locations 722, 724 is known and can be denoted as Ad2(X). The distance along the -X direction between the diagnostic light beams 725 and 730 at the locations 724, 728 is also known and can be denoted as A<B(X). Using this additional information, the control system 870 can calculate a time difference ΔΤ2{Χ) between the time stamps T?;.: and T722 and a time difference AT3(X) between the time stamps T72? and T?^. The control system 870 can therefore determine the velocity V2 of the current target along the -X direction as it travels between location 722 and 724 as Ad2{X)/AT2(X), and the velocity V3 of the current target along the -X direction as it travels between location 724 and 728 as

Δό3(Χ)/ΔΤ3(Χ).

The diagnostic light beam 725 can be used in combination with one or more of the diagnostic light beams 720, 730 to determine a change in a moving property (for example, an acceleration A) of the current target 1 10 along the -X direction. Specifically, the control system 870 determines the time stamp T724 associated with the light 745 produced from tire interaction of the diagnostic light beam 725 and the current target 1 10 at the location 724. in this way, the velocity V2(X) can be determined for the current target 1 10 between the diagnostic light beam 720 and the diagnostic light beam 725 based on a difference ΔΤ2(Χ) between the time stamps T722 and TT24 and a distance Ad2(X) between the locations 722 and 724. Moreover, the velocity V3( X) can be determined for the current target 1 10 between the diagnostic light beam 725 and the diagnostic light beam 730 based on a difference AT3(X) between the time stamps T724 and T728 and a distance Ad3(X) between the locations 724 and 728. The difference between these two velocities (V2(X) - V3(X}} can be divided by the time difference to obtain the acceleration of the current target 1 10 along the X direction. For example, it can be assumed that the current target 1 10 has the velocity V2{X) at time and the velocity V3(X) at time Ί½« and thus the acceleration A can be determined to be (V2(X) - ν3(Χ))/(Τ724-Τ½).

As discussed above, the diagnostic light beams 720, 725, 730 produced by the laser source within the illumination module 700 can be Gaussian beams. In this case, the transverse profile of (he optical intensity of each diagnostic light beam 720, 725, 730 can be described wi th a Gaussian function. In such a function, the optical intensity correlates with the transverse distance from the axis of the light beam 720, 725, or 730. Because the Gaussian shape is relatively simple, this particular aspect of the diagnostic light beam 725 can be used to process data obtained from the interaction between the diagnostic light beams 720, 725, 730 and the current target 1 10.

The diagnostic light beam 725 can be used by the control system 870 to determine a trajectory of the current target 1 10, specifically, to determine a distance or a velocity that the current target 1 10 travels along the Y direction. This can be determined because the diagnostic light beam 725 is directed at an angle in a plane defined by the X and Y directions.

As shown in Fig. 9A, the diagnostic light beam 720 crosses the trajectory TR at the location 722. The diagnostic light beam 720 travels along a direction defined by its axis 920 A, which generally aligns with the -Ύ direction, in Fig. 9 A, the current target 1 10 generally aligns with the X direction (is at Y ^::: 0) and thus the current target 1 10 does not have a measurable Y direction component to it. By contrast, in Fig. 9B, the current target 1 10 is offset from the X direction along the -Y direction by an amount dY, However, because this offset still aligns with the axis 920 A of the diagnostic light beam 720, the reflected light 740 from the current target will not change by a significant amount. Moreover, the time at which the reflected light 740 is detected in both examples (Figs. 9 A. and 9B) is the same or nearly the same because the interaction between the target 1 10 and the diagnostic light beam 720 occurs at approximately the same time. It is noted that the intensity of the diagnostic light beam 720 does change by an amount depending on the distance from the beam waist, but that change may not significant enough to be measurable or to show up as a change in the intensity of the reflected light 740.

By contrast, as shown in Fig. 9C, the diagnostic light beam 725 crosses the trajectory TR at the location 724C and the current target 1 10 interacts with the diagnostic light beam 725 at the time T724C- l.n this case, the diagnostic light beam 725 travels along a direction that is in the XY plane and its axis 925A has components in both the X and Y directions. Thus, the intensity of the beam 725 decreases according to the Gaussian function along both the X and Y directions. The current target 1 10 aligns with the X direction and does not have any appreciable motion along the Y direction. By contrast; as shown in Fig. 9D, the current target 1 10 is shifted along the Y direction by the distance dY. In Fig. 9D, the diagnostic light beam 725 is directed such that its axis 925 A has components in both the X and Y directions, and the offset current target 1 10 would be interacting with the highest intensity of the light beani 725 at a different location 724D and also at a time T?;.u>, which, is later than the time Tn-ic- Therefore, the detection module 735 detects the reflected light 745 D in Fig. 9D at a later time than it would detect the reflected light 745C in Fig. 9C. This difference in time at which the reflected light 745C or 745D is detected by the detection module 735 can be used to determine how far the current target 1 10 has shifted along the Y direction.

Specifically,, i f the time di fference ΛΤ2(Χ ) for a current target 1 30 is greater than the time difference ΔΤ2< X) for a prior target 1 1 OP then this means that the current target 1 10 has moved along the Y direction relative to the prior target 1 iOP. By contrast if the time difference ΔΤ2(.Χ) for a current target 1 10 is less than the time difference ΔΤ2ίΧ) for a prior target i 10P then this means that the current, target 1 10 has moved along the -Y direction relative to the prior target HOP,

Referring to Fig.. 10, in other implementations, an exemplary diagnostic system. 1005 includes an illumination module 1000 that includes a single light source 1002 that produces a light beam 1010. The diagnostic system. 1005 produces a plurality of diagnostic light beams 1020, 1025, 1030 that serve as the diagnostic probe or probes 107. To this end, the illumination module .1000 also includes a difiractive optic 1015 and a refractive optic 10! 7 such as a focusing lens. The light beam 1010 is directed through the ditYraetive optic 1.015, which splits the light beam 1010 into a plurality of light beams, which travel along distinct directions and are directed through the refractive optic 101 7 to produce the diagnostic light beams .1020, 1.025, 1030. The diagnostic light beams 1020. 1025, 1030 are directed toward the trajectory TR of the current target I 10. The difiractive optic 1015 can split the light beam 1010 so that the diagnostic light beams 1020, 1025, 1030 are separated by a set distance (for example, 0.65 mm) at the trajectory TR. Moreover, the refractive optic 1017 can ensure that the foci (or beam waist) of each of the diagnostic light beams 1020,, 1025, 1030 overlaps the trajectory TR. Because of the design of the diffraciive optic 1015 and the refractive optic 1017.. the diagnostic light, beams 1020. 1025, 1030 are directed so that they fan out toward the trajectory TR and intersect the trajectory TR at different and distinct angles. For example, the diagnostic light beam 1025 can intersect the trajectory TR at a right or approximately right angle to the X direction. The diagnostic light beam 1020 caw intersect the trajectory TR at an angle that is less than 90" relative to the -X direction and the diagnostic light beam 1030 can intersect the trajectory TR at an angle that is greater than 90° relative to the -X direction. Each of the diagnostic light beams 1020, 1025, 1030 can be Gaussian beams so that the transverse profile of the optical intensity of each diagnostic light beam .1020, 1025, 1030 can be described with a Gaussian function. The beam waist of each diagnostic light beam 1020, 1025, 1030 can be configured to overlap at the trajectory TR or the -X direction.

The diffracti ve optic 1015 can be a rectangular or binary phase diffraction grating that produces discrete and spatially spaced replicas of the input light beam 1010. The separation between the diagnostic light beams 1020, 1025, 1030 can be adjusted or customized depending on the rate at which the targets are released from the target delivery system 145 as well as the size and material of the targets. It is also possible to produce more than three diagnostic light beams 1020, 1025, 1030 with the diffract) ve optic 101 5. By producing so many diagnostic light beams, it is possible to record or detect the position of the current target 1 10 through the extended target re ^g ion 1 15, thus a!lowina for a more accurate determination of the velocity and acceleration of the current target 1 10 and also providing a tool for understanding the dynamics of the current target 1 10 as a result of the plasma pushback forces 125.

In some implementations, the diffracti ve optic .1015 is a binary phase diffraction grating. The diagnostic system 1005 also includes a detection module 1035 that receives the light 1040, 1045, 1050 reflected from the current target Ϊ 10 as it passes across the respective diagnostic light beams 1020. 1025, 1030. The detection module 1035 can include a detection device that converts the photons of the light 1040, 1045, 1050 into a current, and outputs a one- dimensional voltage signal based on the current. For example, the detection module 1035 can include a photon detection device such as a photodiode that converts the light 1040, 1045, 1050 into an electrical signal.

Referring to Fig. 1 1 , in some implementations, the present target 1 W interacts with two radiation pulses within the target space 120, For example, the optical source 140 can be configured to supply a preliminary radiation pulse 1 1.35 A to a first target location 1 1 22 A within a target space 1 i 20 and a main radiation pulse 1 1 35B to a second target location 1 1 22B within the target space 1 120. The radiation pulses 1 135 A, 1 1 35 B can be directed along the Z direction.

The interaction between the preliminary radiation pulse 1 135A and the present target I ). 10' at the first target, location 1 1 22A causes the present target 1 1 10' to modify its shape so as to deform and to geometrically expand as it moves through the target space 1 120. The interaction between the main radiation pulse 1 1356 and the modified present target 1 1 10 ^T at the second target location Π 22Β converts at least part of the modified present target 1 1 10 ^:' into plasma 1 1 30 that, emits EUV light 1 1 50. It is possible for some of the materia! of the present target 1 1 10 ^' to he converted into plasma when it interacts with the preliminary radiation pulse 1 1 35 A. However., the properties of the preliminary radiation pulse 1 1 35A are selected and controlled so that the predominant action on the present target 1 1 10' by the preliminary radiation pulse 1 .135 A. is the deformation and modification of the geometric distribution of the present target 1 i ! 0\

The interaction between the preliminary radiation pulse 1 335 A and the present target 1 1 10' causes material to ablate from the surface of the present target 1 1 10' and this ablation provides a force that deforms the present target 1 1 10' so that it has a shape that is different than the shape of the present target 1 1 10' prior to interaction with the preliminary radiation pulse 1 135 A. For example, prior to interacting with the preliminary radiation pulse 3 .135 A, the present target 1 1 10' can have a shape that is similar to a droplet upon exiting the target delivery' system 145, while after interaction with the preliminary radiation pulse 1 135 A, the shape of the present target 1 1 10" deforms so that its shape is closer to the shape of a disk {such as a pancake shape) when it reaches the second target location 1 122B. After interaction with the preliminary radiation pulse 1 135A, the present, target 1 1 1 0' can be a material that is not ionized (a material that is not a plasma) or that is minimally ionized. After interaction with the preliminary radiation pulse 1 1 35 A, the present target 1 1 10' can be, for example, a disk of liquid or molten metal, a continuous segment of target material that does not have voids or substantia! gaps, a mist of micro- or nano-partkies, or a cloud of atomic vapor.

Additionally, the interaction between the preliminary radiation pulse 1 135 A and the present target 1 1 10' that causes the materia! to ablate from the surface of the present target. 1 1 10' can provide a force that can cause the present target 1 1 10' to acquire some propulsion or speed along the Z direction, as shown in Fig. 1 1 . The expansion of the present target Π 10' as it travels from the first target location 1 122A to the second target location I 122B in the X direction and the acquired speed in the Z direction depend on an energy of the preliminary radiation pulse i 135A, and in particular, on tire energy delivered to (that is, intercepted by) the present target 1 1 10' .

The optical source .140 can be designed to produce a beam of preliminary radiation pulses

1 135 A and a beam of main radiation pulses 1 135B directed to respective target locations 1 122 A, 1 122B. Moreover, as discussed above, the BUY light source 100 adjusts one or more

characteristics of the radiation pulse 135 that is directed to the target space 120 based on the analysis of the determined moving property or properties of the current target i 10. Accordingly, it is possible for the EU V light source 100 to adjust one or more characteristics of the

preliminary radiation pulse 1 S 35A, one or more characteristics of the main radiation pulse 1 135B. or one or more characteristics of both of the preliminary radiation pulse 1 135A and the main radiation pulse 1 135B.

Referring to Fig.. 12, an exemplary optical source 1240 is designed to produce the beam of preliminary radiation pulses 1 135A and the beam of main radiation pulses I I35B directed toward their respective target locations 1 122 A, 1 122B within the target space 1 120.

The optical source 1240 includes a first optical amplifier system 1200 that includes a series of one or more optical amplifiers through which the beam of preliminary radiation pulses 1 135 A is passed, and a second optical amplifier system 1205 that includes a series of one or more optical amplifiers through which the beam of main radiation pulses 1 135B is passed. One or more amplifiers from the first system 1.200 can be in the second system 1205; or one or more amplifiers in the second system 1205 can be in the first system 1200. Alternatively, it is possible that, the first, optical amplifier system 1200 is entirely separate from the second optical amplifier system 1205.

Additionally, though not required, the optical source 1240 can include a first light generator 1 2 10 that produces a first pulsed light beam 12 1 1 and a second light generator 1215 that produces a second pulsed light beam 1216. The light generators 12 i0, 1215 can each be, for example, a laser, a seed laser such as a master oscillator, or a lamp. An exemplary light generator that can be used as the light generator 1210, 1215 is a Q-switched, radio frequency (RF) pumped. axial flow, carbon dioxide (CO?) oscillator that can operate at a repetition rate of for example, 100 kHz, The optical ampl ifiers within the optical amplifier systems 1200, 1205 each contain a gain medium on a respective beam path, along which a light beam 121 1 , 1 2 16 from the respective light generator 1 210, 121 5 propagates. When the gain medium of the optical amplifier is excited, the gain medium provides photons to the light beam, amplifying the light beam 121 1 , 1216 to produce the amplified light beam that loans the preliminary radiation pulse beam 1 1 35A or the main radiation pulse beam 1 1 35B.

The wavelengths of the light beams 1.21 .1 , 121 6 or the radiation pulse beams 1 1 35A, 1 1 35B can be distinct from each other so that the radiation pulse beams 1. 135 A, 1 135B can be separated from each other, if they are combined at any point within the optical source 1240. If the radiation pulse beams 1 135A, 1 1 35B are produced by CO; amplifiers, then the preliminary radiation pulse beam 1 135 A can have a wavelength of 10.26 micrometers (μηι) or 10.207 μτη, and the main radiation pulse beam i 135B can have a wavelength of 10.59 μηι. The wavelengths are chosen to more easily enable separation of the beams 1 135A, 1 1 35 B using dispersive optics or dichroie mirror or beamsplitter coatings. In the situation in which both beams 1 135 A, 1 135B propagate together in the same amplifier chain (for example, a situation in which some of the amplifiers of optical amplifier system 1200 are in the optical amplifier system 1 205), then the distinct w avelengths can be used to adjust a relative gain between the two beams 1 135 A, Π 35Β even though they are traversing through the same amplifiers.

For example, the beams 1 135 A . 1 135B, once separated, could be steered or focused to two separate locations ( such as the first and second target locations 1 122 A, 1 1 22 B, respectively) within the chamber 175. In particular, the separation of the beams 1 135A, 1 I 35B also enables the target 1 1 10 to expand after interacting with the beam of preliminary radiation pulses 1 1 35 A while it travels from the first target location 1 1.2.2 A to the second target location .1 1 22B.

The optical source 1240 can include a beam path combiner 1225 that overlays the beam of preliminary radiation pulses 1 135 A and the beam of main radiation pulses 3 1 35B and places the beams 1 135 A, 1 1 35B on the same optical path for at least some of the distance between the optical source 1240 and the beam delivers' system 185. Additionally, tire optical source 1240 can include a beam path separator 1226 that separates the beam of preliminary radiation pulses 1 Ϊ 35Α from the beam of main radiation pulses 1 135B so that the two beams 1 135A, 1 135B can be separately steered and focused within the chamber 1 75. Additionally, the beam of preliminary radiation pulses 3 135 A can be configured to have !ess pulse energy than the pulse energy of the beam of main radiation pulses 1 S 35B. This is because the preliminary radiation pulse 1 135 A is used to modify the geometry of the present target 1 1 10' while the main radiation pulse 1 1 35B is used to convert the modified present target 1 1 10' into plasma 1 130. For example, the energy of the preliminary radiation pulse 1 135 A can be 5- 100 times less than the energy of the main radiation pulse 1 135B.

In some implementations, each optical amplifier system .1200, 1205 includes a set of three optical amplifiers, though as few as one amplifier or more than three amplifiers can be used, in some implementations, each of the optical amplifiers in each system 1200, .1205 includes a gain medium thai includes CO? and can amplify light at a wavelength of between about 9. ! μηι and about 1 1 .0 pm, and in particular, at about 10.6 tun, at a gain greater than 1000. It is possible for the optical amplifiers in each system 1200, 1205 to be operated similarly or at different wavelengths. Suitable amplifiers and lasers for use in the optical amplifier systems 1200, 1 205 can include a pulsed laser device such as a pulsed gas-discharge CC¾ amplifier producing radiation at about 9.3 μηι or about 10.6 pm, for example, with DC or RF excitation, operating at relatively high power, for example, 10 kW or higher and high pulse repetition rate, for example, 50 kHz or more. Exemplary optical amplifiers that can be used in each of the systems 1 200, 1205 are axial How high-power CC¾ lasers with wear-free gas circulation and capacitive RF excitation.

Additionally, though not required, one or more of the optical amplifier systems 1200 and

1205 can include a first amplifier that acts as a pre-amplifier. The pre-amplifier, if present, can. be a diffusion -cooled CO? laser system.

The optical amplifier systems 1200, 1.205 can include optical elements that are not shown in Fig. 12 for directing and shaping the respective light beams 121 1 , 1216. For example, the optical amplifier systems 1200, 1205 can include reflective optics such as mirrors, partially- transmissive optics such as beam splitters or paitially-ttansmissive mirrors, and dichroic beam splitters.

The optical source 1240 also includes an optical system 1220 that can include one or more optics (such as reflective optics such as mirrors, partially reflective and partially transmissive optics such, as beamsplitters, refractive optics such as prisms or lenses, passive optics, active optics, etc.) for directing the light beams 12 TL 1216 through the optical source 1240.

Although the optical amplifiers can be separate and dedicated systems, it is possible for at least one of the amplifiers of the optical amplifier system 1200 to be in the optical amplifier system 1205 and for at least one of the amplifiers of the optical ampli fier system 1205 to be in the optical amplifier system 1200. In such a system in which at least some of the amplifiers and optics overlap between the optical amplifier systems 1200, 1.205, it is possible that the beam of preliminary radiation pulses 1 135 A and the beam of main radiation pulses 1 135B are coupled together such that changes of one or more characteristics of the beam 1 135A can cause changes to one or more characteristics of the beam 1 135B. and vice versa.

Referring to Fig. 13, a procedure 1300 is performed by the EUV light source 100 (under control of the control system 170, 470, 670 or 870) for compensating for plasma pushback forces 125 on a present target 1 10'. Other procedures not discussed herein can be performed by the EUV light source 100 during operation. The procedure 1300 includes forming the remaining plasma 130 that at least partially coincides with the extended target region 1 .15, the remaining plasma being a plasma formed from an interaction between a prior target i iOP and a prior radiation pulse I35P in a target space 120 ( 1305). As shown in Figs. 14A and I 4FJ, the prior target 1 I OP is approaching the target location 122 as the prior radiation pulse 335P is

approaching the target location 122. After the prior radiation pulse 135P and the prior target 1 10P have interacted, the remaining plasma 130 is formed and plasma pushback forces 125 are- produced, as shown in Figs. 15 A and 156.

The current target i 10 is released from the target delivery system 145 along the trajectory TR toward the target space 120 ( 1.310). The current target 1 10 can be released (1310) prior to the remaining plasma 130 being formed from the interaction between the prior target 1 1 OP and the prior radiation pulse 135P ( 1305). For example, as shown in Figs. 14A and 14B, the current target 1 10 has been released from the target delivery system 145 along the trajectory TR toward the target space 120 ( 1310).

One or more moving properties of the current target i 30 (when the current target 1 10 is within the extended target region 1 15) are determined ( 1.315). The moving property of the current target can be determined ( 1 315) by detecting a first interaction between a first diagnostic light beam (such as beam 320) and the current target 1 10 at a first location (such as location 322} within the extended target region .1 I 5, detecting a second interaction between a second diagnostic light beam (such as beam 330) and the current target J 10 at a second location (such as location 328) within the extended target region 1 15. The first diagnostic light beam ( such as beam 320) is directed toward the current target I I 0 at the first location (such as location 322)., and the second diagnostic light beam (such as beam 330) is directed toward the current target 1 10 at the second location (such as location 328).

The first interaction can be detected (for example, at the detection module 335 ) by- detecting at least a portion of the first diagnostic light beam (such as light beam 320) that is reflected from the current target (for example, the light 340 is detected). The second interaction can be detected (for example, at the detection module 335) by detecting a portion of the second diagnostic light beam (such as light beam 33) that is reflected from the current target 1 10 (for example, the light 350 is detected) by the detection module 335. The moving property or properties of the current target 1 10 can be determined ( 1315) based on these detections of the reflected portions.

For example, with reference to Figs. 16A- 1.7B, the diagnostic system 305 is used in combination with the control system 170, 470, 670, 870 to determine the one or more moving properties of the current target 1 10. In Figs, 16Λ and I6B, the current target 1 10 interacts with the diagnostic light beam 320, and the light 340 from that interaction is detected by the detection module 335. In Figs. 1 7A and Γ7Β, the current target 1 10 then interacts with the diagnostic light beam 330, and the light 350 from that interaction is detected by the detection module 335. The detection module 335 outputs the data to the control system 170, 470, 670, 870 for processing, as discussed above, to determine the one or more moving properties of the current target 1 10.

The control system 170, 470, 670., 870 determines whether any of the determined moving properties are outside of an acceptable range ( 1320). If any of the moving properties is out of an acceptable range (1320), then the control system .! 70, 470, 670, 870 adjusts one or more characteristics of the radiation pulse 135 (for example, one or more characteristics of one or more of the preliminary radiation pulse 1 135A and the main radiation pulse 1 135B) to thereby control a relative position between the radiation pulse 135 and the present target 1 10 ^J based on the determined moving property or properties of the current target ! 10 ( 1325). The radiation pulse 135 ( which may have been adjusted at 1325) is directed toward the target space 120 so that the radiation pulse 135 and the present target 110 ^* interact in the target space 120 (1330), For example, as shown in Figs. I SA and I SB, the present target 1 10' is approaching the target location 122 within the target space 120 and the adjustments have been made to the radiation pulse 135, which is also directed toward the target location. And, as shown in Figs. 1 9A and 19B. the present target 1 10' is interacting with the current radiation pulse 135 at the target location 1 22.

The moving property or properties that can be determined ( 1315) include one or more of a speed, velocity, direction, acceleration, or location of the current target 1 10 along any of the directions X. Y. or Z of the three dimensional coordinate system.

In some implementations, such as shown in Fig. i I , the radiation pulse 135 can be a preliminary radiation pulse 1 135A that delivers the energy to the present target 1 10' to modify a geometric distribution of the present target 1 S 0\ If this occurs, then the procedure 1300 can also include, after directing the current preliminary radiation pulse ί 1 35A toward the present target 1 1 0 ^' , directing a main radiation pulse 1 135B toward the present target 1 10' to thereby convert at least part of the present, target 1 10' into plasma that emits EUV light 1 1 50. Figs . 19C and 19D show the interaction between the main radiation pulse 1 1 35B and the present target 1 10' to produce the EUV light. 1 150.

The procedure 1300 can also include analyzing the one or more moving properties that were determined (1 31 5 ). For example, the control system 170, 470, 670, 870 can determine the velocity of the current target 1 10 along the -X direction and predict when the present target 1 1 0' will reach the target location 122. The control system 1 70, 470, 670, 870 can adjust when the radiation pulse 135 is released or it can adjust the direction of the radiation pulse 135 so that the radiation pulse 135 and the present target 1 10' efficiently interact at the target location 122 ( 1.325). This adjustment to the relati ve position between the radiation pulse 135 and the present target 1 10' is therefore based on the analysis of the determined moving property of the current target 1 10.

As also shown in Fig. 19C, the next current target 1 I ON is released at a point in. time in. accordance with the rate at which the targets 1 10 are released from the target delivery system 145.

In some implementations, the acceleration A of the current target 1 10 can be determined { 1 3 15) as well as the velocity V . In such implementation, the determination (13 15 ) would additionally include detecting a third interaction between a third diagnostic light beam and the current target ai a third location within the extended target region, the third location being distinct from the first and second locations. For example, as shown in Figs. 20A and 20B, the current target 1 10 is directed toward the target space 120, and, while in the extended target region 1 15, the current target 1 10 would interact sequentially with the diagnostic light beams 720, 725, 730 at respective locations 722, 724, 728. As discussed above, the resultant light 740, 745. 750 is detected by the detection module 735, which outputs data that is analyzed by the control system 1 70, 470, 670, 870, which can. use the data to determine the acceleration A as well as the velocity V of the current target 1 10. Additionally, the control system 170, 470, 670, 870 can use the additional information obtained from the interaction between the current target 1 10 and the third diagnostic beam 725 to determine one or more moving properties of the current target 1 10 along a direction (such as the Y direction) perpendicular to the -X direction.

Other implementations are w ithin the scope of the following claims.

In other implementations, the moving property of the current target 1 10 that is detected is a speed of the current target 1 .10, a direction or trajectory of the current target 1. 10, and an acceleration of the current target 1 10.