[0001] This application claims priority to United States Application Serial No.

62/366,847, filed July 26, 2016 and to United States Application Serial No. 62/394,828, filed September 15, 2016, both of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

[0002] The present disclosure is related to the field of capillaries, more specifically to the field of capillaries suitable for use in droplet generators, which droplet generators are suitable for use in lithographic systems,

DESCRIPTION OF RELATED ART

[0003] As is taught in United States Patent Publication No. US 2015/0293456 Al, entitled "Droplet Generator, EUV Radiation Source, Lithographic Apparatus, Method For Generating Droplets And Device Manufacturing Method", the contents of which are incorporated herein by reference in their entirety, droplet generators generally include a capillary. The capillar}' is generally a tube-like structure having a nozzle at a first end portion thereof, and which is in fluid communication with a reservoir of molten material at an opposite, second end portion. The molten material in the reservoir flows into the second end portion of the capillary and toward the nozzle, and the nozzle generates the formation of droplets of molten material. As noted in the foregoing publication, the capillary is formed of glass and has the following approximate dimensi ons: length of approximately 15-50 millimeters, inner diameter of approximately 0.5 to 0.7 mi llimeters, and wall thickness of approximately 0.15 to 0.25 millimeters. These types of capillaries, however, have suffered from a number of issues. For example, under increased pressures, the capillaries (and thus the droplet generators) may be subject to undesired movement with respect to the reservoir. While attempts have been made to design capillaries that overcome this and other issues, no acceptable solution has yet been provided, primarily due to the extremely small size of the capillar}' and the specific material used to form same. Consequentially, further improvements to the design of capillaries for droplet generators would be appreciated by certain individuals.

SUMMARY

[0004] A capillary includes a main portion with a first aperture and an end portion that is enlarged with a second aperture. The end portion acts as a stop to aid in retaining the capillary in a desired position under increased pressures. The second aperture can be a uniquely sized/shaped aperture for receiving molten material therein and can have funnel characteristics. Advantageously, the entire capillary, including the end portion, is formed as a single piece of material, which is preferably a manufactured glass, such as quartz, and more preferably fused silica. The second aperture tapers from a larger inner diameter to a smaller inner diameter. The second aperture joins to the first aperture and thus allows the smaller inner diameter to join with an inner diameter of the first aperture.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The current disclosure is illustrated by way of example and not limited in the accompanying figured in which like reference numerals indicate similar elements and in which;

[0006] FIG. 1 illustrates a cross-section of an embodiment of a capillary .

[0007] FIG. 2 illustrates an enlarged view of the embodiment depicted in FIG. 1.

[0008] FIG. 3 illustrates a cross section of an embodiment of a capillary in a droplet generator.

DETAILED DESCRIPTION

[0009] The detailed description that follows describes exemplary embodiments and is not intended to be limited to the expressly disclosed combination(s). Therefore, unless otherwise noted, features disclosed herein may be combined to fonn additional combinations that were not otherwise shown for purposes of brevity.

[0010] FIGS. 1-3 illustrate a capillary 20. The capillary 20 has first and second opposite ends 22, 24. The capillary 20 has a main portion 26 (which is sometime referred to as ferrule) and an end portion 28 that is enlarged. The main portion 26 extends from the first end 22 to the end portion 28 and the end portion 28 extends from the main portion 26 to the second end 24. The main and end portions 26, 28 are integrally formed, such that the capillary is monolithic and the material used to form the capillary 20 is continuous throughout the main and end portions 26, 28, In a preferred embodiment, the material used to form the capillar}' 20 is a manufactured glass, preferably quartz, and more preferably fused silica. [0011] The main portion 26 of the capillar}' 20 is generally an elongated tube-like structure, having an outer cylindrical wall 30 having a diameter ODl and an inner cylindrical wall 32 having a diameter ID1. The inner cylindrical wall 32 defines an aperture 34 of the main portion 26 of the capillary 20. The inner cylindrical wail 32 may be formed with a nozzle (not shown) proximate to the first end 22. Diameter ID of the inner cylindrical wall 312 is preferably in the range of 0.001 mm to 10.0 mm.

[0012] The end portion 28 (or inlet flare) of the capillary 20 is flared/knobbed such that an outer wall 36 of the end portion 28 has a diameter OD2 at the second end 24 that is larger than the diameter ODl of the main portion 26. In a preferred embodiment, the diameter OD2 can be as large as ten times the diameter ODl . In a preferred embodiment, the outer wall 36 of the end portion 28 is curved, such that the outer wall 36 of the end portion 28 takes on a generally semi -spherical configuration, although it is to be understood that the outer wall 36 of the end portion 28 could have any other suitable configuration, such as, for example, an angled configuration, a square configuration, an oval configuration, or a triangular configuration.

[0013] The end portion 28 of the capillary 20 further defines an inner wall 38. The inner wall 38 defines an aperture 40 of the end portion 28 which is in communication with the aperture 34 of the main portion 26. The inner wall 38 is preferably conical in configuration and thus tapers from a wider opening to a narrower opening. While the depicted

configuration has a linear taper it is to be understood that the inner wall 38 of the end portion 28 could have any other suitable configuration, such as, for example, a curved configuration.

[0014] The inner wall 38 of the end portion 28 has a diameter ID2' at the second end 24 of the capillary 20. In a preferred embodiment, the diameter ID2' is larger than the diameter ID1 of the main portion 26. The inner wall 38 of the end portion 28 has a diameter ID2" where the aperture 40 meets the aperture 34. Diameter ID2' is preferably equal to or greater than diameter ID2". The diameter ID2" is preferably smaller than the diameter ID1 of the main portion 26, such that a shoulder 42 is defined between the inner wall 32 of the main portion 26 and the inner wall 38 of the end portion 28, however, diameter ID2" could be larger than the diameter ID1 of the main portion 26, such that the shoulder 42 would be provided as part of the aperture 40. The minimum diameter ID2" can be of any diameter to create the aperture 40 that is separate from the outer wall 36 of the end portion 28. As best illustrated in FIG. 2, the location where the inner walls 32, 38 are joined (e.g., at the position of the shoulder 42) may be off-set as compared to the location where the outer walls 30, 36 are joined, with the location where the inner walls 32, 38 are joined is positioned closer to the first end 22 and the location where the outer walls 30, 36 are joined is positioned closer to the second end 24. In view of the foregoing, it is to be understood that the general boundaries of the first and end portions 26, 28 as defined herein are not exact.

[0015] In a preferred embodiment, a wall thickness Tl of the main portion 26 (the distance between the diameter OD1 and the diameter ID1) is less than or equal to a wall thickness T2 of the end portion 28 at the second end 24 (the distance between the diameter OD2 and the diameter ID2'). Furthermore, in a preferred embodiment, the wall thickness Tl of the main portion 26 is always less than or equal to the wall thickness T2 of the end portion 28 along an entire length of the end portion 28 to provide additional structure support. As can be appreciated from FIG. 1 , the aperture 34 is substantially longer than the aperture 40 and while no precise value is required, the aperture is generally expected to be at least four times longer than the aperture 40.

[0016] As illustrated in FIG. 3, the capillary 20 is preferably provided as a part of a droplet generator 60. The droplet generator 60 may include an actuator 62 which surrounds a part (preferably a part of the main portion 26) of the capillary 20 and a controller 64 which is connected to the actuator 62. The controller 64 controls the actuator 62 according to a driving frequency. The general structure and function of the actuator 62 and controller 64 are described and illustrated in United States Patent Publication No. US 2015/0293456 Al, the contents of which are hereby incorporated by reference herein in their entirety,

[0017] The capillary 20 of the droplet generator 60 is preferably secured in place relative to a reservoir 82 formed as a part of a lithographic apparatus 80. The reservoir 82 is configured to house molten material therein. The aperture 40 of the end portion 28 of the capillary 20 is in communication with the reservoir 82 such that molten material from within the reservoir 82 can flow into the aperture 40 of the end portion 28 of the capillar}' 20 and, thereafter, flow into the aperture 34 of the main portion 26 of the capillary 20 and, thereafter, flow/drip/drop out of the aperture 34 of the main portion 26 of the capillar}' 20 at the first end 22 thereof to form the desired droplets of molten material. The aperture 40 of the end portion 28 of the capillary 20 is generally funnel-shaped so as to aid in the flow of molten material into and through the capillary 20.

[0018] The capillary 20 may be secured in position in any manner desired, and the end portion 28 of the capillar}' 20 is sized and configured to aid in the stability of the capillary 20 in its connection to the lithographic apparatus 80. For instance, as described and illustrated in United States Patent Publication No. US 2015/0293456 AL the end portion 28 of the capillary 20 may be positioned and secured within a stiff housing 84 of the lithographic apparatus 80 such that the aperture 34 of the end portion 28 of the capillary 20 is in communication with the reservoir 82. The end portion 28 prevents, or at least substantially inhibits, push/pull out movement of the capillar}' 20 relative to the reservoir 82 when the capillary 20 is subject to an increased pressure. The end portion 28 is essentially stopped from movement by a wall of the stiff housing 84. It is to be understood that, regardless of the specific configuration of the portion of the lithographic apparatus 80 that holds/secures the capillar}' 20 (and thus the droplet generator 60) in place relative to the reservoir 82, whether it be due to the stiff housing 84 or otherwise, the end portion 28 prevents/inhibits such movement.

[0019] The capillar}' 20 provides for numerous improvements over prior art capillaries. For instance, the capillary 20 is not formed with any weak areas due to the fusion or combination of multiple parts. The internal geometry of the aperture 40 of the end portion 28 (which could also be referred to as the inlet) is expanded compared to prior art capillaries, thus allowing for a funnel characteristic in the final application. The internal geometry of the aperture 40 of the end portion 28 is also expanded compared to prior art capillaries, resulting in a "female" mating end-face geometry that is beneficial for certain applications. The internal geometr' of the aperture 40 of the end portion 28 at diameter ID2" is controllable within a specification of ± 0.025 millimeters, which is important for droplet pulse frequency specification. The length of the internal diameter at the end portion 28 (which can be semi- sphere or knob shaped) to the main portion 26 can be specified. The geometry of the internal diameter at the end portion to main portion is an internal wall structure for a ferrule body chamber. It should be noted that the end portion 28 can have various diameters and geometric shapes, and the internal diameter geometries of the walls that define ID2' and ID2" can be varied in both length and size.

[0020] The embodiments provided herein address certain issues that Applicants have determined exist in existing designs. Numerous other embodiments, modifications and variations will occur to persons of ordinary skill in the art from a review of the disclosure. Thus, various versions of capillaries with various levels of features are possible.