INSPECTION

CROSS REFERENCE TO RELATED APPLICATIONS

[001] This patent application claims priority of US provisional patent application No. 61/693,727 filed August 27, 2012, the application is incorporated herein by reference.

FIELD OF THE INVENTION

[002] The present invention relates an object carrier for back light inspection of transparent or semitransparent objects.

[003] The invention relates as well to a system for back light inspection of transparent or semitransparent objects.

[004] Additionally the invention relates to a method for back light inspection.

BACKGROUND OF THE INVENTION

[005] Back light illumination is typically used to detect defects in non-transparent parts of transparent wafers like e.g. finger cuts in LED wafers.

[006] Figure 1 shows a schematic representation of a prior art system 1 for generating back light inspection of transparent or semitransparent objects 2 according to a first concept. A light source 6 is part of an object carrier 10 for the transparent or

semitransparent object 2. The light source 6 is covered with a transparent plate 11 so that the light 5 from the light source 6 reaches the transparent or semitransparent object 2. Only a portion of light 7 of the light source 6 reaches an optical system 8. From there portion of light 7 reaches a sensor 12. The light source 6 is mounted on a stage 9 which is able to position the transparent or semitransparent object 2 with respect to the optical arrangement 8. The size of the light source 6 needs to be at least equal to the size of the transparent or semitransparent object 2. Due to heat dissipation and power requirements the output of the light source 6 and the inspection speed is limited. Since the size of the transparent or semitransparent objects 2 increases, the heat dissipation of the light source 6 increases too. Furthermore, as shown in figure 1 the illumination is insufficient, since most of the light 5 is not captured by the optical arrangement 8. Another problem is that a part of the transparent or semitransparent object 2 is illuminated with a different part of the light source 6. This will result in different image brightness for different parts of the transparent or semitransparent object 2. The movement of the light source 6 and the transparent or semitransparent object 2 is limited due to the cabling (not shown) of the light source 6.

[007] A schematic representation of another a prior art arrangement for back light inspection is shown in Figure 2. Here the light source 6 is not part of the object carrier 10. In this case the light source 6 for back light illumination is a fixed light source 6. The transparent or semitransparent object 2 moves between the light source 6 for back light illumination and the optical system 8. The stage 9 and the carrier 10 need to be designed in such a way that that movement is not blocked by the fixed light source 6. The size of the light source 6 needs to be at least equal to the size of the largest field of view of the optical system 8. The design of the stage 9 is complex in order to enable movement of the carrier 10 and the transparent or semitransparent object 2 around the light source 6. The carrier 10 and the transparent or semitransparent object 2 cannot be supported at the center since this space is taken by the light source 6. The associated bending of the carrier 10 and the transparent or semitransparent object 2 will lead to different focus positions at different locations on the transparent or semitransparent object 2 and image distortion in general.

SUMMARY OF THE INVENTION

[008] It is an object of the invention to provide object carrier for back light inspection of transparent and/or semitransparent objects, which avoids the problems of prior art object carriers.

[009] The above object is achieved by an object carrier for back light inspection of objects comprising:

• a carrier base; and

• a layer with photo luminescent properties for carrying a transparent or semitransparent object on top of the layer. [0010] A further object of the invention is to provide a system for back light inspection of transparent and/or semitransparent objects, which avoids the problems of prior art systems for back light inspection.

[0011] The above object is achieved by a system for back light inspection of transparent or semitransparent objects comprising:

• an object carrier with a carrier base and a layer with photo luminescent

properties;

• at least one light source being arranged above the object carrier such that excitation light emitted from the at least one light source is directed through the transparent or semitransparent object to the layer with photo luminescent properties;

• an optical system, which is adapted to capture emission light emitted from the layer with photo luminescent properties and travelled through the transparent or semitransparent object; and

• a sensor for registering the light captured by the optical system.

[0012] An additional object of the invention to provide a method for back light inspection for transparent and/or semitransparent objects, which avoids the problems of the inspection methods carried out with prior art systems for back light inspection.

[0013] The above object is achieved by a method for back light inspection which comprises the following steps:

• directing at least one illumination light beam with an excitation waveband of λ _α ± Αλ _^ through a transparent or semitransparent object onto a layer with photo luminescent properties;

• capturing light emitted with an emission waveband of _em ± Al _em from the layer with photo luminescent properties and travelled through the transparent or semitransparent object; and

• generating an image from the light with the emission waveband _em ± Al _em and wherein A _em ± AA _em ≠ ± Αλ _^ .

[0014] The object carrier can have as well the form of a wafer chuck and the transparent or semitransparent object is a transparent or semitransparent wafer. The layer with photo luminescent properties of the object carrier is composed of a bulk layer with photo luminescent properties that can have a reflective coating at the side of layer which faces the carrier base. The excitation illumination forces the layer with photo luminescent properties to emit light in a different wave length. According to a preferred embodiment, the bulk layer with photo luminescent properties is a porous layer. The reflective coating on one side of the bulk layer can be an aluminum coating.

[0015] A vacuum means, which is mounted to the porous bulk layer, insures that the transparent or semitransparent object is fixed to the object carrier or chuck. The vacuum is applied to the object through pores and micro holes of the bulk layer, respectively.

[0016] According to another embodiment of the invention the layer with photo luminescent properties is composed of a glass plate with a photo luminescent coating. The photo luminescent coating can be covered with a reflective coating while the reflective coating faces the carrier base. Preferably, the reflective coating is an aluminum coating and the photo luminescent coating is made of phosphor.

[0017] In this embodiment, also vacuum means is mounted to the glass plate so that a vacuum can be applied to the object trough micro holes or micro grooves of the glass plate.

[0018] A size and shape of the layer with photo luminescent properties are at least equal to a size and shape of the transparent or semitransparent object. Furthermore, the layer with photo luminescent properties has a plurality of pin lifting holes, wherein each pin in the pin lifting holes is made of the same photo luminescent material or material composition as the layer with photo luminescent properties.

[0019] The at least one light source of the system being arranged above the object carrier such that excitation light emitted from the at least one light source is directed through the transparent or semitransparent object to the layer with photo luminescent properties. The excitation waveband of λ _α ± Αλ _^ can be generated by a light source that emits this waveband directly, or can be generated by a broadband emitting light source where a filter is applied to. The sensor (camera) is configured such that a registered image is defined by an emission waveband _em ± Α _^ and wherein _em ± A/t _em ≠ λ _α ± Α _^ . The layer with photo luminescent properties converts the excitation waveband of λ _α ± Α _^ into the emission waveband ± A _em where _em > ± Αλ _^ or _em < ± Αλ _^ . At least one optical filter is arranged prior to the sensor, so that only light of the emission waveband _em ± Al _em reaches the sensor. According to a further embodiment, the sensor is insensitive to the excitation waveband of λ _α ± Αλ _^ and sensitive to at least a portion of the emission waveband _em ± Al _em .

[0020] The sensor can be configured in the form of an area scan camera, a line scan camera or a time delay integration line scan camera.

[0021] There are several possibilities to carry out the illumination of the transparent or semitransparent object and the layer with photo luminescent properties. Firstly, the excitation light emitted by the at least one light source travels through the optical system to the layer with photo luminescent properties. Secondly, the excitation light emitted by the at least one light source travels outside the optical system to the layer with photo luminescent properties. Thirdly, the excitation light emitted by the at least one first light source travels through the optical system to the layer with photo luminescent properties and the excitation light emitted by the at least one second light source travels outside the optical system to the layer with photo luminescent properties.

[0022] The at least one first and/or second light source are configured as a lamp or a combination of lamps, as an LED or a combination of LEDs or as a laser or a combination of lasers.

[0023] The optical system of the system has at least one microscope objective and at least one optical filter so that only light with an emission waveband of ± AA _em from the layer with photo luminescent properties reaches the sensor. The microscope objective defines a beam path. A dichroic beam splitter is arranged in the optical system such that light from the at least one first light source with the excitation waveband of λ _α ± Αλ _^ is coupled into the beam path of the microscope objective. According to a different embodiment, the microscope objective defines a beam path and the light from the at least one further light source with the excitation waveband of λ _α ± Αλ _^ defines an illumination beam path which is different from the beam path of the microscope objective. Combinations of the above described embodiment are possible as well. [0024] An embodiment of the inventive system for back light inspection of transparent or semitransparent objects comprising:

• an object carrier with a carrier base and a layer with photo luminescent properties;

• a microscope objective, defining a beam path;

• at least one first light source, wherein illumination light, with an excitation waveband of λ _α ± Αλ _^ , from the at least on light source is directed via the beam path of the microscope objective onto the object carrier such that illumination light emitted from the at least one light source passes through the transparent or semitransparent object to the layer with photo luminescent properties; and

• a sensor is arranged such that only light of the emission waveband ± AA _em reaches the sensor, wherein the light travels through the transparent or semitransparent object and is captured with the microscope objective.

[0025] A further embodiment of the inventive system for back light inspection of transparent or semitransparent objects comprising:

• an object carrier with a carrier base and a bulk material layer with photo

luminescent properties which is coated at the side of the carrier base with a reflective coating;

• a microscope objective, defining an illumination beam path;

• at least one first light source, wherein illumination light, with an excitation

waveband of λ _α ± Α _^ , form the at least on light source is directed via the beam path of the microscope objective onto the object carrier such that illumination light emitted from the at least one light source passes through the transparent or semitransparent object to the layer with photo luminescent properties; and

• a sensor is arranged such that only light of the emission waveband A _em ± AA _em reaches the sensor, wherein the light travels through the transparent or semitransparent object and is captured with the microscope objective.

[0026] An improvement over the prior art is that the light source is not located in the chuck base or object carrier base. Therefore no heat generation takes place below the wafer or the transparent or semitransparent object to be inspected. Accordingly, stronger light sources can be used without affecting the wafer or the transparent or semitransparent object. This leads to higher inspection speeds and an increased throughput. Furthermore, only the inspection spot of the wafer or the transparent or semitransparent object is illuminated which leads to higher efficiency. The homogeneity is improved because only one light source is used instead of an array of different LED's. In case bigger wafer sizes need to be inspected with back light there is only the requirement for a bigger chuck. The light source can stay the same. In case of the prior art design the number of LED's needs to be increased too. A vacuum can be applied through pores or micro holes/grooves of the object carrier, which do not affect the image. Vacuum holes in the prior art design would affect image quality.

[0027] The inventive system allows for illuminating at least partially transparent or semi-transparent (non-opaque) objects such as semiconductor wafers from one side in order to capture the transmitted light from the other side of the object. The light source illuminating the object, the object placed in front of layer with photo luminescent properties. A microscope optic and a camera capture the inspection image.

[0028] The invention allows wafer manufacturers to increase wafer quality and yield. Back light inspection makes defects visible which are otherwise not detectable. The wafer size does not influence the inspection speed which allows the concept to grow together with the customers wafer size.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which

[0030] Figure 1 is a schematic representation of a prior art arrangement for back light inspection;

[0031 ] Figure 2 is a schematic representation of another embodiment of a prior art arrangement for back light inspection;

[0032] Figure 3 is a schematic representation of one inventive embodiment for the back light inspection of objects; [0033] Figure 4 is a schematic representation of a further inventive embodiment for the back light inspection of objects;

[0034] Figure 5 is a schematic representation of an alternative for the illumination in order to achieve the back light illumination of transparent or semitransparent objects;

[0035] Figure 6 is a schematic representation of a system for back light inspection of transparent or semitransparent objects;

[0036] Figure 7 is a schematic representation of another embodiment of the system for back light inspection;

[0037] Figure 8 is a schematic representation of an implementation of the system according to one embodiment of the invention; and

[0038] Figure 9 is a schematic representation of an implementation of the system according to a further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0039] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail to not unnecessarily obscure the present invention. While the invention will be described in conjunction with the specific embodiments, it will be understood that it is not intended to limit the invention to the embodiments.

[0040] Same reference numerals refer to same elements throughout the various figures. Furthermore, only reference numerals necessary for the description of the respective figure are shown in the figures. The shown embodiments represent only examples of how the invention can be carried out. This should not be regarded as limiting the invention.

[0041] Figure 3 is a schematic representation of one inventive embodiment for the back light inspection of transparent or semitransparent objects 2. The transparent or semitransparent object 2 rests on a layer 22 with photo luminescent properties. The layer 22 is composed of a bulk layer 24, having the photo luminescent properties; with a reflective coating 26 at the side of layer 22 which faces the carrier base 18 (see Figures 6 - 8). Opposite to the transparent or semitransparent object 2 an objective lens 25 is arranged. The objective lens 25 can be a microscope objective. Excitation light 30 is emitted from the at least one light source (not shown) and directed via the objective lens 25 to the transparent or semitransparent object 2. The excitation light 30 passes through the transparent or semitransparent object 2 and reaches the bulk layer 24 with photo luminescent properties. In the bulk layer 24 emission light 32 is generated which travels through the transparent or semitransparent object 2 and is captured by the objective lens 25.

[0042] . The embodiment shown in Fig. 3 shows a vacuum means 20, which is mounted to the porous bulk layer so that a vacuum is applied to the object through micro pores 29 of the bulk layer 24. With the application of vacuum the transparent or semitransparent object 2 (wafer) is in firm contact with the layer 22 with photo luminescent properties. In order to facilitate the removal of the transparent or semitransparent object 2, the layer 22 with photo luminescent properties has pin lifting holes 31 and lifting pins 34. The top of the lifting pins 34 is made of the same photo luminescent material as the layer 22 with photo luminescent properties to limit the disturbance of the image.

[0043] Figure 4 shows a schematic representation of an additional inventive embodiment for the back light inspection of transparent or semitransparent objects 2. Here the layer 22 with photo luminescent properties is composed of a glass plate 27 with a photo luminescent coating 28. The material of the photo luminescent coating 28 could be phosphor. The photo luminescent coating 28 is covered with a reflective coating 26 on the coating which faces the carrier base 18 (see Figures 6 - 8). In the embodiments shown in Fig. 3 and Fig. 4 the reflective coating 26 is made of aluminum. Excitation light 30 is emitted from the at least one light source (not shown) and directed via the objective lens 25 to the transparent or semitransparent object 2. The excitation light 30 passes through the transparent or semitransparent object 2, the glass plate 27 and reaches the photo luminescent coating 28. With the luminescent coating 28 emission light 32 is generated which travels through the glass plate 27 and the transparent or semitransparent object 2 and is captured by the objective lens 25. In case the luminescent coating 28 is a phosphor coating the excitation light 30 covers a waveband from ultraviolet to blue and the emission light 32 covers a waveband from green to red.

[0044] In Figure 5 an additional illumination concept for the layer 22 with photo luminescent properties is shown. The layer 22 with photo luminescent properties is identical with the layer 22 shown in Fig. 3. The excitation light 30, having waveband in the ultraviolet region, is emitted from the at least one light source (not shown) and directed via the objective lens 25 to the transparent or semitransparent object 2. The excitation light 30 passes through the transparent or semitransparent object 2 and reaches the bulk layer 24 with photo luminescent properties. Additionally, at least one further light source 60 is provided, which directs its excitation light 62 in the green waveband and/or blue waveband through the transparent or semitransparent object 2 to the bulk layer 24 with photo luminescent properties In the bulk layer 24 emission light 32 is generated which travels through the transparent or semitransparent object 2 and is captured by the objective lens 25.

[0045] Figure 6 is a schematic representation of an embodiment of the inventive system 1 for back light inspection of transparent or semitransparent objects 2. The transparent or semitransparent object 2 is positioned on a stage 9 for moving the transparent or semitransparent object 2 along an X-coordinate direction X and a Y-coordinate direction Y. The stage 9 enables the positioning of various sections of the transparent or semitransparent object 2 in the excitation light 30 emitted by the at least one light source 6. The excitation light 30 exits the light source 6 and enters the optical system 8 and from the optical system 8 the excitation light 30 reaches, via the microscope objective 25 (see Fig. 3 to 5) and the transparent or semitransparent object 2, the layer 22 with photo luminescent properties. The excitation light 30 reaches with a waveband of λ _α ± Αλ _^ layer 22 with photo luminescent properties. From the layer 22 with photo luminescent properties light 32 with an emission waveband of _em ± Αλ _^ reaches the optical system 8 and the associated sensor 12. The sensor 8 is configured such that a registered image is defined by an emission waveband _em ± Α _^ and wherein _em ± Δλ _βιη ≠ λ _α ± Α _^ .

[0046] A further embodiment of the inventive system 1 is shown in Figure 7. A further light source 60 is arranged such that the excitation light 62 emitted by the further light source 60 travels outside the optical system 8 via the transparent or semitransparent object 2 to the layer 22 with photo luminescent properties. The microscope objective 25 of the optical system 8 defines a beam path 25B and the light from the at least one further light source 60 with the excitation waveband of λ _α ± Αλ _^ defines an

illumination beam path 60B which is different from the beam path 25B of the microscope objective 25 (see Fig. 3 to 5). As already mentioned in the description of Fig. 8, the sensor 8 is configured such that a registered image is defined by an emission waveband _em ± Al _em of the emission light 32 exiting the layer 22 with photo luminescent properties through the transparent or semitransparent object 2 and wherein ± Αλ _^ ≠ _ex ± Αλ _^ . A combination of the embodiments shown in Fig. 6 and 7 is possible as well. Here the light 30 from the light source 6 is coupled into the beam path 25B and the light 62 from the at least one further light source 60 is coupled with the excitation waveband of λ _α ± Αλ _^ in the illumination beam path 60B which is different from the beam path 25 B.

[0047] Figure 8 is a schematic representation of an implementation of the system 1 according to one embodiment of the invention. The layer 22 with photo luminescent properties is on a carrier base 26 and the carrier base 26 is positioned on the stage 9. Here one light source 6 is arranged above the transparent or semitransparent object 2. The excitation light 30 emitted from the light source 6 is directed through the transparent or semitransparent object 2 to the layer 22 with photo luminescent properties. As mentioned above the microscope objective 25 (see Fig. 3 to 5) defines the beam path 25B. A dichroic beam splitter 40 is arranged in the optical system 8 such that light from the light source 6 is coupled into the beam path 25 B with the excitation waveband of λ _α ± Αλ _^ . In front of the sensor 12 at least one optical filter 42 is arranged prior to the sensor so that only light 32 of the emission waveband _em ± Al _em reaches the sensor 12. According to a further embodiment, not shown, the sensor 12 is insensitive to the light 30 of the excitation waveband of λ _α ± Αλ _^ and only sensitive to at least a portion of the emission waveband _em ± A _em .

[0048] The light 32 returning from the layer 22 with photo luminescent properties contains the emission waveband _em ± Al _em and light 34 returning from the layer 22 with photo luminescent properties contains as well the excitation waveband λ _α ± Αλ _^ , wherein _em ± A _em ≠ λ _α ± Αλ _^ . The dichroic beam splitter 40 let a portion of the light 34 with the excitation waveband λ _α ± Αλ _^ pass and as mentioned above this portion is blocked by the optical filter 42 so that it does not reach the sensor 12. On the other hand a portion of the light 34 with the excitation waveband λ _α ± Αλ _^ is reflected by the dichroic beam splitter 40 back into the light source 6.

[0049] In case the light source 6 in Fig. 8 emits blue light with a wavelength of 460nm, the dichroic beam splitter 40 in the optical system 8 (microscope) has a cut-on at the wavelength of 514 nm. This light 30 shines through the transparent or semitransparent object 2 (wafer) on the layer 22 with photo luminescent properties. The layer 22 with photo luminescent properties layer emits white light 32 which is sent to the sensor 12 (camera) through the dichroic beam splitter 40 and a high pass filter 42 which has a cut on a wavelength of 514 nm.

[0050] Figure 9 is a schematic representation of an implementation of the system 1 according to a further embodiment of the invention. Here in addition to the light source 6 (excitation light in the UV region) two further light sources 60 are provided. The two further light sources 60 are arranged such that an excitation light 62 from the further light sources 60 travels outside the optical system 8 via the transparent or

semitransparent object 2 to the layer 22 with photo luminescent properties. The number of further light sources 60 shown in this embodiment should not be regarded as limiting the scope of the invention. It is clear for a skilled person that the number of further light sources 60 can be selected according to the inspection requirements.

[0051] In case the further light source 60 is a ring light with an excitation light in the green light region it might be worthwhile to use a different set of filters to have the range UV - green available as excitation wavelengths. The emission filter should only transmit the red. This will block the blue response from the transparent or semitransparent object 2.

[0052] The invention has been described with reference to specific embodiments. It is obvious to a person skilled in the art, however, alterations and modifications can be made without leaving the scope of the subsequent claims. Reference numerals