Patent Application
20190331475
The present invention relates to optical inspection of a mask used in lithograph and, more particularly, to a boundary detector used in an optical inspection apparatus.
A mask is a necessary element used in lithography for raking an integrated circuit (“IC”) on the surface of a wafer. The dimension of the wiring in an IC can be made smaller than 10 nanometers. Hence, any contamination on a mask in a process for making IC products could affect the yield of the production.
Referring to
Referring to
However, according to Snell's Law, some of the incident beam Lo (the “beam Lc”) goes through the face 112 and gets refracted, and then reaches a face 111 of the substrate 110. Some of the beam Lc gets reflected from the face 111. Some of the beam reflected from the face 111 gets refracted by the face 112 and becomes secondary reflected beam Lr2. Such a process continues until the beam is too weak to be detected by the photo sensor C.
There are superimposed images because the photo sensor C receives the secondary reflected beam Lr2 or any other beam reflected from the face 111 and refracted by the face 112 in addition to the primary reflected beam Lr1. For example, the contaminant A is on the face 112 of the substrate 110, and the contaminant B is on the face 151 of the pellicle 150. The real state of contamination cannot be detected effectively because the images of the contaminants A and B are superimposed.
The images are processed to determine the real state of contamination. The boundary of the pellicle 150 should be detected to properly process the images. However, it is difficult to use a conventional optical inspection apparatus to detect the boundary of the face 151 of the pellicle 150.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.
It is the primary objective of the present invention to provide an optical inspection machine with a boundary detector for inspecting a laminate that includes a first layer and a second layer that extends below the first layer.
To achieve the foregoing objective, the boundary detector detects a boundary between a transparent plate and a frame. The boundary detector includes a light source, a shield and two beam-adjusting units. The light source emits an original beam. The shield blocks secondary reflected beam and slits the original beam into a middle incident beam and two lateral incident beams. The middle incident beam gets reflected from the transparent plate and becomes a middle reflected beam. The lateral incident beams get reflected from two lateral portions of the frame and become two lateral reflected beam. The beam-adjusting units direct the lateral incident beams. The intensity of the middle reflected beam is different from that of the lateral reflected beams so that the boundary is detected.
Other objectives, advantages and features of the present invention will be apparent from the following description referring to the attached drawings.
The present invention will be described via detailed illustration of the preferred embodiment in view of the prior art referring to the drawings wherein:
As discussed above in the RELATED PRIOR ART referring to
Referring to
The light source 20 casts an incident beam onto the face 112 of the substrate 110 when used to inspect the face 112 of the substrate 110. The incident beam reaches the faces 112 and 111 of the substrate 110 and gets reflected, thereby providing a primary reflected beam and at least one secondary reflected beam. The shield 30 blocks the secondary reflected beam. Later, the primary reflected beam is received by an image sensor 50.
Referring
The light source 20 is inserted in the chamber 11 of the case 10. The light source 20 includes a light emitter 22 inserted in a shell 21. The light emitter 22 provides a beam with a certain width. The light emitter 22 emits visible or invisible light. The light emitter 22 is a halogen lamp, an LED, a high-frequency fluorescent lamp, a metal light bulb, a neon lamp or a laser lamp for example. The image sensor 50 such as CCD and CMOS must be able to detect the beam emitted from the light emitter 22. The shell 21 of the light source 20 is supported on two brackets 25 attached to an internal face of the chamber 11 of the case 10. Each of the brackets 25 includes axial aperture 26 and coaxial arched slot 27. The shell 21 includes an axle 291 inserted in the axial aperture 26. A fastener 292 is inserted in the shell 21 through the arched slot 27. Thus, the shell 21 can be located in various angles relative to the brackets 25. Hence, the light emitter 22 can cast a beam at different angles.
The shield 30 is attached to a lower portion of the case 10 to cover an open lower end of the chamber 11 and an open lower end of the chamber 12. The shield 30 includes an exit 31 in communication with the chamber 11 and an entrance 32 in communication with the chamber 12. The exit 31 is in the form of a slot, and so is the entrance 32. The beam emitted from the light source 20 goes to an inspected face via the exit 31 and gets reflected from the inspected face. The reflected beam goes into the chamber 12 through the entrance 32. Then, the reflected beam goes out of the chamber 12 through the window 18. Finally, the reflected beam reaches the image sensor 50, which is located out of the case 10.
The shield 30 further includes two slots 33, with each of the slots 33 in the vicinity of a corresponding end of the exit 31. The distance between the axis of the exit 31 and that of the slots 33 is identical to the distance between the face 151 of the pellicle 150 and the face 111 of the substrate 110. The slots 33 extend for 5 to 20 mm. The distance between the centers of the slots 33 is identical to a width of the face 151 of the pellicle 150.
The width of the exit 31 is substantially identical to that of the slots 33. The width of the exit 31 and the width of the slots 33 are preferably 0.1 to 5 mm, smaller than that of the entrance 32. The width of the exit 31, the width of the slots 33 and the width of the entrance 32 are smaller than the thickness of the substrate 110.
Preferably, the positions of the exit 31 and the entrance 32 are adjustable. To this end, the shield 30 includes two plates 35 and 36. The exit 31 and the slots 33 are made in the plate 35. The entrance 32 is made in the plate 36. The case 10 further include two planks 39 on two opposite sides of the shield 30. The plates 35 and 36 are movably supported on the planks 39 so that the positions of the plates 35 and 36 are adjustable. Therefore, the angle of the incident beam onto the substrate 110 and the angle of the reflected beam from the substrate 110 are adjustable.
The beam-adjusting units 40 are inserted in the chamber 11, above the shield 30. Each of the beam-adjusting units 40 includes a tab 41, a mount 42, two reflectors 43 and 47, a supporting element 45 and a board 46. The following description will be given to only one of the beam-adjusting units 40 for clarity. The reflectors 43 and 47 guide the beam emitted from the light source 20 through a corresponding one of the slots 33 of the shield 30. The tab 41 is supported on the plate 35, near a corresponding one of the slots 33. The mount 42 is supported on the tab 41. The reflector 43 is connected to the mount 42. The mount 42 includes an axial aperture 421 and an arched slot 422. Two fasteners 426 and 427 are inserted in tab 41 via the axial aperture 421 and the coaxial arched slot 422, respectively. For the use of the axial aperture 421 and the arched slot 427, the angle of the reflector 43 relative to the light emitter 22 is adjustable. The supporting element 45 is supported on the shield 30 so that the corresponding slot 33 is located between the mount 42 and the supporting element 45. The board 46 is movable on the supporting element 45. The reflector 47 is attached to a lower face of the board 46. The reflector 47 reflects the beam reflected form the reflector 43, thereby guiding the reflected beam out of the case 10 via the corresponding slot 33.
Referring to
In the chamber 11, the light emitter 22 emits a beam (the “original beam”). A middle portion of the original beam travels out of the chamber 11 through the exit 31 and becomes a middle incident beam. Two lateral portions of the original beam get reflected by the beam-adjusting units 40 and travel out of the chamber 11 via the slots 33 and become two lateral incident beams.
The middle incident beam is cast on and reflected from the face 151 of the pellicle 150, thus providing a middle reflected beam. Each of the lateral incident beams is cast on and reflected from a lateral portion of the frame 120 and a lateral portion of the face 151 of the pellicle 150, thus providing a lateral reflected beam. The middle and lateral reflected beams enter the chamber 12 through the entrance 32, and then travel out of the chamber 12 via the window 18. Finally, the middle and lateral reflected beams reach the image sensor 50. An image is produced according to the middle and lateral reflected beams. Due to the width of the exit 31 and the entrance 32, not any secondary reflected beam from the face 151 of the pellicle 150 and the face of the frame 120 can enter the chamber 12 via the entrance 32.
The middle incident beam is cast on the face 151 at an angle θ1 and gets reflected from the face 151 at an angle θ2. Each of the lateral incident beams is cast on the corresponding lateral portion of the frame 120 at an angle θ3 and gets reflected from the corresponding lateral portion of the frame 120 at an angle θ4. The angle θ1 is substantially identical to the angle θ2. The angle θ3 is substantially identical to the angle θ4. The angle θ2 is however different from the angle θ4. Hence, the intensity of the middle reflected beam from the pellicle 150 is different from that of the lateral reflected beams from the frame 120.
The image based on the middle and lateral reflected beams includes a middle portion, two lateral portions and two superimposed portions. The middle portion of the image is obtained from the middle reflected beam and only covers the face 151. Each of the lateral portions of the image is obtained from the corresponding lateral reflected beam and only covers the corresponding lateral portion of the frame 12. Each of the superimposed portions of the image is obtained from the middle reflected beam and the corresponding lateral reflected beam and covers the corresponding lateral portion of the face 151 and the corresponding lateral portion of the frame 12. Then, the image is processed to determine the boundary of the face 151 of the pellicle 150. The precise determination of the face 151 is used to obtain the real state of contamination. Hence, the boundary detector increases precision and reduces the risks of misjudgment.
Referring to
The present invention has been described via the illustration of the preferred embodiment. Those skilled in the art can derive variations from the preferred embodiment without departing from the scope of the present invention. Therefore, the preferred embodiment shall not limit the scope of the present invention defined in the claims.
