Method and apparatus for optical inspection of substrates

• US 4,877,326 A
• Filed: 02/19/1988
• Issued: 10/31/1989
• Est. Priority Date: 02/19/1988
• Status: Expired

• Current Assignee: KLA Instruments, Corporation
• Original Assignee: KLA Instruments, Corporation
• Inventors: Fein, Michael E., Bell, William, Chadwick, Curt H., Greene, John D., Harvey, David J., Jann, P. C., Sholes, Robert R., Tucker, Francis D. III
• Primary Examiner(s): McGraw, Vincent P.
• Assistant Examiner(s): TURNER, SAMUEL A
• Application Number:
  US07/158,289
• Time in Patent Office: 620 Days
• Field of Search: 356/394, 356/386, 356/387, 356/237, 356/446, 356/398, 356/448, 358/101, 358/106, 358/107, 396/398
• US Class Current: 356/394
• CPC Class Codes: G01N 2021/8908 Strip illuminator, e.g. light tube
• CPC Class Codes: G01N 2021/95638 for PCB's
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• CPC Class Codes: G01N 21/956 Inspecting patterns on the surface of objects contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/95684 Patterns showing highly reflecting parts, e.g. metallic elements
• CPC Class Codes: G01R 31/311 of integrated circuits G01R31/31728 takes precedence

Abstract

Substrate inspection apparatus and methods, and illumination apparatus. The inspection apparatus and method includes memory for storing the desired features of the surface of the substrate, focussed illuminator for substantially uniformly illuminating a region of the surface of the substrate to be inspected. Additionally there is a sensor for imaging the region of the substrate illuminated by the illuminator, and a comparator responsive to the memory and sensor for comparing the imaged region of the substrate with the stored desired features of the substrate. The illumination apparatus is designed to provide substantially uniform focussed illumination along a narrow linear region. This apparatus includes first, second and third reflectors elliptically cylindrical in shape, each with its long axis substantially parallel to the long axes of each of the others. Fourth and fifth reflectors are also included with each being flat and mounted parallel to each other and at opposite ends of each of said first, second and third reflectors, and first, second and third linear light sources each mounted parallel to a corresponding one of said first, second and third reflectors with each of the light sources mounted so that it is at the first focus of the corresponding reflector and the illuminated linear region is at the second focus of each of the first, second and third reflectors.

Claims

1. Inspection apparatus for inspecting surface features of a substrate comprising:

memory means for storing the desired features of the surface of the substrate;

focussed quasi-Lambertian illumination means for substantially uniformly illuminating a region of the surface of the substrate to be inspected;

sensor means for imaging the region of the substrate illuminated by the illumination means; and

comparison means responsive to the memory and sensor means for comparing the imaged region of the substrate with the stored desired features of the substrate.

2. An inspection apparatus as in claim 1 wherein said illumination means includes:

first and second reflector means elliptically cylindrical segments in shape, each with its long axis substantially parallel to the long axis of the other, and each being spaced-apart from the other along their closest edges to define a path through which the illuminated linear region can be viewed from above through said illumination means;

third and fourth reflector means each being flat and mounted parallel to the other, at opposite ends of each of said first and second reflector means and substantially perpendicular to the long axis of each of said first and second reflector means;

first and second linear light source means each mounted parallel to a corresponding one of said first and second reflector means, said first and second linear light source means each include a light source having a length that is substantially as long as the illuminated linear region is long, and that is parallel to a corresponding one of said first and second reflector means with each of the light source means mounted so that it is at the first focus of the corresponding reflector means and the illuminated linear region is at the second focus of each of the first and second reflector means;

fifth reflector means elliptically cylindrical segments in shape with its long axis substantially parallel to the long axes of the first and second reflector means, being mounted above said first and second reflector means and away from the path through which the illuminated linear region can be viewed from above through said illumination means;

beamsplitter means mounted in the path through which the illuminated linear region can be viewed from above through said illumination means, tilted to the optical viewing axis, and being positioned to reflect the focussed beam from the fifth reflector means to the illuminated linear region; and

third linear light source means mounted parallel to said fifth reflector means to direct light onto substantially the entire surface of the fifth reflector means with the illuminated linear region at a first focus of the fifth reflector means and the illuminated linear region is at the second focus of the fifth reflector means with the beam from the fifth reflector means being reflected by the beamsplitter means.

3. An inspection apparatus as in claim 2 wherein:

said first and second light source means are water cooled mercury capillary arc lamps; and

said illumination means further includes;

first and second optic filter means being removable and positionable between the illuminated linear region and each of the combinations of the first and second light source means and the first and second reflector means, respectively, for filtering the light delivered to the illuminated linear region from the combination of the first and second light source means and the first and second reflector means;

third optic filter means being a visible light filter positioned on the side of the beamsplitter means that is away from the illuminated linear region and through which light from the illuminated linear region passes to the sensor means for passing only visible light to the sensor means; and

lens means mounted on the side of the third optic filter means away from the beamsplitter means for focusing the light from the illuminated linear region onto the sensor means.

4. An inspection apparatus as in claim 2 wherein each of said first and second light source means include:

an elongated lamp that is substantially as long as the illuminated linear region is long; and

a transparent jacket means for surrounding said lamp.

5. An inspection apparatus as in claim 4 wherein said transparent jacket means is optically coated to filter the light emitted by the enclosed lamp.

6. An inspection apparatus as in claim 4 wherein said transparent jacket means forms a chamber around said lamp to provide a conduit for water cooling of the enclosed lamp.

7. An inspection apparatus as in claim 2 wherein said first and second reflector means include a wavelength-selective coating to cause light of selected wavelengths to be reflected and light of other wavelengths to be transmitted to reduce the heat loading of the substrate.

8. An inspection apparatus as in claim 1 wherein said illumination means includes a slit assembly means disposed to be immediately above said illuminated linear region for reducing the amount of light reflected from regions of the substrate into the sensor means that are not in the imaging region of the substrate by the sensor means.

9. An inspection apparatus as in claim 8 wherein said slit assembly means includes an integral air bearing means for causing the slit assembly means to fly at substantially a uniform height above the surface of the substrate.

10. An inspection apparatus as in claim 8 further including:

a fixed mounting surface to which said sensor means is mounted;

first mounting means for mounting said illumination means to said surface directly below said sensor means, said first mounting means disposed to permit movement of said illumination means only in the vertical direction with respect to the surface of the substrate to be inspected to maintain a relatively fixed distance between the illumination means and the surface of the substrate; and

second mounting means for mounting said slit assembly means to said surface directly below said illumination means, said second mounting means disposed to permit movement of said slit assembly means only in the vertical direction with respect to the surface of the substrate to be inspected to maintain a relatively fixed distance between the slit assembly means and the surface of the substrate.

11. An inspection apparatus as in claim 1 wherein said illumination means includes:

high volume air source means for providing a source of controlled direction moving air; and

ducting means for directing said moving air through the illumination means to minimize the Schlieren effects within the illumination means in the optical path between the substantially uniformly illuminated region of the substrate and the sensor means.

12. Inspection apparatus as in claim 1 wherein said sensor means is a TDI sensor means.

13. Inspection apparatus as in claim 12 wherein said TDI sensor means is a two dimensional charge-coupled device light sensing array.

14. Inspection apparatus as in claim 12 wherein said TDI sensor means has at least two rows of light sensitive areas in a first direction know as the TDI dimension and at least one column of light sensitive areas in a second direction know as the multiplexing dimension.

15. Inspection apparatus as in claim 14 wherein said TDI sensor means includes at least one tap at evenly spaced intervals in the multiplexing dimension.

16. Inspection apparatus for inspecting surface features of a substrate comprising:

memory means for storing the desired features of the surface of the substrate;

illumination means for substantially uniformly illuminating a region of the surface of the substrate to be inspected;

TDI sensor means for imaging the region of the substrate illuminated by the illumination means; and

comparison means responsive to the memory and sensor means for comparing the imaged region of the substrate with the stored desired features of the substrate.

17. An inspection apparatus as in claim 16 wherein said illumination means includes:

first and second reflector means elliptically cylindrical segments in shape, each with its long axis substantially parallel to the long axis of the other, and each being spaced-apart from the other along their closest edges to define a path through which the illuminated linear region can be viewed from above though said illumination means;

third and fourth reflector means each being flat and mounted parallel to the other, at opposite ends of each of said first and second reflector means and substantially perpendicular to the long axis of each of said first and second reflector means; and

first and second linear light source means each mounted parallel to a corresponding one of said first and second reflector means to direct light onto substantially the entire surface of the corresponding reflector means with the illuminated linear region at one focus of each of the first and second reflector means.

18. An inspection apparatus as in claim 17 wherein said first and second linear light source means each include a fiber optic bundle with exit ends that are narrow in height and substantially as wide as the illuminated linear region and an incoherent light source disposed to illuminate the entrance ends of said first and second fiber optic bundle.

19. An inspection apparatus as in claim 17 wherein said first and second linear light source means each include a light source having a length that is substantially as long as the illuminated linear region is long, and that is parallel to a corresponding one of said first and second reflector means with each of the light source means mounted so that it is at the first focus of the corresponding reflector means and the illuminated linear region is at the second focus of each of the first and second reflector means.

20. An inspection apparatus as in claim 19 wherein said illumination means further includes:

fifth reflector means elliptically cylindrical segments in shape with its long axis substantially parallel to the long axes of the first and second reflector means, being mounted above said first and second reflector means and away from the path through which the illuminated linear region can be viewed from above through said illumination means;

beamsplitter means mounted in the path through which the illuminated linear region can be viewed from above through said illumination means, tilted to the optical viewing axis, and being positioned to reflect the focussed beam from the fifth reflector means to the illuminated linear region; and

third linear light source means mounted parallel to said fifth reflector means to direct light onto substantially the entire surface of the fifth reflector means with said third linear light source means at a first focus of the fifth reflector means and the illuminated linear region at the second focus of the fifth reflector means with the beam from the fifth reflector means being reflected by the beamsplitter means.

21. An inspection apparatus as in claim 20 wherein:

said first and second light source means are water cooled mercury capillary arc lamps; and

said illumination means further includes;

first and second optic filter means being removable and positionable between the illuminated linear region and each of the combinations of the first and second light source means and the first and second reflector means, respectively, for filtering the light delivered to the illuminated linear region from the combination of the first and second light source means and the first and second reflector means;

third optic filter means being a visible light filter positioned on the side of the beamsplitter means that is away from the illuminated linear region and through which light from the illuminated linear region passes to the sensor means for passing only visible light to the sensor means; and

lens means mounted on the side of the third optic filter means away from the beamsplitter means for focusing the light from the illuminated linear region onto the sensor means.

22. An inspection apparatus as in claim 17 wherein each of said first and second light source means include:

an elongated lamp that is substantially as long as the illuminated linear region is long; and

a transparent jacket means for surrounding said lamp.

23. An inspection apparatus as in claim 22 wherein said transparent jacket means is optically coated to filter the light emitted by the enclosed lamp.

24. An inspection apparatus as in claim 22 wherein said transparent jacket means forms a chamber around said lamp to provide a conduit for water cooling of the enclosed lamp.

25. An inspection apparatus as in claim 17 wherein said first and second reflector means include a wavelength-selective coating to cause light of selected wavelengths to be reflected and light of other wavelengths to be transmitted to reduce the heat loading of the substrate.

26. An inspection apparatus as in claim 16 wherein said illumination means includes a slit assembly means disposed to be immediately above said illuminated linear region for reducing the amount of light reflected from regions of the substrate into the sensor means that are not in the imaging region of the substrate by the sensor means.

27. An inspection apparatus as in claim 26 wherein said slit assembly means includes an integral air bearing means for causing the slit assembly means to fly at substantially a uniform height above the surface of the substrate.

28. An inspection apparatus as in claim 26 further including:

a fixed mounting surface to which said sensor means is mounted;

first mounting means for mounting said illumination means to said surface directly below said sensor means, said first mounting means disposed to permit movement of said illumination means only in the vertical direction with respect to the surface of the substrate to be inspected to maintain a relatively fixed distance between the illumination means and the surface of the substrate; and

second mounting means for mounting said slit assembly means to said surface directly below said illumination means, said second mounting means disposed to permit movement of said slit assembly means only in the vertical direction with respect to the surface of the substrate to be inspected to maintain a relatively fixed distance between the slit assembly means and the surface of the substrate.

29. An inspection apparatus as in claim 16 wherein said illumination means includes:

high volume air source means for providing a source of controlled direction moving air; and

ducting means for directing said moving air through the illumination means to minimize the Schlieren effects within the illumination means in the optical path between the substantially uniformly illuminated region of the substrate and the sensor means.

30. Inspection apparatus as in claim 16 wherein said TDI sensor means is a two dimensional charge-coupled device light sensing array.

31. Inspection apparatus as in claim 16 wherein said TDI sensor means has at least two rows of light sensitive areas in a first direction know as the TDI dimension and at least one column of light sensitive areas in a second direction know as the multiplexing dimension.

32. Inspection apparatus as in claim 31 wherein said TDI sensor means includes at least one tap at evenly spaced intervals in the multiplexing dimension.

33. A method for inspecting surface features of a substrate, said method comprising the steps of:

a. storing the desired features of the surface of the substrate;

b. substantially uniformly illuminating a region of the surface of the substrate to be inspected with focussed quasi-Lambertian illumination;

c. imaging the region of the substrate illuminated by the illumination means; and

d. comparing the imaged region of the substrate with the stored desired features of the substrate.

34. A method as in claim 33 wherein step b. includes the step of:

e. illuminating a region on the surface of the substrate through a narrow slit disposed above the surface and in close proximity thereto.

35. A method as in claim 33 wherein said method further includes the step of:

f. directing air flow passed the illuminated region to minimize the Schlieren effect in step c.

36. A method as in claim 33 wherein said method further includes the step of:

g. moving the illumination means vertically with respect to the surface to be inspected to maintain a relatively constant spacing therebetween to maintain the surface in focus during step c.

37. A method as in claim 33 wherein step b. includes the steps of:

h. illuminating the surface of the substrate with short-wave incoherent light; and

i. imaging the surface of the substrate with light of a longer wave length than the light of step h.

38. A method as in claim 33 further including the steps of:

i. performing steps a. through d. with the illumination of step b. being short-wave incoherent light and imaging the substrate with light of a longer wave length than the light of the illumination of the substrate; and

j. performing steps a. through d. with the illumination of step b. being quasi Lambertian illumination.

39. A method for inspecting surface features of a substrate, said method comprising the steps of:

a. storing the desired features of the surface of the substrate;

b. substantially uniformly illuminating a region of the surface of the substrate to be inspected;

c. imaging the region of the substrate illuminated by the illumination means with TDI sensor means; and

d. comparing the imaged region of the substrate with the stored desired features of the substrate.

40. A method as in claim 39 wherein step b. includes the step of:

e. illuminating a region on the surface of the substrate through a narrow slit disposed above the surface and in close proximity thereto.

41. A method as is claim 39 wherein said method further includes the step of:

f. directing air flow passed the illuminated region to minimize the Schlieren effect in step c.

42. A method as in claim 39 wherein said method further includes the step of:

g. moving the illumination means vertically with respect to the surface to be inspected to maintain a relatively constant spacing therebetween to maintain the surface in focus during step c.

43. A method as in claim 39 wherein step b. includes the steps of:

h. illuminating the surface of the substrate with short-wave incoherent light; and

i. imaging the surface of the substrate with light of a longer wavelength than the light of step h.

44. A method as in claim 39 further including the steps of:

i. performing steps a. through d. with the illumination of step b. being short-wave incoherent light and imaging the substrate with light of a longer wave length than the light of the illumination of the substrate; and

j. performing steps a. through d. with the illumination of step b. being quasi Lambertian illumination.

45. Illumination apparatus for substantial uniform focussed illumination along a narrow linear region comprising:

first and second reflector means elliptically cylindrical segments in shape, each with its long axis substantially parallel to the long axes of the other, and each being spaced-apart from the other along their closest edges to define a path through which the illuminated linear region can be viewed from above through said illumination apparatus;

third and fourth reflector means each being flat and mounted parallel to the other and at opposite ends of each of said first and second reflector means and substantially perpendicular to the long axis of each of said first and second reflector means; and

first and second linear light source means each mounted parallel to a corresponding one of said first and second reflector means to direct light onto substantially the entire surface of the corresponding reflector means with the illuminated linear region at one focus of each of the first and second reflector means.

46. An inspection apparatus as in claim 45 wherein said first and second linear light source means each include fiber optic bundle with exit ends that are narrow in height and substantially as wide as the illuminated linear region and an incoherent light source disposed to illuminate the entrance ends of said first and second fiber optic bundle.

47. Illumination apparatus as in claim 45 wherein said first and second linear light source means each include a light source having a length that is substantially as long as the illuminated linear region is long, and that is parallel to a corresponding one of said first and second reflector means with each of the light source means mounted so that it is at the first focus of the corresponding reflector means and the illuminated linear region is at the second focus of each of the first and second reflector means.

48. Illumination apparatus as in claim 47 further includes:

fifth reflector means elliptically cylindrical segments in shape with its long axis substantially parallel to the long axes of the first and second reflector means, being mounted above said first and second reflector means and away from the path through which the illuminated linear region can be viewed from above through said illumination apparatus;

beamsplitter means mounted in the path through which the illuminated linear region can be viewed from above through said illumination apparatus, tilted to the optical viewing axis, and being positioned to reflect the focussed beam from the fifth reflector means to the illuminated linear region; and

third linear light source means mounted parallel to said fifth reflector means to direct light onto substantially the entire surface of the fifth reflector means with said third linear light source at a first focus of the fifth reflector means and the illuminated linear region at the second focus of the fifth reflector means with the beam from the fifth reflector means being reflected by the beamsplitter means.

49. Illumination apparatus as in claim 48 wherein:

said first and second light source means are water cooled mercury capillary arc lamps; and

said illumination apparatus further includes;

first and second optic filter means being removable and positionable between the illuminated linear region and each of the combinations of the first and second light source means and the first and second reflector means, respectively, for filtering the light delivered to the illuminated linear region from the combination of the first and second light source means and the first and second reflector means;

third optic filter means being a visible light filter position on the side of the beamsplitter means that is away from the illuminated linear region and through which light from the illuminated linear region passes to the sensor means for passing only visible light to the sensor means; and

lens means mounted on the side of the third optic filter means away from the beamsplitter means for focusing the light from the illuminated linear region.

50. Illumination apparatus as in claim 45 wherein each of said first and second light source means include:

an elongated lamp that is substantially as long as the illuminated linear region is long; and

a transparent jacket means for surrounding said lamp.

51. Illumination apparatus as in claim 50 wherein said transparent jacket means is optically coated to filter the light emitted by the enclosed lamp.

52. Illumination apparatus as in claim 50 wherein said transparent jacket means forms a chamber around said lamp to provide a conduit for water cooling of the enclosed lamp.

53. Illumination apparatus as in claim 45 further includes a slit assembly means disposed to be immediately above said illuminated linear region.

54. Illumination apparatus as in claim 53 wherein said slit assembly means includes an integral air bearing means for causing the slit assembly means to fly at substantially a uniform height above a surface below the illumination apparatus.

55. Illumination apparatus as in claim 45 wherein said first and second reflector means include a wavelength-selective coating to cause light of elected wavelengths to be reflected and light of other wavelengths to be transmitted to reduce the heat loading of a surface below the illumination apparatus.

56. Illumination apparatus as in claim 45 further includes:

high volume air source means for providing a source of controlled direction moving air; and

ducting means for directing said moving air through the illumination apparatus to minimize the Schlieren effects within the illumination apparatus in the region between the substantially uniformly illuminated region and the sensor.