Wafer inspection system for distinguishing pits and particles

• US 6,292,259 B1
• Filed: 07/24/2000
• Issued: 09/18/2001
• Est. Priority Date: 03/06/1995
• Status: Expired due to Term

• Current Assignee: ADE Optical Systems Corporation
• Original Assignee: ADE Optical Systems Corporation
• Inventors: Fossey, Michael E., Stover, John C.
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): Lauchman, Layla
• Application Number:
  US09/624,502
• Time in Patent Office: 421 Days
• Field of Search: 356/237.2, 356/237, 356/364, 356/430, 356/394, 356/338, 356/343, 250/559.18, 250/559-9-5, 250/559-4-5, 250/225
• US Class Current: 356/237.2
• CPC Class Codes: G01N 2021/945 Liquid or solid deposits of macroscopic size on surfaces, e.g. drops, films, or clustered contaminants dust particles and microscopic contaminants in G01N21/94
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: H01L 22/12 for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions electrical measurement of diffusions H01L22/14

Abstract

A surface inspection system and method is provided which detects defects such as particles or pits on the surface of a workpiece, such as a silicon wafer, and also distinguishes between pit defects and particle defects. The surface inspection system comprises an inspection station for receiving a workpiece and a scanner positioned and arranged to scan a surface of the workpiece at the inspection station. The scanner includes a light source arranged to project a beam of P-polarized light and a scanner positioned to scan the P-polarized light beam across the surface of the workpiece. The system further provides for detecting differences in the angular distribution of the light scattered from the workpiece and for distinguishing particle defects from pit defects based upon these differences.

Claims

1. A surface inspection system for distinguishing between particle defects and pit defects on a surface of a workpiece comprising:

an inspection station for receiving the workpiece;

a scanner positioned to scan a surface of the workpiece at the inspection station, the scanner including a light source arranged to project p-polarized light at an angle of incidence oblique to the workpiece surface;

a first collector positioned to collect light scattered from the surface of the workpiece at a central zone;

a second collector positioned to collect light scattered from the surface of the workpiece at an oblique zone offset angularly from the central zone;

one or more converters for converting the collected light components into respective signals representative of the light scattered into the central zone and oblique zone; and

a system controller configured to receive the signals, compare the signals, and classify defects as pits or particles based at least in part on the comparison.

2. The surface inspection station of claim 1 wherein the central zone includes a scattering direction substantially perpendicular to the surface.

3. The surface inspection station of claim 1 wherein the oblique zone is offset at least forwardly of the central zone.

4. The surface inspection station of claim 3 wherein the oblique zone receives substantially only forward scattered light.

5. The surface inspection system of claim 1 wherein the oblique zone is offset at least backwardly of the central zone.

6. The surface inspection system of claim 5 wherein the oblique zone receives substantially only backscattered light.

7. The surface inspection system of claims 1, 2, 3, 4, 5 or 6 wherein the system controller compares the ratio of the signals to a predetermined value.

8. The surface inspection system of claim 7 wherein the collected light components are converted into respective intensity signals representative of the intensity of the light scattered into the central zone and oblique zone and the system controller classifies a defect as a particle if the ratio of the intensity signal from the oblique zone to the intensity signal from the central zone exceeds a threshold value.

9. The surface inspection system of claim 7 wherein the collected light components are converted into respective intensity signals representative of the intensity of the light scattered into the central zone and oblique zone and the system controller classifies a defect as a pit if the ratio of the intensity signal from the central zone to the intensity signal from the oblique zone exceeds a predetermined measure.

10. The surface inspection system of claims 1, 2, 3, 4, 5 or 6 wherein the collected light components are converted into respective intensity signals representative of the intensity of the light scattered into the central zone and oblique zone, and the system controller classifies a defect as a particle if the intensity signal from the oblique zone exceeds the intensity signal from the central zone by a predetermined value.

11. The surface inspection station of claim 1 wherein the oblique zone receives substantially only backscattered light, and the surface inspection station further comprises a third collector positioned to collect light scattered from the surface of the workpiece at a second oblique zone offset angularly from said central zone, wherein the second oblique zone receives substantially only forward scattered light.

12. The surface inspection station of claim 11 wherein the collected light components are converted into respective intensity signals representative of the intensity of the light scattered into the central zone and oblique zone, and the system controller compares the intensity signal from each zone and classifies a defect as a particle if the intensity signal from either of the oblique zones exceeds the intensity signal from the central zone by a predetermined value.

13. The surface inspection system of claim 1 wherein the system controller further counts the number of defects classified as pits.

14. The surface inspection system of claim 1 wherein the system controller further counts the number of defects classified as particles.

15. The surface inspection system of claim 1 wherein the system controller further determines the size of the pits and particles detected on the surface of the workpiece.

16. The surface inspection system of claim 15 wherein the system controller further groups the pits and particles based at least in part on the determination of size.

17. The surface inspection system of claim 16 wherein the system controller further counts the number of pits and particles in each size group.

18. The surface inspection system of claim 1 wherein the system controller further produces a map of the pits and particles on the surface of the workpiece.

19. The surface inspection system of claim 1 wherein the system controller further sorts the workpieces based at least in part on whether the system controller classifies a defect as a pit or a particle.

20. The surface inspection system of claim 19 wherein the system controller sorts the workpieces for recleaning based at least in part on whether the system controller classifies a defect as a pit or a particle.

21. A surface inspection system for distinguishing between particle defects and pit defects on a surface of a workpiece comprising:

an inspection station for receiving the workpiece;

a scanner positioned to scan a surface of the workpiece at the inspection station, the scanner including a light source arranged to project p-polarized light at an angle of incidence oblique to the workpiece surface;

a first collector positioned to collect light scattered from the surface of the workpiece at a central zone;

a second collector positioned to collect light scattered from the surface of the workpiece at an oblique zone offset angularly from the central zone;

one or more converters for converting the collected light components into respective signals representative of the light scattered into the central and oblique zones;

a comparator configured to receive and compare the signals; and

a classifier configured to classify defects as pits or particles based at least in part on the comparison by the comparator.

22. The surface inspection system of claim 21 wherein the comparator compares the ratio of the signals to a predetermined value.

23. The surface inspection system of claim 22 wherein the collected light components are converted into respective intensity signals representative of the intensity of the light scattered into the central zone and oblique zone, and the classifier classifies a defect as a particle if the ratio of the intensity signal from the oblique zone to the intensity signal from the central zone exceeds a threshold value.

24. The surface inspection system of claim 22 wherein the collected light components are converted into respective intensity signals repressentative of the intensity of the light scattered into the central zone and oblique zone, and the classifier classifies a defect as a pit if the ratio of the intensity signal from the central zone to the intensity signal from the oblique zone exceeds a predetermined measure.

25. A surface inspection system for distinguishing between particle defects and pit defects on a surface of a workpiece comprising:

an inspection station for receiving the workpiece;

a scanner positioned to scan a surface of the workpiece at the inspection station, the scanner including a light source arranged to project p-polarized light at an angle of incidence oblique to the workpiece surface;

a first collector positioned to collect light scattered from the surface of the workpiece at a central zone;

a second collector positioned to collect light scattered from the surface of the workpiece at an oblique zone offset angularly from the central zone;

one or more converters for converting the collected light components into respective signals representative of the light scattered into the central and oblique zones;

a system controller configured to receive the signals, compare the signals, classify defects as pits or particles based at least in part on the comparison, and produce a map of the pits and particles on the surface of the workpiece.

26. The surface inspection system of claim 25 wherein the system controller produces a first map identifying the location of pit defects on the workpiece surface.

27. The surface inspection system of claim 26 wherein the system controller produces a second map identifying the location of particle defects on the workpiece surface.

28. The surface inspection system of claim 27 wherein the system controller further displays the first map and second map on a video display.

29. A surface inspection system for distinguishing between particle defects and pit defects on a surface of a workpiece comprising:

an inspection station for receiving the workpiece;

a scanner positioned to scan a surface of the workpiece at the inspection station, the scanner including a light source arranged to project p-polarized light at an angle of incidence oblique to the workpiece surface;

a first collector positioned to collect light scattered from the surface of the workpiece at a central zone;

a second collector positioned to collect light scattered from the surface of the workpiece at an oblique zone offset angularly from said central zone;

one or more converters for converting the collected light components into respective signals representative of the light scattered into said central and oblique zones;

a comparator comprising computer-readable medium which stores computer-executable instructions for distinguishing between particle defects and pit defects on the surface of the workpiece, the instructions causing the comparator to compare the signals and determine whether a defect is one of a pit or a particle based at least in part on the comparison.

30. A surface inspection system for distinguishing between particle defects and pit defects on a surface of a workpiece comprising:

an inspection station for receiving the workpiece;

a scanner positioned to scan a surface of the workpiece at the inspection station, the scanner including a light source arranged to project p-polarized light at an angle of incidence oblique to the workpiece surface;

a first collector positioned to collect light scattered from the surface of the workpiece at a central zone;

a second collector positioned to collect light scattered from the surface of the workpiece at an oblique zone offset angularly from said central zone;

one or more converters for converting the collected light components into respective signals representative of the light scattered into said central and oblique zones; and

a system controller comprising computer-readable medium which stores computer-executable instructions for distinguishing between particle defects and pit defects on the surface of the workpiece, the instructions causing the system controller to compare the signals and classify defects as pits or particles based at least in part on the comparison.

31. The surface inspection system of claim 30 wherein the instructions cause the system controller to compare the ratio of the signals to a predetermined value.

32. The surface inspection system of claim 31 wherein the collected light components are converted into respective intensity signals representative of the intensity of the light scattered into the central zone and oblique zone, and the instructions cause the system controller to classify a defect as a particle if the ratio of the intensity signal from the oblique zone to the intensity signal from the central zone exceeds a threshold value.

33. The surface inspection system of claim 31 wherein the collected light components are converted into respective intensity signals representative of the intensity of the light scattered into the central zone and oblique zone, and the instructions cause the system controller to classify a defect as a pit if the ratio of the intensity signal from the central zone to the intensity signal from the oblique zone exceeds a predetermined measure.

34. The surface inspection system of claim 31 wherein the instructions further cause the system controller to produce a map of the pits and particles on the workpiece surface.

35. The surface inspection system of claim 34 wherein the instructions cause the system controller to produce a first map identifying the location of pit defects on the workpiece surface.

36. The surface inspection system of claim 35 wherein the instructions cause the system controller to produce a second map identifying the location of particle defects on the workpiece surface.

37. The surface inspection system of claim 36 wherein the instructions further cause the system controller to display the first map and second map on a video display.

38. The surface inspection system of claim 30 wherein the instructions further cause the system controller to count the number of defects classified as pits.

39. The surface inspection system of claim 30 wherein the instructions further cause the system controller to count the number of defects classified as particles.

40. The surface inspection system of claim 30 wherein the instructions further cause the system controller to determine the size of the pits and particles detected on the surface of the workpiece.

41. The surface inspection system of claim 40 wherein the instructions further cause the system controller to group the pits and particles based at least in part on the determination of size.

42. The surface inspection system of claim 41 wherein the instructions further cause the system controller to count the number of pits and particles in each size group.