Method and apparatus for particle inspection

• US 5,748,305 A
• Filed: 06/28/1996
• Issued: 05/05/1998
• Est. Priority Date: 06/30/1995
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Ito, Masami, Nagasaki, Tatsuo, Shimono, Ken, Nishii, Kanji, Takamoto, Kenji
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Ratliff, Reginald A.
• Application Number:
  US08/670,851
• Time in Patent Office: 676 Days
• Field of Search: 356/237, 356/335, 356/338, 356/343, 356/340, 356/339, 250/572
• US Class Current: 356/237.2
• CPC Class Codes: G01N 21/94 Investigating contamination, e.g. dust G01N21/85 takes precedence

Abstract

A method for foreign particles inspection includes illuminating an inspection surface of an inspection object with a beam which is, one of s-polarized and p-polarized relative to the inspection surface of the inspection object. The illumination utilizes an optical axis which is generally parallel to the inspection surface or which intersects the inspection surface at an angle that is greater than or equal to 1° and less than 5°. Reflected and scattered light is detected utilizing an optical axis which makes an acute angle with the inspection surface and which makes a differential angle of 30° or less with the optical axis of the illumination beam. The detection of foreign particles is accomplished by detecting the component of the reflected and scattered light which is the other of s-polarized and p-polarized relative to the inspection surface.

Claims

1. A method of foreign particles inspection comprising:

illuminating an inspection surface of an inspected object with a beam, which is one of an s-polarized light and a p-polarized light relative to the inspection surface of the inspection object, in such a manner that an optical axis of the beam intersects the inspection surface at an angle of not less than 1° and

less than 5°

; and

detecting, as an indication of foreign particles, a component of reflected and scattered light which occurs from the beam and which is the other of the s-polarized light and the p-polarized light, wherein said detecting is about a detection optical axis which makes an acute angle with the inspection surface and which makes a differential angle of 30°

or less with the optical axis of the beam.

2. The method of foreign particles inspection as claimed in claim 1, wherein:

the inspection object is a patterned substrate; and

the detecting comprises comparing;

a light quantity of a polarized light component of the reflected light, which indicates the presence of foreign particles with

a light quantity of a polarized light component of the scattered light.

3. The method of foreign particles inspection as claimed in claim 1, wherein said detecting is about a detection optical axis which makes an angle of less than 60°

with the inspection surface of the inspection object.

4. The method of foreign particles inspection as claimed in claim 2, wherein said detecting is about a detection optical axis which makes an angle of less than 60°

with the inspection surface of the inspection object.

5. The method of foreign particles inspection as claimed in claim 3, wherein said detecting is about a detection optical axis which makes an angle of 40°

or less with the inspection surface of the inspection object.

6. The method of foreign particles inspection as claimed in claim 4, wherein said detecting is about a detection optical axis which makes an angle of 40°

or less with the inspection surface of the inspection object.

7. The method of foreign particles inspection as claimed in claim 1, wherein a periodic pattern of the inspection object is eliminated by disposing a spatial filter along the detection optical axis.

8. The method of foreign particles inspection as claimed in claim 2, wherein a periodic pattern of the inspection object is eliminated by disposing a spatial filter along the detection optical axis.

9. The method of foreign particles inspection as claimed in claim 5, wherein a periodic pattern of the inspection object is eliminated by disposing a spatial filter along the detection optical axis.

10. The method of foreign particles inspection as claimed in claim 1, wherein , as an indication of the foreign particles, a p-polarized component of the reflected and scattered light is detected about the detection optical axis and by using an optical system, and a photoelectric conversion element, wherein the optical system comprises an objective lens having a focal length f and an aperture diameter D, and an image forming lens having a principal plane located at a distance L from a principal plane of the objective lens, the image forming lens having an aperture diameter set to be (D-2A+AL/f) or more, where A denotes an inspection width determined based on a magnification relationship between detection ranges of the photoelectric conversion element and the objective and image forming lenses.

11. The method of foreign particles inspection as claimed in claim 2, wherein a, as an indication of the foreign particles, a p-polarized component of the reflected and scattered light is detected about the detection optical axis and by using an optical system, and a photoelectric conversion element, wherein the optical system comprises an objective lens having a focal length f and an aperture diameter D, and an image forming lens having a principal plane located at a distance L from a principal plane of the objective lens, the image forming lens having an aperture diameter set to be (D-2A+AL/f) or more, where A denotes an inspection width determined based on a magnification relationship between detection ranges of the photoelectric conversion element and the objective and image forming lenses.

12. The method of foreign particles inspection as claimed in claim 1, wherein a p-polarized component of the reflected and scattered light is detected, as an indication of the foreign particles, by using a telecentric optical system.

13. The method of foreign particles inspection as claimed in claim 2, wherein a p-polarized component in the reflected and scattered light is detected, as an indication of the foreign particles, by using a telecentric optical system.

14. The method of foreign particles inspection as claimed in claim 1, wherein a half-wave plate for rotating polarized light is added so that an s-polarized component in the reflected and scattered light is converted into a p-polarized component, the p-polarized component is detected as an indication of the foreign particles, about the detection optical axis.

15. The method of foreign particles inspection as claimed in claim 2, wherein a half-wave plate for rotating polarized light is added so that an s-polarized component in the reflected and scattered light is converted into a p-polarized component, the p-polarized light component is detected, as an indication of the foreign particles, about the detection optical axis.

16. The method of foreign particles inspection as claimed in claim 1, wherein beams from an array of point sources are set as a line beam by a cylindrical lens disposed so as to vary a magnification of an image oriented in a direction parallel with the array of point sources.

17. The method of foreign particles inspection as claimed in claim 2, wherein beams from an array of point sources are set as a line beam by a cylindrical lens disposed so as to vary a magnification of an image oriented in a direction parallel with the array of point sources.

18. A foreign particles inspecting apparatus comprising:

an illumination device arranged so as to define an optical axis substantially parallel to an inspection surface of an inspection object, for supplying a beam of light toward the inspection surface of the inspection object wherein the beam is one of s-polarized and ppolarized relative to the inspection surface;

a detection device having a detection optical axis which makes an acute angle with the inspection surface of the inspection object and which makes a differential angle of 30°

or less with the optical axis of the illumination device, such that said detection device can detect a light component in reflected and scattered light produced by the illumination device, which is the other of s-polarized and p-polarized relative to the inspection surface, and performs photoelectric conversion of the light component; and

a signal processing unit for determining foreign particles based on a signal from the photoelectric conversion from the detection device.

19. The foreign particles inspecting apparatus as claimed in claim 18, wherein:

the inspection object is a patterned substrate; and

the detection device is capable of comparing;

a light quantity of a polarized light component of the reflected light, which indicates the presence of foreign particles with

a light quantity of a polarized light component of the scattered light.

20. The foreign particles inspecting apparatus as claimed in claim 18, wherein said detecting device has a detection optical axis which makes an angle of less than 60°

with the inspection surface of the inspection object.

21. The foreign particles inspecting apparatus as claimed in claim 19, wherein said detecting device has a detection optical axis which makes an angle of less than 60°

with the inspection surface of the inspection object.

22. The foreign particles inspecting apparatus as claimed in claim 20, wherein said detecting device has a detection optical axis which makes an angle of 40°

or less with the inspection surface of the inspection object.

23. The foreign particles inspecting apparatus as claimed in claim 21, wherein said detecting device has a detection optical axis which makes an angle of 40<

or less with the inspection surface of the inspection object.

24. The foreign particles inspecting apparatus as claimed in claim 18 further comprising a spatial filter disposed along the detection optical axis.

25. The foreign particles inspecting apparatus as claimed in claim 19 further comprising a spatial filter disposed along the detection optical axis.

26. The foreign particles inspecting apparatus as claimed in claim 22 further comprising a spatial filter disposed along the detection optical axis.

27. The foreign particles inspecting apparatus as claimed in claim 18 further comprising an optical system, and a photoelectric conversion element, wherein the optical system comprises an objective lens having a focal length f and an aperture diameter D, and an image forming lens having a principal plane located at a distance L from a principal plane of the objective lens, the image forming lens having an aperture diameter set to be (D-2A+AL/f) or more, where A denotes an inspection width determined based on a magnification relationship between detection ranges of the photoelectric conversion element and the objective and image forming lenses.

28. The foreign particles inspecting apparatus as claimed in claim 19 further comprising an optical system, and a photoelectric conversion element, wherein the optical system comprises an objective lens having a focal length f and an aperture diameter D, and an image forming lens having a principal plane located at a distance L from a principal plane of the objective lens, the image forming lens having an aperture diameter set to be (D-2A+AL/f) or more, where A denotes an inspection width determined based on a magnification relationship between detection ranges of the photoelectric conversion element and the objective and image forming lenses.

29. The foreign particles inspecting apparatus as claimed in claim 18 further comprising a telecentric optical system for use in detecting a p-polarized component of the reflected and scattered light.

30. The foreign particles inspecting apparatus as claimed in claim 19 further comprising a telecentric optical system for use in detecting a p-polarized component of the reflected and scattered light.

31. The foreign particles inspecting apparatus as claimed in claim 18 further comprising a half-wave plate for rotating polarized light so that an s-polarized component in the reflected and scattered light is converted into a p-polarized component.

32. The foreign particles inspecting apparatus as claimed in claim 19 further comprising a half-wave plate for rotating polarized light so that an s-polarized component in the reflected and scattered light is converted into a p-polarized component.

33. The foreign particles inspecting apparatus as claimed in claim 18 further comprising an array of point sources and a cylindrical lens, wherein beams from the array of point sources are set as a line beam by the cylindrical lens disposed so as to vary a magnification of an image oriented in a direction parallel with the array of point sources.

34. The foreign particles inspecting apparatus as claimed in claim 19 further comprising an array of point sources and a cylindrical lens, wherein beams from the array of point sources are set as a line beam by the cylindrical lens disposed so as to vary a magnification of an image oriented in a direction parallel with the array of point sources.

35. A method of foreign particles inspection comprising:

producing parallel beams by passing laser beams from a laser light source through a collimator lens;

passing only one of s-polarized light and p-polarized light from the parallel beams through a polarizer;

directing the light passed by the polarizer through a cylindrical lens so as to illuminate a line-form region on an inspection surface of an inspection object, on an incident plane, at an incident angle that is greater than or equal to 1° and

less than 5°

with respect to the inspection object;

wherein the light on the incident plane is reflected by a pattern on the inspection surface of the inspection object or is scattered by foreign particles on the inspection surface of the inspection object;

receiving, about a detection optical axis which makes an acute angle with the inspection surface, the reflected and scattered light by an objective lens;

transmitting, through an analyzer, only the other of s-polarized light and p-polarized light from the light received by the objective lens;

focusing the light from the analyzer by an image forming lens onto a line sensor;

photoelectrically converting the focused light into a detection signal by the line sensor; and

detecting the foreign particles based on the detection signal.

36. The method of foreign particles inspection as claimed in claim 35, wherein receiving is about a detection optical axis which makes an angle of less than 60°

with the inspection surface of the inspection object, and which makes a differential of 0°

with the light from the cylindrical lens.