Electron beam inspection system and method

• US 5,578,821 A
• Filed: 01/11/1995
• Issued: 11/26/1996
• Est. Priority Date: 05/27/1992
• Status: Expired due to Term

• Current Assignee: KLA Instruments, Corporation (KLA Corporation)
• Original Assignee: KLA Instruments, Corporation (KLA Corporation)
• Inventors: Chen, Zhong-Wei, Desai, Anil A., Emge, Dennis G., Meisberger, Dan, Smith, Dave E. A., Honfi, Leslie A., Rough, J. Kirkwood H., Dutta, April, Brodie, Alan D., Munro, Eric, Simmons, Richard, Pearce-Percy, Henry, McMurtry, John
• Primary Examiner(s): Berman, Jack I.
• Assistant Examiner(s): NGUYEN, KIET TUAN
• Application Number:
  US08/371,458
• Time in Patent Office: 685 Days
• Field of Search: 250/310, 250/311, 250/346 R, 250/396 ML, 250/392, 250/398, 250/440.11, 250/441.11, 250/442.11
• US Class Current: 250/310
• CPC Class Codes: H01J 2237/2817 Pattern inspection
• CPC Class Codes: H01J 37/28 with scanning beams H01J37/268, H01J37/292, H01J37/2955 take precedence
• CPC Class Codes: H01J 37/3005 Observing the objects or the point of impact on the object

Abstract

A method and apparatus for a charged particle scanning system and an automatic inspection system, including wafers and masks used in microcircuit fabrication. A charged particle beam is directed at the surface of a substrate for scanning that substrate and a selection of detectors are included to detect at least one of the secondary charged particles, back-scattered charged particles and transmitted charged particles from the substrate. The substrate is mounted on an x-y stage to provide at least one degree of freedom while the substrate is being scanned by the charged particle beam. The substrate is also subjected to an electric field on it'"'"'s surface to accelerate the secondary charged particles. The system facilitates inspection at low beam energies on charge sensitive insulating substrates and has the capability to accurately measure the position of the substrate with respect to the charged particle beam. Additionally, there is an optical alignment system for initially aligning the substrate beneath the charged particle beam. To function most efficiently there is also a vacuum system for evacuating and repressurizing a chamber containing the substrate. The vacuum system can be used to hold one substrate at vacuum while a second one is being loaded/unloaded, evacuated or repressurized. Alternately, the vacuum system can simultaneously evacuate a plurality of substrates prior to inspection and repressurize the same plurality of substrates following inspection. In the inspection configuration, there is also a comparison system for comparing the pattern on the substrate with a second pattern.

Claims

1. An automatic system for the automatic inspection of a substantially non-conductive substrate comprising:

a field emission electron source to provide an electron beam;

a charged particle beam column to deliver and scan said electron beam from said field emission electron source on a surface of said substantially non-conductive substrate;

at least one charged particle detector to detect at least one of three types of charged particles emanating from the top and bottom surfaces of said substantially non-conductive substrate, namely, secondary charged particles, back-scattered charged particles and transmitted charged particles;

a continuously moving x-y stage disposed to receive said substantially non-conductive substrate and to provide at least one degree of motion to said substantially non-conductive substrate while the substantially non-conductive substrate is being scanned by the charged particle beam; and

a multi-processor image defect computer coupled to said at least one charged particle detector to identify defects on said substrate.

2. An automatic system for the automatic inspection of a substrate as in claim 1 further comprising at least one electrode disposed to develop a substantially field free region at the surface of the substrate.

3. An automatic system for the automatic inspection of a substrate as in claim 1 further comprising a charged particle deflector to selectively direct said charged particles from the surface of said substrate to said charged particle detector.

4. An automatic system for the automatic inspection of a substrate as in claim 3 wherein said charged particle deflector produces crossed magnetic and electric deflection fields.

5. An automatic system for the automatic inspection of a substrate as in claim 3 wherein said charged particle optical column includes a Wien filter to deflect secondary charged particles from the surface of the substrate to said charged particle detector.

6. An automatic system for the automatic inspection of a substrate as in claim 1 wherein said system further comprises a comparator to compare a pattern on said substrate with a second pattern.

7. An automatic system for the automatic inspection of a substrate as in claim 1 further comprising an interferometer to determine the position of said x-y stage.

8. An automatic system for the automatic inspection of a substrate as in claim 1 further comprising a charged particle optical column, wherein said charged particle optical column has deflection elements to produce fields to control the path of charged particles, wherein said deflection elements include a Wien filter to deflect secondary charge particles from the surface of the substrate to said charged particle detector.

9. An automatic system for the automatic inspection of a substrate as in claim 1 further comprising a vacuum system including first and second chambers in each of which pressurization is performed independently to permit varying of the pressurization environment, and loading or unloading, of a first substrate in one of said first and second chambers while simultaneously inspecting a second substrate in a pressurized other one of said first and second chambers.

10. An automatic system for the automatic inspection of a substrate as in claim 9 wherein said vacuum system further includes two air locks to permit the independent variation of the pressure environment of each of said first and said second substrates while simultaneously inspecting a third substrate.

11. An automatic system for the automatic inspection of substrates as in claim 1 further comprising a vacuum system including a plurality of chambers in each of which pressurization is performed independently for simultaneously permitting the varying of the pressurization environment, loading, unloading or inspecting of up to the same plurality of substrates in a pipeline manner.

12. An automatic system for the automatic inspection of a substrate as in claim 1 wherein said charged particle beam column includes an objective lens having a retardation field to decelerate electrons in said electron beam.

13. An automatic system for the automatic inspection of a substrate as in claim 1 wherein the energy of said electron beam is between 500 and 1,500 volts.

14. An automatic system for the automatic inspection of a substrate as in claim 1 wherein said at least one charged particle detector only includes a charged particle detector to detect secondary electrons.

15. An automatic system for the automatic inspection of a substantially non-conductive substrate comprising:

a charged particle optical column to selectively direct charged particles at a surface of said substrate; and

a high speed semiconductor detector to detect at least one of the three types of charged particles emanating from the top and bottom surfaces of said substrate, namely, secondary charged particles, back-scattered charged particles and transmitted charged particles at a rate of at least 100 MHz.

16. An automatic system for the automatic inspection of a substantially non-conductive substrate comprising:

a charged particle beam column to deliver and scan a charged particle beam on a surface of said substrate;

a charged particle detector to detect at least one of the three types of charged particles emanating from the top and bottom surfaces of said substrate, namely, secondary charged particles, back-scattered charged particles and transmitted charged particles;

an alignment system to align said substrate beneath said charged particle beam; and

a multi-processor image defect computer coupled to said charged particle detector to identify defects on said substrate.

17. An automatic system for the automatic inspection of a substrate as in claim 16 wherein said system further comprises a comparator to compare a pattern on said substrate with a second pattern.

18. An automatic system for the automatic inspection of a substrate as in claim 16 wherein said alignment system automatically aligns the substrate beneath the charged particle beam.

19. An automatic system for the automatic inspection of a substrate as in claim 16 wherein said system further comprises a comparator to compare one pattern on said substrate with a second pattern on said substrate.

20. An automatic system for the automatic inspection of a substrate as in claim 16 wherein said alignment system performs automatically using an image pattern of the substrate being inspected for alignment of the substrate.

21. An automatic system for the automatic inspection of a substrate as in claim 16 wherein said alignment system includes an interferometer to automatically align the substrate being inspected.

22. An automatic system for the automatic inspection of a substrate as in claim 16 wherein:

said systems further includes;

a memory in which an image of the substrate to be inspected is pre-stored; and

said alignment system in communication with said memory uses said stored image to automatically align the substrate being inspected.

23. An automatic system for the automatic inspection of a substrate as in claim 16 further comprising at least one electrode disposed to develop a substantially field free region at the surface of the substrate.

24. An automatic system for the automatic inspection of a substrate as in claim 16 further comprising a charged particle deflector to selectively direct particles from the surface of said substrate to said charged particle detector.

25. An automatic system for the automatic inspection of a substrate as in claim 16 further comprising a vacuum system including first and second chambers in each of which pressurization is performed independently to permit varying of the pressurization environment, and loading or unloading, of a first substrate in one of said first and second chambers while simultaneously inspecting a second substrate in a pressurized other one of said first and second chambers.

26. An automatic system for the automatic inspection of a substrate as in claim 25 wherein said vacuum system further includes two air locks to permit the independent variationof the pressure environment of each of siad first and said second substrates while simultaneously inspecting a third substrate.

27. An automatic system for the automatic inspection of a substrate as in claim 16 further comprising a vacuum system including a plurality of chambers in each of which pressurization is performed independently for simultaneously permitting the varying of the pressurization environment, loading, unloading or inspecting of up to the same plurality of substrates in a pipeline manner.

28. An automatic system for the automatic inspection of a substrate as in claim 16 wherein said charged particle beam column includes an objective lens having a retardation field to decelerate electrons in said electron beam.

29. An automatic system for the automatic inspection of a substrate as in claim 16 wherein the energy of said electron beam is between 500 and 1,500 volts.

30. An automatic system for the automatic inspection of a substrate as in claim 16 wherein said charged particle detector only detects secondary electrons.

31. A method for the automatic inspection of a substantially non-conductive substrate using an electron beam from a field emission source, said method comprising the steps of:

a. positioning the electron beam on the substrate accurately by measuring the position of the substrate;

b. deflecting the electron beam to the desired position of said substrate measured in step a.;

c. scanning the desired position of a surface of the substrate with the electron beam as said substrate is continuously moving with at least one degree of motion in an x-y plane; and

d. detecting at least one of the three types of charged particles emanating from the top and bottom surfaces of said substrate as a result of step c., namely, secondary charged particles, back-scattered charged particles and transmitted charged particles; and

e. identifying defects on said substrate with a multi-processor image defect computer using information from step d.;

wherein step a. includes computing misalignment of an image produced by step d. to control the positioning of said electron beam.

32. A method for the automatic inspection of a substrate as in claim 31 wherein said step a. is performed by detecting a pattern on said substrate for positioning.

33. A method for the automatic inspection of a substrate as in claim 31 wherein:

said method further includes the step of;

e. prestoring the desired surface characteristics of said substrate in a memory means; and

said step a. includes the step of;

f. comparing the surface characteristics of said substrate with the prestored characteristics of step e. to detect the position of said substrate.

34. A method for the automatic inspection of a substrate as in claim 31 wherein said step a. is performed by an interferometer.

35. A method as in claim 31 wherein step b. includes the step of retarding a field to decelerate electrons in said electron beam.

36. A method as in claim 31 wherein the energy of said electron beam is between 500 and 1,500 volts.

37. A method as in claim 31 wherein step d. only detects secondary electrons.

38. An automatic system for the automatic inspection of a substantially non-conductive substrate comprising:

a field emission electron source to provide an electron beam;

a charged particle beam column to deliver and scan said electron beam from said field emission electron source on a surface of said substrate;

a charged particle detector to detect at least one of the three types of charged particles emanating from the top and bottom surfaces of said substrate, namely, secondary charged particles, back-scattered charged particles and transmitted charged particles;

an interferometer to determine the position of said substrate with respect to said electron beam;

a stage disposed to receive said substrate and to provide continuous motion relative to said electron beam; and

a multi-processor image defect computer coupled to said at least one charged particle detector to identify defects on said substrate.

39. An automatic system for the automatic inspection of a substrate as in claim 38 wherein said stage includes a continuously moving x-y stage disposed to receive said substrate and to provide at least one degree of motion to said substrate while the substrate is being scanned by the electron beam.

40. An automatic system for the automatic inspection of a substrate as in claim 38 wherein said charged particle beam column includes an objective lens having a retardation field to decelerate electrons in said electron beam.

41. An automatic system for the automatic inspection of a substrate as in claim 38 wherein the energy of said electron beam is between 500 and 1,500 volts.

42. An automatic system for the automatic inspection of a substrate as in claim 38 wherein said charged particle detector only detects secondary electrons.

43. An automatic system for the automatic inspection of a substantially non-conductive substrate using an electron beam, said system comprising:

a field emission source to provide an electron beam;

means for positioning the electron beam on the substrate accurately by measuring the position of the substrate;

means for deflecting the electron beam to the desired position of said substrate as measured by said positioning means;

means for scanning the desired position of a surface of the substrate with the electron beam;

a charged particle detector to detect at least one of the three types of charged particles emanating from the top and bottom surfaces of said substrate, namely, secondary charged particles, back-scattered charged particles and transmitted charged particles;

a continuously moving x-y stage disposed to receive said substrate and to provide at least one degree of motion to said substrate while the substrate is being scanned by the electron beam; and

a multi-processor image defect computer responsive to said charged particle detector to identify defects on said substrate;

wherein said positioning means includes an alignment computer coupled to said charged particle detector and said x-y stage to determine misalignment of an image produced by said charged particle detector and said x-y stage, and to control the movement of said x-y stage.

44. An automatic system for the automatic inspection of a substrate as in claim 43 wherein said electron deflecting means includes an objective lens having a retardation field to decelerate electrons in said electron beam.

45. An automatic system for the automatic inspection of a substrate as in claim 43 wherein the energy of said electron beam is between 500 and 1,500 volts.

46. An automatic system for the automatic inspection of a substrate as in claim 43 wherein said charged particle detector only detects secondary electrons.

47. An electrostatic immersion objective lens for use within a charged particle beam column wherein said column delivers an electron beam from an electron source to a surface of a specimen through said electrostatic immersion objective lens that is spaced apart from said specimen, said electrostatic immersion objective lens comprising:

a first, a second, and a third electrode, said objective lens disposed to be positioned with said first electrode furthest from said specimen, said third electrode closest to said specimen, and said second electrode intermediate said first and third electrodes;

a first potential adjustment circuit connected between said first and third electrodes with said third electrode at a more negative potential that said first electrode; and

a second potential adjustment circuit connected between said second electrode and one of said first and third electrodes to adjust the potential to create a substantially field free region at said surface of said specimen.

48. An electrostatic objective lens as in claim 47 further including a magnetic field generating subsystem to superimpose a magnetic field on said specimen.

49. A method for scanning an electron beam on the surface of a continuously moving specimen, said method to improve the image contrast, reduce image noise and minimize heating of said specimen, said method comprising the steps of:

a. scanning said electron beam on said specimen in a direction that is substantially perpendicular to the direction of instantaneous motion of said specimen;

b. deflecting said electron beam in the direction of the instantaneous motion of said specimen to scan the same area of said specimen several times;

c. detecting at least one of the three types of charged particles emanating from the top and bottom surfaces of said substrate as a result of step c., namely, secondary charged particles, back-scattered charged particles and transmitted charged particles;

d. identifying defects on said substrate using information from step c.; and

e. repeating steps a. and b. as many times as desired.

50. A method as in claim 49 wherein step b. includes the step of retarding a field to decelerte electrons in said electron beam.

51. A method as in claim 49 wherein the energy of said electron beam is between 500 and 1,500 volts.