Claims
- 1. A small spot ellipsometer for evaluating a sample comprising:a light source for generating a probe beam which is to be directed to the surface of the sample; an analyzer for evaluating the change in polarization state induced in the beam from interacting with the sample; and a lens for focusing the beam to a spot size having a diameter along both axes of less than 25 microns, said lens having a curved focusing surface and being formed from a material whose index of refraction varies along the optical axis in order to substantially reduce spherical aberration.
- 2. An ellipsometer as recited in claim 1, wherein the focal length of the lens is less than 50 mm.
- 3. An ellipsometer as recited in claim 2 wherein the numerical aperture of the lens is less than 0.20.
- 4. An ellipsometer is recited in claim 2 wherein the numerical aperture of the lens is less than 0.15.
- 5. An ellipsometer as recited in claim 2 wherein the effective numerical aperture of the lens is about 0.1.
- 6. A ellipsometer as recited in claim 1 wherein said material has a coefficient of thermal expansion in excess of 1×10−7/K.
- 7. An ellipsometer as recited in claim 1, further including a lens mount including a plurality of flexible O-rings for supporting the lens in a manner to reduce stress birefringence in the lens induced by changes in the ambient temperature.
- 8. An ellipsometer as recited in claim 1, wherein said probe beam is defined by a stable, narrow-bandwidth beam.
- 9. An ellipsometer as recited in claim 8 wherein said light source is a gas-discharge laser.
- 10. An ellipsometer as recited in claim 1 wherein the focused spot on the sample has a diameter along both axes of less than 20 microns.
- 11. A small spot ellipsometer for evaluating a sample comprising:a light source for generating a probe beam which is to be directed to the surface of the sample; an analyzer for evaluating the change in polarization state induced in the beam from interaction with the sample; a lens for focusing the beam to a spot on the sample surface, said lens having a curved focusing surface and being formed from a material whose index of refraction varies along the optical axis in order to substantially reduce spherical aberration; and a low stress lens mount including a resilient member for supporting the lens in a manner to reduce stress birefringence in the lens induced by changes in the ambient temperature.
- 12. An ellipsometer as recited in claim 11, wherein a focal length of the lens is less than 50 mm.
- 13. An ellipsometer as recited in claim 12, wherein a numerical aperture of the lens is less than 0.20.
- 14. An ellipsometer as recited in claim 12, wherein a numerical aperture of the lens is less then 0.15.
- 15. An ellipsometer as recited in claim 12, wherein an effective numerical aperture of the lens is about 0.1.
- 16. An ellipsometer as recited in claim 11, wherein said probe beam is defined by a stable, narrow-bandwidth beam.
- 17. An ellipsometer as recited in claim 16, wherein said light source is a gas-discharge laser.
- 18. An ellipsometer as recited in claim 11, wherein the focused spot on the sample has a diameter along both axes if less 20 microns.
- 19. An ellipsometer as recited in claim 11, wherein the focused spot on the sample has a diameter along one axis of less than 20 microns.
- 20. An ellipsometer as recited in claim 19 wherein the focused spot diameter on the sample has a diameter along one axis of less than 10, microns.
- 21. A small spot ellipsometer for evaluating a sample comprising:a gas discharge laser having a stable, narrow-bandwidth output defining a probe beam directed to reflect off the surface of the sample; an analyzer for evaluating the change in polarization state induced in the beam when the beam reflects off the sample; a lens for focusing the beam to a spot size having a diameter along both axes of less than 20 microns, said lens having a spherical focusing surface, a focal length of less than 50 mm and a numerical aperture less then 0.15 and being formed from a mixture of glass materials arranged so that the index of refraction of the lens varies along the optical axis thereof in order to substantially reduce spherical aberration; and a low stress lens mount including a resilient member for supporting the lens in a manner to reduce stress birefringence in the lens induced by changes in the ambient temperature.
- 22. An ellipsometer as recited in claim 21, wherein the effective numerical aperture of the lens is about 0.1.
- 23. An ellopsometer as recited in claim 21, wherein the focused spot diameter on the sample has a diameter along one axis of less than 10 microns.
Parent Case Info
This application is a continuation application of U.S. patent application 09/779,761, entitled SMALL SPOT ELLIPSOMETER having a filing date of Feb. 8, 2001 now U.S. Pat. No. 6,515,744, and which is hereby incorporated by reference.
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Entry |
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Continuations (1)
|
Number |
Date |
Country |
Parent |
09/779761 |
Feb 2001 |
US |
Child |
10/310195 |
|
US |