Claims
- 1. In a measurement system a method of evaluating a sample comprising:
generating a probe beam which is to be directed to the surface of the sample; analyzing the probe beam after it has been reflected off the sample to determine characteristics of the sample; and focusing the beam to a spot on the sample surface, using a lens, 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 wherein said lens is supported in 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.
- 2. The method of claim 1, wherein a focal length of the lens is less than 50 mm.
- 3. The method of claim 2, wherein a numerical aperture of the lens is less than 0.20.
- 4. The method of claim 2, wherein a numerical aperture of the lens is less than 0.15.
- 5. The method of claim 2, wherein an effective numerical aperture of the lens is about 0.1.
- 6. The method of claim 1, wherein said probe beam is defined by a stable, narrow-bandwidth beam.
- 7. The method of claim 6, wherein said light source is a gas-discharge laser.
- 8. The method of claim 1, wherein the focused spot on the sample has a diameter along both axes of less than 25 microns.
- 9. The method of claim 1, wherein the focused spot on the sample has a diameter along both axes of less than 20 microns.
- 10. The method of claim 9, wherein the focused spot diameter on the sample has a diameter along one axis of less than 10 microns.
- 11. 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 25 microns, said lens having a spherical focusing surface, a focal length of less than 50 mm and a numerical aperture less than 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.
- 12. An ellipsometer as recited in claim 11, wherein the focused spot diameter on the sample has a diameter along one axis of less than 10 microns.
RELATED APPLICATIONS
[0001] This application is a continuation application of U.S. patent application Ser. No. 10/310,195, entitled SMALL SPOT ELLIPSOMETER, having a filing date of Dec. 4, 2002, and which is a continuation of U.S. patent application Ser. No. 09/779,761, now issued U.S. Pat. No. 6,515,744 entitled SMALL SPOT ELLIPSOMETER having a filing date of Feb. 8, 2001, and both of these patent applications are incorporated herein by reference in their entirety.
Continuations (2)
|
Number |
Date |
Country |
Parent |
10310195 |
Dec 2002 |
US |
Child |
10811018 |
Mar 2004 |
US |
Parent |
09779761 |
Feb 2001 |
US |
Child |
10310195 |
Dec 2002 |
US |