Optical metrology tool having improved contrast

• US 20030133102A1
• Filed: 05/28/2002
• Published: 07/17/2003
• Est. Priority Date: 01/16/2002
• Status: Active Grant

• Current Assignee: The Therma-Wave Incorporated (KLA Corporation)
• Original Assignee: The Therma-Wave Incorporated (KLA Corporation)
• Inventors: Opsal, Jon
• Granted Patent: US 7,050,162 B2
• Time in Patent Office: Days
• US Class Current: 356/237.1
• CPC Class Codes: G01N 2021/213 Spectrometric ellipsometry
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/956 Inspecting patterns on the surface of objects contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10

Abstract

The subject invention relates to broadband optical metrology tools for performing measurements of patterned thin films on semiconductor integrated circuits. Particularly a family of optical designs for broadband optical systems wherein the ratio of illumination system to collection system numerical apertures is less than 1. System performance is enhanced through selection and control of the optical system partial coherence; this is accomplished through installation of beam-control apertures within the illumination and collection optical systems. The invention is broadly applicable to a large class of broadband optical wafer metrology techniques including spectrophotometry, spectroscopic reflectometry, spectroscopic ellipsometry and spectroscopic scatterometry.

Claims

1. A method for evaluating a sample with a optical wafer metrology tool employing an incoherent light source, illumination optics that collect a portion of the light from the source and illuminate the sample at a small-spot, the illumination interacting with and reflecting from the sample, collection optics that collect at least a fraction of the reflected illumination, a detection system generating output signals in response to the collected illumination and a processor for recording and analyzing the output signals, said method comprising:

limiting the angular range of the illumination striking the sample to an illumination numerical aperture, NA_I;

limiting the angular variation of the fraction of the reflected radiation collected by the collection optics to a collection numerical aperture, NA_C;

constraining the above described angular limitations to configurations where NA_C>

NA_I, whereby the relative numerical aperture NA_R≡

NA_I/NA_C assumes a value less than 1.

2. The method of claim 1 where NA_R is less than 0.9.

3. The method of claim 1 where NA_R is less than 0.8.

4. The arrangement of claim 1 where 0.50≦

NA_R≦

0.90.

5. The arrangement of claim 1 where 0.70≦

NA_R≦

0.90.

6. The arrangement of either claim 4 or 5 wherein the NA_R is adjustable.

7. The method of any of claims 1 to 5 wherein the light source is a broadband light source and the optical metrology tool employs at least one metrology system selected from the group consisting of spectroscopic reflectometers, polarized beam spectroscopic reflectometers, spectroscopic ellipsometers and spectroscopic scatterometers.

8. An arrangement of an optical metrology tool for evaluating a sample with light, including an incoherent light source, illumination optics that collect a portion of the light from the source and illuminate the sample at a small-spot, the illumination interacting with and reflecting from the sample, collection optics that collect at least a fraction of the reflected illumination, a detection system generating output signals in response to the collected illumination and a processor for recording and analyzing the output signals, said arrangement including:

means for limiting the angular range of the illumination striking the sample to an illumination numerical aperture, NA_I;

means for limiting the angular variation of the fraction of the reflected radiation collected by the collection optics to a collection numerical aperture, NA_C;

selecting NA_C and NA_I such that NA_C>

NA_I, whereby the relative numerical aperture NA_R≡

NA_I/NA_C assumes a value less than 1.

9. The arrangement of claim 8 where NA_R is less than 0.9.

10. The arrangement of claim 8 where NA_R is less than 0.8.

11. The arrangement of claim 8 where 0.50≦

NA_R≦

0.90.

12. The arrangement of claim 8 where 0.70≦

NA_R≦

0.90.

13. The arrangement of either claims 11 or 12 wherein the NA_R is adjustable.

14. The arrangement of any of claims 8 to 12 wherein the light source is a broadband light source and the optical metrology tool employs at least one metrology system selected from the group consisting of spectroscopic reflectometers, polarized beam spectroscopic reflectometers, spectroscopic ellipsometers and spectroscopic scatterometers.

15. An apparatus for evaluating a sample with light including an incoherent light source, illumination optics that collect a portion of the light from the source and illuminate the sample at a small-spot, the illumination interacting with and reflecting from the sample, collection optics that collect at least a fraction of the reflected illumination, a detection system generating output signals in response to the collected illumination and a processor for recording and analyzing the output signals, said apparatus further including:

a first beam-limiting aperture for limiting the angular range of the illumination striking the sample to an illumination numerical aperture, NA_I;

a second beam-limiting aperture for limiting the angular variation of the fraction of the reflected radiation collected by the collection optics to a collection numerical aperture, NA_C;

said first and second apertures configured so that NA_C>

NA_I, whereby the relative numerical aperture NA_R≡

NA_I/NA_C assumes a value less than 1.

16. The apparatus of claim 15 where NA_R is less than 0.9.

17. The apparatus of claim 15 where NA_R is less than 0.8.

18. The apparatus of claim 15 where 0.50≦

NA_R≦

0.90.

19. The apparatus of claim 15 where 0.70≦

NA_R≦

0.90.

20. The apparatus of claims 18 or 19 wherein the NA_R is adjustable.

21. The apparatus of an of claims 15 to 19 wherein the light source is a broadband light source and the optical metrology tool employs at least one metrology system selected from the group consisting of spectroscopic reflectometers, polarized beam spectroscopic reflectometers, spectroscopic ellipsometers and spectroscopic scatterometers.

22. The apparatus of claim 21 wherein the metrology tool employs a plurality of metrology systems selected from the group consisting of reflectometers, polarized beam reflectometers, ellipsometers, scatterometers, optical CD metrology tools, spectroscopic reflectometers, polarized beam spectroscopic reflectometers, spectroscopic ellipsometers, spectroscopic scatterometers and spectroscopic optical CD metrology tools, and the processor analyzes the detector outputs either individually or in combination to evaluate the sample.

23. An apparatus for evaluating characteristics of a sample comprising:

a broad band light source for generating a polychromatic probe beam of radiation;

an optical element for focusing the probe beam to a small spot on the surface of the sample;

collection optics for gathering the reflected probe beam radiation;

a detector system for measuring changes in the probe beam due to interaction with the sample and generating output signals in response thereto;

a processor for evaluating characteristics of the sample based on the output signals and wherein the illumination path is configured to have a numerical aperture (NA_I) less than the numerical aperture of the collection path (NA_C) whereby the relative numerical aperture NA_R≡

NA_I/NA_C assumes a value less than 1.

24. The apparatus of claim 23 where NA_R is less than 0.9.

25. The apparatus of claim 23 where NA_R is less than 0.8.

26. The apparatus of claim 23 where 0.50≦

NA_R≦

0.90.

27. The apparatus of claim 23 where 0.70≦

NA_R≦

0.90.

28. The apparatus of claims 26 or 27 wherein the NA_R is adjustable.