Method and apparatus for using multiple relative reflectance measurements to determine properties of a sample using vacuum ultra violet wavelengths

• US 20090219537A1
• Filed: 02/28/2008
• Published: 09/03/2009
• Est. Priority Date: 02/28/2008
• Status: Abandoned Application

• Current Assignee: Jordan Valley Semiconductors Ltd. (Bruker Corporation)
• Original Assignee: Jordan Valley Semiconductors Ltd. (Bruker Corporation)
• Inventors: Walsh, Phillip
• Application Number:
  US12/072,878
• Publication Number:
  US 20090219537A1
• Time in Patent Office: Days
• US Class Current: 356/445
• CPC Class Codes: G01N 21/33 using ultraviolet light G01N21/39 takes precedence

Abstract

A method and apparatus is disclosed for measuring properties of an unknown sample. A reflectometer and one or more reference pieces is provided. A set of data is collected from the unknown sample and a combination of the reference pieces. A combination of the sample and reference piece data independent of incident intensity is used to determine a property of the unknown sample without calibrating incident reflectometer intensity. The method and apparatus disclosed can measure properties of thin films or scattering structures on semiconductor work pieces. In one embodiment the reflectometer utilizes vacuum ultraviolet (VUV) wavelength reflectometry. Multiple relative reflectance measurements are used to overcome effects of the inevitable contamination buildup that occurs when using optical systems in the VUV region. While advantageous for VUV wavelengths, the method described herein is generally applicable to any wavelength range, and is advantageous in situations where stable reference samples are not available.

Claims

1. A method of measuring properties of an unknown sample, comprising:

providing a reflectometer and at least one reference sample, wherein the at least one reference sample is unstable under conditions in which the reflectometer is operated;

collecting a set of data from the unknown sample and at least one reference sample; and

utilizing a combination of the unknown sample and reference sample data that is independent of incident intensity to determine a property of the unknown sample, without calibrating incident reflectometer intensity.

2. The method of claim 1, wherein the data obtained from the unknown sample and the at least one reference sample includes intensity data.

3. The method of claim 2, wherein reflectance ratios are obtained from the intensity data.

4. The method of claim 3, wherein one or more properties of the unknown sample are obtained by analyzing reflectance ratios using thin film models and a regression analysis to determine one or more properties of one or more of the unknown sample and the at least one reference sample.

5. The method of claim 2, wherein the collecting a set of data from the unknown sample and at least one reference sample comprises collecting a set of data from the unknown sample and a plurality of reference samples.

6. The method of claim 5, wherein plurality of reference samples comprises at least a first and second reference sample wherein the first reference sample comprises a relatively thick SiO₂/Si film structure and the second reference sample comprises a native SiO₂/Si film structure.

7. The method of claim 5, wherein the reflectance ratios comprise at least one ratio with data from the relatively thick SiO₂/Si film structure in the numerator and data from the unknown sample in the denominator and another ratio with data from the relatively thick SiO₂/Si film structure in the numerator and data from the native SiO₂/Si film structure in the denominator.

8. The method of claim 5, wherein a contaminant layer is included in a model for the reference samples.

9. The method of claim 5, wherein the unknown sample is an ultra-thin silicon oxynitride or hafnium-silicide film.

10. The method of claim 1, wherein the reflectometer is operated in at least vacuum ultraviolet (VUV) wavelengths and the at least one reference sample is unstable under VUV conditions.

11. The method of claim 10, wherein the data obtained from the unknown sample and the at least one reference sample includes intensity data.

12. The method of claim 11, wherein reflectance ratios are obtained from the intensity data.

13. The method of claim 12, wherein one or more properties of the unknown sample are obtained by analyzing reflectance ratios using thin film models and a regression analysis to determine one or more properties of one or more of the unknown sample and the at least one reference sample.

14. The method of claim 11, wherein the collecting a set of data from the unknown sample and at least one reference sample comprises collecting a set of data from the unknown sample and a plurality of reference samples.

15. A system for measuring properties of an unknown sample, comprising:

at least one reference sample;

a reflectometer configured for collecting a set of data from the unknown sample and the at least one reference sample wherein the at least one reference sample is unstable under conditions in which the reflectometer is operated; and

a computer operating a software routine configured to utilize a combination of the unknown sample and reference sample data that is independent of incident intensity to determine a property of the unknown sample, without calibrating incident reflectometer intensity.

16. The system of claim 15, wherein the at least one reference sample is a reference piece integrated with a sample holding system.

17. The system of claim 16, further comprising of a plurality of the reference pieces.

18. The system of claim 15, wherein the data obtained from the unknown sample and the at least one reference sample includes intensity data and wherein the software routine is configured to obtain reflectance ratios from the intensity data.

19. The system of claim 15, wherein the at least one reference sample comprises a plurality of reference samples.

20. The system of claim 19, wherein the plurality of reference samples comprises at least a first and second reference sample wherein the first reference sample comprises a relatively thick SiO₂/Si film structure and the second reference sample comprises a native SiO₂/Si film structure.

21. The system of claim 15, wherein the reflectometer is configured to operate in at least vacuum ultraviolet (VUV) wavelengths and the at least one reference sample is unstable under VUV conditions.

22. The system of claim 21, wherein the at least one reference sample is a reference piece integrated with a sample holding system.

23. The system of claim 22, further comprising of a plurality of the reference pieces.

24. The system of claim 21, wherein the data obtained from the unknown sample and the at least one reference sample includes intensity data and wherein the software routine is configured to obtain reflectance ratios from the intensity data.

25. The system of claim 21, wherein the at least one reference sample comprises a plurality of reference samples.

26. A system for measuring properties of an unknown sample, comprising:

at least one reference sample;

a reflectometer, configured for collecting a set of data from the unknown sample and the at least one reference sample wherein the at least one reference sample is unstable under conditions in which the reflectometer is operated; and

a computer operating a software routine that selectably operates in at least one of a plurality of measurement modes, the plurality of measurement modes including at least a first measurement mode and a second measurement mode, wherein,

the first measurement mode is configured to utilize a combination of the unknown sample and reference sample data that is independent of incident intensity to determine a property of the unknown sample, without calibrating incident reflectometer intensity, and

the second measurement mode is configured to utilize the reference sample data in a manner that is independent of incident intensity to determine one or more properties of one or more reference pieces, thereby determining the incident intensity of the reflectometer, after which reflectance of unknown samples may be determined.

27. The system of claim 26, wherein the at least one reference sample is a reference piece integrated with a sample holding system.

28. The system of claim 27, further comprising of a plurality of the reference pieces.

29. The system of claim 26, wherein in the first measurement mode the data obtained from the unknown sample and the at least one reference sample includes intensity data and wherein the software routine is configured to obtain reflectance ratios from the intensity data.

30. The system of claim 26, wherein in at least the first measurement mode the at least one reference sample comprises a plurality of reference samples.

31. The system of claim 30, wherein in the first measurement mode the plurality of reference samples comprises at least a first and second reference sample wherein the first reference sample comprises a relatively thick SiO₂/Si film structure and the second reference sample comprises a native SiO₂/Si film structure.

32. A method of measuring properties of an unknown sample, comprising:

providing a reflectometer and at least one reference sample, wherein the at least one reference sample is unstable under conditions in which the reflectometer is operated;

collecting a set of data from the unknown sample and at least one reference sample; and

selectably operating the system in at least one of a plurality of measurement modes, the plurality of measurement modes including at least a first measurement mode and a second measurement mode, wherein,

the first measurement mode is configured to utilize a combination of the unknown sample and reference sample data that is independent of incident intensity to determine a property of the unknown sample, without calibrating incident reflectometer intensity, and

the second measurement mode is configured to utilize the reference sample data in a manner that is independent of incident intensity to determine one or more properties of one or more reference pieces, thereby determining the incident intensity of the reflectometer, after which reflectance of unknown samples may be determined.

33. The method of claim 32, wherein in the first measurement mode the data obtained from the unknown sample and the at least one reference sample includes intensity data.

34. The method of claim 33, wherein in the first measurement mode reflectance ratios are obtained from the intensity data.

35. The method of claim 34, where the reflectance ratios comprise at least one ratio with data from the relatively thick SiO₂/Si film structure in the numerator and data from the unknown sample in the denominator and another ratio with data from the relatively thick SiO₂/Si film structure in the numerator and data from the native SiO₂/Si film structure in the denominator.

36. The method of claim 32, wherein in the first measurement mode one or more properties of the unknown sample are obtained by analyzing reflectance ratios using thin film models and a regression analysis to determine one or more properties of one or more of the unknown sample and the at least one reference sample.

37. The method of claim 32, wherein the collecting a set of data from the unknown sample and at least one reference sample comprises collecting a set of data from the unknown sample and a plurality of reference samples.

38. The method of claim 32, wherein the at least one reference sample comprises at least a first and second reference sample wherein the first reference sample comprises a relatively thick SiO₂/Si film structure and the second reference sample comprises a native SiO₂/Si film structure.

39. The method of claim 32, where a contaminant layer is included in a model for the reference samples.