Detection of contaminants on low wavelength masks

• US 20020135759A1
• Filed: 03/23/2001
• Published: 09/26/2002
• Est. Priority Date: 03/23/2001
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Dao, Giang, Gerth, Christopher, Ramamoorthy, Arun
• Granted Patent: US 6,611,327 B2
• Time in Patent Office: Days
• US Class Current: 356/237.2
• CPC Class Codes: G01N 21/65 Raman scattering
• CPC Class Codes: G03F 7/70483 Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring

Abstract

Testing of a mask which is intended to be used for low wavelength lithography. At lower wavelengths, e.g., 157 nm, certain contaminants may become visible, even though they were transparent under visible or ultraviolet light. A combination of Raman spectroscopy and infrared absorption spectroscopy are used to identify the contaminants.

Claims

1. A testing method, comprising:

testing a lithography mask using a combination of Raman techniques and infrared absorption techniques; and

using said testing to detect contaminants on said mask, including contaminants which may be substantially transparent at ultraviolet and visible wavelengths.

2. A method as in claim 1, further comprising using said mask for lithography, after said testing.

3. A method as in claim 2, wherein said lithography is carried out using 157 nm light.

4. A method as in claim 3, wherein said using comprises determining materials which are transparent at visible and ultraviolet inspection wavelengths, but opaque at 157 nm.

5. A method as in claim 1, wherein said testing comprises first testing a known cleaned mask, to determine a background spectrum, and second testing a mask to be tested, and subtracting said background spectrum to obtain a resultant absorption spectrum.

6. A method as in claim 1, wherein said testing comprises detecting scattered light and detecting transmitted light.

7. A testing method, comprising:

testing a mask using a first technique which uses a first kind of light to detect interaction with dipole moments of elements on the surface of said mask; and

testing said mask using a second technique simultaneously with the first technique, using a second kind of light different than the first kind of light.

8. A method as in claim 7, wherein said first kind of light is infrared light.

9. A method as in claim 7, wherein said first kind of light is laser light.

10. A method as in claim 8, wherein said second kind of light is laser light.

11. A method as in claim 7, wherein said first technique includes infrared absorption spectroscopy.

12. A method as in claim 11, wherein said second technique includes Raman spectroscopy.

13. A method as in claim 7, wherein said first and second testing comprise finding contaminants which are transparent under visible light.

14. A method as in claim 7, wherein said first and said second testing comprises finding contaminants which are transparent under ultraviolet light.

15. A method as in claim 14, further comprising analyzing said spectrum to be analyzed by comparing said spectrum against other spectra including spectra of possible contaminants.

17. A method as in claim 16, wherein said comparing comprises subtracting a background spectra from an acquired spectra, prior to said comparing.

18. A method as in claim 16, wherein said contaminants include water.

19. A method as in claim 16, wherein said wavelength lower than visible includes a wavelength which is less than 200 nm.

20. A method as in claim 19, wherein said wavelength lower than visible is 157 nm.

28. A method as in claim 7, further comprising testing a mask which is clean, to obtain a spectrum therefrom, and subtracting said spectrum from a final spectrum, to form a spectrum to be analyzed.

16. A method, comprising:

using both of a predetermined first and second measuring techniques to detect spectra of a plurality of different contaminants which are transparent at visible wavelengths, but which are detectable at lower than visible wavelengths to obtain spectra; and

comparing said spectra against said spectra of said plurality of different contaminants.

21. A testing system, comprising:

a light source which produces a Raman laser and an infra red absorption spectroscopy output; and

a detector which detects a result of both IR absorption and Raman spectroscopy on a sample.

22. A system as in claim 21, further comprising an element which forms can absorption spectrum based on a result of said detector.

23. A system as in claim 21, wherein said sample is a lithography mask.

25. A method as in claim 24, wherein said first technique includes a first detecting and a second detecting using a different operation than said first detecting.

26. A method as in claim 24, wherein said first detecting and said second detecting each detect a dipole reaction of said material.

27. A method as in claim 26, wherein said first detecting is infrared absorption, and said second detecting is Raman spectroscopy.

24. A method comprising:

inspecting a mask surface using a first technique that does not depend on interacting with any material on the mask surface in a way that depends on the visible light passing characteristics of the material; and

also inspecting said mask surface using a second technique where the surface is visually inspected.