Method and system for using reflectometry below deep ultra-violet (DUV) wavelengths for measuring properties of diffracting or scattering structures on substrate work pieces
A method and apparatus is disclosed for using below deep ultra-violet (DUV) wavelength reflectometry for measuring properties of diffracting and/or scattering structures on semiconductor work-pieces is disclosed. The system can use polarized light in any incidence configuration, but one technique disclosed herein advantageously uses un-polarized light in a normal incidence configuration. The system thus provides enhanced optical measurement capabilities using below deep ultra-violet (DUV) radiation, while maintaining a small optical module that is easily integrated into other process tools. A further refinement utilizes an r-θ stage to further reduce the footprint.
1. A reflectometer apparatus for analyzing a scattering or diffracting structure, comprising:
a below deep ultra-violet (DUV) wavelength referencing reflectometer configured for normal incidence operation and having a light source that provides light at wavelengths below 190 nm, wherein referencing is configured to account for system and environmental changes to adjust reflectance data obtained through use of the reflectometer; and
at least one computer, which is connected to the reflectometer and is configured to run a computer program which causes the at least one computer to extract structural and optical parameters from a theoretical model of the scattering or diffracting structure,
wherein the computer program uses a reduced RCW calculation for analyzing 2-D periodic structures of the scattering or diffracting structure.
2. The apparatus of claim 1 , wherein an absolute reflectance of the below DUV wavelength referencing reflectometer is calibrated using reflectance ratios of two or more calibration samples in order to account for changing conditions of the calibration samples.
3. The apparatus of claim 1 , wherein the computer program uses a group theoretic approach for analyzing 3-D periodic structures.
4. The apparatus of claim 1 , wherein the light directed on the scattering or diffracting structure is un-polarized.
5. The apparatus of claim 4 , further comprising an r-θ stage for holding the scattering or diffracting structure.
6. The apparatus of claim 5 , wherein a calculated reflectance is obtained from a relationship R=0.5*(R TE +R TM ), regardless of a sample rotation.
7. The apparatus of claim 1 , wherein the reflectometer comprises at least one environmentally controlled chamber in which the light travels, the chamber sufficiently controlled to allow transmission of wavelengths below DUV light.
8. A method of optically measuring diffracting and scattering features on a sample, comprising:
providing an optical signal having at least some light at wavelengths below 190 nm;
directing the light on the sample in a substantially normally incident configuration, wherein the incident light is un-polarized;
utilizing a reduced RCW calculation to analyze 2-D periodic structures; and
utilizing a group theoretic approach to analyze 3-D periodic structures.
9. The method of claim 8 , wherein the diffracting and scattering features on a sample are optically measured via a reflectometer having at least some light below deep ultra-violet wavelengths.
10. The method of claim 9 , wherein referencing is utilized to account for system and environmental changes to adjust reflectance data obtained through use of the reflectometer.
11. The method of claim 9 , wherein the absolute reflectance of the reflectometer is calibrated using reflectance ratios of two or more calibration samples in order to account for changes in calibration sample conditions.
12. The method of claim 8 , wherein the reflectometer employs an r-θ stage.
13. The method of claim 12 , wherein a calculated reflectance is obtained for 2-D and 3-D periodic structures from a relationship R=0.5*(R TE +R TM ), regardless of sample rotation.
14. A method of optically measuring diffracting and scattering features on a sample, comprising:
providing a reflectometer that utilizes at least some light at wavelengths below 190 nm;
measuring intensity data from a plurality of sites within an area of the sample; and
analyzing a combination of the measured intensity data from the plurality of sites that is independent of incident intensity in order to extract structural and/or optical property information regarding the sample.
15. The method of claim 14 , wherein at least one of the sites represents an un-patterned region of the sample and at least one other site represents a patterned region of the sample.
16. The method of claim 15 , where at least one property of a patterned region film and one property of an un-patterned region film are common.
17. The method of claim 16 , wherein the value of the at least one common property is coupled when analyzing the combination of the measured intensity data.
18. The method of claim 14 , wherein the measured intensity data is obtained serially from at least two of the plurality of sites.
19. The method of claim 14 , wherein a reflectance ratio between two or more of the sites is formed from the intensity data.
20. The method of claim 19 , wherein the reflectance ratio is utilized at least in part to avoid calibrating an absolute reflectance of the reflectometer.
21. A method of optically measuring diffracting and scattering features on a sample, comprising:
providing a reflectometer that utilizes at least some light at wavelengths below 190 nm; and
measuring intensity data from a plurality of sites within an area of the sample; wherein at least one of the sites represents an un-patterned region of the sample and at least one other site represents a patterned region of the sample.
22. The method of claim 21 , wherein a reflectance ratio between two or more of the sites is formed from the intensity data.
23. The method of claim 22 , wherein the reflectance ratio is utilized at least in part to avoid calibrating an absolute reflectance of the reflectometer.
24. A reflectometer apparatus for analyzing a scattering or diffracting structure, comprising:
a below deep ultra-violet (DUV) wavelength referencing reflectometer configured for normal incidence operation and having an unpolarized light source and non-polarizing optical system that provides light at wavelengths below 190 nm, wherein referencing is configured to account for system and environmental changes to adjust reflectance data obtained through use of the reflectometer;
at least one computer, which is connected to the reflectometer and is configured to run a computer program which causes the at least one computer to extract structural and optical parameters from a theoretical model of the scattering or diffracting structure; and
an r-θ stage for holding the scattering or diffracting structure, wherein a calculated reflectance is obtained from a relationship that is independent of a sample rotation.
25. The apparatus of claim 24 , wherein an absolute reflectance of the below DUV wavelength referencing reflectometer is calibrated using reflectance ratios of two or more calibration samples in order to account for changing conditions of the calibration samples.
26. The apparatus of claim 24 , wherein the relationship is R=0.5*(R TE +R TM ).