Systems and methods for producing a more uniform intensity wavelength dispersed beam of electromagnetic radiation entering a multielement detector, while maintaining information content therein

• US 10,627,288 B1
• Filed: 04/29/2019
• Issued: 04/21/2020
• Est. Priority Date: 10/06/2015
• Status: Active Grant

• Current Assignee: J.A. Woollam Co., Inc.
• Original Assignee: J.A. Woollam Co., Inc.
• Inventors: Liphardt, Martin M., He, Ping
• Primary Examiner(s): Chowdhury, Tarifur R
• Assistant Examiner(s): Nixon, Omar H
• Application Number:
  US16/501,536
• Time in Patent Office: 358 Days
• Field of Search: 356326
• CPC Class Codes: G01J 2003/1213 Filters in general, e.g. dichroic, band
• CPC Class Codes: G01J 2003/1278 Mask with spectral selection
• CPC Class Codes: G01J 2003/1282 Spectrum tailoring
• CPC Class Codes: G01J 2003/2809 Array and correcting filter
• CPC Class Codes: G01J 2003/282 Modified CCD or like
• CPC Class Codes: G01J 3/0213 using attenuators
• CPC Class Codes: G01J 3/0224 using polarising or depolarising elements
• CPC Class Codes: G01J 3/0229 using masks, aperture plates, spatial light modulators or spatial filters, e.g. reflective filters
• CPC Class Codes: G01J 3/12 Generating the spectrum; Monochromators
• CPC Class Codes: G01J 3/2803 using photoelectric array detector
• CPC Class Codes: G01J 3/433 Modulation spectrometry; Derivative spectrometry
• CPC Class Codes: G01J 4/04 Polarimeters using electric detection means G01J4/02 takes precedence
• CPC Class Codes: G01N 21/21 Polarisation-affecting properties G01N21/19 takes precedence
• CPC Class Codes: G01N 21/211 Ellipsometry optical thickness measurement G01B11/06
• CPC Class Codes: G01N 21/31 Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry G01N21/72 takes precedence
• CPC Class Codes: G01N 21/55 Specular reflectivity

Abstract

Reflectometer, Spectrophotometer, Ellipsometer and Polarimeter Systems that utilize 1) electromagnetic radiation energy absorbing or reflecting material of spatially distributed different optical densities and 2) wavelength dependent electromagnetic radiation energy aperturing, or both, placed near the entry to said multi-element detector, to improve detector capability to monitor intensity vs. wavelength spectra entered thereinto and provide more uniform detector output, while preferably maintaining beam information content.

Claims

1. A reflectometer, spectrophotometer, ellipsometer or polarimeter system comprising:

a) a source of a spectroscopic beam of electromagnetic radiation;

b) a stage for supporting a sample;

c) a wavelength dispersion element; and

d) a multi-element detector for detecting a beam of electromagnetic radiation provided by said source electromagnetic radiation;

such that in use said source provides a spectroscopic beam of electromagnetic radiation which interacts with a sample placed on said stage for supporting a sample, then is dispersed by a dispersion element and enters said multi-element detector;

said multi-element detector of electromagnetic radiation comprising a selection from the group consisting of;

an electromagnetic radiation energy absorbing or reflecting material of spatially varying optical densities, which is designed to attenuate high intensity wavelengths more than low intensity wavelengths on the entry to said detector so that at least one wavelength of relatively higher intensity is more attenuated than is a relatively lower intensity wavelength, and is therefore reduced in intensity more than is the relatively lower intensity wavelength; and

a wavelength dependent electromagnetic radiation energy blocking aperture which is designed to attenuate high intensity wavelengths more than low intensity wavelengths on the entry to said multi-element detector, so that at least one wavelength of relatively higher intensity is subjected to greater aperturing, and thus a smaller area through which to pass, than is a relatively lower intensity wavelength and is therefore reduced in intensity more than is the relatively lower intensity wavelength;

said system being distinguished in that at least one wavelength of relatively higher intensity is more attenuated and/or apertured than are at least two relatively lower intensity wavelengths between which is said at least one wavelength of relatively higher intensity;

the result being a more uniform intensity beam of electromagnetic radiation entering said multi-element detector and more uniform detector output, as a function of wavelength.

2. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 1, wherein said multi-element detector has electromagnetic radiation energy absorbing or reflecting material of spatially varying optical densities on the entry thereto, positioned symmetrically at both top and bottom locations, as viewed in frontal elevation.

3. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 1, wherein said multi-element detector has electromagnetic radiation energy absorbing or reflecting material of spatially varying optical densities on the entry thereto, positioned symmetrically at both left and right locations, as viewed in frontal elevation.

4. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 1, in which the electromagnetic radiation energy absorbing or reflecting material provides spatial variation in optical densities in both vertical and lateral directions, as the multi-element detector is viewed in frontal elevation.

5. A reflectometer, spectrophotometer, ellipsometer or polarimeter system comprising:

a) a source of a spectroscopic beam of electromagnetic radiation;

b) a stage for supporting a sample;

c) a wavelength dispersion element; and

d) a multi-element detector for detecting a beam of electromagnetic radiation provided by said source electromagnetic radiation;

such that in use said source provides a spectroscopic beam of electromagnetic radiation which interacts with a sample placed on said stage for supporting a sample, then is dispersed by a dispersion element and then enters said multi-element detector;

said multi-element detector of electromagnetic radiation comprising a surface having non-uniform optical and/or physical properties, through which surface electromagnetic radiation passes to reach the multiple elements of said detector;

there being at least three different regions of said non-uniform surface optical and/or physical properties, none of which completely blocks electromagnetic radiation incident thereupon, said at least three different regions being variously sensitive to wavelengths in electromagnetic radiation entered thereto, but substantially insensitive to other attributes thereof;

said at least three different regions of said non-uniform surface optical and/or physical properties being characterized in that the more centrally located is of a higher optical density and/or thickness than are the adjacent regions.

6. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein each of said at least three different regions of non-uniform surface optical and/or physical properties interact with electromagnetic radiation which pass therethrough differently, as a function of wavelength.

7. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the at least three different regions of non-uniform surface optical and/or physical properties differ from one another based on optical density properties.

8. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the at least three different regions of non-uniform surface optical and/or physical properties differ from one another based on physical thickness properties.

9. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the at least three different regions of non-uniform surface optical and/or physical properties differ from one another based on both optical density and physical thickness properties.

10. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the at least three different regions of non-uniform surface optical and/or physical properties are different locations in a gradient of optical and/or physical properties.

11. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, which further comprises electromagnetic radiation blocking material at the surface thereof, positioned symmetrically at both upper and lower locations thereof, as viewed in frontal elevation so that said beam of electromagnetic radiation continues to reach said detector elements through said at least three different regions of non-uniform surface optical and/or physical properties, and therefore information content is maintained, said blocking material serving to attenuate all wavelengths substantially equally.

12. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, which further comprises electromagnetic radiation blocking material at the surface thereof, positioned symmetrically at both right and left locations thereof, as viewed in frontal elevation.

13. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the surface has non-uniform optical and/or physical properties that vary symetrically in a vertical direction, as the multi-element detector is viewed in frontal elevation.

14. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the surface has non-uniform optical and/or physical properties that vary symetrically in a lateral direction, as the multi-element detector is viewed in frontal elevation.

15. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the surface has non-uniform optical and/or physical properties that vary symetrically in both vertical and lateral directions, as the multi-element detector is viewed in frontal elevation.

16. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the non-uniform optical and/or physical properties at the surface are achieved by deposition of energy absorbing or reflecting material thereupon.

17. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the non-uniform optical and/or physical properties at the surface are achieved by placement of energy absorbing or reflecting material in contact therewith.

18. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the surface non-uniform optical and/or physical properties serve to attenuate higher intensity wavelengths more than lower intensity wavelengths.

19. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the multi-element detector of electromagnetic radiation is a charge coupled device (CCD).

20. A reflectometer, spectrophotometer, ellipsometer or polarimeter system as in claim 5, wherein the at least two different regions are distinct regions of non-uniform surface optical and/or physical properties present with abrupt property changes at any border therebetween.