Method for in-situ monitoring of patterned substrate processing using reflectometry.

• US 7,019,844 B2
• Filed: 11/01/2002
• Issued: 03/28/2006
• Est. Priority Date: 08/13/2002
• Status: Expired due to Term

• Current Assignee: Lam Research Corporation
• Original Assignee: Lam Research Corporation
• Inventors: Venugopal, Vijayakumar C., Perry, Andrew J.
• Primary Examiner(s): Toatley, Jr., Gregory J.
• Assistant Examiner(s): Lyons, Michael A.
• Application Number:
  US10/286,410
• Publication Number:
  US 20040032592A1
• Time in Patent Office: 1,243 Days
• Field of Search: 356/503, 356/504
• US Class Current: 356/504
• CPC Class Codes: G01B 11/0625 with measurement of absorption or reflection
• CPC Class Codes: G01B 11/0683 measurement during deposition or removal of the layer
• CPC Class Codes: G01N 21/8422 Investigating thin films, e.g. matrix isolation method

Abstract

A method of determining a parameter of interest during fabrication of a patterned substrate includes illuminating at least a portion of the patterned substrate with a normal incident light beam, obtaining a measured net reflectance spectrum of the portion of the patterned substrate from a normal reflected light beam, calculating a modeled net reflectance spectrum of the portion of the patterned substrate, and determining a set of parameters that provides a close match between the measured net reflectance spectrum and the modeled net reflectance spectrum. The modeled net reflectance spectrum is calculated as a weighted incoherent sum of reflectances from n≧1 different regions constituting the portion of the patterned substrate, wherein the reflectance of each of the n different regions is a weighted coherent sum of reflected fields from k≧1 laterally-distinct areas constituting the region.

Claims

1. A method of determining a parameter of interest during fabrication of a patterned substrate, comprising:

illuminating at least a portion of the patterned substrate with a normal incident light beam;

obtaining a measured net reflectance spectrum of the portion of the patterned substrate from a normal reflected light beam;

calculating a modeled net reflectance spectrum of the portion of the patterned substrate as a weighted incoherent sum of reflectances from n≧

1 different regions constituting the portion of the patterned substrate, wherein the reflectance of each of the n different regions is a weighted coherent sum of reflected fields from k≧

1 laterally-distinct areas constituting the region; and

determining a set of parameters that provides a close match between the measured net reflectance spectrum and the modeled net reflectance spectrum.

2. The method of claim 1, further comprising extracting the parameter of interest from the set of parameters.

3. The method of claim 1, wherein each laterally-distinct area is modeled as an isotropic, homogeneous thin-film stack.

4. The method of claim 3, wherein calculating the modeled net reflectance spectrum comprises modeling the patterned substrate as having a nominally polarization-independent reflectance.

5. The method of claim 1, wherein calculating the modeled net reflectance spectrum comprises applying a loss factor to the modeled net reflectance that is proportional to non-specular reflection from the portion of the patterned substrate.

6. The method of claim 1, wherein determining the set of parameters comprises calculating a least squares difference error metric between the measured net reflectance spectrum and the modeled net reflectance spectrum and finding the set of parameters that minimizes the error metric.

7. The method of claim 6, further comprising amplifying an effect of a change in the parameter of interest on the error metric.

8. The method of claim 6, wherein calculating the modeled net reflectance spectrum comprises receiving as input a set of initial guesses for the set of parameters.

9. The method of claim 1, wherein obtaining the measured reflectance spectrum comprises obtaining a set of reflectance spectra of the portion of the patterned substrate over a time interval and setting the measured reflectance spectrum to an average of the set of reflectance spectra.

21. The method of claim 1 wherein the weighted incoherent sum of reflectances is

R=w₁(λ

₀)E₁|²+w₂(λ

₀)|E₂ |² +Λ

+w_n(λ

₀)|E_n|²

where R is the net reflectance measured, E_n are the individual incoherently adding field terms, and w_n(λ

₀) are the weighting factors for the incoherently adding terms.

22. The method of claim 1 wherein the weighted coherent sums of reflected fields is

E_i=α

₁(λ

₀)E_c1+α

₂(λ

₀)E_c2+Λ

+α

_k(λ

₀) E_ck

where α

_k(λ

₀) are the weighting factors for coherently adding field terms E_ck.

10. A process control method for fabrication of a patterned substrate. comprising:

illuminating at least a portion of the patterned substrate with a normal incident light beam while processing the patterned substrate;

obtaining a measured reflectance spectrum of the portion of the patterned substrate over a range of wavelengths;

calculating a modeled reflectance spectrum of the portion of the patterned substrate over a range of wavelengths as a weighted incoherent sum of reflectances from n≧

1 different regions constituting the patterned substrate, wherein the reflectance of each of the n different regions is a weighted coherent sum of reflected fields from k≧

1 laterally-distinct areas constituting the region;

determining a set of parameters that provides a close match between the measured reflectance spectrum and the modeled reflectance spectrum;

deriving a parameter of interest from the set of parameters; and

signaling an endpoint in the processing of the patterned substrate if the value of the parameter of interest satisfies a predetermined endpoint criterion.

11. The process control method of claim 10, wherein calculating the modeled net reflectance spectrum comprises applying a loss factor to the modeled net reflectance that is proportional to non-specular reflection from the patterned substrate.

12. The process control method of claim 10, wherein determining the set of parameters comprises calculating a least squares difference error metric between the measured net reflectance spectrum and the modeled net reflectance spectrum and finding the set of parameters that minimizes the error metric.

13. The process control method of claim 12, further comprising amplifying an effect of a change in the parameter of interest on the error metric.

14. A method for determining a vertical dimension of a feature on a patterned substrate, comprising:

illuminating at least a portion of the patterned substrate including the feature with a normal incident light beam;

obtaining a measured net reflectance spectrum of the portion of the patterned substrate from a normal reflected light beam;

calculating a modeled net reflectance spectrum of the portion of the patterned substrate as a weighted incoherent sum of reflectances from n≧

1 different regions constituting the portion of the patterned substrate, wherein the reflectance of each of the n different regions is a weighted coherent sum of reflected fields from k≧

1 laterally-distinct areas constituting the region;

determining a set of parameters that provides a close match between the measured net reflectance spectrum and the modeled net reflectance spectrum; and

extracting the vertical dimension of the feature from the set of parameters.

15. The method of claim 14, wherein each laterally-distinct area is modeled as a thin-film stack.

16. The method of claim 15, wherein calculating the modeled net reflectance spectrum comprises modeling the patterned substrate as having a nominally polarization-independent reflectance.

17. The method of claim 14, wherein calculating the modeled net reflectance spectrum comprises applying a loss factor to the modeled net reflectance spectrum that is proportional to non-specular reflection from the portion of the patterned substrate.

18. The method of claim 14, wherein determining the set of parameters comprises calculating a least squares difference error metric between the measured net reflectance spectrum and the modeled net reflectance spectrum and finding the set of parameters that minimizes the error metric.

19. The method of claim 18, further comprising amplifying an effect of a change in the vertical dimension of the feature on the error metric.

20. The method of claim 18, wherein calculating the modeled net reflectance spectrum comprises receiving as input a set of initial guesses for the set of parameters.