Process endpoint detection method using broadband reflectometry

• US 20060035395A1
• Filed: 08/12/2005
• Published: 02/16/2006
• Est. Priority Date: 08/13/2002
• Status: Active Grant

• Current Assignee: Lam Research Corporation
• Original Assignee: Lam Research Corporation
• Inventors: Venugopal, Vijayakumar C.
• Granted Patent: US 7,531,369 B2
• Time in Patent Office: Days
• US Class Current: 438/14
• 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 processing of a patterned substrate includes obtaining a measured net reflectance spectrum resulting from illuminating at least a portion of the patterned substrate with a light beam having a broadband spectrum, calculating a modeled net reflectance spectrum as a weighted incoherent sum of reflectances from different regions constituting 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. For wavelengths below a selected transition wavelength, a first optical model is used to calculate the reflectance from each region as a weighted coherent sum of reflected fields from thin film stacks corresponding to laterally distinct areas constituting the region. For wavelengths above the transition wavelength, a second optical model based on effective medium approximation is used to calculate the reflectance from each region.

Claims

1-19. -19. (canceled)

20. A method of determining a vertical dimension of a feature in a portion of the patterned substrate during processing of a patterned substrate, comprising:

obtaining a measured net reflectance spectrum resulting from illuminating at least the portion of the patterned substrate with a light beam having a broadband spectrum;

calculating a modeled net reflectance spectrum as a weighted incoherent sum of reflectances from different regions constituting the portion of the patterned substrate.

for wavelengths below a selected transition wavelength in the broadband spectrum, using a first optical model to calculate the reflectance from each region as a weighted coherent sum of reflected fields from thin film stacks corresponding to 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 in the portion of the patterned substrate from the set of parameters.

21. The method of claim 20 further comprising:

using, for wavelengths above the selected transition wavelength in the broadband spectrum, a second optical model to calculate the reflectance from each region as a reflected field from a thin film stack obtained by replacing layers in the region with effective homogeneous mediums.

22. The method of claim 20, wherein the transition wavelength is functionally dependent on dimensions of dominant features on the patterned substrate.

23. The method of claim 20, wherein determining the set of parameters comprises determining in-situ an optimal value for the transition wavelength.

24. The method of claim 20, wherein a free-space wavelength of the light beam is comparable to or smaller than a characteristic size of dominant features in the portion of the patterned substrate at wavelengths below the transition wavelength.

25. The method of claim 24, wherein the free-space wavelength is at least 2.0 times the characteristic size.

26. The method of claim 24, wherein a free-space wavelength of the light beam is larger than a characteristic size of dominant features in the portion of the patterned substrate at wavelengths above the transition wavelength.

27. The method of claim 26, wherein the free-space wavelength is greater than 2.0 times the characteristic size.

28. The method of claim 20, wherein the thin film stacks corresponding to the laterally distinct areas in the first optical model are isotropic and homogeneous.

29. The method of claim 20, wherein using the first optical model to calculate the reflectance comprises modeling the portion of the patterned substrate as having a nominally polarization-independent reflectance.

30. The method of claim 20, further comprising applying a loss factor to the modeled net reflectance that is proportional to non-specular reflection from the portion of the patterned substrate prior to determining the set of parameters.

31. The method of claim 20, wherein replacing layers in the region with effective homogeneous mediums comprises modeling features in the portion of the patterned substrate as inclusions in the homogeneous mediums.

32. The method of claim 20, 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.

33. The method of claim 32, further comprising amplifying an effect of a change in the parameter of interest on the error metric.

34. The method of claim 32, wherein calculating the modeled net reflectance spectrum comprises receiving a set of initial guesses for the set of parameters.

35. The method of claim 20, wherein obtaining the measured net reflectance spectrum comprises obtaining a set of reflectance spectra of the portion of the patterned substrate over a time interval and setting the measured net reflectance spectrum to an average of the set of reflectance spectra.

36. A method of determining a vertical dimension of a feature in a portion of the patterned substrate during processing of a patterned substrate, comprising:

obtaining a measured net reflectance spectrum resulting from illuminating at least the portion of the patterned substrate with a light beam having a broadband spectrum;

calculating a modeled net reflectance spectrum as a weighted incoherent sum of reflectances from different regions constituting the portion of the patterned substrate.

for wavelengths above a selected transition wavelength in the broadband spectrum, using a first optical model to calculate the reflectance from each region as a reflected field from a thin film stack obtained by replacing layers in the region with effective homogeneous mediums;

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 in the portion of the patterned substrate from the set of parameters.