Method for determining a structure-independent contribution of a lithography mask to a fluctuation of the linewidth

Patent metadata

Field	Value
Publication number	US-11061331-B2
Application number	US-201916280469-A
Country	US
Kind code	B2
Filing date	Feb 20, 2019
Priority date	Feb 21, 2018
Publication date	Jul 13, 2021
Grant date	Jul 13, 2021

Abstract

For determining a structure-independent contribution of a lithography mask to a fluctuation of the linewidth, recorded 2D intensity distributions (15zi) of an unstructured measurement region of a lithography mask are evaluated in a spatially resolved manner.

First claim

What is claimed is:

1. A method for determining a structure-independent contribution of a lithography mask to a fluctuation of the linewidth (LWR, linewidth roughness) comprising the following steps:
1.1. providing an optical system having an imaging optical unit for imaging lithography masks,
1.2. providing a lithography mask having at least one measurement region which is free of structures to be imaged,
1.3. illuminating the at least one measurement region with illumination radiation,
1.4. recording a focus stack of the at least one measurement region of the lithography mask, and
1.5. evaluating 2D intensity distributions of the recorded focus stack in a spatially resolved manner,
1.6. wherein evaluating the 2D intensity distributions comprises ascertaining a defocus dependence of the standard deviation of the detected 2D intensity distributions, and
1.7. wherein evaluating the 2D intensity distributions comprises the following steps:
1.7.1. determining a spectrum S( , z) of the 2D intensity distributions by Fourier transformation of the 2D intensity distributions,
1.7.2. determining a defocus dependence of a plurality of spectral components S(ν xi , ν yi ) of the spectrum S( , z), and
1.7.3. ascertaining a Fourier transform H( ) of a function for describing the optical surface roughness of the lithography mask from the determined defocus dependence of the spectral components S(ν xi , ν yi ).

2. The method according to claim 1 , wherein evaluating the 2D intensity distributions comprises exclusively Fourier transformations and linear algebra.

3. The method according to claim 2 , wherein evaluating the 2D intensity distributions comprises ascertaining intensity fluctuations.

4. The method according to claim 3 , wherein evaluating the 2D intensity distributions comprises ascertaining a speckle contrast (ΔI).

5. The method according to claim 4 , wherein evaluating the 2D intensity distributions comprises ascertaining a speckle correlation factor.

6. The method according to claim 5 , wherein the speckle correlation factor (w) is derived from a known defocus aberration function.

7. The method according to claim 1 , wherein a mirror-symmetrical illumination setting is used for illuminating the measurement region.

8. The method according to claim 1 , wherein at least partially coherent illumination radiation is used for illuminating the measurement region.

9. The method according to claim 1 , wherein coherent illumination radiation is used for illuminating the measurement region.

10. The method according to claim 1 , wherein illumination radiation having a wavelength in the EUV range is used for illuminating the measurement region.

Assignees

• Zeiss Carl Smt Gmbh

Inventors

• Koch Markus
• Hellweg Dirk
• Capelli Renzo
• Dietzel Martin

Classifications

• G03F7/70625 Primary

  Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness · CPC title

• G03F7/70691

  Handling of masks or workpieces · CPC title

• G03F7/70516

  Calibration of components of the microlithographic apparatus, e.g. light sources, addressable masks or detectors · CPC title

• G03F1/84 Primary

  Inspecting · CPC title

• G03F7/70433

  Layout for increasing efficiency or for compensating imaging errors, e.g. layout of exposure fields for reducing focus errors; Use of mask features for increasing efficiency or for compensating imaging errors · CPC title