Metrology method and apparatus, computer program and lithographic system

Patent metadata

Field	Value
Publication number	US-9879988-B2
Application number	US-201615013340-A
Country	US
Kind code	B2
Filing date	Feb 2, 2016
Priority date	Feb 4, 2015
Publication date	Jan 30, 2018
Grant date	Jan 30, 2018

Abstract

Disclosed is a method of measuring a parameter of a lithographic process, and associated computer program and apparatuses. The method comprises providing a plurality of target structures on a substrate, each target structure comprising a first structure and a second structure on different layers of the substrate. Each target structure is measured with measurement radiation to obtain a measurement of target asymmetry in the target structure, the target asymmetry comprising an overlay contribution due to misalignment of the first and second structures, and a structural contribution due to structural asymmetry in at least the first structure. A structural asymmetry characteristic relating to the structural asymmetry in at least the first structure of each target structure is obtained, the structural asymmetry characteristic being independent of at least one selected characteristic of the measurement radiation. The measurement of target asymmetry and the structural asymmetry characteristic is then used to determine the overlay contribution of the target asymmetry of each target structure.

First claim

The invention claimed is:

1. A method comprising:
providing a plurality of target structures on a substrate, each target structure comprising a first structure and a second structure on different layers of the substrate;
measuring each target structure with measurement radiation to obtain a measurement of target asymmetry in the target structure, said target asymmetry comprising an overlay contribution due to misalignment of the first and second structures and a structural contribution due to structural asymmetry in at least said first structure;
obtaining a structural asymmetry characteristic relating to the structural asymmetry in at least the first structure of each target structure, said structural asymmetry characteristic being independent of at least one selected characteristic of said measurement radiation; and
determining the overlay contribution of the target asymmetry of each target structure from said measurement of target asymmetry and said structural asymmetry characteristic.

2. The method as claimed in claim 1 , wherein said structural asymmetry characteristic comprises a dimensionless fingerprint characteristic of at least the first structure of each target structure.

3. The method as claimed in claim 1 , wherein said measuring of said target structure comprises:
illuminating the target structures with said measurement radiation;
detecting the measurement radiation scattered by each target structure; and
measuring intensity asymmetry in corresponding higher orders of the scattered measurement radiation.

4. The method as claimed in claim 3 , wherein said determining the overlay contribution of the target asymmetry comprises:
assuming that there is a non-linear periodic relationship between intensity asymmetry and the overlay contribution of the target asymmetry, said non-linear periodic relationship including an offset term related to the structural asymmetry.

5. The method as claimed in claim 4 , wherein said offset term is composed of said structural asymmetry characteristic, scaled by a scalar factor, wherein said scalar factor is constant for all of said plurality of target structures when measured in at least a first orientation with respect to the measurement radiation, and dependent upon said at least one selected characteristic of the measurement radiation.

6. The method as claimed in claim 5 , comprising constructing an overlay model, said overlay model comprising:
a design matrix parameterized by said structural asymmetry characteristic and a first intensity asymmetry parameter related to the measurements of intensity asymmetry;
a response vector parameterized by a second intensity asymmetry parameter related to the measurements of intensity asymmetry; and
a vector of parameters to be solved for, parameterized by an overlay contribution parameter describing said overlay contribution of the target asymmetry and said scalar factor.

7. The method as claimed in claim 6 , wherein said target structure comprises at least two targets, a first oriented target having a first orientation with respect to the measurement radiation and a second oriented target having a second orientation with respect to the measurement radiation; and
said overlay model comprises a first overlay model for modeling overlay in the direction of said first orientation based on measurements of said first oriented target and a second overlay model for modeling overlay in the direction of said second orientation based on measurements of said second oriented target.

8. The method as claimed in claim 7 , wherein the first overlay model comprises a first scalar factor and said second overlay model comprises a second scalar factor.

9. The method as claimed in claim 7 , wherein the first overlay model comprises a first structural asymmetry characteristic and said second overlay model comprises a second structural asymmetry characteristic.

10. The method as claimed in claim 6 , wherein said determining the overlay contribution of the target asymmetry comprises using said model to solve for said overlay contribution parameter.

11. The method as claimed in claim 6 , wherein:
each of said target structures comprise at least two targets, a first target with a first known imposed bias and a second target with a second known imposed bias,
said first asymmetry parameter comprises the difference of asymmetry measurements obtained from said first target and said second target; and
said second asymmetry parameter comprises the sum of asymmetry measurements obtained from said first target and said second target.

12. The method as claimed in claim 1 , comprising making direct measurements of the first structure, and using said direct measurements to obtain said structural asymmetry characteristic.

13. The method as claimed in claim 12 , wherein:
said first structure is the lowermost structure on the substrate, and
said direct measurement of the first structure prior is made prior to the formation of the second structure.

14. The method as claimed in claim 1 , wherein said overlay contribution of the target asymmetry comprises a contribution due to a known imposed bias and a contribution due to an overlay error, and said method comprises determining the contribution due to an overlay error.

15. The method as claimed in claim 1 , comprising performing said measuring of each target structure a plurality of times, each time using measurement radiation wherein said at least one selected characteristic is varied.

16. The method as claimed in claim 1 , wherein said at least one selected characteristic comprises wavelength and/or polarization.

17. The method as claimed in claim 1 , wherein said obtaining a structural asymmetry characteristic comprises obtaining a linear combination of a plurality of structural asymmetry characteristics, each structural asymmetry characteristic being the result of a different processing step.

18. A metrology apparatus comprising:
a support configured to support a substrate having a plurality of target structures thereon;
an optical system configured to perform measuring of each target structure; and
a processor arranged to determine overlay contribution of the target asymmetry of each target structure by being configured to:
measure each target structure with measurement radiation to obtain a measurement of target asymmetry in the target structure, said target asymmetry comprising an overlay contribution due to misalignment of the first and second structures and a structural contribution due to structural asymmetry in at least said first structure;
obtain a structural asymmetry characteristic relating to the structural asymmetry in at least the first structure of each target structure, said structural asymmetry characteristic being independent of at least one selected characteristic of said measurement radiation; and
determining the overlay contribution of the target asymmetry of each target structure from said measurement of target asymmetry and said structural asymmetry characteristic.

19. A lithographic system comprising:
a lithographic apparatus comprising:
an illumination optical system arranged to illuminate a pattern;
a projection optical system arranged to project an image of the pattern onto a substrate; and
a metrology apparatus comprising,
a support configured to support a substrate having a plurality of target structures thereon,
an optical system configured to perform measuring of each target structure, and

a processor arranged to determine overlay contribution of the target asymmetry of eac

Assignees

• Asml Netherlands Bv

Inventors

• Liu xing lan
• Smilde Hendrik Jan Hidde
• Peng Yue-Lin
• Cekli Hakki Ergün
• Pello Josselin
• Van Haren Richard Johannes Franciscus

Classifications

• G03F7/70633 Primary

  Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching · CPC title

• G03F7/70625

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

• G01B11/272 Primary

  using photoelectric detection means · CPC title

• G03F7/70616

  Monitoring the printed patterns · CPC title

• G03F9/7007

  Alignment other than original with workpiece · CPC title