Metrology method and apparatus, substrate, lithographic system and device manufacturing method

Patent metadata

Field	Value
Publication number	US-9811003-B2
Application number	US-201615355334-A
Country	US
Kind code	B2
Filing date	Nov 18, 2016
Priority date	May 29, 2012
Publication date	Nov 7, 2017
Grant date	Nov 7, 2017

Abstract

A metrology target formed by a lithographic process on a substrate includes a plurality of component gratings. Images of the target are formed using +1 and −1 orders of radiation diffracted by the component gratings. Regions of interest (ROIs) in the detected image are identified corresponding the component gratings. Intensity values within each ROI are processed and compared between images, to obtain a measurement of asymmetry and hence overlay error. Separation zones are formed between the component gratings and design so as to provide dark regions in the image. In an embodiment, the ROIs are selected with their boundaries falling within the image regions corresponding to the separation zones. By this measure, the asymmetry measurement is made more tolerant of variations in the position of the ROI. The dark regions also assist in recognition of the target in the images.

First claim

The invention claimed is:

1. An inspection apparatus for measuring a property of a lithographic process using a composite target structure including a plurality of component structures that have been formed by the lithographic process on a substrate, the apparatus comprising:
a support for the substrate having the composite target structure formed thereon;
an optical system configured to illuminate the composite target structure under predetermined illumination conditions and for forming and detecting an image of the composite target structure using a predetermined portion of radiation diffracted by the plurality of component structures under the illumination conditions;
a processor configured to:
identify one or more regions in the detected image, each region corresponding to a respective one of the plurality of component structures,
process pixel values within the one or more regions to obtain a measurement of the property of the lithographic process, and
identify the one or more regions such that their boundaries fall within image regions corresponding to separation zones between the plurality of component structures within the composite target structure.

2. The apparatus of claim 1 , wherein the plurality of component structures comprise overlaid gratings formed in two layers on the substrate, and wherein different component structures within the composite target structure are formed with different overlay bias values.

3. The apparatus of claim 1 , wherein the optical system is configured to form and detect two or more images of the composite target structure using different portions of the diffracted radiation, and wherein the processor is further configured to compare the pixel values from corresponding regions identified in the two or more images to obtain a measurement of asymmetry of the plurality of component structures.

4. The apparatus of claim 1 , wherein the processor is further configured to identify regions corresponding to at least two component structures in the detected image and to process their pixel values together to obtain the measurement in accordance with a known bias scheme of the composite target structure.

5. 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
an inspection apparatus comprising:
a support for the substrate having a composite target structure including a plurality of component structures formed thereon,
an optical system configured to illuminate the composite target structure under predetermined illumination conditions and for forming and detecting an image of the composite target structure using a predetermined portion of radiation diffracted by the plurality of component structures under the illumination conditions, and
a processor configured to:
identify one or more regions in the detected image, each region corresponding to a respective one of the plurality of component structures,
process pixel values within the one or more regions to obtain a measurement of a property of the plurality of component structures, and
identify the one or more regions such that their boundaries fall within image regions corresponding to separation zones between the plurality of component structures within the composite target structure,

wherein the lithographic apparatus is configured to use the measurement results from the inspection apparatus in applying the pattern to further substrates.

6. The lithographic system of claim 5 , wherein:
the plurality of component structures comprise overlaid gratings formed in two layers on the substrate, and
different component structures within the composite target structure are formed with different overlay bias values.

7. The inspection apparatus of claim 5 , wherein the plurality of component structures comprise overlaid gratings and different component structures within the composite target structure are formed with different orientations to measure overlay in different directions.

8. The lithographic system of claim 5 , wherein:
the optical system is configured to form and detect two or more images of the composite target structure using different portions of the diffracted radiation, and
the processor is further configured to compare the pixel values from corresponding regions identified in the two or more images to obtain a measurement of asymmetry of the plurality of component structures.

9. The lithographic system of claim 5 , wherein the processor is further configured to identify regions corresponding to at least two component structures in the detected image and to process their pixel values together to obtain the measurement in accordance with a known bias scheme of the composite target structure.

10. The apparatus of claim 1 , wherein the plurality of component structures comprise overlaid gratings and different component structures within the composite target structure are formed with different orientations to measure overlay in different directions.

11. The apparatus of claim 1 , wherein the separation zones occupy more than 5% of the composite target structure in a given direction.

12. The apparatus of claim 1 , wherein the separation zones occupy more than 10% of the composite target structure in a given direction.

13. The apparatus of claim 1 , wherein the separation zones occupy more than 15% of the composite target structure in a given direction.

14. The apparatus of claim 1 , wherein the separation zones in the composite target structure contain filling structures having an average density similar to that of the plurality of component structures but with higher spatial frequencies, whereby radiation diffracted by the filling structures falls outside the portion of radiation used in the formation of the detected image.

15. An inspection apparatus for measuring a property of a lithographic process using a composite target structure including a plurality of component structures that have been formed by the lithographic process on a substrate, the apparatus comprising:
a support for the substrate having the composite target structure formed thereon;
an optical system configured to illuminate the composite target structure under predetermined illumination conditions and for forming and detecting an image of the composite target structure using a predetermined portion of radiation diffracted by the plurality of component structures under the illumination conditions;
a processor configured to:
identify one or more regions in the detected image, each region corresponding to a respective one of the plurality of component structures,
process pixel values within the one or more regions to obtain a measurement of the property of the lithographic process, and
recognize the location of the composite target and identify the one or more regions at least in part by recognizing image regions corresponding to separation zones between the plurality of component structures within the composite target structure.

16. The inspection apparatus of claim 15 , wherein the plurality of component structures comprise overlaid gratings formed in two layers on the substrate, and wherein different component structures within the composite target structure are formed with different overlay bias values.

17. The inspection apparatus of claim 15 , wherein the plurality of component structures comprise overlaid gratings and different component structures within the composite target structure are formed with different ori

Assignees

• Asml Netherlands Bv

Inventors

• Jak Martin Jacobus Johan
• Koolen Armand Eugene Albert
• Smilde Hendrik Jan Hidde

Classifications

• H10P74/203

  Structural properties, e.g. testing or measuring thicknesses, line widths, warpage, bond strengths or physical defects · CPC title

• H10P76/2041 Primary

  Photolithographic processes · CPC title

• G03F7/70683

  Mark designs · CPC title

• G03F7/70633

  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 Primary

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