Inspection apparatus, inspection method, lithographic apparatus, patterning device and manufacturing method

Patent metadata

Field	Value
Publication number	US-10054862-B2
Application number	US-201615179509-A
Country	US
Kind code	B2
Filing date	Jun 10, 2016
Priority date	Jun 12, 2015
Publication date	Aug 21, 2018
Grant date	Aug 21, 2018

Abstract

Disclosed is a method of monitoring a focus parameter during a lithographic process. The method comprises acquiring first and second measurements of, respectively first and second targets, wherein the first and second targets have been exposed with a relative best focus offset. The method then comprises determining the focus parameter from first and second measurements. Also disclosed are corresponding measurement and lithographic apparatuses, a computer program and a method of manufacturing devices.

First claim

The invention claimed is:

1. A method of monitoring a focus parameter during a lithographic process, the method comprising:
acquiring a first measurement value, the first measurement value having been obtained from inspection of a first target;
acquiring a second measurement value, the second measurement value having been obtained from inspection of a second target, wherein the first and second targets have been exposed with a relative best focus offset; and
determining the focus parameter from a difference of the first and second measurement values, wherein the difference of the first and second measurement values is divided by an average of the first and second measurement values,
wherein the first and second measurement values comprise intensity values of a diffraction order of radiation scattered by the first and second targets, respectively.

2. The method of claim 1 , wherein the relative best focus offset results from astigmatism in the lithographic apparatus during formation of the first and second targets.

3. The method of claim 1 , further comprising:
forming the first and second targets on a substrate with the relative best focus offset.

4. The method of claim 1 , wherein the first and second targets each comprise line-space grating structures.

5. The method of claim 1 , wherein:
design rules constrain target features to a set critical dimension, and
wherein on a grid of set pitch, the first and second targets are each formed from rows of the grid, such that each line feature of the first target and second targets are formed from one or more adjacent, corresponding target features formed on the grid.

6. The method of claim 1 , wherein patterns defining the first and second targets do not comprise features which purposely introduce focus dependent asymmetry in the first and second targets.

7. The method of claim 1 , further comprising:
acquiring additional measurements of additional targets, the additional targets being additional to the first and second targets, and each of the additional targets having a different best focus to that of the first target and/or the second target; and
using the additional measurements in the step of determining the focus parameter.

8. The method of claim 1 , wherein the diffraction order comprises a first diffraction order of radiation scattered from the first and second targets.

9. The method of claim 1 , wherein the diffraction order comprises a zeroth diffraction order of radiation from the first and second targets.

10. The method of claim 1 , wherein the first and second targets comprise corresponding line and space targets having the same pitch and inverse duty cycles.

11. A method of monitoring a dose parameter during a lithographic process, the method comprising:
acquiring a first measurement value, the first measurement value having been obtained from inspection of a first target;
acquiring a second measurement value, the second measurement value having been obtained from inspection of a second target, and
determining the dose parameter from the first and second measurement values;
wherein the first and second targets comprise corresponding line and space targets having the same pitch and inverse duty cycles.

12. The method of claim 11 , wherein the step of determining the dose parameter comprises:
determining the dose parameter from a difference of the first and second measurement values.

13. The method of claim 11 , wherein the step of determining the dose parameter comprises:
determining a focus parameter of the lithographic process; and
referring to a dose calibration curve corresponding to the determined focus parameter.

14. The method of claim 13 , further comprising:
determining the focus parameter from the first and second measurement values,
wherein the first and second targets have been exposed with a relative best focus offset.

15. A lithographic system comprising:
a lithographic apparatus comprising:
an illumination optical system arranged to illuminate a pattern; and
a projection optical system arranged to project an image of the pattern onto a substrate; and

a metrology apparatus comprising:
a support for the substrate having a plurality of targets thereon;
an optical system for measuring each target; and
a processor configured to:
acquire a first measurement value, the first measurement value having been obtained from inspection of a first target;
acquire a second measurement value, the second measurement value having been obtained from inspection of a second target, wherein the first and second targets have been exposed with a relative best focus offset; and
determine the focus parameter from a difference of the first and second measurement values, wherein the difference of the first and second measurement values is divided by an average of the first and second measurement values, wherein the first and second measurement values comprise intensity values of a diffraction order of radiation scattered by the first and second targets, respectively,

wherein the lithographic apparatus is arranged to use the focus parameter and/or a dose parameter calculated by the metrology apparatus in applying the pattern to further substrates.

16. A non-transitory computer program product comprising processor readable instructions which, when run on suitable processor controlled apparatus, cause the processor controlled apparatus to perform operations comprising:
acquiring a first measurement value, the first measurement value having been obtained from inspection of a first target;
acquiring a second measurement value, the second measurement value having been obtained from inspection of a second target, wherein the first and second targets have been exposed with a relative best focus offset; and
determining the focus parameter from a difference of the first and second measurement values, wherein the difference of the first and second measurement values is divided by an average of the first and second measurement values,
wherein the first and second measurement values comprise intensity values of a diffraction order of radiation scattered by the first and second targets, respectively.

17. The lithographic system of claim 15 , wherein the diffraction order comprises a first diffraction order of radiation scattered from the first and second targets.

18. A method of manufacturing devices wherein a device pattern is applied to a series of substrates using a lithographic process, the method comprising:
monitoring a focus parameter by:
acquiring a first measurement value, the first measurement value having been obtained from inspection of a first target;
acquiring a second measurement value, the second measurement value having been obtained from inspection of a second target, wherein the first and second targets have been exposed with a relative best focus offset; and
determining the focus parameter from a difference of the first and the second measurement values, wherein the difference of the first and second measurement values is divided by an average of the first and second measurement values,
wherein the first and second measurement values comprise intensity values of a diffraction order of radiation scattered by the first and second targets, respectively; and

controlling the lithographic process for later substrates in accordance with the determined focus parameter.

19. The method of claim 18 , wherein the diffraction order comprises a first diffraction order of radiation scattered from the first and second targets.

Assignees

• Asml Netherlands Bv

Inventors

• Van Oosten Anton Bernhard
• Hinnen Paul Christiaan
• De Kruif Robertus Cornelis Martinus
• Socha Robert John

Classifications

• G03F7/70641 Primary

  Focus · CPC title

• G03F1/44 Primary

  Testing or measuring features, e.g. grid patterns, focus monitors, sawtooth scales or notched scales · CPC title

• G03F7/70558 Primary

  Dose control, i.e. achievement of a desired dose · CPC title

• G03F7/70525

  Controlling normal operating mode, e.g. matching different apparatus, remote control or prediction of failure · CPC title

• G03F7/70516

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