Inspection Method and Apparatus, and Corresponding Lithographic Apparatus

• US 20130135600A1
• Filed: 11/02/2012
• Published: 05/30/2013
• Est. Priority Date: 11/30/2011
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: MIDDLEBROOKS, Scott Anderson, Coogans, Martyn John, Pluijms, Rene Andreas Maria, Noot, Marc Johannes
• Granted Patent: US 10,295,913 B2
• Time in Patent Office: Days
• US Class Current: 355/67
• CPC Class Codes: G03F 7/70525 Controlling normal operating mode, e.g. matching different apparatus, remote control or prediction of failure
• CPC Class Codes: G03F 7/70625 Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness
• CPC Class Codes: G03F 7/70641 Focus

Abstract

An inspection method, and corresponding apparatus, enables classification of pupil images according to a process variable. The method comprises acquiring diffraction pupil images of a plurality of structures formed on a substrate during a lithographic process. A process variable of the lithographic process varies between formation of the structures, the variation of the process variable resulting in a variation in the diffraction pupil images. The method further comprises determining at least one discriminant function for the diffraction pupil images, the discriminant function being able to classify the pupil images in terms of the process variable.

Claims

1. An inspection method comprising:

acquiring diffraction pupil images of a plurality of structures formed on a substrate during a lithographic process, a process variable of the lithographic process having been varied between formation of the structures, the variation of the process variable resulting in a variation in the formed structures and consequently the diffraction pupil images; and

determining at least one discriminant function for the diffraction pupil images, the discriminant function being able to classify the pupil images in terms of the process variable.

2. The method of claim 1, wherein the discriminant function is used to classify subsequent measured diffraction pupil images.

3. The method of claim 2, wherein the measured diffraction pupil images are obtained from direct measurement of production structures in-die.

4. The method of claim 1, wherein the discriminant function includes at least one of logistic regression, support vector machines and linear discriminant analysis.

5. The method of claim 1, wherein a plurality of classifications are predetermined for the process variable, the method further comprising:

labeling each pupil image with its corresponding classification, the corresponding classification being the classification that the process variable belonged to when the structure giving rise to the pupil image was formed; and

using the labeled pupil images to determine the discriminant function as one which classifies the pupil images according to the predetermined classifications.

6. The method of claim 5, wherein the using the labeled pupil images to determine the discriminant function comprises defining a cost function and minimizing the cost function over the variable range of the process variable.

7. The method of claim 5, wherein the classifications indicate whether the process is within predetermined control limits or are outside of predetermined control limits.

8. The method of claim 7, wherein the classifications comprise upper control limit, lower control limit and nominal, nominal indicating that the process is within the upper and lower control limits.

9. The method of claim 1, wherein the process variable comprises focus or dose settings during the lithography process.

10. The method of claim 1, wherein the process variable comprises the lithography or scanner tool used to perform the process.

11. The method of claim 1, wherein the diffraction pupil images are obtained using angle resolved scatterometry.

12. The method of claim 1, wherein the method comprises the forming of the plurality of structures using a lithographic process while varying the process variable of the lithographic process between formation of the structures.

13. A lithographic apparatus comprising:

an illumination system configured to condition a radiation beam;

a support configured to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;

a substrate table configured to hold a substrate;

a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and

an inspection tool configured to;

acquire diffraction pupil images of a plurality of structures formed on a substrate during a lithographic process, a process variable of the lithographic process having been varied between formation of the structures, the variation of the process variable resulting in a variation in the formed structures and consequently the diffraction pupil images; and

determine at least one discriminant function for the diffraction pupil images, the discriminant function being able to classify the pupil images in terms of the process variable.

14. A computer program product comprising instructions for causing a programmable data processing apparatus to perform as the data processing apparatus performing a method comprising:

acquiring diffraction pupil images of a plurality of structures formed on a substrate during a lithographic process, a process variable of the lithographic process having been varied between formation of the structures, the variation of the process variable resulting in a variation in the formed structures and consequently the diffraction pupil images; and

determining at least one discriminant function for the diffraction pupil images, the discriminant function being able to classify the pupil images in terms of the process variable.