Imaging performance optimization methods for semiconductor wafer inspection

1. An inspection system, comprising:

an optical component configured to deliver inspection light to a subject;

one or more lens decenter manipulators configured to adjust the optical component when an aberration of the optical component is larger than a selected aberration level, wherein an adjustment of the one or more lens decenter manipulators shifts a focal plane of the inspection light directed through the optical component to overlap with a focal plane of an autofocus light;

a detector configured to obtain an image of the subject at least partially based on the inspection light delivered to the subject; and

a processor in communication with the optical component and the detector, the processor configured to:

generate a model to determine a threshold time when an aberration of the optical component will exceed a selected aberration level, wherein the threshold time is an amount of time elapsed after a measurement of one or more control parameters of the one or more lens decenter manipulators occurs;

adjust the optical component via adjustment of the one or more lens decenter manipulators to reduce the aberration of the optical component to be within the selected aberration level prior to inspection of the subject at the threshold time; and

during inspection of the subject at the threshold time:

measure the one or more control parameters to determine whether the aberration of the optical component is within the selected aberration level, wherein the one or more control parameters are based on at least one of time, power, temperature, or pressure; and

upon determining the aberration of the optical component is larger than the selected aberration level, adjust the optical component via an adjustment of the one or more lens decenter manipulators to compensate for the aberration of the optical component being larger than the selected aberration level.

2. The inspection system of claim 1 , wherein the subject includes a wafer.

3. The inspection system of claim 2 , wherein the subject further includes a reference chip configured to be positioned in the field of view of the detector and configured to be held such that the reference chip is coplanar with the wafer when the inspection light is delivered to the wafer.

4. The inspection system of claim 3 , wherein the processor is configured to measure the aberration of the optical component based on the image of the reference chip obtained by the detector.

5. The inspection system of claim 1 , wherein the processor is further configured to model the aberration of the optical component as a function of the at least one of time, power, temperature, or pressure.

6. The inspection system of claim 5 , wherein the processor is further configured to determine the threshold time based on the at least one of time, power, temperature, or pressure.

7. An inspection system, comprising:

an optical component configured to deliver inspection light to a wafer;

one or more lens decenter manipulators configured to adjust the optical component when an aberration of the optical component is larger than a selected aberration level, wherein an adjustment of the one or more lens decenter manipulators shifts a focal plane of the inspection light directed through the optical component to overlap with a focal plane of an autofocus light;

a detector configured to obtain an image of the wafer at least partially based on the inspection light delivered to the wafer; and

a processor in communication with the optical component and the detector, the processor configured to:

generate a model to determine a threshold time when an aberration of the optical component will exceed a selected aberration level, wherein the threshold time is an amount of time elapsed after a measurement of one or more control parameters of the one or more lens decenter manipulators occurs;

adjust the optical component via adjustment of the one or more lens decenter manipulators to reduce the aberration of the optical component to be within the selected aberration level prior to inspection of the wafer at the threshold time; and

during inspection of the wafer at the threshold time:

measure the one or more control parameters to determine whether the aberration of the optical component is within the selected aberration level; and

upon determining the aberration of the optical component is larger than the selected aberration level, adjust the optical component via an adjustment of the one or more lens decenter manipulators to compensate for the aberration of the optical component being larger than the selected aberration level.

8. The inspection system of claim 7 , further comprising:

a reference chip configured to be positioned in the field of view of the detector and configured to be held such that the reference chip is coplanar with the wafer when the inspection light is delivered to the wafer.

9. The inspection system of claim 8 , wherein the detector is further configured to obtain an image of the reference chip at least partially based on the inspection light delivered by the optical component and wherein the processor is further configured to measure the aberration of the optical component based on the image of the reference chip obtained by the detector.

10. The inspection system of claim 7 , wherein the processor is further configured to model the aberration of the optical component as a function of one or more variables.

11. The inspection system of claim 10 , wherein the aberration of the optical component is modeled as a function of at least one of time, power, temperature, or pressure.

12. The inspection system of claim 11 , wherein the processor is further configured to determine the threshold time based on the at least one of time, power, temperature, or pressure.

13. A method for adjusting imaging performance of an inspection system, the method comprising:

delivering inspection light to a subject through an optical component, wherein one or more lens decenter manipulators are configured to adjust the optical component when an aberration of the optical component is larger than a selected aberration level, wherein an adjustment of the one or more lens decenter manipulators shifts a focal plane of the inspection light directed through the optical component to overlap with a focal plane of an autofocus light;

obtaining an image of the subject at least partially based on the inspection light delivered to the subject;

generating a model to determine a threshold time when an aberration of the optical component will exceed a selected aberration level, wherein the threshold time is an amount of time elapsed after a measurement of one or more control parameters of one or more lens decenter manipulators occurs;

adjusting the optical component via an adjustment of the one or more lens decenter manipulators to reduce the aberration of the optical component to be within the selected aberration level prior to inspection of the subject at the threshold time; and

during inspection of the subject at the threshold time:

measuring the one or more control parameters to determine whether the aberration of the optical component is within the selected aberration level, wherein the one or more control parameters are based on time, temperature, or pressure; and

upon determining the aberration of the optical component is larger than the selected aberration level, adjusting the optical component via an adjustment of the one or more lens decenter manipulators to compensate for the aberration of the optical component being larger than the selected aberration level.

14. The method of claim 13 , wherein the subject includes a reference chip and wherein the aberration of the optical component is measured based on the image of the reference chip.

15. The method of claim 13 , further comprising:

modeling the aberration of the optical component as a function of the time, temperature, or pressure.

16. The method of claim 15 , further comprising:

determining the threshold time at least partially based on the function of the time, temperature, or pressure.

17. The inspection system of claim 1 , wherein the one or more control parameters are based on time, temperature, and pressure.

18. The inspection system of claim 7 , wherein the one or more control parameters are based on time, temperature, and pressure.

19. The method of claim 13 , wherein the one or more control parameters are based on time, temperature, and pressure.