High astigmatism during image shift

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Issue

High astigmatism during image shift was observed during EPU run.

Environment

Krios G2

Resolution

These are possible resolutions for the issue:

Install AFIS.

Cause

These are possible causes for the issue:

Normal for Image shift to cause large aberrations for systems without AFIS.

Details

The astigmatism is quite high during image shift especially in the Y direction. The Y astigmatism is 5x greater than the X astigmatism.

With 4um Image Shift X, the measured astigmatism is 21nm and coma 2432nm in Sherpa.

With 4um Image Shift Y, the measured astigmatism is 111nm and coma 3782nm in Sherpa.

It was quite difficult to find out the root cause of why astigmatism is worse in the Y direction, so in the end FSE installed AFIS (Aberration Free Image Shift) on the system and customer was happy with the system after that.

AFIS is available for Titan from SW 6.15 onwards and should be available for Talos in the future from SW 7.6 onwards. You can refer to WI-308638 for alignment procedure