Patent ID: 9466100
Filing Date: 2016-10-11
CPC Classification: G03F,G06T

Claim Text:
1. An apparatus for monitoring focus during lithography comprising: a processor; memory connected to the processor; and computer executable program code configured to execute on the processor, wherein: the computer executable program code is configured to: receive a first image profile corresponding to a first mask element and a second image profile corresponding to a second mask element comprising a first sub-resolution assist feature, the first image profile and second image profile being asymmetrical; receive a third image profile corresponding to a third mask element and a fourth image profile corresponding to a fourth mask element comprising a second sub-resolution assist feature; measure a first profile asymmetry resulting from the first sub-resolution assist feature based on the first image profile and the second image profile; and measure a second profile asymmetry based on the third image profile and the fourth image profile; and determine a first focus response based on the first profile asymmetry and a second focus response based on the second profile asymmetry.