Patent ID: 9588440
Date: 2017-03-07
CPC Classifications: G03F

Claim:
1. A method for monitoring focus in an EUV lithography comprising: providing a substrate containing a photoresist layer; exposing, with EUV radiation, and printing the photoresist layer at different focus positions with a mask comprising a repeating pattern of two different pitches which include a first pitch and a second pitch, wherein the repeating pattern of at least one of the two different pitches comprises an assist feature; determining a first relationship between printed linewidths of the photoresist layer and the different focus positions under the repeating pattern of the first pitch in the mask; determining a second relationship between printed linewidths of the photoresist layer and the different focus positions under the repeating pattern of the second pitch in the mask; establishing a calibration curve which comprises printed linewidth differences of the two different pitches at the different focus positions; and performing EUV exposure on photoresists or other photo sensitive materials using a focus position which is pre-determined as a focus position on the calibration curve.