Critical dimensions (CD) measured in resist are key to understanding the CD distribution on photomasks. Vital to this
understanding is the separation of spatially random and systematic contributions to the CD distribution. Random
contributions will not appear in post etch CD measurements (final) whereas systematic contributions will strongly impact
final CDs. Resist CD signatures and their variations drive final CD distributions, thus an understanding of the mechanisms
influencing the resist CD signature and its variation play a pivotal role in CD distribution improvements. Current
technological demands require strict control of reticle critical dimension uniformity (CDU) and the Advanced Mask
Technology Center (AMTC) has found significant reductions in reticle CDU are enabled through the statistical analysis of
large data sets. To this end, we employ Principle Component Analysis (PCA) - a methodology well established at the
AMTC1- to show how different portions of the lithographic process contribute to CD variations. These portions include
photomask blank preparation as well as a correction parameter in the front end process. CD variations were markedly
changed by modulating these two lithographic portions, leading to improved final CDU on test reticles in two different
chemically amplified resist (CAR) processes.
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