Influence of writing strategy on CD control for the spatial light modulator-based Sigma7300 DUV laser pattern generator

摘要

Critical dimension control is becoming more and more critical in the mask making industry as the exposure wavelength goes down. For laser pattern generators, the move from traditional DNQ/Novolak based towards DUV chemically amplified resist processing was initially troublesome. The relative long total exposure time of pattern generators in contrast to wafer steppers, in combination with thick quartz substrates with relatively low heat capacity, may result in reduced lithographic performance due to excessive diffusion of photogenerated acid. The photoresist polymer architecture play a large role in determining the acid diffusion characteristics and thereby also the image fidelity and resolution. In the Sigma7300 laser pattern generator the image is created by the spatial light modulator, which acts as a reflective computer-controlled reticle. By adopting a proper writing strategy, the negative effects of acid diffusion could be reduced. One component in the Sigma writing strategy is to expose the pattern in several passes that allows for dose compensation as well as averaging schemes to reduce CD errors. By adjusting the dose per pass and by keeping track of the delay times between each shot as well as the exposure path, a better control of the linewidth may be achieved for certain photoresist chemistry. In this study we present results from investigations of AZ DX 1100P and FEP-171 resists using different writing strategies.