Relationship between Dissolution Property and Molecular Weight of Positive-tone Novolak Resist

Abstract

We demonstrated the relationship between the weight-average molecular weight (M_W) of novolak resin for the positive-tone novolak resist and the dissolution properties of resists obtained by discrimination curves. We subsequently used PROLITH to evaluate the effects of M_W of the resin on the resolution of resists while changing the M_W from 2940 to 13100 as the fixed number-average molecular weight (M_N) of the resin (M_N=605±35). Dissolution contrast (n_D: the ratio of the dissolution rate of the resist in the exposed area to the dissolution rate of the resist in the unexposed area) of the resist was improved with an increase in M_W when M_W was 6370 or less and was saturated (n_D≈ 2.9) when M_W exceeded 6370. Resist development contrast (δ: gradient of change of the dissolution rate from unexposed area to exposed area) improved with an increase in M_W. Using PROLITH, we demonstrated that the resist pattern profile and the process window improved as M_W increased. However, resist sensitivity degraded with an increase in M_W. Therefore, from the perspectives of resist sensitivity, process window, and contrast, a resist pattern with a better profile may be made stably using the positive-tone novolak resist with novolak resin of M_W≈6370.