Effect of low-molecular-weight dissolution-promoting compounds in DNQ-novolac positive resist

Abstract

Effects of a dissolution promoter (DP) on the lithographic behavior of DNQ-novolac resists were investigated. The key structure/property relationships of the DP in relation to other parameters of the resist components were identified. In this work, we observed: (1) A significant improvement in resolution and photospeed when the DP was appropriately used. (2) Improvements in resist profile to increase its steepness. (3) Novolac dispersivity was the key for obtaining a beneficial effect from DP incorporation into the resist matrix. (4) Molecular size of the DP influenced resist resolution. (5) The PEB process effectively acts to improve dissolution discrimination. The dissolution rate analysis indicated that the DP incorporation, when optimized, accelerated dissolution of exposed resist film while decreasing the dissolution rate of unexposed film. This results in resolution improvement by increasing the dissolution contrast. DP also enhanced the surface induction in the resist film dissolution, which resulted in improvement of the profile steepness. We are proposing a 'selective dissolution model' to account for the influence of the DP to the resist dissolution. This model assumes a critical dissolution rate differentiation between the DP and the other components, i.e., a microscopically uneven dissolution of the resist film components at the dissolution front, which leads to the above unique dissolution behavior. PAC or DP diffusion in the resist film were found to be critical in obtaining the discussed DP effect in a real resist film.