Manipulation of Polymer Solubility: Crosslinking, Thermal Activation and Variable-Temperature Bakes

A two-layer polymeric stack is designed to be converted to a three-layer stack using sequential bakes. The three-layer stack is composed of layers that are (bottom to top): insoluble, soluble, and insoluble in 0.26 N TMAH developer. The two-layer stack is composed of a bottom layer that is a 193-nm positive tone resist containing a thermal acid generator (TAG) and, optionally, a crosslinker. The top layer contains a t-butyl acrylate monomer that can be deprotected by catalytic acid. During the sequential bakes, the TAG is designed to decompose to generate an acid that diffuses into the top layer. Diffusion lengths of 20-30 nm have been demonstrated. Additionally, the Arrhenius activation parameters are described for the acid-catalyzed deprotection of two esters in combination with strong and weak sulfonic acids. Surprisingly, the rates of these reactions are dictated more by their entropy than by their enthalpy.