Aqueous developers for positive tone ultrathin chemically amplified EUV resists

Abstract

Dissolution of ultrathin exposed EUV photoresist can deviate from the bulk regime due to the modulating influence of the adjacent top and bottom interfaces, which can eventually dominate the behavior of the entire film. Furthermore, use of TMAH 0.26N as aqueous developer for CARs has remained the industry standard without thorough investigation of other possible aqueous bases and concentrations. In this work, we provide a detailed description of the interfacial dissolution behavior of model ultrathin EUV resists in a variety of tetraalkylammonium-based developers, using a representative open source polymer platform. Dissolution kinetics measured using QCM (quartz crystal microbalance) with and without added PAG highlight the convolution of vertical distribution of resist additives with their dissolution inhibition effect throughout the resist film. Results for the local dissolution at the resist-substrate interface using interrupted development and AFM measurements are provided and explained in terms of confinement effects (polymer chain mobility, vacid diffusion) and polymer-substrate interactions. This work can serve as initial guidance to understand the attainable interfacial dissolution modulation afforded by a rational developer selection and a matching EUV resist design.