Kinetics of chemically amplified resists

Abstract

Deep-UV chemically amplified (CA) resists are among the leading candidates for the manufacture of semiconductors at 0.25 micron ground rules. In systems of this type, a latent image of photogenerated acid is produced in the resist film on pattern- wise exposure to UV light. The subsequent post-exposure bake (PEB) step drives a thermal reaction, causing a change in the aqueous base solubility of the resist in the exposed regions. Due to the fact that the photochemical and thermal images are decoupled it is important to understand the details of the resist thermal chemistry in order to understand how process conditions affect properties such as linewidth control and resolution. We describe here in-situ, high data-rate, accurate measurements of the chemical kinetics that occur in CA resists during post- exposure bake (PEB). The experimental methodology employs IR or UV spectroscopic measurement under carefully controlled isothermal conditions to determine resist film composition as a function of time. The acid-catalyzed deprotection reactions of two candidate deep-UV resist materials, poly(t-butoxy carbony- loxystyrene)(PTBOC) and poly(t-butyl methacrylate)(PTBMA), were characterized. We propose a model for the acidolysis reactions for both polymer systems and extract coefficients using a stochastic kinetics simulator. This model explicitly addresses the effects of photo-acid strength on the efficiency of the deprotection step. Excellent agreement between the model and experimental data is obtained. The derived rate coefficients are shown to be useful for quantitative prediction of the chemical kinetics of related resist systems. Mechanistic implications of the values of the derived rate coefficients are discussed. The influence of chemical kinetics on the resist's lithographic properties is examined.