ACID-DIFFUSION SUPPRESSION IN CHEMICAL AMPLIFICATION RESISTS BY CONTROLLING ACID-DIFFUSION CHANNELS IN BASE MATRIX POLYMERS

We have investigated the suppression of acid diffusion during postexpo sure baking (FEB) of chemical amplification resists in terms of the mo lecular control of base matrix polymers to control acid-diffusion chan nels. According to a previously proposed model, acid diffuses along ac id-diffusion channels in chemical amplification resists. The acid-diff usion channels are composed of OH groups outside the base matrix polym ers (active OH groups) and vacancies in the matrices. The negative-typ e chemical amplification resists used in this work consisted of cresol novolak with controlled molecular-weight distributions as the base ma trix polymers, an acid-catalyzed crosslinker of melamine resin, and ac id generators of onium salt. Measurements of the dependence of the pat tern sizes of isolated lines on the FEB time made it clear that acid d iffusion defines the resist pattern sizes based on Fick's law. The den sities of the active OH groups play a critical role in acid diffusion, and a base matrix polymer with fewer active OH groups is expected to result in less acid diffusion. Therefore, we can suppress acid diffusi on by reducing the number of oligomers in the base matrix polymers by a precipitation method, since these oligomers stereochemically include many active OH groups. We have obtained high resolution by using a re sist with an oligomer-free resin. The acid-diffusion model was also co nfirmed based on infrared absorption spectroscopy and thermal analysis . We conclude that acid diffusion can be suppressed by controlling the acid-diffusion channels. (C) 1996 American Vacuum Society.