Deprotection chemistry resist systems

Acid-C t lyzed Chemistry. Acid-catalyzed reactions form the basis for essentially all chemically amplified resist systems for microlithography appHcations (61). These reactions can be generally classified as either cross-linking (photopolymerization) or deprotection reactions. The latter are used to unmask acidic functionality such as phenohc or pendent carboxyhc acid groups, and thus lend themselves to positive tone resist apphcations. Acid-catalyzed polymer cross-linking and photopolymerization reactions, on the other hand, find appHcation in negative tone resist systems. Representative examples of each type of chemistry are Hsted below. 

The process control of the post-exposure bake that is required for chemically amplified resist systems deserves special attention. Several considerations are apparent from the previous fundamental discussion. In addition for the need to understand the chemical reactions and kinetics of each step, it is important to account for the diffusion of the acid. Not only is the reaction rate of the acid-induced deprotection controlled by temperature but so is the diffusion distance and rate of diffusion of acid. An understanding of the chemistry and chemical kinetics leads one to predict that several process parameters associated with the PEB will need to be optimized if these materials are to be used in a submicron lithographic process. Specific important process parameters include ... 

In this paper, we report an alternative approach to the design of deep UV resist systems combining the desired properties, which involves copolymerization of methacrylic ester with styrenic comonomer and the use of the acid-catalyzed deprotection chemistry. 

In contrast to chain scission, chemical amplification (CA) employs an acid catalyzed deprotection or crossfinking reaction, which changes the solubility of the resist in the exposed areas. Therefore, a typical CA resist consists of a matrix polymer and a photoacid generator (PAG). The PAG is converted into a strong acid on absorption of a photon. The acid catalyzes the deprotection or crosslinking reaction and is regenerated (Scheme 2), which explains the amplification effect in the system. A variety of acid generator chemistries are available, both ionic and nonionic, but are not considered here. 

While recent research regarding base catalyzed systems is now known (13, 14), the predominant diemistiy assodated with chemicalty amplified resists involves addolytic reactions. The add spedes is required for either crosslinking or deprotection reactions and is also often needed for depotymerization mechanisms. Add generator chemistry will be discussed separately since any of the available materials might find application in a chemically amplified resist composition. 

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