Chemical amplification design

Thus, these new copolymers form the basis of a new, deep UV, thermally stable photoresist. This resist combines the high Tg and thermal stability of the styrene-N-(p-hydroxyphenyl)maleimide copolymer and the sensitivity of the chemical amplification design concept. 

A significant part of our recent work with imaging systems which incorporate chemical amplification has involved the design of polymers which can undergo thermally activated multiple main-chain cleavages as the result of a phototriggered process. 

The latest addition to this list of dry developing resist materials is a contribution from IBM s San Jose Research Laboratory (66-67) that evolved from efforts to design positive-tone resist materials that incorporate chemical amplification. These efforts were stimulated by the fact that the quantum yield of typical diazoquinones of the sort used in the formulation of positive photoresists is 0.2 to 0.3 thus, three or four photons are required to transform a single molecule of sensitizer. This places a fundamental limit on the photo-sensitivity of such systems. 

In order to circumvent this sensitivity limitation, the San Jose researchers sought to design resist materials that incorporate chemical amplification of the sort that characterizes the silver halide photographic emulsion system. In these systems a single photo event initiates a cascade of subsequent chemical reactions that ultimately result in the intended function. 

Ito, H. Willson, G., "Chemical Amplification in the Design of Dry Developing Resist Materials," SPE Regional Technical Conference, Ellenville, New York, Nov. 1982. 

Over the past few years we have been interested in the design of new types of resist materials which generally possess high sensitivities due to structural features which allow for the occurrence of radiation initiated repetitive processes. The three main approaches we have investigated to-date all maximize the use of available protons through "chemical amplification" they are the following ... 

In all three of these designs, chemical amplification is the result of photoinitiated chain or catalytic reactions where irradiation is used only to initiate a chain reaction or to generate a catalyst within localised areas of a resist film. 

Chart 3.1. Tertiary butyl ester polymers useful in designing positive-negative resists incorporating chemical amplification. 

The copolymer and blend approaches have been combined to design three-component chemical amplification positive resists, which consist of PHOST partially protected with an acid-labile group (see Fig. 31), an acid-labile dissolution inhibitor, and PAG [124,157,158]. In this scheme both the matrix polymer and... 

Acid-catalyzed rearrangement reactions are also very useful in the design of chemical amplification resists. However, the potential of this imaging mechanism has been exploited only partially so far. 

Attempts have been made to design chemical amplification resists that can be cast from and/or developed with pure water, although casting from a solvent with a high surface tension (such as water) might not produce high quality thin films needed for microlithography. 

The very first chemical amplification resist designed for use in bilayer lithography employed Si-containing polyphthalaldehyde as a top layer resin,... 

H. Ito and C.G. Willson, Chemical amplification in the design of dry developing resist materials, Technical Papers of SPE Regional Technical Conference on Photopolymers, p. 331, Society of Plastics Engineers, Brookfield, CT (1982). 

The design concept of chemical amplification is based on generation of a chemically stable catalytic species (commonly referred to as a photoacid and designated as a proton H, as illustrated in Fig. 17.22 for a resist system comprising a copolymer—poly(4-hydroxystyrene-co-4-t-butyloxycarbonyloxystrene)—in... 

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