Chemical amplification process

A number of new resist materials which provide very high sensitivities have been developed in recent years [1-3]. In general, these systems owe their high sensitivity to the achievement of chemical amplification, a process which ensures that each photoevent is used in a multiplicative fashion to generate a cascade of successive reactions. Examples of such systems include the electron-beam induced [4] ringopening polymerization of oxacyclobutanes, the acid-catalyzed thermolysis of polymer side-chains [5-6] or the acid-catalyzed thermolytic fragmentation of polymer main-chains [7], Other important examples of the chemical amplification process are found in resist systems based on the free-radical photocrosslinking of acrylated polyols [8]. 

Sulfonic (-SO3H) and Sulfinic (-SO2H) Acid-Based Nonsalt Photoinitiators Photosensitive tosylate esters of nitrobenzyl [65] and benzoin [73], sulfonyl ketones [67,68], and diphenyl disulfones [68] can be employed in cationic photopolymerization, especially in photolithography and chemical amplification processes. The advantages of these photoinitiators are the ease of synthesis, the absorption wavelengths suitable for deep-UV curing and the high yield of acid formation [65]. 

The second type of photofunctional change resist involves a catalytic or chemical amplification process to increase the sensitivity. Aspects of this work have been the subject of a recent review." ... 

The chemical amplification process concept has been extended to some of the high phenolic polymers described earlier. For example, high resolution thermally stable images were obtained in both a positive and negative mode for copolymers of N-(p-hydroxyphenyl)maleimide and styrene. 

Protons are regenerated with each addition Process incorporates chemical amplification... 

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. 

One final example of the application of onium salt photochemistry in positive resist materials should be mentioned, because it does not include any postexposure acid-catalyzed processes and therefore does not encompass the principle of chemical amplification (79). Interestingly, Newman (79) has determined that onium salts themselves can inhibit the dissolution of novolac in aqueous base and that irradiation of such an onium salt-novolac resist restores the solubility of the resin in developer and leads to a positive-tone image. In this application, the onium salt behaves like diazonaphthoquinone in a typical positive resist. Recently, Ito (80) has reported also the use of onium salts as novolac dissolution inhibitors. 

Title Monomer Having Fluorine-Containing Acetal or Ketal Structure, Polymer Thereof, and Chemical-Amplification-Type Resist Composition as Well as Process for Formation of Pattern with Use of the Same... 

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 ... 

Postexposure bake of the wafer. A postexposure bake (PEB) improves contrast of the photoresist before its development. The PEB process causes three effects 1) diffusion of the PAC 2) solvent evaporation and 3) thermally induced chemical reactions. In general, the dissolution rate of a resist decreases as a function of a PEB temperature. PEB becomes more important for the photoresists with a chemical amplification (CA) feature. The photoresists need the PEB to complete chemical reactions initiated by exposure. 

Chain reactions, essentially polymerizations, can be achieved with medium doses, as a result of the chemical amplification by purely thermal processes of radiation-induced initiation (Scheme 2). Processes involving single steps or short kinetic chain length reactions require much higher doses.This is generally the case for the radiation cross-linking of rubbers and thermoplastics. 

Understanding how chemical events might initiate the social amplification process is facilitated by elucidating critical aspects of the trust relationship engendered by activities such as the chemical weapons demilitarization pro-... 

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