Electron beam resist reactions

The progress of technology for the high-resolution fabrication of semiconductor and magnetic bubble devices has required sub-micron exposure techniques such as electron beam x-ray and deep UV. Although a number of papers have been published on electron beam resists, reaction mechanisms of electron resists are still largely unknown since few studies on reactive intermediates by means of direct measurements have been done in order to elucidate the reaction mechanisms. 

Electron Beam Resist Reactions of CMS. The lifetime of the excimer fluorescence of CMS observed in pulse radiolysis of CMS solutions in cyclohexane and tetrahydrofuran (THF) is almost independent of chloromethylation ratio from 0% to 24%. The intensity of the excimer fluorescence decreases with increasing degree chloromethylation indicating that the precursor of the excimer is scavenged by the chloromethylated part of CMS. In this case, an electron (quasi-free electron in cyclohexane and solvated electron in tetrahydrofuran, which are the precursors of the excimer), is scavenged by the chloromethyl group. The excited singlet state... 

Although both excited and ionic species play important roles in electron beam resist reactions, the ratio of the contribution of excited and ionic species, which depends on chloromethylation ratio, is not known. 

Electron Beam Resist Reactions of SNR. The transient absorption spectrum observed in pulse radiolysis of SNR (partly chloromethylated diphenyl siloxane) solutions in benzene as shown in Fig. 3 is very similar to that of CMS (of Fig. 2). 

The scheme for the main electron beam resist reactions SNR is as follows ... 

It is important to note in this regard that there are practical limits to sensitivity. For example, an electron-beam resist with a sensitivity greater than 10-8 C/cm2 might well undergo thermal reactions at room temperature and would consequently be unsatisfactory because of an unacceptably short shelf-life of both the resist solution and spun films. The lower limit of sensitivity is governed by throughput considerations. Figure 4 illustrates the sensitivity... 

To achieve a manufacturable system for sub-0.5-pm patterning, extremely precise control of the molecular properties, structure, composition, and purity of the polymer is required (Table 4). Meeting these requirements provides intellectual challenges in ultrapurification reaction engineering and chemical synthesis. An illustration of the control required in this synthesis process can be found in a negative electron beam resist, GMC. 

The major reaction pathways for SNR operating as a negative electron beam resist are general known, but several problems still remain. 

Many reports have been published on negative electron-beam resists. Most of these resists utilize radiation-induced gel-formation as the insolubilzation reaction. However, a major problem with these resists, is that their resolution is limited by swelling which is induced by the developer during development. 

Kozawa T, Nagahara S, Yoshida Y, Tagawa S, Watanabe T, Yamashita Y. (1997) Radiation-induced reactions of chemically amplified X-ray and electron beam resists based on deprotection of t-butoxycarbonyl groups. J Vac Sci Tech 15 2582-2586. 

The polymeric systems are usually composed of a polymer which Imparts the majority of physical properties and actinic additives. In simple systems such as curing films or electron beam resists, the polymer is also the radiation sensitive species. In most cases, the formulations behave simllarily in their response to high energy irradiation. Practically any polymer can be made radiation sensitive by direct exposure to ionizing energies or by formulation with additives such as free radical precursors. Thermally sensitive polymers are also likely to undergo a similar reaction when exposed. 

Photosensitized degradation of poly(olefin sulfones) similar to the Hg(3P) photosensitized reactions of olefin sulfones make them subject to photodegradation in easily accessible wavelength regions. Almost all poly(olefin sulfones) have been reported only as positive tone electron beam resists (4). As the only exception, poly(5-hexene-2-one sulfone) has been reported as a positive tone photoresist with or without a photosensitizer, benzophenone (5). Because this polymer has a carbonyl chromophore, its photosensitivity is clearly derived from the polymer structure itself. 

PET reactions of benzylic silanes with polycyano-aromatic compounds have been applied to photoresist and electron-beam resist technologies. "" The photoreaction of poly(4-trimethylsilyl-methylstyrene) in benzene-acetonitrile with DCB affords insoluble polymer via photo-cross-linking, which contains 4-cyanophenyl-methyl groups. In the case of 1,2,4,5-tetracyanobenzene, soluble 2,4,5-tricyanophenylmethyl-substituted polystyrene is produced. But,... 

The co-condensation at low temperature of a metal vapor (commonly produced by resistance or electron-beam heating of metals) with a vapor of weakly stabilizing organic ligands (such as -pentane, toluene, tetrahydrofu-ran, acetone, or acetonitrile), using commercially available reactors, affords solid matrices, where reactions between the ligand molecules and metal atoms can take place (Scheme 1(A) Figure 1) [5]. 

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]. 

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