Component ratio, negative resists

The relationship between sensitivity and component ratio in copolymer negative resists was studied theoretically on the basis of Charlesby s gel formation theory. The formulas for sensitivity as a function of component weight ratio are derived for a nonchain reaction and for a chain reaction, respectively. Copolymer sensitivities for any component ratio can be estimated numerically using the derived formulas, from the data on sensitivities for homopolymers composed of individual constituent monomers in the copolymer. The calculated results are in good agreement with the experimental data reported. 

In the course of the research on copolymer negative resists, numerous experimental data on sensitivities have been reported as a function of component ratio in order to optimize each resist system. Summarizing these data, it is found that the relationship between sensitivity and component ratio can be divided into two groups. In one group, sensitivity increases steeply at first as the mole fraction of highly sensitive monomer in the copolymer increases, and then it tends to saturate. In the other group, sensitivity saturation does not occur. It has been presumed that these different dependences on component ratio result from the difference in crosslinking reaction scheme, i.e., a nonchain reaction or a chain reaction. 

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