Semiconductor Engineering

"These molecular-scale inhomogeneities are difficult to study. To examine segregation behavior in resists, Gregory Denbeaux, associate professor at SUNY Polytechnic Institute, introduced polystyrene, an intentionally immiscible component, into a model resist system. In a simple ternary phase diagram (see figure 1), he investigated the bottom right corner, with a low polystyrene concentration and most of the solvent evaporated. As he explained in work presented at the recent SPIE Advanced Lithography and Patterning conference in San Jose, this scenario might model segregation of PAG molecules after spin-coating and before exposure, for example. As the solvent concentration dropped and the polystyrene concentration went up, segregation became energetically favorable. The degree of segregation that actually occurred depended on the mobility of individual molecules.

“Reducing the range of molecules after segregation becomes energetically favorable will reduce segregation,” Denbeaux said. Faster drying, for example, causes the mixture to become viscous more quickly, with less time for segregation.

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