Theoretical study on protected unit fluctuation of chemically amplified resists used for photomask production by electron beam lithography

Stochasticity in the sensitization processes of resist materials is a significant concern in fine patterning. Such stochasticity results in protected unit fluctuation in the case of a chemically amplified resist, which is a standard resist for photomask production. After development, protected unit fluctuation comes to the surface as line edge roughness, stochastic pinching, and stochastic bridging. In this study, protected unit fluctuation after postexposure baking was investigated, assuming the fabrication of line-and-space patterns. The standard deviation of the number of protected units connected to a polymer molecule was calculated using a Monte Carlo method on the basis of the sensitization mechanism of chemically amplified electron beam resists. The dependences of the standard deviation on half-pitch, sensitivity, sensitizer concentration, and exposure pattern width were clarified.