Parameters,affecting the sensitivity of poly(methyl methacrylate) as a positive lithographic resist

The contribution of parameters such as molecular weight, molecular weight distribution and stereochemistry to electron beam sensitivity of poly(methyl methacrylate), PMMA, has been investigated. The sensitivity is interpreted here as the minimum radiation dose required to obtain a predetermined solubility rate ratio, S/S_o = S_R, of the exposed, S, and unexposed, S_o, material. The G-value was foam be independent of molecular weight, molecular weight distribution, and stereochemistry. Data indicate that the weight average molecular weight ratio correlates better with S_R than the number average molecular weight ratio. The tacticity of the resist and the developer solvent molecular weight or size have a large effect on solubility rate. Although the solubility rate pf isotactic PMMA is much greater than the syndiotactic and heterotactic stereoforms, the sensitivity appears to be independent of tacticity. In a homologous series of n-alkyl acetate developer solvents, the molecular size of the solvent has a greater effect on the solubility rate than the molecular weight of the resist. A developer solvent has been selected from the n-alkyl acetates which enhanced the sensitivity of PMMA.