1986 Volume 43 Issue 3 Pages 153-160
The relation of monomer ratios in poly (methyl methacrylate-co-t-butyl methacrylate) s to electron beam sensitivities and thermal properties of the heat-treated copolymers was investigated in order to develop a highly sensitive positive electron beam resist. These copolymers sustained weight loss as a result of heat-treatment at 250°C and the evolved gases during this heat-treatment were mainly composed of isobuten. Therefore this weight loss was due to elimination of the t-butyl groupsfrom the t-butyl methacrylate component in the copolymers. Cyclized acid anhydrides mainly formed on such portions of the heat-treated copolymer films. The glass transition temperature of the copolymers increases as a result of the heat-treatment, so that thermal stabilities were improved, with a higher content of t-butyl methacrylate in the copolymers. In these copolymers, a 37 mol%. composition of t-butyl methacrylate, designated CP-3-2, showed the highest sensitivity (0.35 μC/cmcm2) and a high γ-value (1.9). Moreover, the CP-3-2 resolved a micro circuit pattern (less than 1.0μm line width), and the resistance to dry etching of the CP-3-2 are higher than the values for poly (methyl methacrylate). It is clear that CP-3-2 has a higher performance for highly sensitive positive electron beam resist.
