Preparation and lithographic performance of novel copolymers having acid labile pendant alicyclic ether moieties

A series of methacrylic copolymers derived from methacrylic acid (MAA), methyl methacrylate (MMA), n-butyl methacrylate (BM), and bornyl methacrylate (BMA) with various feed molar ratios was synthesized. In order to introduce acid labile alicyclic ether groups, the pendant carboxyl groups of copolymers were further functionalized with unsaturated alicyclic ethers of 2,3-dihydrofuran (DHF), 3,4-dihydro-2H-pyran (DHP), and 3,4-dihydro-2-methoxy-2H-pyran (DHMP). The existence of alicyclic bornyl groups was found to increase the thermal and plasma etching resistance of polymers but to decrease the sensitivity and contrast. Copolymers having pendant carboxyl groups can be crosslinked in the presence of photoacid after sufficient heat treatment. Acid catalyzed dehydration of pendant carboxylic acids may also cause the crosslinking of polymers. The thermogravimetric properties of copolymers, exposure characteristic curves and lithographic evaluation of the positive tone photoresist were all investigated. A line and space pattern resolution of 0.3 μm was also achieved.