Radiation sensitive resist material

A radiation sensitive resist material for photolithography in the manufacture of microelectronic devices. The material comprises a polymerisation product of a substituted styrene in which at least twenty mole percent is a substituted styrene containing a substituent in the ortho-position. The presence of the ortho-substituent gives improved properties such as contrast and resistance to solvent-induced swelling so that an accurate resist pattern can be formed. Preferred monomers include 2:5 dimethylstyrene, 2, 4, 6 trimethylstyrene. Chloromethylstyrenes are also specified. (author)