Conventional acid catalyzed, chemically amplified DUV photoresists are susceptible to environmental contamination and post exposure delay effects resulting in `T-topping' and linewidth variation. These phenomena are directly relatable to uncontrolled diffusion of the photoactive acid generator within the photoresist or from the diffusion of basic contaminants into the resist. The diffusion process can be controlled by a combination of materials and processing optimization. This paper describes a new positive tone DUV photoresist based on poly(4-hydroxystyrene) protected with the isopropyloxycarbonyl (i-POC) functionality. This protecting group is considerably less acid labile than the tert-butyloxycarbonyl (t-BOC) group and the resulting polymer is considerably more thermally stable than a t-BOC protected poly(4-hydroxystyrene). As such, the i-POC based polymer is more amenable to processing at higher temperatures.