Photoacid structure effects on environmental stability of 193 nm chemically amplified positive resists

The effects of a generated photoacid structure on environmental stability a t post-exposure bake (PEB) and during postexposure delay (PED) were investi gated for a 193 nm chemically amplified positive resist composed of an etho xyethyl-blocked alicyclic copolymer and an iodonium sulfonate photoacid gen erator (PAG). It was found that the influence of airborne contaminants at F EB was less than that during FED. The relationship between environmental st ability and generated photoacid properties such as acid strength, reactivit y to amine, acid molecular size, reaction efficiency, and activation energy for the deblocking reaction, are discussed. The environmental stability wa s greatly dominated by the acid strength of generated photoacid, which cont ributed to the reactivity of the acid with base contaminants. In addition, a good correlation was obtained between the acid molecular size and the lit hographic performance. Weak acid (pKa similar to -7) with moderate size (si milar to 100 Angstrom (3)) exhibited both high environmental stability and high lithographic performance. The high environmental stability of the resi st with weak acid was almost the same as that of the 248 nm acetal-type res ist, and it is sufficient for practical use.