A new chemically amplified resist containing a basic monomer, 3-(t-butoxycarbonyl)-1-vinylcaprolactam, in the matrix polymer was prepared for post-exposure delay stability. Poly(3-(t-butoxycarbonyl)-1-vinylcaprolactam-co-t-butyl methacrylate) was synthesized and evaluated as a new matrix resin. The diffusion lengths of photogenerated acid in the resist films were studied for various fractions of the basic monomer in the copolymers. The results show the copolymer with a basic monomer can control the acid diffusion without a severe decrease in sensitivity. This new resist system enables us to form fine patterns and attain 2 h post-exposure delay stability without any additional treatment.