Novel crosslinking method for negative tone photoresist having pendant carboxyl moieties

We have developed a novel photo-crosslinking method for the negative tone photoresist comprising binder resins with pendant carboxyl groups. A series of copolymers have been synthesized deriving from methacrylic acid, methyl methacrylate, n-butyl methacrylate, and alpha -methacryloxy-gamma -butyrolactone with various feed molar ratios. The existence of lactonic methacrylate units in copolymers was found to increase the sensitivity of the photoresist. Increasing photosensitivity was investigated by using a model compound of alpha -acetoxy-gamma -butyrolactone (ACBL). Heat treatment of ACBL compounds in the presence of acid was found to cause the formation of dimers. The following were also investigated: thermogravimetric properties of binder resins, the exposure characteristic curves, and the lithographic evaluation of the negative tone photoresist of copolymers. The existence of alicyclic gamma -butyrolactone groups was found to increase the etching resistance of the resists.