Properties of Cross‐Linked Positive Acting X‐Ray Resists Fabricated on the Basis of Poly(methylmethacrylate‐co‐methacrylyl Chloride)

Abstract

Copolymers of methylmethacrylate (MMA) and methacrylyl chloride (MACl) were cross‐linked under various conditions, in order to obtain intermolecularly cross‐linked polymeric networks having different cross‐linking densities (β). These materials were irradiated with x‐rays generated by an electron‐storage ring or a conventional x‐ray tube. The results showed that there is a critical dose for total solubilization, which can be used to determine the radiation sensitivity of cross‐linked resists. Both the critical dose and the sensitivity obtained from conventional exposure curves depend strongly on β. Optimum sensitivity values were obtained with slightly cross‐linked material produced from copolymers with about 4 m/o MACl. In this case, was up to five times lower than in the case of PMMA. The contrast factor, however, was not significantly affected. The technological properties of this resist were investigated by evaluating influences upon stability due to ion milling, plasma etching , and etchant, as well as by performing adhesion‐sensitive electroplating experiments. The results indicate that this material is at least as good as PMMA resist with regard to etch stability, and that it is superior as concerns adhesion behavior. The storage instability of the uncured (not yet cross‐linked) material, caused by the gradually proceeding hydrolysis of acid‐chloride groups, leads to some problems in practical applications. It was found that reproducible resist performance can only be obtained (after controlled partial conversion of the acid chloride groups) if the material is stored and cross‐linked under total exclusion of water.