A Sensitive Novolac‐Based Positive Electron Resist

Abstract

A positive electron resist has been developed which appears to operate on a different mechanism from conventional positive electron resists. Resists in the latter category such as PBS or PMMA achieve differential solubility primarily as a result of scission of the main chain. In the case of the new resist, differential solubility appears to be achieved by the removal of a polymeric dissolution inhibitor. The resist is a composite system consisting of a novolac resin similar to that used in most positive photoresists in solid solution with poly(2‐methyl‐1‐pentene sulfone) which functions as a dissolution inhibitor of the novolac resin in aqueous base. The process operates by spontaneous depolymerization of the polymeric dissolution inhibitor, a process which is initiated by electron irradiation. The sensitivity of this resist (called NPR) is 3 μC cm−2 at 20 kV and the contrast is 1.0. Submicron features have been delineated in 1.0 μm resist films. The resist withstands Al, poly‐Si, , doped, and plasma etching environments and has been used as a plasma etch mask to transfer submicron features into these film substrates.