Block co-polymerized polyimide resists for KrF lithography and EB lithography with high dry etching resistance

Abstract

We have developed a series of block co-polymerized polyimides for KrF lithography and EB lithography. Block co-polymerization is a synthesis method to control molecular structures. We have developed solvent soluble polyimides in powdered form. We can use these polyimides for dielectric materials in devices, and also can use as a dry etching mask in semiconductor processes. Here we report the details of dry etching properties for the block co-polymerized polyimides by reactive-ion-etching (RIE) using fluoride and chloride gases, typically used for Si etching and GaAs etching, respectively. Etching rates for EB exposed polyimide, photosensitive polyimide, novolac standard photoresist and Si at the condition of 80 W RF power and 60 sccm SF₆ gas flow, were measured as < 1 nm/min, 1.7 nm/min, 34 nm/min and 31 nm/min, respectively. We also checked the etching rate for EB exposed polyimide, photosensitive polyimide, novolac standard photoresist and GaAs at the condition of 50 W RF power and 3 sccm Cl₂ gas flow in the inductive coupled plasma (ICP) RIE, were measured as < 1 nm/min, 50 nm/min, 120 nm/min and 500 nm/min, respectively. Dry etching selectivity of EB exposed polyimide to Si is more than 31, and dry etching selectivity to GaAs is more than 500. These values are much higher compared to novolac standard photoresist. The high resolution EB exposed polyimide is promising for nano-patterning as stable dry etching mask. RIE resistance for polyimide photoresist is 20 times more than novolac standard photoresist for SF₆ etching gas, and more than twice for Cl₂ etching gas.