The effects of polymer film formation on photoresist (OFPR-800) during plasma etching in C2F6/CHF3/He

Abstract

Experiments were performed to study the effects of fluorocarbon erosion of photoresist and the changes in photoresist surface chemistry as a function of the plasma conditions in a commercial etching system using C2H6–CHF3–He gas mixtures used in SiO2 etching. Fluorocarbon thin film formation is observed on the photoresist surface. The composition and thickness of the surface layers are determined using computations from x-ray photoemission data. The composition of the polymer layer is mostly constant within the parameter space studied. It becomes fluorine rich when the source gas is CHF3/He. The measured etch rate of the resist film is correlated to polymer film thickness of the fluorocarbon layer remaining on the surface of the resist in the parameter space studied [total gas flow, C2H6:CHF3 flow (0–40 sccm), variable He flow (40–100 sccm), variable power (350–500 W), and variable pressure (2–2.6 Torr)]. Fluorocarbon polymer deposition is correlated with a zero photoresist erosion rate. In the matrix studied, this occurs when the pressure is maximum, power is minimum, and the He flow is minimum or when the gas is a mixture of CHF3 and He.