Resist etching kinetics and pattern transfer in a helicon plasma

Abstract

We describe the first commercial etching system based on a helicon ion source and characterize it for etching organic films in an oxygen plasma. This single wafer etching system achieves a throughput of at least 30 fully processed 5 in. wafers per hour, which is comparable to the throughput of batch reactors. The etching chamber is equipped with a 13.56-MHz 2500-W helicon source, four low-field magnets to shape the plasma and support the helicon wave mode, and a 600-W radio-frequency chuck with He backside heat exchange and a temperature range from −50 to +125 °C. Etching rates and uniformity were measured on unpatterned resist-coated wafers, while trilayer resist patterns were used to study pattern transfer effects. Under nearly optimum conditions we obtain an etching rate of 1.31 μm/min, a throughput ≥30 wafers/h, nonuniformity ≤± 3%, selectivity ≊70 relative to SiO2 and nearly vertical etching profiles for all types of features having dimensions down to 0.25 μm. We describe the effect of process variables on etching rate, uniformity, selectivity, and etching profiles. We present a model based on multicomponent adsorption kinetics that fits the observed dependence of etching rate on the process variables. This etching system is being applied to several advanced lithographic schemes including dry-developed resists, bilayer lithography, and pattern transfer through organic antireflective coatings and planarizing layers.