POLYSILICON GATE ETCHING IN HIGH-DENSITY PLASMAS .1. PROCESS OPTIMIZATION USING A CHLORINE-BASED CHEMISTRY

High density plasma etching processes using chlorine gas have been dev eloped for 0.25 mu m polysilicon etching. Polysilicon films on SiO2-co vered 200 mm silicon wafers are masked with photoresist patterns, and then etched downstream using a high density helicon source made by Luc as Labs of Sunnyvale, CA. To enhance the anisotropic etching, ion bomb ardment is provided by radio frequency (rf) biasing of the sample. Pol ysilicon trenching can be suppressed by performing a two-step etching process: the first uses a high energy ion bombardment resulting in hig h etch rate (250 nm/min) and anisotropy and the second a lower ion ene rgy. The second etching step shows a high selectivity (>80) of Si over SiO2 and therefore ensures the complete removal of the polysilicon du ring the overetch time. Perfect anisotropic profiles can be obtained w ithout any trenching or other undesirable anomalies. The optimum etch rate nonuniformity is 6.5% (3 sigma) when operating the source at maxi mum rf source power (2500 W), 2 mTorr reactor pressure, and adding 30 seem of helium to a 50 seem chlorine discharge. Polysilicon and gate o xide etch rates have been measured using a real time in situ HeNe elli psometer. Etch rates for polysilicon and oxide increase as a function of rf bias power but show no significant pressure or rf source power d ependence. After etching, the 200 mm wafers can be transferred (under high vacuum) to an ultra high vacuum analysis chamber equipped with a Fisons ESCALAB 220i x-ray photoelectron spectrometer. (C) 1996 America n Vacuum Society.