Hydrogen Plasma Cleaning of the Si(100) Surface: Removal of Oxygen and Carbon and The Etching of Si

Abstract

Silicon etch rates and the in situ remote H plasma cleaning effectiveness in a Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) system have been measured under conditions of varying substrate temperature, exposure time, and hydrogen pressure. An incubation phenomenon is observed in the Si etch rate as a function of exposure time to the plasma species at a substrate temperature of 250°C. The etch rate is observed to increase from 20 A/hr. for 45 min. exposure to 70 A/hr. for a 4 hour exposure. The dependence of the etch rate on the plasma discharge pressure shows the etch rate to decrease from 72 A/hr. at 50-55 mTorr to 4 A/hr. for pressures greater than 125 mTorr. The substrate temperature is found to have the greatest effect on both the cleaning of the surface and the Si etch rate, with 250AC resulting in a surface with oxygen and carbon concentrations less than the detection limit for Auger Electron Spectroscopy. On wafers exposed to atomic H at both 150 and 400AC, oxygen, carbon and nitrogen were detected after 4 hr. exposures. The etch rate is inversely related to temperature, consistent with earlier results. At a substrate temperature of 150AC, Reflection High Energy Electron Diffraction (RHEED) shows the diffraction pattern to change from a streak pattern observed at higher temperatures to a spot pattern, indicating a roughened surface after 4 hrs. of etching. Wafers cleaned at temperatures above 150AC yielded streak patterns even after 4 hr. exposure. Increasing the H pressure during the clean had no effect on the final RHEED pattern.