The Formation of SiO2 in an RF Generated Oxygen Plasma: II. The Pressure Range Above 10 mTorr
Abstract
This paper describes the formation of SiO2 in an rf generated oxygen plasma in the pressure range above 10 mTorr. The experimental setup used for this study is the same as that described in Part I of this study. Using the silicon-mask interface as a marker and examining the cross section of silicon wafers after oxide formation, it was concluded that the mechanism of oxide formation in the pressure range 10-100 mTorr is growth of SiO2. A unique and unexpected result of the plasma process conducted at pressures greater than 10 mTorr is that oxide growth occurs primarily on the surface of the wafer facing away from the plasma, in sharp distinction to the observations made at pressures less than 10 mTorr where the oxide forms only on the surface facing the plasma. A key experimental parameter is the confinement of the plasma by the wafer which was observed only at pressures greater than 10 mTorr and at generator frequencies from 0.5 to 3 MHz. Oxide growth rate was studied as a function of pressure, power, frequency of the applied field, and substrate parameters to determine the optimum growth conditions. The etch rate, refractive index, stress, fixed charge, interface states, and breakdown strength of plasma oxides grown at 500°C compare very favorably to thermal oxides grown at 1100°C. © 1981, The Electrochemical Society, Inc. All rights reserved.