REACTIVE ION ETCHING OF SIC THIN-FILMS BY MIXTURES OF FLUORINATED GASES AND OXYGEN

Reactive ion etching (RIE) of SiC thin films has been investigated in depth in a variety of fluorinated gas plasmas, such as SF6, CBrF3, and CHF3 mixed with oxygen. The optical emission spectrum of the RF plasma and the plasma-induced dc bias were monitored to explore the etching mechanisms. Argon actinometry has been used to convert the plasma emission intensity to relative concentration of plasma species in order to more accurately quantify the etching process. Plasma conditions, such as composition of gas mixture, pressure, and power were investigated in order to achieve selective SiC-to-Si etching and anisotropic patterning of SiC thin films. A SiC:Si etch rate ratio higher than unity was obtained for the first time by using CBrF3/75%02 and CHF3/90%02 at 200W, 20 seem, 20 mtorr plasma conditions. The best anisotropic profile was obtained by using CHF3 gas in the RIE mode. A critical dc bias level, around -300V, appears to separate regimes of chemical and physical rate limiting step domination of the SiC etch rate. A carbon-rich surface on the etched SiC films was found for all gases. The SiC etching mechanisms in fluorinated gases were deduced from loading experiments, surface analysis, and other etching phenomena. Evidence of the chemical reaction between carbon and oxygen is presented. No evidence of chemical reaction between fluorine and carbon has been observed. A combined chemical and physical etching model, supported by experiments, is suggested. A carbon blocking mechanism is proposed to understand the etching profile. © 1990, The Electrochemical Society, Inc. All rights reserved.