XPS CHARACTERIZATION OF SILICON ETCHED IN SF6 plus N2O AND SF6 plus O2 RF PLASMAS.

Dry etching of silicon using a radio-frequency glow discharge in SF6 plus N2O and SF6 plus O2 gas mixtures have been studied. Both N2O and O2 additives can significantly enhance the silicon etch rate. For low RF power, the same amount of N2O enhances silicon etch rate more than O2 does. When the RF power level is increased beyond a value, O2 becomes more efficient in enhancing the silicon etch rate. According to XPS characterization, there is no detectable sulfur contamination on silicon surface after being etched by either plasma. Under some conditions, SF6 plus O2 plasma causes irregular surface etching leaving dark or cloudy islands scattered on the silicon surface. XPS reveals that those darker islands appear to have a much larger carbon and oxygen content. According to XPS after sputtering the sample, it seems to indicate bulk carbon instead of just surface contamination. SF6 plus N2O etches silicon smoothly without dark islands.