REACTIVE ION ETCHING OF SIGE ALLOYS USING FLUORINE-CONTAINING PLASMAS

The dry etching characteristics of strained S0.85Ge0.15 thin films (congruent-to 800 nm thick), elemental Si and Ge in CF4 reactive ion etching (RIE) and electron cyclotron resonance (ECR) plasmas have been studied. The SiGe films were grown on Si substrates by ultrahigh vacuum/chemical vapor deposition. Etch rates were determined by in situ ellipsometry. For RIE, the dependence of the SiGe etch rate on CF4 pressure was studied, the pressure serving as a means to change the ion energy and the ion/neutral ratio of the plasma. In the ECR plasma separate rf biasing of the wafer was used to control the ion energy independent of the production of the plasma. For all conditions, the etch rates of SiGe alloy films are enhanced over the Si etch rates. X-ray photoelectron spectroscopy surface analysis shows that the SiGe surface etched in CF4 is Ge rich. The Ge enrichment increases with decreasing pressure in RIE and increasing rf bias in ECR etching. These results suggest that preferential sputtering is in part responsible for the change in the stoichiometry of the surface.