RESIDUE-FREE REACTIVE ION ETCHING OF SILICON-CARBIDE IN FLUORINATED PLASMAS .2. 6H-SIC

We have previously reported the residue-free reactive ion etching (RIE) of 3C-SiC in CHF3/O-2, SF6/O-2, CF4/O-2, and NF3/O-2 mixtures with H-2 additive. The minimum H-2 concentration for residue prevention was found to vary with the O-2 content of each gas plasma and from gas to gas. In this paper, we report on the reactive ion etching of 6H-SiC in the same gas plasmas. The 6H-SiC etch rate and etched surface morphology under different etching conditions are presented. A similar pattern of minimum H-2 concentrations for the residue-free RIE of 6H-SiC is obtained. This indicates that the process involving H-2 additive in the fluorinated plasma could be applied to other SIC polytypes. A residue-free etching surface can be obtained without the H-2 additive only in pure CHF3 plasma. Other plasma conditions do need various levels of H-2 concentration in the plasma to obtain a clean etched surface. In both 3C- and 6H-SiC the etch rate decreases as the H-2 concentration increases. No etching undercut was found for 6H-SiC with Al as etching mask. A graphite sheet covering the powered electrode also produced residue-free RIE but suffers from undesirable side effects. A comparison of minimum H-2 levels for residue-free etching of 3C- and 6H-SiC in different plasmas is discussed.