EFFECTS OF HYDROGEN ADDITIVE ON OBTAINING RESIDUE-FREE REACTIVE ION ETCHING OF BETA-SIC IN FLUORINATED PLASMAS

In this paper we discuss the formation and prevention of residues during long-term reactive ion etching (RIE) of beta-SiC thin film a variety of fluorinated gas plasmas mixed with oxygen: CHF3, CF4, SF6, and NF3. Without the addition of H2, all fluorinated plasmas produced significant residue for mixtures with O2 ranging from 0 to 90%. Only NF3 and CHF3 at 0% O2 showed a low level, or the absence, of residues. The introduction of a relatively small amount of H-2 additive was observed to prevent residue formation in the etched region during the process. In CHF3 etching, approximately 10% H-2 was sufficient to prevent residues at all values of O2%. A significantly larger (>10%) amount of H-2 is required to prevent residue formation in CF4/O2, SF6/O2, and NF3/O2 plasma. For these gases, the required H-2 additive concentration increases as the oxygen decreases, reaching a maximum for 10% O2. Optimum RIE conditions in different fluorinated gas plasmas are presented for SiC homojunction and heterojunction device fabrication. The effects of covering the powered electrode with graphite or Kapton sheets on residue formation and etch rates were investigated with a variety of fluorinated gas plasmas. The mechanisms of residue formation and prevention through the addition of H-2 are discussed.