POCl3 Annealing as a New Method for Improving 4H-SiC MOS Device Performance

Abstract

Effects of POCl3 annealing on the electrical properties of metal-oxide-semiconductor (MOS) devices on 4H-SiC were investigated. Comparative results of non-annealed, NO-annealed, and POCl3-annealed MOS devices are shown. POCl3 annealing is more effective to reduce interface state density and improve channel mobility than conventional NO annealing. Breakdown characteristics and reliability of annealed oxides were also investigated. POCl3 annealing did not deteriorate oxide breakdown field very much. Time-dependent dielectric breakdown characteristics indicated different behavior due to enhanced electron trapping in the oxide. It is related with uniformly distributed phosphorus in the oxide. Flat-band voltage shift due to interface traps and near-interface traps in the oxide was very small at low oxide fields (< 3 MV/cm), whereas injected electrons were easily trapped in the POCl3 annealed oxide at high oxide fields (> 5 MV/cm). By combination of NO and POCl3 annealing, relatively high channel mobility and stabilized characteristics against electron injection were achieved.