Phosphorus implantation into 4H-silicon carbide

Abstract

Sheet resistances in nitrogen- and phosphorus-implanted 4H-SiC are measured to assess the time and temperature dependencies of this variable. In 4H-SiC implanted with 3 × 1015 cm−2 nitrogen ions to a depth of 2800 A, the minimum sheet resistance observed is 534 Ω/□. The minimum sheet resistance in 4H-SiC implanted with 4 × 1015 cm−2 phosphorus ions to a depth of 4000 A is 51 Ω/□, a record low value for any implanted element into any polytype of SiC. Time-independent sheet resistances are observed following anneals at 1700°C for nitrogen and phosphorus samples. Lower temperature anneals produce sheet resistances which decrease monotonically with increasing time of anneal. Overall, sheet resistances from phosphorus-implanted 4H-SiC are an order of magnitude below those measured from nitrogen implanted samples. The response of phosphorus to low-temperature annealing is significant, and sheet resistances below 500 Ω/□ are achieved at 1200°C. Activation of phosphorus is attempted in an oxidizing atmosphere with and without prior argon annealing. A three-hour gate oxidation in wet O2 at 1150°C, followed by a 30 min argon anneal, produced a sheet resistance of 1081 Ω/□. Oxidation after argon annealing caused sheet resistances to increase by about 20% compared to samples subjected solely to argon annealing. It is also found that oxide growth rates are much higher over phosphorus implanted than over unimplanted 4H-SiC. Reasons for the disparity in sheet resistances between nitrogen and phosphorus implants, and for the difference in oxide growth rates are suggested.