Ion-implantation in bulk semi-insulating 4H-SiC

Multiple energy N (at 500 °C) and Al (at 800 °C) ion implantations were performed into bulk semi-insulating 4H-SiC at various doses to obtain uniform implant concentrations in the range 1 × 10¹⁸-1 × 10²⁰ cm^-3 to a depth of 1.0 μm. Implant anneals were performed at 1400, 1500, and 1600 °C for 15 min. For both N and Al implants, the carrier concentration measured at room temperature for implant concentrations ≤ 10¹⁹ cm^-3 is limited by carrier ionization energies, whereas for the 10²⁰ cm^-3 implant, the carrier concentration is also limited by factors such as the solubility limit of the implanted nitrogen and residual implant damage. Lattice quality of the as-implanted and annealed material was evaluated by Rutherford backscattering spectroscopy measurements. Residual lattice damage was observed in the implanted material even after high temperature annealing. Atomic force microscopy revealed increasing deterioration in surface morphology (due to the evaporation of Si containing species) with increasing annealing temperature. The surface damage is in the form of long furrows running in one direction across the wafer to a depth of ∼25 nm from the surface for samples annealed at 1600 °C for 15 min. We measured room temperature sheet resistivities of ∼70 and 1.2 × 10⁴ Ω/sq., respectively, for 2 × 10¹⁹ cm^-3 N (1500 °C annealing) and 1 × 10²⁰ cm^-3 Al (1600 °C annealing) implanted samples.