Annealing ion implanted SiC with an AlN cap

An AlN cap was used to try to prevent the preferential evaporation of Si during the high temperature anneals required to activate N implanted into a SiC substrate. The process was essentially successful as the electrical measurements showed that the resistivity continued to decrease with increasing annealing temperatures up to 1600°C and times up to 120 min. The changes were, however, marginal when compared to a 1500°C, 30 min anneal suggesting that this anneal would be sufficient to activate most of the N implants. There is evidence for a small amount of Si being lost near the surface. This could occur where the AlN pulled away locally from the SiC wafer; this effect was stronger for patterned substrates where stress concentrations can occur at steps. For the most part, however, the SiC surface retained its integrity even during the process of removing the AlN film with a hot KOH etch. Also, there was no evidence that Al from the AlN contaminated the N implanted region by diffusing in during the anneals. The surface of the AlN retained its integrity during the anneal although topographical changes suggested that considerable atomic motion had occurred. This coincided with the formation of an amorphous AlN layer in the film.