Annealing of Ion Implantation Damage in SiC Using a Graphite Mask
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For p-type ion implanted SiC, temperatures in excess of 1600 'C are required to activate the dopant atoms and to reduce the crystal damage inherent in the implantation process. At these high temperatures, however, macrosteps (periodic welts) develop on the SiC surface. In this work, we investigate the use of a graphite mask as an anneal cap to eliminate the formation of macrosteps. N-type 4H- and 6H-SiC epilayers, both ion implanted with low energy (keV) Boron (B) schedules at 600 'C, and 6H-SiC substrates, ion implanted with Aluminum (Al), were annealed using a Graphite mask as a cap. The anneals were done at 1660 'C for 20 and 40 minutes. Atomic force microscopy (AFM), capacitance-voltage (C-V) and secondary ion mass spectrometry (SIMS) measurements were then taken to investigate the effects of the anneal on the surface morphology and the substitutional activation of the samples. It is shown that, by using the Graphite cap for the 1660 'C anneals, neither polytype developed macrosteps for any of the dopant elements or anneal times. The substitutional activation of Boron in 6H-SiC was about 15%. INTRODUCTION
The improvement of the material quality of SiC and the development of its device technology have been, for the past several years, the focus of intense investigation by research groups from around the world. It is projected that its large bandgap, high electron saturation velocity, exceptional thermal conductivity (greater than copper), and large breakdown field strength will improve the standard commercial benchmarks of high-power and high-frequency devices and allow them to operate in caustic environments and at higher temperatures [1]. Of the three methods of doping--ion implantation, thermal diffusion, and in situ doping--ion implantation will play the most important part in the fabrication of these devices. This is because, unlike Silicon technology, thermal diffusion, due to the low diffusion coefficients of the standard dopants below 1800 'C, is not a viable method for doping SiC [2]. In addition, the in situ doping method, while it is the principal method of preparing doped device quality epitaxial material at present, cannot be used for planar device fabrication and other applications where precision is required in small areas. Still, despite its advantages, ion implantation of SiC is not as mature a technology as it is for Silicon, where ion implantation is routinely used in device fabrication. One of the problems associated with the ion implantation of SiC surrounds its post implant anneal. An anneal is necessary to activate the dopant atoms and to reduce the inherent crystal damage created by the ion implantation process. For p-type SiC, this anneal is usually done at temperatures up to 1700 'C [3]. One side effect of this anneal is that, at these high temperatures, the post anneal surface 45 Mat. Res. Soc. Symp. Proc. Vol. 572 ©1999 Materials Research Society
morphology of the material is dominated by macrosteps. In this paper, we present a technique that eliminates the formation of these macro
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