Surface roughening in ion implanted 4H-silicon carbide

Silicon carbide (SiC) devices have the potential to yield new components wi th functional capabilities that far exceed components based on silicon devi ces. Selective doping of SiC by ion implantation is an important fabricatio n technology that-must be completely understood if SiC devices are to achie ve their potential. One major problem with ion implantation into SiC is the surface roughening that results from annealing SiC at the high temperature s which are needed to activate implanted acceptor ions, boron or aluminum. This paper examines the causes and possible solutions to surface roughening of implanted and annealed 4H-SiC. Samples consisting of n-type epilayers ( 5 x 10(15) cm(-3), 4 mu m thick) on 4H-SiC substrates were implanted with B or Al to a total dose of 4 x 10(14) cm(-2) or 2 x 10(15) cm(-2), respectiv ely. Roughness measurements were made using atomic force microscopy. From t he variation of root mean square (rms) roughness with annealing temperature , apparent activation energies for roughening following implantation with A l and B were 1.1 and 2.2 eV, respectively, when annealed in argon. Time-dep endent activation and surface morphology analyses show a sublinear dependen ce of implant-activation on time; activation percentages after a 5 min anne al following boron implantation are about a factor of two less than after a 40 min anneal. The rms surface roughness remained relatively constant-with time for anneals in argon at 1750 degrees C. Roughness values at this temp erature were approximately 8.0 nm. Annealing experiments performed in diffe rent ambients demonstrated the benefits of using silane to maintain good su rface morphology. Roughnesses were 1.0 nn (rms) when boron or aluminum impl ants were annealed in silane at 1100 degrees C, but were about 8 and 11 nm for B and Al, respectively, when annealed in argon at the same temperature.