Structural and Chemical Comparison of Graphite and BN/AlN Caps Used for Annealing Ion Implanted SiC
The effectiveness of AlN/BN and graphite annealing caps for ion implanted SiC was examined morphologically, structurally, chemically, and electrically. The AlN/BN cap more effectively blocks the out-diffusion of silicon because it is essentially inert. Relatively small amounts of silicon from the SiC diffuse out into the graphite cap and react with it. This has the effect of lowering the Si vapor pressure so that it does not create blow holes in this relatively weak structure. The graphite cap can be removed easily with an oxygen plasma, while warm KOH has to be used to remove the nitride cap, and not all of it can be removed after an 1800°C anneal. The out-diffusion of silicon through the graphite cap is most severe at 1800°C, where it roughens the SiC surface and forms reaction products when the Si reacts with the graphite at a significant rate. At lower temperatures these reaction products form small particulates on the surface that are visible only at higher magnifications. In those regions where the graphite cap crystallized, isolated morphological damage on the SiC surface was also detected, appearing to be in the vicinity of the grain boundaries. Scratches on the substrate surface were not affected even at temperatures as high as 1800°C.