Growth of 6H-SiC crystals with low boron concentration

The effects of growth conditions, diffusion barrier coatings, and alternate hot zone materials on boron incorporation in 6H-SiC boules grown by physical vapor transport were evaluated. Chemical analysis by secondary ion mass spectrometry revealed that commercial source materials combined with standard halogen-purified graphite led to B concentrations on the order of 1.0e17 atoms/cm3. Development of high-purity source material with B concentrations less than 1.8e15 atoms/cm3 subsequently reduced the B concentration in the boule to 3.0e16 atoms/cm3. Application of carbide coatings and the use of pyrolytic graphite components ultimately lead to the growth of SiC boules with B concentrations as low as 2.4e15 atoms/cm3. Changes in growth temperature (2100–2300 °C) and pressure (5–13.5 Torr) had no measurable effect on B incorporation. Changes in the C/Si ratio due to source graphitization and addition of hydrogen gas to the growth atmosphere also had no effect on B incorporation.