The diffusivities of different types of dopant atoms in SiC wafers were generally very low. Nd:YAG and excimer lasers were used to dope SiC with N and Al, respectively. Mathematical models were presented for the temperature distributions in the wafers to understand the diffusion mechanisms in the laser doping process. Since the SiC substrate reaches its peritectic temperature (3100K) at irradiances of 80.6 and 61MW/cm2 for Nd:YAG and excimer lasers, respectively, lower irradiances were used to achieve solid-state diffusion. The Nd:YAG laser doping process doped N to a depth of 800nm; the KrF excimer laser doping process produced Al dopant depths of 200 and 450nm for different numbers of laser pulses. Two distinct diffusion regions, near-surface and far-surface regions, were identified in the dopant concentration profiles, indicating different diffusion mechanisms in these two regions. The effective diffusion coefficients of N and Al were determined for both regions and found to be 2.4 x 10−5 and 9.2 x 10−6cm2/s in the near- and far-surface regions for nitrogen, respectively, and 1.2 x 10−5 and 1.3 x 10−6cm2/s in the near- and far-surface regions for Al, respectively. The calculated diffusivities were at least six orders of magnitude higher than the typical values for N and Al, which indicated that the laser doping process enhanced significantly the diffusion of dopants in SiC .

Laser-Enhanced Diffusion of Nitrogen and Aluminum Dopants in Silicon Carbide. Z.Tian, N.R.Quick, A.Kar: Acta Materialia, 2006, 54[16], 4273-83