Two-step rapid thermal diffusion of B, using a BN solid diffusion source, was described. During the first step, HBO2 glass was deposited onto the Si wafer from the diffusion source by keeping the wafer temperature at 750C and the diffusion source temperature at about 900C. During the second step, the B was diffused into the wafer (from the HBO2 glass) by annealing at 1000C or 1100C in N2. Extremely shallow junctions, with depths of about 20nm and sheet resistances of about 350Ω/square, could be achieved as well as relatively deep junctions with depths of about 175nm and sheet resistances of about 55Ω/square. If diffusion annealing was performed at 1100C, the junction depth and the electrically active B concentration at the surface increased when the ambient gas was changed from N2 and O2. The sheet resistance also decreased. No high-resistivity B-rich layer was formed at the surface when diffusion annealing was performed at 1100C in an O2 ambient.

J.G.Kim, C.K.Kim: Journal of Electronic Materials, 1989, 18[5], 573-8