Zinc Diffusion into Silicon by a Closed-Tube, Two-Temperature Technique

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Abstract
The diffusion of zinc into silicon was investigated by a sealed‐quartz‐tube, two temperature method. The following diffusion variables were considered: time (15 min‐16 h), silicon type (N and P), temperatures (900°–1100°C), zinc temperatures (600°–900°C), and the effect of chemical treatments. A value of 4.4×10−8 cm2/sec was computed for substitutional zinc diffusivity in silicon, with silicon wafers at 1000°C and zinc source at 700°C. While the diffusion of zinc followed the usual square root dependence on time, there was an initial time lag of several minutes very probably due to the ever present thin SiO2 films on the surface of silicon. When these SiO2 surface layers were made intentionally thicker zinc diffusion virtually stopped. In the pressure range between 50 and 760 Torr, the penetration of zinc was found to be a nonlinear function of the vapor pressure of zinc. The effects of heat treatments at 1000°C on electrical resistance of silicon with and without zinc were also studied and compared. Finally, zinc was diffused into N+‐P power diode structures.

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