SOLID-SOLID VACUUM DIFFUSION PROCESSES IN SILICON

Two diffusion techniques are described making use of doped silicon wafers as the diffusion source. The processes are carried out either in an evacuated capsule or inside a high vacuum furnace. In a series of boron diffusions, the high vacuum technique yielded results comparable to the capsule technique. It offers more experimental flexibility but requires masking layers other than SiO//2 for the production of planar devices. A mathematical model based on the various physical processes occurring in a multiphase system is developed to allow the calculation of material exchange in capsule diffusion processes. The influences of three main effects on this exchange are considered: the finite ratio of source to sink surfaces, the limited rate of exchange at the beginning of the process due to the sorption processes at the surfaces, and the disturbance of the exchange process by doping material adsorption at the capsule walls.