Abstract
An apparatus is described for the vapor‐solid diffusion of donors and acceptors into silicon at atmospheric pressure. It consists essentially of a fused silica tube extending through one or more controlled temperature zones. A gas such as nitrogen carries the vapors from the heated impurity element or one of its compounds past the heated silicon.
At temperatures above about 1000 °C, gases such as helium or nitrogen are shown to cause serious pitting or erosion of the silicon surfaces. A thin vitreous silicon dioxide envelope enclosing the silicon during the high temperature heating operation is shown to provide complete protection of the underlying surface against damage. Methods of obtaining surface passivation are described.
In addition to surface protection, a silicon dioxide surface layer also is shown to provide a selective mask against the diffusion into silicon of some donors and acceptors at elevated temperatures. Data are presented showing the masking effectiveness of the silicon dioxide layer against the diffusion of several donors and acceptors into silicon.
The application of the masking technique to produce precise surface patterns of both n‐ and p‐type is described. An example of its feasibility in device considerations is illustrated by the construction of a transistor by double diffusion. This transistor is unique in that both the emitter and base contacts are made at the surface in adjacent areas.
Finally a new predeposition technique is described for controlling the impurity levels in diffused layers over wide ranges. Data are presented to illustrate this technique.