Diffusion of Gallium Through Silicon Dioxide Films into Silicon

Metal‐oxide‐silicon capacitors with shallow (∼0.1 µm) diffusions of gallium through silicon dioxide films into silicon were studied with capacitance voltage techniques. The first part of the paper is a discussion of the ionization of the gallium acceptor in the silicon space charge region, and of the unusual capacitance‐voltage characteristics of very shallow diffused layers. It is concluded that in a space charge region even a comparatively deep level like that of gallium is largely ionized so that nearly all of the dissolved gallium contributes to the signal. Furthermore, very shallow diffusions give curves identical to those of the bulk substrate material. However, the entire curve is shifted on the voltage axis in linear proportion to the amount of indiffused impurity. This voltage shift is used to determine the amount of gallium in silicon. In the second part the following experimental results are reported: After comparatively short diffusion times the concentration of gallium in silicon is linearly proportional to in an ambient gas containing hydrogen and water over . This implies that initially the gallium concentration is a function of rather than . The diffusion coefficient of gallium in the oxide film, derived from the amount of gallium which diffused through the film into the silicon at . The density of mobile charge in the film was found to be higher than 1 × 10¹² cm⁻² under all diffusion conditions except when vapor is suppressed.