Variability of Closed-Box Diffusion of Boron into Silicon

摘要

A study of the variability of the closed-box diffusion of boron into silicon has been made, using boric acid and silicic acid mixtures as boron sources. Two dilute sources (0.1 wt-pct boric acid and 10 wt-pct boric acid) have been examined in detail to determine how well junction depths, sheet resistivities, and surface concentrations could be reproduced. The experiments were designed to emphasize the contribution of the mass transfer and methods of measurement to the error, and to deemphasize the effect of source-to-source variations. In general, the 10 wt-pct source provided the more reproducible performance, allowing the placement of junctions to within =1/3 microns, control of sheet resistivities to within roughly =30 pct and control of surface concentrations to within a factor of 5 at the level of 3x10 to the 19th power atoms/cu cm. Diffusion coefficients and activation energies for the diffusion of boron in silicon calculated from the two sets of data were in acceptable agreement with the published values. (Author)