Quantitative theory of retarded base diffusion in silicon n-p-n structures with arsenic emitters

When As is sequentially diffused into Ga or B-doped Si, a retardation of the p -type base layer is generally observed. This is in contrast to the "emitter-push" effect associated with sequential phosphorus diffusions. In order to simulate transistor profiles it is necessary to be able to quantitatively describe the emmiter-base interactions during diffusion. In this study, the way in which the internal electric field, the equilibrium vacancy density, ion pairing, and the rate of [VSiAS2] complex formation affect the redistribution of the base layer during sequential processing was investigated. Numerical solutions to coupled diffusion equations indicate that the electric field and ion-pairing effects only cause localized retardation of a B profile during the As emitter diffusion. However, the formation of [VSiAs2] complexes causes a vacancy undersaturation in the Si to a distance in the crystal well beyond most practical collector-base junction depths. Since the local-base diffusivity depends upon the vacancy density, this extrinsic vacancy undersaturation effect causes the expected retarded base diffusion. Experimental verification of the correctness of the theory present is given as a function of emitter- and base-surface concentrations, initial base depths, and times and temperatures. © 1973 American Institute of Physics.

Duke Scholars

Author Richard B. Fair Electrical and Computer Engineering