Determination of junction depths for phosphorous diffused in silicon

P was diffused into p-type Si wafers containing B at 1100°C for six different times using a solid state source and a standard pre-deposition process. Secondary ion mass spectrometry (SIMS) provided profiles of dopant concentration versus wafer depth from which both the surface concentration and the junction depths for the six wafers were determined. These profiles were fitted acceptably well by the constant supply model of diffusion in the dilute “tail region” identified by Fair, although indications of concentration-dependent diffusion were observed. Two independent determinations of the sheet resistivity of each sample were made. The results confirmed the correct operation of our custom-built sheet resistivity system. The resulting data allow us to predict the junction depth within 0.2 μm over a range from 1.0 to 2.0 μm. A plot of the dopant surface concentration, N₀, versus the product of the sheet resistivity and the junction depth, R_sx_j, agrees well with data from the Irvin plot