Redistribution of boron and phosphorous in silicon after two oxidation steps used in MOST fabrication

Redistribution of boron and phosphorous impurities in silicon resulting from two consecutive oxidation steps is calculated by using either the method of Green's function or by separating the redistribution after the first oxidation into a constant and error function term. An approximate but analytical solution for redistribution after the second oxidation is then obtainable. Employing a variety of oxidation parameters normally used in several MOS-transistor fabrication processes, the impurity profiles at the end of the second (gate) oxidation process is calculated for each case for both boron- and phosphorous-doped substrates. These profiles compare well with those obtained experimentally fromC-Vmeasurements made on Schottky-barrier diodes deposited on silicon wafers that underwent the same oxidation processes.