INHIBITION OF SILICON OXIDATION DURING LOW-TEMPERATURE EPITAXIAL-GROWTH

Oxidation of silicon surfaces by trace oxygen prior to epitaxial growth is strongly inhibited in a low temperature epitaxial reactor operated in one atmosphere of hydrogen. Oxidation appears to be highly superlinear with dose, but can be interpreted as linear oxidation following an "incubation period." During the "incubation period" the sticking coefficient of oxygen is less than 4 x 10(-6). The duration of the "incubation period" as a function of oxygen concentration from 5 ppb to 6 ppm at 750-degrees-C was investigated. Incorporation of oxygen into growing Si epitaxial layers was also found to be strongly superlinear with oxygen content in the gas phase. To incorporate oxygen in a growing film above a background level of 10(18) atoms/cm3 requires oxygen concentrations of greater than 400 ppb, which is a concentration two orders of magnitude greater than is required to produce detectable surface oxidation for exposures of surfaces for long times (100 to 1000 s) prior to epitaxial growth. We interpret the superlinear oxidation behavior during growth in terms of the "incubation period" observed for oxidation prior to growth. Incorporation of oxygen into growing films is largely avoided when the "incubation period" is longer than the time to grow a monolayer of Si.