surface due to the presence of contaminants from the chamber ambient and residuals from the wafer cleaning process the sims tool uses a cs beam as the sputtering source fig9 shows that there is no further oxygen or carbon contaminations from the earlier use of the ethylene precursor or any associated mixtures of ethylene the uhv cvd chamber remains operational having no background carbon and a base pressure of less than 10 u2212 9 torr with respect to the background contaminates to enable further growth of epitaxial silicon or silicon germanium layers as described in u s pat no 5 298 452 by meyerson which issued mar 29 1994 carbon may be incorporated into silicon layers or silicon germanium only due to the ethylene precursor gas and where no carbon incorporates into the layer from the background when the flow of the ethylene precursor gas is turned off there is no carbon or oxygen memory effect i e no continued incorporation of carbon the fact that there is no memory effect is substantiated by the laboratory data given in table 1 table 1 provides data via sims measurements taken from 14 samples in the first column of table 1 14 different days over six months were used for growing a silicon film on a substrate similar to the.