Impurity profile broadening and shifts by ion beam mixing

Abstract

The broadening and shifts of the profile of a buried impurity layer, caused by heavy ion irradiation, have been measured by backscattering spectrometry. The matrix was amorphous Si and the impurity was a 4 Å thick layer of Pt buried at a depth of 500 Å. The samples were held at a temperature of 90 K and irradiated with 300-keV Xe+ ions to fluences ranging from 0.4 to 12.7×1015 ions/cm2. The broadening was monitored by finding the irradiation-induced increases in the variances of the impurity signals in the backscattering spectra. This quantity appeared to increase linearly with irradiation fluence up to 1×1016 ions/cm2. Shifts were monitored by measuring the movement of both the mean and the peak of the impurity signal relative to the position of the signal from a second thin Pt layer buried beyond the range of the Xe ions. These were corrected for the shifts caused by the Xe atoms buried between the two layers. The net shifts of both the mean and the peak were away from the sample surface, with the magnitude of the shift of the mean being about 100 Å for an irradiation fluence of 1×1016 ions/cm2. The shifts increased roughly linearly with irradiation fluence.