Damage formation and annealing studies of low energy ion implants ...

yield (counts per 5µC)
300
250
200
150
100
50
0
O depth (nm)
3 2 1 0
Si depth (nm)
14 12 10 8 6 4 2 0
150 155 160 165 170 175 180 185
Energy (keV)
RTA at 700 °C causes a substantial change in the spectrum indicating the
completion of the SPER process. The depth of the Si damage peak reduces to 2.8 nm,
which is still somewhat greater than that of the virgin Si peak (2 nm). This larger width
is in part accounted for by the growth of the oxide layer from 1.5 nm (for virgin Si) to
1.8 nm (after 700 °C RTA), also shown in the spectrum. A second reason is given
below. The SPER of the amorphous layer has produced a segregated layer of As, which
has been pushed out of the regrown layer and has piled up at the interface. MEIS
unambiguously shows that this pileup occurs at the interface with the now 1.8 nm thick
oxide (10). This As yield accounts for about 40 % of the implanted dose. Apart from a
visible As profile tail, the remainder has moved into substitutional lattice positions and
is no longer visible to the He + beam. The tail of the As profile indicates that the
regrowth is not perfect and that the layer still contains some non-substitutional As
atoms. RTA at 900 °C causes some further reduction in the visible As profile tail and a
corresponding growth in the segregated As peak to 47 % of the implanted As dose.
Taking the system energy resolution into account, the FWHM width of this peak may be
below 1 nm and in fact the peak may actually be 1 ML thick in agreement with certain
121
virgin
Random
1.8e15 as-impl
600 C 10 sec
700 C 10 sec
900 C 10 sec
1050 C spike
As depth (nm)
10 8 6 4 2 0
Figure 6.1 200 keV He MEIS energy spectra for 2.5 keV 1.8E15 As implants, for various
anneal temperatures.