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

The as-implanted sample, with a broad As distribution (seen from MEIS), does
not provide sufficient density contrast to be visible in SR.
In terms of the behaviour of the oxide layer, both MEIS and SR show the SiO2
layer growing in thickness with increasing thermal budget. The measurements of the
width of the SiO2 are in reasonable agreement, within the experimental accuracy and are
given in Table 6.1. The small differences may be simply due to different measurement
criteria. MEIS shows that the oxide peaks appear to contain a region of suboxide
(Figure 6.4c), which are not included in the oxide widths in Table 6.1, based on FWHM.
It is not clear how the SiO2 layer is defined in the SR measurements.
To conclude this comparison section, it has been shown that the combined use of
MEIS and SR can provided complementary and additional information. MEIS has
provided the essential starting point for an unambiguous modelling of the SR curves.
SR with the better depth resolution gives the width of the segregated As layer to be 0.7
nm. Within the accuracy of the two techniques they give good agreement on the depth
of the segregated peak and the trends in the oxide layer width.
6.2.4 Reduction in implant energy – 1 keV As implantation and annealing
In terms of improvements in junction depth a common trend in manufacturing
has been to reduce the implant energy. In this section the results of 1 keV As
implantation are presented as a comparison to the 3 keV results described in section
6.2.3. It is shown that diffusion is far more critical in determining the final junction
depth than the implantation energy and hence a reduction in beam energy may not
necessarily lead to an improvement in junction depth.
6.2.4.1 Experimental
MEIS and SIMS analysis was carried out on a similar batch of samples to the
previous set but with a 1 keV implant instead of 3 keV. The dose was again 2E15 cm -2 .
As with the previous samples, implants were carried out into crystalline (NoPAI) and
pre-amorphised (PAI) wafers. The pre-amorphising implant was a 130 keV Xe to a dose
of 2E14 cm -2 , producing a 100 nm amorphous layer (13). Samples were annealed with a
furnace anneal at 600 °C for 20 min, rapid thermal annealed at 1000 °C for 5s and
1025 °C for 10s, and spike annealed at 1050 °C. MEIS analysis was performed using a
100 keV He + beam. The results of the [332] blocking direction are presented here. The
shallower implantation does not require as large an energy separation of the peaks as in
the case of a 3 keV implant and so the [332] direction with its better depth resolution
132