Damage formation and annealing studies of low energy ion implants ...
Damage formation and annealing studies of low energy ion implants ... Damage formation and annealing studies of low energy ion implants ...
7.3 Results and discussion Figure 7.1 shows the MEIS energy spectrum of an as-implanted, PAI, 3 keV BF2 + implanted sample, as well as spectra taken after 10 s annealing at 1025 °C for both 1 and 3 keV BF2 + implants. The spectrum of the Xe pre-amorphised, 1 keV BF2 implanted sample is identical to the 3 keV implanted one, as should be expected, and hence is not shown. A virgin Si sample showing scattering from the surface Si and O atoms, at energies of 84 keV and 72 keV, respectively, is included as a reference. The increased random yield between 70 and 84 keV for the pre-amorphised, as-implanted sample is caused by scattering off deeper atoms in the amorphised layer. Spectra obtained after annealing show that SPER has restored the Si crystalline state. The observed increase of the width of the Si peak compared to the virgin sample is largely accounted for by the growth in oxide thickness following implantation and annealing. For all of the anneals investigated here the SPER process was completed. The behaviour of the Xe implant after annealing forms the main interest in this chapter. The Xe is visible in the spectrum between 84 and 95 keV and shown in the inset with the yield multiplied by a factor 10 and the Xe depth scale added. The asimplanted Xe profile extends from ~ 94 keV, down in energy until it merges with the Si surface peak at ~ 84 keV. The TRIM calculated Xe profile, added in the inset, shows good agreement with the as-implanted shape. Approximately half of the Xe profile is visible for energies above the Si peak. TRIM calculations give a mean projected range (Rp) of 18 nm for 20 keV Xe. Following the 1025 °C 10 s anneals, some of the Xe has migrated to a shallower depth where it is trapped, in a relatively narrow distribution, the depths of which are dependant on the BF2 implant energy. For the 1 keV BF2 implanted sample the peak centre is at ~ 7 nm, and for 3 keV BF2 it is at ~ 13 nm, as indicated with arrows. The Si regrowth at all other anneal conditions used is very similar to that shown in Figure 7.1. 175
Yield (counts per 5 µC) 400 300 200 100 0 O 20 keV Xe 1 keV BF 1025 2 o C 20 keV Xe 3 keV BF 1025 2 o virgin 20 keV Xe 3 keV BF as-impl 2 C 70 75 80 85 90 95 Figure 7.2 shows Xe depth profiles before and after SPER for different anneals. Note that here the depth scale is plotted in the opposite direction to the energy scale in Figure 7.1. The Xe concentration scale is also included on the right hand side of the figure. The top of the figure contains Xe profiles for 3 keV samples and the bottom contains those for the 1 keV samples. Both include profiles from as-implanted, 600 °C 20 minutes furnace anneal, 1000 °C 5 s RTA and a high temperature spike annealed sample. As is observed for the 1025 °C 10s sample in Figure 7.1, for all anneals following SPER, Xe has migrated closer to the surface and is trapped in a 5-6 nm wide layer (FWHM). For the 1 keV BF2 implanted samples this is centred at approximately 7 nm, and for 3 keV BF2 at around 13 nm. The location of the Xe is consistent for all anneal conditions used. The different anneals affect the sharpness of the profile but not the depths of the peaks. Lower temperatures generally produced a broader Xe distribution. By referencing the integrated peak areas to the random Si yield, the Xe dose could be calculated. 176 Xe depth Si Energy (keV) 15 10 5 0 (nm) PAI 1 keV BF2 3 keV BF 2 TRIM Figure 7.1 MEIS energy spectra of Xe pre-amorphised Si samples, implanted with 1 and 3 keV BF2, before and after annealing at 1025 °C for 10s. The inset shows the depth Xe depth profiles before and after annealing.
- Page 143 and 144: implantation conditions are those u
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7.3 Results <strong>and</strong> discuss<strong>ion</strong><br />
Figure 7.1 shows the MEIS <strong>energy</strong> spectrum <strong>of</strong> an as-implanted, PAI, 3 keV<br />
BF2 + implanted sample, as well as spectra taken after 10 s <strong>annealing</strong> at 1025 °C for both<br />
1 <strong>and</strong> 3 keV BF2 + <strong>implants</strong>. The spectrum <strong>of</strong> the Xe pre-amorphised, 1 keV BF2<br />
implanted sample is identical to the 3 keV implanted one, as should be expected, <strong>and</strong><br />
hence is not shown. A virgin Si sample showing scattering from the surface Si <strong>and</strong> O<br />
atoms, at energies <strong>of</strong> 84 keV <strong>and</strong> 72 keV, respectively, is included as a reference. The<br />
increased r<strong>and</strong>om yield between 70 <strong>and</strong> 84 keV for the pre-amorphised, as-implanted<br />
sample is caused by scattering <strong>of</strong>f deeper atoms in the amorphised layer. Spectra<br />
obtained after <strong>annealing</strong> show that SPER has restored the Si crystalline state. The<br />
observed increase <strong>of</strong> the width <strong>of</strong> the Si peak compared to the virgin sample is largely<br />
accounted for by the growth in oxide thickness fol<strong>low</strong>ing implantat<strong>ion</strong> <strong>and</strong> <strong>annealing</strong>.<br />
For all <strong>of</strong> the anneals investigated here the SPER process was completed.<br />
The behaviour <strong>of</strong> the Xe implant after <strong>annealing</strong> forms the main interest in this<br />
chapter. The Xe is visible in the spectrum between 84 <strong>and</strong> 95 keV <strong>and</strong> shown in the<br />
inset with the yield multiplied by a factor 10 <strong>and</strong> the Xe depth scale added. The asimplanted<br />
Xe pr<strong>of</strong>ile extends from ~ 94 keV, down in <strong>energy</strong> until it merges with the Si<br />
surface peak at ~ 84 keV. The TRIM calculated Xe pr<strong>of</strong>ile, added in the inset, shows<br />
good agreement with the as-implanted shape. Approximately half <strong>of</strong> the Xe pr<strong>of</strong>ile is<br />
visible for energies above the Si peak. TRIM calculat<strong>ion</strong>s give a mean projected range<br />
(Rp) <strong>of</strong> 18 nm for 20 keV Xe.<br />
Fol<strong>low</strong>ing the 1025 °C 10 s anneals, some <strong>of</strong> the Xe has migrated to a shal<strong>low</strong>er<br />
depth where it is trapped, in a relatively narrow distribut<strong>ion</strong>, the depths <strong>of</strong> which are<br />
dependant on the BF2 implant <strong>energy</strong>. For the 1 keV BF2 implanted sample the peak<br />
centre is at ~ 7 nm, <strong>and</strong> for 3 keV BF2 it is at ~ 13 nm, as indicated with arrows. The Si<br />
regrowth at all other anneal condit<strong>ion</strong>s used is very similar to that shown in Figure 7.1.<br />
175
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