Ion Implantation Damage and B Diffusion in Low Energy B Implantation with Ge Preimplantation
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757 Mat. Res. Soc. Symp. Proc. Vol. 396 ©1996 Materials Research Society
RESULTS Determination of implant conditions We decide first that a B+ implant energy of 6 keV would produce a practical beam current from commercial high current implanters. A dose of 1x1015 cm"2 is sufficient to form a source drain of a MOS transistor. The Ge+ implant energy of 50 keV was decided so that the Ge+ damage layer distributes to a similar depth as the B implanted layer simulated by TRIM. [7] To suppress the leakage current of the pn junction, the Ge+ implant damage should be shallower than the pn junction. [8] The doses of Ge+ preimplant produce either a complete amorphization 2 3 (2x 1013 (2x 1014 cm-2), intermediate (5x 101 cm ), or a damage comparable with the B+ implant cmr2). As-implant damage Figure 1 shows the depth profiles of damage of the as-implanted substrates measured by RBS channeling analysis. As shown in Fig. 1 (a), the substrate implanted with Ge+ to a dose of 2x 1014 cm-2 has a 60 nm thick completely amorphous layer, so a continuous amorphous layer is formed from the surface. The substrates implanted with Ge+ to 5x 1013 cm-2 or only LEB have the damage of a 30 nm thick 60 % amorphized layer and a 15 nm thick 50 % amorphized layer, respectively. These are called sub-amorphous. The substrate implanted with LEB after the implantation of Ge+ to 5x 1013 cm-2 has a 30 rum thick 80 % amorphized layer. It is larger than the total of damage of the LEB and the Ge+ with 5x10 13 cm2 . The damaged crystalline with Ge+ 5x 1013 cm" 2 would tend to collapse when the LEB is implanting. Figure 1 (b) shows that the 3 2 damage of Ge+ of 2x1013 cm"2 is similar to the damage of LEB with Ge+ at 2x101 cm- . The damaged substrate maintains the crystalline structure. The Ge+ dose dependence of damage accumulation would be explained from a stress incorporated in the damaged crystal prior to amorphization. [2] When the Ge+ dose is too low to form an amorphous layer, the damage can be accumulated in the substrate such that the location 120
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Depth (nm)
Depth (nm)
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(a)
Figure 1. the depth profiles of damage of the as-implanted substrates measured by RBS channeling analysis.
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Figure 2. The SIMS profiles of the as-implanted and (b) the after-RTA B profiles. of Si atoms is not shifted from regular sites. For example, the multifold point defects, such as divacancies are generated. The vacancy type multifold point defect is not detected using RBS channeling analysis. As the Ge+ dose increases in the vicinity of amorphization, the substrate is amorphized quickly. The multifold point defects is saturated, so a base
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