Dopant Diffusion and Grain Growth in Arsenic-Implanted Poly-Si
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DOPANT DIFFUSION AND GRAIN GROWTH IN ARSENIC-IMPLANTED POLY-Si L. R. ZHENGa), L. S. HUNGa) AND J. W. MAYER Department of Materials Science and Engineering Cornell University, Ithaca, NY 14853 ABSTRACT The diffusion behavior of arsenic and 4 thl+grain growth of Si in arsenic backscattering techniques and doped poly-Si were investigated by MeV He transmission electron microscopy. By implanting arsenic ions into poly-Si crystallized upon annealing. was made amorphous and films the surface portion In-situ mssurements showed crystal nucleation and growth at temperatures of 650 - 700 C with a dimension comparable to the thickness of the amorphous layer. Annealing at temperatures up to 8500C increased the number of the large grains, but the average grain size did not change significantly. In the unimplanted region grains retained their initial size until 885 C, although implanted arsenic was found to diffuse into this region along grain boundaries. At 8850C penetration of arsenic into the interior of grains caused significant grain growth. We also found that single implants of boron somewhat increased grain size, whereas boron codoped with arsenic appeared to reduce the effect of arsenic doping. These observations support the hypothesis that the enhanced growth rate and the electrical activity of Si near the grain boundary are closely interrelated. INTRODUCTION
Doped poly-Si films are extensively used in both MOSFET and bipolar technologies. High temperature furnace annealing is generally required to activate dopant atoms. This process results in considerable redistribution Therefore, an of dopants as well as grain growth in poly-Si [1-61. understanding of dopant redistribution and its effect on enhancement of grain growth
becomes an important issue for effectively controlling the electrical
and material characteristics of poly-Si. EXPERIMENTAL
Poly-Si 280 nm in thickness was deposited onto SiO using a standard low pressure chemical vapor deposition technique at 620 . Poly-Si and single crystal Siltafers werl simultaneously implanted with 100 keV arsenic at doses of 3 x 10 ions/cm and annealed in an oxygen atmosphere at various temperatures. In-situ annealing was performed at 20-850 C to examine crystal nucleation and crysta{6 gr~wth. In some cases a single boron implant at 30 keV to a dose of 1 x 10 /cm and a dual implant of arsenic and boron were carried out in poly-Si films. The arsenic distribution was studied by Rutherford backscattering (RBS) The microstructure and grain size of the and ion-channeling spectrometry. poly-Si were examined by planar transmission electron microscopy (TEM). RESULTS Arsenic Redistribution Fig. la shows RBS spygtra for 22.8 MeV 4He2+ incident on Si The arsenic signal is increased by a implanted with 3 x 10 ions/cm . factor of 2 for clarity. The full width at half maximum of the arsenic initial distribution corresponds to 80 nm, leading to an average arsenic
Mat. Ras. Soc. Symp. Proc. Vol. 106. @1988 Materials Research Society
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concentration of about 8 at.%. No redistribution of
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