Crystallization of Amorphous Silicon Films by Pulsed Ion Beam Annealing
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J. GYULAI,* R. FASTOW, K. KAVANAGH, M. 0. THOMPSON, C. J. PALMSTROM, C. A. HEWETT,** AND J. W. MAYER Department of Materials Science, Cornell University, Ithaca, NY 14853 *Permanent Address: Central Res. Inst. for Physics, H-1525 Budapest **Permanent Address: Dept. of Elec. Engineering, Univ. of California, San Diego, La Jolla, CA 92093
ABSTRACT Regrowth by pulsed proton beam was studied for evaporated amorphous Si layers, for layers converted to polycrystalline by annealing (both with and without Ge markers) and for implantation-amorphized SOS films. Silicon-on-sapphire showed the lowest threshold for regrowth. Amorphous silicon melted 2 at about 0.2 J/cm lower fluences of protons of 380 keV energy than crystalline Si. Implanted Sb into SOS occupies lattice positions exceeding the solid solubility.
INTRODUCTION Non-equilibrium annealing techniques, e.g. lasers or electron beams have received attention in the past few years [1]. Recently, pulsed ion sources producing protons or heavier particles were used to form metastable layer structures [2] using the equipment in Plasmaphysics Laboratory at Cornell University [3]. Annealing properties of ion beams are analogous to that of the electron beams. The situation closely resembles that of splat cooling, where a molten layer is in good contact with a heat sink. In this study, one approach is described in which markers were used to detect regrowth properties of amorphous and crystalline silicon layers. Parallel to this, the measurement of real-time electrical conductivity of the molten layers was also performed [4]. EXPERIMENTAL In one set of experiments, Si-Si layered structures were produced by vacuum evaporation. Thin layers (=50 A) of germanium were deposited as markers between layers of Si. In some cases, a Ge layer was first deposited, in other instances it was sandwiched between Si layers. All samples were subjected to a 350'C heat treatment for 2 hours to increase stability of the layers. A part of the samples was converted to polycrystalline silicon by an additional anneal at 650*C, 2 hours. A second set of experiments was based on SOS structures, where the amorphous state was reached by room temperature implantation of Xe or Sb at doses of 2 about 1015 ions/cm . Pulsed ion beam annealing was performed on a •450 keV accelerator in Cornell Plasmaphysics Laboratory. The incident energy of protons was chosen between 280 and 400 keV. The total energy flux was tailored by changing the distance between diode and the sample. The incident fluence was measured by an equivalent temperature rise of a free-hanging Ni-platelet spotwelded onto a thermoMat. Res. Soc. Symp.
Proc. Vol. 13 (1983) OElsevier Science Publishing Co., Inc.
456 couple and placed adjacent to the sample. Pulses were of 2-400 nsec duration. The beam contained a high percentage of shallow-penetrating particles, too. This was shown by masking the Ni-platelet with a 5000 X thick, self-supporting Si window. Energy readings in this case dropped to one third of their value. Because of the two beam componen
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