Ion Beam Induced Amorphization and Crystallization Processes in Silicon and GaAs
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ION BEAM INDUCED AMORPHIZATION AND CRYSTALLIZATION PROCESSES IN SILICON AND GaAs J.S. WILLIAMS**, S.T. JOHNSON** AND E. NYGREN** Physics, Clayton 3168, Australia. ** Microelectronics Technology Centre, RMIT, Melbourne 3000, Australia. R.G. ELLIMAN*,
* CSIRO Chemical
ABSTRACT Thin amorphous layers in crystalline Si and GaAs substates have been irradiated at selected temperatures with 1.5 MeV Ne ions to induce either In Si, such irradiation can epitaxial crystallization or amorphization. induce complete epitaxial crystallization of a 1000 A surface amorphous layer for temperatures typically >200'C whereas, at significantly lower temperatures, layer-by-layer amorphization results. Although epitaxial crystallization can also be stimulated in GaAs by ion irradiation at temperatures >65°C, the process is non-linear with ion dose and results in poor quality crystal growth for amorphous layers greater than a few hundred Angstroms in thickness. Layer-by-layer amorphization has not been observed in GaAs. INTRODUCTION Complete epitaxial crystallization of amorphous Si layers can be induced by MeV ion irradiation at temperatures typically greater than 200°C [see for example refs. 1 and 2 and refs. therein]. Recently, a layer-bylayer amorphization process has also been identified for 1.5 MeV Xe* irradiation at temperatures less than about 220'C [31. In this study, we have examined the transition from epitaxial crystallization to layer-bylayer amorphization for silicon layers irradiated with 1.5 MeV Ne+. The existence of similar processes in GaAs has also been explored. EXPERIMENTAL Silicon (1Q0) s~mples were implanted at 77 K with 50 KeV Si+ ions to a dose of 2 x 10 cm- and annealed at 450°C for 15 minutes to create a stable surface amorphous layer - 950A thick. GaAs (100) wafers were similarly 4 irradiated with either 30 to 80 KeV Ar ions I? dosps in the range 1-2 x 10 cm- , or 15 KeV Si ions to a dose of 2 x 10" cm- to generate amorphous layers of varying thicknesses. Samples were subsequently irradiated with 1.5 MeV Ne+ ions at temperatures up to 200'C in an attempt to induce either epitaxial crystallization or layer-by-layer amorphization of the p~s-existing2 near-1 surface amorphous layer. A constant dose rate of 7 x 10 ions cm- sec" was employed for all irradiations. Irradiated samples were subsequently analysed by high depth resolution Rutherford backscattering-channeling (RBS-C) to monitor the extent of epitaxial growth or amorphization. Selected samples were also analysed by transmission electron microscopy (TEM) to identify the defect structures following irradiation.
Mat. Res. Soc. Symp. Proc. Vol. 74. ' 1987 Materials Research Society
472
RESULTS The processes to be discussed in this paper are depicted schematically in fig. 1. A pre-existing surface amorphous layer, fig. la, is irradiated at elevated temperatures with 1.5 MeV Ne*ions. For silicon, such irradiation can induce either epitaxial crystallization, fig. 1b, or layerby-layer growth of the amorphous layer, fig. Ic, depending on the substrate Note that
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