Phase Transformations Induced by Arsenic Implants into Silicon
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Phase Transformations Induced by Arsenic Implants into Silicon James P. Lavine1, David D. Tuschel2, and Donald L. Black2 1
Digital and Applied Imaging, Image Sensor Solutions, Eastman Kodak Company, Rochester, NY 14650-2008, U.S.A. 2 Imaging Materials & Media, R & D, Analytical Technology Division, Eastman Kodak Company, Rochester, NY 14650-2132, U. S. A.
ABSTRACT
Micro-Raman spectroscopic investigations of arsenic-implanted silicon show lines characteristic of silicon crystallites even at implant doses above the amorphization threshold. The intensity and frequency of occurrence of the lines increase with the implanted dose. Polarization/orientation Raman studies indicate the crystallites are silicon in the hexagonal phase (Si-IV) and silicon in the diamond phase (Si-I). The latter are oriented differently than the substrate silicon. Monte Carlo simulations of the arsenic ion energy loss and published molecular dynamics studies suggest that each arsenic ion deposits sufficient energy to locally melt the silicon lattice. This is taken as the basis of the present attempt to explain the origin of the crystallites. A one-dimensional numerical model is developed to determine the time scale for the liquid silicon to solidify. The effect of amorphous silicon on the solidification is also investigated.
INTRODUCTION
As part of a study of ion-implanted silicon, Raman spectroscopy was applied to a series of arsenic-implanted silicon samples [1]. The dose varied from 2 x 1013 to 5 x 1015 As/cm2. Macro-Raman spectroscopy showed the expected amorphous silicon broad band, which strengthened as the dose increased. This was accompanied by the decrease and eventual disappearance of the substrate optical phonon line at 520 cm–1, when the arsenic dose exceeded 5 x 1014 As/cm2. However, micro-Raman spectroscopy revealed narrow lines at ~508 cm-1 and 520 cm-1, even for the 5 x 1015 As/cm2 samples. Additional experimental work appeared to tie the narrow lines to specific locations with observable surface features [2,3]. We became aware that additional phases of silicon exist [4] and that there is a hexagonal phase, Si-IV, with a Raman line at 508 cm-1 [5]. Si-IV had been observed in arsenic-implanted silicon by Tan et al. [6] and in deposited polycrystalline silicon [7]. Tan et al. proposed a transformation from the diamond phase of silicon to Si-IV with the required energy coming from the implanted arsenic as it slowed down in the silicon. In this work, we present Raman spectroscopy results that clarify our earlier observations and further elucidate the phases of silicon present. The second section contains a brief account of the experiments and new data. The third section considers the state of the silicon during the implant. It has a numerical model that simulates the cooling of the implanted silicon region and its phase T8.9.1
transformation from liquid to crystalline silicon. The fourth section describes the effects of increased arsenic implant dose and the appearance of amorphous silicon. The final section has the conclusions
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