Ion Beam Self Annealing in Thin Silicon Films

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ION BEAM SELF ANNEALING IN THIN SILICON FILMS J.D. RUBIO*, R.P. VIJAY*, R.R. HART' AND J.D. PEARCE+ *Dept. of Nuclear Engineering, Texas A&M University, College Station, Texas 77843 +E.I. duPont de Nemours and Company, Atomic Energy Division, Savannah River Laboratory, Aiken, South Carolina 29801 ABSTRACT Residual lattice disorder in lgm-thick silicon films as a function of the dose rate of 120 keV 2Ar+ ion implantations has been investigated. At a fluence of lx1 014 ions/cm , low dose rates produced a highly damaged surface layer as expected; however, at a dose rate sufficient to locally heat the implanted film to a temperature of approximately 700 0K, essentially complete annealing of the lattice disorder was observed. This temperature is significantly less than that normally required for post-implant thermal annealing. Measurements of lattice disorder were based on medium energy Rutherford backscattering and channeling analyses. INTRODUCTION Early investigations [1-3] which demonstrated the annealing effects of ion beams have led to more recent studies of ion beam self annealing [4-9] and ion beam induced epitaxial crystallization [10-12]. The results of the latter investigations have shown that ion bombardment can lead to the recrystallization of an amorphous layer at temperatures much lower than those required for purely thermal processes. The ion beam induced recrystallization takes place in a planar fashion along the amorphous/crystalline interface and has an activation energy which is an order of magnitude smaller than that for thermal regrowth. However, a major drawback to this method is that the annealing ions leave extensive damage at the depth corresponding to their range. Ion beam self annealing studies have relied on poor thermal contact between the target and its holder to allow the power input by the ion beam to raise the temperature of the sample. During the initial stages of these high dose rate implantations, the sample temperature is below a threshold value, and damage accumulates to create an amorphous layer. If the fluence is large enough, however, the sample temperature can reach a point (>5000 K) where ion beam enhanced epitaxial crystallization occurs and the amorphous layer is regrown. Residual damage at the end of range of the ions has also been observed after this type of self-annealing implant. In contrast to previous investigations, the present study focused on selfannealing implantations in which amorphous layers were not formed during the early stages of the implantation. In order to perform high fluence implantations without forming amorphous layers, very thin thermally isolated silicon films were used as targets. The temperature of these thin films can be rapidly increased during implantation, to a level where dynamic annealing dominates the damage production process, before significant resultant damage occurs.

Mat. Res. Soc. Symp. Proc. Vol. 128. C1989 Materials Research Society

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EXPERIMENTAL PROCEDURE The 1lim-thick, 1cm-diameter, self-supporting silicon single crystal fil