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D. L. Kendall and B. Martinez-Tovar Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico 87131

D. S. Simons National Institute of Standards and Technology, Gaithersburg, Maryland 20899

D. R. Myers Sandia National Laboratories, Albuquerque, New Mexico 87185 (Received 27 July 1988; accepted 24 October 1988)

Implantation of nitrogen at 150 KeV and a dose of 1 X 1018/cm2 into (110) silicon results in the formation of an amorphized layer at the mean ion range, and a deeper tail of nitrogen ions. Annealing studies show that the amorphized layer recrystallizes into a continuous polycrystalline Si3N4 layer after annealing for 1 h at 1200 °C. In contrast, the deeper nitrogen fraction forms discrete precipitates (located 1 /xm below the wafer surface) in less than 1 min at this temperature. The areal density of these precipitates is 5 X 107/cm2 compared with a nuclei density of 1.6 x 105/cm2 in the amorphized layer at comparable annealing times. These data suggest that the nucleation step limits the recrystallization rate of amorphous silicon nitride to form continuous buried nitride layers. The nitrogen located within the damaged crystalline silicon lattice precipitates very rapidly, yielding semicoherent crystallites of a-Si 3 N 4 .

I. INTRODUCTION Silicon nitride is used in numerous applications in microelectronics such as dielectric isolation, to provide passivating layers and as a diffusion mask. More recently, there has been interest in silicon nitride to provide insulating layers in silicon-on-insulator technology.1 Buried layers of silicon nitride can be synthesized by ion implantation of N + followed by high-temperature annealing. While implantation at near-stoichiometric doses results in continuous polycrystalline layers upon annealing, implantation at lower doses yields crystalline precipitates of a-Si 3 N 4 which are epitaxial and partially coherent within the silicon matrix.2 While previous studies have involved nitrogen implantation in (100) silicon1"4 and in (111) silicon,5'6 there is little (if any) work on implantation in (110) silicon. This paper describes the results of implantation and annealing studies on near-stoichiometric implants in (110) Si. Nitrogen profiles were studied using Secondary Ion Mass Spectroscopy (SIMS) for as-implanted and annealed samples. Implants in this material were found to result in a deep tail of nitrogen ions along with the main peak. Upon annealing, the main peak formed a continuous layer, while the deeper fraction caused precipitation of silicon nitride at about 0.5 pim below the main peak. The main and deeper nitrogen fractions show very different annealing and growth characteristics. The matrix dependent differences in the kinetics of recrystallization between the two fractions are the subject of this study. Samples annealed for varying time periods have been studied by optical micros394

http://journals.cambridge.org

J. Mater. Res., Vol. 4, No. 2, Mar/Apr 1989

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copy, transmission electron microscopy (TEM) us