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C. Hayzelden Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02138

K. N. Tu IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598 (Received 27 February 1990; accepted 26 June 1990)

The nucleation and growth kinetics of NiSi2 precipitation in amorphous silicon thin films ion implanted with nickel was investigated using scanning transmission electron microscopy. It was found that the nucleation rate could be approximately described by a delta function at time t = 0 when the films were annealed between 325 and 400 °C. The growth kinetics of the precipitates at these temperatures were described by r oc t", where r was the average radius and n was about 1/3. This behavior is consistent with models for growth of three-dimensional particles in a two-dimensional diffusion field. It was also found that the implanted amorphous films displayed an enhanced rate of single crystal silicon formation, apparently catalyzed by migrating silicide precipitates.

I. INTRODUCTION Metal silicides in thin films have a wide range of applications in electronics.1'2 For most of these applications, silicides are formed by interfacial reactions between metal films and silicon.1'2 Recently, metal ion implantation has been employed to produce buried metal silicide layers in single crystal silicon.3 In previous work,4 we have reported the use of ion implantation to produce buried nickel silicide precipitates in amorphous silicon thin films. Unlike the case for interfacial reactions between nickel and silicon,1'2 where the first of several possible intermetallic phases to form is the most nickel-rich phase, Ni2Si, the first (and only) phase to form in the nickel ion implanted films is the most silicon-rich phase, NiSi2. It was suggested that this difference in first phase formation behavior is due to the effect of interfacial energies on the nucleation kinetics.4 In this paper, the kinetics of nucleation and growth of nickel silicide precipitates in ion implanted amorphous silicon thin films are reported. An enhancement in the kinetics of crystallization of amorphous silicon is also reported, apparently owing to the migration of silicide precipitates. II. EXPERIMENTAL PROCEDURE

Amorphous silicon thin films, 95 nm thick, were deposited by low pressure chemical vapor deposition at ''Current address: Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, Maryland 21218. J. Mater. Res., Vol. 5, No. 10, Oct 1990

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565 °C onto 2 in. diameter (100) silicon substrates coated with 100 nm thick thermally grown SiO2 layers. Nickel was then implanted into the amorphous silicon at a dose of 1 x 1015 cm"2 and an energy of 55 keV. This led to a peak concentration of about 4 x 1020 ions/cm3 located at approximately half the thickness of the amorphous silicon films. The temperature range used in the present study was bounded by two experimental factors. When samples were annealed at temperatures of 400 °C or above, the entire pre