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EFFECTS OF IMPURITIES ON THE KINETICS OF NUCLEATION AND GROWTH IN AMORPHOUS SILICON J. A. ROTH and G. L. OLSON Hughes Research Laboratories, Malibu, CA 90265 ABSTRACT The effects of intentionally introduced impurities on the crystallization time, nucleation rate and crystallite growth velocity during solid phase random crystallization of amorphous Si thin films have been determined. Films deposited in UHV onto oxidized Si wafers were subjected to multiple energy ion implantation to introduce uniform distributions of P, B, As, 0 or F at 0.1-1.0 at.%. Crystallization times and growth velocities were determined over the temperature range 650 to 850'C from time-resolved reflectivity measurements, and nucleation rates were determined from these data using a classical, steady state nucleation and growth model. Strong impurity effects are observed: P, B and As all decrease the nucleation rate but accelerate the growth of crystallites, whereas both 0 and F retard growth while enhancing nucleation. The largest effects are for P, which reduces the nucleation rate more than 100 times at 1% concentration, and F, which increases the rate by roughly the same amount. INTRODUCTION Amorphous silicon, Si(a), is metastable and will crystallize in order to lower its free energy. In the absence of a single crystal template, this occurs by the spontaneous nucleation of randomly-oriented crystallites. Once nucleated, each crystallite grows continuously by the addition of atoms to the existing crystalline template. The ongoing formation of new nuclei throughout the sample combined with the progressive growth of previously nucleated crystallites eventually results in complete conversion to (poly)crystalline material. The rates of nucleation and crystallite growth both increase with temperature. The "1'random" crystallization rate of Si(a) thin films has been studied as a function of temperature by several groups [1-4], and various activation energies ranging from 3.1 to 4 eV have been reported for the overall process. Separate studies of the nucleation component have been made by directly measuring the size distribution of observable crystallites as a function of time during isothermal annealing experiments [2,5], and activation energies ranging from 4.4 to 4.9 eV have reported for nucleation. However, no one has yet identified the specific site and mechanism of nucleation in amorphous Si, and it is not known what physical mechanism leads to the reported activation energy. The growth component has also been studied and is reported to have an activation energy of 2.4 to 2.9 eV [2,3,5], compared to the activation energy of 2.7 eV found for solid phase epitaxy (SPE) in pure Si [6]. In SPE the amorphous material is in intimate contact with adjoining crystalline material, and the crystal serves as a template for the layer-by-layer conversion of atoms from the amorphous to the crystalline phase. It is well known that the growth rate of Si SPE is affected dramatically by impurities such as the Group Il and V dopants, and by reactive impurities su