GRAIN GROWTH PROCESSES DURING TRANSIENT ANNEALING OF As-IMPLANTED, POLYCRYSTALLINE-SILICON FILMS S.J. KRAUSE*, S.R. WILSON"*, W.M. PAULSON**, and R.B. GREGORY"* *Dept. of Mechancial and Aerospace Engineering, Arizona State University, Tempe, AZ 85287 "**Semiconductor Research and Development Laboratory, Motorola, Inc., 5005 F. McDowell Road, Phoenix, AZ 85008 ABSTRACT Polycrystalline silicon films of 300 nm thickness were deposited on oxidized wafer surfaces, implanted with As, and annealed on a Varian IA 200 rapid thermal annealer. Transmission electron microscopy was used to study through-thickness and cross sectional views of grain size and morphology of as-deposited and of transient annealed films. A bimoda] distribution of grain sizes was present in as-deposited polycrystalline silicon films. The first population was due to columnar growth of some grains to a final average diameter of 20 rm. The second population of small equiaxed grains of 5 nm average diameter were formed early in the deposition process. During transient annealing grains in the first population grew rapidly up to 280- nm equiaxed grains. After this the growth rate decreased due to the grain size reaching the thickness of the film. Grains in the second population grew rapidly up to a size of 150 nm, after which the growth rate was lowered due to grains impinging upon one another. The grain growth processes for both populations have been described with a modified model for interfacially driven grain growth. This model accounts for diffusion and grain growth which occur with rapidly rising and falling temperatures during short annealing times characteristic of transient annealing processes. INTRODUCTION Polycrystalline silicon is commonly used as an interconnect and as a gate material for most metal-oxide-semiconductor (MOS) devices. To reduce resistivity of polycrystalline silicon, it is ion implanted and annealed during the same steps as are the source and drain of the MOS device. Depending on the temperature of deposition, the silicon may be completely amorphous, partially amorphous and partially crystalline, or entirely crystalline [1]. The polycrystalline silicon itself may have a single or bimodal distribution of grain sizes [2] which may or may not be heavily textured [3]. During furnace annealing of single crystal silicon the diffusion of As and Si may be enhanced by the presence of As dopant [4]. In phosphorous doped polycrystalline silicon, the enhanced diffusion rate of Si (due to P dopant) increases the grain growth rate [5). This process has been modeled by Wads and Nishimatsu [6] by an interfacial energy driven grain growth model. In an earlier paper we described the grain growth of polycrystalline silicon during transient annealing with a modified model for interfacially driven grain growth [7]. In this paper we have characterized dopant enhanced grain growth of a bimodal grain size distribution of As doped polysilicon during the short times and high temperatures characteristic of transient annealing. EXPERIMENTAL The substrates used in these experiments were 3 inch (100) Si wafers on which a 0.1 micron SiO 2 film was grown. Undoped polysilicon, about 300 Mat. Res. Soc. Symp. Proc. Vol. 35. c'1985 Materials Research Society