Using Quantitative TEM Analysis of Implant Damage to Study Surface Recombination Velocity in Silicon
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0913-D05-01
Using Quantitative TEM Analysis of Implant Damage to Study Surface Recombination Velocity in Silicon Jennifer Lee Gasky, Sophya Morghem, and Kevin Jones Materials Science and Engineering, University of Florida, 100 Rhines Hall, P.O. Box 116400, Gainesville, FL, 32611-6400 ABSTRACT Silicon wafers with shallow trench isolation structures 3700Å deep were self-implanted with silicon at 40keV, and a dose of 1E15/cm2. This produced an amorphous layer 1000Å deep. The samples were subsequently annealed at temperatures ranging from 750°C to 900°C. The excess interstitials can recombine at the “surface” created by the proximity to the trench sidewall. Plan-view TEM was used to quantify the dislocation distribution as a function of distance from the trench sidewall. It was found that there was no measurable change in defect density as a function of distance from the trench. This was true for both the 20 minute isochronal anneal, and the isothermal study 750°C. This suggests there is a relatively weak recombination of interstitials at the surface. This is surprising given most of the TCAD models assume a very fast surface recombination velocity. INTRODUCTION In order to model advanced microelectronic devices, an accurate understanding of interstitial recombination at the surface in necessary. The goal of the experiment was to use the evolution of end of range damage in patterned silicon to develop a better understanding of the strength of surface recombination. Ion implantation in semiconductor devices is known to introduce point defects. Upon annealing, these point defects evolve into {311} defects and subsequently dislocation loops. During this process the interstitial population decreases. Surface recombination is believed to account for much of the loss of these interstitials. Previously, surface recombination velocities were measured through various techniques, including the measurement of diffusion near the surface and the monitoring of the dissolution of defects. Previous results on the role of the surface are conflicting. Papers by B. Colombeau et al suggest the surface acts as a strong sink for interstitials. This paper shows a lack of diffusion in the first layer of a boron superlattice. Slow diffusion was attributed to the strong surface recombination of interstitials.1 However both Ganin and Marwick2 and King et al3 showed that lapping the surface to reduce the amorphous layer thickness of an amorphizing implant(there-by bringing the end of range(E.O.R.) damage closer to the surface) had no effect on the evolution of E.O.R. damage upon annealing. King’s experiment involved four samples chemically and mechanically lapped to depths of 180Å, 155Å, 125Å, and 80Å. The results showed no difference in defect evolution, which suggests the surface does not act as a strong sink. However, in both cases an amorphous layer was present between the E.O.R. and the surface until re-crystallization was complete. This experiment attempts to study surface recombination laterally at the trench sidewall since no amorphous la
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