Point Defect Based Two Dimensional Modeling of Dislocation Loops and Stress Effects on Dopant Diffusion in Silicon.
Abstract
Dopant diffusion in silicon is studied and modeled on the basis of point defect kinetics associated with ion implantation damage. Point defect parameters are extracted from the modeling of transient enhanced dopant diffusion due to oxidation and low dose implant damage without extended defects. The theory of dopant-defect pairing is found to be crucial in modeling the implantation damage effects, and the effective binding energies for boron-defect and phosphorus-defect pairs are experimentally determined. The extracted parameters provide an important reference for further modeling of diffusion under high dose implantation conditions involving extended defects. Evolution of dislocation loops through their interaction with point defects is modeled in two dimensions by accounting for the pressure around the ensemble of loops as well as loop coalescence and dissolution as observed in transmission electron microscopy (TEM) measurements. Assuming an asymmetric triangular density distribution of periodically oriented circular dislocation loops leads to estimation of the effective pressure and an efficient model for the statistical loop -to-loop interaction. Simulation with the model correctly predicts variation of the number of captured silicon atoms and the radii and densities of the dislocation loops during oxidation in agreement with the TEM data. It also shows significant reduction in oxidation enhanced diffusion of boron in a buried layer in agreement with measured profiles, confirming the role of dislocation loops as an efficient sink for interstitials. A point-defect-based atomistic model for the stress effects on dopant diffusion is developed by accounting for variation in formation enthalpy of dopant-defect pairs due to the hydrostatic pressure. Binding energies and diffusivities of dopant-defect pairs under the pressure are modeled and incorporated into diffusion equations. Boron segregation around dislocation loops in silicon is explained by the pressure effects, and the simulation agrees with the measured profiles. The model also shows that retarded diffusion of phosphorus under oxide-padded nitride film of various widths is caused by the stress at the film edge. Two -dimensional simulation of diffusion in the pressure field leads to better prediction of threshold voltage shift in short channel MOS transistors.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1993
- Bibcode:
- 1993PhDT.......155P
- Keywords:
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- Engineering: Electronics and Electrical; Engineering: Materials Science; Physics: Condensed Matter