Point Defect Charge-State Effects on Transient Diffusion of Dopants in Si

Ion implantation damage produces point defects during annealing which can significantly enhance dopant diffusion. This diffusion at low temperatures was studied for P, As, and B implants in Si. Enhanced diffusion was observed below certain doping concentrations which depend only on temperature. For As this concentration corresponds to As solid solubility. For P, enhanced diffusion occurs below the well-known kink concentration. For B, diffusion occurs below ni for temperatures below 850°C. A model is presented which correlates the self-interstitial donor level position, E1⁺, in the Si bandgap with the dominance of B diffusion via neutral self-interstitials. It is shown that when self-interstitials are extremely generated, the resulting changes in the free energy of self-interstitial formation force the B diffusion via I^x to be 10–100 times greater than B diffusion via I⁺. This results in significant enhanced diffusion of B in intrinsic Si relative to B layers doped above n1. At temperatures at or above 850°C, thermally-assisted, concentration-dependent diffusion via I⁺ begins to dominate over enhanced diffusion which occurs with an ever decreasing time constant. © 1990, The Electrochemical Society, Inc. All rights reserved.

Duke Scholars

Author Richard B. Fair Electrical and Computer Engineering