EFFECT OF INTERACTION BETWEEN POINT-DEFECTS AND PREEXISTING DISLOCATION LOOPS ON ANOMALOUS-B DIFFUSION IN SILICON

We have studied the interaction between point defects and pre-existing extended defects in silicon, through associated changes in the transi ent enhanced diffusion of boron. The extended defects were produced by Si self-implantation at energies ranging from 40 to 300 keV (one ener gy per wafer) with a constant dose of 2 x 10(15) cm(-2), followed by R TA for 40 s at 1000 degrees C in a nitrogen ambient. Subsequently, B i ons were implanted at an energy of 40 keV to a dose of 4 X 10(14) cm(- 2) and the samples were again annealed by RTA at temperatures from 800 to 1100 degrees C. TEM and SIMS methods have been used to observe the evolution of dislocation loops and changes in B profiles, respectivel y. These loops lie close to the boron distribution. Transient enhanced diffusion of boron during post-implantation annealing is strongly sup pressed: this is attributed to trapping by loops of interstitials asso ciated with the boron implant. The effect upon B diffusivity of increa sing separation between the loop network and B implant is demonstrated and discussed.