Positron annihilation study of defects in boron implanted silicon

Defects and their annealing behavior in boron implanted silicon have been studied using positron annihilation spectroscopy (PAS), ion channeling, nuclear reaction analysis, and transmission electron microscopy. Silicon wafers were implanted with 80 keV boron ions to fluences from 10(12) to 10(15) cm(-2). Furnace annealing or rapid thermal annealing (RTA) of the implanted Si samples was conducted to temperatures in the range 750-950 degrees C in a N-2 ambient. For as-implanted samples, the defect profiles extracted from PAS spectra were found to extend beyond the implanted boron distribution given by TRIM calculations. The S-defect/S-bulk values increased monotonically with increasing boron fluences. For boron fluences greater than or equal to 10(13) cm(-2),S-defect/S-bulk was found to be > 1.04 (the characteristic value for divacancy), while S-defect/S-bulk was found to be < 1.04 for a boron fluence of 10(12) cm(-2). After annealing at 750 degrees C, all B-implanted samples had similar S-parameter values in the near-surface region, while in the deep region the S values for high B fluences (phi greater than or equal to 10(14) cm(-2)) were found to be lower than those for low B fluences (phi less than or equal to 10(13) cm(-2)). Annealing at 950 degrees C did not change the S-parameter data for the lowest boron fluence (10(12) cm(-2)), but caused a slight increase of the S parameters in the deep region for other boron fluences. RTA at 750 degrees C shows that major defects in B-implanted Si are annealed out within the first 3 s. An interesting transient annealing behavior is observed in which the S value decreases in the initial annealing stage, and then increases to a saturating value after prolonged annealing. Possible effects of electric fields resulting from the electrical activation of implanted boron on the behavior of positron annihilation line shapes after annealing are discussed. (C) 2000 American Institute of Physics. [S0021-8979(00)07110-3].