Positron annihilation study of defects in boron implanted silicon

Abstract

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 1012 to 1015 cm−2. Furnace annealing or rapid thermal annealing (RTA) of the implanted Si samples was conducted to temperatures in the range 750–950 °C in a N2 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 Sdefect/Sbulk values increased monotonically with increasing boron fluences. For boron fluences ⩾1013 cm−2,Sdefect/Sbulk was found to be >1.04 (the characteristic value for divacancy), while Sdefect/Sbulk was found to be <1.04 for a boron fluence of 1012 cm−2. After annealing at 750 °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 (φ⩾1014 cm−2) were found to be lower than those for low B fluences (φ⩽1013 cm−2). Annealing at 950 °C did not change the S-parameter data for the lowest boron fluence (1012 cm−2), but caused a slight increase of the S parameters in the deep region for other boron fluences. RTA at 750 °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.