Structural and electrical properties of p+n junctions in Si by low energy Ga+ implantation

Abstract

Ultrashallow p+n junctions have been formed in silicon by low energy (5.5 keV) Ga+ implantation into n-type substrates. This avoids the use implantation of molecular species such as BF2+ or preamorphization with Ge+ or Si+, which degrade the integrity of p+n junctions in metastably strained SixGe1−x layers. High resolution secondary ion mass spectroscopy measurements indicate an implant peak at less than 10 nm, except for postanneal temperatures above 800 °C, for which severe loss of profile control was observed. Electrical characteristics of the implanted junctions were determined from diode current–voltage measurements and Hall data. At low anneal temperatures, these showed good rectification behavior, with an ideality factor of 1.1±0.1 and a reverse bias leakage of ≈3 μA cm−2 in a relatively large junction area of 5×10−2 cm2. The electrical properties of the p+n junctions were found to be sensitive to implant dose, improving with increasing dose. At 580 °C, implant doses were achieved that were completely activated at levels above previously published Ga equilibrium solubility data. For temperatures of 800 °C, reverse annealing occurred, observed as a reduction in carrier concentration with increasing anneal time and severe profile broadening.