Deep p-type layer formation using Al + implantation and diffusion into Si

Abstract

The formation of aluminum-diffused deep layers using Al + ion implantation into Si and low temperature annealing was investigated. The n-type Si (111) wafers were ion implanted with aluminum at 80 and 120 keV and doses in the range of 1 × 10 13–5 × 10 15 cm −2. Good electrical activation was obtained by heating the wafer at low temperatures, (550–650°C). Al diffusion was studied in the range of 900–1200°C. Impurity profiles and electrical activation of Al + ion implanted and annealed layers were measured with secondary ion mass spectroscopy (SIMS) and sheet resistance profiling respectively. The carrier concentration was found to be the solid solubility limit of Al in Si. The diffusion coefficient at 1200°C was determined to be 1.5 × 10 −11 cm 2/s, which is about ten times larger than that of B (1.3 × 10 −12 cm 2/s). A deep diffused p-type layer of 10–35 μm thickness was formed by heating at 1200°C for 2–30 h. A combination of Al + implantation and low temperature diffusion was found to be a superior process to the method of using B + ions for forming deep p-type diffused layers, since they have reduced damage which is of considerable importance for VLSI fabrication.