Reliable Measurements of Defect Profiles in Low-Energy Boron Implanted Silicon

Abstract

Low-energy implantation is one of the most promising options for ultrashallow junction formation for the new generation of bipolar complementary metal oxide semiconductor (BiCMOS) silicon technology. Boron is one of the dopants to be implanted, but is the most problematic because of its low stopping power, and its tendency to undergo transient enhanced diffusion and clustering during thermal activation. In this paper we report an experimental contribution, using secondary defect profiles, to the understanding of low-energy B implants in crystalline silicon. Shallow p+n junctions were formed by low-energy B implantation – 1015 cm-2 at 3 KeV – into n-type crystalline silicon preamorphized with germanium – 1015 cm-2 at 30 KeV, 60 keV and 150 keV. Rapid thermal annealing (RTA) for 15 s at 950°C was then performed to achieve electrical activation of the dopant and implantation damage removal. We propose a reliable approach to the measurement of secondary defect profiles, induced by this process, using isothermal transient capacitance associated with deep-level transient spectroscopy (DLTS). This approach could be generalised to the profile measurement of any defect detected into silicon or III–V semiconductor substrate. In our case, we obtain a relatively high concentration of B-related electrically active defects to a depth of 3.5 µm in the crystalline silicon bulk.