| Over the past 30 years, the semiconductor industry has grown at a tremendous rate, creating faster and cheaper integrated circuits with more functionality. Continued scaling, however, will face some major obstacles in the next several years. In the area of the doping technology, shallow and abrupt dopant profiles with supersaturated dopant concentrations will be required. These kinds of profiles can be obtained through non-equilibrium annealing techniques such as laser annealing, solid phase epitaxy, and molecular beam epitaxy. Unfortunately, these supersaturated dopant concentrations exist in a metastable state and deactivate upon any subsequent thermal processing. In this work, we investigate the thermal stability of supersaturated dopants created through laser annealing. We compare the deactivation behavior of the common dopants in silicon (As, B, P, and Sb) across a range of concentrations and thermal annealing conditions. A number of analytical techniques are used, including Hall effect measurements, secondary ion mass spectroscopy (SIMS), high-resolution x-ray diffraction (HR-XRD), grazing angle diffuse x-ray scattering and transmission electron microscopy (TEM).; Through these analytical techniques, we have developed a picture of the fundamental deactivation mechanism for each dopant and determined the limits to both concentration and annealing conditions to maintain high electrical activation levels. Arsenic and phosphorus have been shown to be highly unstable against deactivation, with severe deactivation occurring at temperatures as low as 500°C. It is proposed that this instability arises due to the formation of small, coherent, inactive clusters of a few dopant atoms and a native vacancy. Upon annealing at higher temperatures during which diffusion occurs, these clusters evolve into precipitates. In contrast, Sb and B are promising n- and p-type candidates for supersaturated dopant concentrations due to their relative stability against deactivation. This stability is believed to exist because these dopants deactivate through the precipitate mechanism. Deactivation does not occur until the dopants are able to diffuse over large distances and agglomerate together into macroscopic precipitates. With this understanding of the underlying deactivation mechanism for each dopant, ways of slowing down or even eliminating deactivation can be investigated. |
