Ion Implantation and Synthesis of Materials - Studium

132 10 Crystallization and Regrowth of Amorphous Si600T (°C)575 550 525 500 400 375 350 325100REGROWTH RATE (A/min)°10SiGe11.1 1.2 1.3 1.53 −1 10 /T (K )1.6 1.7Fig. 10.5. Regrowth rate versus 10 3 /T (K) for different substrate orientations of amorphousimplantedSi and Ge (from Lau et al. 1980)in diffusion of dopants in Si. Consequently, regrowth of implanted amorphouslayers can be accomplished on time scales that are relatively short compared tothose required for appreciable dopant diffusion.During the epitaxial growth process, implanted dopants move onto substitutionallattice sites as the interface between the amorphous and crystalline regionsweeps by their locations. Since the time for regrowth is much shorter that thetime for significant dopant diffusion, the dopants are effectively frozen in thelattice at low regrowth temperatures, and substitutional concentrations of group IIIand V dopants can be increased to exceed the equilibrium solubility limit. A secondannealing treatment at high temperatures of 900 or 1,000°C (carried out to removeresidual defects in the regrown layer) will allow the dopants to diffuse. After thishigh-temperature process, the substitutional concentration of dopants is reduced tothe equilibrium solubility concentration value. The excess concentration ofimplanted ions form nonsubstitutional precipitates or clusters.