Impurity Segregation, Supersaturation and Interface Stability

Abstract

The presence of an interface separating two media, one ordered (crystal) and one disordered (either amorphous or liquid), has a profound influence on dopant depth distribution and lattice location. The differences in dopant behavior between crystallization at the liquid-solid and amorphous-solid interfaces are illustrated by the following example. The implantation of Te in Si produces an amorphous layer which can be crystallized in the liquid or solid phase by laser or furnace annealing, respectively. Figure 1 shows (1) the depth profiles of Te implanted in silicon after pulsed laser annealing and solid-phase regrowth, respectively. In both cases the low aligned yields indicate that almost 100% of the Te atoms which are retained inside the crystal are located on substitutional lattice sites. The concentration of the substitutional Te is about 105 times the maximum equilibrium solubility. Supersaturated solid solutions, therefore, result from both liquid-phase and solid-phase crystallization processes. There is, however, a marked difference in the depth profiles of Te after laser or furnace annealing: In the process involving the liquid phase, part of the dopant is rejected to the sample surface, while after the low-temperature furnace annealing no profile modification is observed.