Thermal annealing and electrical activation of high dose gallium imp lanted silicon

Abstract

Samples of silicon single crystals implanted with 3 × 10¹⁴/ cm², 1 × 10¹⁵/cm² and 6 × 10¹⁵/cm² Ga ions have been investigated by alpha particle back-scattering before and after annealing, differential Hall effect and ellipsometry measurements. The impurity depth profiles as obtained from the analysis of the back-scattering spectra do not show any long tail of Ga atoms even in the high dose as-implanted samples. Upon annealing, the dopant atom distributions are seen to be modified during recrystallization. High levels of electrical activation of Ga atoms (~3 × 10²⁰ cm^-3), exceeding the maximum solid solubility limit of Ga in Si (4.5 × 10¹⁹ cm^-3) and comparable to those obtained by laser annealing have been achieved by conventional thermal annealing. The above three measurements have clearly shown that there is 20% residual damage in the high dose (6 × 10¹⁵ cm²) implanted sample after the recrystallization at about 570°C. This may be related to strain in the lattice at the high concentrations of metastable substitutional Ga atoms. Annealing at higher temperatures reduces the electrical activity of Ga atoms, possibly by driving out the metastable high substitutional concentrations of Ga atoms into electrically inactive clusters or precipitates.