Beam transport

Abstract

Dopant distribution, electrical activity and damage annealing of high-dose (～5 × 10¹⁵ cm²) Ga-implanted silicon samples annealed by conventional thermal annealing have been studied by alpha particle back-scattering, differential Hall effect and ellipsometry measurements. Back-scattering spectra show that there is no long tail of Ga atoms in the as-implanted samples. Upon annealing these samples the damaged amorphous layer recrystallizes at about 570°C by solid phase epitaxy. During the epitaxial regrowth the dopant atom distribution seems to be modified. Further, very high levels of electrical activaton of Ga-atoms (～3 × 10²⁰ cm^?3), much higher than the maximum solubility limit of Ga in Si (4.5 × 10¹⁹ cm^?3), is achieved by thermal annealing of the sample at ～570°C. This is comparable to the doping achieved by laser annealing of the Ga implanted Si. All the above three measurements show that there is residual damage in the high dose (?10¹⁵cm^?2) implanted samples 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 temperature reduces the electrical activity of Ga atoms, possibly by driving out the metastably high substitutional concentrations of Ga-atoms into electrically inactive clusters or precipitates.