Pulsed laser annealing of high-dose Ag+-ion implanted Si layer

Abstract

The formation of a crystalline composite Ag:Si material with Ag nanoparticles by low-energy (E = 30 keV) high-dose (D = 1.5 × 1017 ion cm−2) Ag+ implantation into a monocrystalline c-Si substrate followed by nanosecond pulsed laser annealing (PLA) is demonstrated. Compared to traditional thermal annealing, PLA allows us to perform local heating of the sample both for its depth and area, and eliminate implantation-induced defects more efficiently, due to rapid liquid-phase recrystallization. Moreover, dopant diffusion during a nanosecond laser pulse is mainly limited by the molten region, where the dopant diffusion coefficient is several orders of magnitude higher than in the solid state. During PLA by a ruby laser (λ = 0.694 µm), the optical probing of the irradiated zone at λ = 1.064 µm with registration of time-dependent reflectivity R(t) was carried out. By scanning electron microscopy, it was established that Ag+ implantation leads to the creation of a thin amorphous Ag:Si layer of porous structure, containing Ag nanoparticles with sizes of 10–30 nm. PLA with energy density W = 1.2–1.8 J cm−2 results in the melting of the implanted layer (d ~ 60 nm) and the topmost layers of the c-Si substrate (d < 400 nm), followed by the rapid recrystallization of the Si matrix containing Ag nanoparticles with dominate sizes of 5–15 nm and some fraction of larger particles of 40–60 nm. Energy dispersive x-ray (EDX) spectroscopy did not show a noticeable change of Ag atomic concentration in the implanted layer after PLA. Spectral dependence R(λ) of Ag:Si layers showed the partial recovery of c-Si bands with maxima at 275 and 365 nm with simultaneous weakening of plasmon band for Ag nanoparticles in Si at 835 nm.