Enhanced germanium precipitation and nanocrystal growth in the Ge+ ion-implanted SiO2 films during high-pressure annealing

The effect of pressure employed during subsequent annealing of the Ge+-ion implanted SiO2 layers on the Ge nanocrystal formation was studied. Ge+ ions implanted in the thin SiO2 layers formed Gauss-like profiles with a Ge peak concentration varied from 1 to 12 at%. Subsequent annealing was carried out at temperature 600-1130 °C under pressures 1-1.2×104 bar. Strong effect of the pressure on the Ge atom distribution was obtained. High-temperature annealing under pressure within the range of 1-103 bar resulted in the out-diffusion of germanium from the SiO2 layer to the Si substrate. As the pressure reached 1.2×104 bar, Ge migration to the Si/SiO2 interface was prevented. At that, the Ge nanocrystal growth within the ion-implanted region of the SiO2 film took place. The nanocrystal size was investigated as a function both of the Ge atom concentration and the annealing temperature. The obtained results show a diffusion-controlled nanocrystal growth mechanism. The high-pressure (1.2×104 bar) diffusion coefficient of germanium in silicon dioxide was estimated as a function of the temperature and expressed by D=1.1×10−10 exp(−1.43 eV/kT) cm2/s.