Nanoparticle formation in 25-nm-SiO2 thin layer by germanium negative-ion implantation and its capacitance-voltage characteristics

We have investigated germanium nanoparticle formation in a 25-nm-thick oxide layer on silicon substrate by negative-ion implantation for single electron devices. Ge negative-ions were implanted into the oxide layer at 10 keV with fluences of 1 × 1015 and 5 × 1015 ions/cm2. Then, the samples were annealed at temperatures of 300, 500, 700 and 900 °C for 1 h in vacuum. The implanted Ge atoms and Ge NPs were studied by a high-resolution Rutherford backscattering (HRBS) and cross-sectional TEM. The HRBS revealed that the Ge atoms had an almost Gaussian profile for annealing temperature less than 900 °C. At 900 °C, a part of Ge atoms reached to the Si substrate due to the thermal diffusion. From the TEM, Ge nanoparticles had various diameters in a range of 2-5 nm. The electric property of capacitance-voltage (CV) characteristics was also measured. In CV measurement, two kinds of Ge-implanted SiO2 layers with 1 × 1015 and 5 × 1015 ions/cm2 showed a clear hysteresis in each CV curve with a voltage shift of 0.6 and 6.6 V, respectively, after annealing at 500 °C.