Implantation of 60 keV copper negative ion into thin SiO2 films on Si: Thermal stability of Cu nanoparticles and recovery of radiation damage

Abstract

Implantation of 60 keV copper negative-ion into 115 nm thick amorphous SiO2 films on a Si substrate (SiO2/Si) induces not only Cu nanoparticle formation in SiO2, but also radiation damage. Using ultraviolet, visible, and infrared reflection spectroscopy (0.031–6.52 eV), thermal recovery of the damage and stability of the nanoparticles were evaluated with isochronal annealing in Ar gas flow, from 100 to 1000 °C. The implantation induces Si–O–Si bond breaking in SiO2 layer, and amorphization of Si substrate, in addition to Cu nanoparticle formation in the SiO2 layer. A gradual recovery of the broken bonds in SiO2 was observed in a wide temperature range of 200–700 °C, which is characteristic in amorphous structures. Two-step recoveries at 600 and 900 °C are observed in recrystallization of Si substrate, indicating recoveries of pure and O-recoil rich regions in the Si substrate, respectively. Around 700 °C, intensity of the Cu surface plasmon resonance (SPR) peak drastically increases, suggesting coarsening of Cu nanoparticles. At 1000 °C, most of the Cu atoms escape from the SiO2 layer, probably due to thermally activated diffusion. Annealing temperature of 800–900 °C is adequate for a large SPR peak of Cu nanoparticles in SiO2 thin film on a crystalline Si substrate.