Determination of migration of ion-implanted helium in silica by proton backscattering spectrometry

Understanding the processes caused by ion implantation of light ions in dielectric materials such as silica is important for developing the diagnostic systems used in fusion and fission environments. Recently, it has been shown that ion-implanted helium is able to escape from SiO2 films. To study this process in details, helium was implanted into the central part of a buried SiO2 island up to a fluence of 4 x 1017 He/cm2. The implanted helium could be detected in the SiO2 island, if the oxide was insulated properly from the vacuum. The shape of the helium depth distributions was far from SRIM simulation because helium distributed in the whole 1 μm thick oxide layer. After the ion implantation, helium was observed only on the implanted spot. After nine months the implanted helium filled out the whole oxide island as it was expected from the high diffusivity