Modification of MeV He Implantation-Induced Cavities in Silicon by Hydrogen Plasma Treatment

In this paper, we present results on the formation of He-cavities in Si in the presence of vacancies and hydrogen produced by electron cyclotron resonance (ECR) high-density hydrogen plasma treatment. Epitaxial Si (111) samples were first implanted with 1.55 MeV He ions at a dose of 5×10 ¹⁶cm^-2. Subsequent annealing at 800 °C for 30 min creates a band of cavities around the He projected range. This band is mainly made up of big elongated cavities in the middle surrounded by a high density of small ones. Other defects (mainly dislocations) have also been observed within and beneath the cavity band. Additional hydrogen plasma treatment, however, changes the morphology of the He-cavities. Plasma hydrogenation tends to increase both the width of cavity band and the cavity size, while, the density of cavities decreases. Moreover, with the plasma hydrogenation step, the cavities are accompanied by a significant concentration of dislocation loops. Such effects have been interpreted in terms of the vacancy-type defects and atomic hydrogen introduced by plasma hydrogenation, and thus their interactions with He-cavities. We have confirmed the generation of high concentrations of vacancies by hydrogen plasma treatment through positron annihilation spectroscopy (PAS) measurements.