Single-crystal silicon coimplanted by helium and hydrogen: Evolution of decorated vacancylike defects with thermal treatments

Abstract

Si p -type (100) samples were coimplanted at room temperature with He+ ions at 30 keV with a dose of 1× 1016 ions/cm2 and successively with H+ ions at 24 keV with a dose of 1× 1016 ions/cm2. A series of samples was thermally treated for 2 h from 100 to 900°C at 100°C steps to study the evolution of pointlike and extended defects by two complementary techniques: positron Doppler broadening spectroscopy and transmission electron microscopy. Depth profiling the samples with a positron beam led to the identification of five different traps and the evolution of their profile distributions with thermal treatments. The positron traps were identified as decorated vacancy clusters of different sizes. Their decoration by implanted ions and in some case by oxygen was probed by coincidence Doppler broadening spectroscopy. Up to 300°C annealing temperature positrons probe three distributions of different decorated defects covering regions of the sample down to 400-450 nm. Starting from 300°C annealing temperature no defects were revealed by positrons in the region next to the peak of the implanted ions distributions positioned around 280 nm, where extended defects are expected; this indicates complete filling of the defects by H and He. From 300 to 600°C decorated vacancy clusters of different sizes appear progressively in the region below 280 nm, with a distribution moving deeper into the sample. Comparison with previous measurements on He-implanted samples points out the chemical action of H. Hydrogen atoms interact with the previous damage by He, producing more stabilized vacancylike defects distributed through the damage region of the sample. Electron microscopy shows the transformation of the extended defects from platelets to blisters and cavities.