Reactive-ion- and plasma-etching-induced extended defects in silicon studied with photoluminescence

Abstract

Defects introduced by reactive-ion etching and plasma etching using deuterium have been studied in boron-doped Si with the photoluminescence (PL) technique. We have observed a set of broad luminescence bands in the below-band-gap range between 1.05 and 0.8 eV. These bands change in intensity as well as in photon energy with annealing. This has been studied by isochronal annealing treatments from 75 to 800 °C in steps of 50 °C, each for 30 min. Directly after the plasma treatment we observe overlapping broad bands at liquid-He temperature, with a peak around 0.9 eV and a half-width of about 100 meV. There is a large shift of these bands to higher photon energy after the annealing step at 325 °C, peaking at about 0.925 eV with a half-width of about 60 meV. The intensities of the broad PL bands increase with increasing annealing temperature up to about 375 °C, while they decrease in intensity at higher temperatures. The changes in PL intensity of the broad bands after annealing are shown to be related to the difference in deuterium concentration near the surface, as determined by secondary-ion mass spectrometry, due to the passivation effect the deuterium has on other competing recombination channels. The samples have not completely recovered after annealing at 800 °C, where a broad PL band at 0.96 eV still remains. PL bands observed in hydrogenated samples containing "bubbles" will also be reported. We attribute all these PL bands to electron-hole recombination in heavily damaged regions, where electrons and holes can be localized in potential wells caused by the strain from the hydrogen-induced microscopic defects. This "strain-induced intrinsic quantum well" model is supported by the temperature and excitation intensity dependence of the broad PL bands.