Growth mechanism for solid-phase epitaxy of Si in the Si <100>/Pd2Si/Si(amorphous) system studied by a radioactive tracer technique

Abstract

A tracer technique using radioactive 31Si (T1/2=2.62 h) was used to study solid-phase epitaxial growth (SPEG) of silicon. After depositing Pd and Si onto single-crystal substrates which had been activated in a nuclear reactor, Pd2Si was formed with about equal amounts of radioactive and nonradioactive silicon during heating at 400 °C for 5 min. After a second annealing stage (450 °C-->500 °C in 1 h) the silicide layer which moves to the top of the sample during SPEG was etched off with aqua regia. From the absence of radioactive 31Si in the etchant solution it is concluded that SPEG takes place by dissociation of the Pd2Si layer at the single-crystal interface to provide free Si for epitaxial growth, while new silicide is formed at the interface with the amorphous Si. These results were confirmed by evaporating radioactive silicon onto nonactivated silicon substrates before evaporation of Pd and stable amorphous Si and by measuring the activity in the SPEG sample before and after etching off the silicide layer.