Electron Spin Resonance Probing of Defects in Si Foils Fabricated by the SLIM-Cut Method

Silicon thin (< 100 μm) foils for photovoltaic applications have been fabricated using a novel low-temperature (< 150 °C) lift- off process with the aim of reducing production costs. The quality of the resulting material has been assessed by electron spin resonance (ESR) spectroscopy in terms of occurring paramagnetic defects. For reasons of comparison, foils are prepared from (100) and (111) oriented silicon wafers, for which similar results were obtained. In previous work on the as-cleaved foils, hole traps were detected which could be associated with D-line defects (Si dangling bonds in disordered environment). These traps disappear after vacuum annealing (606 °C), but at the same time new specific defects associated with Si/SiO2 interfaces are detected, in particular, Pb0 and Pb centers in the case of (100) and (111) Si foils, respectively. Silicon etch back experiments indicated all signals to be located only in a top layer (< 4.4 μ m thick) on the crack side of the foil. The data show that the SLIM-Cut fabrication method may result in high quality Si material after etching off a thin damaged surface layer.