Epoxy-Induced Spalling of Silicon

One of the main driving forces to lower the silicon solar cell modules overall cost is to decrease the thickness of the silicon substrate and, at same time, to reduce the material losses caused by the sawing of the silicon ingot. For this reason, a considerable number of methods have been proposed in the last decade to manufacture thin silicon foils which aim to replace the commonly used sawing technique. One of these methods is based on peeling off a thin layer from a silicon substrate by means of the residual stress induced either through the only deposition of a layer on a silicon substrate or through a succeeding thermal cycle of such a bilayer. Up to now, three different materials have been successfully employed in this technique: Nickel, Nickel/Chromium alloy and a Silver/Aluminium system. In this work we demonstrate the possibility to induce the lift-off of a thin silicon foil by means of curing an epoxy layer on top of a silicon wafer. This new method has the advantages of reducing metal contamination in the silicon and lowers the operating temperatures below 150°C.