Comparative study of stress inducing layers to produce kerfless thin wafers by the Slim-cut technique

Abstract

The decrease in wafer thickness seen as a route to cost reductions has raised a growing interest in techniques that allow the preparation of thin wafers without kerf loss. The Slim-cut process [1] is one of these new techniques and comprises mainly three stages: a stress layer deposition step on the top of a monocrystalline silicon sample, a heating step necessary to induce the stress on the silicon sample and detach a thin silicon layer, and a third step to clean the stress-inducing layer to obtain a silicon foil adapted to the fabrication of solar cells. One of the major problems of this technology consists in finding a stress layer that induces a sufficiently high contraction in order to achieve a rupture of the silicon without contamination of the foil. In this work we present a comparison between thin foils obtained by Slim-cut, using three different stress layers: i) a double screen printed Silver/Aluminum layer, ii) a dispensed epoxy paste, iii) an electrodeposited Nickel metallization. Results on lifetime measurements indicate that some of the stress layers, although capable of inducing large stress, severely degrade lifetime of the foil.