Thermomechanical Spalling of Epitaxially Grown Silicon from Porosified Substrates

We combine two kerfless approaches to unite advantages of both processes: the epitaxial layer transfer based on porous silicon (PSI process) and the lift-off of a thin silicon layer from a substrate via controlled spalling by a stress-inducing layer. For this, we deposit an Al stressor layer on top of an epitaxially grown silicon layer. A porous double layer underneath the epitaxial layer serves as determined breaking point. We directionally heat this sample stack and cool it afterwards for controlled spalling of the epitaxial layer from the substrate. We achieve a lift-off rate of 34 out of 36 detached samples. The porous silicon layer enables a smooth surface of the detached epitaxial layer and the remaining substrate. Compared to our standard spalling process the thickness variation of the detached layers is significantly reduced from ≤ 25 μm to less than 2 μm. Furthermore we show that the lifetime of the detached epitaxial layers does not suffer from the Al deposition and the lift-off process