Sub-5 μm-thick spalled single crystal Si foils by decoupling crack initiation and propagation

Abstract

Spalling of a brittle semiconductor substrate is an attractive method for fabricating sub-50 μm thick single crystal semiconductor wafers in large area. Here, a spalling process to fabricate single crystal Si foils with controlled thicknesses ranging from sub-5 to 38 μm is demonstrated using electroplated Ni stressor layers on Si substrates. In this study, the thickness profile of the Ni stressor layer was varied by changing the Ni electroplating current density, and the effect of thickness variation on the crack initiation and propagation in the underlying Si substrate was evaluated. The critical Ni thickness for crack initiation in our Ni/Si bilayer system was determined and we also show that the crack propagation depth, i.e., spalled Si thickness, is proportional to the thickness of the Ni layer at the central area of the Si wafer. Ni layer plated using 40 mA/cm2 resulted in sub-5 μm thick Si foil. In addition, the spalling mechanics of a Ni/Si bilayer system was analytically explored to give insight into the requirements of the Ni stressor layer for crack initiation.