Lift-off of free-standing layers in the kerfless porous silicon process

Abstract

We discuss the lift-off of free-standing epitaxially grown silicon layers from the porous silicon (PSI) process, which is a kerfless wafering technology. The lift-off is a crucial step in the PSI cycle. A high-porosity layer serves as a mechanically weak layer for lift-off and consists of widely spaced silicon bridges with thicknesses of 40-100 nm. The low width leads to a 33-fold stress enhancement in the bridges, making them break when a force is applied while the epitaxial layer and the substrate remain intact. We perform the free-standing lift-off with a curved vacuum chuck. A vacuum pressure of 0.2 bar is sufficient for controlled peeling off of the 30-50 um thick silicon layers. We simulate the stresses and the displacements of the epitaxial layer in the lift-off process close to the first non-broken bridge. We demonstrate the defect-free lift-off of 8 of 9 of 9 × 9 cm2 layers from 6" substrates.