Porous Silicon Films for Thin Film Layer Transfer Applications and Wafer Bonding

Abstract

Porous silicon films were fabricated from p+-Si (0.001-0.005 Ω cm) for their applicability to wafer bonding and layer transfer. Wafer bonding of porous silicon surfaces using silicon nitride interlayers was demonstrated, without the use of high temperature annealing. Conditions for producing porous silicon films compatible with both a) bonding surface requirements and b) layer transfer mechanical requirements were investigated. Nanoindentation showed quadratic dependence of Young's Modulus on relative density; films with mid-range Young's moduli were selected for layer transfer applications. Microstructural changes in annealed porous silicon films were studied using scanning electron microscopy and high resolution x-ray diffraction. Coarsening was observed at temperatures as low as 300 °C, the films remained pseudomorphic after annealing at all temperatures. After subsequent higher temperature annealing, mechanical fracture of the bonded stack occurred through the porous layer. The fracture mechanism for these structures is proposed.