Stress Engineering in Germanium-Silicon Heterostructure Using Surface Activated Hot Bonding

Abstract

The manufacturing of heterostructures is interesting in many fields such as photonics, solar energy production and quantum technologies. This paper, dedicated to germanium on silicon heterostructure manufacturing and stress engineering, builds up on LETI and EVGroup’s hot bonding technology (1). The coefficients of thermal expansion (CTE) mismatch between germanium and silicon is used to induce some in-plane tensile stress in a thin germanium layer transferred by the Smart CutTM technique onto a silicon substrate. In this approach, a bulk germanium wafer is directly bonded on a bulk silicon wafer, using surface activated hot bonding (SAHB). Process integration advantages are the low defect density of bulk germanium and the tensile stress that can be tuned using the bonding temperature. According to X-Ray diffraction measurements, for a bonding performed at 250°C, the lattice parameter deformation reached +0.06%, resulting in a 82 MPa tensile stress in a 370 nm thick germanium layer.