Wafer bonding for III–V on insulator structures

The InP and GaAs wafers were bonded to GaAs substrates using a siliconnitride intermediate layer. Key process parameters include the silicon-nitride surface roughness and density as determined by atomic-force microscopy and x-ray reflectivity. We demonstrate that silicon nitride can be bonded without any chemical-mechanical polishing step. Silicon-nitride films produced by plasma-enhanced chemical-vapor deposition (PECVD) and deposition by sputtering were compared for bonding compatibility. Smooth silicon-nitride layers (root-mean-square roughness <0.7 nm) were found to produce large areas of bonded material and an oxygen-plasma treatment (200 mtorr, 200 W, 60 s) produced strong nitride/nitride bonding. The strain in the InP layer after transfer to the GaAs substrate was determined using x-ray reciprocal-space mapping (RSM). The crystalline quality of the InP layer was examined with high-resolution x-ray scattering.