Progressive materials integration: III-V on insulator by wafer bonding

The development of wafer bonded III-V on insulator structures aims to provide advancements in high-speed electronic applications such as High Electron Mobility Transistors. This study demonstrates the feasibility of hydrogen exfoliated template layers for the growth III-V based device structures. InP layers are transferred to GaAs substrates to assess the suitability of the InP layer as a template for metal-organic vapor phase epitaxial growth. Strong, large area bonds between III-V wafers are achieved using SiN intermediate layers, which provide robust structures at high temperatures. The bonding mechanisms of SiN layers with a short oxygen plasma exposure are found to mimic those of SiO2. These bonds are strong enough to withstand thermal strain imposed by bonded wafers that exhibit appreciable coefficient of thermal expansion mismatch, such as InP and GaAs. These bonded wafers exhibit some stability against defect formation for low thermal strains. However, depending upon the thermal expansion coefficient mismatch and required thermal processing, misfit dislocations can form to relieve this thermal strain. Careful control of both template thickness and annealing temperatures leads to a stable template for subsequent epitaxial growth. Once bonding is complete, the template layer is separated from the bulk by a technique of hydrogen ion implantation and exfoliation. The layer exfoliation from a hydrogen implanted InP substrate is facilitated by the formation of extended defects in a certain temperature regime due to hydrogen trapping. Subsequently increasing the temperature produces rapid planar exfoliation. This two-step annealing scheme simultaneously allows the wafer bond to strengthen during the low temperature defect nucleation phase. After exfoliation, the surface of the template layer is generally very rough, therefore a chemical mechanical polishing step was developed to planarize this layer for subsequent epitaxial growth. Damage-free planarization of the transferred InP layer is achieved with an abrasive free sodium hypochlorite and citric acid solution. The hydrogen implantation process is found to induce crystalline damage throughout the thickness of the transferred layer. This ion damage does not initiate any extended defects into subsequent epitaxial layers; however, a slight mosaic tilt is propagated. The electronic properties of the epitaxial layers grown on these template layers are largely affected by the final surface preparation. The optimized CMP process provides planarization, however, a post-CMP HCl etch improves the surface and produces a high quality growth.