Formation of III–V-on-insulator structures on Si by direct wafer bonding
We have studied the formation of III?V-compound-semiconductors-on-insulator (III?V-OI) structures with thin buried oxide (BOX) layers on Si wafers by using developed direct wafer bonding (DWB). In order to realize III?V-OI MOSFETs with ultrathin body and extremely thin body (ETB) InGaAs-OI channel layers and ultrathin BOX layers, we have developed an electron-cyclotron resonance (ECR) O2?plasma-assisted DWB process with ECR sputtered SiO2?BOX layers and a DWB process based on atomic-layer-deposition Al2O3?(ALD-Al2O3) BOX layers. It is essential to suppress micro-void generation during wafer bonding process to achieve excellent wafer bonding. We have found that major causes of micro-void generation in DWB processes with ECR-SiO2?and ALD-Al2O3?BOX layers are desorption of Ar and H2O gas, respectively. In order to suppress micro-void generation in the ECR-SiO2?BOX layers, it is effective to introduce the outgas process before bonding wafers. On the other hand, it is a possible solution for suppressing micro-void generation in the ALD-Al2O3?BOX layers to increase the deposition temperature of the ALD-Al2O3?BOX layers. It is also another possible solution to deposit ALD-Al2O3?BOX layers on thermally oxidized SiO2?layers, which can absorb the desorption gas from ALD-Al2O3?BOX layers.