Key Process Study Of Si-based GaN Thin Film Substrate Transfer

AlGaN/GaN high electron mobility transistors(HEMTs)have great prospects in high frequency,high power device application area,but the self-heating effects induced temperature enhancement in the channel limited the performance potential and decreases the reliability of devices.Transferring the GaN films from original host substrates to the higher thermal conductivity diamond can effectively improve the thermal transport performance and enhance the output power of devices.In this thesis,the thermal stress in GaN/diamond wafers is simulated,and the key process in substrate transfer is studied for realizing high quality GaN/diamond bonded wafers.The main results are summarized as follows:(1).The thermal stress in GaN-Si-diamond three layered structure is simulated by Comsol software.The results show that the thermal stress in GaN increases with the bonding temperature.The thermal stress in GaN surface induced by heat source offsets that induced by bonding process,and the structure stress minimum can be achieved when the temperature in heat source approximates the bonding temperature.(2).The wet etching process of Si substrates is studied by varying the bonding materials and etching solution.The results show that GaN can be bonded on the sacrifice layer using paraffin,and the mixed solution of HNO3(66%),HF(40%),H2O with a volume ratio of 1:1:1 can transfer a complete GaN film.The measurements of GaN before and after transfer process are performed.(3).The measurements of magnetron sputtering Si films are performed,and the Si-Si low-temperature bonding process is studied.The results show that magnetron sputtering Si films are non-crystalline,and roughness of Si films is critical in bonding.The Si films on Al2O3 substrates are bonded successfully at 200?,and the bonding rate and bending strength are respectively 91.6%and 0.58 MPa.