The Fabrication Of AlGaN/GaN HEMT

AlGaN/GaN HEMT（High Electron Mobility Transistor）is an importantsubstitute for RF and microwave application and other area in high voltage, highfrequency, high temperature, high-power and Radiation-hardened environment. Thisis because its high heat conductivity, corrosion resistance and radiation resistance. Inthis paper, we focus on the key process which affects the performance of theAlGaN/GaN HEMT devices, and fabricate the devices on the basis of theoptimization of process parameters.First，a two-step ICP etching method with a photoresist mask has been used forsolving the electrode climbing problem. This etching can achieve an incline mesarather than steep mesa, improving the adhesion between the mesa and electrodes. Inthe meantime, the two-step ICP etching adds a buffer zone in the middle of the mesa,changing the monolayer to double-deck and equivalent reduces the overall electrodesheight.Second， effects of Rapid Thermal Annealing temperature and time on Ohmiccontact of AlGaN-GaN HEMTs are studied, and obtain an optimum annealingcondition. In order to improve the surface morphology after annealing, differentsource and drain electrodes are reached. It found that the Ti/Al/Ni/Au has a higherannealing temperature than Ti/Al/Ti/Au electrodes, but it can get a better surfacemorphology. In order to reduce the ohmic electrodes with a Ni barrier layer annealingdifficulty, a Ti/Al/Ti/Al/Ti/Al/Ni/Au multilayer ohmic electrodes and lengthwayscontact holes structure. Study found that multi-layer ohmic electrodes structure canobtain a better ohmic contact than traditional four-layer electrodes and surfacemorphology. The lengthways contact holes structure not only reduce the ohmiccontact annealing requirement, but also obtain the better ohmic contact.Third, the gate metal and heat treatment influence on DC performance andschottky contact between gate electrode and AlGaN/GaN epitaxy are reached.Finally, a layout include different structure and different size is designed.Combined with the optimized parameters have achieved, and then fabricate theAlGaN/GaN HEMT devices. To optimize the performance, new structures andoptimized processes are used.