Threshold Voltage Modulation Technique Of Enhancement GaN Trench-Gate MIS-HFET

Power semiconductor devices play an important role in the field of power control and transformation.Reasonable design can improve the efficiency of electric energy conversion,enhance the stability of the system,and transmit energy as a switch element.GaN power switch is a research hotspot in recent years in international academia and industry.With its high breakdown voltage,high working temperature and high switching frequency characteristics,it is expected to become an ideal candidate technology for the next generation of efficient and high-speed power electronics.The Enhancement-mode is the key to ensure the stability,reliability and safety of the power switch device.And high threshold voltage can effectively avoid the“fault turn-on”caused by various problem in the operation of enhanced devices.Trench gate technology is one of the important methods to realize E-mode GaN,and is also a key issues in the field of GaN power devices.Through the method of simulation and experiment,this work studies the threshold voltage regulation technology of enhancement-mode GaN trench gate MIS-HFET.Firstly,this paper introduce the basic working principle of GaN HFET,compare various enhancement-mode implementation methods,explain the basic process flow of the GaN trench gate device,and focuse on the design and working principle of buried-fluorine shallow-trench gate which is a new technical scheme.Laying the foundation of the experiment process the simulation result showed that based on trench gate method the introduction of F~-ions buried layer structure can realize the modulation of the threshold voltage.Secondly,in this work,the process flow of fabrication of buried-fluorine shallow-trench gate device is designed.And in the process of researching the core technology,a high quality wet etching gate method is developed.The barrier layer is oxidized at high temperature,and the oxidation reaction can be automatically terminated at the heterojunction interface.It is possible to obtain the etched low barrier grid by the etching of hot alkali solution.The RMS roughness of the interface is only 0.298nm.This method provides a high precision method and process condition for the trench grate etching.Finally,the experimental conditions for the core process of the trench gate etching and the fluorine ion implantation are optimized.High quality trench gate with threshold voltage hysteresis 0.05V can be obtained through a series of surface treatment processes after the flow of trenching gate,such as remocing the natural oxide,surface treatment by N plasma,inserting the AlN dielectric layer.In the process of etching Si N_x sacrificial layer by F~-based gas of RIE equipment,the F~-ion is introduced into the buried-fluorine layer structure to realize the positive modulation of the threshold voltage.Finally,we get the threshold voltage 5.0V,threshold hysteresis 0.1V,V_G=10V saturation current400mA/mm excellent performance,achieving threshold voltage wide range regulation,while maintaining the strong transport capacity of the device.