Study On Technology And Characteristics Of GaN-Based FinFET

AlGaN/GaN HEMTs have excellent characteristics such as large output current,high breakdown voltage,high temperature resistance,radiation resistance,and it also have a pleasant prospect in microwave power applications.The development of integrated circuits has always followed Moore's law,so it can be foreseen that the AlGaN/GaN HEMTs will continue to shrink in size,and short channel effects will be a major difficulty in this developing period.In the development of Si-based devices,the three-dimensional fin-gate?Fin?structure is a major technological breakthrough to solve the short-channel effect and promote the development of integrated circuits.When it comes to GaN-based devices,the Fin structure can improve gate control ability effectively.Furthermore,the side gate of the Fin structure can deplete a portion of channel electrons,weaken the polarization effect to realize enhanced-mode HEMT.In this paper,based on the Silvaco simulation and laboratory standard process line,aiming at improving gate control ability and realizing enhancement-mode devices,we combined the theoretical research and experimental fabrication,and studyed the process control and characteristics of FinFETs.The main research contents and achievements are:This article explored the process conditions for nanochannel etching of FinFETs firstly.SEM microscope was used to test the nanochannel arrays with different ICP etching conditions.The test results show that the higher the bias source power,the higher the bombardment speed and the rougher the surface of the material.The greater the ICP source power,the greater the chemical reaction rate,and the faster the lateral expansion,the larger the etch angle.The ICP source power used in the final etching scheme was 100 W,the bias source power was 10 W,the Cl₂ flow rate was 25 sccm,the etching rate was as low as 0.5 nm/s,as a result,the etched surface was good,the roughness was small and the array was steep.We simulates AlGaN/GaN FinFETs secondly.Three-dimensional FinFETs with Fin-width of 50nm,100nm,150nm,200nm,400nm,and 800nm are designed.Simulation results show that the threshold voltage of FinFETs shifts positively compared to the conventional HEMT.And with the decrease of Fin-width,threshold voltage also shifts positively.The threshold voltage of FinFETs with 50-nm Fin-width is 0.14V,which realized enhancement-mode.Compared with the conventional HEMT,the transconductance of FinFETs is greatly improved and the transconductance peak value increases firstly and then decreases with the reduction of the Fin-width.The peak transconductance of FinFETs with 100-nm Fin-width is 321 mS/mm.The electron concentration distribution of the device shows that as the Fin-width decreases,the concentration of the 2DEG gradually decreases.And regardless of Fin-width,the depletion width generated by the sidewalls is fixed.The internal potential distribution of the device shows that the potential distribution generated by the Schottky contact is basically the same,and has nothing to do with the Fin-width.FinFETs with different Fin-width were fabricated and tested.The test results show that:Firstly,the threshold voltage of FinFETs shifts positively by approximately 2V compared with the conventional HEMT,and the threshold voltage of the FinFETs further shifts positively as the Fin-width decreases.The threshold voltages of FinFETs with Fin-width of 160nm and 100nm are-1.63V and-0.97,shifted by 0.66V.At the same time,using a theoretical model about threshold voltage,we explained the experimental result successfully.The depletion caused by side gate and the reduction of the piezoelectric polarization lead to a positive shift of threshold voltage in FinFETs.When the Fin-with has reduced to a certain extent,the width depleted by side gate will occupy the entire channel and the device will realize enhancement-mode.Secondly,FinFETs exhibit better gate control capabilities.The FinFETs with 160nm Fin-width have a peak transconductance of 306mS/mm,increase by 41.6%compare with conventional HEMT.Lastly,FinFETs have a higher current density,and the current density of FinFETs with 160nm Fin-width is 996mA/mm(V_G-V_TH=4V),which is 44.5%higher than that of the conventional HEMT.However,the sub-threshold swing and DIBL value of FinFETs are larger than that of the conventional HEMT due to the interface states caused by the device channel etching process.At the same time,the introduction of the interface state increases the forward and reverse Schottky current.This article used ICP equipment to perform oxygen plasma treatment under the gate region of the FinFETs.The test results show that oxidation shifts the threshold voltage of devices,and the threshold voltage of FinFETs with 100nm Fin-width increases from-0.97V to-0.54V,shifted by 0.43V.The oxidation also has the effect of etching,reducing the thickness of the barrier layer,and leads to an increase in the peak transconductance,a decrease in the subthreshold slope and an increase in the gate control capability.An MIS insulating layer is generated in the oxidation process,which reduces the Schottky forward and reverse leakage current by nearly two orders of magnitude.