Fabrication Of GaN Based HEMT Au-free Ohmic Contact Electrode

Gallium Nitride material have wide bandgap,high breakdown field strength,high electron drift velocity,high temperature resistance,high radiation resistance and high thermal conductivity,etc,suitable for high frequency,high power and harsh environments application.Benefit from high electron mobility,Ga N-based HEMT devices have broad application prospects in high-voltage,high-frequency,high-power devices,and optoelectronic integration.Ga N-based devices manufactured in the mature Si-CMOS process line can reduce the difficulty of preparation and production costs,which is beneficial to the industrialization of Ga N-based devices and improves the market competitiveness of Ga N-based HEMT devices.Studying the gold-free ohmic contact technology of Ga N-based HEMT devices is of great practical significance for achieving compatibility between Ga N-based electronic devices and Si-CMOS processes.This work mainly studies Au-free ohmic contact technology of Al Ga N/Ga N heterojunction,the main contents are as follow:1.We propose a preparation method of Ti N-based electrode to replace Au,and conduct in-depth analysis and verification of the gold-free electrode.The method of physical vapor deposition is used to prepare pure Ti films at room temperature,and then the Ti films are converted into Ti N films by rapid thermal nitridation reaction through annealing process compatible with ohm contact.Compared with the traditional method of physical vapor deposition at high temperature?300??,the method of rapid thermal nitridation greatly reduced the preparation time of Ti N films.Based on the Ti/Al/Ni/Ti N structure,the effects of annealing temperature,annealing time and the relative thickness of Ti/Al on contact resistance,specific contact resistivity and root-mean-square surface roughness are studied.And then ohmic contacts comparable to that with Au-based ohmic contacts performance are obtained,but with better electrode better edge acuity and electrode surface morphology.The specific contact resistivity,contact resistance,and root mean square surface roughness of Ti/Al/Ni/Ti N ohmic contacts are 3.47×10^-5??cm²,1.1??mm and 5.89 nm respectively,and that of Ti/Al/Ni/Au ohmic contacts are 3.12×10^-5??cm²,1.05??mm and 26 nm,respectively.On this basis,Al Ga N/Ga N MIS-HEMT devices with Au-free electrodes are fabricated.The maximum current density is 372.7 m A/mm@V_G=0 V,the on-resistance is18.4??mm,and the peak transconductance is 57.0 m S/mm It is equivalent to the DC performance of traditional Au-based Al Ga N/Ga N MIS-HEMT devices.2.Using Ti/Al/W as the Au-free ohmic metal,we first study the non-recessed contact performance of Al Ga N/Ga N under Al-rich structure.After annealing at 600?for 10 min,Ti/Al/W?3/140/40 nm?obtain linear contact.Subsequently,Ti/Al/W low temperature contact is formed by over-recessed Al Ga N/Ga N structure,and the effects of surface treatment process after etching,thickness of Ti in Ti/Al/W and different etching patterns on ohmic contact characteristics are studied.The annealing treatment with oxygen atmosphere after etching can repair the etching damage and increase the current.The specific contact resistivity of Ti/Al/W?20/200/40 nm?after annealing at 750?for 1 min is 6.58×10^-4??cm².After optimizing the thickness of Ti and etching pattern,after annealing at at 550?for 10 min,Ti/Al/W?10/200/40 nm?obtain a specific contact resistance of 3.61×10^-4?·cm².