Research On Fabrication Process Of GaN-on-Si Enhanced MOS-HEMT

GaN High Electron Mobility Transistor?HEMT?has high breakdown voltage,low on resistance,high carrier mobility and high carrier drift speed,which is expected to become a power switch in the semiconductor power field that exceeds the limit performance of Si devices.A lot of researches have been done on the manufacturing process of GaN HEMT at home and abroad,but there are still some problems that need to be solved urgently.Under the above background,GaN HEMT power devices are manufactured in this paper.In-depth research is made specifically on the ohmic contact process and the post gate annealing?PGA?process.The main research content is divided into the following three parts:?1?GaN HEMT devices and transmission line model?TLM?structures with the same channel length and different ohmic contact lengths?L_c?were manufactured.After testing the GaN HEMT device,it was found that the on resistance of the GaN HEMT device with L_c=40?m was 26%lower than that of the GaN HEMT device with L_c=10?m.It shows that L_c will affect ohmic contact resistance?R_c?.The TLM structure with L_c equal to 10?m,40?m,and 100?m was tested,and it was found that the effect of L_c on R_c showed an exponential decay relationship.In order to compromise the relationship between L_c and R_c,and find the design merit of L_c.The effective transmission length of ohmic contacts is calculated in this paper.The calculation results and experimental results show that the modified transmission length of the ohmic contact basically matches the actual transmission length of the ohmic contact.It shows that the correction value of the ohmic contact transmission length can be used to guide the design of L_c.?2?Based on the theoretical analysis of ohmic contact process tolerance optimization,a new ohmic contact pattern with ohmic contact process tolerance capability was proposed.A series of new ohmic contact patterns and traditional TLM structures of ohmic contact patterns have been manufactured.The manufacturing TLM structure is annealed and tested under different annealing conditions,and then the process tolerance capability of all ohmic contact patterns is evaluated.Under different annealing conditions,the standard deviation of the ohmic contact resistance of different ohmic contact patterns is compared to measure the process tolerance of the ohmic contact.Experimental results show that the proposed new ohmic pattern structure has strong ohmic contact process tolerance.Compared with the traditional ohmic pattern structure,the new structure can effectively improve the consistency of ohmic contact resistance.?3?The enhancement mode HfO₂ gate dielectric GaN MOS-HEMT device are manufactured,and the PGA process is optimized.The experimental results show that the N₂ atmosphere at 500?for 1 minute is the optimal PGA process condition.The optimized PGA process condition can repair the HfO₂/AlGaN interface defects and HfO₂ body defects under the gate,and reduce the donor traps under the gate.Electrical performance tests were performed on the manufactured HfO₂ gate dielectric GaN MOS-HEMT device.The test results show that the manufactured HfO₂ gate dielectric enhanced GaN MOS-HEMT device exhibit a threshold voltage of 0.8 V,a maximum on current of 619 mA/mm,a sub-threshold swing of 59.88 mV/dec,and a switching ratio of 10¹⁰.The overall device performance is excellent.