Research On Key Technologies Of Polysilicon Source And Drain SiC N Channel MOSFET

Silicon Carbide metal-oxide-semiconductor field-effect transistor (MOSFET) with polysilicon source/drain is a new kind of SiC MOSFETs. The heavily doped source/drain structure in a traditional MOSFET is totally replaced by polysilicon/SiC heterojunction contact. This device eliminates the steps of ion implantation and annealing at high temperature for conventional SiC MOSFET. At the same time, it has no problems of crystal damage caused by ion implantation and low activation rate of implanted atoms. The complicated process of fabricating sidewall is replaced by simultaneously oxidizing polysilicon and SiC.Because of the thick sidewall, this device has a high threshold voltage. For getting a device with excellent performance, it is necessary to change the process and the structure to eliminate the influence of the sidewall.In this paper, several key technologies of polysilicon source and drain SiC N channel MOSFET are studied:Firstly, the transport characteristics of p+polysilicon/P-4H-SiC heterojunction are analyzed. Both forward and reverse bias I-V characteristics of this heterojunction are simulated by the simulator ISE TCAD. The ohmic contact of n+polysilicon/N+SiC heterojunction has been fabricated. The specific contact resistance as low as 3.82×10-5?cm2 is achieved.Secondly, the effect of interface-state charges and fixed charges on the device is analyzed. The high acceptor-like interface-state charges affect the electrical properties of this device seriously.Finally, the change in structure of this device caused by dqry etching processes is studied. And the characteristics of the device with new structure are simulated. Another process to improve the performance of the device is advanced in this paper. Oxidized polysilicon is used to form the sidewall and the gate insulator in this process. If the thickness of polysilicon and the time of oxidation are controlled perfectly, thin sidewall and gate insulator can be fabricated. And the simulated result shows good performance. In this paper, a method has been proposed to improve the characteristics by using SiON as the insulator layer.