Investigation on the Use of Nitrogen Implantation to Improve the Performance of N-Channel Enhancement 4H-SiC MOSFETs

A gate oxide obtained by wet oxidation of SiC preimplanted with nitrogen has been investigated on MOS capacitors and implemented in a n-channel MOSFET technology. Different implantation fluences and energies in the ranges 1.5 X 10¹³-1 X 10¹⁵ cm ^-2 and 2.5-10 keV, respectively, were used with the aims to study the effect of the nitrogen concentration at the SiO₂/SiC interface on MOSFET performance. The highest dose, which is able to amorphize a surface SiC layer, was also employed to take advantage of the faster oxidation rate of amorphous phase with respect to crystalline one. The electron interface trap density near the conduction band has been evaluated with different techniques both on MOS capacitors and MOSFET devices; a good agreement among the measured values has been attained. A strong reduction of the electron interface traps density located near the conduction band has been obtained in the samples with a high nitrogen concentration at the SiO₂/SiC interface. The MOSFETs with the highest nitrogen concentration at the interface (~1 X 10¹⁹ cm ^-3) present the highest channel mobility (21.9 cm²/V .s), the lowest threshold voltage (2.4 V), and the smallest subthreshold swing (310 mV/decade at drain current of 10 ^-11 A).