Characterization of inversion layers on SiC.

摘要

Silicon carbide (SiC) has been shown to have several advantages as a semiconductor for the fabrication of devices for high power, high temperature and high frequency applications. The advantages of SiC power MOSFETs in terms of the low drift region resistance have also been predicted. However, before this research, the low inversion layer mobility obtained on 6H-SiC and the lack of any report on inversion layer mobility in the c plane on 4H-SiC had been hampering the progress of SiC technology in this area.; During the course of this research, the highest values of inversion layer electron mobility on 6H-SiC were measured and lateral MOSFETs on 4H-SiC with high inversion mobilities were measured and reported for the first time. The choice of gate dielectric for the SiC lateral MOSFETs was found to be important. While MOSFETs with thermally grown oxides fabricated during this research had very low inversion mobilities with positive temperature dependence, MOSFETs with deposited and subsequently annealed oxides had high inversion mobilities with a negative temperature dependence. Such a dependence was also observed for the first time in SiC inversion layers.; Some overview of the existing literature regarding the state of the art in characterization of oxides in SiC is given. While the oxide charges for oxide grown on N-type SiC was found to be comparable to the levels in silicon, oxides grown on P-type SiC show large flatband voltage shifts. These have been reduced through some careful optimization of the oxidation conditions but still more work has to be done in this regard. The kinetics of thermal oxidation in SiC is also briefly outlined and the prior work done in measuring SiC inversion mobilities is also summarized.; The devices required to perform a complete characterization of the various dependences of the inversion mobility as well as a novel Hall inversion mobility structure were designed and laid out.; The process used to obtain the highest reported inversion mobilities in lateral MOSFETs on both 6H-SiC and 4H-SiC was successfully repeated indicating the viability of the process. Measurements on these wafers revealed low effective oxide charge densities and high inversion mobilities (50-70 cm{dollar}sp2{dollar}/V.s). While no clear-cut orientation dependence was measured, negative temperature dependence of mobility suggesting phonon dominated scattering processes were observed in SiC inversion layers for the first time. A temperature dependence for the inversion mobility of about T{dollar}sp{lcub}-1{rcub}{dollar} for 6H-SiC and T{dollar}sp{lcub}-1.5{rcub}{dollar} for 4H-SiC were measured. During this regime the electric field dependence was about E{dollar}sp{lcub}-0.25{rcub}{dollar} corroborating the theory of phonon dominated scattering. (Abstract shortened by UMI.)