Hirohisa Hirai

Structural difference between near interface oxides grown on Si and C faces of 4H-SiC characterized by infrared spectroscopy

Thermal oxides on 4H-SiC (0001) (Si-face) and (0001¯) (C-face) grown at 1100 °C were characterized by Fourier transform infrared spectroscopy attenuated total reflection method. For the films thicker than 5 nm on both faces, the structure of oxide was almost the same as that of the thermal oxide on silicon irrespective of film thickness. For the films thinner than 3 nm, structural transition regions were observed near the interface on both faces, and structural difference was also clearly detected between the oxides in those transition regions on (0001) and on (0001¯) faces.

Difference of near-interface strain in SiO2 between thermal oxides grown on 4H-SiC by dry-O2 oxidation and H2O oxidation characterized by infrared spectroscopy

Structural difference of near-interface oxides at thermally grown SiO2/4H-SiC interfaces between dry-O2 oxidation and H2O oxidation was investigated using infrared spectroscopy for both on Si- and C-faces. We found that H2O oxidation results in a significant reduction of the intrinsic strain of SiO2 in the near-interface region compared to dry-O2 oxidation, while such strain was not affected by the change of oxidation temperature and O2 partial pressure in the case of dry-O2 oxidation. The peak broadness observed in the near-interface region was also smaller for H2O oxidation than for dry-O2 oxidation, which indicated a formation of an oxide with more uniformity in microscopic structures. A strong correlation between the strain of near-interface oxides and the formation of near-interface oxide traps was suggested from the clear difference of the characteristics of metal-oxide-semiconductor capacitors fabricated with different oxidants.

Suppression of byproduct generation at 4H-SiC/SiO2 interface by the control of oxidation conditions characterized by infrared spectroscopy

An oxidation-induced byproduct at the 4H-SiC/SiO2 interface was detected by infrared spectroscopy as a peak in the range of 2100–2150 cm−1. The oxidation condition dependence of the peak intensity revealed that the generation of the byproduct is significantly affected by both the oxidant and the oxidation temperature. Low-temperature oxidation in dry O2 generates the byproduct, whereas employing H2O as the oxidant and oxidation at high temperature are effective ways of suppressing the byproduct generation. Oxygenated compounds including C≡O bonds are attributable to the byproduct, considering the peak frequency shift observed for oxidation with the 18O2 isotope.

Effects of high-temperature diluted-H2 annealing on effective mobility of SiC MOSFETs estimated by split capacitance–voltage technique

The effects of post-oxidation annealing (POA) in diluted-H2 ambient on 4H- and 6H-SiC/SiO2 interfaces were investigated. Effective mobility (μeff) was extracted from lateral metal–oxide–semiconductor field-effect transistors (MOSFETs) by the split capacitance–voltage (C–V) technique to determine the surface charge density and a calibration technique using two MOSFETs with different gate lengths to minimize the contribution of parasitic components. POA at 1150 °C in diluted-H2 ambient resulted in an enhancement of μeff, compared with that in N2 ambient. It was indicated that the effects of POA in diluted-H2 ambient should be attributed to the reduction in the density of near-interface traps in oxide, which disturb the electron transportation in the inversion channel, from the measurement temperature dependence of μeff for 6H-SiC MOSFETs as well as from the C–V curves of MOS capacitors fabricated on n-type 4H-SiC.

Low temperature wet-O2 annealing process for enhancement of inversion channel mobility and suppression of Vfb instability on 4H-SiC (0001) Si-face

For improvement of 4H-SiC metal-oxide-semiconductor field-effect-transistor performance, a post-oxidation annealing (POA) process in a wet environment after dry oxidation was systematically investigated. By tuning the wet-POA conditions, we clarified that wet-POA at low temperatures is more advantageous for both the enhancement of channel mobility and the suppression of flatband voltage instability. One of the mechanisms of channel mobility enhancement is attributed to the decrease in the density of traps in oxide near the MOS interface, rather than conventional interface traps. The effects of the wet environment on interfacial properties were also discussed based on oxide growth kinetics on 4H-SiC.For improvement of 4H-SiC metal-oxide-semiconductor field-effect-transistor performance, a post-oxidation annealing (POA) process in a wet environment after dry oxidation was systematically investigated. By tuning the wet-POA conditions, we clarified that wet-POA at low temperatures is more advantageous for both the enhancement of channel mobility and the suppression of flatband voltage instability. One of the mechanisms of channel mobility enhancement is attributed to the decrease in the density of traps in oxide near the MOS interface, rather than conventional interface traps. The effects of the wet environment on interfacial properties were also discussed based on oxide growth kinetics on 4H-SiC.