Shiro Hino

Remarkable Increase in the Channel Mobility of SiC-MOSFETs by Controlling the Interfacial

The impact of a thin SiO₂ layer inserted between Al₂O₃ and SiC on channel mobility in AI₂O₃/SiC MOSFETs was investigated. The remarkable increase in the channel mobility is demonstrated when the SiO₂ thickness is around 1 nm. The thin SiO₂ layer is formed by the thermal oxidation of the SiC substrate at 600 or 800degC in O₂ atmosphere. The peak value of the field-effect mobility in AI₂O₃/SiO₂/SiC MOSFETs is as high as 300 cm² / (V ldr s). On the other hand, when the SiO₂ layer is 2.0 nm, the field-effect mobility drastically reduces to 40 cm²/ (V ldr s), which is most likely due to the high interface trap density as seen in conventional SiO₂/SiC MOSFETs.

\hbox{SiO}_{2}

Ultrahigh channel mobility is demonstrated for 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) with Al2O3 gate insulators fabricated at low temperatures by metal-organic chemical-vapor deposition. Relatively high field effect channel mobility of 64cm2∕Vs is obtained when the Al2O3 gate insulator is deposited at 190°C. Furthermore, extremely high field effect mobility of 284cm2∕Vs was obtained for a MOSFET fabricated with an ultrathin thermally grown SiOx layer inserted between the Al2O3 and SiC.

Layer Between

We have characterized hafnium oxide thin films grown on SiO2/p-Si(001) by source gas pulse introduced metalorganic chemical vapor deposition (MOCVD) using tetrakis-diethylamido-hafnium (Hf[N(C2H5)2]4) and tetrakis-dimethylamido-hafnium (Hf[N(CH3)2]4). O2 or H2O is used as oxidant gas. It is demonstrated that the use of H2O can reduce the residual impurity concentrations of hafnium oxide films when the deposition temperature is as low as 280°C. In addition, we have found that the residual impurity concentration of hafnium oxide films grown with Hf[N(C2H5)2]4 is lower than that grown with Hf[N(CH3)2]4. This tendency agrees with the leakage current density. An equivalent SiO2 thickness (EOT) of 1.4 nm with 4.7×10-6 A/cm2 @-1 V have been obtained for the hafnium oxide films grown with Hf[N(C2H5)2]4 at 280°C.

\hbox{Al}_{2}\hbox{O}_{3}

We have characterized HfO 2 thin films grown by source gas pulse introduced metallorganic chemical vapor deposition (MOCVD) technique using Hf(O-t-C 4 H 9 ) 4 as a Hf precursor, and H 2 O or O 2 as an oxidization gas. The Hf precursor and H 2 O (or O 2 ) were alternately introduced with N 2 purge step, which is one growth cycle in this experiment. The residual impurity concentration in HfO 2 thin films can be reduced when the film is grown by pulse-MOCVD using H 2 O. In addition, the leakage current density has been improved for the HfO 2 film grown with H 2 O. This low leakage current density is considered to be due to the lower impurity concentration in the film grown with H 2 O as an oxidization gas.

and SiC

Hafnium oxide films were deposited on silicon substrates at deposition temperatures ranging from 190 to 500°C by metalorganic chemical vapor deposition. An oxygen-free precursor, Hf[N(C2H5)2]4, and O2 gas were used as starting materials. The reaction-limited deposition of hafnium oxide films fabricated with Hf[N(C2H5)2]4 was observed for wide temperature region compared with that with the conventional alkoxide precursor. Concentration of contaminated elements, such as carbon, nitrogen and hydrogen, decreased with increasing the deposition temperature, and amorphous films were obtained up to 450°C. Flat surface was obtained between 280 and 450°C. Reduction of hysteresis in capacitance-voltage curve and the increase of the accumulation capacitance were both achieved by the high temperature deposition. Hf[N(C2H5)2]4 is a unique precursor which can produce amorphous hafnium oxide films having very flat surface even at high deposition temperature of 400 and 450°C together with the reduction of the contamination elements.