AlON/SiO₂ Stacked Gate Dielectrics for 4H-SiC MIS Devices

Abstract

We propose the use of an aluminum oxynitride (AlON) gate insulator for 4H-SiC MIS devices. Since direct deposition of AlON on 4H-SiC substrate generates a large amount of interface charge due to an interfacial reaction, a thick AlON layer was deposited on underlying thin SiO2 thermally grown in N2O ambient. To reduce the negative fixed charge density in the aluminum oxide (Al2O3) film, we used reactive sputtering of Al in an N2/O2 gas mixture. The fabricated MIS capacitor with AlON/SiO2 stacked gate dielectric shows no flat band voltage shift and negligible capacitance-voltage hysteresis (30 mV), indicating the dielectric is almost free from both fixed charges and electrical defects. Owing to the high dielectric constant of AlON (k=6.9), as compared to single N2O-SiO2 gate insulator, significant gate leakage reduction was achieved by AlON/SiO2 stacked gate dielectrics even at high-temperature, especially in a high electric field condition (>5 MV/cm).

Effect of nitrogen incorporation into Al-based gate insulators in AlON/AlGaN/GaN metal–oxide–semiconductor structures

“…In the current study, to evaluate the validity of AlON insulators for GaN-based HEMTs, we investigated AlON=AlGaN=GaN MOS structures using the reactive sputtering method. Contrary to our previous research on SiC MOS devices consisting of SiO 2 underlayers beneath the deposited AlON films (AlON=SiO 2 =SiC stacks), [16][17][18] an excellent MOS interface quality, together with suppressed charge injection into the insulators, was successfully achieved even with the direct sputter deposition of AlON films on AlGaN=GaN substrates. On the basis of physical characterizations, the impact of nitrogen incorporation into the Al-based oxides was studied in detail.…”

“…Then, postdeposition annealing (PDA) was conducted in N 2 ambient at 800 °C for 3 min to improve the electrical properties of the Al-based oxides by referring to the optimized PDA conditions in our previous study on SiC MOS devices. 16,17) No significant change in film thickness was observed for both AlON and Al 2 O 3 films after the PDA. The nitrogen atomic concentration in the AlON films determined by conventional X-ray photoelectron spectroscopy (XPS) analysis using Ar ion sputtering was about 18% (atomic concentrations for total Al, O, and N were 38, 44, and 18%, respectively).…”

“…15) We have also implemented AlON gate dielectrics stacked with thin SiO 2 underlayers (AlON=SiO 2 structures) into silicon carbide (SiC) power MOSFETs. [16][17][18] Consequently, a significant reduction in carrier injection into the gate stacks and an improved reliability of SiC MOSFETs were demonstrated using sputter deposition 16,17) and CVD 18) methods. In the current study, to evaluate the validity of AlON insulators for GaN-based HEMTs, we investigated AlON=AlGaN=GaN MOS structures using the reactive sputtering method.…”

Fundamental Aspects of Silicon Carbide Oxidation

“…This enlarged band offset for the thick MOS devices is preferable from the viewpoint of reducing gate leakage, but electrical defects should negatively impact on the device performance and reliability. Therefore, fundamental tactics, such as applying deposited gate oxides and band engineering by utilizing stacked structures, are indispensable to take advantage of C-face SiC-MOS devices [25][26][27][28]. We also evaluated the modulation of energy band alignment of SiO 2 /4H-SiC(0001) structures due to the interface defect passivation [29].…”

Effect of N bonding structure in AlON deposited by plasma-assisted atomic layer deposition on electrical properties of 4H-SiC MOS capacitor

“…In order to improve the interface properties of the AlON=4H-SiC, 13,15) we also inserted a SiO 2 layer into the AlON layer and 4H-SiC interface. After chemical cleaning of the 4H-SiC surface using a standard RCA method, a 10-or 70-nm-thick SiO 2 layer was formed on the SiC substrate by low-pressure chemical vapor deposition.…”