Comprehensive and systematic design of metal/high-k gate stack for high-performance and highly reliable SiC power MOSFET

Abstract

Aluminum-based high-permittivity (high-k) gate dielectrics and suitable metal electrodes were systematically designed for advanced SiC power metal-oxide-semiconductor field-effect transistors (MOSFETs). Although electron injection into alumina (Al2O3) was significantly suppressed by nitrogen incorporation (aluminum oxynitride: AlON), gate leakage current under negative gate bias and hole trapping into the dielectrics were observed. Adding hafnium into the AlON (HfAlON) was investigated to overcome these drawbacks, and an atomic layer deposition-based method for HfAlON was developed in terms of permittivity, energy bandgap, and hole conduction under negative stressing conditions. Consequently, the reliability of metal/high-k gate stacks under both positive and negative bias temperature stresses was improved by using an optimized HfAlON gate dielectric in combination with a high work-function TiN gate electrode. Thanks to the higher permittivity of HfAlON, peak transconductance was successfully enhanced up to 3.4 times with an acceptable reliability margin in the state-of-the-art trench SiC MOSFETs by implementing a TiN/HfAlON gate stack.

Defect engineering in SiC technology for high-voltage power devices

“…Another intrinsic problem of Al 2 O 3 gate dielectric is the charge trapping phenomenon, leading to V T instability. 154,299,300) Figure 32 shows C-V characteristics taken from the SiC MOS capacitors with 65 nm thick Al 2 O 3 or aluminum oxynitride (AlON) grown on 7 nm thick SiO 2 underlayers. Here, the C-V measurements were repeated from −10 V to accumulation (positive bias) and vice versa by changing the maximum accumulation voltage.…”

“…32(b), immunity against positive bias stress was significantly improved by introducing nitrogen atoms at around 10%. 154,299,300) Moreover, firstprinciples calculations have revealed the mechanism by which V O V Al complex formation is suppressed under electrical stressing due to the nitrogen incorporation. 301) There is an ALD-based method of producing high-quality AlON films with suitable nitrogen concentrations ranging from 8% to 17%.…”

“…The nitrogen concentration is 5%, and TiN is used as a high work function (WF) metal electrode. 300) Hafnium incorporation increases permittivity of the dielectric, leading to enhanced drivability of MOSFETs. In addition, defect states near the valence band edge of AlON were passivated by adding Hf atoms to AlON.…”

“…33(a)]. 300) Even though the CET of the high-k devices (28-42 nm) was smaller than that of the standard NO-treated SiO 2 device (49 nm), time zero dielectric breakdown (TZDB) under high positive and negative biases were apparently improved by implementing HfAlON dielectrics. Both the positive and negative gate biases at which leakage current (FN tunneling) starts to flow systematically increased with the thickness of HfAlON layers, leading to enhanced immunity against both PBTI and NBTI, as well as improved TZDB.…”

“…Figure 33(b) summarizes the peak transconductance (g m ) enhancement in planar and trench-type SiC MOSFETs with the TiN/HfAlON/SiO 2 gate stacks relative to values for a standard device with the NO-treated SiO 2 dielectric. 300) The enhancement ratio is plotted as a function of HfAlON thickness. Since CET reduction directly enhances the gate capacitance (inversion carrier density), drivability and reliability of SiC MOSFETs can be improved without any μ FE improvement at the SiO 2 /SiC interface.…”