Highly Reliable SiC MOS Transistors Operated at High Temperatures X.W. Wang, W.J. Zhu, X. Guo, and T.P. MA Department of Electrical Engineering, Yale University A Major Problem of State-of-the-art SiC MOSFETs at High Temperatures: Very Short Operating Lifetimes. C-V and Ig – Vg Fabrication of SiC MOSFET Source Drain Gate 100 3 10 2 10 1 10 0 10 -1 10 -2 10 -3 10 -4 10 -5 10 -6 10 -7 10 -8 10 -9 10 90 LPCVD SiO2 Conventional ONO 5 7 45 min 9 7 75 hour 11.4 6.4 Our Approach Has Resulted in Extrapolated Lifetime of 280 Years Lifetime (sec) 10 n+ n+ 60 50 40 30 P 10 Meas. Freq: 10KHz 0 Temp: 450 C 10 -2 NOT: 5 X 10 cm 0 -12 -10 -8 -6 -4 -2 0 2 4 P+ 6H-SiC JVD O N O 12 10 9 6H-SiC, RCA Cleaning 100 10 6 In-situ, Sequential Deposition of O-N-O Layers, Room Temp. 3 10 0 Anneal: 900 C, N2, 30 min o + 950 C, WV, 30min o Stressed at 450 C E ox=(Vg-Vth)/dox 0 1 16 NA-ND=3x10 /cm 2 3 4 5 6 7 Dielectric Field (MV/cm) Key to success: Dielectric and Interface Engineering 5 Source of O N2 SiH4 He S. of N S. of Si Carrier 80 8 9 10 11 12 13 Low gate current and high breakdown field contribute to the excellent reliability. VG-VT=8V 6V 40 4V 20 2V 20 4V 0 2V 0V 0V 0 0 2 4 6 8 10 14 (a) 60 6V 40 Vd (V) Research done in collaboration with Jesse Tucker and Mulpuri Rao of George Mason University Research supported by ONR 7 NA-ND=3x1016/cm3 @ Room T o 0 (b) Id-Vd Characteeristics at 450 C Key considerations: 1. N2O Treated SiC Surface 2. Room-temp Deposition of SiO2. 3. High-Quality Si3N4 Layer 6 nMISFET on 6H-SiC W/L=250µm/200µm VG -VT=8V 3 Id (µA) N2O Load to Furnace 10 years o 10 4 100 nMISFET on 6H-SiC W/L=250µm/200µm 80 60 SiC Surface Pre-cleaned by N2O / He Plasma 280 years o 450 C Dielectric Field E(MV/cm) @ 450 C dox(equi.)=28nm W/L=200µ/50µ o 400 C SiC MOSFET Id – Vd Curves Load to Deposition Chamber Gate Dielectric: JVD ONO o 450 C o 400 C 3 6 C-V characteristics indicate excellent Gate dielectric and interface properties. Formation of O-N-O Stack Gate Dielectric 18 15 JVD-ONO/6H-SiC (n-type) Substrate Injection Gate Voltage (V) Id (µA) 10 70 20 10 nm 20 nm 10 nm Source: Lipkin, IEEE Trans. on ED, Vol. 46, 1999 10 Ni 2 < 4.8 min Al Ni Current Density J(A/cm ) Dry-Wet SiO2 Dielectric 80 Capacitance (pF) SOA SiO2 Lifetime Breakdown Field (MV/cm)) o o (@ 350 C) RT 350 C JVD Field Oxide 3.2-3.6 4.5-5 < 1.2 min Al/JVD ONO/6H-SiC 2 4 6 Vd (V) 8 10 (a) Id-Vd Characteeristics at R.T. Conclusion: By use of a novel gate dielectric, we have demonstrated highly reliable & highly durable SiC nMOSFETs operating at 450oC with over 4 orders of magnitude longer operating lifetimes than the state-of-the-art.
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