Electrical properties of reactive-ion-sputtered Al2O3 on 4H-SiC

Highlights

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O₂ annealed RIS-Al₂O₃ on 4H-SiC showed better performance than other reported result.

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FN, FN + PF tunneling was found in O₂ annealed RIS-Al₂O₃ for different temp. ranges.

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Al₂O₃/SiC barrier height increased from 1.7 eV to 2.53 eV after O₂ annealing.

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Increase in barrier height is attributed to interfacial SiO₂, confirmed by XPS study.

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Forming gas annealing further improved the C-V hysteresis of these devices.

Abstract

Al₂O₃ was deposited on n-type 4H-SiC by reactive-ion-sputtering (RIS) at room temperature using aluminum target and oxygen as a reactant gas. Post deposition oxygen annealing was carried out at a temperature of 1100 °C. Metal-oxide-semiconductor (MOS) test structures were fabricated on 4H-SiC using RIS-Al₂O₃ as gate dielectric. The C-V characteristics reveal a significant reduction in flat band voltage for oxygen annealed RIS-Al₂O₃ samples (V_fb = 1.95 V) compared to as-deposited Al₂O₃ samples (V_fb > 10 V), suggesting a reduction in negative oxide charge after oxygen annealing. Oxygen annealed RIS-Al₂O₃ samples also showed significant improvement in I-V characteristics compared to as-deposited RIS-Al₂O₃ samples. A systematic analysis was carried out to investigate the leakage current mechanisms present in oxygen annealed RIS-Al₂O₃ on 4H-SiC at higher gate electric field and at different operating temperature. For measurement temperature (T) < 303 K, Fowler–Nordheim (FN) tunneling was found to be the dominant leakage mechanism and for higher temperature (T ≥ 303 K), a combination of FN tunneling and Poole-Frenkel (PF) emission was confirmed. The improvement in I-V characteristics of oxygen annealed RIS-Al₂O₃/4H-SiC MOS devices is attributed to large effective barrier height (Φ_B = 2.53 eV) at Al₂O₃/SiC interface, due to the formation of an interfacial SiO₂ layer during oxygen annealing, as confirmed from X-ray Photoelectron Spectroscopy results. Further improvement in C-V characteristics for oxygen annealed RIS-Al₂O₃/4H-SiC MOS devices was observed after forming gas annealing at 400 °C.

Keywords

• Aluminum oxide; 
• 4H-SiC; 
• Reactive-ion sputtering; 
• Fowler–Nordheim tunneling; 
• Poole-Frenkel tunneling; 
• Oxygen annealing; 
• Forming gas annealing; 
• Metal-oxide-semiconductor capacitor
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