High temperature bias-stress-induced instability in power trench-gated MOSFETs

• Published in: Microelectronics and reliability Vol. 54; no. 2; pp. 374 - 380
• Main Authors: Hao, J., Rioux, M., Suliman, S.A., Awadelkarim, O.O.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.02.2014; Elsevier
• Subjects: Applied sciences; Degradation; Electric power generation; Electrical engineering. Electrical power engineering; Electronic equipment and fabrication. Passive components, printed wiring boards, connectics; Electronics; Exact sciences and technology; Gates; Instability; MOSFETs; Niobium base alloys; Other multijunction devices. Power transistors. Thyristors; Oxides; Power electronics, power supplies; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Stresses; Transistors; Thermal stress; Water; Voltage threshold; MOSFET; Bias temperature instability; Electric stress; Temperature effect; Transistor gate; n channel; High temperature; Power transistor; Degradation; Optical microscopy; Stress effects; Silicon; Damaging; Passivation; Transistor parameter; Scanning electron microscopy; Trench technology; Power electronics; Field effect transistor; Gate oxide; Reliability; Crack
• ISSN: 0026-2714; 1872-941X
• DOI: 10.1016/j.microrel.2013.10.004

•High-temperature reverse-bias stress of trench-gated UMOSFETs causes parameter degradation.•The degradation is particularly large when the stress is applied in a humid ambient.•Stress introduces mobile protons in the gate oxide of the UMOSFET.•The stress configuration and level give rise to negative-bias temperature instability. We report on the high-temperature reverse-bias (HTRB) stress reliability of trench-gated n-channel metal-oxide-silicon field-effect transistors (n-UMOSFETs). The degradation induced by the HTRB is examined using changes in transistor parameters, optical microscopy, and scanning electron microscopy. The HTRB causes degradations in the threshold voltage and drain leakage of the n-UMOSFET and these degradations are particularly large when the stress is applied in a humid ambient. The observations were interpreted in terms of water molecule diffusion into the gate oxide through passivation cracks in the edge termination of the n-UMOSFET during HTRB in a humid ambient. The water molecules catalyze proton (H+) generation through electric-field assisted interactions and hole injection into the gate oxide at the bottom of the trench. Also, H+ is observed to be very stable in the gate oxide and to migrate between the gate-oxide and oxide–Si interfaces driven by an applied gate-voltage. It is proposed that the employed HTRB configuration and level give rise to negative-bias temperature instability (NBTI) in a parasitic p-channel MOSFET structure occurring in the trench base of the n-UMOSFET, and that NBTI is a serious reliability concern in power UMOSFETs subjected to stress in a moist ambient.