Comprehensive BTI reliability study on trench field-stop IGBT under different applications

• Main Author: Sim, Zhi Lin
• Other Authors: Chen Xiaodong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; BTI; IGBT; Trench oxide interface; Interface states; Interface trapped charges; HTRB; Forming gas annealing
• Online Access: https://hdl.handle.net/10356/175646
• Institution: Nanyang Technological University

IGBT is a promising candidate in Si-based device to be used in high-voltage applications due to its low conduction loss and fast switching speed. Recent years, IGBT has become popular as compared to other power discrete devices, such as MOSFET and BJT as IGBT plays a leading role in energy conversation and the potential demand driven by the booming electric vehicle. In 21st century, the evolution of IGBT development has brought Trench Field-Stop to replace the earliest generation of planar Punch-Through IGBT due to its superior performance in terms of lower conduction loss, higher current density and smaller die size. However, one of the drawbacks of employing trench technology is the complexity of fabrication during process. The high-powered plasma of reactive ion etching is used to form trenches would induce a large amount of interface trapped charges in the Si/SiO2. These interfaces trapped charges impose several reliability issues and Bias Temperature Instability (BTI) reliability is one of the main contributors to degrade device’s lifespan. Furthermore, as transistor continues to scale further aggressively, particularly thinning of gate oxide, BTI degradation becomes more alarming to reliability. To solve this, atomic hydrogen from FGA can be employed to neutralise the interface states. However, the behaviour of hydrogen becomes complicated during harsh environments as studies have shown hydrogen can induce its own defects such as proton (H+) to degrade the device. Until now, there has been little reported work on trench-gate interface and its impact on reliability performance. In this work, different hydrogen contents of forming gas annealing were used to assess the BTI reliability and quantification of interface states in the trench-gate IGBT. A carefully designed BTI reliability methodologies with appropriate voltage and time to compare the different hydrogen content were studied in response to positive and negative bias stress. Moreover, 0V and ±5V recovery steps have been incorporated to help distinguish between recoverable and permanent Vth changes. For positive gate bias (PBTI), positive Vth shift is caused by electron trapping while negative gate bias (NBTI) induces negative Vth shift due to generation of interface states. Through the results, a physical model was proposed to explain the BTI test and its impact to the entire trench module, including the sidewall and bottom of the trench.