Edge termination is located at the periphery of the active region in power devices for alleviating junction curvature effect and avoiding premature breakdown. The current density of power devices has been increased a lot during the past decades own to the advancements of device design and fabrication technologies. However, the edge termination does not change much, leading to increasingly large edge termination area to total chip size ratio. It is necessary to reduce the edge termination length for further reduction of chip cost. In this thesis, novel edge termination structures with deep trenches and sloped field plates are proposed and demonstrated for achieving the ideal planar junction breakdown voltage with record-short edge termination lengths.

First, a novel 600 V-class slop...[ Read more ]

Edge termination is located at the periphery of the active region in power devices for alleviating junction curvature effect and avoiding premature breakdown. The current density of power devices has been increased a lot during the past decades own to the advancements of device design and fabrication technologies. However, the edge termination does not change much, leading to increasingly large edge termination area to total chip size ratio. It is necessary to reduce the edge termination length for further reduction of chip cost. In this thesis, novel edge termination structures with deep trenches and sloped field plates are proposed and demonstrated for achieving the ideal planar junction breakdown voltage with record-short edge termination lengths.

First, a novel 600 V-class sloped field plate enhanced ultra-short edge termination structure is proposed and experimentally demonstrated. The structure features a BCB (BenzoCycloButene) dielectric filled trench and a sloped field plate buried inside the trench. Experimental results show that the ideal planar junction breakdown voltage of 755 V can be achieved by the devices with a trench width larger than 20 μm. Furthermore, the high dV/dt measurement results show that the devices with a trench width larger than 25 μm are capable of handling a high dV/dt of 28.9 kV/μs even at a bus voltage of 750 V. The edge termination length is less than one-fifth of conventional guard ring approaches. Second, a new 1200 V-class trench edge termination structure with double field plates is proposed and experimentally demonstrated. One of the field plates is for modulating electric field distributions along the trench and shifting the breakdown point to the active region for achieving the ideal planar junction breakdown voltage, and the other one is for stopping the depletion region extension at the right side of the trench to achieve high dV/dt performance. The fabricated device has a breakdown voltage of 1422 V, which is verified as the ideal planar junction breakdown voltage. Furthermore, it is with a record-short edge termination length of 78 μm which is less than one-fifth of conventional guard ring approaches. Besides, it can handle a high dV/dt value of 73 kV/μs even at a bus voltage of 1400 V. Finally, optimization of the trench sidewall of the termination structures for low leakage current is carried out experimentally. Mechanisms and sources of the leakage current are analyzed. It was found that the leakage current is highly dependent on the trench sidewall treatment. Rough trench sidewall causes large stress during trench sidewall oxidation, thus resulting in large leakage current. Smooth trench sidewall and a thin layer of thermal oxide should be applied to the trench for achieving a significantly lower leakage current.