A novel trench IGBT with a deep P+ layer beneath the trench emitter

The trench insulated gate bipolar transistor (TIGBT) suffers from breakdown voltage degradation due to the electric field crowding at the corner of the trench gate in the forward blocking state. We propose a new TIGBT structure that has a deep p+ layer beneath the trench emitter to distribute the concentrated electric field. The deep p+ layer of the structure is formed by ion implantation at the bottom of the trench after a partial etching of the p-base region. The proposed structure improves the breakdown voltage compared to conventional TIGBTs without changing the threshold voltage and with quite a small change of on-state voltage drop. The distribution of the electric field is also changed by its design parameters. When the positions of the trench gate corner and the deep p+ layer are nearer, the breakdown voltage is higher. The distribution effect operates when the doping level of the deep p+ layer exceeds the appropriate value to prevent punchthrough between the metal electrode and the n-drift region. This structure can be applied easily to various TIGBTs with simple-process additions.