New-Tech Magazine Europe | Dec 2015 Digital edition

4th Generation Field Stop (FS) IGBT with High Performance and Enhanced Latch Up Immunity

Kyuhyun Lee, Sungmin Yang, Sekyeong Lee, Jiyong Lim and Youngchul Choi - Fairchild Semiconductor

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hanks to their low conduction and switching

by a very fine cell pitch design and hole carrier injection was restricted by a new buffer structure, achieving remarkably better trade off performance as well as strong latch up immunity. To realize the narrow mesa or high-density cathode design of the trench IGBT, a self-aligned contact process was applied. This proved to be very effective in optimizing the critical dimension of active cell design for the enhanced on-state performance, as well as to maximize the latch up current capability. In addition, multiple buffer layers were adopted for the anode side of the IGBT in order to not only effectively control the minority carrier injection during the on state, but also to completely block the electric field during the off state [5]. The vertical structures of the proposed IGBT are illustrated in Fig.1 for the cathode and anode side. Figs.1(a) and 1(c) showthat thehighdensity cell design with submicron narrow mesa width is successfully realized by employing a self- aligned contact process, without any photo misalignment. The higher density active pattern shown in this figure is beneficial for extremely enhanced electron injection from the cathode

side and, as a result, the higher electron current density. The new buffer structure with multiple layers, as shown in Fig.1(b), is very helpful for the ideal carrier distribution during IGBT operation. Generally, a single buffer layer with 1~5e15cm–3 is used for both hole injection control and electric field blocking efficiently. In this experiment, a thin buffer layer with a much higher doping concentration was additionally embedded for better trade-off performance. In other words, the higher doping concentration in the double buffer layer is even more effective for the electric field blocking and hole carrier injection control by the first FS layer (L1). The lower doping concentration for the second buffer layer (L2) is preferred for forming a lightly doped p-type collector for high-speed switching performance without any lifetime killing process. In addition, the device switching waveform can be effectively improved by varying the doping concentration and thickness of the double buffer layers, due to proper carrier distribution control during switching ON/OFF operation.

energy loss, IGBTs arewidely used in high power applications such as power supplies, motor driving inverters, electrical vehicles, etc. The requirement for more state of the art power devices for power applications has triggered efforts around novel silicon based development, as well as wide band gap material development, to achieve characteristics that stretchthe ideal limitof silicon. The theoretical silicon limit for IGBTs was investigated by A. Nakagawa, [1] and in order to realize optimal silicon characteristics, various injection methods to enhance IGBT structures were proposed, such as CSTBT, IEGT, and narrow mesa IGBT [2-4]. In order to push IGBT silicon to the limit, extremely high electron injection efficiency from the MOS gate is required, while the hole carrier injection should be restricted to the level of contribution only for the conductivity modulation. [1] For Fairchild’s 4th generation FS IGBTs, electron injection was enhanced

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