Semiconductor switch devices having a region with three distinct zones and their manufacture

Abstract

In a semiconductor switch device such as an NPN transistor (T) or a power switching diode (D), a multiple-zone first region ( ) of one conductivity type forms a switchable p-n junction ( ) with a second region ( ) of opposite conductivity type. In accordance with the invention, this first region ( ) includes three distinct zones, namely a low-doped zone ( ), a high-doped zone ( ), and an intermediate additional zone ( ). The low-doped zone ( ) is provided by a semiconductor body portion ( ) having a substantially uniform p-type doping concentration (P−) and forms the p-n junction ( ) with the second region ( ). The distinct additional zone ( ) is present between the low-doped zone ( ) and the high-doped zone ( ). The high-doped zone ( ) which may form a contact zone has a doping concentration (P++) which is higher than that of the low-doped zone ( ) and which decreases towards the low-doped zone ( ). The distinct additional zone ( ) has an additional doping concentration (P+) which is lower than the doping concentration (P++) of the high-doped zone ( ) and which decreases towards the low-doped zone ( ). This triple-zone formation for the first region ( ) permits an improvement in switching behaviour, e.g. in terms of fall-time and energy dissipation during turn-off of the device (T, D). A very low doping (P−) can be used for low-doped zone ( ) so that, in the off-state of the device (T, D), this zone ( ) and also the additional zone ( ) can be fully depleted. The additional zone ( ) having its additional doping concentration provides a path for extracting residual charge carriers from the low-doped zone ( ) when the device (T, D) is being switched off.