High-frequency semiconductor device with protection device

Abstract

A semiconductor device with a semiconductor body (3) including a surface region (5) of a first conductivity type which adjoins a surface (4) and in which a field effect transistor (1) with insulated gate (6) is provided. The field effect transistor (1) has source and drain regions (7, 8, respectively) of the second, opposed conductivity type situated in the surface region (5), and a channel region (9) of the first conductivity type situated between the source and drain regions. A metal gate electrode (6) separated from the channel region (9) by an insulating layer (10) is provided over the channel region (9) and is provided with a protection device (2) against excessive voltages applied to the gate electrode (6). According to the invention, the surface (4) of the semiconductor body (3) is provided with a locally recessed field oxide (15), and the protection device (2) includes a lateral bipolar transistor with collector and emitter regions (16, 17, respectively) of the second conductivity type which are more strongly doped than the surface region (5) and which adjoin the surface (4) and the field oxide (15), and with a base region (18) of the first conductivity type which is more strongly doped than the surface region (5) and which lies below the field oxide (15), the collector region (16) being electrically connected to the gate electrode (6) and the emitter region (17) being electrically connected to the source region (7). It is achieved thereby that the field effect transistor (1) can switch high frequencies much more quickly.