Varied trench depth for thyristor isolation

Abstract

A semiconductor device is formed having a thyristor and trench arranged to electrically insulate an emitter region of the thyristor from another circuit structure. In one example embodiment of the present invention, a trench having a bottom portion with two different trench depths is etched in the substrate. A thyristor is formed having a control port in a trench and having an emitter region adjacent to the trench and below an upper surface of the substrate. A deeper portion of the trench electrically insulates the emitter region from the other circuit structure. The control port is capacitively coupled to the thyristor and to the other circuit structure (e.g., in response to at least one edge of a voltage pulse applied thereto). In one implementation, the trench further includes an emitter-access connector extending from the emitter region to an upper surface of the substrate. These approaches are also useful in high-density circuit applications, such as memory applications, where the semiconductor device is formed in close proximity with other circuitry, such as with other thyristors. In addition, the isolation approach is useful for applications where a cathode-down thyristor is used, such as when it is desirable to form the thyristor control port near a bottom portion of the thyristor. Moreover, the approaches discussed herein are useful for electrically isolating various portions of the semiconductor device using a relatively limited number of etching steps.