Semiconductor device and method of forming the same

Abstract

A semiconductor device and a method of forming thereof has a base body has a field stopping layer, a drift layer, a current spreading layer, a body region, and a source contact region layered in the order on a substrate. A trench that reaches the field stopping layer or the substrate is provided. A gate electrode is provided in the upper half section in the trench. In a section deeper than the position of the gate electrode in the trench, an insulator is buried that has a normal value of insulation breakdown electric field strength equal to or greater than the value of the insulation breakdown electric field strength of the semiconductor material of the base body. This inhibits short circuit between a gate and a drain due to insulation breakdown of an insulator film at the bottom of the trench to realize a high breakdown voltage in a semiconductor device using a semiconductor material such as SiC.

Description

BACKGROUND [0001] A high breakdown voltage power device fabricated with SiC has the potential of significantly reducing the on-state-resistance. For example, according to the press release from Rohm Co., Ltd., an SiC MOSFET (a Field Effect Transistor with a Metal-Oxide-Semiconductor structure) to be mass-produced by Rohm Co., Ltd. is to have its on-state-resistance becoming a half the on-state-resistance of an Si IGBT (Insulated Gate Bipolar Transistor) having the same breakdown voltage class. See An SiC power MOSFET has been developed with a less power loss of 1 / 40 of conventional one!” at http: / / www.rohm.co.jp / news / sicpower-j.html, circa Jun. 30, 2005. [0002] A high breakdown voltage MOSFET of SiC as a principal material thereof is expected to be shipped from each semiconductor device maker within the next one or two years. In the future, most of IGBTs of Si as inverter parts are expected to be substituted by IGBTs of SiC, while reducing the cost and improving their electrical cha...

AI Technical Summary

Problems solved by technology

Mass producing SiC devices, however, can be problematic in that an SiC wafer is very expensive in comparison with an Si wafer.

Such increase in the JFET resistance is unfavorable because it increases the loss in the on-state.

However, an electric field with high strength applied to the insulator for a long time deteriorates the insulator gradually over time until it eventually breaks down.

Therefore, should the source and the drain be short-circuited, only the device is burnt out, or only a few other power devices operating in cooperation with the device or only passive elements are burnt out.

Therefore, when a high voltage on the drain side is applied to the gate by a short circuit between the gate and the drain, the control circuit on the gate side become damaged.

Then, the destructive high voltage is transmitted from the control circuit to the neighboring low voltage circuits from one to another to possibly causing fatal damages of the entire system using the power device.

This, however, is not only economically undesirable but also decreases performance, such as by increasing the switching loss, reducing the switching speed, and distorting the control signal waveform due to charge and discharge of the Zener diode carried out at each switching.

Thus, it is not desirable to incorporate such a design where the breakdown voltage of the device is determined by the breakdown voltage between the gate and the drain.

However, a vertical trench MISFET using SiC, otherwise having the same structure as the Si device as shown in FIG. 16 causes the following problem.

This, like in the case in the DMOSFET structure, imposes limitation on reducing the cell pitch.

Therefore, as was explained above, in an SiC device using an expensive SiC wafer, despite the importance of cell pitch reduction, the main effect of reducing the cell pitch, which is obtained by providing the trench MOSFET type structure, is lost.

Furthermore, the structure disclosed in JP-A-10-308512 has a drawback in that it prevents realization of a high breakdown voltage expected from the high value of the insulation breakdown electric field strength of SiC.

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