CN-115206803-B - Method for manufacturing a switching device

Abstract

A method for manufacturing a switching device (10) includes forming a trench (22) at a top surface (12 a) of a semiconductor substrate (12), forming a gate insulating film (24) for covering an inner surface of the trench, forming a gate electrode (26) inside the trench to position the top surface of the gate electrode below the top surface of the semiconductor substrate, forming an oxide film (40) by oxidizing the top surface of the gate electrode, forming an interlayer insulating film (28) at the top surface of the oxide film by vapor phase growth so that the top surface of the interlayer insulating film is below the top surface of the semiconductor substrate, and forming an upper electrode (70) in contact with the semiconductor substrate at the top surface of the semiconductor substrate and at a side surface of the trench above the top surface of the interlayer insulating film.

Inventors

• Tome Eiji
• IWAHASHI YOHEI

Assignees

• 株式会社电装
• 丰田自动车株式会社
• 未来瞻科技株式会社

Dates

Publication Date

20260505

Application Date

20220411

Priority Date

20210414

Claims (2)

1. 1. A method for manufacturing a switching device, the method comprising: Forming a trench at a top surface of a semiconductor substrate; Forming a gate insulating film for covering an inner surface of the trench; forming a gate electrode inside the trench to position a top surface of the gate electrode below the top surface of the semiconductor substrate; forming an oxide film by oxidizing the top surface of the gate electrode; Forming an interlayer insulating film by vapor phase growth at a top surface of the oxide film so that the top surface of the interlayer insulating film is located below the top surface of the semiconductor substrate, and An upper electrode in contact with the semiconductor substrate is formed at the top surface of the semiconductor substrate and at a side surface of the trench above the top surface of the interlayer insulating film, Wherein the semiconductor substrate is made of silicon carbide, Wherein the semiconductor substrate comprises: a drift region of n-type conductivity, A body region of p-type conductivity disposed over the drift region, and An n-type conductivity source region disposed over the body region, Wherein the trench is formed to penetrate the source region and the body region and reach the drift region during the formation of the trench, and Wherein, during the formation of the oxide film, the top surface of the gate electrode is oxidized to satisfy a mathematical relationship of L > 2.7xA, Where L represents a distance between the oxide film and the body region along a side surface of the trench, and a represents a diffusion length of an oxide substance into the gate insulating film when the gate electrode is oxidized.
2. 2. The method according to claim 1, Wherein, during the formation of the trench, a boundary portion between the side surface of the trench and the top surface of the semiconductor substrate is formed to be curved.

Description

Method for manufacturing a switching device Technical Field The present disclosure relates to a method for manufacturing a switching device. Background JP 2005-2098057825 discloses a switching device comprising a semiconductor substrate, a trench, a gate insulating film, a gate electrode, and an interlayer insulating film. The trench is disposed at a top surface of the semiconductor substrate. The gate insulating film covers the inner surface of the trench. The interlayer insulating film covers the top surface of the gate electrode. In a method for manufacturing a switching device, a gate electrode is formed such that a top surface of the gate electrode is located below a top surface of a semiconductor substrate after a gate insulating film is formed at an inner surface of a trench. Subsequently, an insulating layer is deposited inside the trench and at the top surface of the semiconductor substrate using Chemical Vapor Deposition (CVD) techniques. Subsequently, the insulating layer is etched to form an interlayer insulating film embedded inside the trench. Disclosure of Invention In the manufacturing method described in JP 2005-209808 209807A, it is necessary to form a thicker interlayer insulating film to ensure the withstand voltage of the interlayer insulating film. An object of the present disclosure is to provide a technique of ensuring withstand voltage of an insulating film while reducing the thickness of the insulating film covering a gate electrode. According to one aspect of the present disclosure, a method for manufacturing a switching device includes forming a trench at a top surface of a semiconductor substrate, forming a gate insulating film for covering an inner surface of the trench, forming a gate electrode inside the trench to position the top surface of the gate electrode below the top surface of the semiconductor substrate, forming an oxide film by oxidizing the top surface of the gate electrode, forming an interlayer insulating film at the top surface of the oxide film by vapor phase growth to position the top surface of the interlayer insulating film below the top surface of the semiconductor substrate, and forming an upper electrode in contact with the semiconductor substrate at the top surface of the semiconductor substrate and a trench side surface located above the top surface of the interlayer insulating film. In the process of forming the interlayer insulating film at the top surface of the oxide film by vapor phase growth, the top surface of the interlayer insulating film may be located below the top surface of the semiconductor substrate by adjusting the time of vapor phase growth. In this process, an interlayer insulating film extending to an upper side of a top surface of a semiconductor substrate is formed by vapor phase growth, and by etching the interlayer insulating film, the top surface of the interlayer insulating film may be located below the top surface of the semiconductor substrate. The vapor phase growth described in this disclosure may also be referred to as vapor phase epitaxial growth or vapor phase deposition. In the above manufacturing method, the oxide film is formed by oxidizing the gate electrode. As a result, the top surface of the gate electrode is covered with the oxide film. Subsequently, an interlayer insulating film is grown at the top surface of the oxide film by vapor phase growth to form a double-layer insulating film for covering the gate electrode. The oxide film formed by oxidizing the gate electrode has a lower impurity content such as hydrogen content and higher compactness than an interlayer insulating film formed by vapor phase growth. Therefore, the oxide film has a high withstand voltage. Since withstand voltage is ensured by the oxide film, the film thickness of the interlayer insulating film formed by the subsequent vapor deposition can be reduced. In the above-described manufacturing method, the film thickness of the entire insulating film can be reduced while ensuring the withstand voltage of the insulating film for covering the gate electrode. Therefore, the contact area between the upper electrode and the trench side surface of the upper portion of the interlayer insulating film can be enlarged. Drawings Other objects, features and advantages of the present disclosure will become more apparent from the following detailed description, which proceeds with reference to the accompanying drawings. In the drawings: fig. 1 is a perspective view of a switching device according to a first embodiment; FIG. 2 is a cross-sectional view taken along plane II in FIG. 1; FIG. 3 is a cross-sectional view taken along plane III in FIG. 1; fig. 4 shows a manufacturing process of a switching device according to a first embodiment; fig. 5 shows a manufacturing process of the switching device according to the first embodiment; fig. 6 shows a manufacturing process of the switching device according to the first embodiment; fig. 7 shows a manufacturing proce