# US 12,191,359 B2 · Method of manufacturing silicon carbide semiconductor device and silicon carbide semiconductor device

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- Number: US 12,191,359 B2
- Document ID: US12191359B2
- Status: Granted
- Kind: B2
- Application number: 17/829,065
- Filed: 2022-05-31
- Published: 2023-01-19
- Granted: 2025-01-07
- Earliest claimed: 2021-07-15
- Assignees: Fuji Electric Co., Ltd.
- Applicants: Fuji Electric Co., Ltd.
- Inventors: Yu Kurioka
- Web page: https://patentgrep.com/patent/US12191359B2

## CPC

- H10D 62/60: Impurity distributions or concentrations
- H10D 12/031: {of IGBTs}
- H10D 30/0297: {using recessing of the gate electrodes, e.g. to form trench gate electrodes}
- H10D 30/668: {having trench gate electrodes, e.g. UMOS transistors}
- H10D 62/8325: {Silicon carbide}
- H10D 64/01366: {the semiconductor being silicon carbide}
- H10D 64/693: {the insulator comprising nitrogen, e.g. nitrides, oxynitrides or nitrogen-doped materials}
- H10D 62/107: {Buried supplementary regions, e.g. buried guard rings (multi-RESURF H10D62/111)}
- H10D 62/157: {Impurity concentrations or distributions}
- H10D 62/393: {Body regions of DMOS transistors or IGBTs (cell layout of DMOS H10D62/127)}
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES

## Abstract

A process of forming a gate insulating film in a silicon carbide semiconductor device. The process includes performing a first stage of a nitriding heat treatment by a gas containing oxygen and nitrogen, followed by depositing an oxide film, and then performing a second stage of the nitriding heat treatment by a gas containing nitric oxide and nitrogen. The amount of nitrogen at the treatment starting point of the first stage of the nitriding heat treatment is greater than the amount of nitrogen at the treatment starting point of the second stage of the nitriding heat treatment. The amount of nitrogen at the treatment ending point of the second stage of the nitriding heat treatment is greater than the amount of nitrogen at the treatment ending point of the first stage of the nitriding heat treatment.

## Claims

### Claim 1

A method of manufacturing a silicon carbide semiconductor device, the method comprising:
preparing a silicon carbide semiconductor substrate of a first conductivity type, the silicon carbide semiconductor substrate having a first surface and a second surface that are opposite to each other;
forming a first semiconductor layer of the first conductivity type on the first surface of the silicon carbide semiconductor substrate, the first semiconductor layer having an impurity concentration that is lower than an impurity concentration of the silicon carbide semiconductor substrate, the first semiconductor layer having a first surface and a second surface that are opposite to each other, the second surface of the first semiconductor layer facing the silicon carbide semiconductor substrate;
forming a second semiconductor layer of a second conductivity type on the first surface of the first semiconductor layer, the second semiconductor layer having a first surface and a second surface that are opposite to each other, the second surface of the second semiconductor layer facing the silicon carbide semiconductor substrate;
selectively forming a plurality of first semiconductor regions of the first conductivity type in the second semiconductor layer, at the first surface of the second semiconductor layer;
forming a plurality of trenches that penetrate through the first semiconductor regions and the second semiconductor layer, and reach the first semiconductor layer;
forming a gate insulating film in the trenches, along sidewalls and bottoms of the trenches;
forming a plurality of gate electrodes on the gate insulating film in the trenches;
forming a first electrode on surfaces of the first semiconductor regions and the first surface of the second semiconductor layer; and
forming a second electrode on the second surface of the silicon carbide semiconductor substrate, wherein
forming the gate insulating film includes forming the gate insulating film using a nitriding heat treatment that has a first stage and a second stage, by
performing the first stage of the nitriding heat treatment by a first gas containing oxygen and nitrogen,
depositing an oxide film after performing the first stage of the nitriding heat treatment, and
performing the second stage of the nitriding heat treatment by a second gas containing nitric oxide and nitrogen, after depositing the oxide film;
an amount of the nitrogen at a treatment starting point of the first stage of the nitriding heat treatment is greater than an amount of the nitrogen at a treatment starting point of the second stage of the nitriding heat treatment; and
an amount of the nitrogen at a treatment ending point of the second stage of the nitriding heat treatment is greater than an amount of the nitrogen at a treatment ending point of the first stage of the nitriding heat treatment.

### Claim 2 (depends on 1)

The method according to claim 1, wherein
the first gas contains 1% to 7% oxygen and 93% to 99% nitrogen.

### Claim 3 (depends on 1)

The method according to claim 1, wherein
the second gas contains 10% nitric oxide and 90% nitrogen at the treatment starting point of the second stage of the nitriding heat treatment, and
a concentration of the nitric oxide gradually decreases until the second gas is 100% nitrogen at the treatment ending point of the second stage of the nitriding heat treatment.

### Claim 4

A silicon carbide semiconductor device, comprising:
a silicon carbide semiconductor substrate of a first conductivity type, the silicon carbide semiconductor substrate having a first surface and a second surface that are opposite to each other;
a first semiconductor layer of the first conductivity type, provided on the first surface of the silicon carbide semiconductor substrate, the first semiconductor layer having an impurity concentration that is lower than an impurity concentration of the silicon carbide semiconductor substrate, the first semiconductor layer having a first surface and a second surface that are opposite to each other, the second surface of the first semiconductor layer facing the silicon carbide semiconductor substrate;
a second semiconductor layer of a second conductivity type, provided on the first surface of the first semiconductor layer, the second semiconductor layer having a first surface and a second surface that are opposite to each other, the second surface of the second semiconductor layer facing the silicon carbide semiconductor substrate;
a plurality of first semiconductor regions of the first conductivity type, selectively provided in the second semiconductor layer, at the first surface of the second semiconductor layer;
a plurality of trenches that penetrate through the first semiconductor regions and the second semiconductor layer, and reach the first semiconductor layer;
a gate insulating film provided in the trenches, along bottoms and sidewalls of the trenches;
a plurality of gate electrodes provided on the gate insulating film in the trenches;
a first electrode provided on surfaces of the first semiconductor regions and the first surface of the second semiconductor layer; and
a second electrode provided on the second surface of silicon carbide semiconductor substrate, wherein
the silicon carbide semiconductor device has a peak nitrogen concentration at interfaces between the gate insulating film and the first semiconductor regions and between the gate insulating film and the second semiconductor layer, in a range of 1×1020 atoms/cm3 to 1×1021 atoms/cm3.

### Claim 5 (depends on 4)

The silicon carbide semiconductor device according to claim 4, wherein
the gate insulating film contains nitrogen at a concentration of at least 5×1019 atoms/cm3.