A silicon carbide semiconductor device includes a silicon carbide substrate having a first main surface and a second main surface opposite to the first main surface. A gate trench is provided in the first main surface. The gate trench is defined by side surfaces and a bottom surface. The side surfaces penetrate the source region and the body region to reach the drift region. The bottom surface connects to the side surfaces. The gate trench extends in a first direction parallel to the first main surface. The silicon carbide substrate further includes an electric field relaxation region that is the second conductive type, the electric field relaxation region being provided between the bottom surface and the second main surface and extending in the first direction, and a connection region that is the second conductive type, the connection region electrically connecting a contact region to the electric field relaxation region. In a plan view in a direction normal to the first main surface, the gate trench and the electric field relaxation region are disposed on a virtual line that extends in the first direction, and the connection region is in contact with the electric field relaxation region on the virtual line.

To provide a technique capable of improving performance and reliability of a semiconductor device. An n.sup.−-type epitaxial layer (12) is formed on an n-type semiconductor substrate (11), and a p.sup.+-type body region (14), n.sup.+-type current spreading regions (16, 17), and a trench. TR are formed in the n.sup.−-type epitaxial layer (12). A bottom surface B1 of the trench TR is located in the p.sup.+-type body region (14), a side surface S1 of the trench TR is in contact with the n.sup.+-type current spreading region (17), and a side surface S2 of the trench TR is in contact with the n.sup.+-type current spreading region (16). Here, a ratio of silicon is higher than a ratio of carbon in an upper surface T1 of the n.sup.−-type epitaxial layer (12), and the bottom surface B1, the side surface S1, and the side surface 32 of the trench. Furthermore, an angle θ1 at which the upper surface T1 of the n.sup.−-type epitaxial layer (12) is inclined with respect to the side surface S1 is smaller than an angle θ2 at which the upper surface T1 of the n.sup.−-type epitaxial layer (12) is inclined with respect to the side surface S2.

A manufacturing method of a silicon carbide semiconductor device may include: forming a gate insulating film on a silicon carbide substrate; and forming a gate electrode on the gate insulating film. The forming of the gate insulating film may include forming an oxide film on the silicon carbide substrate by thermally oxidizing the silicon carbide substrate under a nitrogen atmosphere.

Provided is a method of manufacturing a semiconductor device capable of suppressing variation in thickness of oxide films among a plurality of SiC wafers. Forming first inorganic films on lower surfaces of a plurality of SiC wafer, and then performing etching of the plurality of SiC wafers so that 750 nm or more of the first inorganic film is left in thickness, and then forming oxide films on upper surfaces of the plurality of SiC wafers by performing thermal oxidation treatment in a state in which a first SiC wafer of the plurality of SiC wafers is placed directly below any one of at least one wafer, including at least one of a dummy wafer and a monitor wafer, and a second SiC wafer of the plurality of SiC wafers is placed directly below a third SiC wafer of the plurality of SiC wafers.

A MOSFET includes a gate electrode and an etching stopper layer formed on a field insulating film of a gate pad region, and an interlayer insulating film formed on the gate electrode and the etching stopper layer. The etching stopper layer is made from a substance having a selectivity of 5.0 or more with respect to etching of the interlayer insulating film and the field insulating film, and is provided at a position farthest from the well contact hole of the under-gate well contact region at least in the gate pad region.

A semiconductor device includes an SiC semiconductor layer which has a first main surface on one side and a second main surface on the other side, a semiconductor element which is formed in the first main surface, a raised portion group which includes a plurality of raised portions formed at intervals from each other at the second main surface and has a first portion in which some of the raised portions among the plurality of raised portions overlap each other in a first direction view as viewed in a first direction which is one of the plane directions of the second main surface, and an electrode which is formed on the second main surface and connected to the raised portion group.

A semiconductor device includes a semiconductor layer of a first conductivity type. A well region that is a second conductivity type well region is formed on a surface layer portion of the semiconductor layer and has a channel region defined therein. A source region that is a first conductivity type source region is formed on a surface layer portion of the well region. A gate insulating film is formed on the semiconductor layer and has a multilayer structure. A gate electrode is opposed to the channel region of the well region where a channel is formed through the gate insulating film.

An insulated-gate semiconductor device, which has trenches arranged in a chip structure, the trenches defining both sidewalls in a first and second sidewall surface facing each other, includes: a first unit cell including a main-electrode region in contact with a first sidewall surface of a first trench, a base region in contact with a bottom surface of the main-electrode region and the first sidewall surface, a drift layer in contact with a bottom surface of the base region and the first sidewall surface, and a gate protection-region in contact with the second sidewall surface and a bottom surface of the first trench; and a second unit cell including an operation suppression region in contact with a first sidewall surface and a second sidewall surface of a second trench, wherein the second unit cell includes the second trench located at one end of an array of the trenches.

A drift layer is formed over a semiconductor substrate which is an SiC substrate. The drift layer includes first to third n-type semiconductor layers and a p-type impurity region. Herein, an impurity concentration of the second n-type semiconductor layer is higher than an impurity concentration of the first n-type semiconductor layer and an impurity concentration of the third n-type semiconductor layer. Also, in plan view, the second semiconductor layer located between the p-type impurity regions adjacent to each other overlaps with at least a part of a gate electrode formed in a trench.

A semiconductor device manufacturing method of embodiments includes: forming a silicon oxide film on a surface of a silicon carbide layer; performing a first heat treatment in an atmosphere containing nitrogen gas at a temperature equal to or more than 1200° C. and equal to or less than 1600° C.; and performing a second heat treatment in an atmosphere containing nitrogen oxide gas at a temperature equal to or more than 750° C. and equal to or less than 1050° C.