Mitsubishi Electric Corporation

Koji Sadamatsu

Shiro Hino

Hideyuki Hatta

Yuichi Nagahisa

Kotaro Kawahara

Yasuhiro Yoshiura

Eiko Otsuki

Kohei Ebihara

Katsumi Nakamura

Ze Chen

Shingo Tomohisa

The fabrication method for a silicon carbide semiconductor device according to this disclosure includes a step of forming a dielectric film over part of a silicon carbide layer, a step of forming an ohmic electrode adjoining the dielectric film on the silicon carbide layer, a step of removing an oxidized layer on the ohmic electrode, a step of forming a mask with its opening on the side opposite to the side where the ohmic electrode is adjoining the dielectric film on the ohmic electrode having the oxidized layer removed and on the dielectric film, and a step of wet etching of a film to be etched with hydrofluoric acid with the mask formed. With the fabrication method for a silicon carbide semiconductor device described in this disclosure, it is possible to fabricate a silicon carbide semiconductor device with reduced failure.

Method for fabricating silicon carbide semiconductor device and power conversion device using the silicon carbide semiconductor device

An object of the present invention is to suppress the passage of bipolar current in a silicon carbide semiconductor device by reducing a voltage applied to a terminal well region during reflux operations. An SiC-MOSFET includes a plurality of first well regions, a second well region, a third well region in a surface layer of a drift layer, the first, second, and third well regions being of a second conductivity type. The third well region is provided on the side of the second well region opposite to the first well regions. A unit cell that includes the first well regions includes a unipolar diode. The SiC-MOSFET includes a source electrode connected to the unipolar diode and the ohmic electrode and not having ohmic connection with the second well region and the third well region.

Silicon carbide semiconductor device and power converter

In an SiC-MOSFET with a built-in Schottky diode, a bipolar current may be passed in a second well region formed at a terminal part to reduce the breakdown voltage of the terminal part. In the SiC-MOSFET with the built-in Schottky diode, a source electrode forming non-ohmic connection such as Schottky connection with the second well region is provided on the second well region formed below a gate pad in the terminal part. By the absence of ohmic connection between the second well region and the source electrode, reduction in breakdown voltage is suppressed at the terminal part.

In an SiC-MOSFET with a built-in Schottky diode, a bipolar current may be passed in a second well region formed at a terminal part to reduce a breakdown voltage. In the SiC-MOSFET with the built-in Schottky diode, a conductive layer in Schottky connection with the second well region is provided on the second well region in the terminal part, and the conductive layer is electrically connected with a source electrode of the MOSFET. A conductive layer contact hole is provided for connecting only the conductive layer and the source electrode.

Silicon carbide semiconductor device having a conductive layer formed above a bottom surface of a well region so as not to be in ohmic connection with the well region and power converter including the same

In SiC-MOSFETs including Schottky diodes, passage of a bipolar current to a second well region formed in a terminal portion sometimes reduces a breakdown voltage. In a SiC-MOSFET including Schottky diodes according to the present invention, the second well region formed in the terminal portion has a non-ohmic connection to a source electrode, and a field limiting layer lower in impurity concentration than the second well region is formed in a surface layer area of the second well region which is a region facing a gate electrode through a gate insulating film.

In SiC-MOSFETs including Schottky diodes, passage of a bipolar current to a well region in a terminal region cannot be sufficiently reduced, which may reduce the reliability of elements. A SiC-MOSFET including Schottky diodes includes a gate electrode formed, through a second insulating film thicker than a gate insulating film in an active region, on a separation region between a first well region in the active region that is the closest to the terminal region and a second well region in the terminal region, wherein the second well region has a non-ohmic connection to a source electrode. Thus, a decrease in the reliability of elements is prevented.

A technique is provided for effectively suppressing a forward voltage shift due to occurrence of a stacking fault. A semiconductor device relating to the present technique includes a first well region of a second conductivity type, a second well region of the second conductivity type which is so provided as to sandwich the whole of a plurality of first well regions in a plan view and has an area larger than that of each of the first well regions, a third well region of the second conductivity type which is so provided as to sandwich the second well region in a plan view and has an area larger than that of the second well region, and a dividing region of a first conductivity type provided between the second well region and the third well region, having an upper surface which is in contact with an insulator.

Semiconductor device

In SiC-MOSFETs including Schottky diodes, passage of a bipolar current to a well region in an edge portion of an active region cannot be sufficiently reduced, which may reduce the reliability of elements. In a SiC-MOSFET including Schottky diodes, the Schottky diodes formed in a terminal region are made higher in density in a plane direction than those formed in the active region or intervals between the Schottky diodes in the plane direction are shortened, without an ohmic connection between the well and the source in the terminal region.

A drift layer is made of a wide bandgap semiconductor. First well regions are formed on the drift layer. A source region is formed on each of the first well regions. A gate insulating film is formed on the first well regions. A first electrode is in contact with the source regions, and has diode characteristics allowing unipolar conduction to the drift layer between the first well regions. A second well region is formed on the drift layer. A second electrode is in contact with the second well region, and separated from a gate electrode and the first electrode.

Semiconductor device and semiconductor device manufacturing method

A semiconductor device capable of increasing a value of current that flows through the whole chip until a p-n diode in a unit cell close to a termination operates and reducing a size of the chip and a cost of the chip resulting from the reduced size, and including a second well region formed on both sides, as seen in plan view, of the entirety of a plurality of first well regions, a second ohmic electrode located over the second well region, a third separation region of a first conductivity type that is positioned closer to the first well regions than the second ohmic electrode in the second well region and that is formed to penetrate the second well region from a surface layer of the second well region in a depth direction, and a second Schottky electrode located on the third separation region.

An n-type semiconductor substrate () includes an active region and a terminal region disposed outside the active region. A p-type anode layer () is formed in a portion of an upper surface of the n-type semiconductor substrate () in the active region. A plurality of p-type guard ring layers () are formed in a portion of the upper surface of the n-type semiconductor substrate () in the terminal region. An n-type cathode layer () is formed in a lower surface of the n-type semiconductor substrate (). An anode electrode () is connected to the p-type anode layer (). A metallic cathode electrode () is connected to the n-type cathode layer (). A recess () is formed by trenching the n-type cathode layer () in the terminal region. The cathode electrode () is also formed in the recess ().

A method of testing a semiconductor device having a substrate in and on which a cell structure and a termination structure are formed, the cell structure having a main current flowing therethrough, the termination structure surrounding the cell structure, the method includes a first test step of testing dielectric strength of the semiconductor device, a charge removal step of, after the first test step, removing charge from a top surface layer of the termination structure, the top surface layer being located on the substrate and formed of an insulating film or a semi-insulating film, and a second test step of, after the charge removal step, testing dielectric strength of the semiconductor device.

Method of testing semiconductor device

A semiconductor device includes a semiconductor substrate having one main surface in which an anode of a diode is formed. At a distance from the outer periphery of the anode, a guard ring is formed to surround the anode. The anode includes a p-type diffusion region, a p-type region, and an anode electrode. The p-type region is formed as a region of relatively high electrical resistance sandwiched between the p-type diffusion regions.

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Tokyo, Japan

Koji Sadamatsu