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Semiconductor device and method for manufacturing same

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Semiconductor device and method for manufacturing same


In the present invention, the semiconductor device includes an n+-type GaN substrate 1 having a GaN layer that is in ohmic contact with a supporting substrate, a FET having an n−-type GaN drift layer 2 in a first region R1, and an SBD having an anode electrode in a second region R2, the anode electrode being in Schottky contact with the n−-type GaN drift layer 2. The FET and the SBD are arranged in parallel. A drain electrode D of the FET and a cathode electrode C of the SBD are formed on the back of the n+-type GaN substrate 1. There are provided a semiconductor device that includes a bypass protection unit against surge voltage or the like, achieves good withstand voltage characteristics and low on-resistance (low On-state voltage), has a simple structure, and is used for large-current purpose and a method for producing the semiconductor device.
Related Terms: Semiconductor Layer 2 Electrode Semiconductor Device Cathode Anode

Browse recent Sumitomo Electric Industries, Ltd. patents - Osaka-shi, JP
USPTO Applicaton #: #20130313564 - Class: 257 76 (USPTO) - 11/28/13 - Class 257 
Active Solid-state Devices (e.g., Transistors, Solid-state Diodes) > Specified Wide Band Gap (1.5ev) Semiconductor Material Other Than Gaasp Or Gaalas

Inventors: Masaya Okada, Makato Kiyama, Seiji Yaegashi, Ken Nakata

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The Patent Description & Claims data below is from USPTO Patent Application 20130313564, Semiconductor device and method for manufacturing same.

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CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No. 13/531,279, filed Jun. 22, 2012, which is a Divisional of U.S. patent application Ser. No. 13/126,569, filed Apr. 28, 2011, which is a National Stage of International Application No. PCT/JP2010/061679 filed Jul. 9, 2010, and which claims the benefit of Japanese Patent Application No. 2009-178324, filed Jul. 30, 2009, all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a small semiconductor device that is used for high-power switching and can achieve good withstand voltage characteristics and low On-state voltage, and a method for producing the semiconductor device.

BACKGROUND ART

High reverse breakdown voltage and low on-resistance are required for large current switching elements. To achieve the protection against surge voltage or the like, there has been proposed a structure in which a Schottky barrier diode (SBD) is additionally arranged in parallel between a source and a drain of a power field effect transistor (FET) that functions as a switching element (PTL 1). In a GaN-based semiconductor layer formed on a sapphire substrate, the SBD accompanying the power FET (no specific structure is disclosed in PTL 1) includes an anode electrode that is in Schottky contact with an AlGaN layer and a cathode electrode that is in ohmic contact with a GaN layer, and a two-dimensional electron gas is generated at an interface between the GaN layer and the AlGaN layer.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2008-219021

SUMMARY

OF INVENTION Technical Problem

In the above-described device, the on-resistance and withstand voltage characteristics may be improved, but the entire structure of the device becomes complicated. In a large current switching element, there is a tendency to use a vertical element in which a current flows in the thickness direction of a semiconductor layered body. However, in the case of a vertical element, the current-carrying capacity is determined by the circumference of an SBD, which is a protective element. Therefore, it is difficult to increase the current-carrying capacity and a sufficient amount of current cannot be discharged when a surge voltage or the like with a large current is applied.

An object of the present invention is to provide a semiconductor device that includes a bypass protection unit against surge voltage or the like, achieves good withstand voltage characteristics and low on-resistance (low On-state voltage), has a simple structure, and is used for large-current purpose and a method for producing the semiconductor device.

Solution to Problem

The semiconductor device of the present invention includes a first conductivity type substrate, a FET having a first conductivity type drift layer and constituting a switching element in a first region of the substrate, and an SBD having an electrode that is in Schottky contact with a first conductivity type layer located in a second region of the substrate. The FET and the SBD are arranged in parallel, the substrate is a GaN substrate, and a backside electrode of the FET and a backside electrode (the counterpart of a Schottky electrode) of the SBD are formed on the back of the GaN substrate. Herein, the semiconductor device of the present invention is intended to be any of electrical devices such as electronic apparatuses for light electrical appliances, electrical devices for heavy electrical equipment, electrical devices for car electronics, and electrical devices for electric trains or the like.

In the above-described structure, a vertical FET that is a switching element and a vertical SBD are arranged in parallel on the same GaN substrate, and the SBD functions as a protective element of the FET against surge voltage or the like. The GaN substrate has conductivity, and a backside electrode such as a drain electrode of the FET or a cathode electrode of the SBD can be directly formed on the back of the GaN substrate through ohmic contact. The backside electrode may be an integrated body formed at the same timing and may be a common electrode of the drain electrode and the cathode electrode. In this case, a simple structure having a small size is achieved. The channel of the FET may have a metal oxide semiconductor (MOS) structure or a high electron mobility transistor (HEMT) structure that generates a two-dimensional electron gas or the like.

Furthermore, since a GaN-based drift layer or the like is directly formed on the GaN substrate, there is no need to use a buffer layer or the like. By simplifying the structure of the epitaxial layered body without using a buffer layer, the production process is simplified and thus the production time can be shortened and the production yield can be improved. By combining the above-described advantage with the advantages of the mounting of the FET and the SBD onto the same GaN substrate and the formation of a backside electrode in a shared manner, the entire structure can be simplified and a reduction in size can be achieved.

Since a GaN-based semiconductor layer formed on a GaN substrate is a vertical element and has good withstand voltage characteristics and low on-resistance, a large current can be passed. In the case where the channel has a HEMT structure, among wide gap semiconductors, a hetero device is easily formed using GaN (GaN includes many crystals that are epitaxially grown and have different band gaps) compared with SiC or the like. Therefore, a channel such as a two-dimensional electron gas layer can be easily formed. Thus, significantly low on-resistance can be achieved.

The first conductivity type layer of the SBD that can be called a drift layer is herein simply referred to as a first conductivity type layer without adding “drift” to distinguish the first conductivity type layer of the SBD from a first conductivity type drift layer of the FET. In the description of a production method or the like, there may be the case where a common first conductivity type drift layer is formed in the FET and the SBD in a certain production method. In such a case, “drift” is added to both the first conductivity type layers.

The first conductivity type layer of the SBD and the first conductivity type drift layer of the FET may be formed at the same film formation timing or may be formed separately. As described below, even in the case where they are formed at the same film formation timing, an object that prevents or obstructs passing of current may be disposed between the FET and the SBD.

The semiconductor device may include a second conductivity type layer and a first conductivity type cap layer formed on the first conductivity type drift layer in the first region and each having an opening formed therein, wherein a cylindrical channel-forming portion of the FET is located so as to contact an inside surface of the opening, a gate electrode is located so that the gate electrode and an inside surface of the second conductivity type layer in the opening sandwich the channel-forming portion, and the second conductivity type layer extends from the first region to the second region and contacts a Schottky electrode of the SBD. With this extending second conductivity type layer, a guard ring for the Schottky electrode of the SBD can be formed, which can improve the withstand voltage characteristics of the SBD. The second conductivity type layer is not necessarily in ohmic contact with the Schottky electrode of the SBD, but ohmic contact further improves the withstand voltage characteristics. The channel-forming portion is a regrown layer in the case of a HEMT structure, there are the case (HEMT structure) where the channel-forming portion itself includes a channel and the case (MOS structure) where the channel-forming portion itself does not include a channel and is an insulating film for forming a channel of an inversion layer in the second conductivity type layer.

The channel portion may be a regrown layer that includes a first GaN-based semiconductor layer through which carriers transit and a second GaN-based semiconductor layer having a band gap larger than that of the first GaN-based semiconductor layer. Thus, the channel portion can be constituted by a two-dimensional electron gas with high mobility and the on-resistance can be decreased.



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stats Patent Info
Application #
US 20130313564 A1
Publish Date
11/28/2013
Document #
13954618
File Date
07/30/2013
USPTO Class
257 76
Other USPTO Classes
438237
International Class
/
Drawings
13


Semiconductor
Layer 2
Electrode
Semiconductor Device
Cathode
Anode


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