JP2012049204A - Nitride semiconductor device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor device capable of preventing current collapse and capable of high-output operation.SOLUTION: A silicon film 15 is formed on the surface of a III-V group nitride semiconductor layer 14 between a Schottky-contact electrode 16 (a gate electrode 16) and ohmic-contact electrodes (a source electrode 17a and a drain electrode 17b) by an electron cyclotron resonance (ECR) sputtering method. The silicon film 15 may be formed between the Schottky-contact electrode 16 and the III-V group nitride semiconductor layer 14.

Description

  The present invention relates to a nitride semiconductor device using a nitride semiconductor as an active layer and a method for manufacturing the same, and in particular, the surface of a high electron mobility transistor (HEMT) or a field effect transistor (FET). The present invention relates to a nitride semiconductor device having a protective film and a method for manufacturing the same.

  FIG. 4 shows a cross-sectional view of a conventional semiconductor device made of a group III-V nitride semiconductor. The semiconductor device shown in FIG. 4 has a so-called HEMT structure. On a substrate 101 made of a sapphire substrate, a buffer layer 102 made of gallium nitride (GaN), a channel layer 103 made of gallium nitride, and non-doped aluminum gallium nitride. The barrier layer 104 is sequentially stacked, and a two-dimensional electron gas layer having a very high electron mobility is formed in the vicinity of the heterojunction interface including the channel layer 103 and the barrier layer 104. Yes. In the semiconductor device having such a structure, the carrier (two-dimensional electron) flowing between the source electrode 107a and the drain electrode 107b is controlled by controlling the voltage applied to the gate electrode 106 (control electrode) in Schottky contact with the barrier layer 104. Gas).

For this type of semiconductor device, various structures as disclosed in Patent Document 1, for example, have been proposed in addition to the above structure.

Japanese Patent Laid-Open No. 10-335637

  In a conventional semiconductor device in which a gate electrode is formed on a nitride semiconductor layer such as an aluminum gallium nitride (AlGaN) layer or a gallium nitride (GaN) layer, the surface trapped by electrons trapped in the surface level of the nitride semiconductor layer When the potential fluctuates, there is a problem that a collapse phenomenon (hereinafter referred to as current collapse) occurs in which the drain current decreases under a quasi-static condition (pulse measurement, high-frequency operation) when a high drain voltage is applied. An object of the present invention is to provide a nitride semiconductor device capable of solving such problems and capable of high output operation.

  In order to achieve the above object, the invention according to claim 1 of the present application includes a first electrode in Schottky contact with the nitride semiconductor layer on the group III-V nitride semiconductor layer, and an ohmic contact with the nitride semiconductor layer. And a silicon film between the first electrode and the second electrode, or between the first electrode and the nitride semiconductor layer. It is characterized by having.

  The invention according to claim 2 of the present application includes a group III-V nitride semiconductor layer stacked on a substrate via a buffer layer, a silicon film stacked on the nitride semiconductor layer, and the silicon film, or A gate electrode formed on the nitride semiconductor layer; and a source electrode and a drain electrode formed on the nitride semiconductor layer with the gate electrode interposed therebetween, at least between the source electrode and the drain electrode. The surface of the nitride semiconductor layer is covered with the silicon film.

  The invention according to claim 3 includes a step of forming a first electrode in Schottky contact with the nitride semiconductor layer on the group III-V nitride semiconductor layer, and a second in ohmic contact with the nitride semiconductor layer. And forming a silicon film between the first electrode and the second electrode, or between the first electrode and the nitride semiconductor layer. In the method of manufacturing a nitride semiconductor device including a forming step, the silicon film is formed by an ECR sputtering method.

  The invention according to claim 4 includes a step of stacking a group III-V nitride semiconductor layer on a substrate via a buffer layer, a step of stacking a silicon film on the nitride semiconductor layer, and the silicon Forming a gate electrode on the film or on the nitride semiconductor layer, and forming a source electrode and a drain electrode on the nitride semiconductor layer with the gate electrode interposed therebetween, and at least the source electrode In the method of manufacturing a nitride semiconductor device in which the surface of the nitride semiconductor layer between the electrode and the drain electrode is covered with the silicon film, the silicon film is formed by ECR sputtering.

  The nitride semiconductor device of the present invention is a nitride semiconductor device capable of suppressing current collapse and capable of high output operation by covering the surface of a group III-V nitride semiconductor layer that causes generation of current collapse with a silicon film. It becomes possible to provide.

  The method for manufacturing a nitride semiconductor device according to the present invention is a nitriding method in which a silicon film is formed by an ECR sputtering method used in a normal manufacturing process of a semiconductor device, and is simple, has good controllability, and suppresses current collapse. It becomes possible to manufacture a physical semiconductor device.

It is a figure explaining the Example of this invention. It is a characteristic view of the nitride semiconductor device of this invention. It is a characteristic view of the conventional nitride semiconductor device. It is a figure explaining the conventional nitride semiconductor device.

  Hereinafter, the nitride semiconductor device of the present invention will be described in detail.

  First, the nitride semiconductor device of the present invention will be described in detail by taking a HEMT as a group III-V nitride semiconductor device as an example. FIG. 1 shows a sectional view of a HEMT which is a group III-V nitride semiconductor device according to an embodiment of the present invention. As shown in FIG. 1, a buffer layer 12 made of gallium nitride (GaN) having a thickness of about 30 nm and a non-doped gallium nitride (GaN) having a thickness of 2.5 μm are formed on a substrate 11 made of sapphire, for example, by MOCVD. A barrier layer 14 made of non-doped aluminum gallium nitride (AlGaN) having a thickness of 25 nm, which forms a two-dimensional electron gas layer serving as a carrier, is laminated on the interface between the channel layer 13 and the channel layer 13. On the barrier layer 14, a source electrode 17a and a drain electrode 17b made of titanium (Ti) / aluminum (Al) / titanium (Ti) / gold (Au) are formed.

  In the present invention, an ECR sputtering method is further used to form a silicon (Si) film 15 having a thickness of 30 nm so as to cover at least the barrier layer 14 exposed between the source electrode 17a and the drain electrode 17b. A gate electrode 16 made of nickel (Ni) / gold (Au) is formed on the silicon film 15.

  FIG. 2 is a characteristic diagram of the nitride semiconductor device of the present invention shown in FIG. 1 and shows drain current (Ids) -drain voltage (Vds) characteristics by DC measurement and pulse measurement. For comparison, FIG. 3 shows a characteristic diagram of the conventional nitride semiconductor device shown in FIG. As shown in FIGS. 2 and 3, the drain sweep voltage is 0 to 20 V, and the gate voltage is in the range of −7 V to 0 V in the nitride semiconductor device of the present invention shown in FIG. In a conventional nitride semiconductor device, measurement is performed by applying each voltage in a 1V step within a range of -6V to 0V. In the pulse measurement, a pulse was applied to the gate, the pulse period was 10 ms, and the pulse width was 1 ms.

  As a result, as shown in FIG. 2, in the nitride semiconductor device of the present invention, it can be seen that the drain currents of the DC measurement and the pulse measurement are almost the same, and the characteristic variation is reduced. On the other hand, in the conventional nitride semiconductor device, the drain current greatly decreases in the pulse measurement, and the characteristic deterioration is remarkable. Thus, it can be seen that the current collapse suppressing effect of the present invention is very high.

  Thus, according to the present invention, the instability of the interface state between the silicon film and the nitride semiconductor is eliminated, and the current collapse suppressing effect becomes very high, so that a nitride semiconductor device capable of high output operation can be provided. . In the present embodiment, an example of HEMT is shown, but the same effect can be obtained in MESFET. The same effect can be obtained even when the silicon film 15 does not exist under the gate electrode 16 and the silicon film 15 exists only between the source electrode 17a and the gate electrode 16 and between the gate electrode 16 and the drain electrode 17b. In addition, when the silicon film 15 is present under the gate electrode 16, there is an advantage in manufacturing because it is not necessary to process the silicon film.

  Next, a method for manufacturing the silicon film used in the present invention will be specifically described. The silicon film 15 of the present invention is formed by ECR sputtering. For forming the silicon film 15 by the ECR sputtering method, a Si target can be used, for example, under the conditions of an argon (Ar) gas flow rate of 15 sccm, a microwave power source power of 500 W, and a radio frequency (RF) power source power of 500 W. In an ECR sputtering apparatus, by applying a microwave having the same frequency as the cyclotron frequency of an electron in a magnetic field, cyclotron resonance occurs, and collision between an electron rotating at high speed around a magnetic field line and an argon gas molecule introduced into the plasma chamber occurs. A high density argon plasma is generated. The generated plasma is extracted as a plasma flow, sputters a Si target, and enters the surface of the barrier layer 14 made of non-doped aluminum gallium nitride (AlGaN), thereby forming a silicon film 15.

  The ECR sputtering method can change the energy of particles incident on the sample surface by changing conditions such as pressure. For example, it is possible to maintain a stable high-density plasma at a low pressure on the order of 0.01 Pa, and it is incident on the sample surface with an energy of about 10 to 30 eV. With this level of energy, the damage to the sample surface is small, and by applying energy suitable for film formation to the particles that are incident on the sample surface, a thin film can be formed while the energy-controlled high-density particles are incident on the sample surface. proceed.

  Therefore, the ECR sputtering method can form a chemically stable and thin film having a high bonding force. In addition, since the ECR sputtering method does not involve a surface reaction, nitrogen escape from the surface of the barrier layer 14 made of AlGaN, which is a problem in the CVD method, can be reduced, and contamination by reaction products does not occur. It is suitable as a method for forming a film.

11, 101: substrate, 12, 102: buffer layer, 13, 103: channel layer,
14, 104: barrier layer, 15: surface protective film, 16, 106: gate electrode,
17a, 107a: source electrode, 17b, 107b: drain electrode

Claims (4)

  On the group III-V nitride semiconductor layer, a first electrode in Schottky contact with the nitride semiconductor layer and a second electrode in ohmic contact with the nitride semiconductor layer are provided, the first electrode and the A nitride semiconductor device comprising a silicon film between the surface of the nitride semiconductor layer between the second electrode and further between the first electrode and the nitride semiconductor layer. A group III-V nitride semiconductor layer stacked on a substrate via a buffer layer;
A silicon film laminated on the nitride semiconductor layer;
A gate electrode formed on the silicon film or the nitride semiconductor layer;
A source electrode and a drain electrode formed on the nitride semiconductor layer with the gate electrode interposed therebetween, and at least a surface of the nitride semiconductor layer between the source electrode and the drain electrode is covered with the silicon film; A nitride semiconductor device characterized by the above. Forming a first electrode in Schottky contact with the nitride semiconductor layer on the III-V nitride semiconductor layer; forming a second electrode in ohmic contact with the nitride semiconductor layer; A step of forming a silicon film between the surface of the nitride semiconductor layer between the first electrode and the second electrode, or further between the first electrode and the nitride semiconductor layer. In the device manufacturing method,
The method of manufacturing a nitride semiconductor device, wherein the silicon film is formed by an ECR sputtering method. A step of forming a group III-V nitride semiconductor layer on a substrate via a buffer layer; a step of forming a silicon film on the nitride semiconductor layer; and the silicon film or the nitride semiconductor layer Forming a gate electrode on the nitride semiconductor layer, and forming a source electrode and a drain electrode across the gate electrode on the nitride semiconductor layer, and at least between the source electrode and the drain electrode In the method for manufacturing a nitride semiconductor device, wherein the surface of the nitride semiconductor layer is covered with the silicon film,
The method of manufacturing a nitride semiconductor device, wherein the silicon film is formed by an ECR sputtering method.

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