JP5329606B2 - Manufacturing method of nitride semiconductor device - Google Patents

Description

This invention relates to a method of manufacturing a nitride semiconductor equipment.

  Conventionally, as a nitride semiconductor device, an oxygen plasma treatment is performed on the surface of an n-type GaN contact layer to form an oxygen doped layer, and then an ohmic electrode is formed on the n-type GaN contact layer, thereby forming an n-type GaN. Some reduce the contact resistance between the contact layer and the ohmic electrode (see, for example, Japanese Patent No. 2967743).

  However, with respect to the nitride semiconductor device, when the inventor has actually conducted an experiment and formed an ohmic electrode after performing oxygen plasma treatment on the GaN layer, the ohmic electrode has a high contact resistance and a sufficiently low contact resistance. I just couldn't get it.

Patent No. 2967743

Accordingly, an object of the present invention is to provide a method for manufacturing a nitride semiconductor equipment capable of reducing the contact resistance between the nitride semiconductor layer and the ohmic electrode.

  As a result of earnestly examining the contact resistance of the ohmic electrode formed on the nitride semiconductor layer without doping oxygen on the GaN layer side as in the conventional nitride semiconductor device, the present inventor has found that the TiAl-based material is used. It has been discovered that the contact resistance characteristics of the nitride semiconductor layer and the ohmic electrode change depending on the oxygen concentration in the ohmic electrode when the oxygen atom is contained in the ohmic electrode as an impurity to the extent that an oxide cannot be formed. .

  The present invention has been found for the first time by experiments that the contact resistance is greatly reduced when the oxygen concentration in the ohmic electrode is within a specific range based on the discovery of the present inventors.

Here, if the nitride semiconductor of the nitride semiconductor device of the present invention is represented by Al _x In _y Ga _1-xy N (x ≧ 0, y ≧ 0, 0 ≦ x + y ≦ 1). Good. The TiAl-based material is made of at least Ti / Al, and a TiN cap layer may be laminated thereon, or Au, Ag, Pt, etc. may be laminated on Al.

In the method for manufacturing a nitride semiconductor device of the first invention,
A first semiconductor layer sequentially stacked on the substrate, and a second semiconductor layer forming a heterointerface with the first semiconductor layer, and a two-dimensional electron gas at the heterointerface between the first semiconductor layer and the second semiconductor layer A method for manufacturing a nitride semiconductor device including a nitride semiconductor layer on which is formed,
Forming the nitride semiconductor layer on the substrate;
After forming the nitride semiconductor layer, through the second semiconductor layer by etching, forming a recess in a part of the upper side of the first semiconductor layer;
Forming a metal film made of a TiAl-based material on the nitride semiconductor layer in which the recess is formed by sputtering;
Etching a metal film made of the TiAl-based material to form an ohmic electrode at least partially embedded in the recess;
Annealing the substrate on which the ohmic electrode is formed,
In the step of forming the metal film made of the TiAl-based material, oxygen is allowed to flow into the chamber during sputtering of the Ti layer of the metal film made of the TiAl-based material, whereby the ohmic electrode before the annealing is performed. By making the oxygen concentration of the electrode 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less, the ohmic electrode made of the TiAl-based material contains oxygen atoms that cannot form oxides as impurities. It is characterized by.

According to the above configuration, in the step of forming the metal film made of the TiAl-based material, in the ohmic electrode before annealing by flowing oxygen into the chamber during the sputtering of the Ti layer of the metal film made of the TiAl-based material. By making the oxygen concentration of 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less, the contact resistance between the nitride semiconductor layer and the ohmic electrode can be reduced.
In the nitride semiconductor device having a recess structure in which at least a part of the ohmic electrode is embedded in a recess formed in a part of the upper side of the first semiconductor layer through the second semiconductor layer by etching. The contact resistance between the two-dimensional electron gas and the ohmic electrode at the heterointerface between the layer and the second semiconductor layer can be reduced.

According to a second aspect of the present invention, there is provided a method for manufacturing a nitride semiconductor device, comprising: a first semiconductor layer that is sequentially stacked on a substrate; and a second semiconductor layer that forms a heterointerface with the first semiconductor layer. And a method of manufacturing a nitride semiconductor device including a nitride semiconductor layer in which a two-dimensional electron gas is formed at a heterointerface between the second semiconductor layer and the second semiconductor layer,
Forming the nitride semiconductor layer on the substrate;
After forming the nitride semiconductor layer, through the second semiconductor layer by etching, forming a recess in a part of the upper side of the first semiconductor layer;
Forming a metal film made of a TiAl-based material on the nitride semiconductor layer in which the recess is formed by sputtering;
Etching a metal film made of the TiAl-based material to form an ohmic electrode at least partially embedded in the recess;
Annealing the substrate on which the ohmic electrode is formed,
In the step of forming the metal film made of the TiAl-based material, the next sputtering of the Ti layer is performed by flowing oxygen into the chamber before the sputtering of the Ti layer of the metal film made of the TiAl-based material. The oxygen concentration in the ohmic electrode is 1 × 10 ¹⁶ cm ⁻³ and 1 × 10 ²⁰ cm ^{−3 in the} presence of oxygen in the chamber and before the annealing, The ohmic electrode made of a TiAl-based material contains oxygen atoms as impurities so as not to form oxides.

According to the above configuration, in the step of forming the metal film made of the TiAl-based material, the ohmic electrode before annealing by flowing oxygen into the chamber before sputtering of the Ti layer of the metal film made of the TiAl-based material. The contact resistance between the nitride semiconductor layer and the ohmic electrode can be reduced by setting the oxygen concentration therein to 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less.
In the nitride semiconductor device having a recess structure in which at least a part of the ohmic electrode is embedded in a recess formed in a part of the upper side of the first semiconductor layer through the second semiconductor layer by etching. The contact resistance between the two-dimensional electron gas and the ohmic electrode at the heterointerface between the layer and the second semiconductor layer can be reduced.

According to a third aspect of the present invention, there is provided a method for manufacturing a nitride semiconductor device, comprising: a first semiconductor layer sequentially stacked on a substrate; and a second semiconductor layer that forms a heterointerface with the first semiconductor layer. And a method of manufacturing a nitride semiconductor device including a nitride semiconductor layer in which a two-dimensional electron gas is formed at a heterointerface between the second semiconductor layer and the second semiconductor layer,
Forming the nitride semiconductor layer on the substrate;
After forming the nitride semiconductor layer, through the second semiconductor layer by etching, forming a recess in a part of the upper side of the first semiconductor layer;
Forming a metal film made of a TiAl-based material on the nitride semiconductor layer in which the recess is formed by sputtering;
Etching a metal film made of the TiAl-based material to form an ohmic electrode at least partially embedded in the recess;
Annealing the substrate on which the ohmic electrode is formed,
After the step of forming the metal film made of the TiAl-based material by sputtering and before the step of forming the ohmic electrode, after the Ti layer of the metal film made of the TiAl-based material is sputtered, the Ti layer By performing oxygen plasma treatment on the surface, the oxygen concentration in the ohmic electrode before the annealing is set to 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less, whereby the TiAl The ohmic electrode made of a system material contains oxygen atoms as impurities so as not to form oxides.

According to the above configuration, after the step of forming the metal film made of TiAl-based material by sputtering and before the step of forming the ohmic electrode, after the sputtering of the Ti layer of the metal film made of TiAl-based material, By performing oxygen plasma treatment on the surface of the Ti layer and setting the oxygen concentration in the ohmic electrode before annealing to 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less, the nitride semiconductor Contact resistance between the layer and the ohmic electrode can be reduced.

  In the nitride semiconductor device having a recess structure in which at least a part of the ohmic electrode is embedded in a recess formed in a part of the upper side of the first semiconductor layer through the second semiconductor layer by etching. The contact resistance between the two-dimensional electron gas and the ohmic electrode at the heterointerface between the layer and the second semiconductor layer can be reduced.

In one embodiment of the method of manufacturing a nitride semiconductor device, in the annealing step, the substrate on which the ohmic electrode is formed is heated at 400 ° C. or more and 500 ° C. or less.

  According to the embodiment, in the step of performing the annealing, the substrate on which the ohmic electrode is formed is heated at 400 ° C. or more and 500 ° C. or less, so that the nitride semiconductor is compared with the case where annealing is performed at a high temperature of 500 ° C. or more. The contact resistance between the layer and the ohmic electrode can be greatly reduced.

  As is apparent from the above, according to the nitride semiconductor device and the manufacturing method thereof of the present invention, a nitride semiconductor device capable of reducing the contact resistance between the GaN-based semiconductor layer and the ohmic electrode can be realized.

FIG. 1 is a cross-sectional view of a nitride semiconductor device according to a first embodiment of the present invention. FIG. 2 is a process cross-sectional view for explaining the method of manufacturing the nitride semiconductor device. FIG. 3 is a process cross-sectional view subsequent to FIG. FIG. 4 is a process cross-sectional view subsequent to FIG. FIG. 5 is a process cross-sectional view subsequent to FIG. FIG. 6 is a process sectional view for explaining the method for manufacturing a nitride semiconductor device according to the third embodiment of the present invention. FIG. 7 is a process cross-sectional view subsequent to FIG. FIG. 8 is a process cross-sectional view subsequent to FIG. FIG. 9 is a process cross-sectional view subsequent to FIG. FIG. 10 is a process cross-sectional view subsequent to FIG. FIG. 11 is a diagram showing the relationship between the oxygen concentration in the ohmic electrode and the contact resistance. FIG. 12 is a diagram showing the relationship between the annealing temperature of the ohmic electrode and the contact resistance.

It will be described in detail below by nitride semiconductor equipment manufacturing method illustrated embodiment of the present invention.

[First Embodiment]
FIG. 1 shows a cross-sectional view of a nitride semiconductor device according to the first embodiment of the present invention, which is a GaN-based HFET (Hetero-junction Field Effect Transistor).

  As shown in FIG. 1, the semiconductor device includes an undoped AlGaN buffer layer 15, an undoped GaN layer 1 as an example of a first semiconductor layer, and an undoped AlGaN layer 2 as an example of a second semiconductor layer, on an Si substrate 10. A nitride semiconductor layer 20 made of is formed. 2DEG (two-dimensional electron gas) is generated at the interface between the undoped GaN layer 1 and the undoped AlGaN layer 2.

  Further, a source electrode 11 and a drain electrode 12 are formed on the AlGaN layer 2 at a distance from each other. A gate electrode 13 is formed on the AlGaN layer 2 between the source electrode 11 and the drain electrode 12 and on the source electrode 11 side. The source electrode 11 and the drain electrode 12 are ohmic electrodes, and the gate electrode 13 is a Schottky electrode. The source electrode 11, the drain electrode 12, the gate electrode 13, and the active regions of the GaN layer 1 and the AlGaN layer 2 on which the source electrode 11, the drain electrode 12, and the gate electrode 13 are formed constitute an HFET.

  Here, the active region means that carriers are generated between the source electrode 11 and the drain electrode 12 by the voltage applied to the gate electrode 13 disposed between the source electrode 11 and the drain electrode 12 on the AlGaN layer 2. This is a region of the flowing nitride semiconductor layer 20 (GaN layer 1, AlGaN layer 2).

An insulating film 30 made of SiO ₂ is formed on the AlGaN layer 2 excluding the region where the source electrode 11, the drain electrode 12, and the gate electrode 13 are formed in order to protect the AlGaN layer 2. An interlayer insulating film 40 made of polyimide is formed on the Si substrate 10 on which the source electrode 11, the drain electrode 12, and the gate electrode 13 are formed. In FIG. 1, reference numeral 41 denotes a via as a contact portion, and 42 denotes a drain electrode pad. Note that the insulating film is not limited to SiO ₂ but SiN, Al ₂ O _3, or the like may be used. In particular, the insulating film preferably has a SiN film having a stoichiometric collapse on the surface of the semiconductor layer to suppress collapse and a multilayer structure of SiO ₂ or SiN for surface protection. The interlayer insulating film is not limited to polyimide, but may be an insulating material such as SiO ₂ film manufactured by p-CVD, SOG (Spin On Glass), or BPSG (boron / phosphorus / silicate / glass).

  In the nitride semiconductor device having the above configuration, a two-dimensional electron gas (2DEG) formed at the interface between the GaN layer 1 and the AlGaN layer 2 is generated to form a channel layer. The channel layer is controlled by applying a voltage to the gate electrode 13 to turn on and off the HFET having the source electrode 11, the drain electrode 12, and the gate electrode 13. In the HFET, when a negative voltage is applied to the gate electrode 13, a depletion layer is formed in the GaN layer 1 below the gate electrode 13, and the HFET is turned off. On the other hand, when the voltage of the gate electrode 13 is zero, the HFET 13 is a normally-on type transistor in which the depletion layer disappears in the lower GaN layer 1 and is turned on.

  Next, a method for manufacturing the nitride semiconductor device will be described with reference to FIGS. 2 to 6, the Si substrate and the undoped AlGaN buffer layer are not shown in order to make the drawings easier to see, and the sizes and intervals of the source electrode and the drain electrode are changed.

First, as shown in FIG. 2, an undoped AlGaN buffer layer (not shown), undoped GaN is formed on a Si substrate (not shown) by using a MOCVD (Metal Organic Chemical Vapor Deposition) method. A layer 101 and an undoped AlGaN layer 102 are sequentially formed. The thickness of the undoped GaN layer 101 is 1 μm, for example, and the thickness of the undoped AlGaN layer 102 is 30 nm, for example. The GaN layer 101 and the AlGaN layer 102 constitute a nitride semiconductor layer 120. Next, an insulating film 130 (for example, SiO ₂ ) is formed to a thickness of 200 nm on the AlGaN layer 102 by, for example, a plasma CVD (Chemical Vapor Deposition) method. In FIG. 2, reference numeral 103 denotes a two-dimensional electron gas (2DEG) formed at the heterointerface between the GaN layer 101 and the AlGaN layer 102.

  Next, as shown in FIG. 3, after applying a photoresist on the insulating film 130 and patterning it, a portion where an ohmic electrode is to be formed is removed by dry etching, and the GaN layer 101 penetrates the AlGaN layer 102. A recess 106 is formed in a part on the upper side of the substrate. The depth of the recess 106 may be equal to or greater than the depth from the surface of the AlGaN layer 102 to 2 DEG, for example, 50 nm. Then, annealing is performed after dry etching (for example, 500 to 850 ° C.).

  Next, as shown in FIG. 4, Ti / Al / TiN is laminated on the insulating film 130 and the recess 106 by sputtering to form a laminated metal film 107 to be an ohmic electrode. Here, the TiN layer is a cap layer for protecting the Ti / Al layer from the subsequent step.

  At this time, a small amount (for example, 5 sccm) of oxygen is allowed to flow into the chamber during the Ti film formation. Here, the flow rate of oxygen is set so that Ti oxide is not generated.

  Next, as shown in FIG. 5, patterns of ohmic electrodes 111 and 112 are formed by using normal photolithography and dry etching.

  Then, by annealing the substrate on which the ohmic electrodes 111 and 112 are formed, for example, at 400 ° C. or more and 500 ° C. or less for 10 minutes or more, an ohmic contact is formed between the two-dimensional electron gas (2DEG) and the ohmic electrodes 111 and 112. can get. In this case, the contact resistance can be greatly reduced as compared with the case of annealing at a high temperature of 500 ° C. or higher. Further, annealing at a low temperature of 400 ° C. or higher and 500 ° C. or lower does not adversely affect the characteristics of the insulating film.

  The ohmic electrodes 111 and 112 serve as a source electrode and a drain electrode, and a gate electrode made of TiN or WN is formed between the ohmic electrodes 111 and 112 in a later step.

According to the method of manufacturing the nitride semiconductor device of the first embodiment, when the laminated metal film 107 to be an ohmic electrode is formed, oxygen is flowed into the chamber during the Ti film formation, so that the ohmic contact can be achieved. The oxygen concentration in the ohmic electrodes 111 and 112 before annealing can be set to 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less. Thereby, the contact resistance between 2DEG of the nitride semiconductor layer after annealing and the ohmic electrodes 111 and 112 can be reduced.

  The oxygen concentration in the ohmic electrodes 111 and 112 is measured before alloying by annealing by SIMS (Secondary Ion Mass Spectroscopy).

  According to the present invention, it is a coincidence that the oxygen concentration in the ohmic electrode made of a TiAl-based material affects the contact resistance in the course of various experiments conducted by the present inventor for a GaN-based HFET which is one of the nitride semiconductor devices. Although it is based on the result of research on the headline and its influence, the specific principle is still unclear.

  Further, in a nitride semiconductor device having a recess structure in which the ohmic electrodes 111 and 112 are partially embedded in the recess 106 in a part of the upper side of the GaN layer 101 through the AlGaN layer 102, the GaN layer 101, the AlGaN layer 102, The contact resistance between the two-dimensional electron gas (2DEG) at the heterointerface and the ohmic electrodes 111 and 112 can be reduced.

In addition, by using the ohmic electrodes 111 and 112 which are laminated metal films in which the Ti layer and the Al layer are laminated in order from the substrate side, oxygen is contained in the Ti layer formed first on the AlGaN layer 102, The oxygen concentration in the ohmic electrode can be easily set to 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less.

  According to the method of manufacturing the nitride semiconductor device of the first embodiment, the insulating film 130, the AlGaN layer 102, and the GaN layer 101 are removed by dry etching to form the recess 106, but the insulating film 130 is removed by wet etching. Then, the recess 106 may be formed by removing the AlGaN layer 102 and the GaN layer 101 by dry etching.

  According to the method of manufacturing the nitride semiconductor device of the first embodiment, Ti / Al / TiN is laminated to form an ohmic electrode. However, the present invention is not limited to this, and TiN may be omitted, and Ti / Al is laminated. After that, Au, Ag, Pt or the like may be laminated thereon.

[Second Embodiment]
Next explained is a method for manufacturing a nitride semiconductor device according to the second embodiment of the invention. The nitride semiconductor device of the second embodiment has the same configuration as the nitride semiconductor device of the first embodiment shown in FIG. The nitride semiconductor device manufacturing method of the second embodiment is the same as that of the first embodiment except that oxygen is allowed to flow into the chamber before Ti deposition instead of oxygen to flow into the chamber during Ti deposition. It has the same process as the manufacturing method of the nitride semiconductor device, and FIGS.

  Hereinafter, differences from the method for manufacturing the nitride semiconductor device according to the first embodiment will be described.

In the first embodiment, when Ti / Al / TiN is laminated on the insulating film 130 and the recess 106 by sputtering to form the laminated metal film 107 serving as an ohmic electrode, a small amount of oxygen is introduced into the chamber during the Ti film formation. In contrast, in the method of manufacturing the nitride semiconductor device according to the second embodiment, oxygen is flowed into the chamber, for example, at 50 sccm for 5 minutes before the Ti film is formed. The oxygen concentration can be set to 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less.

  The method for manufacturing a nitride semiconductor device according to the second embodiment has the same effects as the method for manufacturing a nitride semiconductor device according to the first embodiment.

According to the method for manufacturing the nitride semiconductor device of the second embodiment, when the laminated metal film 107 to be an ohmic electrode is formed by sputtering, oxygen is allowed to flow into the chamber before the Ti film is formed. , 112 can be set to 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less. Thereby, the contact resistance between the 2DEG of the nitride semiconductor layer and the ohmic electrodes 111 and 112 can be reduced.

[Third Embodiment]
FIG. 6 is a process sectional view for explaining the method for manufacturing a nitride semiconductor device according to the third embodiment of the invention. The nitride semiconductor device of the third embodiment has the same configuration as the nitride semiconductor device of the first embodiment shown in FIG.

First, as shown in FIG. 6, an undoped GaN layer 201 and an undoped AlGaN layer 202 are sequentially formed on a Si substrate (not shown) by MOCVD. The GaN layer 201 and the AlGaN layer 202 constitute a nitride semiconductor layer 220. Next, an insulating film 230 (for example, SiO ₂ ) is formed on the AlGaN layer 202. In FIG. 2, 203 is a two-dimensional electron gas (2DEG) formed at the heterointerface between the GaN layer 201 and the AlGaN layer 202.

  Next, as shown in FIG. 7, after applying a photoresist on the insulating film 230 and patterning it, the portion where the ohmic electrode is to be formed is removed by dry etching, thereby penetrating the AlGaN layer 202 and forming a GaN layer. A recess 206 is formed in a part of the upper side of 201. And annealing (for example, 500-850 degreeC) is performed after dry etching.

  Next, as shown in FIG. 8, a Ti layer 207 is formed on the insulating film 230 and in the recess 206 by sputtering.

  Next, oxygen plasma treatment is performed on the surface of the Ti layer 207. This oxygen plasma treatment is desirably performed at 60 ° C., for example, with oxygen set at a flow rate of 900 sccm and RF power of 1000 W for 5 minutes.

  Next, as shown in FIG. 9, Al / TiN is laminated on the insulating film 230 and the concave portion 206 by sputtering to form a laminated metal film 208 to be an ohmic electrode.

  Next, as shown in FIG. 10, patterns of ohmic electrodes 211 and 212 are formed by using normal photolithography and dry etching.

  Then, by annealing the substrate on which the ohmic electrodes 111 and 112 are formed, for example, at 400 ° C. or more and 500 ° C. or less for 10 minutes or more, an ohmic contact is obtained between the 2DEG and the ohmic electrodes 111 and 112.

  The nitride semiconductor device manufacturing method of the third embodiment has the same effects as the nitride semiconductor device manufacturing method of the first embodiment.

According to the method of manufacturing the nitride semiconductor device of the third embodiment, when the laminated metal film 107 to be an ohmic electrode is formed, the oxygen plasma treatment is performed on the surface of the Ti layer after the Ti layer is sputtered. Thus, the oxygen concentration in the ohmic electrodes 111 and 112 can be set to 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less. Thereby, the contact resistance between the 2DEG of the nitride semiconductor layer and the ohmic electrodes 111 and 112 can be reduced.

  FIG. 11 is a graph showing the relationship between the oxygen concentration in the ohmic electrode of the nitride semiconductor device and the contact resistance.

  However, for the oxygen concentration (horizontal axis) in FIG. 11, the oxygen concentration in the ohmic electrode before annealing is measured by SIMS. The oxygen concentration may be measured using other measurement methods such as AES (Atomic Emission Spectroscopy).

  On the other hand, the contact resistance (vertical axis) in FIG. 11 is obtained by measuring the contact resistance of the ohmic electrode after annealing.

As is apparent from FIG. 11, the nitride semiconductor device having a contact resistance of 6 Ωmm or less is realized by setting the oxygen concentration in the ohmic electrode to 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less. be able to. In particular, there exists an inflection point at which the contact resistance rapidly increases when the oxygen concentration in the ohmic electrode exceeds 1 × 10 ²⁰ cm ^−3, and the change in contact resistance characteristics depending on the oxygen concentration in the ohmic electrode is present. The music point has never been known.

  Such a nitride semiconductor device having a contact resistance of 6 Ωmm or less has a commercial value in terms of performance and cost as a product that can be driven with a larger current than a silicon element and is suitable for high-temperature operation.

  FIG. 12 is a diagram showing the relationship between the annealing temperature and contact resistance of an ohmic electrode manufactured using the method for manufacturing a nitride semiconductor device shown in the first embodiment.

At this time, sputtering was performed while flowing 5 sccm of oxygen into the chamber during the Ti film formation, and the oxygen concentration in the ohmic electrode before annealing was measured by SIMS and found to be 2 × 10 ¹⁹ cm ⁻³ .

  Thus, it can be seen that the contact resistance between the nitride semiconductor layer and the ohmic electrode can be significantly reduced by annealing at a temperature of 400 ° C. or more and 500 ° C. or less.

  Normally, the annealing temperature of n-type GaN is 600 ° C. and the annealing temperature of non-doped GaN is 800 ° C., whereas in this method of manufacturing a nitride semiconductor device, an ohmic electrode is formed in the annealing step. By heating the substrate at a low temperature of 400 ° C. or more and 500 ° C. or less, the contact resistance between the nitride semiconductor layer and the ohmic electrode is greatly increased as compared with the case where the annealing temperature is lower than 400 ° C. or higher than 500 ° C. Can be reduced.

  In the first to third embodiments, the nitride semiconductor device using the Si substrate has been described. However, the present invention is not limited to the Si substrate, and a sapphire substrate or SiC substrate may be used, and nitriding is performed on the sapphire substrate or SiC substrate. A nitride semiconductor layer may be grown on a substrate made of a nitride semiconductor, such as growing an AlGaN layer on a GaN substrate. Further, a buffer layer may be formed between the substrate and the nitride semiconductor layer, or a hetero improvement layer is formed between the first semiconductor layer, the first semiconductor layer, and the second semiconductor layer of the nitride semiconductor layer. May be.

  In the first to third embodiments, the normally-on type HFET has been described. However, the present invention may be applied to a normally-off type nitride semiconductor device. Further, the present invention may be applied not only to a Schottky electrode but also to a field effect transistor having an insulated gate structure.

The nitride semiconductor of the nitride semiconductor device of the present invention may be any material represented by Al _x In _y Ga _1-xy N (x ≧ 0, y ≧ 0, 0 ≦ x + y ≦ 1).

  Although specific embodiments of the present invention have been described, the present invention is not limited to the first to third embodiments, and various modifications can be made within the scope of the present invention.

1, 101, 201 ... GaN layer 2, 102, 202 ... AlGaN layer 3, 103, 203 ... 2 DEG
DESCRIPTION OF SYMBOLS 11 ... Source electrode 12 ... Drain electrode 13 ... Gate electrode 15 ... AlGaN buffer layer 20 ... Nitride semiconductor layer 30, 130, 230 ... Insulating film 40 ... Interlayer insulating film 41 ... Via 42 ... Drain electrode pad 111, 211, 112, 212 ... Ohmic electrode

Claims (4)

A first semiconductor layer sequentially stacked on the substrate, and a second semiconductor layer forming a heterointerface with the first semiconductor layer, and a two-dimensional electron gas at the heterointerface between the first semiconductor layer and the second semiconductor layer A method for manufacturing a nitride semiconductor device including a nitride semiconductor layer on which is formed,
Forming the nitride semiconductor layer on the substrate;
After forming the nitride semiconductor layer, through the second semiconductor layer by etching, forming a recess in a part of the upper side of the first semiconductor layer;
Forming a metal film made of a TiAl-based material on the nitride semiconductor layer in which the recess is formed by sputtering;
Etching a metal film made of the TiAl-based material to form an ohmic electrode at least partially embedded in the recess;
Annealing the substrate on which the ohmic electrode is formed,
In the step of forming the metal film made of the TiAl-based material, oxygen is allowed to flow into the chamber during sputtering of the Ti layer of the metal film made of the TiAl-based material, whereby the ohmic electrode before the annealing is performed. By making the oxygen concentration of the electrode 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less, the ohmic electrode made of the TiAl-based material contains oxygen atoms that cannot form oxides as impurities. A method for manufacturing a nitride semiconductor device, comprising: A first semiconductor layer sequentially stacked on the substrate, and a second semiconductor layer forming a heterointerface with the first semiconductor layer, and a two-dimensional electron gas at the heterointerface between the first semiconductor layer and the second semiconductor layer A method for manufacturing a nitride semiconductor device including a nitride semiconductor layer on which is formed,
Forming the nitride semiconductor layer on the substrate;
After forming the nitride semiconductor layer, through the second semiconductor layer by etching, forming a recess in a part of the upper side of the first semiconductor layer;
Forming a metal film made of a TiAl-based material on the nitride semiconductor layer in which the recess is formed by sputtering;
Etching a metal film made of the TiAl-based material to form an ohmic electrode at least partially embedded in the recess;
Annealing the substrate on which the ohmic electrode is formed,
In the step of forming the metal film made of the TiAl-based material, the next sputtering of the Ti layer is performed by flowing oxygen into the chamber before the sputtering of the Ti layer of the metal film made of the TiAl-based material. The oxygen concentration in the ohmic electrode is 1 × 10 ¹⁶ cm ⁻³ and 1 × 10 ²⁰ cm ^{−3 in the} presence of oxygen in the chamber and before the annealing, A method for manufacturing a nitride semiconductor device, wherein an oxygen atom that does not form an oxide is contained as an impurity in an ohmic electrode made of a TiAl-based material. A first semiconductor layer sequentially stacked on the substrate, and a second semiconductor layer forming a heterointerface with the first semiconductor layer, and a two-dimensional electron gas at the heterointerface between the first semiconductor layer and the second semiconductor layer A method for manufacturing a nitride semiconductor device including a nitride semiconductor layer on which is formed,
Forming the nitride semiconductor layer on the substrate;
After forming the nitride semiconductor layer, through the second semiconductor layer by etching, forming a recess in a part of the upper side of the first semiconductor layer;
Forming a metal film made of a TiAl-based material on the nitride semiconductor layer in which the recess is formed by sputtering;
Etching a metal film made of the TiAl-based material to form an ohmic electrode at least partially embedded in the recess;
Annealing the substrate on which the ohmic electrode is formed,
After the step of forming the metal film made of the TiAl-based material by sputtering and before the step of forming the ohmic electrode, after the Ti layer of the metal film made of the TiAl-based material is sputtered, the Ti layer By performing oxygen plasma treatment on the surface, the oxygen concentration in the ohmic electrode before the annealing is set to 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less, whereby the TiAl A method for manufacturing a nitride semiconductor device, wherein an ohmic electrode made of a base material contains oxygen atoms as impurities so as not to form an oxide. In the manufacturing method of the nitride semiconductor device according to any one of claims 1 to 3 ,
In the step of performing the annealing, the substrate on which the ohmic electrode is formed is heated at 400 ° C. or higher and 500 ° C. or lower.

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