JP6018809B2 - Nitride semiconductor device - Google Patents

Description

  The present invention relates to a nitride semiconductor device.

  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 There is one that reduces the contact resistance between the contact layer and the ohmic electrode (see Japanese Patent No. 2996743 (Patent Document 1)).

Japanese Patent No. 2967743

  However, for the nitride semiconductor device, when the inventor 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.

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

  As a result of intensive studies on the contact resistance of the ohmic electrode formed on the nitride semiconductor layer, the inventor has found that the substrate side region near the interface between the ohmic electrode made of TiAl-based material and the nitride semiconductor layer is in the vicinity of the interface. It was discovered that the contact resistance characteristics of the nitride semiconductor layer and the ohmic electrode change depending on the oxygen concentration of the generated oxygen concentration peak and the chlorine concentration of the chlorine concentration peak.

  Furthermore, the inventor has experimentally demonstrated that contact resistance is greatly reduced when the oxygen concentration at the oxygen concentration peak near the interface on the substrate side from the interface and the chlorine concentration at the chlorine concentration peak are within a specific range. I found it for the first time.

Based on the above discovery, the nitride semiconductor device of the present invention is
A substrate,
A nitride semiconductor multilayer body formed on the substrate and having a heterointerface;
An ohmic electrode made of a TiAl-based material at least partially formed in the nitride semiconductor laminate,
The nitride semiconductor laminate is
A first nitride semiconductor layer formed on the substrate;
A second nitride semiconductor layer formed on the first nitride semiconductor layer and forming a heterointerface with the first nitride semiconductor layer;
In the oxygen concentration distribution in the depth direction from the ohmic electrode made of the TiAl-based material to the nitride semiconductor laminate,
It has an oxygen concentration peak at a position near the interface in a region closer to the substrate than the interface between the ohmic electrode and the nitride semiconductor laminate,
The oxygen concentration at the oxygen concentration peak is
1.1 × 10 ¹⁸ cm ⁻³ or more and 6.8 × 10 ¹⁸ cm ⁻³ or less,
In the chlorine concentration distribution in the depth direction from the ohmic electrode made of the TiAl-based material to the nitride semiconductor laminate,
It has a chlorine concentration peak at a position near the interface in the region on the substrate side of the interface between the ohmic electrode and the nitride semiconductor laminate,
The chlorine concentration at the above chlorine concentration peak is
It is characterized by being 5.0 × 10 ¹⁶ cm ⁻³ or more and 9.6 × 10 ¹⁷ cm ⁻³ or less.

According to the nitride semiconductor device of the present invention, in the region on the substrate side of the interface between the ohmic electrode made of the TiAl-based material and the nitride semiconductor stacked body, the oxygen concentration at the oxygen concentration peak in the vicinity of the interface is 1.1 × 10 ¹⁸ cm ⁻³ or more and 6.8 × 10 ¹⁸ cm ⁻³ or less, and the chlorine concentration at the chlorine concentration peak in the vicinity of the interface is 5.0 × 10 ¹⁶ cm ⁻³ or more and 9 The contact resistance between the nitride semiconductor multilayer body and the ohmic electrode can be reduced by being not more than 0.6 × 10 ¹⁷ cm ⁻³ .

In one embodiment of the nitride semiconductor device, the nitride semiconductor stack is
Having a recess that penetrates the second nitride semiconductor layer and reaches the two-dimensional electron gas layer near the heterointerface;
At least a part of the ohmic electrode is embedded in the recess.

  According to this embodiment, in the nitride semiconductor device having a recess structure, the contact resistance between the two-dimensional electron gas layer near the heterointerface and the ohmic electrode can be reduced.

According to the nitride semiconductor device of the present invention, in the region on the substrate side of the interface between the ohmic electrode made of a TiAl-based material and the nitride semiconductor multilayer body, the oxygen concentration at the oxygen concentration peak near the interface is 1.1 ×. 10 ¹⁸ cm ⁻³ or more and 6.8 × 10 ¹⁸ cm ⁻³ or less, and the chlorine concentration at the chlorine concentration peak near the interface is 5.0 × 10 ¹⁶ cm ⁻³ or more and 9.6 × 10 ^17. Since it is cm ⁻³ or less, the contact resistance between the nitride semiconductor multilayer body and the ohmic electrode can be reduced.

It is sectional drawing of the nitride semiconductor device of embodiment of this invention. It is process sectional drawing for demonstrating the manufacturing method of the said nitride semiconductor device. FIG. 3 is a process cross-sectional view subsequent to FIG. 2. FIG. 4 is a process cross-sectional view subsequent to FIG. 3. FIG. 5 is a process cross-sectional view subsequent to FIG. 4. It is a graph which shows oxygen concentration distribution in the depth direction from the ohmic electrode side to the GaN layer side of the interface of an ohmic electrode and a GaN layer. It is a graph which shows concentration distribution of oxygen, Al, Ti, Ga in the depth direction from the ohmic electrode side to the GaN layer side at the interface between the ohmic electrode and the GaN layer. It is a graph which shows the density | concentration distribution of the chlorine in the depth direction from the ohmic electrode side to the GaN layer side of the interface of the ohmic electrode of the said embodiment, and a GaN layer. It is a graph which shows the relationship between the oxygen concentration of the oxygen concentration peak of the interface vicinity of an ohmic electrode and a GaN layer, and the contact resistance of an ohmic electrode. It is a graph which shows the relationship between the chlorine concentration of the chlorine concentration peak of the interface vicinity of an ohmic electrode and a GaN layer, and the contact resistance of an ohmic electrode. It is a graph which shows the relationship between the oxygen concentration of the said oxygen concentration peak, the chlorine concentration of the said chlorine concentration peak, and the contact resistance of an ohmic electrode.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1 shows a cross-sectional view of a nitride semiconductor device according to an embodiment of the present invention, and this nitride semiconductor device 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 nitride semiconductor layer, and an example of a second nitride semiconductor layer on a Si substrate 10. As a result, a nitride semiconductor stacked body 20 composed of the undoped AlGaN layer 2 is formed. A 2DEG layer (two-dimensional electron gas layer) 3 is generated in the vicinity of the interface between the undoped GaN layer 1 and the undoped AlGaN layer 2.

  In place of the GaN layer 1, an AlGaN layer having a smaller band gap than the AlGaN layer 2 may be used. Further, a layer having a thickness of about 1 nm made of GaN, for example, may be provided on the AlGaN layer 2 as a cap layer.

  Further, the source electrode 11 and the drain electrode 12 are formed in the recess 106 and the recess 109 that pass through the AlGaN layer 2 and the 2DEG layer 3 and reach the GaN layer 1 with a space therebetween. Further, 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 stacked body 20 (GaN layer 1, AlGaN layer 2).

Then, 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 , and SiN, Al ₂ O _3, or the like may be used. In particular, the insulating film preferably has a multilayer structure of a SiN film having a stoichiometric collapse on the surface of the semiconductor layer to suppress collapse and a SiO ₂ or SiN film structure for surface protection. In addition, the interlayer insulating film is not limited to polyimide, but an insulating material such as SiO ₂ film manufactured by p-CVD (plasma CVD), SOG (Spin On Glass), or BPSG (boron, phosphorus, silicate, glass) is used. Also good.

  In the nitride semiconductor device having the above configuration, a channel is formed by the two-dimensional electron gas layer (2DEG layer) 3 generated near the interface between the GaN layer 1 and the AlGaN layer 2, and a voltage is applied to the gate electrode 13 through this channel. Thus, the HFET having the source electrode 11, the drain electrode 12, and the gate electrode 13 is turned on / off. 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, 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 5, the Si substrate and the undoped AlGaN buffer layer are not shown in order to make the drawings easy 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 are formed on a Si substrate (not shown) using MOCVD (Metal Organic Chemical Vapor Deposition). A layer 101 and an undoped AlGaN layer 102 are formed in this order. 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 stacked body 120.

Next, an insulating film 130 (for example, SiO ₂ ) is formed on the AlGaN layer 102 to a thickness of 200 nm by, for example, a plasma CVD (Chemical Vapor Deposition) method. In FIG. 2, reference numeral 103 denotes a two-dimensional electron gas layer (2DEG layer) formed in the vicinity of the heterointerface between the GaN layer 101 and the AlGaN layer 102.

  Next, after applying and patterning a photoresist (not shown) on the insulating film 130, a portion where an ohmic electrode is to be formed is removed by dry etching, as shown in FIG. Recesses 106 and 109 deeper than the 2DEG layer 103 are formed in a part of the upper side of the GaN layer 101 so as to penetrate therethrough. In the dry etching, a chlorine-based gas is used. The depth of the recesses 106 and 109 may be equal to or greater than the depth from the surface of the AlGaN layer 102 to the 2DEG layer 103, for example, 50 nm.

  In this embodiment, in the dry etching, the self-bias potential Vdc of the RIE (reactive ion etching) apparatus is set to 180 V or more and 240 V or less.

Next, after removing the resist, annealing for reducing etching damage due to the dry etching is performed (for example, 500 to 850 ° C.). Then, O ₂ plasma treatment, cleaning with HCl / H ₂ O ₂ , cleaning with BHF (buffered hydrofluoric acid) or 1% HF (hydrofluoric acid) are sequentially performed.

  Next, as shown in FIG. 4, Ti / Al / TiN are stacked by sequentially stacking Ti, Al, and TiN on the insulating film 130 and the recesses 106 and 109 to form an ohmic electrode. A metal film 107 is formed. Here, the TiN layer is a cap layer for protecting the Ti / Al layer from a subsequent process.

  When the laminated metal film 107 is formed by the sputtering, 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 the oxygen is set so that Ti oxide is not generated. Instead of flowing a small amount of oxygen into the chamber during the Ti film formation, oxygen may be flowed into the chamber at 50 sccm for 5 minutes before the Ti film formation.

  In the sputtering, both Ti and Al may be sputtered simultaneously. Further, Ti and Al may be deposited instead of sputtering.

  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, between the two-dimensional electron gas layer (2DEG layer) 103 and the ohmic electrodes 111 and 112 Ohmic contact is obtained. In this case, the contact resistance can be greatly reduced as compared with the case where annealing is performed at a high temperature exceeding 500 ° C. Further, by annealing at a low temperature of 400 ° C. or more and 500 ° C. or less, the diffusion of the electrode metal into the insulating film 130 can be suppressed, and the characteristics of the insulating film 130 are not adversely affected. In addition, the low temperature annealing can prevent deterioration of current collapse and characteristic fluctuation due to nitrogen desorption from the GaN layer 101. Note that “current collapse” is a phenomenon in which the on-resistance of a transistor in a high-voltage operation becomes higher than the on-resistance of the transistor in a low-voltage operation.

  The ohmic electrodes 111 and 112 become the source electrode 11 and the drain electrode 12, and a gate electrode made of TiN or WN or the like is formed between the ohmic electrodes 111 and 112 in a later step.

  According to the method for manufacturing the nitride semiconductor device of the embodiment, in the oxygen concentration distribution in the depth direction from the source electrode 11 and the drain electrode 12 as the ohmic electrodes to the GaN layer 1, the source electrode 11 and the drain electrode A first oxygen concentration peak P1 is formed at a position near the interfaces S1 and S2 on the undoped GaN layer 1 side of the interfaces S1 and S2 between the GaN layer 1 and the GaN layer 1. A second oxygen concentration peak P2 is formed at a position deeper than the first oxygen concentration peak P1. The vicinity of the interfaces S1 and S2 is, for example, a range of about 33 nm deeper than the interfaces S1 and S2, as will be described later with reference to FIG. The oxygen concentration peak P2 is deeper than the vicinity of the interface.

Moreover, the oxygen concentration of the first oxygen concentration peak can be set to 1.1 × 10 ¹⁸ cm ⁻³ or more and 6.8 × 10 ¹⁸ cm ⁻³ or less by the above manufacturing method, for example. The oxygen concentration at the first oxygen concentration peak is higher than the oxygen concentration at the second oxygen concentration peak.

FIG. 6 is a graph showing an example of the oxygen concentration distribution in the depth direction from the source electrode 11 side to the GaN layer 1 side of the interface S1 between the source electrode 11 and the undoped GaN layer 1. 6, the vertical axis scale 1.E + 00,1.E + 01, ..., 1.E + 06 , respectively, 1.0,1.0 × 10, ..., representative of 1.0 × 10 ^6. This graph shows the results measured by SIMS (secondary ion mass spectrometry) using TEG (test element group), with the horizontal axis representing depth (nm) and the vertical axis representing relative secondary ion intensity. (counts). As shown in FIG. 6, it has a convex oxygen concentration distribution at the position of the interface S1, and as an example, the first oxygen has a depth of about 8 nm from the interface S1 to the GaN layer 1 side. A concentration peak P1 is located, and a second oxygen concentration peak P2 is located at a depth of about 108 nm from the interface S1 to the GaN layer 1 side. In the example of FIG. 6, the oxygen concentration of the first oxygen concentration peak P1 is 2.6 × 10 ¹⁸ cm ⁻³ , and the oxygen concentration of the second oxygen concentration peak P2 is 6.4 × 10 ^17. cm ⁻³ .

  The interface S1 corresponds to the peak position of the relative secondary ion intensity (counts) of the carbon C. The oxygen concentration distribution in the depth direction from the drain electrode 12 side to the GaN layer 1 side at the interface S2 between the drain electrode 12 and the undoped GaN layer 1 was also the same as the graph of FIG.

FIG. 7 is a graph showing oxygen concentration distribution and Al, Ti, Ga concentration distribution in the depth direction from the source electrode side to the GaN layer 1 side of the interface S1 between the source electrode 11 and the undoped GaN layer 1. It is. In Figure 7, the vertical axis scale 1.E + 00,1.E + 01, ..., 1.E + 07 , respectively, 1.0,1.0 × 10, ..., representative of 1.0 × 10 ^7. As in FIG. 6, this graph shows the results of measurement by SIMS (secondary ion mass spectrometry) using TEG (test element group), with the horizontal axis representing depth (nm) and the vertical axis representing Relative secondary ionic strength (counts) is taken. The interface S1 corresponds to the peak position of the relative secondary ion intensity (counts) of the carbon C. In the graph of FIG. 7, as an example, a region having a depth of about 378 nm to a depth of about 438 nm is a region R1 in the vicinity of the interface, and a range of about 27 nm toward the shallower side than the interface S1 and about 33 nm toward the deeper side than the interface S1. Is the region R1 near the interface.

  The concentration distribution of Al, Ti, and Ga in the depth direction from the drain electrode 12 side to the GaN layer 1 side of the interface S2 between the drain electrode 12 and the undoped GaN layer 1 is the same as the graph of FIG. It was.

  Further, according to the method for manufacturing the nitride semiconductor device of the embodiment, in the chlorine concentration distribution in the depth direction from the source electrode 11 and the drain electrode 12 as the ohmic electrode to the GaN layer 1, the source electrode 11, In a region on the undoped GaN layer 1 side of the interfaces S1 and S2 between the drain electrode 12 and the undoped GaN layer 1, a first chlorine concentration peak P10 is formed at a position near the interfaces S1 and S2. A second chlorine concentration peak P20 is formed at a position deeper than the first chlorine concentration peak P10. As described above with reference to FIG. 7, the vicinity of the interfaces S1 and S2 is, for example, a range of about 33 nm deeper than the interfaces S1 and S2. As can be seen from FIG. The chlorine concentration peak P20 is deeper than the vicinity of the interface.

In addition, the chlorine concentration of the first chlorine concentration peak P10 is, for example, 5.0 × 10 ¹⁶ cm ⁻³ or more and 9.6 × 10 ¹⁷ cm ⁻³ or less. The chlorine concentration of the first chlorine concentration peak P10 is higher than the chlorine concentration of the second chlorine concentration peak P20.

FIG. 8 is a graph showing an example of a chlorine concentration distribution in the depth direction from the source electrode 11 to the undoped GaN layer 1. 8, 1.E + 01, 1.E + 02,..., 1.E + 04 on the vertical scale represent 1.0 × 10, 1.0 × 10 ² ,..., 1.0 × 10 ⁴ , respectively. This graph shows the results measured by SIMS (secondary ion mass spectrometry) using TEG (test element group), with the horizontal axis representing depth (nm) and the vertical axis representing relative secondary ion intensity. (counts). As shown in FIG. 8, there is a convex chlorine concentration distribution at the position of the interface S1, and as an example, there is a first chlorine in the vicinity of the interface having a depth of about 10 nm from the interface S1 to the GaN layer 1 side. A concentration peak P10 is located, and a second chlorine concentration peak P20 is located at a depth of about 95 nm from the interface S1 to the GaN layer 1 side. In the example shown in FIG. 8, the chlorine concentration of the first chlorine concentration peak P10 was 1.6 × 10 ¹⁷ cm ⁻³ . The chlorine concentration at the second chlorine concentration peak P20 was 8.4 × 10 ¹⁶ cm ⁻³ .

  Note that the chlorine concentration distribution in the depth direction from the drain electrode 12 side to the GaN layer 1 side of the interface S2 between the drain electrode 12 and the undoped GaN layer 1 was also the same as the graph of FIG.

Next, in FIG. 9, 2DEG layer 3 and the source electrode 11 of the nitride semiconductor stack 20, and the contact resistance between the drain electrode 12 (Ωmm), the oxygen concentration of the first oxygen concentration peak P1 (cm ^{- 3} ) shows the relationship. 9, the horizontal axis scale E + 17, E + 18, E + 19, E + 20 each represent ^{× 10 17, × 10 18,} × 10 19, × 10 20. In FIG. 9, the numerical value written beside each plot of rhombus marks ◇ is the contact resistance (Ωmm) in each plot.

As can be seen from FIG. 9, the oxygen concentration (cm ⁻³ ) of the first oxygen concentration peak P1 is within the range of 1.1 × 10 ¹⁸ cm ^{−3 to} 6.8 × 10 ¹⁸ cm ^−3. By doing so, the contact resistance can be remarkably reduced as compared with the case where the oxygen concentration of the first oxygen concentration peak P1 is outside the above range.

In FIG. 9, the samples in each plot have a chlorine concentration of 5.0 × 10 ¹⁶ (cm ⁻³ ) or more and 9.6 × 10 ¹⁷ (cm ⁻³ ) or less of the first chlorine concentration peak. is there.

Next, in FIG. 10, 2DEG layer 3 and the source electrode 11 of the nitride semiconductor stack 20, and the contact resistance between the drain electrode 12 (Ωmm), the chlorine concentration of the first chlorine concentration peak P10 (cm ^{- 3} ) shows the relationship. In FIG. 10, the horizontal axis scales E + 16, E + 17, E + 18, and E + 19 represent x10 ¹⁶ , x10 ¹⁷ , x10 ¹⁸ , and x10 ¹⁹ , respectively. In FIG. 10, the numerical value indicated beside each plot of diamond marks 印 represents the contact resistance (Ωmm) in each plot.

As can be seen from FIG. 10, the chlorine concentration (cm ⁻³ ) of the first chlorine concentration peak P10 is within the range of 5.0 × 10 ¹⁶ cm ⁻³ or more and 9.6 × 10 ¹⁷ cm ⁻³ or less. As a result, the contact resistance can be significantly reduced as compared with the case where the chlorine concentration of the first chlorine concentration peak P10 is outside the above range.

In addition, in FIG. 10, the sample of each plot has an oxygen concentration of the first oxygen concentration peak of 1.1 × 10 ¹⁸ (cm ⁻³ ) or more and 6.8 × 10 ¹⁸ (cm ⁻³ ) or less. is there.

Next, FIG. 11 shows the oxygen concentration (cm ⁻³ ) of the first oxygen concentration peak P1 and the relationship between the first chlorine concentration peak P10 and the contact resistance (Ωmm). In FIG. 11, the vertical axis represents the oxygen concentration (cm ⁻³ ) of the first oxygen concentration peak P1, the horizontal axis represents the chlorine concentration (cm ⁻³ ) of the first chlorine concentration peak P10, and rhombus marks The numerical value indicated beside each plot of ◇ represents the contact resistance (Ωmm) in each plot. 11, the horizontal axis scale E + 16, E + 17, E + 18, E + 19 , ^{respectively, × 10 16, × 10 17} , × 10 18, represent × ^{10 19,} the vertical axis scale E + 17, E + 18, E + 19, E + 20 is These represent x10 ¹⁷ , x10 ¹⁸ , x10 ¹⁹ , and x10 ²⁰ , respectively.

As can be seen from FIG. 11, the oxygen concentration of the first oxygen concentration peak P1 is in the range of 1.1 × 10 ¹⁸ cm ^{−3 to} 6.8 × 10 ¹⁸ cm ⁻³ , and the first The chlorine concentration peak P10 has a chlorine concentration in the range of 5.0 × 10 ¹⁶ cm ⁻³ or more and 9.6 × 10 ¹⁷ cm ⁻³ or less, so that the oxygen concentration of the first oxygen concentration peak P1 is The contact resistance can be remarkably reduced as compared with the case where is outside the above range and the case where the chlorine concentration of the first chlorine concentration peak P10 is outside the above range.

In the embodiment, as an example, the oxygen concentration of the first oxygen concentration peak is 2.6 × 10 ¹⁸ cm ⁻³ and the chlorine concentration of the first chlorine concentration peak is 1.6 × 10 ¹⁷ cm. ^As a result, the contact resistance between the ohmic electrodes (source electrode 11 and drain electrode 12) and the GaN layer 1 was 1.1 Ωmm.

On the other hand, when the oxygen concentration at the first oxygen concentration peak is less than 1.1 × 10 ¹⁸ cm ⁻³ , the contact resistance rapidly increases to 70 Ωmm. This is presumably because the activation of oxygen, which is a reaction on the GaN layer side necessary for the formation of the ohmic contact, is insufficient. On the other hand, when the oxygen concentration at the first oxygen concentration peak exceeds 6.8 × 10 ¹⁸ cm ⁻³ , the contact resistance rapidly increases to 100 Ωmm. This is because Ti is a reaction on the GaN layer 1 side necessary for ohmic contact formation when excessive oxygen reacts with Ti if the oxygen concentration of the first oxygen concentration peak P1 is too high, even if the chlorine concentration is low. This is considered to be because the N abstraction reaction from GaN by the above is not performed sufficiently.

Further, there is a plot in which the contact resistance increases rapidly to 50 Ωmm when the chlorine concentration of the first chlorine concentration peak P10 exceeds 9.6 × 10 ¹⁷ cm ⁻³ . This is because if the chlorine concentration of the second chlorine concentration peak P20 is too high, even if the oxygen concentration is within a predetermined range (1.1 × 10 ¹⁸ cm ^{−3 to} 6.8 × 10 ¹⁸ cm ⁻³ ), This is thought to be due to the fact that the chlorine reacted with Ga and Ti, and the N extraction reaction from GaN and the activation of oxygen by Ti, which are reactions on the GaN layer 1 side necessary for the ohmic contact formation, were inhibited.

According to this embodiment, the oxygen concentration of the first oxygen concentration peak P1 is in the range of 1.1 × 10 ¹⁸ cm ^{−3 to} 6.8 × 10 ¹⁸ cm ⁻³ , and the first chlorine concentration The chlorine concentration of peak P10 is in the range of 5.0 × 10 ¹⁶ cm ^{−3 to} 9.6 × 10 ¹⁷ cm ⁻³ . Thereby, activation of oxygen on the GaN layer side necessary for forming the ohmic contact and N extraction reaction from GaN can be promoted. When the oxygen concentration of the first oxygen concentration peak P1 is outside the above range, Compared to the case where the chlorine concentration at the chlorine concentration peak P10 is outside the above range, it is considered that an ohmic contact with a much lower resistance can be formed.

  According to the nitride semiconductor device manufacturing method of the above embodiment, the insulating film 130, the AlGaN layer 102, and the GaN layer 101 are removed by dry etching to form the recesses 106 and 109. However, the insulating film 130 is wet etched. The recesses 106 and 109 may be formed by removing the AlGaN layer 102 and the GaN layer 101 by dry etching.

  Further, according to the nitride semiconductor device manufacturing method of the above 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. Then, Au, Ag, Pt or the like may be laminated thereon.

  In the above embodiment, 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 an SiC substrate may be used, and a nitride semiconductor layer is formed on the sapphire substrate or the SiC substrate. The nitride semiconductor layer may be grown on a substrate made of a nitride semiconductor, such as by growing an AlGaN layer on a GaN substrate. In addition, a buffer layer may be formed between the substrate and the nitride semiconductor layer, or a hetero-improvement layer between the first nitride semiconductor layer and the second nitride semiconductor layer of the nitride semiconductor stacked body. May be formed.

  In the above-described embodiment, the recess structure HFET in which the ohmic electrode reaches the GaN layer has been described. However, the present invention is applied to an HFET in which an ohmic electrode serving as a source electrode and a drain electrode is formed on an undoped AlGaN layer without forming a recess. May be applied. In addition, the nitride semiconductor device of the present invention is not limited to an HFET that uses 2DEG, and the same effect can be obtained even with field effect transistors having other configurations.

  In the above embodiment, a 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 present invention is not limited to a field effect transistor, and may be applied to an ohmic electrode of a Schottky diode.

The nitride semiconductor of the nitride semiconductor device according to the present invention may be any material as long as it is 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 above-described embodiments, and various modifications can be made within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1,101 GaN layer 2,102 AlGaN layer 3,103 2DEG layer 10 Si substrate 11 Source electrode 12 Drain electrode 13 Gate electrode 15 AlGaN buffer layer 20,120 Nitride semiconductor laminated body 30,130 Insulating film 40 Interlayer insulating film 41 Via 42 Drain electrode pad 106, 109 Recessed part 111, 112 Ohmic electrode P1 First oxygen concentration peak P2 Second oxygen concentration peak P10 First chlorine concentration peak P20 Second chlorine concentration peak S1 interface

Claims (4)

A substrate,
A nitride semiconductor multilayer body formed on the substrate and having a heterointerface;
An ohmic electrode made of a TiAl-based material at least partially formed in the nitride semiconductor laminate,
The nitride semiconductor laminate is
A first nitride semiconductor layer formed on the substrate;
A second nitride semiconductor layer formed on the first nitride semiconductor layer and forming a heterointerface with the first nitride semiconductor layer;
In the oxygen concentration distribution in the depth direction from the ohmic electrode made of the TiAl-based material to the nitride semiconductor laminate,
It has an oxygen concentration peak at a position near the interface in a region closer to the substrate than the interface between the ohmic electrode and the nitride semiconductor laminate,
The oxygen concentration at the oxygen concentration peak is
1.1 × 10 ¹⁸ cm ⁻³ or more and 6.8 × 10 ¹⁸ cm ⁻³ or less,
In the chlorine concentration distribution in the depth direction from the ohmic electrode made of the TiAl-based material to the nitride semiconductor laminate,
It has a chlorine concentration peak at a position near the interface in the region on the substrate side of the interface between the ohmic electrode and the nitride semiconductor laminate,
The chlorine concentration at the above chlorine concentration peak is
A nitride semiconductor device having a size of 5.0 × 10 ¹⁶ cm ⁻³ or more and 9.6 × 10 ¹⁷ cm ⁻³ or less. The nitride semiconductor device according to claim 1,
The nitride semiconductor laminate is
Having a recess that penetrates the second nitride semiconductor layer and reaches the two-dimensional electron gas layer near the heterointerface;
A nitride semiconductor device, wherein at least part of the ohmic electrode is embedded in the recess.   The nitride semiconductor device according to claim 1 or 2,
  The nitride semiconductor device, wherein the ohmic electrode is annealed at a temperature of 400 ° C. or higher and 500 ° C. or lower.   Forming a nitride semiconductor multilayer body having a heterointerface on a substrate;
  The nitride semiconductor laminate is dry-etched using a chlorine-based gas to form a recess that reaches the two-dimensional electron gas layer near the heterointerface,
  During or before the Ti film formation, an amount of oxygen that does not generate an oxide of Ti is flowed to form an ohmic electrode made of a TiAl-based material with at least a portion embedded in the recess,
  By annealing the ohmic electrode at 400 ° C. or more and 500 ° C. or less, an oxygen concentration peak is obtained at a position near the interface in the region closer to the substrate than the interface between the ohmic electrode and the nitride semiconductor laminate. A chlorine concentration peak is obtained at a position near the interface in a region closer to the substrate than the interface between the ohmic electrode and the nitride semiconductor multilayer body, and the oxygen concentration of the oxygen concentration peak is 1.1 × 10 6. ¹⁸ cm ^-3 And 6.8 × 10 ¹⁸ cm ^-3 The chlorine concentration at the chlorine concentration peak is 5.0 × 10 ¹⁶ cm ^-3 And 9.6 × 10 ¹⁷ cm ^-3 A method for manufacturing a nitride semiconductor device, comprising:

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