JP6139494B2 - Nitride semiconductor device - Google Patents

Description

  Embodiments described herein relate generally to a nitride semiconductor device.

  In a semiconductor device, it is effective to use a material having a high critical electric field in order to realize a high breakdown voltage and a low on-resistance. Since nitride semiconductors have a high critical electric field strength, a semiconductor device that achieves high breakdown voltage and low on-resistance can be obtained by using nitride semiconductors.

  In a nitride semiconductor device, as a method for increasing the avalanche resistance, there are a method of connecting a source electrode to a substrate, a method of using a p-type GaN layer, and a method of using a layer structure that generates a two-dimensional hole gas. .

JP 2008-135575 A

  The problem to be solved by the present invention is to provide a nitride semiconductor device having a high avalanche resistance.

The nitride semiconductor device according to the embodiment includes an underlayer, a semiconductor stacked body, a source electrode, a drain electrode, and a gate electrode. The semiconductor stacked body is provided on the base layer and includes a nitride semiconductor. The source electrode and the drain electrode are provided on the semiconductor stacked body and are in contact with the semiconductor stacked body. The gate electrode is provided on the semiconductor stacked body, and is provided between the source electrode and the drain electrode. The semiconductor stacked body includes a first barrier layer provided on the base layer, a second barrier layer provided on the first barrier layer, the first barrier layer, and the first barrier layer. And a carrier traveling layer provided between the two barrier layers. The carrier traveling layer includes GaN. The thickness of the carrier traveling layer is 50 nm or more and 100 nm or less. The first barrier layer includes Al _X Ga _1-X N (0 <X ≦ 0.1). The second barrier layer includes Al _Y Ga _1-Y N (0.2 ≦ Y <1, Y> X). The drain electrode is in contact with the second barrier layer. The source electrode includes a first source electrode and a second source electrode, the first source electrode is in contact with the first barrier layer, and the second source electrode is the second source electrode. The first source electrode includes any one of Ni, Pt, and Pd, the second source electrode includes any one of Ti and Al, and a lower end of the first source electrode. Is located in the first barrier layer. The thickness of the portion of the carrier transit layer located between the gate electrode and the first barrier layer is between the drain electrode of the carrier transit layer and the first barrier layer. It is thinner than the thickness of the located part.

It is a schematic diagram of the nitride semiconductor device concerning a 1st embodiment, (a) is a plane schematic diagram and (b) is a section schematic diagram in the XY position of (a). 3 is an enlarged view of a source electrode on the gate electrode side of the nitride semiconductor device according to the first embodiment. FIG. It is a figure explaining the band structure of the nitride semiconductor device which concerns on 1st Embodiment. It is a cross-sectional schematic diagram of the nitride semiconductor device according to the second embodiment. It is a cross-sectional schematic diagram of the nitride semiconductor device according to the third embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

(First embodiment)
1A and 1B are schematic views of the nitride semiconductor device according to the first embodiment. FIG. 1A is a schematic plan view, and FIG. 1B is a schematic cross-sectional view at the XY position of FIG.

Nitride semiconductor device 1 according to the first embodiment shown in FIG. 1, the underlayer (for example, Si substrate 10), is provided on the undercoat layer, a semiconductor stacked body 45 including a nitride semiconductor, semiconductor A source electrode 120 and a drain electrode 70 provided on the stacked body 45 and a gate electrode 80 provided on the semiconductor stacked body 45 and provided between the source electrode 120 and the drain electrode 70 are provided.

  The semiconductor stacked body 45 includes a first barrier layer 20, a second barrier layer 40, and a carrier traveling layer 30 sandwiched between the first barrier layer 20 and the second barrier layer 40.

  In the region 46 where the source electrode 120 of the semiconductor stacked body 45 is provided, the second barrier layer 40 and the carrier traveling layer 30 are removed. A part of the source electrode 120 is in contact with the first barrier layer 20. A part of the source electrode 120 other than a part of the source electrode 120 is in contact with the second barrier layer 40.

  When viewed from a direction perpendicular to the main surface of the Si substrate 10, the source electrode 120, the drain electrode 70, and the gate electrode 80 are striped.

  In the nitride semiconductor device 1, the buffer layer 11 is provided on the Si substrate 10. By providing the buffer layer 11, distortion caused by the difference between the lattice constant of the Si substrate 10 and the lattice constant of the nitride semiconductor layer on the buffer layer 11 is relieved.

  Further, the buffer layer 11 is required to have a breakdown voltage equal to or higher than the potential difference between the Si substrate 10 and the electrode in addition to the role of relaxing the lattice constant difference. The buffer layer 11 needs to have a thickness proportional to the breakdown voltage of the nitride semiconductor device 1. For example, when the nitride semiconductor device 1 has a withstand voltage of 600 V, the buffer layer 11 needs to have a thickness of about 5 μm. The buffer layer 11 includes a GaN / AlGaN superlattice on AlN.

A first barrier layer 20 including an Al _X Ga _1-X N layer is provided on the buffer layer 11. On the first barrier layer 20, a carrier traveling layer 30 including a GaN layer is provided. The carrier traveling layer 30 is a non-doped layer. A second barrier layer 40 including an Al _Y Ga _1-Y N layer (Y> X) is provided on the carrier traveling layer 30.

  The film thickness of the first barrier layer 20 is, for example, 20 nm or more and 2 μm or less. When the film thickness of the first barrier layer 20 is smaller than the above-described film thickness, electrons generated in the carrier traveling layer 30 may leak to the buffer layer 11 side. For this reason, it is desirable that the film thickness of the first barrier layer 20 be the above-described film thickness. The film thickness of the carrier traveling layer 30 is, for example, 50 nm. The film thickness of the second barrier layer 40 is not less than 5 nm and not more than 40 nm.

Due to the polarization due to the strain caused by the difference in lattice constant between the GaN layer (carrier traveling layer 30) and the Al _X Ga _1-X N layer (second barrier layer 40), the carrier traveling layer 30 in the carrier traveling layer 30 and the second Near the interface with the barrier layer 40, a two-dimensional electron system 30e is formed. That is, the nitride semiconductor device 1 can form a channel of a transistor. Further, a two-dimensional hole system 30 h is formed near the interface between the carrier traveling layer 30 and the first barrier layer 20 in the carrier traveling layer 30. In this specification, electrons generated in the two-dimensional electron system 30e are two-dimensional electron gas (2DEG), and holes generated in the two-dimensional hole system 30h are two-dimensional hole gas (two-dimensional electron gas). hole gas: 2DHG).

On the second barrier layer 40, a surface protective film 50 including a SiN film is provided. A gate insulating film 60 including at least one selected from the group of SiN film, SiO ₂ film, Al ₂ O ₃ film, and various high-k (high dielectric constant) films is provided on the surface protective film 50. ing.

  In the nitride semiconductor device 1, a part of the surface protective film 50 and the gate insulating film 60 on the part of the surface protective film 50 are removed. A drain electrode 70 is provided at the removed place. The drain electrode 70 is in contact with the second barrier layer 40. The drain electrode 70 is in electrical ohmic contact with the two-dimensional electron system 30e.

  In the nitride semiconductor device 1, a part of the surface protection film 50 in a region different from the region where the drain electrode 70 is provided, and the carrier traveling layer 30 and the second layer under the part of the surface protection film 50. The barrier layer 40 is removed. Further, a part of the surface of the carrier traveling layer 30 under a part of the surface protective film 50 is removed. A gate insulating film 60 is provided in the removed portion. That is, the gate insulating film 60 is formed so as to protrude from the interface position between the carrier traveling layer 30 and the second barrier layer 40 to the carrier traveling layer 30 side. A gate electrode 80 is provided on the gate insulating film 60.

In the nitride semiconductor device 1, a source electrode 120 is provided in addition to the drain electrode 70 and the gate electrode 80. In the region where the source electrode 120 is provided, the second barrier layer 40, the carrier traveling layer 30, and a part of the surface of the first barrier layer 20 are removed. The source electrode 120 includes a first source electrode 100 and a second source electrode 110. At least a part of the first source electrode 100 is in contact with the first barrier layer 20, and at least a part of the second source electrode 110 is in contact with the second barrier layer 40. The first source electrode 100 is a p-side electrode , and the second source electrode 110 is an n-side electrode.

  The source electrode 120 is in ohmic contact with the two-dimensional electron system 30 e by a portion in contact with the second barrier layer 40. The source electrode 120 is in ohmic contact with the two-dimensional hole system 30 h by a portion in contact with the first barrier layer 20.

FIG. 2 is an enlarged cross-sectional view of the source electrode on the gate electrode side of the nitride semiconductor device according to the first embodiment.
In the nitride semiconductor device 1, the second barrier layer 40 and the carrier traveling layer 30 are removed, and the first source electrode 100 is embedded so that the first source electrode 100 and the two-dimensional hole system 30 h are in ohmic contact. I am letting. Further, the second source electrode 110 is in ohmic contact with the two-dimensional electron system 30 e through the second barrier layer 40. L1, L2, and W1 in FIG. 2 will be described later.

  FIG. 3 is a graph illustrating the band structure of the nitride semiconductor device according to the first embodiment.

  FIG. 3 shows the band structure in the vertical direction of the nitride semiconductor device 1 obtained by calculation. That is, the horizontal axis in FIG. 3 represents the depth from the second barrier layer 40 toward the first barrier layer 20, and the vertical axis represents energy. In the direction parallel to the horizontal axis in FIG. 2, ranges of the second barrier layer 40, the carrier traveling layer 30, and the first barrier layer 20 are shown.

As shown in FIG. 3, the interface between the carrier traveling layer 30 and the second barrier layer 40 in the carrier traveling layer 30 is caused by polarization due to distortion due to a lattice constant difference between the GaN layer and the Al _Y Ga _1-Y N layer. A two-dimensional electron system 30e is formed in the vicinity. Further, due to the polarization of the first barrier layer 20 and the carrier traveling layer 30, the vicinity of the interface between the carrier traveling layer 30 and the first barrier layer 20 in the carrier traveling layer 30 is the most for holes. A place with low energy is generated. For this reason, when holes are generated, a two-dimensional hole system 30 h is formed near the interface between the carrier traveling layer 30 and the first barrier layer 20 in the carrier traveling layer 30.

  Thus, in the nitride semiconductor device 1, the two-dimensional electron system 30e and the two-dimensional hole system 30h can be generated simultaneously in the non-doped carrier traveling layer 30. For this reason, in the nitride semiconductor device 1, when a high voltage is applied between the source and drain electrodes and an avalanche breakdown occurs just before the breakdown voltage limit, electrons are in the two-dimensional electron system 30e and holes are in the two-dimensional hole system. Injected for 30 h.

  Electrons move to the drain electrode 70 having a higher potential and are absorbed by the drain electrode 70 that is in ohmic contact with the two-dimensional electron system 30e. Further, the holes move to the source electrode 120 having a lower potential and are absorbed by the source electrode 120 that is in ohmic contact with the two-dimensional hole system 30h. For this reason, since electrons and holes generated by avalanche breakdown in the carrier traveling layer 30 are absorbed by the two-dimensional electron system 30e and the two-dimensional hole system 30h in the same layer, carriers are efficiently transferred from the carrier traveling layer 30. Can be discharged.

  In the nitride semiconductor device 1 capable of simultaneously generating the two-dimensional electron system 30e and the two-dimensional hole system 30h in the non-doped carrier traveling layer 30, the mobility and two-dimensional hole of the two-dimensional electron system 30e are generated. The mobility of the system 30h is increased. Therefore, the nitride semiconductor device 1 can efficiently absorb electrons and holes generated by avalanche breakdown. As a result, a nitride semiconductor device having a high avalanche resistance can be realized.

  In the nitride semiconductor device 1, the first source electrode 100 in contact with the first barrier layer 20 and in ohmic contact with the two-dimensional hole system 30 h and the second barrier layer 40 are in contact with each other. It is desirable to separate the respective materials for the second source electrode 110 that is in ohmic contact with the electron system 30e.

  For example, a material containing Ni, Pt, and Pd is used for the first source electrode 100. Thereby, the contact resistance between the first source electrode 100 and the two-dimensional hole system 30h can be lowered. A material containing Ti and Al is used for the second source electrode 110. Thereby, the contact resistance between the second source electrode 110 and the two-dimensional electron system 30e can be lowered. As a result, when the nitride semiconductor device 1 is in the ON state, a low on-resistance is realized by the two-dimensional electron system 30e, and when avalanche breakdown occurs, the two-dimensional hole system 30h is used to efficiently and positively The hole can be pulled out.

  The second source electrode 110 may be made of the same material as the drain electrode 70. By using the same material, the second source electrode 110 and the drain electrode 70 can be manufactured more easily.

  In the nitride semiconductor device 1, the two-dimensional hole system 30h may be generated only when avalanche breakdown occurs. Therefore, as shown in FIG. 3, it is desirable that the energy of the valence band at the interface between the first barrier layer 20 and the carrier traveling layer 30 is lower than the Fermi energy indicated by zero energy. In order to reduce the on-resistance, it is desirable that the carrier concentration of the two-dimensional electron system 30e is large. Therefore, it is desirable that the polarization generated on the second barrier layer 40 side is larger in the carrier traveling layer 30 than the polarization generated on the first barrier layer 20 side.

Therefore, when a nitride semiconductor layer is composed of GaN and AlGaN, Al _X Ga _1-X N is used for the first barrier layer 20, GaN is used for the carrier travel layer 30, and Al is used for the second barrier layer 40. _Y Ga _1-Y N layer (Y> X) is preferably used. For example, an AlGaN layer having an Al composition ratio with X being 0.1 or less is used for the first barrier layer 20, and an AlGaN layer with Y being 0.2 or more is used for the second barrier layer 40. Further, by forming the nitride semiconductor layer with GaN and AlGaN, the nitride semiconductor layer can be formed with the highest quality film, so that the on-resistance can be lowered.

  Further, the semiconductor layer need not be formed of GaN or AlGaN, and for example, an InAlN layer or a mixture with InAlN may be used.

  Further, in the nitride semiconductor device 1, the film thickness of the carrier traveling layer 30 is desirably 100 nm or less. Holes generated in the carrier traveling layer 30 due to avalanche breakdown are absorbed by the two-dimensional hole system 30 h in the same carrier traveling layer 30. In the nitride semiconductor device 1, since the generation location and the absorption location are in the same layer, holes can be efficiently discharged from the carrier travel layer 30. If the film thickness of the carrier traveling layer 30 is larger than 100 nm and is separated, the effect is reduced. Therefore, the film thickness of the carrier traveling layer 30 is desirably 100 nm or less.

  Further, the first barrier layer 20 has a role of lifting the band structure as a whole as shown in FIG. 3 due to its polarization. In the nitride semiconductor device 1, the second barrier layer 40 in the portion of the gate electrode 80 is removed, and the gate insulating film 60 and the gate electrode 80 are formed in the removed portion, thereby providing an effect of increasing the threshold voltage. ing. Since the effect of increasing the threshold voltage is also reduced when the carrier traveling layer 30 is larger than 100 nm, the thickness of the carrier traveling layer 30 is desirably 100 nm or less.

  As described above, in the nitride semiconductor device 1, by setting the carrier traveling layer 30 to 100 nm or less, a nitride semiconductor device with improved threshold voltage and increased avalanche resistance is realized. Further, by improving the threshold voltage, a normally-off nitride semiconductor device with high avalanche resistance can be realized.

  In the nitride semiconductor device 1, acceptors such as Mg and C can be introduced into the first barrier layer 20 to make the first barrier layer 20 p-type. In this case, the hole concentration of the two-dimensional hole system 30h can be increased, and as a result, the avalanche resistance can be further increased.

  However, it is difficult to activate Mg or C, and there is a concern that the acceptor or the like diffuses into the carrier traveling layer 30. Therefore, in the first embodiment, the first barrier layer 20 is a non-doped layer, the mobility of the two-dimensional hole system 30h is increased, and the bottom of the source electrode 120 is brought into contact with the non-doped first barrier layer 20. As a result, the avalanche resistance is increased.

  Further, as shown in FIG. 2, the first barrier from the surface of the second barrier layer 40 in the region where the second barrier layer 40 and the carrier traveling layer 30 are removed and the first barrier layer 20 is exposed. The depth L2 to the surface of the layer 20 is shorter than the thickness L1 of the source electrode.

  In other words, the total length of the film thickness of the first source electrode 100 and the film thickness of the second source electrode 110 is L1, and this length L1 is equal to the second barrier layer 40 and the carrier. It is longer than the depth L2 from which a part of the surface of the traveling layer 30 and the first barrier layer 20 is removed.

  In addition, the thickness of the source electrode 120 in the region formed on the second barrier layer 40, that is, the total length of the film thickness of the first source electrode 100 and the film thickness of the second source electrode 110 is , Longer than L2. Thereby, the thickness L1 of the source electrode 120 in the region formed on the first barrier layer 20 and the thickness of the source electrode 120 in the region formed on the second barrier layer 40 are formed with the same thickness. Even in this case, disconnection can be suppressed, and a nitride semiconductor device having a high avalanche resistance can be easily manufactured by a simple method.

  In this way, even if the source electrode 120 has a step, a so-called step breakage hardly occurs in the step portion. As a result, the source electrode 120 can simultaneously make ohmic contact with the two-dimensional electron system 30e and the two-dimensional hole system 30h, and a nitride semiconductor device with high avalanche resistance can be easily manufactured.

  For example, the film thickness of the carrier traveling layer 30 is 50 nm, the film thickness of the second barrier layer 40 is 30 nm, L2 is 100 nm, and L1 of the source electrode 120 is 200 nm.

  In addition, a length (width) W1 in a direction from the source electrode 120 to the drain electrode 70 at a boundary where a part of the source electrode 120 and the first barrier layer 20 are in contact is longer than L2. By making the depth L2 smaller than the width W1 at which the bottom 100b of the first source electrode 100 is in contact with the first barrier layer 20, the first source electrode 100 can be easily embedded. A two-dimensional electron system 12 and a two-dimensional hole system 13 can be in ohmic contact simultaneously, and a nitride semiconductor device having a high avalanche resistance can be easily manufactured.

  For example, the thickness of the carrier traveling layer 30 is 50 nm, the thickness of the second barrier layer 40 is 30 nm, L2 is 100 nm, and the width W1 of the bottom 100b of the first source electrode 100 is 2 μm.

(Second Embodiment)
FIG. 4 is a schematic cross-sectional view of the nitride semiconductor device according to the second embodiment.

  The nitride semiconductor device 2 according to the second embodiment is different from the nitride semiconductor device 1 according to the first embodiment in that the source electrode 120 is formed of one kind. By making the material of the source electrode 120 one type, the source electrode 120 can be manufactured more easily.

(Third embodiment)
FIG. 5 is a schematic cross-sectional view of a nitride semiconductor device according to the third embodiment.

  The nitride semiconductor device 3 according to the third embodiment is different from the nitride semiconductor device 1 according to the first embodiment in that the second barrier layer 20 and the carrier traveling layer 30 are not removed in the gate portion. Is a point.

  Thus, in the embodiment, the gate structure is not particularly limited. For example, the gate structure may be a recess structure or may not be a recess structure. The gate structure may be a MIS structure having a gate insulating film 60, a Schottky gate structure that is Schottky connected to a semiconductor layer, or a gate structure that may be a junction gate having a p-type layer and an n-type layer. . Further, the surface protective film 50 may be removed.

In this specification, “nitride semiconductor” refers to B _x In _y Al _z Ga _1-xyz N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z ≦ 1) It is assumed that the semiconductors having all compositions in which the composition ratios x, y, and z are changed within the respective ranges in the following chemical formula Furthermore, in the above chemical formula, those further containing a group V element other than N (nitrogen), those further containing various elements added for controlling various physical properties such as conductivity type, and unintentionally Those further including various elements included are also included in the “nitride semiconductor”.

  The embodiment has been described above with reference to specific examples. However, the embodiments are not limited to these specific examples. In other words, those specific examples that have been appropriately modified by those skilled in the art are also included in the scope of the embodiments as long as they include the features of the embodiments. Each element included in each of the specific examples described above and their arrangement, material, condition, shape, size, and the like are not limited to those illustrated, and can be appropriately changed.

  In addition, each element included in each of the above-described embodiments can be combined as long as technically possible, and combinations thereof are also included in the scope of the embodiment as long as they include the features of the embodiment. In addition, in the category of the idea of the embodiment, those skilled in the art can conceive various changes and modifications, and it is understood that these changes and modifications also belong to the scope of the embodiment. .

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  1, 2, 3 ... Nitride semiconductor device, 10 ... Si substrate, 11 ... Buffer layer, 20 ... First barrier layer, 30 ... Carrier traveling layer, 30e ... 2D electron system, 30h ... -Two-dimensional hole system, 40 ... Second barrier layer, 45 ... Semiconductor stack, 46 ... Area, 50 ... Surface protective film, 60 ... Gate insulating film, 70 ... Drain electrode, 80 ...・ Gate electrode 100 ・ ・ First source electrode 110 ・ ・ Second source electrode 120 ・ ・ Source electrode

Claims (4)

An underlayer,
A semiconductor stacked body provided on the underlayer and including a nitride semiconductor;
A source electrode and a drain electrode provided on the semiconductor stacked body and in contact with the semiconductor stacked body;
A gate electrode provided on the semiconductor stacked body and provided between the source electrode and the drain electrode;
With
The semiconductor stacked body includes a first barrier layer provided on the base layer, a second barrier layer provided on the first barrier layer, the first barrier layer, and the first barrier layer. A carrier traveling layer provided between the two barrier layers,
The carrier traveling layer includes GaN,
The thickness of the carrier traveling layer is 50 nm or more and 100 nm or less,
The first barrier layer includes Al _X Ga _1-X N (0 <X ≦ 0.1),
The second barrier layer includes Al _Y Ga _1-Y N (0.2 ≦ Y <1, Y> X),
The drain electrode is in contact with the second barrier layer;
The source electrode includes a first source electrode and a second source electrode, the first source electrode is in contact with the first barrier layer, and the second source electrode is the second source electrode. In contact with the barrier layer of
The first source electrode includes any one of Ni, Pt, and Pd, and the second source electrode includes any one of Ti and Al,
A lower end of the first source electrode is located in the first barrier layer;
The thickness of the portion of the carrier transit layer located between the gate electrode and the first barrier layer is between the drain electrode of the carrier transit layer and the first barrier layer. A nitride semiconductor device that is thinner than the thickness of the portion where it is located.   The nitride semiconductor device according to claim 1, wherein the first barrier layer is a non-doped layer, and a bottom portion of the source electrode is in contact with the first barrier layer.   3. The nitride semiconductor device according to claim 1, wherein a depth from a surface of the second barrier layer to a surface of the first barrier layer is shorter than a thickness of the source electrode.   The length of the boundary between the source electrode and the first barrier layer in the direction from the source electrode to the drain electrode is the depth from the surface of the second barrier layer to the surface of the first barrier layer. The nitride semiconductor device according to any one of claims 1 to 3, wherein the nitride semiconductor device is longer.

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