Nitride semiconductor devices

Abstract

To provide a nitride semiconductor element that can reduce current collapse and improve breakdown voltage.SOLUTION: A nitride semiconductor element includes a nitride semiconductor structure including an active region where a channel is formed, a transistor unit including a part of the nitride semiconductor structure, a diode unit including another part of the nitride semiconductor structure. The transistor unit includes a source electrode, a drain electrode, a gate electrode, a first field plate electrode. The diode unit includes a first electrode electrically connected to the source electrode, a second electrode electrically connected to the drain electrode, a third electrode, and a second field plate electrode. The first electrode is short-circuited to the third electrode, and the length of the first field plate electrode in a direction where the gate electrode and the drain electrode are connected is larger than the length of the second field plate electrode in a direction where the third electrode and the second electrode are connected.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a nitride semiconductor device. [Background technology]

[0002] There is a demand for transistors using nitride semiconductors to improve the current collapse phenomenon. For example, Patent Document 1 describes a compound semiconductor device provided with a field plate electrode to improve the current collapse phenomenon. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2014-072379 Summary of the Invention [Problem to be solved by the invention]

[0004] In a transistor with a field plate electrode, the electric field is concentrated at the electrode end of the field plate electrode, so the breakdown voltage of the transistor tends to be lower than that of a transistor without a field plate electrode. The longer the distance between the field plate electrode and the drain electrode, the higher the breakdown voltage of the transistor, but the higher the element resistance of the transistor. [Means for solving the problem]

[0005] a first field plate electrode connected to the source electrode and covering the gate electrode in a planar view; and a second field plate electrode connected to the first electrode and covering the third electrode in a planar view. The first electrode is short-circuited to the third electrode. A nitride semiconductor device according to one embodiment of the present invention comprises: a nitride semiconductor structure including an active region in which a channel is formed; a transistor portion including a part of the nitride semiconductor structure; and a diode portion including another part of the nitride semiconductor structure. The transistor portion has a source electrode, a drain electrode, a gate electrode, and a first field plate electrode connected to the source electrode and covering the gate electrode in a planar view. The diode portion has a first electrode electrically connected to the source electrode, a second electrode electrically connected to the drain electrode, a third electrode located between the first electrode and the second electrode in a planar view, and a second field plate electrode connected to the first electrode and covering the third electrode in a planar view. The first electrode is short-circuited to the third electrode. A length of the first field plate electrode in a direction connecting the gate electrode and the drain electrode is greater than a length of the second field plate electrode in a direction connecting the third electrode and the second electrode. Effect of the Invention

[0006] According to the nitride semiconductor device of one aspect of the present invention, it is possible to reduce current collapse and improve the breakdown voltage. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic plan view showing a nitride semiconductor device according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. [Diagram 3] 1 is a graph showing current-voltage characteristics of a nitride semiconductor device according to an example. [Figure 4] 4 is a graph showing current-voltage characteristics of a diode portion of the nitride semiconductor device of the example. [Diagram 5] 4 is a graph showing current-voltage characteristics of a transistor portion of a nitride semiconductor device according to an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals.

[0009] Fig. 1 is a schematic plan view showing the nitride semiconductor device of this embodiment. Fig. 2 is a schematic cross-sectional view taken along line II-II in Fig. 1. As shown in Fig. 1 and Fig. 2, the nitride semiconductor device 100 of this embodiment has a nitride semiconductor structure 10 including an active region in which a channel is formed, a transistor section 20 including a part of the nitride semiconductor structure 10, and a diode section 30 including another part of the nitride semiconductor structure 10.

[0010] The transistor section 20 has a source electrode 21, a drain electrode 22, a gate electrode 23, and a first field plate electrode 24. The first field plate electrode 24 is connected to the source electrode 21, and covers the gate electrode 23 in a plan view. The transistor section can function as a field effect transistor.

[0011] The diode section 30 has a first electrode 31, a second electrode 32, a third electrode 33, and a second field plate electrode 34. The first electrode 31 is electrically connected to the source electrode 21. The second electrode 32 is electrically connected to the drain electrode 22. The third electrode 33 is located between the first electrode 31 and the second electrode 32 in a planar view. The second field plate electrode is connected to the first electrode 31 and covers the third electrode 33 in a planar view. The first electrode 31 is short-circuited with the third electrode 33. As a result, the diode section 30 has a structure similar to that of the transistor section 20, but unlike the transistor section 20, can function as a diode.

[0012] The length L of the first field plate electrode 24 in the direction connecting the gate electrode 23 and the drain electrode 22 b1 is the length L of the second field plate electrode 34 in the direction connecting the third electrode 33 and the second electrode 32. b2is larger than . As a result, the electric field applied to the third electrode 33 can be made stronger than the electric field applied to the gate electrode 23, so that the voltage at which the diode section 30 punches through can be made lower than the voltage at which the transistor section 20 is destroyed. Therefore, when a voltage is applied to the nitride semiconductor device 100, the diode section 30 can be punched through before the transistor section 20 is destroyed. In the diode section 30, a conductive path is substantially formed between the first electrode 31 and the third electrode 33 due to the punch-through phenomenon. Therefore, when the diode section 30 punches through, the source-drain voltage of the transistor section 20 is clamped. Therefore, even if a voltage exceeding the breakdown voltage of the transistor section 20 is applied to the nitride semiconductor device 100, the breakdown of the transistor section 20 can be avoided. That is, the breakdown voltage of the nitride semiconductor device 100 can be improved. Furthermore, by providing the diode section 30, the breakdown voltage of the nitride semiconductor device 100 can be made higher than the breakdown voltage of the transistor section 20, so that the gate-drain distance of the transistor section 20 can be reduced and current collapse can be reduced. Note that the distance refers to the shortest distance.

[0013] The breakdown voltage of the transistor section 20 can be set to 600V or more, and is preferably set to 1200V or more. This allows the transistor section 20 to be used in applications such as in-vehicle applications that require high voltage resistance. The breakdown voltage of the transistor section 20 is, for example, 1500V or less. The breakdown voltage of the transistor section 20 is the voltage between the drain and source of the transistor section 20. The voltage at which the diode section 30 punches through can be set to 300V or more, and is preferably set to 900V or more. This allows the transistor section 20 to be used in applications such as in-vehicle applications that require high voltage resistance. The voltage at which the diode section 30 punches through is, for example, 1200V or less.

[0014] In the nitride semiconductor device 100, the probability of breakdown of the transistor section 20 is reduced by the diode section 30, so that the length L b1This can reduce current collapse in the transistor section 20. b1 is the distance from the gate electrode 23 to the end of the first field plate electrode 24 on the drain electrode 22 side in a plan view. b2 is the distance from the third electrode 33 to the end of the second field plate electrode 34 on the second electrode 32 side in a plan view. The distance refers to the shortest distance.

[0015] The length L of the first field plate electrode 24 b1 is the distance L between the gate electrode 23 and the drain electrode 22 a1 The distance L between the gate electrode 23 and the drain electrode 22 can be less than a1 It is preferable to make the length L of the first field plate electrode 24 smaller than the drain electrode 22 by 0.5 μm or more. This makes it possible to improve the breakdown voltage between the first field plate electrode 24 and the drain electrode 22 and reduce current collapse at the same time. b1 can be 1 μm or more, and the distance L between the gate electrode 23 and the drain electrode 22 a1 It is preferable that the length L of the second field plate electrode 34 is at least half of the length L of the second field plate electrode 34. This makes it possible to effectively reduce current collapse. b2 The length L of the second field plate electrode 34 can be set to 1 μm or more. b2 is the distance L between the third electrode 33 and the second electrode 32 a2 The distance L between the third electrode 33 and the second electrode 32 can be less than a2 This has the advantage that the electric fields applied to the second field plate electrode 34 and the third electrode 33 can be balanced and the distance between the second electrode 32 and the third electrode 33 can be made shorter for a desired punch-through voltage.

[0016] By providing the diode section 30 with the second field plate electrode 34, the electric field near the third electrode 33 can be reduced. This makes it possible to increase the punch-through voltage of the diode section 30 compared to a case in which the second field plate electrode 34 is not provided, and therefore the distance between the second electrode 32 and the third electrode 33 can be shortened. In the nitride semiconductor device 100, the diode section 30 can be turned off regardless of whether the transistor section 20 is on or off, so the length L of the second field plate electrode 34 can be reduced. b2 is the length L of the first field plate electrode 24 b1 It can be smaller than .

[0017] Distance L between the gate electrode 23 and the drain electrode 22 a1 is the distance L between the second electrode 32 and the third electrode 33. a2 Since the diode section 30 reduces the probability of breakdown of the transistor section 20, the distance L between the gate electrode 23 and the drain electrode 22 is smaller than a1 can be reduced, thereby reducing the resistance of the transistor section 20.

[0018] Distance L between the gate electrode 23 and the drain electrode 22 a1 The distance L between the gate electrode 23 and the drain electrode 22 can be set to 1 μm or more, and is preferably set to 10 μm or more. This makes it easier to set the breakdown voltage of the transistor section 20 higher than the voltage at which the diode section 30 punches through. a1 The distance L between the second electrode 32 and the third electrode 33 may be 20 μm or less. This can further reduce the resistance of the transistor section 20. a2 This makes it easy to design the transistor section 20 so that its breakdown voltage is greater than the punch-through voltage of the diode section 30.

[0019] The gate electrode 23 and the third electrode 33 are made of, for example, the same material. This allows them to be formed simultaneously, thereby reducing the number of steps and enabling costs to be reduced. The source electrode 21, the drain electrode 22, the first electrode 31, and the second electrode 32 are made of, for example, the same material. This allows them to be formed simultaneously, thereby reducing the number of steps and enabling costs to be reduced.

[0020] The gate electrode 23 and the third electrode 33 contain, for example, Ni. The gate electrode 23 and the third electrode 33 are composed of, for example, a structure in which Ni / Au / Pt are laminated in this order from the nitride semiconductor structure 10 side, a structure in which Ti / Al are laminated, or a Ni single film. The source electrode 21, the drain electrode 22, the first electrode 31, and the second electrode 32 are composed of, for example, Ti / Al. These electrodes are formed, for example, by removing a part of the nitride semiconductor structure 10 and at a position in contact with the channel. The first field plate electrode 24 and the second field plate electrode 34 are composed of, for example, Al.

[0021] The nitride semiconductor structure 10 may be disposed on a substrate 40. The substrate 40 is, for example, a sapphire substrate. The nitride semiconductor structure 10 may be composed of a plurality of nitride semiconductor layers. Examples of nitride semiconductors that compose the nitride semiconductor structure 10 include Group III nitride semiconductors. Examples of Group III nitride semiconductors include GaN, InGaN, AlGaN, AlN, and AlInGaN.

[0022] The nitride semiconductor structure 10 can have a first nitride semiconductor layer 11, a second nitride semiconductor layer 12, a gate contact layer 13, and a third electrode contact layer 14. The first nitride semiconductor layer 11 is a layer in which a channel is formed. The channel is, for example, a two-dimensional electron gas. The first nitride semiconductor layer 11 is made of, for example, GaN. The second nitride semiconductor layer 12 is provided on the first nitride semiconductor layer 11 and has a band gap energy larger than that of the first nitride semiconductor layer 11. The second nitride semiconductor layer 12 is made of, for example, AlGaN. A thinner AlN layer may be provided below the AlGaN layer. The nitride semiconductor structure 10 can be formed by, for example, metalorganic chemical vapor deposition (MOCVD).

[0023] The gate contact layer 13 is located between a part of the second nitride semiconductor layer 12 and the gate electrode 23. The gate contact layer 13 has a p-type impurity-containing layer that contains a p-type impurity, for example. The p-type impurity is, for example, Mg. The gate contact layer 13 may be composed of a plurality of layers. The gate contact layer 13 is formed, for example, by forming a layer containing a p-type impurity-containing layer on the entire second nitride semiconductor layer 12, and then removing the layer containing the p-type impurity-containing layer other than the part where the gate electrode 23 is to be formed. After removing the part of the layer containing the p-type impurity-containing layer, a heat treatment may be performed. The heat treatment is performed, for example, in an atmosphere containing H2 and NH3 at a temperature of 700 to 800°C for 30 minutes. This heat treatment can promote the generation of two-dimensional electron gas. In addition, after that, a passivation film such as SiO2, SiN, AlN, Al2O3, etc. may be formed, and then a heat treatment may be performed in an N2 atmosphere at a temperature of 550°C. This can further promote the generation of two-dimensional electron gas.

[0024] The third electrode contact layer 14 is located between another part of the second nitride semiconductor layer 12 and the third electrode 33. The third electrode contact layer 14 has, for example, a p-type impurity-containing layer that contains a p-type impurity. The p-type impurity is, for example, Mg. The third electrode contact layer 14 may be composed of a plurality of layers. The gate contact layer 13 and the third electrode contact layer 14 are made of, for example, the same material. The gate contact layer 13 and the third electrode contact layer 14 may have the same layer structure. In this way, if the gate contact layer 13 and the third electrode contact layer 14 are similar, they can be formed at the same time, which reduces the number of steps and allows costs to be reduced.

[0025] The nitride semiconductor structure 10 of the transistor section 20 and the nitride semiconductor structure 10 of the diode section 30 can be the same. For example, the nitride semiconductor structure 10 can be formed on one substrate 40, with a part of the nitride semiconductor structure 10 being part of the transistor section 20 and another part of the nitride semiconductor structure 10 being part of the diode section 30. By simultaneously forming the nitride semiconductor structure 10 of the transistor section 20 and the nitride semiconductor structure 10 of the diode section 30 in this manner, the number of steps can be reduced, enabling costs to be reduced.

[0026] The nitride semiconductor element 100 may be provided with a recess 50 that separates the channel of the transistor section 20 from the channel of the diode section 30. This can reduce the leakage current flowing between the diode section 30 and the transistor section 20. The nitride semiconductor structure 10 of the transistor section 20 and the nitride semiconductor structure 10 of the diode section 30 may be partially connected or completely separated. In FIG. 1 and FIG. 2, the recess 50 is provided at a position that connects the transistor section 20 and the diode section 30 at the shortest distance, and the nitride semiconductor structure 10 is connected at other positions. The bottom surface of the recess 50 may be a part of the nitride semiconductor structure 10 or the surface of the substrate 40. In FIG. 2, the bottom surface of the recess 50 is the surface of the substrate 40. This can more reliably separate the nitride semiconductor structure 10 of the transistor section 20 from the nitride semiconductor structure 10 of the diode section 30, and can further reduce the leakage current.

[0027] The nitride semiconductor device 100 may have a passivation film provided on the surface of the nitride semiconductor device 100. The nitride semiconductor device 100 may also have an insulating film provided between each electrode. Examples of the passivation film and the insulating film include a film containing silicon and nitrogen (e.g., a SiN film), a film containing silicon and oxygen (e.g., a SiO2 film), a film containing aluminum and nitrogen (e.g., an AlN film), or a film containing aluminum and oxygen (e.g., an Al2O3 film). The nitride semiconductor device 100 may have other members such as a pad electrode.

[0028] (Example) As an example, an element having a structure generally the same as that of the nitride semiconductor element 100 shown in Fig. 1 and Fig. 2 was fabricated. First, a buffer layer, a 600 nm undoped GaN layer, a 1 nm undoped AlN layer, a 9 nm undoped AlGaN layer, a 30 nm Mg-doped GaN layer, a 20 nm undoped GaN layer, and a 20 nm undoped AlGaN layer were laminated in this order on a substrate 40 made of sapphire to form a nitride semiconductor structure 10. Ni was formed on the surface of the undoped AlGaN layer as the gate electrode 23 and the third electrode 33. The three layers from the top undoped AlGaN layer to the Mg-doped GaN layer of the nitride semiconductor structure 10 were removed except for the portions immediately below the gate electrode 23 and the third electrode 33. In the formation region of the source electrode 21, the drain electrode 22, the first electrode 31, and the second electrode 32, a part of the nitride semiconductor structure 10 was removed until the undoped GaN layer was exposed, and the source electrode 21, the drain electrode 22, the first electrode 31, and the second electrode 32 were formed at a position covering the side surface formed by the removal. The laminated structure of the source electrode 21, the drain electrode 22, the first electrode 31, and the second electrode 32 was Ti / Al in order from the substrate 40 side. The nitride semiconductor structure 10 between the transistor section 20 and the diode section 30 was partially removed. An Al2O3 film and a SiN film were formed as an insulating film covering the source electrode 21, the drain electrode 22, the gate electrode 23, the first electrode 31, the second electrode 32, and the third electrode 33. A part of the insulating film was removed, and a first field plate electrode 24 connected to the source electrode 21 and a second field plate electrode 34 connected to the first electrode 31 were formed.

[0029] The transistor section 20 had a source-gate distance of 2 μm, a gate length of 1 μm, and a gate-drain distance of 10 μm. The length of the first field plate electrode 24 was 9 μm. The distance between the first field plate electrode 24 and the drain electrode 22 was 1 μm. The diode section 30 had a distance between the first electrode 31 and the third electrode 33 of 2 μm, a length of the third electrode 33 of 1 μm, and a distance between the second electrode 32 and the third electrode 33 of 14 μm. The length of the second field plate electrode 34 was 3 μm. The distance between the second field plate electrode 34 and the second electrode 32 was 11 μm. The nitride semiconductor device 100 thus formed was sealed with polyimide resin.

[0030] Note that the nitride semiconductor element 100 of the embodiment differs from the structure shown in Figures 1 and 2 in that the source electrode 21 of the transistor section 20 and the first electrode 31 of the diode section 30 are not connected, and the drain electrode 22 of the transistor section 20 and the second electrode 32 of the diode section 30 are not connected, so that the characteristics of the transistor section 20 and the diode section 30 can be measured independently.

[0031] Fig. 3 is a graph showing the current-voltage characteristics of the nitride semiconductor device 100 of the example. Fig. 3 was obtained by connecting the source electrode 21 of the transistor section 20 to the first electrode 31 of the diode section 30, connecting the drain electrode 22 of the transistor section 20 to the second electrode 32 of the diode section 30, and shorting the first electrode 31 and third electrode 33 of the diode section 30, and then performing measurements. The gate voltage applied to the nitride semiconductor device 100 was set to 0 V, and the source-drain voltage V ds The current waveform of the entire device was measured by increasing the voltage from 0 V to 2000 V. In Fig. 3, the solid line indicates the drain current I d The dashed line indicates the gate current I g From Figure 3, we can see that the voltage is clamped at around 1200V.

[0032] Fig. 4 is a graph showing the current-voltage characteristics of the diode section 30 of the nitride semiconductor device 100 of the example. Fig. 5 is a graph showing the current-voltage characteristics of the transistor section 20 of the nitride semiconductor device 100 of the example. Figs. 4 and 5 were obtained by individually driving the diode section 30 or the transistor section 20 and measuring the current-voltage characteristics. In Fig. 4, the solid line indicates the current I2 flowing through the second electrode 32, and the dashed line indicates the current I3 flowing through the third electrode 33. In Fig. 5, the solid line indicates the drain current I d The dashed line indicates the gate current I g Shows.

[0033] Fig. 4 shows a current waveform when the first electrode 31 and the second electrode 32 of the diode section 30 are electrically connected and the voltage between the first electrode 31 and the second electrode 32 of the diode section 30 is increased from 0 V to 2000 V. From Fig. 4, it can be seen that the voltage is clamped at around 1200 V, similar to Fig. 3.

[0034] 5 shows a current waveform when the source-drain voltage applied to the transistor section 20 alone is increased from 0 V to 2000 V. In FIG. 5, the drain current I d rises, and the gate current I g is negative. The gate current I g When the potential becomes negative, it indicates that the insulation between the drain electrode 22 and the first field plate electrode 24 has been broken down and a current is flowing in from the drain electrode 22. From this, it is presumed that the transistor section 20 was broken down at around 1700V.

[0035] From the above, it can be said that by electrically connecting the transistor section 20, which will be destroyed when 2000 V is applied, to the diode section 30, the voltage is clamped before it reaches the breakdown voltage of the transistor section 20, making it possible to avoid destruction of the transistor section 20.

[0036] The above describes the embodiments of the present invention with reference to specific examples. However, the present invention is not limited to these specific examples. All forms that can be implemented by a person skilled in the art through appropriate design modifications based on the above-described embodiments of the present invention also fall within the scope of the present invention as long as they include the gist of the present invention. In addition, within the scope of the concept of the present invention, a person skilled in the art may come up with various modified examples and examples of modifications, and it is understood that these modified examples and examples of modifications also fall within the scope of the present invention. [Explanation of symbols]

[0037] 100 Nitride semiconductor device 10. Nitride Semiconductor Structure 11 First nitride semiconductor layer 12 Second nitride semiconductor layer 13 Gate contact layer 14 Third electrode contact layer 20 Transistor section 21 Source electrode 22 Drain electrode 23 Gate electrode 24 First field plate electrode 30 Diode section 31 1st electrode 32 2nd electrode 33 Third electrode 34 Second field plate electrode 40 Substrate 50 Recess

Claims

1. a nitride semiconductor structure including an active region in which a channel is formed; A transistor portion including a part of the nitride semiconductor structure; a diode portion including another part of the nitride semiconductor structure; the transistor portion has a source electrode, a drain electrode, a gate electrode, and a first field plate electrode connected to the source electrode and covering the gate electrode in a plan view; the diode portion includes a first electrode electrically connected to the source electrode, a second electrode electrically connected to the drain electrode, a third electrode located between the first electrode and the second electrode in a plan view, and a second field plate electrode connected to the first electrode and covering the third electrode in a plan view; the first electrode is shorted to the third electrode; a length of the first field plate electrode in a direction connecting the gate electrode and the drain electrode is greater than a length of the second field plate electrode in a direction connecting the third electrode and the second electrode.

2. The nitride semiconductor device according to claim 1 , wherein a distance between the gate electrode and the drain electrode is smaller than a distance between the second electrode and the third electrode.

3. The nitride semiconductor structure comprises: a first nitride semiconductor layer in which a channel is formed; a second nitride semiconductor layer provided on the first nitride semiconductor layer and having a band gap energy larger than that of the first nitride semiconductor layer; a gate contact layer located between a portion of the second nitride semiconductor layer and the gate electrode; 3. The nitride semiconductor device according to claim 1, further comprising: a third electrode contact layer located between another part of said second nitride semiconductor layer and said third electrode.

4. The nitride semiconductor device according to claim 3 , wherein the gate contact layer and the third electrode contact layer are made of the same material.

5. 5. The nitride semiconductor device according to claim 1, wherein the gate electrode and the third electrode are made of the same material.

6. 6. The nitride semiconductor device according to claim 1, wherein the source electrode, the drain electrode, the first electrode and the second electrode are made of the same material.

7. 7. The nitride semiconductor device according to claim 1, further comprising a recess that separates a channel of said transistor portion from a channel of said diode portion.

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