JP6712735B2 - Power device - Google Patents

Description

The present invention relates to a power device, and more particularly to a power device using a diamond semiconductor.

The power element is indispensable for power control of electrical equipment, and energy loss can be significantly reduced by reducing the loss of the power element. Diamond is known as one of the materials from which a power element having characteristics (high withstand voltage and low loss) superior to those of conventional silicon elements can be obtained. Diamond has a large band gap, and by using diamond, it is possible to reduce the size, power consumption, and efficiency of power elements.

By hydrogenating the surface of the diamond substrate to form a hydrogenated layer, a conductive layer is induced immediately below the hydrogenated layer. This conductive layer has high conductivity necessary for field effect transistor (FET) operation, and is expected to be applied to future high efficiency power devices. Recently, a power device that operates stably by providing a protective film on the hydrogenated layer on the surface of the diamond semiconductor has been proposed (for example, Patent Document 1).

JP, 2014-60377, A

The requirements for power devices are becoming even more stringent. For example, a power device is required to have a higher withstand voltage and a lower loss property, and further to have a higher withstand voltage.

Therefore, an object of the present invention is to provide a power element that can operate stably with high breakdown voltage and low loss and can further improve the withstand voltage.

A power device according to the present invention is characterized by including a diamond substrate, a hydrogenation layer formed in a thickness direction of the diamond substrate, and a protective film covering the hydrogenation layer.

According to the present invention, the hydrogenated layer is formed in the thickness direction of the diamond substrate, and the hydrogenated layer is covered with the protective film. Since the hydrogenated layer is protected by being covered with the protective film, it is possible to obtain a power device that operates stably with high breakdown voltage and low loss. Since the hydrogenation layer exists in the thickness direction of the diamond substrate, in the power device of the present invention, the conductive layer (two-dimensional hole layer) also exists in the thickness direction of the diamond substrate. As a result, the distance between the gate and the drain electrode becomes long, so that it is possible to provide a power element with a further improved breakdown voltage.

1 is an external view of a power device according to a first embodiment of the present invention. FIG. 2B is a vertical cross-sectional view showing a method of manufacturing a power device according to the first embodiment of the present invention step by step, FIG. 2A is a step of forming a diamond substrate, FIG. 2B is a step of forming a metal mask, and FIG. It is a figure which shows the step which formed the recessed part in. FIG. 3A is a vertical cross-sectional view showing a method of manufacturing a power device according to the first embodiment of the present invention step by step, FIG. 3A is a step in which a metal mask is removed, FIG. 3B is a step in which a diamond film and a hydrogenated layer are formed FIG. 3C is a diagram showing a stage in which a predetermined region of the hydrogenation layer is oxygen-terminated. FIG. 4B is a vertical cross-sectional view showing a method of manufacturing a power device according to the first embodiment of the present invention step by step, FIG. 4A showing a step of forming a source electrode and a drain electrode, and FIG. 4B showing a step of forming a protective film. Is. FIG. 5B is a vertical cross-sectional view showing a method of manufacturing the power element according to the first exemplary embodiment of the present invention in stages, where FIG. 5A is a stage in which a part of the surface of the source electrode and the drain electrode is exposed, and FIG. It is a figure which shows the formed stage. 6A is a graph showing an operation characteristic of an example of the power device according to the first embodiment, FIG. 6A shows the drain voltage (Vds) dependency of the drain current (Ids), and FIG. 6B is the gate voltage (Ids) of the drain current (Ids). Vgs) dependency is shown. 7A is a graph showing operating characteristics of another example of the power device according to the first embodiment, FIG. 7A shows drain voltage (Vds) dependence of drain current (Ids), and FIG. 7B shows gate of drain current (Ids). The voltage (Vgs) dependence is shown. It is a longitudinal section showing the composition of the power element concerning a 2nd embodiment of the present invention. Is a longitudinal sectional view showing stepwise the manufacturing method of the power device according to a second embodiment of the present invention, FIG. 9A step of forming a drain electrode on the back surface of the p ⁺ diamond layer, FIG. 9B is a p ⁺ diamond layer FIG. 9C is a diagram showing a step of forming an undoped diamond layer on the surface, and FIG. 9C is a step of forming a metal mask. FIG. 10A is a vertical cross-sectional view showing a method of manufacturing a power device according to a second embodiment of the present invention step by step. FIG. 10A shows a step of forming a recess in a diamond substrate, FIG. 10B shows a step of removing a metal mask, and FIG. It is a figure which shows the stage which formed the diamond film and the hydrogenation layer. FIG. 11A is a vertical cross-sectional view showing a method of manufacturing a power device according to a second embodiment of the present invention step by step. FIG. 11A shows a step of forming a protective film, FIG. 11B shows a step of inserting a filler, and FIG. It is a figure which shows the formed stage. 12A and 12B are longitudinal cross-sectional views showing a method of manufacturing a power device according to a second embodiment of the present invention step by step, wherein FIG. 12A is a step in which a gate electrode is embedded and formed, and FIG. 12B is a step in which an insulating film is formed. .. It is a longitudinal section showing the composition of the power element concerning a 3rd embodiment of the present invention. 14A and 14B are vertical cross-sectional views showing a method for manufacturing a power device according to a third embodiment of the present invention step by step. FIG. 14A shows a step of forming a metal mask, FIG. 14B shows a step of forming a recess in a diamond substrate, and FIG. It is a figure which shows the stage which removed the metal mask. FIG. 15A is a vertical cross-sectional view showing a method of manufacturing a power device according to a third embodiment of the present invention in stages, FIG. 15A is a stage in which a diamond film and a hydrogenated layer are formed, and FIG. 15B is a stage in which a protective film is formed. FIG. 15C is a diagram showing a stage where a metal film is formed. 16A and 16B are vertical cross-sectional views showing a method of manufacturing a power device according to a third embodiment of the present invention step by step, wherein FIG. 16A is a step in which a gate electrode is embedded and formed, and FIG. 16B is a step in which an insulating film is formed. .. It is a longitudinal section showing the composition of the power element concerning a 4th embodiment of the present invention. FIG. 18A is a vertical cross-sectional view showing a method for manufacturing a power element according to a fourth embodiment of the present invention step by step. FIG. 18A shows a step of forming a diamond stack on the surface of a p ⁺ diamond layer, and FIG. FIG. 18C is a diagram showing a stage where the recess is formed in the diamond substrate. FIG. 19A is a vertical cross-sectional view showing a method of manufacturing a power device according to a fourth embodiment of the present invention step by step. FIG. 19A shows a step of forming a diamond film and a hydrogenation layer, and FIG. 19B shows a metal film via a protective film. FIG. 19C is a diagram showing a stage where the insulating film is formed on the buried gate electrode. It is a longitudinal section showing the composition of the power element concerning a 5th embodiment of the present invention. FIG. 21A is a vertical cross-sectional view showing a method for manufacturing a power element according to a fifth embodiment of the present invention step by step. FIG. 21A is a step in which a diamond film and a hydrogenation layer are formed on a diamond substrate having recesses, and FIG. FIG. 21C is a diagram showing a stage in which a predetermined region of the hydrogenated layer is terminated with oxygen, and FIG. 21C is a stage in which a source electrode is formed. FIG. 22A is a vertical cross-sectional view showing a method of manufacturing a power device according to a fifth embodiment of the present invention step by step, wherein FIG. 22A is a step in which an insulating film is formed and FIG. FIG. It is a graph which shows the operating characteristic of an example of the power element which concerns on 5th Embodiment, FIG. 23A shows the drain voltage (Vds) dependence of drain current (Ids), and FIG. 23B shows a breakdown voltage.

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

1. First embodiment (overall configuration)
The overall configuration of the power element 30 according to the first embodiment of the present invention will be described with reference to FIG.

The power device 30 according to the present embodiment includes a diamond substrate 6 in which an undoped diamond layer 4 is formed on a semi-insulating n ⁻ diamond layer (hereinafter, also simply referred to as an n ⁻ layer) 2 containing a high concentration of nitrogen. ing. A diamond containing a high concentration of nitrogen is called an Ib type diamond. The undoped diamond layer 4 is formed by epitaxial growth on the n ⁻ layer 2 by a plasma-enhanced chemical vapor deposition (PECVD) method using microwave-excited plasma.

The diamond substrate 6 has a recess 10 on its surface, and a gate electrode 26a is formed on a part of the side surface of the recess 10 with a protective film 24 interposed therebetween. A source electrode 22a and a drain electrode 22b are formed in a predetermined region of the surface of the diamond substrate 6 with a recess 10 having a gate electrode 26a formed on a side surface thereof interposed therebetween. The protective film 24 acts as a gate insulating film below the gate electrode 26a. Further, the protective film 24 covers the surface of the diamond substrate 6, leaving a part of the surface of the source electrode 22a and the drain electrode 22b.

The gate electrode 26a can be formed by vapor-depositing aluminum (Al), for example. The source electrode 22a and the drain electrode 22b can be formed by, for example, a laminated film obtained by sequentially depositing a titanium (Ti) film and a gold (Au) film.

The protective film 24 is made of aluminum oxide (Al ₂ O ₃ ). The composition of the protective film 24 is not necessarily Al:O=2:3, but in the present specification, the protective film is referred to as Al ₂ O ₃ for simplification.

In the power device 30 of the present embodiment, the protective film 24 covers and protects the hydrogenated layer (not shown) on the diamond substrate 6. In regions other than the source electrode 22 a and the drain electrode 22 b, a hydrogenated layer having a C—H bond is present in the lower layer of the protective film 24 including the side surface and the bottom surface of the recess 10. In the hydrogenated layer, the surface of the diamond crystal is hydrogenated. Specifically, hydrogen atoms are bonded to dangling bonds of carbon atoms on the surface of the diamond crystal, that is, extra bonds (unbonded bonds). A two-dimensional hole layer (not shown) exists immediately below the hydrogenated layer. The two-dimensional hole layer has high conductivity and is used as a drift layer of a field effect transistor. The hydrogenated layer and the two-dimensional hole layer will be described in detail later.

(Production method)
Next, a method for manufacturing the power element 30 according to this embodiment will be described.

First, the semi-insulating diamond layer (n ⁻ layer) 2 containing nitrogen at a high concentration is sequentially washed with an ammonia/hydrogen peroxide mixed aqueous solution and a hydrochloric acid/hydrogen peroxide mixed aqueous solution. These are the methods usually performed in the manufacture of semiconductor devices. Further, cleaning is performed using a nitric acid/sulfuric acid mixed aqueous solution heated to 80° C. or higher. This removes or reduces the metal impurities, organic substances, and graphite-like surface layer remaining on the surface.

An undoped diamond layer 4 having a thickness of about 3 to 10 μm is epitaxially grown on the surface of the n ⁻ layer 2 after cleaning by the plasma CVD method. Hydrogen (H ₂ gas) and methane (CH ₄ ) gas as a carbon source are used as the synthesis gas. Thus, the diamond substrate 6 having the undoped diamond layer 4 laminated on the n ⁻ layer 2 as shown in FIG. 2A is obtained.

A metal mask 8 as shown in FIG. 2B is formed on the diamond substrate 6 using Au by a lift-off technique. Specifically, a thick film resist mask is formed in a predetermined region, and an Au film is formed on the entire surface by a sputtering method. When the thick film resist mask is removed using an organic solvent such as acetone, the Au film on the thick film resist mask is also removed by lift-off, and the metal mask 8 is obtained.

Further, the surface of the diamond substrate 6 is processed by Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) using O ₂ plasma to form the recess 10 as shown in FIG. 2C. After that, the metal mask 8 is removed using a gold etching solution (Kanto Chemical Co., Inc.: AURUM series) as shown in FIG. 3A. The size of the recess 10 formed in the diamond substrate 6 can be set appropriately. For example, the depth d ₁ of the recess 10 can be set to about 0.1 to 10 μm, preferably about 1.2 to 2.4 μm. The width w _{1 of the} recess 10 can be about ₁ to 50 μm, preferably about 5 to 20 μm. The aspect ratio (d ₁ /w ₁ ) of the recess 10 is preferably at least 0.1 or more. This is to secure a sufficient channel length with a small area on the substrate to improve the dielectric strength voltage. The distance d ₀ between the bottom surface of the recess 10 and the surface of the n ⁻ layer 2 is not particularly limited. In some cases, the recess 10 may reach the n ⁻ layer 2.

As shown in FIG. 3B, a diamond film 14 is epitaxially grown on the entire surface of the diamond substrate 6 in which the recesses 10 are formed, and then a hydrogenated layer 16 is formed on the surface of the diamond film 14. The diamond film 14 preferably has a thickness of about 50 to 1000 nm. In the diamond film 14, it is desirable that the nitrogen concentration be lower than the boron concentration. The fact that the nitrogen concentration in the diamond film 14 is lower than the boron concentration is advantageous for forming the hydrogenated layer 16 by the hydrogenation treatment which will be performed later and inducing the secondary hole layer directly thereunder. The hydrogenated layer 16 is formed on the surface of the diamond film 14 by irradiating hydrogen plasma while heating at 400 to 700° C. (here, 600° C.). The diamond film 14 epitaxially grown on the diamond substrate 6 can be confirmed by observation with a transmission electron microscope (TEM).

Immediately below the hydrogenated layer 16, a two-dimensional hole layer (not shown) is induced by C—H bonds and impurities in the atmosphere adsorbed on the surface. The two-dimensional hole layer is also called a two-dimensional hole gas (2DHG). The two-dimensional hole layer is a conductive layer in which holes are two-dimensionally distributed, and generally has a thickness of 5 to 20 nm. The two-dimensional hole layer thus formed has high conductivity and is used as a drift layer of a field effect transistor.

Next, as shown in FIG. 3C, a photoresist mask 12 is formed by photolithography to cover at least the hydrogenated layer 16 formed on the side surface and the bottom surface of the recess 10. In this way, a predetermined region of the hydrogenated layer 16 is protected by the photoresist mask 12, and the exposed portion of the hydrogenated layer 16 is oxygen-terminated by an oxygen plasma device (here, oxygen plasma asher) to change into an oxygen-terminated region 18. ..

After that, the source electrode 22a and the drain electrode 22b made of an Au/Ti laminated film as shown in FIG. 4A are formed by a lift-off technique with a thickness of about 50 to 200 nm. For the source electrode 22a and the drain electrode 22b, for example, a photoresist mask is formed in a predetermined region, a Ti film and an Au film are sequentially deposited on the entire surface by an evaporation method to obtain an Au/Ti laminated film, and then the photoresist mask is removed. Then, it can be formed by leaving only the Au/Ti laminated film other than the predetermined region. A TiC film 20 having a thickness of about 3 nm is formed by heating at 450 to 500° C. in the regions below the source electrode 22a and the drain electrode 22b, which were the oxygen termination region 18. This TiC film 20 acts as a source/drain region. As illustrated, the hydrogenated layer 16 is exposed in the regions other than the oxygen termination region 18 and the source electrode 22a and the drain electrode 22b formed on the TiC film 20, including the side surface and the bottom surface of the recess 10.

Next, as shown in FIG. 4B, an Al ₂ O ₃ film as the protective film 24 is formed on the entire surface with a thickness of 10 to 400 nm. The protective film 24 can be formed at a high temperature of 200° C. or higher by an atomic layer deposition (ALD) method. Specifically, the sample is introduced into the reaction chamber in a state in which the amount of air mixed in is reduced, for example, in a non-oxidizing atmosphere (here, nitrogen) that is depressurized using a load lock device, and an Al source and an oxidant as a reaction gas An Al ₂ O ₃ film is deposited on the entire surface by heat treatment at 450° C. Trimethyl aluminum (TMA) is used as the Al source, and a reactive species (here, H ₂ O) that undergoes an endothermic reaction with the C—H bond is used as the oxidizing agent. The heat treatment time can be appropriately selected and is, for example, 20 minutes to 20 hours.

As shown in FIG. 4B, the hydrogenated layer 16 is covered and protected by the protective film 24 not only on the surface of the diamond substrate 6 but also on the side surfaces and the bottom surface of the recess 10. The protective film 24 acts as a gate insulating film below the gate electrode formed later.

After that, the protective film on the surface is etched by a photoresist technique and an etching technique to expose a part of the surface of the source electrode 22a and the drain electrode 22b as shown in FIG. 5A. Finally, as shown in FIG. 5B, an Al film is used to form a gate electrode 26a with a thickness of about 50 nm in a predetermined region of the protective film 24. The gate electrode 26a can be formed by forming a resist mask in a region other than the gate portion, depositing Al on the entire surface to obtain an Al film, and removing the photoresist mask.

Through the above steps, the power element 30 of the first embodiment as shown in FIG. 5B is obtained. The power element 30 is a MISFET (Metal-Insulator-Semiconductor Field Effect Transistor) using a two-dimensional hole layer induced immediately below the hydrogenation layer 16 as a channel layer. In this power element 30, the gate length _{L G} that covers the diamond film 14 may be, for example 1~20μm about. The inter-electrode distance L _SD can be set to, for example, about 10 to 50 μm. As described above, the depth d ₁ of the recess 10 can be, for example, about 0.1 to 10 μm.

(Action and effect)
The power device 30 according to the present embodiment includes the diamond substrate 6 having the recess 10, and the protective film 24 is formed on the side surface and the bottom surface of the recess 10. The protective film 24 covers and protects the hydrogenated layer 16 on the side surface and the bottom surface of the recess 10 of the diamond substrate 6. A two-dimensional hole layer is induced immediately below the hydrogenated layer 16 protected by the protective film 24 on the side surface and the bottom surface of the recess 10. In the power device 30 according to the present embodiment, the two-dimensional hole layer exists in parallel to the main surface of the diamond substrate 6 and also in the thickness direction of the diamond substrate 6. Therefore, the region of the diamond substrate 6 in the thickness direction can also contribute to conduction.

As a result, in the power device 30 according to the present embodiment, the gate-drain electrode distance LG _-D becomes long, so that it is possible to improve the dielectric strength voltage per unit area of the substrate.

The hydrogenated layer 16 is formed on the surface of the diamond film 14 epitaxially grown on the diamond substrate 6 having the recess 10. In many cases, the surface of the diamond substrate 6 is damaged by etching when forming the recess 10 in the diamond substrate 6 and is oxygen-terminated. Due to the presence of the diamond film 14 on the surface of the diamond substrate 6, a stable hydrogenated layer 16 can be reliably formed without being affected by the surface of the diamond substrate 6. Moreover, the stability of the two-dimensional hole layer induced immediately below the hydrogenated layer 16 is also high.

In this embodiment, an Al ₂ O ₃ film formed by the ALD method is used as the protective film 24. Since the protective film 24 made of an Al ₂ O ₃ film formed by the ALD method has excellent step coverage, it is possible to reliably cover and protect the hydrogenated layer 16 on the side surface of the recess 10 of the diamond substrate 6. it can. Moreover, since the protective film made of the Al ₂ O ₃ film is formed in the non-oxidizing atmosphere, the hydrogenated layer 16 is not affected by oxygen in the atmosphere. A part of the hydrogenated layer 16 does not disappear, and a decrease in conductivity of the two-dimensional hole layer induced immediately below the hydrogenated layer 16 can be avoided.

Therefore, the power element 30 according to the present embodiment can have good operating characteristics even after being heated at a high temperature or under a high temperature environment.

In the power device 30 according to this embodiment, the TiC film 20 is formed below the source electrode 22a and the drain electrode 22b. The TiC film 20 here is an extremely shallow source/drain region having extremely lower resistance than the two-dimensional hole layer. Such an ultra-shallow junction is highly resistant to the short channel effect that accompanies the miniaturization of devices, which also enhances the characteristics of the power element 30.

Here, FIG. 6 shows an operation characteristic of an example of the power element 30 according to the first embodiment. The electrode distance L _S-D in FIG. 5B was 40 μm, the gate length L _G was 20 μm, and the depth d ₁ of the recess 10 was 1.2 μm. FIG. 6A shows the drain voltage (V _ds ) dependence of the drain current (I _ds ) at the gate voltage (V _gs ) for each 2 V between −10 V and +10 V. FIG. 6B shows the gate voltage (V _gs ) dependence of the drain current (I _ds ) at the drain voltage (V _ds )=−10V. FIGS. 6A and 6B show typical characteristics of current with respect to voltage between source and drain, and it is shown that current flows through the power element to function as a switch.

Further, FIG. 7 shows operating characteristics of the same power device as described above except that the depth d ₁ of the recess 10 is set to 2.4 μm. FIG. 7A shows the drain voltage (V _ds ) dependence of the drain current (I _ds ) at the gate voltage (V _gs ) for each 2 V between −10 V and +10 V. FIG. 7B shows the gate voltage (V _gs ) dependence of the drain current (I _ds ) at the drain voltage (V _ds )=−10V. 7A and 7B also show typical current characteristics with respect to the voltage between the source and the drain, and it is shown that current flows through the power element to function as a switch.

The power element configured as described above can be applied to a power device that is indispensable for power control of electric devices, and can be applied to motor drive devices such as hybrid cars and control devices for air conditioners.

2. Second embodiment (overall configuration)
Next, the overall configuration of the power element 40 according to the second embodiment of the present invention will be described with reference to FIG. 8 in which the same reference numerals are given to the same configuration as the power element 30 according to the first embodiment.

The power device 40 according to the present embodiment includes a diamond substrate 34 in which an undoped diamond layer 4 is formed on a p ⁺ diamond layer (hereinafter also simply referred to as a p ⁺ layer) 32 containing boron, and a diamond substrate 34 on the surface of the diamond substrate 34. The source electrode 22a made of the formed Au/Ti laminated film and the drain electrode 22b made of the Au/Ti laminated film formed on the back surface of the diamond substrate 34 are provided.

The diamond substrate 34 has a recessed portion 10, and a gate electrode 26a disposed on an insulating filler 36 made of silicon oxide is embedded in the recessed portion 10 via a protective film 24 made of Al ₂ O _3. Has been. The protective film 24 is formed between the filler 36 and the p ⁺ layer 32, and the gate electrode 26a is insulated from the source electrode 22a by the insulating film 38.

The protective film 24 covers and protects the hydrogenated layer 16 on the side surface and a part of the surface of the recess 10 of the diamond substrate 34. Between the undoped diamond layer 4 and the hydrogenated layer 16 on the diamond substrate 34, the diamond film 14 formed by epitaxial growth exists. In the power element 40 according to the second embodiment as well as the power element 30 according to the first embodiment, the surface of the hydrogenated diamond film 14 corresponds to the hydrogenated layer 16.

(Production method)
Next, a method for manufacturing the power device 40 according to this embodiment will be described.

First, as shown in FIG. 9A, a drain electrode 22b having a thickness of about 500 nm is formed on the back surface of a diamond layer (p ⁺ layer) 32 containing boron. The drain electrode 22b can be formed of an Au/Ti laminated film in which a Ti film and an Au film are sequentially laminated by a vapor deposition method.

An undoped diamond layer 4 having a thickness of about 3 to 10 μm is formed on the surface of the p ⁺ layer 32 having the drain electrode 22b on the back surface by the same method as in the first embodiment, as shown in FIG. 9B. .. The p ⁺ layer 32 and the undoped diamond layer 4 constitute the diamond substrate 34 in the power device 40 according to this embodiment.

On the surface of the diamond substrate 34, the metal mask 8 as shown in FIG. 9C is formed using Au by the same method as that of the first embodiment.

Further, after the surface of the diamond substrate 34 is processed by ICP-RIE to form the recesses 10 as shown in FIG. 10A, the same gold etching solution as that in the first embodiment is used, and then the metal mask 8 is provided as shown in FIG. 10B. To remove. In the present embodiment, the p ⁺ layer 32 is exposed on the bottom surface of the recess 10. The width w _{2 of the} recess 10 can be appropriately selected, and can be, for example, about 1 to 50 μm, preferably about _{2 to} 10 μm. The aspect ratio (d ₂ /w ₂ ) of the recess 10 is preferably at least 1 or more.

Then, the diamond film 14 is grown by epitaxial growth by the same method as in the first embodiment, and the hydrogenated layer 16 is formed on the surface of the diamond film 14. In the second embodiment, the diamond film 14 and the hydrogenation layer 16 are not formed on the p ⁺ layer 32 on the bottom surface of the recess 10 as shown in FIG. 10C, but are formed on the surface and side surfaces of the undoped diamond layer 4. To be done. A secondary hole layer (not shown) having a thickness of 5 to 20 nm is induced immediately below the hydrogenation layer 16 as in the case of the first embodiment.

After that, as shown in FIG. 11A, an Al ₂ O ₃ film as the protective film 24 is formed on the entire surface including the side surface and the bottom surface of the recess 10, and thereby the hydrogenated layer 16 is covered and protected. The protective film 24 can be formed with the same thickness by the same method as in the first embodiment.

In the recess 10 whose side surface and bottom surface are covered with the protective film 24, silicon oxide as an insulating material is deposited by a spin coating method, a TEOS-CVD method or the like to form a filler 36 as shown in FIG. 11B. .. To ensure a sufficient dielectric withstand voltage, the distance d _f between the surface and the p ⁺ layer 34 of the filler 36 is preferably at least 3μm approximately.

As shown in FIG. 11C, an Al film as a metal film 26 is formed on the protective film 24 inside the recess 10 in which the filler 36 is formed and outside the recess 10. CMP (Chemical Mechanical Polishing) is performed to remove the metal film 26 outside the recess 10 together with the protective film 24 to expose the hydrogenated layer 16 as shown in FIG. 12A. The metal film 26 left in the recess 10 via the protective film 24 becomes the gate electrode 26a. The protective film 24 in contact with the gate electrode 26a acts as a gate insulating film.

Next, as shown in FIG. 12B, the insulating film 38 is formed on the gate electrode 26a. The insulating film 38 here is required to withstand a voltage of, for example, about 20 V, and can have a thickness of, for example, about 10 to 200 nm. The insulating film 38 does not necessarily have to be an Al ₂ O ₃ film formed by the ALD method, and SiO ₂ or the like can be used as an insulating material. The insulating film 38 can be formed by selectively forming a photoresist mask on the hydrogenated layer 16, depositing an insulating material on the entire surface, and then removing the photoresist mask. A Ti film and an Au film are sequentially deposited on the entire surfaces of the hydrogenated layer 16 and the insulating film 38 by a vapor deposition method to form a source electrode 22a made of an Au/Ti laminated film with a thickness of about 500 nm.

Through the above steps, the power device 40 of the second embodiment as shown in FIG. 8 is obtained.

(Action and effect)
The power device 40 according to the present embodiment includes the diamond substrate 34 having the recess 10, and the side surface of the recess 10 is covered with the hydrogenation layer 16 and protected by the protective film 24 as in the first embodiment. Since the two-dimensional hole layer is induced in the thickness direction of the diamond substrate 34 immediately below the hydrogenated layer 16, the power element 40 according to the present embodiment also has the same effect as that of the first embodiment. Can be obtained.

Further, in the power device 40 according to the present embodiment, since the gate electrode 26a is embedded in the diamond substrate 34, the unit cell area can be reduced. This makes it possible to reduce the on-resistance.

Further, in the power element 40 according to the second embodiment, the filler 36 made of an insulating material (silicon oxide) is arranged below the gate electrode 26a. Since the insulating material has a high thermal conductivity, an effect that heat can be efficiently dissipated can be obtained.

3. Third embodiment (overall configuration)
Next, the overall configuration of the power element 50 according to the third embodiment of the present invention will be described with reference to FIG. 13 in which the same reference numerals are given to the same configuration as the power element 40 according to the second embodiment.

The power device 50 according to the present embodiment has a diamond substrate 34 in which an undoped diamond layer 4 is formed on a p ⁺ diamond layer (hereinafter also simply referred to as a p ⁺ layer) 32 containing boron, and a diamond substrate 34 on the surface of the diamond substrate 34. The source electrode 22a made of the formed Au/Ti laminated film and the drain electrode 22b made of the Au/Ti laminated film formed on the back surface of the diamond substrate 34 are provided.

The diamond substrate 34 has a recess 10, and a gate electrode 26a is embedded in the recess 10 via a protective film 24 made of Al ₂ O ₃ . The gate electrode 26a is insulated from the source electrode 22a by the insulating film 38.

The protective film 24 covers the side surface and the bottom surface of the recess 10 in the diamond substrate 34 to protect the hydrogenated layer 16. Between the hydrogenated layer 16 and the diamond substrate 34, the diamond film 14 formed by epitaxial growth exists. Similar to the first and second embodiments, the surface of the hydrogenated diamond film 14 corresponds to the hydrogenated layer 16.

In the power element 50 according to the third embodiment, the recess 10 provided in the diamond substrate 34 does not reach the p ⁺ layer 32, and the filler 36 is not disposed below the gate electrode 26a, the second embodiment. It is different from the power element 40 according to the embodiment, and is otherwise the same as the power element 40 according to the second embodiment.

(Production method)
Next, a method for manufacturing the power element 50 according to this embodiment will be described.

First, similarly to the second embodiment, the metal mask 8 is formed on the surface of the diamond substrate 34 having the drain electrode 22b formed on the back surface thereof, as shown in FIG. 14A.

Next, after the surface of the diamond substrate 34 is processed by ICP-RIE to form the recesses 10 as shown in FIG. 14B, the metal mask 8 as shown in FIG. 14C is formed using the same gold etching solution as in the first embodiment. To remove.

In this embodiment, the depth d ₃ of the recess 10 may be about 0.1 to 50 μm, preferably about 10 to 30 μm. The width w _{3 of the} recess 10 can be appropriately selected and can be, for example, about 1 to 50 μm, preferably about 2 to 10 μm. The aspect ratio (d ₃ /w ₃ ) of the recess 10 is preferably at least 0.1 or more. This is to suppress the conduction path that is directly conducted to the p ⁺ layer 32 from the upper surface of the diamond substrate 34, not from the bottom surface of the recess 10, and secure a high on/off controllability. Further, in order to improve the withstand voltage, the distance d ₄ between the bottom surface of the recess 10 and the p ⁺ layer 32 is preferably at least about 1 μm. Incidentally, the power device manufactured with the distance d ₄ between the bottom surface of the recess 10 and the p ⁺ layer 32 being 3 μm or more can withstand a voltage of 3000V.

Then, the diamond film 14 and the hydrogenation layer 16 are formed on the entire surface of the diamond substrate 34 in which the recesses 10 are formed by the same method as in the first embodiment, as shown in FIG. 15A. As in the case of the first and second embodiments, also in the third embodiment, a secondary hole layer (not shown) having a thickness of 5 to 20 nm is induced immediately below the hydrogenation layer 16. As shown in FIG. 15B, an Al ₂ O ₃ film as a protective film 24 is formed on the hydrogenated layer 16 to cover and protect the hydrogenated layer 16. The protective film 24 can be formed on the entire surface with the same thickness by the same method as in the first embodiment.

As shown in FIG. 15C, an Al film as a metal film 26 is formed on the protective film 24 inside the concave portion 10 where the protective film 24 is formed and outside the concave portion 10. CMP is performed to remove the metal film 26 outside the recess 10 together with the protective film 24 to expose the hydrogenated layer 16 as shown in FIG. 16A. The metal film 26 left in the recess 10 becomes the gate electrode 26a. The protective film 24 in contact with the gate electrode 26a acts as a gate insulating film.

Next, as shown in FIG. 16B, the insulating film 38 is formed on the gate electrode 26a. The insulating film 38 can be formed by using a material similar to that of the second embodiment and a similar method. After that, a Ti film and an Au film are sequentially deposited on the entire surfaces of the hydrogenated layer 16 and the insulating film 38 by a vapor deposition method to form a source electrode 22a made of an Au/Ti laminated film with a thickness of about 500 nm.

Through the above steps, the power element 50 of the third embodiment shown in FIG. 13 is obtained.

(Action and effect)
The power device 50 according to the present embodiment includes the diamond substrate 34 having the recess 10, and on the side surface of the recess 10, the protective film 24 covers and protects the hydrogenation layer 16 as in the first embodiment. Since the two-dimensional hole layer is induced in the thickness direction of the diamond substrate 34 immediately below the hydrogenation layer 16, the power element 50 according to the present embodiment also has the same effect as that of the first embodiment. Can be obtained.

Further, in the power device 50 according to the present embodiment, the gate electrode 26a is embedded in the diamond substrate 34, so that the unit cell area can be further reduced, and the same effect as the second embodiment can be obtained. can get.

Furthermore, in the power device 50 according to the present embodiment, the carriers are bulk-conducted in the region of the undoped diamond layer 4, so that the carriers are less likely to cause electric field concentration in the crystal and the dielectric strength is easily improved.

4. Fourth embodiment (overall configuration)
Next, the overall configuration of the power element 60 according to the fourth embodiment of the present invention will be described with reference to FIG. 17 in which the same reference numerals are given to the same configuration as the power element 50 according to the third embodiment.

The power device 60 according to the present embodiment includes a diamond substrate 44 in which a diamond laminated body 46 is provided on a p ⁺ diamond layer (hereinafter also simply referred to as a p ⁺ layer) 32 containing boron. A source electrode 22a made of an Au/Ti laminated film is formed on the front surface of the diamond substrate 44, and a drain electrode 22b made of an Au/Ti laminated film is formed on the rear surface of the diamond substrate 44.

In the present embodiment, the diamond laminated body 46 is composed of a first layer 47 made of an undoped diamond layer and an n-type diamond layer (hereinafter, also simply referred to as n layer) laminated on the first layer 47. And a second layer 48. The n-layer as the second layer 48 is a semi-insulating diamond layer containing n-type impurities such as nitrogen.

The boundary between the first layer 47 and the second layer 48 in the diamond stack 46 is provided above the bottom surface of the recess 10, but may be at the same height as the bottom surface of the recess 10.

The diamond substrate 44 has a recess 10, and a gate electrode 26a is embedded in the recess 10 with a protective film 24 made of Al ₂ O ₃ interposed therebetween. The gate electrode 26a is insulated from the source electrode 22a by the insulating film 38.

The protective film 24 covers the side surface and the bottom surface of the recess 10 in the diamond substrate 44 to protect the hydrogenated layer 16. Between the hydrogenated layer 16 and the diamond substrate 44, the diamond film 14 formed by epitaxial growth exists. Similar to the above-described embodiment, the surface of the hydrogenated diamond film 14 corresponds to the hydrogenated layer 16.

In the power device 60 according to the fourth embodiment, the diamond substrate 44 includes a first layer 47 made of an undoped diamond layer and a second layer 48 made of an n layer stacked on the first layer 47. The power element 50 according to the third embodiment is different from the power element 50 according to the third embodiment in that it includes a laminated body 46 of diamond, and is otherwise similar to the power element 50 according to the third embodiment.

(Production method)
Next, a method of manufacturing the power device 60 according to this embodiment will be described.

As shown in FIG. 18A, a first layer 47 made of an undoped diamond layer and a second layer 48 made of an n layer are formed on the surface of the p ⁺ layer 32 having the back surface of the drain electrode 22b made of an Au/Ti laminated film. A diamond laminated body 46 including is formed with a thickness of about 3 to 10 μm to obtain a diamond substrate 44. The undoped diamond layer can be formed by the same method as in the first embodiment. An n-type impurity source is further used to form the n-layer.

A metal mask 8 as shown in FIG. 18B is formed on the diamond substrate 44 by a lift-off technique using Au similarly to the case of the first embodiment. After the surface of the diamond substrate 44 is processed by ICP-RIE to form the recess 10 as shown in FIG. 18C, the metal mask 8 is removed by using the same gold etching solution as in the first embodiment.

As shown in FIG. 19A, the diamond film 14 and the hydrogenation layer 16 are formed on the entire surface of the diamond substrate 44 in which the recesses 10 are formed, by the same method as in the first embodiment. A secondary hole layer (not shown) having a thickness of 5 to 20 nm is induced immediately below the hydrogenation layer 16 as in the above-described embodiment. As shown in FIG. 19B, a metal film 26 is formed on the hydrogenated layer 16 with a protective film 24 interposed therebetween. The protective film 24 and the metal film 26 can be formed similarly to the case of the third embodiment.

The metal film 26 outside the recess 10 is removed together with the protective film 24 by CMP, and an insulating film 38 is formed on the gate electrode 26a made of the remaining metal film 26 as shown in FIG. 19C. The insulating film 38 can be formed by the same method using the same material as that of the third embodiment. After that, the source electrode 22a is formed in the same manner as in the third embodiment.

Through the above steps, the power element 60 of the fourth embodiment shown in FIG. 17 is obtained.

(Action and effect)
The power device 60 according to the present embodiment includes the diamond substrate 44 having the recess 10, and the side surface of the recess 10 has the protective film 24 covering and protecting the hydrogenation layer 16 as in the first embodiment. Since the two-dimensional hole layer is induced in the thickness direction of the diamond substrate 34 immediately below the hydrogenated layer 16, the power element 60 according to the present embodiment also has the same effect as that of the first embodiment. Can be obtained.

Further, in the power device 60 according to the present embodiment, since the gate electrode 26a is embedded in the diamond substrate 44, the unit cell area can be further reduced, and the second embodiment and the third embodiment. The same effect as can be obtained.

Further, in the power device 60 according to the present embodiment, the diamond substrate 44 includes the diamond layered body 46 of the first layer 47 made of the undoped diamond layer and the second layer 48 made of the n layer. Therefore, the leak current can be suppressed more reliably.

5. Fifth embodiment (overall configuration)
Next, the overall configuration of the power element 70 according to the fifth embodiment of the present invention will be described with reference to FIG. 20 in which the same reference numerals are given to the same configuration as the power element 60 according to the fourth embodiment.

The power device 70 according to the present embodiment includes a diamond substrate 44 in which a diamond laminated body 46 is provided on a p ⁺ diamond layer (hereinafter also simply referred to as a p ⁺ layer) 32 containing boron. On the back surface of the diamond substrate 44, a drain electrode 22b made of an Au/Ti laminated film is formed.

The diamond laminated body 46 includes a first layer 47 made of an undoped diamond layer and an n-type diamond layer laminated on the first layer 47 (hereinafter, also simply referred to as n layer) as in the case of the fourth embodiment. And a second layer 48 of

The diamond substrate 44 has a recess 10 on its surface, and a gate electrode 26a is formed on the surface of the recess 10 via a protective film 24 made of Al ₂ O ₃ . The protective film 24 covers the side surface and the bottom surface of the recess 10 in the diamond substrate 44 to protect the hydrogenated layer 16. Between the hydrogenated layer 16 and the diamond substrate 44, the diamond film 14 formed by epitaxial growth exists.

Two source electrodes 22a are formed via the TiC layer 20 on the surface of the diamond substrate 44 that sandwiches the recess 10 in which the gate electrode 26a is formed. The source electrode 22a is covered with a protective film 24 except for a part of the surface.

(Production method)
Next, a method of manufacturing the power device 70 according to this embodiment will be described.

As shown in FIG. 21A, the diamond film 14 and the diamond film 14 are formed on the entire surface of the diamond substrate 44 having the drain electrode 22b on the back surface and the recess 10 formed in a predetermined region on the front surface by the same method as in the fourth embodiment. The hydrogenated layer 16 is formed. A secondary hole layer (not shown) having a thickness of 5 to 20 nm is induced immediately below the hydrogenation layer 16 as in the above-described embodiment.

Next, by a method similar to that of the first embodiment, a photoresist mask 12 as shown in FIG. 21B is formed so as to cover at least the side surface and the bottom surface of the recess 10 and the hydrogenation layer 16 is formed. The exposed portion of is changed to the oxygen termination region 18.

The source electrode 22a made of the Au/Ti laminated film is formed on the oxygen termination region 18 by the same method as in the first embodiment. As shown in FIG. 21C, the oxygen termination region 18 immediately below the source electrode 22a becomes a TiC film 20 by heating. The hydrogenated layer 16 is exposed in the regions other than the oxygen termination region 18 and the source electrode 22a formed on the TiC film 20, including the side surface and the bottom surface of the recess 10.

An Al ₂ O ₃ film as a protective film 24 is formed on the entire surface including the hydrogenated layer 16 as shown in FIG. 22A. The protective film 24 can be formed with the same thickness as in the first embodiment. As shown in FIG. 22A, the hydrogenated layer 16 is covered and protected by the protective film 24 not only on the surface of the diamond substrate 44 but also on the side surface and the bottom surface of the recess 10. The protective film 24 acts as a gate insulating film below the gate electrode formed later.

After that, a part of the protective film 24 is etched by the same method as in the first embodiment to expose a part of the surface of the source electrode 22a as shown in FIG. 22B. Finally, the gate electrode 26a is formed in a predetermined region of the protective film 24 by the same method as in the first embodiment, and the power element 70 of the present embodiment shown in FIG. 20 is obtained.

(Action and effect)
The power device 70 according to the present embodiment includes the diamond substrate 44 having the recess 10, and the side surface of the recess 10 is covered with the hydrogenation layer 16 and protected by the protective film 24 as in the first embodiment. Since the two-dimensional hole layer is induced in the thickness direction of the diamond substrate 34 immediately below the hydrogenated layer 16, the power element 70 according to the present embodiment also has the same effect as that of the first embodiment. Can be obtained.

Further, in the power device 70 according to the present embodiment, since the gate electrode 26a is embedded in the diamond substrate 44, it is possible to further reduce the unit cell area, and the second embodiment and the third embodiment. The same effect as the fourth embodiment can be obtained.

Further, in the power device 70 according to the present embodiment, the diamond substrate 44 includes the diamond laminated body 46 including the first layer 47 made of the undoped diamond layer and the second layer 48 made of the n layer. The leak current can be suppressed more reliably as in the fourth embodiment.

Here, operating characteristics of an example of the power element 70 according to the fifth embodiment are shown in FIGS. 23A and 23B. The interelectrode distance L ₁₁ in FIG. 20 was set to 40 μm, and the distance L ₁₂ between the end portions of the gate electrode 26 a on the surface of the diamond substrate 44 was set to 20 μm. The distance W ₁₁ of the hydrogenated layer 16 on the side surface of the recess 10 was 10 μm, and the depth d ₁₁ of the recess 10 was 2.5 μm. The thickness t ₁₁ of the first layer 47 was 1 μm, and the thickness t ₁₂ of the second layer 48 was 2 μm. The thickness of the diamond film 14 was 100 nm.

FIG. 23A shows the drain voltage (Vds) dependence of the drain current (Ids) at the gate voltage (Vgs) between −20V and +40V. FIG. 23A shows a characteristic of a current with respect to a typical source-drain voltage. The power device 70 according to the fifth embodiment has a breakdown voltage of 634 V (FIG. 23B) and has high withstand voltage. 23A and 23B show that a current flows through the power element 70 of this embodiment to function as a switch.

6. Modifications The present invention is not limited to the above-described embodiment, and can be appropriately modified within the scope of the gist of the present invention. For example, in the above embodiment, the Au film is used as the metal mask when the recess is formed in the diamond substrate by etching. However, any metal that can protect the diamond substrate from etching, for example, an Al film may be used as the metal mask. it can. Further, the gas used for etching the diamond substrate to form the recess may contain a cleaning gas such as octafluoropropane (C ₃ F ₈ ) gas.

In the above embodiment, the hydrogenation layer was formed by epitaxially growing a diamond film on the diamond substrate in which the recess was formed and irradiating the surface of this diamond film with hydrogen plasma, but hydrogen plasma irradiation is not always necessary. Absent. In many cases, the surface of the diamond film is sufficiently hydrogenated without intentionally irradiating it with hydrogen plasma. This is because the diamond film epitaxial growth process itself has a hydrogenation effect, and hydrogen plasma irradiation can be omitted. In this case, the epitaxial growth itself of the diamond film also serves as the hydrogenation treatment step.

A hydrogenation layer may be formed on the surface of the diamond substrate by terminating the surface of the diamond substrate having the recesses with hydrogen without epitaxially growing a diamond film on the diamond substrate having the recesses. In this case, the hydrogenated layer can be formed on the surface of the diamond substrate by irradiating the diamond substrate having the concave portion with hydrogen plasma. This makes it possible to omit the epitaxial growth step of the diamond film.

Further, in the above embodiment, nitrogen was used as the non-oxidizing atmosphere when forming the Al ₂ O ₃ film as the protective film for covering and protecting the hydrogenation layer, but an inert gas such as Ar, Alternatively, a mixed gas of nitrogen and an inert gas may be used. Although H ₂ O was used as the oxidant for forming the Al ₂ O ₃ film, any reactive species that undergoes an endothermic reaction with the C—H bond can be used as the oxidant. For example, methanol _(CH 4 O), ethanol _{(C 2 H} 6 O), propanol _{(C 3 H} 8 O), alcohols such as butanol _{(C 4 H 10} O) may be used as the oxidizing agent.

In order to reliably maintain the two-dimensional hole layer induced immediately below the hydrogenated layer, the protective film is required to be able to protect the hydrogenated layer even after heating at high temperature or during high temperature operation. The film forming method is not limited to the ALD method as long as such a protective film can be formed with good step coverage. For example, it may be formed by a CVD method. Aluminum nitride (AlN) can be used if a suitable protective film is formed.

Further, various materials can be changed. For example, the gate electrode is not limited to the Al film, but may be formed of an Au film or a W film.

In the second embodiment, the filler used in the lower layer of the gate electrode may be made of an insulating material such as phosphorus glass (PSG) or boron phosphorus glass (BPSG) in addition to silicon oxide.

In the second embodiment, the third embodiment, the fourth embodiment and the fifth embodiment, the source electrode and the drain electrode are formed by the Au/Ti laminated film, but the Ti film is not always essential. The source electrode and the drain electrode can be formed by vapor-depositing only Au.

In the fourth and fifth embodiments, a p-type diamond layer may be used as the first layer 47 forming the diamond laminated body 46. The p-type diamond layer can be formed by a general method using a p-type impurity source such as boron.

As described above, in the present invention, the region in the thickness direction of the diamond substrate is used for conduction. In the above-mentioned embodiment, the two-dimensional hole layer was induced in the thickness direction of the diamond substrate by forming the hydrogenated layer on the side surface of the recess provided in the diamond substrate, but the method for forming the hydrogenated layer is not limited to this. Not done. The hydrogenation layer may be present in the thickness direction of the diamond substrate, and may be formed by any method to induce a two-dimensional hole layer in the thickness direction of the diamond substrate to obtain the power device of the present invention. You can

2: n ^- diamond layer 4: undoped diamond layer 6, 34, 44: diamond substrate 14: diamond film 16: hydrogenated layer 22a: source electrode 22b: drain electrode 24: protective film 26a: gate electrode 32: p ⁺ diamond layer 38: Insulating film 30, 40, 50, 60, 70: Power element

Claims (4)

A diamond substrate having a recess, a hydrogenation layer formed on a side surface of the recess, and a protective film covering the hydrogenation layer ,
The diamond substrate includes a diamond stack including a first layer formed of an undoped diamond layer or a p-type diamond layer and a second layer formed on the first layer and formed of an n-type diamond layer. A power element characterized by the above. Between the diamond substrate and the protective film, further comprising a diamond film formed by epitaxial growth,
The power element according to claim 1, wherein the hydrogenated layer is formed by hydrogenating the surface of the diamond film. The power element according to claim 2, wherein the diamond film formed by the epitaxial growth has a thickness of 50 to 1000 nm. The power element according to claim 1, wherein the protective film is formed of an aluminum oxide film.

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