Semiconductor device and manufacturing method of the same
By forming an insulating oxide film on GaN and treating it with nitrogen plasma at controlled microwave power, the method addresses Ga-O bond formation and current leakage, ensuring reduced damage and improved semiconductor device performance.
Patent Information
- Application Number
- JP2024041551
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-03-15
- Publication Date
- 2025-09-29
AI Technical Summary
The formation of Ga-O bonds on the surface of GaN semiconductor materials leads to current leakage, particularly when defects are created during trench formation or when oxygen-based insulating films are used, and existing methods to suppress these bonds can cause damage to the semiconductor with high microwave outputs.
A manufacturing method involving the formation of an insulating first oxide film on a Group III nitride semiconductor, followed by nitrogen plasma treatment with a limited microwave output of 300 W or less, and subsequent heat treatments to nitride the interface, reducing Ga-O bonds to a concentration of 0.8 to 1.2 at%, thereby suppressing current leakage and semiconductor damage.
The method effectively reduces Ga-O bonds and current leakage while minimizing plasma damage to the semiconductor, enhancing the reliability and performance of semiconductor devices.
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Figure 2025141554000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a semiconductor device and a method for manufacturing the same. [Background technology]
[0002] Group III nitride semiconductors, such as GaN, have high dielectric breakdown field strength, making them promising materials for power devices, and semiconductor elements using these semiconductors are being actively researched and developed.
[0003] Patent Document 1 describes a MISFET using GaN, and describes how to form a gate insulating film as follows: First, a first oxide film made of SiO2 is formed on a semiconductor layer made of GaN. Next, nitrogen plasma is irradiated to the first oxide film. The first oxide film is nitrided, and a stack of SiON and SiN is formed in that order from the semiconductor layer side. After that, a first heat treatment is performed. Next, a second oxide film made of SiO2 is formed on the SiN, and a second heat treatment is performed. It is described that the method in Patent Document 1 can suppress oxidation of Ga on the GaN surface. [Prior art documents] [Patent documents]
[0004] [Patent Document 1] Japanese Patent Publication No. 2022-14832 Summary of the Invention [Problem to be solved by the invention]
[0005] When the surface of GaN is exposed to the atmosphere, the outermost surface of the GaN reacts with oxygen, forming Ga-O bonds. These Ga-O bonds cause current leakage. Ga-O bonds are particularly likely to form when defects are created by removing nitrogen from the GaN during etching during trench formation. Furthermore, when an insulating film is formed on GaN using oxygen gas, such as in ALD (atomic layer deposition), Ga-O bonds are likely to form on the GaN surface. However, it has been difficult to remove these Ga-O bonds that form on the GaN surface.
[0006] The method described in Patent Document 1 is said to be able to suppress the oxidation of Ga near the GaN surface under the insulating film. However, the microwave output required for nitriding by irradiating nitrogen plasma is high, which may damage the semiconductor.
[0007] The present invention has been made in view of the above background, and aims to provide a semiconductor element in which damage to the semiconductor is suppressed and current leakage is suppressed, and a method for manufacturing the same. [Means for solving the problem]
[0008] One aspect of the present invention is a first oxide film forming step of forming an insulating first oxide film on a semiconductor layer made of a Group III nitride semiconductor; a nitrogen plasma treatment step of irradiating the first oxide film with nitrogen plasma to inject nitrogen into the first oxide film; a first heat treatment step of heat treating the first oxide film to nitride the first oxide film into an oxynitride film; a second oxide film forming step of forming an insulating second oxide film on the oxynitride film; a second heat treatment step of heat treating the second oxide film, The nitrogen plasma treatment step is performed in a method for manufacturing a semiconductor device, in which a microwave output is set to 300 W or less.
[0009] Another aspect of the present invention is a first oxide film forming step of forming an insulating first oxide film on a semiconductor layer made of a Group III nitride semiconductor; a nitrogen plasma treatment step of irradiating the first oxide film with nitrogen plasma to inject nitrogen into the first oxide film; a first heat treatment step of heat treating the first oxide film to nitride the first oxide film into an oxynitride film; a second oxide film forming step of forming an insulating second oxide film on the oxynitride film; a second heat treatment step of heat treating the second oxide film, In the method for manufacturing a semiconductor element, the first heat treatment step is performed by nitriding the interface between the semiconductor layer and the oxynitride film, so that the concentration of oxygen in Ga—O bonds at the interface is 0.8 to 1.2 at %.
[0010] Another aspect of the present invention is a semiconductor layer made of a Group III nitride semiconductor; a gate insulating film provided on the semiconductor layer; a gate electrode provided on the gate insulating film, The gate insulating film is a SiON film formed on and in contact with the semiconductor layer; an SiO2 film formed on and in contact with the SiON film, In the semiconductor element, the concentration of oxygen atoms in Ga—O bonds at the interface between the semiconductor layer and the SiON film is 0.8 to 1.2 at %. [Effects of the Invention]
[0011] In the above embodiment, the microwave output in the nitrogen plasma treatment step is set to 300 W or less, which makes it possible to reduce Ga-O bonds formed on the surface of the semiconductor layer while suppressing plasma damage to the semiconductor layer, thereby suppressing current leakage.
[0012] As described above, according to the above-described aspects, it is possible to provide a semiconductor element in which damage to the semiconductor is suppressed and current leakage is suppressed, and a method for manufacturing the same. [Brief explanation of the drawings]
[0013] [Figure 1]1 is a cross-sectional view showing the configuration of a semiconductor element according to Embodiment 1, taken along a plane perpendicular to the main surface of a substrate. [Figure 2] FIG. 3 is an enlarged cross-sectional view showing the vicinity of the interface between the second semiconductor layer and the gate insulating film. [Figure 3] 2A to 2C are diagrams illustrating a manufacturing process of a semiconductor element according to the first embodiment. [Figure 4] 1A to 1C are diagrams showing a process of forming a gate insulating film. [Figure 5] 10 is a flowchart showing a process for forming a gate insulating film. [Figure 6] 10 is a graph showing the Id-Vd characteristics of the semiconductor element of Comparative Example 1 when the gate voltage is off. [Figure 7] 4 is a graph showing the Id-Vd characteristics of the semiconductor element of Example 1 when the gate voltage is off. [Figure 8] 1 is a graph showing the distribution of nitrogen concentration and oxygen concentration in the thickness direction. [Figure 9] 6 is a graph showing the distribution of gallium concentration and oxygen concentration in the thickness direction. [Figure 10] A graph showing the CV characteristics when the microwave output is set to 200W. [Figure 11] A graph showing the CV characteristics when the microwave output is 500W. DETAILED DESCRIPTION OF THE INVENTION
[0014] The method for manufacturing a semiconductor device includes a first oxide film formation step of forming an insulating first oxide film on a semiconductor layer made of a group III nitride semiconductor, a nitrogen plasma treatment step of irradiating the first oxide film with nitrogen plasma to inject nitrogen into the first oxide film, a first heat treatment step of heat treating the first oxide film to nitride the first oxide film to form an oxynitride film, a second oxide film formation step of forming an insulating second oxide film on the oxynitride film, and a second heat treatment step of heat treating the second oxide film, wherein the nitrogen plasma treatment step uses a microwave output of 300 W or less.
[0015] The method for manufacturing a semiconductor device includes a first oxide film formation step of forming an insulating first oxide film on a semiconductor layer made of a group III nitride semiconductor, a nitrogen plasma treatment step of irradiating the first oxide film with nitrogen plasma to inject nitrogen into the first oxide film, a first heat treatment step of heat treating the first oxide film to nitride the first oxide film to form an oxynitride film, a second oxide film formation step of forming an insulating second oxide film on the oxynitride film, and a second heat treatment step of heat treating the second oxide film, wherein the first heat treatment step nitrides the interface between the semiconductor layer and the oxynitride film to set the concentration of oxygen in Ga-O bonds at the interface to 0.8 to 1.2 at%.
[0016] In the method for manufacturing a semiconductor device, the first heat treatment step may nitride the interface between the semiconductor layer and the oxynitride film to reduce the concentration of oxygen in Ga-O bonds at the interface compared to before the first heat treatment step. This can sufficiently reduce the Ga-O bonds, thereby further suppressing current leakage.
[0017] In the method for manufacturing a semiconductor element, the concentration of oxygen in Ga-O bonds at the interface between the semiconductor layer and the oxynitride film may be set to 0.8 to 1.2 at % by the first heat treatment step, which can sufficiently reduce the Ga-O bonds and further suppress current leakage.
[0018] In the method for manufacturing a semiconductor device, the nitrogen plasma treatment step is performed to reduce the nitrogen concentration of the first oxide film to 1×10 20 ~1×10 22 / cm 3 The nitrogen concentration may be sufficient to reduce Ga—O bonds.
[0019] In the method for manufacturing a semiconductor device, the nitrogen plasma treatment step is performed to reduce the nitrogen concentration in the first oxide film to 1×10 or less in a region near the interface between the semiconductor layer and the first oxide film. 21 ~1×10 22 / cm 3 The nitrogen concentration may be sufficient to reduce Ga—O bonds.
[0020] In the method for manufacturing a semiconductor device, the first oxide film may be formed to a thickness of 1 nm to 9 nm in the first oxide film forming step, which allows sufficient nitrogen to be implanted and also suppresses plasma damage to the semiconductor layer.
[0021] The semiconductor device includes a semiconductor layer made of a group III nitride semiconductor, a gate insulating film provided on the semiconductor layer, and a gate electrode provided on the gate insulating film. The gate insulating film includes a SiON film formed on the semiconductor layer and a SiO2 film formed on and in contact with the SiON film, and the concentration of oxygen atoms in Ga-O bonds at the interface between the semiconductor layer and the SiON film is 0.8 to 1.2 at%.
[0022] (Embodiment 1) 1. Structure of semiconductor elements 1 is a cross-sectional view perpendicular to a main surface of a substrate showing the configuration of a light-emitting device according to Embodiment 1. As shown in Fig. 1, the semiconductor device according to Embodiment 1 includes a substrate 10, a first semiconductor layer 11, a second semiconductor layer 12, a third semiconductor layer 13, a gate insulating film 14, a gate electrode 15, a source electrode 16, a body electrode 17, and a drain electrode 18.
[0023] The substrate 10 is a Si-doped n-type semiconductor having a c-plane as its principal surface. + The substrate 10 is made of GaN. The Si concentration of the substrate 10 is 1×10 18 / cm 3 That's all.
[0024] The first semiconductor layer 11 is provided on the substrate 10 and is a Si-doped n - The first semiconductor layer 11 functions as a drift layer. The thickness of the first semiconductor layer 11 is 8 to 15 μm. The Si concentration of the first semiconductor layer 11 is 1×10 15 ~2×10 16 / cm 3 is.
[0025] The second semiconductor layer 12 is provided on the first semiconductor layer 11 and is a semiconductor layer made of Mg-doped p-GaN. The second semiconductor layer 12 functions as a channel layer. The thickness of the second semiconductor layer 12 is 0.1 to 1 μm. The Mg concentration of the second semiconductor layer 12 is 1×10 17 ~8×10 19 / cm 3 is.
[0026] The third semiconductor layer 13 is provided on the second semiconductor layer 12 and is a Si-doped n + The third semiconductor layer 13 is a semiconductor layer made of GaN. The third semiconductor layer functions as a source contact layer. The thickness of the third semiconductor layer 13 is 0.1 to 0.5 μm. The Si concentration of the third semiconductor layer 13 is 1×10 18 ~1×10 19 / cm 3 is.
[0027] A trench 20 is provided in a partial region of the surface of the third semiconductor layer 13. The trench 20 is a recess that penetrates the third semiconductor layer 13 and the second semiconductor layer 12 and reaches the first semiconductor layer 11. The first semiconductor layer 11 is exposed at the bottom surface of the trench 20. Furthermore, the first semiconductor layer 11, the second semiconductor layer 12, and the third semiconductor layer 13 are exposed at the side surface of the trench 20 in this order from the bottom side. The second semiconductor layer 12 exposed at the side surface of the trench 20 functions as a channel.
[0028] A recess 21 is provided in a partial region of the third semiconductor layer 13, which is different from the region where the trench 20 is formed. The recess 21 is a recess that penetrates the third semiconductor layer 13 and has a depth that reaches the second semiconductor layer 12.
[0029] The gate insulating film 14 is provided in the form of a film continuously over the bottom, side and top surfaces of the trench 20 (areas of the surface of the third semiconductor layer 13 near the trench 20).
[0030] The structure of the gate insulating film 14 will be described in more detail with reference to Fig. 2. Fig. 2 is an enlarged cross-sectional view of the gate insulating film 14 in a region that is in contact with the second semiconductor layer 12. Note that the structure of the gate insulating film 14 is the same in regions other than the region that is in contact with the second semiconductor layer 12.
[0031] 2, the gate insulating film 14 has an oxynitride film 141 made of SiON provided on and in contact with the second semiconductor layer 12, and an oxide film 142 made of SiO provided on and in contact with the oxynitride film 141. The oxide film 142 corresponds to the second oxide film of the present invention.
[0032] Ga-O bonds exist at the interface 140 between the second semiconductor layer 12 (or the first semiconductor layer 11, or the third semiconductor layer 13) and the oxynitride film 141. These Ga-O bonds are naturally formed on the surface of gallium nitride. That is, they are formed when gallium nitride is exposed to the atmosphere and the outermost surface of the gallium nitride reacts with oxygen. In particular, etching damage is formed on the side and bottom surfaces of the trench 20 by dry etching, and when nitrogen is removed from the gallium nitride and defects are created, Ga-O bonds are more likely to be formed.
[0033] These Ga-O bonds cause current leakage. Therefore, in the first embodiment, the Ga-O bonds are reduced by nitriding the interface 140, thereby reducing current leakage. The method for nitriding the interface 140 will be described later in the method for forming the gate insulating film 14.
[0034] At the interface 140, the concentration of oxygen atoms in Ga—O bonds is 0.8 to 1.2 at %. At the interface 140, the nitrogen concentration is 1×10 21 ~5×10 21 / cm 3 is.
[0035] The oxynitride film 141 is made of SiON and is provided on and in contact with the second semiconductor layer 12. As will be described later, the oxynitride film 141 is a film formed by nitriding an oxide film made of SiO2 by nitrogen plasma treatment and then performing heat treatment. The oxynitride film 141 is thin and has been heat-treated at a high temperature, making it difficult for oxygen atoms to move. Therefore, the oxynitride film 141 functions as a layer that suppresses the diffusion of oxygen atoms into the second semiconductor layer 12. The oxynitride film 141 also suppresses electron injection from the second semiconductor layer 12 into the gate insulating film 14.
[0036] The thickness of the oxynitride film 141 is, for example, 1 to 9 nm. By setting the thickness within this range, the effects of suppressing oxygen diffusion and electron injection can be fully exerted. The thickness is preferably 1 to 6 nm, and more preferably 1 to 4 nm.
[0037] The nitrogen concentration of the oxynitride film 141 is approximately constant in the thickness direction, for example, 1×10 21 ~1×10 22 / cm 3 is.
[0038] The oxygen concentration of the oxynitride film 141 has a distribution in the thickness direction, and the closer to the oxide film 142, the higher the oxygen concentration becomes.
[0039] The oxide film 142 is made of SiO2 and is provided on and in contact with the oxynitride film 141. The thickness of the oxide film 142 is, for example, 40 to 100 nm. By providing the oxide film 142, the gate insulating film 14 has a sufficient thickness.
[0040] The gate electrode 15 is an electrode provided across the bottom, side and top surfaces of the trench 20 via the gate insulating film 14. The gate electrode 15 is made of, for example, TiN.
[0041] The body electrode 17 is an electrode provided on the bottom surface of the recess 21. The body electrode 17 is made of, for example, Ni.
[0042] The source electrode 16 is an electrode provided on the third semiconductor layer 13 and the body electrode 17. The source electrode 16 is made of a multilayer film in which Pd, Al, and Ti are stacked in this order from the third semiconductor layer 13 or body electrode 17 side, for example.
[0043] The drain electrode 18 is an electrode provided on the back surface of the substrate 10. The drain electrode 18 is made of, for example, Pd / Al / Ti.
[0044] As described above, in the semiconductor device of the first embodiment, it is possible to reduce Ga—O bonds at the interface 140 between the oxynitride film 141 and the first semiconductor layer 11, the second semiconductor layer 12, and the third semiconductor layer 13 under the gate insulating film 14. As a result, it is possible to suppress current leakage.
[0045] 2. Manufacturing method of semiconductor element Next, a method for manufacturing the semiconductor device according to the first embodiment will be described with reference to the drawings.
[0046] First, a first semiconductor layer 11, a second semiconductor layer 12, and a third semiconductor layer 13 are formed on a substrate 10 in this order from the substrate 10 side (see FIG. 3(a)). The first semiconductor layer 11, the second semiconductor layer 12, and the third semiconductor layer 13 are formed by, for example, MOCVD.
[0047] Next, a predetermined region on the surface of the third semiconductor layer 13 is dry-etched until it reaches the first semiconductor layer 11, thereby forming a trench 20. Then, a predetermined region on the surface of the third semiconductor layer 13 is dry-etched until it reaches the second semiconductor layer 12, thereby forming a recess 21 (see FIG. 3(b)). After the trench 20 and the recess 21 are formed by dry etching, a wet etching process may be added.
[0048] Next, the gate insulating film 14 is formed continuously in a film shape on the bottom, side and top surfaces of the trench 20 (see FIG. 3(c)). The method for forming the gate insulating film 14 will be described later.
[0049] Next, a gate electrode 15 is formed on the bottom, side, and top surfaces of the trench 20 with a gate insulating film 14 interposed therebetween. Next, a body electrode 17 is formed on the bottom surface of the recess 21, and a source electrode 16 is formed on the third semiconductor layer and on the body electrode 17. Next, a drain electrode 18 is formed on the back surface of the substrate 10. These electrodes are formed by, for example, vapor deposition or sputtering. In this manner, the semiconductor device of embodiment 1 shown in FIG. 1 is manufactured.
[0050] 3. Gate insulating film formation method A method for forming the gate insulating film 14 will be described with reference to Figures 4 and 5. Note that Figure 4 shows an enlarged view of the vicinity of the surface of the second semiconductor layer 12.
[0051] First, an oxide film 143 made of SiO2 is formed on the bottom, side, and top surfaces of the trench 20 (FIG. 4(a), S1 in FIG. 5). The oxide film 143 can be formed by CVD, ALD, sputtering, or the like. The thickness of the oxide film 143 is set to 1 to 9 nm. By setting the thickness to this range, sufficient nitrogen can be implanted in the nitrogen plasma treatment in the next step, and plasma damage to the semiconductor layer can also be suppressed. The thickness is preferably 1 to 6 nm, and more preferably 1 to 4 nm.
[0052] Here, after the trench 20 is formed, the wafer is exposed to the atmosphere. Oxygen in the atmosphere reacts with the surface of the GaN, particularly with nitrogen vacancies formed during the formation of the trench 20. Therefore, after the trench 20 is formed, Ga-O bonds are naturally formed on the surface of the GaN (interface 140 between the GaN and the oxide film 143). Similarly, when a method using oxygen gas is used to form the oxide film 143, Ga-O bonds are also likely to be formed at the interface 140.
[0053] Next, nitrogen plasma treatment is performed by irradiating the surface of the oxide film 143 with nitrogen plasma (S2 in FIG. 5). Nitrogen gas is used as the plasma gas. Any plasma source capable of generating high-density plasma can be used, such as ECR plasma, ICP, CCP, or SWP. This nitrogen plasma treatment implants nitrogen into the oxide film 143 and the interface 140. Because the oxide film 143 is sufficiently thin, the nitrogen reaches the interface 140.
[0054] By nitrogen implantation by nitrogen plasma treatment, the nitrogen concentration (average in the thickness direction) of the oxide film 143 is, for example, 1×10 20 ~1×10 22 / cm 3 This becomes:
[0055] The nitrogen plasma treatment time is, for example, 10 to 50 minutes, and the substrate temperature is, for example, 0 to 300° C., and the bias power to the substrate side is 0 W.
[0056] In the nitrogen plasma irradiation, it is preferable to remove charged particles such as electrons and ions so that only radicals are irradiated. Methods for removing charged particles include using a wire mesh or applying a magnetic field. Alternatively, the substrate and the plasma generation region may be separated sufficiently and the bias applied to the substrate may be weakened to make it difficult for charged particles to reach the substrate.
[0057] The microwave output for generating nitrogen plasma is set to 300 W or less. By sufficiently suppressing the output, it is possible to prevent nitrogen from reaching the first semiconductor layer 11, the second semiconductor layer 12, and the third semiconductor layer and damaging the GaN. However, if the output is too weak, nitrogen will not be sufficiently implanted to the interface 140, so the microwave output is preferably 50 W or more. It is more preferably 100 to 300 W, and even more preferably 100 to 200 W.
[0058] Next, a heat treatment is performed in an inert gas atmosphere (S3 in FIG. 5). Hereinafter, this heat treatment will be referred to as the first heat treatment. The inert gas is nitrogen. The temperature of the first heat treatment is, for example, 800 to 1000° C., and the time of the first heat treatment is 10 to 60 minutes.
[0059] This first heat treatment causes defects in the oxide film 143 and the interface 140 to bond with nitrogen and become nitrided. As a result, the oxide film 143 changes from SiO2 to SiON, becoming the oxynitride film 141. The interface 140 is also nitrided, and the GO bonds present at the interface 140 are reduced. For example, the concentration of oxygen in Ga-O bonds at the interface 140 is reduced from approximately 2 to 3 at % to 0.8 to 1.2 at %. In this way, the first heat treatment reduces the concentration of oxygen in Ga-O bonds at the interface 140, thereby reducing current leakage through the interface 140.
[0060] Furthermore, the nitrogen concentration of the oxynitride film 141 is approximately constant in the thickness direction by the first heat treatment, for example, 1×10 21 ~1×10 22 / cm 3 The nitrogen concentration in the oxynitride film 141 is higher than the nitrogen concentration in the oxide film 143.
[0061] The oxygen concentration in the oxynitride film 141 increases with increasing depth, and is lower than the oxygen concentration before the first heat treatment at any thickness. The concentration of oxygen in Ga-O bonds at the interface 140 is 0.8 to 1.2 at%, which is lower than the concentration before the first heat treatment. The concentration of oxygen in Ga-O bonds at the interface 140 before the first heat treatment is 2 to 3 at%.
[0062] Next, an oxide film 142 is formed on the oxynitride film 141 (FIG. 4(c), S4 in FIG. 5). The oxide film 143 is formed by a method such as a CVD method, an ALD method, or sputtering. The thickness of the oxide film 143 is, for example, 40 to 100 nm.
[0063] Next, a heat treatment is performed in an inert gas atmosphere (S5 in FIG. 5). Hereinafter, this heat treatment will be referred to as the second heat treatment. The inert gas is nitrogen. The temperature of the second heat treatment is lower than that of the first heat treatment, for example, 400 to 600°C. The time of the second heat treatment is, for example, 10 to 30 minutes. The second heat treatment can repair defects in the oxide film 142 and promote recombination within the film, thereby improving the insulation properties.
[0064] The above-described method for forming the gate insulating film 14 can reduce the concentration of oxygen in Ga-O bonds at the interface 140 while suppressing damage to the first semiconductor layer 11, the second semiconductor layer 12, and the third semiconductor layer 13. As a result, current leakage can be suppressed.
[0065] 4. Experimental results Next, various experimental results relating to the first embodiment will be described.
[0066] Experiment 1 A semiconductor device according to the first embodiment (hereinafter referred to as Example 1) was fabricated, and the Id-Vd characteristics were examined. The gate insulating film 14 had an oxide film 143 with a thickness of 53 nm and an oxide film 142 with a thickness of 50 nm. The microwave output for the nitrogen plasma treatment was 200 W. For comparison, the Id-Vd characteristics were also examined for a semiconductor device (hereinafter referred to as Comparative Example 1) fabricated in the same manner as the example, except that the nitrogen plasma treatment and the first heat treatment in the example were not performed.
[0067] 6 is a graph showing the Id-Vd characteristics of the semiconductor device of Comparative Example 1. As shown in FIG. 6, when the gate voltage Vg is −2 V or higher, the drain current Id flows, and it is clear that a current leak occurs. This current leak is thought to be due to the formation of Ga—O bonds at the interface 140 between the second semiconductor layer 12 on the side surface of the trench 20 and the oxynitride film 141.
[0068] 7 is a graph showing the Id-Vd characteristics of the semiconductor device of Example 1. As shown in FIG. 7, even when the gate voltage Vg is set to 0 V, the drain current Id is 0.01 nA or less, and it is clear that no current leakage occurs. This is thought to be because the nitrogen plasma treatment and the first heat treatment reduced Ga-O bonds at the interface 140 between the GaN under the gate insulating film 14 and the oxynitride film 141 (particularly the interface 140 between the second semiconductor layer 12 and the oxynitride film 141).
[0069] Experiment 2 A gate insulating film 14 was formed on n-GaN, and a gate electrode 15 made of TiN was formed on the gate insulating film 14 to fabricate a sample (hereinafter referred to as Example 2). The gate insulating film 14 was the same as in Example 1. Furthermore, the nitrogen plasma treatment and first heat treatment in Example 2 were not performed, but the rest of the fabrication was the same as in Example 2 (Comparative Example 2). For Example 2 and Comparative Example 2, the nitrogen concentration and oxygen concentration in the gate insulating film 14 were measured by SIMS.
[0070] 8 is a graph showing the relationship between depth and nitrogen concentration and oxygen concentration. The depth is measured in the n-GaN direction with the top surface of the gate insulating film 14 as the reference. In Example 2 and Comparative Example 2, the position at a depth of 46 nm is considered to be the interface between the oxide film 142 and the oxynitride film 141 of the gate insulating film 14. This is because the oxygen concentration is approximately constant at depths of 46 nm or less. In Example 2 and Comparative Example 2, the position at a depth of 53 nm is considered to be the interface 140 between the GaN layer and the oxynitride film 141. This is because the nitrogen concentration is constant.
[0071] Furthermore, in the depth range of 45 to 53 nm, the oxygen concentration was lower in Example 2 than in Comparative Example 2. From this, it is considered that the Ga—O bond at the interface 140 is reduced more in Example 2 than in Comparative Example 2.
[0072] In Example 2, near a depth of 46 nm, the nitrogen concentration increased with increasing depth, and the oxygen concentration decreased with increasing depth, and neither the nitrogen nor the oxygen concentration was constant. With SiN, the nitrogen concentration would be approximately constant and the oxygen concentration would be low, so it can be inferred that SiN does not exist between the oxide film 142 and the oxynitride film 141.
[0073] Experiment 3 For Example 2 and Comparative Example 2, the 3d spectrum of Ga and the 1s spectrum of O in the Ga—O bond in the gate insulating film 14 were measured by XPS, and the depth dependence of the gallium concentration and oxygen concentration was measured.
[0074] Figure 9 is a graph showing the relationship between depth and gallium concentration and oxygen concentration. The horizontal axis of Figure 9 indicates the depth in the p-GaN direction, relative to the insulating film surface, for a sample with a 7-nm insulating film on p-GaN. The concentrations indicate the concentrations (at%) of gallium atoms and oxygen atoms in Ga-O bonds. The position at a depth of 7 nm is considered to be the interface 140 between the GaN layer and the oxynitride film 141.
[0075] As shown in Figure 9, Comparative Example 2, which was not subjected to nitrogen plasma treatment, has an oxygen concentration peak at a depth of approximately 2.8 at% near 6 nm. It can also be seen that the gallium concentration increases with depth and becomes approximately constant at around 8 nm. This suggests the presence of Ga-O bonds near a depth of 6 nm. Note that Comparative Example 2 also has an oxygen concentration peak near a depth of 2.5 nm, which may be due to oxygen being mixed in during sputtering of the gate insulating film 14 when measuring the depth direction using the XPS method.
[0076] On the other hand, in Example 2, which was subjected to nitrogen plasma treatment, the peak near a depth of 6 nm seen in Comparative Example 2 was not observed, and instead a peak was observed near a depth of 4 nm. The oxygen concentration at the peak was approximately 1.6 at %, and the oxygen concentration gradually decreased as the depth increased from the peak. Furthermore, the oxygen concentration was generally lower than in Comparative Example 2. Furthermore, it was found that the gallium concentration increased with increasing depth. This suggests that the Ga-O bonds at the interface 140 in Example 2 were reduced compared to Comparative Example 2.
[0077] 8 and 9 reveal the following about the nitrogen concentration and oxygen concentration of the interface 140 and the oxynitride film 141 in Example 2.
[0078] At the interface 140 between the GaN layer and the oxynitride film 141, the concentration of oxygen atoms in Ga—O bonds is 0.8 to 1.2 at %. At the interface 140, the nitrogen concentration is 1×10 21 ~1×10 22 / cm 3 is.
[0079] The oxygen concentration of the oxynitride film 141 has a distribution in the thickness direction, and the oxygen concentration becomes higher closer to the oxide film 142. The nitrogen concentration of the oxynitride film 141 is approximately constant in the thickness direction, and is 1×10 21 ~1×10 22 / cm 3 is.
[0080] Experiment 4 A gate insulating film 14 was formed on n-GaN, and a gate electrode 15 made of TiN was formed on the gate insulating film 14 to fabricate samples. The microwave output for the nitrogen plasma treatment was set to 200 W and 500 W. The CV characteristics of the fabricated samples were then measured. Figure 10 is a graph showing the CV characteristics when the microwave output was set to 200 W. Figure 11 is a graph showing the CV characteristics when the microwave output was set to 500 W.
[0081] As shown in Figure 10, no hysteresis was observed when the microwave power was set to 200 W. In other words, no change was observed in the CV curve when the voltage was swept in the forward direction from negative to positive and when it was swept in the reverse direction from positive to negative.
[0082] On the other hand, when the microwave output was set to 500 W, hysteresis was observed, as shown in Figure 11. In other words, a difference was observed in the CV curve when the voltage was swept in the forward direction and when it was swept in the reverse direction.
[0083] Hysteresis was observed in the CV characteristics when the microwave output was set to 500 W, suggesting the presence of levels (defects) at the interface between the GaN and the insulating film. This is thought to be due to defects formed in the GaN due to plasma damage during nitrogen plasma treatment. No hysteresis was observed when the microwave output was set to 200 W, suggesting that reducing the plasma output reduced plasma damage to the GaN, thereby reducing defects in the GaN.
[0084] (Modification of the first embodiment) Although the semiconductor element in the first embodiment is a MISFET with a trench gate structure, the present invention can be applied to any semiconductor element having a gate insulating film.
[0085] Furthermore, instead of or in addition to the gate insulating film 14, a protective film of the element may have the same structure as the gate insulating film 14. In this case as well, it is possible to suppress damage to the semiconductor and to suppress current leakage at the interface between the semiconductor layer and the protective film. In short, the present invention can be applied to any structure, not limited to gate insulating films and protective films, as long as an insulating film is provided on a semiconductor layer made of a Group III nitride semiconductor.
[0086] The oxide films 142 and 143 may be made of other insulating oxide films instead of SiO2. For example, Al2O3 may be used. In this case, the oxynitride film 141 is AlON. The oxide films 142 and 143 may be made of different materials. [Explanation of symbols]
[0087] 10: Circuit board 11: First semiconductor layer 12: Second semiconductor layer 13: Third semiconductor layer 14: Gate insulating film 15: Gate electrode 16: Source electrode 17: Body electrode 18: Drain electrode 140: Interface 141: Oxynitride film 142, 143: oxide film
Claims
1. a first oxide film forming step of forming an insulating first oxide film on a semiconductor layer made of a Group III nitride semiconductor; a nitrogen plasma treatment step of irradiating the first oxide film with nitrogen plasma to inject nitrogen into the first oxide film; a first heat treatment step of heat treating the first oxide film to nitride the first oxide film into an oxynitride film; a second oxide film forming step of forming an insulating second oxide film on the oxynitride film; a second heat treatment step of heat treating the second oxide film, In the nitrogen plasma treatment step, microwave output is set to 300 W or less.
2. 2. The method for manufacturing a semiconductor element according to claim 1, wherein the first heat treatment step nitrides an interface between the semiconductor layer and the oxynitride film, thereby lowering the concentration of oxygen in Ga—O bonds at the interface compared to before the first heat treatment step.
3. 3. The method for manufacturing a semiconductor element according to claim 2, wherein the concentration of oxygen in Ga—O bonds at the interface between the semiconductor layer and the oxynitride film is set to 0.8 to 1.2 at % by the first heat treatment step.
4. a first oxide film forming step of forming an insulating first oxide film on a semiconductor layer made of a Group III nitride semiconductor; a nitrogen plasma treatment step of irradiating the first oxide film with nitrogen plasma to inject nitrogen into the first oxide film; a first heat treatment step of heat treating the first oxide film to nitride the first oxide film into an oxynitride film; a second oxide film forming step of forming an insulating second oxide film on the oxynitride film; a second heat treatment step of heat treating the second oxide film, The first heat treatment step nitrides the interface between the semiconductor layer and the oxynitride film, so that the concentration of oxygen in Ga—O bonds at the interface is 0.8 to 1.2 at %.
5. In the nitrogen plasma treatment step, the nitrogen concentration of the first oxide film is 1×10 ２０ ~1 x 10 ２２ / cm ３ The method for manufacturing a semiconductor device according to any one of claims 1 to 4, wherein:
6. The nitrogen plasma treatment step is performed so that the nitrogen concentration in the first oxide film in the region near the interface between the semiconductor layer and the first oxide film is 1×10 ２１ ~1 x 10 ２２ / cm ３ The method for manufacturing a semiconductor device according to any one of claims 1 to 4, wherein:
7. 5. The method for manufacturing a semiconductor device according to claim 1, wherein the first oxide film forming step forms the first oxide film to a thickness of 1 nm or more and 9 nm or less.
8. a semiconductor layer made of a Group III nitride semiconductor; a gate insulating film provided on the semiconductor layer; a gate electrode provided on the gate insulating film, The gate insulating film is a SiON film formed on the semiconductor layer; SiO formed on and in contact with the SiON film ２ a membrane; The semiconductor element has a concentration of oxygen atoms in Ga—O bonds at the interface between the semiconductor layer and the SiON film of 0.8 to 1.2 at %.
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Semiconductor device and method for manufacturing the same
JP2022014832A