Method for manufacturing nitride semiconductor substrate

Abstract

To provide a method for manufacturing a nitride semiconductor substrate, by which Al can be prevented from being diffused into a high-resistance single crystal silicon substrate when an AlN layer is epitaxially grown on the high-resistance single crystal silicon substrate and a GaN or AlGaN layer is epitaxially grown thereon.SOLUTION: The present invention provides a method for manufacturing a nitride semiconductor substrate obtained by forming a nitride semiconductor on a film-forming substrate, the method comprising: (1) a step for heating a film-forming substrate formed of single crystal silicon in a nitrogen atmosphere to form a silicon nitride film on the film-forming substrate; (2) a step for growing an AlN film on the silicon nitride film; and (3) a step for growing a GaN film, an AlGaN film, or both on the AlN film.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a nitride semiconductor substrate, and more particularly to a method for manufacturing a nitride semiconductor substrate for use in high frequency devices. [Background technology]

[0002] Nitride semiconductors such as GaN and AlN can be used to fabricate high electron mobility transistors (HEMTs) that use two-dimensional electron gas and high-voltage electronic devices.

[0003] It is difficult to manufacture nitride wafers by growing these nitride semiconductors on a substrate, so sapphire or SiC substrates are used as substrates. However, epitaxial growth by vapor phase growth on silicon substrates is used to increase the diameter and reduce the cost of substrates. The production of epitaxially grown films by vapor phase growth on silicon substrates allows the use of larger diameter substrates compared to sapphire or SiC substrates, which increases the productivity of devices and has the advantage of heat dissipation.

[0004] An AlN buffer layer is stacked on a single crystal silicon substrate, a buffer layer is stacked, and a GaN-HEMT structure epitaxial layer is stacked to produce epitaxial wafers for power devices and RF devices. In particular, a high-resistance substrate is used for the single crystal silicon substrate of the epitaxial wafer for RF devices. An AlN buffer layer is stacked on top of the high-resistance single crystal silicon substrate, and a superlattice structure buffer layer (SLs) is stacked on top of that as a buffer layer, and the HEMT structure is epitaxially grown on top of that.

[0005] However, when an AlN buffer layer is directly stacked on a high-resistance single crystal silicon substrate, and then a buffer layer and a HEMT structure are stacked, it is known that the growth rate of AlN is slow, the total epitaxial growth time is long, and Al from the AlN buffer layer diffuses into the high-resistance single crystal silicon substrate, creating a low-resistance layer and forming a channel. As a method to reduce this Al diffusion, the most recent known method is the epitaxial growth technology of 3C-SiC on Si. In other words, an intermediate 3C-SiC layer is inserted as AlN / 3C-SiC / Si. The 3C-SiC layer introduces an Al diffusion suppression layer more simply and efficiently.

[0006] Patent Document 1 also discloses a semiconductor structure having SiN between a silicon substrate and an aluminum nitride layer. SiN can be formed before the reaction. SiN can be amorphous, have a single-layer crystal structure, or be polycrystalline. In the case of amorphous, anything that grows on it will be polycrystalline and will not grow epitaxially. It is also described that it is formed by a CVD process, but even if a CVD thin film (2 nm) is piled up, it will become polycrystalline. It is also described that ammonia gas is used as a nitrogen source gas to make single-crystal structure SiN, but if ammonia is used, cloudiness will occur on the epitaxial wafer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special table 2008-522447 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above-mentioned problems, and has an object to provide a method for manufacturing a nitride semiconductor substrate that can prevent Al from diffusing into a single crystal silicon substrate when an AlN layer is epitaxially grown on a single crystal silicon substrate and a GaN or AlGaN layer is epitaxially grown thereon. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides A method for manufacturing a nitride semiconductor substrate in which a nitride semiconductor is formed on a film-formation substrate, comprising the steps of: (1) forming a silicon nitride film on a film-formation substrate made of single crystal silicon by heat-treating the film-formation substrate in a nitrogen atmosphere; (2) growing an AlN film on the silicon nitride film; and (3) growing a GaN film, an AlGaN film, or both, on the AlN film; The present invention provides a method for producing a nitride semiconductor substrate, comprising the steps of:

[0010] This manufacturing method can prevent Al from diffusing from the AlN layer into the single crystal silicon substrate, and can also manufacture a nitride semiconductor substrate that is free of cloudiness.

[0011] In the step (1), the heat treatment is preferably performed in an RTA furnace at 1100 to 1300° C. for 1 to 120 seconds.

[0012] Such a heat treatment makes it possible to form a silicon nitride film relatively easily.

[0013] It is also preferable that the silicon nitride film is a single crystal.

[0014] In the present invention, such a silicon nitride film can be formed.

[0015] In the present invention, the Al diffusion concentration on the growth substrate surface is 4e15 atoms / cm 3 It is preferable to manufacture the following nitride semiconductor substrate.

[0016] A nitride semiconductor substrate in which the diffusion of Al into the growth substrate surface is thus suppressed is particularly useful in the fabrication of high frequency devices. Effect of the Invention

[0017] As described above, the present invention can provide a method for manufacturing a nitride semiconductor substrate that can prevent Al from diffusing into the single crystal silicon substrate and is free of cloudiness when an AlN layer is epitaxially grown on a single crystal silicon substrate, particularly a high-resistivity single crystal silicon substrate, and a GaN or AlGaN layer is epitaxially grown thereon. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic diagram showing an example of a flow of a method for producing a nitride semiconductor substrate according to the present invention. [Diagram 2] 3 is a photograph of nitride semiconductor substrates produced in Example and Comparative Examples 1 and 2. [Diagram 3] 1 shows the results of backside SIMS measurement of the nitride semiconductor substrates produced in Example and Comparative Example 3. [Figure 4] 1 is a cross-sectional photograph of a nitride semiconductor substrate produced in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] As described above, there has been a need for a method for manufacturing a nitride semiconductor substrate that prevents Al from diffusing into a high-resistivity single crystal silicon substrate when epitaxially growing a nitride semiconductor consisting of an AlN buffer layer, a buffer layer, and a GaN-HEMT structure on a high-resistivity single crystal silicon substrate.

[0020] As a result of extensive research, the inventors have found that a method for manufacturing a nitride semiconductor substrate including the steps of forming a silicon nitride film by heat treating a film-formation substrate made of single crystal silicon in a nitrogen atmosphere, growing an AlN film on the silicon nitride film, and growing a GaN film, an AlGaN film, or both, on the AlN film can prevent Al from diffusing into a high-resistivity single crystal silicon substrate and can manufacture a nitride semiconductor substrate that is free of cloudiness, and have completed the present invention.

[0021] That is, the present invention is a method for manufacturing a nitride semiconductor substrate in which a nitride semiconductor is formed on a film-formation substrate, the method including: (1) a step of forming a silicon nitride film on the film-formation substrate by heat-treating a film-formation substrate made of single crystal silicon in a nitrogen atmosphere; (2) a step of growing an AlN film on the silicon nitride film; and (3) a step of growing a GaN film, an AlGaN film, or both on the AlN film.

[0022] The present invention will be described in detail below, but the present invention is not limited thereto.

[0023] [Method of manufacturing nitride semiconductor substrate] The method for producing a nitride semiconductor substrate of the present invention includes the following steps (1) to (3). Each step will be described in detail below with reference to the flow of the method for producing a nitride semiconductor of the present invention shown in FIG.

[0024] <Process (1)> The step (1) is a step of forming a silicon nitride film on a film-formation substrate made of single crystal silicon by heat-treating the substrate in a nitrogen atmosphere.

[0025] 1(a), a film-forming substrate (silicon substrate) 1 made of single crystal silicon is placed in an RTA (Rapid Thermal Annealing) furnace and heat-treated in a nitrogen atmosphere at, for example, 1100-1300°C for 1-120 seconds, preferably 1150-1250°C for 2-20 seconds, particularly 1200°C for 10 seconds, to form a silicon nitride film (SiN film) 2 on the surface with a thickness of, for example, 0.2-20 nm, preferably 1-4 nm, particularly about 2 nm. The silicon nitride film 2 may be formed only on the front surface side of the film-forming substrate, but may also be formed on the entire film-forming substrate 1 having a front surface and a back surface.

[0026] The present invention is characterized in that the silicon nitride film is formed in a nitrogen atmosphere. Here, the nitrogen atmosphere refers to a 100% nitrogen gas atmosphere or a mixed atmosphere of nitrogen gas and an inert gas. The silicon nitride film can prevent Al from diffusing from the AlN buffer layer described later to the surface of the substrate for growing high resistance single crystal silicon, which would otherwise cause a low resistance layer to form. However, if the silicon nitride film is formed by heat treatment in a nitrogen atmosphere, a clear epitaxial layer of a nitride semiconductor can be grown on the silicon nitride film in the next step or later. If the silicon nitride film is formed by heat treatment in a CVD process or an ammonia gas atmosphere, rather than in a nitrogen atmosphere, a polycrystalline layer may be formed on the silicon nitride film or the grown epitaxial layer may become cloudy when the nitride semiconductor is grown in the next step or later.

[0027] The substrate for film formation made of single crystal silicon is not particularly limited, and may be CZ single crystal silicon or FZ single crystal silicon, and there is no particular limit to the presence or absence, type, and concentration of a dopant. The substrate for film formation is preferably a high-resistance single crystal silicon substrate. The resistivity is not particularly limited, but the lower limit is, for example, 1 Ωcm or more, preferably 10 Ωcm or more, more preferably 100 Ωcm or more, and the upper limit is, for example, 3000 Ωcm or less, preferably 1000 Ωcm or less, more preferably 500 Ωcm or less.

[0028] <Process (2)> Step (2) is a step of growing an AlN film on the silicon nitride film.

[0029] As shown in FIG. 1(b), an AlN film (AlN buffer layer) 3 is grown on the silicon nitride film 2 by MOVPE to a thickness of, for example, 20 to 500 nm, preferably 50 to 300 nm, more preferably 100 to 200 nm, and particularly preferably 160 nm.

[0030] <Process (3)> Step (3) is a step of growing a GaN film, an AlGaN film, or both, on the AlN film.

[0031] As shown in FIG. 1(c), for example, a buffer layer 4 made of a multilayer film including an AlN layer and a GaN layer, and a nitride semiconductor made of a GaN-HEMT layer 5 are epitaxially grown to a total thickness of 0.1 to 20 μm, preferably 0.5 to 10 μm, more preferably 1 to 5 μm, and particularly about 2.7 μm.

[0032] In this manner, the silicon nitride film can prevent Al from diffusing from the AlN buffer layer onto the surface of the high-resistance single crystal silicon growth substrate to form a low-resistance layer, and a nitride semiconductor substrate can be manufactured in which the epitaxial layer grown on the AlN buffer layer is clear.

[0033] In the present invention, the Al diffusion concentration on the growth substrate surface is 4e15 atoms / cm 3 Less than 3e15atoms / cm 3 Less than or equal to 2e15 atoms / cm 3 The following nitride semiconductor substrate can be manufactured. The lower limit of the Al diffusion concentration is not particularly limited, but for example, 0 atoms / cm 3 or more than 1e13atoms / cm 3 It can be more than that.

[0034] The Al diffusion concentration on the growth substrate surface can be measured by, for example, secondary ion mass spectrometry (SIMS). EXAMPLES

[0035] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0036] (Example) A 2 nm thick SiN film (placed in an RTA furnace and the surface converted to SiN in an N2 atmosphere at 1200°C for 10 seconds) was applied to the surface of a single crystal silicon substrate with a diameter of 150 mm, a surface orientation of (111), and a resistivity of 100 Ωcm, and an AlN buffer layer, buffer layer, and GaN-HEMT structure were epitaxially grown on top of it. Figure 4 shows the cross section of the wafer after epitaxial growth. As can be seen from Figure 4, it can be confirmed that a flat single crystal SiN layer has been formed between the silicon substrate and the AlN film. Electron beam diffraction results showed that the AlN layer was single crystal.

[0037] Also, as shown in Figure 2(a), it can be seen that the epitaxial layer has grown to a mirror finish. Figure 3 shows the results of a backside SIMS investigation of the Al concentration from the back side of the single crystal silicon substrate to the SiN film. In Figure 3, the area where the nitrogen (N) concentration rises sharply represents the interface between the single crystal silicon substrate and the AlN film on top of it (the silicon nitride film is only 2 nm thick), and it can be seen that the Al concentration is lower just below the interface (around SIMS depth of 2.3 to 2.7 μm on the horizontal axis of the graph) compared to Comparative Example 3, which does not have a SiN film, which will be described later.

[0038] Comparative Example 1 An AlN buffer layer, a buffer layer, and a GaN-HEMT structure were epitaxially grown on a Si substrate with a 2 nm thick SiN film (the surface was SiNified in an RTA furnace at 1175°C for 10 seconds in an NH3+Ar atmosphere) on a single crystal silicon substrate with a diameter of 150 mm, a surface orientation of (111), and a resistivity of 100 Ωcm. As shown in Figure 2(b), the epitaxial layer has grown cloudy.

[0039] Comparative Example 2 A 2 nm thick SiN film (placed in a PE-CVD furnace and the surface was converted to SiN in a SiH4+NH3+N2 atmosphere at 300°C for 3 seconds) was applied to the surface of a single crystal silicon substrate with a diameter of 150 mm, a surface orientation of (111), and a resistivity of 100 Ωcm. An AlN buffer layer, a buffer layer, and a GaN-HEMT structure were epitaxially grown on the Si substrate. As shown in Figure 2(c), it can be seen that the epitaxial layer has grown cloudy.

[0040] Comparative Example 3 Without providing a SiN film on the Si substrate surface, the AlN buffer layer, the buffer layer, and the GaN-HEMT structure were epitaxially grown directly on the Si substrate surface. As shown in Figure 3, the nitride semiconductor substrate of Comparative Example 3 has a higher Al concentration on the silicon substrate surface than the Example.

[0041] As described above, it is found that the method for manufacturing a nitride semiconductor substrate according to the present invention can prevent Al from diffusing into the high-resistance single crystal silicon substrate by forming a silicon nitride film between the single crystal silicon substrate and the AlN film by heat treatment in a nitrogen atmosphere, and can manufacture a nitride semiconductor substrate without clouding. On the other hand, in Comparative Examples 1 and 2 in which the silicon nitride film was formed under conditions other than a nitrogen atmosphere, clouding occurred in the epitaxial layer, and in Comparative Example 3 in which the silicon nitride film was not formed, it was not possible to prevent Al from diffusing into the high-resistance single crystal silicon substrate.

[0042] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0043] 1...film-forming substrate made of single crystal silicon, 2...silicon nitride film, 3...AlN film, 4...Buffer layer, 5...GaN-HEMT layer.

Claims

1. A method for manufacturing a nitride semiconductor substrate in which a nitride semiconductor is formed on a film-formation substrate, comprising the steps of: (1) forming a silicon nitride film on a film-formation substrate made of single crystal silicon by heat-treating the film-formation substrate in a nitrogen atmosphere; (2) growing an AlN film on the silicon nitride film; and (3) growing a GaN film, an AlGaN film, or both, on the AlN film; and The method for producing a nitride semiconductor substrate, wherein in the step (1), the heat treatment is performed in an RTA furnace at 1100 to 1300° C. for 1 to 120 seconds.

2. 2. The method for producing a nitride semiconductor substrate according to claim 1, wherein the silicon nitride film is a single crystal.

3. The Al diffusion concentration on the growth substrate surface is 4e15 atoms / cm ３ 3. The method for producing a nitride semiconductor substrate according to claim 1, further comprising producing the following nitride semiconductor substrate:

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