Method for manufacturing nitride semiconductor substrates

Abstract

This invention discloses a method for manufacturing a nitride semiconductor substrate, wherein the nitride semiconductor substrate is formed by forming a nitride semiconductor on a film-forming substrate. The method is characterized by comprising: step (1), heat-treating a film-forming substrate made of single-crystal silicon in a nitrogen atmosphere to form a silicon nitride film on the substrate; step (2), growing an AlN film on the silicon nitride film; and step (3), growing a GaN film, an AlGaN film, or both, on the AlN film. This provides a method for manufacturing a nitride semiconductor substrate that prevents Al diffusion into the high-resistivity single-crystal silicon substrate when epitaxially growing an AlN layer on a high-resistivity single-crystal silicon substrate and epitaxially growing GaN and AlGaN layers on an AlN layer.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a nitride semiconductor substrate. More particularly, it relates to a method for manufacturing a nitride semiconductor substrate for high-frequency devices. Prior Technology

[0002] Nitride semiconductors, primarily GaN and AlN, can be used to fabricate high electron mobility transistors (HEMTs) and high voltage-resistant electronic devices that utilize two-dimensional electron gases.

[0003] Fabricating nitride wafers, which grow such nitride semiconductors on substrates, is difficult. Sapphire and SiC substrates are commonly used as substrates. However, to achieve larger apertures and reduce substrate costs, epitaxial growth via vapor phase growth on silicon substrates is employed. Compared to sapphire and SiC substrates, the fabrication of epitaxial growth films via vapor phase growth on silicon substrates allows for the use of larger aperture substrates, resulting in higher device productivity and advantages in terms of heat dissipation.

[0004] An AlN buffer layer is deposited on a single-crystal silicon substrate, followed by the deposition of a GaN-HEMT epitaxial layer to create an epitaxial wafer for power generation devices and RF devices. Particularly in the single-crystal silicon substrate for the RF device epitaxial wafer, a high-resistivity substrate is used. An AlN buffer layer is deposited on a high-resistivity single-crystal silicon substrate, and then a buffer layer, i.e., a superlattice structure buffer layer (SLs), is epitaxially grown on top of it, followed by the HEMT structure.

[0005] Furthermore, it is known that when an AlN buffer layer is stacked on a high-resistivity single-crystal silicon substrate, along with the buffer layer and HEMT structure, the growth rate of AlN is slower, resulting in a longer total epitaxial growth time. Al from the AlN buffer layer diffuses into the high-resistivity single-crystal silicon substrate, becoming a low-resistivity layer and forming channels. As a method to reduce this Al diffusion, a 3C-SiC on Si epitaxial growth technique has recently been known. That is, an intermediate 3C-SiC layer is inserted to create an AlN / 3C-SiC / Si structure. Using the 3C-SiC layer, an Al diffusion suppression layer can be introduced more easily and efficiently.

[0006] Furthermore, Patent Document 1 discloses a semiconductor structure in which SiN is present between a silicon substrate and an aluminum nitride layer. SiN can be formed before the reaction. SiN has amorphous, monolayer crystalline, and polycrystalline structures. In the case of amorphous SiN, growth on it will result in polymerization instead of epitaxial growth. Furthermore, although there are records of forming SiN using a CVD process, even when a CVD thin film (2 nm) is deposited, polycrystalline formation still occurs. Additionally, although a technique using ammonia as a nitrogen source gas has been described for forming monocrystalline SiN structures, using ammonia will produce cloudiness on the epitaxial wafer. [Previous Technical Documents] (Patent Documents)

[0007] Patent Document 1: Japanese Patent Application Publication No. 2008-522447. Summary of the Invention

[0008] [The problem the invention aims to solve] The present invention was made to solve the above-mentioned problems, and aims to provide a method for manufacturing a nitride semiconductor substrate, which can prevent Al diffusion into the single crystal silicon substrate when an AlN layer is epitaxially grown on a single crystal silicon substrate and GaN and AlGaN layers are epitaxially grown on an AlN layer. [Technical means to solve the problem]

[0009] To address the aforementioned problems, the present invention provides a method for manufacturing a nitride semiconductor substrate, wherein the nitride semiconductor substrate is formed by forming a nitride semiconductor on a film-forming substrate. The manufacturing method is characterized by comprising: Step (1) involves heat-treating a substrate made of single-crystal silicon in a nitrogen atmosphere to form a silicon nitride film on the substrate. Step (2) involves growing an AlN film on the aforementioned silicon nitride film; and, Step (3) involves growing a GaN film, an AlGaN film, or both on the aforementioned AlN film.

[0010] This method can prevent Al from diffusing from the AlN layer into the single-crystal silicon substrate and can also produce nitride semiconductor substrates that do not produce turbidity.

[0011] Furthermore, it is preferable that in the aforementioned step (1), the aforementioned heat treatment is performed in an RTA (Rapid Thermal Anneal) furnace at 1100~1300°C for 1~120 seconds.

[0012] With this kind of heat treatment, silicon nitride film can be formed relatively easily.

[0013] Furthermore, it is preferable that the aforementioned silicon nitride film is a single crystal.

[0014] Such silicon nitride films can be formed in this invention.

[0015] Furthermore, it is preferable that: in this invention, a nitride semiconductor substrate is manufactured, wherein the Al diffusion concentration on the surface of the substrate for growth is 4e15 atoms / cm3 or less.

[0016] Such nitride semiconductor substrates, which suppress Al diffusion to the surface of the substrate used for growth, are particularly useful in the fabrication of high-frequency devices. [The effects of the invention]

[0017] As described above, this invention provides a method for manufacturing a nitride semiconductor substrate that, when epitaxially growing an AlN layer on a single-crystal silicon substrate, particularly a high-resistivity single-crystal silicon substrate, and epitaxially growing GaN and AlGaN layers on an AlN layer, prevents Al diffusion into the single-crystal silicon substrate and does not produce turbidity. Simple Explanation of the Diagram

[0018] Figure 1 is a schematic diagram illustrating an example of the process of manufacturing a nitride semiconductor substrate according to the present invention. Figure 2 is a photograph of the nitride semiconductor substrates prepared in Examples 1 and 2. Figure 3 shows the measurement results of the backside SIMS of the nitride semiconductor substrates prepared in Examples and Comparative Example 3. Figure 4 is a cross-sectional photograph of the nitride semiconductor substrate prepared in Example 1. Implementation

[0019] As mentioned above, it is desirable to develop a method for manufacturing a nitride semiconductor substrate that can prevent Al diffusion into the high-resistivity single-crystal silicon substrate during the epitaxial growth of an AlN buffer layer, a buffer layer, and a nitride semiconductor composed of a GaN-HEMT structure.

[0020] The inventors dedicated themselves to research and discovered that any method for manufacturing a nitride semiconductor substrate that includes the following steps can prevent Al diffusion to a high-resistivity single-crystal silicon substrate and can also manufacture a nitride semiconductor substrate that does not produce turbidity, thereby completing the present invention. The steps are: heat-treating a film-forming substrate made of single-crystal silicon in a nitrogen atmosphere to form a silicon nitride film; growing an AlN film on the silicon nitride film; and growing a GaN film, an AlGaN film, or both on the AlN film.

[0021] That is, the present invention is a method for manufacturing a nitride semiconductor substrate, wherein the nitride semiconductor substrate is formed by forming a nitride semiconductor on a film-forming substrate. The manufacturing method includes: step (1), wherein a film-forming substrate made of single crystal silicon is heat-treated in a nitrogen atmosphere to form a silicon nitride film on the aforementioned film-forming substrate; step (2), wherein an AlN film is grown on the aforementioned silicon nitride film; and step (3), wherein a GaN film, an AlGaN film, or both are grown on the aforementioned AlN film.

[0022] The present invention will now be described in detail, but the present invention is not limited to the following description.

[0023] [Manufacturing method of nitride semiconductor substrate] The method for manufacturing the nitride semiconductor substrate of the present invention includes the following steps (1) to (3). Hereinafter, each step will be described in detail with reference to the flow chart of the method for manufacturing the nitride semiconductor substrate of the present invention shown in Figure 1.

[0024] <Step (1)> Step (1) is to heat-treat a substrate made of single-crystal silicon in a nitrogen atmosphere, thereby forming a silicon nitride film on the substrate.

[0025] As shown in Figure 1(a), the film-forming substrate (silicon substrate) 1, made of single-crystal silicon, is initially placed in an RTA (Rapid Thermal Anneal) furnace and subjected to heat treatment at 1100-1300°C for 1-120 seconds under a nitrogen atmosphere, preferably at 1150-1250°C for 2-20 seconds, and more preferably at 1200°C for 10 seconds, to form a silicon nitride film (SiN film) 2 with a thickness of, for example, 0.2-20 nm, preferably 1-4 nm, and particularly preferably around 2 nm. The silicon nitride film 2 can be formed only on the surface side of the film-forming substrate, but it can also be formed on the entire film-forming substrate 1, which has a front and a back side.

[0026] In this invention, a key feature is the formation of a silicon nitride film under a nitrogen atmosphere. Here, a nitrogen atmosphere refers to a 100% nitrogen atmosphere or a mixture of nitrogen gas and an inert gas. Forming a silicon nitride film prevents Al from diffusing from the AlN buffer layer (described later) to the surface of the high-resistivity single-crystal silicon growth substrate, thus preventing the formation of a low-resistivity layer. However, if further formed using heat treatment under a nitrogen atmosphere, a clear epitaxial layer of the nitride semiconductor can be grown on the silicon nitride film after subsequent steps. When a silicon nitride film is formed using a CVD process and heat treatment under an ammonia atmosphere instead of a nitrogen atmosphere, polycrystalline layers may sometimes form on the silicon nitride film, or the grown epitaxial layer may become cloudy during subsequent nitride semiconductor growth.

[0027] There are no particular limitations on the substrate for film formation made of monocrystalline silicon; it can be CZ monocrystalline silicon or FZ monocrystalline silicon. There are no particular restrictions on the presence, type, or concentration of dopants. However, a high-resistivity monocrystalline silicon substrate is preferred. The resistivity is not particularly limited, but the lower limit is, for example, 1 Ωcm or more, preferably 10 Ωcm or more, and more preferably 100 Ωcm or more. The upper limit is, for example, 3000 Ωcm or less, preferably 1000 Ωcm or less, and more preferably 500 Ωcm or less.

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

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

[0030] <Step (3)> Step (3) is to grow a GaN film, an AlGaN film, or both on an AlN film.

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

[0032] By operating in the manner described above, a low-resistivity layer can be generated by preventing Al from diffusing from the AlN buffer layer to the surface of the high-resistivity single-crystal silicon growth substrate through the silicon nitride film, and a nitride semiconductor substrate can be manufactured in which even the epitaxial layer grown on the AlN buffer layer will not be cloudy.

[0033] Furthermore, the present invention can manufacture a nitride semiconductor substrate in which the Al diffusion concentration on the surface of the substrate for growth is 4e15 atoms / cm3 or less, preferably 3e15 atoms / cm3 or less, and more preferably 2e15 atoms / cm3 or less. There is no particular limitation on the lower limit of the Al diffusion concentration; for example, it can be set to 0 atoms / cm3 or more, or 1e13 atoms / cm3 or more.

[0034] As a method for determining the Al diffusion concentration on the surface of a substrate used for growth, secondary ion mass analysis (SIMS) can be used, for example. [Example]

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

[0036] (Example) A 2 nm thick SiN film was applied to the surface of a single-crystal silicon substrate with a diameter of 150 mm, a planar orientation (111), and a resistivity of 100 Ωcm (the surface was SiNized in an RTA furnace under N2 atmosphere, 1200°C, and for 10 seconds). An AlN buffer layer, a buffer layer, and a GaN-HEMT structure were then epitaxially grown on top of this substrate. Figure 4 shows the wafer cross-section observed after epitaxial growth. As observed in Figure 4, a flat single-crystal SiN layer is confirmed to be formed between the silicon substrate and the AlN film. Electron X-ray diffraction results confirm that the AlN layer is single-crystal.

[0037] Furthermore, as shown in Figure 2(a), it can be seen that the epitaxial layer is grown in a mirror-like manner. Figure 3 shows the results of investigating the Al concentration from the back side of the single-crystal silicon substrate to the SiN film using back-side SIMS. In Figure 3, the point where the nitrogen (N) concentration increases rapidly indicates the interface between the single-crystal silicon substrate and the AlN film thereon (the silicon nitride film is only 2 nm thick). It can be seen that compared to Comparative Example 3 (which does not have a SiN film) described later, the Al concentration is lower directly below the interface (around the SIMS depth of 2.3–2.7 μm on the horizontal axis of the graph).

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

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

[0040] (Comparative Example 3) AlN buffer layer, buffer layer, and GaN-HEMT structure are epitaxially grown directly on the surface of the Si substrate, without depositing a SiN film on the SiN substrate surface. As shown in Figure 3, it can be seen that the Al concentration on the silicon substrate surface of the nitride semiconductor substrate in Comparative Example 3 is higher than that of the embodiment.

[0041] As described above, it can be seen that any method for manufacturing a nitride semiconductor substrate according to the present invention, by forming a silicon nitride film between a single-crystal silicon substrate and an AlN film through heat treatment under a nitrogen atmosphere, can prevent Al diffusion into the high-resistivity single-crystal silicon substrate and can also manufacture a nitride semiconductor substrate that does not produce turbidity. On the other hand, in Comparative Examples 1 and 2, where a silicon nitride film was formed using conditions other than a nitrogen atmosphere, turbidity occurred in the epitaxial layer, and in Comparative Example 3, where a silicon nitride film was not formed, it was not possible to prevent Al diffusion into the high-resistivity single-crystal silicon substrate.

[0042] Furthermore, the present invention is not limited to the embodiments described above. The embodiments described above are examples; any embodiment that has a substantially identical structure and can perform the same function as the technical concept described in the claims of the present invention is included within the technical scope of the present invention.

[0043] 1: Substrate for film formation 2: Silicon nitride film 3: AlN membrane 4: Buffer layer 5:GaN-HEMT layer

[0044] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. A method for manufacturing a nitride semiconductor substrate, wherein the nitride semiconductor substrate is formed by forming a nitride semiconductor on a film-forming substrate, the method being characterized by comprising: step (1), wherein a film-forming substrate made of single-crystal silicon is heat-treated in a nitrogen atmosphere to form a silicon nitride film on the aforementioned film-forming substrate; step (2), wherein an AlN film is grown on the aforementioned silicon nitride film; and step (3), wherein a GaN film, an AlGaN film, or both are grown on the aforementioned AlN film; wherein in step (1), the aforementioned heat treatment is performed in an RTA furnace at 1100–1300°C for 1–120 seconds.

2. A method for manufacturing a nitride semiconductor substrate as described in claim 1, wherein, The aforementioned silicon nitride film is a single crystal.

3. A method for manufacturing a nitride semiconductor substrate as described in claim 1 or claim 2, wherein the Al diffusion concentration on the surface of the substrate for growth of the nitride semiconductor substrate is 4e15 atoms / cm3 or less.

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