Nitride semiconductor epitaxial substrate manufacturing method, nitride semiconductor epitaxial substrate, and platform substrate for nitride semiconductor epitaxial substrate

Abstract

To provide a method for manufacturing a nitride semiconductor epitaxial substrate with less yellow-light emission or non-light emission defects and with a large diameter, when a nitride semiconductor layer is grown on a single crystal silicon substrate.SOLUTION: A method for manufacturing a nitride semiconductor epitaxial substrate 11 includes: an SiC single crystal film formation step of forming a hole on a surface silicon layer of a single crystal silicon substrate 1 immediately below a 3C-SiC single crystal film 2 while epitaxial-growing the 3C-SiC single crystal film 2 on the single crystal silicon substrate 1; and a nitride formation step of forming dislocation on an entire face of the single crystal silicon substrate 1 while epitaxial-growing a nitride semiconductor layer 3 on the 3C-SiC single crystal film 2, and forming the nitride semiconductor layer 3 with a ratio between yellow-light emission strength and band end light emission strength of 0.02 or less.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a nitride semiconductor epitaxial substrate, a nitride semiconductor epitaxial substrate, and a platform substrate for a nitride semiconductor epitaxial substrate. [Background technology]

[0002] GaN is a material that is used very widely in high-speed switches, high-frequency devices, and power devices, as well as light-emitting devices such as LEDs, because its self-polarization creates a two-dimensional electron gas layer that enables extremely high-speed operation.

[0003] Against this background, GaN has been researched for a very long time, and in addition to free-standing substrates, there are also heteroepitaxial substrates grown on substrates such as sapphire. Among these, GaN on Si substrates grown on silicon substrates (Patent Documents 1 to 4) are inexpensive and have high compatibility with Si device processes because they use the highly versatile Si as the substrate, and GaN lateral devices using these have been expanded in application to high-frequency devices that take advantage of their high mobility, in addition to power devices in the medium-voltage range.

[0004] Furthermore, GaN on Si, which uses Si as a base substrate, is expected to be used as a light-emitting element for displays in addition to the above applications, considering that it is easy to make the diameter larger. In order to take advantage of these characteristics, GaN growth on a 300 mm diameter Si substrate is very attractive and is being actively researched.

[0005] GaN is a direct transition semiconductor, and methods such as PL (photoluminescence) and CL (cathodoluminescence) are used to evaluate defects, and are highly sensitive. PL uses light with energy above the band gap to excite carriers, while CL uses an electron beam to excite carriers, and evaluates the process in which the excited carriers relax to the ground state, and is sensitive to recombination centers in the band gap, i.e., defects.

[0006] The spectrum of a GaN substrate is dominated by yellow emission with a wavelength of around 550 nm. It is also possible to evaluate the crystallinity from the intensity of band edge emission (so-called TO line) which is a non-radiative center with a wavelength of around 360 nm. The amount of these defects is compared by taking the ratio of the yellow emission intensity to the band edge emission intensity.

[0007] In other words, the smaller the value of (yellow emission intensity) / (band edge emission intensity), the fewer the defects that are the source of yellow emission and the higher the band edge emission intensity (the fewer the non-radiative centers), making it a better quality GaN layer. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP2011-25421A [Patent Document 2] JP2017-039622A [Patent Document 3] JP 2018-174234 A [Patent Document 4] JP 2016-092169 A [Non-patent literature]

[0009] [Non-Patent Document 1] Sandeep Bahl, “Achieving GaN Products with Lifetime Reliability” (2021), TI Technical White Paper. Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, in order to grow a high-quality GaN layer as described above on a Si substrate, methods such as using AlN as a buffer layer have been proposed. However, as described above, the smaller the (yellow emission intensity) / (band-edge emission intensity), the better the crystallinity. Therefore, at present, yellow emission (high yellow emission intensity indicates poor crystallinity) and non-radiative defects (low band-edge emission intensity) are observed, and there is a demand to reduce yellow emission and non-radiative defects.

[0011] The present invention has been made to solve the above problems, and has an object to provide a method for manufacturing a large-diameter nitride semiconductor epitaxial substrate which produces less yellow emission and non-radiative defects even when a nitride semiconductor layer is grown on a single crystal silicon substrate.

[0012] Another object of the present invention is to provide a nitride semiconductor epitaxial substrate that has less yellow luminescence and less non-radiative defects and has a large diameter. Another object of the present invention is to provide a platform substrate for a nitride semiconductor epitaxial substrate, which can provide a large-diameter nitride semiconductor epitaxial substrate with fewer yellow luminescence and non-radiative defects when a nitride semiconductor layer is epitaxially grown on the substrate. [Means for solving the problem]

[0013] The present invention has been made to achieve the above-mentioned object, and provides a method for manufacturing a nitride semiconductor epitaxial substrate, comprising: a SiC single crystal film formation step of epitaxially growing a 3C-SiC single crystal film on a single crystal silicon substrate, while further forming vacancies in a surface silicon layer of the single crystal silicon substrate directly below the 3C-SiC single crystal film; and a nitride formation step of epitaxially growing a nitride semiconductor layer on the 3C-SiC single crystal film, while forming dislocations over the entire surface of the single crystal silicon substrate, to form the nitride semiconductor layer having a ratio of Yellow emission intensity to band edge emission intensity of 0.02 or less.

[0014] According to this method for manufacturing a nitride semiconductor epitaxial substrate, when a nitride semiconductor layer is grown on a single crystal silicon substrate, a thin 3C-SiC single crystal film is inserted as an intermediate layer, and voids are provided in the surface layer of the single crystal silicon substrate directly below this 3C-SiC single crystal film. Furthermore, when the nitride semiconductor layer is epitaxially grown, dislocations are formed all over the single crystal silicon substrate to alleviate deformation of the substrate, thereby making the ratio of Yellow emission intensity to band edge emission intensity 0.02 or less, thereby improving the crystallinity of the nitride semiconductor layer.

[0015] Therefore, even when a nitride semiconductor layer is grown on a single crystal silicon substrate, a large-diameter nitride semiconductor epitaxial substrate with fewer yellow emission and non-radiative defects can be manufactured.

[0016] At this time, the surface orientation of the single crystal silicon substrate is <111> The diameter can also be 300mm or more.

[0017] This means: <111> The substrate is, for example, <100> Compared to the substrate, there are fewer directions (slip planes) in which dislocations can slide, ensuring strength against deformation of the substrate. In addition, by making the diameter 300 mm or more, it is possible to manufacture large-diameter nitride semiconductor epitaxial substrates.

[0018] In this case, the thickness of the 3C-SiC single crystal film can be set to 50 nm or more and 200 nm or less.

[0019] By making the 3C-SiC single crystal film 50 nm or thicker, meltback during the subsequent nitride semiconductor growth can be sufficiently prevented, while by making the film 200 nm or thicker, it becomes easier to introduce dislocations over the entire surface of the single crystal silicon substrate when epitaxially growing the nitride semiconductor layer.

[0020] In this case, the thickness of the single crystal silicon substrate can be set to 775 μm or more.

[0021] This eliminates the need for special processing, and also eliminates the need to worry about various problems that may occur when substrates of different thicknesses are used in device processes using nitride semiconductor epitaxial substrates.

[0022] The present invention has been made to achieve the above-mentioned object, and provides a nitride semiconductor epitaxial substrate comprising a single crystal silicon substrate, a 3C-SiC single crystal film epitaxially grown on the single crystal silicon substrate, and a nitride semiconductor layer epitaxially grown on the 3C-SiC single crystal film, wherein the single crystal silicon substrate has vacancies formed in a surface silicon layer immediately below the 3C-SiC single crystal film and dislocations formed over the entire surface, and the nitride semiconductor layer has a ratio of Yellow emission intensity to band edge emission intensity of 0.02 or less.

[0023] With such a nitride semiconductor epitaxial substrate, a thin 3C-SiC single crystal film is inserted as an intermediate layer between the single crystal silicon substrate and the nitride semiconductor layer, and voids are provided in the surface layer of the single crystal silicon substrate directly below this 3C-SiC single crystal film. Furthermore, dislocations are provided all over the single crystal silicon substrate to reduce deformation of the substrate, thereby making the intensity ratio of band edge emission to defect-induced emission (yellow emission) 0.02 or less, thereby improving the crystallinity of the nitride semiconductor layer.

[0024] This results in a nitride semiconductor epitaxial substrate with less yellow emission and less non-radiative defects and a large diameter.

[0025] The present invention has been made to achieve the above object, and provides a platform substrate for a nitride semiconductor epitaxial substrate, comprising a single crystal silicon substrate and a 3C-SiC single crystal film epitaxially grown on the single crystal silicon substrate, the single crystal silicon substrate having a surface silicon layer immediately below the 3C-SiC single crystal film with a density of 100 / cm 2 The present invention provides a platform substrate for a nitride semiconductor epitaxial substrate, which is characterized in that a large number of vacancies are formed therein.

[0026] According to such a platform substrate for nitride semiconductor epitaxial substrates, a thin 3C-SiC single crystal film is provided on a single crystal silicon substrate, and voids are further provided in the surface layer of the single crystal silicon substrate directly below this 3C-SiC single crystal film. This makes it possible to improve the crystallinity of the nitride semiconductor layer when the nitride semiconductor layer is grown.

[0027] Therefore, when a nitride semiconductor layer is epitaxially grown, a large-diameter nitride semiconductor epitaxial substrate with fewer yellow emission and non-radiative defects can be obtained. Effect of the Invention

[0028] As described above, according to the method for manufacturing a nitride semiconductor epitaxial substrate of the present invention, it is possible to manufacture a large-diameter nitride semiconductor epitaxial substrate with fewer yellow luminescence and non-radiative defects, even when a nitride semiconductor layer is grown on a single crystal silicon substrate.

[0029] Furthermore, the nitride semiconductor epitaxial substrate of the present invention has fewer yellow luminescence and non-radiative defects and has a large diameter.

[0030] Furthermore, according to the platform substrate for nitride semiconductor epitaxial substrates of the present invention, when a nitride semiconductor layer is epitaxially grown, a large-diameter nitride semiconductor epitaxial substrate with fewer yellow luminescence and non-radiative defects can be obtained. [Brief description of the drawings]

[0031] [Figure 1] 1 shows an example of a cross-sectional structure of a nitride semiconductor epitaxial substrate according to an embodiment of the present invention. [Diagram 2] 1 shows an example of a cross-sectional structure of a platform substrate for a nitride semiconductor epitaxial substrate according to an embodiment of the present invention. [Diagram 3]1 shows an outline of a flow of a method for manufacturing a nitride semiconductor epitaxial substrate according to an embodiment of the present invention. [Figure 4] An example of XRT measurement of a GaN substrate (nitride semiconductor epitaxial substrate) produced in the example is shown. [Diagram 5] 1 shows CL spectra of GaN substrates (nitride semiconductor epitaxial substrates) of an example and a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The present invention will be described in detail below, but the present invention is not limited thereto.

[0033] As described above, there has been a demand for a method for producing a large-diameter nitride semiconductor epitaxial substrate with fewer yellow emission and non-radiative defects even when a nitride semiconductor layer is grown on a single crystal silicon substrate.

[0034] As a result of intensive investigations into the above-mentioned problems, the inventors have found that a large-diameter nitride semiconductor epitaxial substrate with less yellow emission and non-radiative defects can be manufactured even when a nitride semiconductor layer is grown on a single crystal silicon substrate by a method for manufacturing a nitride semiconductor epitaxial substrate comprising: a SiC single crystal film formation step of epitaxially growing a 3C-SiC single crystal film on a single crystal silicon substrate while further forming vacancies in a surface silicon layer of the single crystal silicon substrate directly below the 3C-SiC single crystal film; and a nitride formation step of epitaxially growing a nitride semiconductor layer on the 3C-SiC single crystal film while forming dislocations over the entire surface of the single crystal silicon substrate to form the nitride semiconductor layer having a ratio of Yellow emission intensity to band edge emission intensity of 0.02 or less, thereby completing the present invention.

[0035] As described above, there has also been a demand for a nitride semiconductor epitaxial substrate with a large diameter and with fewer yellow emission and non-radiative defects.

[0036] As a result of intensive investigations into the above-mentioned problems, the inventors have found that a nitride semiconductor epitaxial substrate comprising a single crystal silicon substrate, a 3C-SiC single crystal film epitaxially grown on the single crystal silicon substrate, and a nitride semiconductor layer epitaxially grown on the 3C-SiC single crystal film, wherein the single crystal silicon substrate has vacancies formed in a surface silicon layer directly below the 3C-SiC single crystal film and dislocations formed over the entire surface, and the nitride semiconductor layer has a ratio of Yellow emission intensity to band edge emission intensity of 0.02 or less, thereby achieving fewer Yellow emission and non-radiative defects and a large diameter, and have completed the present invention.

[0037] Furthermore, as described above, there has been a demand for a platform substrate for nitride semiconductor epitaxial substrates that can produce large-diameter nitride semiconductor epitaxial substrates with fewer yellow luminescence and non-radiative defects when a nitride semiconductor layer is epitaxially grown.

[0038] As a result of intensive research into the above-mentioned problems, the present inventors have discovered a platform substrate for a nitride semiconductor epitaxial substrate, comprising a single crystal silicon substrate and a 3C-SiC single crystal film epitaxially grown on the single crystal silicon substrate, the single crystal silicon substrate having a surface silicon layer immediately below the 3C-SiC single crystal film with a density of 100 / cm 2 The present inventors have found that a large-diameter nitride semiconductor epitaxial substrate with fewer yellow luminescence and non-luminescent defects can be obtained when a nitride semiconductor layer is epitaxially grown by using a platform substrate for nitride semiconductor epitaxial substrates, characterized by having ultra-large vacancies formed therein, and have completed the present invention.

[0039] Hereinafter, a method for manufacturing a nitride semiconductor epitaxial substrate, a nitride semiconductor epitaxial substrate, and a platform substrate for a nitride semiconductor epitaxial substrate according to an embodiment of the present invention will be described with reference to the drawings, with reference to FIGS.

[0040] First, a schematic configuration of a nitride semiconductor epitaxial substrate according to an embodiment of the present invention will be described with reference to Fig. 1. The nitride semiconductor epitaxial substrate 11 shown in Fig. 1 includes a single crystal silicon substrate 1, a 3C-SiC single crystal film 2, and a nitride semiconductor layer 3.

[0041] The single crystal silicon substrate 1 supports other members constituting the nitride semiconductor epitaxial substrate 11 and serves as a base for growing the nitride semiconductor layer 3. The single crystal silicon substrate 1 has a plane orientation of <111> It is also preferable that the diameter is 300 mm or more.

[0042] <111> The substrate is, for example, <100> Compared to the substrate, there are fewer directions (slip planes) in which dislocations tend to slip, so it is possible to ensure strength against deformation of the nitride semiconductor epitaxial substrate 11. Furthermore, by making the diameter 300 mm or more, a nitride semiconductor epitaxial substrate 11 with a large diameter can be manufactured.

[0043] It is preferable that the thickness of the single crystal silicon substrate 1 be 775 μm or more, since this does not require special processing and also eliminates the need to worry about various problems that may occur when substrates of different thicknesses are used in device processes using the nitride semiconductor epitaxial substrate 11.

[0044] The 3C-SiC single crystal film 2 is an intermediate layer epitaxially grown on the single crystal silicon substrate 1, and serves as a base layer on which the nitride semiconductor layer 3 grows.

[0045] The thickness of the 3C-SiC single crystal film 2 can be, for example, 50 nm or more and 200 nm or less. By making the thickness of the 3C-SiC single crystal film 2 50 nm or more, meltback during nitride semiconductor growth can be sufficiently prevented. Also, by making the thickness 200 nm or less, it becomes easy to introduce dislocations into the entire surface of the single crystal silicon substrate 1 when epitaxially growing the nitride semiconductor layer 3.

[0046] The nitride semiconductor layer 3 is a device layer in which elements are formed in the nitride semiconductor epitaxial substrate 11, and is a layer epitaxially grown on the 3C-SiC single crystal film. Specific examples of the nitride semiconductor layer 3 that can be used include GaN, AlN, InN, AlGaN, InGaN, AlInN, and AlScN.

[0047] The thickness of the nitride semiconductor layer 3 is, for example, 0.1 to 10 μm, and can be designed according to the device to be formed. For example, in a high mobility transistor (HEMT) structure, the nitride semiconductor layer 3, which is a device layer, is composed of a gallium nitride layer and an electron supply layer made of AlGaN formed thereon. To improve device characteristics, the nitride semiconductor layer 3 is desirably made of crystals with few crystal defects and few impurities such as carbon and oxygen.

[0048] Specifically, the ratio of the yellow emission intensity to the band edge emission intensity, specifically (yellow emission intensity) / (band edge emission intensity), is 0.02 or less in the nitride semiconductor layer 3. If this ratio exceeds 0.02, the number of defects and non-radiative defects that become the source of yellow emission increases, resulting in a low-quality nitride semiconductor layer 3 with low band edge emission intensity (large number of non-radiative centers).

[0049] Here, the single crystal silicon substrate 1 has a vacancy layer 4 in which vacancies are formed in the surface silicon layer immediately below the 3C-SiC single crystal film 2, and dislocations are formed all over the surface. This makes it possible to improve the crystallinity of the nitride semiconductor layer 3 when the nitride semiconductor layer 3 is grown.

[0050] The vacancy density of the vacancy layer 4 in the nitride semiconductor epitaxial substrate 11 is not particularly limited, but may be, for example, 100 / cm 2 The thickness of the hole layer 4 is not particularly limited, but is about 10 to 1000 nm. The dislocation density is not particularly limited, but is, for example, 1 / cm 2 It's super. The above is a description of the schematic configuration of the nitride semiconductor epitaxial substrate 11.

[0051] Next, the configuration of a platform substrate for nitride semiconductor epitaxial substrates according to an embodiment of the present invention will be described with reference to Fig. 2. A platform substrate 13 shown in Fig. 2 comprises a single crystal silicon substrate 1 and a 3C-SiC single crystal film 2.

[0052] The single crystal silicon substrate 1 and the 3C-SiC single crystal film 2 of the platform substrate 13 perform the same functions as the single crystal silicon substrate 1 and the 3C-SiC single crystal film 2 of the nitride semiconductor epitaxial substrate 11, and also have the same configuration.

[0053] However, the single crystal silicon substrate 1 of the platform substrate 13 has a surface silicon layer immediately below the 3C-SiC single crystal film 2 with a density of 100 / cm 2 As a result, when the nitride semiconductor layer 3 is grown, the crystallinity of the nitride semiconductor layer 3 can be improved.

[0054] Moreover, no dislocations are formed over the entire surface of the single crystal silicon substrate 1 of the platform substrate 13. This is because dislocations in the single crystal silicon substrate 1 of the nitride semiconductor epitaxial substrate 11 are introduced when the nitride semiconductor layer 3 is formed, whereas the platform substrate 13 is in a state prior to the formation of the nitride semiconductor layer 3. The above is an explanation of the schematic configuration of the platform substrate 13.

[0055] Next, a method for manufacturing the nitride semiconductor epitaxial substrate 11 and the platform substrate 13 will be described with reference to FIG.

[0056] FIG. 3 shows an outline of the flow of this embodiment, illustrating an example of a method for manufacturing the nitride semiconductor epitaxial substrate 11 shown in FIG. 1 and the platform substrate 13 shown in FIG.

[0057] First, a single crystal silicon substrate 1 is prepared as shown in FIG. If the single crystal silicon substrate 1 has a thickness of 775 μm or more, no special processing is required, and there is no need to worry about various problems that may occur when substrates of different thicknesses are used in device processing.

[0058] In particular, when a silicon substrate having a thickness of 775 μm is used, no special processing is required, and also in the device process using the nitride semiconductor epitaxial substrate 11, there is no need to worry about various problems caused by the use of a thick substrate, which are a concern when using substrates of different thicknesses.

[0059] The surface orientation of the single crystal silicon substrate 1 is <111> It is preferable to set the above. <111> The substrate is, for example, <100> This is because, compared to the substrate, there are fewer directions (slip planes) in which dislocations tend to slip, and the substrate has strength against deformation. Furthermore, if the diameter of the single crystal silicon substrate 1 is 300 mm or more, the nitride semiconductor epitaxial substrate 11 can have a large diameter.

[0060] Next, the single crystal silicon substrate 1 is placed in a reduced pressure (RP)-CVD device, and the native oxide film on the surface is removed by hydrogen baking (H2 annealing) as necessary. By removing the oxide film, it becomes easier for SiC nuclei to form when forming the 3C-SiC single crystal film 2 on the single crystal silicon substrate 1 in a later process.

[0061] The H2 annealing temperature at this time is preferably set to 1000°C or higher and 1200°C or lower. By setting the temperature at 1000°C or higher, the H2 annealing time required to prevent the natural oxide film from remaining can be shortened. Also, by setting the temperature at 1200°C or lower, the occurrence of slip starting from the substrate support part of the RP-CVD device can be reliably suppressed.

[0062] There are no particular restrictions on the pressure and time of the H2 annealing as long as the native oxide film can be removed.

[0063] Next, as shown in FIG. 3(b), in order to form SiC nuclei on the surface of the single crystal silicon substrate 1 and subsequently form a 3C-SiC single crystal film 2, a carbonizing gas such as propane gas is introduced as a raw material gas into a reduced pressure (RP)-CVD apparatus while gradually increasing the temperature, for example, from a range of 300° C. to 950° C. to a range of 1000° C. to less than 1200° C.

[0064] The rate of temperature rise is, for example, in the range of 0.5 to 5° C. / min, and preferably about 1° C. / min. At this time, after the temperature is raised to a predetermined temperature, the growth may be stopped at that point, or the growth may be continued until a predetermined film thickness is reached.

[0065] Alternatively, when a predetermined film thickness is reached during the temperature rise, the growth may be stopped at that point. By growing the film while changing the temperature, the film growth rate can be gradually increased by continuously changing the growth mode.

[0066] During this process, the 3C-SiC single crystal film 2 is epitaxially grown on the single crystal silicon substrate 1, while a void layer 4 having voids is formed in the silicon layer on the surface of the single crystal silicon substrate 1 directly below the 3C-SiC single crystal film 2 (SiC single crystal film formation process). Upon completion of this process, the platform substrate 13 is manufactured.

[0067] The vacancies are formed in situ in a reduced pressure (RP)-CVD apparatus during the growth of the 3C-SiC single crystal film 2. Specifically, the single crystal silicon substrate 1 is used as a supply source of Si, one of the elements that make up the 3C-SiC single crystal film 2, and the Si in the single crystal silicon substrate 1 is diffused into the 3C-SiC single crystal film 2, causing the vacancies to form in the spaces left by the missing Si.

[0068] The density of the voids is, for example, 100 / cm 2 The thickness of the hole layer 4 is about 10 to 1000 nm.

[0069] The thickness of the 3C-SiC single crystal film 2 formed at this time is, for example, 50 nm to 200 nm, more specifically, approximately 100 nm. A thickness of 50 nm or more can adequately prevent meltback of Al and Ga contained in the nitride semiconductor layer 3 during growth of the nitride semiconductor layer 3 in a later process. Prevention of meltback by the 3C-SiC single crystal film 2 is considered to be very important in improving the characteristics of the nitride semiconductor epitaxial substrate 11.

[0070] Furthermore, if the thickness is 200 nm or less, dislocations can be easily introduced into the entire surface of the single crystal silicon substrate 1 when the nitride semiconductor layer 3 is grown in a later step, and the nitride semiconductor epitaxial substrate 11 becomes less likely to crack.

[0071] Regarding the growth of the 3C-SiC single crystal film 2, the structure for growing SiC on a silicon substrate has already been disclosed in Patent Documents 1 to 4. In particular, Patent Document 4 discloses in paragraphs

[0030] and

[0031] that the thickness of the SiC is 2 nm or more and 3.5 μm or less, but makes no mention of the dislocation density.

[0072] Furthermore, the original idea behind using a thick single crystal silicon substrate is to use the single crystal silicon substrate to absorb stress and prevent deformation. However, the present invention conversely provides a method for mitigating deformation of the substrate by uniformly introducing dislocations into the single crystal silicon substrate 1, which is a completely new concept and method not seen in the past.

[0073] Next, using a reactor or the like of an MOVPE apparatus, a nitride semiconductor layer 3 is epitaxially grown on the 3C-SiC single crystal film 2 as shown in Figure 3(c), while forming dislocations over the entire surface of the single crystal silicon substrate 1, thereby forming a nitride semiconductor layer 3 with a ratio of Yellow emission intensity to band edge emission intensity of 0.02 or less (nitride formation process).

[0074] For example, the nitride semiconductor layer 3 is formed by vapor phase growth on the 3C-SiC single crystal film 2. The following method for forming the nitride semiconductor layer 3 is merely an example, and the present invention is not limited to this method.

[0075] In general, a nitride semiconductor layer 3 is formed by first forming a buffer layer on the 3C-SiC single crystal film 2. The buffer layer acts as a layer based on a buffer effect that is inserted to improve the crystallinity of the device layer and control stress. It is desirable to manufacture the buffer layer as a nitride, since it can be manufactured in the same facility as the nitride semiconductor layer 3.

[0076] Next, a device layer (nitride semiconductor layer 3) made of a thin film of a nitride semiconductor is formed on the 3C-SiC single crystal film 2 and the intermediate layer by vapor phase growth such as MOVPE or sputtering. The nitride semiconductor layer 3 can be made of, for example, GaN, AlN, InN, AlGaN, InGaN, AlInN, AlScN, or the like. The nitride thin film is 0.1 to 10 μm thick and can be designed to suit the device.

[0077] The device layer can have a multi-layer structure. For example, in a high mobility transistor (HEMT) structure, the device layer is composed of a gallium nitride layer and an electron supply layer made of AlGaN formed on top of it. To improve device characteristics, the device layer is preferably made of crystals with few crystal defects and few impurities such as carbon and oxygen, and is manufactured, for example, at 900℃ to 1350℃ using the MOVPE method.

[0078] Incidentally, nitride semiconductor devices are lateral devices because they form and utilize a two-dimensional electron gas layer. Therefore, as described in Non-Patent Document 1, defects that impair reliability become an issue only in the nitride semiconductor layer 3. Therefore, it can be seen that even if a large number of dislocations exist in the single crystal silicon substrate 1 directly below the 3C-SiC single crystal film 2 underlying the nitride semiconductor layer 3, it does not become an issue of reliability.

[0079] A method for growing the nitride semiconductor layer 3 suitable for carrying out the present invention will be described more specifically below.

[0080] [1] Introduction into the reactor The single crystal silicon substrate 1 on which the 3C-SiC single crystal film 2 has been grown, i.e., the platform substrate 13, is introduced into the reactor of the MOVPE apparatus. Before the substrate is introduced into the reactor, it is cleaned with chemicals such as hydrofluoric acid. After the substrate is introduced into the reactor, the inside of the reactor is filled with a high-purity inert gas such as nitrogen to replace the atmosphere inside the reactor.

[0081] [2] The process of cleaning the substrate surface in a furnace The surface of the platform substrate 13 is cleaned by heating it in a reaction furnace. The temperature at which cleaning is performed can be determined as the temperature of the substrate surface between 1000° C. and 1200° C., but a particularly clean surface can be obtained by performing cleaning at 1050° C.

[0082] Cleaning is performed after the pressure inside the furnace is reduced, and the pressure inside the furnace can be set between 200 mbar (20 kPa) and 30 mbar (3 kPa). For example, cleaning can be performed at a pressure of 50 mbar (5 kPa). Cleaning is performed for about 10 minutes while hydrogen or nitrogen is supplied into the furnace.

[0083] [3] Step of growing the buffer layer In this process, AlN or Al is deposited on the substrate by introducing gases that are the raw materials Al, Ga, and N at a specified furnace pressure and substrate temperature. x Ga 1-x N (0≦x<1) can be grown epitaxially.

[0084] In this process, growth can be performed, for example, with a furnace pressure of 50 mbar (5 kPa) and a substrate temperature of 1120° C. Trimethylaluminum (TMAl) can be used as the Al source, trimethylgallium (TMGa) can be used as the Ga source, and ammonia (NH3) can be used as the N source.

[0085] Also, in order to obtain a mixed crystal with a desired Al composition, considering the material efficiency of the source gas, the flow rates of TMAl and TMGa as raw materials are set so that the Al / Ga ratio incorporated into the thin film becomes the set ratio. In this step, the growth of AlN can be carried out with the flow rate of TMAl being 0.24 L / min (240 sccm) under standard conditions and the flow rate of NH3 being 2 l / min (2000 sccm). As the carrier gas for TMAl, TMGa, and NH3, for example, hydrogen can be used. These conditions are just examples and are not particularly limited.

[0086] [4] Step of growing a gallium nitride layer In this step, at a specified furnace pressure and substrate temperature, by introducing the raw materials Ga and the gas serving as the N source, GaN or Al x Ga 1-x N(0 < x ≦ 1) can be epitaxially grown.

[0087] In this step, for example, the growth can be carried out at a furnace pressure of 200 mbar and a substrate temperature of 1120°C. As the Ga source, trimethylgallium (TMGa) and as the N source, ammonia (NH3) can be used.

[0088] Also, in order to obtain a mixed crystal with a desired Al composition, considering the material efficiency of the source gas, the flow rates of TMAl and TMGa as raw materials are set so that the Al / Ga ratio incorporated into the thin film becomes the set ratio. As the carrier gas for TMA, TMGa, and NH3, for example, hydrogen can be used. These conditions are just examples and are not particularly limited.

[0089] [6] Step of growing an electron supply layer In this step, at a specified furnace pressure and substrate temperature, by introducing the raw materials Al, Ga, and the gas serving as the N source, Al x Ga 1-x N(0 < x ≦ 1) can be epitaxially grown on the gallium nitride layer.

[0090] In this process, growth can be performed, for example, at a furnace pressure of 150 mbar and a substrate temperature of 1120° C. Trimethylaluminum (TMAl) can be used as the Al source, trimethylgallium (TMGa) can be used as the Ga source, and ammonia (NH3) can be used as the N source.

[0091] In addition, in order to obtain a mixed crystal with a desired Al composition, the flow rates of the raw materials TMAl and TMGa are set so that the Al / Ga ratio incorporated in the thin film is the set ratio, taking into consideration the material efficiency of the raw material gas. Hydrogen, for example, can be used as a carrier gas for TMAl, TMGa, and NH3. These conditions are merely examples and are not particularly limited.

[0092] With this process, it is possible to generate dislocations all over the surface of the single crystal silicon substrate 1, and an example of XRT of a single crystal silicon substrate 1 with dislocations all over is shown in Figure 4. There are no cracks, and it can be seen that dislocations exist all over the single crystal silicon substrate 1.

[0093] An example of CL measurement at room temperature of a GaN substrate (nitride semiconductor epitaxial substrate 11) in which dislocations are generated all over the single crystal silicon substrate 1 by such a process is shown in the embodiment of FIG. 5. As shown in FIG. 5, it can be seen that the substrate has a strong band edge emission intensity (reference symbol 5) and a small yellow emission (reference symbol 6). This is the effect of the platform substrate for nitride semiconductor epitaxial substrates having a 3C-SiC single crystal film 2 on its surface according to the present invention. EXAMPLES

[0094] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

[0095] (Example) A boron-doped normal resistance single crystal silicon substrate (resistivity: 10 Ω·cm) with a diameter of 300 mm and a (111) surface orientation on its main surface was prepared as single crystal silicon substrate 1. Single crystal silicon substrate 1 was placed on a susceptor in the reactor of an RP-CVD apparatus and subjected to H annealing at 1080 °C for 1 minute.

[0096] Next, the temperature inside the furnace was lowered to 300°C, and then the temperature was increased to 1130°C at a rate of 1°C / sec while introducing trimethylsilane gas to carry out the SiC nucleation process, followed by the formation of the 3C-SiC single crystal film 2 and the formation of the void layer 4.

[0097] The growth pressure at this time was uniformly 100 Torr (13332.2 Pa). After reaching 1130°C, the temperature was held for 10 minutes to grow the 3C-SiC single crystal film 2 (film thickness: 100 nm). As a result, the vacancy density became 200 / cm 2 Thus, a platform substrate 13 having a 50 nm thick air hole layer 4 was obtained.

[0098] Next, the platform substrate 13 was introduced into the reactor of the MOCVD apparatus, and the gas in the reactor was replaced with nitrogen to remove oxygen and moisture from the atmosphere. After that, the pressure in the reactor was reduced to 50 mbar, and the temperature was raised to 1050° C. and the substrate was kept in a hydrogen atmosphere for 10 minutes to clean the surface layer.

[0099] Furthermore, to deposit a buffer layer, the pressure inside the furnace was kept at 50 mbar and the substrate temperature at 1020°C, and trimethylaluminum as the Al source, trimethylgallium as the Ga source, and ammonia as the nitrogen source were introduced into the furnace to deposit AlN to a thickness of 180 nm and AlGaN to a thickness of 580 nm.

[0100] To grow the gallium nitride layer, the pressure in the furnace was kept at 200 mbar and the substrate temperature at 1120°C, trimethylgallium and ammonia were introduced into the furnace, and GaN was grown to 900 nm. 0.25 Ga 0.75 N) was grown to 25 nm at a furnace pressure of 200 mbar and a substrate temperature of 1120°C.

[0101] The results of measurement of the nitride semiconductor epitaxial substrate 11 of the embodiment manufactured by the above steps using a known XRT device are shown in FIG. 4. It was found that there were no cracks and that dislocations were present all over the surface of the single crystal silicon substrate 1. The dislocation density of these dislocations was 3 / cm.2 It was super.

[0102] The CL spectrum of the nitride semiconductor epitaxial substrate 11 of the example was measured using a known CL device and the result is shown in Fig. 5. In Fig. 5, the peak indicated by reference number 5 indicates the band edge emission (TO line) of GaN, the peak indicated by reference number 6 indicates the yellow emission of GaN, and the peak indicated by reference number 7 indicates a harmonic of the band edge emission of GaN.

[0103] 5, the nitride semiconductor epitaxial substrate 11 of the example has a large band edge emission intensity (small non-radiative centers) and a small yellow emission intensity. The ratio of the yellow emission intensity to the band edge emission intensity was calculated from this spectrum, and was found to be small at 0.019, indicating that the quality of the nitride semiconductor layer 3 is good.

[0104] (Comparative Example) In the example, the thickness of the single crystal silicon substrate 1 was set to 1.5 mm, and GaN was grown without growing the 3C-SiC single crystal film 2, to produce a nitride semiconductor epitaxial substrate. The CL measurement results of the nitride semiconductor epitaxial substrate at this time are shown in FIG.

[0105] 5, the comparative example had a low band edge emission intensity (large non-radiative centers) and a high yellow emission intensity. The ratio of the yellow emission intensity to the band edge emission intensity was as high as 0.145, and the dislocation density of the single crystal silicon substrate 1 at this time was 0 / cm 2 It was also found that the quality of the nitride semiconductor layer 3 was worse than that of the example.

[0106] The present specification includes the following aspects. [1]: a SiC single crystal film formation process in which a 3C-SiC single crystal film is epitaxially grown on a single crystal silicon substrate, and voids are formed in a silicon layer on the surface of the single crystal silicon substrate directly below the 3C-SiC single crystal film; a nitride formation step of epitaxially growing a nitride semiconductor layer on the 3C-SiC single crystal film while forming dislocations on the entire surface of the single crystal silicon substrate to form the nitride semiconductor layer having a ratio of Yellow emission intensity to band edge emission intensity of 0.02 or less; 2. A method for producing a nitride semiconductor epitaxial substrate comprising the steps of: [2]: The surface orientation of the single crystal silicon substrate is <111> The method for producing a nitride semiconductor epitaxial substrate according to [1] above, characterized in that the diameter of the substrate is 300 mm or more. [3]: The method for producing a nitride semiconductor epitaxial substrate according to [1] or [2] above, characterized in that the thickness of the 3C-SiC single crystal film is 50 nm or more and 200 nm or less. [4]: The method for producing a nitride semiconductor epitaxial substrate according to any one of [1] to [3] above, wherein the single crystal silicon substrate has a thickness of 775 μm or more. [5]: A nitride semiconductor epitaxial substrate comprising a single crystal silicon substrate, a 3C-SiC single crystal film epitaxially grown on the single crystal silicon substrate, and a nitride semiconductor layer epitaxially grown on the 3C-SiC single crystal film, wherein the single crystal silicon substrate has vacancies formed in a surface silicon layer directly below the 3C-SiC single crystal film and dislocations formed over the entire surface, and the nitride semiconductor layer has a ratio of Yellow emission intensity to band edge emission intensity of 0.02 or less. [6]: A platform substrate for a nitride semiconductor epitaxial substrate comprising a single crystal silicon substrate and a 3C-SiC single crystal film epitaxially grown on the single crystal silicon substrate, the single crystal silicon substrate having a surface silicon layer directly below the 3C-SiC single crystal film with a density of 100 / cm 2 A platform substrate for a nitride semiconductor epitaxial substrate, characterized in that ultra-high vacancies are formed therein.

[0107] 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]

[0108] 1...single crystal silicon substrate, 2...3C-SiC single crystal film, 3...nitride semiconductor layer, 4...vacancy layer, 5...GaN band edge emission, 6...GaN yellow emission, 7...harmonics of GaN band edge emission, 11...nitride semiconductor epitaxial substrate, 13...platform substrate.

Claims

1. a SiC single crystal film formation step of epitaxially growing a 3C-SiC single crystal film on a single crystal silicon substrate and forming voids in a silicon layer on the surface of the single crystal silicon substrate directly below the 3C-SiC single crystal film; a nitride formation step of epitaxially growing a nitride semiconductor layer on the 3C-SiC single crystal film while forming dislocations on the entire surface of the single crystal silicon substrate to form the nitride semiconductor layer having a ratio of yellow emission intensity to band edge emission intensity of 0.02 or less; 2. A method for producing a nitride semiconductor epitaxial substrate comprising the steps of:

2. 2. The method for producing a nitride semiconductor epitaxial substrate according to claim 1, wherein the single crystal silicon substrate has a surface orientation of <111> and a diameter of 300 mm or more.

3. 2. The method for producing a nitride semiconductor epitaxial substrate according to claim 1, wherein the thickness of the 3C-SiC single crystal film is set to be 50 nm or more and 200 nm or less.

4. 2. The method for producing a nitride semiconductor epitaxial substrate according to claim 1, wherein the single crystal silicon substrate has a thickness of 775 μm or more.

5. A nitride semiconductor epitaxial substrate comprising: a single crystal silicon substrate; a 3C-SiC single crystal film epitaxially grown on the single crystal silicon substrate; and a nitride semiconductor layer epitaxially grown on the 3C-SiC single crystal film, the single crystal silicon substrate has vacancies formed in a surface silicon layer directly below the 3C-SiC single crystal film and dislocations formed over the entire surface; A nitride semiconductor epitaxial substrate, wherein the nitride semiconductor layer has a ratio of yellow emission intensity to band edge emission intensity of 0.02 or less.

6. A platform substrate for a nitride semiconductor epitaxial substrate, comprising a single crystal silicon substrate and a 3C-SiC single crystal film epitaxially grown on the single crystal silicon substrate, The single crystal silicon substrate has a surface silicon layer directly below the 3C-SiC single crystal film with a density of 100 / cm ２ A platform substrate for a nitride semiconductor epitaxial substrate, characterized in that ultra-high vacancies are formed therein.

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