Manufacturing method for nitride semiconductor epitaxial substrate, nitride semiconductor epitaxial substrate, and platform substrate for nitride semiconductor epitaxial substrate

Abstract

The present invention is a manufacturing method for a nitride semiconductor epitaxial substrate, said method being characterized by comprising: a SiC single crystal film formation step in which, while epitaxially growing a 3C-SiC single crystal film on a single crystal silicon substrate, a vacancy is additionally formed in a silicon layer on a surface layer of the single crystal silicon substrate directly below the 3C-SiC single crystal film; and a nitride formation step in which, while epitaxially growing a nitride semiconductor layer on the 3C-SiC single crystal film, dislocations are formed over the entire surface of the single crystal silicon substrate, and the nitride semiconductor layer having a ratio of yellow light emission intensity to band edge emission intensity of 0.02 or less is formed. In this way, a manufacturing method is provided for a large-diameter nitride semiconductor epitaxial substrate having reduced yellow light emission and non-light emission defects even when a nitride semiconductor layer is grown on a single crystal silicon substrate.

Description

Method for manufacturing nitride semiconductor epitaxial substrate, nitride semiconductor epitaxial substrate, and platform substrate for nitride semiconductor epitaxial substrate

[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.

[0002] GaN is a material that is widely used in high-speed switches, high-frequency devices, power devices, and light-emitting devices such as LEDs, because it is capable of extremely high-speed operation due to a two-dimensional electron gas layer caused by self-polarization.

[0003] Against this background, GaN has been researched for a very long time, and in addition to freestanding 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 not only power devices in the medium voltage range due to their high mobility, but also high-frequency devices that take advantage of this characteristic.

[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 large. 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 photoluminescence (PL) and cathodoluminescence (CL) 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 by which excited carriers relax to the ground state. These methods are 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 around 550 nm. It is also possible to evaluate the crystallinity based on the intensity of band-edge emission (the so-called TO line), a non-radiative center with a wavelength around 360 nm. The amount of these defects is compared by calculating 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 defects that can be sources of yellow emission and the higher the band edge emission intensity (the fewer non-radiative centers), which means the better the GaN layer quality.

[0008] JP 2011-25421 A JP 2017-039622 A JP 2018-174234 A JP 2016-092169 A

[0009] Sandeep Bahl, “Achieving GaN Products with Lifetime Reliability” (2021), TI Technical White Paper.

[0010] Therefore, in order to grow a high-quality GaN layer as described above on a Si substrate, a method has been proposed in which AlN is used as a buffer layer. However, as described above, the smaller the value of (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 for reducing Yellow emission and non-radiative defects.

[0011] The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing a large-diameter nitride semiconductor epitaxial substrate that has fewer yellow luminescence 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 having a large diameter and fewer yellow luminescence and non-radiative defects.A further object of the present invention is to provide a platform substrate for a nitride semiconductor epitaxial substrate, which, when a nitride semiconductor layer is epitaxially grown, allows for a large diameter nitride semiconductor epitaxial substrate having fewer yellow luminescence and non-radiative defects.

[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 immediately 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 growing a nitride semiconductor layer on a single crystal silicon substrate, a thin 3C-SiC single crystal film is inserted as an intermediate layer, and further, vacancies are provided in the surface layer of the single crystal silicon substrate directly below this 3C-SiC single crystal film. Furthermore, when epitaxially growing the nitride semiconductor layer, dislocations are formed all over the surface of 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 and 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 luminescence and non-radiative defects can be manufactured.

[0016] In this case, the single crystal silicon substrate may have a plane orientation of <111> and a diameter of 300 mm or more.

[0017] As a result, the <111> substrate has fewer directions (slip planes) in which dislocations tend to slip compared to, for example, a <100> substrate, ensuring strength against deformation of the substrate. Furthermore, by making the diameter 300 mm or more, a nitride semiconductor epitaxial substrate with a large diameter can be manufactured.

[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 thickness of the 3C-SiC single crystal film 50 nm or more, meltback during the subsequent nitride semiconductor growth can be sufficiently prevented, and by making the thickness 200 nm or less, it becomes easier to introduce dislocations into 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 arise 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] In 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 vacancies are further 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 surface of the single crystal silicon substrate to mitigate deformation of the substrate, thereby reducing the intensity ratio between band edge emission and defect-induced emission (yellow emission) to 0.02 or less, thereby improving the crystallinity of the nitride semiconductor layer.

[0024] This results in a nitride semiconductor epitaxial substrate with fewer yellow luminescence and non-luminescent 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, wherein the single crystal silicon substrate has a silicon layer having a density of 100 / cm in a surface layer directly below the 3C-SiC single crystal film. ２ The present invention provides a platform substrate for a nitride semiconductor epitaxial substrate, characterized in that a large number of vacancies are formed therein.

[0026] This type of platform substrate for nitride semiconductor epitaxial substrates has a thin 3C-SiC single crystal film formed on a single crystal silicon substrate, and voids formed in the surface layer of the single crystal silicon substrate directly below the 3C-SiC single crystal film, which allows for improved crystallinity of the nitride semiconductor layer grown thereon.

[0027] Therefore, 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.

[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 a larger 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.

[0031] 1 shows an example of a cross-sectional structure of a nitride semiconductor epitaxial substrate according to an embodiment of the present invention; 2 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; 3 shows an outline of a flow of a method for manufacturing a nitride semiconductor epitaxial substrate according to an embodiment of the present invention; 4 shows an example of XRT measurement of a GaN substrate (nitride semiconductor epitaxial substrate) manufactured in an example; and 5 shows CL spectra of GaN substrates (nitride semiconductor epitaxial substrates) of an example and a comparative example.

[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 luminescence and non-radiative defects, even when a nitride semiconductor layer is grown on a single-crystal silicon substrate.

[0034] As a result of extensive research into the above-mentioned problems, the present inventors have found that a large-diameter nitride semiconductor epitaxial substrate with fewer 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 immediately 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 mentioned above, there has also been a demand for a nitride semiconductor epitaxial substrate with a large diameter and fewer yellow emitting and non-radiative defects.

[0036] As a result of extensive research 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 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, and has fewer yellow emission and non-radiative defects and a larger diameter, thereby completing the present invention.

[0037] Furthermore, as described above, there has been a demand for a platform substrate for nitride semiconductor epitaxial substrates that can be used to 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 extensive research into the above-mentioned problems, the present inventors have discovered a platform substrate for a nitride semiconductor epitaxial substrate, which comprises a single crystal silicon substrate and a 3C-SiC single crystal film epitaxially grown on the single crystal silicon substrate, wherein the single crystal silicon substrate has 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 a large number of 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 embodiments of the present invention will be described with reference to FIGS.

[0040] First, the 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 the 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 preferably has a plane orientation of <111> and a diameter of 300 mm or more.

[0042] The <111> substrate has fewer directions (slip planes) in which dislocations tend to slip compared to, for example, a <100> substrate, and therefore can ensure strength against deformation of the nitride semiconductor epitaxial substrate 11. Furthermore, by making the diameter 300 mm or more, a large-diameter nitride semiconductor epitaxial substrate 11 can be manufactured. The upper limit of the diameter of the <111> substrate is not particularly limited, but can be, for example, 450 mm or less.

[0043] It is preferable that the thickness of the single crystal silicon substrate 1 is 775 μm or more, since this does not require special processing and eliminates concerns about various problems that may arise when substrates of different thicknesses are used in device processes using the nitride semiconductor epitaxial substrate 11. The upper limit of the substrate thickness is not particularly limited, but can be, for example, 2 mm or less.

[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. Furthermore, by making the thickness 200 nm or less, it becomes easier 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 to suit the device to be formed. For example, in a high-electron mobility transistor (HEMT) structure, the nitride semiconductor layer 3, which is the device layer, is composed of a gallium nitride layer and an electron supply layer made of AlGaN formed thereon. To improve device characteristics, it is desirable that the nitride semiconductor layer 3 be a crystal with few crystal defects and few impurities such as carbon and oxygen.

[0048] Specifically, the nitride semiconductor layer 3 has a ratio of yellow emission intensity to band edge emission intensity, specifically (yellow emission intensity) / (band edge emission intensity), of 0.02 or less. If this ratio exceeds 0.02, the number of defects and non-radiative defects that serve as sources of yellow emission increases, resulting in a low band edge emission intensity (large number of non-radiative centers) and a poor quality nitride semiconductor layer 3. The lower limit of the ratio of yellow emission intensity to band edge emission intensity is not particularly limited, but is, for example, 0.01 or more.

[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, which 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 vacancy layer 4 is not particularly limited, but is about 10 to 1000 nm. The dislocation density is also not particularly limited, but is, for example, 1 / cm ２ The above is a description of the general 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. The 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 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 This allows the crystallinity of the nitride semiconductor layer 3 to be improved when the nitride semiconductor layer 3 is grown. The upper limit of the vacancy density is not particularly limited, but may be, for example, 500 / cm ２ It can be as follows:

[0054] Furthermore, 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. This concludes the description 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 a general 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. 3(a). 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 there is no need to worry about various problems caused by using a thick substrate, which are a concern when using substrates of different thicknesses in device processes using nitride semiconductor epitaxial substrate 11.

[0059] The plane orientation of the single crystal silicon substrate 1 is preferably <111>. This is because a <111> substrate has fewer directions (slip planes) in which dislocations tend to slip compared to, for example, a <100> substrate, and is therefore more resistant to deformation of the substrate. Furthermore, if the diameter of the single crystal silicon substrate 1 is 300 mm or more, the diameter of the nitride semiconductor epitaxial substrate 11 can be increased.

[0060] Next, the single crystal silicon substrate 1 is placed in a reduced pressure (RP)-CVD apparatus, and the native oxide film on the surface is hydrogen baked (H ２ By removing the oxide film, SiC nuclei can be easily formed when the 3C-SiC single crystal film 2 is formed on the single crystal silicon substrate 1 in a later step.

[0061] H at this time ２ The annealing temperature is preferably set to 1000° C. or higher and 1200° C. or lower. By setting the temperature to 1000° C. or higher, H ２ The annealing time can be shortened. In addition, by setting the temperature at 1200° C. or less, it is possible to reliably suppress the occurrence of slippage originating from the substrate support portion of the RP-CVD device.

[0062] At this time, H ２There are no particular restrictions on the pressure and time of the 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 source gas into a reduced pressure (RP)-CVD apparatus, and the temperature is gradually increased, for example, from a temperature in the range of 300° C. to 950° C. to a temperature in the range of 1000° C. to 1200° C.

[0064] The temperature rise rate is, for example, in the range of 0.5 to 5° C. / min, 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, growth can be stopped when a predetermined film thickness is reached during the temperature increase. By growing the film while changing the temperature, the growth mode can be continuously changed, thereby gradually increasing the film formation rate.

[0066] During this process, the 3C-SiC single crystal film 2 is epitaxially grown on the single crystal silicon substrate 1, and a pore layer 4 having pores is formed in the silicon layer on the surface of the single crystal silicon substrate 1 immediately 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 voids 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, leaving vacancies where the Si has been removed.

[0068] The density of the holes is, for example, 100 / cm ２ The thickness of the porous 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 sufficiently prevent meltback of Al and Ga contained in the nitride semiconductor layer 3 during growth of the nitride semiconductor layer 3 in a subsequent 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 growing the nitride semiconductor layer 3 in a later step, making the nitride semiconductor epitaxial substrate 11 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 does not mention 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, but the present invention conversely provides a method for alleviating 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 Fig. 3(c), while dislocations are formed all over the surface of the single crystal silicon substrate 1, to form a nitride semiconductor layer 3 having a ratio of yellow emission intensity to band edge emission intensity of 0.02 or less (nitride formation step). The lower limit of the ratio of yellow emission intensity to band edge emission intensity is not particularly limited, but can be, for example, 0.01 or more.

[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, the 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 with a buffering effect that is inserted to improve the crystallinity of the device layer and control stress. If the buffer layer is manufactured as a nitride, it can be manufactured using the same equipment as that for forming the nitride semiconductor layer 3, which is desirable.

[0076] Next, a device layer (nitride semiconductor layer 3) made of a nitride semiconductor thin film is formed on the 3C-SiC single crystal film 2 and the intermediate layer by vapor phase growth such as MOVPE or sputtering. For the nitride semiconductor layer 3, for example, GaN, AlN, InN, AlGaN, InGaN, AlInN, AlScN, etc. can be used. 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-electron mobility transistor (HEMT) structure, the device layer is composed of a gallium nitride layer and an AlGaN electron supply layer formed on top of it. To improve device characteristics, the device layer is preferably made of a crystal with few crystal defects and few impurities such as carbon and oxygen. For example, it is manufactured using the MOVPE method at 900°C to 1350°C.

[0078] It should be noted that 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 are a problem 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, this does not pose a reliability problem.

[0079] A method for growing the nitride semiconductor layer 3 suitable for carrying out the present invention will be described in more detail 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 introducing the substrate into the reactor, it is cleaned with a chemical such as hydrofluoric acid. After the substrate is introduced into the reactor, the furnace is filled with a high-purity inert gas such as nitrogen to replace the atmosphere inside the furnace.

[0081] [2] Step of cleaning the substrate surface in a furnace The platform substrate 13 is heated in a reactor to clean the surface of the substrate. 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 with hydrogen or nitrogen supplied into the furnace.

[0083] [3] Step of growing a buffer layer In this step, AlN or Al is grown on the substrate by introducing gases that are the raw materials of 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, at a furnace pressure of 50 mbar (5 kPa) and a substrate temperature of 1120° C. Trimethylaluminum (TMAl) is used as the Al source, trimethylgallium (TMGa) is used as the Ga source, and ammonia (NH ３ ) can be used.

[0085] In order to obtain a mixed crystal with a desired Al composition, the flow rates of the TMAl and TMGa raw materials are set so that the Al / Ga ratio incorporated into the thin film is the set ratio, taking into consideration the material efficiency of the raw material gases. In this process, the flow rate of TMAl is set to 0.24 L / min (240 sccm) under standard conditions, and NH ３ The flow rate of TMAl, TMGa, NH can be set to 2 l / min (2000 sccm) to grow AlN. ３ The carrier gas may be hydrogen, for example. These conditions are merely examples and are not particularly limited.

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

[0087] In this process, growth can be performed, for example, at a furnace pressure of 200 mbar and a substrate temperature of 1120° C. Trimethylgallium (TMGa) is used as the Ga source, and ammonia (NH ３ ) can be used.

[0088] In addition, in order to obtain a mixed crystal with a desired Al composition, the flow rates of the source gases TMAl and TMGa are set so that the Al / Ga ratio incorporated into the thin film is the set ratio, taking into consideration the material efficiency of the source gases. ３ The carrier gas may be hydrogen, for example. These conditions are merely examples and are not particularly limited.

[0089] [5] Step of growing electron supply layer In this step, Al, Ga, and N source gases are introduced at a specified furnace pressure and substrate temperature to form an Al, Ga, and N source layer on the gallium nitride layer. ｘ Ga １－ｘ N (0<x≦1) can be grown epitaxially.

[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) is used as the Al source, trimethylgallium (TMGa) is used as the Ga source, and ammonia (NH ３ ) can be used.

[0091] In addition, in order to obtain a mixed crystal with a desired Al composition, the flow rates of the source gases TMAl and TMGa are set so that the Al / Ga ratio incorporated into the thin film is the set ratio, taking into consideration the material efficiency of the source gases. ３ The carrier gas may be hydrogen, for example. These conditions are merely examples and are not particularly limited.

[0092] This process makes it possible to generate dislocations over the entire surface of the single crystal silicon substrate 1. An example of XRT of the single crystal silicon substrate 1 with dislocations generated over the entire surface is shown in Figure 4. It can be seen that there are no cracks and that dislocations are present over the entire surface of 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 were generated throughout the single crystal silicon substrate 1 using this process is shown in the example in Figure 5. As shown in Figure 5, the substrate exhibits strong band-edge emission intensity (reference numeral 5) and low yellow emission (reference numeral 6). This is due to 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.

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

[0095] (Example) A boron-doped normal resistance single crystal silicon substrate (resistivity: 10 Ω·cm) having a diameter of 300 mm and a main surface with a (111) plane orientation was prepared as the single crystal silicon substrate 1. The single crystal silicon substrate 1 was placed on a susceptor in a reactor of an RP-CVD apparatus and heated to 1080° C. for 1 minute under H ２ Annealing was performed.

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

[0097] The growth pressure at this time was uniformly set to 100 Torr (13332.2 Pa). After reaching 1130°C, the temperature was maintained for 10 minutes, and a 3C-SiC single crystal film 2 was grown (film thickness: 100 nm). This resulted in a vacancy density of 200 / cm ２ Thus, a platform substrate 13 having a 50 nm thick porous layer 4 was obtained.

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

[0099] Furthermore, to deposit a buffer layer, the furnace pressure was maintained at 50 mbar, the substrate temperature was maintained at 1020°C, and trimethylaluminum as an Al source, trimethylgallium as a Ga source, and ammonia as a 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 inside the furnace was kept at 200 mbar and the substrate temperature at 1120° C., trimethylgallium and ammonia were introduced into the furnace, and a GaN film was formed to a thickness of 900 nm. ０．２５ Ga ０．７５ N) was grown to a thickness of 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 example manufactured by the above process using a known XRT device are shown in Figure 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 results are shown in Figure 5. In Figure 5, the peak indicated by reference numeral 5 represents the band edge emission (TO line) of GaN, the peak indicated by reference numeral 6 represents the yellow emission of GaN, and the peak indicated by reference numeral 7 represents a harmonic of the band edge emission of GaN.

[0103] 5, the nitride semiconductor epitaxial substrate 11 of the example has a high band edge luminescence intensity (small non-radiative centers) and a low yellow luminescence intensity. The ratio of the yellow luminescence intensity to the band edge luminescence 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, thereby producing 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 luminescence intensity (large non-radiative centers) and a high yellow luminescence intensity. The ratio of the yellow luminescence intensity to the band edge luminescence 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] This specification includes the following aspects. [1]: 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. [2]: A method for manufacturing a nitride semiconductor epitaxial substrate according to [1], wherein the single crystal silicon substrate has a <111> plane orientation and a diameter of 300 mm or more. [3]: A method for manufacturing a nitride semiconductor epitaxial substrate according to [1] or [2], wherein the 3C-SiC single crystal film has a thickness of 50 nm to 200 nm. [4]: A method for manufacturing a nitride semiconductor epitaxial substrate according to any one of [1] to [3] above, characterized in that the thickness of the single crystal silicon substrate is 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, wherein 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 it has ultra-high vacancies formed therein.

[0107] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. 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 forming voids 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 all over the surface of the single crystal silicon substrate, thereby forming the nitride semiconductor layer having a ratio of Yellow emission intensity to band edge emission intensity of 0.02 or less.

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