Group iii nitride laminate and method for manufacturing group iii nitride laminate

Abstract

To improve crystal quality in a group III nitride laminate.SOLUTION: A group III nitride laminate includes a SiC substrate and a laminate structure provided on the substrate and formed by epitaxially growing a group III nitride crystal. The laminate structure has 1.30 or less of a relative yellow intensity being the ratio of yellow light-emitting intensity to photoluminescence band end light-emitting intensity in the surface center of the laminate structure; and when setting the maximum to Xmax, the minimum to Xmin and the average thereof to Xavg in the relative yellow intensity in three or more places arbitrarily selected along the central line and including the center and two or more places separated from the center in an inner area except a width of 5 mm from the outer edge of the surface of the laminate structure, the variation (Xmax-Xmin) / Xavg of the relative yellow intensity is 20% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a group III nitride laminate and a method for manufacturing the group III nitride laminate.

Background Art

[0002] Group III nitride-based high electron mobility transistors (HEMTs) are widely used as power amplifiers for base stations of mobile phones (for example, Patent Document 1). In group III nitride-based HEMTs, the power that can be input per element can be significantly increased compared to conventionally used Si-based devices. As a result, the base station can be miniaturized, and the installation cost can be significantly reduced.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Semiconductor devices such as HEMTs are manufactured from group III nitride laminates. From the viewpoint of improving the device characteristics of semiconductor devices, it is required to improve the quality of group III nitride crystals.

[0005] An object of the present invention is to provide a technique for improving crystal quality in a group III nitride laminate.

Means for Solving the Problems

[0006] According to one aspect of the present invention, a SiC substrate, a laminated structure provided on the substrate and formed by epitaxially growing a group III nitride crystal, and The laminated structure is at the center of the surface of the laminated structure, the relative yellow intensity, which is the ratio of the yellow emission intensity to the band-edge emission intensity of photoluminescence, is 1.30 or less, and in the internal region excluding a width of 5 mm from the outer edge of the surface of the laminated structure, for the relative yellow intensity at three or more locations arbitrarily selected along the center line and including two or more locations spaced apart from the center, the maximum value is X max , the minimum value is X min , and the average is X avg When this is done, the coefficient of variation of the relative yellow intensity (X max -X min ) / X avg is 20% or less, A group-III nitride laminate is provided.

[0007] According to another aspect of the present invention, (a) A step of preparing a SiC substrate; (b) A step of supplying a halogen-containing gas to the SiC substrate to desorb Si from the main surface of the SiC substrate and forming a Si-deficient region in the surface layer of the main surface; (c) A step of supplying a hydrogen-containing gas to the SiC substrate in which the Si-deficient region is formed to remove the Si-deficient region and performing surface treatment on the main surface; (d) A step of growing a group-III nitride crystal on the main surface after the treatment; A method for manufacturing a group-III nitride laminate having the above is provided.

Advantages of the Invention

[0008] According to the present invention, the crystal quality of the group-III nitride laminate can be improved.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4A

Figure 4B

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0010] <One Embodiment> Next, one embodiment of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to these examples, and is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0011] (1) Group-III Nitride Laminate The group-III nitride laminate according to this embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view showing the group-III nitride laminate according to this embodiment.

[0012] Hereinafter, in a crystal such as a group-III nitride semiconductor having a wurtzite structure, the <0001> axis is referred to as the "c-axis", and the (0001) plane is referred to as the "c-plane".

[0013] As shown in FIG. 1, the group-III nitride laminate 1 (hereinafter also referred to as "laminate 1") includes, for example, an SiC substrate 10 and a laminate structure 20 formed by epitaxially growing a group-III nitride crystal. The laminate structure 20 is formed by crystal growth of a group-III nitride crystal represented by the composition formula of In x Al y GaN (0≦x≦1, 0≦y≦1, x + y≦1). In the present embodiment, a case where the laminate structure 20 includes a nucleation layer 30, a channel layer 40, a barrier layer 50 and a cap layer 60 as functional layers will be described as an example.

[0014] (SiC substrate) The SiC substrate 10 is a base substrate for epitaxially growing the laminate structure 20. As will be described later, the SiC substrate 10 is configured such that its main surface 11 is surface-treated so that the laminate structure 20 can be formed with high crystal quality and little yellow emission. At least a part of the main surface 11 is surface-treated, and preferably the whole of it is surface-treated. As the SiC constituting the SiC substrate 10, for example, semi-insulating SiC of polytype 4H or polytype 6H is used. Here, "semi-insulating" means, for example, a state where the specific resistance is 10 5 Ωcm or more. The surface of the SiC substrate 10 that serves as the base for growing the laminate structure 20 is, for example, the (0001) plane (the silicon plane of the c-plane).

[0015] The SiC substrate 10 preferably has a large area, for example, to improve the productivity in manufacturing semiconductor elements. Specifically, the diameter of the SiC substrate 10 is, for example, 2 inches (50 mm) or more, preferably 4 inches (100 mm) or more, and more preferably 6 inches (150 mm) or more.

[0016] The thickness of the SiC substrate 10 is not particularly limited, but depends on the diameter of the SiC substrate 10. Specifically, the thickness of the SiC substrate 10 with a diameter of 2 inches is, for example, 300 μm or more and 500 μm or less (typically 430 μm), the thickness of the SiC substrate 10 with a diameter of 4 inches is, for example, 400 μm or more and 1000 μm or less (typically 500 μm), and the thickness of the SiC substrate 10 with a diameter of 6 inches is, for example, 400 μm or more and 1500 μm or less (typically 500 μm).

[0017] (Nucleation layer) The nucleation layer 30 is provided on the SiC substrate 10. The nucleation layer 30 functions as a nucleation layer that generates crystal nuclei for growing the channel layer 40 described later. The nucleation layer 30 is formed by epitaxially growing a group III nitride crystal on the main surface 11 of the SiC substrate 10 that has been surface-treated. For example, the nucleation layer 30 is composed of AlN. The thickness of the nucleation layer 30 is not particularly limited, but is preferably, for example, 1 nm or more and 100 nm or less.

[0018] (Channel layer) The channel layer 40 is provided on the nucleation layer 30. The channel layer 40 functions as a channel layer through which electrons travel during the operation of a semiconductor device such as a HEMT. The channel layer 40 is formed, for example, by epitaxially growing a group III nitride crystal on the main surface of the nucleation layer 30. The channel layer 40 is In x Al y Ga (1-x-y)It is composed of a group-III nitride represented by the compositional formula of N(0≦x≦1, 0≦y≦1, x + y≦1), and is composed of, for example, GaN. The low-index crystal plane closest to the main surface of the channel layer 40 is, for example, the c-plane ((0001) plane, Ga plane). The thickness of the channel layer 40 is not particularly limited, but is preferably, for example, 3 nm or more and less than 1 μm. The thickness of the channel layer 40 can be appropriately changed according to the characteristics required for the semiconductor device. For example, it should be thick when reducing the leakage current, and thin when improving the RF response speed. Note that the channel layer 40 may be provided directly on the nucleation layer 30, but for example, a known buffer layer may be provided on the nucleation layer 30, and it may be provided on the nucleation layer 30 via the buffer layer.

[0019] (Barrier layer) The barrier layer 50 is provided on the channel layer 40. The barrier layer 50 functions as a barrier layer that generates a two-dimensional electron gas (2DEG) in the channel layer 40 and spatially confines the 2DEG in the channel layer 40. The barrier layer 50 is formed, for example, by heteroepitaxially growing a group-III nitride crystal on the main surface of the channel layer 40. For example, the barrier layer 50 is composed of a group-III nitride having a smaller electron affinity than the group-III nitride crystal constituting the channel layer 40, such as AlGaN containing aluminum (Al) and gallium (Ga). The thickness of the barrier layer 50 is preferably, for example, 1 nm or more and 80 nm or less.

[0020] (Cap layer) The cap layer 60 is provided on the barrier layer 50. The cap layer 60 is interposed between the barrier layer 50 and the electrode provided thereon in order to improve the device characteristics (such as controllability of the threshold voltage) of a semiconductor device such as a HEMT. The cap layer 60 is formed as needed and may be omitted.

[0021] (Relative yellow intensity) In the group-III nitride crystal that constitutes the stacked structure 20, the crystal quality may vary significantly due to the generation of defects or the incorporation of impurities caused by the surface state of the underlying SiC substrate 10. In the present embodiment, since the stacked structure 20 is formed on the surface-treated SiC substrate 10, the generation of defects and the incorporation of impurities are suppressed, and it has high crystal quality. Generally, the higher the crystal quality of the group-III nitride crystal, the easier it is for band-edge emission having a wavelength corresponding to the bandgap to emit light. On the other hand, when the crystal quality deteriorates due to defects or impurities, light having a wavelength longer than the band-edge emission and having a yellow color (yellow emission) is more likely to emit. That is, the intensity of the yellow emission increases according to the crystal quality. In this regard, the stacked structure 20 is configured such that the intensity of the yellow emission is low, specifically, the relative yellow intensity is 1.30 or less at the center of its surface.

[0022] Here, the relative yellow intensity will be described.

[0023] The relative yellow intensity can be calculated from the PL emission spectrum obtained by performing photoluminescence (PL) mapping measurement on the stacked structure 20. In the PL mapping measurement, laser light is irradiated from a light source to the measurement positions defined on the surface of the stacked structure 20. The irradiation diameter of the irradiated laser light corresponds to the size of the measurement region. By the irradiation of the laser light, PL light is emitted from the measurement positions. This PL light is detected by a detector. Thereby, a PL emission spectrum corresponding to the measurement positions as shown in FIG. 5 can be obtained. FIG. 5 is a schematic diagram of the photoluminescence emission spectrum obtained from the group-III nitride crystal. Note that the irradiation diameter of the laser light may be, for example, 1 mm. With such an irradiation diameter, the average crystal quality in the measurement region can be evaluated.

[0024] As shown in FIG. 5, the PL emission spectrum shows the correlation between the wavelength and the intensity, where the horizontal axis is the wavelength [nm] and the vertical axis is the intensity represented in arbitrary units. The PL emission spectrum has a peak P of the band-edge emission NBE and a peak P of the yellow emission. YL The peak P of the yellow emissionYL This becomes a peak corresponding to a deep level caused by the low crystallinity of the stacked structure 20.

[0025] Peak P of band-edge emission NBE The peak wavelength λ at NBE can vary depending on the composition of the group-III nitride crystal. For example, in the case of GaN, the peak wavelength λ NBE is 365 nm, and the corresponding energy is 3.4 eV. Peak P of yellow emission YL The peak wavelength λ at YL can vary depending on the composition, growth conditions, etc. of the group-III nitride crystal, but it can be said that the wavelength is in the range of 500 nm or more and 650 nm or less. For example, in the case of GaN, the peak wavelength λ YL is 564 nm, and the corresponding energy is 2.2 eV.

[0026] Peak P of band-edge emission NBE and peak P of yellow emission YL each have a predetermined emission intensity. Yellow emission changes according to the quality of the group-III nitride crystal constituting the stacked structure 20, and the higher the quality, the lower the emission intensity of yellow emission tends to be. That is, the higher the quality, the lower the relative yellow intensity, which is the ratio of the yellow emission intensity to the band-edge emission intensity.

[0027] Thus, the stacked structure 20 has a high crystal quality and is configured such that the relative yellow intensity of photoluminescence is 1.30 or less at the center of the sample. The relative yellow intensity is preferably 1.25 or less, and more preferably 1.20 or less. Note that the center of the surface of the stacked structure 20 refers to the center of the surface of the uppermost layer of the stacked structure 20. In this embodiment, since the uppermost layer of the stacked structure 20 is the cap layer 60, the relative yellow intensity at the center of the surface of the cap layer 60 is 1.30 or less.

[0028] In addition, the laminated structure 20 is configured such that the crystal quality is high and uniform in the layer. That is, in the laminated structure 20, the occurrence of locations where the crystal quality is locally prominent and low is suppressed. Specifically, in the internal region of the laminated structure 20 excluding a width of 5 mm from the outer edge of its surface, for the relative yellow intensity at three or more locations selected along the center line of the surface and including any two or more locations spaced apart from the center, when the maximum value is X max , the minimum value is X min , and the average is X avg , the coefficient of variation of the relative yellow intensity (X max - X min ) / X avg is preferably 20% or less. This coefficient of variation is more preferably 15% or less, and even more preferably 10% or less. Note that on the surface of the laminated structure 20, growth in the outer edge region is unstable and the crystal quality tends to be low. Therefore, as shown in the examples described later, the relative yellow intensity is preferably measured in the internal region excluding the outer edge region. The width of the outer edge region is not particularly limited, but may be, for example, 5 mm.

[0029] The coefficient of variation of the relative yellow intensity can be obtained, for example, as shown in FIG. 6. FIG. 6 is a schematic diagram for explaining the case of calculating the coefficient of variation of the relative yellow intensity and is a top view of the laminated structure 20. In FIG. 6, on the surface 21 of the laminated structure 20, three locations, i.e., the center 21A, a location 21B, and a location 21C spaced apart from the center 21A by a predetermined distance, are selected along the center line (the dashed line in the figure). Generally, the relative yellow intensity tends to be lower at the center of the laminated structure 20 and higher toward the outer edge. Therefore, in this embodiment, three or more locations including the center are selected. Then, the relative yellow intensity at each location is obtained, and X max , X min and X avg are calculated from these values, and the coefficient of variation of the relative yellow intensity can be calculated. Note that when calculating the coefficient of variation, at least three locations including the center may be selected, or four or more locations may be selected.

[0030] Thus, according to the laminate structure 20 configured such that the rate of change in relative yellow intensity is 20% or less, the variation in relative yellow intensity within the plane of its surface 21 is small, and the crystal quality is uniformly high throughout the layer.

[0031] (2) Method for manufacturing a group-III nitride laminate and method for manufacturing a semiconductor device Next, with reference to FIG. 2, a method for manufacturing a group-III nitride laminate and a method for manufacturing a semiconductor device according to the present embodiment will be described. FIG. 2 is a flowchart showing the method for manufacturing a group-III nitride laminate and the method for manufacturing a semiconductor device according to the present embodiment.

[0032] The method for manufacturing a semiconductor device according to the present embodiment includes, for example, an SiC substrate preparation step S10, a loading step S20, a cleaning and degreasing step S30, a hydrogen annealing step S40, a conversion layer formation step S50, a conversion layer removal step S60, a nucleation layer formation step S70, a channel layer formation step S80, a barrier layer formation step S90, a cap layer formation step S100, and an unloading step S110.

[0033] (S10: SiC substrate preparation step) First, an SiC substrate 10 is prepared. As the SiC substrate 10, a substrate having SiC exposed on its surface and substantially no components other than SiC laminated on the surface can be used. As the SiC substrate 10, for example, a polytype 4H or 6H semi-insulating SiC substrate can be used.

[0034] (S20: Cleaning and degreasing step) Subsequently, the SiC substrate 10 may be subjected to, for example, known cleaning and degreasing treatments. For cleaning and degreasing, acids, alkaline aqueous solutions, organic solvents, surfactants, pure water, etc. can be used.

[0035] (S30: Loading step) Subsequently, the SiC substrate 10 that has undergone cleaning and degreasing treatment is carried into the processing chamber of a known film deposition apparatus. In this embodiment, surface treatment including the hydrogen annealing step S40 to the altered layer removal step S60 described later is continuously performed using a film deposition apparatus that performs crystal growth such as the nucleation layer formation step S70 to the cap layer formation step S100.

[0036] The film deposition apparatus includes a processing chamber, a gas supply mechanism, a susceptor, and a heater. The susceptor is disposed within the processing chamber, is capable of placing the SiC substrate 10 thereon, and is configured to heat the SiC substrate 10 with the heater. The gas supply mechanism is configured to supply a predetermined processing gas into the processing chamber. As the film deposition apparatus, either a hot wall type or a cold wall type may be used. From the viewpoint of sufficiently increasing the processing temperature of the surface treatment described later and performing the surface treatment more reliably, a cold wall type processing apparatus is preferred.

[0037] As the film deposition apparatus, for example, a MOVPE (Metalorganic Vapor Phase Epitaxy) apparatus that grows by the metalorganic vapor phase epitaxy method, an HVPE (Hydride Vapor Phase Epitaxy) apparatus that grows by the hydride vapor phase epitaxy method, etc. can be used. Hereinafter, the case of using a MOVPE apparatus will be described as an example.

[0038] (S40: Hydrogen Annealing Step) Subsequently, the SiC substrate 10 placed on the susceptor in the processing chamber is annealed in a reducing atmosphere. The SiC substrate 10 is heated, for example, in a hydrogen gas (H2 gas) atmosphere, and hydrogen annealing treatment is performed. According to the hydrogen annealing treatment, the oxide film (natural oxide film, etc.) formed on the surface of the SiC substrate 10 can be removed, and the surface treatment in the altered layer formation step S50 and the altered layer removal step S60 described later can be performed more reliably. In the hydrogen annealing treatment, the treatment temperature is, for example, 950°C or higher and 1300°C or lower, and the treatment time is, for example, 10 seconds or longer and 600 seconds or shorter.

[0039] (S50: Altered Layer Formation Step) Next, a Si-deficient region is formed as a modified layer on the main surface 11 of the SiC substrate 10 before growing the group-III nitride crystal. Specifically, the SiC substrate 10 placed on the susceptor is heated to a predetermined temperature by a heater, and a halogen-containing gas is supplied as a processing gas by a gas supply mechanism. By this supply, silicon (Si) can be desorbed from the main surface 11, and a Si-deficient region can be formed on the main surface 11. It is presumed that the Si-deficient region is formed by the reaction of SiC constituting the main surface 11 with the halogen-containing gas to generate a silicon halide gas and the desorption of Si. The carbon (C) remaining in the Si-deficient region may be graphitized.

[0040] The Si-deficient region is a region corresponding to the surface layer portion of the main surface 11 in the SiC substrate 10. Its thickness may be at least one atomic layer and is not particularly limited.

[0041] In the modified layer formation step S50, it is preferable to perform the treatment under conditions such that the Si-deficient region is formed over the entire area of the main surface 11 of the SiC substrate 10. For example, as shown in FIG. 3A, when the Si-deficient region 12 is formed on a part of the main surface 11 of the SiC substrate 10, as shown in FIG. 3B, only a part of the main surface 11 will be surface-modified in the modified layer removal step S60 described later. When crystal growth is performed on the main surface 11 where only a part is modified, the quality of the crystal formed on the unmodified portion may be lowered. On the other hand, for example, as shown in FIG. 4A, when the Si-deficient region 12 is formed over the entire area of the main surface 11, as shown in FIG. 4B, it becomes possible to modify the entire main surface 11 in the modified layer removal step S60. As a result, the crystal quality can be uniformly improved in the layers of the laminated structure 20.

[0042] As the processing conditions for the deteriorated layer formation step S50, there are, for example, the processing temperature (heating temperature of the SiC substrate 10) and the processing time. From the viewpoint of forming the Si-deficient region over the entire main surface 11 and suppressing the variation in the in-plane distribution of surface defects, the processing temperature is preferably 850°C or higher and 1150°C or lower, and more preferably 900°C or higher and 1050°C or lower. As the processing time, for example, it is preferably 120 seconds or longer and 720 seconds or shorter. Further, from the viewpoint of forming the Si-deficient region over the entire main surface 11, it is preferable to control the processing temperature to be uniform over the entire surface of the SiC substrate 10.

[0043] Also, in the deteriorated layer formation step S50, the halogen-containing gas may be supplied, for example, mixed with an inert gas such as nitrogen gas (N 2 ) in order to adjust the reactivity. In the processing container, the supplied halogen-containing gas is mixed with a carrier gas or the like and diluted to a predetermined concentration. The concentration of the halogen-containing gas indicates the molar ratio of the halogen-containing gas in the atmosphere in the reaction vessel. Although this concentration is not particularly limited, from the viewpoint of desorbing Si from the entire main surface 11 of the SiC substrate 10 while not desorbing it excessively in the thickness direction, it is preferably 0.1% or higher and less than 2%, and more preferably 0.1% or higher and 1.5% or lower.

[0044] As the halogen-containing gas, it is preferable to use at least one gas selected from the group consisting of F2 gas, Cl2 gas, Br2 gas, I2 gas, NF3 gas, ClF3 gas, HF gas, HCl gas, HBr gas, and HI gas. According to these gases, Si can be desorbed from SiC and the Si-deficient region can be formed more reliably. Note that, for example, nitrogen gas (N2 gas) may be used as the atmosphere gas for the Si desorption treatment.

[0045] (S60: Deteriorated layer removal step) Subsequently, within the processing vessel of the same MOVPE apparatus, a Si-deficient region as a deteriorated layer is removed from the main surface 11 of the SiC substrate 10. Here, since the inside of the processing vessel is in a halogen-containing gas atmosphere due to the deteriorated layer formation step S50, for example, after replacing the inside of the processing vessel with N2 gas, while heating the SiC substrate 10, a hydrogen-containing gas is supplied as a processing gas into the processing vessel by a gas supply mechanism. By this supply, the Si-deficient region formed on the surface of the main surface 11 is removed. It is presumed that the removal of the Si-deficient region is performed by the C component contained in the Si-deficient region reacting with the hydrogen-containing gas to generate a hydrocarbon gas and the C desorbing. Since the Si-deficient region can be a factor causing surface defects, by removing the Si-deficient region, the crystal quality of the laminated structure 20 can be uniformly improved. Note that the replacement of the gas inside the processing vessel may be performed, for example, by stopping the supply of the halogen-containing gas, temporarily increasing the pressure while raising the temperature inside the processing vessel, and then lowering the pressure again.

[0046] In the deteriorated layer removal step S60, it is preferable to perform the treatment under conditions such that the Si-deficient region is removed from the entire area of the main surface 11. Thereby, the Si-deficient region can be removed over the entire area of the main surface 11, and a decrease in crystal quality due to the Si-deficient region can be suppressed. As a result, the relative yellow intensity and its variation rate of the laminated structure 20 can be suppressed to be low.

[0047] Examples of the processing conditions for the deteriorated layer removal step S60 include the processing temperature (heating temperature of the SiC substrate 10) and the processing time. From the viewpoint of removing the Si-deficient region from the entire area of the main surface 11, the processing temperature is preferably 1050°C or higher and 1250°C or lower, and more preferably 1100°C or higher and 1200°C or lower. The processing time is preferably, for example, 150 seconds or more and 600 seconds or less. Further, from the viewpoint of removing the Si-deficient region over the entire area of the main surface 11, it is preferable to control the processing temperature to be uniform over the entire surface of the SiC substrate 10.

[0048] Also, from the perspective of more surely removing the Si-deficient region, as the processing temperature for removing the Si-deficient region, it is preferable to set the processing temperature of the Si-deficient region removal process higher than the processing temperature of the Si desorption process described above. Thereby, the desorption of C can be promoted, and the Si-deficient region can be more surely removed. By setting the processing temperature relatively low in the altered layer formation step S50, excessive desorption of Si on the surface of the SiC substrate 10 is suppressed, while by setting the processing temperature relatively high in the altered layer removal step S60, the Si-deficient region formed in the altered layer formation step S50 can be more surely removed.

[0049] From the perspective of suitably removing the Si-deficient region, as the hydrogen-containing gas, it is preferable to use at least any one gas selected from the group consisting of H2 gas, NH3 gas, N2H2 gas, N2H4 gas, and N3H8 gas. Note that, as the atmosphere gas for the Si-deficient region removal process, for example, N2 gas or H2 gas may be used.

[0050] (S70: Nucleation layer formation step) Next, a group III nitride crystal is grown epitaxially on the main surface 11 of the SiC substrate 10 in the processing container continuously with the altered layer removal step S60. Here, for example, a single crystal of AlN is heteroepitaxially grown to form a nucleation layer 30. Since the main surface 11 of the SiC substrate 10 is surface-modified by surface treatment, a nucleation layer 30 with high crystal quality can be formed.

[0051] When the nucleation layer 30 is formed of, for example, AlN, as the group III (Al) source gas, for example, trimethylaluminum (TMA) gas is used. As the N source gas, for example, NH3 gas is used. These source gases may be mixed with a carrier gas using hydrogen (H2) gas, nitrogen (N2) gas, or a mixed gas thereof and supplied.

[0052] As crystal growth conditions for forming the nucleation layer 30, there are, for example, growth temperature, V / III ratio, and growth pressure. These may be set to conventionally known numerical values. Here, the "V / III ratio" refers to the ratio of the supply amount (partial pressure) of group V (N) source gas to the supply amount (partial pressure) of group III (Al) source gas.

[0053] (S80: Channel layer formation step) Next, a group III nitride crystal is grown epitaxially on the upper surface of the nucleation layer 30 in the processing vessel of the same MOVPE apparatus. Here, for example, a single crystal of GaN is heteroepitaxially grown to form the channel layer 40.

[0054] When the channel layer 40 is formed of, for example, GaN, as the group III (Ga) source gas, for example, trimethylgallium (Ga(CH3)3, TMG) gas is used. As the N source gas, for example, NH3 gas is used. These source gases may be mixed with a carrier gas using hydrogen (H2) gas, nitrogen (N2) gas, or a mixed gas thereof and supplied.

[0055] As crystal growth conditions for forming the channel layer 40, there are, for example, growth temperature, V / III ratio, and growth pressure. These may be set to conventionally known numerical values.

[0056] (S90: Barrier layer formation step) Next, in the processing vessel of the same MOVPE apparatus, a single crystal of a group III nitride having a smaller electron affinity than GaN constituting the channel layer 40 is heteroepitaxially grown on the upper surface of the channel layer 40 to form the barrier layer 50.

[0057] When the barrier layer 50 is formed of a single crystal of, for example, AlN, AlGaN, InAlN, or AlInGaN, as the Al source gas, for example, trimethylaluminum (Al(CH3)3, TMA) gas is used. As the In source gas, for example, trimethylindium (In(CH3)3, TMI) gas is used. For other gases, the same gases as in the channel layer formation step S80 are used.

[0058] (S100: Cap layer formation step) Next, in the processing container of the same MOVPE apparatus, for example, GaN is heteroepitaxially grown as a single crystal of group III nitride on the upper surface of the barrier layer 50 to form a cap layer 60.

[0059] (S110: Unloading step) Subsequently, the laminate 1 is unloaded from the processing container. Thus, the laminate 1 of the present embodiment is obtained.

[0060] (3) Effects obtained by this embodiment According to this embodiment, one or more of the following effects can be obtained.

[0061] (a) In the SiC substrate 10, even if cleaning, degreasing, and hydrogen annealing treatment are performed before crystal growth, when the laminated structure 20 is formed, the crystal quality may not be stably and highly improved. According to the study by the present inventors, this problem is less likely to occur in GaN substrates and the like, and is found to be specific to the SiC substrate 10. In this regard, in this embodiment, before growing a group III nitride crystal on the main surface 11 of the SiC substrate 10, the formation and removal of an Si-deficient region as a modified layer are performed on the SiC substrate 10 in advance. In the modified layer formation step S50, Si is desorbed from the main surface 11 of the SiC substrate 10 by supplying a halogen-containing gas to form an Si-deficient region on the main surface 11. Further, in the modified layer removal step S60, the Si-deficient region is removed by supplying a hydrogen-containing gas. Thereby, the main surface 11 can be modified at the atomic layer level. By performing crystal growth on this surface-modified main surface 11, the crystal quality of the laminated structure 20 can be improved, and the occurrence of portions where the crystal quality locally decreases can be suppressed.

[0062] (b) The stacked structure 20 of the laminate 1 is formed by growing a group III nitride crystal on the main surface 11 subjected to the surface treatment shown in (a) above. As a result, at the center of its surface, the relative yellow intensity becomes 1.30 or less. Further, when three or more locations including the center of the surface are selected, the variation rate of their relative yellow intensities becomes 20% or less. According to such a laminate 1, since it has a high crystal quality in which yellow light emission is suppressed, high device characteristics can be realized when a semiconductor device is manufactured. Further, since the crystal quality is uniformly high in the layer and the occurrence of locations where the crystal quality is locally low is suppressed, the yield of the semiconductor device can be improved.

[0063] (c) It is preferable to perform the altered layer removal step S60 under conditions such that the Si-deficient region as the altered layer is removed from the entire area of the main surface 11. Thereby, the Si-deficient region that can reduce the crystal quality is removed, and the relative yellow intensity and its variation rate can be further reduced. Specifically, the relative yellow intensity at the center of the surface of the stacked structure 20 can be made 1.25 or less, and the variation rate can be made 15% or less.

[0064] (d) From the viewpoint of more surely realizing the effect of (c) above, it is preferable that the processing temperature in the altered layer removal step S60 is 1050 °C or higher and 1250 °C or lower. Further, it is preferable that the processing time is 150 seconds or longer and 600 seconds or shorter.

[0065] (e) Further, together with the processing of (c) above, it is preferable to perform the altered layer formation step S50 under conditions such that the Si-deficient region is formed over the entire area of the main surface 11 of the SiC substrate 10. Thereby, it becomes possible to modify the entire area of the main surface 11. Therefore, the crystal quality can be made higher on the surface of the stacked structure 20, and the occurrence of locations where the crystal quality is locally low can be more surely reduced. Specifically, the relative yellow intensity at the center of the surface of the stacked structure 20 can be made 1.20 or less, and the variation rate can be made 10% or less.

[0066] (f) From the viewpoint of more surely realizing the effect according to (e) above, it is preferable that the processing temperature in the altered layer formation step S50 be 850°C or higher and 1150°C or lower. Further, it is preferable that the processing time be 150 seconds or longer and 600 seconds or shorter.

[0067] (g) It is preferable that the processing temperature in the altered layer removal step S60 be higher than that in the altered layer formation step S50. Thereby, while suppressing excessive formation of the Si-deficient region as the altered layer, the activity of C desorption in the altered layer removal step S60 can be enhanced, and the Si-deficient region can be more surely removed.

[0068] (h) It is preferable that the surface treatment including the altered layer formation step S50 and the altered layer removal step S60 and the crystal growth of the laminated structure 20 be continuously performed in the same film forming apparatus. Thereby, the productivity when manufacturing the laminate 1 can be improved. Further, contamination due to exposure of the SiC substrate 10 to the atmosphere can be avoided, and the crystal quality can be further improved. As a result, the device characteristics and reliability of the semiconductor device manufactured using the laminate 1 can be improved.

[0069] <Other Embodiments> As described above, the embodiments of the present invention have been specifically described. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist thereof.

[0070] In the above-described embodiment, the case where the laminate 1 includes the laminated structure 20 composed of the nucleation layer 30, the channel layer 40, the barrier layer 50, and the cap layer 60 has been described. However, the present invention is not limited to this. For example, the laminated structure 20 may be formed by laminating the nucleation layer 30 and the channel layer 40. Further, for example, the laminated structure 20 may be formed by laminating the nucleation layer 30, the channel layer 40, and the barrier layer 50. Further, for example, the laminated structure 20 may be configured such that an AlN layer is interposed between the channel layer 40 and the barrier layer 50. Further, for example, the laminated structure 20 may be configured such that an InGaN layer or AlGaN is interposed in the channel layer 40. In any case, since the crystal quality of the laminated structure 20 is improved, the relative yellow intensity and its variation rate satisfy the above predetermined values in the layer constituting the uppermost surface thereof.

[0071] In the above-described embodiment, the case where the growth of the nucleation layer 30 and the channel layer 40 is performed by the MOVPE method has been described. However, the growth of one or both of them may be performed by, for example, the hydride vapor phase epitaxy (HVPE) method.

[0072] In the above-described embodiment, the case of HEMT as a semiconductor device has been described. However, the present invention is not limited to this. It is also possible to fabricate a vertical power semiconductor from the above-described laminate 1.

[0073] Further, the Si desorption treatment and the Si defect region removal treatment may be performed alternately a plurality of times. Although the desired effect can be obtained even when these treatments are performed only once, by repeating these treatments, the main surface 11 of the SiC substrate 10 can be more reliably surface-treated, and the crystal quality can be more reliably improved.

Examples

[0074] Next, examples according to the present disclosure will be described. These examples are an example of the present disclosure, and the present disclosure is not limited by these examples.

[0075] In this example, a group-III nitride laminate was fabricated and the defect density on its surface was evaluated. This will be specifically described below.

[0076] (1) Fabrication of group-III nitride laminate In this example, as shown below, group-III nitride crystals were grown on a prepared SiC substrate to fabricate a laminate.

[0077] In this example, first, an SiC substrate was prepared. Subsequently, the SiC substrate was cleaned and degreased. The degreased SiC substrate was introduced into the processing chamber of a MOVPE apparatus. Subsequently, in a hydrogen annealing process, the SiC substrate was heated with the inside of the processing chamber in an H2 gas atmosphere. Subsequently, in an alteration layer formation process, with the inside of the processing chamber in an N2 gas atmosphere, the SiC substrate was heated at a predetermined processing temperature while Cl2 gas was supplied as a chlorine-containing gas. At this time, the supply amount of Cl2 gas was adjusted so that the concentration of Cl2 gas in the atmosphere inside the processing chamber became 1.1%. As a result, Si was desorbed from the main surface of the SiC substrate, and an Si-deficient region was formed as an alteration layer on its surface. After the alteration layer formation process, the inside of the processing chamber was replaced with an inert gas. Subsequently, in an alteration layer removal process, with the inside of the processing chamber in an N2 gas atmosphere, the SiC substrate was heated at a predetermined processing temperature while NH3 gas was supplied as a hydrogen-containing gas. As a result, C was desorbed from the main surface of the SiC substrate, and the Si-deficient region was removed. Subsequently, in the same processing chamber, a laminated structure composed of a nucleation layer, a channel layer, a barrier layer, and a cap layer was crystal-grown on the main surface of the SiC substrate under the following growth conditions to fabricate a laminate. In this example, the processing temperature and processing time of the alteration layer formation process and the alteration layer removal process were appropriately changed as shown in Table 1 below, and laminates of Samples 1 to 3 were fabricated. Also, the laminate of Sample 4 was fabricated by the same operations as Samples 1 to 3 except that the alteration layer formation process and the alteration layer removal process were not performed.

[0078]

Table 1

[0079] The SiC substrate, the processing conditions of the hydrogen annealing treatment, and the growth conditions of each layer of the laminated structure are as follows.

[0080] (SiC substrate) Material: SiC (semi-insulating) Diameter: 6 inches Thickness: 500 μm The low-index crystal plane closest to the bottom surface: c-plane (no pattern processing of the bottom surface) Polytype: 6H

[0081] (Processing conditions in the hydrogen annealing process) Processing temperature: 950 °C to 1300 °C Processing time: 10 seconds to 600 seconds Gas atmosphere: H2 gas

[0082] (Growth conditions of the nucleation layer) Material: AlN Growth method: MOVPE method Growth temperature: 1200 °C to 1290 °C Designed film thickness: 10 nm to 13 nm V / III ratio: 5000 to 25000 Growth pressure: 0.059 atm to 0.098 atm

[0083] (Growth conditions of the channel layer) Material: GaN Growth method: MOVPE method Growth temperature: 1100 °C to 1200 °C V / III ratio: 1000 to 3000 Growth pressure: 0.098 atm to 0.197 atm Designed film thickness: 400 nm

[0084] (Growth conditions of the barrier layer) Material: AlGaN Growth method: MOVPE method Growth temperature: 1100 °C to 1200 °C Growth pressure: 0.098 atm to 0.197 atm Designed film thickness: 20 nm

[0085] (Cap layer) Material: GaN Growth method: MOVPE method Designed film thickness: 2 nm

[0086] (2) Evaluation For the fabricated Samples 1 to 4, the relative yellow intensity and its variation rate on the surface of the laminated structure were evaluated. Here, the relative yellow intensity and its variation rate were measured using a photoluminescence (PL) measurement device ("Photoluminor-D" manufactured by Horiba, Ltd.). Specifically, first, on the surface of the laminate, along its center line, three locations were selected as measurement positions: the center (Location A), a location 60 mm away from Location A toward the outer edge side (Location B), and a location 60 mm away from Location A toward the side opposite to Location B (Location C). Next, using the PL measurement device, laser light was irradiated at each measurement position to obtain the PL emission spectrum. The PL emission spectra of each sample are shown in FIGS. 7 and 8. In FIGS. 7 and 8, the emission spectra measured at the three locations of Sample 1 and Sample 4 are shown respectively. In each figure, the PL emission spectrum at Location A where (0,0) is the center, Location B where (0,60) is the position, and Location C where (0, -60) is the position is shown. Then, from the emission spectrum, for each sample, the relative yellow intensity and the variation rate of the relative yellow intensity at the measurement position were calculated.

[0087] In the PL measurement, a He-Cd laser was used, with a laser wavelength of 325 nm, a laser output of 25 - 30 mW, and a laser beam irradiation diameter of 1 mm.

[0088] (3) Evaluation results The results of the above-mentioned evaluation are summarized in Table 1.

[0089] As shown in Table 1, in Samples 1 to 3, by previously forming a modified layer (formation of an Si-deficient region by Si desorption) and removing the modified layer (removing the Si-deficient region by C desorption) before crystal growth, it was confirmed that both the relative yellow intensity at the surface center (location A) of the laminated structure and the fluctuation rate calculated from the relative yellow intensities at multiple locations (locations A to C) could be lowered. On the other hand, in Sample 4, although cleaning, degreasing, and hydrogen annealing treatments were performed, crystal growth was carried out without forming and removing the modified layer, and thus it was confirmed that the relative yellow intensity and its fluctuation rate became higher compared to Samples 1 to 3. That is, in Samples 1 to 3, it was confirmed that the crystal quality of the laminated structure could be increased and the occurrence of locations where the crystal quality locally decreased could be suppressed.

[0090] Also, in Sample 2, it was confirmed that the relative yellow intensity and its fluctuation rate could be further reduced compared to Sample 3. This is presumably because by setting the processing temperature in the modified layer removal step to 1120°C, which is higher than 1050°C of Sample 3, the removal of the modified layer could be promoted more. That is, in Sample 2, it is presumably because the modified layer formed on the main surface of the SiC substrate could be removed more reliably and its remaining could be suppressed compared to Sample 3. As a result, it was confirmed that the crystal quality of the laminated structure could be formed higher and more uniformly.

[0091] Furthermore, in Sample 1, it was confirmed that the relative yellow intensity and its fluctuation rate could be further reduced compared to Sample 2. This is presumably because by setting the processing temperature in the modified layer formation step to 970°C, which is higher than 890°C of Sample 2, a modified layer was formed over the entire main surface of the SiC substrate and all of the formed modified layer could be removed. That is, in Sample 1, it is presumably because the main surface of the SiC substrate could be surface-treated more reliably over the entire area compared to Sample 2. As a result, it was confirmed that the crystal quality of the laminated structure could be formed higher and more uniformly.

[0092] As described above, by modifying the main surface of the SiC substrate through surface treatment, it was confirmed that when a laminated structure was crystal-grown on the main surface, the crystal quality of the laminated structure could be improved, and the occurrence of locations where the crystal quality locally decreased could be suppressed.

[0093] <Preferred Embodiment of the Present Invention> Hereinafter, preferred embodiments of the present invention will be appended.

[0094] (Appendix 1) An SiC substrate, A laminated structure provided on the substrate and formed by epitaxially growing a group III nitride crystal, comprising the laminated structure The relative yellow intensity, which is the ratio of the yellow luminescence intensity to the band-edge luminescence intensity of photoluminescence at the surface center of the laminated structure, is 1.30 or less. In the internal region of the surface of the laminated structure excluding a width of 5 mm from the outer edge, for the relative yellow intensity at three or more locations arbitrarily selected along the center line and including two or more locations spaced apart from the center, with the maximum value being X max , the minimum value being X min , and the average being X avg When set as such, the coefficient of variation of the relative yellow intensity (X max -X min ) / X avg is 20% or less, Group III nitride laminate.

[0095] (Appendix 2) The relative yellow intensity at the surface center is 1.25 or less, The coefficient of variation of the relative yellow intensity is 15% or less, The group III nitride laminate according to Appendix 1.

[0096] (Appendix 3) The relative yellow intensity at the surface center is 1.20 or less, The coefficient of variation of the relative yellow intensity is 10% or less, The group III nitride laminate according to Appendix 1.

[0097] (Appendix 4) The stacked structure is a nucleation layer provided on the SiC substrate, and a channel layer provided on the nucleation layer and represented by the composition formula of In x Al y GaN (0≦x≦1, 0≦y≦1, x + y≦1), wherein the surface of the stacked structure is the channel layer. The group III nitride laminate according to any one of Appendices 1 to 3.

[0098] (Appendix 5) The stacked structure is a nucleation layer provided on the SiC substrate, and a channel layer provided on the nucleation layer and represented by the composition formula of In x Al y GaN (0≦x≦1, 0≦y≦1, x + y≦1), and a functional layer provided on the channel layer and containing a group III nitride having a bandgap wider than that of gallium nitride. wherein the surface of the stacked structure is the functional layer. The group III nitride laminate according to any one of Appendices 1 to 3.

[0099] (Appendix 6) having a diameter of 4 inches or more, The group III nitride laminate according to any one of Appendices 1 to 5.

[0100] (Appendix 7) (a) A step of preparing a SiC substrate; (b) A step of supplying a halogen-containing gas to the SiC substrate to desorb Si from the main surface of the SiC substrate and forming a Si-deficient region on the surface layer of the main surface; (c) A step of supplying a hydrogen-containing gas to the SiC substrate having the Si-deficient region formed thereon to remove the Si-deficient region and performing surface treatment on the main surface; (d) A step of growing a group III nitride crystal on the main surface after the treatment; Method for manufacturing a group-III nitride laminate having

[0101] (Appendix 8) Perform the step (c) under conditions such that the Si-deficient region is removed from the entire main surface of the SiC substrate. Method for manufacturing a group-III nitride laminate according to Appendix 7.

[0102] (Appendix 9) Perform the step (b) under conditions such that the Si-deficient region is formed over the entire main surface of the SiC substrate. Method for manufacturing a group-III nitride laminate according to Appendix 7 or 8.

[0103] (Appendix 10) Perform the step (c) at a temperature higher than that of the step (b). Method for manufacturing a group-III nitride laminate according to any one of Appendices 7 to 9.

[0104] (Appendix 11) Perform the step (b) at a temperature of 850°C to 1150°C. Method for manufacturing a group-III nitride laminate according to any one of Appendices 7 to 10.

[0105] (Appendix 12) Perform the steps (b), (c), and (d) continuously in the same processing vessel. Method for manufacturing a group-III nitride laminate according to any one of Appendices 7 to 11.

[0106] (Appendix 13) Perform the steps (b) and (c) alternately a plurality of times. Method for manufacturing a group-III nitride laminate according to any one of Appendices 7 to 12.

[0107] (Appendix 14) Before performing the step (b), include a step of annealing the SiC substrate in a reducing atmosphere. Method for manufacturing a group-III nitride laminate according to any one of Appendices 7 to 13.

[0108] (Supplementary Note 15) In the above (d), as the group III nitride crystal, In x Al y a substance represented by the composition formula of GaN (0 ≤ x ≤ 1, 0 ≤ y ≤ 1, x + y ≤ 1) is grown The method for manufacturing a group III nitride laminate according to any one of Supplementary Notes 7 to 14.

Explanation of Symbols

[0109] 1 Group III nitride laminate (laminate) 10 SiC substrate 20 Laminated structure 30 Nucleation layer 40 Channel layer 50 Barrier layer 60 Cap layer

Claims

1. An SiC substrate, A stacked structure provided on the substrate and formed by epitaxially growing a group-III nitride crystal, Comprising, The stacked structure is, The relative yellow intensity, which is the ratio of the yellow emission intensity to the band-edge emission intensity of photoluminescence at the center of the surface of the laminated structure, is 1.30 or less. In the internal region excluding a width of 5 mm from the outer edge of the surface of the laminated structure, for the relative yellow intensity at three or more locations arbitrarily selected along the center line and including two or more locations spaced apart from the center, when the maximum value is X ｍａｘ , the minimum value is X ｍｉｎ , and the average is X ａｖｇ , the coefficient of variation of the relative yellow intensity (X ｍａｘ - X ｍｉｎ ) / X ａｖｇ is 20% or less. A group-III nitride laminate.

2. The relative yellow intensity at the center of the surface is 1.25 or less, The rate of change of the relative yellow intensity is 15% or less, The group-III nitride laminate according to Claim 1.

3. The relative yellow intensity at the center of the surface is 1.20 or less, The rate of change of the relative yellow intensity is 10% or less, The group-III nitride laminate according to Claim 1.

4. The stacked structure is, A nucleation layer provided on the SiC substrate, Provided on the core generation layer, In ｘ Al ｙ a channel layer represented by the composition formula of GaN (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1), and is provided with The surface of the stacked structure is the channel layer, The group-III nitride laminate according to Claim 1 or Claim 2.

5. The stacked structure is, A nucleation layer provided on the SiC substrate, Provided on the core generation layer, In ｘ Al ｙ a channel layer represented by the composition formula of GaN (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1), A functional layer provided on the channel layer and containing a group-III nitride having a wider bandgap than gallium nitride, The surface of the stacked structure is the functional layer, The group-III nitride laminate according to Claim 1 or Claim 2.

6. The diameter is 4 inches or more, The group-III nitride laminate according to Claim 1 or Claim 2.

7. (a) A step of preparing an SiC substrate, (b) A step of supplying a halogen-containing gas to the SiC substrate to desorb Si from the main surface of the SiC substrate and form an Si-deficient region on the surface layer of the main surface, (c) A step of supplying a hydrogen-containing gas to the SiC substrate having the Si-deficient region formed thereon to remove the Si-deficient region and perform surface treatment on the main surface, (d) A step of growing a group-III nitride crystal on the main surface after the treatment, A method for manufacturing a group-III nitride laminate having.

8. Performing the step (c) under conditions such that the Si-deficient region is removed from the entire area of the main surface of the SiC substrate, The method for manufacturing a group-III nitride laminate according to Claim 7.

9. Performing the step (b) under conditions such that the Si-deficient region is formed over the entire area of the main surface of the SiC substrate, The method for manufacturing a group-III nitride laminate according to Claim 8.

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