Group 13 element nitride single crystal substrate

Abstract

[Problem] To increase the specific resistance of a group 13 nitride single crystal substrate and inhibit warping and cracking. [Solution] This group 13 nitride single crystal substrate 2 comprises a group 13 nitride single crystal and has a first main surface 2a and a second main surface 2b. The group 13 nitride single crystal contains manganese and zinc as doping components.

Description

[Technical Field]

[0001] This invention relates to a single crystal substrate made of Group 13 element nitrides. [Background technology]

[0002] Gallium nitride self-supporting substrates are used to fabricate various devices such as ultra-high-brightness LEDs, high-power LDs, and high-efficiency power ICs using gallium nitride compound semiconductors. For power devices such as power ICs, it is preferable to increase the size of the element as the power handled increases. This is because increasing the device area reduces the current density, making device failure less likely. For this reason, the development of large-diameter gallium nitride self-supporting substrates, such as 4-inch and 6-inch substrates, is active. Known methods for manufacturing gallium nitride self-supporting substrates include the HVPE method, the amonothermal method, and the flux method.

[0003] In recent years, with the acceleration of the digitalization of social infrastructure, the need for high-speed transmission of large volumes of communication data has increased, and wireless communication is also moving towards higher frequencies. Gallium nitride, which has material properties that result in high electron mobility, is suitable for high-electron-mobility transistors (HEMTs) used in power amplifiers for wireless base stations, etc., and the adoption of HEMT devices with a GaN-on-SiC structure, in which a gallium nitride functional layer is laminated on a high-resistance silicon carbide substrate, is increasing. Since the functional layer is gallium nitride, the practical application of high-resistance gallium nitride self-supporting substrates is awaited in order to fabricate even higher-performance HEMT elements. If a high-resistance gallium nitride self-supporting substrate exists, it will be possible to form a gallium nitride functional layer with fewer defects, and this is expected to lead to the realization of higher-performance HEMT elements. Here, high performance refers to a high output of communication waves and high energy conversion efficiency.

[0004] To date, high-resistance gallium nitride substrates with zinc doping and high-resistance gallium nitride substrates with iron doping have been reported (Patent Documents 1, 2, and 3). [Prior art documents]

Patent Document

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] [[ID=]26]However, for example, a high-resistance gallium nitride substrate with a size of 4 inches or more, which is required for manufacturing HEMT devices used in power amplifiers and the like in wireless base stations, is difficult to manufacture and has not yet been put into practical use.

[0007] The problem of the present invention is to increase the resistivity of the group 13 element nitride single crystal substrate while suppressing warping and cracking.

Means for Solving the Problems

[0008] The present invention relates to a group 13 element nitride single crystal substrate composed of a group 13 element nitride single crystal and having a first main surface and a second main surface Method of manufacturing wherein A seed substrate is immersed in a flux containing manganese and zinc, and a group 13 element nitride single crystal is grown on the seed substrate by the flux method to obtain the group 13 element nitride single crystal substrate. the group 13 element nitride single crystal to contains manganese and zinc as doping components Let and the manganese concentration in the group 13 element nitride single crystal of is 1×10 Let's assume , 3 , 18 , atoms / cm 3 ~5×10<000000]3atoms / cm 3 year and the zinc concentration in the group 13 element nitride single crystal of is 1×10 17 atoms / cm 3 ~3×10 18 atoms / cm 3 Let's assume This is the gist of the present invention.

[0009] Furthermore, the present invention relates to a method for manufacturing the above-mentioned Group 13 element nitride single crystal substrate, A method for producing a group 13 element nitride single crystal substrate, characterized by immersing a seed substrate in a flux containing manganese and zinc, and growing the group 13 element nitride single crystal on the seed substrate by the flux method. [Effects of the Invention]

[0010] According to the present invention, it is possible to increase the resistivity of a group 13 element nitride single crystal substrate while also controlling warping and cracking.

[0011] Here, it was found that when only zinc is added to a group 13 element nitride single crystal, the resistivity of the group 13 element nitride single crystal substrate increases, but the group 13 element nitride single crystal tends to warp into a concave shape when viewed from the growth surface, and is also prone to cracking. Furthermore, in order to obtain the high resistance values ​​required for the fabrication of HEMT devices, for example, it was necessary to increase the amount of zinc doping, but increasing the amount of zinc doping made the aforementioned warping and cracking even more likely.

[0012] On the other hand, the inventors also considered doping the group 13 element nitride single crystal with manganese. In this case, adding a small amount of manganese significantly increased the resistance of the group 13 element nitride single crystal. However, it was found that the grown group 13 element nitride single crystal tended to warp into a convex shape when viewed from the growth surface, and was also prone to cracking. When the amount of manganese added was further reduced to suppress warping and cracking, it was found that the resistance did not become sufficiently high throughout the group 13 element nitride single crystal.

[0013] Thus, it was found that both zinc and manganese have the effect of increasing the resistance of a group 13 element nitride single crystal substrate, while simultaneously exhibiting contradictory behaviors in terms of warping during heteroepitaxial growth of the group 13 element nitride single crystal on the underlying substrate. Focusing on these behaviors, the inventors succeeded in realizing a group 13 element nitride single crystal substrate that exhibits high resistance, small warping, and resistance despite having a large diameter, and is less prone to cracking, by simultaneously adding zinc and manganese. [Brief explanation of the drawing]

[0014] [Figure 1] (a) is a schematic diagram showing an epitaxial substrate 1 for a semiconductor device according to one embodiment, and (b) is a schematic diagram showing a composite substrate 8 for epitaxial growth layer deposition. [Modes for carrying out the invention]

[0015] Figure 1(a) is a schematic diagram of an epitaxial substrate 1 for a semiconductor device according to one embodiment. The Group 13 element nitride single crystal substrate 2 of the present invention has a first main surface 2a and a second main surface 2b. The first main surface 2a of the Group 13 element nitride single crystal substrate 2 is selected as the film deposition surface, and an epitaxial growth layer is deposited on the first main surface 2a. Specifically, in this example, a buffer layer 3 is formed on the first main surface 2a of the Group 13 element nitride single crystal substrate 2, a channel layer 4 is formed on the main surface 3a of the buffer layer 3, and a barrier layer 5 is formed on the main surface 4a of the channel layer 4. A predetermined electrode or the like can be provided on the main surface 5a of the barrier layer 5.

[0016] The Group 13 element nitride single crystal substrate 2 is made of a Group 13 element nitride single crystal and has a first main surface 2a and a second main surface 2b. The Group 13 element is a Group 13 element defined by the IUPAC, and particularly preferably gallium, aluminum and / or indium. Further, as the Group 13 element nitride single crystal, a Group 13 element nitride single crystal selected from gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof is preferable. More specifically, GaN, AlN, InN, Ga x Al 1-x N(1>x>0), Ga x In 1-x N(1>x>0), Al x In 1-x N(1>x>0), Ga x Al y In z N(1>x>0, 1>y>0, x + y + z = 1).

[0017] In a preferred embodiment, the ratio of the manganese concentration to the zinc concentration (manganese concentration / zinc concentration) is 0.5 or more and 30 or less. By setting this ratio to 0.5 or more, the concave warp of the Group 13 element nitride single crystal substrate and the cracks associated with the concave warp can be suppressed, and the resistivity value can be further increased. On the other hand, by setting the ratio to 30 or less, the convex warp of the Group 13 element nitride single crystal substrate and the cracks associated with the convex warp can be suppressed. From these viewpoints, it is more preferable that the ratio of the manganese concentration to the zinc concentration (manganese concentration / zinc concentration) is 3.0 or more, and even more preferable that it is 5.0 or more. Further, it is more preferable that the ratio of the manganese concentration to the zinc concentration (manganese concentration / zinc concentration) is 25 or less, and even more preferable that it is 20 or less. <​​​​​​​​​​​​​​​​​It is even more preferable that this is the case. Also, from the viewpoint of the present invention, the zinc concentration in the group 13 element nitride single crystal is 1 × 10 17 atoms / cm 3 ~3×10 18 atoms / cm 3 It is preferable that it be 2 × 10 17 atoms / cm 3 ~1 × 10 18 atoms / cm 3 It is even more preferable that this is the case. The manganese and zinc concentrations in the group 13 element nitride single crystal shall be measured by SIMS (secondary ion mass spectrometry).

[0019] Note that Group 13 element nitride single crystals may contain elements other than zinc and manganese. Examples of such elements include hydrogen (H), oxygen (O), silicon (Si), iron (Fe), and chromium (Cr).

[0020] Let me explain the definition of a single crystal. It includes textbook-style single crystals in which atoms are arranged regularly throughout the entire crystal, but it is not limited to just that; it refers to single crystals that are commonly used in industry. In other words, the crystal may contain some defects, inherent distortions, or impurities.

[0021] Furthermore, the group 13 element nitride single crystal substrate may be a self-supporting substrate. A "self-supporting substrate" means a substrate that does not deform or break under its own weight when handled and can be handled as a solid object. The self-supporting substrate of the present invention can be used as a substrate for various semiconductor devices such as light-emitting elements. In a preferred embodiment, the thickness of the self-supporting substrate after polishing is preferably 300 μm or more, and preferably 1000 μm or less. The size of the freestanding circuit board is not particularly limited, but it is 4 inches or larger, may be 6 inches or larger, or may be 8 inches or larger.

[0022] Furthermore, as shown in Figure 1(b), a composite substrate 8 for epitaxial growth layer deposition can be obtained by directly bonding a base substrate 7 made of a material with a higher thermal conductivity than the group 13 element nitride single crystal to the second main surface 2b side of the group 13 element nitride single crystal substrate 2. SiC, AlN, and diamond are preferred materials for such a base substrate. The thermal conductivity of the base substrate is preferably 200 W / m·K or higher, and more preferably 500 W / m·K or higher.

[0023] By using the Group 13 element nitride single crystal substrate of the present invention as a template, a HEMT element capable of high-power operation can be realized. Using such a HEMT element, a high-power, high-frequency, and highly efficient power amplifier required for base stations for next-generation wireless communication can be realized.

[0024] In a preferred embodiment, the resistivity of the group 13 element nitride single crystal substrate at room temperature is 1 × 10⁻⁶ 6 The resistivity is greater than Ωcm. In other words, this group 13 element nitride single crystal substrate is semi-insulating. From this perspective, the resistivity of the group 13 element nitride single crystal substrate at room temperature is 1 × 10⁻⁶. 7 Preferably, it is Ωcm or more, 1 × 10 9 It is even more preferable that the resistivity is Ωcm or greater. Also, the resistivity of the group 13 element nitride single crystal substrate at room temperature is 1 × 10⁻⁶ 13 It is often less than Ωcm.

[0025] (Manufacturing of Group 13 element nitride single crystal substrates) Methods for producing Group 13 element nitride single crystal substrates include vapor phase methods such as metal-organic chemical vapor deposition (MOCVD), hydride vapor deposition (HVPE), pulsed excitation deposition (PXD), metal-beam deposition (MBE), and sublimation, as well as liquid phase methods such as amonothermal deposition and flux deposition. Particularly preferred are Group 13 element nitride single crystals produced by flux deposition.

[0026] In the flux method, it is preferable to obtain a group 13 element nitride single crystal substrate by immersing a seed substrate in a flux containing manganese and zinc, and growing a group 13 element nitride single crystal on the seed substrate by the flux method. Particularly preferable is to form a seed substrate by providing a seed crystal film on the surface of a support substrate such as sapphire or a group 13 element nitride single crystal, and then growing a group 13 element nitride single crystal on the seed crystal film by the flux method.

[0027] It is preferable that the material of the support substrate and the material of the group 13 element nitride single crystal substrate of the present invention be different, but they may be the same. One method for fabricating a Group 13 element nitride single crystal substrate involves using a substrate made of a different material, such as sapphire, as a base substrate, performing heteroepitaxial growth to produce a Group 13 element nitride single crystal, and then processing this to obtain a Group 13 element nitride crystal substrate. However, with this manufacturing method, the mismatch in lattice constants between the group 13 element nitride single crystal and sapphire, as well as the difference in thermal expansion coefficients, can easily cause warping and cracking in the group 13 element nitride single crystal substrate. In particular, as the size of the group 13 element nitride single crystal substrate increases, the difference in thermal expansion coefficients with the underlying substrate accumulates and has a greater effect, resulting in a larger absolute value of warping and making cracking more likely.

[0028] The material of the seed crystal film is Al x Ga 1-x N(0≦x≦1) and In x Ga 1-x N(0≦x≦1) can be used as a preferred example, and gallium nitride is particularly preferred. The preferred method for forming the seed crystal film is vapor deposition, but examples include metal-organic chemical vapor deposition (MOCVD), hydride vapor deposition (HVPE), pulsed excitation deposition (PXD), metal-beam deposition (MBE), and sublimation. Metal-organic chemical vapor deposition is particularly preferred. The growth temperature is preferably 950 to 1200°C.

[0029] When growing a group 13 element nitride single crystal by the flux method, the type of flux is not particularly limited as long as it is capable of producing the single crystal. In preferred embodiments, the flux contains at least one of an alkali metal and an alkaline earth metal, and a flux containing sodium metal is particularly preferred. The flux is used by mixing it with metal raw materials. While elemental metals, alloys, and metal compounds can be used as metal raw materials, elemental metals are preferable due to their ease of handling.

[0030] The growth temperature and holding time for single crystals of group 13 element nitrides in the flux method are not particularly limited and can be appropriately changed depending on the composition of the flux. For example, when growing gallium nitride crystals using a sodium or lithium-containing flux, the growth temperature is preferably 800 to 950°C, and more preferably 850 to 900°C.

[0031] In the flux method, single crystals of group 13 element nitrides are grown in an atmosphere containing a gas with nitrogen atoms. Nitrogen gas is preferred, but ammonia may also be used. The atmospheric pressure is not particularly limited, but from the viewpoint of preventing evaporation of the flux, 10 atmospheres or more is preferred, and 30 atmospheres or more is more preferred. However, since high pressure requires a large-scale apparatus, the total atmospheric pressure is preferably 2000 atmospheres or less, and more preferably 500 atmospheres or less. The gas in the atmosphere other than the gas containing nitrogen atoms is not limited, but an inert gas is preferred, and argon, helium, and neon are particularly preferred.

[0032] In a particularly preferred embodiment, a seed crystal film made of gallium nitride is grown on a sapphire substrate by MOCVD to obtain a seed substrate. This seed substrate is placed in a crucible, and then the crucible is filled with 10 to 50 mol% of metallic Ga, 50 to 90 parts by mass of metallic Na, 0.0001 to 1 mol% of metallic Mn, and 0.0001 to 1 mol% of metallic Zn. By appropriately controlling the amount of metallic Mn and metallic Zn added within the aforementioned ranges, it is possible to control the concentration of each element in the group 13 element nitride single crystal. This crucible is placed in a heating furnace, the furnace temperature is set to 800°C to 950°C, the furnace pressure to 3 MPa to 5 MPa, and it is heated for about 20 to 400 hours, after which it is cooled to room temperature. After cooling is complete, the crucible is removed from the furnace. The gallium nitride single crystal obtained in this way is polished using diamond abrasive grains to flatten its surface. This forms a gallium nitride single crystal on the seed crystal film.

[0033] (Formation of epitaxial growth layer) Examples of epitaxial growth layers grown on a Group 13 element nitride single crystal substrate include gallium nitride, aluminum nitride, indium nitride, or mixed crystals thereof. Specifically, GaN, AlN, InN, Ga x Al 1-x N(1>x>0), Ga x In 1-x N(1>x>0), Al x In 1-x N(1>x>0), Ga x Al y In z One example is N(1>x>0, 1>y>0, x+y+z=1). In addition, examples of functional layers provided on a group 13 element nitride single crystal substrate include not only light-emitting layers, but also rectifier layers and switching element layers.

[0034] In a preferred embodiment, for example, as shown in Figure 1(a), a buffer layer 3, a channel layer 4, and a barrier layer 5 are formed on the first main surface 2a of the group 13 element nitride single crystal substrate 2. The buffer layer 3, channel layer 4, and barrier layer 5 can be formed, for example, by metal-organic chemical vapor deposition (MOCVD). In MOCVD layer formation, metal-organic raw material gases (such as TMG (trimethylgallium), TMA (trimethylaluminum), and TMI (trimethylindium)) corresponding to the desired composition, along with ammonia gas, hydrogen gas, and nitrogen gas, are supplied into the reactor of an MOCVD furnace. While heating a group 13 element nitride single crystal substrate placed in the reactor to a predetermined temperature, group 13 element nitride single crystals are sequentially generated by gas-phase reactions between the metal-organic raw material gas and ammonia gas corresponding to each layer.

[0035] (Measurement of cross-sectional shape and warpage) The cross-sectional shape and warpage of the Group 13 element nitride single crystal substrate shall be measured as follows. Using Tropel's "FlatMaster200," the Group 13 element nitride single crystal substrate is placed on the sample stage with the Group 13 element polarity face upwards, and the shape of the substrate is measured in the medium range to obtain a gently curved surface shape. A concave shape is defined as when the height of the outer periphery is greater than the height of the center of the Group 13 element nitride single crystal substrate (wafer), and a convex shape is defined as when the height of the outer periphery is lower than the height of the center of the Group 13 element nitride single crystal substrate (wafer). Furthermore, the sum of the distance from the least-squares plane of the aforementioned curved surface to the highest point on the wafer surface and the distance from the least-squares plane to the lowest point on the wafer surface was defined as the warpage value. However, if the diameter of the Group 13 element nitride single crystal substrate is 4 inches or larger, the absolute value of the warp is measured and calculated within a 4-inch diameter range from the center of the substrate. If the diameter of the Group 13 element nitride single crystal is less than 4 inches, the absolute value of the warp is measured and calculated within a 2-inch diameter range from the center of the substrate. Furthermore, when the diameter of the group 13 element nitride single crystal substrate is 4 inches or more, the absolute value of the warpage is preferably 50 μm or less, more preferably 25 μm or less, and particularly preferably 15 μm or less. When the diameter of the group 13 element nitride single crystal substrate is 2 inches, the absolute value of the warpage is preferably 20 μm or less. [Examples]

[0036] The gallium nitride single crystal substrates shown in Examples 1-4 and Comparative Examples 1 and 2 in Table 1 were prepared, and the manganese concentration, zinc concentration, cross-sectional shape, warpage, presence or absence of cracks, and resistivity were measured for each. These results are shown in Table 1.

[0037] (Fabrication of gallium nitride single crystal substrates) (Preparation of seed substrates) A seed crystal film made of gallium nitride with a thickness of 2 μm was deposited on the surface of a 4-inch diameter c-plane sapphire substrate (underlying substrate) by MOCVD, and this was used as the seed substrate.

[0038] (Growth of gallium nitride single crystals using the Na flux method) Gallium nitride single crystals were formed on the above-mentioned seed substrate using the Na flux method. Specifically, 50 g of metallic Ga, 100 g of metallic Na, metallic Mn, and metallic Zn were packed into an alumina crucible, and the crucible was covered with an alumina lid. The amounts of metallic Mn and metallic Zn were adjusted as appropriate within the range of 1 mg to 10 g. The crucible was placed in a heating furnace, the furnace temperature was set to 850°C, the furnace pressure to 4.0 MPa, and it was heated for 100 hours, after which it was cooled to room temperature. After cooling, when the alumina crucible was removed from the furnace, a brown gallium nitride single crystal was found deposited on the surface of the seed substrate to a thickness of approximately 1000 μm.

[0039] (Fabrication of self-supporting circuit boards) The gallium nitride single crystal obtained in this manner was polished using diamond abrasive grains to flatten its surface, and the total thickness of the gallium nitride single crystal formed on the substrate was set to 700 μm.

[0040] A seed substrate was separated from a gallium nitride single crystal using the laser lift-off method to obtain a gallium nitride single crystal substrate.

[0041] By polishing the first and second main surfaces of a gallium nitride single crystal substrate, a self-supporting substrate made of a gallium nitride single crystal with a thickness of 400 μm was obtained.

[0042] (Measurement of manganese and zinc concentrations) The manganese and zinc concentrations in each obtained gallium nitride single crystal substrate were measured by SIMS (Secondary Ion Mass Spectrometry). The specific measurement conditions are as follows. Measurement device: CAMECA IMA-6f, Primary ion species: Cs+, Acceleration voltage: 15kV, Detection area: 30μmΦ

[0043] (Measurement of cross-sectional shape and warpage) For each example of gallium nitride single crystal substrate, the cross-sectional shape and warpage were measured as described above.

[0044] (Measurement of resistivity) The resistivity of each gallium nitride single crystal substrate was measured using the capacitance method (COREMA-WT, manufactured by SEMIMAP).

[0045] (Observation of cracks) The base substrate and gallium nitride single crystal substrate of each obtained example were visually inspected to check for the presence or absence of cracks.

[0046] [Table 1]

[0047] As shown in Table 1, the gallium nitride single crystal substrate of the present invention exhibits a small absolute value of warpage, no cracks are observed, and a resistivity of 10 6 It was found that the value was high, exceeding Ω·cm.

[0048] On the other hand, in Comparative Example 1, 3.9 × 10⁻¹⁶ gallium nitride single crystal 18 / cm 3 It contains zinc, but not manganese. As a result, the resistivity is 10 5 The resistivity was Ω·cm, and the gallium nitride single crystal substrate was warped concavely when viewed from the growth surface, with a warp reaching -80 μm, and cracks were also observed. If the zinc concentration is increased further to achieve an increase in resistivity, the warp will become even greater.

[0049] On the other hand, in Comparative Example 2, 4 × 10⁶ gallium nitride single crystals were used. 18 / cm 3 It contains manganese but no zinc. As a result, the resistivity is 10 11 Although the resistance was high at Ω·cm, the gallium nitride single crystal substrate was convex when viewed from the growth surface, with a warp reaching +60 μm, and cracks were also observed.

Claims

1. A method for manufacturing a group 13 element nitride single crystal substrate, comprising a group 13 element nitride single crystal and having a first main surface and a second main surface, A seed substrate is immersed in a flux containing manganese and zinc, and a group 13 element nitride single crystal is grown on the seed substrate by the flux method to obtain the group 13 element nitride single crystal substrate, in which case manganese and zinc are included as doping components in the group 13 element nitride single crystal, and the manganese concentration in the group 13 element nitride single crystal is 1 × 10⁻⁶ １８ atoms / cm ３ ~5 x 10 １８ atoms / cm ３ The zinc concentration in the group 13 element nitride single crystal is set to 1 × 10⁻⁶. １７ atoms / cm ３ ~3 x 10 １８ atoms / cm ３ A method for manufacturing a group 13 element nitride single crystal substrate, characterized by the following:

2. A method for manufacturing a group 13 element nitride single crystal substrate according to claim 1, characterized in that the ratio of manganese concentration to zinc concentration (manganese concentration / zinc concentration) is 0.5 or more and 30 or less.

3. The resistivity of the Group 13 element nitride single crystal substrate at room temperature is 1×10 ６ Ωcm or more, and the method for manufacturing a Group 13 element nitride single crystal substrate according to claim 1 or 2.

4. A method for manufacturing a group 13 element nitride single crystal substrate according to claim 1 or 2, characterized in that the absolute value of the warpage of the group 13 element nitride single crystal substrate is 50 μm or less.

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