Substrate set, single crystal substrate, method for producing substrate set, and method for producing semiconductor element

Abstract

Provided is a substrate that suppresses processing losses when used in the production of a semiconductor element. A substrate set according to an embodiment of the present invention includes a first substrate and a second substrate composed of the same type of single crystal. The first substrate has a first main surface and a second main surface facing each other. The second substrate has a third main surface and a fourth main surface facing each other. The first main surface of the first substrate and the third main surface of the second substrate each have a maximum roughness Rz of 5 μm or less. The first main surface in the first substrate is arranged on a first crystal face side of the single crystal body. The third main surface in the second substrate is arranged on a second crystal face of the single crystal body.

Description

Substrate set, single crystal substrate, method for manufacturing the substrate set, and method for manufacturing semiconductor device

[0001] The present invention relates to a substrate set, a single crystal substrate, a method for manufacturing a substrate set, and a method for manufacturing a semiconductor device.

[0002] Typical methods for manufacturing substrates used in semiconductor device manufacturing include, as described in Patent Document 1, slicing from an ingot with a wire saw and polishing the sliced ​​surface. Additionally, as described in Patent Document 2, a method has been proposed in which a laser beam is irradiated from a focal point at a predetermined depth from the surface of the ingot to form a modified layer and cracks, and then the substrate is separated from the ingot by fracture using a strong external force.

[0003] Japanese Patent Publication No. 2000-94221, Japanese Patent Publication No. 2016-111143

[0004] The wire saw method described above has the problem of significant substrate loss due to kerf loss and processing required to smooth the sliced ​​surface. Furthermore, the method of forming a modified layer and cracks by irradiating with a laser beam, which separates the substrate by connecting discontinuous cracks, results in a rough surface on the resulting separation surface. This poses a problem in that a large amount of processing is required on the separation surface of the substrate when forming the device layer of the semiconductor element. For example, grinding and polishing to a depth of tens to hundreds of micrometers may be necessary to smooth the separation surface of the substrate.

[0005] In view of the above, one of the objectives of the present invention is to provide a substrate used in the manufacture of semiconductor devices while suppressing processing losses.

[0006] 1. A substrate set according to an embodiment of the present invention includes a first substrate and a second substrate made of the same type of single crystal, wherein the first substrate has a first principal surface and a second principal surface facing each other, and the second substrate has a third principal surface and a fourth principal surface facing each other, and the first principal surface of the first substrate and the third principal surface of the second substrate each have a maximum roughness Rz of 5 μm or less, and in the first substrate, the first principal surface is located on the side of the first crystal plane of the single crystal, and in the second substrate, the third principal surface is located on the side of the second crystal plane of the single crystal. 2. In the substrate set described in 1 above, the first substrate and the second substrate may each be made of a material selected from group III element oxides, group III element nitrides, silicon carbide, and indium phosphide. 3. In the substrate set described in 1 or 2 above, the first substrate and the second substrate may each be made of a crystal having a hexagonal crystal structure. 4. In the substrate set described in any of 1 to 3 above, the first substrate and the second substrate are each composed of a compound containing a metal element, and in the first substrate, a metal region containing the metal element may be formed on the first main surface, and in the second substrate, a metal region containing the metal element may be formed on the third main surface. 5. A single crystal substrate according to another embodiment of the present invention is a single crystal substrate composed of a compound containing a metal element, having an upper surface and a lower surface facing each other, wherein the maximum roughness Rz of the upper surface is 5 μm or less, and a metal region containing the metal element is formed on the upper surface. 6. A method for manufacturing a substrate set according to yet another embodiment of the present invention includes preparing a base substrate having a first substrate layer, an intermediate layer, and a second substrate layer in that order, wherein the first substrate layer and the second substrate layer are made of the same type of single crystal, and irradiating the intermediate layer of the base substrate with laser light to decompose the intermediate layer and separate the first substrate layer and the second substrate layer to obtain a first substrate and a second substrate, wherein the maximum roughness Rz of the first main surface of the first substrate and the third main surface of the second substrate formed by decomposing the intermediate layer is 5 μm or less, respectively.7. In the method for manufacturing a substrate set described in 6 above, the light absorption rate of the intermediate layer to the laser light may be higher than the light absorption rate of the substrate layer to the laser light. 8. In the method for manufacturing a substrate set described in 6 or 7 above, the diameter of the irradiated laser light may be 50 μm or more. 9. In the method for manufacturing a substrate set described in any of 6 to 8 above, the first substrate layer and the second substrate layer may each be composed of a material selected from group III element oxides, group III element nitrides, silicon carbide, diamond, silicon, and indium phosphide. 10. A method for manufacturing a semiconductor device according to yet another embodiment of the present invention includes polishing the first main surface of the first substrate or the third main surface of the second substrate obtained by the method for manufacturing a substrate set described in any of 6 to 9 above, and forming a device layer on the polished main surface.

[0007] According to embodiments of the present invention, processing losses can be suppressed when obtaining substrates used in the manufacture of semiconductor devices.

[0008] This is a schematic cross-sectional view showing an example of the manufacturing process of a base substrate used in a method for manufacturing a substrate set according to an embodiment of the present invention. This figure follows Figure 1A. This figure follows Figure 1B. This figure follows Figure 1C. This figure follows Figure 1D. This is a schematic cross-sectional view showing another example of the manufacturing process of a base substrate used in a method for manufacturing a substrate set according to an embodiment of the present invention. This figure follows Figure 2A. This figure follows Figure 2B. This figure follows Figure 2C. This is a schematic cross-sectional view showing an example of the manufacturing process of a substrate set according to an embodiment of the present invention. This is a schematic cross-sectional view showing the general configuration of a substrate set according to one embodiment of the present invention. This figure is for explaining the scan feed and beam diameter in laser light irradiation. These are SEM images of the peeled surfaces of two substrates in Example 1 and a mapping image of the element Ga.

[0009] The embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. In order to clarify the explanation, the drawings may schematically represent the width, thickness, shape, etc., of each part compared to the embodiments, but these are merely examples and do not limit the interpretation of the present invention. Furthermore, in the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant explanations may be omitted.

[0010] A method for manufacturing a substrate set according to an embodiment of the present invention includes preparing a base substrate having a first substrate layer, an intermediate layer, and a second substrate layer in that order, and irradiating the intermediate layer of the base substrate with laser light to decompose the intermediate layer, separating the first substrate layer and the second substrate layer to obtain a first substrate and a second substrate. The first substrate and the second substrate may be composed of the same type of single crystal. Here, the same type of single crystal means that the crystal system of the single crystal is the same, and it is preferable that the material constituting the first substrate and the material constituting the second substrate are substantially the same.

[0011] <Base Substrate> The base substrate can typically be manufactured using a base substrate. Specifically, at least some of the layers constituting the base substrate can be formed using a base substrate.

[0012] For example, a base substrate can be formed by epitaxially growing crystals on a substrate. Figures 1A to 1E show an example of the manufacturing process for a base substrate.

[0013] Figure 1A shows a base substrate 30 having an upper surface 30a and a lower surface 30b facing each other. As the base substrate 30, for example, a substrate having a shape and size that allows for the manufacture of a base substrate of a desired shape and size is used. For example, the base substrate 30 is disc-shaped with a diameter of 50 mm to 200 mm. The thickness of the base substrate 30 is, for example, 200 μm to 2000 μm.

[0014] The base substrate 30 is typically composed of a single crystal. The base substrate 30 can be composed of any suitable material capable of forming the desired base substrate. Examples of materials that constitute the base substrate 30 include sapphire, crystal-oriented alumina, silicon, gallium oxide, aluminum nitride, aluminum gallium nitride, gallium arsenide, and silicon carbide.

[0015] Although not shown in the figures, the base substrate 30 may have a seed crystal film on its upper surface 30a, where a base substrate can be formed. The thickness of the seed crystal film is, for example, 0.2 μm to 10 μm, preferably 1 μm to 5 μm. The material constituting the seed crystal film can typically be any suitable material capable of forming the desired base substrate. For example, when forming a base substrate made of a group III element nitride, a group III element nitride is preferably used as the material constituting the seed crystal film. Details of group III element nitrides will be described later.

[0016] Typical methods for depositing seed crystal films include vapor deposition (VPD). Specific examples of VPD methods include metal-organic chemical vapor deposition (MOCVD), hydride vapor deposition (HVPE), pulsed excitation deposition (PXD), molecular beam epitaxy (MBE), vapor deposition, and sublimation. Among these, MOCVD is preferred.

[0017] Figure 1B shows the state in which a crystal has been grown on the upper surface 30a of the base substrate 30 to form the first substrate layer 31.

[0018] The first substrate layer 31 is made of any suitable material according to the desired first substrate. Examples of materials that make up the first substrate layer 31 (the first substrate) include, for example, group III element oxides such as aluminum oxide and gallium oxide, group III element nitrides, silicon carbide, diamond, silicon, and indium phosphide. As the group III element that makes up the group III element nitride, for example, aluminum (Al), gallium (Ga), and indium (In) are used. These can be used alone or in combination of two or more. Specific examples of group III element nitrides include aluminum nitride (Al ｘ N), gallium nitride (Ga ｙ N), indium nitride (In ｚ N), aluminum gallium nitride (Al ｘ Ga ｙ N), gallium indium nitride (Ga ｙ In ｚ N), aluminum indium nitride (Al ｘ In ｚ N), aluminum gallium indium nitride (Al ｘ Ga ｙ In ｚ N). In each chemical formula in parentheses, typically, x + y + z = 1.

[0019] The material that makes up the first substrate layer 31 (the first substrate) may contain a dopant. As the dopant, for example, transition elements such as zinc (Zn), iron (Fe), manganese (Mn), vanadium (V), chromium (Cr), cobalt (Co), and nickel (Ni) are used. Also, as the dopant, carbon (C), oxygen (O), nitrogen (N), phosphorus (P), boron (B), magnesium (Mg), silicon (Si), and germanium (Ge) can also be used. These can be used alone or in combination of two or more.

[0020] The degree of crystal growth can be adjusted according to the desired thickness of the first substrate layer 31 and / or the thickness of the first substrate. Any appropriate direction can be selected for the crystal growth direction depending on the application, purpose, etc. For example, when growing a crystal having a hexagonal crystal structure such as a group III element nitride, the normal directions of the c-plane, a-plane, and m-plane, respectively, and the normal directions of the planes inclined with respect to the c-plane, a-plane, and m-plane can be mentioned.

[0021] The first substrate layer 31 can be formed by any suitable method. The method for growing the crystals constituting the first substrate layer 31 is not particularly limited, as long as it can achieve a crystal orientation that generally follows the crystal orientation of the underlying substrate 30. Specific examples of methods for growing the crystals constituting the first substrate layer 31 (method for forming the first substrate layer 31) include vapor phase growth methods such as metal-organic chemical vapor deposition (MOCVD), hydride vapor deposition (HVPE), pulsed excitation deposition (PXD), molecular beam epitaxy (MBE), and sublimation; and liquid phase growth methods such as flux, amonothermal, hydrothermal, sol-gel, Czochralski (CZ) method, liquid-encapsulated Czochralski (LEC) method, floating zone melting (FZ) method, Bridgman (VB) method, and EFG (Edge-defined Film-fed Growth) method. These can be used individually or in combination of two or more.

[0022] For example, when the first substrate layer 31 is composed of a group III element nitride crystal, the flux method (e.g., the Na flux method) or the MOCVD method is preferably used as the growth method. Details of the method for growing a group III element nitride crystal by the flux method are described, for example, in Japanese Patent Publication No. 5451085, and the crystal may be grown by adjusting the various conditions of the growth method described therein as appropriate. Specifically, the growth of a group III element nitride crystal can be carried out by adjusting various conditions using a crystal manufacturing apparatus that includes a pressure vessel capable of supplying high-pressure nitrogen gas, a turntable that can rotate within the pressure vessel, and an outer container placed on the turntable.

[0023] The growth of Group III element nitride crystals by the flux method is typically carried out using a crucible as the growth container. Specifically, a substrate 30 is placed in a predetermined position within the crucible, and then the raw material is filled in. The crucible containing the substrate 30 is typically placed with a lid on, under a nitrogen-containing atmosphere, and under predetermined pressure and temperature, and subjected to the growth process.

[0024] The above raw materials are, for example, a molten composition containing flux, a Group III element, and optionally a dopant. The flux preferably contains at least one of an alkali metal and an alkaline earth metal, and more preferably contains metallic sodium. Typically, the flux and the metal raw material are used in mixture form. As the metal raw material, elemental metals, alloys, metal compounds, etc., can be used, but from the viewpoint of handling, elemental metals are preferably used.

[0025] The crucible (including the lid) can be formed from any suitable material that can be used in the flux process. Examples of crucible materials include alumina, yttria, and YAG (yttrium aluminum garnet). The crucible material may be single crystal or polycrystalline (ceramic). The ceramic may have its relative density increased by HIP treatment or other methods, giving it so-called translucency.

[0026] As described above, growth can be carried out in a nitrogen-containing atmosphere. In addition to nitrogen, the growth atmosphere may contain other gases. Inert gases such as argon, helium, and neon are preferably used as other gases.

[0027] The atmospheric pressure during growth can be set to any appropriate pressure. For example, from the viewpoint of preventing flux evaporation, the atmospheric pressure during growth may be 1 MPa or more, but may also be 2 MPa or more, or 3 MPa or more. On the other hand, from the viewpoint of preventing the manufacturing equipment from becoming too large, the atmospheric pressure during growth may be 50 MPa or less, or 10 MPa or less.

[0028] The temperature of the atmosphere during growth can be set to any appropriate temperature. The temperature of the atmosphere during growth is preferably 700°C to 1000°C, more preferably 800°C to 900°C.

[0029] For example, from the viewpoint of promoting the dissolution of high-pressure nitrogen gas into the above melt composition, it is preferable to perform the growth while rotating the lower base plate (crucible). For example, a covered crucible is housed in the outer container of the above crystal manufacturing apparatus and placed on a turntable, and in this state, the crucible is rotated by rotating the turntable (for example, rotating on its own axis).

[0030] FIG. 1C shows a state in which an intermediate layer 33 is formed via a first substrate layer 31 on the upper surface 30a side of the lower base plate 30, and FIG. 1D shows a state in which crystals are grown on the intermediate layer 33 to form a second substrate layer 32.

[0031] As described above, the second substrate layer 32 can be composed of a single crystal of the same type as the first substrate layer 31. Examples of the material constituting the second substrate layer 32 (second substrate) include group III element oxides such as aluminum oxide and gallium oxide, group III element nitrides, silicon carbide, diamond, silicon, and indium phosphide. The thickness of the second substrate layer 32 can be adjusted according to the desired thickness of the second substrate. When the thickness of the second substrate layer 32 is thin (for example, when it is 100 μm or less), a support substrate (not shown) may be bonded to the second substrate layer 32. As the crystal growth direction of the second substrate layer 32, any appropriate direction can be selected according to the use, purpose, etc. In one embodiment, the crystal growth direction of the second substrate layer 32 is substantially the same as the crystal growth direction of the first substrate layer 31. The method of forming the second substrate layer 32 may be the same as or different from the method of forming the first substrate layer 31.

[0032] The thickness of the intermediate layer 33 is preferably 5 nm or more, more preferably 20 nm or more. According to such a thickness, the desired light absorption rate described later can be achieved well. On the other hand, the thickness of the intermediate layer 33 is preferably 5 μm or less, more preferably 1 μm or less. According to such a thickness, a second substrate layer 32 having excellent quality (for example, crystallinity) can be formed.

[0033] The intermediate layer 33 may be configured to satisfy a desired light absorption rate for light of wavelength λ. In one embodiment, the light absorption rate of the intermediate layer 33 for light of wavelength λ may be configured to be higher than the light absorption rate of the first substrate layer 31 and / or the second substrate layer 32 for light of wavelength λ. For example, the intermediate layer 33 can absorb light of wavelength λ that can be transmitted through the first substrate layer 31 and / or the second substrate layer 32.

[0034] The wavelength λ can be set, for example, depending on the material constituting the first substrate layer 31 and / or the second substrate layer 32. The first substrate layer 31 and / or the second substrate layer 32 may exhibit high light absorption for light having wavelengths below the wavelength corresponding to the bandgap energy of their constituent material. Therefore, the wavelength λ can be set to a wavelength exceeding the wavelength corresponding to the bandgap energy of the constituent material of the first substrate layer 31 and / or the second substrate layer 32. For example, if the constituent material of the first substrate layer 31 and / or the second substrate layer 32 is gallium nitride, it may exhibit high light absorption for light with a wavelength of 365 nm or less. In this case, the wavelength λ is, for example, in the range of 370 nm to 1070 nm, preferably 400 nm or more. As a specific example, light with a wavelength of about 532 nm can be used as the light with wavelength λ. Also, for example, if the constituent material of the first substrate layer 31 and / or the second substrate layer 32 is aluminum nitride, it may exhibit high light absorption for light with a wavelength of 210 nm or less. In this case, the wavelength λ is, for example, in the range of 220 nm to 1070 nm, and preferably 250 nm or more. As a specific example, light with a wavelength of about 355 nm can be used as the light with wavelength λ.

[0035] The light absorption rate of the intermediate layer 33 at wavelength λ is, for example, 10% or more, preferably 20% or more, more preferably 30% or more, still more preferably 40% or more, and particularly preferably 50% or more. By having such light absorption characteristics, for example, the intermediate layer 33 can be decomposed by light at wavelength λ (typically, laser light). On the other hand, the light absorption rate of the intermediate layer 33 at wavelength λ is, for example, 80% or less, and may be 70% or less. The light absorption rate of the first substrate layer 31 and / or the second substrate layer 32 at wavelength λ is, for example, less than 10%, preferably 5% or less, and more preferably 1% or less.

[0036] The intermediate layer 33 can be formed by any suitable method. In the illustrated example, the intermediate layer 33 is formed by growing crystals on the first substrate layer 31. In this case, the formation method of the intermediate layer 33 may be the same as or different from the formation method of the first substrate layer 31. For example, when the intermediate layer 33 is formed using the same crystal growth method as the first substrate layer 31, after forming the first substrate layer 31, the crystal growth conditions (e.g., crystal growth temperature) can be changed to form the intermediate layer 33. Specifically, the intermediate layer 33 may be formed under crystal growth conditions that can include defects such as impurities and voids. Also, for example, when the intermediate layer 33 is formed using a crystal growth method different from the first substrate layer 31, after forming the first substrate layer 31, the intermediate layer 33 may be formed of a material different from the first substrate layer 31.

[0037] Unlike the illustrated example, an intermediate layer may be formed inside a crystalline layer obtained by growing crystals in the thickness direction on a base substrate, a first substrate layer may be formed below the intermediate layer, and then a second substrate layer may be formed by further growing crystals in the thickness direction on this crystalline layer, thereby obtaining a laminated structure as shown in Figure 1D. In this case, the intermediate layer may be, for example, a modified layer due to laser irradiation or an ion implantation layer. Preferably, an intermediate layer is obtained by implanting ions to a certain depth (for example, 0.1 μm to 3 μm) from the surface of the crystalline layer. In ion implantation, an intermediate layer can be formed inside the crystalline layer, so the surface of the crystalline layer can maintain its crystalline structure, and after forming the intermediate layer, further crystals can be grown on the crystalline layer. Examples of ions used for implantation include hydrogen ions, nitrogen ions, boron ions, and silicon ions. The dose of ions in the ion implantation layer can be set, for example, according to a desired light absorption rate. The dose of ions in the ion implantation layer may be, for example, 1 × 10⁻⁶ １５ cm －２ The above 1 x 10 １８ cm －２ The following, preferably 1 × 10 １６ cm －２ The above 5 x 10 １７ cm －２ The following applies. The ion dose can be confirmed, for example, by secondary ion mass spectrometry (SIMS). It is preferable that the surface of the crystal layer be polished during ion implantation.

[0038] After forming the second substrate layer 32, the base substrate 40 is obtained by removing the underlayment substrate 30 from the first substrate layer 31, as shown in Figure 1E. Typically, the base substrate 40 is obtained by separating the underlayment substrate 30 from the first substrate layer 31, as shown in the figure. The underlayment substrate 30 can be separated from the first substrate layer 31 by any suitable method. Examples of methods for separating the underlayment substrate 30 include the laser lift-off (LLO) method using laser light irradiation and chemical etching. Alternatively, the base substrate 40 may be obtained by methods such as grinding the underlayment substrate 30 away or slicing it using a wire saw.

[0039] The base substrate 40 may be processed. Examples of processing that can be applied to the base substrate 40 include planarization of the main surface (bottom surface) 31a of the first substrate layer 31 by polishing (e.g., chemical mechanical polishing (CMP), lapping). Typically, the substrate is planarized to a desired thickness by grinding and polishing.

[0040] Other examples of processing that can be applied to the base substrate 40 include grinding of the peripheral edges (for example, grinding using a diamond grinding wheel). Typically, the substrate is processed by grinding to achieve the desired shape and size (for example, a disc shape with a desired diameter). Other processing that can be applied to the base substrate 40 include chamfering of the outer edge, removal of the processed altered layer formed on the surface by polishing, and removal of residual stress that may be caused by the processed altered layer.

[0041] In the example shown in Figure 1, the base substrate 30 is removed from the first substrate layer 31 after the second substrate layer 32 has been formed. However, the base substrate 30 may be removed from the first substrate layer 31 before forming the intermediate layer 33 or the second substrate layer 32. In this case, the first substrate layer 31 may be processed after the base substrate 30 has been removed. Specifically, this includes processing the main surface (upper surface and / or lower surface) and the peripheral edge of the first substrate layer 31. Details of these processes can be described in the same way as the processing that can be applied to the base substrate 40 described above.

[0042] Figures 2A to 2D show another example of the manufacturing process for a base substrate. In the example shown in Figure 2, as shown in Figure 2A, a crystal is grown on the upper surface 30a of the base substrate 30 to form a first substrate layer 31, and then as shown in Figure 2B, the base substrate 30 is removed from the first substrate layer 31. After that, the main surface (preferably both main surfaces) of the first substrate layer 31 is subjected to processing such as grinding and polishing to obtain a first substrate layer 31 having a desired thickness as shown in Figure 2C, and then as shown in Figure 2D, an intermediate layer 33 and a second substrate layer 32 are formed on the first substrate layer 31 to obtain a base substrate 40. When the main surface of the first substrate layer 31 is processed before forming the intermediate layer 33, as in this illustrated example, it is preferable to form a thick (for example, 500 μm or more) first substrate layer 31 on the base substrate 30.

[0043] <Disassembly of the Intermediate Layer> Next, as shown in Figure 3, the intermediate layer 33 of the base substrate 40 is disassembled to separate the first substrate layer 31 and the second substrate layer 32. Then, as shown in Figure 4, the first substrate 10 is obtained from the first substrate layer 31, and the second substrate 20 is obtained from the second substrate layer 32, and a substrate set 100 including these is obtained. The thickness of the first substrate layer 31 included in the base substrate 40 is, for example, 100 μm to 1000 μm, preferably 200 μm to 800 μm, and more preferably 300 μm to 800 μm. The thickness of the second substrate layer 32 included in the base substrate 40 is, for example, 1 μm to 1000 μm, preferably 2 μm to 800 μm. The thickness of the first substrate layer 31 and the second substrate layer 32 included in the base substrate 40 can each be set to any appropriate value, and the thickness of the first substrate layer 31 and the second substrate layer 32 may be the same or different.

[0044] The decomposition of the intermediate layer 33 is preferably carried out by irradiating it with laser light L of wavelength λ, as shown in Figure 3. By decomposing the intermediate layer 33 by irradiation with laser light L, the first main surface 11 of the first substrate 10 and the third main surface 23 of the second substrate 20 can be made flat. Specifically, the maximum roughness Rz of the first main surface 11 of the first substrate 10 and the third main surface 23 of the second substrate 20 can be made 5 μm or less, preferably 3 μm or less. The maximum roughness Rz can be measured in accordance with ISO 1997.

[0045] In one embodiment, the wavelength λ of the laser light L is, for example, 400 nm or more. Specifically, a visible light laser and / or an infrared light laser are used for laser irradiation. For example, the wavelength of the laser light L may be around 532 nm. Light of such a wavelength can penetrate, for example, the first substrate layer 31 and / or the second substrate layer 32 made of gallium nitride, and the intermediate layer 33 can be decomposed well. In another embodiment, the wavelength λ of the laser light L is, for example, 250 nm or more and less than 400 nm. Specifically, an ultraviolet laser is used for laser irradiation. For example, the wavelength of the laser light L may be around 355 nm. Light of such a wavelength can penetrate, for example, the first substrate layer 31 and / or the second substrate layer 32 made of aluminum nitride, and the intermediate layer 33 can be decomposed well. Examples of laser light sources include solid-state lasers (DPSS: Diode Pumped Solid State) that use semiconductor lasers as excitation light, fiber lasers, semiconductor lasers, and dye lasers.

[0046] As shown in the figure, the laser light L may be irradiated from the first substrate layer 31 side (lower side of Figure 3) or from the second substrate layer 32 side (upper side of Figure 3). As described above, if a support substrate (not shown) is bonded to the second substrate layer 32, it is preferable to irradiate the laser light L from the first substrate layer 31 side.

[0047] The irradiation conditions for the laser light L can be set to any appropriate conditions. For example, the irradiation conditions for the laser light can be any appropriate conditions depending on the laser used. When using the above solid-state laser, the pulse frequency is, for example, 5 kHz to 100 kHz. The pulse width is, for example, 1 nS to 100 nS. The average power is, for example, 1 W to 20 W. The diameter of the laser light irradiated onto the intermediate layer 33 (hereinafter referred to as the beam diameter) is, for example, 10 μm or more, preferably 50 μm or more, and more preferably 100 μm or more. Since the laser light L is irradiated for the purpose of decomposing the intermediate layer 33, the beam diameter can be widened. With such a beam diameter, the first main surface 11 of the formed first substrate 10 and the third main surface 23 of the second substrate 20 can be made flatter. Moreover, with such a beam diameter, the decomposition area of ​​the intermediate layer 33 per unit pulse can be increased, and the time required for decomposition of the intermediate layer 33 can be shortened. The beam diameter is, for example, 1000 μm or less. Methods for increasing the beam diameter include, for example, changing the beam shape with a beam shaping machine, shifting the focus of the laser beam (defocusing), and scattering the laser beam. The laser beam can be scattered, for example, by roughening the incident surface of the laser beam (e.g., the surface of the substrate layer) or by using a separate diffuser plate.

[0048] The scanning speed of the laser beam during irradiation of the intermediate layer 33 is, for example, 50 mm / sec to 1000 mm / sec, preferably 100 mm / sec to 300 mm / sec. The laser beam scanning is typically performed in a linear (raster scan) or spiral (spiral scan) manner. The scanning interval is preferably 500 μm or less, more preferably 200 μm or less. On the other hand, from the viewpoint of productivity, the scanning interval is preferably 5 μm or more, more preferably 20 μm or more.

[0049] After the intermediate layer 33 is decomposed, the first substrate layer 31 and the second substrate layer 32 can be easily separated. Specifically, the first substrate layer 31 and the second substrate layer 32 can be separated without applying substantially any external force. Furthermore, the main surface formed by the decomposition of the intermediate layer 33 can be extremely flat (for example, with a maximum roughness Rz of 5 μm or less).

[0050] <Substrate Set> The substrate set 100 includes a first substrate 10 and a second substrate 20, both composed of the same type of single crystal. The first substrate 10 has a first main surface 11 formed by the decomposition of the intermediate layer 33 and a second main surface 12 facing the first main surface 11. The second substrate 20 has a third main surface 23 formed by the decomposition of the intermediate layer 33 and a fourth main surface 24 facing the third main surface 23. The thicknesses of the first substrate 10 and the second substrate 20 may substantially correspond to the thickness of the first substrate layer 31 and the second substrate layer 32 contained in the base substrate 40, respectively. The thicknesses of the first substrate 10 and the second substrate 20 may be the same or different. Although not shown, the support substrate may be bonded to the fourth main surface 24 side of the second substrate 20.

[0051] The first main surface 11 of the first substrate 10 and the third main surface 23 of the second substrate 20, formed by the decomposition of the intermediate layer 33, may each have a maximum roughness Rz of 5 μm or less. Having such flat main surfaces significantly reduces substrate loss due to processing such as polishing. For example, substrate loss due to processing can be reduced to about 5 μm.

[0052] The first substrate 10 and / or the second substrate 20 (hereinafter sometimes simply referred to as a single-crystal substrate) can typically be used to manufacture semiconductor devices. Specifically, any suitable device layer can be formed on the single-crystal substrate. The device layer can function, for example, as a light-emitting layer, a rectifier layer, a switching element layer, or a power semiconductor layer. The device layer is typically formed by epitaxial growth of a crystal. Depending on its function, application, etc., it can be determined which main surface of the single-crystal substrate the device layer will be formed on. In one embodiment, the first main surface 11 of the first substrate 10 and / or the third main surface 23 of the second substrate 20, which are formed by decomposition of the intermediate layer 33, are polished, and a device layer is formed on this polished surface to obtain a semiconductor device.

[0053] The first substrate 10 and the second substrate 20 can be manufactured in any suitable shape. In one embodiment, they can be manufactured in the form of a so-called wafer. The sizes of the first substrate 10 and the second substrate 20 can be appropriately set according to the purpose. For example, the diameter of the wafer is 50 mm to 200 mm. The first substrate 10 and the second substrate 20 may each have orientation flats or notches formed on a part of them to indicate the crystal orientation (e.g., the crystal orientation of the wafer). Processing to give the first substrate 10 and the second substrate 20 the desired shape and size may be performed on each of the first substrate 10 and the second substrate 20 after the decomposition of the intermediate layer 33, or on the base substrate 40 before the decomposition of the intermediate layer 33.

[0054] In one embodiment, in the first substrate 10, the first principal surface 11 is located on the side of the first crystal plane of the single crystal, and in the second substrate 20, the third principal surface 23 is located on the side of the second crystal plane of the single crystal. For example, when the first substrate 10 and the second substrate 20 are composed of a compound semiconductor, in the first substrate 10, the first principal surface 11 is located on the side of the first crystal plane of the single crystal, and in the second substrate 20, the third principal surface 23 is located on the side of the second crystal plane of the single crystal. Examples of compound semiconductors include group III element oxides, group III element nitrides, silicon carbide, and indium phosphide. As a specific example, when the first substrate 10 and the second substrate 20 are composed of crystals having a hexagonal crystal structure, for example, the first crystal plane may be the (0001) plane and the second crystal plane may be the (000-1) plane.

[0055] For example, the first substrate 10 and the second substrate 20 may be composed of Group III element nitride crystals. Group III element nitride crystals typically have a hexagonal wurtzite-type crystal structure. In Group III element nitride crystals, typically the <0001> direction is the c-axis direction, the <1-100> direction is the m-axis direction, and the <11-20> direction is the a-axis direction. Furthermore, a crystal plane perpendicular to the c-axis is a c-plane, a crystal plane perpendicular to the m-axis is an m-plane, and a crystal plane perpendicular to the a-axis is an a-plane. In one embodiment, the thickness directions of the first substrate 10 and the second substrate 20 are parallel or substantially parallel to the c-axis, the first principal surface 11 of the first substrate 10 is the Group III element polarity plane on the (0001) plane side, and the third principal surface 23 of the second substrate 20 is the nitrogen polarity plane on the (000-1) plane side. The first main surface 11 may be parallel to the (0001) plane, or it may be inclined with respect to the (0001) plane. The inclination angle of the first main surface 11 with respect to the (0001) plane is, for example, 10° or less, may be 5° or less, may be 2° or less, or may be 1° or less. The third main surface 23 may be parallel to the (000-1) plane, or it may be inclined with respect to the (000-1) plane. The inclination angle of the third main surface 23 with respect to the (000-1) plane is, for example, 10° or less, may be 5° or less, may be 2° or less, or may be 1° or less.

[0056] When the first substrate 10 and the second substrate 20 are composed of compounds containing metal elements, metallic regions containing the metal elements may be formed on the first main surface 11 of the first substrate 10 and the third main surface 23 of the second substrate 20, respectively, which are formed by laser irradiation during the decomposition of the intermediate layer 33.

[0057] For example, when the first substrate 10 and the second substrate 20 are made of gallium nitride, the metallic region contains metallic gallium. In this case, the proportion of the metallic gallium-containing region on the first main surface 11 of the first substrate 10 and the third main surface 23 of the second substrate 20 (the proportion of metallic gallium) may be 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more. The metallic region can function as a protective film on the substrate surface. In particular, the formation of a metallic region on nitrogen polar surfaces, which tend to be chemically brittle, can contribute to improving the chemical durability of the substrate.

[0058] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The light absorption rate and maximum roughness Rz are values ​​measured by the following measurement methods. <Light Absorption Rate> The total light transmittance and total light reflectance of the object to be measured were measured using an ultraviolet-visible-near-infrared spectrophotometer (Hitachi High-Techno-Science Co., Ltd., "UH4150"), and the light absorption rate was calculated by subtracting the total light reflectance from the total light transmittance. <Maximum Roughness Rz> The maximum roughness Rz was measured using a surface roughness measuring instrument (Mitutoyo Corporation, SURFTEST SJ-410). As measurement conditions, the standard conditions were set to ISO 1997, the cutoff value (λc) to 0.8 mm, the measurement length to 4.0 mm, the number of measurement intervals (N) to 5, and the measurement speed to 0.2 mm / s. During measurement, the measurement location was near the center of the planar view of the substrate.

[0059] [Example 1] 1. Fabrication of base substrate A c-plane sapphire substrate with a diameter of 4 inches was prepared as the base substrate, and a gallium nitride film with a thickness of 2 μm was deposited on the sapphire substrate as a seed crystal film by MOCVD to fabricate a seed crystal substrate.

[0060] Gallium nitride crystals were grown on a seed crystal substrate using a crystal manufacturing apparatus (by flux method) comprising a pressure vessel capable of supplying high-pressure nitrogen gas, a rotating platform rotatable within the pressure vessel, an outer container placed on the rotating platform, and a crystal growth furnace for placing the outer container under a desired temperature environment. The obtained seed crystal substrate was placed in an alumina crucible in a glove box under a nitrogen atmosphere. Next, 40 g of metallic gallium, 80 g of metallic sodium, and germanium as a doping element were melted in the glove box and filled into the crucible. The amount of germanium added was adjusted within the range of 0.5 g to 10 g. The seed crystal substrate was then immersed in the flux molten solution and covered with an alumina plate. In this state, the crucible was placed in a stainless steel inner container, which was then placed in a stainless steel outer container capable of housing the inner container, and the outer container was closed with a lid equipped with a nitrogen introduction pipe. In this state, the outer container was placed on a rotating platform located inside the crystal manufacturing apparatus, and the pressure vessel of the crystal manufacturing apparatus was sealed with a lid. Next, the heating element was operated to heat the crystal growth furnace inside the crystal manufacturing apparatus to a uniform temperature of 850°C, while nitrogen gas was introduced into the pressure vessel from a nitrogen gas cylinder until the pressure reached 4 MPa, and the outer container was rotated horizontally. This state was maintained for 35 hours to grow gallium nitride crystals with a thickness of approximately 600 μm.

[0061] (Formation of the intermediate layer 1) During the crystal growth process described above, specifically when the crystal had grown to a thickness of approximately 300 μm, the temperature of the crystal growth furnace was temporarily lowered by 5°C to grow an intermediate layer containing a large amount of sodium to a thickness of 100 nm. The light absorption rate of the sodium-rich intermediate layer at a wavelength of 532 nm was 50%. Subsequently, the temperature of the crystal growth furnace was returned to 850°C, and the gallium nitride crystal was grown to a thickness of approximately 300 μm. The light absorption rate of the gallium nitride crystal grown at 850°C at a wavelength of 532 nm was 1%.

[0062] Subsequently, under an atmospheric environment of 800°C, a 355 nm ultraviolet laser was irradiated from the sapphire substrate side of the seed crystal substrate on which the gallium nitride crystal had grown to decompose the gallium nitride film on the seed crystal substrate, and the grown gallium nitride crystal was separated from the sapphire substrate. The separated gallium nitride crystal was fixed to a ceramic processing plate, and the surface from which the sapphire substrate had been separated (the nitrogen polarity side of the gallium nitride) was polished and flattened using a grinder and lapping device. The maximum roughness Rz of the polished surface was 10 nm. In this way, a base substrate with a diameter of 4 inches and a thickness of 600 μm was fabricated.

[0063] 2. Decomposition of the Intermediate Layer The obtained base substrate was irradiated with laser light from the polished surface side under the following conditions to selectively decompose the intermediate layer: • Laser wavelength: 532 nm • Pulse width: 40 nS • Pulse frequency: 10 kHz • Beam diameter: Adjusted to 50 μm by defocusing • Scan speed: 200 mm / sec • Scan line feed (scan interval): 25 μm pitch • Scan method: Raster scan The scan line feed and beam diameter during laser irradiation are shown in Figure 5.

[0064] After irradiation with laser light, two substrates (substrate set) were obtained from the base substrate. The two substrates could be easily separated from each other without the use of any tools. The maximum roughness Rz of the separated surfaces of the two obtained substrates was less than 2 μm for each.

[0065] [Example 2] A substrate set was obtained in the same manner as in Example 1, except that the intermediate layer was formed as described below in the preparation of the base substrate. The maximum roughness Rz of the peeled surface of the two obtained substrates was less than 5 μm for each.

[0066] (Formation of the intermediate layer 2) After growing a gallium nitride crystal to a thickness of approximately 700 μm on a seed crystal substrate using the flux method, the seed crystal substrate was removed from the crystal manufacturing apparatus, and the sapphire substrate of the seed crystal substrate was separated by the LLO method. After separation, both main surfaces of the remaining portion were ground and polished to obtain a gallium nitride crystal 1 with a thickness of 300 μm. Subsequently, hydrogen ions were implanted from the surface of the gallium nitride crystal 1 on the side where the sapphire substrate was not placed. Here, the ion implantation depth was 1 μm, and the dose was 1 × 10⁻⁶. １７ cm －２ The ion-implanted layer (intermediate layer) had a thickness of 500 nm, and its light absorption rate for light at a wavelength of 532 nm was 40%. Subsequently, the gallium nitride crystal 1 was returned to the crystal growth furnace of the crystal manufacturing apparatus, and the gallium nitride crystal was further grown to a thickness of approximately 300 μm on the side of the gallium nitride crystal 1 where the sapphire substrate had not been placed.

[0067] [Example 3] A substrate set was obtained in the same manner as in Example 1, except that the intermediate layer was formed as described below in the preparation of the base substrate. The maximum roughness Rz of the peeled surface of the two obtained substrates was less than 5 μm for each.

[0068] (Formation of the intermediate layer 3) After growing a gallium nitride crystal to a thickness of approximately 700 μm on the seed crystal substrate using the flux method, the seed crystal substrate was temporarily removed from the crystal manufacturing apparatus, and the sapphire substrate of the seed crystal substrate was separated by the LLO method. After separation, both main surfaces of the remaining portion were ground and polished to obtain a gallium nitride crystal 1 with a thickness of 300 μm. Subsequently, a 100 nm thick group III element nitride layer was formed on the surface of the gallium nitride crystal 1 where the sapphire substrate was not placed, using the MOCVD method. The light absorption rate of the formed group III element nitride layer at a wavelength of 532 nm was 40%. Then, the sapphire substrate was returned to the crystal growth furnace of the crystal manufacturing apparatus, and a gallium nitride crystal was further grown on the group III element nitride layer to a thickness of approximately 300 μm.

[0069] Elemental mapping was performed on the delamination surfaces of the two substrates obtained in Example 1 using energy-dispersive X-ray spectroscopy (SEM-EDX) with a scanning electron microscope (SEM). Specifically, using a scanning electron microscope (JMS-IT500LA manufactured by JEOL Ltd.), 1) images were acquired under the conditions of an acceleration voltage of 15 kV, a magnification of 500x, and a working distance of 10 nm, and 2) a mapping image of the element Ga was obtained in elemental mapping analysis mode.

[0070] As shown in Figure 6, the proportion of metallic Ga was calculated by image analysis from the Ga element mapping images of the delamination surfaces of the two substrates obtained in Example 1. As a result, the proportion of metallic Ga on the delamination surface on the gallium polar side was 30.4%, and the proportion of metallic Ga on the delamination surface on the nitrogen polar side was 18.7%.

[0071] [Example 4] A silicon carbide single crystal substrate with a diameter of 4 inches, a thickness of approximately 700 μm, and a light absorption rate of 1% at a wavelength of 532 nm, fabricated by sublimation, was planarized to a thickness of 300 μm by grinding and polishing of both main surfaces. Subsequently, hydrogen ions were implanted from the Si polar surface side of the silicon carbide single crystal substrate. Here, the ion implantation depth was 1 μm, and the dose was 1 × 10⁻¹⁶. １７ cm －２ The ion-implanted layer (intermediate layer) had a thickness of 500 nm, and its light absorption rate for light at a wavelength of 532 nm was 40%. Subsequently, silicon carbide crystals were further grown on the Si polar side of the silicon carbide single crystal substrate to a thickness of approximately 300 μm by sublimation. In this way, a base substrate with a diameter of 4 inches and a thickness of 600 μm was obtained. The intermediate layer of the obtained base substrate was decomposed under the same conditions as in Example 1, and two substrates (substrate set) were obtained from the base substrate. The maximum roughness Rz of the delamination surface of the two obtained substrates was less than 5 μm for each.

[0072] [Example 5] An aluminum nitride single crystal substrate with a diameter of 2 inches, a thickness of approximately 700 μm, and a light absorption rate of 1% at a wavelength of 532 nm, fabricated by sublimation, was planarized to a thickness of 300 μm by grinding and polishing of both main surfaces. Subsequently, hydrogen ions were implanted from the surface on the Al polarity side of the aluminum nitride single crystal substrate. Here, the ion implantation depth was 1 μm, and the dose was 1 × 10⁻¹⁶. １７ cm －２ The ion-implanted layer (intermediate layer) had a thickness of 500 nm, and its light absorption rate for light at a wavelength of 532 nm was 40%. Subsequently, aluminum nitride crystals were further grown on the Al polarity side of the aluminum nitride single crystal substrate to a thickness of approximately 300 μm by sublimation. In this way, a base substrate with a diameter of 2 inches and a thickness of 600 μm was obtained. The intermediate layer of the obtained base substrate was decomposed under the same conditions as in Example 1, and two substrates (substrate set) were obtained from the base substrate. The maximum roughness Rz of the delamination surface of the two obtained substrates was less than 5 μm for each.

[0073] [Example 6] An aluminum nitride single crystal substrate with a diameter of 2 inches, a thickness of approximately 700 μm, and a light absorption rate of 1% at a wavelength of 355 nm, fabricated by sublimation, was planarized to a thickness of 300 μm by grinding and polishing of both main surfaces. Subsequently, a gallium nitride layer with a thickness of 100 nm was formed on the Al polarity side of the aluminum nitride single crystal substrate by MOCVD. The light absorption rate of the formed gallium nitride layer at a wavelength of 355 nm was 40%. Subsequently, aluminum nitride crystals were further grown to a thickness of approximately 300 μm on the Al polarity side of the aluminum nitride substrate by sublimation. In this way, a base substrate with a diameter of 2 inches and a thickness of 600 μm was obtained. The decomposition of the intermediate layer of the obtained base substrate was carried out in the same manner as in Example 1, except that the wavelength of the irradiated laser light was changed to 355 nm, to obtain two substrates (substrate set) from the base substrate. The maximum roughness Rz of the decomposed surface of the two obtained substrates was less than 5 μm each.

[0074] The substrates included in the substrate set according to the embodiment of the present invention can be used, for example, in the manufacture of semiconductor devices.

[0075] 10 First substrate, 20 Second substrate, 11 First main surface, 12 Second main surface, 23 Third main surface, 24 Fourth main surface, 30 Underlay substrate, 30a Top surface, 30b Bottom surface, 31 First substrate layer, 32 Second substrate layer, 33 Intermediate layer, 40 Base substrate, 100 Substrate set, L Laser light.

Claims

1. A substrate set comprising a first substrate and a second substrate made of the same type of single crystal, wherein the first substrate has a first principal surface and a second principal surface facing each other, the second substrate has a third principal surface and a fourth principal surface facing each other, the first principal surface of the first substrate and the third principal surface of the second substrate each have a maximum roughness Rz of 5 μm or less, the first principal surface of the first substrate is positioned on the side of the first crystal plane of the single crystal, and the third principal surface of the second substrate is positioned on the side of the second crystal plane of the single crystal.

2. The substrate set according to claim 1, wherein the first substrate and the second substrate are each composed of a material selected from a group III element oxide, a group III element nitride, silicon carbide, and indium phosphide.

3. The substrate set according to claim 1, wherein the first substrate and the second substrate are each composed of crystals having a hexagonal crystal structure.

4. The substrate set according to claim 1, wherein the first substrate and the second substrate are each composed of a compound containing a metal element, a metallic region containing the metal element is formed on the first main surface of the first substrate, and a metallic region containing the metal element is formed on the third main surface of the second substrate.

5. A single crystal substrate comprising a compound containing a metal element, having an upper surface and a lower surface facing each other, wherein the maximum roughness Rz of the upper surface is 5 μm or less, and a metallic region containing the metal element is formed on the upper surface.

6. A method for manufacturing a substrate set, comprising: preparing a base substrate having a first substrate layer, an intermediate layer, and a second substrate layer in that order, wherein the first substrate layer and the second substrate layer are made of the same type of single crystal; and irradiating the intermediate layer of the base substrate with laser light to decompose the intermediate layer and separate the first substrate layer and the second substrate layer to obtain a first substrate and a second substrate, wherein the maximum roughness Rz of the first main surface of the first substrate and the third main surface of the second substrate formed by decomposing the intermediate layer is 5 μm or less, respectively.

7. The method for manufacturing a substrate set according to claim 6, wherein the light absorption rate of the intermediate layer to the laser light is higher than the light absorption rate of the substrate layer to the laser light.

8. The method for manufacturing a substrate set according to claim 6, wherein the diameter of the laser beam to be irradiated is 50 μm or more.

9. The method for manufacturing a substrate set according to claim 6, wherein the first substrate layer and the second substrate layer are each composed of a material selected from a group III element oxide, a group III element nitride, silicon carbide, diamond, silicon, and indium phosphide.

10. A method for manufacturing a semiconductor device, comprising polishing the first main surface of a first substrate or the third main surface of a second substrate obtained by the method for manufacturing a substrate set according to claim 6, and forming a device layer on the polished main surface.

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