Methods for manufacturing aluminum nitride substrates, aluminum nitride substrates, and methods for removing strain layers introduced into aluminum nitride substrates by laser processing.

Abstract

The problem this invention aims to solve is to provide a novel technique for removing strain layers introduced into aluminum nitride substrates. This invention is a method for manufacturing an aluminum nitride substrate, comprising a strain layer removal step that removes the strain layer of the aluminum nitride substrate by heat treatment under a nitrogen atmosphere. Thus, this invention can remove the strain layer introduced into the aluminum nitride substrate.

Description

Technical Field

[0001] This invention relates to a method for manufacturing an aluminum nitride substrate, an aluminum nitride substrate, and a method for removing a strain layer introduced into an aluminum nitride substrate by laser processing. Background Technology

[0002] Previously, semiconductor substrates were manufactured by irradiating them with lasers.

[0003] Patent Document 1 discloses an invention in which a laser beam of a wavelength that absorbs light from the workpiece is focused onto the upper surface of the workpiece, and the workpiece is irradiated with the laser beam to perform an ablation process, thereby forming a groove on the upper surface of the workpiece. Furthermore, it can be understood that the invention described in Patent Document 1 is a method applicable to known semiconductor materials.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 10-305420 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Furthermore, in the aforementioned method of irradiating the workpiece with a laser beam, the irradiation introduces strain into the semiconductor substrate, which is the workpiece. Since strain is a major cause of dislocation generation in the semiconductor substrate, it is desirable to remove it. The main cause of this strain introduction is estimated to be not limited to laser beam irradiation, but also includes known semiconductor processes such as mechanical polishing.

[0009] For example, when dislocations are generated in an aluminum nitride substrate, these dislocations may continue in a growth layer formed by epitaxial growth using the aluminum nitride substrate as the base substrate. Therefore, it is desirable to remove the aforementioned strain.

[0010] The problem to be solved by the present invention is to provide a novel technique for removing strain layers introduced into aluminum nitride substrates.

[0011] Problem-solving methods

[0012] To address the aforementioned problems, the present invention provides a method for manufacturing an aluminum nitride substrate, comprising a strain layer removal step of removing the strain layer of the aluminum nitride substrate by heat treatment under a nitrogen atmosphere. Thus, the present invention can remove the strain layer introduced into the aluminum nitride substrate.

[0013] In a preferred embodiment of the invention, the strain layer removal step involves heat-treating the aluminum nitride substrate at a heating temperature below 1900°C. This allows the present invention to remove the strain layer from the AlN substrate while suppressing Al droplet formation.

[0014] In a preferred embodiment of the present invention, the strain layer removal step involves heat-treating the aluminum nitride substrate under a nitrogen back pressure of 10 kPa or higher. This allows the present invention to remove the strain layer from the AlN substrate while suppressing Al droplet formation.

[0015] In a preferred embodiment of the invention, a processing step is further included: performing laser processing to remove a portion of the aluminum nitride substrate by irradiating the aluminum nitride substrate with a laser. Thus, the present invention can remove the strain layer of the AlN substrate while suppressing the formation of Al droplets.

[0016] In a preferred embodiment of the invention, the processing step forms through-holes on the aluminum nitride substrate. Thus, the invention helps to suppress dislocation introduction during epitaxial growth because it removes the strain layer of the aluminum nitride substrate that serves as the base for epitaxial growth.

[0017] The effects of the invention

[0018] According to the disclosed technology, a novel technique can be provided to remove the strain layer introduced into an aluminum nitride substrate.

[0019] Other issues, features, and advantages will become apparent from reading the embodiments of the invention described below, in conjunction with the accompanying drawings and claims. Attached Figure Description

[0020] Figure 1 This is an explanatory diagram illustrating a method for manufacturing an AlN substrate according to an embodiment.

[0021] Figure 2 This is an explanatory diagram illustrating the processing steps and strain layer removal steps according to the implementation method.

[0022] Figure 3 The observed images and Raman spectroscopic measurements of the AlN substrate according to Example 1 are shown.

[0023] Figure 4 The observed images and Raman spectroscopic measurements of the AlN substrate according to Example 1 are shown.

[0024] Figure 5 An observation image of an AlN substrate heat-treated under heating condition 1 according to Example 2 is shown.

[0025] Figure 6An observation image of an AlN substrate heat-treated under heating condition 2 according to Example 2 is shown.

[0026] Figure 7 An observation image of an AlN substrate heat-treated under heating condition 3 according to Example 2 is shown.

[0027] Figure 8 An observation image of an AlN substrate heat-treated under heating condition 4 according to Example 2 is shown. Detailed Implementation

[0028] The preferred embodiments of the aluminum nitride substrate manufacturing method according to the present invention are described below with reference to the accompanying drawings.

[0029] The technical scope of this invention is not limited to the embodiments shown in the accompanying drawings, and can be appropriately modified within the scope of the claims.

[0030] The accompanying drawings in this specification are conceptual diagrams, and the relative dimensions of the components do not limit the invention.

[0031] In this specification, the terms "up" or "down" may be used to refer to the upper or lower parts of the drawings for the purpose of illustrating the present invention, but the upper or lower parts are not limited in relation to the use of the aluminum nitride substrate of the present invention.

[0032] Furthermore, in the following description and accompanying drawings of the embodiments, the same reference numerals are used for the same structures, and repeated descriptions are omitted.

[0033] Manufacturing Method of Aluminum Nitride Substrates

[0034] Figure 1 and Figure 2 The steps of a method for manufacturing an aluminum nitride substrate (hereinafter referred to as "AlN substrate") according to an embodiment of the present invention are shown.

[0035] The method for manufacturing an AlN substrate according to an embodiment includes a strain layer removal step S12, which removes the strain layer 12 introduced into the AlN substrate 10 through processing step S11 by heat treatment of the AlN substrate 10.

[0036] Furthermore, the AlN substrate manufacturing method according to the embodiment may also include a processing step S11 of performing laser processing to remove a portion of the AlN substrate 10 by irradiating the AlN substrate 10 with laser L.

[0037] Furthermore, this embodiment can be understood as a method for removing the strain layer 12 introduced into the AlN substrate 10 by laser processing, including a strain layer removal step S12 of heat treatment of the AlN substrate 10 after laser processing.

[0038] The AlN substrate 10 (equivalent to an AlN wafer) can be a single-crystal AlN substrate, a polycrystalline AlN substrate, a wafer or substrate processed from bulk crystals, a wafer or substrate including an epitaxial growth layer, or a square wafer.

[0039] The crystal polymorphism of the AlN substrate 10 is not restricted. Furthermore, the deviation direction or deviation angle of the AlN substrate 10 is not restricted.

[0040] Furthermore, the wafer size of the AlN substrate 10 is not limited. Additionally, the film thickness of the AlN substrate 10 is not limited.

[0041] Furthermore, the doping concentration of the AlN substrate 10 is not limited. Additionally, the doping elements of the AlN substrate 10 are not limited.

[0042] The following is a detailed description of each step of the implementation method.

[0043] Processing step S11 is a step of performing laser processing to remove a portion of the AlN substrate 10 by irradiating the AlN substrate 10 with laser L.

[0044] In this specification, "laser processing" refers to a process in which a groove is formed on the upper surface of the AlN substrate 10 or a damaged area is formed inside the AlN substrate 10 by focusing a laser beam of a wavelength that is absorbent to the AlN substrate 10 on the upper surface or inside the AlN substrate 10 and irradiating the AlN substrate 10 with the laser beam.

[0045] In addition, laser processing refers to a method in which a portion of the object is selectively processed by irradiating and focusing a light wave with the same energy as the binding energy in the material constituting the object while controlling the laser irradiation part (equivalent to the focal point).

[0046] Furthermore, processing step S11 is preferably a step of irradiating the AlN substrate 10 with a laser L having a wavelength of 532 nm.

[0047] The wavelength of the laser L is preferably below 808nm, preferably below 650nm, more preferably below 635nm, more preferably below 589nm, more preferably below 532nm, more preferably below 473nm, more preferably below 460nm, more preferably below 445nm, and more preferably below 405nm.

[0048] Furthermore, the wavelength of the laser L is preferably 355nm or higher, more preferably 405nm or higher, more preferably 445nm or higher, more preferably 460nm or higher, more preferably 532nm or higher, more preferably 589nm or higher, more preferably 635nm or higher, and more preferably 650nm or higher.

[0049] The wavelength of laser L is, for example, a wavelength within the wavelength band classified as the visible light range.

[0050] Furthermore, the processing step S11 can be implemented based on a known or commonly used optical system.

[0051] Processing step S11 can appropriately use a known light source, such as the wavelength of the laser L.

[0052] The laser L used in processing step S11 has no restrictions on its active medium, oscillation mode, repetition frequency, pulse width, beam diameter, output power, and polarization characteristics.

[0053] The optical system used in processing step S11 appropriately includes known or commonly used mirrors, a scanner equipped with an axis rotary motor for alignment, a condenser lens, and a grating.

[0054] The magnification and numerical aperture (NA) of the condenser lens of the optical system used in processing step S11 are not limited.

[0055] In addition, processing step S11 is the step of forming a through hole 11 on the AlN substrate 10.

[0056] Here, processing step S11 can be understood as an embrittlement process that reduces the strength of the AlN substrate 10 by forming through holes 11.

[0057] In addition, during the formation of the through hole 11, the laser irradiation portion (equivalent to the focusing point) is scanned in the film thickness direction of the AlN substrate 10 in the processing step S11.

[0058] The through-hole 11 can be any shape (pattern) that can reduce the strength of the AlN substrate 10.

[0059] Furthermore, it is desirable to set the desired shape (pattern) of the growth layer in epitaxial growth using AlN substrate 10 as the substrate.

[0060] At this point, in processing step S11, the interior of the AlN substrate 10 is scanned with laser L according to the shape (pattern) described above.

[0061] Furthermore, it is desirable that the implementation employs an optimal pattern based on the physical properties (crystal orientation, etc.) of the AlN substrate 10 or the semiconductor material of the growth layer, or the growth method. Additionally, the width and depth of the shape (pattern) are not limited.

[0062] In addition, processing step S11 is a step of processing the surface of AlN substrate 10 into a mesa shape.

[0063] In this specification, "table-shaped" is equivalent to a concave-convex shape, and the angle between the upper wall and the side wall in such a concave-convex shape is not limited.

[0064] Furthermore, the processing depth in processing step S11 is not limited. In addition, when processing step S11 is to process the surface of AlN substrate 10 into a mesa shape, processing step S11 forms a recess on the surface of AlN substrate 10 instead of the aforementioned through hole 11.

[0065] In addition, the processing step S11 forms a through hole 11 or a protrusion by scanning the focal point of the laser L from the surface (corresponding to the upper surface) of the AlN substrate 10 to the bottom surface (corresponding to the lower surface).

[0066] Furthermore, the processing step S11 may employ at least a portion of known technologies, such as those described in Japanese Patent Application Publication No. 10-305420, Japanese Patent Application Publication No. 2002-192370, and Japanese Patent Application Publication No. 2016-111147.

[0067] It can be understood that processing step S11 in the embodiments of the present invention is, for example, equivalent to the embrittlement processing step.

[0068] The strain layer removal step S12 is a step of removing the strain layer 12 introduced into the AlN substrate 10 through processing step S11 by heat treatment of the AlN substrate 10.

[0069] In addition, the strain layer 12 can be understood as being equivalent to the damage layer, for example.

[0070] The strain layer removal step S12 can be performed by etching the AlN substrate 10 through heat treatment. In this case, a known or commonly used heat treatment mechanism can be appropriately employed for the strain layer removal step S12.

[0071] Furthermore, any means that can remove the strain layer 12 can be used as the strain layer removal step S12.

[0072] Furthermore, the strain layer removal step S12 is a step of removing the strain layer 12 by thermal etching.

[0073] Furthermore, the strain layer removal step S12 is a step of etching the AlN substrate 10 under a nitrogen atmosphere (N2 atmosphere). Additionally, "nitrogen atmosphere" in this specification refers to the vapor pressure of a gaseous species containing nitrogen.

[0074] Furthermore, the strain layer removal step S12 is, for example, a step of placing the AlN substrate 10 inside the aforementioned high-melting-point container and heat-treating the high-melting-point container including the AlN substrate 10. Additionally, in the heated environment of the AlN substrate 10, the generated gases are appropriately vented.

[0075] Furthermore, the thickness of the strain layer 12 removed in the strain layer removal step S12 can be appropriately set. In this case, it can be understood that the strain layer removal step S12 achieves the desired etching rate by adjusting various parameters such as heating temperature and nitrogen back pressure.

[0076] The heating temperature of the AlN substrate 10 in the strain layer removal step S12 is preferably below 2000°C, more preferably below 1900°C, more preferably below 1800°C, and even more preferably below 1700°C.

[0077] Furthermore, the heating temperature is preferably 1400°C or higher, more preferably 1500°C or higher, and even more preferably 1600°C or higher.

[0078] The nitrogen back pressure during the heat treatment of the AlN substrate 10 in the strain layer removal step S12 is preferably 10. 2 Below kPa, more preferably below 90 kPa, more preferably below 70 kPa, more preferably below 50 kPa, more preferably below 20 kPa, more preferably below 10 kPa, more preferably below 1 kPa, more preferably below 102 kPa, more preferably below 10 kPa, more preferably below 1 kPa, more preferably below 10 kPa, more preferably below 10 kPa, more preferably below 10 kPa, more preferably below 10 kPa -1 Pa or less, more preferably 10 Pa -2 Below Pa.

[0079] Furthermore, the nitrogen back pressure is preferably 10. -3 Pa or higher, more preferably 10 Pa -2 Pa or higher, more preferably 10 Pa -1 Pa or higher, more preferably 10 Pa or higher, even more preferably 10 Pa 2 Pa or higher, more preferably 1 kPa or higher, more preferably 10 kPa or higher, more preferably 20 kPa or higher, more preferably 50 kPa or higher, more preferably 70 kPa or higher, and more preferably 90 kPa or higher.

[0080] According to the present invention, the strain layer 12 introduced into the AlN substrate 10 by laser processing can be removed by including a strain layer removal step S12 that involves heat treatment of the AlN substrate 10.

[0081] Furthermore, according to an embodiment of the present invention, the AlN substrate 10 with the strain layer 12 removed is, for example, a substrate substrate for the epitaxial growth of semiconductor materials such as silicon carbide (SiC) and AlN.

[0082] Example 1

[0083] The present invention will be described in more detail by way of example 1.

[0084] (AlN substrate 10)

[0085] Semiconductor material: AlN

[0086] Substrate dimensions: 10mm wide × 10mm deep × 524μm thick

[0087] (Processing step S11)

[0088] According to the embodiment, processing step S11 is the step of irradiating the AlN substrate 10 with a laser to form a through hole 11.

[0089] (Laser processing conditions)

[0090] Wavelength: 532nm

[0091] Output power: 3W / cm 2

[0092] Spot diameter: 40μm

[0093] (Heating conditions)

[0094] The AlN substrate 10 configured under the above conditions will be subjected to heat treatment under the following conditions.

[0095] Heating temperature: 1800℃

[0096] Heating time: 10 min

[0097] Etching depth: 10μm

[0098] Nitrogen back pressure: 30 kPa

[0099] In addition, the strain layer removal step S12 appropriately sets the temperature gradient to achieve the following etching amount.

[0100] Figure 3 Cross-sectional optical microscope images and Raman spectrophotometric images of the AlN substrate 10 after processing step S11 are shown.

[0101] Figure 4 Cross-sectional optical microscope images and Raman spectrophotometric images of the AlN substrate 10 after processing step S11 and strain layer removal step S12 are shown.

[0102] Figure 3 and Figure 4 AlN surfaces 1000 and 1001 are shown respectively. Additionally, Figure 4 The process of etching AlN surface 1000 and forming AlN surface 1001 by removing the strain layer in step S12 is shown.

[0103] Additionally, the "Raman spectrophotometric image" here refers to the peak value at E2 (equivalent to ~660 cm⁻¹). -1 The mapping result of the full width at half maximum (FWHM) when ).

[0104] according to Figure 3 and Figure 4 This can be understood as the strain layer 12 (equivalent to the region with large FWHM and poor crystallinity near the AlN surface 1000) generated in the processing step S11 is removed by the strain layer removal step S12.

[0105] Example 2

[0106] Example 2 is provided to illustrate the present invention in more detail.

[0107] (AlN substrate 10)

[0108] Semiconductor material: AlN

[0109] Substrate dimensions: 10mm wide × 10mm long × 524μm thick

[0110] The Al surface (0001) of the AlN substrate 10 configured under the above conditions is subjected to heat treatment under the following conditions in the strain layer removal step S12.

[0111] (Heating condition 1)

[0112] Heating temperature: 1900℃

[0113] Heating time: 10 min

[0114] Nitrogen back pressure: 90 kPa

[0115] (Heating condition 2)

[0116] Heating temperature: 1700℃

[0117] Heating time: 10 min

[0118] Nitrogen back pressure: 10 kPa

[0119] (Heating condition 3)

[0120] Heating temperature: 1700℃

[0121] Heating time: 10 min

[0122] Nitrogen back pressure: 90 kPa

[0123] (Heating condition 4)

[0124] Heating temperature: 1800℃

[0125] Heating time: 10 min

[0126] Nitrogen back pressure: 10 kPa

[0127] Figure 5 SEM images of the AlN substrate 10 thermally etched under heating condition 1 are shown. According to... Figure 5 This can be understood as suppressing the formation of Al droplets accompanying nitrogen detachment on the surface of the AlN substrate 10, which is thermally etched under heating condition 1.

[0128] Figure 6 SEM images of the AlN substrate 10 thermally etched under heating condition 2 are shown. According to... Figure 6 This can be understood as suppressing the formation of Al droplets on the surface of the AlN substrate 10 that is thermally etched under heating condition 2.

[0129] Figure 7 SEM images of the AlN substrate 10 thermally etched under heating condition 3 are shown. According to... Figure 7 This can be understood as suppressing the formation of Al droplets on the surface of the AlN substrate 10 that is thermally etched under heating condition 3.

[0130] Figure 8 SEM images of the AlN substrate 10 thermally etched under heating condition 4 are shown. According to... Figure 8 This can be understood as Al forming more Al droplets on the surface of the AlN substrate 10 under heating condition 4 than under other heating conditions 1 to 3.

[0131] according to Figure 5 , Figure 6 , Figure 7 and Figure 8 It is understandable that the formation of Al droplets during thermal etching of AlN substrate 10 under a nitrogen atmosphere can be suppressed by low heating temperature and / or high nitrogen back pressure.

[0132] Furthermore, it can be understood that the formation of Al microdroplets on the AlN substrate 10 according to the embodiments of the present invention, for example, hinders the improvement of the quality of the growth layer in the epitaxial growth on the AlN substrate.

[0133] According to the present invention, the strain layer introduced into the aluminum nitride substrate during the patterning process can be removed.

[0134] This reduces the density of defects such as dislocations near the top and sidewalls of the pattern and suppresses the continuation of defects such as dislocations during crystal growth (equivalent to epitaxial growth) from the top and / or sidewalls of the growth surface.

[0135] Explanation of reference numerals in the attached figures

[0136] 10 AlN substrate

[0137] 11 Through Holes

[0138] 12 Strain Layer

[0139] 30 crucibles

[0140] 31 Raw material conveying space

[0141] 40 Semiconductor Materials

[0142] 50 SiC container

[0143] 60 TaC container

[0144] S11 Processing Steps

[0145] S12 Strain Layer Removal Steps

Claims

1. A method for manufacturing an aluminum nitride substrate, comprising a strain layer removing step of removing a strain layer of an aluminum nitride substrate by heat etching the aluminum nitride substrate under a nitrogen atmosphere, the heating temperature of the aluminum nitride substrate in the strain layer removing step is 1400°C or higher, and the heating temperature of the aluminum nitride substrate is 1700°C or lower and / or the nitrogen back pressure is 20 kPa or higher.

2. The method of producing an aluminum nitride substrate according to claim 1, wherein, the strain layer removing step heat-treats the aluminum nitride substrate under a heating temperature of 1900°C or lower.

3. The method of producing an aluminum nitride substrate according to claim 1 or 2, wherein, the strain layer removing step heat-treats the aluminum nitride substrate under a nitrogen back pressure of 10 kPa or higher.

4. The method for manufacturing an aluminum nitride substrate according to claim 1 or 2, further comprising a processing step of performing laser processing to remove a portion of the aluminum nitride substrate by irradiating laser light to the aluminum nitride substrate.

5. The method of producing an aluminum nitride substrate according to claim 4, wherein, the processing step forms a through-hole on the aluminum nitride substrate.

6. An aluminum nitride substrate manufactured by the method for manufacturing an aluminum nitride substrate according to any one of claims 1 to 5.

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