Method for manufacturing an aluminum nitride substrate, aluminum nitride substrate, and method for removing a strain layer introduced into an aluminum nitride substrate by laser processing

Abstract

The problem to be solved by the present invention is to provide a novel technique that can remove a strain layer introduced into an aluminum nitride substrate. In order to solve this problem, the present aluminum nitride substrate manufacturing method involves a strain layer removal step for removing a strain layer in an aluminum nitride substrate by heat treatment of the aluminum nitride substrate in a nitrogen atmosphere. In this way, the present invention can remove a strain layer that has been introduced into an aluminum nitride substrate.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an aluminum nitride substrate, an aluminum nitride substrate, and a method for removing a strained layer introduced into an aluminum nitride substrate by laser processing. [Background technology]

[0002] 2. Description of the Related Art In the manufacture of semiconductor substrates, a method of processing a semiconductor substrate by irradiating the semiconductor substrate with a laser has been conventionally employed.

[0003] Patent Document 1 discloses an invention in which a focus point of a laser beam having a wavelength absorbed by the workpiece is positioned on the upper surface of the workpiece, the laser beam is irradiated onto the workpiece, and ablation processing is performed to form a groove on the upper surface of the workpiece. Note that the invention described in Patent Document 1 can be understood as a method that can be applied to known semiconductor materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-305420 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-described method of irradiating a workpiece with a laser beam, distortion may be introduced into the semiconductor substrate, which is the workpiece, due to the irradiation. Since the distortion can cause dislocations in the semiconductor substrate, it is desirable to remove the distortion. The distortion may be introduced not only by laser beam irradiation but also by known semiconductor processes such as mechanical polishing.

[0006] For example, if dislocations occur in an aluminum nitride substrate, there is a risk that the dislocations will be inherited by a growth layer formed by epitaxial growth using the aluminum nitride substrate as a base substrate. Therefore, it is desirable to remove the above-mentioned distortions.

[0007] An object of the present invention is to provide a novel technique capable of removing a strained layer introduced into an aluminum nitride substrate. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a method for manufacturing an aluminum nitride substrate, which includes a strained layer removal step of removing a strained layer from the aluminum nitride substrate by heat treating the aluminum nitride substrate in a nitrogen atmosphere. In this way, the present invention can remove a strained layer introduced into an aluminum nitride substrate.

[0009] In a preferred embodiment of the present invention, the strained layer removal step involves heat treating the aluminum nitride substrate at a heating temperature of not more than 1900° C. In this manner, the present invention can remove the strained layer of an AlN substrate while suppressing the generation of Al droplets.

[0010] In a preferred embodiment of the present invention, the strained layer removal step comprises heat treating the aluminum nitride substrate under a nitrogen back pressure of 10 kPa or more. In this manner, the present invention can remove the strained layer of the AlN substrate while suppressing the generation of Al droplets.

[0011] In a preferred embodiment of the present invention, the method further includes a laser processing step of removing a portion of the aluminum nitride substrate by irradiating the aluminum nitride substrate with a laser. In this way, the present invention can remove the strained layer of the AlN substrate while suppressing the generation of Al droplets.

[0012] In a preferred embodiment of the present invention, the processing step is a step of forming through holes in the aluminum nitride substrate. As described above, the present invention can remove a strained layer in an aluminum nitride substrate used as a base substrate for epitaxial growth, thereby contributing to suppressing the introduction of dislocations during epitaxial growth. [Effects of the Invention]

[0013] The disclosed technology can provide a novel technology that can remove a strained layer introduced into an aluminum nitride substrate.

[0014] Other objects, features and advantages will become apparent from a reading of the following detailed description when taken in conjunction with the drawings and claims. [Brief explanation of the drawings]

[0015] [Figure 1] 1A to 1C are explanatory diagrams illustrating a method for manufacturing an AlN substrate according to an embodiment. [Figure 2] 10A to 10C are explanatory views illustrating a processing step and a strained layer removing step according to an embodiment. [Figure 3] 1 shows an observation image and Raman spectroscopy results of an AlN substrate according to Example 1. [Figure 4] 1 shows an observation image and Raman spectroscopy results of an AlN substrate according to Example 1. [Figure 5] 10 is an observation image of an AlN substrate heat-treated under heating condition 1 according to Example 2. [Figure 6] 10 is an observation image of an AlN substrate heat-treated under heating condition 2 according to Example 2. [Figure 7] 10 is an observation image of an AlN substrate heat-treated under heating condition 3 according to Example 2. [Figure 8] 10 is an observation image of an AlN substrate heat-treated under heating condition 4 according to Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the method for manufacturing an aluminum nitride substrate according to the present invention will be described in detail below with reference to the accompanying drawings.

[0017] The technical scope of the present invention is not limited to the embodiments shown in the accompanying drawings, and can be modified as appropriate within the scope of the claims.

[0018] The drawings attached to this specification are conceptual diagrams, and the relative dimensions of each component and the like do not limit the present invention.

[0019] For the purpose of explaining the invention, this specification may refer to the top or bottom based on the top and bottom of the drawings, but this does not limit the top or bottom in relation to the use mode of the aluminum nitride substrate of the present invention, etc.

[0020] In the following description of the embodiments and the accompanying drawings, the same components are denoted by the same reference numerals, and duplicated descriptions will be omitted.

[0021] <<Method for manufacturing aluminum nitride substrate>> 1 and 2 show steps in a method for manufacturing an aluminum nitride substrate (hereinafter simply referred to as an "AlN substrate") according to an embodiment of the present invention.

[0022] The method for manufacturing an AlN substrate according to the embodiment includes a strained layer removing step S12 in which the AlN substrate 10 is heat-treated to remove the strained layer 12 introduced into the AlN substrate 10 in the processing step S11.

[0023] The method for manufacturing an AlN substrate according to the embodiment may further include a processing step S11 in which laser processing is performed to remove a part of the AlN substrate 10 by irradiating the AlN substrate 10 with a laser L.

[0024] Furthermore, this embodiment can be understood as a method for removing the strained layer 12 introduced into the AlN substrate 10 by laser processing, which includes a strained layer removal step S12 in which the AlN substrate 10 is heat-treated after laser processing of the AlN substrate 10.

[0025] The AlN substrate 10 (corresponding to an AlN wafer) may be a single crystal AlN substrate, a polycrystalline AlN substrate, a wafer or substrate processed from a bulk crystal, a wafer or substrate including an epitaxially grown layer, or a square wafer.

[0026] There is no limitation on the crystal polytype of the AlN substrate 10. Furthermore, there is no limitation on the off direction or off angle of the AlN substrate 10.

[0027] There is no limit to the wafer size of the AlN substrate 10. There is no limit to the film thickness of the AlN substrate 10.

[0028] There is no limit to the doping concentration of the AlN substrate 10. There is no limit to the dopant element of the AlN substrate 10.

[0029] Each step of the embodiment will be described in detail below.

[0030] The processing step S11 is a step of performing laser processing to remove a part of the AlN substrate 10 by irradiating the AlN substrate 10 with a laser L.

[0031] In the description in this specification, "laser processing" refers to processing in which a laser beam having a wavelength that is absorbed by the AlN substrate 10, which is the object to be processed, is focused on the upper surface or inside the AlN substrate 10, and the laser beam is irradiated onto the AlN substrate 10, thereby forming a groove on the upper surface of the AlN substrate 10 or forming a damaged region inside the AlN substrate 10.

[0032] Laser processing refers to a technique for selectively processing a portion of an object by controlling the laser irradiation area (corresponding to the focal point) and focusing the light waves, which have energy equivalent to the bond energy of the material that makes up the object.

[0033] Furthermore, the processing step S11 is preferably a step of irradiating the AlN substrate 10 with a laser L having a wavelength of 532 nm.

[0034] The wavelength of the laser L is preferably 808 nm or less, preferably 650 nm or less, preferably 635 nm or less, preferably 589 nm or less, preferably 532 nm or less, preferably 473 nm or less, preferably 460 nm or less, preferably 445 nm or less, and preferably 405 nm or less.

[0035] Furthermore, the wavelength of the laser L is preferably 355 nm or more, preferably 405 nm or more, preferably 445 nm or more, preferably 460 nm or more, preferably 532 nm or more, preferably 589 nm or more, preferably 635 nm or more, and preferably 650 nm or more.

[0036] The wavelength of the laser L is, for example, a wavelength in a wavelength band classified as the visible light range.

[0037] Furthermore, the processing step S11 can be performed based on a known or conventional optical system.

[0038] In the processing step S11, a known light source can be used appropriately depending on the wavelength of the laser L, etc.

[0039] The laser L used in the processing step S11 is not limited in terms of its active medium, oscillation mode, repetition frequency, pulse width, beam spot diameter, output power, and polarization characteristics.

[0040] The optical system used in the processing step S11 suitably includes known or conventional mirrors, a scanner with a shaft rotation motor for alignment, a condenser lens, and a grating.

[0041] The condenser lens of the optical system used in the processing step S11 has no limitations on its magnification and numerical aperture (NA).

[0042] The processing step S11 is a step of forming through holes 11 in the AlN substrate 10.

[0043] Here, the processing step S11 can be understood as an embrittlement processing step in which the strength of the AlN substrate 10 is reduced by forming the through holes 11.

[0044] In the processing step S11, when forming the through-holes 11, the laser irradiation portion (corresponding to the focal point) is scanned in the film thickness direction of the AlN substrate 10.

[0045] The through holes 11 can have any shape (pattern) that reduces the strength of the AlN substrate 10.

[0046] Furthermore, it is desirable to set a shape (pattern) that will allow a desired growth layer to be obtained during epitaxial growth using the AlN substrate 10 as a base substrate.

[0047] At this time, in the processing step S11, the laser L is scanned within the surface of the AlN substrate 10 in accordance with the above-mentioned shape (pattern).

[0048] In this embodiment, it is desirable to adopt an optimum pattern depending on the physical properties (crystal orientation, etc.) of the AlN substrate 10 and the semiconductor material of the growth layer, and the growth method. There is no limitation on the width and depth of the shape (pattern).

[0049] The processing step S11 is a step of processing the surface of the AlN substrate 10 into a mesa shape.

[0050] The term "mesa shape" in the description of this specification corresponds to a concave-convex shape, and there is no limitation on the angle formed by the top wall and the side wall of the concave-convex shape.

[0051] Furthermore, there is no limit to the processing depth in processing step S11. When processing step S11 is a step of processing the surface of AlN substrate 10 into a mesa shape, processing step S11 forms recesses in the surface of AlN substrate 10 instead of through holes 11 described above.

[0052] In the processing step S11, the focus of the laser L is scanned from the surface (corresponding to the upper surface) of the AlN substrate 10 to the bottom surface (corresponding to the lower surface) to form the through-holes 11 or the protrusions.

[0053] The processing step S11 can appropriately employ at least a part of known techniques such as those described in, for example, Japanese Patent Application Laid-Open Nos. 10-305420, 2002-192370, and 2016-111147.

[0054] The processing step S11 in the embodiment of the present invention can be understood to correspond to a brittle processing step, for example.

[0055] The strained layer removing step S12 is a step of removing the strained layer 12 introduced into the AlN substrate 10 in the processing step S11 by heat treating the AlN substrate 10.

[0056] The strained layer 12 can be understood to correspond to a damaged layer, for example.

[0057] The strained layer removal step S12 can employ a means for etching the AlN substrate 10 by heat treating the AlN substrate 10. In this case, the strained layer removal step S12 can employ a known or commonly used heat treatment mechanism as appropriate.

[0058] Furthermore, in the strained layer removing step S12, any means capable of removing the strained layer 12 can naturally be employed.

[0059] The strained layer removal step S12 is a step of removing the strained layer 12 by thermal etching.

[0060] The strained layer removal step S12 is a step of etching the AlN substrate 10 in a nitrogen atmosphere (N2 atmosphere). Note that the "nitrogen atmosphere" in the description herein corresponds to the vapor pressure of gaseous species containing nitrogen.

[0061] The strained layer removing step S12 is, for example, a step of placing the AlN substrate 10 in the high-melting-point container and heat-treating the high-melting-point container containing the AlN substrate 10. In the heating environment of the AlN substrate 10, generated gas is appropriately exhausted.

[0062] The thickness of the strained layer 12 removed in the strained layer removal step S12 can be set as appropriate. In this case, it can be understood that the strained layer removal step S12 achieves a desired etching rate by adjusting various parameters such as the heating temperature and the nitrogen back pressure.

[0063] The heating temperature of the AlN substrate 10 in the strained layer removing step S12 is preferably 2000°C or less, more preferably 1900°C or less, more preferably 1800°C or less, and more preferably 1700°C or less.

[0064] The heating temperature is preferably 1400°C or higher, more preferably 1500°C or higher, and even more preferably 1600°C or higher.

[0065] The nitrogen back pressure in the heat treatment of the AlN substrate 10 in the strained layer removal step S12 is preferably 10 2 kPa or less, and preferably 90 kPa or less, and preferably 70 kPa or less, and preferably 50 kPa or less, and preferably 20 kPa or less, and preferably 10 kPa or less, and preferably 1 kPa or less, and preferably 10 2 Pa or less, and preferably 10 Pa or less, and preferably 1 Pa or less, and preferably 10 -1 Pa or less, and preferably 10 -2 Pa or less.

[0066] The nitrogen back pressure is preferably 10 -3 Pa or more, and preferably 10 -2 Pa or more, and preferably 10 -1 Pa or more, and preferably 10 Pa or more, and preferably 10 2Pa or more, and preferably 1 kPa or more, and preferably 10 kPa or more, and preferably 20 kPa or more, and preferably 50 kPa or more, and preferably 70 kPa or more, and preferably 90 kPa or more.

[0067] According to the present invention, by including the strained layer removing step S12 of heat-treating the AlN substrate 10, the strained layer 12 introduced into the AlN substrate 10 by laser processing can be removed.

[0068] According to the embodiment of the present invention, the AlN substrate 10 from which the strained layer 12 has been removed can be used as a base substrate for epitaxial growth of semiconductor materials such as silicon carbide (SiC) and AlN.

[0069] Example 1 The present invention will be explained more specifically with reference to Example 1.

[0070] (AlN substrate 10) Semiconductor material: AlN Board size: 10mm wide x 10mm long x 524μm thick

[0071] (Processing process S11) The processing step S11 according to the embodiment is a step of irradiating the AlN substrate 10 with a laser L to form the through-holes 11.

[0072] (Laser processing conditions) Wavelength: 532nm Output power: 3W / cm 2 Spot diameter: 40 μm

[0073] (Heating conditions) The AlN substrate 10 arranged under the above conditions was subjected to a heat treatment under the following conditions. Heating temperature: 1800℃ Heating time: 10min Etching amount: 10 μm Nitrogen back pressure: 30kPa In the strained layer removing step S12, the temperature gradient is appropriately set to achieve the following etching amount.

[0074] FIG. 3 shows a cross-sectional optical microscope image and a Raman spectroscopic mapping image of the AlN substrate 10 after the processing step S11.

[0075] FIG. 4 shows a cross-sectional optical microscope image and a Raman spectroscopic mapping image of the AlN substrate 10 that has undergone the processing step S11 and the strained layer removing step S12.

[0076] 3 and 4 respectively show AlN surfaces 1000 and 1001. Note that Fig. 4 shows that AlN surface 1001 is formed by etching AlN surface 1000 in strained layer removal step S12.

[0077] The "Raman spectroscopic mapping image" here refers to the E2 high peak (~660 cm -1 The full width at half maximum (FWHM) mapping results are shown.

[0078] 3 and 4, it can be seen that the strained layer 12 (corresponding to the region with large FWHM and poor crystallinity near the AlN surface 1000) that occurs near the recesses on the AlN surface 1000 in the processing step S11 is removed by the strained layer removal step S12.

[0079] Example 2 The present invention will be explained more specifically with reference to Example 2.

[0080] (AlN substrate 10) Semiconductor material: AlN Board size: 10mm wide x 10mm long x 524μm thick

[0081] The Al surface (0001) of the AlN substrate 10 arranged under the above-mentioned conditions was heat-treated under the following conditions in the strained layer removing step S12.

[0082] (Heating condition 1) Heating temperature: 1900℃ Heating time: 10min Nitrogen back pressure: 90kPa

[0083] (Heating condition 2) Heating temperature: 1700℃ Heating time: 10min Nitrogen back pressure: 10kPa

[0084] (Heating condition 3) Heating temperature: 1700℃ Heating time: 10min Nitrogen back pressure: 90kPa

[0085] (Heating condition 4) Heating temperature: 1800℃ Heating time: 10min Nitrogen back pressure: 10kPa

[0086] Fig. 5 shows an SEM image of the AlN substrate 10 thermally etched under heating condition 1. From Fig. 5, it can be seen that the formation of Al droplets due to nitrogen desorption was suppressed on the surface of the AlN substrate 10 thermally etched under heating condition 1.

[0087] Fig. 6 shows an SEM image of the AlN substrate 10 that was thermally etched under heating condition 2. From Fig. 6, it can be seen that the formation of Al droplets was suppressed on the surface of the AlN substrate 10 that was thermally etched under heating condition 2.

[0088] Fig. 7 shows an SEM image of the AlN substrate 10 thermally etched under heating condition 3. From Fig. 7, it can be seen that the formation of Al droplets was suppressed on the surface of the AlN substrate 10 thermally etched under heating condition 3.

[0089] Fig. 8 shows an SEM image of the AlN substrate 10 thermally etched under heating condition 4. From Fig. 8, it can be seen that more Al droplets were formed on the surface of the AlN substrate 10 thermally etched under heating condition 4 than under the other heating conditions 1 to 3.

[0090] 5, 6, 7, and 8, it can be seen that the formation of Al droplets during thermal etching of an AlN substrate 10 in a nitrogen atmosphere can be suppressed by using a low heating temperature and / or a high nitrogen back pressure.

[0091] It can be understood that the formation of Al droplets on the AlN substrate 10 according to the embodiment of the present invention, for example, hinders the improvement of the quality of the grown layer in epitaxial growth on the AlN substrate.

[0092] According to the present invention, it is possible to remove the strain layer introduced into the aluminum nitride substrate during the pattern formation process by processing.

[0093] This reduces the density of defects such as dislocations near the top wall and side wall of the pattern, and suppresses the inheritance of defects such as dislocations during crystal growth (equivalent to epitaxial growth) in which the growth surface progresses from the top wall and / or side wall.

[0094] 10 AlN substrate 11 Through hole 12 Strain layer 30 Crucible 31 Raw material transportation space 40 Semiconductor Materials 50 SiC container 60 TaC container S11 Processing process S12 Strained layer removal process

Claims

1. a strained layer removal step of removing a strained layer from the aluminum nitride substrate by heat treating the aluminum nitride substrate in a nitrogen atmosphere, the strained layer removing step is a step of thermally etching the aluminum nitride substrate; the heating temperature of the aluminum nitride substrate in the strained layer removal step is 1700°C or less, and the nitrogen back pressure is 1 kPa or more; Alternatively, in the method for producing an aluminum nitride substrate, the nitrogen back pressure on the aluminum nitride substrate in the strained layer removing step is 20 kPa or more.

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

3. The method for manufacturing an aluminum nitride substrate according to claim 2 , wherein the processing step is a step of forming a through hole in the aluminum nitride substrate.

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