JP2015224145A - Sapphire substrate and production method of sapphire substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sapphire substrate capable of suppressing generation of a crack caused by a temperature gradient in the sapphire substrate.SOLUTION: There is provided a sapphire substrate having a main surface, a rear surface facing to the main surface, and an end surface, and provided with chamfered parts between the main surface and the end surface, and between the rear surface and the end surface, to which a heat treatment is applied so that the end surface and at least a part of the surface of the chamfered parts are melted.

Description

  The present invention relates to a sapphire substrate and a method for manufacturing a sapphire substrate.

  Sapphire substrates are attracting attention because of their excellent mechanical and thermal properties, chemical stability, etc. In recent years, they have been used as substrates for growing GaN-based thin film elements such as GaN used for blue and white light-emitting diodes. It is supposed to be.

  The sapphire substrate has a disk shape, and has a main surface for epitaxially growing a GaN-based thin film element such as GaN, a back surface facing the main surface, and an end surface positioned between the main surface and the back surface, As for the main surface, a mirror-polished surface is often used.

  Conventionally, since a sapphire substrate has higher hardness than a silicon substrate or the like, an end surface portion is not subjected to edge processing (chamfering processing), and a sapphire substrate having an end surface substantially perpendicular to the main surface has been used. .

  However, when a GaN-based semiconductor layer is grown on a sapphire substrate not subjected to edge processing by a vapor phase growth method such as MOCVD, the flow of the source gas is disturbed in the vicinity of the edge. For this reason, abnormal growth occurs in this portion, and as a result, there is a problem that a convex portion higher than the central flat portion is formed in the GaN-based semiconductor layer in the vicinity of the edge. Thus, for example, Patent Document 1 discloses a sapphire substrate in which the edge of the crystal growth surface is chamfered. Recently, a sapphire substrate that is chamfered between a main surface and a back surface and an end surface is mainly used.

JP 2000-331940 A

  As described above, the sapphire substrate cut out from the ingot into a disk shape and subjected to mirror polishing of the main surface, chamfering of the end surface, etc., is subjected to various processes to form a GaN-based thin film element on the main surface. To be served.

  However, when a large temperature gradient is generated in the sapphire substrate during various processing steps for forming a GaN-based thin film element or the like, the sapphire substrate may break. When the sapphire substrate is cracked in this way, the sapphire substrate subjected to the treatment cannot be used for the product and needs to be discarded, so that the yield of the product is lowered.

  Then, in view of the problem which the said prior art has, this invention aims at providing the sapphire substrate which suppressed generation | occurrence | production of the crack by the temperature gradient in a sapphire substrate.

In order to solve the above problems, the present invention has a main surface, a back surface facing the main surface, and an end surface.
A chamfer is provided between the main surface and the end surface, and between the back surface and the end surface,
Provided is a sapphire substrate that has been heat-treated so that at least a part of the end face and the surface of the chamfered portion are melted.

  ADVANTAGE OF THE INVENTION According to this invention, the sapphire substrate which suppressed generation | occurrence | production of the crack by the temperature gradient in a sapphire substrate can be provided.

Sectional drawing of the sapphire substrate which concerns on embodiment of this invention. The flowchart of the manufacturing method of the sapphire substrate which concerns on embodiment of this invention. The stereoscopic microscope photograph of the end surface before and behind heat processing in Example 1 of the present invention. Explanatory drawing of the evaluation method in an Example and a comparative example.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.
(Sapphire substrate)
A configuration example of the sapphire substrate of this embodiment will be described.

  The sapphire substrate of the present embodiment has a main surface, a back surface opposite to the main surface, and an end surface, and a chamfered portion is provided between the main surface and the end surface and between the back surface and the end surface. It can be. And it can heat-process so that at least one part of the end surface and the surface of a chamfer part may fuse | melt.

  In various processing steps for forming a GaN-based thin film element or the like as described above, for example, a part of the sapphire substrate is heated, or the heated sapphire substrate is in contact with a jig having a low temperature, so that a large temperature gradient is generated in the substrate. This has caused a problem that the sapphire substrate may break. When the inventors of the present invention examined the cause of cracking when a large temperature gradient occurs in the sapphire substrate, the chamfered part of the sapphire substrate and the wrinkles at the end surface part started as a starting point, and cracks occurred. I found out. Therefore, in the sapphire substrate of the present embodiment, wrinkles are reduced and removed by performing heat treatment so that at least a part of the surface of the end face and the chamfered portion of the sapphire substrate is melted. For this reason, it became possible to provide the sapphire substrate which suppressed generation | occurrence | production of the crack by the temperature gradient in a sapphire substrate.

  First, the sapphire substrate of this embodiment will be described with reference to FIG. FIG. 1 is a sectional view taken along a plane perpendicular to the main surface passing through the central axis of the sapphire substrate 10.

  As shown in FIG. 1, the sapphire substrate 10 of the present embodiment has a main surface 11 and a back surface 12 that faces the main surface 11. An end face 13 is provided, and a chamfered portion 14 </ b> A is provided between the main surface 11 and the end face 13. Further, a chamfer 14 </ b> B is provided between the back surface 12 and the end surface 13.

  The main surface 11 is a surface for epitaxially growing a GaN-based thin film element such as GaN, and is preferably mirror-polished. The surface roughness (arithmetic average roughness) Ra of the main surface 11 is not particularly limited, and can be arbitrarily selected according to the use etc., but the surface roughness Ra of the main surface 11 is, for example, 0.30 nm. Or less, and more preferably 0.15 nm or less. The surface roughness Ra is defined in JIS B 0601 and can be evaluated by a stylus method or an optical method, for example.

  The back surface 12 is a surface at a position facing the main surface 11 as shown in FIG. 1, and can be processed into, for example, satin so as to be distinguishable from the main surface 11. The back surface 12 can be processed into a satin finish, for example, by sandblasting or single-side polishing using loose abrasive grains. Note that the back surface 12 may be mirror-polished similarly to the main surface 11 without using the back surface 12 as a matte surface.

  The end surface 13 is an outer peripheral end surface (side surface) of the sapphire substrate 10 disposed between the main surface 11 and the back surface 12 and can be a surface substantially perpendicular to the main surface 11 and the back surface 12.

  The chamfered portion 14 </ b> A and the chamfered portion 14 </ b> B are disposed between the main surface 11 and the back surface 12 and the end surface 13.

  In FIG. 1, the cross sections of the chamfered portions 14A and 14B are linear. That is, the chamfered portions 14A and 14B are formed by taper processing, and are inclined surfaces. However, the shape of the chamfered portions 14A and 14B is not limited to such a form. The chamfered portions 14A and 14B may be formed by rounded chamfering, for example, to have a rounded curved shape. In this case, the cross sections of the chamfered portions 14A and 14B are curved.

  And in the sapphire substrate 10 of this embodiment, it can heat-process so that at least one part of the surface may melt | dissolve about the end surface 13 and chamfering part 14A, 14B.

  By performing heat treatment so that at least a part of the surface of the end surface 13 and the chamfered portions 14A and 14B is melted, wrinkles can be reduced and removed from the end surface 13 and the chamfered portions 14A and 14B.

  Thus, in the sapphire substrate 10 of this embodiment, since wrinkles are reduced and removed from the end face 13 and the chamfered portions 14A and 14B, even when a temperature gradient occurs in the sapphire substrate 10, the sapphire substrate 10 It can suppress that a crack arises.

  The sapphire substrate 10 may be provided with notches and orientation flats (not shown) indicating a specific surface direction. The notch is a notch provided in the end face of the sapphire substrate, and has, for example, a V-shaped narrow shape. And the notch surface also contains wrinkles, and when a temperature gradient occurs in the sapphire substrate, cracks may occur from the notch portion. However, in the sapphire substrate of the present embodiment, heat treatment is performed so that at least a part of the surface of the end face 13 and the chamfered portions 14A and 14B is melted by the heat treatment. Can be removed. For this reason, it can also suppress that a crack arises in the sapphire substrate 10 from the wrinkle contained in a notch part.

  The conditions for the heat treatment are not particularly limited, and the conditions can be arbitrarily selected so that at least a part of the end face 13 and the chamfered portions 14A and 14B are melted. The heat treatment is performed so that at least a part of the end face 13 and the chamfered portions 14A and 14B are melted. At least a part of the end face 13 and the chamfered parts 14A and 14B is melted by the heat treatment, and the melted surface is solidified again. This is because the surface layer of the ridge is closed like a scab and cannot become the starting point of cracking. However, the heat treatment is preferably performed under conditions that allow the shape of the sapphire substrate 10 to be maintained. For this reason, it is preferable to implement heat processing below 2050 degreeC which is melting | fusing point of sapphire. In particular, the heating is preferably performed at 1600 ° C. or more and less than 2050 ° C., more preferably 1800 ° C. or more and 2000 ° C. or less.

According to the sapphire substrate of the present embodiment described above, since heat treatment is performed on the end face and the chamfered portion, wrinkles are reduced and removed from the end face and the chamfered portion. For this reason, even when a temperature gradient is generated in the sapphire substrate, it is possible to suppress the substrate from being cracked.
(Method for manufacturing sapphire substrate)
Next, a configuration example of the method for manufacturing the sapphire substrate of this embodiment will be described.

  The manufacturing method of the sapphire substrate of this embodiment can have the following processes, for example.

  The cutting process which makes a sapphire substrate which slices a sapphire ingot and has a main surface, a back surface opposite to the main surface, and an end surface.

  A chamfering step of forming a chamfered portion between the main surface and the end surface and between the back surface and the end surface of the sapphire substrate.

  A heat treatment step for heat-treating the sapphire substrate so that at least a part of the end face and the surface of the chamfered portion is melted.

  In addition, the above-mentioned sapphire substrate can be suitably manufactured with the manufacturing method of the sapphire substrate of this embodiment. For this reason, it can be set as the structure similar to the above-mentioned sapphire board | substrate except the point demonstrated below.

  Each step will be described below.

  First, the cutting process will be described.

  A cutting process is a process of making a sapphire substrate which has a main surface, a back surface opposite to the main surface, and an end surface by slicing a sapphire ingot. Although the method of slicing a sapphire ingot is not particularly limited, for example, it can be sliced with a wire saw. Further, the thickness of the sapphire substrate obtained by slicing is not particularly limited, and may be any thickness depending on the application, for example, 0.40 mm to 4.0 mm. Preferably, it is 1.0 mm or more and 2.0 mm or less.

  In addition, it is preferable to form the notch and / or orientation flat which show a specific surface direction previously in the side part of the sapphire ingot used for a cutting process. The size of the notch and the orientation flat is not particularly limited, but it is preferable to determine the size in consideration of the polishing amount of the end face in a chamfering process or the like described later. Further, the shape of the notch can be any shape.

  Next, the chamfering process will be described.

  The chamfering step is a step of forming a chamfered portion between the main surface and the end surface of the sapphire substrate and between the back surface and the end surface.

  The shape of the chamfered portion formed by the chamfering process is not particularly limited. For example, the cross section can be a linear shape like the chamfered portions 14A and 14B shown in FIG. That is, the chamfered portions 14A and 14B can be formed by taper processing to form inclined surfaces. Further, the chamfered portions 14A and 14B may be formed by rounded chamfering, for example, to have a rounded curved surface shape. In this case, the cross sections of the chamfered portions 14A and 14B are curved.

  In the chamfering step, for example, a cylindrical grindstone in which a groove having a cross-sectional shape corresponding to the shape of the end surface to be formed and the chamfered portion is formed along the peripheral surface can be used. Then, the chamfering can be performed by rotating the sapphire substrate while pressing the grindstone against the sapphire substrate so that the end portion of the sapphire substrate is accommodated in the groove of the grindstone. Thus, the groove | channel surface formed in the above-mentioned grindstone contacts the end surface of a sapphire substrate, and the part corresponding to the chamfering parts 14A and 14B is formed by grind | polishing the end surface of a sapphire substrate.

  Examples of the grindstone used in the chamfering process include a metal bond grindstone and the like. The abrasive grains contained in the grindstone are not particularly limited, but for example, diamond abrasive grains or SiC abrasive grains are preferable. As a grindstone, it is preferable to use the thing of # 200 or more and # 800 or less, and it is more preferable to use a thing of # 400 or more and # 600 or less.

  Next, the heat treatment process will be described.

  The heat treatment step is a step of performing a heat treatment of the sapphire substrate so that at least a part of the surfaces of the end face 13 and the chamfered portions 14A and 14B are melted. By performing heat treatment so as to melt at least part of the surfaces of the end surface 13 and the chamfered portions 14A and 14B, wrinkles on the end surface 13 and the chamfered portions 14A and 14B, and in some cases, the surface of the notched portion can be further reduced and removed. .

  In the heat treatment step, the temperature at which the sapphire substrate is heated is not particularly limited, but at least part of the end surface 13 of the sapphire substrate 10 and the surfaces of the chamfered portions 14A and 14B is melted while maintaining the shape of the sapphire substrate. It is preferable to do so. Since the melting point of sapphire is 2050 ° C., it is preferable to heat the sapphire substrate at less than 2050 ° C., more preferably at 1600 ° C. to less than 2050 ° C., and more preferably at 1800 ° C. to 2000 ° C. in the heat treatment step. Is more preferable.

  The heat treatment time in the heat treatment step is not particularly limited. For example, the heat treatment time is preferably maintained for 1 hour or more after reaching a predetermined heat treatment temperature, and more preferably 2 hours or more. However, if held at a high temperature for a long time, the sapphire substrate may be deformed or the productivity may be lowered. Therefore, the heat treatment time of the heat treatment step is preferably 5 hours or less.

  The atmosphere of the heat treatment step is not particularly limited, and may be, for example, an air atmosphere, an oxygen atmosphere, or an inert gas atmosphere.

  In the sapphire substrate manufacturing method of the present embodiment, it is preferable that the end face 13 and the chamfered portions 14A and 14B are not polished or ground after the heat treatment step. For this reason, in the sapphire substrate obtained by the method for manufacturing a sapphire substrate of the present embodiment, the end face 13 and the chamfered portions 14A and 14B preferably have the same characteristics as those after the heat treatment step.

  By performing the heat treatment step as described above, wrinkles can be reduced and removed from the end face 13 and the chamfered portions 14A and 14B. Moreover, the wrinkle formed in the notch part can be reduced and removed by performing the heat treatment process. For this reason, the sapphire substrate obtained by the manufacturing method of the sapphire substrate of this embodiment can suppress the generation of cracks due to the temperature gradient in the sapphire substrate.

  In the manufacturing method of the sapphire substrate of this embodiment, an arbitrary process can be further added. For example, it can be implemented according to the flowchart shown in FIG.

  The flowchart shown in FIG. 2 will be described.

  First, a cutting process (S21) can be implemented. Since the cutting process is as described above, the description is omitted here.

  Next, a wrapping step (S22) can be performed. In the lapping step (S22), the main surface 11 and the back surface 12 of the sapphire substrate are polished to form a substantially flat surface, and the surface roughness Ra of the main surface 11 and the back surface 12 can be reduced. The lapping step (S22) can be performed using, for example, a double-side polishing apparatus.

  Next, a chamfering step (S23) can be performed. Since the chamfering step (S23) has already been described, the description thereof is omitted.

  Next, a heat treatment step (S24) can be performed. Since the heat treatment step (S24) has already been described, the description thereof is omitted. As described above, in the method for manufacturing a sapphire substrate of this embodiment, it is preferable that the end face 13 and the chamfered portions 14A and 14B are not polished or ground after the heat treatment step (S24).

  Next, a back surface polishing step (S25) can be performed. The back surface polishing step (S25) can be performed when the back surface 12 of the sapphire substrate has a surface roughness Ra different from the main surface 11. For example, in the back surface polishing step (S25), the back surface 12 can be a satin finish.

  In the back surface polishing step (S25), the back surface 12 of the sapphire substrate 10 can be subjected to, for example, sandblasting or polishing with free abrasive grains. The polishing conditions in the back surface polishing step are not particularly limited, and it is preferable to polish the back surface 12 so as to have an arbitrary surface roughness Ra required for the product.

  When the back surface 12 has the same surface roughness Ra as the main surface 11, that is, a mirror surface, the back surface polishing step is not performed and the back surface 12 is also polished in the main surface polishing step (S27) described later. good.

  Next, a low-temperature heat treatment step (S26) can be performed. When the back surface polishing step (S25) is performed as described above and the surface state is different between the main surface 11 and the back surface 12, stress is generated in the sapphire substrate 10, and thus the sapphire substrate 10 may be warped. Therefore, this step is a step of removing the warp generated in the sapphire substrate 10 by performing a heat treatment. The specific heat treatment conditions are not particularly limited, and can be arbitrarily selected depending on the warpage state of the sapphire substrate 10 or the degree of warpage allowed for the product. For example, the heat treatment conditions are 1200 ° C. or higher and 1600 ° C. or lower. It is preferable to implement.

  Note that when the degree of warping of the sapphire substrate 10 is within a range allowed for the product, the low-temperature heat treatment step (S26) may not be performed.

  Next, a main surface polishing step (S27) can be performed. In the main surface polishing step (S27), the main surface 11 can be mirror-polished by, for example, a single-side polishing apparatus so as to be a mirror surface. The polishing conditions in the main surface polishing step are not particularly limited, and it is preferable to polish the main surface 11 so as to have an arbitrary surface roughness Ra required for the product.

  Furthermore, a cleaning process or the like can be performed to remove abrasive grains, grinding debris, and the like attached to the surface of the sapphire substrate 10 as necessary.

  In the manufacturing method of the sapphire substrate of the present embodiment described above, after the chamfering process is performed, the heat treatment process is performed so that at least a part of the end surface and the surface of the chamfered portion is melted. For this reason, wrinkles can be reduced and removed from the end face and the chamfered portion of the sapphire substrate obtained by the manufacturing method. Therefore, even when a temperature gradient occurs in the sapphire substrate, it is possible to suppress the substrate from being cracked.

Specific examples and comparative examples will be described below, but the present invention is not limited to these examples.
[Example 1]
(Manufacture of sapphire substrate)
In this example, the sapphire substrate produced by the following procedure was evaluated.

  First, a method for manufacturing a sapphire substrate will be described.

  A cylindrical sapphire ingot, in which a notch is formed in advance in one place on the side surface in parallel with the central axis of the sapphire ingot, is 150 mm in diameter and 1.5 mm in thickness, and has a main surface and a back surface facing the main surface And 162 disc-shaped sapphire substrates having an end face (cutting step).

  Next, the main surface and the back surface were polished by a double-side polishing apparatus (Type: 16B, manufactured by Hamai Sangyo Co., Ltd.) so that the main surface and the back surface were flat (lapping step). At this time, the main surface and the back surface of each sapphire substrate were each polished by 30 μm.

  Next, a chamfering process for forming a chamfered portion between the main surface and the end surface of the sapphire substrate and between the back surface and the end surface was performed. In the chamfering process, the chamfered portions 14A and 14B were chamfered with a grindstone so that the cross sections of the chamfered portions 14A and 14B were linear as shown in FIG. 1, that is, the chamfered portions 14A and 14B were inclined surfaces.

  In the chamfering step, a cylindrical metal bond grindstone having a count of # 400 including diamond abrasive grains having an average particle diameter of 40 μm was used. In addition, the groove | channel which has a cross-sectional shape corresponding to the shape of the end surface to form and the chamfering part was previously formed along the surrounding surface of this grindstone. And the chamfering process was implemented by rotating a sapphire substrate, pressing a grindstone against a sapphire substrate so that the edge part of a sapphire substrate might be accommodated in the groove | channel of the said grindstone.

  Next, the sapphire substrate after the chamfering process was heat-treated at 2000 ° C. for 5 hours under an argon atmosphere (heat treatment process). The above time includes the temperature raising time and is maintained for 2 hours after reaching 2000 ° C.

  Next, the back surface of the sapphire substrate was polished by a sand blast method (back surface polishing step). Specifically, GC abrasive grains having an average particle size of 49 μm are sprayed on the entire back surface of the sapphire substrate with 0.2 MPa air so that the back surface of the sapphire substrate has a satin finish (surface roughness Ra 0.8 μm). processed.

  Next, in order to remove the warp generated in the sapphire substrate, heat treatment was performed at 1400 ° C. for 12 hours in an air atmosphere (low temperature heat treatment step).

  And about the main surface 11 of the sapphire substrate 10, it grind | polished with the single-side polish apparatus (Fujikoshi Machine Industry Co., Ltd. make: SPM-19A) using the slurry containing colloidal silica with an average particle diameter of 100 nm (main surface polishing process) ). In the main surface polishing step, the main surface 11 was removed by 15 μm polishing. The surface roughness Ra of the main surface after the main surface polishing step was 0.15 nm.

The obtained sapphire substrate 10 was washed, dried, and evaluated by an evaluation method described later.
(Evaluation method, results)
(1) Measurement of surface roughness of end surface The surface roughness Ra of the end surface 13 of the produced sapphire substrate was measured.

  The surface roughness Ra was measured by a surface roughness measuring device (manufactured by Kosaka Laboratory Co., Ltd., Surfcoder SE3500) and measured by a method based on JIS B 0651 2001.

  It was confirmed that any of the 162 sapphire substrates produced had a surface roughness Ra of 0.38 μm.

  Here, the surface roughness of the end face portion was measured, but it can be said that the chamfered portion has the same surface roughness because the chamfered portion is heat-treated in the same manner as the end face.

Moreover, about the produced sapphire board | substrate, the state of the board | substrate end surface was expanded and observed 50 times with the stereomicroscope before and after the heat treatment process. A photograph taken at the time of observation is shown in FIG. 3A shows the state of the end face before the heat treatment step, and FIG. 3B shows the state of the end face after the heat treatment step. As shown in FIG. 3, the surface property of the substrate end face 13 is changed before and after the heat treatment step, and the substrate after the heat treatment step can be confirmed to have melted on the substrate end face 13 as shown in FIG. It was.
(2) Evaluation of generation of cracks A temperature gradient was formed in the substrate of the produced sapphire substrate, and the number of sapphire substrates on which cracks occurred was evaluated.

  4A and 4B show the configuration of an evaluation apparatus that cools a part of a sapphire substrate and forms a temperature gradient in the substrate in this evaluation method. 4A schematically shows a cross-sectional view of the evaluation apparatus, and FIG. 4B schematically shows a top view when the evaluation apparatus is viewed along the arrow A in FIG. 4A.

  As shown in FIGS. 4 (A) and 4 (B), this evaluation apparatus has a rectangular parallelepiped aluminum support portion 42 in a bat 40 containing water 41 maintained at a water temperature of 21.0 (± 1 ° C.). The aluminum support part 42 is kept at about 21 ° C. by heat exchange with water.

  And about the sapphire board | substrate produced by the above-mentioned procedure, after heating the whole sapphire board | substrate to 240 degreeC with a hotplate, as shown to FIG. 4 (A) and (B), the sapphire board | substrate 43 is two aluminum support parts. It is placed on the upper surface of 42. By placing the sapphire substrate 43 on the aluminum support portion 42, the sapphire substrate 43 has a temperature of about 21 ° C. at the portion in contact with the aluminum support portion 42. And since the other part which is not in contact with the aluminum support part 42 is 240 degreeC, the temperature gradient of about 220 degreeC can be formed in the sapphire substrate 43. FIG.

  And it was left until the temperature of the sapphire substrate 43 became 40 degreeC, and it was observed whether the sapphire substrate 43 cracked.

In this example, when the above evaluation was performed on a total of 162 sapphire substrates produced, only 5 pieces were cracked, and 157 pieces were cracked even if left until the temperature of the sapphire substrate 43 reached 40 ° C. Did not occur. That is, the probability of occurrence of cracking was 3.1%.
[Comparative Example 1]
The heat treatment step was performed in the same manner as in Example 1 except that the heat treatment step was performed after the cutting step and before the lapping step, and the mirror polishing step was performed after the low temperature heat treatment step and before the main surface polishing step. 165 sapphire substrates were produced. That is, each process was implemented in order of the cutting process, the heat treatment process, the lapping process, the chamfering process, the back surface polishing process, the low temperature heat treatment process, the mirror surface polishing process, and the main surface polishing process.

  In the mirror polishing step, the brush is pressed against the end surface 13 and the chamfered portions 14A and 14B of the sapphire substrate, and the slurry containing abrasive grains is supplied between the end surface 13 and the chamfered portions 14A and 14B and the brush, The sapphire substrate 10 was rotated. As the slurry containing the abrasive grains, a slurry containing diamond abrasive grains having an average particle diameter of 2 μm was used. In the mirror polishing step, the end face 13 and the chamfered portions 14A and 14B were each removed by 20 μm. When 20 μm is removed from the end face 13 by polishing, the end face 13 exists along the peripheral surface of the sapphire substrate, so that the diameter of the sapphire substrate is reduced by 40 μm compared to before polishing.

  Each process other than the mirror polishing process is performed under the same conditions as in Example 1. And about the produced sapphire substrate, the above-mentioned (1) measurement of the surface roughness of an end surface and (2) generation | occurrence | production evaluation of a crack were performed like Example 1. FIG.

  (1) When the surface roughness of the end face was measured, it was confirmed that the surface roughness Ra of the end face was 0.12 μm for any of the 165 sapphire substrates produced. Further, it can be said that the chamfered portion has the same surface roughness Ra as the end surface.

  (2) As a result of evaluation of occurrence of cracks, it was confirmed that 43 out of 165 sapphire substrates were cracked. That is, the probability of occurrence of cracking was about 26%, which was confirmed to be higher than that in Example 1.

Although the heat treatment process is performed in Comparative Example 1, the chamfering process is performed after the heat treatment process, and only the mirror polishing process is performed after the chamfering process. In the mirror polishing step, the notch portion and its periphery may not be sufficiently polished. Therefore, the wrinkles formed in the periphery of the notch portion in the chamfering process were not sufficiently removed in the mirror polishing process, and it is considered that the probability of occurrence of cracking was higher than that in Example 1.
[Comparative Example 2]
A total of six sapphire substrates were produced in the same manner as Comparative Example 1 except that the mirror polishing process was not performed. And about the produced sapphire substrate, the above-mentioned (1) measurement of the surface roughness of an end surface and (2) generation | occurrence | production evaluation of a crack were performed like Example 1. FIG.

  (1) When the surface roughness of the end face was measured, it was confirmed that the surface roughness Ra of the end face was 0.38 μm for any of the six produced sapphire substrates. Further, it can be said that the chamfered portion has the same surface roughness Ra as the end surface.

  (2) As a result of evaluation of occurrence of cracks, cracks occurred in all six sapphire substrates. That is, the probability of occurrence of cracks was 100%.

  In Comparative Example 2, although the heat treatment process is performed in the same manner as in Comparative Example 1, since the chamfering process is performed after the heat treatment process, it is considered that wrinkles are formed on the end face and the chamfered portion in the chamfering process. And since the mirror polishing process and the heat treatment process are not carried out after the chamfering process, it is considered that many cracks remaining on the end surface and the chamfered part started as cracks.

  From the above results, it was confirmed that the end face of the sapphire substrate and the chamfered portion have a particularly high cracking suppression effect when heat treatment is performed.

10, 43 Sapphire substrate 11 Main surface 12 Back surface 13 End surface 14A, 14B Chamfer

Claims (3)

A main surface, a back surface facing the main surface, and an end surface;
A chamfer is provided between the main surface and the end surface, and between the back surface and the end surface,
A sapphire substrate that has been heat-treated so that at least a part of the end face and the surface of the chamfered portion are melted. Slicing sapphire ingot, cutting step to be a sapphire substrate having a main surface, a back surface facing the main surface, and an end surface;
A chamfering step of forming a chamfered portion between the main surface and the end surface of the sapphire substrate and between the back surface and the end surface;
A heat treatment step of heat-treating the sapphire substrate so that at least a part of the end face and the surface of the chamfered portion is melted.   The method for manufacturing a sapphire substrate according to claim 2, wherein in the heat treatment step, the sapphire substrate is heat-treated at a temperature of 1600 ° C or higher and lower than 2050 ° C.