Seed crystal substrate with adhesive layer, and seed crystal unit

Abstract

The present invention both improves the strength of adhesion between a main surface of a seed crystal substrate and an adhesive layer and inhibits the seed crystal substrate from cracking. A seed crystal substrate 60 (seed crystal substrate with an adhesive layer) includes a main surface 60A and an adhesive layer 65 formed on the main surface 60A. The adhesive layer 65 is made of an adhesive containing phenol, and the adhesive layer 65 has a thickness of 3 μm or larger. The main surface 60A has a roughness of 10 nm or less.

Description

Seed crystal substrate with adhesive layer and seed crystal unit

[0001] The present invention relates to a seed crystal substrate with an adhesive layer and a seed crystal unit, and relates to a technique that is effective when applied to a seed crystal substrate with an adhesive layer and a seed crystal unit for growing a single crystal by a solution growth method, for example.

[0002] Japanese Patent Laid-Open Publication No. 2015-30659 (Patent Document 1) describes a technique for improving adhesive strength by roughening the adhesive surface of a seed crystal substrate made of silicon carbide (roughness: Ra>500 nm) by electrical discharge machining.

[0003] JP 2015-30659 A

[0004] For example, to grow a single crystal by a solution growth method, a seed crystal unit that provides a growth nucleus is used. This seed crystal unit includes, for example, a seed crystal substrate having a main surface, a sheet-like member that is bonded to the main surface of the seed crystal substrate via an adhesive layer, and a jig that bonds the sheet-like member. In this case, the seed crystal substrate and the sheet-like member are bonded by the adhesive layer, and the roughness of the main surface of the seed crystal substrate is increased (Ra > 30 nm) to improve the adhesive strength between the main surface of the seed crystal substrate and the adhesive layer.

[0005] However, when the seed crystal substrate and the sheet-like member are bonded via the adhesive layer, heating is performed, and the present inventors have newly discovered that this heating process can cause the seed crystal substrate to crack. Therefore, based on the new discovery made by the present inventors, it is necessary to improve the adhesive strength between the main surface of the seed crystal substrate and the adhesive layer, while it is also desirable to suppress cracking of the seed crystal substrate. In other words, it is desirable to achieve both an improvement in the adhesive strength between the main surface of the seed crystal substrate and the adhesive layer and suppression of cracking of the seed crystal substrate.

[0006] In one embodiment, the seed crystal substrate with an adhesive layer includes a main surface and an adhesive layer formed on the main surface, wherein the adhesive layer is made of a phenol-containing adhesive, the thickness of the adhesive layer is 3 μm or more, and the roughness of the main surface is 10 nm or less.

[0007] In one embodiment, the seed crystal unit includes a seed crystal substrate having a main surface, a sheet-like member bonded to the main surface of the seed crystal substrate via an adhesive layer, and a jig for bonding the sheet-like member, wherein the adhesive layer is made of a phenol-containing adhesive, the thickness of the adhesive layer is 3 μm or more, and the roughness of the main surface is 10 nm or less.

[0008] According to one embodiment, it is possible to improve the adhesive strength between the main surface of the seed crystal substrate and the adhesive layer, while also suppressing cracking of the seed crystal substrate.

[0009] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments and is not to be construed as limiting the invention.

[0010] In all the drawings for explaining the embodiments, the same components are generally designated by the same reference numerals, and repeated explanations thereof will be omitted. In addition, hatching may be used even in plan views to make the drawings easier to understand.

[0011] <Configuration of Single Crystal Manufacturing Apparatus> FIG. 1 is a diagram showing the configuration of a single crystal manufacturing apparatus 100 according to this embodiment.

[0012] 1, a single crystal manufacturing apparatus 100 has a container 10. The internal space of this container 10 is filled with, for example, argon gas. An insulating member 13c is provided inside the container 10, and a pedestal 11 that can rotate horizontally is disposed inside the insulating member 13c. The container 10 is made of, for example, an iron-based material such as SUS.

[0013] As an argon gas filling structure, for example, a structure can be adopted in which a quartz tube is passed between the insulating member 13c and the coil 14a and between the insulating member 13c and the coil 14b, and the upper and lower ends of the quartz tube are sealed with flanges to fill the argon gas.

[0014] Next, crucible 12 is placed on pedestal 11. This crucible 12 is made of, for example, graphite, and contains a high-temperature solution 20 containing silicon (Si) inside. Specifically, crucible 12 includes a main body portion capable of containing solution 20 containing carbon and silicon, and a heat transfer portion 12a protruding from the bottom of the main body portion.

[0015] In the crucible 12 configured as described above, the heat transfer portion 12a also functions as a "foot," and therefore the heat transfer portion 12a can be said to have a secondary function of stably standing the crucible 12 upright. The heat transfer portion 12a is configured to contact a pedestal 11 on which the crucible 12 can be placed. For example, as shown in FIG. 1 , the pedestal 11 includes a first region R1 in contact with the heat transfer portion 12a, a second region R2 surrounded by the first region R1, and a third region R3 surrounding the first region R1. A heat insulating member 13a is provided so as to contact the second region R2, and a heat insulating member 13b is provided so as to contact the third region R3.

[0016] The pedestal 11 is connected to a crucible-holding shaft 18 that holds the pedestal 11. The crucible-holding shaft 18 is configured to be movable up and down and to rotate either clockwise or counterclockwise. As a result, the pedestal 11 attached to the crucible-holding shaft 18 and the crucible 12 placed on the pedestal 11 can be moved up and down and rotated horizontally by the crucible-holding shaft 18. The crucible-holding shaft 18 has a hollow interior, allowing a thermocouple or a radiation thermometer to be inserted therein for temperature measurement.

[0017] A coil through which a high-frequency current flows is provided on the outer periphery of the vessel 10 of the single crystal manufacturing apparatus 100, and the crucible 12 is heated by induction heating based on the high-frequency current flowing through the coil. Specifically, the single crystal manufacturing apparatus 100 has a heating unit 25a and a heating unit 25b. The heating unit 25a is configured to heat the crucible 12 by an induction heating phenomenon caused by passing a high-frequency current through a coil 14a provided in a position facing the side of the crucible 12. In other words, since the coil 14a functions as the heating unit 25a that heats the crucible 12, the heating unit 25a is also shown in FIG. 1 in addition to the coil 14a. On the other hand, the heating unit 25b is configured to heat the pedestal 11 that supports the crucible 12 by an induction heating phenomenon caused by passing a high-frequency current through a coil 14b provided in a position facing the pedestal 11 that supports the crucible 12. The crucible 12 is then heated by thermal conduction from the heated pedestal 11. Specifically, heat is transferred from the pedestal 11, which is heated by the heating unit 25b, to the heat transfer unit 12a, and then from the heat transfer unit 12a to the crucible 12 (main body), thereby heating the crucible 12. In this manner, the heating unit 25b is configured to indirectly heat the crucible 12 via the pedestal 11 by an induction heating phenomenon caused by passing a high-frequency current through the coil 14b, which is disposed opposite the pedestal 11 supporting the crucible 12. For this reason, the coil 14b functions as the heating unit 25b that heats the crucible 12, and therefore the heating unit 25b is also shown in FIG. 1 in addition to the coil 14b. Although not shown in FIG. 1, the coils 14b and 14a are configured to allow cooling water to flow therethrough.

[0018] In this way, the single crystal manufacturing apparatus 100 is configured so that not only is the crucible 12 itself heated by the heating section 25a, but the crucible 12 is also heated by thermal conduction from the pedestal 11 heated by the heating section 25b, and it can be said that the heat transfer section 12a of the crucible 12 has the function of thermally conducting the heat from the pedestal 11 heated by the heating section 25b to the main body section.

[0019] Here, in order to make it easier to heat pedestal 11 by heating portion 25b, pedestal 11 is thickened so that the portion facing coil 14b is large. Pedestal 11 can be integrated with crucible 12; however, considering the need to replace crucible 12 every time a silicon carbide single crystal is produced and the high manufacturing cost of an integrated product, it is desirable to configure pedestal 11 and crucible 12 as separate bodies. When pedestal 11 and crucible 12 are configured as separate bodies, the heat transfer portion 12a of crucible 12 may simply be disposed on pedestal 11, or pedestal 11 may be configured so that heat transfer portion 12a can be fitted into pedestal 11.

[0020] These heating units 25a and 25b are controlled by a control unit 50. That is, the single crystal manufacturing apparatus 100 has a control unit 50 that controls the power supplied to the heating units 25a and 25b. For example, the power supply that supplies power to the heating units 25a and the power supply that supplies power to the heating units 25b are separate power supplies, and the control unit 50 is configured to be able to separately control the heating units 25a and 25b, which are powered by different power supplies.

[0021] The control unit 50 is configured to be able to alternate between a first operation of adjusting the power supplied to the heating unit 25a and the power supplied to the heating unit 25b so that the temperature of the solution 20 in contact with the side of the crucible 12 is higher than the temperature of the solution 20 in contact with the bottom of the crucible 12, and a second operation of adjusting the power supplied to the heating unit 25a and the power supplied to the heating unit 25b so that the temperature of the solution 20 in contact with the bottom of the crucible 12 is higher than the temperature of the solution 20 in contact with the side of the crucible 12.

[0022] The solution 20 contained in the crucible 12 heated by the heating units 25a and 25b reaches a high temperature, and the graphite (C) constituting the crucible 12 melts, resulting in the solution 20 containing carbon and silicon. A crucible lid 15 is attached to the crucible 12, and the crucible lid 15 has a cylindrical member 15a and a connecting member 15b connected to the cylindrical member 15a. The connecting member 15b has the function of fixing and supporting the cylindrical member 15a and is configured to be able to come into contact with the crucible 12, for example.

[0023] Next, the single crystal manufacturing apparatus 100 is provided with a crystal holding shaft 16 that can move up and down. This crystal holding shaft 16 may also be configured to be rotatable clockwise or counterclockwise, similar to the crucible holding shaft 18. In other words, the crystal holding shaft 16 and the crucible holding shaft 18 may or may not have a rotation mechanism.

[0024] A seed crystal unit 40 is attached to the tip of the crystal holding shaft 16. The crystal holding shaft 16 also has a fin structure 16a attached to it so as to intersect with the extension direction of the crystal holding shaft 16. Furthermore, the interior of the crystal holding shaft 16 has a hollow structure, and a thermocouple 17 is inserted into the crystal holding shaft 16 to measure the temperature near the seed crystal unit 40. Instead of inserting the thermocouple 17, the temperature near the seed crystal unit 40 can also be measured by placing a radiation thermometer with a measuring diameter smaller than the inner diameter of the crystal holding shaft 16 at the upper end of the crystal holding shaft 16.

[0025] The control unit 50 of the single crystal manufacturing apparatus 100 is also configured to control the crystal holding shaft 16 having the fin structure 16a to move vertically. Specifically, the control unit 50 is configured to control the crystal holding shaft 16 so that the crystal holding shaft 16 having the fin structure 16a moves vertically through the interior of the cylindrical member 15a. The control unit 50 is configured to move the crystal holding shaft 16, to which the seed crystal unit 40 is attached at its tip, downward to bring the lower surface of the seed crystal unit 40 into contact with the surface of the solution 20 contained in the crucible 12, and to grow a silicon carbide single crystal on the lower surface of the seed crystal unit 40 by moving the crystal holding shaft 16 upward after bringing the lower surface of the seed crystal unit 40 into contact with the surface of the solution 20. Note that the seed crystal unit 40 may be brought into contact with the solution 20, but it is particularly desirable that the seed crystal unit 40 be brought into contact with the surface of the solution 20.

[0026] Note that the configuration in which a single crystal of silicon carbide can be grown on the underside of the seed crystal unit 40 by moving the crystal holding shaft 16 upward is one example. For example, the configuration may be such that a single crystal of silicon carbide is grown on the underside of the seed crystal unit 40 while the crystal holding shaft 16 is stopped (maintained), or the configuration may be such that a single crystal of silicon carbide is grown on the underside of the seed crystal unit 40 by moving the crystal holding shaft 16 downward. This configuration takes into consideration, for example, the possibility that the surface of the solution 20 may drop due to evaporation of the solution 20. That is, if the surface of the solution 20 recedes due to evaporation of the solution 20, the single crystal can be reliably grown on the seed crystal unit 40 by growing the single crystal while moving the crystal holding shaft 16 downward.

[0027] The single crystal manufacturing apparatus 100 is configured as described above.

[0028] <Modifications> In the single crystal manufacturing apparatus 100 shown in FIG. 1, the heating unit 25b for heating the pedestal 11 is an example that utilizes the induction heating phenomenon that occurs when a high-frequency current is passed through the coil 14b. However, the heating unit 25b for heating the pedestal 11 is not limited to this, and may be composed of, for example, a resistance heater provided below the pedestal 11.

[0029] However, if the heating unit 25b is configured from a resistance heater, it is necessary to provide a "hole" in the insulating material in order to route a pair of wires used to energize the resistance heater. In particular, if the crucible 12 itself is configured to rotate, it is necessary to provide a circumferential opening in the insulating material in order to route the pair of wires. As a result, it may become difficult to ensure the high-temperature retention properties of the crucible 12. Therefore, from the viewpoint of improving the insulating effect of the insulating material and simplifying the configuration of the single crystal manufacturing apparatus 100, it is desirable that the heating unit 25b that heats the pedestal 11 be configured from an induction heater that utilizes the induction heating phenomenon as shown in FIG. 1.

[0030] <Operation of Single Crystal Manufacturing Apparatus (Single Crystal Manufacturing Method)> Next, the operation of the single crystal manufacturing apparatus 100 will be described.

[0031] First, the control unit 50 lowers the crystal holding shaft 16, to which the seed crystal unit 40 is attached at the tip. As a result, the seed crystal unit 40 attached to the crystal holding shaft 16 passes through the inside of the cylindrical member 15a provided on the crucible lid 15, and then comes into contact with the surface of the solution 20 containing carbon and silicon contained in the crucible 12. At this time, the fin structure 16a attached to the crystal holding shaft 16 is positioned opposite the inner wall of the cylindrical member 15a.

[0032] Next, the control unit 50 slowly raises the crystal holding shaft 16. As a result, a silicon carbide single crystal grows on the underside of the pulled-up seed crystal unit 40. At this time, the fin structure 16a attached to the crystal holding shaft 16 moves while maintaining its position facing the inner wall of the cylindrical member 15a. If the crystal growth is to continue, the pulling operation of the crystal holding shaft 16 continues. On the other hand, if the crystal growth is to be terminated, the control unit 50 further raises the crystal holding shaft 16 to separate the silicon carbide single crystal from the solution 20. This terminates the growth of the silicon carbide single crystal. At this time, the fin structure 16a attached to the crystal holding shaft 16 remains positioned facing the inner wall of the cylindrical member 15a.

[0033] In the above manner, a silicon carbide single crystal can be produced by operating single crystal production apparatus 100. While it has been described that crystal growth is terminated by further pulling up crystal holding shaft 16 to separate the silicon carbide single crystal from solution 20, the present invention is not limited to this, and for example, instead of pulling up crystal holding shaft 16, crucible holding shaft 18 can be pulled down to separate the silicon carbide single crystal from solution 20, thereby terminating crystal growth.

[0034] <Configuration of Seed Crystal Unit> Next, the configuration of the seed crystal unit 40 will be described.

[0035] Fig. 2 is a diagram showing the configuration of seed crystal unit 40. As shown in Fig. 2, seed crystal unit 40 is composed of seed crystal substrate 60 formed from a silicon carbide single crystal, carbon sheet 70 made of carbon, and carbon jig 80 made of carbon. Seed crystal substrate 60 and carbon sheet 70 are bonded together with an adhesive. Similarly, carbon sheet 70 and carbon jig 80 are bonded together with an adhesive.

[0036] The seed crystal substrate 60 is, for example, a wafer formed from a silicon carbide single crystal. The seed crystal substrate 60 has a main surface (upper surface) to be bonded to the carbon sheet 70 and a lower surface (rear surface) located opposite the main surface. The lower surface of the seed crystal substrate 60 is brought into contact with the solution 20 shown in FIG. 1 . This allows a silicon carbide single crystal to grow on the lower surface of the seed crystal substrate 60.

[0037] Carbon sheet 70 is a sheet-like member made of carbon, and is disposed so as to be interposed between seed crystal substrate 60 and carbon jig 80. Carbon sheet 70 is provided to relieve stress acting between seed crystal substrate 60 and carbon jig 80. In other words, carbon sheet 70 functions as a stress relief sheet that relieves stress that occurs due to the difference in thermal expansion coefficient between seed crystal substrate 60 and carbon jig 80.

[0038] The carbon jig 80 has, for example, a screw hole (not shown) and is configured so that, for example, the crystal holder shaft 16 shown in Fig. 1 can be inserted therein. In other words, the carbon jig 80 has the function of fixing the seed crystal unit 40 to the tip end of the crystal holder shaft 16.

[0039] FIG. 3 is a cross-sectional view showing the seed crystal unit 40.

[0040] 3, seed crystal substrate 60 has a main surface 60A and a bottom surface 60B. Bottom surface 60B is the surface that comes into contact with solution 20 shown in FIG. 1 . Meanwhile, an adhesive layer 65 is formed on main surface 60A. As described above, seed crystal substrate 60 includes main surface 60A and adhesive layer 65 formed on main surface 60A. Carbon sheet 70 is disposed so as to be adhered to main surface 60A of seed crystal substrate 60 via adhesive layer 65. Furthermore, carbon jig 80 is disposed so as to be adhered to carbon sheet 70 via adhesive layer 75.

[0041] Here, each of the adhesive layers 65 and 75 is made of, for example, an adhesive containing phenol, such as a photoresist.

[0042] Photoresist is usually used for patterning using photolithography technology, but in this embodiment, photoresist is used as an adhesive because it has the following advantages: (1) it has low viscosity and is therefore easy to apply, and (2) a method for controlling the thickness of the applied layer using a spin coater has been established, allowing for accurate control of the thickness of the adhesive layer.

[0043] The seed crystal unit 40 is constructed as described above.

[0044] <Consideration of Improvements> In the above-described seed crystal unit 40, it is necessary to ensure the adhesive strength between the seed crystal substrate 60 and the carbon sheet 70 via the adhesive layer 65. For this reason, the roughness of the main surface 60A of the seed crystal substrate 60 is increased. This is because increasing the roughness of the main surface 60A increases the surface area of ​​the main surface 60A, thereby improving the adhesive strength between the main surface 60A of the seed crystal substrate 60 and the adhesive layer 65. That is, in conventional techniques, it is common to roughen the main surface 60A of the seed crystal substrate 60 constituting the seed crystal unit 40 from the viewpoint of ensuring adhesive strength, as in, for example, Patent Document 1 described in the background art.

[0045] In this regard, the present inventors have newly discovered that roughening main surface 60A of seed crystal substrate 60 by performing a surface-roughening treatment increases the likelihood of cracks occurring in seed crystal substrate 60. Specifically, when the roughness of main surface 60A is increased, the difference in roughness between main surface 60A and lower surface 60B, which has not been subjected to a surface-roughening treatment (for example, about 1 nm), increases.

[0046] As a result, the present inventors speculate that stress is generated in the seed crystal substrate 60 due to the Twyman effect, and that cracks occur in the seed crystal substrate 60 due to heating performed when bonding the seed crystal substrate 60 and the carbon sheet 70 via the adhesive layer 65. That is, it is common knowledge among those skilled in the art that, from the viewpoint of ensuring adhesive strength, the main surface 60A of the seed crystal substrate 60 constituting the seed crystal unit 40 should be roughened. However, the present inventors have newly discovered that this common knowledge increases the likelihood of cracks occurring in the seed crystal substrate 60. That is, while roughening the main surface 60A is useful from the viewpoint of ensuring adhesive strength, there is room for improvement in that the side effect of cracks occurring in the seed crystal substrate 60 becomes apparent. Therefore, ingenuity is required to simultaneously improve the adhesive strength between the main surface of the seed crystal substrate and the adhesive layer and suppress cracks in the seed crystal substrate.

[0047] Therefore, in this embodiment, an innovation is made to achieve both an improvement in the adhesive strength between the main surface of the seed crystal substrate and the adhesive layer and a suppression of cracking of the seed crystal substrate. The technical concept of this innovation in this embodiment will be described below.

[0048] <Basic Concept of the Embodiment> The basic concept of the present embodiment is to reduce the roughness of the main surface 60A of the seed crystal substrate 60 while increasing the thickness of the adhesive layer 65. This reduces the roughness of the main surface 60A, thereby reducing the difference in roughness with the lower surface 60B, and as a result, the occurrence of the Twyman effect, which causes stress, can be suppressed. Therefore, according to the basic concept, the occurrence of cracks in the seed crystal substrate 60 can be suppressed. However, in this case, the surface area of ​​the main surface 60A is reduced, which may reduce the adhesive strength between the main surface 60A and the adhesive layer 65. In this regard, the basic concept is to increase the thickness of the adhesive layer 65. This can suppress a decrease in the adhesive strength between the main surface 60A and the adhesive layer 65. That is, the basic idea is to first reduce the roughness of main surface 60A to suppress the occurrence of cracks in seed crystal substrate 60, and to prevent a decrease in the adhesive strength between main surface 60A and adhesive layer 65, which becomes apparent when the roughness of main surface 60A is reduced, by increasing the thickness of adhesive layer 65. From the above, according to the basic idea, it is possible to achieve both an improvement in the adhesive strength between main surface 60A of seed crystal substrate 60 and adhesive layer 65 and suppression of cracks in seed crystal substrate 60.

[0049] In this specification, roughness refers to "Ra." "Ra" is a height-direction parameter known as "arithmetic mean roughness." "Ra" is obtained by extracting a portion of the roughness curve measured with a roughness meter over a reference length and expressing the unevenness of that section as an average value. Because "Ra" uses an average value, it is less susceptible to the influence of a single protruding scratch, and has the advantage of providing stable results when evaluating surface roughness.

[0050] <Embodiments> Hereinafter, embodiments that embody the above-described basic concept will be described.

[0051] First, a brief description will be given of a method for manufacturing the seed crystal unit 40. For example, an example will be described in which a seed crystal substrate 60 with a diameter of 150 mm is used.

[0052] 5 ml of photoresist is dropped onto the center of the seed crystal substrate 60. The photoresist is then spread by rotating the substrate with a spin coater under the conditions of (1) 600 rpm x 20 seconds, and then (2) 1500 rpm x 20 seconds. As a result, an adhesive layer 65 made of photoresist is formed on the main surface 60A of the seed crystal substrate 60. At this time, the thickness of the adhesive layer 65 is 3 μm to 4 μm.

[0053] Next, the photoresist-coated main surface 60A of the seed crystal substrate 60 and the carbon sheet 70 are bonded together, and heated on a hot plate to 200° C. or higher. This allows the seed crystal substrate 60 and the carbon sheet 70 to be bonded together via the adhesive layer 65.

[0054] Next, the carbon sheet 70 and the carbon jig 80 are bonded together via the adhesive layer 75. After that, the carbon sheet 70 is heated and fired at 1000° C. or higher in an inert atmosphere. In this way, the seed crystal unit 40 can be manufactured.

[0055] Here, the characteristic features of the embodied embodiment are that the roughness of the main surface 60A of the seed crystal substrate 60 is 10 nm or less, and the thickness of the adhesive layer 65 that bonds the seed crystal substrate 60 and the carbon sheet 70 is 3 μm or more and 30 μm or less.

[0056] As a result, first, the roughness of main surface 60A of seed crystal substrate 60 is 10 nm or less, and because the roughness of main surface 60A is small, the difference in roughness between main surface 60A and bottom surface 60B is small, which results in suppressing the occurrence of the Twyman effect, which causes stress. Therefore, according to the feature of the embodied aspect, the occurrence of cracks in seed crystal substrate 60 can be suppressed.

[0057] Here, the roughness Ra (arithmetic mean roughness) is calculated by evaluating the center of the seed crystal substrate 60 using a Bruker optical interference microscope (Contour GT-K) with a 50x lens and a VXI (Vertical Scan Interferometry) method.

[0058] According to a feature of the embodied aspect, the thickness of the adhesive layer 65 that bonds the seed crystal substrate 60 and the carbon sheet 70 is 3 μm or more and 30 μm or less. Therefore, even if the roughness of the main surface 60A is small, the thick adhesive layer 65 can suppress a decrease in the adhesive strength between the main surface 60A and the adhesive layer 65. In this way, according to the feature, it is possible to improve the adhesive strength between the main surface 60A of the seed crystal substrate 60 and the adhesive layer 65 and suppress cracking of the seed crystal substrate 60. As a result, according to the feature, it is possible to improve the adhesive strength between the seed crystal substrate 60 and the carbon sheet 70 and suppress cracking of the seed crystal substrate 60.

[0059] As described above, the characteristic features of the embodied mode are that the roughness of main surface 60A of seed crystal substrate 60 is 10 nm or less and that the thickness of adhesive layer 65 that bonds seed crystal substrate 60 and carbon sheet 70 is 3 μm or more and 30 μm or less, but below, if the numerical ranges defined by these characteristic features are not met, cracking of seed crystal substrate 60 or peeling of carbon sheet 70 from seed crystal substrate 60 may occur. This example will be described.

[0060] First, an example in which the seed crystal substrate cracked as a result of high roughness will be described.

[0061] For example, using a copper surface plate, the main surface of the seed crystal substrate was processed with diamond abrasive grains having a particle size of 5s (3 μm to 8 μm) to achieve a roughness of the main surface of Ra = 33.5 nm. Then, 5 ml of photoresist was dropped onto the center of the seed crystal substrate, and the substrate was rotated under the conditions of (1) 600 rpm x 20 seconds, and then (2) 1500 rpm x 20 seconds, thereby spreading the photoresist. Then, when the seed crystal substrate and a carbon sheet were bonded together and prebaked, cracks occurred in the seed crystal substrate. This is thought to be because the roughness of the main surface was Ra = 33.5 nm, which is greater than Ra = 10 nm, and cracks occurred in the seed crystal substrate.

[0062] Next, an example will be described in which a carbon sheet peeled off from a seed crystal substrate due to a thin photoresist thickness. For example, using a Pla-Pad surface plate, the main surface of the seed crystal substrate was processed with diamond abrasive grains having a particle size of 5s (3 μm to 8 μm) to achieve a main surface roughness of Ra = 5.9 nm. Then, 5 ml of photoresist was dropped onto the center of the seed crystal substrate, and the substrate was rotated under the conditions of (1) 600 rpm × 20 seconds, and then (2) 3000 rpm × 20 seconds, thereby spreading the photoresist. At this time, the thickness of the photoresist was less than 3 μm (approximately 2 μm). Then, when the seed crystal substrate and the carbon sheet were bonded together and prebaked, the carbon sheet peeled off from the seed crystal substrate. This is thought to be due to the photoresist thickness being approximately 2 μm, which is less than 3 μm, resulting in a decrease in the adhesive strength between the main surface of the seed crystal substrate and the adhesive layer, resulting in the carbon sheet peeling off.

[0063] For the above reasons, if the numerical range defined by the characteristic points in the embodiment is not met, cracking of the seed crystal substrate or peeling of the carbon sheet from the seed crystal substrate may occur. Therefore, in order to simultaneously improve the adhesive strength between the seed crystal substrate and the carbon sheet and suppress cracking of the seed crystal substrate, it is useful to realize the characteristic points in the embodiment.

[0064] The invention made by the inventor has been specifically described above based on the embodiments thereof, but it goes without saying that the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the invention.

[0065] DESCRIPTION OF SYMBOLS 10 Container 11 Base 12 Crucible 12a Heat transfer section 13a Heat insulating member 13b Heat insulating member 13c Heat insulating member 14a Coil 14b Coil 15 Crucible lid 15a Cylindrical member 15b Connection member 16 Crystal holding shaft 16a Fin structure 17 Thermocouple 18 Crucible holding shaft 20 Solution 25a Heating section 25b Heating section 40 Seed crystal unit 50 Control section 60 Seed crystal substrate 60A Main surface 60B Lower surface 65 Adhesive layer 70 Carbon sheet 75 Adhesive layer 80 Carbon jig 100 Single crystal manufacturing apparatus R1 First region R2 Second region R3 Third region

Claims

1. A seed crystal substrate with an adhesive layer, comprising: a main surface; and an adhesive layer formed on the main surface, wherein the adhesive layer is made of an adhesive containing phenol, the thickness of the adhesive layer is 3 μm or more, and the roughness of the main surface is 10 nm or less.

2. In the seed crystal substrate with an adhesive layer according to claim 1, the adhesive layer is made of a photoresist.

3. In the seed crystal substrate with an adhesive layer according to claim 1, the thickness of the adhesive layer is 30 μm or less.

4. A seed crystal substrate with an adhesive layer according to claim 1, wherein the seed crystal substrate with an adhesive layer is made of silicon carbide.

5. A seed crystal unit comprising: a seed crystal substrate having a main surface; a sheet-like member adhered to the main surface of the seed crystal substrate via an adhesive layer; and a jig adhered to the sheet-like member, wherein the adhesive layer is made of an adhesive containing phenol, the thickness of the adhesive layer is 3 μm or more, and the roughness of the main surface is 10 nm or less.

6. In the seed crystal unit according to claim 5, the adhesive layer is made of a photoresist.

7. A seed crystal unit as described in claim 5, wherein the thickness of the adhesive layer is 30 μm or less.

8. A seed crystal unit as described in claim 5, wherein the seed crystal substrate is made of silicon carbide, the sheet-like member is a carbon sheet, and the jig is a carbon jig.

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