WO2007123093A1 - Single crystal sapphire substrate - Google Patents

Abstract

[PROBLEMS] To solve a problem involved in a prior art technique using a single-crystal sapphire substrate as a substrate for epitaxially growing gallium nitride (GaN) or the like used in blue light emitting LEDs, which prior art technique cannot provide a single-crystal sapphire substrate having a regular step shape capable of growing a good epitaxial film of gallium nitride or the like. [MEANS FOR SOLVING PROBLEMS] There is provided a single-crystal sapphire substrate which can be used for providing a crystal film, which has a more flat terrace face and has no significant crystal defect, and for providing a GaN crystal film having a flat surface and no significant crystal defect. The GaN crystal film, when used as a luminescent element, has better luminescence characteristics. There is also provided a method for manufacturing a single-crystal sapphire substrate that can closely control an inclination angle of the surface of a sapphire single crystal and can reliably provide a single-crystal sapphire substrate according to the purpose.

Description

 Specification

 Single crystal sapphire substrate

 Technical field

 [0001] The present invention is suitable for forming elements such as LEDs (Light Emitting Diodes), LDs (Laser Diodes), HEMTs (High Electron Mobility Transistors), FETs (Field Effect Transistors), and SOS (Silicon-ON-Sapphire). The present invention relates to a method for manufacturing a single crystal sapphire substrate having crystal quality and surface condition.

 Background art

 [0002] Currently, blue and white light-emitting diodes (LEDs) are used for light sources such as traffic signals, automobile instrument panels, and backlights for liquid crystal panels of mobile phones. Gallium nitride (GaN) crystals used for blue and white LEDs are sapphire (Al 2 O 3) and silicon carbide (SiC)

 twenty three

 It is manufactured by epitaxial growth through a buffer layer on a substrate. In particular, sapphire substrates have recently become widely used because they have been mass-produced in recent years and are thermally and chemically stable. Single crystal sapphire substrates are also used as substrates for manufacturing various electronic devices, not just LEDs.

[0003] When a GaN crystal or the like is grown on a single crystal sapphire substrate, it is generally performed at an angle of about 0.01 to 2.0 degrees with respect to the C plane of the sapphire crystal. When a GaN crystal is grown on the C-plane of the sapphire single crystal surface, the resulting GaN crystal becomes a crystal with many crystal defects and unevenness. Therefore, as shown in Fig. 1, by using a single crystal sapphire substrate in which the surface of the sapphire single crystal is inclined at a predetermined angle with respect to the C plane, a GaN crystal having a flat surface with few crystal defects can be obtained. (Patent Document 1). At this time, the surface of the sapphire substrate is formed in microscopic steps as shown in FIG. The higher the regularity of this step shape, the more powerful GaN crystals grow on the substrate.

 Patent Document 1: JP 2002-293692 A

Non-Patent Document 1: SASAKI Atsushi, HARA Wakana, MATSUDA Akilumi, AKIBA Shusak u, TATEDA Norihiro, YOSHIMOTO Mamoru, Nucl Instrum Methods Phys Res Sect B, VOL. 232 NO. 1-4; PAGE. 305-311; (2005/05).

 f ^^ j¾2: http://foundry.sanken.osaka-u.ac.jp/report/H15-010.pdf Invention Disclosure

 Problems to be solved by the invention

[0004] However, when processing as a wafer to form a GaN crystal thin film on the single crystal sapphire substrate of Patent Document 1, the steps are not linear and the step height is not uniform at the atomic level. The steps were not parallel, and the terrace surface was uneven. In particular, when the inclination angle of the surface was increased, the unevenness of the steps became prominent and the unevenness of the terrace surface became severe. That is, the single crystal sapphire substrate described in Patent Document 1 has a problem in that oxygen atoms and aluminum atoms constituting the sapphire crystal are not regularly arranged, and a high-quality crystal cannot be obtained.

 Means for solving the problem

[0005] In order to solve the above problems, the present invention provides a single crystal sapphire substrate having a step shape and a flatter terrace surface than a conventional single crystal sapphire substrate, and a method for manufacturing the same.

 [0006] That is, the first invention is a single crystal sapphire substrate in which a regular step having a terrace surface is formed on the single crystal sapphire surface, and the macro surface roughness (Ra) of the substrate is 0. Inm. The terrace surface roughness (Ra) is 0.03 nm or less, the step height is 0.3 Inm or more and 0.3 nm or less, and the difference between the maximum and minimum terrace width is 500 nm or less. A single crystal sapphire substrate is provided.

 [0007] The second invention provides a single crystal sapphire substrate in which the macroscopic surface of the single crystal sapphire substrate is inclined at an angle of 0.1 to 0.6 degrees with respect to the main surface.

 [0008] A third invention provides a single-crystal sapphire substrate configured such that oxygen atoms terminate on a terrace surface to form a monoatomic layer of oxygen.

[0009] A fourth invention includes a vacuum heating step of heating the single crystal sapphire substrate in a vacuum atmosphere, a first atmospheric heating step of heating the sapphire substrate taken out after the vacuum heating step in an atmospheric atmosphere, and a first atmosphere After the heating step, there is provided a method for manufacturing a single crystal sapphire substrate comprising a second atmospheric heating step in which the furnace temperature is raised and further heated. Provide.

 [0010] The fifth invention includes a vacuum heating step for heating the single crystal sapphire substrate in a vacuum atmosphere, and a first atmosphere for heating the sapphire substrate taken out after the vacuum heating step at a low temperature in a component atmosphere contained in the atmosphere. Provided is a method for producing a single crystal difference sapphire substrate comprising: a heating step; and a second atmospheric heating step in which, after the first atmospheric heating step, the furnace temperature is raised and further heated in a component atmosphere contained in the atmosphere. To do.

 [0011] In a sixth invention, the heating temperature in the vacuum heating step is 1000 ° C or higher and 1300 ° C or lower, the holding time is 2 hours or longer, and the heating temperature in the first atmospheric heating step is 800 ° C or higher. Single crystal sapphire having a temperature of 1 ° C or less, a holding time of 2 hours or more and 5 hours or less, a heating temperature of the second atmospheric heating step of 1300 ° C or more and 1600 ° C or less, and a holding time of 1 hour or more and 5 hours or less A method for manufacturing a substrate is provided.

 [0012] A seventh invention provides an electronic device manufacturing method for manufacturing an electronic device by epitaxially growing an electronic device material on a surface side including a terrace surface of a single crystal sapphire substrate.

 [0013] An eighth invention provides a method of manufacturing an electronic device, wherein the electronic device material is gallium nitride.

 A ninth invention provides an electronic device intermediate structure in which an electronic device material is epitaxially grown on a surface side including a terrace surface using a single crystal sapphire substrate. The invention's effect

 By using the single crystal sapphire substrate of the present invention, it is possible to obtain a crystal film having a flatter terrace surface and few crystal defects. Further, it is possible to obtain a GaN crystal film having a flat surface and few crystal defects, and this GaN crystal film exhibits better light emission characteristics when used as a light emitting device. Further, according to the method for producing a single crystal sapphire substrate of the present invention, the tilt angle of the sapphire single crystal surface can be precisely controlled, and a single crystal sapphire substrate suitable for the purpose can be obtained with certainty.

 BEST MODE FOR CARRYING OUT THE INVENTION

[0016] The best mode for carrying out each invention will be described below. It should be noted that the present invention is not limited to these embodiments, and is within the scope not departing from the gist thereof. It can be implemented in various ways.

 [0017] The first embodiment will mainly describe claims 1, 2 and 3. The second embodiment will mainly describe claim 4. The third embodiment will mainly describe claims 5, 6, 7, 8, and 9. Embodiment 4 will mainly describe claims 10, 11 and 12.

 Embodiment 1>

 Embodiment 1: Concept>

 [0018] The single crystal sapphire substrate of the present embodiment controls the surface roughness of the substrate, the shape of the steps, etc., and improves the quality of the crystal grown on the substrate.

 <Embodiment 1: Configuration>

 FIG. 2 is a diagram schematically showing a macroscopic surface of a single crystal sapphire substrate. In the single crystal sapphire substrate, regular steps having a flat terrace surface (0201) are formed on the single crystal sapphire surface. The terrace surface (0201) is the larger part of the flat part of the substrate surface, and the step surface (0202) is the smaller part of the flat part of the substrate surface, that is, one terrace surface and it. It is a surface that connects the following terrace surface. As shown in Fig. 2, the vertical distance between one terrace surface and the following terrace surface is the step height (h), and the horizontal distance between the terrace surface and the subsequent terrace surface is the terrace width (w), The angle between the terrace surface and the end line (0203) of the macroscopic surface of the single crystal sapphire substrate is called the offset angle (Θ). Also, the edge (0204) t is the angle at which the glass surface and the step surface meet.

 [0020] Single crystal sapphire is made of sapphire (a Al O), ideally sapphire

 twenty three

 When focusing on an arbitrary crystal axis, it is a substance whose orientation is the same in any part of the sample. However, since it usually contains dislocations, the direction of the crystal axis may partially change.

FIG. 3 shows a unit cell of a sapphire single crystal. A sapphire single crystal has a hexagonal crystal structure. Hexagonal crystal with C-plane (Miller index notation: (0001)) and side-faced (Mira one-index notation: 10-10)) (Miller index minus sign notation method should be written above the number However, here, the minus sign is written in front of the numbers for the sake of simplicity), and the hatched surface is the Α surface (Miller index notation: 11 20)) and R surface (Miller index notation: 10—12) ) [0022] The characteristics of the single crystal sapphire substrate of the present embodiment are as follows.

[0023] First, the surface roughness (Ra) of the substrate is 0.1 nm or less. The surface roughness (Ra) is expressed by Equation 1 where f (X) is the height of an arbitrary line (length L) on the substrate surface relative to the average line at X. The smaller the Ra value, the smoother the step surface. The surface roughness of the substrate is the roughness of the entire substrate surface and is different from the surface roughness of a specific terrace surface described later. In other words, when measuring the surface roughness of the substrate, it is better to measure the surface height in the X direction in Fig. 2.

 [Number 1]

[0024] Second, the surface roughness (Ra) of the terrace surface is 0.03 nm or less. The surface roughness of the terrace surface is the surface roughness of a specific terrace surface. Therefore, when measuring the surface roughness of the terrace surface, the surface height should be measured in the y direction in Fig. 2.

 [0025] Third, the step height is 0.1 nm or more and 0.3 nm or less. When the terrace surface is the C surface, the step height is preferably the distance between the oxygen atomic layer and the adjacent aluminum atomic layer (about 0.22 nm). This height is also the force that becomes the minimum unit of the step height. The step height is the distance between the oxygen atomic layer and the adjacent aluminum atomic layer.

 [0026] Fourth, on one terrace surface, the difference between the maximum value and the minimum value of the terrace width is 500 nm or less. That is, it is necessary that the edge of the terrace surface has a shape close to a straight line.

By defining the characteristics of the single crystal sapphire substrate surface as described above, the crystal surface of GaN or the like grown on the substrate surface can be flattened and the dislocation density can be reduced.

[0028] In addition, it is preferable that the terrace surface is parallel to the main surface. The main surface is one of the C-plane, A-plane, M-plane, and R-plane of the sapphire single crystal. This is because the terrace surface is parallel to the main surface because it is the most stable in terms of energy. [0029] Further, the macroscopic surface force of the single crystal sapphire substrate is preferably inclined at an angle of 0.1 degree force 0.6 degree with respect to the main surface. Further, it is more preferable that the main surface is inclined with respect to a specific direction rather than with respect to an arbitrary direction. For example, when the main surface is the C surface, it is preferable that the 0.1 degree force is inclined at an angle of 0.6 degrees when directed from the C surface toward the A surface direction or the M surface direction.

 FIG. 4 is a diagram illustrating a macroscopic surface. As shown by the dotted line in Fig. 4, the macroscopic surface represents the average surface when the single crystal sapphire substrate is viewed macroscopically. If the tilt angle is 0.1 degrees or less, the step surface and the terrace surface cannot be clearly formed. If the tilt angle is 0.6 degrees or more, the step height is required to be 0.3 nm or more, and the step is good. Not formed.

 Embodiment 1: Example>

 [0031] FIG. 5 shows an example of an AFM measurement result of a single crystal sapphire substrate with the C-plane as the main surface of the present embodiment. As shown in FIG. 5, it can be seen that the single crystal sapphire substrate of this embodiment has steps with a uniform shape. As a result of measuring the surface shape of this single crystal sapphire substrate, it was found that the surface roughness of the terrace surface was 0.013 nm, the terrace width was 400 to 600 nm, and the step height was about 0.2 nm.

 <Embodiment 1: Effect>

 By using the sapphire substrate of this embodiment, an epitaxial film having a flat surface and a low dislocation density can be obtained. An epitaxial film with good crystallinity shows good light emission characteristics even when used as a light emitting element.

 Embodiment 2>

 Embodiment 2: Overview>

 [0033] The sapphire single crystal of this embodiment is characterized in that the substrate surface is composed of oxygen atoms, and the oxygen atoms are regularly arranged. As a result, it is possible to form an epitaxial film with good crystallinity on the sapphire substrate.

 <Embodiment 2: Configuration>

[0034] The single crystal sapphire substrate of the present embodiment is configured such that oxygen atoms terminate on the terrace surface to form a monoatomic layer of oxygen. Here, the oxygen atom ends here The structure in which an oxygen monoatomic layer is formed is considered to form an oxygen monoatomic layer if aluminum atoms are exposed on the surface due to crystal defects or manufacturing errors in the manufacturing process. This is because perfect crystals are theoretically difficult to manufacture industrially. In addition, these crystal defects and the degree of error in the manufacturing process cause the product yield to deteriorate, but if the concept of discarding defective products is used, the defects and defects are within a certain extent within the range of commercial rationality. Permissible.

 [0035] The single crystal sapphire substrate of this embodiment is composed of a C-plane (mirror index notation: (0001)) whose terrace surface is a sapphire crystal. Figure 6 shows a conceptual diagram of the sapphire crystal. In the figure, aluminum atoms are omitted for the force oxygen atoms indicated by black circles because the figure becomes complicated. The sapphire crystal has a regular octahedral structure with oxygen atoms at the apexes as shown in Fig. 6 (a) or (b). (A) is a regular octahedral structure composed only of oxygen atoms, and (b) is a regular octahedral structure having aluminum atoms in the regular octahedral structure. As shown in these regular octahedron structural forces (c), a large number of sapphire crystals constitute a sapphire crystal. The surface indicated by the oblique lines in (c) is a surface constituting a part of the C surface of the sapphire crystal.

 In this embodiment, a terrace surface is constituted by the C surface. The crystal grown on the sapphire substrate is greatly influenced by the atoms located on the outermost surface of the sapphire crystal. Therefore, first, the outermost surface of the single crystal sapphire substrate was examined. Figure 7 shows the atoms on the outermost surface from the top in the C-plane direction, which is the outermost surface of the single crystal sapphire substrate. The triangle indicated by the diagonal line in Fig. 7 corresponds to the one side indicated by the diagonal line in the octahedral structure of the sapphire crystal shown in Fig. 6. The hexagon (0701) shown in Fig. 7 corresponds to the C-plane part of the hexagonal column shown in Fig. 3.

[0037] FIG. 8 shows a cross-sectional view taken along the line A—B (0702) shown in FIG. 7 (that is, the A plane (Miller index notation: (11 20))) and viewed from the direction of the arrow. By constructing the sapphire crystal with the C-plane as the main surface, it is clear from Fig. 7 that the atomic layer on the outermost surface also has a monoatomic layer force consisting of only oxygen atoms. Figure 9 shows a cross-sectional view of the terrace surface and steps formed in the same direction as in Fig. 8. The edge of the step has an obtuse angle, an acute angle, or a right angle, as shown in (a), (b), or (c), depending on the cutting angle and the conditions during polishing and heat treatment. Also, as shown in (d) May have either an obtuse angle or a right angle. As shown in (a) to (d), the surface composed of straight lines connecting only oxygen atoms is assumed to have oxygen atoms terminated or outermost in any case. Therefore, in the single crystal sapphire substrate of the present embodiment, the terrace surface is formed by the C surface, and the surface is composed only of oxygen atoms. The step surface is also composed of oxygen atoms, and in principle, aluminum atoms are not arranged on the surface.

 Embodiment 2: Example>

 [0038] In order to measure the atomic arrangement on the surface of the single crystal sapphire substrate shown in the present embodiment, the measurement was performed by low-energy ion scattering spectroscopy (LEISb). As described in Non-Patent Document 1, LEISS can measure the composition and arrangement of surface atoms of a crystal and is an analytical technique used for crystal evaluation. LEISS irradiates the sample surface with a low-energy ion beam, detects scattered ions, and measures changes in the energy spectrum. By changing the energy spectrum of the scattered ions detected by changing the incident angle and the incident direction of the ion beam and changing the atomic arrangement as seen from the irradiation direction of the ion beam, Measure the atomic arrangement of the material. Scattered ions are detected by a time-of-flight measuring device installed coaxially with the ion source. In addition, the time-of-flight measurement device qualifies atoms to be irradiated. In the single crystal sapphire substrate of this embodiment, measurement was performed by irradiating a helium ion pulse as an incident ion beam. The spectrum measured by LEISS is compared with the simulation result obtained by calculation based on the atomic arrangement in the ideal form of the crystal, and the arrangement position of the atom is estimated and evaluated by the position and intensity where the peak appears. Is done.

[0039] Fig. 10 shows the spectrum results of measuring the single crystal sapphire substrate with the main surface of the present embodiment as the C-plane by LEISS. The spectrum shown at the bottom is the simulation result obtained based on the ideal atomic arrangement of the C-plane of the sapphire crystal. Comparing the spectrum obtained from the single crystal sapphire substrate force of this embodiment with the spectrum obtained by simulation, the spectrum and peak detection position force of the incident azimuth angle ranged from 30 degrees to 360 degrees. Crystal sapphire substrate and spatter obtained by simulation Are detected at almost the same angle. In addition, in the peaks (a) to (f) in FIG. 10, the “shoulder” of the peak seen in the simulation results is detected as a small peak or “shoulder” in the single crystal sapphire substrate of this embodiment. It can be seen that a single crystal sapphire substrate having an atomic arrangement very close to the ideal shape is obtained.

[0040] Fig. 25 shows the spectrum results of the single crystal sapphire substrate measured by LEISS when the principal surface is the A-plane. In the LEISS measurement, Heon is irradiated at an angle of 15 degrees to the substrate, and the sapphire substrate to be measured is rotated 360 degrees. In this case, if it is an ideal A-plane, the measurement results have a periodic peak every 180 degrees. In Figure 25, peaks (c) and (d) appear at an angle shifted by 180 degrees with respect to peaks (a) and (b), which are periodic peaks every 180 degrees. . Furthermore, these results show the same spectrum as when the LEISS measurement was performed on the orientation flat of the substrate, and the results for the substrate with the sapphire substrate force A surface shown in Fig. 25 as the main surface. It shows that there is.

 <Embodiment 2: Effect>

 By using the sapphire substrate of this embodiment, an epitaxial film having a flat surface and a low dislocation density can be obtained. An epitaxial film with good crystallinity shows good light emission characteristics even when used as a light emitting element.

 Embodiment 3>

 <Embodiment 3: Concept>

 The present embodiment relates to a heat treatment method for a single crystal sapphire substrate of Embodiment 1 or 2. There are two types of heat treatment methods: a heat treatment method that has a three-step force of a vacuum heating step, a first atmospheric heating step, and a second air heating step, and a heat treatment method that has a two-step force of a vacuum heating step and an atmospheric heating step. is there.

 <Embodiment 3: Configuration>

[0043] In the method for manufacturing a single crystal sapphire substrate of the present embodiment, the heat treatment method includes a heat treatment method having three steps of a vacuum heating step, a first atmospheric heating step, and a second atmospheric heating step, and a vacuum heating step. There are two types of heat treatment methods, a heat treatment method consisting of two steps, an atmospheric heating step. FIG. 11 and FIG. 12 show an example of a heating furnace that performs the heat treatment of the present embodiment. Fig. 11 shows a vacuum heating furnace that performs the vacuum heating step of the heat treatment method with three-stage and two-stage power. The heating furnace (1101) is heated by the heating element (1102). The sample is carried into and out of the heating furnace as the sample stage (1103) moves up and down from below the sample carry-in / out port (1104). The heated sample is set on the sample table while the sample table is lowered, and the sample table is moved in the direction of the arrow and is carried into the heating furnace. Conversely, when unloading, move the sample table in the direction opposite to the arrow and unload it. A cryopump (1105) and a vacuum pump (1106) are attached to the heating furnace, and the inside of the heating furnace is depressurized by the vacuum pump. In order to raise the degree of vacuum, a cryopump for cooling is provided. These controls are performed by the control device (1107).

 FIG. 12 shows an atmospheric heating furnace that performs a first atmospheric heating step and a second atmospheric heating step of a heat treatment method having a three-stage force, and an atmospheric heating step of a heat treatment method having a two-stage force. The Karo heating furnace (1201) is heated by the heating element (1202). The sample is loaded and unloaded from the sample loading / unloading port (1203). A control device (1204) for temperature control and the like is provided to the right of the sample loading / unloading port. In addition, the first and second air heating steps of the heat treatment method with a three-stage force, and the air heat step of the heat treatment method with a two-step force are performed in an air atmosphere or a component atmosphere contained in the air. A flow meter (1205) is provided to check the flow rate of the incoming air.

[0046] In both the three-step heat treatment method and the two-step heat treatment method, heat treatment is first performed in the vacuum heating furnace of FIG. 11, and after the heat treatment is completed, heat treatment is performed in the air atmosphere of the air heating furnace of FIG. I do.

FIG. 13 is a diagram illustrating the flow of heat treatment that also has a three-stage force according to this embodiment. The heat treatment method for the single crystal sapphire substrate according to the present embodiment also includes a vacuum heating step (S1301), a first atmospheric heating step (S1302), and a second atmospheric heating step (S1303). These heat treatments are performed after manufacturing the single crystal sapphire ingot, followed by slicing and polishing, in order to secure a complete crystal layer on the surface of the single crystal sapphire substrate. [0048] In the vacuum heating step (S1301), the single crystal sapphire substrate is heated in a vacuum atmosphere. The purpose of the vacuum heating step is to remove excess oxygen before the alumina sublimation temperature and to vaporize impurities such as sulfides, chlorides and hydroxides mixed during the polishing operation above the melting point. The heating temperature in the vacuum heating step is preferably 1600 ° C or more and 2000 ° C or less, and the holding time is preferably 2 hours or more. This is because when the heating temperature is 1600 ° C or lower or the holding time is less than force time, the single crystal sapphire substrate is greatly deformed when the heating temperature is 2000 ° C or higher, at which impurities are not sufficiently removed. The atmospheric pressure in the vacuum atmosphere is preferably 10 " ⁵ Torr or less U. If the atmospheric pressure is higher than this, the effect of removing impurities is reduced.

 In the first atmospheric heating step (S 1302), the sapphire substrate taken out after the vacuum heating step (S 1301) is heated at a low temperature in an atmospheric atmosphere or a component contained in the atmospheric air. The purpose of the first atmospheric heating step is to acidify and remove carbon as diacid carbon. Low-temperature heating in the atmosphere and components contained in the atmosphere is sufficient if the atmosphere contains sufficient oxygen to oxidize carbon to carbon dioxide. The heating temperature of the first atmospheric heating step is preferably 800 ° C. or higher and 1000 ° C. or lower, and the holding time is 2 hours or longer and 5 hours or shorter. If the heating temperature is 800 ° C or less or the holding time is 2 hours or less, the carbon cannot be sufficiently oxidized to carbon dioxide, and if the heating temperature is 1000 ° C or more or the holding time is 5 hours or more. This is because the single crystal sapphire substrate is deformed. The furnaces used for the vacuum heating step (S1 301) and the first atmospheric heating step (S1302) are preferably different furnaces.

[0050] In the second atmospheric heating step (S1303), after the first atmospheric heating step (S1302), the furnace temperature is raised and further heated. The second air heating step is performed in an air atmosphere or in a component contained in the air. In this step, the steps on the surface of the single crystal sapphire substrate can be regularly arranged. The heating temperature in the second atmospheric heating step is preferably 1000 ° C. or higher and 1300 ° C. or lower, and the holding time is preferably 1 hour or longer and 5 hours or shorter. This is because the steps do not align when the calo heat temperature is 1000 ° C or less or the holding time is 1 hour or less, and the single crystal sapphire substrate is deformed when the calo heat temperature is 1300 ° C or more or the holding time is 5 hours or more. . [0051] In the first atmospheric heating step (SI 302) and the second atmospheric heating step (SI 303), since the temperature distribution depending on the loading position occurs when the substrate is affected by the air flow, the substrate is fixed in the holder. Above, it is better to seal with a sapphire block. The temperature and holding time are varied within the above range according to the tilt angle of the substrate. If the temperature and holding time are out of the above ranges, the step height uniformity and straightness, the flatness of the terrace surface will be impaired, and aluminum atoms will be associated with each other. The correct arrangement may be lost.

 FIG. 14 is a diagram illustrating the flow of heat treatment that also has a two-stage force in the present embodiment. The heat treatment method for the single crystal sapphire substrate of the present embodiment consists of a vacuum heating step (S1401) and an atmospheric calorie heating step (S1402). These heat treatments are performed after slicing and polishing after the production of the single crystal sapphire ingot.

 In the vacuum heating step (S1401), the single crystal sapphire substrate is heated in a vacuum atmosphere.

The heating temperature in the vacuum heating step is preferably 1600 ° C or more and 2000 ° C or less, and the holding time is preferably 2 hours or more. The pressure of the vacuum atmosphere is preferably 10 _ ⁵ Torr or less, as in the heat treatment method with three-stage force.

 In the air heating step (S 1402), the sapphire substrate taken out after the vacuum heating step (S 1401) is heated in an air atmosphere or a component contained in the air. The heating temperature in the atmospheric heating step is preferably 1200 ° C to 1400 ° C, and the holding time is 1 hour to 5 hours. The heat treatment in the air atmosphere and the components contained in the air may be performed in an atmosphere containing sufficient oxygen to oxidize carbon to diacid-carbon. In addition, the atmospheric heating step is performed in an air atmosphere or in a component contained in the air, and regularly arranges steps on the surface of the single crystal sapphire substrate.

 [0055] The purpose of the two-stage heat treatment method and the effect of the heat treatment on the single crystal sapphire substrate are substantially the same as those of the three-stage heat treatment method, and a detailed description thereof will be omitted.

 <Embodiment 3: Specific example>

FIG. 15 shows an example of a specific example of the heat treatment method having a three-stage force according to this embodiment. Using (a), a three-stage heat treatment method will be described. First, in the vacuum heating step, Raise the temperature from room temperature (RT) to 1700 ° C over 7 hours. Hold the temperature at 1700 ° C for 2 hours after raising the temperature, and then lower the temperature to room temperature over 12 hours after holding. After the vacuum heating step is completed, the superheating furnace is changed from the vacuum heating furnace to the atmospheric heating furnace. In the first atmospheric heating step, the temperature is raised from room temperature to 900 ° C over 4 hours and held at 900 ° C for 3 hours. Allow to cool to room temperature over 6 hours after holding. After the first atmospheric heating step, the heating furnace may be changed to another atmospheric heating furnace, or the same heating furnace may be used as it is. In the second heating step, first, the temperature is raised from room temperature to 1200 ° C over 5 hours and held at 1200 ° C for 2 hours. After holding, the temperature is lowered to room temperature over 10 hours to complete the heat treatment. In the heat treatment method with three-stage power, after the first atmospheric heating step is completed, the temperature of the second atmospheric heating step may be started after the temperature is once lowered to room temperature (RT) as shown in (a). Then, as shown in (b), after the first atmospheric heating step, the temperature increase in the second atmospheric heating step may be started without lowering the temperature.

 FIG. 16 shows an example of a specific example of the heat treatment method having a two-step force according to this embodiment. First, in the vacuum heating step, the temperature is raised from room temperature (RT) to 1700 ° C over 7 hours. After raising the temperature, hold it at 1700 ° C for 2 hours and let it cool down to room temperature over 12 hours. After the vacuum calorie heat step, the superheater is changed from a vacuum furnace to an atmospheric furnace. In the atmospheric heating step, the temperature is raised from room temperature to 1300 ° C over 5 hours and held at 1300 ° C for 4 hours. After holding, the temperature is lowered to room temperature over 10 hours to complete the heat treatment.

 [0058] In both the three-stage heat treatment method and the two-stage heat treatment method, the temperature increase rate and the temperature decrease rate are changed according to the performance of the heating furnace to be used.

 <Embodiment 3: Effect>

FIG. 17 shows an AFM measurement image of the surface of the single crystal sapphire substrate obtained by the three-stage heat treatment method of the present embodiment. a) is a single crystal sapphire substrate before heat treatment. In the image of a), it can be seen that the edge of the terrace surface is a curve where the interval between the terrace surfaces is not constant. When this is heat-treated by the three-stage heat treatment method shown in Embodiment 3, b) is obtained. In (b), it can be seen that the terrace surface has almost constant intervals, and the edge of the terrace surface is also composed of a linear force. For reference, c) shows an image of the surface of the single-crystal sapphire substrate obtained by the conventional technique described in Non-Patent Document 2. In the surface of c), the edge of the terrace surface is curved and the interval between the terrace surfaces is not constant. The surface is the same as that of the single crystal sapphire substrate before the bright heat treatment method. Therefore, by carrying out the heat treatment method of the present embodiment, a single crystal sapphire substrate having a straight line and step surfaces with a constant interval could be obtained by a method suitable for mass production.

 Embodiment 4>

 Embodiment 4: Overview>

 In this embodiment, an electronic device or an intermediate structure of an electronic device is manufactured by epitaxially growing an electronic device material on the single crystal sapphire substrate.

 <Embodiment 4: Configuration>

 The electronic device manufacturing method of this embodiment manufactures an electronic device by epitaxially growing an electronic device material on the surface side including the terrace surface of the single crystal sapphire substrate.

 [0062] Epitaxial growth is a method of forming a new crystal layer by aligning the crystal direction with the crystal on the surface of a single crystal substrate, which has been intensively produced in the thin film growth technology. . Since crystal growth by epitaxy can be performed at a temperature lower than the melting point of the crystal, it is used as a means for producing a high-purity crystal with few impurities. In this embodiment, a target crystal film is epitaxially grown using a crystal of a base substrate as a single crystal sapphire substrate. Epitaxial growth methods include vapor phase epitaxy (VPE), molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), and solid phase epitaxy (SPE). There are methods such as Phase Epitaxy).

 As an electronic device material to be epitaxially grown on a single crystal sapphire substrate, there are materials as shown in FIG. Unit elements include silicon (Si), germanium (Ge), and selenium (Se), and compounds include zinc compounds (ZnO, ZnS, ZnSb), barium oxide (BaO), and cadmium compounds (CdS). , CdSe), gallium compounds (GaN ゝ GaAs), indium compounds (InP, InAs, InSb), germanium compounds (GeTe), lead compounds (PbS, PbSe, PbTe), vanadium compounds (VO), antimony compounds (Sb Te ), Bismuth

 2 2 3

 Compound (BiSe, BiTe), Cesium compound (Cs Sb), Copper oxide (Cu 2 O), Silicon compound

 3 2 3 3 2

(SiC), silver compounds (AgSbTe, AgBiS). [0064] These electronic device materials are epitaxially grown on a single crystal sapphire substrate, and diodes (LEDs and LDs), transistors (such as HEMDTs and FETs), ICs, LSIs, photoelectric devices, and rectifiers as shown in Figure 18 Processed into elements, hot cathodes, piezoelectric elements, lasers, Hall elements, thermoelectric elements, varistors, thermistors, etc. It is also possible to manufacture SOS (silicon-ON-Sapphire).

 [0065] In particular, gallium nitride (GaN) is attracting attention as it is used for blue-violet diodes and white diodes. For gallium nitride semiconductors, blue-violet diodes have been put into practical use, and full-color displays using light-emitting diodes have been born. In addition, it is expected to be used as a light source with low power consumption to replace ultraviolet lamps by emitting ultraviolet light and combining with white phosphors. This gallium nitride is the same semiconductor as the gallium arsenide (GaAs), which has been put to practical use as an ultra-high frequency transistor, and has the same group 3 and 5 elemental power. For this reason, in addition to ultrahigh frequency transistors that have made the most of the high carrier mobility of gallium arsenide and gallium nitride, gallium nitride is being considered for use in devices capable of high power operation.

 [0066] An electronic device is generally manufactured by a process as shown in FIG. Electronic device manufacturing consists of four processes: a substrate manufacturing process (1901), a mask manufacturing process (1902), a wafer process (1903), and a thread-and-stand process (1904).

 [0067] The substrate manufacturing process also has four process forces: a substrate manufacturing process (1916), a slicing process (1917), a polishing process (1918), and a heat treatment process (1919). In the substrate manufacturing process, first, a substrate manufacturing process (1916) is performed to manufacture an ingot such as single crystal sapphire, which is a base of an electronic device substrate. Ingots with single-crystal sapphire power are produced by crystal growth methods such as the Chiyoklarsky method (CZ method) and the Kilopros method (kyropoulusu method). An ingot is a cylindrical mass of crystals that serve as a substrate, approximately 2 meters in length and 8 to 12 inches in thickness. These dimensions are for the purpose of electronic devices and on a single wafer. Vary depending on the number of electronic devices created.

Next, a slicing step (1917) for cutting the single crystal sapphire ingot into a thin plate-like wafer is performed. In the slicing process, the ingot is cut into a disk shape with a thickness of about 1 mm. There are two main cutting methods used in the slicing process: blade saw method and wire saw method. The blade saw method is shown in Fig. 20 a). The ingot (2002) is cut by rotating the inner peripheral blade (2001) of high hardness stainless steel. The feature is that the flatness of the cut surface is good. In the wire saw method, as shown in b), ingots (2004) are cut while the diamond particles on the slurry are passed through a plurality of tensioned piano wires (2003) and reciprocating the piano wires. Compared to the blade saw method, the wire saw method has the same flatness of the cut surface as the blade saw method, but is advantageous in terms of cost because the slice speed is high, and is advantageous for manufacturing large-diameter wafers. When cutting an ingot made of a single crystal sapphire cover, if the ingot is fixed with glass or carbon as a holding material, the ingot may be displaced with respect to the cutting direction. Therefore, by using hard calcium carbonate as the material of the holding material, it is possible to keep the deviation of the cutting angle within 0.01 degrees.

[0069] When the slicing step is completed, the next step is a polishing step (1918). In the polishing process, first, the side surface of the wafer is polished by mechanical polishing. For mechanical polishing, polishing is performed using a polishing liquid of an abrasive with a fine particle size. After the side surfaces are polished, mirror polishing, which is polishing of the cross section cut in the slicing process, is performed. The mirror polishing is performed by the apparatus shown in FIG. The polishing head (2104) attached with the wafer (2103) is brought into contact with the polishing pad (2102) affixed on the rotating surface plate (2101) with a constant pressure to polish the wafer. The polishing agent is a slurry-like polishing liquid.

[0070] The wafer that has undergone the polishing step is subjected to a heat treatment step after washing. The heat treatment process is performed in order to secure a complete crystal layer near the surface of the wafer that also has a single crystal sapphire force. The detailed heat treatment method in the heat treatment step has been described in Embodiment 3, and will be omitted.

 On the other hand, in the mask manufacturing process, a circuit is first designed (1905), and then a circuit pattern for designing the designed circuit on the wafer is designed (1906). Then, a mask for transferring the designed pattern onto the wafer is manufactured (1907). The mask is used in a lithography process for transferring the circuit onto the thin film. The mask has a circuit formed on the thin film with chromium or the like on the surface of the quartz plate.

[0072] When the wafer and the mask are completed, a wafer process, which is a process for forming a circuit on the wafer, is performed. The wafer process consists of a substrate process (1908) and a lithography process (19 09) The wiring process (1910) has three major process forces. The substrate process, the lithography process, and the wiring process are repeated several times depending on the complexity of the target electronic device, as shown in FIG.

 [0073] The substrate process also has process powers such as a cleaning process (2201), a heat treatment process (2202), an impurity introduction process (2203), a film formation process (2204), and a flattening process (2205).

 The cleaning process is a process for surface cleaning that is always performed between each process including the lithography process and the wiring process. In this process, cleaning is often performed using a combination of chemicals such as sulfuric acid, hydrochloric acid, ammonia, hydrogen fluoride, and hydrogen peroxide. The object of removal by washing is organic residue, oxide residue, metal contamination and so on. In some cases, removal of damage such as crystal defects may also be a cleaning step.

 [0075] The heat treatment step is not necessarily a step that must be performed, which is an essential step in the case of a silicon substrate or the like. A very clean furnace is used for the heat treatment process, and a carefully cleaned wafer is used. By heat treatment, several hundreds of oxide films are formed on the wafer surface. This film becomes an insulating film and is the starting point for semiconductor device manufacturing using silicon.

 [0076] The impurity introduction step is a technique for introducing a trivalent or pentavalent element such as boron arsenic or phosphorus as an impurity into a silicon substrate or the like to form a pn bond or control the impurity concentration. Impurity introduction methods include ion implantation, thermal diffusion, and ion doping. Currently, ion implantation is the mainstream. In the ion implantation method, ions such as boron and arsenic phosphorus separated in a vacuum are accelerated by applying a high voltage and implanted into a substrate.

 [0077] The film formation process is performed on a wafer by vapor phase epitaxy (VPE), molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), solid phase epitaxy (SPE). : Solid Phase Epitaxy) is a process of epitaxially growing various substances to form thin films.

[0078] Figure 23 shows a schematic diagram of an example of an epitaxial growth method of GaN crystals on a single crystal sapphire substrate by the halogen vapor phase epitaxy (HVPE), which is one of the vapor phase growth methods. In (a), the metal-organic vapor phase growth method (Meta 卜 Organic Vapor Phase Fig. 23 (b) shows a schematic diagram of an example of an epitaxy growth method of GaN crystals on a single crystal sapphire substrate by Epitaxy (MOVPE). In the HVPE method, metallic gallium held at a high temperature of about 900 ° C and a hydrogen chloride gas are reacted in an internal reaction tube to mainly produce gallium chloride, and a single unit maintained at about 1000 ° C. A GaN crystal is grown by reacting with ammonia near the crystal sapphire substrate. Ammonia and hydrogen chloride are supplied with the carrier gas. In this method, it is essential to control the temperature at two locations, the salt gallium generator and the single crystal sapphire substrate, and the flow rate control of the salt hydrogen gas and ammonia. In the MOV PE method, generally, only a single crystal sapphire substrate is heated to about 1000 ° C by a substrate heating heater, and there is an organic metal compound, which is a compound of gallium and an organic material, and nitrogen. The raw ammonia is transported with the carrier gas, and GaN crystals grow. In this case, only the single crystal sapphire substrate needs heating and temperature control.

 [0079] The flattening process is a process in which unevenness on the wafer surface is eliminated and a uniform surface shape is obtained.

 As a method used in the flattening step, there is an etch back method, but a typical method is chemical mechanical polishing. The flattening process is an exposure process in the lithography process, which is an important process for securing a deep depth of focus (a focused area), exposing fine patterns, and improving the level difference that occurs in the film formation process. .

 The lithography process also includes photoresist application (2206), exposure (2207), development (2208), etching (2209), and resist removal (2210). Various other processes may be included in the lithography process. In the lithography process, first, a photoresist, which is a photosensitive resin, is coated on a thin film such as a GaN crystal, and then passed through a mask on which a circuit pattern such as an IC is formed. Then, an ultraviolet ray, excimer laser beam, electron beam, X The mask pattern is transferred onto the thin film by exposing it to light. Development is then performed to form a circuit on the thin film, and etching and resist removal are performed.

When the circuit is formed on the thin film, wiring is performed next. Since the wiring process is almost the same as the above-described substrate process in detail, the description thereof will be omitted because the film forming process (2 211), the flattening process (2212), the cleaning process (2213), etc. have the same force. The wiring process is repeated many times depending on the number of electronic device layers. When the wiring is completed and the wafer process is completed, the assembly process is started. The assembly process consists of dicing (1911), mounting (1 912) mounting the electronic device on the frame, and cutting the wafer on which a large number of electronic devices are formed into individual electronic devices. And a frame (1913) in which the frame is connected with a thin gold wire, an encapsulation process (1914) in which the electronic device is encapsulated with grease, and an inspection process (1915) in which the quality of the electronic device is checked. When the inspection is completed, it is shipped as an electronic device. <Embodiment 4: Effect>

 FIG. 24 shows the relationship of the output with respect to the forward voltage of the blue LED produced by the single crystal sapphire substrate of this embodiment. The forward voltage (Vf) is the voltage when a constant current flows through the P → N junction, and the output was measured with a photodetector using an integrating sphere. A blue LED was manufactured by epitaxially growing a gallium nitride thin film on the single crystal sapphire substrate of this embodiment. The blue LED fabricated with the single crystal sapphire substrate of the present embodiment clearly has a higher output than the blue LED manufactured by the conventional technology. This is because the crystal orientation is strictly controlled, and the electronic device material is grown on the monolayer sapphire substrate terminated with a straight step, flat terrace, and oxygen atoms terminated in a constant direction and uniform height. This is because a single-crystal sapphire substrate that is formed and has a crystal orientation and a flat layer that are closer to the ideal and has no defects is manufactured.

 Brief Description of Drawings

[0084] [Fig.1] Conceptual diagram of the surface of single crystal sapphire substrate

 FIG. 2 shows a surface of a single crystal sapphire substrate of Embodiment 1.

 [Figure 3] Diagram showing the crystal morphology of single crystal sapphire

 圆 4] Diagram explaining macroscopic surface

 [Figure 5] AFM measurement data of single crystal sapphire substrate

 [Fig.6] Conceptual diagram explaining the crystal structure of sapphire

 [Fig.7] Conceptual diagram of the C-plane outermost surface of a sapphire single crystal

 [Fig.8] Cross section perspective when sapphire single crystal is cut

 [Fig.9] Cross-sectional perspective view of a sapphire single crystal with a step cut

[Fig.10] LEISS measurement data of single crystal sapphire substrate with C-plane as main surface [Fig. 11] Example of vacuum heating furnace of Embodiment 3

[Fig. 12] Example of atmospheric heating furnace of Embodiment 3

圆 13] Flow chart showing the method of manufacturing the single crystal sapphire substrate of Embodiment 3 圆 14] Flow chart showing the method of manufacturing the single crystal sapphire substrate of Embodiment 3 圆 15] Change in heat treatment temperature of the single crystal sapphire substrate of Embodiment 3 圆16] Change in heat treatment temperature of single crystal sapphire substrate of embodiment 3

 FIG. 17: AFM measurement image of single crystal sapphire substrate of Embodiment 3.

圆 18] Diagram for explaining the electronic device manufacturing method of Embodiment 4 実 施 19] Diagram for explaining the flow of the electronic device manufacturing method of Embodiment 4 の 20] The wafer cutting method of Embodiment 4 FIG. 21] A diagram for explaining the wafer polishing method of the fourth embodiment. FIG. 22] A diagram for explaining the electronic device manufacturing method of the fourth embodiment. FIG. 23] The electronic device manufacturing method of the fourth embodiment. Illustration 圆 24] Maximum forward voltage measurement result of electronic device of Embodiment 4

 [Fig.25] LEISS measurement data of single crystal sapphire substrate with A-plane as main surface Explanation of symbols

 0201 Terrace

 0202 Step side

 0203 Macroscopic edge

 0204 Edge

 0205 Macroscopic surface

Claims

The scope of the claims  [1] A single crystal sapphire substrate in which regular steps having a terrace surface are formed on a single crystal sapphire surface,  The surface roughness (Ra) of the terrace surface is 0.03 nm or less,  The step height is from 0.1 nm to 0.3 nm,  The terrace width is 500nm ± 50nm,  Single crystal sapphire substrate. [2] The macroscopic surface of the single crystal sapphire substrate is tilted at an angle of 0.1 degree force and 0.6 degree relative to the main surface.  The single crystal sapphire substrate according to claim 1. [3] The main surface of the single crystal sapphire substrate is the C / A / R / M plane!  The single crystal sapphire substrate according to claim 1 or 2. [4] The terrace surface is configured so that oxygen atoms terminate and form a monoatomic layer of oxygen.  The single crystal sapphire substrate according to any one of claims 1 to 3. [5] a vacuum heating step for heating the single crystal sapphire substrate in a vacuum atmosphere;  An atmospheric heating step of heating the sapphire substrate taken out after the vacuum heating step in an air atmosphere, and a method for manufacturing a single crystal sapphire substrate. [6] A vacuum heating step for heating the single crystal sapphire substrate in a vacuum atmosphere, and a first atmospheric caloric heating step for heating the sapphire substrate taken out after the vacuum caloric heating step in an air atmosphere at a low temperature;  After the first atmospheric heating step, a second atmospheric heating step in which the furnace temperature is raised and further heated, and a powerful method for producing a single crystal sapphire substrate. [7] a vacuum heating step of heating the single crystal sapphire substrate in a vacuum atmosphere;  A first atmospheric heating step of heating the sapphire substrate taken out after the vacuum heating step at a low temperature under a component atmosphere contained in the atmosphere; After the first atmospheric heating step, a second atmospheric heating step of raising the furnace temperature and further heating in a component atmosphere contained in the atmosphere; A method for producing a single crystal sapphire substrate.  [8] The heating temperature in the vacuum heating step is 1600 ° C or more and 2000 ° C or less, and the holding time is 2 hours or more,  The heating temperature of the first atmospheric heating step is 800 ° C or higher and 1000 ° C or lower, the holding time is 2 hours or longer and 5 hours or shorter,  The heating temperature of the second atmospheric heating step is 1000 ° C or higher and 1300 ° C or lower, and the holding time is 1 hour or longer and 5 hours or shorter,  The method for producing a single crystal sapphire substrate according to claim 6. [9] The heating temperature of the vacuum heating step is 1600 ° C or more and 2000 ° C or less, and the holding time is 2 hours or more,  The heating temperature of the atmospheric heating step is 1200 ° C or higher and 1400 ° C or lower, and the holding time is 1 hour or longer and 5 hours or shorter,  The method for producing a single crystal sapphire substrate according to claim 5. [10] An electronic device manufacturing method for manufacturing an electronic device by epitaxially growing an electronic device material on a surface side including a terrace surface of the single crystal sapphire substrate according to any one of [1] to [4].  11. The method for manufacturing an electronic device according to claim 10, wherein the electronic device material is gallium nitride.  [12] An electronic device intermediate structure using the single crystal sapphire substrate according to any one of claims 1 to 4 and epitaxially growing an electronic device material on a surface side including the terrace surface.