WO2012008208A1

WO2012008208A1 - Process for producing single-crystal sapphire, and single-crystal sapphire substrate

Info

Publication number: WO2012008208A1
Application number: PCT/JP2011/060642
Authority: WO
Inventors: 智博庄内
Original assignee: 昭和電工株式会社
Priority date: 2010-07-16
Filing date: 2011-05-09
Publication date: 2012-01-19
Also published as: TW201204881A; JP2012020916A

Abstract

A process for producing a sapphire ingot includes: a heating step (S101) in the solid phase in which solid aluminum oxide (alumina) filled in a crucible in a heating furnace is heated and held at a temperature less than the melting point (2050°C); a melting step (S102) in which the aluminum oxide in the crucible is melted; a heating step (S103) in the liquid phase in which the aluminum oxide is heated and held at a temperature higher than the melting point thereof; a shoulder-part formation step (S105) in which a seed crystal is pulled up while being rotated to form a shoulder part beneath the seed crystal; and a straight-part formation step (S106) in which the shoulder-part is pulled up while being rotated via the seed crystal while the lower end part of the shoulder-part is kept in contact with the alumina melt to form a straight part beneath the shoulder part. Thus, a process for producing a single-crystal sapphire substrate with few metal impurities and crystal defects (air bubbles), and a single-crystal sapphire substrate are provided.

Description

Sapphire single crystal manufacturing method and sapphire single crystal substrate

The present invention relates to a method for producing a sapphire single crystal and a sapphire single crystal substrate.

In general, a semiconductor light emitting device having a compound semiconductor layer such as a III-V group compound semiconductor layer is formed after a compound semiconductor layer is formed on a substrate made of a sapphire single crystal and a positive electrode, a negative electrode, and the like are further provided thereon. The surface to be ground of the substrate is ground and polished, and then cut into an appropriate shape to prepare a light emitting element chip (Patent Document 1).
As a technique for growing a high-quality sapphire single crystal, a production method using a seed crystal with a low Si concentration (Patent Document 2), a production method with reduced zirconium (Zr) impurities in an alumina melt (Patent Document 3), etc. have been proposed. ing.

JP 2008-177525 A JP 2008-260640 A JP 2008-081370 A

By the way, the sapphire single crystal substrate on which the compound semiconductor layers are stacked is obtained by cutting out a single crystal ingot manufactured by the Czochralski method (CZ method), for example. In general, in the CZ method, it is known that when a sapphire single crystal is grown from an alumina melt, crystal defects and strain are generated in the sapphire single crystal due to slight fluctuations in manufacturing conditions. In particular, a large-diameter sapphire ingot having a diameter of 100 mm or more requires precise control of impurity control, strain relaxation technology, temperature uniformity, temperature gradient, etc., and produces a crystal with few crystal defects, strain, and impurities throughout the ingot. Therefore, it is necessary to examine and optimize new breeding conditions.
Among these, reduction of crystal defects such as bubbles is important. In particular, the large-diameter substrate was easy to entrap bubbles in the crystal, which was a major factor in quality degradation. In addition, air bubbles may cause cracks and cracks in the cutting process and the like, and also cause a reduction in surface processing yield. The inventor has found that the cause of bubble generation is mainly a specific metal element. Specifically, it has been derived that reduction measures for sodium (Na), barium (Ba), vanadium (V), and these compounds whose oxide decomposition temperatures are close to the melting point of sapphire are important issues.
Among the metal elements, Na is contained in the high-purity alumina, which is a raw material, in an amount of about 1 to 20 ppm, and is present in a large amount in the work environment and the human body.
On the other hand, in a sapphire single crystal substrate with many crystal defects (bubbles) and metal impurities, a high-quality compound semiconductor layer may not be formed in the step of epitaxially growing the compound semiconductor layer. That is, the quality of the compound semiconductor layer affects the light emission efficiency and electrical characteristics of the semiconductor light emitting device.
An object of the present invention is to provide a method for manufacturing a sapphire single crystal substrate with few metal impurities and crystal defects (bubbles), and a sapphire single crystal substrate.

According to the present invention, the following inventions [1] to [7] are provided.
[1] In a sapphire single crystal pulling apparatus using the Czochralski method (CZ method), a melt obtained by melting a raw material of aluminum oxide having a sodium (Na) concentration of 1 ppm or more in a crucible at a temperature exceeding the melting point of aluminum oxide. A heating step in a liquid phase held in a liquid state and a seed crystal attached to the melt of aluminum oxide in the crucible are pulled up while rotating, so that the diameter increases toward the lower side of the seed crystal. A shoulder forming step of forming a shoulder, and a barrel forming step of forming a cylindrical trunk under the shoulder by pulling up the shoulder attached to the melt while rotating. A method for producing a sapphire single crystal.
[2] The method for producing a sapphire single crystal according to [1], wherein the heating step in the liquid phase is performed at a temperature higher than the melting point of aluminum oxide by 30 ° C. or more and 300 ° C. or less. .
[3] The above item [1], wherein the melt in the heating step in the liquid phase is formed by melting the raw material of aluminum oxide in the crucible from the lower part to the upper part of the crucible. Or the manufacturing method of the sapphire single crystal as described in [2].
[4] The heating method in a solid phase in which the aluminum oxide raw material in the crucible is kept at a temperature lower than the melting point of aluminum oxide before the heating step in the liquid phase. [1] The method for producing a sapphire single crystal according to any one of [3].
[5] The method for producing a sapphire single crystal as described in [4] above, wherein the heating step in the solid phase is performed at a temperature of 1200 ° C. or higher and lower than 2050 ° C.
[6] The above item [4] or [5], wherein the raw material of aluminum oxide in the crucible in the heating step in the solid phase is heated from the lower part to the upper part of the crucible. Of producing a single crystal of sapphire.
[7] Concentrations of sodium (Na), barium (Ba), and vanadium (V) produced by the method for producing a sapphire single crystal described in any one of [1] to [6] above are , A sapphire single crystal substrate having a diameter of 100 mm or more, both of which are less than 1 ppm.

According to the present invention, a sapphire single crystal with few metal impurities and crystal defects (bubbles) can be obtained as compared with the case without this configuration, the surface processing yield can be improved, and the compound semiconductor is formed on the sapphire single crystal substrate. A semiconductor light emitting device manufactured by forming a layer has improved light emitting characteristics and electrical characteristics.

It is a figure explaining an example of a single crystal pulling device. The example of a structure of the sapphire ingot manufactured using the single crystal pulling apparatus shown in FIG. 1 is shown. It is a flowchart for demonstrating the procedure which manufactures the sapphire ingot shown in FIG. 2 using the single crystal pulling apparatus shown in FIG. It is a figure explaining an example of the semiconductor light emitting element manufactured by this Embodiment. The temperature, time, and evaluation results in the heating step in the solid phase and the heating step in the liquid phase in Examples 1 to 3 and Comparative Examples 1 to 3 are shown.

Hereinafter, embodiments of the present invention will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary. The drawings used are examples for explaining the present embodiment and do not represent actual sizes.

<Single crystal pulling device I>
In the present embodiment, a predetermined single crystal pulling apparatus (sapphire single crystal pulling apparatus) I capable of growing a large-diameter sapphire single crystal of 100 mm or more is used, and a sapphire single crystal ingot (sapphire ingot 30) is manufactured by the CZ method. To do. Here, manufacturing the sapphire ingot 30 is expressed as manufacturing a sapphire single crystal.
FIG. 1 is a diagram illustrating an example of a single crystal pulling apparatus I. As shown in FIG. 1, the single crystal pulling apparatus I includes a heating furnace 10 for growing a sapphire ingot 30 made of a single crystal of sapphire. The heating furnace 10 includes a heat insulating container 11. The heat insulating container 11 has a columnar outer shape, and a columnar space is formed therein. The heat insulating container 11 is configured by assembling parts made of a heat insulating material made of zirconia (ZrO ₂ ), for example. The heating furnace 10 includes a chamber 14 that accommodates the heat insulating container 11 in an internal space. The heating furnace 10 includes a gas supply pipe 12 that is formed through the side surface of the chamber 14 and supplies gas from the outside of the chamber 14 to the inside of the heat insulating container 11 through the chamber 14. Similarly, a gas exhaust pipe 13 that is formed through the side surface of the chamber 14 and exhausts gas from the inside of the heat insulating container 11 to the outside through the chamber 14 is further provided.

The crucible 15 is arrange | positioned so that it may open toward the vertically upward direction below the inner side of the heat insulation container 11. FIG. The crucible 15 is made of, for example, iridium (Ir), and contains an alumina melt 35 formed by melting aluminum oxide.

The heating furnace 10 includes a metal heating coil 16. The heating coil 16 is wound around a portion that is outside the side surface on the lower side of the heat insulating container 11 and inside the side surface on the lower side of the chamber 14. The heating coil 16 faces the wall surface of the crucible 15 through the heat insulating container 11 and is arranged so as to be movable in the vertical direction.

The heating coil 16 is constituted by, for example, a hollow copper tube, wound spirally, and has a cylindrical shape when viewed as a whole. In the present embodiment, the inner diameter on the upper side and the inner diameter on the lower side of the heating coil 16 are substantially the same. Thereby, the space formed in the inside by the wound heating coil 16 is cylindrical. Further, the central axis of the heating coil 16 passing through the cylindrical space is substantially perpendicular to the horizontal direction, that is, along the vertical direction. The crucible 15 is disposed inside a cylindrical space formed by the heating coil 16. Then, the crucible 15 is placed at a site that is substantially at the center of the circular region formed by the heating coil 16.

The heating furnace 10 includes a lifting rod 17 that extends downward from above through through holes provided in the upper surfaces of the heat insulating container 11 and the chamber 14, respectively. The pulling rod 17 is attached so as to be able to move in the vertical direction and rotate around the axis. A sealing material (not shown) is provided between the through hole provided in the chamber 14 and the lifting rod 17. A holding member 18 for attaching and holding a seed crystal 31 (see FIG. 2 described later) serving as a base for growing the sapphire ingot 30 is attached to an end portion on the vertically lower side of the pulling rod 17. Yes.

The single crystal pulling apparatus I includes a pulling drive unit 19 for pulling up the pulling bar 17 vertically upward and a rotation driving unit 20 for rotating the pulling bar 17. Here, the pulling drive unit 19 is constituted by a motor or the like, and the pulling speed of the pulling rod 17 can be adjusted. The rotation drive unit 20 is also composed of a motor or the like so that the rotation speed of the lifting rod 17 can be adjusted.
The single crystal pulling apparatus I includes a gas supply unit 21 that supplies gas into the chamber 14 via the gas supply pipe 12. In the present embodiment, the gas supply unit 21 supplies a mixed gas in which oxygen supplied from the O ₂ source 22 and nitrogen as an example of an inert gas supplied from the N ₂ source 23 are mixed. And the gas supply part 21 adjusts the oxygen concentration in mixed gas by changing the mixing ratio of oxygen and nitrogen. The flow rate of the mixed gas supplied into the chamber 14 is also adjusted.

The single crystal pulling apparatus I includes an exhaust unit 24 that exhausts gas from the inside of the chamber 14 via the gas exhaust pipe 13. The exhaust unit 24 includes, for example, a vacuum pump or the like, and is capable of decompressing the chamber 14 and exhausting the gas supplied from the gas supply unit 21.
The single crystal pulling apparatus I includes a coil power supply 25 that supplies current to the heating coil 16. The coil power supply 25 sets whether to supply current to the heating coil 16 and the amount of current to be supplied.
In addition, a weight detection unit 27 that detects the weight of the sapphire ingot 30 that grows on the lower side of the lifting rod 17 through the lifting rod 17 is provided. The weight detection unit 27 includes, for example, a known weight sensor.
Furthermore, the single crystal pulling apparatus I includes a coil driving unit 28 that moves the heating coil 16 in the vertical direction. Instead of moving the heating coil 16 in the vertical direction, the crucible 15 may be moved in the vertical direction.

The single crystal pulling apparatus I includes a control unit 26 that controls the pulling drive unit 19, the rotation drive unit 20, the gas supply unit 21, the exhaust unit 24, the coil power supply 25, and the coil drive unit 28 described above. Further, the control unit 26 calculates the crystal diameter of the sapphire ingot 30 to be pulled up based on the weight signal output from the weight detection unit 27 and feeds it back to the coil power supply 25.

<Sapphire Ingot 30>
FIG. 2 shows an example of the configuration of the sapphire ingot 30 manufactured using the single crystal pulling apparatus I shown in FIG.
The sapphire ingot 30 includes a seed crystal 31 that is a base for growing the sapphire ingot 30, a shoulder portion 32 that extends under the seed crystal 31 and is integrated with the seed crystal 31, and a lower portion of the shoulder portion 32. A straight body portion (body portion) 33 extending and integrated with the shoulder portion 32, and a tail portion 34 extending under the straight body portion 33 and integrated with the straight body portion 33 are provided. In the present embodiment, in this sapphire ingot 30, a single crystal of sapphire grows in the c-axis direction from the upper seed crystal 31 side toward the lower tail portion 34 side.

Here, the shoulder portion 32 has a shape in which the diameter gradually increases from the seed crystal 31 side toward the straight body portion 33 side. Further, the straight body portion 33 has a shape such that the diameters thereof are substantially the same from the top to the bottom. The diameter of the straight body portion 33 is set to a value slightly larger than the diameter of the sapphire single crystal substrate 110 (see FIG. 4 described later) designed in advance.
The straight body portion 33 is a body portion. However, since it is cylindrical, it is called a straight body part.

The inventor has found that the generation of bubbles is due to the decomposition of a metal compound contained as an oxide and the like, and has found that crystal defects can be reduced by paying attention to the concentration of a specific element.
That is, before the growth of the sapphire ingot 30, metal impurities that exist in the raw material aluminum oxide (alumina) and decompose at a temperature close to the crystal growth temperature of the sapphire ingot 30, such as sodium (Na) and barium (Ba). It is important to remove vanadium (V). Among these, it has been found that Na which is easily mixed into the alumina melt 35 and is present in a large amount in the environment is particularly important. Many of these metal impurities are contained as oxides. The cause of the bubble was derived from the fact that the gas in which these oxides were decomposed and evaporated was taken into the sapphire ingot 30 which is a sapphire single crystal.

As one means for removing these metal compounds, it is effective to heat (bake) aluminum oxide (alumina) as a raw material of the sapphire ingot 30 at a high temperature before the sapphire ingot 30 is grown.
Heating at a high temperature is desirably performed under reduced pressure. It is also a suitable method to promote convection by heating the crucible 15 with an upper and lower temperature difference.
Na ₂ O has a decomposition temperature of 1950 ° C., BaO has a boiling point of 2000 ° C., and V ₂ O ₅ has a decomposition temperature of 1750 ° C. Therefore, by taking these metal oxides decompose or volatilize before the growth of the sapphire ingot 30 by heating at a high temperature, it is possible to suppress the incorporation of bubbles and metals into the sapphire ingot 30.
On the other hand, sodium chloride (NaCl), which is a source of Na, may be mixed into the raw material from the environment or an operator. NaCl has a melting point of 801 ° C. and a boiling point of 1413 ° C. It can evaporate by heating in the state of the solid phase before a raw material melt | dissolves mainly, and the uptake | capture to the sapphire ingot 30 can be suppressed.

In addition to this method, it is also effective to take measures to suppress the mixing of impurities, such as refining and pretreatment of the raw material aluminum oxide, increasing the purity of the heat insulating material constituting the heat insulating container 11, and purifying the atmosphere in the chamber 14. is there.

When the aluminum oxide is heated in a solid state, the heating temperature is preferably a temperature at which the three metal oxides start to decompose or evaporate, and considering that NaCl evaporates under reduced pressure, at least 1200 ° C. or higher, Desirably, it is 1750 degreeC or more. Since it is carried out in a solid phase, it is preferably less than the melting point (2050 ° C.) of aluminum oxide, desirably less than 2000 ° C., and even less than 1800 ° C. In the case of heating in a solid state, there is an advantage that decomposition products and evaporation products are easily released into the atmosphere.

As a result, it has been found that the bubbles in the sapphire single crystal substrate 110 can be reduced along with the reduction of the metal impurity concentration of the sapphire single crystal substrate 110 (see FIG. 4 described later). It is considered that fine bubbles also affect the film quality of the group III compound semiconductor layer 100 (see FIG. 4 described later) epitaxially grown on the sapphire single crystal substrate 110. By these methods, the Na concentration in the large-diameter sapphire ingot 30 was reduced, and it was possible to stably grow a high-purity sapphire single crystal of less than 1 ppm. Furthermore, by optimizing the conditions, a Na concentration of less than 0.5 ppm was achieved.

<Procedure for Producing Sapphire Ingot 30>
FIG. 3 is a flowchart for explaining a procedure for manufacturing the sapphire ingot 30 shown in FIG. 2 using the single crystal pulling apparatus I shown in FIG.
In manufacturing the sapphire ingot 30, first, a solid aluminum oxide (alumina) filled in the crucible 15 in the heating furnace 10 is heated (baked) and held at a temperature lower than the melting point (2050 ° C.). The heating process at is performed (step 101).
Next, a melting step for melting the aluminum oxide in the crucible 15 is executed (step 102).
And the heating process in the liquid phase hold | maintained while heating (baking) in the temperature higher than melting | fusing point of aluminum oxide is performed (step 103).
Next, the lower end portion of the seed crystal 31 is brought into contact with the aluminum oxide melt, that is, the alumina melt 35 (step 104). In this state, the shoulder crystal forming step of forming the shoulder portion 32 below the seed crystal 31 is performed by pulling up the seed crystal 31 while rotating the seed crystal 31 (step 105).
Subsequently, in a state where the lower end portion of the shoulder portion 32 is in contact with the alumina melt 35, the shoulder portion 32 is pulled upward while rotating through the seed crystal 31, so that the straight body portion ( A straight body forming process (body forming process) for forming the body part 33 is executed (step 106).
Subsequently, in a state where the lower end portion of the straight body portion 33 is in contact with the alumina melt 35, the straight body portion 33 is pulled upward while rotating through the seed crystal 31 and the shoulder portion 32. By performing the separation, a tail forming process for forming the tail 34 below the straight body 33 is executed (step 107).
Then, after the obtained sapphire ingot 30 is cooled, it is taken out of the heating furnace 10 to complete a series of manufacturing steps.

Next, in the ingot state, the sapphire ingot 30 is heat-treated to relieve strain caused by the temperature distribution in the ingot. For example, if the sapphire ingot 30 corresponds to a diameter of 100 mm, the heat treatment is performed under conditions of 1200 ° C. or higher and 3 hours or longer, preferably 1500 ° C. or higher and 5 hours or longer. The temperature increase / decrease rate is 1.0 ° C./min to 10.0 ° C./min, preferably 2.0 ° C./min to 7.0 ° C./min.
For these conditions, if the diameter (size) of the sapphire single crystal substrate 110 (see FIG. 4 to be described later) is increased, for example, if the diameter is 150 mm, the temperature is increased and the time is increased. .
Next, the sapphire ingot 30 obtained in this way is first cut at the boundary between the shoulder portion 32 and the straight body portion 33 and at the boundary between the straight body portion 33 and the tail portion 34, and the straight body portion 33 is cut out. It is. Next, the cut out straight body portion 33 is further cut in a direction orthogonal to the longitudinal direction of the sapphire ingot 30 by, for example, a multi-wire saw, and the surface is polished to become the sapphire single crystal substrate 110. At this time, since the sapphire ingot 30 of this embodiment is grown in the c-axis direction of the sapphire single crystal, the main surface of the obtained sapphire single crystal substrate 110 is the C plane of the sapphire single crystal ((0001 ) Surface).
Depending on the growth conditions of the compound semiconductor layer, the main surface of the substrate may be processed with an off-angle from the C plane. In addition, it is possible to cut out other than the C plane.

Now, the above steps will be described in detail. However, here, the description will be given in order from the preparation process executed before the heating process in the solid phase of Step 101.

(Preparation process)
In the preparation step, first, the seed crystal 31 is attached to the holding member 18 of the pulling rod 17 and set at a predetermined position. At this time, the C plane ((0001) plane) of sapphire is exposed at the lower end of the seed crystal 31. Next, the crucible 15 is filled with a raw material of aluminum oxide, and the heat insulating container 11 is assembled using components made of a heat insulating material made of zirconia. Note that aluminum oxide as a raw material is powder or fine crystal pieces. The Na concentration in the starting aluminum oxide is about 1 to 10 ppm. Furthermore, in order to increase the purity to less than 1 ppm, advanced techniques such as a purification treatment are required, the productivity is lowered, and the cost of raw materials is increased. In addition, the maintenance of work environments and work methods with thorough countermeasures against Na contamination also lead to a decrease in productivity.
On the other hand, V and Ba in the raw material have a low concentration of less than 1 ppm, but the concentration may vary depending on the manufacturer, production time, and the like.
And the inside of the heat insulation container 11 is pressure-reduced using the exhaust part 24 in the state which does not supply the gas from the gas supply part 21. FIG.
At this time, the pressure inside the heat insulating container 11 is reduced to 1 Pa or less, preferably 10 ⁻³ Pa or less, and more preferably 10 ⁻⁵ Pa or less.

(Heating process in solid phase)
Next, the solid aluminum oxide filled in the crucible 15 is heated (baked) at a temperature of 1200 ° C. or higher and lower than the melting point of aluminum oxide (2050 ° C.). That is, since aluminum oxide does not dissolve, it becomes heating in the solid phase. In addition, when the temperature to heat exceeds 1800 degreeC, the powder or crystal | crystallization piece of the aluminum oxide which is a raw material of the sapphire ingot 30 fuse | melts, and decomposition | disassembly of a metal compound and volatilization of a metal compound are inhibited. Therefore, the heating temperature is preferably 1200 ° C. or higher and lower than 1800 ° C.
Moreover, in the heating step in the solid phase, it is preferable that heating is performed from the lowermost end of the crucible 15 filled with the raw material aluminum oxide, and the raw material aluminum oxide is sequentially heated from the bottom to the top of the crucible 15. This promotes the volatilization of a metal compound such as NaCl and a metal formed by decomposition of the metal compound and a gas such as oxygen, which is preferable.

The crucible 15 is heated by the coil power supply 25 supplying a high-frequency alternating current (hereinafter referred to as a high-frequency current) to the heating coil 16. When a high frequency current is supplied from the coil power supply 25 to the heating coil 16, the magnetic flux repeatedly generates and disappears around the heating coil 16. When the magnetic flux generated by the heating coil 16 crosses the crucible 15 through the heat insulating container 11, a magnetic field is generated on the wall surface of the crucible 15 so as to prevent the change of the magnetic field, thereby causing a vortex in the crucible 15. Electric current is generated. The crucible 15 generates Joule heat (W = I ² R) proportional to the skin resistance (R) of the crucible 15 by the eddy current (I), and the crucible 15 is heated. The crucible 15 is heated, and accordingly, the aluminum oxide accommodated in the crucible 15 is heated.

In order to heat the crucible 15 from below to above, the coil drive unit 28 moves the center position of the heating coil 16 in the vertical direction to the lower end of the crucible 15, and then the coil power supply 25 moves to the heating coil 16. The energization is started and induction heating of the crucible 15 is started, and the heating coil 16 may be gradually moved upward by the coil driving unit 28.
The crucible 15 is most heated at a portion adjacent to the heating coil 16, but the temperature of the entire crucible 15 also rises due to heat conduction.
The heating step in the solid phase is preferably performed for at least 1 hour or more, preferably 2 hours or more. Considering productivity, less than 10 hours is desirable.
In addition, in order to promote volatilization of gas, such as a metal compound and the metal formed by the decomposition | disassembly of a metal compound, oxygen, it is preferable to maintain the inside of the heat insulation container 11 in a pressure-reduced state. It is also desirable to flow an inert gas.

(Melting process)
Next, the aluminum oxide in the crucible 15 is completely melted to form an alumina melt 35.
It is preferable that the melting of aluminum oxide is started from the lowermost end of the crucible 15 filled with the raw material aluminum oxide and the raw material aluminum oxide is melted sequentially from the bottom to the top of the crucible 15. For this purpose, after the heating step in the solid phase is completed, the coil driving unit 28 moves the center position in the vertical direction of the heating coil 16 to the lower end of the crucible 15 and then completely melts the aluminum oxide. The heating coil 16 may be gradually moved upward by the coil driving unit 28 while the coil power source 25 supplies current to the heating coil 16.
Thereby, the volatilization of the metal compound and the gas formed by decomposing the metal compound, such as oxygen, is promoted. At this time, if the aluminum oxide is rapidly melted, it is left in the alumina melt 35 before the metal compound and the metal, gas such as oxygen generated by the decomposition of the metal compound are discharged. Therefore, it is necessary to spend at least 3 hours, preferably 10 hours or more, until aluminum oxide as a raw material is completely melted.
Even in the melting step, it is preferable to keep the inside of the heat insulating container 11 in a reduced pressure state in order to promote the volatilization of the metal compound and the gas formed by decomposing the metal compound, such as oxygen. It is also desirable to flow an inert gas.

(Heating process in liquid phase)
Next, the alumina melt 35 is held at a temperature 30 ° C. to 300 ° C. higher than the melting point of aluminum oxide. If the heating temperature is lower than this temperature range, decomposition products and bubbles are difficult to escape, so that the treatment for several hours is not effective, and it is considered that heating for a long time is required, and the productivity is remarkably lowered. On the other hand, when the heating temperature is higher than this temperature range, damage to the heating furnace 10 such as the crucible 15 and the heat insulating container 11 increases, and there is a limit on the apparatus. At this time, aluminum oxide as a raw material is melted to form a liquid phase. The holding time is, for example, 2 to 20 hours.
In the heating step in the liquid phase, it is preferable to keep the inside of the heat insulating container 11 in a reduced pressure state in order to promote the volatilization of a metal compound, a metal formed by decomposing the metal compound, gas such as oxygen. It is also desirable to flow an inert gas.

The temperature and time in the solid-phase heating step and the liquid-phase heating step are the material of the crucible 15 containing the raw material aluminum oxide, and the metal compound as an impurity contained in the raw material aluminum oxide powder or crystal piece. What is necessary is just to change with the density | concentration of.

(Shoulder formation process)
In the shoulder forming step, the gas supply unit 21 supplies a mixed gas in which nitrogen and oxygen are mixed at a predetermined ratio into the heat insulating container 11 using the O ₂ source 22 and the N ₂ source 23. However, in the shoulder forming step, as described later, it is not always necessary to supply a mixed gas of oxygen and nitrogen. For example, only nitrogen may be supplied.
The coil power supply 25 continues to supply a high-frequency current to the heating coil 16 to heat the alumina melt 35 via the crucible 15.
Further, the pulling drive unit 19 lowers the pulling rod 17 to a position where the lower end of the seed crystal 31 attached to the holding member 18 contacts the alumina melt 35 in the crucible 15 and then stops the pulling rod 17. Pull up at the first pulling speed.
Furthermore, the rotation drive unit 20 rotates the pulling rod 17 at the first rotation speed.

Then, the seed crystal 31 is pulled up while being rotated with its lower end immersed in the alumina melt 35, and a shoulder 32 that expands vertically downward is formed at the lower end of the seed crystal 31. It will be done.
When manufacturing a sapphire ingot 30 for obtaining a so-called 4 inch (diameter 100 mm) wafer, the shoulder forming step is completed when the diameter of the shoulder 32 becomes approximately 120 mm. Bubbles are easily taken in as the diameter increases.

(Straight body part forming process)
In the straight body forming step, the gas supply unit 21 mixes nitrogen and oxygen at a predetermined ratio using the O ₂ source 22 and the N ₂ source 23, and the oxygen concentration is in the range of 0.6% to 3.0%. The mixed gas set to 1 is supplied into the heat insulating container 11.
The coil power supply 25 continues to supply a high-frequency current to the heating coil 16 to heat the alumina melt 35 via the crucible 15.
Further, the pulling drive unit 19 pulls the pulling rod 17 at the second pulling speed. Here, the second pulling speed may be the same as or different from the first pulling speed in the shoulder forming step.
Furthermore, the rotation drive unit 20 rotates the pulling rod 17 at the second rotation speed. Here, the second rotation speed may be the same speed as the first rotation speed in the shoulder forming step, or may be a different speed.

The shoulder portion 32 integrated with the seed crystal 31 is pulled up while being rotated with its lower end portion immersed in the alumina melt 35, so that the lower end portion of the shoulder portion 32 is preferably a cylindrical straight portion. The body portion 33 is formed. The diameter of the straight body part 33 should just be more than a predetermined aperture.
In the straight body portion forming step, the lower end of the straight body portion 33 pulled up vertically is maintained in contact with the alumina melt 35.

(Tail formation process)
In the tail forming step, the gas supply unit 21 mixes nitrogen and oxygen at a predetermined ratio using the O ₂ source 22 and the N ₂ source 23, and a mixed gas in which the oxygen concentration is set higher than that in the straight body forming step. It supplies in the heat insulation container 11. However, the oxygen concentration in the mixed gas in the tail forming step is set in the range of 1.0% to 5.0%.
The coil power supply 25 continues to supply a high-frequency current to the heating coil 16 to heat the alumina melt 35 via the crucible 15.
Further, the pulling drive unit 19 pulls the pulling rod 17 at the third pulling speed. Here, the third pulling speed may be the same as the first pulling speed in the shoulder forming process or the second pulling speed in the straight body forming process, or may be a speed different from these. Good.
Furthermore, the rotation drive unit 20 rotates the pulling rod 17 at the third rotation speed. Here, the third rotation speed may be the same as the first rotation speed in the shoulder forming process or the second rotation speed in the straight body forming process, or may be different from these. Also good.
Note that the lower end of the tail 34 is kept in contact with the alumina melt 35 in the early stage of the tail formation step.
Then, at the final stage of the tail forming process after a predetermined time has elapsed, the pulling drive unit 19 increases the pulling speed of the pulling bar 17 and pulls the lifting bar 17 further upward, thereby lowering the lower end of the tail 34. Is pulled away from the alumina melt 35. Thereby, the sapphire ingot 30 shown in FIG. 2 is obtained.

In this embodiment, a mixed gas in which oxygen and nitrogen are mixed is used. However, the present invention is not limited to this. For example, a mixture of oxygen and argon as an example of an inert gas is used. It doesn't matter.
In the present embodiment, the crucible 15 is heated using a so-called electromagnetic induction heating method. However, the present invention is not limited to this. For example, a resistance heating method may be adopted. In the case of a structure in which the crucible 15 can be rotated by the resistance heating method, it is desirable to rotate the crucible 15 for stirring in each heating step.

From the sapphire ingot 30 manufactured as described above, the sapphire single crystal substrate 110 is manufactured as described above. The sapphire single crystal substrate 110 was visually observed for the presence or absence of bubbles with an optical microscope, and the presence or absence of bubbles was determined. At this time, the size of the observable bubbles was 1 μm or more.
In addition, when the surface of the sapphire single crystal substrate 110 is used as a semiconductor light emitting device (LC), it is desirable that the surface of the sapphire single crystal substrate 110 be smoothed or unevenly processed in order to improve the crystallinity of the compound semiconductor layer and the luminous efficiency.
Note that the sapphire ingot 30 manufactured as described above has a very small generation of cracks and cracks in the step of cutting in the direction perpendicular to the longitudinal direction of the sapphire ingot 30 and the step of polishing the surface, and has good processing yield. It was rate.

<Semiconductor light emitting device (LC)>
Next, a semiconductor light emitting device (LC) manufactured using the sapphire single crystal substrate 110 manufactured by the method for manufacturing the sapphire ingot 30 described above will be described.
In this embodiment mode, a semiconductor light emitting element (LC) has a group III compound semiconductor layer formed on a sapphire single crystal substrate 110 (see FIG. 4 described later) having a diameter of 100 mm and a thickness of about 900 μm, and then a group III compound The back surface of the sapphire single crystal substrate 110 on which the semiconductor layer is formed is ground so as to have a predetermined thickness, is subjected to a lapping process, and is cut into a chip size.

Next, the configuration of the semiconductor light emitting device (LC) manufactured by the method of manufacturing the semiconductor light emitting device (LC) to which the present embodiment is applied will be described. The semiconductor light emitting device (LC) manufactured in the present embodiment has a sapphire single crystal substrate 110 and a compound semiconductor layer formed on the substrate. Examples of the compound semiconductor constituting the compound semiconductor layer include a III-V group compound semiconductor, a II-VI group compound semiconductor, a IV-IV group compound semiconductor, and the like. In the present embodiment, a III-V group compound semiconductor is preferable, and among these, a group III nitride compound semiconductor is preferable. A semiconductor light emitting device (LC) having a compound semiconductor layer composed of a group III nitride compound semiconductor will be described below as an example.

FIG. 4 is a diagram illustrating an example of a semiconductor light emitting device (LC) manufactured in the present embodiment.
As shown in FIG. 4, the semiconductor light emitting device (LC) has a base layer 130 and a group III compound semiconductor layer 100 on an intermediate layer 120 formed on a sapphire single crystal substrate 110. In the group III compound semiconductor layer 100, an n-type semiconductor layer 140, a light emitting layer 150, and a p-type semiconductor layer 160 are sequentially stacked. It is desirable to process the surface of the sapphire single crystal substrate 110 forming the semiconductor layer so as to arrange a large number of fine convex shapes because it has an effect of improving the light emission output.
Further, a transparent positive electrode 170 is laminated on the p-type semiconductor layer 160, a positive electrode bonding pad 180 is formed thereon, and a negative electrode 190 is formed in the exposed region 140c formed in the n-type contact layer 140a of the n-type semiconductor layer 140. Are stacked.

Here, the n-type semiconductor layer 140 formed on the base layer 130 includes an n-type contact layer 140a and an n-type cladding layer 140b. The light emitting layer 150 has a structure in which barrier layers 150a and well layers 150b are alternately stacked. In the p-type semiconductor layer 160, a p-type cladding layer 160a and a p-type contact layer 160b are stacked.
In the present embodiment, the total thickness of the compound semiconductor layers (a combination of the intermediate layer 120, the base layer 130, and the group III compound semiconductor layer 100) formed on the sapphire single crystal substrate 110 is preferably 3 μm. More preferably, it is 5 μm or more, and more desirably 8 μm or more. The total thickness of these is preferably 15 μm or less.
Next, the material of each layer constituting the semiconductor light emitting element (LC) will be described.

(Intermediate layer 120)
In the present embodiment, it is preferable to provide an intermediate layer 120 that exhibits a buffer function on the sapphire single crystal substrate 110 when the group III compound semiconductor layer 100 is formed by metal organic chemical vapor deposition (MOCVD). . In particular, the intermediate layer 120 preferably has a single crystal structure from the viewpoint of the buffer function. When the intermediate layer 120 having a single crystal structure is formed on the sapphire single crystal substrate 110, the buffer function of the intermediate layer 120 acts effectively, and the base layer 130 and the group III compound semiconductor formed on the intermediate layer 120 The layer 100 is a crystal film having good orientation and crystallinity.
The intermediate layer 120 preferably contains Al, and particularly preferably contains AlN which is a group III nitride. The material constituting the intermediate layer 120 is not particularly limited as long as it is a group III nitride compound semiconductor represented by the general formula AlGaInN. Furthermore, As and P may be contained as a group V. In the case where the intermediate layer 120 has a composition containing Al, it is preferably AlGaN, and the composition of Al among the group III elements is preferably 50% or more.

(Underlayer 130)
As a material used for the underlayer 130, a group III nitride (GaN-based compound semiconductor) containing Ga is used, and in particular, AlGaN or GaN can be preferably used. The film thickness of the underlayer 130 is 0.1 μm or more, preferably 0.5 μm or more, and more preferably 1 μm or more.

(N-type semiconductor layer 140)
The n-type semiconductor layer 140 includes an n-type contact layer 140a and an n-type cladding layer 140b. As the n-type contact layer 140a, a GaN-based compound semiconductor is used in the same manner as the base layer 130. Further, the gallium nitride compound semiconductor constituting the base layer 130 and the n-type contact layer 140a preferably has the same composition, and the total film thickness thereof is 0.1 μm to 20 μm, preferably 0.5 μm to 15 μm, The thickness is preferably set in the range of 1 μm to 12 μm. Since current flows in the n-type contact layer 140a, if it is thin, the resistance becomes high, which is not preferable in terms of electrical characteristics. On the other hand, when it is thick, the growth time and material cost increase, which is not preferable in terms of productivity and cost.

The n-type cladding layer 140b can be formed of AlGaN, GaN, GaInN, or the like. Alternatively, a heterojunction of these structures or a superlattice structure in which a plurality of layers are stacked may be used. In the case of using GaInN, it is desirable to make it larger than the GaInN band gap of the well layer 150b constituting the light emitting layer 150 described later. The film thickness of the n-type cladding layer 140b is preferably in the range of 5 nm to 500 nm, more preferably 5 nm to 100 nm.

(Light emitting layer 150)
The light emitting layer 150 includes a barrier layer 150a made of a gallium nitride-based compound semiconductor and a well layer 150b made of a gallium nitride-based compound semiconductor containing indium, which are alternately stacked, and the n-type semiconductor layer 140 side and the p-type layer. The barrier layers 150a are stacked in the order in which the barrier layers 150a are disposed on the type semiconductor layer 160 side. In the present embodiment, the light emitting layer 150 includes six barrier layers 150a and five well layers 150b that are alternately and repeatedly stacked.

For the well layer 150b, for example, gallium indium nitride such as Ga _1-s In _s N (0 <s <0.4) can be used as a gallium nitride compound semiconductor containing indium.
As the barrier layer 150a, a gallium nitride compound semiconductor such as Al _c Ga _1-c N (0 ≦ c ≦ 0.3) having a larger band gap energy than the well layer 150b made of a gallium nitride compound semiconductor containing indium. Can be suitably used.

(P-type semiconductor layer 160)
The p-type semiconductor layer 160 includes a p-type cladding layer 160a and a p-type contact layer 160b. The p-type cladding layer 160a is preferably Al _d Ga _1-d N (0 <d ≦ 0.4). The film thickness of the p-type cladding layer 160a is preferably 1 nm to 400 nm, more preferably 5 nm to 100 nm.
Examples of the p-type contact layer 160b include a gallium nitride compound semiconductor layer containing at least Al _e Ga _1-e N (0 ≦ e <0.5). The thickness of the p-type contact layer 160b is not particularly limited, but is preferably 10 nm to 500 nm, and more preferably 50 nm to 200 nm.

(Transparent positive electrode 170)
Examples of the material constituting the transparent positive electrode 170 include ITO (In ₂ O ₃ —SnO ₂ ), AZO (ZnO—Al ₂ O ₃ ), IZO (In ₂ O ₃ —ZnO), and GZO (ZnO—Ga ₂ O). Conventionally known materials such as ₃ ) may be mentioned. Moreover, the structure of the transparent positive electrode 170 is not specifically limited, A conventionally well-known structure is employable. The transparent positive electrode 170 may be formed so as to cover almost the entire surface of the p-type semiconductor layer 160, or may be formed in a lattice shape or a tree shape.

(Positive electrode bonding pad 180)
The positive electrode bonding pad 180 as an electrode formed on the transparent positive electrode 170 is made of, for example, a conventionally known material such as Au, Al, Ni, or Cu. The structure of the positive electrode bonding pad 180 is not particularly limited, and a conventionally known structure can be adopted.
The thickness of the positive electrode bonding pad 180 is in the range of 100 nm to 1,000 nm, preferably in the range of 300 nm to 500 nm.

(Negative electrode 190)
As shown in FIG. 4, the negative electrode 190 includes a group III compound semiconductor layer 100 (n-type semiconductor layer 140, n-type semiconductor layer 140) further formed on the intermediate layer 120 and the base layer 130 formed on the sapphire single crystal substrate 110. The light emitting layer 150 and the p-type semiconductor layer 160 are formed so as to be in contact with the n-type contact layer 140a of the n-type semiconductor layer 140. Therefore, when forming the negative electrode 190, the p-type semiconductor layer 160, the light emitting layer 150, and the n-type semiconductor layer 140 are partially removed to form an exposed region 140c of the n-type contact layer 140a, and the negative electrode is formed thereon. 190 is formed.
As the material of the negative electrode 190, negative electrodes having various compositions and structures are well known, and these well-known negative electrodes can be used without any limitation, and can be provided by conventional means well known in this technical field.

In this embodiment, first, an intermediate layer 120 made of a group III nitride is formed on a sapphire single crystal substrate 110 by activating and reacting a gas containing a group V element with a metal material. Subsequently, the base layer 130, the n-type semiconductor layer 140, the light emitting layer 150, and the p-type semiconductor layer 160 are sequentially stacked on the formed intermediate layer 120.

In the present embodiment, when a group III nitride compound semiconductor crystal is epitaxially grown on the sapphire single crystal substrate 110, the intermediate layer 120 uses a sputtering method to activate the raw material that has been activated and reacted with the sapphire single crystal substrate 110. It is preferable to form a film on top. Here, the group V element is nitrogen, the nitrogen gas fraction in the gas when forming the intermediate layer 120 is in the range of 50% to 99% or less, and the intermediate layer 120 is formed as a single crystal structure. . Thereby, the intermediate layer 120 having good crystallinity is formed on the sapphire single crystal substrate 110 as an oriented film having anisotropy in a short time. As a result, a Group III nitride compound semiconductor with good crystallinity grows on the intermediate layer 120 as compared with the case where the intermediate layer 120 is not provided.

In this embodiment, after the intermediate layer 120 is formed by a sputtering method, an underlying layer 130, an n-type semiconductor layer 140, a light-emitting layer 150, and a p-type semiconductor are formed thereon by metal organic chemical vapor deposition (MOCVD). It is preferable to sequentially form the layer 160.
In the MOCVD method, for example, hydrogen (H ₂ ) or nitrogen (N ₂ ) is used as a carrier gas. Trimethylgallium (TMG), triethylgallium (TEG), or the like is used as a Ga source that is a group III raw material. As the Al source, trimethylaluminum (TMA), triethylaluminum (TEA), or the like is used. As the In source, trimethylindium (TMI), triethylindium (TEI), or the like is used. Ammonia (NH ₃ ), hydrazine (N ₂ H ₄ ), or the like is used as an N source that is a group V raw material.
As the dopant, monosilane (SiH ₄ ), disilane (Si ₂ H ₆ ), or the like is used as the Si raw material for the n-type. An organic germanium compound such as germane gas (GeH ₄ ), tetramethyl germanium ((CH ₃ ) ₄ Ge), tetraethyl germanium ((C ₂ H ₅ ) ₄ Ge) can be used as the Ge raw material.

In addition, the gallium nitride compound semiconductor may contain other elements in addition to Al, Ga, and In. For example, dopant elements such as Ge, Si, Mg, Ca, Zn, and Be can be given. Furthermore, it is not limited to the element added intentionally, but may include impurities that are inevitably included depending on the film forming conditions, etc., and trace impurities that are included in the raw materials and reaction tube materials.

In addition, after forming the base layer 130 by the MOCVD method, each layer of the n-type contact layer 140a and the n-type cladding layer 140b is formed by the sputtering method, and the light emitting layer 150 thereon is formed by the MOCVD method, and then the p-type Each layer of the p-type cladding layer 160a and the p-type contact layer 160b constituting the semiconductor layer 160 may be formed by reactive sputtering.

After the intermediate layer 120, the underlayer 130, and the group III compound semiconductor layer 100 are formed on the sapphire single crystal substrate 110 having a diameter of 100 mm and a thickness of about 900 μm, the p-type semiconductor layer 160 of the group III compound semiconductor layer 100 is formed. A transparent positive electrode 170 is laminated thereon, and a positive electrode bonding pad 180 is formed thereon. Further, a wafer in which the negative electrode 190 is provided in the exposed region 140c formed in the n-type contact layer 140a of the n-type semiconductor layer 140 is formed.

The sapphire single crystal substrate 110 on which the compound semiconductor layer described above is formed is then ground and polished until the surface to be ground (back surface) of the sapphire single crystal substrate 110 has a predetermined thickness. In the present embodiment, the wafer is attached to a commercially available grinder (not shown), and the thickness of the sapphire single crystal substrate 110 of the wafer is reduced from, for example, about 900 μm to about 120 μm by the grinding process.

Next, the wafer whose thickness of the sapphire single crystal substrate 110 is adjusted is cut into a square of 350 μm square, for example, so that the intermediate layer 120, the base layer 130, and the group III compound semiconductor layer 100 are formed on the sapphire single crystal substrate 110. A semiconductor light emitting device (LC) is formed.

As described above, in the present embodiment, the sapphire single crystal substrate 110 having a predetermined thickness cut out from the single crystal sapphire ingot 30 is used, and the group III compound semiconductor layer is epitaxially grown on the deposition surface. Done well. A semiconductor light emitting device (LC) having such a sapphire single crystal substrate 110 and a group III compound semiconductor layer 100 has good light emission characteristics and electrical characteristics.

Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

Example 1
A sapphire ingot 30 was produced using the single crystal pulling apparatus I (see FIG. 1) described in the embodiment.
First, as a preparation step, a high-purity aluminum oxide raw material (Na concentration = 5 ppm) was introduced into an iridium (Ir) crucible 15 and the heat insulating container 11 was depressurized to 0.1 Pa.
Thereafter, as a heating process in the solid phase shown in FIG. 3, a high-frequency current was supplied to the heating coil 16 to maintain the heating at 1700 ° C., which is a temperature lower than the melting point (2050 ° C.) of aluminum oxide, for 2 hours. (Step 101).
Thereafter, as the melting step shown in FIG. 3, the temperature of the crucible 15 was raised to 2100 ° C. to melt the aluminum oxide to obtain the alumina melt 35 (step 102).
Next, as the heating process in the liquid phase shown in FIG. 3, the temperature of the crucible 15 was maintained at 2150 ° C. for 4 hours, and the temperature at the bottom of the crucible 15 was increased by 20 ° C. relative to 2150 ° C. to promote convection ( Step 103).

Thereafter, as the seeding step of FIG. 3, the temperature of the crucible 15 is lowered to 2050 ° C., the pressure of the heat insulating container 11 is increased to atmospheric pressure, and the pulling up of the sapphire ingot 30 is started in a state where nitrogen gas is supplied (step 104). .
The shoulder portion 32 was formed (step 105), the straight body portion 33 having a diameter of about 100 mm was formed (step 106), and the sapphire ingot 30 having a length of about 20 cm was produced.
The sapphire ingot 30 was taken out from the single crystal pulling apparatus I and heat treated (annealed) at 1200 ° C. for 4 hours to remove the thermal strain of the sapphire ingot 30.
A plate having a thickness of about 1 mm was cut out from the sapphire ingot 30 and the front and back surfaces were polished to obtain a sapphire single crystal substrate 110 having a thickness of about 900 μm.

Next, the presence or absence of bubbles was observed with an optical microscope. Further, impurities in the sapphire single crystal substrate 110 were analyzed by glow discharge mass spectrometry (GD-MS).
FIG. 5 shows the temperature, time and evaluation results in Examples 1 to 3 and Comparative Examples 1 to 3 in the heating step in the solid phase and the heating step in the liquid phase.
The evaluation results are the presence or absence of bubbles observed with an optical microscope, the concentration of Na, V, and Ba in the sapphire single crystal substrate 110 analyzed by the GD-MS method, the semiconductor light emitting device (LC ) Characteristics. The characteristics of the semiconductor light emitting device (LC) are emission intensity Po (mW), forward voltage VF (V) when the forward current is 20 mA, and reverse current Ir (μA) when the reverse voltage is 20 V.
Here, the larger the emission intensity Po, the smaller the forward voltage VF, and the smaller the reverse current Ir, the better the characteristics of the semiconductor light emitting element (LC).
Note that it was difficult to find fine bubbles (for example, less than 1 μm) by observation with an optical microscope.

The diameter of the sapphire single crystal substrate 110 in Examples 1 to 3 and Comparative Examples 1 to 3 is 100 mm.
The semiconductor light emitting devices (LC) in Examples 1 to 3 and Comparative Examples 1 to 3 are manufactured under the conditions described in the embodiment and have the same shape. And the characteristic of a semiconductor light emitting element (LC) is an average value of the characteristic which took out and measured 20 semiconductor light emitting elements (LC) equally from the wafer surface in which the semiconductor light emitting element (LC) was formed.
The central wavelength λd of light emission of the semiconductor light emitting devices (LC) in Examples 1 to 3 and Comparative Examples 1 to 3 was 450 nm.

In Example 1, no bubbles were observed, and Na, which is a metal impurity that easily generates crystal defects, was 0.3 ppm, and V and Ba were low in the detection limit of 0.1 ppm or less.
In Example 1, the characteristics of the semiconductor light emitting device (LC) reflect the fact that no bubbles are observed and the concentrations of Na, V, and Ba are low, that is, there are few crystal defects, and the light emission output Po = 20 mW. VF (20 mA) = 3.1 V and Ir (20 V) = 0 μA.

In Example 2, the heating temperature in the solid phase was 2000 ° C. for 2 hours, and the heating temperature in the liquid phase was 2100 ° C. for 4 hours. Bubbles were not observed, and Na, which is a metal impurity that easily causes crystal defects, was 0.6 ppm, and V and Ba were low in the detection limit of 0.1 ppm or less. The characteristics of the semiconductor light emitting device (LC) were as follows: light emission output Po = 20 mW, VF (20 mA) = 3.1 V, and Ir (20 V) = 0 μA.
In Example 3, the heating step in the solid phase was eliminated, and the heating temperature in the liquid phase was changed to 2080 ° C. for 4 hours. No bubbles were observed, and Na, which is a metal impurity that easily causes crystal defects, was 0.9 ppm, and V and Ba were low in the detection limit of 0.1 ppm or less. The characteristics of the semiconductor light emitting device (LC) were as follows: light emission output Po = 20 mW, VF (20 mA) = 3.1 V, and Ir (20 V) = 1 μA.

On the other hand, Comparative Example 1 does not provide a heating step in the solid phase and a heating step in the liquid phase. Bubbles were observed, and Na, which is a metal impurity that easily generates crystal defects, was 3 ppm, V was 0.5 ppm, and Ba was 0.4 ppm. The characteristics of the semiconductor light emitting device (LC) were light emission output Po = 15 mW, VF (20 mA) = 3.3 V, and Ir (20 V) = 4 μA, which were inferior to Examples 1 to 3.
Moreover, the comparative example 2 changed the conditions of the heating process in a solid phase at 1100 degreeC for 2 hours. There is no heating step in the liquid phase. Bubbles were observed, and Na, which is a metal impurity that easily generates crystal defects, was 2 ppm, V was 0.2 ppm, and Ba was 0.4 ppm. The characteristics of the semiconductor light emitting device (LC) were light output Po = 16 mW, VF (20 mA) = 3.2 V, and Ir (20 V) = 3 μA, which were inferior to Examples 1 to 3.
In Comparative Example 3, there was no heating step in the solid phase, and the conditions of the heating step in the liquid phase were changed at 2060 ° C. for 4 hours. Bubbles were observed, and Na, which is a metal impurity that easily generates crystal defects, was 1.3 ppm, and V and Ba were detection limits of 0.1 ppm or less. The characteristics of the semiconductor light emitting device (LC) were light emission output Po = 18 mW, VF (20 mA) = 3.2 V, and Ir (20 V) = 2 μA, which were inferior to Examples 1 to 3.

As summarized in FIG. 5, in Examples 1 to 3, no bubbles were observed, the concentrations of Na, V, and Ba were low, and the characteristics of the semiconductor light emitting device (LC) were good.
On the other hand, in Comparative Examples 1 to 3, generation of bubbles is observed and the concentrations of Na, V, and Ba are higher than those in Examples 1 to 3. Further, the semiconductor light emitting element (LC) also has a lower light emission output Po and a higher reverse current Ir as compared with the first to third embodiments.

As described above, bubbles observed in the sapphire single crystal substrate 110 are generated due to metal compounds such as oxides of Na, V, and Ba contained as impurities. And the density | concentration of the metal compound contained as these impurities is heated at the temperature of the solid phase heating process heated at a temperature lower than the melting point of the raw material aluminum oxide and the melting point or higher before the sapphire ingot 30 is pulled up. It can be reduced by providing a heating step in the liquid phase.
Note that it is possible to use only the heating process in the liquid phase without providing the heating process in the solid phase.
Thereby, the characteristic of the semiconductor light emitting element (LC) formed in the sapphire single crystal substrate 110 improves by suppressing the crystal defect and bubble generation of the sapphire single crystal substrate 110.

DESCRIPTION OF SYMBOLS 10 ... Heating furnace, 11 ... Thermal insulation container, 12 ... Gas supply pipe, 13 ... Gas discharge pipe, 14 ... Chamber, 15 ... Crucible, 16 ... Heating coil, 17 ... Lifting rod, 19 ... Drive part, 30 ... Sapphire ingot, DESCRIPTION OF SYMBOLS 31 ... Seed crystal, 32 ... Shoulder part, 33 ... Straight body part, 34 ... Tail part, 35 ... Alumina melt, 100 ... III group compound semiconductor layer, 110 ... Substrate, 120 ... Intermediate layer, 130 ... Underlayer, 140 ... n-type semiconductor layer, 150 ... light-emitting layer, 160 ... p-type semiconductor layer, 170 ... transparent positive electrode, 180 ... positive electrode bonding pad, 190 ... negative electrode, I ... single crystal pulling device, LC ... semiconductor light-emitting element

Claims

In the sapphire single crystal pulling device by the Czochralski method (CZ method),
A heating step in a liquid phase in which a raw material of aluminum oxide having a sodium (Na) concentration of 1 ppm or more is maintained in a molten state melted in a crucible at a temperature exceeding the melting point of aluminum oxide;
A shoulder forming step of forming a shoulder having a diameter increasing toward the bottom of the seed crystal by pulling up the seed crystal attached to the melt of aluminum oxide in the crucible while rotating;
A method for producing a sapphire single crystal, comprising: a body forming step of forming a cylindrical body below the shoulder by pulling up the shoulder attached to the melt while rotating.
2. The method for producing a sapphire single crystal according to claim 1, wherein the heating step in the liquid phase is performed at a temperature higher than the melting point of aluminum oxide by 30 ° C. or more and 300 ° C. or less.
The melt in the heating step in the liquid phase is formed by melting a raw material of aluminum oxide in the crucible from the bottom to the top of the crucible. Of producing a single crystal of sapphire.
4. The method according to claim 1, further comprising a heating step in a solid phase in which the raw material of aluminum oxide in the crucible is held at a temperature lower than the melting point of aluminum oxide before the heating step in the liquid phase. The manufacturing method of the sapphire single crystal of any one of these.
The method for producing a sapphire single crystal according to claim 4, wherein the heating step in the solid phase is performed at a temperature of 1200 ° C or higher and lower than 2050 ° C.
The sapphire single crystal production according to claim 4 or 5, wherein the temperature of the raw material of aluminum oxide in the crucible in the heating step in the solid phase is increased from the lower part to the upper part of the crucible. Method.
Each of the concentrations of sodium (Na), barium (Ba) and vanadium (V) produced by the method for producing a sapphire single crystal according to any one of claims 1 to 6 is less than 1 ppm. A sapphire single crystal substrate having a diameter of 100 mm or more.