JP4905138B2 - Method for producing aluminum oxide single crystal - Google Patents

Description

  The present invention relates to a method for producing an aluminum oxide single crystal. More specifically, the temperature at which the raw material is allowed to melt is precisely controlled, and the crucible is not heated more than necessary, thereby suppressing the occurrence of inclusion and efficiently producing high quality. The present invention relates to a method for producing a simple aluminum oxide single crystal.

  Aluminum oxide single crystals are widely used as an epi growth substrate for producing blue LEDs and white LEDs. These LEDs are expected to spread in the lighting field from the viewpoint of energy saving, and are attracting attention from various fields.

There are various methods for growing oxide single crystals, but most of the oxide single crystal materials such as LN, LT, YAG and aluminum oxide are obtained by melt solidification because their crystal characteristics and large crystal diameters are obtained. It is nurtured. In particular, the Czochralski method (Cz method), which is one of the melt solidification methods, is most widely used because of its versatility and high technical perfection.
In order to produce an oxide single crystal by the Czochralski method, first, an oxide raw material is filled in a crucible, and the raw material is melted by heating the crucible by a high frequency induction heating method or a resistance heating method. After the raw material is melted, the seed crystal cut in a predetermined crystal orientation is brought into contact with the surface of the raw material melt, and the single crystal is grown by pulling upward at a predetermined speed while rotating the seed crystal at a predetermined rotation speed.

However, when an aluminum oxide single crystal is grown by the Czochralski method, innumerable minute bubbles are likely to be generated in the crystal. In these minute bubbles, pits (minute dents with a diameter of several μm) are developed when a wafer to be an epitaxial growth substrate is polished.
Until now, when growing aluminum oxide single crystals, oxygen atoms (O) and oxygen molecules (O ₂ ) generated by decomposition of the raw material at high temperature exist in the supersaturated state in the melt. It is known that it is taken in and becomes a bubble in the single crystal. In order to avoid this, it has been proposed to grow a single crystal in a reducing atmosphere using hydrogen gas or carbon monoxide gas (see Patent Document 1).
As a result, oxygen atoms (O) and oxygen molecules (O ₂ ) present in the melt are removed by reaction with hydrogen gas or carbon monoxide gas, so the amount of bubbles taken into the grown single crystal is certain. To decrease. However, when a wafer is cut out from the grown single crystal and polished and polished, a large number of pits exist on the surface of the wafer, and the amount of bubbles taken in cannot be sufficiently suppressed.

In addition, gas components that are in equilibrium with the melt tend to be discharged from the melt at the solid-liquid interface where crystallization occurs, and in the melt near the interface, gas components become supersaturated and bubbles are generated. Cheap. However, by enhancing the convection of the melt, it is said that the supersaturation of the gas component that occurs near the interface can be suppressed and the amount of the gas component taken into the crystal can be reduced (see Non-Patent Document 1).
Therefore, if the gas component contained in the raw material is removed as much as possible before melting to reduce the supersaturated gas component present in the melt and the amount of minute bubbles taken into the crystal during single crystal growth is reduced, pits can be obtained. It is thought that the occurrence of the occurrence can be suppressed.

  From such a viewpoint, when heating the raw material, the inventors reduced the pressure in the furnace body to a pressure sufficient to remove the gas generated from the crystallization raw material by heating, and then the gas The raw material for crystallization is gradually melted while removing the oxygen, and subsequently, a mixed gas consisting of oxygen and nitrogen or an inert gas is introduced, and the pressure inside the furnace is returned to atmospheric pressure under a sufficient partial pressure of oxygen, and then the grown crystal is It has been found that pulling up can suppress the occurrence of pits.

In addition to the generation of microbubbles, inclusion is known as a micro defect generated in an aluminum oxide single crystal. The size of this inclusion is from several μm to several tens of μm in diameter. However, when a wafer obtained from a crystal containing such inclusions is polished, many protrusions with a diameter of several μm to several tens of μm appear on the wafer surface. .
Inclusions are found in oxide crystals with a high melting point. In addition to aluminum oxide, single crystals of alexandrite used in the oscillation base of GGG (gadolinium gallium garnet) single crystals used in optical isolators and tunable lasers are used. There are also reports on crystals.

  In the production of an aluminum oxide single crystal using an iridium crucible, it has been reported by COCKEYNE et al. That the cause of inclusion is that the iridium crucible is oxidized and evaporated, and this is taken into the melt and becomes a single crystal inclusion. (See Non-Patent Document 2). Accordingly, it is important to suppress the oxygen concentration during growth to 0.5 vol% or less and to quickly remove the iridium oxide evaporated by flowing nitrogen from the crucible.

However, iridium is incorporated into the crystal even when it is melted and grown while removing the gas generated from the raw material by heating in an atmosphere of nitrogen or an inert gas. When a wafer obtained from such a crystal is polished and polished, There may be many small protrusions with a diameter of several μm on the surface. When a wafer obtained from such a crystal is polished and polished, a protrusion with a diameter of several μm is formed on the wafer surface, and a defect remains as a protrusion-like defect even when epitaxially grown on the wafer substrate. For this reason, it has been proposed to suppress excessive convection of the melt by increasing the number of rotations of the growth crystal to, for example, 20 rotations / minute or more, particularly 30 to 120 rotations / minute (see Patent Document 2). . However, with such means, even if the crystal yield can be increased, the generation of fine bubbles in the single crystal cannot be sufficiently suppressed.
Japanese Patent Laid-Open No. 04-132695 JP 09-278592 A Proceedings of the 28th National Conference on Crystal Growth, 22Pa2 1997 P15 “JOURNAL OF MATERIALS SCIENCE” COCKANYE, M.C. CHESSSWAS, D.C. B. GASSON 2 (1967) P.M. 7-11

  In view of the above-mentioned problems of the prior art, the object of the present invention is to precisely control the temperature at which the raw material is allowed to melt and not to heat the crucible more than necessary, thereby suppressing the occurrence of inclusion and efficiently producing high quality aluminum oxide. The object is to provide a method for producing a single crystal.

  The inventors heated the raw material in an atmosphere containing only nitrogen or an inert gas inside the furnace, and after melting the raw material, introduced oxygen into the atmospheric gas and continued heating, and then left the melt at a specific temperature. In addition, by not heating the crucible more than necessary, it is possible to sufficiently suppress the crucible from being oxidized by oxygen contained in the raw material or the atmosphere, and as a result, it is found that the melting of the crucible material into the melt can be reduced. The present invention has been completed.

That is, according to the first invention of the present invention, an aluminum oxide single crystal is produced by a melt solidification method in which a raw material for a single crystal is put in an iridium crucible in a furnace body and heated and melted, and a grown crystal is pulled up from the raw material melt. In the method, when the single crystal raw material is heated and melted, a gas generated from the single crystal raw material by first gradually heating the single crystal raw material over a period of 10 hours or more in a nitrogen or inert gas atmosphere until the melting point is reached. melted while removing, then introducing 0.01-0.5 volume% oxygen with respect to the gas mixture into the furnace, oxygen and nitrogen, or under a mixed gas atmosphere composed of inert gas, subsequently the material melt It was heated to adjust the oxygen concentration to 0.01 to 0.5 vol% retained within 20 hours so as not to oxidize the crucible at 2,050-2150 ° C., then, this performing pulling the growing crystal Method of manufacturing a single crystalline aluminum oxide, characterized in are provided.

According to a second aspect of the present invention, there is provided the aluminum oxide single crystal according to the first aspect, wherein the heating temperature is measured by a thermocouple installed at a position within 20 mm from the bottom of the crucible. A manufacturing method is provided.
According to a third aspect of the present invention, there is provided the method for producing an aluminum oxide single crystal according to the second aspect , wherein the thermocouple is a B thermocouple made of a platinum rhodium alloy. .
According to a fourth aspect of the present invention, there is provided the method for producing an aluminum oxide single crystal according to the first aspect, wherein the holding time is 5 to 20 hours.

  According to the present invention, when the raw material is heated in a crucible such as iridium, the oxygen adsorbed or contained in the raw material is eliminated by setting the atmosphere to only nitrogen or an inert gas, and then the atmospheric gas When oxygen is introduced into the glass and the heating is continued and then left to stand, the generation of iridium oxide is suppressed by maintaining the crucible temperature at an appropriate temperature for an appropriate time, and the dissolution of iridium into the melt can be suppressed. The single crystal obtained in this way is of high quality because there is no inclusion, and if this single crystal is used, electronic component materials and optical component materials having excellent characteristics can be provided.

Hereinafter, the manufacturing method of the aluminum oxide single crystal of this invention is demonstrated in detail using drawing.
The method for producing an aluminum oxide single crystal according to the present invention is a method for producing an aluminum oxide single crystal by a melt solidification method in which a raw material for a single crystal is put in an iridium crucible in a furnace and heated and melted, and a grown crystal is pulled up from the raw material melt. When the single crystal raw material is heated and melted, first, the gas generated from the single crystal raw material is gradually heated in a nitrogen or inert gas atmosphere over 10 hours until the single crystal raw material reaches the melting point. Melting while removing, then introducing 0.01 to 0.5% by volume of oxygen with respect to the mixed gas into the furnace, and subsequently continuing the raw material melt in a mixed gas atmosphere consisting of oxygen and nitrogen or inert gas heating, to adjust the oxygen concentration to 0.01 to 0.5 vol% retained within 20 hours so as not to oxidize the crucible at 2050 to 2,150 ° C., then the pulling of the growing crystal And wherein the Ukoto.

1. Relationship between heating temperature of single crystal raw material and oxygen concentration generated from melt The raw material is put in a crucible in the furnace as in the present invention, heated and melted, and the aluminum oxide single crystal is melted and solidified by pulling up the grown crystal from the raw material melt. In the method for producing a crystal, when a raw material is heated, the atmosphere in the furnace body is only nitrogen or an inert gas, and melting is performed while removing gas generated from the raw material by heating. In this way, when the raw material is heated in the crucible, the gas component adsorbed or contained in the raw material is eliminated by setting the atmosphere of only nitrogen or an inert gas. One of the gas components is oxygen.

  FIG. 1 shows the results of measuring the temperature and oxygen concentration when a typical material, aluminum oxide, was heated while introducing nitrogen from the top of the furnace 3 liters per minute in a high-frequency induction heating furnace and flowing in the furnace. Is shown. The measured temperature is the temperature of a thermocouple placed 10 mm below the bottom of the iridium crucible. The oxygen concentration is measured at the outlet of the nitrogen flow installed at the lower part of the furnace body.

  According to this graph, it can be seen that as the temperature in the furnace is increased, the oxygen concentration increases to about 600 ppm and then decreases (first peak). This temporary increase in oxygen concentration is oxygen from zirconium oxide or alumina used as a heat insulating material, and oxygen adsorbed on the surface of the raw material. Although the temperature is measured by installing a thermocouple at the bottom of the crucible, the temperature at which the zirconium oxide and oxygen adsorbed on the raw material start to be released can be estimated to be 1500 ° C. or lower. In this temperature range, the iridium crucible is hardly oxidized in an atmosphere of nitrogen flow.

When the temperature is further raised to a temperature at which the raw material melts, the oxygen concentration rises again to 750 ppm or more, but then decreases (second peak). This is because oxygen contained in the raw material was released with melting. Since the oxygen concentration is measured at the gas outlet at the bottom of the furnace body, it is considered that the oxygen concentration in the vicinity of the crucible has reached at least 0.5% by volume or more.
In this way, when the raw material melts, a gas typified by oxygen is released and discharged from the outlet to the outside of the furnace body. However, the highest temperature in the high-frequency heating furnace is the surface of the crucible side, so the raw material is completely melted. At that time, the temperature of the inner wall of the crucible is estimated to be about 50 to 100 ° C. higher than the melting point. If this temperature is higher than necessary, the crucible is oxidized and becomes iridium oxide, which dissolves in the raw material. Further, at higher temperatures, the raw material aluminum oxide is decomposed to generate new gas components, which react with the crucible.

  Therefore, when a raw material is put into a crucible in the furnace body by the melt solidification method and heated and melted, and the growth crystal is pulled up from the raw material melt to produce an aluminum oxide single crystal, the inside of the furnace body for growing the single crystal A means for monitoring the oxygen concentration is provided, and the release of oxygen from the zirconium oxide used as a heat insulating material and the oxygen adsorbed on the raw material surface when the raw material is heated is confirmed by the behavior of the oximeter, It is desirable to prevent oxygen from being rapidly released at a high temperature by controlling the temperature rise while confirming the amount of released oxygen contained in the raw material when the raw material is melted. After melting the raw material, the high frequency output is adjusted while suppressing the temperature rise to 2150 ° C. or lower, and the work of holding the melt for a predetermined time is performed to release the gas components including oxygen contained in the raw material. Can be said to be effective.

2. In the present invention, in order to grow an aluminum oxide single crystal, an oxide single crystal growing apparatus by a conventional Czochralski method, for example, a crucible formed of a noble metal, and alumina as a heat insulating material around the crucible Can be used, and a device in which a high-frequency coil as a heating device is disposed outside the furnace material. From the above, the oxygen concentration in the furnace body for growing the single crystal is monitored. Means are provided so that release of oxygen from zirconium oxide used as a heat insulating material and oxygen adsorbed on the surface of the raw material when the raw material is heated can be confirmed by the behavior of the oxygen concentration meter.

  Since the melting point of alumina as a raw material is about 2050 ° C., it is preferable to use an iridium-made crucible. Further, the thermocouple installed at the bottom of the crucible must be installed away from the bottom of the crucible even if it is a high temperature thermocouple. However, if the distance is too large, behaviors such as temperature rise and heat of fusion cannot be observed precisely, so the distance away from the crucible bottom is 20 mm or less. The thermocouple used here is preferably a platinum rhodium alloy thermocouple (B thermocouple). The B thermocouple is a platinum rhodium alloy whose + leg contains 30% rhodium, and a platinum rhodium alloy whose-leg contains 6% rhodium (see JIS C1602-1995: Thermocouple Constituent Materials). This thermocouple is suitable for high temperature measurement of 1000 ° C. or higher, and has a very low thermoelectric power at room temperature, so that no compensation lead wire is required, and oxidation resistance and chemical resistance are good.

  A heat insulating material covering the periphery of the crucible may be filled with a heat insulating material such as foamed zirconia, but it is important to keep the temperature maintaining condition as constant as possible. Then, it is necessary to investigate the relationship between the thermocouple temperature at the bottom of the crucible and the actual melt temperature by actually measuring the melting state of the raw material and the melt temperature with a radiation thermometer. Above the crucible, a pulling device for pulling up the single crystal from the material melt is provided, and the furnace material is shielded by a shielding plate.

3. Next, a preferred embodiment of the single crystal raw material melting step in the present invention will be described. The raw material melting step includes (1) a stage of heating a single crystal raw material with an atmosphere of only nitrogen or an inert gas while removing the gas generated from the raw material by heating, and (2) thereafter And a step of heating and melting the single crystal raw material which is further heated and held in a mixed atmosphere of oxygen and nitrogen or an inert gas, followed by (3) a single crystal growth step of the melt for crystal growth. In the present invention, the temperature at which the raw material is melted and left in the heating and holding stage is precisely controlled, and the crucible is not heated more than necessary, thereby suppressing the occurrence of inclusion and efficiently producing a high-quality aluminum oxide single crystal. To do.

(1) First, in the heating and melting stage of the single crystal raw material, the above-mentioned raw material is put in a crucible, evacuation is started before the raw material is heated, and the evacuation is stopped when the pressure in the furnace is reduced to 20 Pa. Nitrogen gas is introduced. After the pressure in the furnace reaches 0.1 MPa, only nitrogen gas is allowed to flow at a flow rate of 1 to 5 liters per minute.

In the present invention, aluminum oxide powder may be used as the single crystal raw material, but it is desirable to use a sintered body or a crackle raw material. Since normal aluminum oxide powder has a large specific surface area of about 5 to 10 m ² / g, many gas components are adsorbed or encapsulated, but the sintering raw material has a specific surface area of 0.1 to 10 m ² / g. The gas adsorbed on the surface is small and effective for outgassing.
The crackle raw material is obtained by pulverizing an aluminum oxide single crystal raw material produced by the Bernoulli method to a diameter of 20 mm or less. However, the specific surface area is very small, less than 0.1 m ² / g, and the adsorbed gas is small. However, since the aluminum oxide powder is dissolved and the single crystal produced from the obtained melt is pulverized, innumerable bubbles are often included therein. In the crackle raw material, although the viscosity of the aluminum oxide melt is high and the surface tension is large, by leaving the melt after heating and melting, the gas components dissolved in the melt as microbubbles are almost removed. Since the crackle raw material has a high density, there is an advantage that the number of raw material inputs before the growth can be reduced as compared with other raw material forms such as aluminum oxide powder.
Aluminum oxide is composed of two elements, Al and O, but may contain Ti, Cr, Si, Ca, Mg, etc. in addition to Al and O in accordance with the type of target aluminum oxide single crystal. Among these, Si, Ca, Mg and the like can be inevitably contained as components of the sintering aid, but the content is desirably as small as possible. The diameter and density of aluminum oxide are not particularly limited, but for handling, for example, the diameter is preferably 10 mm or less, preferably 5 mm or less, and the density is 5 g / cm ³ or less, preferably 3 g / cm. What is ³ or less is good.

Next, the crucible is heated by the high frequency coil, and the heating of the raw material is started. As can be understood from the principle of the high-frequency induction heating furnace, the crucible induces a high frequency, and the crucible generates heat by the eddy current generated on the surface of the crucible to melt the raw material. Therefore, it is the crucible surface that has the highest temperature inside the furnace body.
In the heating and melting stage of the raw material, the raw material is gradually heated over 10 hours or more, preferably 12 hours or more until reaching the melting point. Although the heating rate until the raw material reaches the melting point is not particularly limited, the rapid generation of oxygen is suppressed by heating gradually over a long period of time without rapidly heating, and a rapid increase in the vicinity of the crucible. There is no increase in oxygen concentration. As a result, gas uptake into the melt and oxidation of the crucible can be suppressed.
As described above, when the temperature rises to about 1500 ° C., oxygen from zirconium oxide or alumina used as a heat insulating material and oxygen adsorbed on the surface of the raw material are generated. In this temperature range, the crucible is oxidized. It doesn't progress very much.

(2) In the heating and holding stage, the temperature is further increased. When the temperature reaches 2050 ° C., the raw material starts to melt, but is further raised to a temperature at which it completely melts.
At this time, the inside of the crucible is not oxidized while the oxygen concentration is adjusted to 0.01 to 0.5% by volume, preferably 0.1 to 0.3% by volume, and the temperature of the melt is suppressed to 2150 ° C. or lower. Hold for a sufficient amount of time. The holding time varies depending on the apparatus and raw materials used, and therefore cannot be specified unconditionally, but it is preferably held for 5 to 20 hours. If the raw material is melted under such conditions, gas components in the raw material are sufficiently removed, and inclusion due to oxidation of the crucible can be suppressed. On the other hand, if the oxygen concentration is less than 0.01% by volume, oxygen is insufficient and a single crystal of good quality cannot be obtained. If the oxygen concentration exceeds 0.5% by volume or is left for 20 hours or more, the crucible There is concern about oxidation.

(3) In the growth of the single crystal, which is the next stage, according to a normal method, the rotation speed and the pulling speed are adjusted to form the neck portion and the shoulder portion, and subsequently the straight body portion is formed. The crystal shape is adjusted by measuring the weight of the crystal during growth, deriving the diameter, growth speed, and the like by calculation, and adjusting the rotation speed and pulling speed. In addition, the melt temperature is controlled by feeding back the change in crystal weight to the power applied to the high frequency induction coil.

Also during the growth of the single crystal, the oxygen concentration is adjusted to a range of 0.01 to 0.5% by volume, preferably 0.1 to 0.3% by volume. When the crystal is grown in this oxygen concentration range, generation of minute bubbles can be suppressed. In addition, since the crucible is hardly oxidized, no inclusion occurs. Further, within this oxygen concentration range, the growth interface does not protrude significantly on the melt side, and the problem that crystals obtained with respect to the raw material cannot be made so large is solved.
In this way, by melting the raw material in a mixed gas atmosphere, controlling the melt temperature to 2150 ° C. or less and allowing it to stand at an oxygen concentration of 0.01 to 0.5% by volume, and growing a single crystal, The occurrence of inclusion due to the oxidation of the crucible can be suppressed, and the excess gas contained in the melt can be reduced, so that the number of minute bubbles taken into the crystal during single crystal growth can be reduced. And the pit and protrusion in a single crystal obtained under such conditions can be decreased.

Next, when the grown single crystal is cut, a wafer having a diameter of about 3 inches, for example, is obtained and polished to check the occurrence of pits, the number of occurrences of pits and protrusions is 5 or less for all wafers.
Since the aluminum oxide single crystal produced by such a manufacturing method has very few microbubbles and inclusions, it is possible to provide electronic component materials and optical component materials having few pits and protrusions and having excellent characteristics.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Evaluation of pits]
Fifty wafers were sliced from the grown single crystal and polished to determine how many pits and protrusions exist. The smaller the number of pits and protrusions, the better the single crystal is grown.

[Example 1]
Using a high-frequency induction heating type growth furnace with a maximum output of 40 kW, a B thermocouple was installed in an iridium crucible 10 mm away from the crucible bottom. The apparatus was provided with means for depressurizing the furnace body, means for monitoring the degree of decompression, means for supplying a mixed gas of oxygen and nitrogen or an inert gas, and means for monitoring the oxygen concentration.
First, 10 kg of 4N (99.99%) aluminum oxide raw material was charged into the crucible. The aluminum oxide raw material is called crackle, which is obtained by grinding an aluminum oxide single crystal grown by Bernoulli method to a size of about 20 mm square.
Vacuuming was started before the raw material was heated, and when the pressure in the furnace was reduced to 20 Pa, the vacuuming was stopped and nitrogen gas was introduced. After the pressure in the furnace reached 0.1 MPa, only nitrogen gas was allowed to flow at a flow rate of 3 liters per minute to start heating the raw material. At this time, the oxygen concentration in the furnace was 0.1 ppm. The raw material was gradually heated for 12 hours until reaching the melting point. When the thermocouple installed 10 mm away from the bottom of the crucible reached about 1000 ° C., the increase in oxygen concentration measured at the gas outlet of the furnace body began, and the oxygen concentration exceeded 500 ppm at 1500 ° C. Thereafter, when the temperature was further increased, the oxygen concentration began to decrease and decreased to 400 ppm. When the temperature was further increased and the raw material was melted, the oxygen concentration rapidly increased again from 400 ppm to 750 ppm. Thirty minutes after melting the raw material, when the oxygen concentration decreased to 500 ppm, oxygen gas was introduced into the furnace to make a mixed gas atmosphere of oxygen and nitrogen, and the oxygen concentration at the gas outlet was adjusted to 0.3%.
After leaving the material in a molten state for 5 hours so that the temperature does not exceed 50 ° C. from the melting point, the aluminum oxide single crystal cut in the a-axis direction is used as a seed crystal, and the seed crystal is lowered to near the melt. It was. The seed crystal is gradually lowered while rotating at a speed of 2 revolutions per minute, and the seed crystal is raised at a pulling speed of 2 mm / h while gradually lowering the temperature by bringing the tip of the seed crystal into contact with the melt. Crystal growth was performed.
As a result, a crystal having a diameter of 102 mm and a length of the straight body portion of 135 mm, in which bubbles were not observed visually, was obtained. Further, when the growth interface at the bottom of the crystal was measured, it was 50 mm convex. When this crystal was made into a wafer and polished, no pits and protrusions could be confirmed.

[Example 2]
This was carried out in the same manner as in Example 1 except that powdered aluminum oxide raw material was used as the raw material. As a result, a crystal having a diameter of 100 mm and a length of the straight body portion of 119 mm, in which bubbles were not observed visually, was obtained. Further, when the growth interface at the bottom of the crystal was measured, it was 42 mm convex. When this crystal was made into a wafer and polished, no pits and protrusions could be confirmed.

[Comparative Example 1]
For comparison, when the raw material was heated and melted, the mixed oxygen and nitrogen atmosphere was started from the start of heating, and the raw material was melted and the temperature was 120 ° C. higher than the melting point, that is, the sample was left at 2170 ° C. for 5 hours. 1 was 121 mm, the length of the straight body was 120 mm, and the growth interface at the bottom of the crystal was 49 mm convex. When this crystal was polished to a wafer and polished, no pits could be confirmed, but several protruding foreign matters having a size of several μm were observed on the wafer. When this was analyzed by EPMA, it was iridium.

[Comparative Example 2]
For comparison, the same procedure as in Example 1 was performed except that the atmosphere was 0.7% oxygen concentration from the start of heating to the end of crystal growth.
As a result, a crystal having a diameter of 120 mm and a length of the straight body part of 121 mm was obtained. When the growth interface at the bottom of the crystal was measured, it was as small as 33 mm convex. When this crystal was polished to a wafer and polished, no pits could be confirmed, but several protruding foreign matters having a size of several μm were observed on the wafer.

[Comparative Example 3]
For comparison, the same procedure as in Example 1 was performed except that the crystal growth was left for 30 hours.
As a result, a crystal having a diameter of 120 mm and a length of the straight body portion of 120 mm was obtained. Further, the growth interface convexity at the bottom of the crystal was 50 mm convex, which was almost the same as the result of Example 1. When this crystal was polished with a wafer, no pits could be confirmed, but several protruding foreign matters having a size of several μm were observed on the wafer.

As described above, in the examples, the atmosphere in the furnace is only nitrogen or an inert gas while the raw material is heated in the crucible, and after the raw material is melted, the oxygen concentration is 0.01 to 0.5 with respect to the mixed gas. By removing the gas adsorbed or contained in the raw material by maintaining the melt for a certain period of time at a temperature not exceeding 2150 ° C. in a mixed atmosphere of oxygen and nitrogen or an inert gas that makes volume% In addition, iridium was prevented from dissolving into the raw material due to the oxidation of the crucible. As a result, it was possible to suppress the gas uptake into the grown single crystal and to suppress the occurrence of inclusion.
On the other hand, in the comparative example, as a result of heating the melt excessively or setting the oxygen excess, the oxidation of the crucible was promoted, iridium was mixed into the melt, and this was taken into the crystal and included.

FIG. 1 shows the results of measuring the thermocouple temperature and oxygen concentration at the bottom of the crucible when nitrogen was introduced from the top of the furnace 3 liters per minute and aluminum oxide was heated while flowing in the furnace in a high frequency induction heating furnace. It is explanatory drawing shown.

Claims (4)

In a method for producing an aluminum oxide single crystal by a melt solidification method in which a raw material for a single crystal is placed in an iridium crucible in a furnace and heated and melted, and a growth crystal is pulled up from the raw material melt,
When the single crystal raw material is heated and melted, the gas generated from the single crystal raw material is removed by gradually heating the single crystal raw material over a period of 10 hours or more in a nitrogen or inert gas atmosphere until the melting point is reached. while melted, then introducing 0.01-0.5 volume% oxygen with respect to the gas mixture into the furnace, oxygen and nitrogen, or under a mixed gas atmosphere composed of inert gas, and subsequently heating the raw material melt The aluminum oxide is characterized in that the oxygen concentration is adjusted to 0.01 to 0.5% by volume at 2050 to 2150 ° C. and kept within 20 hours so as not to oxidize the crucible, and then the grown crystal is pulled up. Crystal production method.   The method for producing an aluminum oxide single crystal according to claim 1, wherein the heating temperature is measured by a thermocouple installed at a position within 20 mm from the bottom of the crucible. The said thermocouple is B thermocouple made from a platinum rhodium alloy, The manufacturing method of the aluminum oxide single crystal of Claim 2 characterized by the above-mentioned. The method for producing an aluminum oxide single crystal according to claim 1, wherein the holding time is 5 to 20 hours.

Images