JPH05319976A - Ultra-low-carbon crystal growing apparatus and production of silicon single crystal - Google Patents

Abstract

PURPOSE:To obtain a silicon single crystal with reduced carbon content by growing a crystal from its melt while heating a crucible by a heater and bringing a carbon-contg. gas generated from a thermal insulating material to outlets to prevent the gas from being allowed to flow into a growing chamber. CONSTITUTION:A crucible 2 and a heater 3 are placed in a crystal growing chamber 1 and a thermal insulating material 4 consisting of inorganic fibers are provided around the chamber; the resulting assembly is put into a refractory member 5. Gas outlets 10 are provided at both lower ends of the wall of the chamber 1, and a carbon-contg. gas generated from the thermal insulating material 4 is forcedly brought, via a gas passage 15, to the outlets 10 to prevent the gas from being allowed to flow into the chamber 1. And, owing to a trimmed flow of an Ar gas stream through a purge tube 16 toward the melt surface, the CO2 and SiO produced can quickly be discharged. With this system, the crucible 2 is charged with a Si polycrystal material which is then heated and melted. A seed crystal is then immersed in the melt 6 and continuously pulled up while rotating, thus obtaining the objective Si single crystal 7 with reduced carbon content.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the Czochralski method (C
The present invention relates to a crystal growth apparatus according to the Z method), and more specifically, to a crystal growth apparatus according to the CZ method capable of reducing carbon taken into the crystal during the crystal growth process according to the CZ method to 1/5 or less of the conventional concentration.

[0002]

2. Description of the Related Art An example of a conventional general CZ method crystal growth apparatus is shown in FIG. Carbon crucible 2 in the center of the growth chamber 1,
There is a carbon heater 3 surrounding this, and a heat insulating material 4 is arranged on the inner wall of the growth chamber 1. The heat insulating material 4 is made of carbon fiber and is housed in the carbon member 5 and attached to the inner wall surface.

The silicon in the crucible 2 is heated and melted,
The seed crystal 1 is pulled out of the melt 6 to obtain a single crystal 7. During this time, an inert gas such as Ar is introduced from the gas inlet 8 into the growth chamber 1.
It is introduced into the chamber and is discharged from the gas discharge port 10 by the vacuum pump 9. The gas outlets 10 are provided in one or two places on the floor surface of the furnace. In the figure, the heater 3 including the crucible 2 and the inside thereof have a high temperature, and are called hot zones.

[0004]

It is a well-known fact that the higher performance and lower cost of VLSIs increasingly require lower defect densities and larger diameters of silicon wafers as substrates.

The characteristic of DRAM, which is a typical VLSI, is given by the length of its refresh time. The refresh time is proportional to the time that the capacitor in the DRAM can store charges. If a precipitate (also called an oxygen precipitate because it is an aggregate of oxygen atoms) is present in the silicon crystal, the charge to be accumulated is transferred to the DRAM via the precipitate.
Since it escapes from the cell, the charge retention time becomes shorter and the refresh time becomes shorter. This causes a refresh failure. On the other hand, the precipitate serves as a recombination center and thus reduces the lifetime of the crystal. That is, a DRAM formed by using a crystal with a long lifetime has a long refresh time and becomes a high quality DRAM. The authors found that carbon in crystals promotes the formation of oxygen precipitates (see below).
Focusing on, the relationship between the carbon concentration and the lifetime was investigated, and it was clarified that the lifetime is improved as the low carbon crystal is shown in FIG. As described above, a low carbon concentration crystal must be used to improve the performance of the VLSI.

The increase in the diameter of the wafer causes an increase in thermal stress acting on the wafer in the heat treatment process. It is well known that when the thermal stress exceeds the yield stress of a wafer (crystal), a large number of dislocations are introduced, the warp of the wafer increases, and lithography and subsequent processing become difficult.

There are many heat treatment processes in the VLSI manufacturing process, so that precipitates are spontaneously formed in the wafer. When a precipitate is formed in the crystal,
It has been reported that the yield stress is reduced. It has also been reported that the warp of the wafer increases when the precipitate is formed in the crystal. Therefore, considering that the thermal stress will increase more and more as the diameter increases in the future, it is necessary to reduce the precipitate density to prevent the yield stress from lowering and develop a crystal that is strong against the thermal stress, that is, does not easily warp.

The density of the precipitate depends on the concentration of point defects and carbon. The present inventors have made the crystal 129 as shown in FIG.
It was clarified that the formation of oxygen precipitates is promoted by quenching from 0 ° C. and introducing point defects. The horizontal axis of FIG. 7 represents the cooling rate, and it is considered that the higher the cooling rate, the higher the point defect concentration. The vertical axis represents the amount of precipitated oxygen, and the larger this amount, the higher the density of oxygen precipitates. That is, it is considered that FIG. 7 shows that the more point defects, the more easily oxygen precipitation occurs. However, since the cooling rate of the wafer is 30 ° C./min or less in the normal thermal process, it cannot be considered that the point defect concentration determines the precipitate density. Also, during the crystal growth, the crystal grows while being cooled, but at a normal growth rate (up to 1 mm / min), the cooling rate is still 30 ° C./min or less.

When the present inventors investigated the relationship between the carbon concentration and the density of oxygen precipitates, they were in a substantially proportional relationship as shown in FIG. FIG. 8 shows a conventional crystal (carbon concentration ~ 3 × 1).
0 ¹⁵ cm ^-3 ) and the result of carbon doping (carbon concentration 10
¹⁶ to 10 ¹⁷ cm ⁻³ ) is heat-treated at 800 ° C. for 100 hours and then the density of oxygen precipitates is measured. The precipitate density is obviously higher depending on the carbon concentration.

From the above, it was found that it is necessary to remove carbon in the crystal in order to reduce the defect density and increase the diameter of the silicon wafer. Therefore, the crystal for reducing the carbon in the crystal It is an object of the present invention to provide a growth device.

[0011]

FIG. 1 is a schematic sectional view of a crystal growth apparatus of the present invention, and FIG. 10 is a schematic sectional view of another crystal growth apparatus of the present invention.

In order to achieve the above object, the present invention has a crucible 2 for a crystal melt in a crystal growth chamber 1 and a heater 3 for heating the crucible 2 with reference to FIGS. 1 and 10. In the crystal growth device by the Czochralski method, in which the heat insulating material 4 is arranged on the inner wall of the crystal growth chamber 1, the heat insulating material 4 is made of inorganic fiber and is housed in the refractory member 5 and The refractory member 5 is provided with an opening, and the gas exhaust port 1 is provided on the wall of the crystal growth chamber 1 behind the heat insulating material 4.
0, so that the carbon-containing gas generated from the heat insulating material 4 is forcibly guided to the gas exhaust port 10 to prevent the carbon-containing gas from flowing into the growth chamber 1, or According to the Czochralski method, in which a crystal melt crucible 2 is provided in a crystal growth chamber 1, a heater 3 for heating the crucible 2 is arranged, and a heat insulating material 4 is arranged on an inner wall of the crystal growth chamber (1). In the crystal growth apparatus, the heat insulating material 4 is made of an inorganic fiber, is housed in the refractory member 5 and is attached in close contact with the inner wall of the crystal growth chamber 1, and the crystal growth chamber 1 exposed above the refractory member 5 is exposed. A gas discharge port 10 is arranged on the bottom wall of the crystal growth chamber 1 exposed below the wall and the refractory member 5, so that the carbon-containing gas generated from the heat insulating material 4 is forcibly discharged.
0, and a crystal growth apparatus having a structure for preventing the carbon-containing gas from flowing into the growth chamber 1, or charcoal having the structure of the above two crystal growth apparatuses and exposed in the crystal growth apparatus chamber. A crystal growth apparatus characterized by coating all or part of the surface of the material with SiC, TiC, NbC, TaC, ZrC, or BN, or having the structure of the two crystal growth apparatuses and growing Or a crystal growth device having the structure of the above-mentioned two crystal growth devices, which is provided with a purge tube 16 for covering the outside of the existing crystals and for flowing the purge gas in the growth furnace toward the free surface of the melt. , And all or part of the surface of the carbon material exposed in the chamber of the crystal growth apparatus is SiC or TiC or NbC or T
A crystal growth apparatus characterized by being coated with aC or ZrC or BN, and provided with a purge tube 16 which covers the outside of a growing crystal and causes the purge gas in the growth furnace to flow toward the melt free surface. Alternatively, a Czochralski crystal growth in which a crucible 2 for a crystal melt and a heater 3 for heating the crucible 2 are arranged in the crystal growth chamber 1 and a heat insulating material 4 is arranged on the inner wall of the crystal growth chamber 1 In a method for producing a silicon single crystal using an apparatus, the crystal growth chamber 1 is located above the heat insulating material 4 made of inorganic fiber, and the heat insulating material 4 is housed and attached to the inner wall of the crystal growing chamber 1. A gas outlet 10 provided in any of the fireproof members 5 provided, the crucible 2 is heated by the heater 3, and the carbon-containing gas generated from the heat insulating material 4 is forcibly forced to the gas outlet 10; Leading to the carbon-containing gas While preventing entry into the crucible 2, it provides a method for manufacturing a silicon single crystal, which comprises growing a crystal of ultra low carbon from the crystal melt in the crucible 2.

[0013]

EXAMPLE FIG. 1 shows a schematic cross section of a crystal growth apparatus of the present invention. The same members as those in the conventional device have the same reference numerals as those in FIG. This device has the following features as compared with the conventional device.

The heat insulating material does not come into contact with the furnace wall, and the ventilation path 1
5 is provided. The surface of the hot zone is made of silicon carbide (Si
C) or Titanium Carbide (TiC) or Niobium Carbide (NbC) or Tantalum
Coated with Carbide (TaC) or Zirconium Carbide (ZrC) or Boron Nitride (BN).

A purge tube 16 is provided which covers the outside of the growing crystal and causes the purge gas in the growth furnace to flow toward the free surface of the melt. The exhaust port 10 to the vacuum pump is provided in the furnace wall and exhausted from at least two locations. However, the position of the outlet is shown in Figure 2.
As shown in (1), (2), and (3), when viewed from the top of the furnace, the angle α is expressed by 2π / n (n: number of exhaust holes), and the exhaust gas is discharged at two or more locations. Design the vacuum piping system so that the suction force at each of the outlets is the same.

First, the mechanism of carbon incorporation into the crystal during CZ growth will be explained, and then the present invention will describe how the carbon concentration can be reduced. There is considerable oxygen in the growth reactor. Most of it is SiO that evaporates from the melt. In addition to this, a small amount of oxygen due to leakage and oxygen contained in argon are present. These oxygen reacts with carbon to generate CO and CO ₂ .

C + nO → CO _n (n = 1, 2) Next, CO and CO ₂ are taken into the melt, reach the growth interface, and are mixed into the crystal. Therefore, there are the following two methods for reducing the carbon concentration of the crystal.

(A) The generated CO _n is exhausted before it is taken into the melt. (B) Separates carbon from oxygen to prevent the generation of CO _n . The main feature of the present invention is (A). A heat insulating material is set between the heater and the furnace wall, but since it is made of a material called carbon fiber, it has numerous voids and cannot be coated. Therefore, the generation of CO _n cannot be suppressed. Therefore, as shown in FIG. 1, the suction force of the vacuum pump is used to exhaust CO _n before it is taken into the melt. For this purpose, a ventilation path for argon gas is provided between the heat insulating material and the furnace wall so that CO
Exhaust _n . The points to be noted at this time are
The position of the outlet is to be provided on the furnace wall, and as shown in FIG. 2, the number n of outlets is 2 or more and the angle is α = 2π / n, and the suction force is the same for all outlets. Is. That is, if the balance of the suction force is lost, there is a risk that CO _{n in} the ventilation path sandwiched between the heat insulating material and the furnace wall will flow backward and rise to the upper part of the furnace to be taken into the melt. In the conventional furnace (FIG. 9), since the heat insulating material is completely in contact with the furnace wall, it is considered that CO _n generated from the heat insulating material is not efficiently exhausted and is taken into the melt. In order to more thoroughly implement the feature (A) of the present invention, if the purge tube 16 shown in FIG. 1 is used, the exhaust of CO _n is further accelerated, and it is effective in reducing carbon. A growth apparatus using a purge tube is disclosed in JP-A-55-113695, JP-A-55-140797, and JP-A-55-15819.
No. 7, Japanese Patent Publication No. 57-15076, etc., and it has been put to practical use today. It is well known among crystal manufacturers that SiO gas is exhausted faster and more efficiently than in a growth apparatus without the purge tube as a result of the Ar gas flow being rectified toward the melt surface by this purge tube. Has been. Therefore, it can be easily understood that CO _n generated in the growth furnace is quickly exhausted together with Ar and SiO. The material of the purge tube is S
iC or TiC or NbC or TaC or ZrC or B
A carbon material coated with N or a refractory metal such as tungsten (W) or molybdenum (Mo), which generates less impurities even at high temperatures, is desirable.

The second feature (B) of the present invention is carried out by coating carbon with SiC, TiC, NbC, TaC, ZrC, BN or the like. FIG. 3 shows the oxidation rate when these coating materials were heated in air. For example, at 1000 ° C., the oxidation rate of BN is about 1/10 ³ of the value of carbon (graphite), SiC, TiC, N
bC and ZrC are lower by a fraction to 1/10.
Therefore, these coatings sequester oxygen from carbon.

Improvement of the present invention described above, namely, by providing an Ar ventilation furnace between the heat insulating material and the furnace wall, or by providing an Ar ventilation furnace between the heat insulating material and the furnace wall, and Coating the carbon hot zone,
Or-providing an Ar ventilation furnace between the heat insulating material and the furnace wall, and providing a purge tube, or-providing an Ar ventilation furnace between the heat insulating material and the furnace wall, and carbon .Coating the hot zone,
Moreover, by providing a purge tube, the vapor pressure of CO _n in the growth furnace can be made lower than that in the conventional furnace. This is easily concluded from the facts described below.

FIG. 4 shows a zone melting method (FZ) which does not use polycrystalline silicon as a raw material and a carbon hot zone at all.
The result of our analysis of the carbon concentration of the crystal is shown (the analysis method is the activation analysis method as before). The carbon concentration in the portion of the FZ crystal having a solidification rate of 10% is 1. 7 × 10 ¹⁵ cm ^-3
It was 1/10 of that of polycrystalline silicon. On the other hand, the segregation coefficient of carbon impurities in the growth from silicon melt is 0. 0
7-0. It is 1. Therefore, in the FZ crystal, the carbon concentration of the solidified portion (the portion having a small solidification rate) at the initial stage of growth is determined by only segregation without any contamination from the atmosphere of the FZ growth furnace. This is a natural consequence of the fact that the FZ furnace does not use any carbon hot zone.

However, as shown in FIG. 5, the carbon concentration of the solidified portion of the CZ crystal in the initial stage is 4 even if only the ventilation furnace of Ar is provided between the heat insulating material and the furnace wall in the present invention. × 10 ¹⁴ cm ^-3, which is 1 of the concentration of the same part of the FZ crystal.
/ 4 or less. That is, it is even lower than the carbon concentration expected from simply segregation. From this result, it is concluded that segregation of carbon impurities also occurs in CZ growth, but a new mechanism for lowering carbon acts in addition to that. As the latter mechanism, it is most rational to think that carbon is evaporating from the melt. Since the carbon in the melt is from easy to take the form of CO _n Since the melt abundant supply oxygen from the quartz crucible, and when the CO _n is out diffused into direct atmosphere from the crystal Is unthinkable. If it is assumed that CO _n diffuses out of the crystal directly into the atmosphere, the carbon content of the FZ crystal must be reduced to a level lower than that expected from segregation. Since there is no such fact in the FZ crystal, it is not considered that CO _n directly diffuses out of the crystal into the atmosphere. From the above, it is most reasonable to think that carbon is evaporating from the melt. (In FZ growth, it is concluded that the melt is extremely high in purity because it does not come into contact with other substances, but it has the drawback that the carbon contained in polycrystalline silicon cannot be evaporated). Accordingly, even if only the improvement of the present invention in which an Ar ventilation furnace is provided between the heat insulating material and the furnace wall is performed, the CZ
The vapor pressure of CO _{n in} the furnace can be made lower than that in the conventional furnace, and as a result, the evaporation of carbon from the melt is promoted more than in the conventional furnace, so that crystals with a low carbon concentration can be obtained. It is clear that the effect of promoting carbon evaporation is further enhanced by using a purge tube or coating hot zone.

The crystal growth method using the apparatus of the present invention is the same as the case of using the conventional apparatus. The most popular size CZ type growth apparatus at present has a 16-inch quartz crucible inside.

First, 45 kg of polycrystalline silicon as a raw material is charged in a quartz crucible and heated and melted by a heater. Next, a seed crystal (single crystal) prepared in advance is immersed in the surface of the melt, and is continuously pulled up while rotating to grow the seed crystal. Crystals grown from a 16 inch quartz crucible have a standard diameter of 6 inches. It should be noted here that when the coating hot zone is used, its surface is vulnerable to mechanical shock and is easily peeled off, so that it should not come into strong contact with other parts in the preparation step for growth. When the coating is peeled off, carbon is exposed and CO _n is generated.

FIG. 5 shows the respective carbon concentration distributions of the silicon crystal grown in the conventional furnace and the silicon crystal grown in the furnace of the present invention (however, only the heat insulating material is improved) with respect to the solidification rate. The analytical method for both is activation analysis. The detection limit is 2. It is 5 × 10 ¹⁴ cm ^-3 .

The total carbon concentration is about 1 as compared with the conventional crystal.
It has been reduced to / 5, demonstrating the effectiveness of the present invention. It is clear that crystals with a lower carbon concentration can be grown by combining a purge tube and a coating hot zone. The effect of the coating hot zone has been confirmed by coating carbon with BN, but on the growth of gallium arsenide (T. Inada, T. Fujii, T. Kikuta and T. Fukuda, App.
L. Phys. Lett., 50 (1987) 143).

Further, in the conventional crystal, a portion having a high solidification rate (for example, 80% or more) cannot be used for ULSI because of a high carbon concentration, but the crystal grown in the furnace of the present invention is compared with the conventional crystal. Since the carbon concentration is low, a portion having a high solidification rate (for example, 80 to 95%) can be used for ULSI. Therefore, the yield in growth is improved.

FIG. 10 is a schematic sectional view of another crystal growth apparatus according to the present invention. The same members as those of the crystal growth apparatus of the present invention described above are denoted by the same reference numerals as in FIG. This device has the following features as compared with the conventional device.

The heat insulating material 4 is provided in close contact with the furnace wall,
Ventilation is prevented during that time. Further, a gas outlet 10 to the vacuum pump is provided at a position higher than the heat insulating material 4 on the upper furnace wall of the furnace and on the bottom wall of the furnace.

Discharge port 1 to a vacuum pump provided on the furnace wall
0 shall be at least two places. However, outlet 10
When viewed from the top of the furnace, the angle α is 2π / n (n:
The vacuum piping system is designed so that the suction force at each of the two or more outlets 10 is the same.

The surface of the hot zone is coated with silicon carbide or titanium carbide or niobium carbide or tantalum carbide or zirconium carbide or boron nitride so that the material carbon is not exposed. ..

The main feature of this embodiment is the discharge port 10 provided in the upper furnace wall. The argon gas containing oxygen generated from the crucible is hot and easily flows into the upper part of the furnace. Therefore, by exhausting the argon gas from the exhaust port 10 provided in the upper part of the furnace, the argon gas which has flown into the upper part of the furnace due to the high temperature and comes into contact with the heat insulating material to contain CO _n is effectively removed. Can be discharged to. Of course, the consideration of the arrangement of the outlets 10 and the balance of the suction force are the same as those of the device of the present invention. What is more important is to balance the exhaust from the top of the furnace with each other, as well as the exhaust from the top of the furnace and the exhaust from the bottom of the furnace. If this balance is lost, there is a risk that the argon gas containing CO _n will flow back to the center of the furnace in contact with the heat insulating material and carbon will be taken into the melt. Such a balance is experimentally established by making the suction force suitable for the configuration of the furnace. It should be noted that the generation of CO _n can be reduced by coating the surface of the carbon member forming the hot zone, as in the above-described device.

The silicon crystal grown using this other growth apparatus according to the present invention had a carbon concentration equivalent to that of the silicon crystal grown using the above-described growth apparatus according to the present invention. The characteristics related to lifetime and oxygen precipitation were also the same.

In this embodiment, the argon gas containing CO _n can be effectively exhausted, and the SiO evaporated from the melt surface can also be efficiently exhausted.
A silicon single crystal with few crystal defects can be manufactured.

[0035]

According to the present invention, it becomes possible to grow a single crystal having a reduced carbon concentration in the crystal in the Czochralski method.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a crystal growth apparatus according to the present invention.

FIG. 2 is a schematic diagram showing the arrangement of gas outlets of the crystal growth apparatus of the present invention.

FIG. 3 is a diagram showing oxidation rates of various coating materials.

FIG. 4 is a diagram showing carbon concentrations of polycrystalline silicon and FZ grown crystals.

FIG. 5 is a diagram showing carbon concentrations in crystals grown by the present invention and a conventional apparatus.

FIG. 6 is a diagram showing a relationship between a crystal lifetime and a carbon concentration.

FIG. 7 is a diagram showing the relationship between the cooling rate of crystals and the amount of precipitated oxygen.

FIG. 8 is a diagram showing the carbon concentration dependence of the amount of precipitated oxygen.

FIG. 9 is a sectional view showing a conventional CZ method crystal growth apparatus.

FIG. 10 is a schematic sectional view of another crystal growth apparatus according to the present invention.

[Explanation of symbols]

 1 ... Growth chamber (furnace) 2 ... Crucible 3 ... Heater 4 ... Insulating material 5 ... Refractory member 6 ... Melt liquid 7 ... Single crystal 8 ... Gas inlet 9 ... Vacuum pump 10 ... Discharge port 15 ... Gas passage 16 ... Purge tube

Claims (6)

[Claims] 1. A crystal melting chamber (1) has a crucible (2) for crystal melt, and a heater (3) for heating the crucible (2).
In the crystal growth device by the Czochralski method in which the heat insulating material (4) is arranged on the inner wall of the crystal growth chamber (1), the heat insulating material (4) is made of inorganic fiber It is housed and attached to the inner wall of the crystal growth chamber (1), an opening is provided in the refractory member (5), and a gas outlet (10) is provided on the wall of the crystal growth chamber (1) behind the heat insulating material (4). Arrange
Therefore, the crystal growth apparatus having a structure for forcibly guiding the carbon-containing gas generated from the heat insulating material (4) to the gas outlet (10) and preventing the carbon-containing gas from flowing into the growth chamber (1). 2. A heater (3) for heating a crucible (2) having a crucible (2) for a crystal melt in a crystal growth chamber (1).
In the crystal growth device by the Czochralski method in which the heat insulating material (4) is arranged on the inner wall of the crystal growth chamber (1), the heat insulating material (4) is made of inorganic fiber It is housed and attached closely to the inner wall of the crystal growth chamber (1), and is exposed above the refractory member (5) and below the crystal growth chamber (1) wall and the refractory member (5). A gas exhaust port (10) is arranged on the bottom wall of the crystal growth chamber (1), and thus the carbon-containing gas generated from the heat insulating material (4) is forcibly guided to the gas exhaust port (10) to A crystal growth apparatus having a structure for preventing gas from flowing into a growth chamber (1). 3. A carbon material having the structure according to claim 1 or 2, and exposing all or part of the surface of the carbon material exposed in the crystal growth apparatus chamber to SiC, TiC, NbC, TaC or Zr.
A crystal growth apparatus characterized by being coated with C or BN. 4. A purge tube (16) having the structure according to claim 1 or 2, which covers the outside of a growing crystal and causes the purge gas in the growth furnace to flow toward the melt free surface. A crystal growth apparatus comprising: 5. The carbon material having the structure according to claim 1 or 2, and exposing all or part of the surface of the carbon material exposed in the chamber of the crystal growth apparatus is SiC, TiC, NbC, TaC, or Zr.
A crystal growth apparatus, which is coated with C or BN, and which is provided with a purge tube (16) which covers the outside of a growing crystal and causes the purge gas in the growth furnace to flow toward the free surface of the melt. .. 6. A crystal melting crucible (2) and a heater (3) for heating the crucible (2) are arranged in the crystal growth chamber (1), and heat insulation is provided on an inner wall of the crystal growth chamber (1). In the method for producing a silicon single crystal using a Czochralski crystal growth apparatus in which the material (4) is arranged, the crystal growth chamber (1) is located above the heat insulating material (4) made of inorganic fiber. The heater (3) is provided with a gas discharge port (10) opened in any of the refractory members (5) that are mounted on the inner wall of the crystal growth chamber (1) that houses the wall or the heat insulating material (4). ) Heats the crucible (2) and forcibly guides the carbon-containing gas generated from the heat insulating material (4) to the gas discharge port (10) to introduce the carbon-containing gas into the crucible (2). A method for growing ultra-low carbon crystals from a crystal melt in the crucible (2) while preventing inflow. Method for producing con single crystal.