JPH09263490A - Graphite crucible and production of silicon single crystal by czochralski method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control technique which is used for controlling the oxygen concn. in a single crystal produced by a CZ(Czochralski) method and a novel technique different from any conventional technique and by which the control can simply and surely be performed in particular without being restricted by any heat shielding member used in recent yarns. SOLUTION: This graphite crucible used at the time of producing a silicon single crystal by a CZ method, has a thickness of its cylindrical section, that is not constant in the vertical direction, or is provided with a part having a reduced thickness, which is formed along the vertical direction in the cylindrical section. The production of a silicon single crystal by a CZ method using this crucible is also provided.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a graphite crucible used for producing a silicon single crystal by the Czochralski method, and a method for producing a silicon single crystal by the Czochralski method using the graphite crucible. .

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have become more highly integrated and more highly accurate, semiconductor crystal substrates have also become larger in diameter and higher in quality. Semiconductor crystals are mainly manufactured by the Czochralski method (hereinafter referred to as the CZ method), and efforts are being made to further increase the diameter and quality.

A case of manufacturing a silicon single crystal ingot by the CZ method will be described with reference to FIG. 6, in which a quartz crucible 3 held by a graphite crucible 2 is provided substantially in the center of a pulling chamber (metal chamber) 1. The center of the bottom of the graphite crucible 2 is supported from below by a support shaft 4 which is rotatable and vertically movable. Polycrystalline silicon as a raw material is filled in a quartz crucible, which is heated and melted by a graphite heater 6 surrounded by a heat retaining body 5 to form a melt 7. A pulling shaft 11 having an opening 8 at the center of the ceiling of the pulling chamber 1 and passing through a sub-chamber 9 connected to the pulling chamber 1 and holding a seed crystal 10 at the tip, which is rotatable and vertically movable.
And the seed crystal is dipped in the melt 7, and then the seed crystal is pulled up while rotating the pulling shaft 11 and the quartz crucible, the single crystal ingot 12 can be grown under the seed crystal. In addition,
The pulling up is performed while introducing argon gas from the upper part of the pulling chamber and discharging it from the exhaust port 15 at the lower part.

A conventional problem in growing a large-diameter silicon single crystal by the CZ method is that the pulling rate should be as high as possible in order to improve the productivity, but When the aperture is increased, the latent heat of crystallization is increased and the radiant heat to the crystals is also increased, so that the pulling rate is rapidly decreased and the productivity is significantly deteriorated. Further, when the crystal has a large diameter, it becomes difficult to make the temperature uniform throughout the solid-liquid interface, the single crystallization rate decreases, and the yield remarkably decreases.

In terms of crystal quality, the demand for high quality of semiconductor crystals has become strict due to the recent trend toward higher integration and higher precision of semiconductor elements, resulting in higher crystal purity.
Low defects and homogenization are required, but recently, in particular, not only high-purity raw materials, high-purity materials used, and high-precision equipment, but also the thermal history of crystals during growth causes crystal defects. It has turned out to have a significant impact. For example, in silicon, oxidation-induced stacking faults (OSF oxidation)
Induced Stacking Fault),
Swirl Defects, other small defects, oxygen precipitation, BMD (Bulk Micro-)
Defect), FPD (Flow Pattern D)
effect), LSTD (Laser Scatter)
ingTomography Defect), COP
(Crystal Originated Parti
Cle) and various characteristics such as breakdown voltage of oxide film are affected by thermal history, and therefore, pulling up with various internal structures to control defects in crystal by adjusting thermal history during crystal growth. A device has been proposed.

In order to solve the problems listed above, a heat shield member is often provided so as to surround the single crystal in order to control the temperature distribution and heat history of the growing single crystal ingot. It was For example, the following proposals have been made as typical ones.

As shown in FIG. 7, this is an apparatus for partially covering the crucible 3 and the melt 7 in the crucible, and the upper portion protruding from the edge of the crucible 3. Flat annular rim 30 and a connecting part 3 attached to this annular rim, which is cylindrically inclined downwards from its inner edge or is conically tapered
1 is a single crystal pulling apparatus, which is provided with a member having an internal height of 0.1 to 1.2 times the depth of the crucible. As shown in FIG. 8, a cylinder 19 that coaxially surrounds the pulling single crystal rod 12 is provided, and one end of the cylinder 19 is airtightly coupled to the opening edge at the center of the pulling chamber ceiling. However, the other end has a collar 20 that is hung down toward the surface of the melt 7 in the quartz crucible 3 and folded back outward to expand. As described above, the use of the heat shielding member is becoming indispensable for the CZ method device in recent years.

On the other hand, when the growth of a silicon single crystal is carried out by the CZ method, in addition to the oxygen originally contained in the raw material, oxygen as a constituent component of the quartz crucible in which the raw material for crystal growth is accommodated is obtained in the obtained crystal. It is widely known to mix. The amount of oxygen impurities mixed in this crystal is the silicon raw material melt amount (melt depth), the furnace pressure, the amount of inert gas introduced into the furnace, or the number of rotations of the crystal to be pulled,
It is affected by the rotation speed (rotation speed) of the crucible, temperature distribution in the raw material melt, and so on. These factors affect the convection in the melt and the oxygen concentration itself in the melt, and thus affect the oxygen concentration in the crystal. Therefore, by controlling these various factors in combination, it is possible to freely adjust the oxygen concentration in the crystal.

However, as described above, the use of the heat shield member is becoming indispensable in the recent CZ method apparatus. When such heat shield member 19, 20, 30, 31 is used, as shown in FIG. As shown in No. 8, since the lower end of the heat shield member and the melt surface are close to each other, and the crystal temperature distribution is greatly affected by this interval, this interval can hardly be changed. However, even if it is changed, only a slight change can be made. Therefore, since the position of the melt surface is uniquely determined and cannot be moved, considerable factors among the factors that affect the oxygen concentration are restricted, making it difficult to control the oxygen concentration. The control range is becoming narrower.

That is, regarding the pressure in the furnace and the amount of inert gas introduced into the furnace, since there is a heat shield member just above the melt surface, if the pressure in the furnace is raised too much and the gas amount is decreased, SiO adheres to this heat shield member and disturbs the crystal, resulting in deterioration of the single crystallization rate. If the amount of gas is increased too much, the melt surface swells and disturbs the crystal.
Also, regarding the temperature distribution in the raw material melt, since the position of the melt surface cannot be changed, the temperature distribution of the melt in the crucible can be easily changed by simply raising or lowering the crucible as in the conventional case. This is not possible, and in order to change the position of the melt surface, it is necessary to change the design of at least the heat shield member, and it is necessary to change other members accordingly.

On the other hand, the demand for single crystal materials is becoming more and more stringent due to higher precision and higher integration of devices. It is known that the oxygen concentration in the semiconductor silicon single crystal also has a great influence on the characteristics of the semiconductor element obtained by the concentration and distribution. That is, if the oxygen concentration is too high, crystal defects and oxygen precipitates are generated, which adversely affects the characteristics of the semiconductor device. However, when such crystal defects and oxygen precipitates are generated in regions other than the active region of the semiconductor device, they function as sites for gettering heavy metal impurities, and the characteristics of the semiconductor device can be improved (intrinsic getter). ring). Therefore, even if the oxygen concentration is too low, the device characteristics cannot be improved.

Therefore, the crystalline material is required to contain an appropriate amount of oxygen impurities in a proper amount according to the intended device, and the standard of the permissible concentration is remarkably narrowed. As described above, in order to highly control the impurity concentration in the crystal and satisfy the standard, the requirement cannot be met only by adjusting and controlling the restricted factor.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a novel control technique which has never been used as a technique for controlling the oxygen concentration of a single crystal by the CZ method. It is an object of the present invention to provide a technique capable of performing simple and reliable control without being restricted by a heat shield member used in recent years.

[0014]

In order to solve the above-mentioned problems, the present invention has been devised in a graphite crucible that directly affects the raw material melt. The described invention is a graphite crucible used in producing a silicon single crystal by the Czochralski method,
The thickness of the cylindrical portion of the graphite crucible is not constant in the vertical direction,
Alternatively, it is characterized in that a part of the cylindrical portion of the graphite crucible has a thinned portion along the vertical direction.

As described above, the wall thickness of the cylindrical portion of the graphite crucible, which has conventionally been considered to be uniform in the vertical direction, is not constant in the vertical direction, or a part of the cylindrical portion along the vertical direction. By having a thinned portion, the heat supplied to the melt can be locally changed, and the temperature distribution of the raw material melt can be directly affected, and convection of the melt can be changed and controlled. Therefore, the concentration of oxygen taken into the crystal can be controlled.

Further, the invention described in claim 3 and claim 4 of the present invention is a graphite crucible used when a silicon single crystal is manufactured by the Czochralski method, wherein the graphite crucible is a lower part of a cylindrical portion. The upper part is thinner,
Alternatively, the upper end portion of the graphite crucible is tapered so that the outer shape is reduced toward the upper portion.

As described above, the thickness of the cylindrical portion of the graphite crucible is thinner in the upper portion than in the lower portion, or the upper end portion of the graphite crucible is tapered so that the outer shape is reduced toward the upper portion. It is suitable for producing a low-oxygen silicon single crystal, which has been particularly required in recent years because the heat flow is improved.

The invention described in claim 5 of the present invention is a graphite crucible used when a silicon single crystal is manufactured by the Czochralski method according to any one of claims 1 to 4. The graphite crucible is characterized in that the bottom part and the cylindrical part are divided and the cylindrical part is replaceable. In this way, if the bottom part and the cylindrical part are divided and the cylindrical part is configured to be replaceable, the oxygen concentration can be freely controlled by replacing the cylindrical part according to the purpose, and at the same time, at a simple and low cost. It can be carried out.

The inventions described in claims 6 and 7 of the present invention are methods for manufacturing a silicon single crystal by the Czochralski method.
The graphite crucible according to any one of claims 1 to 5 is used, or the graphite crucible according to any one of claims 1 to 5 is used, and a heat shield member of a grown silicon single crystal rod is used. And

As described above, by using the graphite crucible according to any one of claims 1 to 5 of the present invention, the convection of the raw material melt can be directly controlled. It is possible to accurately control the oxygen concentration of. In this case, the present invention which is not affected by the heat shielding member of the grown silicon single crystal ingot, which limits other oxygen concentration control factors, is particularly effective.

The present invention will be described in more detail below. The oxygen distribution in the single crystal is affected by the temperature distribution in the raw material melt because convection in the raw material melt changes.

FIG. 1 is a conceptual diagram showing the state of convection in the raw material melt 7 during the growth of the single crystal 12 by the CZ method. The raw material melt is roughly divided into forced convection 51 and natural convection 51. It is known that there is a convection flow 52, and the oxygen concentration in the crystal changes depending on the balance between these convection flows. That is, when the forced convection flow 51 becomes strong, this silicon melt does not cause evaporation of SiO 2 on the melt surface.
Since the oxygen concentration is high, the oxygen concentration of the grown silicon single crystal also tends to increase. On the other hand, natural convection 52
Becomes stronger, the silicon melt becomes Si on the surface of the melt.
Oxygen is evaporated, so that the oxygen concentration is low, so that the grown silicon single crystal also tends to have a low oxygen concentration.

The forced convection 51 and the natural convection 52
As shown in FIG. 2, the strength of each of the above is due to the relative positional relationship between the heater 6 surrounding the crucible and the quartz crucible 3 and the graphite crucible 2. That is, when the crucibles 2 and 3 are raised by the support shaft 4 as shown in FIG. 2 (A) and the crucible is positioned relatively higher than the heater, the forced convection 51 becomes strong and the oxygen concentration rises. Become. On the other hand, FIG.
When the crucibles 2 and 3 are lowered by the support shaft 4 as shown in (B) and the crucible is positioned relatively lower than the heater, the natural convection 52 becomes stronger and the oxygen concentration lowers.

However, as described above, the vertical movement of the crucible cannot be performed when the heat shield member is used. Therefore, in the present invention, the graphite crucible has the function of producing the same effects as the above, and moreover, the graphite crucible acts more directly on the melt and can be accurately controlled. It was successful. And
Thus, devising the shape of the graphite crucible is not restricted by the heat shield member.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. Here, FIG. 3 is a schematic cross-sectional shape of a conventional graphite crucible, where (A) is a flat bottom and (B) is a round bottom. 4 (A) to 4 (F) are diagrams showing cross-sectional shapes in a typical example of the graphite crucible according to the present invention.

FIG. 3 shows a schematic cross-sectional shape of a conventional graphite crucible. In the case of a flat bottom (A) or a round bottom (B), the wall thickness of the cylindrical portion H is vertical. It is constant. When pulling a single crystal by the CZ method using such a graphite crucible having a cylindrical portion H having a uniform thickness in the vertical direction, the heat from the heater is uniformly distributed in the quartz crucible supported by the graphite crucible. The temperature distribution of the melt that is transmitted to the raw material melt is governed by the positional relationship between the heater and the crucible as described above, and reflects this.

Therefore, according to the present invention, it was common knowledge that the vertical direction is uniform, and the wall thickness of the cylindrical portion H is variously changed according to the purpose, so that the heat flow from the heater in that portion is locally changed. The temperature distribution in the melt was changed, and the convection was changed to control the oxygen concentration incorporated in the single crystal.

FIG. 4 shows a sectional shape of a typical example of the graphite crucible according to the present invention. In these graphite crucibles, as shown in FIGS. 4A to 4F, the wall thickness of the hollow cylindrical portion is not constant in the vertical direction. (A) is an example in which a part of the cylindrical portion of the graphite crucible has a thinned portion along the vertical direction, and in particular, the upper portion is thinner than the lower portion of the cylindrical portion. In such a graphite crucible, since heat passes better in the upper part of the crucible, the temperature distribution of the melt becomes higher in the upper part, and the crucible is relatively lowered in FIG. 2 (B). The same effect as in the state of is obtained. Therefore, the oxygen concentration of the grown single crystal can be reduced only by using the crucible of FIG. 4A without changing the position of the crucible. Then, the oxygen concentration can be changed and controlled by changing and adjusting the width and depth of the thinned portion G. That is, the oxygen concentration can be controlled only by replacing the graphite crucible.

On the other hand, (B) is an example in which a part of the cylindrical portion of the graphite crucible has a thinned portion along the vertical direction, and in particular, the lower portion is thinner than the upper portion of the cylindrical portion. . In such a graphite crucible, heat passes better in the lower part of the crucible, so that the temperature distribution of the melt becomes higher in the lower part, and the crucible is relatively raised in FIG. 2 (A). The same effect as in the state of is obtained. Therefore, the oxygen concentration of the single crystal to be grown can be increased simply by using the crucible of FIG. 4B without changing the position of the crucible. Also in this case, the oxygen concentration can be finely adjusted by adjusting the width and depth of the thinned portion G.

The graphite crucible of the present invention is not limited to these, and the wall thickness is not constant in the vertical direction, and as an example having a thinned portion in a part of the cylindrical portion along the vertical direction. Depending on the desired temperature distribution and oxygen concentration, the thinned portion may be provided at the center of the cylindrical portion (C), or the thinned portion may be provided at two locations (D) or more. Then, the number, width, depth, position, etc. of the thinned portions may be variously changed according to the target oxygen concentration.

Further, the present invention can be more simply described by referring to FIG.
As shown in FIG. 3, the upper end of the graphite crucible may be tapered so that the outer shape is reduced toward the upper side. Also in this case, as a result of the heat passing through the upper end portion of the graphite crucible being improved, the same effect as in FIG. 4A can be obtained. As described above, it is believed that the taper of the upper end is effective, because the present invention devises the shape of the graphite crucible and thus acts directly on the raw material melt. Be done.

The graphite crucible having the features of the cylindrical portion of the present invention has a configuration in which the bottom portion S and the cylindrical portion R are divided and the cylindrical portion R is fitted into the bottom portion S as shown in FIG. 4 (F). ,
The cylindrical portion R can be exchanged and used according to the target oxygen concentration, and the oxygen concentration can be controlled extremely easily and at low cost.

Therefore, if a silicon single crystal is produced by the Czochralski method using the graphite crucible of the present invention, the convection of the raw material melt can be directly controlled, so that the oxygen concentration in the crystal can be controlled. It can be controlled precisely. In this case, just replace the graphite crucible used,
Since the oxygen concentration can be changed and controlled, it is extremely simple and low-cost, and as mentioned above, the raw material melt surface cannot be changed, and other oxygen concentration control factors are restricted. The present invention can be carried out and is particularly beneficial when the heat shield member of the single crystal ingot is used without being affected by this.

The thinned portion G is made as thin as possible,
That is, by lowering the height of the graphite crucible, or by creating a part where there is no graphite crucible in the vertical direction, it is possible to improve the heat flow and control the temperature distribution of the melt. Since the quartz crucible softens at a high temperature, the raw material melt cannot be held only by the quartz crucible, and these are mainly held by the graphite crucible.
Therefore, the thinned portion of the present invention is merely a thinned portion, and for safety reasons, the height of the graphite crucible must not be lowered or completely penetrated.

[0035]

Embodiments of the present invention will be described below. (Examples and Comparative Examples) As shown in FIG. 8, a single crystal manufacturing apparatus using the Czochralski method having a heat shield member was used.
An 8-inch quartz crucible was filled with 70 kg of polycrystal, and a silicon single crystal having a diameter of 6 inches was produced from this. As the graphite crucible used, the graphite crucible shown in FIG. 4 (E) has a tapered upper end portion over 40 mm (Example), and the conventional cylindrical portion shown in FIG. 3 (A). The one having a uniform wall thickness (comparative example) was used. As other conditions, the crucible rotation during crystal growth was kept constant at 8 rpm, the seed rotation was kept constant at 22 rpm, and the atmosphere was a reduced pressure atmosphere of argon gas. The conditions other than the graphite crucible were the same in the examples and the comparative examples. The oxygen concentration of the crystal thus obtained is
It measured by FT-IR for every crystal position, and the result was shown in FIG.

As is apparent from FIG. 5, when a single crystal is grown using a graphite crucible having a tapered upper end according to the present invention, heat easily passes through the upper part of the crucible, so that the oxygen of the entire crystal is increased. It can be seen that the concentration is lowered by about 0.5 to 1 ppma.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

For example, the "Czochralski method" referred to in the present invention includes a so-called MCZ method of growing a crystal while applying a magnetic field to the melt in the crucible, and the graphite crucible of the present invention and the same. The method using is naturally applicable to the MCZ method and can exert its effect.

In the above-mentioned embodiment, the graphite crucible having a diameter of 18 inches for holding the quartz crucible has been described as an example. However, the present invention is not limited to this, and the diameter of the crucible may be changed. Needless to say, the present invention can be applied to a graphite crucible holding a quartz crucible of 24 inches or more, further 30 inches or more, as a matter of course.

[0040]

According to the present invention, when a silicon single crystal is produced by the CZ method, the oxygen concentration in the single crystal can be controlled by the unprecedented factor such as the shape of the graphite crucible. Moreover, this is simple and low-cost, and the oxygen concentration can be reliably controlled without being restricted by the heat shield member used in recent years.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a state of convection in a raw material melt during crystal growth by the CZ method.

FIG. 2 is an explanatory diagram for explaining a positional relationship between a crucible and a heater and a relationship between convection. (A) When the crucible is raised, (B) When the crucible is lowered.

FIG. 3 is a schematic cross-sectional shape of a conventional graphite crucible. (A) Flat bottom, (B) Round bottom.

4 (A) to (F) are diagrams showing cross-sectional shapes in a typical example of the graphite crucible according to the present invention.

FIG. 5 is a diagram showing the results of measuring the oxygen concentration of crystals produced in Examples and Comparative Examples for each crystal position.

FIG. 6 is a schematic sectional view of an apparatus for manufacturing a silicon single crystal ingot by a conventional Czochralski method.

FIG. 7 is a schematic cross-sectional view of a Czochralski method device having a heat shield, partially covering the device.

FIG. 8 is a schematic cross-sectional view of a Czochralski method device having a heat shield, the device having a collar.

[Explanation of symbols]

1 ... Pulling chamber, 2 ... Graphite crucible, 3 ... Quartz crucible, 4 ... Support shaft, 5 ... Insulator,
6 ... Graphite heater, 7 ... Melt,
8 ... Opening part, 9 ... Sub chamber, 10 ... Seed crystal,
11 ... Pull-up shaft, 12 ... Single crystal rod, 15 ... Exhaust port, 19 ... Cylinder, 20 ... Collar, 30
... annular rim, 31 ... connecting part, 51 ... forced convection, 52 ... natural convection, G ... thinning part,
H ... Cylindrical part, S ... Bottom part, R ... Cylindrical part.

Claims (7)

[Claims] 1. A graphite crucible used when a silicon single crystal is produced by the Czochralski method, wherein the thickness of the cylindrical portion of the graphite crucible is not constant in the vertical direction. A graphite crucible used when manufacturing a silicon single crystal by the method. 2. A graphite crucible used for producing a silicon single crystal by the Czochralski method, wherein a part of the cylindrical portion of the graphite crucible has a thinned portion along the vertical direction. Graphite crucible used when producing silicon single crystals by the Czochralski method. 3. The silicon according to the Czochralski method according to claim 1, wherein the graphite crucible has a thinner wall thickness in the upper portion than in the lower portion of the cylindrical portion. Graphite crucible used when manufacturing single crystals. 4. The Czochralski method according to claim 1, wherein an upper end portion of the graphite crucible has a taper shape whose outer shape is reduced toward an upper portion. Crucible used for manufacturing silicon single crystals by 5. The Czochralski according to any one of claims 1 to 4, wherein the graphite crucible has a bottom portion and a cylindrical portion which are divided and the cylindrical portion is replaceable. A graphite crucible used when manufacturing a silicon single crystal by the method. 6. A method for producing a silicon single crystal by the Czochralski method, which comprises using the graphite crucible according to any one of claims 1 to 5. 7. A silicon single crystal by the Czochralski method, characterized in that the graphite crucible according to any one of claims 1 to 5 is used and a heat shielding member of a grown silicon single crystal rod is used. A method of producing crystals.