JP3744053B2 - Graphite crucible and method for producing silicon single crystal by using Czochralski method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a graphite crucible used when a silicon single crystal is produced by the Czochralski method, and a method for producing a silicon single crystal by the Czochralski method using the graphite crucible.
[0002]
[Prior art]
In recent years, higher integration and higher accuracy of semiconductor devices have been progressed, and semiconductor crystal substrates have been increasing in diameter and quality. Semiconductor crystals are mainly manufactured by the Czochralski method (hereinafter referred to as CZ method), and efforts to further increase the diameter and quality are being continued.
[0003]
A case where a silicon single crystal rod is manufactured by the CZ method will be described with reference to FIG. 6. A quartz crucible 3 held by a graphite crucible 2 is provided at substantially the center of a pulling chamber (metal chamber) 1. The center of the bottom of the crucible 2 is supported from below by a support shaft 4 that can rotate and move up and down. A quartz crucible is filled with polycrystalline silicon as a raw material, and this is heated and melted by a graphite heater 6 surrounded by a heat retaining body 5 to obtain a melt 7. There is an opening 8 at the center of the ceiling of the pulling chamber 1, and a rotating and vertically movable pulling shaft 11 holding a seed crystal 10 at the tip through a subchamber 9 connected thereto is lowered, After the seed crystal is immersed in the melt 7, when the seed crystal is pulled while rotating the pulling shaft 11 and the quartz crucible, the single crystal rod 12 can be grown thereunder. The pulling-up is performed while introducing argon gas from the upper part of the upper chamber and exhausting it from the lower exhaust port 15.
[0004]
As a conventional problem in growing a large-diameter silicon single crystal by such a CZ method, the pulling speed should be as fast as possible in order to improve productivity, but the pulling single crystal has a large diameter. As a result, the latent heat of crystallization increases and the radiant heat to the crystals also increases, so the pulling speed is reduced and the productivity is remarkably deteriorated. In addition, when the diameter of the crystal is increased, it is difficult to make the temperature uniform across the solid-liquid interface, the single crystallization rate is reduced, and the yield is significantly reduced.
[0005]
In terms of crystal quality, the demand for semiconductor crystal quality has become stricter due to the recent high integration and high precision of semiconductor elements, and further refinement of crystals, reduction of defects, and homogeneity of crystals. Recently, in particular, it has been found that not only the purity of raw materials, the purity of materials used, and the accuracy of equipment, but also the thermal history of the growing crystal greatly affects crystal defects. ing. For example, in silicon, oxidation-induced stacking fault (OSF Oxidation Induced Stacking Fault), swirl defect (Swirl Defect), other micro defects, oxygen precipitation, BMD (Bulk Micro-Defect), FPD (Flow Pattern Defect), LSTD Various properties such as Scattering Tomography Defect (COP), COP (Crystal Originated Particle), and oxide film breakdown voltage are affected by the thermal history. Therefore, to control defects in the crystal by adjusting the thermal history during crystal growth, A pulling apparatus having various in-furnace structures has been proposed.
[0006]
In order to solve the problems listed above, a heat shielding member is often provided so as to surround the single crystal rod in order to control the temperature distribution and thermal history of the growing single crystal rod. For example, the following proposals have been made as typical ones.
[0007]
(1) Japanese Patent Publication No. 57-40119 As shown in FIG. 7, this is an apparatus for partially covering the crucible 3 and the melt 7 in the crucible. A flat annular rim 30 and a connecting portion 31 attached to the annular rim and inclined downwardly in a cylindrical shape or tapered in a conical shape from the inner edge, and the internal height of the connecting portion A single crystal pulling apparatus characterized in that a member having a depth of 0.1 to 1.2 times the depth of the crucible is provided.
(2) Japanese Patent Application Laid-Open No. 64-65086 This is, as shown in FIG. 8, provided with a cylinder 19 that coaxially surrounds the pulling single crystal rod 12, one end of which is an opening edge at the center of the pulling chamber ceiling The single crystal rod manufacturing apparatus is characterized in that it has a collar 20 that is hermetically bonded to the other end and that hangs down toward the surface of the melt 7 in the quartz crucible 3 and is folded outward and expanded. It is.
As described above, the use of a heat shielding member is becoming indispensable in recent CZ method apparatuses.
[0008]
On the other hand, in the case of growing a silicon single crystal by this CZ method, in addition to what was originally included in the raw material, oxygen that is a constituent component of the quartz crucible in which the raw material for crystal growth is contained is mixed in the obtained crystal. Is widely known.
The amount of oxygen impurities mixed in this crystal is the amount of silicon raw material melt (melt depth), furnace pressure, amount of inert gas introduced into the furnace, or the number of revolutions of the crystal to be pulled up, the number of revolutions of the crucible. (Rotational speed), affected by temperature distribution in the raw material melt. These factors influence the oxygen concentration in the crystal because they affect the convection in the melt and the oxygen concentration in the melt itself. Therefore, the oxygen concentration in the crystal can be freely adjusted by controlling these various factors in combination.
[0009]
However, as described above, the use of a heat shielding member is becoming indispensable in recent CZ method apparatuses, and when such heat shielding members 19, 20, 30, 31 are used, they are shown in FIGS. Thus, since the lower end of the heat shielding 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. Even so, only minor changes can be made. Therefore, since the position of the melt surface is uniquely determined and cannot be moved, a considerable number of factors affecting the oxygen concentration are restricted, making it difficult to control the oxygen concentration. The control range is narrowing.
[0010]
In other words, regarding the pressure inside the furnace and the amount of inert gas introduced into the furnace, there is a heat shielding member directly above the melt surface. SiO adheres to the member, the crystal is disturbed, the single crystallization rate is deteriorated, and if the amount of gas is excessively increased, the melt surface is waved and the crystal is also disturbed. Also, regarding the temperature distribution in the raw material melt, as long as the position of the melt surface cannot be changed, the temperature distribution of the melt in the crucible is simply changed by simply raising or lowering the crucible as in the past. This is impossible, and in order to change the position of the melt surface, at least the design of the heat shielding member needs to be changed, and other members need to be changed accordingly.
[0011]
On the other hand, the demand for single crystal materials is becoming more and more strict due to the 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 element. However, when such crystal defects and oxygen precipitates are generated outside the active region of the semiconductor element, it acts as a site for gettering heavy metal impurities, and the characteristics of the semiconductor element can be improved (intrinsic getter). ring). Therefore, the device characteristics cannot be improved even if the oxygen concentration is too low.
[0012]
Therefore, the crystal material is required to contain an appropriate amount of oxygen impurities in accordance with the target device, and the standard of allowable concentration has been remarkably narrowed. Thus, in order to control the impurity concentration in the crystal at a high level and satisfy the standard, it is impossible to meet the requirement only by adjusting and controlling the restricted factor.
[0013]
[Problems to be solved by the invention]
The present invention has been made in view of such problems, and aims to provide an unprecedented new control technique 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 that can be easily and reliably controlled without being restricted by members.
[0014]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention is a devised graphite crucible that directly affects the raw material melt, and the present invention is a graphite used in producing a silicon single crystal by the Czochralski method. A crucible having a thinned portion along a vertical direction in a part of a cylindrical portion of the graphite crucible, and having a smaller thickness at the lower portion than the upper portion of the cylindrical portion. It is characterized by.
[0015]
As described above, the thickness of the cylindrical portion of the graphite crucible that has conventionally been known to be uniform in the vertical direction is not constant in the vertical direction, or a reduced thickness portion along the vertical direction in a part of the cylindrical portion. Therefore, the heat supplied to the melt can be locally changed, the temperature distribution of the raw material melt can be directly affected, and the convection of the melt can be changed and controlled. Therefore, the oxygen concentration taken into the crystal can be controlled.
[0016]
Further, the present invention is a graphite crucible used when producing a silicon single crystal by the Czochralski method, wherein the graphite crucible is thinner at the upper part than the lower part of the cylindrical part, or the graphite crucible The upper end portion has a taper shape whose outer shape is reduced toward the upper portion.
[0017]
In this way, the thickness of the cylindrical part of the graphite crucible is thinner at the upper part than the lower part, or the upper end part of the graphite crucible is tapered so that the outer shape is reduced toward the upper part. Therefore, it is suitable for producing a low-oxygen silicon single crystal that is particularly necessary in recent years.
[0018]
The present invention is a graphite crucible used when producing a silicon single crystal by any of the Czochralski methods described above, wherein the graphite crucible is divided into a bottom part and a cylindrical part, and the cylindrical part can be replaced. It is characterized by being.
Thus, 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 exchanging the cylindrical part according to the purpose, and at a simple and low cost. Can be implemented.
[0019]
The present invention is a method for producing a silicon single crystal by the Czochralski method, wherein the graphite crucible described above is used, or the graphite crucible described above is used, and a grown silicon single crystal A heat shielding member of a rod is used.
[0020]
Thus, since the convection of the raw material melt can be directly controlled by using the graphite crucible according to any one of the present invention, the oxygen concentration in the crystal can be accurately controlled. In this case, the present invention which is not affected at all by the use of a heat shielding member of a grown silicon single crystal rod, in which other oxygen concentration control factors are restricted, is particularly effective.
[0021]
Hereinafter, the present invention will be described in more detail.
The oxygen concentration in the single crystal is influenced by the temperature distribution in the raw material melt because the convection in the raw material melt changes.
[0022]
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 52. Therefore, it is known that the oxygen concentration in the crystal changes depending on the balance of these convections. That is, when the forced convection 51 becomes strong, the silicon melt has no oxygen evaporation on the melt surface, so that the oxygen concentration is high, and therefore the silicon single crystal to be grown also has an oxygen concentration. It tends to rise. On the other hand, when the natural convection 52 becomes strong, the silicon melt has a low oxygen concentration because of the evaporation of SiO on the surface of the melt, and therefore the grown silicon single crystal also tends to have a low oxygen concentration. It becomes.
[0023]
The strength of the forced convection 51 and the natural convection 52 depends on the relative positional relationship between the heater 6, the quartz crucible 3 and the graphite crucible 2 arranged so as to surround the crucible, as shown in FIG. That is, when the crucibles 2 and 3 are lifted by the support shaft 4 as shown in FIG. 2A and the crucible is relatively high with respect to the heater, the forced convection 51 becomes strong and the oxygen concentration increases. Become. On the other hand, when the crucibles 2 and 3 are lowered by the support shaft 4 as shown in FIG. 2B and the crucible is relatively low with respect to the heater, the natural convection 52 becomes stronger and the oxygen concentration decreases. It becomes.
[0024]
However, as described above, the vertical movement of the crucible cannot be carried out when a heat shielding member is used. Therefore, in the present invention, the graphite crucible has a function having the same effect as this, and moreover, it acts directly on the melt and can be accurately controlled. It was a success.
And devising the shape of the graphite crucible in this way is not restricted by the heat shielding member.
[0025]
DETAILED DESCRIPTION OF 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 the cross-sectional shapes in a representative example of the graphite crucible according to the present invention.
[0026]
FIG. 3 shows a schematic cross-sectional shape of a conventional graphite crucible. Even in the case of a flat bottom (A) or a round bottom (B), the thickness of the cylindrical portion H is constant in the vertical direction. . When a single crystal is pulled up by the CZ method using the graphite crucible of the cylindrical portion H having a uniform wall thickness in the vertical direction, heat from the heater is uniformly contained 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.
[0027]
Therefore, in the present invention, it has been common knowledge that the vertical part is uniform in the vertical direction, and the thickness of the cylindrical portion H is changed according to the purpose, so that the heat from the heater is locally changed. The oxygen concentration taken into the single crystal can be controlled by changing the temperature distribution in the melt and changing the convection.
[0028]
FIG. 4 shows a cross-sectional shape of a typical example of the graphite crucible according to the present invention.
When these graphite crucibles are in FIGS. 4A to 4F, the thickness of the hollow cylindrical portion is not constant in the vertical direction. (A) is an example which has a thinning part along a perpendicular direction in a part of cylindrical part of a graphite crucible, and is a shape where the thickness is especially thinner in the upper part than the lower part of the cylindrical part. In such a graphite crucible, since heat passes through the upper part of the crucible, the temperature distribution of the melt becomes a higher temperature in the upper part, and the crucible is relatively lowered as shown in FIG. The same effect as in the state is achieved. Therefore, the oxygen concentration of the single crystal to be grown can be reduced only by using the crucible of FIG. 4A without changing the position of the crucible. Then, by changing and adjusting the width and depth of the thinned portion G, the oxygen concentration can be changed and controlled. That is, the oxygen concentration can be controlled simply by replacing the graphite crucible.
[0029]
On the other hand, (B) is an example in which a thinned portion is provided along a vertical direction in a part of a cylindrical portion of the graphite crucible, and in particular, the lower portion is thinner than the upper portion of the cylindrical portion. In such a graphite crucible, since heat passes through the lower part of the crucible, the temperature distribution of the melt is higher in the lower part, and the crucible is relatively raised as shown in FIG. The same effect as in the state is achieved. Therefore, the oxygen concentration of the grown single crystal can be increased only by using the crucible of FIG. 4B without changing the position of the crucible. In this case, the oxygen concentration can be finely adjusted by adjusting the width, depth, etc. of the thinned portion G.
[0030]
And, the graphite crucible of the present invention is not limited to these, as an example in which the thickness is not constant in the vertical direction, and the reduced thickness portion along the vertical direction is part of the cylindrical portion. Depending on the 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. The number, width, depth, position, etc. of the thinned portions may be variously changed according to the target oxygen concentration.
[0031]
In addition, the present invention can be implemented more simply by making the upper end of the graphite crucible into a tapered shape whose outer shape decreases toward the top as shown in FIG. Also in this case, as a result of improved heat passage at the upper end of the graphite crucible, the same effect as in FIG. 4A can be obtained. As described above, the reason why the upper end portion is merely tapered is that it is effective in the present invention because it works directly on the raw material melt because the shape of the graphite crucible is devised. It is.
[0032]
And the graphite crucible having the feature in the cylindrical portion of the present invention can be obtained by dividing the bottom S and the cylindrical portion R and fitting the cylindrical portion R into the bottom S as shown in FIG. Depending on the concentration, the cylindrical portion R can be exchanged and used, and the oxygen concentration can be controlled extremely easily and at low cost.
[0033]
Therefore, if a silicon single crystal is produced by the Czochralski method using the graphite crucible according to the present invention, the convection of the raw material melt can be directly controlled, so that the oxygen concentration in the crystal is accurately controlled. can do. In this case, the oxygen concentration can be changed and controlled simply by replacing the graphite crucible to be used, so it is extremely simple and low cost, and the raw material melt surface cannot be changed as described above. In the case of using a heat shielding member of a grown silicon single crystal rod that restricts the oxygen concentration control factor of the present invention, the present invention can be carried out without being affected at all, and acts particularly beneficially. .
[0034]
In addition, by reducing the thickness of the thinned portion G as much as possible, that is, by reducing the height of the graphite crucible, or by generating a portion where there is no graphite crucible in the vertical direction, the passage of heat is improved and the melting is improved. Although it is conceivable to control the temperature distribution of the liquid, since the quartz crucible is softened 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 should not be lowered or completely penetrated.
[0035]
【Example】
Examples of the present invention will be described below.
(Examples and comparative examples)
As shown in FIG. 8, an 18-inch quartz crucible was filled with 70 kg of polycrystals using a Czochralski method single crystal manufacturing apparatus having a heat shielding member, and a 6-inch diameter silicon single crystal was manufactured therefrom. As the graphite crucible used, a graphite crucible having an upper end of 40 mm tapered as shown in FIG. 4 (E) (Example) and a conventional cylindrical portion shown in FIG. 3 (A). The one having a uniform thickness (comparative example) was used. In addition, 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 under a reduced pressure atmosphere of argon gas, and the conditions other than the graphite crucible were the same in the examples and comparative examples.
The oxygen concentration of the crystal thus obtained was measured by FT-IR for each crystal position, and the result is shown in FIG.
[0036]
As is clear from FIG. 5, when a single crystal is grown using a graphite crucible having an upper end according to the present invention having a tapered shape, heat easily passes from the upper part of the crucible. It turns out that it has fallen by 0.5-1 ppma.
[0037]
In addition, this invention is not limited to the said embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
[0038]
For example, the “Czochralski method” referred to in the present invention includes a so-called MCZ method in which a crystal is grown while applying a magnetic field to the melt in the crucible. The graphite crucible of the present invention and a method using the same Naturally, it can be applied to the MCZ method and can exhibit its effect.
[0039]
In the above embodiment, the diameter of the graphite crucible is described as an example for holding an 18-inch quartz crucible. However, the present invention is not limited to this, and the effect is obtained regardless of the diameter of the crucible. Needless to say, the present invention can also be applied to a graphite crucible holding a quartz crucible of 24 inches or more, or even 30 inches or more.
[0040]
【The invention's effect】
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 an unconventional factor such as the shape of a graphite crucible. Moreover, this is simple and low-cost, and the oxygen concentration can be reliably controlled without being restricted by a heat shielding member used in recent years.
[Brief description of the 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 relationship between a positional relationship between a crucible and a heater and 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) For flat bottom,
(B) Round bottom.
FIGS. 4A to 4F are diagrams showing cross-sectional shapes in a typical example of a graphite crucible according to the present invention.
FIG. 5 is a graph 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 cross-sectional view of an apparatus for producing a silicon single crystal rod by a conventional Czochralski method.
FIG. 7 is a schematic cross-sectional view of a Czochralski apparatus having a heat shielding member, which is a partially covering apparatus.
FIG. 8 is a schematic cross-sectional view of a Czochralski apparatus having a heat shielding member, which has a collar.
[Explanation of symbols]
1 ... Lifting chamber, 2 ... Graphite crucible,
3 ... quartz crucible, 4 ... support shaft,
5 ... thermal insulator, 6 ... graphite heater,
7 ... melt, 8 ... opening,
9 ... Subchamber, 10 ... Seed crystal,
11 ... Pull-up shaft, 12 ... Single crystal rod,
15 ... exhaust port,
19 ... Cylinder, 20 ... Color,
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 (5)

A graphite crucible used for producing a silicon single crystal by the Czochralski method, comprising a thinned portion along a vertical direction in a part of a cylindrical portion of the graphite crucible, and lower than the upper portion of the cylindrical portion A graphite crucible used for producing a silicon single crystal by the Czochralski method, characterized in that is a shape having a smaller outer diameter and a smaller wall thickness.   The graphite crucible used when producing a silicon single crystal by the Czochralski method according to claim 1, wherein an upper end portion of the graphite crucible has a tapered shape whose outer shape is reduced toward an upper portion.   The graphite crucible is divided into a bottom part and a cylindrical part, and the cylindrical part is replaceable. When producing a silicon single crystal by the Czochralski method according to claim 1 or 2, Graphite crucible used.   A method for producing a silicon single crystal by the Czochralski method, wherein the graphite crucible according to any one of claims 1 to 3 is used.   A method for producing a silicon single crystal by the Czochralski method, wherein the graphite crucible according to any one of claims 1 to 3 is used and a heat shielding member of a grown silicon single crystal rod is used. .

Images