JP3991813B2 - Silicon single crystal growth method - Google Patents

Description

【００４０】
また、絞り工程で磁場を印加しても、その強度が０．１テスラを超える例えば０．３テスラの場合は、増径工程への移行時に磁場印加を停止したにもかわらず、結晶径が１００ｍｍに達するまでの間に有転位化が生じた。なお、ルツボ回転数は図２のパターンとした。
【００４１】
また、絞り工程で印加する磁場強度が０．１テスラ以下の例えば０．０５テスラであり、且つ増径工程への移行時に磁場印加を停止した場合であっても、絞り工程でのルツボ回転数が１ｒｐｍを超える例えば３ｒｐｍの場合は絞り工程における径変動が大きくなり、大重量結晶を保持することが困難となる。
【００４２】
また、絞り工程で印加する磁場強度が０．１テスラ以下の例えば０．０５テスラで、且つ絞り工程でのルツボ回転数が１．０ｒｐｍの場合であっても、増径工程で引き続き磁場印加を行った場合は増径工程の初期において有転位化が頻発した。なお、ルツボ回転数は図２のパターンとした。
【００４３】
【発明の効果】
以上に説明したとおり、本発明のシリコン単結晶成長方法は、転位を除去するための絞り工程でルツボ回転数を１ｒｐｍ以下に制限すると共に、水平方向に０．１テスラ以下の微弱磁場を印加し、且つ、絞り工程から増径工程に移行する段階でその磁場印加を停止することにより、絞り工程での径変動を安定的に抑制でき、増径工程での有転位化及び制御不能も回避できる。
【図面の簡単な説明】
【図１】本発明のシリコン単結晶成長方法の実施に適したＣＺ引上げ炉の縦断面図である。
【図２】ルツボ回転数の変更パターンを例示するグラフである。
【図３】ＣＺ法によるシリコン単結晶成長方法の説明図である。
【符号の説明】
１ ルツボ
２ ヒータ
５ 引上げ軸
６ 支持軸
７ チャンバ
１２ 単結晶
１３ 溶融液
１５ 種結晶
３０ 超電導磁石[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a silicon single crystal growth method using a CZ method (Czochralski method), and more particularly to a silicon single crystal growth method in which a magnetic field is applied in order to prevent fluctuations in crystal diameter in a drawing process.
[0002]
[Prior art]
There are various methods for producing a silicon single crystal used for a semiconductor substrate. A widely used industrial method is the CZ method which is a rotary pulling method. In the manufacture of a silicon single crystal by the CZ method, as shown in FIG. 3, a crucible 1 disposed in a chamber is used. The crucible 1 has a double structure in which a quartz crucible 1a that contains a silicon melt 13 is held from the outside by a graphite crucible 1b, and is fixed on a support shaft 6 that can be rotated and moved up and down.
[0003]
In operation, first, the silicon material for crystallization filled in the crucible 1 is melted in a predetermined atmosphere by a cylindrical resistance heating heater 2 disposed substantially concentrically outside the crucible 1, and a molten solution 13 is obtained. Form. Next, the pulling shaft 5 disposed on the central axis of the crucible 1 and having the seed crystal 15 attached to the lower end thereof is lowered to immerse the seed crystal 15 in the melt 13. Then, while rotating the crucible 1 and the pulling shaft 5 in a predetermined direction at a predetermined speed, the pulling shaft 5 is pulled upward to grow a silicon single crystal 12 below the seed crystal 15.
[0004]
In such a CZ method, in order to remove dislocations originally contained in the seed crystal 15 and dislocations introduced by heat shock at the time of landing, an operation of narrowing the seed crystal 15 to about 3 mm in diameter after landing is performed. Is called. This is a drawing process. Thereafter, the crystal diameter is gradually increased and finally converged to the product diameter. As a result, a shoulder portion having a gradually increasing diameter is formed under the narrow throttle portion, and a straight body portion having a constant diameter is further formed thereunder. The step of forming the shoulder portion by gradually increasing the crystal diameter is the diameter increasing step, and the step of forming the straight body portion having the constant diameter is the constant diameter step.
[0005]
A quartz crucible used for the production of a silicon single crystal by the CZ method is brought into contact with a silicon melt, whereby the surface thereof is dissolved in the melt and oxygen is released into the melt. A part of the oxygen dissolved in the molten liquid is taken into the silicon single crystal and affects the quality of the silicon single crystal in various ways. Therefore, in the CZ method, controlling the amount of oxygen taken into the silicon single crystal is an important technical issue.
[0006]
As one of the methods for controlling the oxygen concentration, there is a magnetic field application CZ method called MCZ (Magnetic-field-applied CZ) method. This method suppresses and controls convection in a direction perpendicular to the magnetic field lines by applying a magnetic field to the melt in the quartz crucible. There are various methods for applying a magnetic field, and in particular, the practical application of the HMCZ (Horizontal MCZ) method in which a magnetic field is applied in the horizontal direction is in progress. The magnetic field strength used here is usually 0.3 to 0.4 Tesla.
[0007]
By the way, as a recent trend, the diameter and weight of a grown single crystal are rapidly increasing. At present, crystals having a diameter of 300 mm and a weight exceeding 200 kg are also produced. And the crystal weight tends to increase further. However, it is difficult to hold such a heavy crystal with the diameter of the squeezed portion (about 3 mm) in the squeezing process of the normal CZ method. In addition, when the liquid temperature varies due to the convection of the melt, the diameter of the constricted part also varies, and as a result, when the diameter is partially reduced, it becomes more difficult to hold the heavy crystal.
[0008]
As means for solving such a problem of diameter variation of the throttle part, a magnetic field in the throttle process, which is presented by JP-A-10-7487, JP-A-9-165298, JP-A-11-209197, etc. There is application.
[0009]
Specifically, in Japanese Patent Application Laid-Open No. 10-7487, a magnetic field of 0.2 Tesla or less is applied in the MCZ method in the drawing process, and in the diameter increasing process following the drawing process, 0.2 is directed toward the constant diameter process. It is explained that the magnetic field is strengthened up to Tesla.
[0010]
In Japanese Patent Application Laid-Open No. 9-165298, a magnetic field of 0.15 Tesla or more is applied in the normal CZ method in the drawing process, and in the diameter increasing process following the drawing process, the magnetic field is weakened to a non-magnetic field toward the constant diameter process. Has been explained.
[0011]
In JP-A 11-209197, JP-has been disclosed that a non-magnetic field whether to weak magnetic field applied from the constant-radius step at higher drawing process and increasing径工in MCZ method, specific examples in the drawing step 0.1 It is shown that a horizontal magnetic field of Tesla is applied, the magnetic field is increased from 0.1 Tesla to 0.4 Tesla in the diameter increasing process, and a magnetic field of 0.4 Tesla is applied in the constant diameter process.
[0012]
[Problems to be solved by the invention]
As can be seen, magnetic field application in the narrowing step is roughly divided into two methods, a method for increasing the magnetic field and a method for weakening the magnetic field by manipulating the magnetic field in the diameter increasing step following the throttling step. In any method, by applying a magnetic field in the squeezing step, the convection of the melt is suppressed and the diameter variation of the squeezed portion is suppressed.
[0013]
However, if the magnetic field is strengthened in the diameter increasing process subsequent to the diameter reducing process or the magnetic field strength in the diameter reducing process is maintained as it is, there is a problem that dislocations frequently occur in the diameter increasing process. The reason is considered as follows.
[0014]
When a magnetic field is applied to the silicon melt, as described in "Hiroshi Nogami: Proceedings of the 11th Computational Mechanics Lecture Meeting of the Japan Society of Mechanical Engineers (1998) P414", the direction of magnetic field application passes through the center of the crucible. A roll-like flow is generated which is symmetric with respect to parallel planes. In a state where the temperature of the melt is relatively high as in the initial stage of the diameter increasing process, this flow is also strong, and foreign matters present in the melt are transported to the growth interface, and the formation of dislocations is promoted.
[0015]
On the other hand, when the magnetic field application is stopped in the diameter increasing process as described in JP-A-9-165298, the above-described roll-shaped convection disappears, and foreign matter transport to the growth interface by this convection is caused. Dislocation is prevented. However, on the other hand, it has been found that there is a risk that the temperature difference due to the convection change accompanying demagnetization increases, and the crystal diameter rapidly increases, resulting in uncontrollability.
[0016]
Also, in the squeezing process in which a magnetic field is applied, depending on the number of rotations of the crucible, the temperature fluctuation of the molten liquid increases due to the interaction between the molten liquid restrained by the magnetic field and the crucible rotation, and the diameter fluctuation of the squeezed portion is sufficient. The problem which is not restrained occurs. This problem becomes prominent when a large-diameter crystal having a diameter of 200 mm or more is pulled using a large-diameter crucible having a diameter of 700 mm or more.
[0017]
An object of the present invention is to provide a silicon single crystal growth method that can stably suppress diameter fluctuations in the drawing step and can avoid dislocations and uncontrollability in the diameter increasing step.
[0018]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present inventors have investigated and examined in detail the influence of the magnetic field application on the formation of the throttle portion, and further the influence of various factors other than the magnetic field. As a result, the following facts were found.
[0019]
First, in order to suppress the diameter variation of the throttle portion, it is effective to apply a magnetic field to the melt, particularly to apply a magnetic field in the horizontal direction. Secondly, in order to suppress dislocation formation in the diameter increasing process, which becomes a problem when a magnetic field is applied in the drawing process, it is essential to stop the magnetic field application in the diameter increasing process. Thirdly, for destabilizing the diameter control accompanying demagnetization in the diameter increasing process, it is effective to make the magnetic field applied in the squeezing process as weak as possible so as to reduce the physical change when demagnetizing. . Fourthly, when the diameter variation of the throttle portion is suppressed by applying a magnetic field, the rotational speed of the crucible is also an important factor for suppressing the diameter fluctuation, and it is necessary to keep the rotational speed as small as possible.
[0020]
The silicon single crystal growth method of the present invention has been completed on the basis of such knowledge. The silicon raw material for crystal is filled in the crucible and melted, and the seed crystal immersed in the melt is pulled up while rotating. Thus, in the silicon single crystal growth method based on the CZ method in which a silicon single crystal is grown below the seed crystal, the crucible rotation speed is set to 1 rpm or less in the drawing process for removing dislocations, and the horizontal direction is 0.1 Tesla. The following magnetic field is applied, and the application of the magnetic field is stopped at the stage of shifting from the drawing step to the diameter increasing step.
[0021]
In order to suppress the diameter variation of the throttle portion, it is effective to suppress the convection of the melt by applying a horizontal magnetic field. However, when a magnetic field exceeding 0.1 Tesla is used, when the application of the magnetic field is stopped, the temperature difference associated with the convection change increases, and the crystal diameter increases rapidly, resulting in uncontrollability. Accordingly, the magnetic field strength used in the drawing step is 0.1 Tesla or less, and 0.08 Tesla or less is particularly preferable. Note that a weak magnetic field of about 0.03 Tesla is sufficiently effective in order to suppress the convection of the melt, which is the main cause of the diameter fluctuation of the throttle portion. From this viewpoint, the lower limit of the magnetic field strength is preferably 0.01 Tesla or more, and particularly preferably 0.03 Tesla or more.
[0022]
When applying a magnetic field in the drawing process to pulling up a large single crystal with a large diameter using a large-diameter crucible, if the crucible rotation speed in the drawing process is large, the interaction between the melt and the crucible rotation that is restrained by the magnetic field As a result, the temperature variation of the melt increases, and even though a magnetic field is applied, the reverse effect is rather increased and the diameter variation of the constricted portion increases, making it difficult to hold a large crystal. For this reason, under the application of a magnetic field, the crucible rotation speed in the drawing step is 1 rpm or less. The lower limit of the crucible rotation speed is not particularly limited, and it is only necessary to stop the crucible rotation. In view of device accuracy, 0.2 rpm or more is preferable from the viewpoint of maintaining stable rotation of the crucible.
[0023]
After stopping the magnetic field, if the diameter increasing process is performed with such a low crucible rotation, natural convection from the outer periphery to the center occurs in the crucible, and dislocations are generated in order to transport foreign matter to the growth interface. It tends to occur. For this problem, it is effective to increase the number of crucible rotations and to prevent foreign substances from being transported by centrifugal force or forced convection. Specifically, it is preferable to change the crucible rotation speed to 3 rpm or more before the crystal diameter reaches 100 mm in the diameter increasing step.
[0024]
As described above, a stable squeezing process and a diameter increasing process are possible. Further, when the magnetic field is applied again during the transition from the diameter increasing process to the constant diameter process, and the crucible rotation speed is changed to a predetermined rotation speed, a large weight is obtained. The HMCZ method is also possible. The magnetic field strength in the constant diameter process is preferably 0.1 to 0.4 Tesla, and the crucible rotation speed is preferably 0.2 to 10 rpm.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a CZ pulling furnace suitable for carrying out the silicon single crystal growth method of the present invention, and FIG. 2 is a graph illustrating a change pattern of the crucible rotation speed.
[0026]
First, the structure of the CZ pulling furnace used in the silicon single crystal growth method of this embodiment will be described.
[0027]
The CZ pulling furnace includes a cylindrical main chamber 7a and a small-diameter pull chamber 7b mounted on the main chamber 7a as a chamber 7 serving as a furnace body.
[0028]
A crucible 1 is disposed in the center of the main chamber 7a. The crucible 1 has a double structure in which a quartz crucible 1a containing a silicon melt 13 is held from the outside by a graphite crucible 1b, and is fixed on a support shaft 6 that can be rotated and moved up and down.
[0029]
On the outside of the crucible 1, a cylindrical resistance heating heater 2 is arranged substantially concentrically. On the further outer side of the heater 2, a cylindrical heat insulating cylinder 8a is disposed along the inner surface of the main chamber 7a. A heat insulating plate 8b is disposed on the bottom of the main chamber 7a.
[0030]
On the central axis of the crucible 1, a wire that is a pulling shaft 5 is concentrically suspended through a pull chamber 7b. The pulling shaft 5 holds a seed crystal 15 at the lower end, and is driven to rotate and to be moved up and down by a winding mechanism provided at the uppermost part of the pull chamber 7b.
[0031]
On the other hand, a pair of superconducting magnets 30a and 30b are arranged opposite to each other to apply a horizontal magnetic field to the melt 13 in the crucible 1 outside the main chamber 7a.
[0032]
Next, a method for growing the silicon single crystal 12 having a diameter of 300 mm using such a pulling furnace will be described.
[0033]
A crucible 1 filled with 300 kg of silicon raw material for crystal and added with phosphorus as an impurity is set in the chamber 7. The diameter of the quartz crucible 1a is 750 mm. The inside of the chamber 7 is decompressed to 25 Torr, and 100 L / min Ar gas is introduced as an inert gas. The crystal silicon material and phosphorus in the crucible 1 are heated and melted by the heater 2 to form a melt 13.
[0034]
After forming the melt 13, a horizontal magnetic field of 0.05 Tesla is applied to the melt 13 by the superconducting magnets 30 a and 30 b, and after the melt temperature is stabilized, the seed crystal 15 is immersed in the melt 13. While the crucible 1 and the pulling shaft 5 were rotated in a predetermined direction at a predetermined speed, the pulling shaft 5 was pulled upward to reduce the crystal diameter from 15 mm to 5 mm. In this drawing step, the rotational speed of the crucible 1 was 1.0 rpm, and the rotational speed of the pulling shaft 5 was 10 rpm. The magnetic field strength was maintained at 0.05 Tesla.
[0035]
Immediately after the squeezing process, the application of the magnetic field was stopped and the process increased to a diameter increasing process. In the diameter increasing step, the crucible rotation speed was increased as the crystal diameter increased so that the crucible rotation speed became 5 rpm when the crystal diameter reached 100 mm. Thereafter, while maintaining the crucible rotation speed at 5 rpm, the crystal diameter was increased to 310 mm to complete the increased diameter portion (shoulder portion) 12a.
[0036]
Then, when the crystal diameter reached 310 mm, the process shifted to a constant diameter process, and a straight body portion 12b having a length of 1400 mm was grown. The total weight of the grown single crystal 12 is 270 kg. By reducing the applied magnetic field strength in the squeezing process to 0.1 Tesla or less, and reducing the crucible rotation speed to 1 rpm or less and demagnetizing in the diameter increasing process, the diameter fluctuation of the squeezing part is slightly suppressed, which is the target value. While 5 mm was maintained over almost the entire length, stable diameter control was continued even in the diameter increasing process, and as a result, stable pulling was performed. The crystal quality was also good.
[0037]
As another example, the process up to the diameter increasing process is the same as the previous example. When the crystal diameter reaches 300 mm, a horizontal magnetic field of 0.03 Tesla is applied, and the crucible rotation speed is changed from 5 rpm to 1 rpm. changed. Then, a straight body portion of 1400 mm was grown. There was no problem in terms of DF and quality as well as stable pulling.
[0038]
For comparison, when a tensile test was performed on a constricted portion formed by a normal CZ method (no magnetic field), as shown in Table 1, fracture occurred at a load of less than 300 mm, and a single crystal of 300 kg or more was pulled. It turned out that it could not be raised.
[0039]
[Table 1]

[0040]
In addition, even when a magnetic field is applied in the drawing process, if the strength exceeds 0.1 Tesla, for example 0.3 Tesla, the crystal diameter is reduced even though the application of the magnetic field is stopped when the process proceeds to the diameter increasing process. Dislocations occurred until reaching 100 mm. The crucible rotation speed was the pattern shown in FIG.
[0041]
Even if the magnetic field strength applied in the drawing process is 0.1 Tesla or less, for example, 0.05 Tesla, and the application of the magnetic field is stopped when shifting to the diameter increasing process, the number of crucible rotations in the drawing process In the case of 3 rpm exceeding 1 rpm, for example, the diameter variation in the drawing process becomes large, and it becomes difficult to hold the heavy crystal.
[0042]
Further, even when the magnetic field strength applied in the drawing process is 0.1 Tesla or less, for example 0.05 Tesla, and the crucible rotation speed in the drawing process is 1.0 rpm, the magnetic field application is continued in the diameter increasing process. When performed, dislocations frequently occurred in the initial stage of the diameter increasing process. The crucible rotation speed was the pattern shown in FIG.
[0043]
【The invention's effect】
As described above, the silicon single crystal growth method of the present invention limits the crucible rotation speed to 1 rpm or less in the drawing process for removing dislocations and applies a weak magnetic field of 0.1 Tesla or less in the horizontal direction. In addition, by stopping the application of the magnetic field at the stage of shifting from the drawing process to the diameter increasing process, it is possible to stably suppress diameter fluctuations in the drawing process, and to avoid dislocations and uncontrollability in the diameter increasing process. .
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a CZ pulling furnace suitable for carrying out a silicon single crystal growth method of the present invention.
FIG. 2 is a graph illustrating a crucible rotation speed change pattern.
FIG. 3 is an explanatory diagram of a silicon single crystal growth method by a CZ method.
[Explanation of symbols]
1 crucible 2 heater 5 pulling shaft 6 support shaft 7 chamber 12 single crystal 13 melt 15 seed crystal 30 superconducting magnet

Claims (4)

  A silicon single crystal growth method by a CZ method in which a silicon raw material for crystal is filled in a crucible and melted, and a seed crystal immersed in the melt is pulled up while rotating to grow a silicon single crystal below the seed crystal. In the drawing process for removing dislocation, the crucible rotation speed is set to 1 rpm or less, a magnetic field of 0.1 Tesla or less is applied in the horizontal direction, and the magnetic field application is performed at the stage of shifting from the drawing process to the diameter increasing process. A silicon single crystal growth method characterized by stopping.   2. The silicon single crystal growth method according to claim 1, wherein the crucible rotation speed is changed to 3 rpm or more when the crystal diameter is 100 mm or less in the diameter increasing step.   3. The silicon single crystal growth method according to claim 1, wherein a magnetic field is applied again at the time of transition from the diameter increasing step to the constant diameter step, and the crucible rotation speed is changed to a predetermined rotation speed.   4. The method for growing a silicon single crystal according to claim 1, wherein a large-diameter crystal having a diameter of 200 mm or more is pulled using a large-diameter crucible having a diameter of 700 mm or more.

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