JP2012012257A - Method for growing single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for growing a single crystal which is based on a melted layer method (DLCZ (Double Layer Czochralsi) method) and by which a single crystal is grown at a desired initial solid layer rate by controlling the initial solid layer rate to any value including 0.SOLUTION: There is provided the method for growing a single crystal by using a single crystal growth apparatus including, in a chamber: a crucible into which a material for the single crystal is charged; a heater arranged in the periphery of the crucible; a crucible shaft for rotating the crucible; a heat-insulating material arranged at least on the side wall of the chamber; and a cooling body which is located on the outer side of the crucible shaft and on the inner side of the heater in the radial direction of the chamber and which supplies a cooling medium for cooling the crucible. In the method, the initial solid layer rate of the material for the single crystal is controlled by controlling the supply and stop of the cooling medium to the cooling body and the up and down movement, in the height direction of the chamber, of the cooling medium.

Description

  The present invention relates to a single crystal growth method, and more particularly to a single crystal growth method that enables control of an initial solid layer ratio during single crystal growth.

In general, the Czochralski method (CZ method) is widely used as a method for producing a single crystal such as silicon.
In this CZ method, for example, a crystal material is charged in a quartz crucible, melted, the seed crystal is immersed in the melt, and the seed crystal is pulled up, so that the melt is added to the lower end of the seed crystal. This is a method of solidifying and sequentially growing single crystals downward.

When a silicon single crystal is grown by the CZ method, an impurity element is usually added to the melt before pulling in order to adjust the electrical resistivity and conductivity type of the single crystal.
However, since the added impurity segregates in the crystal growth direction of the single crystal, there is a problem that the electrical resistivity becomes nonuniform in the crystal growth direction.
This segregation is caused by an increase in the impurity concentration in the melt as the single crystal grows.

As a method for suppressing such segregation, a molten layer method (DLCZ method) is known (see, for example, Patent Document 1).
In the molten layer method, the crystal material in the crucible is melted so that the lower solid layer and the upper molten layer coexist, and the seed crystal is maintained in a state where the impurity concentration in the molten layer (melt) is kept constant. This is a method of growing a single crystal by immersing the substrate.
In the molten layer method, the solid layer is melted as it is pulled, so that the impurity concentration in the molten layer is kept constant, so that segregation of the single crystal can be prevented and the electrical resistivity is uniform in the crystal growth direction. In other words, a single crystal having a high resistance yield can be grown.

Here, the single crystal pulled by the CZ method and the DLCZ method is inevitably supplied with oxygen dissolved from a quartz crucible in direct contact with the molten layer. Part of the oxygen dissolved from the crucible is transported to the crystal growth interface by convection of the melt and taken into the single crystal.
In the DLCZ method, the lower temperature of the molten layer is lower than the melt of the CZ method due to the influence of the solid layer, so the thermal convection of the molten layer is suppressed. A single crystal of a concentration is obtained.

  Therefore, for example, in the case of producing a single crystal having a uniform electrical resistivity and in the case of producing a single crystal having a high oxygen concentration in order to produce a wafer having a high substrate gettering capability, the former is a DLCZ method, The latter has been manufactured according to another method called the CZ method.

Japanese Patent Laid-Open No. 10-324592

  By the way, in recent years, there has been an increasing demand for reduction in the cost and cycle time of single crystal production, and in particular, there has been a demand for proposals of specific methods, especially when sharing production lines is effective.

  In order to meet the above requirements, it is important to control the initial solid layer ratio during single crystal growth to an arbitrary value including zero. Accordingly, an object of the present invention is to provide a single crystal growth method capable of performing single crystal growth under a desired initial solid layer ratio.

The inventor has intensively studied to solve the above problems.
As a result, based on the growth equipment used for the DLCZ method, we also obtained the knowledge that by using this also for the CZ method, the production line can be shared and the cost and cycle time of single crystal production can be reduced.
The inventor has investigated a method for combining the DLCZ method and the CZ method. In order to achieve the initial solid layer ratio of 0, which is a condition for performing the CZ method, the cooling for cooling the crucible is performed. In addition to adjusting the position of the body, it has been found important to stop the cooling capacity of the cooling body, and the present invention has been completed.

This invention is based on said knowledge, The summary structure is as follows.
(1) A crucible for charging a single crystal material inside the chamber, a heater disposed around the crucible, a crucible shaft for rotating the crucible, and heat insulation disposed at least on the side wall of the chamber. A single crystal growth apparatus using a single crystal growth apparatus comprising: a material; and a cooling body that is positioned outside the crucible shaft and inside the heater in a radial direction of the chamber and capable of supplying a coolant for cooling the crucible. In performing, the initial solid layer ratio of the single crystal material is controlled by controlling both the supply and stop of the refrigerant to the cooling body and the vertical movement of the cooling body in the height direction of the chamber. A method for growing a single crystal.

  (2) The single crystal growth method according to (1), wherein the initial solid layer ratio is 0% or more.

  (3) The single crystal growth method according to (1) or (2), wherein the cooling body is formed by coating a material made of copper or stainless steel with graphite carbon.

According to the present invention, by controlling the supply and stop of the refrigerant to the cooling body and the vertical movement of the cooling body in the height direction, the single crystal growth according to the production method according to each of the DLCZ method and the CZ method. It is possible to provide a method for growing a single crystal that can be carried out using the same apparatus.
Therefore, since various types of single crystal products can be made separately with the same apparatus, single crystal growth with low cost and short cycle time is possible.
Furthermore, according to the present invention, a variety of single crystals having a high resistance yield can be manufactured by arbitrarily controlling the initial solid layer ratio in the DLCZ method.

(a) It is sectional drawing of the single crystal growth apparatus at the time of performing DLCZ method in the single crystal growth method of this invention. (b) It is sectional drawing of the single crystal growth apparatus at the time of performing CZ method in the single crystal growth method of this invention. It is a figure which shows the relationship between a cooling body height and an initial stage solid layer rate in the method of this invention.

Hereinafter, the present invention will be described in detail with reference to the drawings.
1 (a) and 1 (b) are cross-sectional views showing a single crystal growth apparatus used in the single crystal growth method of the present invention.
As shown in FIGS. 1 (a) and 1 (b), the single crystal growth apparatus used in the single crystal growth method of the present invention has a crucible 2 charged with a material for single crystal placed inside a chamber 1, and a crucible 2 A heater 3 for heating the crucible 2 is installed on the outside in the radial direction.
A crucible shaft 4 for rotating the crucible 2 at a predetermined speed is provided at the bottom 1a of the chamber 1, and a heat insulating material 5 is disposed at least on the side wall of the chamber 1, in the illustrated example, the side wall and the bottom.

  1A and 1B, in the illustrated example, the chamber 1 is a cylindrical vacuum container, and the crucible 2 is a bottomed cylindrical container. The heater 3 has a cylindrical shape, the crucible shaft 4 has a cylindrical shape, and the heat insulating material 5 has a substantially bottomed cylindrical shape.

Here, in the apparatus used for the single crystal growth method of the present invention, in the radial direction of the chamber 1, the cooling body 6 that is located outside the crucible shaft 4 and inside the heater 3 and cools the crucible 2, and cooling A cooling body moving device 7 for moving the body 6 in the height direction of the chamber 1 and a refrigerant control means 8 for controlling supply and stop of the refrigerant to the cooling body 6 are provided.
In the illustrated example, the cooling body 6 is formed by coating stainless steel with graphite carbon.
The method of the present invention using the above apparatus will be described below.

In growing a single crystal using the above apparatus, it is important to control both of the following two elements in order to control the initial solid layer ratio.
The first element is to supply or stop a coolant of 27 ° C. or more and less than 100 ° C. such as water, for example, inside the cooling body 6 to control the cooling capacity of the cooling body itself that cools the crucible.
As shown in FIGS. 1 (a) and 1 (b), the second element moves the cooling body 6 up and down in the height direction of the chamber 1 in a state where the refrigerant is being supplied to the cooling body 6 or stopped. By controlling, the positional relationship with the crucible is controlled, and the cooling ability for the crucible is controlled based on this positional relationship.
Here, “cooling” means that the cooling body not only shields the heat from the heater but also rapidly cools the crucible by heat exchange with the cooling body.

Fig. 2 shows the use of a general-purpose single crystal growth apparatus for growing a single crystal with a diameter of 200 mm, water at 27 ° C as the refrigerant, and the heater temperature at a maximum of 1600 ° C. It is a figure which shows the change of the initial stage solid layer rate at the time of controlling both supply and a stop, and the height of a cooling body.
As shown in FIG. 2, in the state in which the refrigerant is supplied, the initial solid layer ratio can be arbitrarily controlled in the range of 1.5% to 20% depending on the height of the cooling body 6.
That is, the closer the cooling body 6 is to the upper side of the chamber 1, the closer the cooling body 6 is to the crucible 2 and the more heat exchange is performed between them. When the cooling body 6 is moved away from the crucible 2, the initial solid layer ratio is lowered.
Similarly, as shown in FIG. 2, in a state where the refrigerant is stopped, the initial solid layer ratio is reduced from 0% by moving the cooling body that is relatively cooler than the crucible even when the refrigerant is not supplied up and down. It can be arbitrarily controlled within the range of 8%.
Therefore, according to the method of the present invention, by controlling both the supply and stop of the coolant to the cooling body and the vertical movement of the cooling body in the height direction, the initial solid layer ratio can be arbitrarily set as shown in FIG. In the example shown in (2), it can be controlled in the range of 0% to 20%.

As described above, according to the present invention, as shown in FIGS. 1 (b) and 2, the supply of the refrigerant to the cooling body is stopped, and the cooling body is moved below a certain level of the chamber, FIG. In the example shown in FIG. 1, since the initial solid layer ratio can be set to 0% by being positioned at the lowest limit position, single crystal growth by the CZ method is possible.
Here, the `` initial solid layer ratio '' is the ratio of the mass (g) of the solid layer to the total mass (g) of the single crystal growth material consisting of the molten layer (melt) 9a and the solid layer 9b. They were calculated using FEMAG, a comprehensive heat transfer calculation tool.
Here, the “minimum position” refers to a position spaced apart from the heat insulating material upper portion 5a by a certain distance so that the heat insulating material upper portion 5a and the cooling body 6 do not contact each other.
Similarly, the maximum upper limit position refers to a position at a certain distance downward from the crucible bottom 2a so that the crucible bottom 2a and the cooling body 6 do not contact each other.
The fixed interval can be set to, for example, 40 mm for both the upper limit and the lower limit.

In addition, according to the present invention, in the DLCZ method, it is possible to control an arbitrary initial solid layer ratio and to improve the resistance yield of single crystals over a wide variety.
According to the present invention, since the production lines by the DLCZ method and the CZ method can be shared, the cost can be reduced.
Furthermore, the cooling body of the present invention not only simply shields the heat from the heater, but also cools the crucible with a coolant such as water, so a solid layer can be formed in a short time, reducing heater power and shortening the cycle. Single crystal growth in time can be realized.
Further, according to this method, since there is no need to divide the heater, there is no fear of quartz deformation due to thermal stress caused by turning on only one of the divided heaters.

By the way, in the present invention, the cooling body is preferably formed by coating a material made of copper or stainless steel with graphite carbon.
This is because in the present invention, it is important that the cooling body not only shields heat from the heater but also cools the crucible with a coolant such as water. It is because it is preferable to use. Further, the coating with graphite carbon is for preventing metal contamination.

Example 1
First, in order to confirm that the initial solid layer ratio during single crystal growth can be arbitrarily controlled by the method according to the present invention, the following simulation was performed.
The initial solid layer ratio is the H (mm) distance between the upper part of the cooling body and the upper part 5a of the heat insulating material 5 below the cooling body in the 200 mm single crystal growth hot zone having the configuration shown in FIG. ), And the initial solid layer ratio when the distance was changed was calculated using FEMAG, which is a comprehensive heat transfer calculation tool.
In this simulation, the cooling body is made of stainless steel covered with graphite carbon and the length in the chamber height direction is 96 mm. In addition, water at 27 ° C. was used as the refrigerant, and the water was positioned in a range of 40 mm (lowest limit position) to 160 mm (maximum upper limit position) from the heat insulating material upper part 5a. The maximum temperature of the heater was 1697 ° C.
The evaluation results are summarized in Table 1 below.

From Table 1, it can be seen that the initial solid layer ratio of the single crystal material can be arbitrarily controlled to 0% or more by the method of the present invention.
Therefore, according to the method of the present invention, it is possible to grow a variety of single crystals with a high resistance yield by the DLCZ method.
It can also be seen that the initial solid layer ratio can be reduced to 0% by stopping the supply of the refrigerant to the cooling body and keeping the cooling body at a certain distance from the crucible.
Therefore, it can be seen that the method of the present invention can be used for single crystal growth by the CZ method in the same apparatus as that for performing the DLCZ method.

  According to the present invention, it is possible to provide a single crystal growth method capable of performing single crystal growth under a desired initial solid layer ratio by controlling the initial solid layer ratio to an arbitrary value including 0. .

1 chamber
1a Chamber bottom
2 crucible
3 Heater
4 Crucible shaft
5 Insulation
5a Insulation top
6 Cooling body
7 Cooling body moving device
8 Refrigerant control means
9a Molten layer (melt)
9b solid layer
H Cooling body height (mm)

Claims (3)

  A crucible for charging a single crystal material inside the chamber, a heater disposed around the crucible, a crucible shaft for rotating the crucible, and a heat insulating material disposed at least on the side wall of the chamber; In performing the growth of a single crystal using a single crystal growth apparatus, which is provided outside the crucible shaft in the radial direction of the chamber and inside the heater, and provided with a coolant supply capable of cooling the crucible. The initial solid layer ratio of the single crystal material is controlled by controlling both the supply and stop of the refrigerant to the cooling body and the vertical movement of the cooling body in the height direction of the chamber. Single crystal growth method.   2. The single crystal growth method according to claim 1, wherein the initial solid layer ratio is 0% or more.   3. The single crystal growth method according to claim 1, wherein the cooling body is formed by coating a material made of copper or stainless steel with graphite carbon.

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