JPH09235181A - Pulling of single crystal and single crystal pull apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the concentration of oxygen trapped in a single crystal to be controlled by altering the number of laminating sheets of thermal insulation plate located under a crucible. SOLUTION: A crucible 11 is packed with a stock for the aimed single crystal followed by injecting electric current into a heater 12 to melt the stock. Thereafter, the number of laminating sheets of thermal insulation plate 170 constituting a thermal insulation laminate 17 located under the crucible 11 is altered to lower the temperature of the lower portion of the melt and produce a solid layer 19 of desired thickness and melt layer 13 at the bottom of the crucible 11. Next, a seed crystal 15 attached to the tip of a pull shaft 14 is brought into contact with the surface of the melt 13. Subsequently, the power of the heater 12 is controlled; concurrently, the crucible 11 is raised via a support shaft 18 in a specified speed pattern to relatively move the position of the heater 12 bit by bit under the crucible 11, and a single crystal 16 is pulled while keeping the melt layer 13 at a specified thickness and revolving the pull shaft 14 at a specified rate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a single crystal pulling method and a single crystal pulling apparatus, and more particularly to a single crystal pulling method and a single crystal pulling apparatus for pulling a single crystal such as silicon by using a melt layer method.

[0002]

2. Description of the Related Art There are various methods for growing a single crystal, one of which is the Czochralski method (hereinafter referred to as the CZ method). FIG. 7 is a cross-sectional view schematically showing a single crystal pulling apparatus used for the CZ method, and 11 in the figure shows a crucible.

The crucible 11 comprises a bottomed cylindrical quartz inner layer holding container 11a and a bottomed cylindrical graphite outer layer holding container 11b fitted to the outside of the inner layer holding container 11a. The crucible 11 is supported by a support shaft 18 that rotates at a predetermined speed in the direction of the arrow in the figure. Outside the crucible 11, a resistance heating type heater 12,
A heat-retaining cylinder 21 is concentrically arranged outside the heater 12, and the crucible 11 is filled with a melt 23 of a raw material for crystallization melted by the heater 12. Further, a pulling shaft 14 made of a pulling rod or a wire is hung on the central axis of the crucible 11, and a seed crystal 15 is attached to the tip of the pulling shaft 14 via a seed chuck 14a. There is.

These members are housed in a chamber 20 whose pressure can be controlled. When pulling the single crystal 26, the inside of the chamber 20 is depressurized and then an inert gas is introduced to depressurize it. Use a gas atmosphere. Next, the seed crystal 15 attached to the tip of the pull-up shaft 14 is brought into contact with the surface of the melt 23, and the pull-up shaft 14 is rotated while rotating at the same speed as the support shaft 18 in the same direction or in the opposite direction at a predetermined speed. By pulling up, the melt 23 is solidified and the single crystal 2
Grow 6.

When the semiconductor single crystal 26 is pulled by this pulling method, impurities are often added to the melt 23 before the pulling in order to adjust the electrical resistivity and electric conductivity type of the single crystal 26. . However, in the usual CZ method, it is said that a single crystal having a uniform electric resistivity in the growth axis direction of the single crystal 26 cannot be obtained due to a so-called segregation phenomenon occurring between the single crystal 26 and the melt 23. There was a problem.

The segregation phenomenon means that the concentration of impurities taken into the single crystal 26 at the interface between the single crystal 26 and the melt 23 when the single crystal 26 grows does not match the impurity concentration in the melt 23. That is, the effective distribution coefficient ke
(Impurity concentration in single crystal 26 / impurity concentration in melt 23) is often less than 1. In this case, the single crystal 26 grows and the melt 2 is melted due to the segregation phenomenon.
The impurity concentration in 3 gradually increases. Along with this, the impurity concentration in the single crystal 26 also gradually increases, and the electrical resistivity decreases. Therefore, in the single crystal 26 grown by the CZ method, some of the single crystals which do not satisfy the standard in electrical resistivity are produced, and there is a problem that the yield is reduced.

Therefore, a melt layer method has been developed as a method for pulling a single crystal for preventing a decrease in yield due to the above-mentioned segregation phenomenon and increasing a yield related to electrical resistivity. FIG. 8 is a sectional view schematically showing a single crystal pulling apparatus used in the melt layer method. It should be noted that components having the same functions as those of the single crystal pulling apparatus shown in FIG. 7 are designated by the same reference numerals.

The melting layer method is characterized in that the raw material for crystallization filled in the crucible 11 is melted by the heater 12, and then a part of the molten liquid is solidified, so that the melting layer 13 is on the upper side and the solid is on the lower side. The layer 19 is formed, and with the growth of the single crystal 36,
Melt layer 13 by gradually melting solid layer 19
It is to keep the impurity concentration in the inside almost constant. The structure of the apparatus used for the melted layer method is almost the same as that of the apparatus used for the CZ method, and the pulling method of the single crystal 36 is almost the same as the pulling method by the CZ method except for the above description.

According to the above-mentioned molten layer method, since the molten liquid having a low impurity concentration is constantly supplied from the solid layer 19 to the molten layer 13 during the growth of the single crystal 36, the concentration of impurities in the molten layer 13 is high. Therefore, the concentration of impurities taken in the single crystal 36 can be maintained at a substantially constant value.

By the way, another major factor affecting the characteristics of the single crystals 26, 36 is the oxygen concentration in the single crystals 26, 36. When the crystal raw material is melted in the quartz inner layer holding container 11a, SiO ₂ is eluted in the melt 23 (melted layer 13), and this SiO ₂ is a single crystal 26, 36.
By being taken into the inside, oxygen comes to be contained in the single crystals 26 and 36. The oxygen concentration in the single crystals 26, 36 is determined by the oxygen concentration in the melt 23 (melt layer 13), and the melt 23 from the quartz inner layer holding container 11a is determined.
As the amount of oxygen eluted into the (molten layer 13) increases, the concentration of oxygen contained in the single crystals 26 and 36 increases.

The oxygen concentration in the single crystals 26 and 36 affects the device characteristics, the mechanical strength of the wafer, the gettering ability of metal impurities, and the like. Therefore, the required oxygen concentration varies depending on the type of semiconductor manufacturer's production line and product characteristics, and the required oxygen concentration range is narrow. Therefore, the control of the oxygen concentration in the single crystals 26 and 36 is
It is extremely important for manufacturing the single crystals 26 and 36.

In the above CZ method, the inner layer holding container 11
Since most of the inner surface of a is in contact with the melt 23 and oxygen is supplied from the inner surface, the oxygen concentration in the melt 23 depends on the temperature of the inner layer holding container 11a. On the other hand,
Since the heater 12 is not provided near the bottom of the inner layer holding container 11a, its temperature is likely to change, and therefore the oxygen concentration in the melt 23 changes depending on the temperature of this bottom. Therefore, in the conventional CZ method, the temperature of the bottom portion of the inner layer holding container 11a is changed by changing the heat retention state in the apparatus to control the oxygen concentration in the melt 23.

On the other hand, in the above-mentioned molten layer method, a part of the inner layer holding container 11a is in contact with the solid layer 19 and oxygen does not elute from that part, so that the oxygen concentration in the molten layer 13 is the same. It greatly depends on the area of the inner layer holding container 11a in contact with (the thickness of the molten layer 13). Therefore, in the above-mentioned molten layer method, the inner layer holding container is usually controlled by controlling the thickness of the solid layer 19 formed after melting the crystallization raw material as a method for controlling the oxygen concentration in the single crystals 26 and 36. The thickness of the molten layer 13 in contact with 11a was controlled.

Specifically, based on the temperature of the bottom of the inner layer holding container 11a to be set in the single crystal pulling apparatus shown in FIG. 7, the single crystal pulling apparatus shown in FIG. Based on the thickness of the solid layer 19 (thickness of the molten layer 13), heat transfer simulations are carried out for the heat insulating members 22 arranged in the lower part of the device.
The shape (thickness) and the like were calculated.

[0015]

However, in the heat transfer simulation, the modeled crucible 11 and heater 1 are used.
2, based on the heat insulating cylinder 21, the heat insulating member 22, and the like.
Therefore, it is unavoidable to make a difference between the heat transfer state in the device actually designed and manufactured and the heat transfer state calculated by the heat transfer simulation, and in the actual device, the temperature of the bottom of the inner layer holding container 11a is inevitable. Does not follow the set value,
In addition, there is a problem that the molten layer 13 having the thickness as set is not formed. If the difference from the set value does not fall within the predetermined range, the temperature of the bottom of the inner layer holding container 11a and the molten layer thickness cannot be adjusted by controlling the power of the heater 12 and the like, and the temperature of the heat insulating member 22 is again set. The design and production will be redone. In this case, the manufacturing cost of the heat insulating member 22 becomes high and the manufacturing period thereof becomes long, so that a large loss is incurred.

In order to solve the above problems relating to the melt layer method, Japanese Patent Laid-Open No. 6-85365 discloses an apparatus for forming a solid layer 19 by moving a heat shield plate.
A single crystal pulling apparatus is disclosed in which a heat shield plate is arranged between two heaters so that the heat shield plate can move in and out. According to this single crystal pulling apparatus, after completely melting the crystallization raw material in the crucible, by inserting the heat shield plate between the upper heater and the lower heater, the formation speed of the solid layer is increased. The amount of solid layer formed (thickness of molten layer) can be controlled.

However, in the single crystal pulling apparatus described in the above publication, since the heat shield plate is inserted from the lateral direction of the crucible, the mechanism for inserting the heat shield plate becomes very complicated, and the device There was a problem that was expensive.

The present invention has been made in view of the above problems, and controls the temperature of the bottom of the crucible to control the oxygen concentration of the melt, and finally controls the oxygen concentration of the single crystal to be pulled up. It is an object.

Another object of the present invention is to control the thickness of the molten layer formed in the upper portion of the crucible by the amount of the solid layer formed, and finally to control the oxygen concentration in the pulled single crystal. There is.

[0020]

Means for Solving the Problems and Effects Thereof In order to achieve the above object, a single crystal pulling method according to the present invention (1)
Is characterized in that the concentration of oxygen taken into the crystal is controlled by changing the number of laminated heat insulating plates arranged below the crucible.

The reason why the invention is constructed as described above is that the supply of oxygen to the molten liquid is performed by a quartz crucible.
This is because the bottom temperature of the quartz crucible is largely related to the oxygen supply rate, and in the present invention, the bottom temperature of the quartz crucible can be controlled, so that the concentration of oxygen taken into the crystal can be controlled.

Further, the single crystal pulling method (2) according to the present invention is not limited to the usual CZ method, but a single crystal is pulled by forming a solid layer in the lower part of the crucible and a molten layer in the upper part of the crucible. In the pulling up method, the thickness of the molten layer formed in the upper part of the crucible is changed by changing the number of laminated heat insulating plates arranged below the crucible, and the concentration of oxygen taken into the single crystal by the change of the molten layer thickness. It is characterized by controlling.

The reason why the invention is configured as described above is that the heat quantity radiated from the bottom of the crucible can be changed by changing the number of laminated heat insulating plates, and the change of the radiated heat quantity causes the heat quantity to be changed. It is possible to control the thickness of the solid layer formed when the crystallization raw material is melted, that is, the thickness of the molten layer. By controlling the melt layer thickness by the above method,
It is possible to control the amount of oxygen eluted from the crucible into the molten layer,
As a result, the concentration of oxygen taken into the pulled single crystal can be controlled.

Further, the single crystal pulling apparatus according to the present invention is characterized in that a detachable heat insulating laminate is arranged below the crucible.

According to the above single crystal pulling apparatus, the amount of heat released from the bottom of the crucible can be easily changed by changing the number of laminated heat insulating plates constituting the heat insulating laminate. As a result, the oxygen concentration in the pulled single crystal can be controlled.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION A single crystal pulling method and a single crystal pulling apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view schematically showing a single crystal pulling apparatus according to an embodiment. The single crystal pulling apparatus has the same structure as the single crystal pulling apparatus shown in FIG. 8 except that the heat insulating laminate 17 is arranged below the crucible 11. Therefore, here, description of the configuration of the other portions of the single crystal pulling apparatus according to the embodiment will be omitted, and the heat insulating laminate 17 will be described.

FIG. 2 is a partially enlarged cross-sectional view showing an enlarged part of the heat insulating laminate 17 in the single crystal pulling apparatus shown in FIG. 1. This heat insulating laminate 17 is a heat insulating member 2.
2 (consisting of the heat-resistant covering material 22a and the heat insulating material 22b), and is formed by stacking a plurality of removable heat insulating plates 170. The heat insulating plate 170 includes a heat insulating material 170b and a heat resistant coating material 17 formed on the heat insulating material 170b.
0a has a two-layer structure, the shape is an annular shape, and can be further divided into several fan-shaped divided pieces. Therefore, when attaching / detaching the heat insulating plate 170, the heat insulating plate 170 may be divided into divided pieces and attached / detached. The heat-resistant covering material 170a is formed to protect the heat insulating material 170b and prevent impurities from diffusing into the device from the heat insulating material 170b. As the material, a heat resistant metal such as Mo is not processed. A carbon material such as graphite is preferable because it is difficult and the single crystal 16 may be contaminated by the metal. The heat insulating material 170b may be made of any material as long as it has a low thermal conductivity and can efficiently block heat from the heater 12 and the like, and specific examples thereof include carbon fiber and rock wool.
The carbon fiber is particularly preferable because it has a thermal conductivity of about 0.27 kcal / m · hr · ° C at 1000 ° C and about 0.40 kcal / m · hr · ° C at 1800 ° C.

As shown in FIG. 2, the heat insulating plate 170 may have a layer of the heat resistant coating material 170a formed only on the surface facing the crucible 11, but in another embodiment, as shown in FIG. As shown in FIG. 5, a layer of the heat resistant coating material 270a may be formed on the entire surface of the heat insulating material 270b that constitutes the heat insulating laminate 27. Further, in still another embodiment, as shown in FIG. 4, a heat resistant spacer 171 such as a carbon material is inserted between each heat insulating plate 170 constituting the heat insulating laminate 37, whereby a heat insulating plate is formed. A space may be formed between 170 and the heat insulating plate 170.

The thickness of the heat insulating plates 170 and 270 is not particularly limited, but it is easy to handle and the molten layer 13 to be formed.
Considering that the thickness is finely controlled, the thickness is 8
It is preferably about 50 mm. In this case, the heat resistant coating 1
The thickness of 70a, 270a is preferably thin from the viewpoint of weight reduction, but is preferably 2 to 15 mm from the viewpoint of strength, workability, etc., and the thickness of the heat insulating materials 170b, 270b is 5 from the viewpoint of heat insulation, etc. ~ 35 mm is preferred. The thickness of the spacer 171 is preferably 1 to 10 mm from the viewpoint of heat insulation. Although the number of heat insulating plates 170 and 270 to be laminated is not particularly limited, the thickness of the molten layer 13 and the oxygen concentration are usually controlled by laminating about 3 to 6 sheets. The thickness of each heat insulating plate 170, 270 forming the heat insulating laminate 17, 27,
The types and structures do not necessarily have to be the same.

Next, a single crystal pulling method according to the embodiment will be described. First, the crucible 11 is filled with the crystallization raw material, the heater 12 is energized to heat the crystallization raw material in the crucible 11, and all the crystallization raw materials are once melted into a molten liquid,
Then, the temperature of the lower portion of the melt is lowered to form a solid layer 19 (also referred to as an initial solid layer). In this case, since it is necessary to form the solid layer 19 while adjusting the temperature of the molten liquid so that a solidified film does not form on the surface of the molten liquid, the amount of the solid layer 19, that is, the melting of the solid layer 19, is controlled only by controlling the power of the heater 12. It is difficult to precisely control the layer 13 thickness. Therefore, in the present embodiment, the thickness of the melted layer 13 is controlled by changing the number of laminated heat insulating plates 170 constituting the heat insulating laminate 17 arranged below the crucible 11. In this case, the control of the heater 12 power is set to have the same pattern, an experiment is performed in which the number of laminated heat insulating plates 170 is changed to measure the thickness of the molten layer 13, and the number of laminated heat insulating plates 170 and the thickness of the molten layer 13 are measured. Find out the relationship with. Based on the results of the above experiment, before melting the crystal raw material,
A predetermined number of heat insulating plates 170 are laminated on the heat insulating member 22 so that the target thickness of the molten layer 13 is obtained.

Next, by controlling the power of the heater 12 in a predetermined pattern, the molten layer 13 and the solid layer 19 having a predetermined thickness can be formed in the crucible 11. Next, the lifting shaft 1
The seed crystal 15 attached to the tip of No. 4 is brought into contact with the surface of the molten layer 13, and is pulled while rotating the pulling shaft 14 at a predetermined speed, thereby solidifying the molten layer 13 and growing the single crystal 16. When growing the single crystal 16,
The solid layer 19 is gradually melted to control the thickness of the molten layer 13. For this purpose, the power of the heater 12 is controlled and at the same time,
The crucible 11 is raised in a predetermined speed pattern via the support shaft 18, and the position of the heater 12 is relatively moved to the lower side of the crucible 11 little by little. By the above operation, the single crystal 16 can be grown while keeping the molten layer 13 at a desired thickness, and the single crystal 16 having a predetermined oxygen concentration can be pulled up.

In another embodiment, the heat insulating laminate 17 can be disposed in the single crystal pulling apparatus even when pulling the single crystal by the CZ method.

[0034]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of a single crystal pulling method and a single crystal pulling apparatus according to the present invention will be described below with reference to the drawings. The conditions in the case of the example are described below.

Examples 1 to 6 (1) Characteristics of single crystal to be pulled and conditions of single crystal pulling apparatus (apparatus shown in FIG. 1) Single crystal 16: 8 inch N-type silicon heater 12 Heating method: resistance heating Formula Dimension Inner diameter: 650 mm, Outer diameter: 700 mm, Height: 1
50 mm Dimensions of inner layer holding container 11a (made of quartz) Inner diameter: 560 mm, depth: 350 mm, thickness: 7.0 m
m Dimensions of the heat insulating cylinder 21 Inner diameter: 770 mm, outer diameter: 970 mm Dimensions of the heat insulating member 22 (the heat insulating member 22 of the same shape shown in FIG. 8)
D ₁ = 750 mm (φ), d ₂ = 970 mm (φ), d
₃ = 50 mm, d ₄ = 150 mm Heat insulating plate 170 Heat resistant coating material 170a Material: Graphite (density: 1.85 g / cm ³ ) Thickness: 3 m
m heat insulating material 170b carbon fibers (density 0.15g / cm ^3), Thickness:
7 mm Thickness of heat insulating plate 170: 10 mm (2) Pulling condition of single crystal 16 Charge amount of crystal raw material: 110 kg Charge amount of impurities (P): 2.180 g Atmosphere in chamber 20: Ar atmosphere Ar flow rate: 30 L / min Pressure: 1.33 × 10 ³ Pa Output of heater 12: Relationship between output of heater 12 and elapsed time after starting melting of the raw material for crystallization is shown in FIG. Rotation speed of the pulling shaft 14: 20 rpm Rotation speed of the crucible 11: 8 rpm Single crystal 16 pulling speed: 0.5 mm / min Crystal length of the single crystal to be pulled: 300 mm Number of laminated heat insulating plates 170: 1 to 6 P (phosphorus) effective Partition coefficient (Ke) = 0.35 (3) Measurement of thickness of initial solid layer 19 and measurement of oxygen concentration in single crystal 16 Measurement of thickness of molten layer 13 Attachment of quartz pipe to seed chuck (seed crystal not attached) The quartz pipe is lowered until it hits the solid layer 19, and the thickness of the solid layer 19 and the thickness of the molten layer 13 are calculated from the stroke of the quartz pipe.
The single crystal 16 is cut at a pitch of 50 mm up to 300 mm,
The oxygen concentration of the cleaved portion was measured by the FTIR method (ASTMF-121 (1979)), and the average oxygen concentration was calculated from the arithmetic average value of these.

[Embodiments 7 to 9] The furnace structure of the single crystal pulling apparatus, the charged amount of raw materials for crystal, the pulling conditions, and the crystalline oxygen concentration evaluation method are the same as those in the molten layer method, but the heater is used. The dimensions of 12 were set as follows, and the solid layer 19 was not formed. FIG. 6 shows the relationship between the output of the heater 12 and the elapsed time after the melting of the crystallization raw material is started. Dimensions of heater 12 Inner diameter: 650 mm, Outer diameter: 700 mm, Height: 300 m
m [Comparative Examples 1 to 3] The shape (thickness) of the heat retaining member 22 with respect to the target solid layer thickness (target molten layer thickness) was set by heat transfer simulation (Fig. 8). The heat transfer simulation was performed by using a workstation and a two-dimensional cylindrical coordinate system model that can consider multiple radiation. Conditions for pulling single crystal,
The measuring method and the like are the same as those in the example.

[Comparative Example 4] The furnace structure of the single crystal pulling apparatus, the charged amount of the raw materials for the crystal, the pulling conditions, and the crystalline oxygen concentration evaluation method were the same as those of the comparative example of the molten layer method, but the heater 12 Set the dimensions as follows, and solid layer 1
9 was not formed. FIG. 6 shows the relationship between the output of the heater 12 and the elapsed time after the melting of the crystallization raw material is started.

Dimensions of Heater 12 Inner Diameter: 650 mm, Outer Diameter: 700 mm, Height: 300 m
m Thickness of initial solid layer 19 in the case of Examples 1 to 6 and Comparative Examples 1 to 3 (thickness of molten layer 13), pulled single crystal 1
The average oxygen concentrations (atom / cm ³ ) of 6, 36 (FIG. 8) are shown in Table 1 below.

The average oxygen concentration (atom / cm ³ ) of the pulled single crystals 16 and 36 in Examples 7 to 9 and Comparative Example 4 are also shown in Table 1 below.

[0040]

[Table 1]

As is clear from the results shown in Table 1 above, the thickness of the molten layer 13 and the temperature at the bottom of the crucible 11 can be changed by changing the number of laminated heat insulating plates 170 arranged at the bottom of the chamber 20. As a result, the oxygen concentration in the single crystal 16 (silicon single crystal) can also be controlled.

On the other hand, in the case of Comparative Examples 1 to 3, in order to form the molten layer 13 having a predetermined thickness, the thickness of the heat insulating member 22 below the crucible 11 was determined by heat transfer simulation. Even if it is calculated, the target thickness of the molten layer 13 is not necessarily obtained, and therefore the oxygen concentration in the single crystal 16 does not reach the target value. In particular, when a relatively thick molten layer 13 is formed as in the case of Comparative Example 1, the solid layer 19 may not be formed at all, and the oxygen concentration in the single crystal 16 largely deviates from the target value. It is necessary to redesign the heat insulating member 22.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a single crystal pulling apparatus according to an embodiment of the present invention.

2 is a partially enlarged cross-sectional view showing an enlarged part of a heat insulating laminate in the single crystal pulling apparatus shown in FIG.

FIG. 3 is a cross-sectional view schematically showing a heat insulating laminate according to another embodiment.

FIG. 4 is a cross-sectional view schematically showing a heat insulating laminate according to still another embodiment.

FIG. 5 is a graph showing the relationship between the output of the heater and the elapsed time after starting the melting of the crystallization raw material in Examples 1 to 6 and Comparative Examples 1 to 3.

FIG. 6 is a graph showing the relationship between the output of the heater and the elapsed time after the melting of the crystallization raw material was started in Examples 7 to 9 and Comparative Example 4.

FIG. 7 is a sectional view schematically showing a single crystal pulling apparatus used in a conventional CZ method.

FIG. 8 is a sectional view schematically showing a single crystal pulling apparatus used in a conventional melt layer method.

[Explanation of symbols]

 11 Crucible 13 Molten Layer 16 Single Crystal 17, 27, 37 Heat-insulating Laminate 170, 270 Heat-insulating Plate 170a, 270a Heat-resistant Coating Material 170b, 270b Heat-insulating Material 171 Spacer 19 Solid Layer

Claims (3)

[Claims] 1. A method for pulling a single crystal, characterized in that the concentration of oxygen taken into the single crystal is controlled by changing the number of laminated heat insulating plates arranged below the crucible. 2. The single crystal pulling method according to claim 1, wherein a solid layer is formed in the lower part of the crucible, a molten layer is formed in the upper part of the crucible, and the pulling method is used to change the thickness of the molten layer. Crystal pulling method. 3. A single crystal pulling apparatus, wherein a detachable heat insulating laminate is disposed below the crucible.