JP2940461B2 - Single crystal growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for growing a single crystal such as a silicon single crystal used as a semiconductor material.

[0002]

2. Description of the Related Art In general, the Czochralski method (CZ method) is widely used as a method for producing a silicon single crystal.
In the CZ method, a melt of a crystal raw material is filled in a bottomed cylindrical quartz crucible, a seed crystal fixed to a pulling shaft is immersed in the melt, and the melt is drawn to the lower end of the seed crystal. Is solidified to grow a single crystal. A heater is arranged concentrically outside the crucible so as to melt the crystal raw material in the crucible.

In order to pull up a silicon single crystal without dislocations, when pulling up a seed crystal, a necking step is performed in which the lower end is gradually narrowed down to form a tapered portion and a narrowed portion having a predetermined diameter is grown. . This is a step necessary for removing high-density dislocations caused by thermal shock, which are introduced into the solidified and crystallized portion when the seed crystal is pulled up, and is called a so-called dash method. In order to eliminate dislocations in the silicon single crystal, the constricted part should be 30 mm with a diameter of 3 mm or less.
It is necessary to grow it to about the same length (Maruzen's "Silicon Crystal and Doping", p.14).

Further, when forming the tapered portion and the constricted portion, it is said that it is necessary to quickly solidify the molten portion at the growth interface, and to form the constricted portion thin and long (Kawamura, Matsui). Author, "Dislocation-free silicon single crystal and its properties," Applied Physics, Vol. 88, No. 4, 1969. As a result, dislocations in the crystal escape from the crystal surface. In addition, by growing the crystal at a high speed, excessive vacancies are taken into the crystal, and the dislocations easily overlap with the dislocation portions and disappear.
Furthermore, by growing thinly, the amount of heat removed from the crystal surface increases, the growth interface becomes convex toward the melt, and dislocations are easily removed from the surface. This is because dislocations are considered to be formed perpendicular to the growth interface.If the shear force is assumed to be zero at the growth interface on the melt side, the dislocations are aligned perpendicular to the growth interface. Gradually escapes from the crystal surface (Takao Abe, “Silicon”, page 26, published by Baifukan). Here, it is assumed that the diameter of the narrowed portion is 3 mm.

[0005]

As described above, a dislocation-free silicon single crystal can be grown by forming a narrowed portion, but the crystal weight increases with the recent demand for a large-diameter single crystal. Then, the required strength for holding the heavy crystal on the pulling shaft increases. Various reports have been made on the strength of dislocation-free silicon single crystals.
It considered kgf / mm ^2. According to this, the maximum weight of 140 kg can be held in the narrowed portion having a diameter of 3 mm, and the limit weight is further reduced in consideration of the safety factor against shaking.

[0006] Recently, silicon single crystals required in recent years mainly have a diameter of 8 inches, and the weight exceeds 100 kg. In addition, a 12 inch diameter has been developed, weighing 300 k
g. In order to hold the crystal, the diameter of the constricted portion needs to be at least 4.5 mm, preferably 6 mm or more.

However, as described above, when the diameter of the constricted portion becomes large, dislocation is likely to occur. Further, when the diameter of the constricted portion becomes large, the temperature gradient in the radial direction of the crystal increases, and thermal stress is generated, which causes a problem that dislocations multiply.

A method for solving this problem is disclosed in Japanese Unexamined Patent Publication No.
This is proposed in Japanese Patent Publication No. 300388. This method defines the diameter ratio of the seed crystal and the narrowed portion, the ratio of the diameter of the seed crystal and the length of the tapered portion, and the length of the narrowed portion, whereby the narrowed diameter can hold a high-weight single crystal. A dislocation-free single crystal is grown while forming a portion. However, even with this method, dislocations in the crystal are difficult to escape, which is insufficient for obtaining a crystal without dislocations, and the productivity is inferior because the tapered portion and the constricted portion are extremely long at 250 mm to 750 mm. there were.

The present invention has been made in view of the above circumstances, and a single crystal is firmly held by forming a narrowing angle of a tapered portion smaller than an angle formed between a growth orientation and a crystal dislocation plane. Another object is to provide a method capable of growing a single crystal without dislocations.

[0010]

According to a first aspect of the present invention, there is provided a method for growing a single crystal, wherein a crucible is filled with a raw material for crystal and melted, and a seed crystal is brought into contact with a molten liquid and pulled up. Forming a tapered portion by gradually reducing the diameter of the crystal to be grown, pulling the crystal to have a predetermined diameter, and then gradually increasing the diameter of the growth end, wherein the tapered portion is formed. The tapered portion is formed so that the constriction angle formed between the radial direction and the generatrix direction is smaller than the angle formed by the growth orientation of the single crystal with the crystal dislocation plane.

Since the aperture angle is smaller than the angle between the single crystal growth orientation and the crystal dislocation plane, the dislocations can easily escape from the crystal surface. Further, since the narrowing angle is smaller than the angle at which the growth direction of the single crystal forms with the crystal dislocation plane, the tapered portion has a steep gradient, and the crystal surface area grown in a unit time is large. As a result, the amount of heat removed from the crystal is large, the growth interface becomes convex toward the melt, and dislocations are more likely to escape.

In the method for growing a single crystal according to the second invention, a crucible is filled with a raw material for crystal and melted, a seed crystal is brought into contact with a molten liquid and pulled up, and the diameter of a crystal growing on the seed crystal is increased. In the method of growing a single crystal in which the size is gradually reduced to form a tapered portion, which is then pulled up with a predetermined diameter, and then the diameter at the growth end is gradually increased, prior to the step of forming the tapered portion, A step of increasing the diameter of a crystal grown on the seed crystal.

Since the tapered portion is formed after the diameter of the seed crystal is enlarged, it is possible to form the tapered portion in a wide range of the constriction angle. Further, since the diameter dimension is increased, the crystal surface area that grows in a unit time is large, and dislocations are easily removed. Further, since the seed crystal to be prepared has a small size, the cost of the seed crystal is low.

According to a third aspect of the present invention, there is provided a single crystal growing method comprising:
The invention is characterized in that the seed crystal is pulled up so that a constriction angle formed between a radial direction and a generatrix direction of the tapered portion is smaller than an angle formed by a growth orientation of the single crystal with a crystal dislocation plane. .

When the aperture angle is such that the growth orientation of the single crystal cannot be smaller than the angle formed by the crystal dislocation plane, the diameter of the seed crystal is enlarged before forming the tapered portion. Can be formed.

A method for growing a single crystal according to a fourth invention is characterized in that, in the first, second or third invention, the tapered portion is formed at a pulling rate of 3 mm / min to 6 mm / min.

Since the growth rate of the crystal is high, vacancies are easily taken into the crystal, and the excess vacancies on the periphery of the crystal overlap with the dislocations, so that the dislocations tend to disappear.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. Embodiment 1 FIG. FIG. 1 is a schematic cross-sectional view showing the structure of a single crystal growth apparatus for implementing the method of the present invention. In the figure, reference numeral 1 denotes a chamber. The chamber 1 is a substantially cylindrical vacuum vessel, and a crucible 2 is provided at a substantially central position of the chamber 1. The crucible 2 comprises a bottomed cylindrical quartz inner layer holding container 2a and a bottomed cylindrical outer layer holding container 2b fitted to the outside of the inner layer holding container 2a. A shaft 3 for rotating and raising and lowering the crucible 2 is provided on the lower surface of the outer layer holding container 2b.
Is mounted on the outer periphery of the side wall of the outer layer holding container 2b,
For example, a resistance heating type side heater 4 is provided so as to be able to move up and down. The side heater 4 has a cylindrical shape concentric with the crucible 2, and a heat retaining cylinder 5 is arranged on the outer periphery and below the side heater 4. By adjusting the relative vertical position of the crucible 2 and the side heater 4, the molten layer 11 and the solid layer 12 can be formed in the crucible 2 by relatively adjusting the respective thicknesses.

On the other hand, a small, substantially cylindrical pull chamber 6 is formed continuously above the crucible 2 above the chamber 1, and a pulling shaft 7 penetrates through the pull chamber 6 so as to be rotatable and vertically movable. At the lower end of the pulling shaft 7, a seed crystal 8a is mounted. Then, after the lower end of the seed crystal 8a is immersed in the molten liquid 10, the single crystal 9
To grow.

A procedure for growing a silicon single crystal using the apparatus configured as described above will be described. First, the crucible 2 is filled with polycrystalline silicon as a raw material for crystallization, and the raw material for crystallization is melted by the side heater 4. By controlling the position of the side heater 4 and the crucible 2 and the power of the side heater 4, the temperature of the melt 10 is kept constant. Next, the crucible 2 is rotated and the lower end of the seed crystal 8a is immersed in the melt 10 to perform a necking step.

FIG. 2 is a sectional view showing a crystal shape in a necking step according to the method of the present invention. While rotating the pulling shaft 7, the seed crystal 8a is pulled up so that the diameter of the crystal growing on the lower end of the seed crystal 8a is gradually reduced, and the tapered portion 8b
To form At this time, the stop angle θ formed between the radial direction and the generatrix direction of the tapered portion 8b is tan θ = 2L / (D−d)
Is established. D is the diameter D of the seed crystal 8a, d
Is the lower diameter of the tapered portion 8b, and L is the length of the tapered portion 8b. These are set so that the constriction angle θ is smaller than the angle θ ₀ between the single crystal growth orientation and the crystal dislocation plane.
For example, when producing a single crystal having a <100> growth orientation, θ ₀ = 54.74 °, and the diameter D of the seed crystal 8a, the lower diameter d of the tapered portion 8b, and the length L satisfy θ <54.74 °. Formed. When a single crystal having a <111> growth orientation is produced, θ ₀ = 70.53 °, and the seed crystal 8a
D, the lower diameter d and the length L of the tapered portion 8b are θ <7.
Formed to satisfy 0.53 °.

After the tapered portion 8b is formed, a crystal having a constant diameter d is grown to form a narrowed portion 8c. The aperture 8c is grown to a predetermined length, and the silicon single crystal 9 is grown by gradually increasing the crystal diameter. Since the reduction angle θ is smaller than the angle θ _{0 at} which the growth orientation of the single crystal forms with the crystal dislocation plane, the dislocations introduced in the necking step are likely to escape from the crystal surface, and the diameter of the reduction portion 8c is larger than 3 mm. However, a single crystal can be grown without dislocations. The tapered portion 8b and the narrowed portion 8c are pulled up at a high speed, so that vacancies are easily taken into the crystal and dislocations can be prevented. The pulling speed is preferably 3 to 6 mm / min, and if it is higher than 6 mm / min, the melt is hard to be solidified and dislocations are hardly removed from the crystal surface.

Embodiment 2 FIG. In the second embodiment, the seed crystal 8a
A method of forming a tapered portion having a predetermined aperture angle when it is impossible to satisfy θ <θ ₀ because the diameter of the taper is small. FIG. 3 is a cross-sectional view showing a crystal shape in the necking step in this case. The seed crystal 8a is immersed in the melt 10 using an apparatus similar to that shown in FIG. Pulling shaft 7
The seed crystal 8a is pulled up so that the diameter of the crystal growing on the lower end of the seed crystal 8a gradually increases while rotating the seed crystal 8a.
₁ (D <D ₁ ). Next, the tapered portion 8b is formed by pulling up so that the diameter of the crystal is gradually reduced. At this time, squeeze angle theta ₁ formed by the upper radial and generatrix direction of the tapered portion 8b is to establish a _{tan θ 1 = 2L / (D} 1 -d) relationship. The upper diameter D ₁ , the lower diameter d, and the length L of the tapered portion 8b are set so that the aperture angle θ ₁ is smaller than the angle θ _{0 at} which the growth orientation of the single crystal forms the crystal dislocation plane.

After the tapered portion 8b is formed, a crystal having a constant diameter d is grown to form a narrowed portion 8c. The aperture 8c is grown to a predetermined length, and the silicon single crystal 9 is grown by gradually increasing the crystal diameter. The structure of the device and other manufacturing procedures are the same as those in the first embodiment, and the same portions are denoted by the same reference numerals and description thereof will be omitted.

In the second embodiment, even if the diameter of the seed crystal 8a is too small to form the aperture angle θ of the first embodiment, the diameter of the lower end of the seed crystal 8a is enlarged. can be grown tapered portion 8b has an aperture angle theta _1. Thus, as in the first embodiment, even when the diameter of the narrowed portion 8c is larger than 3 mm, a single crystal can be grown without dislocation. Further, since the size of the seed crystal is small, the manufacturing cost can be reduced. Even when the seed crystal 8a has a size sufficient to form the aperture angle θ of the first embodiment, the diameter of the lower end is enlarged to grow the tapered portion 8b, so that the aperture 8c has a desired diameter. And a single crystal can be grown without dislocations.

[0026]

[Embodiment] In the above procedure, the condition shown in Table 1 was set to <10.
0> A tapered portion 8b and a narrowed portion 8c having a growth orientation were formed, and a silicon single crystal 9 was grown. As shown in Table 2, seed crystal 8a
The diameter D, the length L of the tapered portion 8b, the diameter d of the constricted portion, and the constriction angles θ and θ ₁ were varied to perform the necking step. The presence or absence of dislocation was confirmed by cutting out the tapered portion 8b and the constricted portion 8c along the <110> growth direction and using an X-ray topograph. In Examples 1, 3 and 4 so as to satisfy the theta <theta _0, Examples 2, 5 forms a diaphragm angle so as to satisfy θ ₁ <θ _0.

[0027]

[Table 1]

[0028]

[Table 2]

As is clear from Table 2, Examples 1, 3,
4 satisfies θ <54.74 °, and Examples 2 and 5 satisfy θ ₁
Since it satisfies <54.74 °, it was dislocation-free.
In the first conventional example, θ <54.74 ° is not satisfied. However, since the diameter d of the narrowed portion 8c is 3 mm and is sufficiently thin, no dislocation is formed. However, in the conventional examples 2 and 3, the throttle section 8c
Has a large diameter d of 5 mm or 6 mm and does not satisfy θ <54.74 °, indicating that dislocation has occurred.

[0030]

As described above, in the present invention, since the taper portion is formed such that the narrowing angle of the taper portion is smaller than the angle between the single crystal growth direction and the crystal dislocation plane, the dislocation is formed on the surface. Even if the diameter of the narrowed portion is made larger than 3 mm in order to hold a heavy single crystal, dislocation does not occur. In addition, even when the diameter of the seed crystal is small, the tapered portion is formed after growing the seed crystal so as to enlarge the diameter of the seed crystal, so that the tapered portion can be formed at a predetermined constriction angle, and the dislocation-free crystal can be grown. It is possible to make it. Further, by increasing the pulling speed of the tapered portion, holes are easily taken in and the dislocation disappears, and the present invention has excellent effects.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a structure of a single crystal growing apparatus for implementing a method of the present invention.

FIG. 2 is a cross-sectional view showing a crystal shape in a necking step of the first embodiment.

FIG. 3 is a cross-sectional view showing a crystal shape in a necking step according to a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Chamber 2 Crucible 4 Side heater 7 Pulling shaft 8a Seed crystal 8b Taper part 8c Restriction part 9 Single crystal 10 Melt

Claims (4)

(57) [Claims] Claims 1. A crucible is charged with a crystal raw material and melted.
The seed crystal is brought into contact with the melt and pulled up, and the diameter of the crystal growing on the seed crystal is gradually reduced to form a tapered portion. In the method for growing a single crystal, the size of which is gradually increased, such that the constriction angle formed between the radial direction of the tapered portion and the generatrix direction is smaller than the angle formed by the growth orientation of the single crystal with the crystal dislocation plane. A method for growing a single crystal, comprising forming the tapered portion. 2. A crucible is charged with a raw material for crystallization and melted.
The seed crystal is brought into contact with the melt and pulled up, and the diameter of the crystal growing on the seed crystal is gradually reduced to form a tapered portion. A method for growing a single crystal, wherein the size is gradually increased, comprising, prior to the step of forming the tapered portion, a step of increasing the diameter of a crystal grown on the seed crystal. Growth method. 3. The taper portion is formed such that a constriction angle formed between a radial direction and a generatrix direction of the taper portion is smaller than an angle between a growth orientation of the single crystal and a crystal dislocation plane. 3. The method for growing a single crystal according to 2. 4. The method for growing a single crystal according to claim 1, wherein said tapered portion is formed at a pulling rate of 3 mm / min to 6 mm / min.