JPH10310486A - Production of single crystal and apparatus for pulling up single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a single crystal which produces a single crystal having a uniform oxygen concn. SOLUTION: A pair of first and second electromagnets 8, 9 and an auxiliary third electromagnet 24 are disposed on the outer side of a chamber 2 of the apparatus 20 for pulling up the single crystal. A quartz crucible 3 is risen as the single crystal grows. A magnetic field is impressed thereon by the third electromagnet 24 so as to make up the cusp magnetic field by the second electromagnet 8. As a result, the intensity of the perpendicular magnetic field crossing the base of the quartz crucible 3 is kept approximately constant and even if a solidification rate rises, the convection near the base of the quartz crucible 3 is suppressed, by which the elution of the oxygen is substantially prevented and eventually the single crystal having the oxygen concn. uniform in an axial direction is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for pulling a single crystal from a semiconductor melt contained in a quartz crucible using an MCZ method (magnetic field applying Czochralski method). The present invention relates to a single crystal manufacturing method and a single crystal pulling apparatus capable of obtaining a single crystal.

[0002]

2. Description of the Related Art Conventionally, as a device for growing a semiconductor single crystal such as silicon (Si) or gallium arsenide (GaAs), a single crystal pulling device using an MCZ method (magnetic field applying Czochralski method) is known. I have.

In such a single crystal pulling apparatus, a quartz crucible 3 and a heater 4 are provided inside a chamber 2 as shown in FIG. The quartz crucible 3 is a double crucible, and a lower shaft 6 that can be raised and lowered and rotatable via a susceptor 5.
It is supported by. The heater 4 is for heating the semiconductor melt, and is disposed around the quartz crucible 3.

A wire 7 for holding a seed crystal at a lower end thereof is suspended from the upper portion of the chamber 2 so as to be able to move up and down and rotate freely. Electromagnets 8 and 9 for applying a cusp magnetic field for suppressing convection of the semiconductor melt are provided outside the chamber 2.

In the conventional single crystal manufacturing method, the seed crystal is immersed in the semiconductor melt from above while supplying argon gas from the upper part of the furnace, and the seed crystal is pulled up while rotating the quartz crucible 3 to obtain a single crystal of the semiconductor. A crystal 13 is obtained.

During the pulling of the single crystal, as shown in FIG. 6 (A), the wall surface of the quartz crucible 3 reacts with the semiconductor melt, and oxygen is eluted in the semiconductor melt. When a cusp magnetic field 11 (shown by a dotted line) is applied by 9, a magnetic field component perpendicular to both the bottom surface and the side surface of the quartz crucible 3 is applied, so that convection near the inner wall of the quartz crucible is suppressed. In other words, the dissolved oxygen stays in the vicinity of the wall surface of the quartz crucible 3, so that it is difficult for oxygen to be further dissolved.

On the other hand, since the magnetic field is parallel to the surface of the semiconductor melt and there is no right-angle component, stagnation on the surface is hardly suppressed, oxygen is easily evaporated, and the oxygen concentration decreases. . As described above, by applying the cusp magnetic field 11, the oxygen concentration in the single crystal can be controlled to be uniform to some extent along the axial direction. In addition,
As shown in FIG. 6B, the quartz crucible 3 is raised by the lower shaft 6 so as to compensate for the lowering of the liquid level 12 of the semiconductor melt as the single crystal grows.

[0008]

Incidentally, the oxygen concentration in a silicon single crystal is an important quality factor that must be strictly controlled, and particularly required is that the oxygen concentration distribution is uniform. .

However, in the conventional single crystal pulling apparatus 10,
As shown in FIG. 3, as the quartz crucible 3 rises and the solidification rate g (0 ≦ g ≦ 1) of the single crystal increases, the magnetic field strength across the bottom surface of the quartz crucible 3 gradually decreases. A decrease in the magnetic field strength causes an increase in the amount of oxygen eluted. For example, as shown in FIG. 4, when the solidification rate exceeds 0.4, the oxygen concentration (Oi) increases. In other words, the obtained single crystal has a disadvantage that the oxygen concentration is higher at the bottom side than at the top side, that is, the oxygen concentration in the axial direction is not uniform.

During the pulling of the single crystal, the pulling speed of the pulling mechanism is changed so that the diameter of the single crystal is controlled to be always constant. For example, the lifting speed is 0.5 mm
When the speed is reduced to not more than / min, the free ratio (single crystal ratio) is reduced, and there is also a disadvantage that a single crystal of high quality cannot be obtained.

Accordingly, the present invention has been made in view of the above circumstances, and a method for producing a single crystal capable of obtaining a single crystal having a uniform oxygen concentration in the axial direction and a small decrease in the free ratio is provided. A lifting device is provided.

[0012]

According to the first and third aspects of the present invention, when a single crystal is pulled from a semiconductor melt contained in a crucible, the single crystal is disposed above and below the crucible. A cusp magnetic field is applied to the crucible by the first and second electromagnets, and further, by a third electromagnet provided below the second electromagnet to reinforce the cusp magnetic field by the second magnet. A magnetic field is applied to the crucible.

In the present invention, an exciting current is supplied to the first and second electromagnets, and a cusp magnetic field is applied to the crucible. Further, the crucible is raised so as to compensate for the lowering of the liquid level of the semiconductor melt as the single crystal grows, and the cusp magnetic field generated by the third electromagnet reduces the magnetic field of the second electromagnet. Applied to the crucible to reinforce. Therefore, even if the position of the crucible rises, the strength of the vertical magnetic field passing through the wall of the crucible does not decrease, and convection in the crucible is suppressed, making it difficult for oxygen to elute, and as a result, the oxygen concentration is uniform in the axial direction. A single crystal can be obtained.

According to a second aspect of the present invention, the exciting current for the third electromagnet is increased in proportion to an increase in the solidification rate of the single crystal. That is, by gradually increasing the cusp magnetic field generated by the third electromagnet so as to supplement the magnetic field of the second electromagnet, the intensity of the vertical magnetic field passing through the bottom surface of the crucible is maintained substantially constant, and as a result, A single crystal having a uniform oxygen concentration can be obtained.

[0015]

Next, a single crystal pulling apparatus and a single crystal pulling method according to the present invention will be described in detail with reference to the drawings. In a single crystal pulling apparatus 20 according to the present invention, a quartz crucible 3 and a heater 4 are provided inside a chamber 2.

The quartz crucible 3 is a double crucible having a bowl shape or a bottomed cylindrical shape, and is disposed at a substantially central portion inside the chamber 2.
The susceptor 5 is connected to a vertically movable and rotatable lower shaft 6. A semiconductor melt (a raw material of a semiconductor single crystal melted by heating) 21 is stored in the quartz crucible 3.

The heater 4 serves to heat and melt the semiconductor raw material and keep the semiconductor melt 21 generated thereby, and is installed around the quartz crucible 3. A heat shield 22 is arranged between the heater 4 and the chamber 2.

The upper portion of the chamber 2 is provided with a single crystal pulling mechanism and an inlet 23 for introducing an inert gas such as an argon gas (Ar) into the chamber 2. The wire 7 which is a part of the single crystal pulling mechanism is configured to move up and down while rotating. A seed crystal is attached to the lower end of the wire 7.

In the single crystal pulling apparatus 20, a pair of first and second electromagnets 8 and 9 are provided outside the chamber 2.
An auxiliary third electromagnet 24 is provided. The first and second electromagnets 8 and 9 are ring-shaped, and the quartz crucible 3
Are vertically spaced apart by a distance d so as to be equidistant with respect to the melt surface 12. The direction of the exciting current is different between the first electromagnet 8 and the second electromagnet 9,
The same poles face each other.

The third electromagnet 24 also has a ring shape,
Is installed at a distance d ′ from the electromagnet 9. The exciting current applied to the third electromagnet 24 is set in the same direction as the second electromagnet 9 and is varied by control means (not shown) in response to the rise of the quartz crucible 3.

Single crystal pulling apparatus 2 constructed as described above
A method for producing a single crystal according to Example 0 will be described. In FIG. 1, while supplying argon gas from the upper part of the chamber 2 to the furnace bottom, the semiconductor raw material in the quartz crucible 3 is melted by the heater 4, and the seed crystal held at the lower end of the wire 7 is lowered to form a semiconductor melt. Let it soak. Next, while rotating the quartz crucible 3 by the lower shaft 6, the seed crystal is pulled up while rotating in the opposite direction to grow the single crystal 13.

As shown in FIG. 2A, an exciting current is supplied to the first and second electromagnets 8 and 9, and a cusp magnetic field 11 is applied to the quartz crucible 3. As shown in FIG. 2B, the liquid level 12 of the semiconductor melt is increased with the growth of the single crystal 13.
The quartz crucible 3 is raised by the lower shaft 6 so as to compensate for the lowering of the position, and the liquid level 12 of the semiconductor melt is maintained at a constant position with respect to the cusp magnetic field 11.

The excitation current is supplied to the third electromagnet 24 when the single crystal 13 exceeds, for example, the solidification rate of 0.35. The time when the solidification rate is 0.35 is based on the fact that the oxygen concentration (Oi) increases when the solidification rate exceeds 0.4, as shown in FIG.

Then, the exciting current I2 to the third electromagnet 24 is increased in proportion to the increase in the solidification rate. Specifically, the solidification rate is g, the exciting current value I1 of the second electromagnet 9, the coefficient is k (for example, 2.0 ≦ k ≦ 3.0), and the first electromagnet 8 and the second electromagnet 9 Is the distance d and the distance between the second electromagnet 9 and the third electromagnet 24 is d ′, the exciting current I2 to the third electromagnet 24 is I2 = g × I1 × k × (d ′ / d ) …… (1) Variable so that

That is, as shown in FIG. 3, the magnetic field strength across the bottom surface of the quartz crucible 3 gradually decreases as the solidification rate increases in the related art, but the magnetic field generated by the third electromagnet 24 becomes the second magnetic field. Is gradually increased so as to reinforce the magnetic field of the electromagnet 9, the intensity of the vertical magnetic field passing through the bottom surface of the quartz crucible 3 is maintained substantially constant.

The ratio of the distance d 'from the second electromagnet 9 to the third electromagnet 24 with respect to the distance d between the first and second electromagnets 8 and 9, that is, the third ratio corresponding to d' / d. By controlling the exciting current value I2 of the electromagnet 24, the third
When the installation position of the electromagnet 24 is set arbitrarily, a substantially constant magnetic field strength can be obtained. For example, as shown in FIG.
When d ′ = d, and d ′ = 0.7 × d,
In each case where d ′ = 0.3 × d, a substantially constant magnetic field intensity could be obtained with respect to the increase in the solidification rate g.

As described above, as the solidification rate increases, the third
By applying a magnetic field from the electromagnet 24, the vertical magnetic field strength across the bottom surface of the quartz crucible 3 can be made substantially constant, and even if the solidification rate increases, convection near the bottom surface of the quartz crucible 3 is suppressed to reduce oxygen. Is difficult to elute, and as a result, a single crystal 13 having a uniform oxygen concentration in the axial direction can be obtained.

During the pulling of the single crystal, the pulling speed of the pulling mechanism is changed so that the diameter of the single crystal is controlled to be always constant. Table 1 shows a change in the free ratio (single crystal ratio) with respect to the pulling speed when the standard value is set to 1. When the pulling speed is, for example, 0.65 mm / min or less, the freeing rate is reduced in the conventional single crystal pulling apparatus, but the freeing rate is not reduced in the single crystal pulling apparatus of the present invention. A high quality single crystal can be obtained.

[0029]

[Table 1]

In this embodiment, the case where the present invention is applied to a single crystal production method by the MCZ method using a double crucible has been described. However, the present invention is also applicable to the production of a single crystal by a batch method using a single crucible. It goes without saying that it can be applied.

[0031]

As described above, according to the first and third aspects of the present invention, even if the crucible rises as the single crystal grows, the vertical magnetic field crossing the bottom of the crucible does not decrease.
The convection inside the crucible is suppressed, making it difficult for oxygen to elute, and a single crystal with a uniform oxygen concentration in the axial direction can be obtained. Can be obtained.

According to the second and third aspects of the present invention, the cusp magnetic field generated by the third electromagnet can be gradually increased so as to supplement the magnetic field of the second electromagnet. Is maintained substantially constant, and as a result, a single crystal having a uniform oxygen concentration in the axial direction can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of a single crystal pulling apparatus of the present invention.

FIG. 2 is a diagram showing a cusp magnetic field applied to a crucible according to the present invention.

FIG. 3 is a graph showing a relationship between a solidification rate and a magnetic field.

FIG. 4 is a graph showing a relationship between a solidification rate and an oxygen concentration.

FIG. 5 is a cross-sectional view showing a configuration of a conventional single crystal pulling apparatus.

FIG. 6 is a diagram showing a conventional cusp magnetic field applied to a crucible.

[Explanation of symbols]

 2 Chamber 3 Quartz crucible 4 Heater 6 Lower shaft 8 First electromagnet 9 Second electromagnet 10, 20 Single crystal pulling device 13 Single crystal 24 Third electromagnet

Claims (4)

[Claims] When a single crystal is pulled from a semiconductor melt contained in a crucible, a cusp magnetic field is applied to the crucible by first and second electromagnets disposed above and below the crucible; A method for producing a single crystal, wherein a magnetic field is applied to the crucible by a third electromagnet provided below the second electromagnet in order to reinforce a cusp magnetic field generated by the second magnet. 2. In proportion to an increase in the solidification rate of the single crystal,
2. The method according to claim 1, wherein the exciting current for the third electromagnet is increased. 3. A single crystal pulling apparatus for pulling a single crystal from a semiconductor melt contained in a crucible, wherein the first and second crystals are arranged above and below the crucible and apply a cusp magnetic field to the semiconductor melt. And a third electromagnet provided below the second electromagnet for applying a magnetic field to the crucible to reinforce a cusp magnetic field generated by the second magnet. Single crystal pulling device. 4. In proportion to an increase in the solidification rate of the single crystal,
The single crystal pulling apparatus according to claim 3, further comprising control means for increasing an exciting current to the third electromagnet.