JPH08208369A - Method for growing single crystal - Google Patents

Abstract

PURPOSE: To control the concn. of oxygen in a single crystal without causing the dislocation lowering of the single crystal by accelerating the rotation of a crucible up to a required velocity while pulling up the single crystal from a crucible. CONSTITUTION: Polycrystalline silicone is charged into the crucible 1 and a phosphorus-silicon alloy is added as an impurity thereto. The pressure in a chamber is reduced and gaseous argon is supplied thereto. All of both raw materials are melted by adjusting the power of an upper heater 3a and a lower heater 3b and thereafter a solid layer S is gradually grown up to a prescribed amt. from the bottom of the crucible 1 by adjusting the power of the upper heater 3a and the lower heater 3b. Dipping of a seed crystal 5 is executed by setting the rotating velocity of a pulling-up shaft 4/the rotating speed of the crucible 1 at 10rpm/0rpm after the solid layer S and the molten layer L attains a stationary state. The seed crystal 5 is then pulled up at a prescribed pulling-up speed, by which the neck and shoulder of the seed crystal 6 are grown at the bottom end of the seed crystal 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a single crystal such as silicon by using a rotary pulling method.

[0002]

2. Description of the Related Art There are various methods for producing a silicon single crystal used for a semiconductor substrate, and one of them is the Czochralski method (hereinafter referred to as CZ method) which is a rotary pulling method. FIG. 3 is a schematic view showing an embodiment of the CZ method,
In the figure, 1 is a crucible arranged in the chamber. The crucible 1 is provided with an inner container 1a made of quartz and having a cylindrical shape with a bottom, and an outer container 1b made of graphite adapted to hold the outside of the inner container 1a. It is fixed to the upper end. A resistance heating type heater 3 is arranged substantially concentrically outside the crucible 1, and the crucible 1 is filled with a melt 9 of a raw material for crystal melted by the heater 3.
On the central axis of the crucible 1, there is provided a pulling shaft 4 such as a wire that rotates at a predetermined speed with the same axis as the supporting shaft 2,
A seed crystal 5 is suspended on the pulling shaft 4.

In such a crystal growth apparatus, a raw material for crystal is charged into the crucible 1 and melted by a heater 3 arranged around the crucible 1 under reduced pressure in an inert gas atmosphere. After that, the seed crystal 5 suspended on the pulling shaft 4 is immersed in the melt 9 and the crucible 1 and the pulling shaft 4 are rotated, and the pulling shaft 4 is pulled up to the lower end of the seed crystal 5. The crystal 6 is grown.

When the grown single crystal is used as a semiconductor substrate or the like, an impurity element is added to the melt in the crucible before pulling in order to adjust the electric resistivity and electric conductivity type of the single crystal. However, as described above, in the method of pulling a single crystal from a melt obtained by melting all the crystal raw materials in the crucible, the impurity concentration C _S in the crystal at the interface between the melt and the crystal and the impurity concentration C in the melt are _The effective segregation coefficient K _e (K _e = C _S / C _L ) represented by the ratio with _L is smaller than 1, and the impurities in the melt and the impurities in the crystal are concentrated as the crystal grows. There has been a problem that the impurities segregate in the pulling direction of the single crystal, and it is difficult to obtain a single crystal having a uniform impurity concentration distribution over the entire length thereof.

A melt layer method is known as a method of pulling a single crystal by suppressing such segregation of impurities. FIG.
FIG. 3 is a schematic view showing an embodiment of a conventional melt layer method described in Japanese Patent Laid-Open No. 6-80495, in which parts corresponding to those in FIG. 3 are given the same numbers. After the crystallization raw material and the impurities are put into the crucible 1 and all of them are melted by the heater 3, for example, the output of the heater 3 is reduced to reduce the solid layer S from the bottom of the crucible 1.
Grow gradually.

When the growth of the solid layer S and the formation of the molten layer L by the melting of the solid layer S reach a steady state, the seed crystal 5 attached to the lower end of the pulling shaft 4 is immersed in the molten layer L, After acclimatizing the interface of the seed crystal and the interface of the molten layer L so as to be integrated, the power of the heater 3 is adjusted so that the interface between the seed crystal 5 and the molten layer L has a temperature suitable for pulling up ( Dip process). Then, in order to eliminate dislocations, the seed crystal 5 is pulled up so that the pulling speed is approximately 3 mm / min, and the diameter of the neck 6a is narrowed to approximately 3 mm.
Are formed (neck process). When the neck 6a is formed,
The pulling speed is reduced to about 1 mm / min or less to form a shoulder 6b having a gradually increasing diameter (shoulder step), and then a body 6c having a constant diameter is pulled up to a predetermined length (body step).

During the body process, the crucible 1 is raised so that the position of the surface of the molten layer L becomes constant. Therefore, the solid layer S formed on the bottom of the crucible 1 is eluted, the increase of the impurity concentration in the molten layer L due to segregation is prevented, and the single crystal 6 having a uniform impurity concentration in the pulling direction is obtained.

On the other hand, in the portion of the inner container 1a made of quartz which is in contact with the molten layer L, the inner container 1a reacts with the molten layer L as shown in the following formula (1) and gradually melts to form a molten layer. SiO is mixed in L. SiO ₂ + Si → 2SiO (1)

Most of the SiO mixed in the melted layer L evaporates as SiO from the surface of the melted layer L, but a part thereof mixes in the single crystal 6 from the solid-liquid interface to become impurity oxygen. Oxygen in the single crystal 6 takes in crystal defects on the wafer surface and impurities such as heavy metals in the heat treatment in the device process, forms a defect-free and clean wafer surface layer, and has the effect of increasing the strength of the wafer. There is. On the other hand, there is a problem that excessive oxygen causes crystal defects due to oxygen precipitation in the heat treatment in the device process.

In order to solve this problem, Japanese Patent Laid-Open No. 3248/1993
As described in Japanese Patent No. 0, a method of rotating the crucible 1 in a direction opposite to the rotation direction of the pulling shaft 4 is implemented. In this method, as the rotation speed of the crucible 1 is increased, the concentration of oxygen in the single crystal 6 can be reduced, and the crucible 21 can be rotated at a rotation speed determined to reach a predetermined oxygen concentration.
The oxygen concentration in the single crystal 6 was controlled by rotating the.

[0011]

However, in the conventional method as described above, since the crucible is rotated from the initial stage of single crystal growth forming the neck and the shoulder, the temperature fluctuation of the molten layer due to the rotation of the crucible is caused. Due to the influence, it becomes difficult to form a neck with a diameter smaller than a predetermined diameter, and there is a problem that the grown crystal is likely to have dislocations. The present invention has been made in view of the above circumstances, and an object thereof is to bring a single crystal into a dislocation state by accelerating the rotation of the crucible to a required speed while pulling the single crystal. The purpose of the present invention is to provide a single crystal growth method capable of controlling the concentration of oxygen in a single crystal.

[0012]

A method for growing a single crystal according to a first aspect of the present invention is to melt a raw material for a crystal in a crucible to form a molten layer, and immerse the seed crystal in the molten layer to form the seed crystal. In the method of pulling while rotating and growing a single crystal on the lower side, the rotation of the crucible is accelerated to a required speed while pulling the single crystal.

In the method for growing a single crystal according to the second aspect of the invention, the crystal raw material in the crucible is melted to form a molten layer, the seed crystal is immersed in the molten layer, and the seed crystal is pulled up while rotating.
A method of growing a single crystal neck, a shoulder and a body thereunder, characterized in that the rotation of the crucible is accelerated to a required speed during the transition from the growth of the single crystal shoulder to the growth of the body. .

The single crystal growth method according to the third invention is characterized in that, in the first or second invention, the rotation of the crucible is accelerated within about 5 minutes.

A method for growing a single crystal according to a fourth aspect of the present invention is the method for growing a single crystal according to the first or second aspect, wherein the rotation of the crucible is accelerated.
The heating amount of the crucible is increased, and after the rotation of the crucible is accelerated to a required speed, the heating amount of the crucible is decreased.

[0016]

In the single crystal growth method according to the first and second aspects of the present invention, at the stage of growth of the neck and the shoulder where the dislocation is likely to occur in the grown crystal due to the influence of the temperature change of the molten layer due to the rotation of the crucible, the crucible is grown. Is not rotated, or is rotated at a speed at which dislocation does not occur, for example, at a rotation speed of 1 rpm or less. After that, the rotation of the crucible is accelerated to the rotation speed determined to bring the oxygen concentration to a predetermined value. In particular, if acceleration is performed during the transition from the growth of a single-crystal shoulder to the growth of a body, there is no effect on the formation of the neck and shoulder due to the acceleration, there is no dislocation over the entire length, and the oxygen concentration from the beginning of the body is high. , A single crystal having a favorable control can be obtained.

In the single crystal growth method of the third aspect of the invention, the rotation of the crucible is accelerated within about 5 minutes. If the rotation of the crucible is gradually accelerated, the flow and temperature of the molten layer are not stabilized for a long time, and thus pulling control related to crystal diameter control and the like becomes difficult. On the other hand, in the present invention, when accelerating the rotation of the crucible from, for example, 1 rpm or less to 5 to 20 rpm at which the oxygen concentration in the single crystal can be controlled to a required value, the acceleration operation is performed within about 5 minutes. The flow and temperature of the molten layer are controlled in a short time, and pulling control is not hindered.

In the single crystal growth method of the fourth invention, the heating amount of the crucible is increased before the rotation of the crucible is accelerated. Therefore, the rotation speed of the crucible is increased and the temperature of the molten layer is lowered. Is prevented. Then, after accelerating the rotation of the crucible to the required speed, the heating amount of the crucible is reduced,
The temperature of the molten layer is made substantially the same before and after the rotation speed of the crucible is increased.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a schematic sectional view of a crystal growth apparatus for carrying out the single crystal growth method according to the present invention,
In the figure, reference numeral 7 indicates a hollow cylindrical chamber, and 1 indicates a crucible disposed in the chamber 7 at substantially the center thereof. The chamber 7 is composed of a main chamber 7a having a cylindrical shape, a cylindrical pull chamber 7b connected and fixed to the upper end of the main chamber 7a, and the like. Further, the crucible 1 is configured by concentrically arranging a quartz inner container 1a and a graphite outer container 1b, each of which has a bottomed cylindrical shape, and is fixed to an upper end portion of a support shaft 2 which can be rotated and moved up and down. It is set up.

A heater 3 composed of an upper heater 3a and a lower heater 3b having a short heat generation length is concentrically arranged outside the crucible 1, and a heat insulating cylinder 8 is arranged outside the heater 3. Has been done. Inside the crucible 1, a molten layer L of the crystallization raw material is formed on the upper side thereof, and a solid layer S of the crystallization raw material is formed on the lower side thereof. The relative amounts of the molten layer L and the solid layer S in the crucible 1 are adjusted by adjusting the relative vertical positions of the crucible 1 and the heater 3 and adjusting the power of the upper heater 3a and the lower heater 3b. It has become. On a central axis of the crucible 1, a pulling shaft 4 capable of rotating and ascending / descending with the same axis as the support shaft 2 is suspended through a pull chamber 7a, and a seed crystal 5 is attached to a lower end of the pulling shaft 4. .

Next, a method for growing a single crystal by using such a crystal growth apparatus will be described. For example, as shown in Table 1, the inner container has a diameter of 400 mm and a height of 350 m.
65 kg of polycrystalline silicon is put into the crucible 1 of m, and 0.6 g of phosphorus-silicon alloy is added as an impurity.
The pressure inside the chamber 7 is reduced to 10 Torr, and argon gas is supplied at a flow rate of 40 liters / minute.

[0022]

[Table 1]

Then, the powers of the upper heater 3a and the lower heater 3b are adjusted to melt both raw materials, and then the powers of the upper heater 3a and the lower heater 3b are adjusted to make a solid layer from the bottom of the crucible 1. S is gradually grown to a predetermined amount. After the solid layer S and the molten layer L reached a steady state, the seed crystal 5 was dipped with the rotation speed of the pulling shaft 4 / the rotation speed of the crucible 1 = 10 rpm / 0 rpm. Then, the neck of the single crystal 6 and the shoulder are grown at the lower end of the seed crystal 5 by pulling the seed crystal 5 at a predetermined pulling rate.

When the power of the upper heater 3a is increased by 10 kW when the diameter of the single crystal 6 becomes 140 mm, the diameter of the single crystal 6 stops at about 154 mm after about 7 minutes. Therefore, the crucible 1 starts to rotate in the direction opposite to the pulling shaft 4, and
The rotation speed is changed from 0 rpm to 5 to 20 rp within about 5 minutes.
Accelerate to about m. Then, the power of the upper heater 3a is reduced by, for example, 8 kW, and the body of the single crystal 6 is pulled up.
As a result, the temperature rise of the molten layer L due to the increase in the power of the upper heater 3a and the temperature decrease of the molten layer L due to the increase in the rotation speed of the crucible 1 are offset, and the temperature of the molten layer L is the rotation of the crucible 1 after acceleration. The temperature is suitable at the speed. The timing and the degree of increase or decrease in the power of the upper heater 3a are determined in advance by experiments according to the raw material capacity in the crucible 1, the amount of change in the rotation speed, and the like.

Next, the result of growing a single crystal by the method of the present invention will be described. FIG. 2 is a graph showing changes in the diameter of a single crystal and changes in the power of the upper heater when the method of the present invention is carried out, where the horizontal axis represents the crystal length of the body and the vertical axis represents the diameter of the body and the power of the heater. Are shown respectively. In the figure, the solid line represents the change in the diameter of the single crystal, and the broken line represents the change in the power of the upper heater. Figure 2
As shown in the figure, the power of the upper heater is increased during the transition from the shoulder process to the body process, and the rotation speed of the crucible is set to 0 rpm.
To 15 rpm for 30 seconds and then the power of the upper heater was reduced.

As a result, as is apparent from FIG. 2, there was no problem in shifting from the shoulder process to the body process. And
After the transition, all the bodies were dislocation-free, their diameters were almost constant over the entire length and were stable, and it can be seen that the aforementioned changes in acceleration and heater power have little effect on the pulling up of the body. The oxygen concentration in the single crystal was the required value from the beginning of the body.

Although the molten layer method has been described in the present embodiment, it is needless to say that the present invention is not limited to this and can be applied to other rotary pulling methods such as the CZ method.

[0028]

As described in detail above, in the single crystal growth method according to the first aspect of the present invention, a single crystal having a required oxygen concentration can be obtained without causing dislocations along the entire length thereof.

In the single crystal growth method according to the second aspect of the invention, a single crystal having a required oxygen concentration can be obtained from the top of the body, and the product yield is high.

In the single crystal growth method according to the third aspect of the invention, the molten layer is stabilized in a short time, and a single crystal having a stable diameter can be obtained.

In the single crystal growth method according to the fourth aspect of the present invention, the temperature of the molten layer can be stabilized before and after the acceleration of rotation, and a high quality product can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a crystal growth apparatus for carrying out a single crystal growth method according to the present invention.

FIG. 2 is a graph showing changes in the body diameter and changes in the power of the upper heater when the method of the present invention is performed.

FIG. 3 is a schematic view showing an embodiment of the CZ method.

FIG. 4 is a schematic view showing an embodiment of a melt layer method.

[Explanation of symbols]

 1 Crucible 2 Support Shaft 3 Heater 4 Pulling Shaft 5 Seed Crystal 6 Single Crystal 6a Neck 6b Shoulder 6c Body 7 Chamber L Molten Layer S Solid Layer

Front Page Continuation (72) Inventor Shuichi Inami 4-5-3 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd. (72) Masahiko Okui 4-53-3 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd.

Claims (4)

[Claims] 1. A method of melting a raw material for a crystal in a crucible to form a molten layer, immersing the seed crystal in the molten layer, pulling the seed crystal while rotating, and growing a single crystal on the lower side thereof. 2. The method for growing a single crystal, wherein the rotation of the crucible is accelerated to a required speed while pulling the single crystal. 2. A raw material for crystallization in a crucible is melted to form a molten layer, a seed crystal is immersed in the molten layer, the seed crystal is pulled up while being rotated, and a neck of a single crystal and a shoulder are provided below the seed crystal. And a method of growing a body, wherein the rotation of the crucible is accelerated to a required speed during the transition from the growth of the shoulder of the single crystal to the growth of the body. 3. The method for growing a single crystal according to claim 1, wherein the rotation of the crucible is accelerated within about 5 minutes. 4. The heating amount of the crucible is increased before the rotation of the crucible is accelerated, and the heating amount of the crucible is decreased after the rotation of the crucible is accelerated to a required speed. Single crystal growth method.