JP2007176717A - Manufacturing method for silicon single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for silicon single crystal at a low cost which has high quality and in which the generation of OSF is suppressed, by removing impurities in the graphite member mounted in the chamber by short time heating. <P>SOLUTION: When growing silicon single crystal by the Czochralski method, the manufacturing method comprises mounting a heat shielding member that is composed of graphite and a heat insulating material into the chamber, and heating the inside of the chamber in a state where a graphite susceptor is removed, then carrying out a single crystal-pulling operation by charging the graphite susceptor and a quartz crucible filled with polycrystal silicon into the chamber. Wherein the impurities contained in the heat shielding member can be removed in a short time because the heat of a heater can be directly irradiated to the heat shielding member by removing the susceptor that has a relatively large heat capacity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a silicon single crystal in which generation of OSF defects due to impurities contained in a graphite member or the like constituting a single crystal pulling apparatus is small.

A silicon single crystal used in a semiconductor device is manufactured by a so-called Czochralski method (hereinafter CZ method) using an apparatus as shown in FIG.
The outline of the CZ method will be described as follows. That is, first, a polycrystalline silicon lump (or granular polycrystalline silicon) is filled in a quartz crucible and melted to obtain a silicon melt. Thereafter, a dislocation-free crystal seed suspended from the lower end of the pulling wire is immersed in the silicon melt, and the pulling is started after melting the tip of the seed crystal itself. The crystal diameter is gradually increased by continuing the pulling, and the constant diameter portion is pulled through the neck, cone and shoulder forming steps to obtain a silicon single crystal having a predetermined length.

In the pulling apparatus that performs the CZ method, the polycrystalline silicon lump in the quartz crucible is melted by the carbon heater disposed in the chamber, but the heat from the carbon heater is absorbed in the chamber or in the generated silicon unit. In order to prevent radiation to the crystal, or to efficiently supply heat from the carbon heater to the polycrystalline silicon lump or silicon melt, and to block the supply to the generated silicon single crystal, a heat shielding member Is arranged.
Further, the quartz crucible filled with a polycrystalline silicon lump or silicon melt is accommodated in a susceptor that is supported by a shaft so as to be rotatable about its axis in order to prevent soft deformation due to thermal deformation. And this susceptor is divided | segmented into the circumferential direction and assembled | attached to the outer periphery of the quartz crucible in order to prevent the crack at the time of cooling.
Generally, the heat shielding member is made of graphite and a heat insulating material, and graphite is used for the susceptor.

  On the other hand, in the process of manufacturing a semiconductor integrated circuit, as a cause of lowering the yield, oxygen precipitate micro-defects that form the nucleus of oxidation-induced stacking fault (hereinafter referred to as OSF) or crystals Examples include the presence of particles (Crystal Originated Particles, hereinafter referred to as COP) or the presence of interstitial-type large dislocation (hereinafter referred to as L / D). In particular, OSF introduces a micro defect that becomes the nucleus during crystal growth, and is manifested in a thermal oxidation process or the like when manufacturing a semiconductor device, and causes a defect such as an increase in leakage current of the manufactured device. There is a need to reduce OSF from silicon wafers used to manufacture integrated circuits.

It is known that the micro defect that becomes the nucleus of the OSF is formed during crystal growth, and the formation of the OSF nucleus is known to have the following characteristics. (For example, see Patent Document 1)
-OSF nuclei are easily formed when the concentration of heavy metals contained in a silicon single crystal increases.
・ OSF nuclei are easily formed when the oxygen concentration is high.
・ OSF nuclei are easily formed when the thermal donor concentration is increased.
Here, a thermal donor is a crystal defect having the properties of a donor that occurs when it slowly passes through a temperature range of about 450 ° C. during crystal pulling, and is considered to be a collection of solid solution oxygen atoms in the silicon crystal. Yes. During crystal growth, cooling at around 450 ° C. is applied for a long time, and OSF nuclei are likely to be generated at a crystal portion having a high thermal donor concentration.
However, a clear correlation between the above three factors affecting OSF development is not known.

Based on these findings, the following measures have been conventionally taken to suppress OSF. That is, (a) the metal impurity concentration is reduced. (B) Decrease the oxygen concentration. (C) Control heat history around 450 ° C.
Even in Patent Document 1, since the metal impurity of the measure (a) is mixed from the quartz crucible, it cannot be reduced unless the purity of the quartz crucible is improved. Since the oxygen concentration of the measure (b) is a condition set by the user as the product specification of the silicon wafer, it cannot be freely changed. If the thermal history control of the measure (c) is performed, not only the thermal donor but also other qualities are affected. Thus, after describing that the conventionally known methods (a) to (c) are not sufficient methods, the following techniques are proposed.

  That is, in Patent Document 1, generation of OSF is suppressed even when the silicon single crystal after pulling is processed into a wafer shape and subjected to heat treatment by a simpler method without being restricted in manufacturing the silicon single crystal. In order to produce a high-quality silicon single crystal, when growing the silicon single crystal by the CZ method, the atmospheric gas supply conduit to the chamber is used as the atmospheric gas in the chamber defining the region where the silicon single crystal is pulled up It is proposed to use argon gas purified by a gas purification facility installed in the factory.

On the other hand, the applicant of the present invention considers that impurities such as moisture and oxygen contained in a graphite member or the like arranged in the chamber are one of the causes of OSF generation. Prior to inserting the quartz crucible filled with the graphite, the graphite member and the heat insulating material including the graphite susceptor were heated at a high temperature for a certain period of time.
Japanese Patent No. 3709307

However, purifying the argon gas fed into the chamber requires an expensive gas purification facility to be installed in the atmospheric gas supply pipe line, resulting in a significant increase in cost. Moreover, even if the argon gas is purified, the generation of OSF cannot be completely suppressed.
Further, heating the graphite member for a predetermined time in advance not only causes a time loss due to a long cycle time, but also increases the amount of power and argon gas used, leading to an increase in cost. For this reason, shortening of a heating time is calculated | required.
The present invention has been devised in order to solve such a problem, and the impurities in the graphite member and the heat insulating material attached in the chamber are removed by a simpler method, and the generation of OSF is suppressed. Another object of the present invention is to provide a method for producing a high-quality silicon single crystal at low cost.

  In order to achieve the object of the method for producing a silicon single crystal of the present invention, when the silicon single crystal is grown by the Czochralski method, a heat shielding member made of graphite and a heat insulating material is attached to the chamber, and the graphite susceptor is attached. The inside of the chamber is heated in the removed state, and thereafter, a graphite susceptor and a polycrystalline silicon filled quartz crucible are loaded into the chamber and a single crystal pulling operation is performed.

  In the present invention, by heating with the graphite susceptor removed, the heat from the heater directly hits the heat shielding member made of graphite and a heat insulating material, and is heated to a higher temperature. For this reason, impurities such as moisture and oxygen contained in the heat shielding member made of graphite and a heat insulating material can be removed in a short time, and as a result, a high-quality silicon single crystal in which generation of OSF is suppressed is reduced in cost. Can be manufactured.

  As described in Patent Document 1, a silicon single crystal grown using an argon gas containing moisture or oxygen as an atmospheric gas pulled by the CZ method is processed into a wafer shape and subjected to an oxidation heat treatment. If it does, OSF will generate | occur | produce in a silicon wafer. The formation of a thermal donor can be considered as a cause of this OSF generation. The moisture in the atmosphere argon reacts with the graphite in the furnace to generate CO gas and hydrogen, and this hydrogen is taken into the single crystal from the silicon melt or single crystal surface. If hydrogen incorporated during growth exists inside the single crystal, it is assumed that a large amount of oxygen-related clusters are formed inside the single crystal during the cooling process that the crystal receives from the high temperature to the low temperature during growth.

In other words, moisture in the growth atmosphere is thought to accelerate the formation of thermal donors. When the concentration of the thermal donor increases, OSF nuclei are likely to be formed. It is not clear how oxygen in the atmosphere argon affects the formation of thermal donors, but CO generated by the reaction between oxygen and graphite, or the reaction between moisture and graphite, or CO ₂ gas is a silicon melt. If it is taken in and further mixed as carbon in the silicon single crystal, it can be a factor for forming OSF nuclei. Thus, there is a possibility that OSF nuclei are formed by the presence of moisture or oxygen in argon. Alternatively, OSF nuclei may be formed by the coexistence of moisture and oxygen in argon. This is as described in Patent Document 1.

By the way, argon gas is not the only source of impurities such as moisture and oxygen in the silicon single crystal growth atmosphere in the chamber. As described above, it is volatilized and mixed from graphite constituting the heat shielding member, heat insulating material, and graphite constituting the susceptor.
For this reason, the present applicant employs means for heating the heat insulating material and the graphite member at a high temperature for a predetermined time in advance to remove impurities contained in the heat insulating material and the graphite member.
However, it is not efficient because it takes a long time.
Accordingly, the present inventors have repeatedly studied various means for efficiently removing impurities that adversely affect the silicon single crystal from the heat insulating material and the graphite member loaded in the chamber, and have reached the present invention. It is. Details will be described below.

In a chamber for performing the CZ method, an argon gas is generally introduced from above and discharged from a discharge port provided at the lower end.
Moreover, the argon gas usually introduced from above passes through the gap between the growing silicon single crystal and the heat shielding member, and after the flow is changed at the upper end of the quartz crucible, it passes through the gap between the susceptor and the heater. And discharged downward. If argon gas is constantly flowing, impurities such as moisture and oxygen from the graphite susceptor do not have a great influence on the growing silicon single crystal.

On the other hand, in the embodiment shown in FIG. 2, for example, as shown in FIG. 2, the applicant of the present application performs the removal of the influence of impurities from the heat shielding member and the susceptor, and the heat from the heater is used to heat the susceptor having a large heat capacity. In addition, the shield member is shielded by the susceptor and cannot be used to efficiently heat the shield member.
Moreover, as described above, the impurities discharged from the susceptor do not greatly affect the growing silicon single crystal.

Therefore, in the present invention, an impurity that adversely affects the growing silicon single crystal is determined to be from the heat shielding member, and only this impurity is removed in advance before the single crystal growing operation. It is.
That is, as shown in FIG. 3, the chamber is heated with the heat shielding member attached to the chamber and the graphite susceptor is removed, and then the graphite susceptor and the polycrystalline silicon filled quartz crucible are loaded into the chamber. Thus, the single crystal pulling operation is started.
Heat from the heater is efficiently applied to the heat shielding member, and impurities such as moisture and oxygen contained in the member are efficiently removed in a short time. For this reason, compared with the conventional heating mode, the heating time can be greatly shortened, and not only the working time but also the energy cost can be greatly reduced.

Next, examples of the present invention will be described together with comparative examples.
1. A silicon single crystal pulling apparatus having the structure shown in FIG. 1, and using a device having the following size, when a silicon single crystal having a diameter of 200 mm is pulled, a heat treatment previously applied to the used graphite member The effect of was investigated.
That is, a graphite susceptor having an inner diameter of 600 mm, a wall thickness of 40 mm, and a height of 450 mm and a quartz crucible having an outer diameter of 950 mm are arranged in a chamber having a diameter of 1000 mm and a height of 4000 mm, and an upper portion of the quartz crucible. In addition, a silicon single crystal having a diameter of 200 mm was pulled with an apparatus in which a heat shielding member having a wall thickness of 40 mm and a cylindrical portion height of 650 mm was disposed.
Note that the pressure in the chamber was reduced to 100 torr or less in advance, and Ar gas having an oxygen content of 0.5 vol% or less and a dew point of −76 ° C. or less was supplied into the chamber from the top at a flow rate of 100 L / min. The oxygen content and water content in the Ar gas used were values that are said to be levels that normally do not affect the formation of OSF.
Further, the ash content of the material graphite from which the heat shielding member and the susceptor were produced was 400 ppm, and the water content was 0.1 mass%.

Comparative Example 1:
Using the above pulling apparatus, as shown in FIG. 1, a susceptor containing a quartz crucible filled with polycrystalline silicon was loaded in the chamber without being subjected to heat treatment in advance, and the pulling operation was performed by heating as it was.
Comparative Example 2:
As shown in FIG. 2, with a susceptor loaded together with a heat shielding member, after a heat treatment of 2000 ° C. × 12 h, a quartz crucible filled with polycrystalline silicon is loaded into the susceptor and heated to perform a pulling operation. went.
Example:
As shown in FIG. 3, with the susceptor removed and only the heat shielding member attached, a heat treatment of 2000 ° C. × 6 h was performed, and then a quartz crucible filled with susceptor and polycrystalline silicon was loaded into the chamber and heated. Then the pulling operation was performed.

Using the wafers cut out from the three types of silicon single crystals obtained in the above embodiment as a sample, the occurrence of OSF was observed.
That is, a sample cut from each silicon single crystal was heat-treated at 1100 ° C. for 5 hours in a wet oxygen atmosphere, and then the surface condition was observed with a microscope.
As a result, in the wafer of Comparative Example 1, generation of OSF was recognized in about 5%. On the other hand, in the wafers of Comparative Example 2 and Invention Example, the occurrence of OSF was below the detection limit.

From the above Examples and Comparative Examples, it can be seen that a silicon single crystal having excellent quality can be obtained by previously heat-treating the graphite constituting the susceptor and the heat shielding member and removing impurities contained therein.
Even if heat treatment is performed with the susceptor loaded in the chamber as in Comparative Example 2, the impurity removal effect can be obtained. However, as in the embodiment of the present invention, when the heat treatment is performed with only the heat shielding member attached without loading the graphite susceptor, the heating time is about half that when the graphite susceptor is loaded. It can be seen that the impurities in the graphite can be removed to the extent that the single crystal is not affected. By adopting the method of the present invention, energy efficiency can be greatly improved, and as a result, manufacturing costs can be reduced.

Diagram explaining the pulling situation with a silicon single crystal pulling device The figure explaining the conventional aspect of the graphite member preheating in a silicon single crystal pulling device The figure explaining this invention method of graphite member preheating in a silicon single crystal pulling device

Claims (1)

  When growing a silicon single crystal by the Czochralski method, a heat shielding member made of graphite and a heat insulating material is attached to the chamber, and the inside of the chamber is heated with the graphite susceptor removed, and then the graphite susceptor and polycrystalline A method for producing a silicon single crystal, wherein a silicon filled quartz crucible is loaded into a chamber and a single crystal pulling operation is performed.

Images