JPH11236294A - Device for producing silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce a silicon single crystal having excellent device properties by preventing metal contamination from being caused and enhancing the pulling-up rate, in the process of silicon single crystal pulling-up. SOLUTION: This device for producing a silicon single crystal by a Czochralski method is provided with: a graphite shielding member 8 that is a cylindrical or downwardly tapered inverted-conical member placed so as to encircle the periphery of a single crystal pulling-up zone; and a cylindrical or inverted-conical metallic reflection member 9 coaxially placed with the graphite shielding member 8; wherein the metallic reflection member 9 is covered with quartz glass 10. In the device, at the time of covering the metallic reflection member 9 with the quartz glass 10, desirably, a space is formed between them, or the metallic reflection member 9 is subjected to vacuum encapsulation. Further, the material of the metallic reflection member 9 is desirably molybdenum(Mo).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for manufacturing a silicon single crystal in which a radiant heat shielding member is provided in a single crystal pulling region, and more particularly, to eliminating contamination from the shielding member and improving device characteristics as a semiconductor substrate. The present invention relates to a manufacturing apparatus capable of efficiently growing an excellent silicon single crystal.

[0002]

2. Description of the Related Art There are various methods for producing single crystals for semiconductors. Among them, the Czochralski method (hereinafter referred to as "silicon single crystal") is widely used in a method capable of industrially efficient production. Hereinafter, there is simply “CZ method”).

FIG. 5 is a view for explaining a situation in which a silicon single crystal is pulled by the CZ method. The crucible 2 arranged in the center of the apparatus has a double structure, the inside is a quartz crucible,
The outside is made of graphite crucible. A heater 3 and a heat insulating material 4 are provided outside the crucible 2, and a material for crystal formation melted by the heater, that is, a raw material melt 7 is accommodated in the crucible 2. The lower end of the seed crystal 5 attached to the tip of the pull rod or the wire 11 is brought into contact with the surface of the melt 7 and the seed crystal 5 is pulled upward, so that the lower end of the single crystal 6 To grow. These parts and members are housed in a water-cooled metal chamber 1 and constitute a silicon single crystal manufacturing apparatus as a whole.

[0004] In industrial production of single crystals, high-speed pulling is an effective means for improving productivity. Also, in terms of manufacturing costs, pulling a single crystal requires a large amount of power and inert gas costs per unit time, so increasing the pulling speed is necessary for the production of inexpensive silicon single crystals. It is. As described above, high-speed pulling is indispensable for efficient production of a silicon single crystal, but the pulling speed largely depends on the temperature gradient in the pulling direction of the single crystal.

In other words, the temperature gradient referred to here is the rate at which the single crystal to be pulled is cooled on the melt (° C./unit length of the crystal). Need to be promoted. However, as shown in FIG. 5, in the CZ method, there are radiant heat sources such as the crucible 2, the heater 3 and the melt 7 around the single crystal 6 to be pulled up. The temperature gradient in the pulling direction becomes small, and the pulling speed cannot be increased.

Conventionally, measures to solve such a problem and increase the pulling speed of the single crystal have been studied. For example, in Japanese Patent Application No. 54-41161, the pulling region of the single crystal is exposed to the surrounding radiant heat. In order to shield from a source, an apparatus provided with a shielding member has been proposed.

FIG. 6 is a diagram showing a device structure proposed in Japanese Patent Application No. 54-41161. As is clear from the figure,
The shielding device 8 of the proposed device has an upper flat annular rim 8a protruding from the edge of the crucible and is attached to this annular rim 8a and is tapered conically tapering downward from the inner edge. The crucible has a connecting portion 8b, and the inside height of the connecting portion 8b is 0.2 to 1.2 times the crucible depth. Therefore, in this apparatus, the amount of heat input to the single crystal is reduced by reflecting the radiant heat from the exposed wall surface of the crucible, the heater, and the melt contained in the crucible, and the cooling rate of the single crystal is improved. can do. And as a shielding member that reflects radiant heat,
It is stated that a metal material such as tungsten or tantalum is optimal.

[0008]

In recent years, in the field of semiconductor manufacturing, as the degree of integration of IC and LSI devices has increased,
Various characteristics are required for a silicon wafer processed after pulling a single crystal by the Z method. In particular, metal impurities contained in the silicon single crystal increase the reverse leakage current of the PN junction in the device, so that the carrier recombination lifetime is shortened and the current-
It becomes clear that the voltage characteristics deteriorate. For this reason,
There has been a strong demand for the production of silicon single crystals free of metal contamination during the pulling process.

As described above, in the apparatus shown in FIG. 6, a metal material is used as the shielding member. At this time, considering the silicon melt exceeding the melting point of silicon (about 1400 ° C) and the radiant heat from the heater, etc.,
The shielding member provided in the single crystal pulling region is exposed to a high temperature environment of about 1500 ° C. For this reason, in the pulling process, the metal diffuses from the metal shielding member, and a part of the metal is taken into the silicon single crystal surrounded by the shielding member.

[0010] In order to prevent metal diffusion from the shielding member,
Attempts have been made to control the temperature of the shielding member by circulating cooling water by using a double structure, but it is difficult to adopt this method in actual operation if troubles such as crushing of cooling water are assumed.
In some cases, graphite is used as a material of the shielding member simply to avoid metal diffusion.However, graphite has a lower radiant heat reflectance than metal, and thus has the effect of shielding a single crystal from radiant heat. descend. For this reason, when a graphite shielding member is used, a certain limitation is imposed on efficient production by high-speed pulling of a silicon single crystal.

The present invention has been made in view of the above-mentioned conventional problems,
It is an object of the present invention to improve the structure of a shielding member arranged in a single crystal pulling region and to provide an apparatus for efficiently producing a silicon single crystal having no metal contamination and having excellent device characteristics.

[0012]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have proposed a combination of a graphite shielding member and a metal reflecting member for shielding radiant heat and exhibiting their respective characteristics. It was clarified that although simple combination enables high-speed pulling, metal contamination of the single crystal from the metal reflecting member is inevitable. Further, on the premise that a graphite shielding member and a metal reflecting member are combined, the following findings were obtained as a result of further studies.

(1) In a high-temperature environment, it is effective to coat a metal reflecting material with a coating material having excellent high-temperature characteristics in order to prevent metal diffusion while securing the thermal reflectance of the metal material.

(2) Quartz glass is most suitable as a coating material for the metal reflecting member. This is because even when exposed to a high-temperature environment, the fluctuation of the viscosity of quartz glass is small, there is no possibility of softening deformation as a coating material, the diffusion amount of impurities is extremely small, and the light transmittance is low. This is because it is a material that is high, around 80%, and does not hinder the heat radiation of the metal reflection member.

(3) The thermal expansion coefficient of quartz glass in a high-temperature environment is smaller than that of a metal material serving as a reflection member. In order to prevent the quartz glass from being damaged due to the difference in the coefficient of thermal expansion, when covering the metal reflecting member with the quartz glass, a gap may be provided between the two.

(4) In the process of pulling the single crystal, the inside of the metal chamber is kept in a vacuum state. For this reason, the stress caused by the pressure difference between the inside and the outside of the quartz glass can be reduced by enclosing the metal reflecting member with the quartz glass in a vacuum when covering the same.

The present invention has been completed on the basis of the above findings, and has a gist of the following silicon single crystal manufacturing apparatus as shown in FIG.

That is, a crucible 2 containing a raw material melt 7 of a single crystal to be grown, a means 3 for heating the melt, and a seed crystal 5 contacting the surface of the melt in the crucible with a single crystal 6 In a single crystal manufacturing apparatus comprising pulling means 11 for growing the crystal, and a metal chamber 1 for accommodating the above members, the diameter of the single crystal is reduced from the top to the bottom in a cylindrical shape surrounding the periphery of the pulling region of the single crystal. An inverted conical graphite shielding member 8 and a cylindrical or inverted conical metal reflecting member 9 which is coaxially arranged with the graphite shielding member and whose diameter decreases from the upper side to the lower side.
Wherein the metal reflecting member is covered with quartz glass 10.

In the above-mentioned silicon single crystal manufacturing apparatus, when covering the metal reflecting member with quartz glass, it is desirable to provide a gap or to vacuum-enclose the metal reflecting member. Further, it is desirable that the material of the metal reflecting member be molybdenum (Mo).

[0020]

FIG. 1 is a longitudinal sectional view showing a configuration example of a manufacturing apparatus according to the present invention. The main device configuration is a normal CZ
As in the case of the manufacturing apparatus by the method, the exterior is constituted by a water-cooled metal chamber 1, a crucible 2 is provided at a central position of the metal chamber 1, and a heater 3 and a heat insulating material 4 are provided on the outer periphery of the crucible 2. It is arranged. On the other hand, above the crucible 2, a pulling means 11 is vertically suspended from the center of the ceiling of the metal chamber 1 so as to be rotatable and vertically movable, and a seed crystal 5 is mounted at a lower end thereof. The seed crystal 5 rises while rotating as the pulling means 11 rotates, and the single crystal 6 grows at the lower end portion which is the contact surface with the melt 7.

A feature of the manufacturing apparatus of the present invention is that a graphite shielding member 8 and a metal reflecting member 9 surround the periphery of the single crystal pulling region above the surface of the melt 7 contained in the crucible 2. And are arranged coaxially.
The reason why the shielding of the radiant heat is performed by combining the graphite shielding member and the metal reflecting member is to exhibit characteristics as the respective shielding members or reflecting members. That is, since the shielding member is made of graphite, sufficient high-temperature strength can be ensured and a high-purity member can be provided, so that there is no need to worry about contamination of the single crystal. Further, the reason why the metal reflecting member is provided is that the radiant heat shielding effect is greater than any material.

The shape of the graphite shielding member and the metal reflecting member is appropriately designed from a cylindrical or inverted conical shape so as to effectively shield and reflect radiant heat from a radiant heat source. In addition, in combination of these, as shown in FIG. 1, the configuration of both may be provided with a metal reflecting member on the inner peripheral side of the graphite shielding member,
Alternatively, a metal reflecting member may be provided on the outer peripheral side of the graphite shielding member.

Further, other features of the manufacturing apparatus of the present invention are as follows.
That is, the metal reflecting member 9 is covered with the quartz glass 10. As a material of the reflection member, for example, molybdenum (Mo) can be used. Mo has excellent heat resistance,
This is because the heat reflectance is high. In order to increase the heat reflectance of the reflecting member, the surface of the member may be sufficiently polished. However, the material of the reflection member is not limited to Mo, and any material may be used as long as it has heat resistance during the process of pulling the single crystal and has little deterioration.

As described above, quartz glass having excellent characteristics at high temperatures is used as a coating material for the metal reflecting member. Also,
When air bubbles are contained in quartz glass, radiant heat is uniformly reflected and scattered. Therefore, when quartz glass is used as the coating material, opaque quartz glass containing some air bubbles is desirably used.

FIG. 2 is a diagram showing the configuration of a metal reflecting member coated on quartz glass. It is desirable that the total thickness t of the quartz glass 10 covering the metal reflecting member 9 be about 3 to 30 mm. At this time, when Mo is used as the reflection member, it is desirable that its thickness be 1 mm or more in terms of strength.

In order to prevent the quartz glass from being damaged due to a difference in the coefficient of thermal expansion in a high temperature environment, a gap is provided between the metal reflecting member and the quartz glass when the member is covered with the quartz glass. Although it depends on the size of the reflecting member, it is preferable that the gap is provided at about 1/300 to 1/50 of the maximum diameter of the reflecting member. Further, since the metal reflecting member is placed in a reduced-pressure atmosphere in the metal chamber, the metal reflecting member is vacuum-sealed when the metal reflecting member is covered with quartz glass in order to eliminate a pressure difference between the inside and outside of the quartz glass.

The effects of the apparatus for manufacturing a silicon single crystal of the present invention will be described in detail below based on examples.

[0028]

EXAMPLE Using a silicon single crystal manufacturing apparatus according to the CZ method shown in FIG. 5, the shielding members of the present invention and Comparative Examples 1 and 2 were provided in the single crystal pulling region, and boron (B) was produced at a product diameter of 8 inches. ) Doping was performed to grow a P-type single crystal of 15 to 10 Ωcm. As shown in FIG. 1, the shielding member used in the example of the present invention is composed of an inverted conical graphite shielding member and an inverted conical Mo reflecting member coated with quartz glass on the inner peripheral side thereof and a coaxial member. It is arranged in. On the other hand, as shown in FIG. 6, the shielding member used in Comparative Example 1 is one in which an inverted conical Mo reflecting member is independently arranged. Further, Comparative Example 2
The shielding member used in (1) is one in which an inverted conical graphite shielding member is independently disposed.

The procedure for pulling a single crystal is as follows. A crucible is filled with 80 kg of polycrystalline silicon as a raw material, melted with a heater to stabilize the melt surface, and then seed-drawn to eliminate dislocations in the crystal. I do. Next, a shoulder portion was formed so that the product could be grown with a target product diameter of 8 inches, the body length was raised by 80 cm while maintaining the target product diameter, and then cut off from the silicon melt surface and squeezed.

In the process of pulling a single crystal, the pulling speeds when the shielding members of the present invention and Comparative Examples 1 and 2 were provided were compared. Next, the silicon single crystal grown by providing the shielding members of the present invention example and comparative examples 1 and 2 is subjected to a predetermined slicing process and the like to be finished into a single crystal wafer, and then subjected to the reflected microwave photoconductive attenuation method ( μPCD) was used to measure the lifetime.

FIG. 3 is a diagram showing the result of comparison of the pulling speed of a single crystal in the example. Regardless of which shielding member is used, the single crystal body is pulled up at the maximum pulling speed. The maximum pulling speed when pulling a single crystal is determined by the heat input and heat dissipation of the single crystal,
If the single crystal is continuously pulled at a speed higher than the pulling speed, the single crystal is supercooled, and the single crystal is understood to be deformed into a quadrangle or to be twisted. Therefore, in the embodiment, the body is grown at the maximum pulling speed over the entire length of the body portion, and the average value is shown in FIG. As is clear from the figure, the pulling speed can be increased in Comparative Example 1 and the present invention example using the Mo reflecting member, and in Comparative Example 2, 1.
While it stays at 0 mm / min, it can speed up to 1.7 mm / min.

FIG. 4 is a diagram showing the results of comparing the lifetimes of single crystal wafers in the example. The measurement position of the lifetime was 10 mm from the outer periphery of the wafer. First, in Comparative Example 1 using the Mo reflection member alone, the lifetime was 0 μsec, which was below the detection limit due to the factor of metal contamination. On the other hand, in Comparative Example 2 and the present invention example, the lifetime is about 400 μsec, which indicates that the device characteristics are excellent.

[0033]

According to the apparatus for manufacturing a silicon single crystal of the present invention, it is possible to prevent metal contamination in the process of pulling a single crystal and to increase the pulling speed, so that silicon having excellent device characteristics required as a semiconductor substrate can be obtained. A single crystal can be manufactured efficiently.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration example of a manufacturing apparatus of the present invention.

FIG. 2 is a diagram showing a configuration of a metal reflecting member coated on quartz glass of the present invention.

FIG. 3 is a view showing a result of comparing pulling speeds of single crystals in Examples.

FIG. 4 is a diagram showing the results of comparing the lifetimes of single crystal wafers in Examples.

FIG. 5 is a diagram illustrating a situation in which a silicon single crystal is pulled by a CZ method.

FIG. 6 is a diagram showing an apparatus structure proposed as a prior art (Japanese Patent Application No. 54-41161).

[Description of Signs] 1: Metal chamber, 2: Crucible 3: Heater, 4: Heat insulator 5: Seed crystal, 6: Single crystal 7: Silicon melt 8: Graphite shielding member 9: Metal reflection member, 10 : Quartz glass 11: Pulling means

Claims (4)

[Claims] 1. A crucible containing a raw material melt of a single crystal to be grown, a means for heating the melt, and a pulling means for growing a single crystal by bringing a seed crystal into contact with the surface of the melt in the crucible. And a metal chamber for accommodating the above-mentioned members, wherein a single-crystal graphite shield having a cylindrical shape surrounding the pulling region of the single crystal or an inverted conical shape having a diameter reduced from above to below. A member, and a cylindrical or inverted conical metal reflecting member whose diameter is reduced from the top to the bottom disposed coaxially with the graphite shielding member, wherein the metal reflecting member is quartz glass. An apparatus for producing a silicon single crystal, which is coated. 2. The silicon single crystal manufacturing apparatus according to claim 1, wherein said metal reflecting member is covered with quartz glass with a gap provided. 3. The metal reflecting member is vacuum-enclosed and covered with quartz glass.
An apparatus for producing a silicon single crystal according to the above. 4. The apparatus for manufacturing a silicon single crystal according to claim 1, wherein the material of the metal reflecting member is molybdenum (Mo).