JPH05163095A - Apparatus for pulling up single crystal - Google Patents

Abstract

PURPOSE:To provide an apparatus for pulling up a single crystal capable of suppressing the conversion of the single crystal into a polycrystal, affording the single crystal of high grade at a low oxygen concentration, improving the durability of a crucible and reducing the cost. CONSTITUTION:Unevennesses are formed in the periphery of the lower end of a quartz partition wall 10 held at the lower end of a purge tube in an apparatus for pulling up a single crystal. In pulling up the single crystal, the tip of a protruding part (10c) in unevennesses of the quartz partition wall 10 is partially immersed in a melt (12A) at a depth (d) within the range of (d)=<=5mm. The immersion depth (d) of the quartz partition wall 10 in the melt (12A) is extremely shallow according to this invention and the contact area of the quartz partition wall 10 with the melt (12A) is suppressed to a small value. Thereby, the oxygen concentration in the melt (12A) is suppressed to a low value and the objective high grade single crystal at a low oxygen concentration is obtained. Since communicating holes 16 are opened in the quartz partition wall 10, SiO evaporated from the surface of the melt (12A) is passed through the communicating holes 16 and rapidly discharged to prevent the single crystal from converting into a polycrystal with the SiO.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the CZ method (Czochr
single crystal pulling apparatus for pulling a single crystal from a polycrystalline melt by the Alski method).

[0002]

2. Description of the Related Art Such a single crystal pulling apparatus is constructed by accommodating a quartz crucible, a heater, etc. in a chamber. In the single crystal pulling apparatus, a polycrystalline raw material such as silicon supplied to the quartz crucible is It is heated by the heater and melts,
A polycrystalline melt (hereinafter referred to as a melt) is contained in the quartz crucible. Then, a seed crystal attached to the lower end of the upper shaft of the wire or the like is immersed in this melt, and the single crystal is grown at the tip of the seed crystal by pulling it up at a predetermined speed while rotating the upper shaft. be able to.

By the way, in growing a single crystal by the above-mentioned CZ method, the resistivity in the single crystal gradually decreases as the single crystal is pulled up due to the segregation phenomenon of the dopant and the yield deteriorates. A continuous charge method in which a raw material and a dopant are continuously supplied is adopted. Then, in this continuous charge method, when the single crystal growth region and the raw material supply section coexist in the melt in the quartz crucible, the temperature distribution of the melt becomes non-uniform, and the single crystal is adhered to the single crystal by the granular raw material. Therefore, a quartz inner crucible is provided in the quartz crucible to have a double structure, and a double crucible system in which an appropriate amount of granular raw material is supplied to the outside of the inner crucible is adopted.

[0004]

However, in the above double crucible system, the inner crucible made of quartz is fixed to the quartz crucible by welding or the like and is always immersed in the melt. The contact area of
There has been a problem that the amount of oxygen contained in quartz dissolved into the melt increases and the interstitial oxygen concentration in the single crystal increases, making it difficult to obtain a single crystal with a low oxygen concentration.

Further, since the inner crucible requires a height higher than the melt depth, there is a problem that the amount of thermal deformation is large and the material cost and the processing cost are high.

Further, there is a problem that SiO evaporated from the surface of the melt adheres to the chamber to cause polycrystallization of a single crystal.

The present invention has been made in view of the above problems, and an object of the present invention is to suppress the polycrystallization of a single crystal to obtain a high-quality single crystal with a low oxygen concentration and to obtain a crucible. An object of the present invention is to provide a single crystal pulling apparatus capable of improving the durability and reducing the cost.

[0008]

In order to achieve the above object, the present invention is to suspend a carbon tube from the upper part in a chamber accommodating a quartz crucible, a heater, etc.
In the single crystal pulling apparatus configured by holding a cylindrical quartz partition wall at the lower end of the carbon cylinder, unevenness is formed around the lower end portion of the quartz partition wall.

The present invention also provides a method for pulling a single crystal,
The tips of the convex and concave portions formed around the lower end of the quartz partition wall are partially immersed in the melt in the quartz crucible within a depth of 5 mm or less, and an inert gas is supplied into the carbon cylinder. The granular raw material is continuously supplied to the outside of the quartz partition wall in the quartz crucible.

[0010]

According to the present invention, since the quartz partition wall only has the convex and concave portions formed around the lower end portion thereof partially immersed in the melt, the immersion depth of the quartz partition wall in the melt is large. Is very shallow and the contact area with the melt can be kept small. Therefore, the oxygen concentration in the melt can be suppressed low, and a high-quality single crystal with a low oxygen concentration can be obtained. In this case, the flow velocity on the melt surface is suppressed by the quartz partition wall, and the stirring layer of oxygen under the solid-liquid interface becomes thick, so that the oxygen concentration distribution in the cross section of the single crystal becomes uniform. The drift of the granular raw material in the single crystal direction due to the surface convection of the melt is suppressed by the quartz partition walls, so that the polycrystallization of the single crystal due to the adhesion of the granular raw material to the single crystal is prevented.

Further, as described above, since the convex and concave portions of the quartz partition wall are partially immersed in the melt, a communication hole defined by the concave portion and the melt surface is opened around the lower end portion of the quartz partition wall. This means that SiO evaporated from the melt surface inside the quartz partition wall quickly flows into the chamber through the communication hole and is then discharged to the outside of the chamber. Therefore, it is possible to prevent the single crystal from being polycrystallized by SiO, which also improves the quality of the single crystal.

Further, since the quartz partition wall forming the inner crucible is only partially immersed in the melt,
Its length is short, its thermal deformation is suppressed to be small, its durability is enhanced, and its material cost and processing cost are reduced.

[0013]

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional view of a main portion of a single crystal pulling apparatus according to the present invention, FIG. 2 is an enlarged detailed view of a portion A of FIG. 1, and FIG. 3 is an exploded perspective view of the main portion of the single crystal pulling apparatus. FIG. 4 is a side view showing a state where the quartz partition wall is immersed in the melt.

In the single crystal pulling apparatus 1 shown in FIG. 1, reference numeral 2 is a stainless steel chamber in which a quartz crucible 3 is mounted on a shaft 4 and housed therein. The shaft 4 is rotationally driven around its central axis at a predetermined speed by a driving unit (not shown).

A cylindrical heater 5 made of carbon is arranged around the quartz crucible 3 in the chamber 2, and a heat insulating material 6 made of carbon is also arranged around the heater 5.

By the way, a carbon purge tube 7 is suspended from the upper part of the chamber 2 so as to be vertically movable, and a carbon heat shield ring 8 is provided at the lower end of the purge tube 7 which faces the chamber 2. Is held. Further, a carbon cylindrical holder 9 is screwed onto the heat shield ring 8, and a cylindrical quartz partition wall 10 is held on the cylindrical holder 9. The purge tube 7
Is moved up and down by a drive means (not shown) provided on the upper part of the device.

Here, the mounting structure of the heat shield ring 8, the tubular holder 9 and the quartz partition wall 10 will be described with reference to FIGS. 2 and 3.

As shown in FIG. 3, the purge tube 7 is used.
Has two large and small viewing windows 7a and 7b, and three key-like grooves 7c are formed on the outer periphery of the lower portion thereof.
The small viewing window 7b is for an image sensor for measuring the diameter of a single crystal.

The heat shield ring 8 is formed by combining a funnel-shaped inner ring 8A and an outer ring 8B, and an outer ring 8B.
By engaging three protrusions 8a (see FIG. 3) projecting on the inner peripheral portion of the lock groove 7c formed in the purge tube 7, the heat shield ring 8 is attached to the lower end of the purge tube 7. Retained.

By the way, an outer peripheral surface of the outer ring 8B is formed with an inclined surface 8b which spreads upward, and the inclined surface 8b has a predetermined angle θ (= 30 ° to 45 °) with respect to the horizontal.
It is only inclined (see Fig. 2). And this inclined surface 8
A projection 8c is formed on a part of b over the entire circumference,
The tubular holder 9 is screwed onto the protrusion 8c in a reverse screw relationship (a relationship in which the quartz crucible 3 is tightened in the rotational direction).

Further, a total of six gas vent holes 9a and a key-shaped groove 9b are formed on the peripheral wall of the tubular holder 9. In this embodiment, the entire surface of the heat shield ring 8 and the tubular holder 9 is coated with SiC.

Further, 6 is formed on the outer periphery of the upper part of the quartz partition wall 10.
Two protrusions 10a are provided in a protruding manner, and wavy unevenness is formed on the periphery of the lower end portion. That is, a recess 10b having a depth D is formed around the lower end of the quartz partition wall 10.
The portion excluding 0b forms the convex portion 10c (see FIG. 4). In this embodiment, the depth D of the recess 10b is 10
It is set to mm or less.

The quartz partition wall 10 is held by the tubular holder 9 by engaging the protrusion 10a formed on the quartz partition wall 10 with the key-shaped groove 9b formed in the tubular holder 9. It

Next, the operation of the single crystal pulling apparatus 1 according to the present invention will be described.

For example, when pulling a silicon single crystal, the inside of the chamber 2 is kept under a reduced pressure (for example, 30 mbar) under an Ar gas atmosphere, and the quartz crucible 3 is filled with granular polysilicon 12 from the raw material supply pipe 11. Supplied,
The polysilicon 12 supplied into the quartz crucible 3 is heated and melted by the heater 5, and the melt 12A is accommodated in the quartz crucible 3.

Next, the purge tube 7 is lowered together with the quartz partition wall 10 and the like, and as shown in FIGS. 1, 2 and 4, the quartz partition wall 10 has the projections and depressions formed on the lower end thereof. Part of the portion 10c is the melt 12A in the quartz crucible 3.
Is partially immersed in the upper part of the plate in the range of depth d = 5 mm or less. Then, as shown in FIG. 2 and FIG.
Around the lower end of the melt, the recess 10b of the quartz partition wall 10 and the melt 1
The communication hole 16 defined by the surface of 2A opens.

Thereafter, the seed crystal 14 bound to the lower end of the wire 13 suspended in the purge tube 7 is immersed in the melt 12A in the quartz crucible 3, and the quartz crucible 3 is shown by the shaft 4 in the arrow CR (clock). When the seed crystal 14 is pulled at a predetermined speed SE while being rotated in the arrow SR direction (counterclockwise direction) at the same time as being driven to rotate in the direction), a single crystal 15 grows on the seed crystal 14 as shown in the figure. To do. At this time, Ar gas is caused to flow downward in the purge tube 7, and the Ar gas is supplied with the gas vent hole 9a formed in the cylindrical holder 9 and the quartz partition wall 10 as shown by the arrow in FIG. SiO that has flowed out into the chamber 2 through the communication hole 16 that opens in the
Along with this, it is discharged to the outside of the chamber 2. As described above, when Ar gas is caused to flow in the purge tube 7, SiO passes through the gas vent hole 9a and the communication hole 16 and is effectively discharged to the outside of the chamber 2, so that the single crystal 15 is polycrystallized by SiO. In addition to being prevented, since the vicinity of the growth interface of the single crystal 15 is forcibly cooled by Ar gas, the growth rate (pulling rate) of the single crystal 15 without lowering the temperature of the melt 12A.
SE can be raised.

Further, according to this embodiment, the quartz partition wall 10 is
The uneven convex portion 10c formed around the lower end portion of the melt 1
Since it is only partially immersed in 2A at a depth d of 5 mm or less, the immersion depth d of the quartz partition wall 10 in the melt 12A is very shallow, and the contact area with the melt 12A can be kept small. Therefore, the oxygen concentration in the melt 12A is suppressed to be low, and a high-quality single crystal 15 having a low oxygen concentration can be obtained. In this case, since the flow velocity on the surface of the melt 12A is suppressed by the quartz partition wall 10 and the oxygen stirring layer at the solid-liquid interface becomes thick, the oxygen concentration distribution in the cross section of the single crystal 15 becomes uniform. The drift of the polysilicon 12 in the direction of the single crystal 15 due to the surface convection of the melt 12A causes the quartz partition wall 1 to move.
Since it is suppressed by 0, polycrystallization of the single crystal 15 due to the adhesion of the polysilicon 12 to the single crystal 15 is prevented.

FIG. 5 shows the effect of the immersion depth d of the quartz partition wall 10 in the melt 12A on the interstitial oxygen concentration of the single crystal 15.

FIG. 5 is a view showing the interstitial oxygen concentration of the single crystal 15 against the solidification rate of the single crystal with the immersion depth d of the quartz partition wall 10 in the melt 12A as a parameter. According to this figure, the immersion depth of the quartz partition wall d = 5, 10, 20 mm
In the case of, the interstitial oxygen concentration of the single crystal 15 is kept substantially constant with respect to the crystal solidification rate (pulling length), but the interstitial oxygen concentration of the single crystal 15 becomes smaller as the immersion depth d is set smaller. It turns out that it can be kept low.

Further, according to the present embodiment, the quartz partition wall 10 forming the inner crucible is only partly immersed in the melt 12A, so that the length thereof can be short.
The thermal deformation of this is suppressed to be small, the durability is enhanced, and the material cost and the processing cost are reduced.

While the single crystal 15 is being pulled, the polysilicon 12 is continuously supplied to the quartz crucible 3. Since the polysilicon 12 is supplied to the outside of the quartz partition wall 10,
When the polysilicon 12 falls into the melt 12A, it does not adhere to the single crystal 15, and the immersion of the quartz partition wall 10 into the melt 12A suppresses the surface convection on the surface of the melt 12A toward the single crystal 15. Therefore, the polysilicon 12 can be stably and continuously supplied, and the resistivity of the single crystal 15 becomes uniform in the growth axis direction.

In addition, according to this embodiment, the melt 12A
Radiation from the heat shield ring 8 is reflected by the inclined surface 8b of the heat shield ring 8 and heats the vicinity of the interface between the quartz partition wall 10 and the melt 12A, so that the solidification of the melt 12A is prevented and, as a result, the single crystal 1
It is possible to improve the production efficiency by increasing the growing speed (pulling speed) SE of No. 5. The heat shield ring 8 and the tubular holder 9 are always exposed to an ultrahigh temperature of 1400 ° C. or higher. However, since their entire surfaces are coated with SiC as described above, the strength at the ultrahigh temperature is increased. As a result, the carbon does not drop due to deterioration thereof, and the growth of the single crystal 15 is not hindered by the carbon.

Further, in this embodiment, as described above, since the tubular holder 9 is screwed to the heat shield ring 8 in a reverse screw relationship, it is assumed that the melt 12A is solidified. Also, the cylindrical holder 9 and the quartz partition wall 10 do not come off and fall off, which is safe.

[0036]

As is apparent from the above description, according to the present invention, a carbon tube is movably suspended from the upper part in a chamber containing a quartz crucible, a heater, etc. In a single crystal pulling apparatus configured to hold a cylindrical quartz partition wall, since unevenness is formed around the lower end portion of the quartz partition wall, polycrystallization of the single crystal is suppressed and a high-quality single crystal with a low oxygen concentration is suppressed. It is possible to obtain crystals, and it is possible to improve the durability of the crucible and reduce the cost.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a main part of a single crystal pulling apparatus according to the present invention.

FIG. 2 is an enlarged detailed view of a portion A in FIG.

FIG. 3 is an exploded perspective view of a main part of a single crystal pulling apparatus according to the present invention.

FIG. 4 is a side view showing a state where a quartz partition wall is immersed in a melt.

FIG. 5 is a diagram showing the interstitial oxygen concentration of a single crystal against the solidification rate of the single crystal with the immersion depth of a quartz partition wall in the melt as a parameter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single-crystal pulling apparatus 2 Chamber 3 Quartz crucible 5 Heater 7 Purge tube (carbon cylinder) 10 Quartz partition 10b Quartz partition recess 10c Quartz partition projection 12 Polysilicon (granular material) 12A Melt d Quartz partition melt Immersion depth

Claims (4)

[Claims] 1. A single crystal formed by suspending a carbon cylinder vertically from the upper part of a chamber containing a quartz crucible, a heater, etc., and holding a cylindrical quartz partition wall at the lower end of the carbon cylinder. In the pulling apparatus, the single crystal pulling apparatus is characterized in that irregularities are formed around the lower end portion of the quartz partition wall. 2. When pulling a single crystal, at the lower end portion of the quartz partition wall, the convex and concave portions formed around the lower end portion are partially immersed near the melt surface in the quartz crucible,
2. The apparatus for pulling a single crystal according to claim 1, wherein the concave and convex portions form a communication hole for venting an atmospheric gas along the circumference of the melt partition boundary of the quartz partition wall. 3. The quartz crucible is characterized in that the tip of the convex portion formed on the lower end portion of the quartz partition wall is partially immersed in the melt in the quartz crucible within a depth of 5 mm or less. 2. The single crystal pulling apparatus according to 2. 4. When pulling a single crystal, an inert gas is supplied into the carbon cylinder, and a granular raw material is continuously supplied to the outside of the quartz partition wall in the quartz crucible. Item 1. A single crystal pulling apparatus according to item 1 or 2.