JPH01317189A - Production of single crystal of silicon and device therefor - Google Patents

Abstract

PURPOSE:To obtain a continuous silicon crystal having uniform characteristics in the long direction of crystal by setting a covering plate for heat insulation at the upper part of a double crucible and feeding a raw material of silicon during pulling of single crystal. CONSTITUTION:A double crucible 3 consisting of an outer crucible 4 and an inner crucible 5 having a flow hole 6 at the bottom is set in a supporting crucible 7 vertically movably and rotatably sustained on a pedestal 8, a raw material of silicon is fed to the crucible 3 and then part higher than silicon melt in the crucible 5 and upper part of silicon melt at the outside of the crucible 5 are enveloped with a covering plate 11. Then the raw material of silicon is heated and melted by a heater 9, single crystal 1 of silicon is pulled up from a silicon melt 2 in the crucible 5 and the raw material of silicon in a granular state or in a small lump state is supplied through a feed pipe 14 to the semiconductor melt of a feed part B of raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a silicon single crystal by the Czochralski method and a silicon single crystal producing apparatus used for carrying out the method.

[Prior art] Silicon single crystals (hereinafter sometimes simply referred to as single crystals) are manufactured using the so-called Czochralski method, in which a single crystal is pulled from a silicon melt held in a crucible using a seed crystal. (CZ Law) is widely implemented.

In this method, for the purpose of controlling the resistivity of the silicon single crystal, boron for the n-type semiconductor, phosphorus, antimony, etc. for the n-type semiconductor are added to the silicon melt in advance. However, when the silicon melt solidifies into a single crystal, these additive elements are incorporated into the single crystal at a constant rate, and the remainder is discharged into the remaining silicon melt. and,
As the silicon melt decreases as the single crystal is pulled, the concentration of added elements in the silicon melt increases, and therefore the concentration of added elements in the pulled single crystal gradually increases from the top to the base of the single crystal. Therefore, the resistivity will also change, and when silicon wafers are manufactured from single crystals, the conductivity will vary from wafer to wafer, and if requirements are strict, the yield of usable wafers may be less than 50%. .

A double crucible method has been proposed to solve these problems and to equalize the concentration of added elements in a silicon single crystal (W, P, Leverton, J, Appl, Phys.
s.

29.1241 (195B), and K.E.Ben
5on, V, Lin, E, P.

Martjn, Sem1Conductor 5j11
Con, 33 (1981)). FIG. 5 schematically shows the structure of a double crucible used in this method. A second crucible 5 is provided inside the first crucible 4, and this second crucible 5 floats in the silicon melt due to the balance with buoyancy. As the single crystal is pulled up from the silicon melt inside the second crucible 5, the melt inside the first crucible 4 passes through the flow hole 6 provided at the lower part (bottom or lower side) of the second crucible 5. is the second crucible 5
gradually and unilaterally flows into the melt inside the second
The amount of melt in the crucible 5 is always kept constant. Usually the first
The concentration of added elements in the melt between the crucible 4 and the second crucible 5 is set to be approximately equal to the concentration of added elements CO taken into the single crystal 1 to be pulled.
The concentration of added elements in the melt in the second crucible 5 is a constant concentration Co/K regardless of the amount of silicon single crystal pulled.
It is kept at o. However, KO is the equilibrium distribution coefficient of the additive element to silicon.

By the means described above, when pulling a silicon single crystal using a double crucible, the concentration of added elements in the pulled single crystal, and therefore the resistivity, can be kept almost constant, thereby improving the yield of wafers. I can do it.

[Problems to be Solved by the Invention] In the method of pulling a silicon single crystal using a double crucible as shown in FIG. 5, as the pulling of the single crystal progresses, the total amount of silicon melt decreases, The position of the melt level decreases. As described above, even if the total amount of silicon melt decreases, the amount of melt in the inner second crucible 5 is kept constant. However, this condition breaks down when the bottom of the inner second crucible 5 touches the bottom of the first crucible 4, and silicon melt corresponding to the amount of single crystal pulled is replenished into the second crucible 5. It will no longer be done. For this reason, the amount and concentration of the silicon melt in the second lubrication chamber 5 change, making it impossible to pull a silicon single crystal with a constant concentration of added elements. For this reason, even if a double crucible is used, the ratio of single crystal pulling to the silicon raw material initially charged and melted in the crucible will be the same as, or even lower than, the normal Czochralski method. However, overall yield improvement is insufficient.

Furthermore, when pulling a silicon single crystal using a double crucible, the temperature of the silicon melt near the inner crucible wall tends to drop due to heat radiation from the inner crucible wall. In other words, the crucible, silicon melt, etc. installed in the pulling furnace are heated by a heating means using an electrical heating method using a resistance heating element usually made of graphite installed surrounding the crucible, while the heat is transferred to the furnace body. Heat is removed by conduction and radiation.

In particular, the upper part of the crucible is covered with water-cooled furnace walls and a furnace lid, and heat is removed by radiation from these. The rutsuho used to pull silicon single crystals is usually made of quartz glass, but while the emissivity of silicon melt is about 0.3, that of silica glass is about 0.6 or even higher. The heat dissipation from the crucible wall is quite large.

Moreover, since the crucible has a double structure, convection of the silicon melt is suppressed, and heat conduction from the outer circumference to the inner circumference of the double structure is suppressed. In addition, when making a double structure of the crucible, the diameter of the crucible and the diameter of the heating means (heater) are larger than in the case of the normal Czochralski method, so the heat dissipation from the crucible and the melt is even more effective. promoted. For the above reasons, due to heat radiation from the inner crucible wall,
The temperature of the silicon melt near this wall surface decreases.

This causes the following problems.

(1) The silicon melt surface near the wall of the inner melt wall solidifies (freezes). In some cases, even if the temperature of the silicon melt in the center of the crucible is at or above the optimum temperature for pulling a single crystal, solidification may occur near the wall of the crucible. Once coagulation occurs, heat dissipation from that area also increases, and coagulation progresses further.

(2) In the normal Czochralski method, the silicon melt in the crucible has a temperature gradient that is higher at the periphery and lower at the center, but in the case of a double-structured crucible, from the wall of the inner crucible to The temperature of the surrounding area decreases due to heat dissipation. This makes single crystal growth difficult, such as making it difficult to control the diameter during silicon single crystal growth.

(3) In order to suppress the occurrence of solidification on the silicon melt surface, increasing the temperature of the heating means (heater) requires more current, which not only increases electricity costs but also causes the heater itself to deteriorate. . Moreover, overheating significantly reduces the pulling speed of the single crystal, or makes it difficult to grow the single crystal itself.

There are methods for pulling silicon single crystals using a double crucible or using a crucible with a double structure on the side surface, such as the method disclosed in JP-A-58-130195. However, the problem of heat dissipation from the inner crucible wall has not been solved.

[Object of the Invention] The present invention has been made to solve the above-mentioned problems and achieve the objects. An object of the present invention is to provide a method and apparatus capable of reliably dissolving an input silicon raw material without inhibiting the growth of a silicon single crystal, and producing a silicon single crystal with a substantially constant concentration of added elements in the pulling direction. This is the purpose.

[Means for Solving the Problems] The present invention has been made to solve the above problems and achieve the objectives, and includes a second crucible having a flow hole provided in the first crucible. Using a double-structured Luho, the portion of the side surface of the second crucible above the silicon melt surface and the silicon melt outside the second crucible are kept warm by a cover plate provided above, and the A method for producing a silicon single crystal, wherein the single crystal is pulled from a silicon melt in a second crucible, and a silicon raw material is supplied to the outside of the second crucible in accordance with the pulling of the single crystal; In order to carry out this method, a double structure crucible in which a second crucible having a flow hole is disposed in a first crucible, and a second crucible disposed above the double structure crucible, A silicon single crystal production apparatus comprising: a heat-retaining cover plate that covers from the upper part of the first crucible to the upper part of the inner wall of the second crucible; and a supply device that supplies silicon raw material to the outside of the second crucible. This is what we provide.

[Operation 8--Pulling up the silicon single crystal from the second crucible and supplying silicon raw material to the silicon melt between the first crucible and the second crucible. The supplied silicon raw material is melted and mixed into the silicon melt, and gradually moves into the second crucible through the flow hole, so that the silicon melt levels in both crucibles are always kept constant.

On the other hand, the heat insulation effect of the cover plate installed above the double crucible suppresses heat radiation from the crucible wall, etc., and the silicon melt in this area is kept at a high temperature, preventing the temperature of the silicon melt from decreasing and solidifying. This can be prevented and the supplied silicon raw material can be easily dissolved.

[Example] FIG. 1 is a sectional view schematically showing an example of an apparatus for carrying out the present invention. In the figure, reference numeral 3 denotes a double crucible made of quartz glass that is placed in the center of the pulling furnace for silicon single crystal 1, and is composed of an outer crucible 4 and an inner crucible 5, and is placed on a pedestal 8. It is set in a supporting crucible 7 made of graphite and supported so as to be vertically movable and rotatable. A flow hole 6 is provided in the lower part (bottom or lower side surface) of the inner crucible 5, and the silicon melt 2 can flow through the flow hole 6.

In the example, the diameter of the outer crucible 4 was 50 clT11, the diameter of the inner crucible 5 was 40 cm, and two communication holes 6 were provided, each having a diameter of 5 mm.

Reference numeral 9 denotes a heating means (heater) such as a resistance heating element installed on the outer periphery of the supporting crucible 7 to melt the silicon raw material charged in the double crucible 3 and bring the silicon melt 2 to a predetermined temperature. Hold. 10 is a hot zone insulation material surrounding the heater 9. Reference numeral 11 denotes a cover plate, as shown in FIGS. 3 and 4, for example, which includes a disc-shaped flange 12 having a hole in the center, and a cover plate that is aligned with the hole and is integrally fixed to the flange 12. It consists of a cylindrical part or an inverted conical part (hereinafter collectively referred to as the cylindrical part) 13, and the cylindrical part 13 is located above the double crucible 3 in close proximity to the upper part of the inner wall of the inner crucible 5. and is attached to, for example, the hot zone insulation 10 by a flange 12.

The cover plate 11 is made of graphite, and its outer surface is coated with quartz glass to prevent contamination. Reference numeral 14 denotes a supply pipe provided above between the inner crucible 5 and the outer crucible 4 (hereinafter referred to as raw material supply section B), and is connected to a hopper etc. provided outside the pulling furnace. The filled new silicon raw material is supplied to the silicon melt in the raw material supply section B.

Next, the present invention configured as described above will be explained in detail.

First, a polycrystalline silicon lump is charged into the double crucible 3, and the silicon lump is heated and melted by the heater 9. At this time, the liquid levels of the silicon melt in the inner crucible 4 (hereinafter referred to as the single crystal growth section) and the silicon melt in the raw material supply section B are kept almost the same, and the cylindrical section 13 of the cover plate 11 The lower end portion of is located above the liquid level of the silicon melt. Next, the seed crystal is brought into contact with the surface of the silicon melt in the single crystal growth section A and then gradually pulled up while being rotated, whereby crystal growth occurs due to solidification of the contact liquid surface, and a cylindrical silicon single crystal 1 is obtained. .

On the other hand, while pulling the silicon single crystal 1, a granular or small-sized silicon raw material (hereinafter referred to as granular silicon) is introduced into the silicon melt in the raw material supply section B from the supply pipe 14. Specifically, the input amount of granular silicon is the amount (weight) calculated by (diameter of silicon single crystal) x (pulling speed) x (density of silicon) so that it is equal to the amount of pulled silicon single crystal 1. ) is added continuously. Further, the dopant is added so that the concentration of the added element is also constant. Specifically, the concentration of the additive element in the continuously supplied granular silicon may be made equal to the concentration of the additive element in the silicon single crystal to be pulled.

The introduced granular silicon is immediately melted in the raw material supply section B, and gradually flows into the single crystal growth section A through the flow hole 6, so that the silicon melt level in both parts is always kept constant. In this case, the wall surface of the inner crucible 5 and the raw material supply part B are kept at a high temperature because they are insulated by the cover plate 11, so that the silicon raw material charged therein is not only easily melted, but also double Solidification on the silicon melt surface in crucible 3 (
Stable single silicon without any freezing
12 - Crystal pulling can be achieved.

According to the apparatus configured as described above, silicon single crystal 1
It is possible to pull a silicon single crystal while continuously supplying new granular silicon according to the amount of pulling. Therefore, even if a silicon single crystal is pulled, a corresponding amount of granular silicon is replenished into the crucible 3, and the amount of silicon melt 2 in the crucible 3 is always kept constant. Furthermore, by controlling the concentration of added elements in the silicon raw material to be supplied, the concentration of the melt in the crucible 3 can also be kept constant. Thereby, the additive element concentration, that is, the resistivity and oxygen concentration of the silicon single crystal to be pulled, can always be maintained substantially constant regardless of the amount of silicon single crystal pulled. Furthermore, according to this method, there are mechanical constraints on the length that the silicon single crystal 1 can be pulled, limits on the tensile strength of the seed crystal used for pulling, wear and tear on the double crucible 3, and silicon oxide deposits in the furnace. It is possible to continuously pull a long silicon single crystal for a long time within the limits determined by contamination by (S i O) products. For this reason, not only the yield of silicon wafers for pulled silicon single crystals, but also the yield for charged silicon raw materials are dramatically improved. In addition, this method does not change the silicon melt amount or the liquid level position and is extremely thermally stable, so it is not only easy to operate during silicon single crystal pulling operation, but also The possibility of introducing dislocations and inhibiting single crystallization is extremely small.

On the other hand, the inner crucible 5 from the upper outer periphery of the double crucible 3
By covering the upper part of the inner wall of the crucible 5, the cover plate 11 can prevent the temperature drop and solidification (freeze) of the silicon melt near the wall surface of the inner crucible 5 described above. That is, the heat insulation effect of the cover plate 11 suppresses heat radiation from the crucible wall, etc., and the silicon melt in this area is maintained at a considerably high temperature.

The cover plate 11 is desirably made of a material that takes into consideration use under high temperatures and prevention of silicon contamination, such as graphite coated with quartz glass or graphite coated with SiC.

By providing this cover plate 11, even if granular silicon is continuously or intermittently replenished during single crystal pulling, the temperature of the silicon melt at the outer periphery can be easily maintained at a high temperature, and the introduced granular silicon can be easily maintained at a high temperature. Dissolve and mix immediately. Note that the temperature of the silicon melt at the center of the crucible 5 inside the cover plate 11 is relatively low, and can be maintained at an optimum temperature for pulling a silicon single crystal.

In the apparatus shown in FIG. 1, the inner crucible 5 is floating in the silicon melt 2, so the position of the inner crucible 5 may be affected by the rotation of the crucible 3 during pulling of the silicon single crystal. This movement may make the pulling of the silicon single crystal 1 unstable. Furthermore, in order to control the oxygen concentration taken into the silicon single crystal, it may be necessary to completely control the rotation speed of the inner crucible 5.

The embodiment shown in FIG. 2 was made to deal with the above-mentioned problems. This example is based on the inner layer.
One type is a support member 15 provided on the lower surface of crucible 5, which allows the inner crucible 5 to be stably held within the outer crucible 4. Further, in this case, the rotation speed of the inner crucible 5 completely matches that of the outer crucible 4, and the rotation speed can be controlled very easily.

[Effects of the Invention] As described above, according to the present invention, a cover plate for heat insulation is provided above the double crucible, and granular silicon is supplied continuously or intermittently during pulling of a silicon single crystal. Since the temperature is set at the optimum temperature for pulling silicon single crystals, there is no need to worry about solidification (freezing) of the silicon melt surface near the wall of the double crucible or the remaining melt of replenished granular silicon. The conditions can be realized, stable operation is possible, and high quality silicon single crystals can be obtained. Furthermore, it is now possible to always pull silicon single crystals under the same conditions regardless of the amount of pulling, which not only greatly improves work efficiency, but also enables the production of long silicon single crystals with uniform properties in the crystal length direction. Since it can be pulled up, the yield can be greatly improved.

As described above, according to the present invention, it is possible to achieve significant improvements in quality, productivity, and workability in pulling silicon single crystals.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of an embodiment schematically showing an apparatus for implementing the present invention, and FIGS. 3 and 4 show an embodiment of a cover plate forming a part of the above-mentioned apparatus. (a) is a perspective view, and (b) is a cross-sectional view. FIG. 5 is a schematic diagram showing an example of a conventional double crucible type silicon single crystal pulling apparatus. 1: Silicon single crystal, 2 = Silicon melt, 3° double crucible, 4: Outer crucible, 5: Inner crucible, 6: Communication hole, 9: Heater, 11 Cover plate, 14: Supply pipe, 15:
Support member. Agent Patent Attorney Soji Sasaki Figure 4

Claims (2)

[Claims] (1) A method for producing a silicon single crystal by pulling up molten silicon placed in a crucible, using a double-structured crucible in which a second crucible having a communication hole is disposed in the first crucible, The silicon melt on the side surface of the second crucible above the silicon melt surface and the silicon melt on the outside of the second crucible are kept warm by a cover plate provided above, and the silicon melt in the second crucible is heated. A method for producing a silicon single crystal, which comprises pulling the crystal and supplying a silicon raw material to the outside of the second crucible in accordance with the pulling of the single crystal. (2) In an apparatus for producing a silicon single crystal by heating molten silicon placed in a crucible with a heater provided outside the crucible and pulling up the molten silicon in the crucible, a communication hole is provided in the first crucible. a double-structure crucible in which a second crucible is disposed; A silicon single crystal production apparatus comprising: a cover plate; and a supply device for supplying a silicon raw material to the outside of the second crucible.