JP5941384B2 - Method for producing silica glass crucible for pulling silicon single crystal - Google Patents

Description

  The present invention relates to a method for producing a silica glass crucible for containing a raw material silicon melt used when pulling up a silicon single crystal by the Czochralski method (hereinafter referred to as CZ method). More specifically, the present invention relates to a method for producing a silica glass crucible that can pull up a silicon single crystal with a high yield by suppressing bubble generation and expansion in the inner layer of the crucible that is generated when pulling up the silicon single crystal.

  The Czochralski method (CZ method) is widely used in the production of silicon single crystals. In this method, the seed crystal is brought into contact with the surface of the raw material silicon melt contained in the crucible, the crucible is rotated, and the seed crystal is pulled upward while rotating the seed crystal in the opposite direction. Single crystal ingots are nurtured.

In the above method, a silica glass crucible is used as a crucible for containing the raw material silicon melt. This silica glass crucible generally has a two-layer structure as disclosed in Patent Document 1, with the outer layer being an opaque layer and the inner layer being a transparent layer.
The outer opaque layer has a lower purity than synthetic silica glass, but is formed of a natural silica material excellent in heat resistance and contains a large number of bubbles. On the other hand, the transparent layer of the inner layer is formed of a high-purity synthetic silica raw material in order to suppress impurity contamination on the pulled silicon single crystal ingot, and from the viewpoint of improving the crystallization rate of the single crystal ingot, etc. The inner surface of the crucible is formed smoothly.
The inner layer of such a silica glass crucible is a substantially bubble-free transparent layer before starting the pulling of the silicon single crystal, but bubbles are generated when exposed to reduced pressure and high temperature for pulling the silicon single crystal. In some cases, the inner surface of the crucible peels due to expansion of the gas, or the gas inside the bubbles becomes gas bubbles and is released into the raw silicon melt. There has been a problem that the quality of the silicon single crystal is lowered when the peeled pieces and gas bubbles reach the growth interface of the silicon single crystal by convection of the raw material silicon melt and are taken in.

  In order to solve the above-mentioned problem, a transparent quartz glass layer is formed by heating and melting the hydrogen-doped silica powder and the hydrogen-undoped quartz powder on the inner surface side of the translucent quartz glass crucible base. A method for producing such a quartz glass crucible has been proposed. Patent Document 3 discloses a quartz glass crucible in which the expansion rate of bubbles contained in the inner surface transparent layer is controlled at a pulling equivalent temperature.

JP 5-105577 JP2007-326780 JP 2009-132567 A

  However, even when the quartz glass crucible as described above is used, when the silicon single crystal is pulled by the CZ method, bubbles are generated in the transparent layer in a state where the raw material silicon is melted and held and expands. was there. When the expanded bubbles open to the inner surface of the crucible in contact with the raw material silicon melt, gas bubbles and silica glass fragments enter the raw material silicon melt and reach the pulling interface of the silicon single crystal by the convection of the raw material silicon melt. In some cases, it is taken into the silicon single crystal. When the gas bubbles are taken in, the defect cannot be confirmed from the appearance of the pulled silicon single crystal, and it is found as a pinhole, foreign object defect, etc. after slicing and polishing the silicon single crystal to form a silicon wafer. When the silica glass piece is taken in, dislocation occurs in the pulled silicon single crystal and the quality of the silicon single crystal is deteriorated.

  In the substantially bubble-free transparent layer before use, it is impossible to confirm where the bubbles are generated and how much the bubbles are expanded, and there is a problem that the generation and expansion of bubbles during use cannot be controlled.

In view of the current situation, the present inventor has conducted extensive research, and as a result, bubble generation and expansion in the transparent layer are caused by oxygen excess defects in the silica glass of the transparent layer, and oxygen excess defects are heated and melted by arc discharge. It was found that the oxygen was increased by oxygen incorporated into the silica glass structure.
In order to prevent carbon particles generated from the carbon electrode from adhering to the inner surface of the crucible during heating and melting by arc discharge, oxygen supply during heating and melting cannot be eliminated, but hydrogen is supplied along the inner surface of the crucible. Thus, the present invention has been completed by finding that oxygen excess defects can be suppressed.

That is, according to the present invention, in the transparent layer which is the inner layer, bubbles are generated and expanded during use, that is, from the start of heating to melt the polycrystalline silicon contained in the crucible until the end of pulling of the silicon single crystal. An object of the present invention is to provide a silica glass crucible for pulling up a silicon single crystal capable of suppressing the above.

The method for producing a silica glass crucible for pulling up a silicon single crystal according to the present invention supplies a quartz raw material powder into a molding die to form a silica powder molded body having a straight body portion, a corner portion and a bottom portion, and this silica powder molding This is a manufacturing method for obtaining a silica glass crucible by heating and melting the body by arc discharge, and supplying hydrogen gas along the inner surface of the straight body of the silica powder molded body during heating and melting by arc discharge in an oxygen atmosphere It is characterized by doing.
According to such a manufacturing method, it is possible to suppress oxygen from being taken into the silica glass structure of the transparent layer during heating and melting, and to reduce oxygen excess defects in the transparent layer.

In the method for producing a silica glass crucible for pulling a silicon single crystal, the supply amount of hydrogen gas is preferably 40 liter / min or more and 60 liter / min or less.
By setting the hydrogen flow rate in such a range, the OH concentration in the silica glass is increased and the high-temperature strength of the transparent layer is not lowered, and oxygen is taken into the silica glass structure of the transparent layer during heating and melting. It is possible to suppress and reduce oxygen excess defects in the transparent layer.

According to the method for producing a silica glass crucible for pulling up a silicon single crystal according to the present invention, it is possible to suppress oxygen from being taken into the silica glass structure of a substantially bubble-free transparent layer during heating and melting, and oxygen in the transparent layer. By reducing excessive defects, bubble expansion during pulling of the silicon single crystal can be suppressed.

It is a schematic sectional drawing of the silica glass crucible by the manufacturing method of this invention. It is a schematic sectional drawing of the silica glass crucible manufacturing apparatus used for the manufacturing method of this invention.

As shown in FIG. 1, a silica glass crucible 1 for pulling a silicon single crystal obtained by the manufacturing method according to the present invention has a U-shaped cross section having a rounded corner portion between a bottom portion and a cylindrical side wall portion. It consists of the shape. The outer layer 3 is an opaque layer and the inner layer 2 is a transparent layer.
Here, the opaque layer is a silica glass layer that contains many bubbles (preferably 20 / mm ³ or more) in the silica glass and is apparently clouded, and the transparent layer is in the silica glass. Means a silica glass layer substantially free of bubbles (preferably 2 / mm ³ or less) and substantially transparent.

The method for producing a silica glass crucible for pulling up a silicon single crystal according to the present invention is characterized in that hydrogen gas is supplied along the inner surface of a straight body portion of a silica powder molded body during heating and melting by arc discharge in an oxygen atmosphere. The conventional general method is used as the method for producing the silica glass crucible.
In general, the opaque layer is formed of a natural silica material such as quartz, which is low in purity but excellent in heat resistance, and the transparent layer is formed of a high-purity synthetic silica material obtained by hydrolysis of silicon alkoxide. To do.

Using a silica glass crucible manufacturing apparatus as shown in FIG. 2, a crucible molding die 11 is operated while operating a rotational drive source (not shown) and rotating the crucible molding die 11 at a high speed in the direction of the arrow. First, natural silica raw material powder is charged from the upper part inside, and further, synthetic silica raw material powder is charged on the inner surface thereof.

The initially supplied natural silica raw material powder is pressed against the inner member 12 of the crucible molding die 11 by centrifugal force to form one natural silica raw material powder layer 20b.
Then, following this natural silica raw material powder, a synthetic silica raw material powder is supplied into the crucible molding die 11, and the synthetic silica raw material powder is pressed against the natural silica raw material powder layer by centrifugal force to form one synthetic silica raw material powder layer. 20a is formed, and a two-layered silica powder molded body 20 having a crucible shape as a whole is formed.
Thereafter, the pressure is reduced by the operation of the pressure reducing mechanism 18 in the air atmosphere, the carbon electrode 19 is energized and heated from the inside of the silica powder molded body 20, and the silica powder molded body 20 is sequentially melted from the inside. After the energization of the carbon electrode 19 is started, the supply of hydrogen gas is started from the opening of the silica powder molded body 20 along the inner surface of the straight body portion, and the supply of the hydrogen gas is stopped after the energization of the carbon electrode 19 is completed.

Thereafter, by cooling, a transparent silica glass layer 2 in which oxygen excess defects are suppressed in a substantially bubble-free state on the inner surface side, and an opaque silica glass layer 3 in which a large number of bubbles exist on the outer surface side is formed. A silica glass crucible 1 having a double layer structure is formed.

Thus, by supplying hydrogen gas from the opening of the silica powder molded body 20 along the inner surface of the straight body portion, a substantially bubble-free transparent layer is formed during heating and melting by arc discharge in an oxygen-containing atmosphere. By suppressing oxygen incorporation into the silica glass structure and reducing oxygen excess defects, it is possible to suppress bubble generation and expansion of the generated bubbles during pulling of the silicon single crystal.

It is preferable to supply the hydrogen gas from the opening of the silica powder molded body 20 along the inner surface of the straight body portion, and to supply the hydrogen gas so as not to contact the carbon electrode 19 as much as possible. When the supplied hydrogen gas comes into contact with the carbon electrode 19, carbon particles generated from the carbon electrode 19 do not react with oxygen in the atmosphere and adhere to the inner surface of the crucible.

Further, it is preferable to supply the hydrogen gas so as not to be blown directly onto the silica powder molded body 20 as much as possible. When the supplied hydrogen gas is directly blown onto the silica powder molded body 20, it deeply penetrates into the inner surface layer of the silica powder molded body 20 to be a transparent layer, and the OH group concentration in the transparent layer becomes high.

The supplied hydrogen flow rate is preferably 40 liters / min or more and 60 liters / min or less. When the hydrogen flow rate is less than 40 liters / min, the effect of suppressing the bubble generation and expansion of the transparent layer is reduced, and defects such as dislocations and air pockets may occur in the pulled silicon single crystal ingot. It is not preferable. On the other hand, when the hydrogen flow rate exceeds 60 liters / min, the OH group concentration in the transparent layer increases, and the high-temperature strength of the transparent layer is reduced, which is not preferable.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by the following Example.
[Example 1]
By a manufacturing method similar to the method described in the above embodiment, a silica powder molded body having an outer diameter of about 600 mm and a height of about 500 mm is formed, and arc discharge while supplying hydrogen gas at a flow rate of 40 liters / min. A silica glass crucible was produced by heating and melting.
The silica glass crucible was fitted into a carbon crucible, set, heated with a heater from the outer periphery of the crucible, the polycrystalline silicon raw material was melted in the crucible, and a silicon single crystal having a diameter of 8 inches was pulled by the CZ method.

[Example 2]
In Example 1 above, a silica glass crucible was produced in the same manner as in Example 1 except that the flow rate of hydrogen gas was changed to 60 liters / min. Using this crucible, in the same manner as in Example 1, the silicon single crystal was pulled up. Went.

[Comparative Example 1]
In Example 1 above, a silica glass crucible was produced without supplying hydrogen gas, and using this crucible, a silicon single crystal was pulled in the same manner as in Example 1.

[Comparative Examples 2 to 4]
A silica glass crucible was produced in the same manner as in Example 1 except that the flow rate of hydrogen gas was changed as shown in Comparative Examples 2 to 4 in Table 1 below. Example 1 was made using each of these crucibles. In the same manner, the silicon single crystal was pulled.

About the silica glass crucible manufactured in the said Example and comparative example, the density | concentration increase amount of OH group content was evaluated on the basis of transparent layer OH group content of the silica glass crucible of the comparative example 1 which did not supply hydrogen gas. Further, the bubble density of the transparent layer after use for pulling the silicon single crystal and the crystallization rate of the pulled silicon single crystal ingot were evaluated.
These evaluation results are summarized in Table 1.

The OH group concentration in the silica glass crucible was measured by infrared spectroscopy. Specifically, first, a silica glass piece having only a transparent layer was cut out from a silica glass crucible, and the surface was polished to obtain a measurement sample. Next, using an infrared spectrophotometer (light transmittance measuring device), infrared light is incident on the surface of the measurement sample, the transmitted light emitted from the back surface of the measurement sample is received, and the measured infrared absorption Select the infrared absorption peak due to the OH group in the spectrum, and calculate the OH group concentration in the transparent layer by comparing the transmittance at the wavelength of the peak with the transmittance at a wavelength not affected by infrared absorption. did.

The density of bubbles formed in the silica glass crucible after pulling the silicon single crystal is measured using a CCD camera and a halogen lamp to capture an image from the inner surface of the crucible and binarize the resulting image. It went by. The measurement field of view was 500 μm ² or more (preferably 1.0 mm × 1.4 mm), and the recognizable minimum bubble diameter was 4.6 μm or more. The thickness direction was measured from the surface layer to a thickness of 1.0 mm by moving the CCD camera at a pitch of 20 μm.
This measurement was performed on four points (at intervals of 90 °) at substantially equal intervals in the circumferential direction of the crucible.

The crystallization rate is calculated based on the amount of the polycrystalline silicon raw material used and the crucible shape, and the length of the silicon single crystal ingot (including the straight body portion, top portion, and tail portion) that is actually set is increased. It was defined as the length of the crystal ingot.

  From the results of the above Examples and Comparative Examples, hydrogen gas was used in an amount of 40 liters / min or more and 60 liters / min or less so as to come into contact with the inner surface of the straight body portion of the silica powder molded body during heating and melting by arc discharge in an oxygen atmosphere. By supplying at a flow rate of, the generation of bubbles in the transparent layer was suppressed, the crucible was not deformed, and the crystallization rate of the pulled silicon single crystal ingot was good.

DESCRIPTION OF SYMBOLS 1 Silica glass crucible 2 Transparent silica glass layer 3 Opaque silica glass layer 10 Silica glass crucible manufacturing apparatus 11 Crucible mold 12 Inner member 13 Ventilation part 14 Holding body 15 Rotating shaft 16 Opening part 17 Exhaust port 18 Decompression mechanism 19 Carbon electrode 20 Silica powder molding 21 Hydrogen gas supply nozzle

Claims (2)

A production method for obtaining a silica glass crucible by supplying quartz raw material powder into a mold to form a silica powder molded body having a straight body portion, a corner portion and a bottom portion, and heating and melting the silica powder molded body by arc discharge. There,
A method for producing a silica glass crucible for pulling up a silicon single crystal, characterized in that hydrogen gas is supplied along the inner surface of the straight body portion of a silica powder molded body during heating and melting by arc discharge in an oxygen atmosphere.   The method for producing a silica glass crucible for pulling up a silicon single crystal according to claim 1, wherein the supply amount of the hydrogen gas is 40 liter / min or more and 60 liter / min or less.