JP5473002B2 - Silica glass crucible for silicon single crystal pulling - Google Patents

Description

  The present invention relates to 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).

The 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 made of transparent silica glass for the inner layer and opaque silica glass containing many bubbles for the outer layer is generally used for the crucible for containing the silicon melt.

When the silica glass crucible contains polysilicon therein and is heated to a temperature equal to or higher than the melting point of silicon (about 1400 ° C.), a brown ring is usually formed on the inner surface of the crucible by crystallization of silica glass. Shaped cristobalite, so-called brown mold (also called brown ring or brown mark) is produced.
In this brown mold, crystal nuclei of the generated cristobalite are gradually grown and expanded by heating, and the inner surface of the crucible is roughened and peeled off. As a result, exfoliated crystal pieces and the like are mixed into the silicon melt, causing dislocations in the silicon single crystal, leading to a decrease in the yield of the silicon single crystal.

  The occurrence of the brown mold is generally considered to be caused by impurities on the inner surface of the silica glass crucible, and the inner layer of the crucible is composed of high-purity synthetic silica glass, or the nucleation factor of cristobalite A method of removing impurities such as Na and K by washing or the like is employed (see, for example, Patent Document 1).

On the other hand, there is an air pocket (also referred to as a pinhole) as a cause of a decrease in yield of pulling a silicon single crystal due to a silica glass crucible. This is mainly because Ar contained in the crucible adheres or floats on the inner surface of the crucible by heating, and is generated as bubbles in the silicon melt in the crucible. It is generated by being incorporated into a single crystal.
Such an air pocket degrades the device characteristics of a silicon wafer produced by slicing the silicon single crystal. In particular, it has been regarded as a problem with the recent thinning and high integration of semiconductor wafers, which is one of the causes of lowering the yield of wafers.

  For this purpose, for example, in Patent Document 2, the depth from the inner surface of the bottom of the crucible is aimed at increasing the wettability of the inner surface of the silicon with respect to the silicon melt and making it difficult for Ar to adhere to the inner surface of the crucible. A silica glass crucible having an OH group concentration contained in a region up to 1 mm in a range of 30 ppm to 500 ppm is disclosed.

  Further, in Patent Document 3, for the purpose of reducing the number of brown marks, a layer having high reactivity with a silicon melt is formed within 150 μm from the surface of the crucible, and the layer having high reactivity is synthesized quartz glass. A quartz crucible is disclosed as a layer or a natural quartz glass layer containing 100 ppm or less of one or more of alkali metals and alkaline earth metals. That is, it is disclosed that an upper limit value of the impurity metal content is defined to make the layer highly reactive with the silicon melt.

Japanese Patent Laid-Open No. 11-43392 JP 2010-168240 A JP-A-2005-306708

  As described above, although there are proposals for suppressing the occurrence of brown mold on the inner surface of the crucible or for solving individual problems of reducing air pockets due to Ar bubbles, the conventional crucible has both of these problems. It was difficult to solve at the same time.

  In addition, as described in Patent Document 3, there is a limit to increasing the reactivity with the silicon melt simply by defining the upper limit value of the impurity metal content, and this occurred on the surface of the quartz crucible. The cristobalite crystal nucleus does not have a dissolution rate higher than the growth rate, and a brown mark may remain even after all layers having high reactivity with the silicon melt are dissolved.

  Accordingly, there is a need for a silica glass crucible having a configuration capable of suppressing both the brown mold and the generation of air pockets, which are the cause of a decrease in the yield of silicon single crystals due to the crucible.

  The present invention has been made to solve the above technical problem, and the occurrence of brown mold is suppressed, and the generation of air pockets in the silicon single crystal is also suppressed, thereby improving the yield of pulling up the silicon single crystal. An object of the present invention is to provide a silica glass crucible for pulling a silicon single crystal that can be achieved.

A silica glass crucible for pulling a silicon single crystal according to the present invention is a silica glass crucible having a straight body and a bottom, and is a transparent silica glass having a chlorine or fluorine concentration of 50 to 10,000 ppm and a thickness of 0.05 to 0.2 mm. An inner layer made of transparent silica glass having a region in contact with the innermost layer having an OH group concentration of less than 30 ppm and a thickness of 3 to 5 mm, and an outer layer made of opaque silica glass. To do.
According to the silica glass crucible having such an innermost layer and the inner layer, generation of brown mold can be suppressed and generation of air pockets in the silicon single crystal can also be suppressed.

It is preferable that the innermost layer can be dissolved within 2 hours in a state where the silicon melt is in contact with the innermost surface of the crucible.
The innermost layer only needs to cover the inner surface of the crucible until all the polysilicon in the crucible is melted. Thus, the dissolution rate of the innermost layer is high, so that the generation of the brown mold is effectively prevented. It can be suppressed, and the effect of suppressing air pockets by the inner layer can also be suitably exhibited.

According to the silica glass crucible for pulling a silicon single crystal according to the present invention, the innermost layer having a high dissolution rate with respect to the silicon melt can suppress the occurrence of brown mold on the inner surface. In addition, by providing a highly viscous inner layer immediately below the innermost layer, generation of large cavities that cause the generation of air pockets can be suppressed, and generation of air pockets in the pulled silicon single crystal can be suppressed.
Therefore, the silica glass crucible according to the present invention can contribute to the improvement of the yield of silicon single crystal pulling.

Hereinafter, the present invention will be described in more detail.
The silica glass crucible according to the present invention is a silica glass crucible used in pulling a silicon single crystal by a CZ method having a straight body portion and a bottom portion, and is a multilayer in which an innermost layer and an inner layer are transparent silica glass, and an outer layer is an opaque silica glass It consists of a structure. The innermost layer has a chlorine or fluorine concentration of 50 to 10,000 ppm and a thickness of 0.05 to 0.2 mm, and the inner layer is in contact with the innermost layer having an OH group concentration of less than 30 ppm and a thickness of 3 to 5 mm. Has an area.

As described above, the brown mold is produced by crystallizing silica glass into cristobalite on the inner surface of the crucible. The cristobalite crystal nucleus on the inner surface of the crucible is formed before the solid polysilicon contained in the crucible melts and comes into contact with the silicon melt. Thereafter, the number of crystal nuclei hardly increases, and the crystal nuclei formed initially grow with the progress of pulling the single crystal, that is, with the lapse of the contact time with the silicon melt.
On the other hand, the crystal nuclei are etched by reaction with the silicon melt in contact with them, but the etch rate is usually smaller than the etch rate of silica glass. For this reason, the crystal nuclei of cristobalite that have not been etched are produced as a brown mold, and then the crystal pieces are peeled off and mixed into the silicon melt and taken into the silicon single crystal.

From such knowledge, even if cristobalite crystal nuclei are formed on the innermost layer surface by coating the innermost layer, which is a sacrificial layer, on the inner surface of the crucible in advance, the crystal in the vicinity is formed. If the innermost layer is dissolved in the silicon melt faster than the rate of crystallization, the formation of cristobalite crystal nuclei on the inner layer surface exposed after the innermost layer dissolution is suppressed, and the yield of silicon single crystal pulling is reduced. It is considered that the occurrence and growth of the brown mold that is the cause can be suppressed.
That is, according to the present invention, the inner surface of the crucible in which the crystal nuclei of cristobalite are formed is formed before the crystal nuclei of cristobalite are formed on the inner surface of the crucible exposed to the silicon melt when the silicon single crystal is pulled. This is based on the view that the brown mold generation point disappears if it is damaged.

Therefore, in the silica glass crucible according to the present invention, from the viewpoint of increasing the dissolution rate of the inner surface of the crucible in contact with the silicon melt before pulling the silicon single crystal, the innermost layer has a chlorine or fluorine concentration of 50 to 10,000 ppm. And the thickness is 0.05 to 0.2 mm.
By introducing chlorine or fluorine into the silica glass, Si—O—Si bonds in the silica glass network can be easily broken, and the dissolution rate can be increased.
When the chlorine or fluorine concentration is less than 50 ppm, the effect of increasing the dissolution rate is insufficient, and it is difficult to sufficiently inhibit the formation of crystal nuclei of cristobalite on the inner surface of the crucible.
On the other hand, when the chlorine or fluorine concentration exceeds 10,000 ppm, precipitates in the furnace are generated due to the influence of the halide gas generated in the silicon single crystal pulling process. In addition, there is a risk of causing troubles in the constituent materials in the furnace, particularly metal parts.
In order to dissolve the innermost layer quickly during the melt line formation period, the chlorine or fluorine concentration is more preferably 500 to 2000 ppm.

The innermost layer made of the transparent silica glass has a thickness of 0.05 to 0.2 mm.
When the thickness is less than 0.05 mm, the innermost layer is dissolved before the polysilicon accommodated in the crucible is completely melted, and the cristobalite crystal nucleus formation inhibition effect by the innermost layer cannot be obtained. It will be.
On the other hand, when the thickness exceeds 0.2 mm, the innermost layer remains even after all the polysilicon is melted, and thus the melting may continue, which may affect the oxygen concentration of the silicon single crystal. . In addition, since the innermost layer has low viscosity, Ar enters the cavity (indentation) formed by hitting the inner surface of the crucible and remains in the innermost layer that remains undissolved in the initial contact with the silicon melt. However, air bubbles are generated from the inner surface of the crucible starting from this cavity, and there is a risk of causing air pockets in the silicon single crystal.

In addition to the Ar bubbles described above, the air pockets are also caused by SiO gas bubbles generated by the reaction between the silica glass crucible and the silicon melt. These bubbles are likely to be generated starting from scratches or cavities on the inner surface of the crucible generated during crucible manufacture, when the polysilicon is accommodated in the crucible, or when the polysilicon is melted.
For this reason, it is preferable that the thickness of the innermost layer is such that it can be completely melted at the initial stage of contact with the silicon melt from the viewpoint of suppressing the generation of air pockets.
The thickness of the innermost layer is more preferably 0.05 to 0.1 mm.

The innermost layer only needs to cover the surface of the inner crucible layer until the polysilicon is completely melted, and can be dissolved within 2 hours in a state where the silicon melt is in contact with the inner surface of the crucible. Is preferred. That is, the initial contact with the silicon melt is preferably within 2 hours, and more preferably within 0.5 hours.
In this way, due to the high dissolution rate of the innermost layer, together with the suppression effect of brown mold generation by inhibiting the formation of cristobalite crystal nuclei on the inner surface of the crucible exposed to the silicon melt when the silicon single crystal is pulled up In addition, the effect of suppressing the occurrence of air pockets can also be achieved.

On the other hand, the inner layer of the silica glass crucible according to the present invention is configured to have a region in contact with the innermost layer having an OH group concentration of less than 30 ppm and a thickness of 3 to 5 mm.
Since the innermost layer melts in the initial contact with the silicon melt, the region of the inner layer that is in contact with the innermost layer, that is, the region immediately below the innermost layer, is in contact with the silicon melt during pulling of the silicon single crystal.
As described above, since the innermost layer has a high dissolution rate in the silicon melt, the viscosity near the silicon melting temperature is low, and the inner surface of the crucible, in particular, by the load of the polysilicon before the polysilicon is completely dissolved. A cavity is easily formed at the bottom of the crucible.
For this reason, by providing a highly viscous inner layer immediately below the innermost layer, viscous deformation is suppressed even before the polysilicon is completely melted, and generation of large cavities that cause air pockets can be suppressed. .

For this reason, OH group concentration shall be less than 30 ppm.
When the OH group concentration exceeds 30 ppm, the volume of the cavity from the inner surface of the crucible formed by polysilicon increases, and it becomes difficult to sufficiently suppress the generation of bubbles that cause air pockets.
The OH group concentration is more preferably 1 ppm or less.
In addition, since the innermost layer is more easily dissolved by contact with the silicon melt as the OH group concentration is higher, the innermost layer is preferably made higher than the OH group concentration of the inner layer.

The thickness of the region where the OH group concentration is less than 30 ppm is 3 to 5 mm.
When the thickness is less than 3 mm, the volume of the cavity from the inner surface of the crucible formed by polysilicon increases, and it becomes difficult to sufficiently suppress the generation of bubbles that cause air pockets.
On the other hand, even if the thickness exceeds 5 mm, the improvement of the air pocket suppression effect commensurate with the thickness cannot be achieved. Therefore, the thickness of the region should be 5 mm or less.

  Of the inner layer, the outside of the region where the OH group concentration is less than 30 ppm is a portion that does not come into contact with the silicon melt in the crucible, so that it can maintain the shape and strength as a silicon single crystal pulling crucible. If it is silica glass, the OH concentration is not particularly limited. Of course, the entire inner layer may be a region having an OH group concentration of less than 30 ppm.

  The thickness of the entire crucible including the inner layer and the outer layer is preferably about 7 to 25 mm in consideration of the thickness of the region where the OH group concentration is less than 30 ppm and the strength and weight of the crucible. Usually about 15 mm.

The silica glass crucible according to the present invention as described above can be manufactured by a rotational molding method, but the manufacturing method is not particularly limited.
In general, the opaque silica glass of the outer layer is formed of a natural silica material such as quartz, which has low heat but excellent heat resistance. The transparent silica glass of the innermost layer and the inner layer is obtained by hydrolysis of silicon alkoxide or the like. Formed from a high purity synthetic silica raw material.
Moreover, the silica glass raw material whose chlorine or fluorine concentration is 50 to 10,000 ppm can be obtained by doping chlorine or fluorine in the VAD method or the flame melting method.

Below, an example of a manufacturing method is shown.
First, in a rotating crucible molding die, natural silica raw material powder for constituting the outer layer, synthetic silica raw material powder for constituting the inner layer inside thereof, and then synthetic silica raw material powder having an OH group concentration of less than 30 ppm Furthermore, a synthetic silica raw material powder having a chlorine or fluorine concentration of 50 to 10000 ppm for constituting the innermost layer is loaded at a predetermined thickness inside and molded.
And the silica glass crucible which concerns on this invention is obtained by inserting an arc electrode in this and vitrifying by pressure reduction arc melting.
The innermost layer can also be formed by directly depositing the outer layer after the outer layer is formed by a flame melting method.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not restrict | limited by the following Example.
[Example 1]
By the rotational molding method, the inner diameter layer is made of transparent silica glass having an outer diameter of 610 mm and a height of 380 mm, a chlorine concentration of 500 ppm and a thickness of 0.1 mm, and a region in contact with the innermost layer is an OH group concentration of 20 ppm and a thickness of 3 mm. A silica glass crucible having an inner layer made of a certain transparent silica glass and an outer layer made of an opaque silica glass in contact with the inner layer and having a total thickness of 15 mm was produced.

[Comparative Example 1]
In Example 1, a silica glass crucible was produced in the same manner as in Example 1 except that the innermost layer was not formed.

[Comparative Example 2]
In Example 1, a silica glass crucible was produced in the same manner as in Example 1 except that the innermost layer was not formed and the OH group concentration in a region 3 mm from the inner surface was 70 ppm.

[Examples 2 to 4, Comparative Examples 3 to 7]
In Example 1, the chlorine concentration and thickness of the innermost layer and the OH group concentration and thickness of the region in contact with the innermost layer were set to the numerical values shown in Table 1, and the other cases were the same as in Example 1. Thus, a silica glass crucible was produced.

[Example 5]
In Example 1, a silica glass crucible was produced in the same manner as in Example 1 except that chlorine added to the innermost layer was replaced with fluorine.

[Examples 6 to 8, Comparative Examples 8 to 12]
In Example 5, the fluorine concentration and thickness of the innermost layer, and the OH group concentration and thickness of the region in contact with the innermost layer were set to the numerical values shown in Table 2, and the others were the same as in Example 5. Thus, a silica glass crucible was produced.

Each of the 20 silica glass crucibles prepared in the above examples and comparative examples was fitted into a carbon crucible and heated from the outer periphery of the crucible to melt about 150 kg of raw silicon in the crucible. A silicon single crystal having a diameter of 8 inches was pulled up.
Then, the inner surface of the crucible after the pulling of the silicon single crystal was observed, the presence or absence of the innermost layer was confirmed, and the number of brown molds generated was measured with a stereomicroscope.
Further, the dislocation-free rate (DF rate) in pulling the silicon single crystal was determined. The dislocation-free rate is the ratio of the number of silicon single crystals in which dislocations did not occur to the number of pulled up.
Moreover, the air pocket generation rate was measured about the wafer which sliced the pulled silicon single crystal. The air pocket generation rate was a value obtained by dividing the total number of air pockets generated in the wafer obtained from the straight body portion of the pulled silicon single crystal by the number of wafers. The number of air pockets was determined by measuring the number of air pockets on the wafer surface after wafer polishing with a particle measuring device.
These evaluation and measurement results are summarized in Tables 1 and 2. Table 1 shows examples and comparative examples when chlorine is added to the innermost layer, and Table 2 shows cases where fluorine is added to the innermost layer.

As can be seen from the results shown in Tables 1 and 2, according to the silica glass crucible (Examples 1 to 8) according to the present invention, the occurrence of brown mold is suppressed and the dislocation-free silicon single crystal is reliably pulled up. It was confirmed that the generation of air pockets in the silicon single crystal can be suppressed.
In Comparative Examples 7 and 12, precipitates were observed in the furnace. This is considered to be due to the fact that the concentration of chlorine or fluorine in the innermost layer was too high, and the halide gas was generated.

Claims (2)

A silica glass crucible having a straight body and a bottom,
An innermost layer made of transparent silica glass having a chlorine or fluorine concentration of 50 to 10,000 ppm and a thickness of 0.05 to 0.2 mm;
An inner layer composed of a transparent silica glass having a region in contact with the innermost layer having an OH group concentration of less than 30 ppm and a thickness of 3 to 5 mm;
A silica glass crucible for pulling up a silicon single crystal, comprising an outer layer made of opaque silica glass.   2. The silica glass crucible for pulling up a silicon single crystal according to claim 1, wherein the innermost layer can be dissolved within 2 hours in a state where a silicon melt is in contact with the surface of the innermost layer of the crucible.