JPH01148783A - Quartz crucible for pulling up single crystal - Google Patents

Abstract

PURPOSE:To provide the title quartz crucible for pulling up a single crystal having excellent heat resistance and capable of stably maintaining a high degree of crystallization by providing a transparent quartz glass layer having a smooth surface and free of bubbles on the inner surface of a translucent quartz glass layer contg. many bubbles and contg. a crystalline quartz component. CONSTITUTION:The quartz crucible 1 having a translucent quartz glass layer 2 contg. many bubbles 4 and a crystalline quartz component is prepared. The transparent glass layer 3 having a smooth surface and free of bubbles is formed on the whole inner surface of the crucible 1 and fused to the inner surface. As a result, since the crystalline quartz component is contained in the translucent quartz glass layer 2, the heat resistance of the crucible 1 can be increased, and the local deformation of the crucible 1 generated when a single crystal is pulled up is reduced. In addition, the generation of ruggednesses on the inner surface of the crucible 1 due to the local erosion is reduced, and a stable and high degree of crystallization can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a quartz crucible for pulling single crystals such as silicon single crystals.

[Conventional technology]

Conventionally, silicon semiconductor single crystals are manufactured by melting polycrystalline silicon in a container and producing high-purity single crystal silicon (seed crystal).
The so-called Czochralski method, in which the tip is immersed and pulled up while rotating to grow a single crystal with the same orientation as the seed crystal, is widely used.

The containers used for this single crystal pulling are usually
A quartz crucible is used, but because of the difference in appearance due to the manufacturing method, it is different from a transparent quartz crucible, which has an opaque or translucent appearance due to the large amount of microscopic air bubbles contained within the fabric. There is a quartz crucible (hereinafter referred to as a translucent quartz crucible).

Translucent quartz crucibles can be manufactured with higher strength than transparent quartz crucibles by using powder as raw material.
In addition, large-diameter crucibles can be manufactured at relatively low cost, and the microbubbles contained in crucibles provide a more uniform heat distribution than transparent quartz crucibles, so they are widely used industrially.

However, in the conventional translucent quartz crucible, during the production of single crystals, (1) single crystallization often becomes unstable and defects occur, reducing the yield of single crystals;

(2) The stability of the shape against high temperatures during pulling is insufficient, leading to problems such as deformation along the shape of the carbon sussegrator supporting the quartz crucible.

Various factors are thought to be responsible for the instability of single crystallization during pulling, in addition to the pulling equipment and conditions. According to the inventor's study, the following three points are caused by the quartz crucible. This is the main thing that we are doing.

First, if the quartz crucible becomes partially deformed due to prolonged exposure to high temperatures during pulling, the convection of the silicon melt will be disrupted and single crystallization will be inhibited.

Second, the reaction between silicon melt and quartz glass at high temperatures can cause the inner surface to erode and become rough, or even if the erosion progresses further and exposes internal microbubbles, single crystal formation may occur. To become unstable.

That is, because the surface of the crucible in the part that comes into contact with the silicon melt surface is rough, the liquid level does not fall smoothly due to the reduction of raw materials, and the liquid level vibrates, inhibiting crystal growth.

Thirdly, in conventional translucent quartz crucibles, the size and density of the bubbles they contain are not necessarily uniform, and there are variations, especially in the cylindrical part. This actually makes heat transfer uneven, disrupts the convection of the silicon melt, and impedes single crystallization. Furthermore, minute protrusions, scratches, etc. on the surface of the quartz glass become nuclei for crystallization reactions due to high-temperature heating, producing spots of cristobalite, which cause the crystals to fall into the silicon melt, inhibiting crystal growth. However, when the inner surface becomes rough due to erosion, it is also a problem that many points that become nuclei for this crystallization reaction are generated.

According to the inventor's study, it was estimated that the above-mentioned erosion is promoted by the structural non-uniformity of the quartz glass.

Several inventions have been made regarding quartz crucibles. For example, in Japanese Patent Application Laid-open No. 59-213697, a crucible is heated from the inside for a long time, or a transparent quartz tube is melted to form a part of the cylindrical part into a transparent tube. Accordingly, it is described that at least the portion in contact with the raw material melt is made of a transparent quartz glass layer with a thickness of one layer or more. Furthermore, US Pat. No. 4,528,163 discloses a quartz crucible in which the outside is formed of natural quartz particles, the inside is lined with synthetic quartz particles, and a smooth thin amorphous IJf layer is formed on the surface of this lining layer. Are listed.

Additionally, U.S. Pat. Nos. 4,416,680 and 4.632
, No. 686 describes a method for reducing air bubbles in a quartz crucible, in which the outside pressure is reduced and melting is performed.

[Problem that the invention seeks to solve]

However, these prior documents contain specific measures to simultaneously solve a number of technical problems, such as preventing crucible deformation due to high temperatures during single crystal pulling, and characteristics required for the surface condition of the inner surface of the crucible. No disclosure has been made.

Specifically, Japanese Patent Application Laid-Open No. 59-213697 discloses that, among the characteristics required for the surface condition of the inner surface of the crucible, the inner surface of the translucent quartz glass layer is further heated to prevent corrosion of the portion in contact with the raw material melt. However, in the former method, the unmelted portion inside the quartz glass layer is further melted, and in some cases, the inner surface of the crucible may be melted. This method heats and expands the bubbles in the vicinity and ruptures them to release the bubbles inside, but with this method, it is almost impossible to remove the bubbles, and a large amount of the bubbles are removed from the transparent quartz glass layer. Since traces of air bubbles remain, a large amount of air bubbles will expand again during semiconductor pulling, especially when exposed to reduced pressure. Also,
The latter method, in which transparent tubes are melted, is complicated and the joints prevent the inner surface of the crucible from becoming a perfectly smooth surface.Also, it is difficult to completely weld the joint surfaces, and the joints are difficult to weld. Due to the difference in thermal expansion coefficients on both sides, destruction occurs during heating and cooling, reducing productivity.

Further, US Pat. No. 4,528,163 does not mention anything about preventing deformation during high-temperature lifting, but describes simultaneously melting the inner and outer layers of the kata.

In this case, although the characteristics of the crucible inner surface are improved by using synthetic quartz for the inner part, it is inevitable that a large number of bubbles and voids remain in the inner part, and the molten material becomes bubbles when pulling the single crystal. , become trapped in the pores of the air gap and significantly impede the lifting operation.

Additionally, U.S. Pat. Nos. 4,416,680 and 4.632
, No. 686 only describes that air bubbles in a quartz crucible are reduced by evacuation, but does not consider the deformation of the crucible during high temperature heating.

The present invention exhibits excellent heat resistance against high temperatures during single crystal pulling, and its inner surface is smooth and has few irregularities, so that air bubbles are not exposed in molten silicon and do not cause cristobalite generation. An object of the present invention is to provide a quartz crucible in which single crystal pulling can be performed extremely stably.

[Means for solving problems]

Therefore, the present invention integrally forms a transparent quartz glass layer that is substantially bubble-free and has a smooth surface on the inner surface of a translucent quartz glass layer containing a large number of bubbles. The structure should include a mixture of crystalline quartz components.

[Effect]

A transparent quartz glass layer with no bubbles and a smooth surface is formed on a translucent quartz glass layer containing a large number of bubbles, and a crystalline quartz component is present in this translucent quartz glass layer.

The crystalline quartz component significantly increases the heat resistance strength of the crucible, minimizes the deformation of the crucible during single crystal pulling, and prevents disturbance of convection of the silicon melt. Not only does it not cause vibrations, but it also does not cause vibrations on the surface of the silicon melt.

〔Example〕

Examples of the present invention will be described below.

In FIG. 1, the quartz crucible 1 of the present invention comprises an outer semi-transparent quartz glass layer 2 and a thin, substantially free layer formed integrally by continuously growing a completely molten layer on the inner surface of this layer. A crystalline quartz component (not shown) is mixed in the opaque quartz glass layer 2, and preferably, this crystalline quartz component is included in the translucent quartz glass layer 2. The same night near the outer surface.

The above-mentioned crystalline quartz component is dispersed in the semi-transparent quartz glass layer 2 in the form of particles, so that when the crucible is used,
For example, the deformation resistance near 1450'C, which is the melting point of silicon, is greatly improved.

Even if there is a gap between the crucible and the carbon susceptor that supports it, the crucible will not be deformed by the load of the raw material silicon charged into the crucible.

In other words, when a crucible is used for a long time at a high temperature such as 1450°C, if the crucible is locally deformed or distorted, the transfer of thermal energy to the inner surface of the crucible at the deformed part is reduced to other parts. It will be different. Therefore, the raw material melt undergoes different thermal histories in different parts of the inner surface of the crucible, which causes disturbances in the convection of the melt, making single crystal pulling unstable. Further, the deformation of the crucible itself causes trouble in pulling the single crystal.

The criteria for the transparent quartz glass layer 3 to be substantially bubble-free is that it contains extremely few bubbles compared to ordinary transparent quartz glass for semiconductors. Ordinary quartz glass for semiconductors contains a large amount of bubbles that are 100 μm to 1 block in size and can be observed with the naked eye, as well as microbubbles that can be observed by light scattering by the bubbles. . A specific example of no bubbles in the present invention is a visual field of 8 n+n+2 of a microscopic microscope with a magnification of 30 times.
As a result of observing 6 unused quartz crucibles at 30 locations in total (4 locations on the inner surface of the side wall and 1 location on the bottom of each crucible), two bubbles with a diameter of 20 μm or more were observed.
It is only slightly observed in ~3 locations. As an example, out of the 30 measurement points mentioned above, two bubbles with a diameter of 20 μm or more were observed at one point, and two bubbles were observed at one point, and the density of bubbles was 0.13 bubbles/bubble. 811” (1-
This is approximately 1.6 pieces/-), making the layer extremely homogeneous. As this transparent quartz glass layer,
As mentioned above, glass that is extremely homogeneous in terms of structure is used. Due to the presence of this transparent quartz glass layer, even if the inner surface of the crucible is eroded by a reaction at the contact interface with the silicon melt, the transparent layer itself has active centers and structural factors that can promote the reaction. Because there is no cristobalite, only a uniform and slow reaction occurs, and only a small amount of cristobalite is produced, maintaining the smoothness of the newly formed surface.
It is possible to always obtain a stable interface between the silicon melt and the crucible. Therefore, stable quality can be guaranteed even during long-term pulling. This transparent quartz glass layer is necessary until the use of the crucible is completely completed, and it is desirable that the thickness be at least 0.3 degrees, in fact, 0.8 to 1 degrees or more. Also, since each part of the crucible has different contact times with the silicon melt, the thickness of the transparent quartz glass layer should be adjusted accordingly, for example, the top of the cylindrical part is thin and the thickness increases towards the bottom. It is also possible to provide a distribution of

The translucent quartz glass layer 2 has a diameter of 10 to 250 μm.
m bubbles 4 exist, preferably 20,000 or more per ICl3, more preferably 60% or more of the translucent quartz glass layer 2 in the cylindrical portion in the thickness direction. It is distributed at an abundance density of 40,000 to 70,000.

A large number of bubbles 4 in such a translucent quartz glass N2
Due to the presence of
Temperature unevenness due to variations in the wall thickness of the crucible is also reduced.

As a result, during single crystal pulling, the raw polycrystalline melt undergoes a constant thermal history over the entire inner surface of the crucible, and single crystal pulling is performed extremely stably.

Next, an example of manufacturing the quartz crucible of the present invention will be described below. First, as the raw material powder used, purified powder such as natural crystal is used. This powder is fed into a rotating crucible manufacturing mold, and after a layer is formed to a predetermined thickness by centrifugal force, melting is started from the inside by means such as arc discharge.

At this stage, translucent quartz glass N2 is formed. At this time, the melting conditions are controlled so that the entire formed powder layer is not vitrified. By cooling the outside of the mold as necessary, It is possible to remove excess heat and leave the crystalline quartz component in the vicinity of the outer surface of the translucent quartz glass layer 2.

In the present invention, the size of the bubbles is preferably within the above range, that is, 10 to 250 μm in diameter, and the density of the bubbles is preferably 20,000 bubbles/C113 or more, more preferably translucent quartz glass. 60% of layer thickness
In the above portion, it is 40,000 to 70,000 pieces/CI3. This can be achieved by using crystalline quartz powder containing no crystal water as the raw material powder, controlling its particle size distribution within the range of 300 to 100 μm, and controlling the heating and melting conditions.

The transparent quartz glass layer in the present invention can be formed by incorporating a desirable high-quality quartz glass layer into a molded powder layer and melting it into one, or by additionally melting the powder. can. The transparent layer formed in this way does not have any traces of air bubbles, so it does not expand under reduced pressure.
In particular, quartz powder is fed into a rotating mold to create a preform of an outer quartz powder layer on the wall of the mold by centrifugal force, and then the quartz powder is passed through a high-temperature gas atmosphere such as an arc discharge to make it semi-molten. If the powder is continuously adhered to the inner surface of the outer wall quartz powder layer using discharge energy to form a substantially bubble-free completely melted layer, the outer wall quartz powder layer and the transparent quartz glass layer on the inner surface will melt simultaneously. As a result, a bubble-free transparent quartz glass layer having a desired thickness is firmly formed on the translucent quartz glass layer.

(Experiment example) Next, an experimental example of the present invention will be explained.

First, by the method described above, the raw material powder is adjusted to have a diameter of 1
A 4-inch quartz crucible of the present invention (sample 1.2 of the present invention) was produced.

In addition, for comparison, a quartz crucible with a diameter of 14 inches (F11.2) was prepared.

Table 1 shows the presence or absence of crystalline quartz components in the translucent quartz glass layer of these quartz crucibles, the bubble diameter, and the bubble density.

In addition, FIG. 2 shows the results of X-ray diffraction of the outer surface of the quartz crucible and the portion where one cocoon was ground in the thickness direction.

The following experiment was conducted on the above sample.

(Experiment example 1) Effect of crystalline quartz components in the translucent quartz glass layer.

In order to investigate this, inventive sample 1.2 and comparative sample 1 were prepared.
1.2 was compared in terms of heat resistance. That is, the crucible was placed in a carbon susceptor with a gap of 10 degrees between the cylindrical part and the curved part of the bottom, and 10 ksr of polycrystalline silicon was placed in the crucible and melted at 1450° C. and held for 20 hours. 4. As a result, inventive samples 1 and 2 had small deformations, with the gaps being only 8 and 7, respectively, whereas comparative samples 1 and 2 had large deformations at the bottom, and The gap became 2m+n and 1m, resulting in large deformation. Delicious,
Samples 1 and 2 of the present invention and comparative samples 1 and 2 were prepared so that the outer diameter of the crucible was 150 mm, and these were cut into rings with a length of 2 mm, and placed in an electric furnace with the wall facing down. After heating at 1300℃ for 18 hours and 6 hours, we investigated the change in the diameter of the tube.
The diameter changed by about 30fflII+ and 35 degrees due to collapse, but the diameter was smaller by about 7 mm in sample 1 of the present invention and by about 8 mm in Akira Motokawa sample 2, and the crystalline quartz component was due to the strength of the crucible. It can be seen that this significantly increases the

(Experimental Example 2) To investigate the effect of the transparent quartz glass layer according to the present invention, changes in surface roughness of the inner surface of the crucible due to single crystal pulling were measured. That is, the roughness of the inner surface of the crucible was measured after single crystal growth was performed for 50 hours using Sample atB of the present invention and Comparative Sample 1.

Measurements were made using a stylus type surface roughness meter (manufactured by vIJ Kosaka Koitasho). Figure 3 shows the surface roughness of sample 1 of the present invention before use, Figure 4 shows the surface roughness of Akira Motokawa sample 1 after single crystal growth, and Figure 5 shows the surface roughness of sample 1 of the present invention before use. Comparison sample 1 after crystal growth
Check the surface thickness measurement results.

As is clear from each figure, after using the quartz crucible of the present invention, it maintains a fairly flat inner surface with a maximum roughness of 29 μm, whereas in the conventional crucible, It can be seen that this makes it difficult for the melting surface of silicon to be disturbed in the crucible of the present invention.

Furthermore, the state of point devitrification on the inner surface of the crucible after the completion of crystal growth is shown in photographs in FIGS. 6A and 6B.

FIG. 6A shows the inner surface of inventive sample 1, and FIG. 6B shows the inner surface of comparative sample 1. According to this, it can be seen that the occurrence of cristobalite on the inner surface of the crucible of the present invention is significantly less than that of the conventional crucible.

That is, the inner surface of the quartz crucible of the present invention is extremely homogeneous and has few protrusions that serve as nuclei for crystallization reactions, so that point devitrification due to cristobalite is less likely to occur.

(Experimental Example 3) In order to investigate the effect of the presence of air bubbles, crucibles of the present invention sample 1.2 and comparative sample 1.2 were set in a normal single crystal pulling apparatus, and the crucibles were baked to determine the temperature of the inner surface of the crucible. We investigated the variation in

As a result, with respect to the set temperature, sample 1 of the present invention had a temperature of ±3°C.
, was within the range of ±5°C for Inventive Sample 2, whereas there was a large variation of ±12°C for Comparative Sample 1 and ±13°C for Comparative Sample 2. This shows that the crucible of the present invention is heated uniformly throughout, that is, uniform heat transfer is performed.

On the other hand, in Comparative Sample 1, the bubble diameter is too small and cannot contribute to uniform heat diffusion.
The bubble diameter was too large, and giant bubbles were generated due to the fusion of bubbles at high temperatures, resulting in large temperature variations as described above.

(Experimental Example 4) Next, the results of silicon single crystal production using the quartz crucible of the present invention will be shown.

The production conditions were such that two single crystal ingots each having a diameter of 150 mm and a length of 70 cm were continuously produced in each crucible under reduced pressure (10 mb) under an argon atmosphere.

The average value of the single crystallization rate was determined for the manufactured single crystal ingots. The results are shown in Table 2.

Table 2 Single crystallization rate of single crystal ingot From the results shown in Table 2, it is clear that the crucible of the present invention always produces stable single crystals.

Next, Table 3 shows the number of bubbles with a diameter of 20 μm or more in the transparent quartz glass layer of the quartz crucible of the present invention and the conventional quartz crucible used for pulling the silicon single crystal, and
7 and 8 show longitudinal cross-sections of the body and bottom.

Table 3 Physical properties of quartz crucible after single crystal pulling Measurements were taken at a total of 5 locations (30 locations in total).

It is important to note that the temperature of the quartz crucible is approximately 1450°C.
Because it is heated at high temperatures for long periods of time and under reduced pressure, even if it is considered bubble-free before its use, these individual bubbles expand due to the softening of the quartz glass, making it easier to observe. It is.

In other words, the bubbles that are melt-sealed in the quartz glass layer during quartz crucible manufacturing are filled with atmospheric gas under atmospheric pressure (air if quartz crucible manufacturing is performed in air).
Naturally, it expands under high temperature and reduced pressure. however,
As shown in Table 3 and FIGS. 7A and 7B, the quartz crucible according to the present invention has a clearly bubble-free transparent quartz glass layer on its inner surface even after use. On the other hand, a quartz crucible made using the conventional method has a thin transparent quartz glass layer on its inner surface that is bubble-free to some extent before pulling the silicon single crystal, but when the silicon single crystal is pulled, the bubbles expand and these bubbles interact with each other. As a result, a clearly dense state of bubbles can be seen on the inner surface of the quartz crucible after pulling the silicon single crystal. (Table 3 and Figures 8A and 8B).

〔Effect of the invention〕

According to the quartz crucible of the present invention, the heat resistance strength of the crucible is extremely high, so that the local deformation of the crucible that occurs during single crystal pulling is extremely small, and the occurrence of surface roughness due to partial erosion of the inner surface of the crucible is minimized. becomes extremely small.

Therefore, even if the single crystal is pulled multiple times, a higher single crystal ratio can be maintained than in conventional crucibles.

In addition to single crystal pulling under atmospheric pressure,
Even when single crystals are pulled under reduced pressure, a stable and high single crystallization rate can be maintained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the quartz crucible of the present invention, FIG. 2 is a drawing showing the results of X-ray diffraction of the quartz crucible before single crystal growth, FIG. 2A is an outer surface of the crucible of the present invention, and FIG. The figure shows the results of X-ray diffraction of the outer surface of the crucible of the present invention after IIW+ grinding, FIG. 2C shows the outer surface of a conventional crucible, and FIG. 2D shows the results of X-ray diffraction of the outer surface of the conventional crucible after IIW+ grinding. FIG. 3 is a graph showing the roughness of the inner surface of the quartz crucible of the present invention before single crystal growth, FIG. 4 is a graph showing the roughness of the inner surface of the quartz crucible of the present invention after single crystal growth, and FIG. 5 6A and 6B are graphs showing the roughness of the inner surface of a conventional quartz crucible after single crystal growth; FIGS. 6A and 6B are drawings showing the state of point devitrification on the inner surface of the crucible after single crystal growth; Figure 6B shows the inner surface of the crucible of the present invention, Figure 6B shows the inner surface of a conventional crucible, Figures 7A and 7B are drawings showing longitudinal sections of the walls of the crucible of the present invention, and Figure 8A shows the inner surface of the crucible of the present invention. Fig. 8B and Fig. 8B are drawings showing a longitudinal section of a wall of a conventional crucible. 1... Quartz crucible, 2... Translucent quartz glass layer, 3
... Transparent quartz glass layer, 4... Air bubbles. Applicant Yasushi Ishikawa Figure 1 2θ [°] Figure 2A Figure 2B X-ray diffraction of the quartz crucible of the present invention (outer surface) Figure 2B 2θ [°] Fig. 2C Xi diffraction (outer surface) of a conventional quartz crucible Fig. 2D X-ray diffraction of a conventional quartz crucible Human surface II
II+I+Grinding) mm I'-"1 Roughness of the inner surface of the quartz crucible of the present invention (before single crystal growth) m
m Measurement length (rnm) Figure 4 Roughness of the inner surface of the quartz crucible of the present invention (after single crystal growth) m
m i Height of the inner surface of a conventional quartz crucible (after single crystal growth) 6th
Figure A Inner surface after i1 crystal growth of the quartz crucible of the present invention Figure 6B Inner surface of conventional quartz crucible after single crystal growth Figure 7A External softness Figure 7B Figure 8A Outside Figure 8B

Claims (1)

[Claims] 1. A translucent quartz glass layer containing a large number of bubbles, and a substantially bubble-free transparent quartz glass layer with a smooth surface integrally formed on the inner surface of this layer. A quartz crucible for pulling a single crystal, characterized in that a crystalline quartz component is present in the translucent quartz glass layer. 2. The transparent quartz glass layer is formed by depositing quartz powder on a preform of the translucent quartz glass layer through a high-temperature gas atmosphere and melting the same with the preform. A quartz crucible for pulling single crystals as described in scope 1. 3. Claim 1, characterized in that crystalline quartz components are unevenly distributed near the outer surface of the translucent quartz glass layer.
A quartz crucible for pulling a single crystal according to any one of items 1 to 2. 4. The bubbles in the translucent quartz glass layer have a diameter of 10
A quartz crucible for pulling a single crystal according to any one of claims 1 to 3, characterized in that the diameter is 250 μm.