JP2000016896A - Quartz crucible for pulling silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the thickness of a synthetic quartz layer to be measured simply without breaking a crucible by forming an oxygen-deficient type quartz glass at the interface part of an inner layer part composed of a synthetic quartz glass, and an outer layer composed of a molten quartz glass. SOLUTION: An oxygen-deficient type quartz glass is allowed to be present at the interface of an inner layer part and an outer layer of a quartz crucible for pulling a single crystal, having a double layered structure so that the position of the interface of the inner layer part and the outer layer part may be clearly detected. The inner layer part contacting a silicon molten liquid is composed of a synthetic quartz glass having small impurity content. The outer layer part is composed of a cheap molten quartz glass excellent in thermal stability. The oxygen-deficient type quartz glass can be obtained by mixing a small amount of Si with a raw material of the quartz glass, and is opaque and colored brown even if the thickness is very thin. The oxygen- deficient type quartz can clearly show the interface of the inner and outer layers, and the thickness of the synthetic quartz glass layer of the inner layer can be measured by an optical micrometer without destroying the crucible. The objective crucible can be molded by using three kinds of glass raw materials by a rotating melting method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a quartz crucible used for solidifying and growing a single crystal from a melt in the production of a silicon single crystal used for a substrate material of a semiconductor.

[0002]

2. Description of the Related Art A silicon single crystal as a semiconductor substrate material is mostly manufactured by the Czochralski method (CZ method). In this method, polycrystalline high-purity silicon as a raw material is heated and melted in a quartz crucible in an atmosphere-controlled chamber under reduced pressure, and a seed crystal is immersed in the melt surface of the silicon, and then gradually pulled up. It grows and produces a single crystal by solidifying based on a seed crystal.

During pulling and growing of a single crystal, a quartz crucible
It gradually erodes and dissolves into the silicon melt. Oxygen content in the silicon melt increases due to the incorporation of quartz, but most of it becomes SiO and is vaporized and eliminated from the melt surface. However, impurities contained in the quartz of the crucible
When mixed and taken into the melt, it causes a single crystal defect, and deteriorates the quality of a silicon wafer as a substrate material collected from the single crystal.

[0004] With the recent miniaturization and high integration of semiconductor devices, the demands on the quality of silicon wafers, which are the raw materials thereof, have become more and more severe. For this reason, a higher purity quartz crucible used for pulling a silicon single crystal is required.

[0005] Conventional fused quartz glass made from natural quartz has a limit in purification for removing impurities, and cannot respond to such high purity. In contrast,
Synthetic silica glass artificially synthesized by a sol-gel method, a gas phase method, or the like can have much higher purity than fused silica glass. However, this synthetic quartz glass generally has a low viscosity at high temperatures compared to fused quartz, and is likely to be deformed. Therefore, as the configuration of the crucible, for example, as in the invention disclosed in JP-A-56-17996,
Synthetic quartz lining on the inner wall of a crucible made of fused silica glass, or the invention of Japanese Patent Application Laid-Open No. 1-261293, and the invention of Japanese Patent Application Laid-Open No. 6-279167 in which the shape of the inner layer portion is devised A crucible having a two-layer structure in which the inner layer portion is made of synthetic quartz glass and the outer layer portion is made of fused quartz glass has been used.

If the outer layer for maintaining the shape and strength of the crucible is made of fused silica glass which is conventionally used and the inner layer in contact with the silicon melt is made of synthetic quartz glass as described above, the crucible is made to have a two-layer structure. Of the impurities can be suppressed while maintaining the shape and strength of the substrate. However, as the diameter of a single crystal increases due to the recent demand for an increase in the diameter of a silicon wafer, the amount of silicon melt used at a time increases, and the crucible wall becomes larger due to the crucible wall becoming larger. The contact time is getting longer. As a result, the erosion of the layer of the synthetic quartz glass increases, and the silicon melt comes into direct contact with the fused quartz glass, so that impurity contamination cannot be sufficiently suppressed. On the other hand, it is considered that the thickness of the synthetic quartz glass layer should be increased. However, if the ratio of the synthetic quartz glass layer increases, the deformation of the crucible during use increases. In addition, synthetic quartz glass is expensive, and quartz crucibles are usually discarded after a single use. Therefore, it is not preferable to add a synthetic quartz glass layer having an unnecessarily thick thickness due to an increase in cost.

In a quartz crucible having a two-layer structure, it is extremely important that the synthetic quartz glass layer has a minimum necessary thickness and that the thickness of the synthetic quartz glass layer is sufficiently understood in advance. Quartz crucibles having a two-layer structure are usually manufactured by a rotary melting method. That is, fused silica glass raw material powder,
Deposited in a crucible shape by centrifugal force in a rotating hollow mold,
Next, a raw material powder of synthetic quartz glass is introduced and deposited inside. Thereafter, the exhausted material is heated and melted by arc discharge from the inside while discharging the material from the mold surface side to form a crucible.

[0008] The interface between the fused silica glass layer and the synthetic silica glass layer of the crucible thus obtained cannot be discerned with the naked eye or an optical microscope. However,
The synthetic quartz glass layer is difficult to control stably to a constant thickness, and is not always uniform over the entire crucible wall, and the thickness of the synthetic quartz glass layer of the manufactured crucible is insufficient. In this case, impurities in the fused silica glass may be mixed at an early stage, which may lower the yield of non-defective silicon single crystals.

In the measurement of the thickness of a synthetic quartz glass layer of a crucible, which is currently used, chemical etching is performed in the depth direction from the surface, the amount of impurities contained therein is analyzed, and the content changes. It depends on the method of knowing the thickness from the position. For this purpose, the completed crucible must be destroyed, and is unsuitable for use in production as a product inspection.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a silicon single crystal pulling quartz crucible having a two-layer structure in which an inner layer is made of synthetic quartz glass and an outer layer is made of fused silica glass. Another object of the present invention is to provide a quartz crucible that can easily measure without destroying the quartz crucible.

[0011]

Means for Solving the Problems The inventors of the present invention have pressed for a quartz crucible having a two-layer structure, and need for a method capable of confirming the thickness of a synthetic quartz glass layer as an inner layer after production without breaking the crucible. Was done. Both fused quartz glass and synthetic quartz glass have almost the same chemical and physical properties and cannot be distinguished by ordinary means. From the standpoint of manufacturing silicon single crystals for semiconductor substrates, fused silica glass may contain many impurities, but is of extremely high purity from the viewpoint of general industrial materials.

As one method, it is considered to insert a certain marker. However, if the erosion proceeds to that part, a large amount of impurities of the marker may be mixed into the silicon melt. Thus, the use of oxygen-deficient quartz glass as a marker was studied. Quartz is Si as a chemical symbol
It can be represented by O ₂ , but when a small amount of Si is mixed into a quartz raw material and heated and melted, a black and opaque oxygen-deficient quartz glass SiO
_2-x (where x is a small number less than or equal to 1) is obtained. When a two-layer crucible is manufactured, a fused silica glass powder to be an outer layer is deposited in a hollow mold, a small amount of the oxygen-deficient quartz glass powder is introduced, and then a synthetic quartz glass to be an inner layer is filled. By this method, a quartz crucible in which the interface between the fused quartz glass and the synthetic quartz glass is colored,
In addition, it was found that it had the same performance as the conventional two-layer quartz crucible.

Oxygen-deficient quartz glass has almost the same properties as fused quartz glass or synthetic quartz glass except that it is opaque.
It has no effect on the performance as a conventional two-layer quartz crucible. Further, if oxygen-deficient quartz glass is prepared by mixing high-purity silicon for producing a single crystal with synthetic quartz glass, there is no risk of impurity contamination even if it is mixed in the silicon melt. For example, by measuring the depth of the colored surface from the inner surface of the crucible using an optical microscope or the like, the thickness of the synthetic quartz glass layer can be measured without breaking the crucible.

That is, the gist of the present invention is as follows.
Synthetic quartz glass for the inner layer and fused silica glass for the outer layer
A quartz crucible for pulling a silicon single crystal, wherein the quartz crucible has a layer structure, and has oxygen-deficient quartz glass at an interface between an inner layer portion and an outer layer portion.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is applied to a quartz crucible having a two-layer structure using quartz glass in which an inner layer and an outer layer are different from each other. No limitation. However, such a quartz crucible is mainly used for pulling a silicon single crystal by the CZ method. In this case, the inner layer in contact with the silicon melt is made of synthetic quartz glass having as low an impurity content as possible, and the outer layer is made of a heat resistant material. It should be excellent and inexpensive fused silica glass. In addition, the interface between the different types of silica glass of the inner layer and the outer layer, or the position of the boundary surface is made to be clearly detectable, and the thickness of each of those layers is not particularly limited. Absent.

Oxygen-deficient quartz glass is present at the interface between the inner layer and the outer layer. This oxygen-deficient quartz glass is opaque, and can be colored brown to clearly show the boundary between the inner and outer layers even when the thickness of the interface is extremely thin.
For example, when measuring the thickness of the synthetic silica glass inner layer of the crucible, using an optical microscope that can measure the moving distance of the lens barrel,
First, focus on the crucible surface, and then move the lens barrel in a direction perpendicular to the surface to focus on the colored portion of the interface. If the moving distance a at this time is obtained, the refractive index of the quartz glass is 1.
Since it is 43, the thickness b of the synthetic quartz glass layer can be obtained by b = a / 1.43.

Oxygen-deficient quartz glass is obtained by mixing a small amount of Si with a quartz glass raw material and heating and melting the material. The amount is not limited. However, the quartz glass raw material should be high-purity synthetic quartz glass, and Si should be high-purity Si, a raw material for single crystal production, so that even if this oxygen-deficient quartz glass is mixed into the silicon melt, it will not cause impurity contamination. It is desirable to use. Further, in the process of manufacturing the crucible, Si may be supplied to the interface between the inner and outer layers, and at the time of subsequent heating and melting, Si may react with surrounding quartz to generate oxygen-deficient quartz glass.

The crucible manufacturing method of the present invention is not particularly limited as long as oxygen-deficient quartz glass can be present between the inner layer and the outer layer. For example, if a normal rotary melting method is used, a rotating hollow mold is first filled with a raw material powder of fused silica glass, and then Si powder or an oxygen-deficient fused silica glass powder prepared in advance. Is introduced, a synthetic quartz glass powder to be an inner layer is filled, and heated and melted by arc discharge or the like to form a crucible.

[0019]

EXAMPLES Example 1 A two-layer crucible was manufactured by a rotary melting method generally used for manufacturing a quartz crucible. The dimensions of the crucible after completion are shown in Fig. 1 (a). First, a mold having a predetermined shape is rotated, and fused silica glass powder having an average particle size of 200 µm is formed into a crucible having a thickness of about 40 mm. Filled. A total of 0.5 g of granular Si (particle diameter: about 3.5 mm) is poured evenly over the bottom and side walls of the crucible, and then a synthetic quartz glass powder having an average particle diameter of 200 μm is added to a thickness of about 0.5 μm. It was filled on it to be 8 mm. Then, according to a normal operation method, the inner surface was subjected to arc discharge heating, degassing from the inner surface side to the outer surface side, and the like, followed by melting to obtain a quartz crucible.

In the obtained crucible, oxygen-deficient quartz 6, which appears black, was scattered at the interface 3 between the inner layer 1 and the outer layer 2. The cross section of the crucible wall is enlarged as shown in FIG. 1 (b), and the opaque layer 5 remains on the outer surface side of the outer layer portion. If there is no black oxygen-deficient quartz glass grain 6 as the above, the position of the interface 3 cannot be detected at all.

Using a 50 × optical microscope, the distance from the inner surface of the crucible to the inner colored portion or black particles was measured, and the thickness of the inner layer portion was determined. Further, a specimen was cut out from the portion where the thickness was measured with this optical microscope, and was gradually dissolved with hydrofluoric acid from the inner surface side of the crucible, and A at the position in the thickness direction was removed.
The l (aluminum) content was chemically analyzed. The difference between fused silica glass and synthetic quartz glass can be easily detected from the concentration of Al. A for the depth from the crucible inner surface
FIG. 2 shows an example of the analysis result of l. In this case, the position where the analysis value of Al was exactly the middle value between the fused quartz concentration and the synthetic quartz concentration was defined as the depth from the surface, that is, the thickness of the synthetic quartz layer.

Table 1 shows the measurement locations of the crucible and the thickness of the synthetic quartz glass layer at those locations in comparison with those measured by an optical microscope and those measured by chemical analysis. From this, it can be seen that in the crucible of the present invention in which oxygen-deficient quartz is present at the interface between the inner layer and the outer layer, the thickness of the inner synthetic quartz glass layer can be accurately measured without breaking the crucible.

[0023]

[Table 1]

[0024]

The quartz crucible of the present invention having a two-layer structure of synthetic quartz glass as the inner layer and fused silica glass as the outer layer breaks the crucible because the marker exists at the interface between the inner layer and the outer layer. The thickness of the inner layer portion can be easily known without any need. As a result, the quality of the product can be determined, the optimum inner layer thickness can be selected, and the use condition of the crucible free from impurity contamination can be set, so that an excellent silicon single crystal can be more rationally manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a two-layer quartz crucible manufactured in an example, in which (a) is a sectional shape and dimensions, and (b) is a diagram.
Indicates the enlargement of the wall section.

FIG. 2 is a diagram showing an example of a change in an analytical value of Al at a depth position in a cross-sectional direction from an inner surface of a quartz crucible wall having a two-layer structure.

[Explanation of symbols]

1 inner layer of quartz crucible 2 outer layer of quartz crucible 3 interface where oxygen-deficient quartz exists 4 transparent layer 5 opaque layer 6 black oxygen-deficient quartz grains

Continuation of the front page (72) Inventor Tadahisa Arahori 1-8 Fuso-cho, Amagasaki-shi, Hyogo Sumitomo Metal Industries, Ltd. Electronics Technology Research Laboratory F term (reference) 4G014 AH08 4G050 FD01 FD05 4G077 AA02 BA04 CF00 EG02

Claims (1)

[Claims] Synthetic quartz glass for the inner layer and fused silica glass for the outer layer
A quartz crucible for pulling a silicon single crystal, wherein the quartz crucible has a layered structure and oxygen-deficient quartz glass is present at an interface between an inner layer portion and an outer layer portion.