JPH11292694A - Quartz crucible for pulling up silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the subject quartz crucible intended for standing its use for a long time by setting the surface roughness inside the crucible at least coming into contact with silicon melt within a specific range so as to uniformly produce silica glass crystal phase on the inside surface in a short time. SOLUTION: This quartz crucible is so designed that the arithmetically mean roughness (Ra) of the surface inside the crucible satisfies the relationship: 0.02 μm<=Ra<=20.0 μm; preferably, the maximum roughness (Rmax) and the minimum roughness (Rmin) satisfy the relationship: Rmax/Rmin<=10; that is, the surface inside the crucible is made uneven to afford the nucleus-forming sites for silica glass crystal phase intentionally uniformly and also in high density so as to ensure the surface to be entirely covered in a short time with silica glass crystal phase (e.g. cristobalite phase) forming on the surface on contacting it with sinicon melt; therefore, even if the crucible is used for a ling time, the surface uniformly dissolves in the silicon melt, and the resulting silicon single crystal is free from surface roughness with slight section debonding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz glass crucible used for pulling a silicon single crystal by the Czochralski method (hereinafter referred to as CZ method).

[0002]

2. Description of the Related Art Conventionally, in the production of silicon single crystals, a single crystal pulling method called a so-called CZ method has been widely and industrially employed. In this method, polycrystalline silicon is heated and melted in a container, and the end of the seed crystal is immersed in the molten bath and pulled up while rotating. A single crystal having the same crystal orientation grows on the seed crystal. . A quartz glass crucible is generally used for the single crystal pulling container.
A quartz glass crucible containing polycrystalline silicon is heated for a long time to a temperature higher than the melting point of silicon (about 1414 ° C) and is exposed to a silicon melt. Therefore, the inner surface of the crucible gradually undergoes a chemical reaction with the molten silicon at a high temperature. Wake up. As a result, when a crucible is used for a long time, erosion or devitrification (crystallization) occurs,
This will have a significant effect on the production of silicon single crystals. In particular, if a large amount of impurities are mixed in the quartz glass crucible, this is taken into the silicon melt and causes impurity contamination of the silicon single crystal, or the impurities promote the crystallization of the quartz glass and cause the quartz glass to devitrify. This causes deterioration of the characteristics of the glass crucible. For this reason, quartz glass crucibles are manufactured using high-purity quartz powder as a raw material. Currently, natural quartz powder is mainly used as the quartz powder for crucibles, but synthetic quartz powder having a purity higher than that of natural quartz is used, and great care has been taken to mix impurities. .

In recent years, as the diameter of silicon wafers has increased, the diameter of quartz glass crucibles for pulling single crystals has also increased, and the diameter has increased from 18 inches (457.2 mm) to 22 inches.
~ 24 inches (558.8-609.6mm)
There is also a demand for large diameter crucibles. The quartz crucible inner surface has a function of holding the melt and transmitting heat from a carbon heater provided outside the crucible to the silicon melt. As the diameter of the quartz crucible increases, the amount of dissolved silicon also increases, and the heat load from the heater to the crucible inner wall increases. Furthermore, since a single crystal is pulled while holding a large amount of melt, the contact time between the melt and the crucible inner surface is prolonged. For this reason,
Even with a quartz crucible with reduced impurity contamination, the amount of erosion from the inner surface of the crucible into the melt increases, the crystallization of the quartz glass on the crucible surface is promoted, and the crystal phase of the spotted quartz glass on the inner surface of the crucible is increased. (Cristobalite or tridymite) is easily formed and grown. The location where the crystal phase of quartz glass is generated is not always constant, and is often concentrated at a specific location or uneven. The dissolution rate in silicon melt is higher for quartz glass that is not crystallized.
The inner surface of the quartz glass crucible, which is faster than the crystal phase of the quartz glass and has been in contact with the silicon melt for a long time, undergoes non-uniform melting, and the surface roughness increases. In some cases, bubbles are present inside the quartz glass crucible and are released into the silicon melt as the quartz glass dissolves, thereby increasing the surface roughness. The portion where the surface irregularities are locally large in this way is easily detached from the crucible surface, and the detached section floats in the melt. This attaches to the single crystal to be pulled, causing serious quality defects such as polycrystallization, and greatly hinders the productivity of the silicon single crystal. In other words, long-term use of a large-diameter quartz crucible becomes difficult, which has led to an increase in silicon single crystal production costs.

[0004] In order to solve such a problem, methods for lowering the OH concentration or alkali concentration in the quartz glass to make the quartz glass highly purified and difficult to crystallize are disclosed in JP-A-3-208880, JP-A-8-133719, and JP-A-8-133719. 5-301731
It is proposed in Japanese Patent Publication No. However, even if the content of impurities in the quartz glass crucible is reduced, the crystallization of the quartz glass is slightly suppressed because the quartz glass crucible is used for a long time at a temperature equal to or higher than the melting point of silicon. Roughening of the inner surface of quartz glass due to crystallization and melting was inevitable.

On the other hand, a method of applying or solid-solving a Group 2a element or a Group 3b element such as magnesium, strontium, calcium, barium, or aluminum on the inner surface of a quartz glass crucible to form a quartz glass crystal layer easily is particularly featured. It has been proposed in Japanese Unexamined Patent Publication No. Hei 8-2932, Japanese Unexamined Patent Publication No. Hei 9-110590 and the like. However, the main effect is to lower the crystallization temperature of quartz glass, or to increase the crystal growth rate, and when the inner surface of quartz glass is poor in cleanliness, for example, when there are many things that should be the cores of crystal growth. Can be expected to produce a crystal layer on the glass surface, but when cleaning is rapid and there are few nuclei to be formed, the crystallization promoting effect cannot be expected much. Furthermore, the adhesion between the coating film and the quartz glass surface is usually weak, and the coating film is easy to peel off when setting the silicon to be dissolved, and it is difficult to control the thickness and distribution of the coating film. However, there are drawbacks such as that the number of work steps is large and the cost is increased.

[0006] There is a need for further improvements to essentially control the formation and growth of the quartz glass crystal phase on the inner surface of the crucible so that the crystal layer is formed uniformly and uniformly.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems in the conventional quartz glass crucible, and forms a quartz glass crystal phase uniformly on the inner surface of the quartz glass crucible in a short time. It is an object of the present invention to provide a quartz glass crucible that can withstand use.

[0008]

Means for Solving the Problems The present inventors have made extensive studies and conducted extensive studies, and as a result, have found that the nucleation density of the crystal phase of quartz glass can be remarkably increased so that quartz crystal The inventors have found that a uniform crucible surface can be obtained even by long-term contact with a silicon melt, thereby completing the present invention.

According to the present invention, the arithmetic mean roughness (Ra) is measured at least on the inner surface of a quartz crucible in contact with a silicon melt.
Is a quartz crucible characterized by satisfying a relationship of 0.02 μm ≦ Ra ≦ 20.0 μm. Further, the maximum roughness (Rmax) and the minimum roughness (Rmin) are Rmax / Rm.
It is desirable to have a surface roughness that satisfies the relationship of in ≦ 10.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In order to pull a silicon single crystal for a long time, it is important to keep the melting of the inner surface of the quartz glass crucible by contact with the molten silicon and to keep the inner surface of the quartz glass crucible uniform. However, quartz glass is not inherently stable as a glass phase in a temperature range in which a silicon single crystal is pulled, and a cristobalite phase or a tridymite phase is thermodynamically stable. Therefore, even if there is no impurity in the quartz glass, crystallization of the quartz glass surface is essentially unavoidable. Crystallization of quartz glass is more likely to occur at the interface with the melt where interfacial energy is greater and material diffusion is more frequent than inside the glass.

The crystal phase of quartz glass is formed in spots on the surface of quartz glass, and its formation can be considered as nucleation and crystal growth. That is, the number of spots on the quartz glass surface corresponds to the amount of nuclei generated, and the change in the size of the spots corresponds to the nucleus growth rate. Then, from the immersion experiment of quartz glass of various surface states in silicon melt, nuclei of the quartz glass crystal phase were generated on the surface of quartz glass immersed in the melt before or just after immersion, It grows in proportion to the immersion time, and the spots of the crystal phase of quartz glass formed on the quartz glass surface show the size according to the immersion time, and it is clear from the fact that the crystal growth rate is constant with quartz glass of the same composition did. This indicates that after nucleation occurs on the quartz glass surface at one time, new nucleation does not occur, and the total amount of the crystal phase of the quartz glass increases only by crystal growth. The nucleation of the crystal phase of the quartz glass is greatly affected by the surface state of the quartz glass. That is, by controlling the amount of nuclei generated on the quartz glass surface, the total amount of the quartz glass crystal phase formed in the crucible during the single crystal pulling operation can be increased or decreased.

The nucleation of the crystal phase of quartz glass is likely to occur at a portion where the surface energy or interface energy on the quartz glass surface changes greatly. Specifically, it is a portion where impurity particles are adsorbed or a portion having a structural defect. In order to consciously make this change in surface energy, it is effective and simple to provide uniform and fine irregularities on the surface.

According to the present invention, the inner surface of a quartz glass crucible is made uneven and the density of nucleation sites of the crystal phase of the quartz glass is intentionally made uniform and at a high density. A silicon single crystal in which the crystal phase of the quartz glass to be formed covers the surface in a short time, and even when used for a long time, there is no surface roughness due to the difference in the dissolution rate of the quartz glass crucible surface in silicon, and there is little peeling of slices. It is a quartz crucible for lifting.

The rough surface of the rough surface for promoting the nucleation must have an arithmetic mean roughness of 0.02 to 20.0 μm. Preferably, 0.04 to 0.1 μm
The surface roughness is controlled so as to fall within the range described above. The arithmetic average roughness is expressed as Ra and is known as a parameter representing the surface roughness of various industrial products. The definition and indication are described in detail in JIS B-0601.
International standards include ISO468, ISO3274, IS
O 4287, ISO 4288, etc. R
a is extracted from the roughness curve by the reference length in the direction of the average line, the X axis is taken in the direction of the average line of the extracted portion, the Y axis is taken in the direction of the vertical magnification, and the roughness curve is taken with respect to the center line. The integrated value is expressed in micrometers (μm). For the measurement of the surface roughness, a non-contact method using light, laser, or the like, or a contact method in which measurement is performed by bringing the surface of the sample into contact with a needle using a stable material such as diamond are known.

The inner surface of a conventional quartz glass crucible is a smooth surface having an arithmetic average roughness of about 0.002 to 0.01 μmRa. This is to supply silica powder into a rotating mold to form a silica powder filling layer, which is melted and solid-dissolved by arc heating with atmosphere control to form a crucible inner surface, which is inevitably smooth, The surface roughness cannot be controlled by this method alone. Here, a surface having a surface that is intentionally roughened is referred to as a rough surface. If the arithmetic mean roughness of the rough surface is less than 0.02 μm, the effect of promoting nucleation is small, and if it is more than 20.0 μm, the uniformity of nucleation is impaired, and in each case, a crystal phase is formed unevenly on the quartz glass surface. This causes uneven dissolution of the crucible.

It is necessary that the roughness of the rough surface does not greatly differ within the same crucible. This is important for forming a uniform quartz glass crystal phase in the same crucible, since the nucleation density of the quartz glass crystal phase is affected by surface irregularities. Therefore, it is desirable that the ratio of the maximum value to the minimum value of the roughness of the rough surface is 10 or less. If the ratio exceeds 10, the crystal phase formed in the portion having a large roughness tends to be easily separated, which is not preferable.

The rough surface may be applied only to a portion of the crucible that is desired to be crystallized uniformly, but at least a portion in contact with the silicon melt is rough. In particular, since the bottom inner surface of the crucible always comes into contact with the silicon melt and the contact time is longer than that of the inner surface in another crucible, the bottom inner surface needs to be roughened. In a portion close to the opening of the quartz crucible and not in contact with the silicon melt, it is not necessary to make the surface uneven, and the surface may not be roughened if extra processing cost and labor are required.

In such a quartz crucible for pulling a silicon single crystal, particles or materials having a surface hardness higher than that of quartz glass are brought into contact with the quartz crucible inner surface with a constant stress to make the quartz crucible inner surface uneven. Can be manufactured. At this time, by using hard particles having a particle size of 0.01 μm to 40 μm, Ra of the quartz crucible is set to 0.02 μm to 2 μm.
A 0.0 μm rough surface is obtained. Alternatively, a hard material having an arithmetic average roughness of 0.01 μm to 40 μm may be used. The formation of the rough surface needs to be performed with a constant stress so that the variation of the arithmetic average roughness within a single crucible satisfies Rmax / Rmin ≦ 10. For this purpose, for example, sandpaper is used. A belt sander or a grinding wheel using an electric motor is preferable to a method of roughening the surface by hand using the method. The formation of the rough surface may be performed in a dry atmosphere or in a solution. Further, in a solution which chemically reacts with quartz glass, the hard particles and the hard material may be brought into contact with each other to make the surface uneven by utilizing a chemical mechanical polishing action.

As a material having a higher surface hardness than quartz glass, carbides, nitrides, carbonitrides of silicon and titanium, alumina, diamond, boron nitride, high-purity quartz, and the like can be used industrially. These can be simple or particulate
It may be in a coated state. In addition, as a method of mechanically forming irregularities, for example, a grinding machine can be installed in a quartz crucible, the quartz crucible can be rotated, and a grinding tool made of a material having a higher surface hardness than the quartz glass can be used.
Alternatively, a method is also possible in which the hard particles are sprayed together with a high-pressure gas onto the inner surface of the quartz glass crucible to make the surface uneven. It is also possible to disperse the hard particles in a solution and use an ultrasonic cleaner to cause the particles to collide with the inner surface of the quartz glass crucible to form irregularities.

In the method of roughening the inner surface of the crucible, when the hard material or a part thereof adheres to the inner surface of the quartz crucible, it is necessary to take care that the adhered material does not adversely affect the pulling of the silicon single crystal. is there. For example, if silicon carbide adheres and dissolves in the silicon melt during the pulling, raises the carbon concentration in the silicon single crystal and degrades the quality, reduce the amount of adhesion and perform cleaning. In addition, it is necessary to devise processes and materials to be used, such as using other hard materials. Conversely, there is no effect on the quality of the silicon single crystal, and when the nucleation or growth of cristobalite is promoted by the deposit, the deposit may be actively used. In the case where the surface is made uneven by using a chemical action, it is effective to use a solution that chemically reacts with quartz glass and dissolves or erodes. As such a solution, a solution containing hydrofluoric acid is suitable. The concentration and temperature of hydrofluoric acid are determined according to the surface roughness and the processing time. In this solution, the hard substance is included,
The surface may be made uneven by using both chemical and mechanical actions.

[0021]

EXAMPLES Examples of the present invention and comparative examples are shown below.
The quartz glass crucible used was a crucible having a diameter of 558.8 mm manufactured from high-purity synthetic quartz powder, and the composition of the quartz glass on the inner surface of the crucible was Al, Ca, Cu, Fe in a thickness range of 200 μm from the surface. , Na, K,
The content of each element of Li, Mg, Mn, and Ti is 0.1.
At less than 01 wt%, the OH concentration was 50 ppm. Surface roughness of crucible inner surface is 0.003-0.007μ
mRa range. In Comparative Examples in Table 1, the surface roughness before use of a crucible that has not been roughened is shown in parentheses.

Then, with respect to the inner surface of the crucible,
Various rough surface treatments as shown in Table 1 were performed. The range of the rough surface processing is a portion in contact with the silicon melt in the case of the grinding wheel and the ultrasonic treatment, and is the entire inner surface of the crucible in the case of the blast treatment. As a method of cleaning the inner surface of the crucible before and after the treatment, cleaning with a 5% hydrofluoric acid solution and pure water was appropriately combined. In the treatment with the grinding wheel, the crucible was rotated, the grinding wheel was put in the crucible, and ground with a # 1000 grinding wheel to form a rough surface. In the ultrasonic treatment, 1 g of a 1% HF solution contained 100 g of diamond particles having a diameter of 1 μm to 30 μm and was subjected to ultrasonic waves. Blasting is a method in which silicon carbide powder is sprayed at high pressure from a nozzle together with argon gas.

These crucibles were filled with granular polycrystalline silicon and heated and melted, and the temporal change of the crystal phase (spotted cristobalite) of the quartz glass formed on the inner surface of the quartz glass crucible was examined. Cristobalite had a larger diameter in proportion to the contact time with the melt.

Table 1 shows the results of analysis of the cristobalite formation state 4 hours and 10 hours after the silicon melt came into contact with the crucible inner surface. As the number of nuclei of the generated crystals, cristobalite spots intersect as crystallization progresses, and accurate measurement is not always possible. Therefore, the area occupancy was compared here. As the amount of generated nuclei increases, the area occupancy also increases. Here, the area occupancy is 1 cm ²
Is the ratio of crystals (cristobalite) occupying the surface of quartz glass, and can be compared by observing and analyzing with an optical microscope. The crystallized portion has a brown to white color, and can be easily distinguished by light reflection under an optical microscope.
The evaluation of the inner surface Ra and the area occupancy of the crucible after use is based on the analysis of a portion that has come into contact with the silicon melt, pulled out of the silicon single crystal after a certain period of time, and no longer contacts the silicon melt, and cooled. is there.

As shown in Table 1, in the crucible having an arithmetic average roughness of 0.02 to 20.0 μm Ra, which is an embodiment of the present invention, the formed cristobalite has
The area occupancy after time was 90% or more in each case, and it can be seen that nucleation was significantly promoted as compared with the comparative example. For this reason, in the crucible whose inner surface has been covered with cristobalite at an early stage, the change in the surface roughness Ra value after 10 hours is small, and uneven melting does not occur even when the crucible is in contact with the silicon melt for a long time. It is shown that. The surface roughness of the inner surface of the quartz crucible that is in contact with the silicon melt is currently difficult to measure directly during use, but the silicon single crystal is pulled up and the part that no longer contacts the silicon melt is reduced. By observing and comparing after cooling, the effect of the present invention can be confirmed as described above.

Further, since the same synthetic quartz powder is used as a raw material for the quartz glass, the diameter of cristobalite does not differ between the examples and the comparative examples, and the crystal growth rate of cristobalite is estimated to be 150 to 200 μm / hr. I got it. Since nucleation is promoted in the crucible of the present invention,
The total amount of formed cristobalite (the area occupation ratio of the generated crystal) increases to about 2 to 3 times in a short time as compared with the conventional crucible of the comparative example, so that the change in surface roughness is extremely small. became.

Further, by using these crucibles, 8
When the silicon single crystal having an inch diameter was pulled, in the crucible of the example, desorption of cristobalite from the crucible was not observed until the pulling of the silicon single crystal was completed, and all were pulled as good single crystal ingots. However, in the crucible of the comparative example, partial detachment of cristobalite was observed during the pulling operation, and the detached cristobalite floated on the melt and adhered to the silicon single crystal, causing polycrystallization. Of these, those which were not pulled up as good silicon single crystals frequently occurred.

[0028]

[Table 1]

[0029]

According to the present invention, the formation of a crystal phase of quartz glass by contact with a silicon melt is promoted, and the uniform melting of the inner surface of the crucible allows the silicon to withstand a longer use than conventional crucibles. A quartz crucible for pulling a single crystal can be provided. As a result, a large-diameter long silicon single crystal that requires a long time to be pulled can be pulled with good yield, and has an industrially advantageous effect that a silicon single crystal can be manufactured at a lower manufacturing cost than before. .

Claims (2)

[Claims] 1. A quartz crucible for pulling a silicon single crystal, wherein at least an inner surface of the quartz crucible in contact with the silicon melt has a surface roughness whose arithmetic average roughness (Ra) satisfies the following relationship. 0.02 μm ≦ Ra ≦ 20.0 μm 2. The method according to claim 1, wherein at least the inner surface of the quartz crucible in contact with the silicon melt has a surface roughness whose maximum roughness (Rmax) and minimum roughness (Rmin) satisfy the following relationship. The described quartz crucible for pulling a silicon single crystal. Rmax / Rmin ≦ 10