JPH11292695A - 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 bearing a crystalline film having each specific thickness and melting point on the surface inside the crucible at least coming into contact with silicon melt 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 a crystalline film 0.01-50 μm thick with the melting point higher than that (about 1,414 deg.C) of silicon and a crystal grain size of pref. 0.005-1 μm is borne on the surface inside the crucible, and it is preferable in terms of improving the adhesiveness of the crystalline film to the silica glass and high-temperature durability of the film that the composition of the crystalline film is a compound consisting of titanium and carbon and/or nitrogen and/or titanium and also the contents of elements other than titanium, carbon and nitrogen in the crystalline film is <=1 wt.%; the crystalline film may be either a film of a single composition or in the form of a multilayered film made by being laminated with a plurality of the film mentioned above. The above film can be produced by any of various techniques including vacuum vapor deposition, sputtering and ion plating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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, a single crystal pulling method called a so-called CZ method has been widely and industrially employed for producing a silicon single crystal. 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, which has 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 a quartz glass crucible for pulling a single crystal has also increased, and the diameter has changed 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 in a quartz crucible in which contamination is suppressed, the amount of erosion from the inner surface of the crucible to the melt increases, and crystallization of the quartz glass on the crucible surface is promoted. (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 rate of dissolution in the silicon melt is faster in the non-crystallized quartz glass than in the crystal phase of the crystallized quartz glass, and the inner surface of the quartz glass crucible that has been in contact with the silicon melt for a long time undergoes uneven dissolution. The surface roughness increases. Bubbles are present inside the quartz glass crucible and are released into the silicon melt as the quartz glass dissolves, which may increase the surface roughness. The portion where the unevenness of the surface becomes 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 adhesion between the coating film and the quartz glass surface is weak, the coating film is easy to peel off when setting the silicon to be dissolved, it is difficult to control the thickness and distribution of the coating film, However, there are drawbacks such as that the number of working steps is large and cost is increased, but a uniform crystallization effect cannot be obtained early.

[0006] There is a need for further improvements in controlling the generation and growth of the crystal phase of quartz glass on the inner surface of the crucible essentially and for uniformly generating the crystal phase in a short time.

[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 present inventors have found that a phase is uniformly formed, and that a crucible surface with a small change in surface roughness can be obtained even by long-term contact with a silicon melt, thereby completing the present invention.

According to the present invention, at least a thickness of 0.01 μm to 50 μm is provided on the inner surface of a quartz crucible in contact with a silicon melt.
And a melting point of the film is higher than a melting point of silicon. Further, the crystal grain size is 0.00
5 μm to 1 μm, the composition of which is a compound of titanium and carbon and / or nitrogen and / or titanium, wherein the content of elements other than titanium, carbon and nitrogen in the coating is 1% by weight or less. It is a quartz crucible having.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In order to pull up a silicon single crystal for a long time, it is important to control the total amount of the crystal phase of quartz glass formed on the inner surface of the crucible. Quartz glass is not inherently stable as a glass phase in a temperature range where a silicon single crystal is pulled up, and thermodynamically a cristobalite phase or a tridymite phase is 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. From the experiment of immersion of quartz glass of various surface states in silicon melt, nuclei of quartz glass crystal phase were generated on the surface of quartz glass immersed in the melt immediately after immersion, and then, in proportion to the immersion time. The crystal phase of the quartz glass formed on the surface of the quartz glass showed a size corresponding to the immersion time, and it was found that the quartz glass of the same composition had a constant crystal growth rate. this is,
After nucleation occurs on the quartz glass surface at one time, new nucleation does not occur, indicating that the mechanism is that the total amount of the crystal phase of 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. For example, the amount of crystal phase generation of quartz glass differs depending on the method of cleaning the inner surface of the crucible before dissolving the polycrystalline silicon. The usual cleaning includes a step of cleaning with a solution containing HF, and when this is brought into contact with, for example, tap water and naturally dried in a room (as a result, the inner surface of the crucible is contaminated). The crystal phase of quartz glass formed on the inner surface of a quartz glass crucible is significantly increased. This is a phenomenon that occurs because impurities remain attached to the inner surface of the crucible before use and serve as nuclei for generating a crystal phase of quartz glass. In the present invention, in order to consciously control and promote the nucleation, the inner surface of the crucible is coated.

When the surface of the quartz glass comes into contact with the silicon melt, mass transfer at this interface takes place vigorously, and a location where the change in interface energy is large may be a crystal nucleus generation location.
It is preferable that the crystal nucleus generation sites are uniformly distributed on the quartz glass surface and have a density as high as possible. When crystal growth occurs from these nuclei, the quartz glass surface is early covered with a crystal phase. In order to uniformly distribute the crystal nucleation sites at a high density, it is effective to apply a dense film having a small crystal grain size. Since the crystals in such a film have already grown from the nuclei on the substrate at the time of crystal grain growth, they can also become crystal nuclei when the quartz glass in contact with the silicon melt crystallizes. It is desirable that the crystal grains of the film be 1 μm or less for high-density distribution of generated nuclei. In addition, since the effect is not exhibited if the crystal grain is smaller than 0.005 μm, the crystal grain needs to be 0.005 μm to 1 μm.
In order to maintain fine crystal grains even when contacting the silicon melt,
At least, the film must have a higher melting point than silicon.

[0013] The quartz glass crucible for coating the inner surface is not particularly limited, and it may be made of natural quartz powder or synthetic quartz powder. Can be.

A sufficient effect is exhibited when the thickness of the film is 0.1 μm to 50 μm. If the thickness is less than 0.1 μm, the effect of forming a nucleus of a quartz glass crystal phase cannot be seen, and
If the thickness exceeds 0 μm, the effect is saturated, the cost of forming the film increases, and the internal stress of the film increases, making it difficult to secure adhesion. Further, the silicon melt and the film react with each other, and the film may be dissolved or melted down. The dissolved component changes the composition of the silicon melt and affects the properties of the silicon single crystal to be pulled. Thick films are not preferred.

[0015] As such a film, specifically, the composition of the film is a compound of titanium and carbon and / or nitrogen and / or
Alternatively, a film in which titanium is contained and the content of elements other than titanium, carbon and nitrogen in the film is 1% by weight or less is preferable because it has excellent adhesion to quartz glass and high durability at high temperatures. It may be a film having a single composition or a multilayer film in which a plurality of these films are laminated. Further, these are preferable because they are fine grains and are easily crystallized, and have a melting point of 2000 ° C. or higher, which is much higher than the melting point of silicon (about 1414 ° C.). These crystalline films can have a wide range of composition ratios of titanium, carbon, and nitrogen. For example, in the case of titanium nitride, the chemical formula is TiN, Ti ₂ N, Ti ₃ N
There is a crystal phase such as No. _4, and it can be a composite phase of these depending on the film forming conditions. Also, TiN is nitrogen 28 atm.
% To 60 atm% to form a crystalline phase in a wide range of compositions.

These films are relatively stable at the melt holding temperature during the operation of pulling the silicon single crystal, but when they are in contact with the silicon melt for a long time, all or a part of the film is dissolved in the melt. Therefore, it is necessary that the quality of the silicon single crystal is not affected, and it is desirable that impurities contained in the film be as small as possible. Therefore, the content of elements other than titanium, carbon and nitrogen is 1 w
It is preferably at most t%.

Such a quartz crucible for pulling a silicon single crystal has a crystalline film of 0.1 μm to 50 μm coated by PVD.
(Physical Vapor Deposition) method and the like can be manufactured by forming it on the inner surface of a quartz crucible. The PVD method is characterized in that a load due to temperature on a substrate such as thermal deformation is small, and a crystalline film composed of dense and fine grains can be formed, and as this PVD method suitable for forming a thin film on the inner surface of a quartz crucible, Specifically, various techniques such as vacuum deposition, sputtering, and ion plating are suitably used. In any case, the base material can be coated at a temperature of 500 ° C. or less and does not deform the quartz glass crucible due to heat. Quartz glass is 10
It is known that the viscosity increases at a high temperature of 00 ° C. or higher. Particularly, a heavy quartz glass is deformed by its own weight at a high temperature. Therefore, the surface treatment needs to be performed at a temperature as low as possible. In the above three methods, the film formation rate is 0.02 μm per minute.
About 0.2 μm, for example, 5 μm to obtain a film of 1 μm.
Minutes to 50 minutes are practical.

In vacuum deposition, titanium is melted under a vacuum using a heat source such as an electron beam to generate titanium vapor,
This is a method of depositing this on a substrate. The apparatus configuration is relatively simple, and the film formation cost is the lowest among the above three methods. Sputtering is a method in which a target is irradiated with a gas component such as ionized argon or the like, and a component beaten from the target is formed on a substrate. Since a film close to the composition of the target is obtained, it is advantageous for forming a composite film. Ion plating is a method in which a component ionized by plasma is reacted on a substrate to form a film. By applying a charge to the substrate, ions are attracted, and it is advantageous for forming a dense film, and the substrate temperature is low. High adhesion is obtained. In the ion plating method, it is easy to form a film composed of fine-grained crystals. For example, an arc discharge activated ion plating method, which is a kind of the ion plating method, is used. In a titanium nitride film having a thickness of 1 μm formed at a pressure of 05 Pa, the crystal grains become fine particles of about 0.01 μm. As described above, a film formation method can be selected according to the characteristics of a target film.

The part covered by PVD is not necessarily
It is not necessary to cover the entire inner surface of the quartz glass crucible. In particular, there is a portion near the opening of the quartz crucible that does not come into contact with the silicon melt, and it is not necessary to cover this portion. In order to efficiently dissolve the silicon raw material in the crucible, it may be better to not apply the above-mentioned coating on the portion that does not come into contact with the silicon melt, in some cases. If the coating prevents heat radiation from the heater outside the quartz crucible, it is preferable not to cover the vicinity of the opening. Such a quartz crucible can be easily manufactured by masking a portion not to be covered with, for example, a stainless steel plate or an aluminum wheel and applying the PVD coating described above.

[0020]

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, L
i, Mg, Mn, the content of each element of Ti is 0.0
At 1 wt% or less, the OH concentration was 50 ppm.

Then, for the inner surface of the crucible,
Various treatments as shown in Table 1 were performed. Here, as a method of cleaning the inner surface of the crucible before use, cleaning with a 5% hydrofluoric acid solution and pure water was appropriately combined. Each coating was formed on the lower half including the bottom of the quartz glass crucible, and the portion corresponding to half the crucible height including the opening was not treated. When the polycrystalline silicon was melted, the amount of the polycrystalline silicon used was about の of the crucible height from the bottom of the quartz glass crucible.

The preparation of a film of each composition on the inner surface of the crucible is as follows:
The cleaned crucible was set in a vacuum chamber and subjected to various PVD methods. Ion plating is
This was performed using an arc discharge activated ion plating apparatus. This is an apparatus used for coating tools and blades (Journal of the Japan Institute of Metals, Vol. 58, p. 6).
42, 1994). TiN, Ti
In the case of forming a C, Ti-CN film, metallic titanium was dissolved and evaporated by an electron beam, then ionized, and nitrogen and acetylene gas were introduced as a reaction gas as needed. A current of 50 A was obtained at a voltage of 40 V at the ionization electrode. The output of the electron beam was 2 kW. The pressure during film formation was 4 × 10 ⁻⁴ Torr. The inside of the quartz crucible was kept at 200 ° C. or lower to form a film.

In sputtering, a film was formed by introducing an argon gas and using the same material as the film composition to be formed as a target. The inside of the quartz crucible is 50 ° C to 100 ° C
To form a film.

The vacuum deposition was performed using the same apparatus as the above-mentioned ion plating film formation, without performing ionization.

In the thermal spraying, plasma spraying was performed using WC powder and argon gas as a carrier gas.

If necessary, an argon gas was introduced before film formation, and ion cleaning was performed at 0.2 Torr and 500 V for 5 minutes.

These crucibles were filled with granular polycrystalline silicon, and were heated and melted. The time-dependent changes in the crystal phase of spotted quartz glass formed on the inner surface of the quartz glass crucible were examined. The crystal phase of quartz glass had a larger diameter in proportion to the contact time with the melt.

Table 1 shows the results of analyzing the state of formation of the crystal phase of quartz glass 4 hours and 10 hours after the contact of the silicon melt with the crucible inner surface. Here, the area occupancy is the ratio of crystal (cristobalite) occupying 1 cm ² of quartz glass surface, 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. After use, the inner surface roughness Ra and the area occupancy of the crucible were analyzed after contacting with the silicon melt, pulling the silicon single crystal after a certain period of time, and cooling the portion that no longer contacted the silicon melt. is there. The surface roughness and film thickness are measured by a contact type surface roughness meter DEKTAK303.
0 was used. The melting point was investigated by peeling and pulverizing the film and analyzing the peak of the DTA apparatus. At temperatures up to 1600 ° C, no peaks due to melting were observed.
When the sample after the test is not dissolved, the melting point is 1600.
° C or higher. The determination of crystalline or amorphous was made amorphous when peak intensity was not obtained by X-ray diffraction or electron beam diffraction. The crystal grain size was determined by observing the coating with a transmission electron microscope and measuring the average grain size.

As shown in Table 1, in the crucible having the coating according to the embodiment of the present invention, the area occupation ratio of the crystal phase of the formed quartz glass exceeds 90% after 4 hours, and the crystal phase is quickly formed. It can be seen that they are formed. Also, the change of the roughness of the crucible inner surface with time is smaller than that of the comparative example.
This is because the crystal phase is formed early on the crucible surface and maintains a uniform dissolution rate even if it is in contact with the silicon melt for a long time.
It is considered that the change in the surface roughness was reduced.

Further, since the same synthetic quartz powder is used as the raw material for the quartz glass, the diameter of the crystal phase of the quartz glass does not differ between the embodiment and the comparative example, and is 0.66 to 0.69 m.
m, from which the crystal growth rate of the crystal phase of quartz glass was estimated to be 150 to 200 μm / hr. In the crucible of the present invention, since nucleation is remarkably promoted, the change in surface roughness is reduced to about 10 times as compared with the conventional crucible of the comparative example due to the uniform solubility of the crystal phase of the formed quartz glass. The use time of the crucible was found to be at least several times longer.

Also, by using these crucibles, 8
When the silicon single crystal having an inch diameter was pulled, in the crucible of the example, no detachment of the crystal phase of quartz glass from the crucible was observed until the pulling of the silicon single crystal was completed, and all were pulled as good single crystal ingots. Was done. However, in the crucible of the comparative example, partial detachment of the quartz glass crystal phase was observed during the pulling operation, and the detached quartz glass crystal phase floated on the melt and adhered to the silicon single crystal. As a result, polycrystallization occurred, and some of them were not pulled as good silicon single crystals.

[0032]

[Table 1]

[0033]

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 (4)

[Claims] 1. A silicon single crystal having a crystalline film having a thickness of 0.01 μm to 50 μm on at least an inner surface of a quartz crucible in contact with a silicon melt, and having a melting point higher than that of silicon. Quartz crucible for lifting. 2. The crystalline coating has a crystal grain size of 0.005 μm.
The quartz crucible according to claim 1, which has a thickness of from 1 to 1 µm. 3. The composition of a crystalline film, wherein titanium and carbon and / or
3. The quartz crucible according to claim 1, wherein the quartz crucible is a compound of nitrogen and / or titanium. 4. The quartz crucible according to claim 3, wherein the content of elements other than titanium, carbon and nitrogen in the crystalline film is 1% by weight or less.