JPH11199370A - Quartz glass crucible and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a quartz glass crucible capable of suppressing local corrosion and crystallization of an inner surface, and impurity contamination of a silicon molten liquid, and ensiling the corrective action against deterioration of the surface of the crucible, and overcoming of inconvenience of treatment by forming the inner surface of a crucible wall out of a transparent quartz glass layer covering a layer containing a crystallization improver. SOLUTION: A metal ion (e.g. an alkali ion) is used as a crystallization improver. The concentration to be used is over 0 ppm but not over 500 ppm (e.g. 50 ppm). The thickness of a transparent quartz glass layer is over 0 mm and not over 1 mm (e.t. 6-800 μm). A layer containing the crystallization improver is rapidly crystallized before the pulling-up of the single crystal when a polycrystal silicon is melted at a high temperature of >=1,400 deg.C because of the double layered structure of the inner surface of the crucible. When the single crystal is pulled up thereafter, the transparent quartz glass layer is slowly crystallized on the surface layer side by using such crystallized layer as a nuclear and as a result, the whole surface of the crucible is in a state covered with the crystal.

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 for melting silicon used in pulling a silicon single crystal and a method for producing the same, and more particularly to a crucible structure capable of pulling a high-purity single crystal for a long time.

[0002]

2. Description of the Related Art In recent semiconductor manufacturing technology, it is required to grow a large-diameter silicon single crystal by a pulling method. A quartz glass crucible used to generate and hold a silicon melt during the crystal growth process is required. In addition, the diameter required for the lifting process tends to be longer in accordance with the increase in diameter.

When a silicon single crystal is pulled over a long time using a large-diameter crucible as described above, the heat load applied to the crucible wall surface and the weight of the silicon melt itself increase. As a result, the inner surface of the crucible subjected to a large heat load while holding the increased silicon melt is susceptible to corrosion due to the reaction with the melt and local crystallization proceeds. The portion crystallized in this way is more likely to peel off than the other portions. Once released for some reason and released into the melt, it moves in the melt and adheres to the solid-liquid interface between the single crystal. Here, the adhered portion forms nuclei to induce polycrystallization, which is one of the factors inhibiting single crystal formation.

In order to increase the diameter of a silicon single crystal, it is necessary to suppress crystallization on the inner surface of the crucible, which is considered to be a factor that causes the deterioration of the inner surface of the crucible and a decrease in the rate of single crystallization. Therefore, as a countermeasure, there is known a method in which a crystallization accelerator is applied to the inner surface of the crucible in advance, and the crystallization accelerator is nucleated at the time of use to crystallize the entire inner surface of the crucible early. I have.

[0005]

In the above-mentioned method using a crystallization accelerator of the prior art, a high concentration of impurities is contained in the crucible wall as the crystallization accelerator. If such impurities dissolve into the silicon melt along with the melting of the crucible wall during the growth of the single crystal, the impurities contaminate the single crystal generated from the melt and deteriorate the silicon characteristics (lifetime, etc.). There's a problem. In addition, when a special layer such as a coating layer is formed on the crucible surface, problems such as peeling and scratching are generally likely to occur, and special handling is often required during use. Occasionally, a new problem such as surface roughness may occur, resulting in a result opposite to the original purpose.

Therefore, according to the present invention, a quartz crucible for pulling a silicon single crystal having a large diameter and a long life is embodied, so that the inner surface of the crucible is locally corroded and crystallized, and impurities from the inner surface of the crucible to the silicon melt are melted. An object of the present invention is to suppress contamination, and to prevent deterioration of crucible surface and inconvenience of handling.

[0007]

As a result of repeated studies to achieve the above object, the outer surface of the layer containing the crystallization accelerator is covered with a transparent quartz glass layer containing no foreign matter, and the transparent quartz glass layer The present inventor has found for the first time a fact that, when the inner surface of the crucible wall is constituted by the outer surface, the original role of the crystallization accelerator for crystallizing the inner surface of the crucible is effectively utilized.

That is, a quartz glass crucible according to the present invention includes a layer containing a crystallization accelerator and a transparent quartz glass layer covering the layer containing the crystallization accelerator, and the transparent quartz glass layer is used to form an inner surface of the crucible wall. Is constituted.

According to such a two-layer structure on the inner surface of the crucible, when the polycrystalline silicon is melted at a high temperature of 1400 ° C. or more before the single crystal is pulled, the layer containing the crystallization accelerator is rapidly crystallized. . At the start of the subsequent pulling of the single crystal, the transparent quartz glass layer on the surface layer slowly crystallizes with the crystallized layer as a nucleus, and as a result, the entire inner surface of the crucible is effectively covered with crystals. become.

Therefore, local corrosion on the surface layer of the crucible can be suppressed by the crystal layer covering almost the entire inner surface of the crucible, thereby extending the life of the crucible. Further, since the crystal grown on the inner surface of the crucible does not contain impurities, contamination of silicon can be prevented. Further, since the transparent quartz glass is used, labor required for countermeasures for deterioration and handling on the inner surface of the crucible is greatly reduced as compared with the conventional case.

According to the present invention, the crystal growing from the layer containing the crystallization accelerator is formed on the outer surface of the transparent quartz glass layer, ie, in the crucible, in order to most effectively exert the effect of the double structure on the inner surface of the crucible. It is desirable that the time to reach the surface position be when the crucible is used, that is, before starting the pulling of the silicon single crystal.

Therefore, it is desirable to set the thickness of the transparent quartz glass layer in consideration of such crystal growth conditions on the inner surface of the crucible. The crystal growth rate in this case varies depending on conditions such as the heat history when using the crucible and the type of nucleating material used as a crystallization accelerator. For example, when the concentration of the crystallization accelerator is set to 50 ppm and Na ion is used as the type, the growth rate of the crystal (cristobalite) is 1 to 1 under the condition that the temperature is maintained at 1500 ° C.
2 μm / min. Under the same conditions, the type of the crystallization accelerator was changed to Ba.
When ionized, the crystal growth rate is 0.1 to 0.0
It is 1 μm / min. Here, when the maintenance temperature is raised or lowered by 50 ° C. from 1500 ° C., the crystal growth rate is approximately doubled or halved. Other conditions were changed to produce a prototype crucible, and experiments were conducted to pull up a silicon crystal using the prototype crucible.As a result of accumulating data, the thickness of the transparent glass layer was required to fully demonstrate the effects of the present invention. It was found that “more than 0 mm and 1 mm or less” is desirable.

Since the concentration of the crystallization accelerator is also an important factor for the crystal growth conditions on the inner surface of the crucible similarly to the above, it is necessary to set the concentration within a predetermined range in order to sufficiently exert the effect of the present invention. desirable. For example, the higher the concentration of the crystallization accelerator, the faster the crystals are formed, but if the concentration exceeds a certain level, the viscosity of the glass is reduced so as to adversely affect the actual use, or the desired crucible structure is formed. Crystal precipitation occurs more than necessary in the process, and the desired characteristics may not be obtained. Therefore, the results of experiments were confirmed, and it was found that the concentration of the crystallization promoter was desirably "more than 0 ppm and not more than 500 ppm" for practical use.

As a method for forming the structure of the quartz glass crucible according to the present invention, a voltage application method is desirable as one of extremely effective examples. This voltage application method preferably employs the following four steps (1) to (4).

(1): A crucible made of quartz glass is prepared by a predetermined method. As an example of the crucible forming method, there is a method in which a rotating crucible is filled with silica powder and melted by a heat source such as an arc to form the crucible. In this method, when pulling a single crystal using the obtained crucible, a large number of bubbles are often contained in the vicinity of the outer surface of the crucible so that the distribution of radiant heat to the silicon raw material becomes uniform. In any case, in the present invention, the method of forming the crucible itself is not particularly limited, and it goes without saying that other methods may be used.

(2): A layer containing a crystallization promoter, that is, a crystal nucleating material, is formed on the inner surface of the obtained quartz glass crucible. Examples of the crystallization promoter include metal ions (crystallization promotion ions). When this metal ion is used, for example, a compound of the corresponding metal or a paste containing the compound is applied to the inner surface of the crucible, and the temperature is increased to diffuse the ions into the glass. A metal ion-containing layer is formed on the inner surface of the crucible by a washing method. Other forming methods include, for example, a method in which a crucible is exposed to an air stream containing crystallization-promoting ions and adheres to the surface, or a method in which crystallization-promoting ions are previously contained in an electrode material and transferred when a voltage is applied. Methods and the like can be mentioned.

(3) A DC voltage is applied in the thickness direction of the crucible so that the inside becomes (-), thereby moving metal ions into the crucible. At this time, the temperature of the crucible is increased so that the movement of ions is facilitated. When this voltage is applied, it is desirable to use a noble metal such as graphite or platinum that does not react with the crucible as an electrode material.
A buffer such as silica powder or graphite powder may be inserted between the electrode and the crucible. As a condition of the applied voltage method, it was confirmed by experiments that the most desirable crucible structure was obtained when the temperature was 600 ° C. or more and the applied voltage was 100 V / cm or more (Experiment No. 1 in Table 1 described later).
-No. 9). According to this method, in the vicinity of the entire inner peripheral wall of the crucible, the metal ions can be interposed in a substantially uniform distribution, and the crystallization of the transparent quartz glass layer can be uniformly promoted throughout the entire inner peripheral wall of the crucible. .

(4): Thereafter, the crucible is cooled and the electrode is removed. When this method is used, it is necessary to use a metal ion nucleating material that can move when a voltage is applied as a crystallization accelerator. This metal ion contains Na.
An alkali metal ion such as K or an alkaline earth metal ion such as Mg.Ca.Ba is suitable.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a quartz glass crucible and a method of manufacturing the same according to the present invention will be specifically described.

(First Embodiment) In this embodiment, K ion which is an alkali metal ion is used as a crystallization accelerator. A 5% ethanol solution of potassium nitrate as the crystallization promoting ion material and a quartz glass crucible having a diameter of 18 inches are prepared in advance. The quartz glass crucible was obtained by filling a silica crucible in a mold of a rotating crucible and melting it using an arc heat source.

A 5% ethanol solution of potassium nitrate was applied to the inner surface of the quartz glass crucible, and the solution was dried. Thereafter, the crucible was heated to 400 ° C. and kept at that temperature for 1 hour. The crucible was cooled, and the adhered substance was removed by washing the inner surface with hydrochloric acid.

[0022] Carbon powder as a pair of electrode materials is brought into contact with the inside and outside facing each other with the crucible therebetween,
Heating was performed in a nitrogen atmosphere while applying a voltage in a state where the electrode disposed inside the crucible wall was a positive electrode and the electrode disposed outside was a negative electrode. Table 1 shows a basic experiment example of the voltage application.

[0023]

[Table 1]

In the basic experiment of voltage application shown in Table 1, the experiment No. 1 to No. The temperature is 600 ° C as represented by 9.
The crucible is processed under the conditions of 1300 ° C., the applied voltage of 0.1 kV to 25 kV, and the maintenance time in various ranges within the range of 30 minutes to 5 hours. The thickness of the transparent quartz glass layer covering the ion-containing layer was measured, and visual observation was performed.

As a result, when the concentration distribution of K ions was measured by the step etching method, it was confirmed that the maximum concentration of the layer having a high concentration was in the range of 10 ppm to 300 ppm. This K ion concentration is 0.1 ppm
When the thickness of the outermost layer which is not substantially present was measured as a transparent quartz glass layer, the thickness was 6 μm as shown in Table 1.
m to 800 μm. Visual observation of the surface and the inside of the crucible after treatment under each of these conditions revealed no precipitation of crystals.

Using each crucible obtained by this voltage application method, a pulling test of a silicon single crystal was conducted under the condition of maintaining at 1480 ° C. for 6 hours. It was confirmed that the crystal had grown to the inner surface of the crucible.

(Second Embodiment) Here, as crystallization promoters, alkaline earth metal ions Ca, Mg,
Each ion of Ba was used. A paste in which 10 parts of an aqueous solution of 0.3 M / l of each hydroxide of Ca, Mg and Ba serving as each crystallization promoting ionic material is mixed with colloidal silica at a weight ratio of 2 and polyethylene glycol at a weight ratio of 0.1. And the paste was applied to the inner surface of the same 18-inch quartz glass crucible as described above. After the coating solution was dried, it was maintained at 700 ° C. for 1 hour. After cooling, the applied layer was washed off with an aqueous alkali solution or the like.

Platinum foil is applied as a pair of electrode materials to the inside and outside of the crucible, and a voltage of 10 kV is applied in a state where the electrode arranged inside the crucible wall becomes a positive pole and the electrode arranged outside becomes a negative pole. Maintained at 1200 ° C. for 1 hour.

The inner surface of the obtained crucible has a thickness of about 5
It was confirmed that a μm transparent quartz glass layer was formed. When silicon was put in this crucible and melted at 1500 ° C. for 1 hour, it was confirmed that crystals were deposited over the entire inner surface of the crucible.

(Third Embodiment) Here, Na ion which is an alkali metal ion was used as a crystallization accelerator. The salt serving as the crystallization-promoting ionic material is placed in a dish, the dish is placed in the center of a quartz glass plate, and the same 18-inch quartz glass crucible as above is turned down, and the whole is placed in an electric furnace at 900 ° C. For 5 minutes, and thus a crucible having Na ions applied to the inner surface of the crucible was prepared.

The mixture of silica powder and graphite powder as a pair of electrode materials was brought into contact with the inside and outside of the obtained crucible wall, respectively. The electrode arranged inside the crucible wall was a positive electrode, and the electrode arranged outside was a positive electrode. A voltage of 1 kV was applied in the state of a negative pole, and the temperature was maintained at 1000 ° C. for 15 minutes.

The inner surface of the obtained crucible has a thickness of about 1 m.
It was confirmed that the m transparent quartz glass layer was formed. When pulling a silicon single crystal with this crucible,
It was confirmed that crystals were precipitated over the entire inner surface of the crucible. In addition, as compared with the case where an untreated crucible was used, it was found that the defective rate due to polycrystallization was reduced by about 10%. When the concentration of Na impurities in the silicon single crystal obtained using this crucible was measured,
0.01 ppb or less, showing almost the same level as compared with the case of using an untreated crucible.
It was confirmed that contamination by impurities was effectively suppressed.

[0033]

As described above, according to the present invention, the inner surface of the crucible can be crystallized almost over the entire surface, and the local corrosion on the surface layer of the crucible can be more effectively prevented by the crystal layer. A longer crucible life can be achieved. Further, since the crystal grown on the inner surface of the crucible does not contain impurities, contamination of silicon can be prevented. Further, since the transparent quartz glass is used, labor required for countermeasures for deterioration and handling on the inner surface of the crucible is greatly reduced as compared with the conventional case.

Claims (6)

[Claims] 1. A layer comprising a crystallization accelerator, and a transparent quartz glass layer covering the layer containing the crystallization accelerator, wherein the inner surface of the crucible wall is constituted by the transparent quartz glass layer. Quartz glass crucible. 2. The quartz glass crucible according to claim 1, wherein the thickness of the transparent quartz glass layer is more than 0 mm and 1 mm or less. 3. The quartz glass crucible according to claim 1, wherein the concentration of the crystallization promoter is more than 0 ppm and 500 ppm or less. 4. The quartz glass crucible according to claim 1, wherein the crystallization promoter is an alkali metal ion. 5. The quartz glass crucible according to claim 1, wherein the crystallization promoter is an alkaline earth metal ion. 6. A layer containing metal ions that promotes crystallization is formed on the inner surface of the crucible wall, and a pair of electrodes are respectively disposed inside and outside the crucible wall including this layer. The metal ions are moved to the inner surface side of the crucible wall by heating while applying a DC voltage to the crucible wall via the pair of electrodes in a state where the electrode disposed outside the crucible wall is a negative electrode. A method for producing a quartz glass crucible, characterized in that: