JP2000143386A - Method of cleaning quartz crucible - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for cleaning a quartz crucible comprising such a practice as to satisfactorily remove organic matter, microparticles and metallic impurities as well as debonded quartz powder and dusts adhered to the surface of the crucible. SOLUTION: This method for cleaning a quartz crucible comprises such a practice as to conduct a process 12 where the crucible used in producing semiconductor single crystals by Czochralski method are cleaned with an aqueous ozone solution and then a process 13 where the crucible thus cleaned is further cleaned with hydrofluoric acid, or repeat these processes at least twice; wherein it is preferable to involve processes 11 and 14 for cleaning the crucible with pure water prior to the process 12 and after the process 13, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a quartz crucible used for producing a semiconductor single crystal by the Czochralski method.

[0002]

2. Description of the Related Art A silicon single crystal for a semiconductor device is manufactured mainly by a Czochralski method (hereinafter, referred to as a CZ method). In the CZ method, a lump or granular polycrystalline silicon of polycrystalline silicon is melted in a quartz crucible in a furnace, a seed crystal is immersed in the obtained melt, and the seed crystal is pulled up to grow a silicon single crystal. Is the way. This CZ
The quartz crucible used in the method has a bad influence on the growth of silicon single crystal when dust is attached.Therefore, quartz crucible manufacturers clean the crucible thoroughly in the final crucible manufacturing process, dry it, and then transport it. To prevent contamination inside, crucibles are shipped sealed in plastic bags. However, the inside of the quartz crucible that contains the raw materials is finished to a smooth surface, but the outside is a rough surface state where the raw material powder of quartz is fixed, so the outer surfaces of the plastic bag and the crucible rub during transportation and the quartz Threshing powder is generated and wraps around and adheres to the inner surface of the crucible. When the quartz crucible after shipment is actually used, polycrystalline silicon is charged and melted while the above-mentioned quartz-milled powder remains attached to its inner surface, and then the single crystal is pulled up. The powder causes dislocations in the growing single crystal, thereby inhibiting growth.

[0003] A washing and drying apparatus for removing dust adhering to a quartz crucible before polycrystalline silicon is introduced has been disclosed (JP-A-10-7225). This cleaning device is a nozzle that ejects a fluid to the outer and inner surfaces of the crucible, a liquid tank that stores a cleaning liquid of the crucible, an air tank that stores air for drying, and selectively one of the cleaning liquid and the air. Means for supplying to the nozzle. In this cleaning / drying apparatus, first, ion-exchanged water, distilled water, hydrofluoric acid, nitric acid, or the like is spouted from a nozzle as a cleaning liquid without moving the crucible to wash the outer and inner surfaces of the crucible, and then air is blown from the nozzle. Spout to dry the outer and inner surfaces of the crucible. In addition, a cleaning method for removing crushed powder of quartz adhering to the inner surface of a quartz crucible before pouring polycrystalline silicon is disclosed (Japanese Patent Application Laid-Open No. 9-1997).
255478). In this cleaning method, the quartz crucible cleaned in the predetermined cleaning step is heated with pure water of 50 ° C. or higher,
Air dry. According to this method, the quartz crucible can be washed and dried with simplified equipment.

[0004]

However, before the manufactured quartz crucible is sealed with a plastic bag or after opening, organic substances, fine particles and metal impurities may adhere to the surface of the crucible. It has been difficult to remove organic substances, fine particles and metal impurities by the conventional techniques disclosed in the two publications. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for cleaning a quartz crucible capable of satisfactorily removing organic substances, fine particles and metal impurities attached to the surface of the quartz crucible. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for cleaning a quartz crucible that satisfactorily removes dust and dedusted quartz powder adhering to the surface of the quartz crucible.

[0005]

The invention according to claim 1 is
As shown in FIGS. 1 and 2, in a method of cleaning a quartz crucible used when a semiconductor single crystal is manufactured by the Czochralski method, a step 12 of cleaning the quartz crucible 22 with a dissolved ozone aqueous solution, and a step of cleaning with a dissolved ozone aqueous solution Cleaning the quartz crucible 22 with hydrofluoric acid is performed once in this order or repeated one or more times in this order. The cleaning of hydrofluoric acid can remove dust, crushed powder of quartz, fine particles, and metal impurities, and can remove organic substances with dissolved ozone water. Step 12 and Step 1
By repeating Step 3 once or more, the removal effect is further enhanced.

A second aspect of the present invention is the invention according to the first aspect, wherein the first cleaning step 1 using a dissolved ozone aqueous solution is performed.
Before and after the final cleaning step 13 using hydrofluoric acid, steps 11 and 14 for cleaning the quartz crucible 22 with pure water, respectively.
This is a method for cleaning a quartz crucible containing: By further adding steps 11 and 14 for cleaning the quartz crucible with pure water,
The effect of removing organic substances, fine particles and metal impurities, such as crushed quartz powder and dust, can be further enhanced.

A third aspect of the present invention is the invention according to the first or second aspect, wherein the dissolved ozone aqueous solution has an ozone concentration of 3%.
２０20 ppm, and the concentration of hydrofluoric acid is 0.1-5 wt%
This is a method for cleaning a quartz crucible. By setting the ozone concentration of the dissolved ozone aqueous solution and the concentration of hydrofluoric acid respectively in the above ranges, the effect of removing organic substances, fine particles and metal impurities can be further enhanced.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The dissolved ozone aqueous solution used in step 12 of the method for cleaning a quartz crucible of the present invention has high purity, low concentration, high oxidizing power, and easy availability. The dissolved ozone aqueous solution preferably has an ozone concentration of 3 ppm or more. If it is less than 3 ppm, the ability to decompose organic substances will be insufficient, and if it exceeds 20 ppm, the corrosion resistance of the cleaning device will be reduced, which is not preferable. Since the solubility limit of ozone in pure water is about 25 ppm, the ozone concentration of the dissolved ozone aqueous solution is more preferably 5 to 15 ppm. The concentration of hydrofluoric acid used in step 13 is 0.1 to 5% by weight. In particular, 1 to 2% by weight is preferable. If it is less than 0.1% by weight, it is insufficient to remove fine particles and metal impurities, and if it exceeds 5% by weight, the washing cost is undesirably increased.

An apparatus for cleaning a quartz crucible according to an embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 2, in a chamber 21 filled with clean air, a quartz crucible 22 is placed on a table 23 with its inner surface facing downward. Inside spray nozzle 2 inside and outside of quartz crucible 22
4a and the outer surface injection nozzle 24b are respectively arranged. A dissolved ozone aqueous solution, hydrofluoric acid, or pure water is selectively injected from the inner surface spray nozzle 24a and the outer surface spray nozzle 24b to the inner surface and the outer surface of the quartz crucible 22, respectively. The HEPA filter (hi
A gh efficiency particulate air filter) 26 is provided to keep the inside of the chamber 21 in the cleanliness class 100. The table 23 is configured to be rotatable about the center of the quartz crucible 22, and its rotation direction and speed are controlled by an electric motor 27 provided below the table 23.

As shown in FIG. 3, four projections 23a are formed on the upper surface of the base 23 to engage with the quartz crucible 22, and the quartz crucible 22 is placed on these projections 23a. Further, a drain port 28 for discharging the dissolved ozone aqueous solution, hydrofluoric acid or pure water injected from the inner surface injection nozzle 24 a to the inner surface of the quartz crucible 22 to the outside of the table 23 is provided inside the convex portion 23 a of the table 23. . As shown in FIG. 2, conduits 24 c and 24 d connected to the inner ejection nozzle 24 a and the outer ejection nozzle 24 b respectively are united, led out of the chamber 21, and connected to the pump 31. The pump 31 is connected to the electromagnetic switching valve 29a, the electromagnetic switching valve 29b, and the electromagnetic switching valve 29c, respectively. Solenoid switching valve 29
a is connected to a tank 32 containing a dissolved ozone aqueous solution. The electromagnetic switching valve 29b is connected to a tank 33 containing hydrofluoric acid. The electromagnetic switching valve 29c is connected to a tank 34 containing pure water. The controller 37 is connected to the pump 31 and the electromagnetic switching valves 29a to 29c, respectively.

When the quartz crucible is cleaned using the cleaning apparatus constructed as described above, first, a predetermined amount of pure water is supplied from the pure water tank 34 based on the control of the controller 37 to the inner surface spray nozzle 24a and the outer surface spray nozzle. The inner surface and the outer surface of the quartz crucible 22 are sprayed from 24b for cleaning. On this occasion,
The table 23 is simultaneously rotated by the electric motor 27, whereby pure water is evenly sprayed on the entire surface of the quartz crucible 22 to perform cleaning. Next, based on the control of the controller 37, a predetermined amount of the dissolved ozone aqueous solution is sprayed from the tank 32 of the dissolved ozone aqueous solution from the inner surface spray nozzle 24a and the outer surface spray nozzle 24b to the inner surface and the outer surface of the quartz crucible 22, and is washed. In the same manner, the washing process using the dissolved ozone aqueous solution and the washing process using hydrofluoric acid are repeated at least once, and then the inner and outer surfaces of the quartz crucible 22 are washed with pure water. After washing, the quartz crucible 22 is sufficiently dried, and then naturally dried. Although not shown, the final drying of the quartz crucible is performed by the inner jet nozzle 24a and the outer jet nozzle 2a.
4b may be performed by injecting dry air.

[0012]

Next, examples of the present invention will be described together with comparative examples. <Example 1> A quartz crucible was cleaned using the cleaning apparatus shown in Figs. 2 and 3 under the following conditions. All the processing liquids were jetted from the inner jet nozzle and the outer jet nozzle toward the quartz crucible. First, 3000 ml of pure water in the pure water tank
/ Min for 3 minutes to spray and clean the inner and outer surfaces of the quartz crucible. Next, an aqueous solution of dissolved ozone having an ozone concentration of 10 ppm was sprayed onto the inner surface and the outer surface of the quartz crucible at a rate of 3000 ml / min for 5 minutes for cleaning. Then, concentration 2
The hydrofluoric acid was sprayed onto the inner and outer surfaces of the quartz crucible at a rate of 3000 ml / min for 5 minutes for cleaning. Subsequently, the washing step using a dissolved ozone aqueous solution and the washing step using hydrofluoric acid were repeated once more under the same conditions as described above. Then, pure water was sprayed onto the inner and outer surfaces of the quartz crucible at a rate of 8000 ml / min for 10 minutes for cleaning. After the washing, the quartz crucible was naturally dried.

Comparative Example 1 A quartz crucible was washed by substantially repeating the washing method of Example 1 except that the step of washing with a dissolved ozone aqueous solution was omitted. <Comparative test and evaluation> Pure water was applied to both the quartz crucible washed by the method of Comparative Example 1 and the quartz crucible washed by the method of Example 1, and the degree of water wetting was visually compared. While the quartz crucible washed by the method partially repelled water due to the remaining organic matter, the quartz crucible washed by the method of Example 1 had a uniform water film formed on the entire surface, and Excellent in effect.

[0014]

As described above, in the cleaning method of the present invention, the step of cleaning the quartz crucible with the aqueous solution of dissolved ozone and then cleaning it with hydrofluoric acid is performed once in this order or is repeated one or more times. In addition, organic substances, fine particles, and metal impurities, such as crushed quartz powder and dust adhering to the surface of the quartz crucible, can be satisfactorily removed. In particular, when dust, crushed powder of quartz, fine particles or metal impurities are covered with or mixed with organic substances on the surface of the quartz crucible, the organic substances block hydrofluoric acid and cause dust and the like when conventionally washed with hydrofluoric acid. In the present invention, since the dissolved ozone aqueous solution removes the organic matter in advance, the hydrofluoric acid can more reliably remove dust and the like, which has prevented the washing.

[Brief description of the drawings]

FIG. 1 is a view showing a quartz crucible cleaning step of the present invention.

FIG. 2 is a configuration diagram of an apparatus for cleaning a quartz crucible according to an embodiment of the present invention.

FIG. 3 is a plan view of a base included in the cleaning apparatus of FIG. 2;

[Explanation of symbols]

 11 Cleaning Step Using Pure Water 12 Cleaning Step Using Dissolved Ozone Solution 13 Cleaning Step Using Hydrofluoric Acid 14 Cleaning Step Using Pure Water

Claims (3)

[Claims] 1. A method for cleaning a quartz crucible used when manufacturing a semiconductor single crystal by the Czochralski method, wherein a step (12) of washing the quartz crucible (22) with a dissolved ozone aqueous solution, A step (13) of washing the washed quartz crucible (22) with hydrofluoric acid once in this order or repeating it one or more times. 2. A first cleaning step using a dissolved ozone aqueous solution.
Before (12) and after the last hydrofluoric acid washing step (13),
The method for cleaning a quartz crucible according to claim 1, further comprising a step of cleaning the quartz crucible (22) with pure water. 3. The dissolved ozone aqueous solution has an ozone concentration of 3 to 2.
The method for cleaning a quartz crucible according to claim 1 or 2, wherein the concentration is 0 ppm and the concentration of hydrofluoric acid is 0.1 to 5% by weight.