JP2005288333A - Washing method and washing apparatus of polycrystalline silicon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a washing method and a washing apparatus of a polycrystalline silicon rod which are excellent in washing effect and prevents an acidic liquid from being carried over to pure water washing after acid washing, therefore raises no risk of forming washing spot, and prevents pollution attributed to washing tools. <P>SOLUTION: The polycrystalline silicon washing method and apparatus are characterized by washing the rod-like polycrystalline silicon forgoingly washed with an acid, with pure water while hanging the polycrystalline silicon directly on a hanger without putting in a basket, and the washing is preferably carried out by using the hanger having a plurality of arms made of a thin L-shaped plate material, putting polycrystalline silicon rods on the rims of the thin arms for hanging the rods, washing the rods with an acid and successively with pure water by swinging the rods in pure water, showering pure water on the rods after pulling out the rods, immersing the rods in pure water and carrying out ultrasonic washing, and showering pure water on the rods after pulling out the rods. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for cleaning polycrystalline silicon used as a raw material for single crystal silicon for semiconductors. More specifically, a cleaning method and a cleaning device for a polycrystalline silicon rod excellent in a cleaning effect in which pure acid cleaning after acid cleaning is less likely to bring in an acid solution, there is no fear of causing cleaning spots, and contamination from cleaning tools is also prevented. About.

  Single crystal silicon is mainly manufactured by polycrystalline silicon as a raw material by the Czochralski method (CZ method) or floating zone method (FZ method). In order to increase the purity of single crystal silicon, high purity polycrystalline silicon is used. It has been demanded. However, usually, the surface of the polycrystalline silicon is oxidized, and impurities are attached. Therefore, it is necessary to remove the oxide film on the surface and the attached impurities from the polycrystalline silicon used as the raw material for the single crystal silicon.

  Conventionally, as a method for cleaning polycrystalline silicon, hydrogen fluoride water, nitric acid, hydrochloric acid, hydrogen peroxide, ammonia water, hydrogen peroxide, or a mixed solution thereof is used as a cleaning liquid, and a cleaning tank filled with this cleaning liquid is often used. Crystal silicon is immersed and washed. As an example of a cleaning method, a cleaning apparatus is known in which a basket containing polycrystalline silicon is moved along a plurality of cleaning tanks, and the baskets are sequentially immersed in the cleaning tank for cleaning (Patent Document 1).

  In the polycrystalline silicon cleaning method, acid cleaning (acid etching) using hydrofluoric acid or nitric acid is a step of removing the oxide film by dissolving the surface of the polycrystalline silicon with an acid solution. Therefore, the acid solution after washing contains a large amount of impurities, and it is necessary to wash away this acid solution sufficiently after washing. Conventionally, after washing with an acid solution, the pure water washing process in which the acid solution is washed away with pure water is performed by oscillating the polycrystalline silicon placed in the pure water washing tank and then immersed in pure water for a certain period of time. doing.

  However, since there are many fine irregularities and pores on the surface of the polycrystalline silicon, the acid solution adhering to the surface of the polycrystalline silicon cannot be completely washed away to the extent that it swings in the washing tank. , Washing spots may occur. Also, it takes time to clean with pure water and productivity is low. Further, in the conventional cleaning method, the polycrystalline silicon is immersed in a cleaning tank in a state where the basket is perforated, and acid cleaning and pure water cleaning are performed, and the basket containing the polycrystalline silicon is stored in the acid cleaning tank. After being soaked in and cleaned, the whole basket is pulled up and immersed in a pure water cleaning tank to perform pure water cleaning. For this reason, there is a problem that the amount of the acid solution brought into the pure water cleaning tank is large and the cleaning effect is lowered, and the surface of the polycrystalline silicon is stained with a crust and the equipment becomes large.

Specifically, in the conventional cleaning method, rod-shaped polycrystalline silicon is put into a bowl-shaped container having a hole, and the container is shaken to perform cleaning in an acid solution and pure water. However, in cleaning using a container, since the silicon rod is in contact with the bottom or side of the container, the contact part is not evenly contacted with pure water compared to other parts, and the rod surface cleaning effect Decreases and causes cleaning spots. Moreover, when washing | cleaning using a container, when putting the container taken out from the acid solution tank in a pure water tank, there exists an acid solution adhering to a container and a pure water washing | cleaning effect reduces.
Japanese Unexamined Patent Publication No. 63-285938

  The present invention solves the above-mentioned problem in the conventional polycrystalline silicon cleaning method, in which there is little carry-in of acid solution in pure water cleaning after acid cleaning, so there is no concern of generating cleaning spots, and further from the cleaning tool. A cleaning method and a cleaning device for a polycrystalline silicon rod excellent in cleaning effect that prevent contamination of the metal are provided.

According to the present invention, the following polycrystalline silicon cleaning method is provided.
(1) A method for cleaning polycrystalline silicon, characterized in that the acid-cleaned rod-shaped polycrystalline silicon is cleaned with pure water in a state where it is suspended directly on a hanger without being put in a basket.
(2) A polycrystalline silicon cleaning method in which acid cleaning and / or acid cleaning and pure water cleaning are performed in a state where the polycrystalline silicon rod is directly suspended from a hanger without being placed in a basket.
(3) In the cleaning method of (1) or (2) above, a hanger having a comb-shaped arm with a plurality of thin L-shaped plate members arranged side by side is used, and a polycrystal is formed on the upper edge of the thin arm. A method for cleaning polycrystalline silicon in which a silicon rod is placed and suspended while being cleaned.
(4) In the cleaning method of any of (1) to (3) above, the acid-cleaned polycrystalline silicon rod is subjected to pure water swinging, pure water shower cleaning, and ultrasonic cleaning in pure water. A method for cleaning polycrystalline silicon, which is pulled up and cleaned with a pure water shower.
(5) In the cleaning method of (4) above, a cleaning tank is provided with a comb-like table with a plurality of thin plates standing in parallel, and the polycrystalline silicon rod is suspended on a hanger. In addition, a method for cleaning polycrystalline silicon, which is transferred to a table and cleaned.
(6) In the cleaning method of (5) above, an ultrasonic cleaning tank is provided with a table having a comb-like cross section formed by standing a plurality of thin plates in parallel, and the polycrystalline silicon rod is placed between the hanger and the table. A method for cleaning a polycrystalline silicon rod in which the rod rotates the top surface of the pedestal and the ultrasonic vibration is uniformly applied to the side surface of the rod when transferring between them.

Furthermore, according to the present invention, the following polycrystalline silicon cleaning apparatus and the like are provided.
(7) A washing tank and a hanger for hanging a polycrystalline silicon rod are provided, the hanger has a comb-shaped arm having a plurality of thin L-shaped plate members arranged side by side, and the upper edge of the arm A polycrystalline silicon cleaning apparatus, wherein a polycrystalline silicon rod is placed on and suspended from the cleaning tank.
(8) A cleaning apparatus in which a table having a comb-like cross section formed by standing a plurality of thin plates in parallel is provided in a cleaning tank, and a polycrystalline silicon rod is placed on the table and cleaned.
(9) A hanger that hangs the polycrystalline silicon rod and a washing tank provided with a table on which the rod is placed. The polycrystalline silicon rod is washed while being hung on the hanger. Cleaning equipment that transfers and cleans.
(10) A hanger having a comb-shaped arm with a plurality of thin L-shaped plate members arranged side by side, and a table having a comb-shaped cross-section with a plurality of thin plates standing in parallel A polycrystalline silicon cleaning apparatus having a cleaning tank and capable of transferring a polycrystalline silicon rod without contacting each other by inserting an arm of a hanger into a gap of a table.
(11) A cross section comprising a hanger for hanging a polycrystalline silicon rod, a pure water cleaning tank, an acid cleaning tank, and an ultrasonic cleaning tank, wherein the hanger is provided with a plurality of thin L-shaped plate members arranged in parallel. Has a comb-shaped arm and moving means that moves up and down and moves back and forth, and is provided with an acid-resistant resin coat, or is formed of an acid-resistant resin. Is provided with a comb-shaped pedestal having a plurality of thin plates standing in parallel, and is washed with a polycrystalline silicon rod suspended on the upper edge of the arm of the hanger, A cleaning apparatus for a polycrystalline silicon rod, wherein the polycrystalline silicon rod is moved to a table and cleaned in the ultrasonic cleaning tank.
(12) A circulation path for extracting the cleaning liquid from the cleaning tank and returning it back to the cleaning tank is provided, and in the circulation path, a liquid purification means including a pre-filtration part and a filtration part and a liquid feed pump are provided (7 ) To (11).
(13) The cleaning apparatus according to any one of (7) to (12), wherein means for injecting a pure water shower into the pure water cleaning tank is provided.
(14) Polycrystalline silicon rods cleaned by the cleaning method of any one of (1) to (6) above, or single crystal silicon produced using this polycrystalline silicon rod as a raw material.

[Specific description]
An example of the cleaning system of the present invention is shown in FIG. As shown in the figure, the cleaning method of the present invention is a cleaning method of polycrystalline silicon characterized in that pure water cleaning is performed in a state in which acid-washed rod-shaped polycrystalline silicon is directly suspended from a hanger without being placed in a basket. Preferably, for example, a method for cleaning polycrystalline silicon in which acid cleaning and / or acid cleaning and pure water cleaning are performed in a state in which a polycrystalline silicon rod is directly hung on a hanger without being placed in a basket.

  In the cleaning method of the present invention, the polycrystalline silicon rod to be cleaned is generally referred to as a cut rod, and is approximately rod-shaped having a length of 50 mm to 500 mm. Note that the cleaning method of the present invention is not limited to such a cut rod as long as it can be hung on a hanger.

  An example of the hanger used for the cleaning method of the present invention is shown in FIG. The hanger 10 shown in the figure has a plurality of arms 11 made of a thin L-shaped plate material, and the plurality of arms 11 are arranged at appropriate intervals so that the liquid runs out. ) Is formed in a comb shape. The upper part of each arm 11 is integrally and swingably attached to a moving means (not shown). The polycrystalline silicon rod 20 is suspended on the upper edge of the arm 11 in a horizontal direction. If the hanger 10 is used, the polycrystalline silicon rod 20 is stable because it is supported by a plurality of arms 11, and the polycrystalline silicon 20 is placed on the upper edge of a thin plate arm, so that the contact area is extremely small, and Since an appropriate space is provided between the arms 11, the cleaning effect is excellent and the liquid breakage is very good.

  The hanger 10 has moving means (not shown) that moves up and down and moves back and forth. The hanger 10 moves up and down with a polycrystalline silicon rod suspended from the arm 11 and moves between a plurality of washing tanks. A polycrystalline silicon rod is taken in and out of each washing tank. When this hanger 10 is also used for acid cleaning, each arm 11 is preferably provided with an acid-resistant resin coat or formed with an acid-resistant resin.

  The cleaning system of the present invention shown in FIG. 1 includes a cleaning process 30 using a pure water shower, an acid cleaning process 40, a process 50 for rinsing an acid solution with pure water, and a process 60 for performing ultrasonic cleaning in pure water in this order. The cleaning tanks 31 to 61 are arranged in each cleaning process. In the illustrated example, the cleaning steps are arranged in the above order, but the installation order can be appropriately changed as necessary. Moreover, if the said washing | cleaning processes 30-60 are made into 1 set and it is set as the structure which repeats this, the washing | cleaning effect will improve further.

  The acid cleaning tank 41 and the pure water cleaning tank 51 are provided with circulation paths 15 and 16 for extracting the cleaning liquid from the bottom of each tank and performing the cleaning process, and then returning the cleaning liquid to the cleaning tanks 41 and 51 again. In 16, a liquid purification means having a pre-filtration unit 12 and a filtration unit 14 and a liquid feed pump 13 are interposed. The acid solution or pure water in each cleaning tank is circulated through the cleaning means to remove fine particles and impurities in the solution, and used in acid cleaning or pure water cleaning in a clean state.

  The pure water cleaning tanks 31, 51, 61 are each provided with means for injecting a pure water shower, and the pure water cleaning tank 61 in the final step is provided with ultrasonic vibration means. Specifically, ultrasonic transducers 63 are attached to both side wall portions of the pure water cleaning tank 61.

  First, the polycrystalline silicon rod 20 is put in the washing tank 31 while being suspended on the hanger 10, and dust, dirt, impurities, etc. adhering to the rod surface are washed away by a pure water shower. Note that the first pure water shower cleaning may be replaced with pure water immersion cleaning or ultrasonic cleaning. Next, the rod 20 is lifted from the washing tank 31 while being hung on the hanger 10, put into the acid washing tank 41, and immersed in the acid solution. The acid solution uses a mixed acid of nitric acid and hydrofluoric acid, but is not limited thereto. The rod 20 is immersed in the acid solution while being hung on the hanger 10, and after a predetermined time has elapsed, the rod 20 is pulled up from the acid cleaning tank 41 and transferred to the pure water cleaning tank 51.

  In the pure water washing tank 51, the rod 20 is swung in the pure water while being hung on the hanger 10, and the acid solution adhering to the rod 20 is removed. Thereafter, the rod 20 is pulled up from the acid solution, and the rod 20 is subjected to a pure water shower on the upper portion of the pure water washing tank while being hung on the hanger 10 to wash away the remaining acid solution. Next, the rod 20 hung on the hanger 10 is moved to another pure water cleaning tank 61 to perform ultrasonic cleaning.

  As shown in the figure, a liquid feed pump 62 for supplying pure water into the tank is connected to the pure water cleaning tank 61, and a drainage channel for guiding the cleaning liquid overflowing from the upper end of the tank to the outside is provided. In addition, a stand 64 on which the polycrystalline silicon rod 20 is placed is provided in the tank. As shown in FIG. 2, the pedestal 64 is formed by standing a plurality of thin plates in parallel, with an appropriate interval between the thin plates, and the entire cross section (in the parallel direction). The cross section is comb-like. The rod 20 is placed on the tip of this comb. Furthermore, the upper end portion of the pedestal 64 is processed into a V-groove shape along the plate width direction, and is formed so as to stably support the rod 20 placed on the upper end portion. The ultrasonic transducers 63 are preferably provided so as to be positioned on both sides with respect to the longitudinal direction (parallel direction) of the pedestal 64.

  The rod 20 is put in the pure water washing tank 61 while being hung on the hanger 10, the arm 11 of the hanger 10 is inserted between the placing tables 64, and the rod 20 is moved to the placing table 64. Since the hanger 10 and the pedestal 64 are each formed in a comb shape, the rod 20 is transferred to the upper end portion of the pedestal 64 without contact by being inserted into the gap between the teeth so that the teeth of the combs mesh with each other. be able to. In order to transfer the rod 20 of the cradle 64 to the hanger 10, the rod 20 is transferred to the arm 11 by inserting the arm 11 of the hanger 10 into the gap of the cradle 64 and pulling it up as in the above case.

  Further, since the upper end portion of the pedestal 64 is processed into a V-groove shape, by placing the rod 20 on the inclined surface of the V-groove, the rod 20 moves along the inclination and is fitted in the V-groove. It is fixed with. Ultrasonic vibration is uniformly applied to the entire side surface of the rod 20 from both sides by the vibrator 63 with respect to the rod 20, and ultrasonic cleaning is performed in pure water. When the rod 20 is transferred from the hanger 10 to the mounting table 64 or when the rod 20 is transferred from the mounting table 64 to the hanger 10, the rod 20 rotates along the inclined surface of the mounting table 64 or the inclined surface of the arm 11. Since the position of the part that has been in contact with the arm or the pedestal is shifted, the side surface of the rod is uniformly cleaned, and the ultrasonic wave is uniformly applied, so that the cleaning effect can be enhanced.

  After ultrasonic cleaning, the arm 11 is inserted into the pedestal 64 to raise the hanger 10, and the rod 20 is transferred from the pedestal 64 to the hanger 10 and pulled up. The rod 20 is washed with a pure water shower on the upper side of the washing tank. If necessary, the impurity level on the surface of the polycrystalline silicon rod can be further reduced by repeating the acid cleaning, ultrasonic cleaning and pure water shower.

  In the above cleaning method and cleaning apparatus of the present invention, the ultrasonic vibration means is not limited to the cleaning tank 61 and may be installed in the pure water shower cleaning tank 31 and the pure water cleaning tank 51. Further, the cradle 64 may be installed not only in the cleaning tank 61 but also in the acid cleaning tank 41 and the pure water cleaning tank 51. If the cradle 64 is installed in these washing tanks 41 and 51, the rod 20 rotates on the cradle upper end surface as described above, and the cleaning effect can be enhanced. Further, the pure water shower cleaning 30 may be pure water immersion cleaning. Moreover, the installation order of the pure water shower cleaning process 30, the acid cleaning process 40, the pure water immersion cleaning process 50, and the ultrasonic cleaning process 60 is not limited to the illustrated example. If necessary, the order of the cleaning steps may be appropriately changed, and some cleaning steps may be omitted.

  In the cleaning system of the present invention, the polycrystalline silicon is directly hung on the hanger, the acid solution is cleaned, and then ultrasonic pure water cleaning is performed. Preferably, the hanger has a comb-shaped cross section formed by arranging thin plates side by side. Since the cleaning is performed in a suspended state, the acid solution is not brought into the pure water cleaning, so that there is no fear of generating cleaning spots, contamination from the cleaning tool is prevented, and an excellent cleaning effect can be obtained. Incidentally, according to the cleaning method of the present invention, the amount of the acid solution brought into the pure water cleaning tank can be reduced by about 70% as compared with the case where a conventional container for horizontally storing a rod is used. As a result, since the consumption amount of the acid solution is reduced, the use amount of the acid solution can be reduced, and the use amount of pure water can also be reduced.

  Furthermore, the cleaning system of the present invention includes a hanger having a comb-shaped arm formed by arranging thin plates, and a cleaning tank provided with a comb-shaped table having a plurality of thin plates standing in parallel. And the polycrystalline silicon rod is washed while hung on the hanger and placed on the cradle for washing, so the position of the part that was in contact with the hanger arm and the cradle is displaced and washed uniformly. , No cleaning spots. In addition, by inserting the arm of the hanger into the gap of the pedestal, it is possible to transfer the polycrystalline silicon rod without contacting each other, so it can be washed smoothly and the contamination of the equipment is reliably prevented can do. Furthermore, by transferring the polycrystalline silicon rod between the hanger and the cradle, the rod rotates on the cradle upper surface and the hanger arm, and the ultrasonic waves uniformly strike the rod side surface, so a uniform cleaning effect is obtained. .

  Furthermore, according to the cleaning method of the present invention, a high-purity polycrystalline silicon rod with few impurities can be obtained. By using this polycrystalline silicon rod as a raw material, the single crystallization rate of single crystalline silicon can be increased. it can.

  Hereinafter, the present invention will be described specifically by way of examples.

  The polycrystalline silicon is cut into five rods, and three of them are cleaned in accordance with the cleaning process shown in FIG. 1 using a mixed acid of hydrofluoric acid and nitric acid as the acid cleaning cleaning liquid for the time indicated in Table 1 in each cleaning process. The amount of impurities on the surface of the washed polycrystalline silicon rod was measured. The results are shown in Table 2 (Test No1 to No3). Furthermore, the result of repeating the illustrated washing process twice for one of the remaining two was also shown in Table 2 (Test No. 4). The last one was subjected to a conventional cleaning method, and the amount of impurities was measured. This is shown in comparison with Table 2 as a comparative example. In this conventional cleaning method, a polycrystalline silicon rod was placed in a perforated basket, and the entire basket was cleaned in the order of pure water shower → acid cleaning tank → pure water shower → pure water cleaning tank immersion. As shown in this result, according to the cleaning method of the present invention, the amount of impurities can be greatly reduced as compared with the conventional cleaning method. Impurities were measured with an ICP mass spectrometer.

  As shown in Table 2, according to the cleaning method of the present invention, the impurity amount is significantly small, and an excellent cleaning effect can be obtained. In addition, the cleaning methods of the present invention all have a level of impurities that are close to each other and show a stable cleaning effect. On the other hand, the amount of impurities in the comparative example is much larger than in the present invention.

Process drawing showing an example of the cleaning method of the present invention Schematic of hanger and pedestal used in the present invention

Explanation of symbols

10-hangers, 11-arms, 12-prefiltration sections, 13-pumps, 14-filtration sections, 15-circulation paths, 16-circulation paths, 20-polycrystalline silicon rods, 30-pure water cleaning steps, 31-cleanings Tank, 40-acid cleaning process, 41-cleaning tank, 50-pure water cleaning process, 51-cleaning tank, 60-ultrasonic pure water cleaning process, 61-cleaning tank, 62-pump, 63-vibrator, 64- Stand.

Claims (14)

  A method for cleaning polycrystalline silicon, characterized in that acid-washed rod-shaped polycrystalline silicon is washed with pure water in a state of being suspended directly on a hanger without being put in a basket.   A method for cleaning polycrystalline silicon, in which acid cleaning and / or acid cleaning and pure water cleaning are performed in a state in which a polycrystalline silicon rod is suspended directly on a hanger without being placed in a basket.   3. The cleaning method according to claim 1 or 2, wherein a hanger having a comb-shaped arm with a plurality of thin L-shaped plate members arranged side by side is used, and a polycrystalline silicon rod is placed on the upper edge of the thin arm and suspended. A method for cleaning polycrystalline silicon in which cleaning is performed in a lowered state.   4. The cleaning method according to claim 1, wherein the acid-cleaned polycrystalline silicon rod is subjected to swinging in pure water, pure water shower cleaning, and ultrasonic cleaning in pure water, and the resultant is pulled up to be purified. A method for cleaning polycrystalline silicon in which water is washed.   5. A cleaning method according to claim 4, wherein the cleaning tank is provided with a comb-like pedestal having a plurality of thin plates arranged in parallel, and the polycrystalline silicon rod is washed and hung on the hanger. A method for cleaning polycrystalline silicon that is transferred to a table and cleaned.   6. The cleaning method according to claim 5, wherein a table having a comb-like cross section formed by arranging a plurality of thin plates in parallel in an ultrasonic cleaning tank is provided, and the polycrystalline silicon rod is transferred between the hanger and the table. In this case, a method for cleaning a polycrystalline silicon rod in which the rod rotates on the top surface of the pedestal and ultrasonic vibration is uniformly applied to the side surface of the rod.   A washing tank and a hanger for hanging a polycrystalline silicon rod are provided. The hanger has a comb-shaped arm in which a plurality of thin L-shaped plate members are juxtaposed, and a polycrystal is formed on the upper edge of the arm. A polycrystalline silicon cleaning apparatus, wherein a silicon rod is placed on and suspended from the cleaning tank.   A cleaning apparatus in which a pedestal having a comb-like cross section formed by standing a plurality of thin plates in parallel is provided in a cleaning tank, and a polycrystalline silicon rod is placed on the pedestal and cleaned.   It has a hanger that hangs the polycrystalline silicon rod, and a washing tank provided with a table on which the rod is placed. The polycrystalline silicon rod is washed while hung on the hanger, and transferred to the table. Cleaning device for cleaning.   A hanger having a comb-shaped arm with a plurality of thin L-shaped plates arranged side by side, and a washing tank having a comb-shaped table with a plurality of thin plates standing in parallel. And a polycrystalline silicon cleaning apparatus capable of transferring the polycrystalline silicon rod without contacting each other by inserting the arm of the hanger into the gap of the pedestal.   A hanger for hanging a polycrystalline silicon rod, a pure water cleaning tank, an acid cleaning tank, and an ultrasonic cleaning tank are provided, and the hanger has a comb-like cross section formed by juxtaposing a plurality of thin L-shaped plates. And a movement means that moves up and down and forwards and backwards, and is provided with an acid-resistant resin coat or is formed of an acid-resistant resin. A table having a comb-like cross-section formed by standing a plurality of thin plates in parallel is provided, and the ultrasonic wave is washed while the polycrystalline silicon rod is suspended and hung on the upper edge of the arm of the hanger. An apparatus for cleaning a polycrystalline silicon rod, wherein the polycrystalline silicon rod is moved to a table and cleaned in a cleaning tank.   12. A circulation path is provided in the washing tank for extracting the washing liquid and returning it to the washing tank again, and the circulation path is provided with a liquid purification means comprising a pre-filtration part and a filtration part and a liquid feed pump. The cleaning apparatus described in any one.   The cleaning apparatus according to any one of claims 7 to 12, wherein means for injecting a pure water shower is provided in the pure water cleaning tank. A polycrystalline silicon rod cleaned by the cleaning method according to claim 1, or single crystal silicon produced using the polycrystalline silicon rod as a raw material.

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