JP6329920B2 - Method for evaluating polycrystalline silicon mass - Google Patents

Method for evaluating polycrystalline silicon mass Download PDF

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JP6329920B2
JP6329920B2 JP2015082332A JP2015082332A JP6329920B2 JP 6329920 B2 JP6329920 B2 JP 6329920B2 JP 2015082332 A JP2015082332 A JP 2015082332A JP 2015082332 A JP2015082332 A JP 2015082332A JP 6329920 B2 JP6329920 B2 JP 6329920B2
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polycrystalline silicon
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JP2016199448A (en
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秀一 宮尾
秀一 宮尾
祢津 茂義
茂義 祢津
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信越化学工業株式会社
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  The present invention relates to a technique for evaluating a polycrystalline silicon lump, and relates to a technique for evaluating the cleanliness of a polycrystalline silicon lump obtained by crushing polycrystalline silicon synthesized by the Siemens method, and a polycrystalline silicon lump selected by the technique. About.
  A polycrystalline silicon lump as a raw material for producing single crystal silicon by the CZ method is obtained by removing a polycrystalline silicon rod synthesized by the Siemens method from a reaction furnace and then crushing it. After the pulverization operation, the product is manufactured by performing chemical etching with hydrofluoric acid or the like in order to clean the surface.
  When single crystal silicon is grown by the CZ method, the polycrystalline silicon lump is melted in a quartz crucible, and the seed crystal (seed) of the single crystal silicon is brought into contact with the silicon melt, so that the growth is performed. In order to make the subsequent single crystal silicon highly pure, it is necessary to reduce impurities contained in the silicon melt as much as possible. This means that it is necessary to reduce both the bulk impurity concentration of the polycrystalline silicon lump and the concentration of impurities adhering to the surface as much as possible.
  In general, atomic absorption analysis, ICP-AES, ICP-MS, etc. are used for metal impurities as a method for evaluating the bulk and surface impurity concentration of a polycrystalline silicon lump. Diameter elements such as oxygen and carbon are used. For this, an infrared absorption method is used. After evaluating the cleanliness of the polycrystalline silicon lump by these methods, it is classified by product rank.
  In order to reduce bulk impurities in the polycrystalline silicon lump, not only gas purification technology such as trichlorosilane and hydrogen, which are raw materials used in the production of polycrystalline silicon rods, and removal technology of impurities contained in the raw material gas, but also reaction Considerations have been made on the furnace components. On the other hand, the reduction of the surface impurities of the polycrystalline silicon lump has been promoted exclusively by examining the etching conditions of the surface, and semiconductor grade products are generally distributed in the market of 2000 pptw or less.
JP2013-143549A
  As described above, in order to achieve high purity single crystal silicon grown by the CZ method, it is necessary to reduce both the bulk impurity concentration of the polycrystalline silicon lump and the concentration of impurities adhering to the surface as much as possible. is there. That is, even if the bulk impurity concentration of the polycrystalline silicon block is low, the polycrystalline silicon block having a high surface impurity concentration is not suitable as a raw material for production. Similarly, the bulk impurity concentration is low even if the surface impurity concentration of the polycrystalline silicon block is low. High polycrystalline silicon lumps are also unsuitable as raw materials for production.
  However, if the surface impurity concentration and the bulk impurity concentration of the polycrystalline silicon lump are separately evaluated, the evaluation work becomes complicated, and as a result, the manufacturing cost of the polycrystalline silicon lump becomes high. For example, the surface impurity concentration is obtained from the analysis of the first extract obtained by etching the extreme surface region of the polycrystalline silicon lump, and the bulk impurity concentration is obtained from the analysis of the second extract obtained by etching a deeper region. In such a method, it is necessary to perform the etching operation and the impurity measurement operation a plurality of times.
  The present invention has been made in view of such problems, and the object thereof is to determine and select a polycrystalline silicon lump suitable as a raw material for producing single crystal silicon by the CZ method by a single impurity measurement. It is to provide a technique for making this possible.
  In order to solve the above problems, the polycrystalline silicon lump according to the present invention has an impurity concentration obtained by analyzing an extract obtained by etching a region of at least 30 μm from the surface with a mixed aqueous solution of hydrofluoric acid and nitric acid. Is less than 100 pptw per metal element and less than 10 ppbw per carbon concentration.
  For example, the metal element is any one of Li, B, Na, Mg, Al, P, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Sn, W, and Pb. is there.
  Further, for example, the metal element is any one of six types of Na, Cr, Fe, Ni, Cu, and Zn.
  Preferably, the total concentration of the six elements is less than 100 pptw.
  More preferably, the total concentration of the six elements is less than 80 pptw.
  The method for evaluating a polycrystalline silicon lump according to the present invention is a method for evaluating the cleanliness of a polycrystalline silicon lump, wherein an area of at least 30 μm from the surface of the polycrystalline silicon lump is mixed with a mixed aqueous solution of hydrofluoric acid and nitric acid. When the impurity concentration obtained by etching and analyzing the extract obtained by the etching is less than 100 pptw per metal element and less than 20 ppba per carbon concentration, it is determined to be clean.
  Preferably, the etching is performed while controlling the temperature of the etching solution to 39 ° C. or lower.
  Preferably, the etching is performed by setting the circulating flow rate (liter / minute) of the etching solution to 1.3 or more of the volume (liter) of the chemical bath.
  The present invention provides a technique for enabling determination and selection of a polycrystalline silicon lump suitable as a raw material for producing single crystal silicon by the CZ method.
[Occurrence of spots and etching chemical temperature]
When etching a region having a predetermined depth from the surface of the polycrystalline silicon block, a mixed acid of hydrofluoric acid (HF) and nitric acid (HNO 3 ) is generally used as an etchant. This reaction between the hydrofluoric acid solution and silicon is an exothermic reaction, and there is an exotherm of 85.2 kcal per mole of silicon. For this reason, the amount of heat generation increases as the etching dissolution amount increases, and the reaction at the silicon surface proceeds violently as the liquid temperature rises. If the etchant is not flowing in such a state, brown spots are generated on the silicon surface, resulting in a deterioration in quality.
  On the other hand, if the chemical concentration of the etchant is lowered, a sufficient allowance for etching cannot be secured. Therefore, the chemical concentration of the etchant is set to a relatively high level, and the etchant flows (circulates) to efficiently remove heat from the silicon lump surface and to quickly remove reaction products generated by etching. It becomes necessary to do.
  Therefore, the circulating flow rate (liter / minute) of the etchant was set to 1.3 of the volume (liter) of the chemical bath, and the influence of the etchant temperature on the occurrence of spots was examined.
The experimental conditions are as follows. A chemical tank with an internal volume of 60 liters is filled with a 50 wt% aqueous solution of hydrofluoric acid (HF) and a 70 wt% aqueous solution of nitric acid (HNO 3 ) as an etchant (volume ratio 1: 9), and the flow rate is 78 liters. / Min. The etchant was circulated by a pump and overflowed at the upper part of the tank. The “circulation flow rate” is 1.3 (/ min) which is a value obtained by dividing 78 liters / minute by 60 liters. Note that both HF and HNO 3 are grades for the electronics industry.
  In this chemical tank, the polycrystal silicon lump with a total amount of 13 kg is stored in a PP bag and etched, and the upper limit temperature of the etchant in the chemical tank is controlled by cooling a part of the flow path (pipe). did. The cooling structure is the same as that disclosed in JP2013-143549A (Patent Document 1).
  Table 1 summarizes the results of examining the etchant temperature in the chemical bath and the presence or absence of spot generation under 6 conditions. From this result, no stain is observed under the condition that the etchant temperature (upper limit) in the chemical bath is controlled to 39 ° C. or lower. On the other hand, when the temperature exceeds this, brown stain is generated as the etchant temperature increases. The degree of is also high.
  When the etchant temperature is 39 ° C., the etching allowance when etching is performed for 120 seconds is 60 μm, and a sufficient allowance is secured.
  Based on the above results, the inventors of the present invention are effective in controlling the etching solution temperature to be 39 ° C. or lower, which is effective in suppressing the occurrence of stains while ensuring a sufficient machining allowance. I concluded that there was.
[Influence of metal impurity concentration in bulk on surface metal impurity concentration]
Subsequently, during the etching process, the influence of the metal impurity concentration in the bulk on the surface metal impurity concentration was examined by setting six conditions. Under any conditions, the upper limit temperature of the etching solution was controlled at 39 ° C., and the circulating amount of the etchant (liter / minute) was set to 1.5 of the volume (liter) of the chemical bath. The other conditions were as described above.
  First, in the first batch, in order to evaluate the total amount of metal impurity concentration in the bulk and surface metal impurity concentration, an area of at least 30 μm from the surface is etched with a mixed aqueous solution of hydrofluoric acid and nitric acid, and 5.0 ml of the resulting extract is obtained. Was collected in a clean Teflon (registered trademark) container, evaporated to dryness in a temperature range of 85 ± 5 ° C., 1.0 ml of 1 wt% nitric acid aqueous solution was added to make the volume constant, and ICP-MS measurement was performed.
  The metal elements to be analyzed are Li, B, Na, Mg, Al, P, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Sn, W, Pb, and P analysis. An ICP-MS / MS apparatus (8800) manufactured by Agilent was used for the analysis, and an ICP-MS apparatus (7500CS) manufactured by Agilent was used for the other metal element analysis.
  Following this, in the second batch, in order to evaluate the total amount of metal impurity concentration in the bulk, an area of at least 30 μm from the surface was etched with a mixed aqueous solution of hydrofluoric acid and nitric acid, and 5.0 ml of the extract was added in the same manner as above. The sample was collected in a clean Teflon (registered trademark) container, evaporated to dryness in the temperature range of 85 ± 5 ° C., and 1.0 ml of 1 wt% nitric acid aqueous solution was added to make a constant volume, and ICP-MS measurement was performed.
Table 2 shows the total amount of metal impurity concentrations in the six types of bulk of Na, Cr, Fe, Ni, Cu, and Zn, the total amount of the above six types of metal impurities in the bulk and the surface concentration, and Na, Cr, Fe It is the table | surface which put together the density | concentration of the element which showed the highest density | concentration among Ni, Cu, and Zn. The unit of concentration is pptw.
In all of Examples 4 to 6 , the maximum value of one element of the metal element is less than 100 pptw, and the total concentration of the six elements (Na, Cr, Fe, Ni, Cu, Zn) is less than 100 pptw. In the case of 4 , the total concentration of 6 elements is less than 80pptw.
  From the results shown in this table, it can be seen that the higher the metal impurity concentration in the bulk, the higher the surface metal impurity concentration. This is obtained by adding and quantifying the metal impurity elements in the bulk dissolved in the etchant during etching.
[Effect of circulating flow rate of etchant on the amount of metal impurities]
Subsequently, the influence of the circulating flow rate of the etchant on the amount of metal impurities was examined by setting six conditions. Under any condition, the upper limit temperature of the etching solution was controlled at 39 ° C., and the circulating amount of the etchant (liter / minute) was set in the range of 0.8 to 1.7 of the volume (liter) of the chemical bath. The other conditions were as described above.
  First, in a first batch, an area of at least 30 μm from the surface is etched with a mixed aqueous solution of hydrofluoric acid and nitric acid. Subsequently, in a second batch, an area of at least 20 μm from the surface is etched with a mixed aqueous solution of hydrofluoric acid and nitric acid. In the same manner as above, 5.0 ml of the extract was dispensed into a clean Teflon (registered trademark) container, evaporated to dryness in a temperature range of 85 ± 5 ° C., and 1.0 ml of a 1 wt% nitric acid aqueous solution was added to a constant volume. ICP-MS measurement was performed.
  Table 3 shows the total amount of metal impurity concentrations in the six bulks of Na, Cr, Fe, Ni, Cu, and Zn, and the element that showed the highest concentration among Na, Cr, Fe, Ni, Cu, and Zn. It is the table | surface which summarized the density | concentration and the yield (%) at the time of using these as a raw material for CZ silicon crystal growth. The unit of machining allowance is μm, and the unit of concentration is pptw.
In all of Examples 7 to 9 , the maximum value of one element of the metal element is less than 100 pptw, and the total concentration of the six elements (Na, Cr, Fe, Ni, Cu, Zn) is less than 100 pptw. In the case of 7 , the total concentration of 6 elements is less than 80pptw.
Each of Examples 7 to 9 has a CZ yield of 100%, and as a result of its high purity, it shows a very good yield.
[Effect of circulating flow rate of etchant on the amount of carbon impurities]
Subsequently, the influence of the circulating flow rate of the etchant on the amount of carbon impurities was examined by setting six conditions. Under any condition, the upper limit temperature of the etching solution was controlled at 39 ° C., and the circulating amount of the etchant (liter / minute) was set in the range of 0.8 to 1.7 of the volume (liter) of the chemical bath. The other conditions were as described above.
  First, in a first batch, an area of at least 30 μm from the surface is etched with a mixed aqueous solution of hydrofluoric acid and nitric acid. Subsequently, in a second batch, an area of at least 20 μm from the surface is etched with a mixed aqueous solution of hydrofluoric acid and nitric acid. The organic matter adhering to the surface of the obtained polycrystalline silicon lump was driven off by raising the heating temperature to 350 ° C. while passing an inert gas through the sealed container, and adsorbed on the adsorbent.
The adsorbent is Tenax-TA, which is a weakly polar porous polymer bead based on 2,6-diphenyl-p-phenylene oxide, having a surface area of 35 m 2 / g and a pore area of 2. 4 cm 2 / g, average pore size 200 nm, a specific gravity of 0.25 g / cm 3.
  Thereafter, the adsorbent was heated to desorb the components and introduced into GC-MS to quantify the carbon components.
The adsorption conditions are as follows.
-Sample amount: 5g
Sample size: major axis 20-30 mm, minor axis 5-10 mm
・ Sample heating temperature and time: 250 ° C. × 10 minutes ・ Aeration gas type: helium (50 ml / min)
-Capture of released components: -60 ° C (liquid nitrogen)
-Heating (desorption) of the adsorbent: The temperature rising rate is -60 ° C to 250 ° C for 25 seconds
Moreover, GC-MS measurement conditions are as follows.
-Device name: 5975C-MSD manufactured by Agilent
Separation column: Agilent-5, HP-5MS, 25 m × 0.2 mm diameter, film thickness 0.33 μm
-Temperature conditions: 50 ° C x 5 minutes → 300 ° C (+ 10 ° C / min)
Injection port: 300 ° C. (split ratio = 20: 1)
-Carrier gas flow rate: Helium 1 ml / min-Mass spectrometry detector: EI (electron impact ionization) mode
  On the other hand, the total of surface and bulk carbon was measured by inserting a 19 mm diameter × 140 mm rod-like sample into an etching trough, taking it out after etching, single crystallization with a small FZ apparatus, and measuring by an infrared absorption method. .
  Table 4 is a table summarizing the surface carbon impurity concentration, the total surface and bulk carbon impurities, and the carbon concentration in the crystals when these polycrystalline silicon blocks were used as raw materials for CZ silicon crystal growth. is there. The unit of the machining allowance is μm, the unit of the total surface carbon impurity concentration and the surface and bulk carbon impurities is pptw, and the unit of carbon concentration in the CZ silicon crystal is ppba.
In any of Examples 10 to 12 , the carbon concentration in the CZ crystal was less than 5 ppba, indicating a very good result.
  As for organic substances on the surface, etching is incomplete, or many organic substances are adsorbed and adhered due to contamination from the environment, handling, and packing material after etching. Since these organic substances on the surface are taken in together with carbon as a bulk during the production of a single crystal, it is necessary to reduce the concentration of both, like the metal element.
  Based on the above results, in the present invention, an impurity obtained by etching a region of at least 30 μm from the surface of the polycrystalline silicon lump with a mixed aqueous solution of hydrofluoric acid and nitric acid and analyzing the extract obtained by the etching. When the concentration is less than 100 pptw per element of the metal element and less than 10 ppbw per carbon concentration, it is determined to be clean.
  Therefore, the impurity concentration obtained by analyzing the extract obtained by etching a region of at least 30 μm from the surface with a mixed aqueous solution of hydrofluoric acid and nitric acid is less than 100 ptw per metal element, A polycrystalline silicon mass that is less than 10 ppbw can be obtained.
  By selecting the conditions, the total concentration of the six elements can be less than 100 pptw, preferably less than 80 pptw.
  In the present invention, the etching is performed with the circulating amount (liter / minute) of the etching solution being 1.3 or more of the volume (liter) of the chemical bath.
  The present invention provides a technique for enabling determination and selection of a polycrystalline silicon lump suitable as a raw material for producing single crystal silicon by the CZ method.

Claims (5)

  1. A method for evaluating the cleanliness of a polycrystalline silicon lump, wherein a region at least 30 μm from the surface of the polycrystalline silicon lump is made of 50 wt% aqueous hydrofluoric acid (HF) and 70 wt% aqueous nitric acid (HNO 3 ). Etching with a mixed acid (volume ratio of 1: 9) as an etchant and controlling the temperature of the etchant to 39 ° C. or less, with a circulation flow rate (liter / minute) of 1.3 or more of the volume (liter) of the chemical bath Then, the extract obtained by the etching was evaporated to dryness in a temperature range of 85 ± 5 ° C., and the volume was adjusted by adding 1.0 ml of 1 wt% -nitric acid aqueous solution, and the ICP-MS measurement was performed . metal impurity concentration is less than 100pptw per element of the metal element, leaving the heating component adsorbent after the organic substances adhering to the surface of the polycrystalline silicon chunks after the etching was adsorbed by the adsorbent Carbon concentration obtained by performing the determination of the introduced carbon component is allowed by GC-MS determines the cleaned is less than 20Ppba, the evaluation method of the polycrystalline silicon chunks.
  2.   The metal element is any one of Li, B, Na, Mg, Al, P, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Sn, W, and Pb. The method for evaluating a polycrystalline silicon lump according to claim 1.
  3.   The method for evaluating a polycrystalline silicon lump according to claim 2, wherein the metal element is any one of six types of Na, Cr, Fe, Ni, Cu, and Zn.
  4.   The method for evaluating a polycrystalline silicon lump according to claim 3, wherein the total concentration of the six elements is less than 100pptw.
  5.   The method for evaluating a polycrystalline silicon lump according to claim 4, wherein the total concentration of the six elements is less than 80pptw.
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DE19741465A1 (en) * 1997-09-19 1999-03-25 Wacker Chemie Gmbh Polycrystalline silicon
JPH11195637A (en) * 1998-01-06 1999-07-21 Toshiba Ceramics Co Ltd Etching of silicon wafer and device
JP4200107B2 (en) * 2004-01-09 2008-12-24 株式会社トクヤマ Method for analyzing impurities in silicon
JP3804864B2 (en) * 2004-05-24 2006-08-02 株式会社Sumco Impurity analysis method
JP4877897B2 (en) * 2004-07-21 2012-02-15 シルトロニック・ジャパン株式会社 Method for removing impurities from silicon wafer and analysis method
US7905963B2 (en) * 2008-11-28 2011-03-15 Mitsubishi Materials Corporation Apparatus and method for washing polycrystalline silicon
JP5816562B2 (en) * 2012-01-12 2015-11-18 信越化学工業株式会社 Heat exchanger and heat removal method for etching solution for silicon-based material

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