JP6693575B2 - Silicon nitride powder, release agent for polycrystalline silicon ingot, and method for producing polycrystalline silicon ingot - Google Patents

Description

  The present invention relates to a silicon nitride powder capable of forming a mold release layer having good adhesion to a mold and good mold releasability on a mold, and particularly to a silicon nitride powder suitable as a mold release agent for a polycrystalline silicon ingot.

  A polycrystalline silicon substrate used for a solar cell is usually obtained from a polycrystalline silicon ingot produced by unidirectionally solidifying molten silicon using a vertical Bridgman furnace. High performance and low cost are required for polycrystalline silicon substrates, and in order to meet these demands, suppression of impurity mixing into polycrystalline silicon ingots during directional solidification of molten silicon and polycrystalline silicon ingots are required. It is important to improve the yield of In unidirectional solidification of molten silicon by the vertical Bridgman method, a mold such as quartz is used, but in order to increase the yield of the polycrystalline silicon ingot, the mold has a good mold release property of the polycrystalline silicon ingot. Therefore, a mold in which a release agent containing silicon nitride powder is applied to the inner wall (the surface in contact with molten silicon) is generally used.

  Due to the structure of the vertical Bridgman furnace, heat escapes downward from the bottom of the mold, so that a large temperature gradient occurs in the mold in the vertical direction, and the temperature of the upper part of the mold becomes relatively high. In recent years, polycrystalline silicon ingots for solar cell substrates have tended to become larger and larger. If the temperature at the bottom of the mold (melting point: 1414 ° C) is sufficiently melted, depending on the structure of the Bridgman furnace, the upper part of the mold The temperature may be as high as 1500 ° C. or higher. In such a case, in the upper part of the mold where the temperature is high, there may be problems such that the releasability of the polycrystalline silicon ingot deteriorates, and the release layer peels off from the mold and adheres to the polycrystalline silicon ingot. Therefore, even if the release layer of the polycrystalline silicon ingot is unidirectionally solidified at a high temperature, for example, 1500 ° C. or higher, the release property of the polycrystalline silicon ingot and the adhesion of the release layer to the mold are good. Is required.

  From such a background, even if the melting temperature of silicon during directional solidification is increased to improve the yield of the polycrystalline silicon ingot applicable to the substrate of the solar cell, the releasability of the polycrystalline silicon ingot, and Development of a silicon nitride powder capable of forming a release layer having good adhesion to a mold has been desired. Further, in order to obtain a long polycrystalline silicon ingot, when a mold having a large size in the vertical direction is used, the upper part of the mold is exposed to high temperature for a particularly long time, so the melting time of silicon during unidirectional solidification It is desired to develop a silicon nitride powder capable of forming a mold release layer having a good mold releasability of a polycrystalline silicon ingot and a good adhesion to a mold even if the length is long.

JP, 2007-261832, A JP, 2013-71864, A

  Patent Document 1 discloses that a silicon nitride powder having Fe concentration and D50 within a specific range can form a strong release layer and is useful for production of polycrystalline silicon having high conversion efficiency of a solar cell. Although described, the crystal structure and crystallite size of the silicon nitride powder is not described, and the polycrystalline silicon ingot in the case of increasing the melting temperature of silicon or increasing the melting time of silicon It does not describe the releasability or the adhesion of the release layer to the mold.

  Further, in Patent Document 2, a silicon nitride powder having a particle size distribution, a β phase ratio, and a specific metal impurity in a specific range reduces the amount of impurities mixed into a polycrystalline silicon ingot and suppresses peeling of a release agent. Although shown to be possible, it is only shown that a silicon nitride powder having a relatively small D50 and D90 or a silicon nitride powder having a β phase ratio of 50 mass% can most suppress the release agent from peeling off. However, the crystallite diameter of the silicon nitride powder is not described, and the release property of the polycrystalline silicon ingot and the release layer of the polycrystalline silicon ingot when the melting temperature of silicon is increased or the melting time of silicon is lengthened. No mention is made of adhesion to the mold.

  Therefore, the present invention has a good releasability of a polycrystalline silicon ingot, even if the melting temperature of silicon during unidirectional solidification is increased or the melting time of silicon is lengthened. An object of the present invention is to provide a silicon nitride powder that can be suitably used as an agent.

  The present inventors have conducted extensive studies to solve the above problems, have a specific specific surface area, a specific β-type silicon nitride ratio and a specific particle size distribution, and have a specific metal impurity and other metal impurities. When the mold release layer of the polycrystalline silicon ingot casting mold is formed by using a silicon nitride powder having a content ratio of less than a specific ratio and a crystallite diameter larger than a specific value, the melting temperature of silicon during unidirectional solidification is increased. The inventors have found that the mold release property of the polycrystalline silicon ingot and the adhesion of the mold release layer to the mold are good even if they are increased, and have completed the present invention. That is, the present invention relates to the following matters.

(1) Silicon nitride powder having a specific surface area of 0.4 m ² / g or more and 5 m ² / g or less as measured by the BET method, a proportion of β-type silicon nitride of 70% by mass or more, and laser diffraction When D50 is the volume-based 50% particle diameter measured by the scattering method and 90% particle diameter is D90, D50 is 2 μm or more and 20 μm or less, D90 is 8 μm or more and 60 μm or less, and the Fe content ratio is Is 100 ppm or less, the content ratio of Al is 100 ppm or less, the total content ratio of metal impurities other than Fe and Al is 100 ppm or less, and the Williamson-Hall equation is calculated from the powder X-ray diffraction pattern of β-type silicon nitride. the crystallite size of β-type silicon nitride which is calculated using when a D _C, silicon nitride powder, characterized in that D _C is 300nm or more .

(2) The crystal strain of β-type silicon nitride calculated from the powder X-ray diffraction pattern of β-type silicon nitride using the Williamson-Hall equation is 0.8 × 10 ⁻⁴ or less, (1) ) Silicon nitride powder.

(3) When the specific surface area equivalent diameter calculated from the specific surface area is D _BET , D _BET / D _C (nm / nm) is 5 or less, (1) or (2) above Of silicon nitride powder.

  (4) D50 is 3 micrometers or more, The silicon nitride powder in any one of said (1)-(3) characterized by the above-mentioned.

  (5) D90 is 50 micrometers or less, The silicon nitride powder in any one of said (1)-(4) characterized by the above-mentioned.

  (6) D90 is 13 micrometers or more, The silicon nitride powder in any one of said (1)-(5) characterized by the above-mentioned.

  (7) The silicon nitride powder according to any one of (1) to (6) above, wherein the proportion of β-type silicon nitride is greater than 80% by mass.

  (8) The Fe content is 20 ppm or less, the Al content is 20 ppm or less, and the total content of metal impurities other than Fe and Al is 20 ppm or less. (7) Any of the silicon nitride powders.

  (9) Any of the above (1) to (8), wherein D10 is 0.5 μm or more and 8 μm or less, where D10 is a volume-based 10% particle diameter measured by a laser diffraction scattering method. Silicon nitride powder.

  (10) A mold release agent for a polycrystalline silicon ingot, which contains the silicon nitride powder according to any one of (1) to (9) above.

  (11) A method for producing a polycrystalline silicon ingot, in which molten silicon contained in a mold is solidified, wherein the mold has a silicon nitride contact surface contacting with the molten silicon. A method for producing a silicon ingot, which comprises using a mold coated with powder.

  According to the silicon nitride powder of the present invention, even if the melting temperature of silicon during unidirectional solidification is increased or the melting time of silicon is lengthened, the releasability of the polycrystalline silicon ingot and the release layer It is possible to provide a silicon nitride powder which can improve the adhesion to a mold and is suitable as a mold release agent for a polycrystalline silicon ingot.

It is a schematic diagram of the combustion synthesis reaction device used for manufacture of the silicon nitride powder of Examples 1-13 and Comparative Examples 1-10.

  An embodiment of the silicon nitride powder of the present invention will be described in detail.

(Silicon nitride powder)
The silicon nitride powder of the present invention is a silicon nitride powder having a specific surface area measured by the BET method of 0.4 m ² / g or more and 5 m ² / g or less, and the proportion of β-type silicon nitride is 70% by mass or more. , D50 is 2 μm or more and 20 μm or less, D90 is 8 μm or more and 60 μm or less, and D50 is 50% by volume, and D90 is 50% by volume. Content of 100 ppm or less, Al content of 100 ppm or less, the total content of metal impurities other than Fe and Al is 100 ppm or less, from the powder X-ray diffraction pattern of β-type silicon nitride Williamson- the crystallite size of β-type silicon nitride which is calculated using the Hall type is taken as D _C, to wherein the D _C is 300nm or more .

The silicon nitride powder of the present invention has a specific surface area measured by the BET method of 0.4 m ² / g or more and 5 m ² / g or less. When the specific surface area is within this range, it is possible to form a release layer having good adhesion to the mold. The specific surface area of the silicon nitride powder measured by the BET method may be 4.0 m ² / g or less, 3.0 m ² / g or less, and 2.0 m ² / g or less.

  In the silicon nitride powder of the present invention, the proportion of β-type silicon nitride is 70% by mass or more. When the proportion of β-type silicon nitride is within this range, it is possible to form a release layer having good release properties of the polycrystalline silicon ingot and good adhesion to the mold. From this viewpoint, the proportion of β-type silicon nitride is more preferably more than 80% by mass. The proportion of β-type silicon nitride can be greater than 85% by weight, greater than 90% by weight, greater than 95% by weight and even 100% by weight.

  Components other than silicon nitride are less than 3% by mass, more preferably less than 1% by mass, and particularly preferably less than 0.1% by mass. When a component other than silicon nitride is present, good releasability of the polycrystalline silicon ingot is obtained even when the melting temperature of silicon during unidirectional solidification as in the present invention is increased or when the melting time of silicon is lengthened. May not be obtained.

  The silicon nitride powder of the present invention has a D50 of 2 μm or more and 20 μm or less, where D50 is a volume-based 50% particle diameter measured by a laser diffraction scattering method. When D50 is in this range, the adhesion between the silicon nitride particles and the adhesion between the silicon nitride particles and the mold are likely to be improved, and a dense release layer is easily formed, so that the release of the polycrystalline silicon ingot is facilitated. It is possible to form a release layer having excellent properties and good adhesion to the mold. D50 is preferably 3 μm or more. D50 may be 5 μm or more, 10 μm or more, and 15 μm or more. When the 90% particle size is D90, D90 is 8 μm or more and 60 μm or less. When D90 is in this range, the surface of the release layer is likely to be smooth, and a release layer with good release properties of the polycrystalline silicon ingot can be formed. D90 is more preferably 50 μm or less, and particularly preferably 40 μm or less. D90 may be 13 μm or more, 14 μm or more, 15 μm or more, 17 μm or more, 20 μm or more, 30 μm or more.

  The silicon nitride powder of the present invention preferably has D10 of 0.5 μm or more and 8 μm or less, where D10 is a volume-based 10% particle diameter measured by a laser diffraction scattering method. D10 may be 0.6 μm or more, 0.7 μm or more, 1.0 μm or more, 2.0 μm or more, 4.0 μm or more, 6.0 μm or more. When D10 is in this range, the release layer is more easily densified, and the release layer of the polycrystalline silicon ingot and the adhesiveness to the mold can be formed further excellently.

  The silicon nitride powder of the present invention has a Fe content of 100 ppm or less. When the content ratio of Fe is within this range, it is possible to suppress the mixing of Fe into the polycrystalline silicon ingot, so that the yield of the polycrystalline silicon ingot applicable to the solar cell application is increased. The content ratio of Fe is preferably 20 ppm or less, particularly preferably 10 ppm or less and 5 ppm or less. Further, the silicon nitride powder of the present invention has an Al content of 100 ppm or less. When the content ratio of Al is within this range, it is possible to suppress the mixing of Al into the polycrystalline silicon ingot, so that the yield of the polycrystalline silicon ingot applicable to the solar cell application is increased. The content ratio of Al is preferably 20 ppm or less, particularly preferably 10 ppm or less and 5 ppm or less. Further, the total content ratio of metal impurities other than Fe and Al is 100 ppm or less. If the content ratio of the metal impurities other than Fe and Al is within this range, it is possible to suppress the mixing of the metal impurities other than Fe and Al into the polycrystalline silicon ingot, and therefore the polycrystalline silicon applicable to the solar cell application Higher ingot yield. The content ratio of metal impurities other than Fe and Al is preferably 20 ppm or less, particularly preferably 10 ppm or less and 5 ppm or less.

When the crystallite diameter of the β-type silicon nitride which is calculated using the Williamson-Hall type from powder X-ray diffraction pattern of β-type silicon nitride was _{D C,} silicon nitride powder of the present invention is a _{D C} is 300nm or more is there. When D _C is in this range, a release layer having good release properties of the polycrystalline silicon ingot and good adhesion to the mold even if the melting temperature of silicon is increased or the melting time is lengthened is obtained. Can be formed. By the D _C and above 300 nm, even if prolonged contact with the molten silicon, for example 1500 ° C. or more high temperature, silicon nitride powder of the present invention is presumed to maintain the structural stability of the crystal. From this viewpoint, it is preferable that _{D C} is 600nm or more, 1000 nm or more, and more preferably 1500nm or more.

In the silicon nitride powder of the present invention, the crystal strain of β-type silicon nitride calculated from the powder X-ray diffraction pattern of β-type silicon nitride using the Williamson-Hall equation is preferably 0.8 × 10 ⁻⁴ or less. .. If the crystal strain of β-type silicon nitride is within this range, it is necessary to form a release layer that has good mold release properties of the polycrystalline silicon ingot and good adhesion to the mold even if the melting temperature of silicon is raised. You can By setting the crystal strain to 0.8 × 10 ⁻⁴ or less, it is presumed that the silicon nitride powder of the present invention can maintain the structural stability of crystals even if it is in contact with molten silicon at a higher temperature for a long time. It From this viewpoint, the crystal strain is more preferably 0.6 × 10 ⁻⁴ or less, and 0.5 × 10 ⁻⁴ or less, 0.4 × 10 ⁻⁴ or less, 0.3 × 10 ⁻⁴ or less. It is particularly preferable that

It is preferable that the silicon nitride powder of the present invention has D _BET / D _C (nm / nm) of 5 or less, where D _BET is a specific surface area equivalent diameter calculated from the specific surface area. D _BET / D _C (nm / nm) may be 4 or less and 3 or less. If D _BET / D _C (nm / nm) is in this range, a release layer having good mold releasability of the polycrystalline silicon ingot and good adhesion to the mold can be obtained even if the melting temperature of silicon is increased. Can be formed. The reason is not clear, but the smaller the area of the interface of the crystallites in one particle of silicon nitride constituting the silicon nitride powder, the structure of the crystal of silicon nitride when it is in contact with molten silicon for a long time at high temperature. It is presumed that the social stability will be further enhanced.

(Release agent for polycrystalline silicon ingot)
The release agent for polycrystalline silicon ingots of the present invention contains the silicon nitride powder of the present invention. The release agent for a polycrystalline silicon ingot of the present invention may be the silicon nitride powder of the present invention as a main component, and may contain a component other than silicon nitride, but is composed only of the silicon nitride powder of the present invention. May be.

(Method for manufacturing polycrystalline silicon ingot)
The method for producing the polycrystalline silicon ingot of the present invention will be described below. The method for producing a polycrystalline silicon ingot of the present invention is a method for producing a polycrystalline silicon ingot in which molten silicon contained in a mold is solidified (particularly unidirectionally solidified), and as the mold, contact with the molten silicon is performed. It is characterized by using a mold whose surface is coated with the silicon nitride powder of the present invention.

(Method for producing silicon nitride powder)
An example of the method for producing the silicon nitride powder of the present invention will be described below. The silicon nitride powder of the present invention, for example, in a silicon nitride combustion synthesis process for synthesizing silicon nitride by a combustion synthesis method utilizing a self-heating and propagation phenomenon associated with a combustion reaction of silicon, using specific manufacturing conditions, Is mixed with silicon nitride powder as a diluent to the raw material silicon powder at a specific ratio to reduce the content ratio of the metal impurities of the raw material silicon powder and the silicon nitride powder as the diluent, and the silicon powder and the silicon nitride powder. A method of producing a combustion product with a low crushing strength by performing a combustion reaction with a small packing density of the mixture of By crushing using, the content of metal impurities is small, the content of β-type silicon nitride is large, and the specific surface area specified in the present invention A beauty particle size distribution, it is possible to produce a silicon nitride powder having a characteristic such as large crystal strains crystallite size is smaller. Hereinafter, an example of the manufacturing method will be specifically described.

<Preparation process of mixed raw material powder>
First, a silicon powder and a silicon nitride powder as a diluent are mixed to prepare a mixed raw material powder. Since the combustion synthesis reaction has a high temperature of 1800 ° C. or higher, silicon may be melted / welded in a portion where the combustion reaction occurs. For the purpose of suppressing this, it is preferable to add silicon nitride powder as a diluent to the raw material powder within a range that does not prevent self-propagation of the combustion reaction. The addition rate of the diluent is usually 10 to 50% by mass (the mass ratio of silicon: silicon nitride is 90:10 to 50:50), and further 15 to 40% by mass. Further, in adjusting the proportion of β-type silicon nitride in the combustion product obtained by the combustion synthesis reaction, NH ₄ Cl, NaCl or the like may be added. These additives have the effect of lowering the reaction temperature by sensible heat, latent heat and endothermic reaction. Here, the content ratio of Fe, the content ratio of Al, and the content ratio of metal impurities other than Fe and Al in the obtained mixed raw material powder are preferably 100 ppm or less, more preferably 50 ppm or less and 10 ppm or less, respectively. Therefore, it is preferable to use a high-purity powder containing a small amount of metal impurities as both the silicon powder and the silicon nitride powder as a diluent. In addition, it is preferable that the inner surface of the mixing container used for mixing the raw material powders and the portion such as the mixing medium which come into contact with the raw material powders are made of a non-metallic material having a small content ratio of Al and Fe. The method of mixing the raw material powders is not particularly limited, but when ball mill mixing is adopted, for example, the inner surface of the mixing container is preferably made of resin, and the outer surface of the mixing medium is preferably made of silicon nitride. Further, the bulk density of the mixed raw material powder is preferably less than 0.5 g / cm ³ . The bulk density of the mixed raw material powder to be less than 0.5 g / cm ^3, it is preferable that the bulk density is used 0.45 g / cm ³ or less of the silicon powder as the raw material powder. If the bulk density of the mixed raw material powder is less than 0.5 g / cm ³ , it is easy to make the crushing strength of the lumpy combustion product obtained in the <combustion synthesis reaction step> described below 4 MPa or less.

<Combustion synthesis reaction process>
Then, the obtained mixed raw material powder is burned in a nitrogen-containing atmosphere to produce a lumpy combustion product made of silicon nitride. For example, the mixed raw material powder is placed in a container such as graphite together with the igniting agent, the igniting agent is ignited in the combustion synthesis reaction device, and the nitriding reaction of silicon in the mixed raw material powder is performed by the nitriding combustion heat of the igniting agent. The reaction is initiated and the reaction is self-propagated through the silicon to complete the combustion synthesis reaction to obtain a bulk combustion product of silicon nitride.

  The crush strength of the obtained combustion product is preferably 4 MPa or less. If the crush strength of the combustion product is 4 MPa or less, crushing that will increase the amount of metal impurities mixed in and will reduce the crystallinity of the silicon nitride powder in the <crushing and classifying process of combustion product> described below. It becomes easy to obtain a silicon nitride powder having a specific surface area or particle size distribution (D50, D90 or D10) specified in the present invention without performing grinding with a large amount of energy.

<Crushing and classification process of combustion products>
The lumpy combustion product obtained is then coarsely crushed. The crushing means for coarse crushing is not particularly limited, but as the crushing medium, it is preferable to use a hard non-metallic material having a small content ratio of Al and Fe, and it is more preferable to use a crushing medium made of silicon nitride. .. Since the combustion products are lumpy, the crushing by the roll crusher is efficient, and it is preferable that the roll crusher is provided with a roll made of ceramics such as silicon nitride.

  The silicon nitride powder of the present invention can be obtained by sieving the silicon nitride powder obtained by the above coarse pulverization to remove particularly coarse particles. The sieve used for sieving is preferably made of a non-metal having a low content ratio of Al and Fe, and is preferably made of a resin.

  Further, the obtained silicon nitride powder can be finely pulverized depending on the desired specific surface area, D50 or D90. The pulverizing means for fine pulverization is not particularly limited, but pulverization with a vibration mill is preferable. The portion of the inner surface of the pot for the vibration mill that contacts the raw material powder, such as the mixed medium, is preferably made of a non-metallic material having a small content ratio of Al and Fe. The inner surface of the pot is preferably made of resin, and the mixed medium is preferably made of silicon nitride. The conditions (amplitude, frequency, grinding time) of the vibration mill can be adjusted appropriately to obtain the silicon nitride powder of the present invention having a desired specific surface area or particle size distribution (D50, D90 or D10).

As described above, the silicon nitride powder of the present invention is a mixture of a silicon powder and a silicon nitride powder as a diluent, and the resulting mixed raw material powder is filled in a container to prevent self-heating and propagation phenomena associated with combustion reaction. In the method for producing a silicon nitride powder in which the silicon powder is burned by a combustion synthesis method used and the obtained combustion product is crushed, the mixed raw material powder contains Fe content, Al content, and Fe and Al. The content of metal impurities other than is preferably 100 ppm or less, and is preferably produced by a method for producing a silicon nitride powder having a bulk density of less than 0.5 g / cm ³ , and further, the crush strength of the combustion product is It is preferably 4 MPa or less, and it is particularly preferable to use a grinding medium made of silicon nitride for grinding the combustion product.

  Hereinafter, the present invention will be described in more detail with reference to specific examples. Silicon nitride powder of the present invention, silicon powder used as a raw material powder, raw material mixed powder and measurement of physical properties of combustion products, and release of polycrystalline silicon ingot when the silicon nitride powder of the present invention is applied to a mold release agent The moldability was evaluated by the following method.

(Method of measuring specific surface area of silicon nitride powder and method of calculating specific surface area equivalent diameter D _BET )
The specific surface area of the silicon nitride powder of the present invention was obtained by measuring with a BET one-point method by nitrogen gas adsorption using Macsorb manufactured by Mountech.

Further, the specific surface area equivalent diameter D _BET was calculated by the following formula (1), assuming that all particles constituting the powder are spheres having the same diameter.
D _BET = 6 / (ρ _S × S) (1)

Here, ρ _S is the true density of silicon nitride (the true density of α-Si ₃ N ₄ is 3186 kg / m ³ , the true density of β-Si ₃ N ₄ is 3192 kg / m ³ , and the ratio of α phase to β phase The average true density was calculated and defined as the true density.) And S is the specific surface area (m ² / g).

(Method for measuring proportion of β-type silicon nitride in silicon nitride powder)
The proportion of β-type silicon nitride powder in the silicon nitride powder of the present invention was calculated as follows. For the silicon nitride powder of the present invention, a step consisting of a target made of a copper tube and a graphite monochromator is used to step-scan an X-ray detector in a diffraction angle (2θ) range of 15 to 80 ° in 0.02 ° steps. X-ray diffraction measurement was performed by the regular step scanning method. When the silicon nitride powder contains components other than silicon nitride, the peaks of those components can be compared with the corresponding peaks of a standard sample of those components to determine the proportions of those components. In all the following Examples and Comparative Examples, it was confirmed from the obtained powder X-ray diffraction patterns that the silicon nitride powder of the present invention was composed of only α-type silicon nitride and β-type silicon nitride. In addition, the proportion of β-type silicon nitride in the silicon nitride powder of the present invention is G. P. Gazzara and D.M. P. Messier, "Determination of Phase Content of Si3N4 by X-ray Diffraction Analysis", Am. Ceram. Soc. Bull. , 56 [9] 777-80 (1977) and by the method of Gazzara & Messier.

(Method of measuring D10, D50 and D90 of silicon nitride powder)
The particle size distributions of the silicon nitride powder of the present invention and the silicon powder used as a raw material in the present invention were measured as follows. The powder was put into a 0.2 mass% aqueous solution of sodium hexametaphosphate and dispersed for 6 minutes at an output of 300 W using an ultrasonic homogenizer equipped with a stainless steel center cone having a diameter of 26 mm to prepare a dilute solution. , And used as a measurement sample. The particle size distribution of the measurement sample was measured using a laser diffraction / scattering particle size distribution measuring device (Microtrac MT3000 manufactured by Nikkiso Co., Ltd.) to obtain a volume-based particle size distribution curve and its data. From the obtained particle size distribution curve and its data, D50, D90 and D10 of the silicon nitride powder of the present invention and D50 of the silicon powder used as a raw material in the present invention were calculated.

(Method for measuring the content ratio of Fe, Al, and metal impurities other than Fe and Al in silicon nitride powder, silicon powder, and raw material mixed powder)
Content ratios of Fe and Al, and metal impurities other than Fe and Al in the silicon nitride powder of the present invention, the silicon powder used as a raw material in the present invention, and the raw material mixed powder were measured as follows. In a container containing a liquid mixture of hydrofluoric acid and nitric acid, put the above powder into a tightly closed container, irradiate microwaves in the container and heat to completely decompose silicon nitride or silicon, and obtain the decomposition The solution was made up to volume with ultrapure water to give a test solution. Using ICP-AES (SPS5100 type) manufactured by SII Nanotechnology Inc., Fe, Al, and Fe and Al other than Al in the test solution were quantified from the detected wavelength and its emission intensity, and Fe, Al , And the content ratio of metal impurities other than Fe and Al were calculated.

(Method for measuring crystallite diameter D _C and crystal strain of β-type silicon nitride)
The crystallite diameter D _C and crystal strain of β-type silicon nitride of the silicon nitride powder of the present invention were measured as follows. With respect to the silicon nitride powder of the present invention, a target made of a copper tube and a graphite monochromator are used to step-scan an X-ray detector in a diffraction angle (2θ) range of 15 to 80 ° in 0.02 ° steps. X-ray diffraction measurement was performed by the regular step scanning method. From the X-ray diffraction pattern of the obtained silicon nitride powder of the present invention, the respective integral widths of the (101), (110), (200), (201) and (210) planes of β-type silicon nitride were calculated, The integration width was substituted into the Williamson-Hall formula of the following formula (2). In the following equation (2), “2 sin θ / λ” is plotted as the x-axis and “β cos θ / λ” is plotted as the y-axis, and the least squares method is used to obtain the intercept and slope of the straight line obtained from the Williamson-Hall equation. It was Then, the crystallite diameter Dc of β-type silicon nitride was calculated from the intercept, and the crystal strain of β-type silicon nitride was calculated from the slope.
β cos θ / λ = η × (2 sin θ / λ) + (1 / Dc) (2)
(Β: integral width (rad), θ: Bragg angle (rad), η: crystal strain, λ: wavelength of X-ray source (nm), Dc: crystallite diameter (nm))

(Measurement method of bulk density of mixed raw material powder)
The bulk density of the mixed raw material powder obtained in the present invention was determined by a method according to JIS R1628 "Measurement method of bulk density of fine ceramic powder".

(Method of measuring the crush strength of combustion products)
The crush strength of the combustion product obtained by the present invention was measured as follows. Five cubes each having a side of 10 mm were cut out from the combustion product to obtain measurement samples. The crushing strength of the measurement sample was measured using a manual crushing strength measuring device (Model 1334, manufactured by Aiko Engineering Co., Ltd.). A compression test was conducted by applying a load to the measurement sample placed on the pedestal, and the crush strength was calculated from the measured maximum load. The crushing strength of the combustion product obtained in the present invention was an average value of the crushing strength of five measurement samples.

(Evaluation method of releasability of polycrystalline silicon ingot)
In the present invention, a unidirectional solidification experiment of a polycrystalline silicon ingot using a mold produced by applying the silicon nitride powder of the present invention as a release agent, and releasing the polycrystalline silicon ingot from the mold, Thus, the silicon nitride powder of the present invention was evaluated. When the polycrystalline silicon ingot can be released from the mold and the release layer is not confirmed to be attached to the polycrystalline silicon ingot, ○, the polycrystalline silicon ingot can be released from the mold, but the release layer is attached to the polycrystalline silicon ingot. The case was confirmed as Δ, and the case where the polycrystalline silicon ingot could not be released from the mold, or the polycrystalline silicon ingot was cracked or chipped even if it could be released was taken as ×.

(Measuring method of metal impurities contained in polycrystalline silicon ingot)
Fe, Al, and metal impurities other than Fe and Al contained in the polycrystalline silicon ingot obtained by the directional solidification experiment were measured as follows. The obtained polycrystalline silicon ingot was divided into two parts so that the cut surface was parallel to the solidification direction, and the time of flight was measured on the central axis of the cut surface at a position 1 cm above the bottom as the measurement position. Surface analysis was performed by a secondary ion mass spectrometry method (manufactured by ULVAC-PHI, Inc. (TRIFT V nano TOF type)). Normalized secondary mass spectra of Fe, Al, and metallic impurities other than Fe and Al were detected to have a secondary ion intensity of 1 × 10 ⁻⁴ or more and to have no detection of less than 1 × 10 ⁻⁴ . Here, the normalized secondary ion intensity is the secondary ion intensity of each spectrum divided by the secondary ion intensity of all detected spectra.

(Example 1-1)
D50 is 4.0 μm, bulk density is 0.40 g / cm ³ , Fe content is 3 ppm, Al content is 4 ppm, and content of metal impurities other than Fe and Al is 3 ppm. As a silicon nitride powder (manufactured by Ube Industries, Ltd., product name "SN-E10" (content ratio of Fe; 9 ppm, content ratio of Al; 2 ppm, content ratio of metal impurities other than Fe and Al; 4 ppm)), A raw material powder was obtained by adding silicon nitride so that the addition ratio was 20 mass% (the mass ratio of silicon: silicon nitride was 80:20). The raw material powder was stored in a nylon pot filled with silicon nitride balls and having an inner wall surface lined with urethane, and a batch type vibrating mill was used to obtain a frequency of 1200 cpm and an amplitude of 8 mm for 0.5 hours. The mixture was mixed to obtain a mixed raw material powder.

FIG. 1 shows a combustion synthesis reaction apparatus 1 used in the combustion synthesis reaction of silicon in this example. The mixed raw material powder 2 obtained by mixing the raw material powders was housed in a square sheath-shaped graphite container 3 having a bottom surface of 200 × 400 mm, a depth of 30 mm, and a thickness of 10 mm. At this time, the bulk density of the mixed raw material powder was 0.45 g / cm ³ . Titanium powder and carbon powder were mixed at a mass ratio of titanium: carbon of 4: 1 and molded to prepare an igniting agent 4 used in the combustion synthesis reaction, and the igniting agent 4 was placed on the mixed raw material powder 2. .. Next, the graphite container 3 containing the mixed raw material powder 2 and the igniting agent 4 is placed in a pressure resistant container 6 equipped with a carbon heater 5 for heating the igniting agent, and the carbon heater 5 is positioned directly above the igniting agent 4. So housed.

  After degassing the inside of the pressure-resistant container 6 using the vacuum pump 7, nitrogen gas was introduced from the nitrogen cylinder 8 into the reaction container to set the atmospheric pressure to 0.6 MPa. Next, the carbon heater 5 was energized to heat the igniting agent 4 to ignite the mixed raw material powder to start the combustion synthesis reaction. During the combustion synthesis reaction, the pressure of the nitrogen atmosphere in the pressure resistant container 6 was 0.6 MPa, which was almost constant. When the inside of the pressure resistant container 6 was observed through the viewing window 9, the combustion synthesis reaction was completed after continuing for about 20 minutes. After the reaction was completed, the graphite container 3 was taken out from the pressure resistant container 6 and the lumpy combustion product was collected.

  A portion near the igniting agent was removed from the obtained combustion product, and the remaining portion was coarsely pulverized with a roll crusher having an inner surface coated with urethane and equipped with a roll made of silicon nitride, and then a nylon sieve having an opening of 100 μm was used. After passing through a sieve, the powder under the sieve was collected to obtain a silicon nitride powder of Example 1-1.

  Table 1 shows the physical property values of the silicon powder and the diluent used for the raw material powder, the physical property values of the mixed raw material powder, and the crush strength of the combustion products in Example 1-1, and the physical property values of the silicon nitride powder. It shows in Table 2.

  Evaluation of the silicon nitride powder of Example 1-1 as a mold release agent for the casting mold for polycrystalline silicon ingots was carried out as follows.

  The silicon nitride powder of Example 1-1 was housed in a polyethylene container capable of being hermetically sealed, and water was added to prepare a mixture ratio of the silicon nitride powder of 20 mass%. A silicon nitride ball was placed in a container containing silicon nitride powder and water, and the container was tightly stoppered and mixed with a batch type vibration mill at an amplitude of 5 mm and a frequency of 1780 cpm for 5 minutes to obtain a silicon nitride slurry.

  The obtained silicon nitride slurry of Example 1-1 was spray-applied to the inner surface of a quartz crucible having a square shape having a porosity of 16% and a bottom surface of 100 mm and a depth of 100 mm, which had been heated in advance to 90 ° C. It was dried at 90 ° C. for 15 hours. At this time, the release layer had a thickness of about 0.2 mm. Further, using an air atmosphere furnace, the mold was held in air at 1100 ° C. for 3 hours for heat treatment to obtain a polycrystalline silicon ingot casting mold in which the silicon nitride powder of Example 1-1 was applied to the release layer.

  The mold was filled with 300 g of silicon granules having a purity of 7 N and a size of 2 to 5 mm and housed in a Bridgman furnace. Under argon flow at atmospheric pressure, the temperature in the furnace was raised to 1500 ° C. over 5 hours to melt the silicon granules. After holding at 1500 ° C. for 24 hours, the molten silicon was unidirectionally solidified by pulling down the mold at a pulling rate of 50 mm / h, and further cooled to room temperature. Further, another method for casting the polycrystalline silicon ingot of Example 1-1 was prepared, and the holding temperature was changed to 1550 ° C. by using the mold, by the same method as in the unidirectional solidification experiment. A unidirectional solidification experiment was conducted.

  The polycrystalline silicon ingot is released from the taken-out mold, and the polycrystalline silicon ingot casting mold and the polycrystalline silicon ingot of Example 1-1 are manufactured by the method described in "Evaluation method of polycrystalline silicon ingot casting mold". Was evaluated. The results are shown in Table 3.

(Example 1-2)
A silicon nitride powder of Example 1-2 was produced in the same manner as in Example 1-1, except that the sieving after coarse pulverization was performed using a sieve having an opening of 120 μm. Then, using the silicon nitride powder of Example 1-2, two polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. Unidirectional solidification experiments at two furnace temperatures of 1500 ° C. and 1525 ° C. were performed in the same manner as in Example 1-1 using these molds, and polycrystals were performed in the same manner as in Example 1-1. A silicon ingot casting mold was evaluated.

(Example 1-3)
A silicon nitride powder of Example 1-3 was produced in the same manner as in Example 1-1, except that the sieving after coarse crushing was performed using a sieve having an opening of 80 μm. Then, using the silicon nitride powder of Example 1-3, two polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. Directional solidification experiments at two different furnace temperatures similar to those of Example 1-1 were performed in the same manner as in Example 1-1 using those molds, and in the same manner as in Example 1-1. A casting mold for polycrystalline silicon ingots was evaluated.

(Example 1-4)
A silicon nitride powder of Example 1-4 was produced in the same manner as in Example 1-1, except that the sieving after coarse pulverization was performed using a sieve having an opening of 125 μm. Then, using the silicon nitride powder of Example 1-4, three polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. Directional solidification experiments at three furnace temperatures of 1500 ° C., 1525 ° C. and 1550 ° C. were carried out in the same manner as in Example 1-1 using those molds, and the same method as in Example 1-1. Evaluated the casting mold for polycrystalline silicon ingot.

(Example 1-5)
The silicon nitride powder obtained by coarsely crushing and sieving was housed in a nylon pot whose inner wall surface filled with silicon nitride balls was lined with urethane, and the vibration frequency was 1780 cpm using a batch type vibration mill. A silicon nitride powder of Example 1-5 was produced in the same manner as in Example 1-1, except that the powder was pulverized with an amplitude of 5 mm for 20 minutes. In addition, at the time of pulverization with a batch type vibration mill, 1% by mass of ethanol was added to the combustion product as a pulverization aid. Then, using the silicon nitride powder of Example 1-5, two polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. Directional solidification experiments at two different furnace temperatures similar to those of Example 1-1 were performed in the same manner as in Example 1-1 using those molds, and in the same manner as in Example 1-1. A casting mold for polycrystalline silicon ingots was evaluated.

(Example 1-6)
A silicon nitride powder of Example 1-6 was produced in the same manner as in Example 1-5, except that the pulverization time was 40 minutes. Then, using the silicon nitride powder of Example 1-6, two polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. Directional solidification experiments at two different furnace temperatures similar to those of Example 1-1 were performed in the same manner as in Example 1-1 using those molds, and in the same manner as in Example 1-1. A casting mold for polycrystalline silicon ingots was evaluated.

(Example 1-7)
A silicon nitride powder of Example 1-7 was produced in the same manner as in Example 1-5, except that the pulverization time was 50 minutes. Then, using the silicon nitride powder of Example 1-7, two polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. Directional solidification experiments at two different furnace temperatures similar to those of Example 1-1 were performed in the same manner as in Example 1-1 using those molds, and in the same manner as in Example 1-1. A casting mold for polycrystalline silicon ingots was evaluated.

(Example 1-8)
A silicon nitride powder of Example 1-8 was produced in the same manner as in Example 1-7, except that the sieving after coarse crushing was performed using a sieve having an opening of 20 μm. Then, using the silicon nitride powder of Example 1-8, two polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. A directional solidification experiment at two different furnace temperatures similar to that of Example 1-2 was performed in the same manner as in Example 1-2 using those molds, and in the same manner as in Example 1-1. A casting mold for polycrystalline silicon ingots was evaluated.

(Example 1-9)
The silicon nitride powder obtained by coarse crushing was used with an air flow type crusher (SJ-1500 type manufactured by Nisshin Engineering Co., Ltd.) equipped with a silicon nitride liner at the kissing portion to obtain the required air volume of 3. The silicon nitride powder of Example 1-9 was produced by crushing under conditions of 0 m ³ / min and a raw material supply rate of about 250 g / min. Then, using the silicon nitride powder of Example 1-9, two polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. Directional solidification experiments at two different furnace temperatures similar to those of Example 1-1 were performed in the same manner as in Example 1-1 using those molds, and in the same manner as in Example 1-1. A casting mold for polycrystalline silicon ingots was evaluated.

(Example 1-10)
Ammonium chloride (manufactured by Wako Pure Chemical Industries, purity 99.9%) was added to the raw material powder as an additive at 6.9 mass% (the mass ratio of the mixed powder of silicon and silicon nitride and ammonium chloride was 93.1: 6. The silicon nitride powder of Example 1-10 was prepared in the same manner as in Example 1-6, except that it was further added. Then, using the silicon nitride powder of Example 1-10, two polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. Directional solidification experiments at two different furnace temperatures similar to those of Example 1-1 were performed in the same manner as in Example 1-1 using those molds, and in the same manner as in Example 1-1. A casting mold for polycrystalline silicon ingots was evaluated.

(Example 1-11)
Example except that the addition ratio of ammonium chloride as an additive was set to 9.2 mass% (so that the mass ratio of the mixed powder of silicon and silicon nitride and ammonium chloride was 90.8: 9.2). A silicon nitride powder of Example 1-11 was produced in the same manner as 1-10. Then, using the silicon nitride powder of Example 1-11, three polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. Directional solidification experiments at three furnace temperatures similar to those in Example 1-4 were performed in the same manner as in Example 1-1 using these molds, and in the same manner as in Example 1-1. A casting mold for polycrystalline silicon ingots was evaluated.

(Example 1-12)
The silicon powder of the raw material powder is made into silicon powder having D50 of 3.3 μm, bulk density of 0.36 g / cm ³ , and Fe content of 3 ppm, and Al content of 3 ppm, and Fe and metal impurities other than Al. Example except that the content ratio was 3 ppm and the diluent was silicon nitride powder manufactured by SKW (content ratio of Fe: 310 ppm, content ratio of Al: 145 ppm, content ratio of metal impurities other than Fe and Al: 42 ppm) The silicon nitride powder of Example 1-12 was produced in the same manner as in 1-1. Then, using the silicon nitride powder of Example 1-12, two polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. Directional solidification experiments at two different furnace temperatures similar to those of Example 1-1 were performed in the same manner as in Example 1-1 using those molds, and in the same manner as in Example 1-1. A casting mold for polycrystalline silicon ingots was evaluated.

(Examples 1-13)
The silicon powder of the raw material powder has a D50 of 3.3 μm, a bulk density of 0.36 g / cm ³ , an Fe content of 3 ppm, an Al content of 3 ppm, and a metal impurity content of 3 ppm other than Fe and Al. Except that the silicon powder of No. 1 was used and the diluent was silicon nitride powder (Fe content ratio: 224 ppm, Al content ratio: 500 ppm, metal impurity content ratio other than Fe and Al: 174 ppm) manufactured by VESTA Si. The silicon nitride powder of Example 1-13 was produced in the same manner as in Example 1-7. Then, using the silicon nitride powder of Example 1-13, two polycrystalline silicon casting molds were produced in the same manner as in Example 1-1. Directional solidification experiments at two different furnace temperatures similar to those of Example 1-1 were performed in the same manner as in Example 1-1 using those molds, and in the same manner as in Example 1-1. A casting mold for polycrystalline silicon ingots was evaluated.

(Comparative Example 1-1)
A silicon nitride powder of Comparative Example 1-1 was produced in the same manner as in Example 1-1, except that sieving after coarse pulverization was not performed. As seen in Table 2, the specific surface area of the silicon nitride powder obtained in Comparative Example 1-1 was as small as 0.25 m ² / g, and D10, D50, and D90 were 15.50 μm, 26.34 μm, and 62, respectively. It was as large as 0.34 μm. Then, using the silicon nitride powder of Comparative Example 1-1, one polycrystalline silicon casting mold was produced in the same manner as in Example 1-1. Only the unidirectional solidification experiment at a furnace temperature of 1500 ° C. was performed in the same manner as in Example 1-1 using the mold, and a polycrystalline silicon ingot casting mold was prepared in the same manner as in Example 1-1. evaluated.

(Comparative Example 1-2)
A silicon nitride powder of Comparative Example 1-2 was produced in the same manner as in Example 1-5, except that the pulverization time was 60 minutes. As shown in Table 2, the silicon nitride powder obtained in Comparative Example 1-2 had a specific surface area of 5.70 m ² / g, D90 of 5.69 μm, and was a powder having a small particle size. Then, using the silicon nitride powder of Comparative Example 1-2, one polycrystalline silicon casting mold was produced in the same manner as in Example 1-1. A unidirectional solidification experiment at the same furnace temperature as in Comparative Example 1-1 was performed in the same manner as in Comparative Example 1-1 using the mold, and a polycrystalline silicon ingot was obtained in the same manner as in Example 1-1. The casting mold was evaluated.

(Comparative Example 1-3)
Ammonium chloride (manufactured by Wako Pure Chemical Industries, purity 99.9%) as an additive was added to the raw material powder in an amount of 12.3% by mass (the mass ratio of the mixed powder of silicon and silicon nitride and ammonium chloride was 87.7: 12. A silicon nitride powder of Comparative Example 1-3 was prepared in the same manner as in Example 1-7 except that it was further added. As shown in Table 2, the silicon nitride powder obtained in Comparative Example 1-3 was a powder having a small proportion of β-type silicon nitride of 64%. Then, using the silicon nitride powder of Comparative Example 1-3, one polycrystalline silicon casting mold was produced in the same manner as in Example 1-1. A unidirectional solidification experiment at the same furnace temperature as in Comparative Example 1-1 was performed in the same manner as in Comparative Example 1-1 using the mold, and a polycrystalline silicon ingot was obtained in the same manner as in Example 1-1. The casting mold was evaluated.

(Comparative Example 1-4)
Silicon powder having D50 of 6.0 μm, bulk density of 0.60 g / cm ³ , Fe content of 4 ppm, Al content of 4 ppm, and metal impurities other than Fe and Al content of 4 ppm. A silicon nitride powder of Comparative Example 1-4 was produced in the same manner as in Example 1-7 except that the above was used. Silicon nitride powder obtained in Comparative Example 1-4, as seen in Table 2, the crystallite diameter _{D c} is as small as 290 nm, crystal strains were big powder and 0.92 × ^{10 -4.} Then, using the silicon nitride powder of Comparative Example 1-4, one polycrystalline silicon casting mold was produced in the same manner as in Example 1-1. A unidirectional solidification experiment at the same furnace temperature as in Comparative Example 1-1 was performed in the same manner as in Comparative Example 1-1 using the mold, and a polycrystalline silicon ingot was obtained in the same manner as in Example 1-1. The casting mold was evaluated.

(Comparative Example 1-5)
A silicon nitride powder of Comparative Example 1-5 was produced in the same manner as Comparative Example 1-4, except that the pulverizing time was 100 minutes. As seen in Table 2, the silicon nitride powder obtained in Comparative Example 1-5 was a powder having a small crystallite diameter D _c of 182 nm and a large crystal strain of 1.25 × 10 ⁻⁴ . Then, using the silicon nitride powder of Comparative Example 1-5, one polycrystalline silicon casting mold was produced in the same manner as in Example 1-1. A unidirectional solidification experiment at the same furnace temperature as in Comparative Example 1-1 was performed in the same manner as in Comparative Example 1-1 using the mold, and a polycrystalline silicon ingot was obtained in the same manner as in Example 1-1. The casting mold was evaluated.

(Comparative Example 1-6)
Silicon powder having D50 of 5.0 μm, bulk density of 0.50 g / cm ³ , Fe content of 205 ppm, Al content of 220 ppm, and metal impurities other than Fe and Al content of 503 ppm. A silicon nitride powder of Comparative Example 1-6 was produced in the same manner as Comparative Example 1-4 except that was used. The silicon nitride powder obtained in Comparative Example 1-6, as shown in Table 2, the content ratio of Fe is 109 ppm, the content ratio of Al is 127 ppm, the content ratio of metal impurities other than Fe and Al is 271 ppm, The powder contained a large proportion of metal impurities. Then, using the silicon nitride powder of Comparative Example 1-6, one polycrystalline silicon casting mold was produced in the same manner as in Example 1-1. A unidirectional solidification experiment at the same furnace temperature as in Comparative Example 1-1 was performed in the same manner as in Comparative Example 1-1 using the mold, and a polycrystalline silicon ingot was obtained in the same manner as in Example 1-1. The casting mold was evaluated.

(Comparative Example 1-7)
Silicon powder with D50 of 8.5 μm, bulk density of 0.70 g / cm ³ , Fe content of 2 ppm, Al content of 1 ppm, and metal impurities other than Fe and Al content of 2 ppm. Was used, and the raw material powder was placed in a nylon pot filled with alumina balls and ball-milled for 24 hours using ethanol as a solvent. Comparative Example 1 was carried out in the same manner as in Example 1-1, except that the roll crusher provided with the above was used, and that the sieving after coarse crushing was performed using a stainless steel sieve having an opening of 150 μm. A -7 silicon nitride powder was prepared. As shown in Table 2, the silicon nitride powder obtained in Comparative Example 1-7 had a content ratio of Al of 846 ppm, a high content ratio of metal impurities, and a small specific surface area of 0.21 m ² / g. D10, D50, and D90 were large powders of 15.43 μm, 26.50 μm, and 62.44 μm, respectively. Then, using the silicon nitride powder of Comparative Example 1-7, one polycrystalline silicon casting mold was produced in the same manner as in Example 1-1. A unidirectional solidification experiment at the same furnace temperature as in Comparative Example 1-1 was performed in the same manner as in Comparative Example 1-1 using the mold, and a polycrystalline silicon ingot was obtained in the same manner as in Example 1-1. The casting mold was evaluated.

(Comparative Example 1-8)
Silicon powder having D50 of 5.0 μm, bulk density of 0.50 g / cm ³ , Fe content of 205 ppm, Al content of 220 ppm, and metal impurities other than Fe and Al content of 503 ppm. Was used, and the raw material powder was mixed for 1 hour in a planetary ball mill filled with alumina balls to prepare a silicon nitride powder of Comparative Example 1-8 in the same manner as in Example 1-6. .. The silicon nitride powder obtained in Comparative Example 1-8, as shown in Table 2, the content ratio of Fe is 109 ppm, the content ratio of Al is 420 ppm, the content ratio of metal impurities other than Fe and Al is 312 ppm, the content of metal impurities is large and had a crystallite size _D c 290 nm and smaller powder. Then, using the silicon nitride powder of Comparative Example 1-8, one polycrystalline silicon casting mold was produced in the same manner as in Example 1-1. A unidirectional solidification experiment at the same furnace temperature as in Comparative Example 1-1 was performed in the same manner as in Comparative Example 1-1 using the mold, and a polycrystalline silicon ingot was obtained in the same manner as in Example 1-1. The casting mold was evaluated.

(Comparative Example 1-9)
D50 is 2.5 μm, bulk density is 0.26 g / cm ³ , content ratio of Fe is 2 ppm, content ratio of Al is 3 ppm, and content ratio of metal impurities other than Fe and Al is 3 ppm. The mold was filled and uniaxially molded at a pressure of 1500 kg / cm ² , to obtain a uniaxially molded body of silicon powder. The molded body was filled in a graphite container, housed in a batch type nitriding furnace, the atmosphere in the furnace was replaced with a nitrogen atmosphere, and then the temperature was raised to 1450 ° C. in a nitrogen atmosphere and kept for 3 hours. After cooling to room temperature, the nitriding product was taken out. The obtained nitriding product was coarsely crushed by a roll crusher having a urethane nitride inner surface and provided with a roll made of silicon nitride, and sieved with a nylon sieve having an opening of 100 μm to collect powder under the sieve. .. Next, the powder is stored in an alumina pot filled with silicon nitride balls and whose inner surface is lined with urethane, and finely pulverized for 30 minutes with a batch type vibration mill at a vibration frequency of 1780 cpm and an amplitude of 5 mm. Then, a silicon nitride powder of Comparative Example 1-9 was produced. As shown in Table 2, the silicon nitride powder obtained in Comparative Example 1-9, which is a direct nitriding method without combustion synthesis, has a large specific surface area of 6.10 m ² / g and a ratio of β-type silicon nitride of 50. %, D10 and D50 are as small as 0.40 μm and 1.60 μm, respectively, the crystallite diameter D _c is as small as 55 nm, the crystal strain is large as 3.01 × 10 ^−4, and the D _BET / D _c is The powder was as large as 5.6. Then, using the silicon nitride powder of Comparative Example 1-9, one polycrystalline silicon casting mold was produced in the same manner as in Example 1-1. A unidirectional solidification experiment at the same furnace temperature as in Comparative Example 1-1 was performed in the same manner as in Comparative Example 1-1 using the mold, and a polycrystalline silicon ingot was obtained in the same manner as in Example 1-1. The casting mold was evaluated.

(Comparative Example 1-10)
A silicon nitride powder of Comparative Example 1-10 was produced in the same manner as Comparative Example 1-9, except that the pulverization time was 10 minutes. As shown in Table 2, the silicon nitride powder obtained in Comparative Example 1-10, which is a direct nitriding method without combustion synthesis, has a small proportion of β-type silicon nitride of 58% and D15 and D90 of 1.60 μm each. The powder was as small as 5.90 μm, the crystallite diameter Dc was as small as 88 nm, the crystal strain was large as 1.90 × 10 ^−4, and the D _BET / D _c was as large as 6.7. Then, using the silicon nitride powder of Comparative Example 1-10, one polycrystalline silicon casting mold was produced in the same manner as in Example 1-1. A unidirectional solidification experiment at the same furnace temperature as in Comparative Example 1-1 was performed in the same manner as in Comparative Example 1-1 using the mold, and a polycrystalline silicon ingot was obtained in the same manner as in Example 1-1. The casting mold was evaluated.

  In Examples 1-2 to 1-13 and Comparative Examples 1-1 to 1-10, the physical property values of the silicon powder and the diluent used as the raw material powder, the physical property values of the mixed raw material powder, and the crushing strength of the combustion product. Is shown in Table 1, and the physical properties of the silicon nitride powder are shown in Table 2. Table 3 shows the evaluation results of the polycrystalline silicon ingot casting molds and the polycrystalline silicon ingots of Examples 1-2 to 1-13 and Comparative examples 1-1 to 1-10.

(Example 2-1)
According to the method described below, a polycrystalline silicon ingot casting mold having a release layer containing the silicon nitride powder of Example 1-1 was prepared, and the polycrystalline silicon ingot casting mold and the silicon ingot were evaluated. ..

  The silicon nitride powder of Example 1-1 was placed in a sealable polyethylene container, and silica sol having a silica concentration of 20 mass% (Fuso Chemical Co., Ltd., product name “PL-3”) and water were added. At this time, silicon nitride: silica sol: water were mixed in a mass ratio of 20: 8: 72. Next, in a container containing silicon nitride powder, silica sol, and water, balls made of silicon nitride were placed and hermetically sealed, and a batch type vibration mill was used to mix for 5 minutes with a vibration mill having an amplitude of 5 mm and a frequency of 1780 rpm, A silicon nitride slurry was obtained.

  The obtained silicon nitride slurry of Example 2-1 was sprayed on the inner wall surface of a quartz crucible having a square shape having a porosity of 16%, a bottom surface of 100 mm and a depth of 100 mm, which had been heated to 90 ° C. in advance, It was dried at 90 ° C. for 15 hours to obtain a polycrystalline silicon ingot casting mold having a release layer containing the silicon nitride powder of Example 2-1. The thickness of the release layer at this time was about 0.2 mm.

  Using the obtained casting mold for polycrystalline silicon of Example 2-1, a unidirectional solidification experiment was conducted in the same manner as in Example 1-1, and a method similar to that in Example 1-1 was used. A casting mold for polycrystalline silicon and a polycrystalline silicon ingot were evaluated. The results are shown in Table 4.

(Examples 2-2 to 2-13, Comparative examples 2-1 to 2-10)
A silicon nitride slurry was produced in the same manner as in Example 2-1, except that the silicon nitride powder shown in Table 4 was used, to produce a polycrystalline silicon casting mold. Using the obtained polycrystalline silicon casting molds of Examples and Comparative Examples, a directional solidification experiment was conducted in the same manner as in Example 1-1, and polycrystalline silicon was produced in the same manner as in Example 1-1. The ingot casting mold and the silicon ingot were evaluated. The results are shown in Table 4.

  As described above, the silicon nitride powder of the present invention, by applying a heat treatment at a high temperature after coating the mold, it is possible to form a mold release layer having good adhesion and releasability substantially by itself. It was also found that by mixing with silica sol and coating it on a mold, a mold release layer having good adhesion and mold releasability can be formed on the mold without heat treatment at high temperature.

  INDUSTRIAL APPLICABILITY The silicon nitride powder of the present invention is useful as a mold release agent capable of forming a mold release layer having good adhesion and mold releasability to a mold, and particularly high quality silicon substrates for solar cells. It is useful as a release agent for polycrystalline silicon ingots that can be collected at a yield. Further, the silicon nitride powder of the present invention is capable of forming a dense release layer and has high crystallinity, and therefore is useful as a raw material for a silicon nitride sintered body that exhibits high strength at high temperatures.

1 Combustion Synthesis Reaction Device 2 Mixed Raw Material Powder 3 Graphite Container 4 Ignition Agent 5 Carbon Heater 6 Pressure Resistant Container 7 Vacuum Pump 8 Nitrogen Cylinder 9 Peep Window

Claims (11)

Silicon nitride powder,
The specific surface area measured by the BET method is 0.4 m ² / g or more and 5 m ² / g or less,
The proportion of β-type silicon nitride is 70% by mass or more,
When the volume-based 50% particle diameter measured by the laser diffraction scattering method is D50 and the 90% particle diameter is D90, D50 is 2 μm or more and 20 μm or less, and D90 is 8 μm or more and 60 μm or less,
Fe content ratio is 100 ppm or less,
Al content is 100 ppm or less,
The total content of metal impurities other than Fe and Al is 100 ppm or less,
When the crystallite diameter of β-type silicon nitride calculated from the powder X-ray diffraction pattern of β-type silicon nitride using the Williamson-Hall equation is D _C , D _C is 300 nm or more. Silicon powder. The crystal strain of β-type silicon nitride calculated from the powder X-ray diffraction pattern of β-type silicon nitride using the Williamson-Hall formula is 0.8 × 10 ⁻⁴ or less, and the nitriding according to claim 1. Silicon powder. D _BET / D _C (nm / nm) is 5 or less when the specific surface area equivalent diameter calculated from the specific surface area is D _BET, and the silicon nitride powder according to claim 1 or 2. ..   D50 is 3 micrometers or more, The silicon nitride powder as described in any one of Claims 1-3 characterized by the above-mentioned.   D90 is 50 micrometers or less, The silicon nitride powder as described in any one of Claims 1-4.   D90 is 13 micrometers or more, The silicon nitride powder as described in any one of Claims 1-5 characterized by the above-mentioned.   The ratio of β-type silicon nitride is greater than 80% by mass, and the silicon nitride powder according to claim 1. Fe content ratio is 20 ppm or less,
Al content ratio is 20 ppm or less,
The silicon nitride powder according to any one of claims 1 to 7, wherein the total content of metal impurities other than Fe and Al is 20 ppm or less.   D10 is 0.5 μm or more and 8 μm or less, where D10 is a volume-based 10% particle diameter measured by a laser diffraction / scattering method, and nitriding according to any one of claims 1 to 8. Silicon powder.   A mold release agent for a polycrystalline silicon ingot, comprising the silicon nitride powder according to claim 1.   A method for manufacturing a silicon ingot for solidifying molten silicon contained in a mold, wherein the silicon nitride powder according to any one of claims 1 to 9 is applied to the contact surface with the molten silicon as the mold. A method for manufacturing a silicon ingot, which comprises using a mold.

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