JPWO2018110560A1 - Silicon nitride powder, mold release agent for polycrystalline silicon ingot, and method for producing polycrystalline silicon ingot - Google Patents

Abstract

Even when the melting temperature of silicon at the time of unidirectional solidification is increased or when the melting time of silicon is extended, it is suitably used as a mold release agent for polycrystalline silicon ingots having good releasability of polycrystalline silicon ingots. It is an object of the present invention to provide a silicon nitride powder that can be Silicon nitride powder with a specific surface area of 0.4 m 2 / g to 5 m 2 / g and a ratio of β-type silicon nitride of 70 mass% or more, D 50 of 2 μm to 20 μm, D 90 of 8 μm to 60 μm The content ratio of Fe 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 crystallite diameter of β-type silicon nitride is Provided is a silicon nitride powder characterized in that DC is 300 nm or more when DC is taken.

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, and in particular to a silicon nitride powder suitable as a mold release agent for polycrystalline silicon ingots.

  A polycrystalline silicon substrate used for a solar cell is generally obtained from a polycrystalline silicon ingot manufactured by unidirectionally solidifying molten silicon using a vertical Bridgman furnace. In the polycrystalline silicon substrate, higher performance and lower cost are required, and in order to meet the requirements, suppression of mixing of impurities into the polycrystalline silicon ingot at the time of unidirectional solidification of molten silicon, and polycrystalline silicon ingot are required. It is important to improve the yield of In unidirectional solidification of molten silicon by the vertical Bridgman method, a mold made of quartz or the like is used, but in order to increase the yield of polycrystalline silicon ingot, the mold has good releasability of polycrystalline silicon ingot. In general, a mold in which a release agent containing silicon nitride powder is applied to an inner wall (surface in contact with molten silicon) is generally used.

  In the vertical Bridgman furnace, the heat escapes downward from the bottom of the mold due to its structure, so that a large temperature gradient is generated in the mold in the vertical direction, and the temperature at the top of the mold becomes relatively high. In recent years, polycrystalline silicon ingots for solar cell substrates tend to be larger, and raising the temperature until the silicon (melting point; 1414 ° C) at the bottom of the mold 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 more. In such a case, problems such as mold releasability of the polycrystalline silicon ingot deteriorating at the upper part of the mold at a high temperature, and the mold releasing layer peeling from the mold and adhering to the polycrystalline silicon ingot may occur. Therefore, even if the mold release layer of the polycrystalline silicon ingot is unidirectionally solidified at a high temperature, for example, 1500 ° C. or more, the releasability of the polycrystalline silicon ingot is good and the adhesion of the mold release layer to the mold is good. Is required.

  From such a background, the releasability of the polycrystalline silicon ingot, even if the melting temperature of silicon at the time of unidirectional solidification is raised to improve the yield of polycrystalline silicon ingot applicable to the substrate of the solar cell, It is desired to develop a silicon nitride powder that can form a release layer with good adhesion to a mold. In addition, if a mold having a large size in the vertical direction is used to obtain a long polycrystalline silicon ingot, the upper part of the mold is exposed to a high temperature particularly for a long time, and therefore the melting time of silicon during unidirectional solidification It is desired to develop a silicon nitride powder capable of forming a release layer having good releasability of polycrystalline silicon ingot and good adhesion to a mold, even though the length of the film is long.

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

  In Patent Document 1, it is possible that a silicon nitride powder having a Fe concentration and D50 in a specific range can form a strong release layer and is useful for producing polycrystalline silicon having a high conversion efficiency of a solar cell. Although described, the crystal structure and crystallite diameter of the silicon nitride powder are not described, and the polycrystalline silicon ingot when the melting temperature of silicon is increased or the melting time of silicon is extended. There is no description about the releasability or the adhesion of the releasable layer to the mold.

  Further, according to Patent Document 2, silicon nitride powder whose particle size distribution, the ratio of β phase and specific metal impurities are in a specific range reduces the amount of impurities mixed in the polycrystalline silicon ingot and suppresses peeling of the release agent. Although it has been shown that it can be done, it has only been shown that silicon nitride powder having relatively small D50 and D90 and silicon nitride powder having a proportion of 50% by mass of .beta. Therefore, the crystallite diameter of silicon nitride powder is not described, and the releasability and release layer of polycrystalline silicon ingot when raising the melting temperature of silicon or prolonging the melting time of silicon. The adhesion to the mold is not described.

  Therefore, according to the present invention, even if the melting temperature of silicon in one direction solidification is increased or the melting time of silicon is extended, the mold releasability of the polycrystalline silicon ingot is excellent. It is an object of the present invention to provide a silicon nitride powder that can be suitably used as an agent.

  The present inventors have intensively studied to solve the above-mentioned problems, and have a specific specific surface area, a specific ratio of β-type silicon nitride and a specific particle size distribution, and specific metal impurities and metal impurities other than them. When the mold release layer of polycrystalline silicon ingot casting mold is formed using silicon nitride powder having a content ratio of less than a specified ratio and a crystallite diameter larger than a specified value, the melting temperature of silicon at the time of unidirectional solidification is It has been found that the releasability of the polycrystalline silicon ingot and the adhesion of the releasable layer to the mold are good even at high temperatures, and the present invention has been completed. 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 measured by BET method, and having a proportion of β-type silicon nitride of 70 mass% or more; Assuming that the volume-based 50% particle diameter measured by the scattering method is D50 and the 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 Fe content ratio 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 Willison-Hall equation is obtained 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. ) 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, the above (1) or (2) Silicon nitride powder.

  (4) The silicon nitride powder according to any one of the above (1) to (3), wherein D50 is 3 μm or more.

  (5) The silicon nitride powder according to any one of the above (1) to (4), wherein D90 is 50 μm or less.

  (6) The silicon nitride powder according to any one of the above (1) to (5), wherein D90 is 13 μm or more.

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

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

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

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

  (11) A method for producing a polycrystalline silicon ingot for solidifying molten silicon contained in a mold, comprising the silicon nitride according to any one of the above (1) to (9) on the contact surface with the molten silicon as the mold. A manufacturing method of a silicon ingot characterized by using a mold to which powder was applied.

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

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

  The 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 of 0.4 m ² / g or more and 5 m ² / g or less measured by BET method, and the proportion of β-type silicon nitride is 70 mass% or more Assuming that the 50% particle diameter based on volume 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, D90 is 8 μm or more and 60 μm or less, Fe The content ratio of Al is 100 ppm or less, the content ratio of Al is 100 ppm or less, and the total content of metal impurities other than Fe and Al is 100 ppm or less. According to the powder X-ray diffraction pattern of β-type silicon nitride 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 of 0.4 m ² / g or more and 5 m ² / g or less measured by BET method. If the specific surface area is in 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, or 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. If the ratio of β-type silicon nitride is in this range, it is possible to form a release layer having good releasability of the polycrystalline silicon ingot and good adhesion to the mold. From this viewpoint, the proportion of β-type silicon nitride is more preferably greater than 80% by mass. The proportion of β-type silicon nitride may be greater than 85% by weight, greater than 90% by weight, greater than 95% by weight, and may be 100% by weight.

  The content of components other than silicon nitride is preferably less than 3% by mass, more preferably less than 1% by mass, and particularly preferably less than 0.1% by mass. If a component other than silicon nitride is present, good releasability of polycrystalline silicon ingot is obtained even when the melting temperature of silicon is increased during unidirectional solidification as in the present invention, or even when the melting time of silicon is increased. There is a risk that you will not get

  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 50% particle diameter on a volume basis measured by a laser diffraction scattering method. If D50 is in this range, the adhesion between the silicon nitride particles and the adhesion between the silicon nitride particles and the mold tend to be good, and it is easy to form a fine release layer, so the release of polycrystalline silicon ingot It is possible to form a release layer having good properties as well as adhesion to the mold. It is preferable that D50 is 3 micrometers or more. D50 may be 5 μm or more, 10 μm or more, 15 μm or more. When the 90% particle diameter is D90, D90 is 8 μm or more and 60 μm or less. If D90 is in this range, the surface of the release layer is likely to be smooth, and a release layer having good releasability 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 a 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. If D10 is in this range, the release layer is more easily densified, and the release layer of the polycrystalline silicon ingot and the adhesion to the mold can be further formed.

  The silicon nitride powder of the present invention has an Fe content of 100 ppm or less. If the content ratio of Fe is in this range, the mixing of Fe into the polycrystalline silicon ingot can be suppressed, so the yield of polycrystalline silicon ingot applicable to solar cell applications is increased. The content ratio of Fe is preferably 20 ppm or less, and particularly preferably 10 ppm or less and 5 ppm or less. Moreover, the silicon nitride powder of this invention is 100 ppm or less in content rate of Al. If the content ratio of Al is in this range, the mixing of Al into the polycrystalline silicon ingot can be suppressed, and the yield of polycrystalline silicon ingots applicable to solar cell applications is increased. The content ratio of Al is preferably 20 ppm or less, and particularly preferably 10 ppm or less and 5 ppm or less. Moreover, the sum total of the content rate of metal impurities other than Fe and Al is 100 ppm or less. If the content ratio of metal impurities other than Fe and Al is in this range, the mixture of metal impurities other than Fe and Al in the polycrystalline silicon ingot can be suppressed, so polycrystalline silicon applicable to solar cell applications The yield of ingots is increased. The content of metal impurities other than Fe and Al is preferably 20 ppm or less, and more 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. If D _C is in this range, the release layer of the polycrystalline silicon ingot exhibits good releasability and adhesion to the mold even if the melting temperature of silicon is increased or the melting time is increased. It can be formed. By the D _C and above 300 nm, even 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.

The silicon nitride powder of the present invention preferably has a crystal strain of 0.8 × 10 ^-4 or less of β-type silicon nitride calculated from the powder X-ray diffraction pattern of β-type silicon nitride using the Williamson-Hall equation. . If the crystal strain of β-type silicon nitride is in this range, a release layer is formed which has good releasability of the polycrystalline silicon ingot and adhesion to the mold even if the melting temperature of silicon is higher. Can. By setting the crystal strain to 0.8 × 10 ^-4 or less, it is surmised that the silicon nitride powder of the present invention can maintain the structural stability of the crystal even if it contacts the molten silicon for a long time at a higher temperature. Ru. 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 Being particularly preferred.

In the silicon nitride powder of the present invention, it is preferable that D _BET / D _C (nm / nm) is 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, the release layer has good releasability of polycrystalline silicon ingot and good adhesion to the mold even if the melting temperature of silicon is higher. It can be formed. The reason is not clear, but the smaller the area of the interface of crystallites in one particle of silicon nitride constituting the silicon nitride powder, the structure of the crystal of silicon nitride when it contacts with molten silicon for a long time at high temperature It is surmised that the

(Release agent for polycrystalline silicon ingot)
The mold release agent for polycrystalline silicon ingots of the present invention comprises the silicon nitride powder of the present invention. The releasing agent for polycrystalline silicon ingot of the present invention may be any main component of the silicon nitride powder of the present invention, and may contain components other than silicon nitride, but is composed only of the silicon nitride powder of the present invention It is good.

(Manufacturing method of 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 according to the present invention is a method for producing a polycrystalline silicon ingot for solidifying (especially directionally solidifying) molten silicon contained in a mold, wherein the mold is in contact with the molten silicon as the mold. It is characterized by using a mold coated with the silicon nitride powder of the present invention on the surface.

(Method of 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 can be produced, for example, by using specific production conditions in the process of synthesis of silicon nitride which synthesizes silicon nitride by a combustion synthesis method utilizing self-heating and propagation phenomena accompanying combustion reaction of silicon. The silicon powder of the raw material is mixed with the silicon powder as a diluent at a specific ratio to reduce the content of metal impurities in the silicon powder of the raw material and the silicon nitride powder as the diluent, and the silicon powder and the silicon nitride powder The packing density of the mixture is reduced and combustion reaction is carried out to produce a combustion product having a small crushing strength, and the obtained combustion product having a small crushing strength is subjected to a method having a small crushing energy and being hard to mix with metal impurities. By using and grinding, the content ratio of metal impurities is small, the content ratio 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, silicon powder and silicon nitride powder as a diluent are mixed to prepare mixed raw material powder. Since the combustion synthesis reaction has a high temperature of 1,800 ° C. or more, melting and deposition of silicon may occur in the 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, as long as the self propagation of the combustion reaction is not hindered. 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. In addition, NH ₄ Cl or NaCl may be added to adjust the ratio of β-type silicon nitride of the combustion product obtained by the combustion synthesis reaction. These additives have the effect of lowering the reaction temperature by sensible heat, latent heat and endothermic reaction. Here, in the mixed raw material powder to be obtained, the content ratio of Fe, the content ratio of Al, and the content ratio of metal impurities other than Fe and Al are preferably 100 ppm or less, more preferably 50 ppm or less, and 10 ppm or less. Therefore, it is preferable to use a high purity powder having a low content of metal impurities, both for silicon powder and silicon nitride powder as a diluent. Moreover, it is preferable that the location which contacts raw material powder, such as the inner surface of a mixing container used for mixing of raw material powder, and mixing media, is a nonmetallic raw material with few content ratios, such as Al and Fe. The mixing method of the raw material powder is not particularly limited, but for example, in the case of employing ball mill mixing, the inner surface of the mixing container is preferably made of resin, and the outer surface of the mixed medium is preferably made of silicon nitride. Moreover, it is preferable to make bulk density of mixed raw material powder 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 set the crush strength of the massive combustion product obtained in <combustion synthesis reaction step> to 4 MPa or less.

<Combustion synthesis reaction process>
Next, the mixed raw material powder obtained is burned in a nitrogen-containing atmosphere to produce a massive combustion product of silicon nitride. For example, mixed raw material powder is accommodated together with an ignition agent in a container made of graphite or the like, the ignition agent is ignited in the combustion synthesis reactor, and the nitriding reaction of silicon in the mixed raw material powder is carried out by the nitriding combustion heat of the ignition agent. The reaction is self-propagated throughout the silicon to complete the combustion synthesis reaction to obtain a massive combustion product of silicon nitride.

  Here, the combustion product obtained preferably has a crushing strength of 4 MPa or less. If the crushing strength of the combustion product is 4 MPa or less, grinding is performed such that the mixing of metal impurities is increased in the <grind and classification step of combustion product> described later, and the crystallinity of the silicon nitride powder is reduced. It becomes easy to obtain the silicon nitride powder having the specific surface area or the particle size distribution (D50, D90 or D10) specified in the present invention even if the pulverization with high energy is not performed.

<Pulverization and classification process of combustion products>
The resulting massive combustion products are then coarsely crushed. There is no particular limitation on the grinding means of the coarse grinding, but it is preferable to use a hard nonmetallic material having a small content ratio such as Al and Fe as a grinding medium, and it is more preferable to use a grinding medium made of silicon nitride . Since the combustion products are massive, grinding by a roll crusher is efficient, and it is preferable that a roll made of a ceramic such as silicon nitride be provided as the roll crusher.

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

  In addition, depending on the desired specific surface area, D50 or D90, the obtained silicon nitride powder can be pulverized. There is no particular limitation on the pulverizing means of pulverizing, but pulverizing with a vibration mill is preferable. It is preferable that the locations in contact with the raw material powder, such as the inner surface of the pot for the vibration mill and the mixed media, be nonmetallic materials having a small content ratio of Al, Fe and the like. 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 as appropriate 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 obtained by mixing the silicon powder and the silicon nitride powder as a diluent, filling the obtained mixed raw material powder in a container, and generating self-heating and propagation phenomena associated with the combustion reaction. In the method for producing a silicon nitride powder in which the silicon powder is burned by the combustion synthesis method used and the obtained combustion product is crushed, the mixed raw material powder includes a content ratio of Fe, a content ratio of Al, and Fe and Al It is preferable to manufacture by the manufacturing method of the silicon nitride powder whose content rates of metal impurities other than 100 ppm or less, respectively, and bulk density is less than 0.5 g / cm ³ , and further, crushing strength of the said combustion product is The pressure is preferably 4 MPa or less, and in particular, it is preferable to use a grinding media made of silicon nitride for grinding the combustion product.

  The present invention will be described in more detail by way of specific examples. Physical property measurement of silicon nitride powder of the present invention, silicon powder used as raw material powder, raw material mixed powder and combustion product, and release of polycrystalline silicon ingot when silicon nitride powder of the present invention is applied to mold release agent The evaluation of the moldability was performed 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 determined by measuring with a BET one-point method by nitrogen gas adsorption using Macsorb manufactured by Mountech.

The specific surface area equivalent diameter D _BET was obtained from the following equation (1), assuming that all particles constituting the powder are spheres of the same diameter.
D _BET = 6 / (ρ _S × S) (1)

Here, [rho _S is the true density of silicon nitride _(α-Si 3 _{N 4} of the true density 3186kg / ^{m 3,} the true density of 3192kg / ^{m 3} of _β-Si 3 _{N 4,} the ratio of the alpha phase and beta phase The average true density was calculated and taken as the true density), S is the specific surface area (m ² / g).

(Method of measuring proportion of β-type silicon nitride in silicon nitride powder)
The ratio of β-type silicon nitride powder of the silicon nitride powder of the present invention was calculated as follows. For the silicon nitride powder of the present invention, using a target made of a copper tube and a graphite monochrome meter, step scan the X-ray detector in the range of diffraction angles (2θ) of 15-80 ° in steps of 0.02 ° The X-ray diffraction measurement was performed by the fixed step scanning method. When the silicon nitride powder contains components other than silicon nitride, the ratio of those components can be determined by comparing the peaks of those components with the corresponding peaks of the standard samples of those components. In all of 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 only of α-type silicon nitride and β-type silicon nitride. In addition, the proportion of β-type silicon nitride in the silicon nitride powder according to the invention is as described in G.I. P. Gazzara and D. P. Messier, "Determination of Phase Content of Si3N4 by X-ray Diffraction Analysis", Am. Ceram. Soc. Bull. , 56 [9] 777-80 (1977), calculated by the method of Gazzara & Messier.

(Method of measuring D10, D50 and D90 of silicon nitride powder)
The particle size distribution of the silicon nitride powder of the present invention and the silicon powder used as a raw material in the present invention was measured as follows. The above powder is put into a 0.2% by mass aqueous solution of sodium hexametaphosphate, and dispersed for 6 minutes at a power of 300 W using an ultrasonic homogenizer equipped with a stainless steel center cone 26 mm in diameter to prepare a dilute solution. , And the measurement sample. The particle size distribution of the measurement sample was measured using a laser diffraction / scattering type particle size distribution measuring apparatus (Microtrac MT 3000, manufactured by Nikkiso Co., Ltd.), and a volume-based particle size distribution curve and its data were obtained. From the obtained particle size distribution curve and the data thereof, 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 of measuring the content ratio of Fe, Al, and metallic impurities other than Fe and Al of silicon nitride powder, silicon powder and raw material mixed powder)
The content ratios of the silicon nitride powder of the present invention, the silicon powder used as a raw material in the present invention, and Fe and Al, Fe, and metal impurities other than Al in the raw material mixed powder were measured as follows. The above powder is charged into a container containing a mixture of hydrofluoric acid and nitric acid and sealed up, and the container is irradiated with microwaves and heated to completely decompose silicon nitride or silicon, and the obtained decomposition is obtained. The solution was adjusted to volume with ultrapure water to prepare a test solution. Fe, Al, and metallic impurities other than Fe and Al in the test solution are quantified from the detected wavelength and its emission intensity using ICP-AES (SPS 5100 type) manufactured by SII Nano Technology Inc., Fe, Al The content ratio of metal impurities other than Fe and Al was calculated.

(Method of measuring crystallite diameter D _C and crystal strain of β-type silicon nitride)
Crystallite diameter D _C and crystal distortion β-type silicon nitride of the silicon nitride powder of the present invention was measured as follows. For the silicon nitride powder of the present invention, using a target made of a copper tube and a graphite monochrome meter, step scan the X-ray detector in the range of diffraction angles (2θ) of 15-80 ° in steps of 0.02 ° The X-ray diffraction measurement was performed by the fixed step scanning method. From the X-ray diffraction pattern of the obtained silicon nitride powder of the present invention, the respective integral widths of (101), (110), (200), (201) and (210) planes of β-type silicon nitride are calculated, The integration width was substituted into the Williamson-Hall equation of the following equation (2). Plot “2 sin θ / λ” in the following equation (2) with x axis and “β cos θ / λ” as y axis, and use the least squares method to find the intercept and slope of the straight line obtained from this Williamson-Hall equation The Then, the crystallite diameter Dc of β-type silicon nitride was calculated from the section, and the crystal strain of β-type silicon nitride was calculated from the inclination.
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))

(Method of measuring 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 in accordance with JIS R1628 "Method for measuring bulk density of fine ceramic powder".

(Method of measuring crushing strength of combustion products)
The crushing strength of the combustion product obtained in the present invention was measured as follows. From the combustion product, five cubes each having a side of 10 mm were cut out and used as 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 load was applied to the measurement sample placed on the pedestal to perform a compression test, and the crushing strength was calculated from the measured maximum load. The crushing strength of the combustion product obtained in the present invention was taken as an average value of crushing strengths 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 is conducted using a mold produced by applying the silicon nitride powder of the present invention as a mold release agent, and the polycrystalline silicon ingot is released from the mold. The silicon nitride powder of the present invention was evaluated as follows. When the polycrystalline silicon ingot can be released from the mold and adhesion of the release layer is not confirmed in the polycrystalline silicon ingot, ○, although the polycrystalline silicon ingot can be released from the mold, adhesion of the release layer to the polycrystalline silicon ingot In the case where is confirmed, the case in which the polycrystalline silicon ingot can not be released from the mold, or in the case where it can be released, cracking or chipping in the polycrystalline silicon ingot is regarded as ×.

(Method of measuring metal impurities contained in polycrystalline silicon ingot)
Fe, Al, and metal impurities other than Fe and Al contained in the polycrystalline silicon ingot obtained in the directional solidification experiment were measured as follows. The obtained polycrystalline silicon ingot is divided into two so that the cut surface is parallel to the solidification direction, and a position 1 cm from the bottom on the central axis of the cut surface is taken as a measurement position. Surface analysis was performed by next ion mass spectrometry (manufactured by ULVAC-PHI, Inc. (TRIFT V nano TOF type)). The case where the secondary ion intensity of secondary mass spectra of Fe, Al, and metal impurities other than Fe and Al was 1 × 10 ⁻⁴ or more was detected, and the case of less than 1 × 10 ⁴ was not detected. Here, the normalized secondary ion intensity is obtained by dividing the secondary ion intensity of each spectrum by the secondary ion intensity of all detected spectra.

Example 1-1
Diluent to silicon powder with D50 of 4.0 μm, bulk density of 0.40 g / cm ³ , Fe content rate of 3 ppm, Al content rate of 4 ppm, and Fe and other metal impurities content rate of 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)), It was added as the raw material powder so that the addition rate of silicon nitride might be 20 mass% (the mass ratio of silicon: silicon nitride is 80:20). The raw material powder is accommodated in a nylon pot filled with silicon nitride balls and whose inner wall is urethane-lined, and a batch type vibration mill is used for 0.5 hours with a frequency of 1200 cpm and an amplitude of 8 mm. It mixed and obtained mixed raw material powder.

FIG. 1 shows a combustion synthesis reaction apparatus 1 used for the combustion synthesis reaction of silicon in the present embodiment. The mixed raw material powder 2 obtained by mixing the above raw material powder was accommodated in a square-sheared 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 . A mixture of titanium powder and carbon powder in a mass ratio of titanium to carbon of 4: 1 was formed to prepare an ignition agent 4 used for the combustion synthesis reaction, and the ignition agent 4 was placed on the mixed raw material powder 2 . Next, the carbon heater 5 is positioned immediately above the ignition agent 4 in the pressure-resistant container 6 provided with the carbon heater 5 for heating the ignition agent, and the graphite container 3 containing the mixed raw material powder 2 and the ignition agent 4. So housed.

  After degassing the inside of the pressure resistant container 6 using the vacuum pump 7, nitrogen gas was introduced into the reaction container from the nitrogen cylinder 8 to set the atmospheric pressure to 0.6 MPa. Next, the carbon heater 5 was energized to heat the ignition agent 4, and the mixed raw material powder was ignited to start the combustion synthesis reaction. During the combustion synthesis reaction, the nitrogen atmosphere pressure of the pressure resistant container 6 was substantially constant at 0.6 MPa. When the inside of the pressure-resistant container 6 was observed from the observation window 9, the combustion synthesis reaction ended after continuing for about 20 minutes. After completion of the reaction, the container 3 made of graphite was taken out from the pressure-resistant container 6 to recover a massive combustion product.

  A portion near the ignition agent is removed from the obtained combustion product, and the remaining portion is roughly crushed with a roll crusher having a urethane-coated inner surface and equipped with a silicon nitride roll, and a nylon sieve with an opening of 100 μm. The powder was sieved and the powder under the sieve was collected to obtain a silicon nitride powder of Example 1-1.

  Physical properties of silicon powder and diluent used for raw material powder, physical properties of mixed raw material powder, crushing strength of combustion product, and physical properties of silicon nitride powder in Example 1-1 It shows in Table 2.

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

  The silicon nitride powder of Example 1-1 was accommodated in a pluggable polyethylene container, and water was added to adjust the mixing ratio of the silicon nitride powder to be 20% by mass. A silicon nitride ball was charged into a container containing silicon nitride powder and water, and sealed up, and mixed for 5 minutes with an amplitude of 5 mm and a frequency of 1780 cpm using a batch-type vibration mill to obtain a silicon nitride slurry.

  The obtained silicon nitride slurry of Example 1-1 was spray-coated on the inner surface of a quartz crucible having a porosity of 16%, a bottom of 100 mm and a depth of 100 mm, which had been heated to 90 ° C. in advance, and then It dried at 90 degreeC for 15 hours. The thickness of the release layer at this time was about 0.2 mm. Furthermore, it heat-processed by hold | maintaining in the air for 3 hours at 1100 degreeC using air atmosphere furnace, and the mold for polycrystalline silicon ingot casting which applied the silicon nitride powder of Example 1-1 to the mold release layer was obtained.

  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 was housed in a Bridgman furnace. The temperature in the furnace was raised to 1500 ° C. under argon flow at atmospheric pressure for 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. Also, another polycrystalline silicon ingot casting mold of Example 1-1 was produced, and the same method as the unidirectional solidification experiment was used except that the holding temperature was changed to 1550 ° C. using the mold. One-way coagulation experiments were performed.

  The polycrystalline silicon ingot is released from the mold taken out, and the mold for polycrystalline silicon ingot casting of Example 1-1 and the polycrystalline silicon ingot according to the method described in "Method for evaluating mold for polycrystalline silicon ingot". 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 sieving after coarse grinding was performed using a sieve with 120 μm openings. And two casting molds for polycrystalline silicon casting were produced by the method similar to Example 1-1 using the silicon nitride powder of Example 1-2. Two-way solidification experiments at two furnace temperatures of 1500 ° C. and 1525 ° C. are conducted using these molds in the same manner as in Example 1-1, and polycrystalline in the same manner as in Example 1-1. The 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 sieving after coarse grinding was performed using a sieve with an aperture 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. The same two-way solidification experiments at the same furnace temperature as in Example 1-1 are carried out in the same manner as in Example 1-1 using these molds, and in the same manner as in Example 1-1. The polycrystalline silicon ingot casting mold was evaluated.

(Example 1-4)
The silicon nitride powder of Example 1-4 was produced in the same manner as in Example 1-1 except that sieving after coarse grinding was performed using a sieve with an opening of 125 μm. And three casting molds for polycrystalline silicon casting were produced by the method similar to Example 1-1 using the silicon nitride powder of Example 1-4. Three-way solidification experiments at three furnace temperatures of 1500 ° C., 1525 ° C. and 1550 ° C. were carried out using these molds in the same manner as in Example 1-1, and in the same manner as Example 1-1. The mold for casting of polycrystalline silicon ingot was evaluated.

(Example 1-5)
The silicon nitride powder obtained by coarse crushing and sieving is housed in a nylon pot lined with a urethane nitride on the inner wall surface filled with silicon nitride balls, and using a batch type vibration mill, the frequency 1780 cpm The silicon nitride powder of Example 1-5 was produced in the same manner as Example 1-1 except that the fine grinding was performed for 20 minutes with an amplitude of 5 mm. In addition, in the case of grinding | pulverization with a batch type vibration mill, 1 mass% of ethanol was added with respect to the combustion product as a grinding | pulverization auxiliary agent. And two casting molds for polycrystalline silicon casting were produced by the method similar to Example 1-1 using the silicon nitride powder of Example 1-5. The same two-way solidification experiments at the same furnace temperature as in Example 1-1 are carried out in the same manner as in Example 1-1 using these molds, and in the same manner as in Example 1-1. The polycrystalline silicon ingot casting mold was evaluated.

(Example 1-6)
The silicon nitride powder of Example 1-6 was produced in the same manner as in Example 1-5 except that the pulverizing time was 40 minutes. And two casting molds for polycrystalline silicon casting were produced by the method similar to Example 1-1 using the silicon nitride powder of Example 1-6. The same two-way solidification experiments at the same furnace temperature as in Example 1-1 are carried out in the same manner as in Example 1-1 using these molds, and in the same manner as in Example 1-1. The polycrystalline silicon ingot casting mold 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 time for pulverization was set to 50 minutes. And two casting molds for polycrystalline silicon casting were produced by the method similar to Example 1-1 using the silicon nitride powder of Example 1-7. The same two-way solidification experiments at the same furnace temperature as in Example 1-1 are carried out in the same manner as in Example 1-1 using these molds, and in the same manner as in Example 1-1. The polycrystalline silicon ingot casting mold was evaluated.

(Example 1-8)
The silicon nitride powder of Example 1-8 was produced in the same manner as in Example 1-7 except that sieving after coarse grinding was performed using a sieve with an aperture of 20 μm. And two casting molds for polycrystalline silicon casting were produced by the method similar to Example 1-1 using the silicon nitride powder of Example 1-8. The same two-way solidification experiments at the same furnace temperature as in Example 1-2 are carried out using those molds in the same manner as in Example 1-2, and in the same manner as in Example 1-1. The polycrystalline silicon ingot casting mold was evaluated.

(Example 1-9)
The silicon nitride powder obtained by the coarse grinding is used with an air flow crusher (SJ-1500 manufactured by Nisshin Engineering Co., Ltd.) equipped with a silicon nitride liner at the kiss part, and the required air amount is 3. The silicon nitride powder of Example 1-9 was produced by grinding under the conditions of 0 m ³ / min and a raw material feed rate of about 250 g / min. And two casting molds for polycrystalline silicon casting were produced by the method similar to Example 1-1 using the silicon nitride powder of Example 1-9. The same two-way solidification experiments at the same furnace temperature as in Example 1-1 are carried out in the same manner as in Example 1-1 using these molds, and in the same manner as in Example 1-1. The polycrystalline silicon ingot casting mold was evaluated.

(Example 1-10)
In the raw material powder, ammonium chloride (manufactured by Wako Pure Chemical Industries, purity 99.9%) as an additive, 6.9% by mass (mixed powder of silicon and silicon nitride and ammonium chloride in a mass ratio of 93.1: 6. The silicon nitride powder of Example 1-10 was produced in the same manner as in Example 1-6 except that 9) was further added. And two casting molds for polycrystalline silicon casting were produced by the method similar to Example 1-1 using the silicon nitride powder of Example 1-10. The same two-way solidification experiments at the same furnace temperature as in Example 1-1 are carried out in the same manner as in Example 1-1 using these molds, and in the same manner as in Example 1-1. The polycrystalline silicon ingot casting mold was evaluated.

(Example 1-11)
Example except that the addition ratio of ammonium chloride of the additive was 9.2 mass% (the mass ratio of the mixed powder of silicon and silicon nitride and ammonium chloride is 90.8: 9.2) The silicon nitride powder of Example 1-11 was produced in the same manner as in 1-10. And three casting molds for polycrystalline silicon casting were produced by the method similar to Example 1-1 using the silicon nitride powder of Example 1-11. The same three-way solidification experiments at the same furnace temperature as in Example 1-4 are carried out using those molds in the same manner as in Example 1-1, and in the same manner as in Example 1-1. The polycrystalline silicon ingot casting mold was evaluated.

(Example 1-12)
The silicon powder of the raw material powder is converted to a silicon powder having a D50 of 3.3 μm, a bulk density of 0.36 g / cm ³ and a Fe content of 3 ppm, an Al content of 3 ppm, Fe and metallic impurities other than Al Example except that the content ratio was 3 ppm, and the diluent was made to silicon nitride powder (content ratio of Fe: 310 ppm, content ratio of Al: 145 ppm, content ratio of metallic impurities other than Fe and Al; 42 ppm) manufactured by SKW. The silicon nitride powder of Example 1-12 was produced in the same manner as 1-1. And two casting molds for polycrystalline silicon casting were produced by the method similar to Example 1-1 using the silicon nitride powder of Example 1-12. The same two-way solidification experiments at the same furnace temperature as in Example 1-1 are carried out in the same manner as in Example 1-1 using these molds, and in the same manner as in Example 1-1. The polycrystalline silicon ingot casting mold was evaluated.

(Example 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 content of metal impurities other than Fe and Al 3 ppm Silicon powder, and the diluent used was silicon nitride powder (Fe content: 224 ppm, Al content: 500 ppm, Fe and metal impurities other than 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. And two casting molds for polycrystalline silicon casting were produced by the method similar to Example 1-1 using the silicon nitride powder of Example 1-13. The same two-way solidification experiments at the same furnace temperature as in Example 1-1 are carried out in the same manner as in Example 1-1 using these molds, and in the same manner as in Example 1-1. The polycrystalline silicon ingot casting mold was evaluated.

(Comparative Example 1-1)
A silicon nitride powder of Comparative Example 1-1 was produced in the same manner as Example 1-1 except that sieving after coarse grinding was not performed. As shown in Table 2, the silicon nitride powder obtained in Comparative Example 1-1 has a small specific surface area of 0.25 m ² / g, and D10, D50, D90 are 15.50 μm, 26.34 μm, 62 respectively. Both were as large as .34 μm. And one mold for polycrystalline silicon casting was produced by the method similar to Example 1-1 using the silicon nitride powder of comparative example 1-1. A unidirectional solidification experiment at a furnace temperature of 1500 ° C. is performed using the mold in the same manner as in Example 1-1, and a mold for casting polycrystalline silicon ingots in the same manner as in Example 1-1. evaluated.

(Comparative example 1-2)
The silicon nitride powder of Comparative Example 1-2 was produced in the same manner as in Example 1-5 except that the time for pulverization was set to 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 with 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. The same direction solidification experiment in the same furnace temperature as Comparative Example 1-1 is conducted by the same method as Comparative Example 1-1 using its mold, and a polycrystalline silicon ingot is produced by the same method as Example 1-1. The casting molds were evaluated.

(Comparative example 1-3)
In the raw material powder, ammonium chloride (manufactured by Wako Pure Chemical Industries, purity 99.9%) as an additive, 12.3 mass% (mixed powder of silicon and silicon nitride and mass ratio of ammonium chloride to ammonium chloride) is 87.7: 12. The silicon nitride powder of Comparative Example 1-3 was produced in the same manner as in Example 1-7 except that it was 3). As shown in Table 2, the silicon nitride powder obtained in Comparative Example 1-3 was a powder in which the proportion of β-type silicon nitride was as low as 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. The same direction solidification experiment in the same furnace temperature as Comparative Example 1-1 is conducted by the same method as Comparative Example 1-1 using its mold, and a polycrystalline silicon ingot is produced by the same method as Example 1-1. The casting molds were evaluated.

(Comparative Example 1-4)
Silicon powder with D50 of 6.0 μm, bulk density of 0.60 g / cm ³ , Fe content of 4 ppm, Al content of 4 ppm, Fe and metal impurities other than Al content of 4 ppm in raw material powder A silicon nitride powder of Comparative Example 1-4 was produced in the same manner as in Example 1-7 except for using. As shown in Table 2, the silicon nitride powder obtained in Comparative Example 1-4 was a powder with a small crystallite diameter D _c of 290 nm and a large crystal strain of 0.92 × 10 ⁻⁴ . And one mold for polycrystalline silicon casting was produced by the method similar to Example 1-1 using the silicon nitride powder of Comparative Example 1-4. The same direction solidification experiment in the same furnace temperature as Comparative Example 1-1 is conducted by the same method as Comparative Example 1-1 using its mold, and a polycrystalline silicon ingot is produced by the same method as Example 1-1. The casting molds were evaluated.

(Comparative Example 1-5)
A silicon nitride powder of Comparative Example 1-5 was produced in the same manner as in Comparative Example 1-4 except that the pulverizing time was changed to 100 minutes. As shown 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 . And one mold for polycrystalline silicon casting was produced by the method similar to Example 1-1 using the silicon nitride powder of Comparative Example 1-5. The same direction solidification experiment in the same furnace temperature as Comparative Example 1-1 is conducted by the same method as Comparative Example 1-1 using its mold, and a polycrystalline silicon ingot is produced by the same method as Example 1-1. The casting molds were evaluated.

(Comparative example 1-6)
Silicon powder having a D50 of 5.0 μm, a bulk density of 0.50 g / cm ³ , an Fe content of 205 ppm, an Al content of 220 ppm, and a content of metal impurities other than Fe and Al of 503 ppm in the raw material powder A silicon nitride powder of Comparative Example 1-6 was produced in the same manner as in Comparative Example 1-4 except for using. As shown in Table 2, the silicon nitride powder obtained in Comparative Example 1-6 had a content of Fe of 109 ppm, a content of Al of 127 ppm, and a content of metal impurities other than Fe and Al of 271 ppm, It was a powder having a high content 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. The same direction solidification experiment in the same furnace temperature as Comparative Example 1-1 is conducted by the same method as Comparative Example 1-1 using its mold, and a polycrystalline silicon ingot is produced by the same method as Example 1-1. The casting molds were evaluated.

(Comparative Example 1-7)
Raw material powder: 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, Fe and metal impurities other than Al content ratio of 2 ppm The raw material powder was placed in a nylon pot filled with alumina balls and ball mill mixed for 24 hours using ethanol as a solvent, and the coarse grinding of the combustion product was carried out using an alumina roll. Comparative Example 1 was carried out in the same manner as Example 1-1 except that the process was carried out using a roll crusher equipped with the above, and the coarse-crushed sieve was carried out using a stainless steel sieve with a 150 .mu.m opening. A silicon nitride powder of -7 was produced. As shown in Table 2, the silicon nitride powder obtained in Comparative Example 1-7 has a high content of Al at 846 ppm, a high content of metal impurities, and a low specific surface area of 0.21 m ² / g, Each of D10, D50 and D90 was a large powder 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. The same direction solidification experiment in the same furnace temperature as Comparative Example 1-1 is conducted by the same method as Comparative Example 1-1 using its mold, and a polycrystalline silicon ingot is produced by the same method as Example 1-1. The casting molds were evaluated.

(Comparative Example 1-8)
Silicon powder having a D50 of 5.0 μm, a bulk density of 0.50 g / cm ³ , an Fe content of 205 ppm, an Al content of 220 ppm, and a content of metal impurities other than Fe and Al of 503 ppm in the raw material powder A silicon nitride powder of Comparative Example 1-8 was produced in the same manner as in Example 1-6 except that the raw material powder was mixed for 1 hour in a planetary ball mill filled with alumina balls. . As shown in Table 2, the silicon nitride powder obtained in Comparative Example 1-8 had a content of Fe of 109 ppm, a content of Al of 420 ppm, and a content of metal impurities other than Fe and Al of 312 ppm, The powder contained a large amount of metal impurities and a small crystallite diameter D _{c of} 290 nm. 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. The same direction solidification experiment in the same furnace temperature as Comparative Example 1-1 is conducted by the same method as Comparative Example 1-1 using its mold, and a polycrystalline silicon ingot is produced by the same method as Example 1-1. The casting molds were evaluated.

(Comparative Example 1-9)
Silicon powder with a D50 of 2.5 μm, a bulk density of 0.26 g / cm ³ , an Fe content of 2 ppm, an Al content of 3 ppm, and a content of metallic impurities other than Fe and Al of 3 ppm, inner diameter 30 mm The mold was filled and uniaxially molded at a pressure of 1,500 kg / cm ² to obtain a uniaxially molded silicon powder. The molded body was filled in a container made of graphite, housed in a batch type nitriding furnace, and the inside of the furnace was replaced with a nitrogen atmosphere, and then the temperature was raised to 1450 ° C. under a nitrogen atmosphere and held for 3 hours. After cooling to room temperature, the nitrided product was removed. The obtained nitrided product was roughly crushed with a roll crusher equipped with a silicon nitride roll whose inner surface was urethane coated, and sieved through a nylon screen with a 100 μm mesh to recover the powder under the sieve. . Next, the powder is contained in a pot made of alumina which is filled with silicon nitride balls and whose inner surface is lined with urethane, and finely ground for 30 minutes with a frequency of 1780 cpm and an amplitude of 5 mm with a batch type vibration mill. The 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 that is not 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 as large as 3.01 × 10 ^−4, and D _BET / D _c is as small as It was a large powder of 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. The same direction solidification experiment in the same furnace temperature as Comparative Example 1-1 is conducted by the same method as Comparative Example 1-1 using its mold, and a polycrystalline silicon ingot is produced by the same method as Example 1-1. The casting molds were evaluated.

(Comparative Example 1-10)
A silicon nitride powder of Comparative Example 1-10 was produced in the same manner as in Comparative Example 1-9 except that the milling 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 that is not combustion synthesis, has a low proportion of β-type silicon nitride of 58%, and D15 and D90 are each 1.60 μm. The powder was as small as 5.90 μm, the crystallite diameter Dc was as small as 88 nm, the crystal strain was as 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. The same direction solidification experiment in the same furnace temperature as Comparative Example 1-1 is conducted by the same method as Comparative Example 1-1 using its mold, and a polycrystalline silicon ingot is produced by the same method as Example 1-1. The casting molds were evaluated.

  Physical property values of silicon powder and diluent used for raw material powder, physical property values of mixed raw material powder, and crushing strength of combustion products in Examples 1-2 to 1-13 and Comparative examples 1-1 to 1-10 Table 1 shows the physical properties of the silicon nitride powder and Table 2 shows the physical properties of the silicon nitride powder. The evaluation results of the mold for casting polycrystalline silicon ingots and the polycrystalline silicon ingots of Examples 1-2 to 1-13 and Comparative Examples 1-1 to 1-10 are shown in Table 3.

(Example 2-1)
A mold for casting a polycrystalline silicon ingot having a release layer containing the silicon nitride powder of Example 1-1 was produced by the method described below, and the mold for casting a polycrystalline silicon ingot and the evaluation of the silicon ingot were carried out. .

  The silicon nitride powder of Example 1-1 was housed in a sealable polyethylene container, and a silica sol having a silica concentration of 20% by mass (manufactured by Sakai Chemical Co., Ltd., product name "PL-3") and water were added. At this time, they were mixed so that the mass ratio of silicon nitride: silica sol: water was 20: 8: 72. Next, a silicon nitride ball is charged into a container containing silicon nitride powder, silica sol and water, and sealed, and mixed for 5 minutes with a vibration mill with an amplitude of 5 mm and a frequency of 1780 rpm using a batch vibration mill. A silicon nitride slurry was obtained.

  The resulting silicon nitride slurry of Example 2-1 was spray-applied to the inner wall surface of a quartz crucible having a porosity of 16%, a bottom of 100 mm square, and a depth of 100 mm, which had been preheated to 90 ° C., It was dried at 90 ° C. for 15 hours to obtain a polycrystalline silicon ingot casting mold provided with 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.

  A unidirectional solidification experiment is carried out in the same manner as in Example 1-1 using the obtained mold for casting of polycrystalline silicon in Example 2-1, and the same procedure as in Example 1-1 is carried out in the same manner as in Example 1-1. Polycrystalline silicon casting molds and polycrystalline silicon ingots 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. A unidirectional solidification experiment is conducted in the same manner as in Example 1-1 using the mold for casting polycrystalline silicon in each of the obtained Examples and Comparative Examples, and polycrystalline silicon is obtained in the same manner as in Example 1-1. Ingot casting molds and silicon ingots were evaluated. The results are shown in Table 4.

  As described above, the silicon nitride powder of the present invention can form a release layer having excellent adhesion and releasability on its mold by heat treatment at high temperature after being applied to the mold. Moreover, it turned out that a mold release layer with favorable adhesiveness and releasability can be formed in a casting_mold | template by mix | blending with a silica sol and apply | coating to a casting_mold | template without heat-processing at high temperature.

  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 to the mold and good mold release property to the mold, and in particular, high quality silicon substrates for solar cells. It is useful as a mold release agent for polycrystalline silicon ingots that can be collected at a yield. The silicon nitride powder of the present invention is also useful as a raw material of a silicon nitride sintered body that exhibits high strength at high temperature because it can form a compact release layer and has high crystallinity.

Reference Signs List 1 combustion synthesis reactor 2 mixed raw material powder 3 container made of graphite 4 ignition agent 5 carbon heater 6 pressure resistant container 7 vacuum pump 8 nitrogen cylinder 9 porthole

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,
Assuming that the 50% particle diameter based on volume measured by the laser diffraction scattering method is D50 and the 90% particle diameter is D90, D50 is 2 μm to 20 μm, and D90 is 8 μm to 60 μm,
The content of Fe is 100 ppm or less,
The content ratio of Al is 100 ppm or less,
The total content of metal impurities other than Fe and Al is 100 ppm or less,
The crystallite size of β-type silicon nitride which is calculated using the Williamson-Hall type from powder X-ray diffraction pattern of β-type silicon nitride is taken as _{D C,} nitriding, characterized in that _{D C} is 300nm or more Silicon powder. The nitride crystal according to claim 1, characterized in that 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. Silicon powder. 3. The silicon nitride powder according to claim 1, wherein D _BET / D _C (nm / nm) is 5 or less, where D _BET is a specific surface area equivalent diameter calculated from the specific surface area. .   The silicon nitride powder according to any one of claims 1 to 3, wherein D50 is 3 μm or more.   The silicon nitride powder according to any one of claims 1 to 4, wherein D90 is 50 μm or less.   The silicon nitride powder according to any one of claims 1 to 5, wherein D90 is 13 μm or more.   The silicon nitride powder according to any one of claims 1 to 6, wherein the proportion of β-type silicon nitride is greater than 80% by mass. The content of Fe is 20 ppm or less,
The content ratio of Al 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.   The nitriding according to any one of claims 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 powder.   A mold release agent for polycrystalline silicon ingot comprising the silicon nitride powder according to any one of claims 1 to 9.   A method for producing 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. Method for producing a silicon ingot characterized by using a mold.

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