JP2010077003A - Crucible for melting silicon and release agent used for the same - Google Patents

Abstract

[PROBLEMS] To release a silicon block from the crucible so as to suppress the occurrence of chipping or cracking of the silicon block due to adhesion between the protective film and the silicon block by breaking the protective film itself. The present invention provides a silicon melting crucible having an excellent protective film and a release material used therefor.
A silicon melting crucible according to the present invention is a silicon melting crucible in which a protective film 2 is provided on at least an inner surface 1a of a crucible body 1 made of a heat resistant member, and the protective film 2 has at least a surface. contains an _{SiO X N Y (X> 0} , Y> 0) the second solid particles having a first solid particles having a composition, the content of SiO ₂ particle size is smaller than the first solid particles Thus, the second solid particles connect the first solid particles at a part of the interface between the first solid particles.
[Selection] Figure 2

Description

  The present invention particularly relates to a silicon melting crucible used for manufacturing a polycrystalline silicon substrate used for forming a solar cell and a mold release material used therefor.

  As a substrate for forming a solar cell, a single crystal silicon substrate manufactured by the Czochralski method and a polycrystalline silicon substrate that can be easily enlarged are used. In such a polycrystalline silicon substrate, high-purity silicon is melted in a silicon melting crucible (hereinafter also simply referred to as a crucible), or a silicon melt melted at a high temperature is poured into the crucible. Thereafter, the silicon crystal formed by solidification (hereinafter referred to as silicon block) is removed from the crucible, and the silicon block thus taken out is sliced to a certain thickness.

As such a crucible, silicon nitride (Si ₃ N ₄ ), silica (SiO ₂ ) or the like is separated on the inner surface of the crucible holding the silicon melt so that the silicon block can be easily removed from the crucible. In general, a mold material is applied or coated to form a protective film (hereinafter also referred to as a mold release material layer).

  However, since the protective film using only silicon nitride as the release material is weak in strength, the protective film itself is easily damaged, and the damaged silicon nitride is mixed into the silicon melt, and the silicon nitride precipitate is removed. There is a problem of generating. Therefore, a technique for improving the strength as a protective film by mixing silica in a specific weight ratio with silicon nitride is generally known (for example, Patent Document 1).

  However, since silica has high adhesion to the silicon block, when there is a large amount of silica component on the outermost surface of the protective film in contact with the silicon block, the adhesion between the silicon block and the protective film increases, and silicon When the block is removed from the crucible, there is a high risk of chipping or cracking in the silicon block.

  In order to solve these problems, a crucible has been proposed in which two layers of release material layers having different silicon nitride powder content ratios are formed using silicon nitride powder having a silica layer formed on the surface. (For example, patent document 2).

In addition, the present inventor has found that SiO _X N _Y (X ≠ 0, Y ≠ 0) is effective as a material difficult to wet with molten silicon, and SiO _X N _Y (X ≠ 0, Y ≠ 0) composition. A silicon melting crucible provided with a protective film having the above has been proposed (for example, Patent Document 3).
JP-A-9-175809 ([Claim 1] etc.) JP 2005-95924 A ([Claim 1] etc.) Japanese Patent Laid-Open No. 2008-115056 ([Claim 1] etc.)

  However, the technique described in Patent Document 2 has a silica layer between the outermost surface of the protective film in contact with the silicon melt and the silicon nitride powder, so that the crucible is substantially from the outermost surface of the protective film. A silica layer is formed to be connected in a matrix in the thickness direction of the protective film up to the portion in contact with the surface. Therefore, since the strength as a protective film is high, the silica layer and the silicon block existing on the outermost surface of the protective film adhere to each other, and the protective film itself is not destroyed and the adhesion between the silica layer and the silicon block can be maintained As a result, when the silicon block is removed from the crucible, there is a risk that the silicon block may be broken or cracked.

  Further, as described in Patent Document 2, when the protective film is composed of multiple layers, the release materials used for the respective layers must be prepared and formed, resulting in poor productivity and labor. Furthermore, a thermal shock (for example, pouring a silicon melt melted at high temperature into the crucible) or a physical shock (for example, when placing a polycrystalline silicon lump in the crucible, When the lump and the protective film come into contact with each other), there is a risk that the protective film is peeled off between the laminated layers.

  The present invention has been made in view of such circumstances, and when removing the silicon block from the crucible, the protective film itself breaks the occurrence of chipping or cracking of the silicon block due to adhesion between the protective film and the silicon block. It aims at providing the silicon fusion crucible provided with the protective film excellent in the mold release property which can be suppressed by this.

  Another object of the present invention is to provide a mold release material used for manufacturing a silicon melting crucible having such effects.

The silicon melting crucible according to the present invention is a silicon melting crucible in which a protective film is provided on at least the inner surface of a crucible body made of a heat-resistant member, and at least the surface of the protective film is SiO _X N _Y (X> 0, Y> 0) containing a first solid particle having a composition and a second solid particle having a SiO ₂ composition having a smaller particle size than the first solid particle, the second solid The particles are characterized in that the first solid particles are connected to each other at a part of the interface between the first solid particles.

  By adopting such a configuration, when removing the silicon block from the crucible, the generation of chipping or cracking of the silicon block due to adhesion between the protective film and the silicon block is suppressed by breaking the protective film itself. It is possible to obtain a silicon melting crucible provided with a protective film excellent in releasability.

  The heat resistant member is preferably quartz.

  By adopting such a configuration, the thermal expansion coefficients of the first solid particles or the second solid particles and the crucible body are close to or the same as those of other materials, and the thermal stress caused by the composition difference is reduced. Since the generation is suppressed, even when a thermal shock or a physical shock is generated in the silicon melting crucible, it is possible to prevent the entire protective film from being broken or peeled off.

The mold release material according to the present invention is a mold release material used to form a protective film provided on at least the inner surface of a silicon melting crucible, and at least the surface has a SiO _X N _Y (X> 0, Y> 0) composition. And a second solid particle having a SiO ₂ composition having a particle size smaller than that of the first solid particle. .

  By using a release material having such a configuration, a silicon melting crucible having a protective film having the above-described effects can be obtained.

  In the present invention, when the silicon block is removed from the crucible, the release property that can suppress the occurrence of chipping or cracking of the silicon block due to the adhesion between the protective film and the silicon block by breaking the protective film itself. A silicon melting crucible having an excellent protective film is provided.

  Moreover, this invention provides the mold release material used for manufacture of the silicon fusion crucible which has such an effect.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 is a perspective view showing an example of a silicon melting crucible according to the present invention, and FIG. 2 is a cross-sectional view in the AA direction of FIG.

  As shown in FIGS. 1 and 2, the silicon melting crucible according to the present embodiment includes a crucible body 1 and a protective film 2 provided on the inner surface 1 a of the crucible body 1.

  The crucible body 1 is made of a heat-resistant member, and as shown in FIG. 1, for example, the crucible body 1 is composed of an integrally molded crucible that is integrally molded as a whole. Note that quartz is preferably used as the heat-resistant member. This quartz includes not only quartz glass but also fused quartz.

  As shown in FIG. 2, the protective film 2 is composed of a single layer provided on the inner surface 1 a of the crucible body 1.

  FIG. 3 is an enlarged schematic cross-sectional view in which a region in the vicinity of the protective film 2 in FIG. 2 is enlarged. 3 is merely schematic, and the shape and size of the solid particles and the thickness of the protective film 2 formed by the solid particles are different from actual dimensions.

  As shown in FIG. 3, the protective film 2 contains the first solid particles 2a and the second solid particles 2b having a particle size smaller than that of the first solid particles 2a. 2b has a configuration in which the first solid particles 2a are connected to each other at a part of the interface 3 between the first solid particles 2a.

At least the surface of the first solid particles 2a has a composition of SiO _X N _Y (X> 0, Y> 0).

  FIG. 4 is a schematic cross-sectional view showing a specific configuration of the first solid particles 2a according to the present invention.

Specifically, in the first solid particle 2a, as shown in FIG. 4A, the surface layer 2a1 is composed of SiO _X N _Y (X> 0, Y> 0), and the core 2a2 is silica ( solid particles 2aa composed of SiO _2), or, as shown in FIG. 4 (b), the surface layer 2a1 is constituted by _{SiO X N Y (X> 0} , Y> 0), the core portion 2a3 is silicon nitride Solid particles 2ab composed of (Si ₃ N ₄ ) or solid particles 2ac composed entirely of SiO _X N _Y (X> 0, Y> 0) as shown in FIG. 4C. Consists of either.

The second solid particles 2b are composed of solid particles having a SiO ₂ composition, that is, silica particles.

  Since the silicon melting crucible according to the present invention has the above-described configuration, when the silicon block is removed from the crucible, the silicon block is not broken or cracked due to the adhesion between the protective film and the silicon block. And a protective film excellent in releasability that can be suppressed by breaking the protective film itself.

That is, as described above, at least the surface of the first solid particles 2a constituting the protective film of the silicon melting crucible according to the present invention has a composition of SiO _X N _Y (X> 0, Y> 0). Therefore, it has an effect that it is less likely to get wet with molten silicon than SiO ₂ and Si ₃ N ₄ . In addition, since the second solid particles 2b connect the first solid particles 2a to each other at a part of the interface 3 between the first solid particles 2a, the protective film 2 includes the first solid particles 2a. It has high strength to such an extent that peeling between them does not occur. Furthermore, as described above, the second solid particles 2b are not a whole of the interface 3 between the first solid particles 2a but a part thereof, and the first solid particles 2a are connected to each other. The strength is lower than the overall connection. Therefore, even if the second solid particles 2b existing on the outermost surface of the protective film 2 or the first solid particles 2a and the silicon block are attached, the protective film is removed when the silicon block is removed from the crucible. Since 2 is broken first, it is possible to prevent the silicon block from being broken or cracked due to the adhesion between the protective film 2 and the silicon block.

The composition of SiO _X N _Y (X> 0, Y> 0) provided on at least the surface of the first solid particle 2a is, for example, 0.2 ≦ X ≦ 0.8, 0.8 ≦ Y ≦ 1. 2. The analysis of X and Y can be obtained by the oxygen / nitrogen simultaneous analysis method.

  The particle size and weight ratio of the first solid particles 2a and the second solid particles 2b are not particularly limited as long as the protective film 2 as described above can be formed. The particle size of the first solid particles 2a is, for example, 100 nm or more and 1000 nm or less, the particle size of the second solid particles 2b is, for example, 1 nm or more and 10 nm or less, and the weight ratio of the second solid particles 2b is For example, they are 0.1 wt% or more and 5 wt% or less with respect to the 1st solid particle 2a.

The release material according to the present invention is made of a material that can include the protective film 2 as described above. That is, the release material according to the present invention has a first solid particle 2a having at least a surface having a SiO _X N _Y (X> 0, Y> 0) composition, and a particle size smaller than that of the first solid particle 2a. And a second solid particle 2b having a SiO ₂ composition.

  By using a release material having such a configuration, a silicon melting crucible having a protective film having the above-described effects can be obtained.

  Next, a manufacturing method for manufacturing the silicon melting crucible according to the present embodiment by forming the protective film 2 on the crucible body 1 will be described.

For the production of the first solid particles 2a used for the protective film 2, a powder which is an aggregate of silica fine particles of high purity (for example, purity 99.9% or more) is used as a raw material, and this is nitrided Thus, a powder of solid particles (FIGS. 4 (a) and 4 (c)) having at least a surface having a SiO _X N _Y (X> 0, Y> 0) composition is produced and used as a release material. Alternatively, a powder which is an aggregate of high-purity (for example, purity 99.9% or more) silicon nitride fine particles is used as a raw material, and this is subjected to an oxidation treatment, so that at least the surface has SiO _X N _Y (X> 0, Y> 0) A powder of solid particles (FIGS. 4B and 4C) having a composition is produced and used as a release material (first solid particles 2a).

The nitriding treatment of the silica fine particles is performed by performing a heat treatment for a predetermined time at a high temperature (for example, 1100 ° C.) in a nitrogen-based gas-containing atmosphere (for example, in a mixed gas atmosphere of hydrogen gas and ammonia gas). The surface can be nitrided. By controlling the treatment conditions (for example, heat treatment time) of this nitriding treatment, silica fine particles having different nitriding rates, that is, SiO _X N _Y powder can be obtained. Furthermore, by making the heat treatment time longer, solid particles (FIG. 4C) in which the entire particles are composed of SiO _X N _Y (X> 0, Y> 0) can be produced.

In the oxidation treatment of the silicon nitride fine particles, at least the surface of the silicon nitride fine particles is oxidized by performing a heat treatment for a predetermined time at a high temperature (for example, 800 ° C.) in an oxidizing gas-containing atmosphere (for example, in an air atmosphere). it can. In addition, by controlling the treatment conditions (for example, heat treatment time) of this oxidation treatment, silicon nitride fine particles having different oxidation rates, that is, SiO _X N _Y powder can be obtained. Furthermore, by making the heat treatment time longer, solid particles (FIG. 4C) in which the entire particles are composed of SiO _X N _Y (X> 0, Y> 0) can be produced. When the oxide film SiO ₂ (X = 2, Y = 0) is formed on the solid particle surface by the oxidation treatment, the oxide film can be removed by performing dilute HF treatment.

  Further, as the second solid particles 2b used for the protective film 2, a powder of silica fine particles having a high purity (for example, a purity of 99.9% or more) having a smaller particle diameter than the first solid particles 2a is used.

  The formation of the protective film 2 on the inner surface 1a of the crucible body 1 can be performed as follows.

First, a first solid particle 2 a having at least a surface composed of SiO _X N _Y (X> 0, Y> 0), a _second composition having a SiO ₂ composition having a particle size smaller than that of the first solid particle 2 a A suspension is prepared using the solid particles 2b, pure water, and a binder (for example, polyvinyl alcohol (PVA)). For example, this suspension is spray-coated on the inner surface 1a of the concave crucible body 1 and dried. This spray coating and drying are repeated until the coating film has a desired thickness.

  Subsequently, the crucible body 1 on which the coating film is formed is heated to a predetermined temperature (for example, 800 ° C.) in a non-oxidizing atmosphere (for example, under an argon atmosphere) and baked.

  At this time, the binder (for example, PVA) is gasified (burned out) in the temperature rising process. In addition, the solid particles remain in a state where a certain gap remains in the coating film so that the solid particles do not melt and sag downward due to the action of gravity and the film does not slide down or change in film thickness. It is preferable to fire and weld each other. Thus, the protective film 2 in close contact with the crucible body 1 can be formed.

  Since the silicon melting crucible according to the present embodiment can be obtained by the manufacturing method as described above, it is easy to form a protective film on the crucible body without using post-processing such as polishing or CVD. Production economy is good and can be manufactured at low cost.

  Further, the crucible body 1 has been described so far by taking the integrally molded crucible as an example, but the present invention is not limited to this, and a divided crucible may be used. In addition, when manufacturing the silicon fusion crucible concerning this embodiment in the case of using a split crucible, a plurality of plate-like bodies (not shown) made of a heat-resistant member are prepared, and at least one of the plate-like bodies is prepared. After the above-described spray coating, drying, and baking are performed on each of the surfaces, and each of the protective films is formed, at least when the surface on which the protective film is formed has a crucible shape, the plurality of the plurality The plate-like body can be manufactured by being combined through a joint portion or the like.

  The crucible body is preferably made of quartz.

  By adopting such a configuration, the thermal expansion coefficients of the first solid particles 2a and the second solid particles 2b and the crucible body 1 are close to or the same as those of other materials, resulting in a difference in composition. Since the generation of thermal stress is suppressed, even when a thermal shock or a physical shock is generated in the silicon melting crucible, it is possible to prevent the protective film 2 from being broken or peeled off.

Example 1
High purity SiO ₂ powder (purity of 99.9% or more, average particle size of 100 nm, alkali metal, alkaline earth metal, fluoride, chloride, carbon, iron, chromium, cobalt, nickel, tungsten, molybdenum, titanium The total concentration was 2 ppm), and the mixture was held at 1100 ° C. for 5 hours in a mixed gas atmosphere in which hydrogen and ammonia were adjusted to a volume ratio of 1: 3 to prepare SiO _X N _Y powder.

With respect to the SiO _X N _Y powder thus obtained, high-purity SiO ₂ powder (purity 99.9% or more, average particle size 5 nm, alkali metal, alkaline earth metal, fluoride, chloride, carbon, iron , Chromium, cobalt, nickel, tungsten, molybdenum, and titanium are mixed at a weight ratio of 0.1 wt% with respect to the SiO _X N _Y powder, and a suspension is prepared using pure water and PVA. Was made.

  Next, spray coating and drying of the prepared suspensions are repeatedly performed on the inner surface of the fused silica crucible body having an internal volume of 678 mm × 678 mm × 400 mm until the film thickness reaches 500 μm to form a coating film. did.

The crucible thus formed with the coating film is held at 800 ° C. for 60 minutes in a non-oxidizing atmosphere (argon atmosphere) with a certain gap remaining inside the coating film to form a protective film, and SiO _X A crucible in which a protective film comprising _NY particles and SiO ₂ particles was formed was produced.

(Example 2)
High purity Si ₃ N ₄ powder (purity 99.9% or more, average particle size 100 nm, alkali metal, alkaline earth metal, fluoride, chloride, carbon, iron, chromium, cobalt, nickel, tungsten, molybdenum, The total concentration of titanium was maintained at 800 ° C. for about 5 hours in an air atmosphere to prepare SiO _X N _Y powder.

Others were carried out in the same manner as in Example 1 to produce a crucible on which a protective film comprising SiO _X N _Y particles and SiO ₂ particles was formed.

(Comparative Example 1)
A crucible on which a protective film having only SiO _X N _Y particles was formed was produced in the same manner as in Example 1 except that high-purity SiO ₂ powder having an average particle diameter of 5 nm was not used.

(Comparative Example 2)
A crucible on which a protective film having only SiO _X N _Y particles was formed was produced in the same manner as in Example 2 except that high-purity SiO ₂ powder having an average particle diameter of 5 nm was not used.

(Comparative Example 3)
High purity Si ₃ N ₄ powder (purity 99.9% or more, average particle size 100 nm, alkali metal, alkaline earth metal, fluoride, chloride, carbon, iron, chromium, cobalt, nickel, tungsten, molybdenum, Si ₃ N ₄ powder in which an oxide film (SiO ₂ ) was formed on the surface of Si ₃ N ₄ particles was manufactured by heating 3 hours at 1000 ° C. in an air atmosphere.

With respect to the Si ₃ N ₄ powder thus obtained, a suspension was prepared using pure water and PVA without using the high-purity SiO ₂ powder having an average particle diameter of 5 nm.

  Next, spray coating and drying of the prepared suspensions are repeatedly performed on the inner surface of the fused silica crucible body having an internal volume of 678 mm × 678 mm × 400 mm until the film thickness reaches 500 μm to form a coating film. did.

The crucible on which the coating film has been formed in this way is held at 800 ° C. for 60 minutes in a non-oxidizing atmosphere (argon atmosphere) so that the Si ₃ N ₄ powders are welded with a certain gap remaining inside the coating film. Then, a protective film was formed, and a crucible in which a protective film having only the Si ₃ N ₄ powder was formed was produced.

(Comparative Example 4)
Without producing SiO _X N _Y powder, high purity SiO ₂ powder (purity 99.9% or more, average particle size 100 nm, alkali metal, alkaline earth metal, fluoride, chloride, carbon, iron, chromium, A crucible on which a protective film having only the SiO ₂ particles was formed was produced in the same manner as in Example 1 except that the total concentration of cobalt, nickel, tungsten, molybdenum, and titanium was used.

(Evaluation of wettability of protective film with silicon)
Next, a lump of polycrystalline silicon was loaded on the crucible produced above, heated to form a silicon melt, and then cooled and solidified. “Evaluation“ A ”” which was able to remove the crucible fragment from the silicon block thus produced without difficulty, and “Evaluation“ B ”” which was able to remove the crucible fragment with a slight crack in the final solidified portion of the silicon block. "Evaluation" C "" was a case where the silicon block and the crucible adhered in a wide range and the crucible fragments could not be easily removed, and the silicon block was considerably damaged.

以上の結果からわかるように、実施例１、２の結果が最も良く、比較例１から比較例３はほぼ同レベルであった。 (Evaluation results)
Table 1 shows the evaluation results of the wettability of the formed protective film with silicon.

As can be seen from the above results, the results of Examples 1 and 2 were the best, and Comparative Examples 1 to 3 were almost at the same level.

  In addition, when the cross section of the protective film in Example 1, 2 was observed with SEM, it was confirmed that it has the particle structure as shown in FIG.

It is a perspective view showing an example of a silicon fusion crucible concerning the present invention. It is sectional drawing of the AA direction of FIG. FIG. 3 is an enlarged schematic cross-sectional view in which a region in the vicinity of the protective film 2 in FIG. 2 is enlarged. It is a schematic sectional drawing which shows the specific structure of the 1st solid particle 2a which concerns on this invention.

Explanation of symbols

1 Crucible body 2 Protective film 3 Interface

Claims (3)

A silicon melting crucible provided with a protective film on at least the inner surface of a crucible body made of a heat-resistant member,
The protective film includes at least a first solid particle having a SiO _X N _Y (X> 0, Y> 0) composition on the surface, and a _second SiO ₂ composition having a particle size smaller than that of the first solid particle. Solid particles of
The silicon solid crucible characterized in that the second solid particles connect the first solid particles at a part of the interface between the first solid particles.   2. The silicon melting crucible according to claim 1, wherein the heat resistant member is quartz. A release material used for forming a protective film provided on at least an inner surface of a silicon melting crucible, wherein at least the surface has a first solid particle having a composition of SiO _X N _Y (X> 0, Y> 0) A mold release material comprising: a second solid particle having a SiO ₂ composition having a particle size smaller than that of the first solid particle.

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