CN102898034A - Method for manufacturing silicon nitride coating of crucible for crystalline silicon ingot casting - Google Patents

Abstract

The invention discloses a method for manufacturing a silicon nitride coating on a crucible for crystalline silicon ingots. After the silicon nitride coating is prepared on the easily sticky crucible area of the inner wall of the crucible by a liquid phase deposition method, the silicon nitride coating on the area is The coating is subjected to densification and non-wetting treatment, and the silicon nitride coating is prepared on other areas of the inner wall of the crucible by liquid phase deposition, and finally the silicon nitride coating is subjected to low-temperature baking or sintering-free treatment to obtain a crystal Silicon ingots are coated with silicon nitride on crucibles. This method can significantly improve the overall strength of the silicon nitride coating, especially the strength of the coating in the easy-sticking crucible area and its non-wetting property to the silicon melt, which can effectively avoid the occurrence of the sticking pot phenomenon and avoid silicon nitride dust. The production of silicon nitride powder further improves the effective utilization rate of silicon nitride powder, reduces production costs, enhances the environmental friendliness in the operation process, and reduces the damage to the human body; and because no or only low-temperature baking is required, energy is reduced The waste shortens the production cycle.

Description

A kind of manufacturing method of crucible silicon nitride coating for crystalline silicon ingot

technical field

The invention belongs to the technical field of solar cells, and in particular relates to a method for manufacturing a crucible silicon nitride coating for crystalline silicon ingots.

Background technique

In the production of crystalline silicon ingots, the silicon nitride coating serves to isolate the silicon melt from the fused silica crucible, thereby preventing the impurities in the crucible body from diffusing into the silicon material and contaminating the silicon material, while ensuring that the silicon ingot and the crucible are Silicon nitride coating is essential in crystalline silicon ingot casting because of the important role of non-sticking and thus smooth demolding.

For crystalline silicon ingots, different regions of the silicon nitride coating are in different environments, as shown in Figure 1, where the silicon liquid line is at the junction of solid, liquid, and gas phases, where silicon melt and nitride For the substrate of silicon coating, the reaction of fused silica crucible is relatively the strongest. At the same time, the silicon nitride coating here is also eroded by the fluctuation of silicon liquid, and the silicon liquid line rises gradually during the growth of silicon crystal. The coating produces a certain physical impact, so the silicon nitride coating here is most likely to peel off and fail. The most important influencing factor is the degree of reaction between the silicon melt and the fused silica crucible, and this reaction has an interactive relationship with the density of the silicon nitride coating here.

Therefore, how to enhance the density of silicon nitride coating in this area is one of the keys to solve the problem of sticky pot.

For the silicon nitride coating prepared by the spraying and sintering method commonly used in conventional ingots, its disadvantages are obvious: during the spraying operation, a relatively part of the silicon nitride powder is lost with the exhaust air, which causes silicon nitride The waste of powder causes environmental pollution, and the sintering temperature of about 1100°C requires a lot of electric energy and running time, so it needs to be improved urgently.

At present, there have been related research reports on improving the early strength of silicon nitride coatings by introducing binders into silicon nitride slurries at home and abroad. For example, R.Einhaus et al. introduced PVA into silicon nitride coatings as a film-forming agent. , an experimental study of silicon nitride coating prepared by spraying, but due to the damage of non-wetting between the silicon nitride coating and the silicon melt, the silicon ingot cracked, as shown in Figure 2.

In addition, according to the report in the patent application number 201110258563.7, polyvinyl alcohol, polyacrylic acid, etc. are used as bonding materials to prepare non-sintering silicon nitride coatings by spraying, but experiments have proved that the silicon nitride coatings prepared by this method have poor strength. , the sticky crucible phenomenon is serious and cannot be used normally.

In summary, improving the strength of silicon nitride coatings is still an important topic in this field. Although there have been studies on improving the film-forming performance and early strength of coatings by introducing binders, due to uncontrollable The influence of organic matter on the non-wetting properties of the coating is still not available for actual production; and the related patents mention the method of using binders in the spraying process, which cannot fundamentally improve the nitrogen content due to the fact that the particle arrangement structure has not been fundamentally improved. The strength of silicon dioxide coating.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for making a silicon nitride coating on a crucible for crystalline silicon ingots. This method can avoid the generation of dust in the spraying process of the silicon nitride coating, and further improve the silicon nitride powder. The effective utilization rate reduces the amount of silicon nitride powder, thereby reducing production costs; at the same time, due to the avoidance of dust generation, the environmental friendliness in the operation process is enhanced and the harm to the human body is reduced; the prepared silicon nitride coating is Strong density and non-wetting properties, not easy to stick to the crucible, and the silicon ingots made are good.

The above-mentioned technical problems of the present invention are achieved by the following technical scheme: a method for manufacturing a crucible silicon nitride coating for crystalline silicon ingots. After the silicon coating, the silicon nitride coating in this area is densified and non-wetting, and the silicon nitride coating is prepared on other areas of the inner wall of the crucible by liquid phase deposition, and finally the silicon nitride coating Low-temperature baking or non-sintering treatment is carried out to obtain a silicon nitride coating on a crucible for crystalline silicon ingots.

The sticky crucible area of the inner wall of the crucible in the present invention is mainly the silicon liquid line area of the crucible and the edge and corner areas inside the crucible.

The method of preparing the silicon nitride coating in the present invention is: directly coating the silicon nitride slurry on the sticky crucible area or other areas of the inner wall of the crucible, and coating the silicon nitride slurry through the automatic deposition of silicon nitride particles. On the inner wall of the crucible, also known as the liquid phase deposition method.

Compared with the usual method of spraying gas spray in the prior art, the present invention adopts the above-mentioned liquid phase deposition method, which can better coat the silicon nitride slurry on the sticky crucible area, and the coated nitrogen The silicon carbide coating has low porosity and high strength.

Generally speaking, the methods of coating silicon nitride slurry generally include the following types: brushing, roller coating, spraying and pouring, etc. Most of the existing technologies use gas spraying for spraying. In fact, brushing and The porosity of the silicon nitride coating prepared by roller coating is much smaller than that of spraying and pouring. In comparison, the method of brushing is better than that of roller coating, and the method of roller coating is better than that of spraying. Spraying is better than pouring, and the silicon nitride coating obtained by brushing is denser. The present invention adopts the brushing method for the silicon nitride coating in the crucible inner wall, which is easy to stick to the crucible area. In other areas, where the requirements for silicon nitride coating are not too high, spraying, roller coating and pouring or a combination of the two methods are used.

The silicon nitride slurry of the present invention is prepared from silicon nitride powder, pure water and a binder in a weight ratio of 100:70-450:0.1-15.

The binder in the present invention is one or more of methyl methacrylate, acrylic acid, polyvinyl alcohol and colloidal silicon dioxide.

The densification treatment in the present invention is: during the drying process of the silicon nitride slurry in the sticky crucible area of the crucible, the silicon nitride particles in the sticky crucible area of the crucible are densified by agitation, vibration or extrusion mechanical action Arranged to obtain a dense silicon nitride coating.

The non-wetting treatment of the present invention is to perform surface grinding, polishing, and adsorption and drying of silicon nitride powder on the surface of the densified silicon nitride coating to obtain a non-wetting silicon nitride coating. The so-called non-wetting means that during the ingot casting process of silicon crystals, the molten silicon material is not easy to enter the silicon nitride coating. Through non-wetting treatment, the non-wetting between the silicon melt and the silicon nitride coating can be improved. properties, prevent the occurrence of sticky pot phenomenon, and ensure the purity of silicon crystals.

Regarding the definition of non-wetting, non-wetting and wetting are relative indicators, mainly referring to the wetting degree of liquid to solid, and the main standard is the size of the wetting angle, as shown in Figure 7, for silicon melt ( Liquid) and silicon nitride coating (solid), the non-wetting between the two refers to the contact between the edge of the liquid and the silicon nitride coating when the silicon melt contacts the surface of the silicon nitride coating The size of the angle, the larger the angle (>90°), the better the non-wetting between the two, on the contrary, the smaller the angle between the two, the worse the non-wetting between the two (as shown in Figure 7 shown in C). For silicon nitride coatings, the greater the non-wetting property between the two, the better, so that the silicon melt can be completely separated from the coating after solidification. May cause sticky pot.

The silicon nitride coating prepared by the method of the present invention does not need sintering due to its low porosity and good strength. If baking is required, the temperature for the low-temperature baking treatment of the present invention is lower than 500° C.; and Compared with conventional silicon nitride coatings that require a sintering temperature of around 1100°C, the sintering temperature is reduced by nearly 600°C.

The present invention has the following advantages:

(1) The present invention densifies the silicon nitride coating in the sticky crucible area (mainly referring to the silicon liquid line), and the obtained silicon nitride coating is compared with the silicon nitride coating obtained by traditional methods such as spraying The porosity of the coating can be reduced by more than 40%; in terms of strength, the strength of the silicon nitride coating prepared by the present invention is improved by one to two grades, especially the strength of the coating before sintering is significantly improved, which can greatly reduce the process of charging. Coating damage caused by silicon material collision, the specific hardness performance is shown in Table 1 below;

Table 1 Different methods to prepare silicon nitride coating pencil hardness test

(2) The silicon nitride coating prepared by the present invention can be used only by baking at a low temperature below 500°C;

(3) The silicon nitride coating obtained by the method of the present invention can significantly reduce the proportion of the sticking phenomenon under conditions such as quasi-single crystal ingots with large temperature gradients and harsh crystal growth conditions, and basically eliminate polycrystalline ingots. Sticky pot phenomenon in ingot;

(4) adopt the inventive method to prepare silicon nitride coating, can avoid the generation of silicon nitride dust in the spraying process, from further improving the effective utilization rate of silicon nitride powder, reduce the consumption of silicon nitride powder, thereby reduce production cost; at the same time, due to the avoidance of dust generation, the environmental friendliness in the operation process is enhanced and the harm to the human body is reduced;

(5) Adopting the method of the present invention to prepare the silicon nitride coating can greatly shorten the production cycle, reduce energy consumption, and reduce production costs.

Description of drawings

Fig. 1 is the position of the silicon liquid line formed in the solid, liquid and gas three-phase boundary area in the crucible when the silicon material of the present invention is melted;

Figure 2 is a schematic representation of silicon crystals formed during ingot casting using a crucible with a prior art silicon nitride coating;

Fig. 3 is a schematic diagram of the manufacturing process of the silicon nitride coating in the crucible of the present invention;

Fig. 4 is a schematic diagram of comparison between a crucible coated with silicon nitride according to Example 1 of the present invention and a crucible coated with conventional silicon nitride for polysilicon ingot casting;

Fig. 5 is a schematic diagram of comparison between a crucible coated with silicon nitride according to Example 2 of the present invention and a crucible coated with conventional silicon nitride when casting monocrystalline silicon;

Fig. 6 is a schematic diagram of comparison between a crucible with a silicon nitride coating according to Example 3 of the present invention and a crucible with a conventional silicon nitride coating for casting high-efficiency polysilicon;

Fig. 7 is a schematic diagram for explaining non-wetting property in the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

Example 1

The manufacturing method of the crucible silicon nitride coating for crystalline silicon ingot provided in this embodiment, the preparation process is shown in Figure 2:

Firstly, a silicon nitride slurry is prepared, wherein the silicon nitride slurry is prepared from silicon nitride powder, pure water and a binder in a weight ratio of 100:150:5. Wherein the binder is methyl methacrylate, acrylic acid, polyvinyl alcohol, colloidal silicon dioxide, the mass ratio is 1:1:10:10, and the sticky crucible area coated by the above-mentioned liquid phase deposition method, It mainly refers to the silicon liquid line area of the crucible.

Next, a silicon nitride coating made in the sticky crucible region of the crucible, typically a fused silica crucible, is densified and non-wetting. The densification treatment is as follows: during the drying process of the silicon nitride slurry in the sticky crucible area of the crucible, the silicon nitride particles in the sticky crucible area of the crucible are densified and arranged by mechanical action such as agitation, vibration or extrusion, to obtain Densified silicon nitride coating, mechanical actions such as stirring, vibration and extrusion can be carried out by the equipment with the patent number ZL201120254516.0, or other equipment can be used. The non-wetting treatment is to perform surface grinding, polishing and adsorption drying of silicon nitride powder on the surface of the densified silicon nitride coating to obtain a non-wetting silicon nitride coating.

Then, the silicon nitride coating is prepared on other areas of the inner wall of the crucible. Since the other areas of the inner wall of the crucible have relatively low requirements on the density and strength of the silicon nitride coating, it can be prepared by casting or casting + roller coating.

Finally, the above-mentioned silicon nitride coating is sinter-free (dried without baking), that is, the silicon nitride coating of the crucible for obtaining crystalline silicon ingots is produced.

After ingot casting and demolding by ordinary polycrystalline technology, the obtained polycrystalline silicon ingot is shown in Figure 4, where a picture in Figure 4 is a crucible coated with a conventional silicon nitride coating and sintered at 1100 ° C for casting The picture of the ingot polysilicon, the picture b is the picture of the polysilicon used for casting the ingot after the silicon nitride prepared by the present invention is free from sintering treatment, as can be seen from Fig. The crucible piece over 30mm adheres to the surface of the silicon ingot, which is likely to cause hidden cracks or even cracks in the silicon ingot. At the same time, a large amount of silicon nitride powder adheres to the side of the silicon ingot, which shows that the coating is incompatible with the silicon ingot during use. The inner wall of the crucible has low adhesion and low stability; in figure b, only a small amount of silicon nitride powder is attached to the surface of the silicon ingot, and there is no sticking area, and the silicon ingot and the crucible are completely separated. This proves that the silicon nitride coating of the present invention has stronger adsorption capacity on the inner wall of the crucible than the conventional sprayed silicon nitride coating in the demolding of polycrystalline ingots, and the demoulding performance is more stable.

Example 2

The manufacturing method of the crucible silicon nitride coating for crystalline silicon ingot provided in this embodiment, the preparation process is shown in Figure 2:

First, a silicon nitride slurry is prepared, wherein the silicon nitride slurry is prepared from silicon nitride powder, pure water and a binder in a weight ratio of 100:150:10. Among them, the binder is methyl methacrylate, acrylic acid, polyvinyl alcohol, and colloidal silicon dioxide, the mass ratio of which is 0.1:1:10:10, and the above-mentioned silicon nitride slurry is used to brush the silicon nitride easily. The sticky crucible area mainly refers to the silicon liquid line area of the crucible.

Next, a silicon nitride coating made in the sticky crucible region of the crucible, typically a fused silica crucible, is densified and non-wetting. The densification treatment is as follows: during the drying process of the silicon nitride slurry in the sticky crucible area of the crucible, the silicon nitride particles in the sticky crucible area of the crucible are densified and arranged by mechanical action such as agitation, vibration or extrusion, to obtain Densified silicon nitride coating; mechanical actions such as stirring, vibration and extrusion can be carried out with the equipment with patent number ZL 201120254516.0, or other equipment; non-wetting treatment is for the surface of the densified silicon nitride coating Surface grinding, polishing, and adsorption drying of silicon nitride powder are carried out to obtain a non-wetting silicon nitride coating.

Then, the silicon nitride coating is prepared on other areas of the inner wall of the crucible. Since the other areas of the inner wall of the crucible have relatively low requirements on the density and strength of the silicon nitride coating, it can be prepared by casting or casting + roller coating.

Finally, the above-mentioned silicon nitride coating is baked at 500° C., that is, the silicon nitride coating of the crucible for obtaining the crystalline silicon ingot is fabricated.

After ingot casting under the quasi-single crystal process conditions, the formed polycrystalline silicon ingot is shown in Figure 5, in which Figure a in Figure 5 is the one used for quasi-single crystal ingot after sintering at 1100°C with a conventional sprayed silicon nitride coating. The picture of the silicon ingot, the picture b is the picture of the silicon ingot used for the quasi-single crystal ingot after the silicon nitride coating of the present invention is baked at 500 ° C, as can be seen from Figure 5, the silicon liquid level in the picture a Significant sticking occurs, leading to cracking of the silicon ingot, which shows that the conventional sprayed silicon nitride coating cannot meet the requirements of quasi-single crystal ingots with relatively harsh growth conditions; The crucible is completely separated. This proves that the silicon nitride coating of the present invention has more reliable mold release performance than conventional sprayed silicon nitride coatings in the use of quasi-single crystal ingot mold release under harsh conditions.

Example 3

The manufacturing method of the crucible silicon nitride coating for crystalline silicon ingot provided in this embodiment, the preparation process is as shown in Figure 2:

Firstly, a silicon nitride slurry is prepared, wherein the silicon nitride slurry is prepared from silicon nitride powder, pure water and a binder at a weight ratio of 100:150:15. Among them, the binder is methyl methacrylate, acrylic acid, polyvinyl alcohol, and colloidal silicon dioxide, the mass ratio of which is 1:0.1:10:10, and the above-mentioned silicon nitride slurry is used to brush the silicon nitride easily. The sticky crucible area mainly refers to the silicon liquid line area of the crucible. If a square crucible is used, the silicon nitride slurry is also brushed on the edges and corners inside the crucible.

Next, a silicon nitride coating made in the sticky crucible region of the crucible, typically a fused silica crucible, is densified and non-wetting. The densification treatment is as follows: during the drying process of the silicon nitride slurry in the sticky crucible area of the crucible, the silicon nitride particles in the sticky crucible area of the crucible are densified and arranged by mechanical action such as agitation, vibration or extrusion, to obtain Densified silicon nitride coating; mechanical actions such as stirring, vibration and extrusion can be carried out by the equipment with the patent number ZL 201120254516.0, or by other equipment. The non-wetting treatment is to perform surface grinding, polishing and adsorption drying of silicon nitride powder on the surface of the densified silicon nitride coating to obtain a non-wetting silicon nitride coating.

Then, the silicon nitride coating is prepared on other areas of the inner wall of the crucible. Since the other areas of the inner wall of the crucible have relatively low requirements on the density and strength of the silicon nitride coating, it can be prepared by casting or casting + roller coating.

Finally, the above-mentioned silicon nitride coating is baked at 500° C., that is, the silicon nitride coating of the crucible for obtaining the crystalline silicon ingot is produced.

High-efficiency polycrystalline silicon ingots formed after ingot casting under high-efficiency polycrystalline process conditions. As shown in Figure 6, Figure a in Figure 6 is a picture of high-efficiency polysilicon ingots after sintering at 1100 ° C using a conventional sprayed silicon nitride coating, and Figure b is a picture of a silicon nitride coating of the present invention baked at 500 ° C. After the baking treatment, the pictures used for high-efficiency polycrystalline, as can be seen from Figure 6, there is a partial sticky pot at the silicon liquid level in figure a, indicating that the use of conventional spray coating will bring hidden dangers of sticky pot to high-efficiency polycrystalline; b In the figure, the silicon ingot does not have any sticky crucible area, and the silicon ingot is completely separated from the crucible. This proves that the silicon nitride coating of the present invention has more reliable demoulding performance than the conventional sprayed silicon nitride coating in the high-efficiency polycrystalline ingot demoulding use.

Example 4

The manufacturing method of the crucible silicon nitride coating for crystalline silicon ingot provided in this embodiment, the preparation process is as shown in Figure 2:

First, a silicon nitride slurry is prepared, wherein the silicon nitride slurry is prepared from silicon nitride powder, pure water and a binder in a weight ratio of 100:450:0.1. The binder can be any one of methyl methacrylate, acrylic acid, polyvinyl alcohol or colloidal silicon dioxide. In this embodiment, acrylic acid is used, and the above-mentioned silicon nitride slurry is used to brush silicon nitride The sticky crucible area mainly refers to the silicon liquid line area of the crucible.

Next, a silicon nitride coating made in the sticky crucible region of the crucible, typically a fused silica crucible, is densified and non-wetting. The densification treatment is as follows: during the drying process of the silicon nitride slurry in the sticky crucible area of the crucible, the silicon nitride particles in the sticky crucible area of the crucible are densified and arranged by mechanical action such as agitation, vibration or extrusion, to obtain Densified silicon nitride coating; mechanical actions such as stirring, vibration and extrusion can be carried out by the equipment with the patent number ZL 201120254516.0, or by other equipment. The non-wetting treatment is to perform surface grinding, polishing and adsorption drying of silicon nitride powder on the surface of the densified silicon nitride coating to obtain a non-wetting silicon nitride coating.

Then, the silicon nitride coating is prepared on other areas of the inner wall of the crucible, and since the other areas of the inner wall of the crucible have relatively low requirements on the density and strength of the silicon nitride coating, it can be prepared by casting.

Finally, the above-mentioned silicon nitride coating is baked at 300° C., that is, the silicon nitride coating of the crucible for obtaining the crystalline silicon ingot is fabricated.

The present invention has been described by citing specific examples above. It should be pointed out that the above examples are only used to further illustrate the present invention, and do not represent the protection scope of the present invention. Non-essential modifications and adjustments made by others according to the hints of the present invention still belong to the protection scope of the present invention.

Claims (8)

1. the making method of a crystalline silicon crucible for casting ingots silicon nitride coating, it is characterized in that: adopt the method for liquid deposition after the easily sticking crucible zone of crucible inwall makes silicon nitride coating, this zone silicon nitride coating is carried out densification and non-infiltration processing, and adopt the method for liquid deposition to make silicon nitride coating in other zone of crucible inwall, at last silicon nitride coating is carried out low-temperature bake or non-sintered processing, obtain crystalline silicon crucible for casting ingots silicon nitride coating.

2. the making method of crystalline silicon crucible for casting ingots silicon nitride coating according to claim 1 is characterized in that: the easily sticking crucible zone of described crucible inwall is mainly rib, the angular zone of silicon liquidus zone and the crucible inside of crucible.

3. the making method of crystalline silicon crucible for casting ingots silicon nitride coating according to claim 1 and 2, it is characterized in that: the mode that makes silicon nitride coating is: directly Silicon Nitride is coated on the easily sticking crucible zone of crucible inwall or other zone of crucible inwall, silicon nitride particle autodeposition in the Silicon Nitride is coated Silicon Nitride on the inwall of crucible.

4. the making method of crystalline silicon crucible for casting ingots silicon nitride coating according to claim 3 is characterized in that: described Silicon Nitride by alpha-silicon nitride powders, pure water and binding agent by weight than for 100:70 ~ 450:0.1 ~ 15 formulated.

5. the making method of crystalline silicon crucible for casting ingots silicon nitride coating according to claim 4, it is characterized in that: described binding agent is one or more in methyl methacrylate, vinylformic acid, polyvinyl alcohol and the colloid silica.

6. the making method of crystalline silicon crucible for casting ingots silicon nitride coating according to claim 1 and 2, it is characterized in that: described densification is: in the drying process of the easily Silicon Nitride in sticking crucible zone of crucible, the silicon nitride particle that makes crucible easily glue the crucible zone by stirring, vibration or extrusion machinery effect is the densification arrangement, obtains the densification silicon nitride coating.

7. the making method of crystalline silicon crucible for casting ingots silicon nitride coating according to claim 1 and 2, it is characterized in that: described non-infiltration is treated to surface finish, polishing and adsorption dry silicon nitride powder is carried out in the silicon nitride coating surface of densification, obtains the non-infiltration silicon nitride coating.

8. the making method of crystalline silicon crucible for casting ingots silicon nitride coating according to claim 1 and 2 is characterized in that: the temperature when low-temperature bake is processed is for being lower than 500 ℃.

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