CN101433890A - Method and device for spraying silicon nitride coating on inner wall of quartz crucible under low pressure - Google Patents

Abstract

The invention relates to a method for spraying a silicon nitride coating layer on the inner wall of a quartz crucible at low pressure and a device thereof. The method comprises the following process course: silicon nitride particles with particle diameter of between 5 and 200 microns and deionized water are stirred into an emulsion slurry shaped solution; the emulsion slurry shaped solution is continuously stirred in the spraying process; the solution forms silicon nitride mist through an atomization head under the function of inner and outer pressure difference; at low pressure of between 10 and 100 Pa, the mist is evenly and continuously sprayed on the inner wall of the quartz crucible; after moisture is dried, a dry and thin silicon nitride layer of between 1 and 2 mm is formed; and the quartz crucible coated with the silicon nitride coating layer is sintered at temperature of between 950 and 1,050 DEG C to form a silicon nitride layer with more compact structure. The method can prepare the silicon nitride layer with even thickness, small pollution and compact structure and can reduce environmental pollution and harm to the health of operators.

Description

Under the low pressure on inner wall of quartz crucible the method for spraying silicon nitride coating and device

(1) technical field

The present invention relates to a kind of on the inner wall of quartz crucible that is used for the casting polycrystalline silicon ingot method and the spraying silicon nitride coating device of spraying silicon nitride coating.

(2) background technology

The polycrystalline ingot casting is earlier the silicon material to be put in the silica crucible, and electricity consumption is heated to the silicon in the silica crucible more than the silicon fusing point then, after insulation a period of time, begins to cool down to head from the silica crucible bottom and to solidify, and has promptly formed polycrystal silicon ingot at last.If the inwall of silica crucible does not have coating, can take place after the molten silicon cooled and solidified and silica crucible sticks together, cause silica crucible to reuse.If on the inwall of silica crucible, be coated with the recycling that the last layer silicon nitride can be realized silica crucible, reduce production costs.

At present spraying silicon nitride coating on the used inner wall of quartz crucible of polycrystalline ingot casting is in normal pressure (atmospheric pressure) spraying down.The normal pressure spraying has following shortcoming: silicon nitride is vulnerable to pollute; Silicon nitride coating is in uneven thickness; Silicon nitride coating is fine and close inadequately; Easy contaminated environment and harm operating personnel health in the spraying operation process.

(3) summary of the invention

The objective of the invention is to overcome above-mentioned deficiency, provide a kind of can prepare thickness evenly, pollute silicon nitride layer little, compact structure, and can reduce environmental pollution and reduce under the low pressure of operating personnel's health hazard on inner wall of quartz crucible the method for spraying silicon nitride coating and device.

The object of the present invention is achieved like this: under a kind of low pressure on inner wall of quartz crucible the method for spraying silicon nitride coating, described method comprises that technical process is as follows: the silicon nitride particle of 5～200 microns of particle diameters is become Mag solution and remains on constantly stirring in the spraying process with deionized water and stirring, this solution forms the silicon nitride mist through atomising head under the inside and outside differential pressure effect, in low pressure (10～100Pa) times evenly continuous spraying on the inner wall of quartz crucible of this mist, moisture content is promptly formed dry 1～2mm thin layer of sin after drying, the silica crucible that will scribble again at silicon nitride coating carries out sintering under 950～1050 ℃, form the fine and close more silicon nitride layer of structure.

Pressure is lower in the process of the inventive method spraying silicon nitride, has only the one thousandth of normal pressure spraying method.Low pressure has higher cleanliness factor in the container mutually with normal pressure, and the silicon nitride of spraying can be clean more, can reduce the pollution to the polycrystalline ingot casting.

The following table data are selected from 49 pages of GB50073-2001 versions

Atmosphere dust content mean value is (more than or equal to 0.5m, pc/L)

The area	Annual	The monthly average maximum	The monthly average minimum of a value
				Beijing (urban district)	190956	293481	9274
Beijing (rural area, Changping)	35643	156620	4591
				Shanghai (urban district)	128052	365103	34327
Xi'an (urban district)	131644	317561	29738

The air a large amount of dust is arranged as can be seen from last table data, vacuum coating, the pressure when supposing plated film is 100Pa, normal pressure is 1.01 * 10 ⁵Pa is according to the imperial equation PV=nRT estimation of carat uncle, 1/1000 the when molal quantity of gas becomes normal pressure, can estimate that airborne dust particle also is kept to original 1/1000 approximately, therefore cleanliness factor improves greatly, has reduced the pollution of air to silicon nitride, thereby reduces the pollution to the polycrystalline ingot casting.

Under the low pressure, the vaporific particle of silicon nitride has longer mean free path, and what promptly combine between silicon nitride particle and silica crucible and silicon nitride particle is tightr.According to formula $\stackrel{\‾}{\mathrm{\λ}}=\frac{1}{\sqrt{2}\mathrm{\π}{d}^{2}n},$ Wherein λ is a molecule mean free path, and π is a constant, and d is that the molecule effective diameter is considered as definite value, and n is the number density of molecule; In conjunction with carat imperial equation PV=nRT of uncle, V is that the plated film volume of a container is a certain value, and R is a perfect gas state constant, and T also is constant under certain conditions, so n is directly proportional low pressure (10-100Pa) and normal pressure (1.01 * 10 with P ⁵Pa) compare, molecule mean free path can be increased to original 1000 times, so silicon nitride particle has when arriving silica crucible surperficial bigger actively, makes that silicon nitride film compactness is better.

Vavuum pump is worked under manometric monitoring, keep the work under the less pressure reduction that is sprayed at, the inside and outside differential pressure fluctuation is little to make that the initial kinetic energy fluctuation of silicon nitride spraying is little, and therefore silicon nitride atomizing high conformity makes that the silicon nitride coating that sprays on the inner wall of quartz crucible is more even.

The low pressure spraying operation is operation in airtight space, has avoided the diffusion of silicon nitride mist outside confined space, has reduced to the harmful effect of environment and to operative employee's harm.

To sum up, the inventive method has following characteristics:

1, environment is cleaner under the low pressure, and the pollution that the silicon nitride of spraying is subjected to still less;

2, the vaporific grain structure of silicon nitride is finer and close; Silicon nitride coating is more even;

3, can reduce operation process to the pollution of environment and to operator's harm.

(4) description of drawings

Fig. 1 under the low pressure of the present invention on inner wall of quartz crucible the apparatus structure schematic diagram of spraying silicon nitride coating.

Among the figure: silica crucible 1, atomising head 2, vavuum pump 3, vacuum meter 4, low pressure vessel 5, valve 6, pipeline 7, agitator 8, Sheng silicon nitride slurry container 9.

(5) specific embodiment

Referring to Fig. 1, under the low pressure involved in the present invention on inner wall of quartz crucible the device of spraying silicon nitride coating, mainly by silica crucible 1, atomising head 2, vavuum pump 3, vacuum meter 4, low pressure vessel 5, valve 6, agitator 8 with contain silicon nitride slurry container 9 and form.Described low pressure vessel 5 links to each other with vavuum pump 3, vacuum meter 4 is installed on the low pressure vessel 5, pressure in the control low pressure vessel 5 is 10-100Pa, described silica crucible 1 places in the airtight low pressure vessel 5, atomising head 2 is arranged in the silica crucible 1, atomising head 2 links to each other with Sheng silicon nitride slurry container 9 by pipeline 7, and pipeline 7 is provided with valve 6, contains in the silicon nitride slurry container 9 and is provided with agitator 8.

Spraying method of the present invention is as follows:

The deionized water and stirring of silicon nitride particle (5～200 microns of particle diameters) and 15～18M Ω cm is become Mag solution and remains on constantly stirring in the spraying process, this solution forms the silicon nitride mist through atomising head under the inside and outside differential pressure effect, (10～100Pa) times evenly continuous spraying on the inner wall of quartz crucible of this mist, moisture content is promptly formed dry silicon nitride (1～2mm) thin layer after drying in low pressure.This coating also need be carried out sintering under (950～1050) ℃ before being used for the casting polycrystalline silicon ingot, forms the fine and close more silicon nitride layer of structure.

Claims (2)

1, under a kind of low pressure on inner wall of quartz crucible the method for spraying silicon nitride coating, it is characterized in that: described method comprises that technical process is as follows: the silicon nitride particle of 5～200 microns of particle diameters is become Mag solution and remains on constantly stirring in the spraying process with deionized water and stirring, this solution forms the silicon nitride mist through atomising head under the inside and outside differential pressure effect, evenly continuous spraying on the inner wall of quartz crucible of this mist under 10～100Pa low pressure, moisture content is promptly formed dry 1～2mm thin layer of sin after drying, the silica crucible that will scribble again at silicon nitride coating carries out sintering under 950～1050 ℃, form the fine and close more silicon nitride layer of structure.

2, under a kind of low pressure according to claim 1 on inner wall of quartz crucible the used device of the method for spraying silicon nitride coating, it is characterized in that described device comprises silica crucible (1), atomising head (2), vavuum pump (3), vacuum meter (4), low pressure vessel (5), valve (6), agitator (8) and Sheng silicon nitride slurry container (9), described low pressure vessel (5) links to each other with vavuum pump (3), low pressure vessel (5) is gone up vacuum meter (4) is installed, pressure in the control low pressure vessel (5) is 10-100Pa, described silica crucible (1) places in the airtight low pressure vessel (5), atomising head (2) is arranged in the silica crucible (1), atomising head (2) links to each other with Sheng silicon nitride slurry container (9) by pipeline (7), pipeline (7) is provided with valve (6), contains in the silicon nitride slurry container (9) and is provided with agitator (8).

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