CN201267022Y - Heating coil for purifying polycrystalline silicon empty space melt - Google Patents

Abstract

The utility model discloses a heating coil for melting and purifying polysilicon in a vacuum zone, which comprises a coil frame and a coil water-cooled tube. The slope formed by connecting one end of the bottom with the inner circle edge of the coil frame forms a second inclination angle with the horizontal plane. The inner circle of the coil frame is an eccentric structure, and an eccentric groove is provided on the lower surface of the coil. The heating coil described in the utility model overcomes the defect that burrs are easy to appear on the edge of polysilicon with larger diameter during the process of melting and purifying in the vacuum zone. The eccentric structure of the inner diameter greatly reduces the possibility of a belt in the melting zone, and the inclined design of the upper surface of the coil enhances the fluidity of the molten silicon at the polycrystalline melting interface. On the side of the coil frame close to the upper flange of the electrode and the lower flange of the electrode, an oblique cut with cut planes parallel to each other is provided to reduce electromagnetic leakage.

Description

A heating coil for polysilicon vacuum zone melting purification

technical field

The utility model relates to the field of vacuum purification of polysilicon, in particular to a heating coil for melting and purifying polysilicon in a vacuum zone.

Background technique

Zone melting, referred to as zone melting, refers to the preparation of high-purity metals, semiconductor materials and A method of purification of organic compounds. The typical method of zone melting is to make the purified material into a thin rod with a length of 0.5 ~ 3m or longer, and through high-frequency induction heating, a small section of solid is melted into a liquid state, and the liquid phase temperature in the melting zone is only higher than that of the solid material. The melting point is a few degrees higher, and a solid phase will precipitate out after a little cooling. The melting zone moves slowly along the axial direction, a few to ten centimeters per hour. As the melting zone moves forward, the impurities also move along, and are finally enriched at one end of the rod and removed. One-time zone smelting often cannot meet the required purity, and usually has to be repeated many times, or several melting zones are formed sequentially along the length of the thin rod in one operation.

Utilizing the evaporation and segregation effects of impurities, multiple times of vacuum melting and purification of polysilicon is a necessary step for preparing low compensation, high purity and high resistance melting silicon materials. During the purification process of polysilicon, the crystallization rate of polysilicon is inconsistent in all directions, and the release of latent heat of crystallization can easily cause cracks in the large-diameter polysilicon, which makes it unusable. Therefore, the diameter of polysilicon purified by vacuum zone melting is generally controlled below 50±2mm. Since the preparation of high-resistance silicon materials requires multiple purifications of polysilicon, the stability of the purification is particularly important, that is, during the preparation, if there are thorns on the edge of the polysilicon, solidification in the melting zone, belts in the melting zone, and furnace collapse, the entire process will be interrupted. In the preparation process, the belt is generally formed in the shoulder stage of polycrystalline purification. Due to the mismatch between the heating power, the shape of the thermal field, and the shape of the polycrystal, a belt-shaped non-melting solid is formed in the center of the melting zone, commonly known as "belt". ", therefore, a stable thermal field for melting and purification in the vacuum zone is particularly important, and the core part of the thermal field is the heating coil.

The traditional heating coil used for the growth of silicon single crystals below 52mm is generally a flat "duckbill coil". The surface is an inclined surface, and a flange is used to fix the coil water-cooling tube at the end of the coil. At present, this "duckbill coil" is usually directly used for polysilicon vacuum purification, but due to polysilicon vacuum purification and single crystal silicon growth process The characteristics are not the same. When the polycrystalline diameter gradually increases, the fluidity of the molten silicon at the polycrystalline melting interface becomes poor, and the polycrystalline melting edge is prone to burrs due to overcooling. When the polycrystalline diameter is greater than 45mm, this phenomenon is particularly obvious. It is difficult to apply to the process that requires multiple vacuum zone melting and purification. Experiments have proved that this kind of heating coil is not suitable for vacuum zone melting and purification.

There is also a Danish coil that can be used for melting and purifying polysilicon in a vacuum zone. As shown in Figure 3 and Figure 4, a step is engraved on the upper surface of the coil, the lower surface of the coil has an inclined design, and the inner circle of the coil skeleton adopts an eccentric design, that is, it is close to the flange. One side is a rectangle plus a positive semicircle, and the other side is a positive semicircle. The experiment proves that the effect of this coil is not good. Although the single-step design reduces the probability of thorns on the edge of polycrystalline melting to a certain extent, due to the step energy The radiation range is limited, which can easily cause uneven local energy distribution and local overcooling to produce burrs. At the same time, during the purification process using this coil, the fluidity of molten silicon at the polycrystalline melting interface is still poor, and there is a hidden danger of furnace collapse. In addition, the eccentric design of the coil can reduce the probability of belt generation in theory, but due to the large degree of asymmetry in the center of the coil, the energy distribution is relatively uneven, and the local energy is too low, which is not effective in removing the belt. obvious.

Utility model content

The technical problem solved by the utility model is to provide a heating coil for melting and purifying polysilicon in a vacuum zone, which can provide a thermal field for melting and purifying in a vacuum zone, and can overcome the tendency of the polysilicon edge with a larger diameter to appear during the process of melting and purifying in a vacuum zone Glitch defect.

The technical solution adopted by the utility model is that the heating coil used for melting and purifying polysilicon in a vacuum zone includes a coil frame and a coil water-cooled tube, the coil water-cooled tube is welded and embedded in the coil frame, and one end of the lower edge of the inner circle of the coil frame and the lower surface of the coil The connected inclined plane and the horizontal plane form a first inclined angle. The coil adopts a flat single-turn structure, and the upper surface around the inner circle of the coil bobbin is provided with a first step and a second step. The diameter of the circle where the first step is located is greater than The diameter of the circle where the second step is located, and the slope formed by connecting the bottom end of the second step with the edge of the inner circle of the coil bobbin form a second inclination angle with the horizontal plane.

The coil further includes an electrode upper flange and an electrode lower flange. The electrode upper flange and the electrode lower flange have electrode connection holes and water cooling tube holes. The coil water cooling tube passes through the water cooling tube hole and connects with the electrode upper flange and the electrode respectively. The lower flanges are welded together, and the circulating cooling water enters and exits the coil frame through the coil water cooling tube, and a cutout is set on the side of the coil frame close to the electrode upper flange and the electrode lower flange.

As a preferred technical solution, the inner circle of the coil frame is an eccentric structure, which may be composed of a semicircle and a half ellipse, and an eccentric groove is provided on the lower surface of the coil.

As another preferred technical solution, the cut is an oblique cut with cut planes parallel to each other.

By adopting the above-mentioned technical scheme, the utility model has at least the following advantages:

The heating coil used for melting and purifying polysilicon in a vacuum zone described in the utility model is suitable for multiple vacuum zone melting and purification. There are two steps on the upper surface of the coil, which overcomes the defect that burrs are easy to appear on the edge of polysilicon with a large diameter during the process of melting and purifying in a vacuum zone. The eccentric design of the inner diameter greatly reduces the possibility of a belt in the melting zone, and the inclined design of the upper surface of the coil enhances the fluidity of the molten silicon at the polycrystalline melting interface. The inclined design of the lower surface of the coil is conducive to the release of latent heat of polycrystalline crystallization. On the side of the coil frame close to the upper flange of the electrode and the lower flange of the electrode, an oblique cut with cut planes parallel to each other is arranged to reduce electromagnetic leakage.

Description of drawings

Fig. 1 is a schematic diagram of the duckbill coil structure;

Fig. 2 is the A-A plane sectional view of Fig. 1;

Fig. 3 is a schematic diagram of the Danish coil structure;

Fig. 4 is a sectional view of plane A-A of Fig. 3;

Fig. 5 is a schematic structural diagram of the heating coil of the first embodiment of the utility model;

Fig. 6 is a sectional view of plane A-A of Fig. 5;

Fig. 7 is the B direction view of Fig. 5;

Fig. 8 is a schematic structural diagram of the heating coil used for melting and purifying polysilicon in a vacuum zone according to the third embodiment of the present invention;

Fig. 9 is a sectional view of plane A-A of Fig. 7;

Fig. 10 is the B direction view of Fig. 7;

Fig. 11 is a schematic diagram of the cutout of the heating coil in the fourth embodiment of the utility model.

Detailed ways

In order to further explain the technical means and effects adopted by the utility model to achieve the intended purpose, the heating coil for polysilicon vacuum zone melting and purification proposed by the utility model will be described in detail as follows in conjunction with the accompanying drawings and preferred embodiments. .

In the first embodiment of the present utility model, the structure of the heating coil used for melting and purifying polysilicon in a vacuum zone is shown in Figure 5. The basic structure of the pancake-type flat single-turn coil is adopted, and the thickness of the pancake-type single-turn structure is 7-7. 9mm. The heating coil includes a coil frame 501, a coil water cooling tube 502, an electrode upper flange 503, and an electrode lower flange 504. The coil water cooling tube 502 is welded and embedded in the coil frame 501. This structure can improve the effect of water cooling, and at the same time, it is easy to For processing, the coil bobbin 501 and the coil water-cooled tube 502 are all made of red copper T2 grade. As shown in Figure 7, the electrode upper flange 503 and the electrode lower flange 504 have an electrode connection hole 701 and a water cooling pipe hole 702 for the coil water cooling pipe 502 to pass through, and the coil water cooling pipe 502 passes through the water cooling pipe hole 702 and respectively The electrode upper flange 503 and the electrode lower flange 504 are welded together. Circulating cooling water enters and exits the coil through the water-cooling pipe hole 702 to cool it.

As shown in Figure 6, the upper surface around the inner circle of the coil bobbin adopts a two-level stepped structure, including a first level step 601 and a second level step 602, the diameters of the two steps are slightly larger than the diameter of polysilicon, for example, if the polysilicon The diameter is 2 inches, i.e. 50.8mm, then the diameter of the circle where the first step 601 is located is 52-54mm, the diameter of the circle where the second step 602 is located is 48-50mm, the first step 601 and the second step 602 The height is 1-1.5mm. The structure of two steps strengthens the electromagnetic field generated locally by the heating coil used for polysilicon vacuum zone melting and purification, and at the same time improves the melting interface between the inner and outer sides of the outer edge of the polysilicon, and eliminates the outer edge of the polysilicon with a larger diameter during the vacuum purification process. Burrs that are prone to appear, polysilicon with a diameter of 45mm to 52mm belong to polysilicon with a larger diameter. The upper surface of the coil is a downward inclined surface 603, that is, the inclined surface formed by connecting the bottom end of the second step and the inner circle edge of the coil bobbin forms a second inclined angle with the horizontal plane. The second inclined angle can be 6-9 degrees, which can make the electromagnetic field The energy does not gradually decrease from the inside to the outside, so that the polycrystalline melting interface is flat and inclined from the outside to the inside, and the molten silicon on the melting interface tends to flow to the center of the melting zone, which increases the fluidity of the molten silicon. The lower surface of the coil is an upwardly inclined surface 604, that is, the inclined plane formed by connecting the lower edge of the inner circle of the coil frame with the lower surface of the coil forms a first inclined angle with the horizontal plane. The first inclined angle can be 7 to 10 degrees, which can increase energy radiation Reduce the temperature gradient of the polycrystalline solidification interface, which is conducive to the release of stress during the polycrystalline crystallization process, and reduces the risk of fractures inside the polycrystalline silicon. A cutout 703 is provided on the side of the coil frame 501 close to the electrode upper flange and the electrode lower flange. The cutout 703 is located on the extension line of the inner diameter of the coil frame.

In the second embodiment of the present utility model, the structure of the heating coil used for melting and purifying polysilicon in a vacuum zone is substantially the same as that of the first embodiment, except that the diameter of the circle where the first step used in this embodiment is 53 mm, and the second The diameter of the circle where the first step is located is 49 mm, and the height of the first step and the second step are both 1 mm.

In the third embodiment of the present utility model, the structure of the heating coil used for melting and purifying polysilicon in a vacuum zone is shown in Figure 8. The heating coil used for melting and purifying polysilicon in a vacuum zone includes an electrode upper flange 803 and an electrode lower flange. 804, coil bobbin 801, coil water-cooled tube 802, the structure of the coil is basically the same as that of the first embodiment, the coil has an inclined surface 903 on the upper surface, an inclined surface 904 on the lower surface, and two steps on the upper surface: the first step 901 and The difference of the second step 902 is that the inner circle of the coil bobbin adopts an eccentric structure, and the arc of the inner circle is enlarged on the side close to the flange to form an eccentricity 805 . In practical applications, the inner circle of the coil bobbin with eccentric structure can be composed of half a perfect circle and half an ellipse close to the flange side. The ratio of the radii of the circles may be 1.15:1. As shown in FIG. 9 , an eccentric notch 905 is provided on the inclined surface 904 of the lower surface of the coil, and the eccentric notch 905 is carved 4-6 mm horizontally from the lower edge of the inner circle of the coil frame to the direction of the flange. The eccentric structure can make the heating power, the shape of the thermal field, and the polycrystalline shape more matched, reducing the possibility of belts, and because the ellipse is eccentric, it will not make the electromagnetic field distribution too asymmetric and cause the local energy to be too low , and at the same time increase the stirring of the melting zone to improve the non-uniformity of polysilicon radial resistivity. The eccentric notch 905 can keep the lower interface of the melting zone flat and stable. As shown in Figure 10, a cutout 1003 with cut planes parallel to each other and perpendicular to the horizontal plane is provided on the side of the coil bobbin close to the upper flange of the electrode and the lower flange of the electrode, and the cutout 1003 is located on the extension line of the semi-major axis of the ellipse near the flange side.

In the fourth embodiment of the present utility model, the structure of the heating coil used for melting and purifying polysilicon in a vacuum zone is basically the same as that in the third embodiment, except that this embodiment, as shown in Figure 11, is on the coil skeleton close to the electrode One side of the flange and the lower flange of the electrode is provided with an inclined notch 1103 with cut planes parallel to each other. The inclined notch 1103 is located on the extension line of the semi-major axis of the ellipse close to the side of the flange to reduce electromagnetic leakage.

Through the description of specific implementation methods, the technical means and effects of the utility model to achieve the intended purpose can be more deeply and specifically understood. However, the attached drawings are only for reference and description, and are not used to explain the utility model. be restricted.

Claims (10)

1, a kind of heater coil that is used for the polysilicon vacuum zone refining, comprise coil rack and coil water cooling tube, the welding of coil water cooling tube embeds in the coil rack, the inclined-plane that circle lower edge one end and coil lower surface connect in the described coil rack is horizontal by first angle of inclination, it is characterized in that, described coil adopts dull and stereotyped single turn structure, the upper surface that encloses at the coil rack inner periphery is provided with first order step and second level step, first order step place diameter of a circle is greater than second step place diameter of a circle, and the inclined-plane that bottom one end of second level step and coil rack internal circle edge connect into is horizontal by second angle of inclination.

2, heater coil according to claim 1, it is characterized in that, this coil further comprises electrode upper flange and electrode lower flange, electrode connecting hole and water-cooled pore are arranged on electrode upper flange and the electrode lower flange, the coil water cooling tube pass the water-cooled pore and respectively with electrode on method and electrode lower flange weld mutually, recirculated cooling water is by coil water cooling tube turnover coil rack, and the side near electrode upper flange and electrode lower flange on described coil rack offers an otch.

3, heater coil according to claim 1 and 2 is characterized in that, described coil rack and coil water cooling tube all adopt red copper T2 level material to make.

4, heater coil according to claim 3 is characterized in that, described pancake formula single turn thickness of structure is 7～9mm.

5, heater coil according to claim 4 is characterized in that, described first angle of inclination is 7～10 degree.

6, heater coil according to claim 5 is characterized in that, described second angle of inclination is 6～9 degree.

7, heater coil according to claim 6 is characterized in that, first order step place diameter of a circle is 52～54mm, and step place, second level diameter of a circle is 48～50mm, and the height of first order step and second level step is 1～1.5mm.

8, heater coil according to claim 6 is characterized in that, first order step place diameter of a circle is 53mm, and step place, second level diameter of a circle is 49mm, and the height of first order step and second level step is 1mm.

9, heater coil according to claim 7, it is characterized in that, circle is the centering type structure in the coil rack, by half just circle form with a semiellipse, oval semi-minor axis equates with positive radius of a circle, the length of oval major semiaxis is 1.15:1 with the ratio of positive radius of a circle, and the coil lower surface is provided with an eccentric cutting, and described eccentric cutting is to justify the lower edge level to carve 4～6mm to the flange direction in coil rack.

10, heater coil according to claim 9 is characterized in that, described otch is an angular cutouts that tangent plane is parallel to each other, and is positioned on the extended line of oval major semiaxis near flange one side.

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