JP2009184917A - Apparatus for preventing contamination of silicon melt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for preventing contamination of a silicon melt, where falling of dust to a silicon melt from a heat shielding body surrounding a passage for pulling single-crystal silicon is prevented. <P>SOLUTION: The heat shielding body 55 whose opening at an upper side is larger than that at a lower side, has a slope 55a between the upper opening and the lower opening, facing to the passage for pulling single-crystal silicon. The slope 55a has a convex-concave shape with difference of height of about 0.5-10.0 mm. Where, falling of the dust to the silicon melt is reduced by the structure, to thereby prevent the single-crystal silicon from quality degradation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a silicon melt contamination prevention device for preventing silicon melt from being contaminated by the fall of dust from a heat shield to the silicon melt.

FIG. 1 is a schematic view of a single crystal silicon pulling apparatus.
Inside the furnace body 1 of the single crystal pulling apparatus 10, a heat insulating material 2 disposed inside the inner wall surface of the furnace body 1 to block heat transfer outside the furnace body and a silicon material such as polycrystalline silicon are held. The crucible 3 for storing the silicon melt after dissolution of the silicon raw material, the heater 4 disposed so as to surround the crucible 3 and heating the silicon material via the crucible 3, and the pulling path of the single crystal silicon 8 are surrounded. And a heat shield 5 disposed above the crucible 3.

  Further, the cooling coil 6 may be provided above the crucible 3 so as to surround the pulling path of the single crystal silicon 8. The cooling coil 6 is formed by spirally winding a pipeline through which cooling water flows, and the overall shape is cylindrical. The cooling coil 6 is disposed above the crucible 3 so that the crystal pulling path is located inside the spiral. When the cooling rate of the single crystal silicon 8 is increased by the cooling coil 6, the crystal quality is improved because the size of the so-called COPs of voids contained in the single crystal silicon 8 is reduced. Further, since the manufacturing cycle of the single crystal silicon 8 is accelerated, the manufacturing efficiency is improved. In some cases, oxygen precipitates in the single crystal silicon 8 are controlled or the oxide film breakdown voltage may be improved, and a cylindrical heater or purge tube is provided at substantially the same position as the cooling coil 6 instead of the cooling coil. There is also.

  Here, the procedure of the single crystal silicon manufacturing process using the single crystal pulling apparatus 10 will be briefly described. Silicon material is put into the crucible 3 and the heater 4 is started. Then, the silicon material is heated and melted to generate a silicon melt. A silicon seed crystal is immersed in the produced silicon melt. When this seed crystal is pulled up, single crystal silicon 8 is grown around the seed crystal. When pulling up the single crystal silicon 8, the pulling speed, the position of the heat shield 5 and the like are adjusted. Further, the single crystal silicon 8 is forcibly cooled by flowing cooling water through the pipe of the cooling coil 6.

  Ar gas is supplied from above in the furnace body 1 when the single crystal silicon 8 is grown. FIG. 5 is a diagram showing a gas flow in a general furnace body. 5A shows a gas flow at the initial stage of single crystal silicon growth, and FIG. 5B shows a gas flow after the initial stage of single crystal silicon growth.

  As shown in FIG. 5A, at the initial stage of growth of the single crystal silicon 8, Ar gas supplied from above in the furnace body 1 passes through the inside of the cooling coil 6 and descends to the vicinity of the silicon melt. Further, the gap between the crucible 3 and the heater 4 is lowered and flows out of the furnace body 1 from a gas discharge port 1 a provided in the lower part of the furnace body 1. A part of Ar gas supplied from above in the furnace body 1 passes through the inside of the cooling coil 6 and then passes through the gap between the lower end 6 a of the cooling coil 6 and the heat shield 5 to shield the cooling coil 6 from the heat. The gap between the bodies 5 rises and merges with Ar gas supplied from above the furnace body 1.

  As shown in FIG. 5B, after the initial growth of the single crystal silicon 8, a part of Ar gas supplied from above in the furnace body 1 is inside the cooling coil 6, that is, the cooling coil 6 and the single crystal silicon. Passes through the gap 8 and descends to the vicinity of the silicon melt. Further, the gap between the crucible 3 and the heater 4 is lowered and flows out of the furnace body 1 from a gas discharge port 1 a provided in the lower part of the furnace body 1. Further, a part of Ar gas supplied from above in the furnace body 1 descends the gap between the cooling coil 6 and the heat shield 5 and passes through the gap between the lower end 6a of the cooling coil 6 and the heat shield 5, and the cooling coil. 6 merges with the Ar gas that has passed through the inside of 6.

As shown in FIGS. 5A and 5B, the traveling direction of Ar gas flowing through the gap between the lower end 6 a of the cooling coil 6 and the thermal shield 5 changes between the initial stage of growth of the single crystal silicon 8 and thereafter. At this time, if the amount of change in the flow velocity is large, dust adhering to the heat shield 5 may be peeled off. The separated dust falls along the heat shield 5 and falls into the silicon melt.
Moreover, the dust adhering to the upper part of the furnace body 1 may fall. The dust falls on the heat shield 5, falls along the heat shield 5, and falls into the silicon melt.

  When dust falls on the silicon melt, the silicon melt is contaminated. In particular, when dust in the silicon melt is taken into the crystal to be grown, there is a problem that the single crystallization of the crystal is hindered and the quality of the single crystal silicon is lowered. Therefore, it is necessary to prevent the dust from falling into the silicon melt.

  The present invention has been made in view of such a situation, and an object of the present invention is to reduce the fall of dust into the silicon melt and prevent the deterioration of the quality of single crystal silicon.

The present invention
In the silicon melt contamination prevention device for preventing dust from falling from the heat shield surrounding the single crystal silicon pulling path to the silicon melt,
The thermal shield has an upper opening larger than the lower opening, and has a slope between the upper opening and the lower opening and facing the pulling path side of the single crystal silicon. It has unevenness of about 10.0 mm.

  The dust on the heat shield is retained by the uneven portions on the surface of the heat shield and does not fall into the silicon melt. If the height difference of the unevenness is too large, the heat shield itself will be enlarged, and if it is too small, it will not play a role to keep dust. Therefore, about 0.5 to 10.0 mm is appropriate.

  According to the present invention, dust falling on the heat shield from the upper part of the furnace body and dust on the heat shield can be retained on the heat shield. Therefore, the fall of the dust from the heat shield to the silicon melt is reduced, and the deterioration of the quality of the single crystal silicon is prevented.

FIG. 1 is a schematic view of a single crystal silicon pulling apparatus. FIG. 2 is a diagram showing the areas S1 and S2 used in the first embodiment. FIG. 3 is a view showing a gas flow in the furnace body according to the first embodiment. FIG. 4 is a schematic view of a cross section of the heat shield. FIG. 5 is a diagram showing a gas flow in a general furnace body. FIG. 6 is a schematic diagram of a general cooling coil. 7A and 7B are schematic views of a cooling coil to which a coil complementing member is attached.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Example 1 relates to control of the gas flow passing through the gap between the lower end of the cooling coil and the heat shield, and Examples 2 and 3 relate to the shape of the heat shield.

  The apparatus configuration of the present embodiment is the same as that of the single crystal pulling apparatus 10 shown in FIG. 1, but the arrangement of the pulling paths of the heat shield 5, the cooling coil 6, and the single crystal silicon 8 is based on areas S1 and S2, which will be described later. It is different in that it is determined.

  The relative position of the heat shield 5, the cooling coil 6, and the single crystal silicon 8 pulling path is such that the flow velocity of the gas passing through the gap between the lower end 6 a of the cooling coil 6 and the heat shield 5 It adjusts so that it may not be made to peel. The position is determined, for example, by determining an area ratio S2 / S1, which will be described later, according to the size and shape of each component in the manufacturing stage of the single crystal pulling apparatus 10.

  Further, at least one of the cooling coil 6 and the heat shield 5 may be movable up and down, and the relative positions of the cooling coil 6 and the heat shield 5 may be changed as appropriate. In this case, the raising / lowering operation of the cooling coil 6 and the heat shield 5 is controlled by a controller (not shown). In this embodiment, the cylindrical body surrounding the pulling path of the single crystal silicon 8 will be described as the cooling coil 6. However, the present invention is also applied to a case where a heater or a purge tube is provided instead of the cooling coil 6. Is possible.

FIG. 2 is a diagram showing the areas S1 and S2 used in the present embodiment.
In the present embodiment, the relative positions of the pulling path of the single crystal silicon 8 and the cooling coil 6 and the heat shield 5 are adjusted based on the elements of areas S1 and S2.

  An annular space 21 is formed between the side surface of the single crystal silicon 8 and the inner wall surface of the cooling coil 6. In the annular space 21, a cross section 21a of a cross section included in a plane orthogonal to the axis is shown in FIG. The area of the cross section 21a is S1. Next, it is assumed that the cooling coil 6 extends downward. In such a case, a cylindrical space 22 is assumed below the cooling coil 6. In this cylindrical space 22, a portion 22a formed between the cooling coil 6 and the heat shield 5 is shown in FIG. The area of the peripheral surface of this portion 22a is S2.

  The area S1 is determined according to the diameter of the single crystal silicon 8 to be pulled up and the diameter of the cooling coil 6. The area S2 is determined according to the shape of the heat shield 5, the diameter of the cooling coil 6, and the positions of the heat shield 5 and the cooling coil 6. What is important here is not the values of the areas S1 and S2, but the ratio S2 / S1 (or S1 / S2).

  Table 1 shows the inventor's experimental data regarding the area ratio S2 / S1. Table 1 shows data when a crystal having a diameter of 200 mm is pulled up.

  Dust in the silicon melt affects the quality of single crystal silicon. Specifically, dust inhibits single crystallization of crystals. The greater the amount of dust in the silicon melt, the lower the single crystallization rate of the generated crystal, and the higher the polycrystallization rate. Crystals produced when the area ratio S2 / S1 was 1.15 had a low rate of single crystallization and were not acceptable as a product. Crystals produced when the area ratio S2 / S1 is less than 1.15 (1.01, 0.8) have a high single crystallization rate. The present inventor believes that the single crystallization rate of crystals generated when the area ratio S2 / S1 is 1.15 is a threshold value as to whether or not the product is acceptable. Therefore, if the relative positions of the pulling paths of the heat shield 5, the cooling coil 6 and the single crystal silicon 8 are adjusted so that the area ratio S2 / S1 is less than 1.15, a good crystal can be produced as a product. Can do.

  Table 1 shows data with a diameter of 200 mm, but similar results can be obtained with crystals of other diameters.

FIG. 3 is a view showing a gas flow in the furnace according to the present embodiment. FIG. 3A shows a gas flow at the initial stage of single crystal silicon growth, and FIG. 3B shows a gas flow after the initial stage of single crystal silicon growth.
When Ar gas is supplied from above the furnace body of the single crystal silicon pulling apparatus, the Ar gas descends along the pulling path of the single crystal silicon 8. As shown in FIG. 3, when the area ratio S2 / S1 is an appropriate value, the flow rate of the gas passing through the gap between the lower end 6a of the cooling coil 6 and the heat shield 5 becomes small. If the flow rate of Ar gas passing through the gap between the lower end 6a of the cooling coil 6 and the heat shield 5 is small, the amount of change in flow rate is small even if there is a change in the Ar gas traveling direction. Therefore, the fall of the dust from the heat shield 5 due to the change in the traveling direction of Ar gas is suppressed.

  According to the present embodiment, the flow rate of Ar gas passing through the gap between the lower end of a cylindrical body such as a cooling coil and the heat shield can be reduced. For this reason, the separation of dust from the surface of the heat shield due to the change of the gas flow is reduced. Therefore, the fall of the dust to a silicon melt is reduced, and the quality fall of a single crystal silicon is prevented.

FIG. 4 is a schematic view of a cross section of the heat shield.
In the heat shield 55, the surface 55a on the single crystal silicon 58 side is uneven. The level difference of the unevenness is such that dust falling along the surface 55a of the heat shield 55 can be retained. Specifically, it is about 0.5 to 10.0 mm.

  According to this embodiment, dust falling on the heat shield from the upper part of the furnace body and dust on the heat shield can be retained on the heat shield. Therefore, the fall of the dust from the heat shield to the silicon melt is reduced, and the deterioration of the quality of the single crystal silicon is prevented.

  Incidentally, as shown in FIG. 6, the actual cooling coil 6 has a cooling pipe 6 b spirally wound around the pulling path of the single crystal silicon 8. Cooling water as a cooling medium is supplied into the cooling pipe 6b from a cooling water supply mechanism (not shown). When the cylindrical cooling coil 6 is formed by spirally forming the cooling pipe 6b as described above, the lower end 6a of the cooling coil 6 is not flat, and a height difference L1-L2 corresponding to one pipe is generated at the maximum. For this reason, the gap between the lower end 6a of the cooling coil 6 and the heat shield 5 varies depending on the location, and a portion where the gas flow is fast and a portion where the gas flow is slow are generated, resulting in non-uniform gas flow. If the gas flow becomes non-uniform in the gap between the lower end 6a of the cooling coil 6 and the heat shield 5 in this way, when the gas flow changes as the single crystal silicon 8 is pulled up, the minute amount deposited on the upper part of the furnace body. May cause falling of heavy dust (carbon etc.).

  In the present embodiment, in order to prevent the dust from falling due to such a height difference, a coil complementing member 61 is attached along a part of the lower end 6a of the cooling coil 6 as shown in FIG. ing. The coil complementing member 61 has the same curvature as that of the cooling coil 6. The cooling coil 6 and the coil complementing member 61 are integrated. Here, the integrated structure is referred to as a coil body 60. The coil complementing member 61 complements the height difference of the lower end 6a of the cooling coil 6 to make the lower end of the coil body 60 substantially flat. The material of the coil complementing member 61 may be any material as long as it does not hinder the formation and quality of the single crystal silicon 8.

  As shown in FIG. 7A, the coil complementing member 61 is not attached to a part of the lower end 6a of the cooling coil 6, but the lower end 6a of the cooling coil 6 is not attached as shown in FIG. The coil complementing member 62 may be attached to the entirety.

  In this embodiment, the coil complementing member 61 is provided on the cylindrical cooling pipe 6. However, the present invention is not limited to this, and the coil complementing member 61 is provided on a cylindrical coil that allows a temperature adjusting medium to flow through the spiral pipe. Also good.

  According to this embodiment, a coil complement member is attached to the lower end of a temperature adjustment coil such as a cooling coil to form a coil body, so that the gap between the lower end of the coil body and the heat shield is constant in all parts. be able to. Therefore, nonuniform gas flow does not occur in the gap between the coil body and the heat shield. Therefore, it does not induce the fall of the minute dust deposited on the upper part of the furnace body, the fall of the dust to the silicon melt is reduced, and the quality deterioration of the single crystal silicon is prevented.

DESCRIPTION OF SYMBOLS 1 Furnace 5, 45, 55 Thermal shield 6 Cooling coil 8 Single crystal silicon 10 Single crystal pulling device 60 Coil body 61 Coil complementary member

Claims (1)

In the silicon melt contamination prevention device for preventing dust from falling from the heat shield surrounding the single crystal silicon pulling path to the silicon melt,
The thermal shield has an upper opening larger than the lower opening, and has a slope between the upper opening and the lower opening and facing the pulling path side of the single crystal silicon. An apparatus for preventing contamination of silicon melt, which has irregularities of about 10.0 mm.

Images