JP2021075421A - Carbon crucible - Google Patents

Abstract

To reduce the amount of carbon incorporated into silicon monocrystals being pulled up.SOLUTION: When monocrystals S are produced by the Czochralski method, a carbon crucible 5 supports a quartz crucible 3A to store raw material melt M. The carbon crucible 5 has a straight body part 51, a bent part 52, and a bottom part 53. The bent part 52 has a through hole 12 that penetrates from the outer surface of the bent part 52 to the inner surface.SELECTED DRAWING: Figure 2

Description

The present invention relates to a carbon crucible that supports a quartz crucible that houses a raw material melt when producing a single crystal by the Czochralski method.

As a method for producing a single crystal such as a silicon single crystal, a method called a Czochralski method (hereinafter referred to as a CZ method) is known. The crucible used for accommodating the raw material melt in the CZ method has a double structure in which the inside is a quartz crucible and the outside is a carbon crucible such as a graphite crucible. The quartz crucible is used by being installed in a pulling device while being housed in a carbon crucible (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2018-43890

By the way, in wafers for power devices such as insulated gate bipolar transistors (IGBTs), reduction of carbon concentration in a single crystal is required. The cause of carbon contamination is that carbon monoxide gas or the like (hereinafter referred to as CO gas) generated in the furnace when the single crystal is pulled up dissolves in the raw material melt.

The following two sources can be considered as the sources of CO gas. The first source is the reaction between silicon monoxide gas (SiO) generated from the silicon melt and carbon (C) contained in the carbon product arranged around the crucible when the raw material melt is a silicon melt. Is. The second source is _{the reaction between the quartz (SiO 2} ) of the quartz crucible and the carbon (C) contained in the carbon crucible.
Regarding the second source, the CO gas generated between the quartz crucible and the carbon crucible is discharged from the vicinity of the upper end of the crucible, and a part of the discharged CO gas is introduced into the quartz crucible. It is considered that it is incorporated into the raw material melt and increases the carbon concentration in the single crystal.

An object of the present invention is to provide a carbon crucible capable of reducing carbon incorporated into a single crystal being pulled up when a single crystal is produced by the Czochralski method.

The carbon crucible of the present invention is a carbon crucible that supports a quartz crucible that houses a raw material melt when a single crystal is produced by the Czochralski method, and has a straight body portion, a curved portion, and a bottom portion. The curved portion is characterized by having a through hole penetrating from the outer surface to the inner surface of the curved portion.

In the carbon crucible, the through hole has a bent portion.

The carbon crucible has an annular groove extending in the circumferential direction on the inner surface of the curved portion, and the end portion of the through hole on the inner surface side is located in the annular groove.

In the carbon crucible, the annular groove has a first annular groove formed above the curved portion and a second annular groove formed below the curved portion, and the through hole is formed. The carbon having a first through hole whose inner surface side end is located in the first annular groove and a second through hole whose inner surface side end is located in the second annular groove. The crucible is formed on the inner surface of the curved portion and has a vertical groove extending in the vertical direction to connect the first annular groove and the second annular groove.

In the carbon crucible, a plurality of through holes are provided in the circumferential direction.

The carbon crucible is divided into a plurality of carbon crucible pieces at a dividing surface including the central axis, and the through hole is formed on the dividing surface of the carbon crucible pieces adjacent in the circumferential direction.

According to the present invention, the CO gas generated at the contact interface between the quartz crucible and the carbon crucible is discharged from the through hole formed in the curved portion of the carbon crucible, so that the CO gas taken into the raw material melt is reduced. It is possible to reduce the carbon incorporated into the single crystal being pulled up.

It is the schematic sectional drawing of the pulling device which concerns on embodiment of this invention. It is a side view which cut out a part of the carbon crucible which concerns on embodiment of this invention. FIG. 5 is an enlarged cross-sectional view of a through hole according to an embodiment of the present invention. It is a top view of the carbon crucible of the embodiment of this invention. It is a side view of the carbon crucible piece of the embodiment of this invention. It is sectional drawing explaining the operation of the pulling device of embodiment of this invention. It is sectional drawing which shows the modification of the through hole of embodiment of this invention. It is a graph which shows the result of the experiment performed for confirming the CO gas emission effect of the ordinary carbon crucible and the carbon crucible of the embodiment of the present invention.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[Pulling device]
FIG. 1 is a schematic cross-sectional view of the pulling device 1 according to the embodiment of the present invention.
The pulling device 1 is a device for pulling and growing a silicon single crystal S by the Czochralski method. As shown in FIG. 1, the pulling device 1 includes a chamber 2 constituting an outer shell, a crucible 3 arranged in a central portion of the chamber 2, and a heater 4.

The crucible 3 is a container in which a silicon melt M (raw material melt), which is circular when viewed from above, is housed. The crucible 3 has a double structure composed of an inner quartz crucible 3A and an outer carbon crucible 5. The crucible 3 is fixed to the upper end of a support shaft 6 that can rotate and move up and down and extends in the vertical direction.

The quartz crucible 3A is a container made of quartz glass having a bottomed cylindrical shape.
The carbon crucible 5 is a container made of graphite (graphite) having a bottomed cylindrical shape, and the quartz crucible 3A is placed so as to cover the outer surface of the quartz crucible 3A so that the shape of the quartz crucible 3A softened by heating is maintained. To support.

The heater 4 is a heating device that heats the silicon melt M in the crucible 3. The heater 4 has a cylindrical shape and is arranged coaxially with the central axis A of the crucible 3 on the outside of the crucible 3. The heater 4 is a resistance heating type so-called carbon heater. A heat insulating material 7 is provided on the outside of the heater 4 along the inner surface of the chamber 2.

Above the crucible 3, a pull-up shaft 8 is arranged coaxially with the support shaft 6. The pull-up shaft 8 is formed of a wire or the like. The pull-up shaft 8 rotates around the shaft at a predetermined speed. A seed crystal SC is attached to the lower end of the pulling shaft 8. The pulling shaft 8 rotates the seed crystal SC (silicon single crystal S).

A heat shield 9 is arranged in the chamber 2. The heat shield 9 has a tubular shape and surrounds the silicon single crystal S being grown above the silicon melt M in the crucible 3.
The heat shield 9 blocks high-temperature radiant heat from the silicon melt M in the crucible 3, the heater 4, and the side wall of the crucible 3 with respect to the growing silicon single crystal S.

A gas introduction port 10 is provided in the upper part of the chamber 2. The gas introduction port 10 introduces an inert gas G1 such as argon gas into the chamber 2. An exhaust port 11 is provided in the lower part of the chamber 2. The exhaust port 11 sucks and discharges the gas in the chamber 2 by driving a vacuum pump (not shown). The inert gas G1 introduced into the chamber 2 from the gas introduction port 10 descends between the growing silicon single crystal S and the heat shield 9. Next, the inert gas G1 passes through the gap between the lower end of the heat shield 9 and the liquid surface of the silicon melt M, and then flows toward the outside of the heat shield 9 and further toward the outside of the crucible 3. After that, the inert gas G1 descends outside the crucible 3 and is discharged from the exhaust port 11.

As shown in FIG. 2, the carbon crucible 5 includes a cylindrical straight body portion 51, a cylindrical curved portion 52, and a circular bottom portion 53. The curved portion 52 smoothly connects the straight body portion 51 and the bottom portion 53. The bottom 53 is curved. The curvature of the curved portion 52 is larger than the curvature of the bottom portion 53.
The straight body portion 51 is a cylindrical portion formed with a substantially constant thickness. The straight body portion 51 does not have to have a completely cylindrical shape, and may have, for example, a tapered shape such that the inner diameter gradually increases upward.

The curved portion 52 is a portion between the straight body portion 51 and the bottom portion 53. The inner surface of the curved portion 52 is smoothly connected to the inner surface of the straight body portion 51 at the upper end portion of the curved portion 52, and is smoothly connected to the inner surface of the bottom portion 53 at the lower end portion of the curved portion 52.

The carbon crucible 5 is formed so that 0.3HP <HC <0.5HP, where HP is the height of the carbon crucible 5 and HC is the height of the upper end of the curved portion 52. Further, the carbon crucible 5 is formed so that 0.5 DP <DC <0.7 DP, where DP is the diameter of the carbon crucible 5 and DC is the diameter of the bottom 53.
The straight body portion 51, the curved portion 52, and the bottom portion 53 are formed so that their inner surfaces are smoothly connected to each other to form a bottomed tubular shape.

The carbon crucible 5 of the present embodiment has a circular opening 5H formed in the center of the bottom 53. By combining the opening 5H with the support shaft 6 (see FIG. 1), the carbon crucible 5 can be easily installed.

The curved portion 52 of the carbon crucible 5 has a plurality of through holes 12 (in the carbon crucible 5 of the present embodiment, six through holes 12 each of three at the top and bottom). These through holes 12 penetrate from the outer surface to the inner surface of the curved portion 52. The cross-sectional shape of the through hole 12 is circular.
The through hole 12 has three first through holes 12A formed above the curved portion 52 and three second through holes 12B formed below the curved portion 52.
The three first through holes 12A are formed at equal intervals in the circumferential direction. Similarly, the three second through holes 12B are formed at equal intervals in the circumferential direction.
The number of through holes 12 is not limited to this, and at least one through hole 12 may be formed. Further, the cross-sectional shape of the through hole 12 is not limited to a circular shape, and may be a rectangular shape.

The carbon crucible 5 has two upper and lower annular grooves 13 extending in the circumferential direction on the inner surface of the curved portion 52. The annular groove 13 has a notched groove shape formed so as to be recessed in the inner surface of the curved portion 52 of the carbon crucible 5. The annular groove 13 is continuously formed over the entire circumference of the curved portion 52.
The annular groove 13 has a first annular groove 13A extending in the circumferential direction so as to pass through the first through hole 12A, and a second annular groove 13B extending in the circumferential direction so as to pass through the second through hole 12B. In other words, the end of the through hole 12 on the inner surface side is located in the annular groove 13.
The annular groove 13 does not have to be continuously formed over the entire circumference, and may be formed in a part in the circumferential direction.

The carbon crucible 5 has a vertical groove 14 that extends in the vertical direction and connects the first annular groove 13A and the second annular groove 13B. The vertical groove 14 is formed on the inner surface of the curved portion 52. The carbon crucible 5 of the present embodiment has a plurality of vertical grooves 14 (12 in the present embodiment), and the plurality of vertical grooves 14 are formed at equal intervals in the circumferential direction.

As shown in FIG. 3, each through hole 12 is not formed linearly and has a bent portion 15. The through hole 12 of the present embodiment is composed of a horizontal portion 123 extending in the horizontal direction (direction orthogonal to the central axis A) from the outer opening 121 and an inclined portion 124 extending from the inner opening 122. The inclined portion 124 is formed so that the angle θ formed by the central axis A and the central axis AT of the inclined portion 124 is 20 ° to 30 ° and becomes lower toward the outer side in the radial direction.
The through hole 12 is formed so that the inclined portion 124 and the horizontal portion 123 intersect at the bent portion 15 in the vicinity of the middle in the thickness direction of the curved portion 52.
As a result, each through hole 12 has a shape in which the inside of the carbon crucible 5 cannot be visually recognized from the outside through the through hole 12. That is, when light is irradiated from the outside of the carbon crucible 5, the light is formed so as not to directly reach the inside of the carbon crucible 5.

It is preferable that the inner diameter of the through hole 12, the width of the annular groove 13, and the width of the vertical groove 14 are the same. The width of the groove is preferably set to, for example, 1 mm to 20 mm, and particularly preferably 2 mm to 10 mm. Further, the groove depth is preferably set to 20% to 40% of the plate thickness of the carbon crucible 5.
If the width of the groove is too narrow, the gas discharge effect due to the gas being guided through the groove cannot be obtained. If the width of the groove is too wide, the quartz crucible 3A will enter the groove due to the softening deformation of the quartz crucible 3A, and the cooling of each crucible due to the difference in thermal expansion between the carbon crucible 5 and the quartz crucible 3A. Sometimes the carbon crucible 5 may crack.

FIG. 4 is a plan view of the carbon crucible 5 as viewed from above. However, in FIG. 4, the through hole 12, the annular groove 13, and the vertical groove 14 are not shown.
As shown in FIG. 4, the carbon crucible 5 of the present embodiment is divided into a plurality of carbon crucible pieces 5P. Each carbon crucible piece 5P has a shape in which the carbon crucible 5 is divided by a dividing surface P including the central axis A. The carbon crucible 5 of the present embodiment is evenly divided into three in the circumferential direction.

FIG. 5 is a side view of the carbon crucible piece 5P. As shown in FIG. 5, the through hole 12 is formed by a through hole groove 12G having a semicircular cross section formed on the dividing surface P of the carbon crucible piece 5P. The through hole 12 is for a through hole groove 12G formed on the dividing surface P of one carbon crucible piece 5P adjacent in the circumferential direction and for a through hole formed on the dividing surface P of the other carbon crucible piece 5P. The groove 12G is formed so as to form a through hole 12 having a circular cross section.
The through hole 12 of the present embodiment is formed by a pair of through hole grooves 12G, but is not limited to this, and is formed on the dividing surface P of one carbon crucible piece 5P adjacent in the circumferential direction. The through hole 12 may be formed only by the through hole groove 12G. Further, the cross-sectional shape of the through hole 12 is not limited to a circular shape, but may be a rectangular shape or another shape.

Next, the operation of the pulling device 1 having the carbon crucible 5 of the present embodiment will be described.
During the production of the silicon single crystal S by the Czochralski method, while the silicon single crystal S is being pulled up, the heat of the heater 4 causes silicon dioxide (SiO ₂ ) constituting the quartz rutsubo 3A and carbon (SiO 2) constituting the carbon rutsubo 5 (). By reacting with C), carbon monoxide gas (CO gas) is generated. The inventors presume that among the straight body portion 51, the curved portion 52, and the bottom portion 53, the curved portion 52 is the portion where the temperature is highest and the deterioration is large, so that CO gas is generated most in this portion. , A through hole 12 was formed in the curved portion 52.

As shown in FIG. 6, the CO gas G2 generated at the curved portion 52 is discharged to the outside of the crucible 3 from the through hole 12. On the outside of the rutsubo 3 (outward in the radial direction of the straight body portion 51), the inert gas G1 introduced from the gas introduction port 10 flows downward, and the CO gas G2 discharged from the through hole 12 is discharged. The gas is discharged from the exhaust port 11 together with the inert gas G1 without flowing toward the silicon melt M.
However, if the through hole has a linear shape, the radiant heat from the heater 4 directly hits the quartz crucible 3A, so that a local temperature rise occurs in the quartz crucible 3A, resulting in softening deformation of the quartz crucible 3A and silicon melting. There is a risk that the liquid will vary. Therefore, the bent portion 15 is formed in the through hole 12 of the present embodiment.

According to the above embodiment, since the through hole 12 is formed in the curved portion 52, the CO gas taken into the silicon melt M is reduced, and by extension, the carbon taken into the silicon single crystal S being pulled up is reduced. can do. In other words, by using the pulling device 1 of the present embodiment, the discharge path of CO gas, which was conventionally between the quartz crucible 3A and the carbon crucible 5, and was discharged from the upper edge of the crucible 3, is changed. can do.

Further, since the through hole 12 is formed, the radiant heat from the heater 4 acts on the contact surface between the quartz crucible 3A and the carbon crucible 5 through the through hole 12, and the amount of CO gas emitted increases. At the same time, it is considered that the temperature of the portion corresponding to the through hole 12 rises and an unintended heat generation distribution occurs in the silicon melt M. However, in the carbon crucible 5 of the present embodiment, since the through hole 12 has the bent portion 15, the radiant heat from the heater 4 does not directly hit the quartz crucible 3A. As a result, local heating from the heater 4 to the quartz crucible 3A can be suppressed, softening and deformation of the quartz crucible 3A, and temperature variation of the silicon melt M can be suppressed.

Further, since the carbon crucible 5 has a three-divided structure and the through hole 12 is formed on the divided surface P of the carbon crucible piece 5P, even the through hole 12 having the bent portion 15 can be easily formed. be able to.

Further, by forming an annular groove 13 passing through the through hole 12 on the inner surface of the carbon crucible 5 and connecting the annular grooves 13 with each other by a vertical groove 14, the CO gas emission effect can be enhanced. it can.
Further, by providing a plurality of through holes 12 in the circumferential direction, the CO gas discharge effect can be enhanced.

In the above embodiment, the carbon crucible 5 has a three-divided structure, but the number of divisions is not limited to this. Further, the crucible 3 may be integrally molded without being divided. In this case, the through hole 12 can be formed from the inner peripheral side and the outer peripheral side of the carbon crucible 5 by using a tool such as an end mill so as to have the shape shown in FIG.
Further, the carbon crucible 5 is not limited to the graphite crucible as long as it is formed of a material containing carbon, and may be formed of, for example, a carbon composite.

Further, the shape of the through hole 12 is not limited to this as long as it has a bent portion. For example, the through hole 12 may have a meandering shape as shown in FIG.
Further, the through holes 12 and the vertical grooves 14 do not have to be evenly spaced in the circumferential direction.

Next, an experiment conducted to confirm the CO gas emission effect of the carbon crucible 5 of the present embodiment will be described. In the experiment, a quartz crucible 3A and a carbon crucible were installed in the furnace and air-baked (heating the crucible 3 without accommodating the silicon melt in the crucible 3) was performed to determine the CO concentration of the gas exhausted from the furnace. It was done by analysis.
Piping for gas analysis was arranged near the upper end of the crucible 3 (inside the furnace) and at the exhaust port 11. Three pipes for gas analysis were installed near the upper end of the crucible 3.

In FIG. 8, the horizontal axis represents the installation location of the gas analysis piping (three locations in the furnace and the exhaust port), the vertical axis represents the CO gas concentration [ppm], and the through hole 12, the annular groove 13, and the vertical groove 14 are shown. It is a graph which shows the comparison between the ordinary carbon-made rubbing pot (normal product) in which is not formed, and the carbon-made rubbing pot 5 of this embodiment.
As shown in FIG. 8, it was possible to reduce the CO gas particularly in the vicinity of the upper end of the crucible 3 in the furnace, and it was possible to reduce the CO concentration by 20% on average.

In the above embodiment, the silicon single crystal is produced by using the pulling device 1, but the present invention is not limited to this. That is, the carbon crucible of the present invention can be widely used as a crucible that supports a quartz crucible used when producing a single crystal by the Czochralski method.

1 ... Pulling device, 2 ... Chamber, crucible ... 3, 3A ... Quartz crucible, 5 ... Carbon crucible, 5P ... Carbon crucible piece, 12 ... Through hole, 12A ... First through hole, 12B ... Second through hole, 13 ... annular groove, 14 ... vertical groove, 15 ... bent part, 51 ... straight body part, 52 ... curved part, 53 ... bottom, M ... silicon melt, P ... divided surface, S ... silicon single crystal.

Claims (6)

A carbon crucible that supports a quartz crucible that houses a raw material melt when a single crystal is produced by the Czochralski method, and consists of a straight body, a curved part, and a bottom.
The curved portion is a carbon crucible characterized by having a through hole penetrating from the outer surface to the inner surface of the curved portion. The carbon crucible according to claim 1, wherein the through hole has a bent portion. It has an annular groove extending in the circumferential direction on the inner surface of the curved portion.
The carbon crucible according to claim 1 or 2, wherein the end of the through hole on the inner surface side is located in the annular groove. The annular groove has a first annular groove formed above the curved portion and a second annular groove formed below the curved portion.
The through hole includes a first through hole whose inner surface side end is located in the first annular groove and a second through hole whose inner surface side end is located in the second annular groove. Have
The third aspect of claim 3, wherein the carbon crucible is formed on the inner surface of the curved portion and has a vertical groove extending in the vertical direction to connect the first annular groove and the second annular groove. Carbon crucible. The carbon crucible according to any one of claims 1 to 4, wherein a plurality of through holes are provided in the circumferential direction. The carbon crucible is divided into a plurality of carbon crucible pieces at a dividing surface including the central axis.
The carbon crucible according to any one of claims 1 to 4, wherein the through hole is formed on a divided surface of the carbon crucible pieces adjacent to each other in the circumferential direction.

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