An apparatus for growing a silicon crystal ingot by the Czochralski method

Abstract

The present application relates to a device for growing silicon ingot by Czochralski method, comprising a crucible for containing a silicon ingot raw material melt; a heating mechanism for heating the crucible; a silicon ingot raw material melt supplementing mechanism for supplementing the silicon ingot raw material melt into the crucible; a rotating magnetic field at the periphery of the crucible; a seed rod above the crucible, with a containing area for loading a seed at the lower end of the seed rod; a rotating and lifting mechanism for the seed rod; a mechanism for providing a protective gas to provide a protective atmosphere for the ingot growth space formed by the crucible and the seed rod; wherein the vertical central axis of the seed rod does not coincide with the vertical central axis of the crucible. The device of the present application can produce ingots with larger size and higher quality wafers, for example, the doping concentration, mechanical strength, dislocation density, electrical conductivity and resistivity of the wafers are more uniform, which is of great significance for the production of large-scale integrated circuits.

Description

Technical Field

[0001] This invention relates to an apparatus for growing large-size silicon ingots using the Czochralski method. Background Technology

[0002] The production of semiconductor silicon wafers includes steps such as silicon ingot growth, silicon ingot cutting into rough wafers, rough wafer grinding, edge grinding, rough polishing, fine polishing, cleaning, drying, and final packaging. One method for silicon ingot growth is the Czochralski process. Its working principle is as follows: Figure 1 As shown, under a suitable temperature field, silicon ingot raw material melts in a crucible. A rotating magnetic field around the crucible prevents the silicon melt from tumbling. The lower end of the seed crystal, mounted on a seed crystal rod, is lowered into the molten raw material. The seed crystal rod, driven by a rotating motor and lifting mechanism, is slowly pulled upwards while rotating. Through several process stages including necking, shoulder expansion, shoulder rotation, equal diameter formation, tailing, and pull-out, a single-crystal ingot with acceptable geometry and internal quality is grown. During the ingot growth process, a silicon ingot raw material replenishment container continuously adds molten silicon ingot raw material to the crucible to ensure the growth of the ingot to the required length. This method allows for convenient observation of the ingot growth process. The ingot grows on the free surface of the melt without contacting the crucible, significantly reducing stress on the ingot and preventing parasitic nucleation on the crucible wall. Furthermore, it allows for convenient use of oriented seed crystals and the "necking" process to obtain a complete seed crystal and an ingot with the desired orientation. The entire system is protected by a protective atmosphere. The biggest advantage of the Czochralski method is that it can grow high-quality silicon ingots at a relatively fast rate.

[0003] The industry continues to make improvements to the Czochralski method for growing silicon ingots in order to enhance product quality. Summary of the Invention

[0004] The inventors discovered that when growing silicon ingots using the Czochralski method, the longitudinal axis of the seed crystal rod generally coincides with the central axis of the crucible. This results in the part of the grown silicon ingot near the central axis actually originating from the raw material melt located in the center of the crucible. Because this part of the raw material melt is near the center of the crucible, it is actually least affected by the external magnetic field. As a result, the central and edge parts of the radial section (for the ingot during growth, the corresponding direction is the horizontal plane) of the grown silicon ingot do not always achieve acceptable consistency in composition and electrical properties with the user, which affects the overall stability of the product.

[0005] Based on the above problems, the inventors propose a new apparatus for growing silicon ingots using the Czochralski method, including...

[0006] - A crucible for containing the molten silicon crystal rod raw material;

[0007] - Heating mechanism for heating the crucible;

[0008] - A silicon ingot raw material melt replenishment mechanism replenishes the silicon ingot raw material melt into the crucible;

[0009] - A rotating magnetic field surrounding the crucible;

[0010] - Seed crystal rod, located above the crucible, with a receiving area at its lower end for filling the seed crystal;

[0011] - Mechanism for rotating and lifting seed crystal rods;

[0012] - A mechanism that provides a protective gas to the growth space of the crystal rod formed by the crucible and the seed rod;

[0013] The vertical central axis of the seed crystal rod does not coincide with the vertical central axis of the crucible.

[0014] In the apparatus of this invention, the mechanism for controlling the seed crystal rod ensures that its vertical central axis does not coincide with the vertical central axis of the crucible. Thus, during actual use, the molten raw material at the center of the crucible is driven by the lower end of the growing silicon ingot, resulting in appropriate exchange and mixing with the molten raw material at the non-central part of the crucible. This makes it easier for the silicon ingot portion corresponding to this molten raw material to achieve consistency in composition and electrical properties with other parts of the silicon ingot, thereby improving product consistency and uniformity. Especially when growing large-size silicon ingots, as the crucible increases in size, the heating of the molten silicon ingot within the crucible becomes uneven, and the apparatus of this invention can compensate for this. Compared to the prior art method where the vertical central axis of the seed crystal rod coincides with the central axis of the crucible, the apparatus of this invention produces larger and higher-quality wafers. For example, the wafers exhibit more uniform doping concentration, mechanical strength, dislocation density, conductivity, and resistivity, which is of great significance for the fabrication of large-scale integrated circuits. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a conventional Czochralski silicon ingot growth apparatus.

[0016] Figure 2 This is a schematic diagram of the silicon ingot growth apparatus of the present invention. Detailed Implementation

[0017] The apparatus for growing silicon ingots by the Czochralski method of the present invention includes

[0018] - A crucible for containing the molten silicon crystal rod raw material;

[0019] - Heating mechanism for heating the crucible;

[0020] - A silicon ingot raw material melt replenishment mechanism replenishes the silicon ingot raw material melt into the crucible;

[0021] - A rotating magnetic field surrounding the crucible;

[0022] - Seed crystal rod, located above the crucible, with a receiving area at its lower end for filling the seed crystal;

[0023] - Mechanism for rotating and lifting seed crystal rods;

[0024] - A mechanism that provides a protective gas to the growth space of the crystal rod formed by the crucible and the seed rod;

[0025] The vertical central axis of the seed crystal rod does not coincide with the vertical central axis of the crucible.

[0026] The apparatus for growing silicon ingots using the Czochralski method of the present invention is not necessarily a completely closed system. In fact, during the actual use of the apparatus of the present invention, the apparatus includes a mechanism for providing a protective gas to provide a protective atmosphere, such as a high-purity nitrogen or argon protective atmosphere. Therefore, although the present invention uses the name "apparatus," it does not indicate that the name has a specific limitation on the overall structure. As long as the components or mechanisms included in the broadest definition of the apparatus of the present invention, and other corresponding conditions defined therein, constitute the apparatus of the present invention.

[0027] In the apparatus of the present invention, preferably, the distance between the vertical central axis of the crucible and the vertical central axis of the seed crystal rod on the horizontal plane is greater than 0.5 cm, more preferably greater than 0.7 cm, and even more preferably greater than 1 cm. Considering the crucible size and corresponding cost, and especially considering the diameter of the silicon ingot being grown, the distance between the vertical central axis of the crucible and the vertical central axis of the seed crystal rod on the horizontal plane is generally no greater than 40 cm, preferably no greater than 35 cm, and even more preferably no greater than 30 cm. Therefore, preferably, the distance between the vertical central axis of the crucible and the vertical central axis of the seed crystal rod on the horizontal plane is 0.5-40 cm, preferably 1-35 cm, and even more preferably 1.5-30 cm. However, it should be understood that this specific value can be changed according to actual needs. For example, the distance between the vertical central axis of the crucible and the vertical central axis of the seed crystal rod on the horizontal plane may be the same as, less than, or greater than the radius of the silicon ingot being grown.

[0028] In a preferred embodiment of the device of the present invention, the rotation and lifting mechanism for the seed crystal rod also has the function of adjusting the position of the seed crystal rod in the horizontal direction. In this way, the distance between the vertical central axis of the crucible and the vertical central axis of the seed crystal rod on the horizontal plane can be flexibly adjusted by means of this mechanism.

[0029] In practical applications, the diameter of the grown silicon ingot (for silicon ingots during growth, measured along the horizontal plane perpendicular to the vertical axis) can be 4, 6, 8, 12, or even 20 inches or more. The ingot growth rate is 0.2-0.7 mm / min, for example, 0.5 mm / min, measured by the axial height (or length) of the ingot.

[0030] In the apparatus of the present invention, the crucible body is usually made of graphite and serves as a support, while the inner surface of the crucible in contact with the molten silicon crystal rod is a quartz inner liner; the surface of the quartz inner liner is generally subjected to a strengthening treatment to form a high-strength, dense surface layer.

[0031] In the apparatus of this invention, the silicon ingot raw material melt replenishment mechanism is typically made of graphite and serves a supporting function. The inner surface of the silicon ingot raw material melt is in contact with a quartz inner liner; the surface of the quartz inner liner is generally strengthened to form a high-strength, dense surface layer. The silicon ingot raw material melt replenishment mechanism has its own heating device and replenishes the silicon ingot raw material melt into the crucible through a quartz-lined pipe.

[0032] As will be understood by those skilled in the art, in order to use the device of the present invention, necessary pipes and other components need to be adopted according to the actual situation. Although not listed one by one in this specification, these pipes and components can be determined and adopted by those skilled in the art.

[0033] In the apparatus of the present invention, the heating mechanism is an electric heating mechanism, such as an electric heating wire heating mechanism or an electromagnetic induction heating mechanism, preferably an electromagnetic induction heating mechanism, which surrounds the crucible to ensure uniform heating.

[0034] The crucible is surrounded by insulating material, made of zirconium oxide, aluminum oxide, etc., which is distributed around the periphery of the crucible, preferably evenly distributed around the periphery of the crucible.

[0035] The rotating magnetic field surrounding the crucible is a high-intensity magnetic field, such as a superconducting magnetic field. The magnetic field strength is, for example, 1500-4500 Gauss (0.15-0.45 Tesla), preferably 2500-3500 Gauss (0.15-0.45 Tesla), and particularly about 3000 Gauss (0.3 Tesla). The rotation of the magnetic field around the molten silicon ingot within the crucible is achieved by controlling the current in the coil that generates the magnetic field. With the help of the magnetic field, the bubbles in the molten silicon ingot, particularly the oxygen content, can be controlled.

[0036] In actual use, the rotation direction of the rotating magnetic field around the crucible is opposite to the rotation direction of the seed crystal rod.

[0037] The rotating magnetic field surrounding the crucible is preferably located inside the insulation material of the crucible (i.e., closer to the outer periphery of the crucible than the insulation material itself), but outside the heating mechanism. Thus, the preferred arrangement is, from the center of the crucible outwards, the following sequence: crucible, heating mechanism, rotating magnetic field, insulation material. This optimizes the effectiveness of each of the heating, magnetic field, and insulation functions.

[0038] In the device of the present invention, the seed crystal rod is made of a material known for use in similar systems, such as metal, particularly stainless steel, and the area containing the seed crystal can be made of quartz.

[0039] Preferably, the apparatus of the present invention further includes a mechanism for lifting the crucible. Thus, at the end of the silicon ingot growth process, as the amount of molten silicon decreases, the crucible is raised using this lifting mechanism. This maintains the distance between the cross-section of the single crystal and the original molten material, and the temperature gradient remains unchanged, thereby preventing any impact on the normal growth of the crystal. Near the end of the growth process, the molten silicon ingot replenishment process ends, the feeding stops, and then the crucible is raised at a rate of 0.05-0.2 mm / min, for example, 0.1 mm / min.

[0040] In the apparatus of the present invention, the mechanism for providing the protective gas can be a known mechanism for providing a protective atmosphere for similar systems. This mechanism can be connected to a protective gas source, such as high-purity nitrogen or argon, thereby providing a protective atmosphere to the crucible and seed rod, particularly to the ingot growth space formed by the crucible and seed rod, ensuring that the areas in contact with the ingot and the molten ingot raw material during silicon ingot growth are protected by the protective atmosphere. Alternatively, the protective atmosphere can be extended to the area surrounding the entire periphery of the apparatus of the present invention.

[0041] The apparatus of the present invention is also applicable to various crystal rods that can be grown by the Czochralski method, such as Ge crystal rods.

[0042] The obtained silicon crystal rods are then processed and treated in a conventional manner, including cutting, grinding, edge grinding, rough polishing, fine polishing, washing, drying, and packaging.

[0043] The present invention will be described by way of example below with reference to the accompanying drawings, which are not necessarily drawn to scale.

[0044] Figure 1This is a schematic diagram of an apparatus for growing silicon ingots using the existing Czochralski method, shown as a cross-sectional view along the vertical direction (based on the actual positioning during use, the same below). The apparatus 1 for growing silicon ingots includes a crucible 10 containing molten silicon ingot material 2; a heating element 7, typically an electric heating wire or an electromagnetic induction heating element, is located around the crucible; a rotating magnetic field (not shown) surrounds the heating element 7 to prevent tumbling within the molten silicon. The lower end of the seed crystal rod 5 has a portion 4 for receiving the seed crystal. Induced by the seed crystal contained in portion 4, the seed crystal rod 5 rotates (for example, from right to left, but it can also rotate in the opposite direction) and is lifted, growing the silicon ingot 3. In addition, a silicon ingot material molten material replenishment mechanism (not shown) is provided to replenish the molten silicon ingot material into the crucible. The longitudinal axis A-A' is the central axis of the seed crystal rod 5, the silicon ingot 3, and the crucible 10, i.e., the central axes of the seed crystal rod 5, the silicon ingot 3, and the crucible 10 coincide. The crucible 10 is made of graphite as its main body and lined with quartz. The seed rod 5 is made of metal or other materials commonly used in the industry, and the seed receiving area 4 at its end is made of quartz. The entire apparatus also includes a mechanism (not shown) for providing a protective gas to the ingot growth space formed by the crucible 10 and the seed rod 5.

[0045] Figure 2 This is a schematic diagram of the apparatus for growing silicon ingots using the Czochralski method according to the present invention, and also a cross-sectional view along the vertical direction (based on the actual positioning in use, the same below). The apparatus 11 for growing silicon ingots according to the present invention includes a crucible 20 for containing raw material melt 12; a heating element 17 is located around the crucible, typically an electric heating wire or an electromagnetic induction heating element; a rotating magnetic field (not shown) is located around the heating element 17 to prevent tumbling within the silicon melt. The lower end of the seed crystal rod 15 has a portion 14 for containing the seed crystal. Induced by the seed crystal contained in portion 14, as the seed crystal rod 15 rotates (for example, from right to left, but it can also rotate in the opposite direction) and is lifted, a silicon ingot 13 is grown. In addition, a silicon ingot raw material melt replenishment mechanism (not shown) is provided to replenish the silicon ingot raw material melt into the crucible. The longitudinal axis B-B' is the central axis of the crucible 20; the longitudinal axis C-C' is the central axis of the seed crystal rod 15 and the silicon ingot 13. The longitudinal axes B-B' and C-C' maintain a distance, for example, in terms of horizontal distance (as measured in this invention), this distance is 0.5-40 cm, preferably 1-35 cm, and more preferably 1.5-30 cm. The crucible 20 is mainly made of graphite with a quartz liner, the seed crystal rod 15 is made of stainless steel, and the area 14 containing the seed crystal is made of quartz. The remaining components are made of metal or materials commonly used in the industry. The entire apparatus also includes a mechanism (not shown) for providing a protective gas to the crystal growth space formed by the crucible 20 and the seed crystal rod 15.

[0046] Figure 2In the example apparatus, a crucible lifting mechanism (not shown) can be added. In this way, at the end of the silicon ingot growth, as the silicon raw material melt decreases, the crucible can be raised by the crucible lifting mechanism. This can keep the distance between the cross section of the single crystal and the original melt body unchanged, and the temperature gradient will not change, thus not affecting the normal growth of the crystal.

[0047] Although the present invention has been described with reference to certain embodiments, those skilled in the art will recognize that modifications or equivalent substitutions may be made to the embodiments without departing from the spirit and scope of the present invention, the scope of which is defined by the appended claims.

Claims

1. An apparatus for growing silicon ingots by the Czochralski method, comprising: - A crucible for containing molten silicon ingot raw material; - Heating mechanism for heating the crucible; - A silicon ingot raw material melt replenishment mechanism that replenishes the silicon ingot raw material melt into the crucible; - A rotating magnetic field surrounding the crucible; - Seed rod, located above the crucible, with a receiving area at its lower end for filling the seed crystal; - Mechanism for rotating and lifting seed crystal rods; - A mechanism that provides a protective gas to the growth space of the crystal rod formed by the crucible and the seed rod; in, The vertical central axis of the seed crystal rod does not coincide with the vertical central axis of the crucible.

2. The apparatus for growing silicon ingots by the Czochralski method according to claim 1, characterized in that, The horizontal distance between the vertical central axis of the crucible and the vertical central axis of the seed crystal rod is between 0.5 cm and 40 cm.

3. The apparatus for growing silicon ingots by the Czochralski method according to claim 1, characterized in that, The horizontal distance between the vertical central axis of the crucible and the vertical central axis of the seed crystal rod is between 1 cm and 35 cm.

4. The apparatus for growing silicon ingots by the Czochralski method according to claim 1, characterized in that, The horizontal distance between the vertical central axis of the crucible and the vertical central axis of the seed crystal rod is between 1.5 cm and 30 cm.

5. The apparatus for growing silicon ingots by the Czochralski method according to any one of claims 1-4, characterized in that, The rotating and lifting mechanism for the seed crystal rod also has the function of adjusting the horizontal position of the seed crystal rod.

6. The apparatus for growing silicon ingots by the Czochralski method according to any one of claims 1-4, characterized in that, The crucible body is made of graphite, and the inner surface of the crucible in contact with the molten silicon crystal rod is made of quartz.

7. The apparatus for growing silicon ingots by the Czochralski method according to any one of claims 1-4, characterized in that, The heating mechanism is an electric heating wire or an electromagnetic induction heating mechanism, which surrounds the crucible to ensure uniform heating.

8. The apparatus for growing silicon ingots by the Czochralski method according to any one of claims 1-4, characterized in that, The crucible is surrounded by insulating material, which is distributed around the perimeter of the crucible.

9. The apparatus for growing silicon ingots by the Czochralski method according to any one of claims 1-4, characterized in that, The rotating magnetic field surrounding the crucible is a superconducting magnetic field with a strength of 1500-4500 Gauss (0.15-0.45 Tesla).

10. The apparatus for growing silicon ingots by the Czochralski method according to any one of claims 1-4, characterized in that, The rotating magnetic field surrounding the crucible is a superconducting magnetic field with a strength of 2500-3500 Gauss (0.15-0.45 Tesla).

11. The apparatus for growing silicon ingots by the Czochralski method according to any one of claims 1-4, characterized in that, The rotating magnetic field surrounding the crucible is a superconducting magnetic field with a strength of 3000 Gauss (0.3 Tesla).

12. The apparatus for growing silicon ingots by the Czochralski method according to any one of claims 1-4, characterized in that, The arrangement of the heating mechanism, rotating magnetic field, and heat insulation material around the crucible, from the center of the crucible outwards, is as follows: crucible, heating mechanism, rotating magnetic field, and heat insulation material.

13. The apparatus for growing silicon ingots by the Czochralski method according to any one of claims 1-4, characterized in that, It also includes a mechanism for lifting the crucible.

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