Apparatus and method for producing single crystal rods from silicon in a zone pulling facility

Abstract

A method and device for pulling single crystal rods from silicon in a zone melt pulling facility comprising: (1) providing a silicon feed rod including azimuth grooves at one end; (2) attaching a lower portion with three gripping arms, one gripping arm configured to fit into the azimuth groove of the feed rod at one end and to be rotatably attached to the lower portion at the other end, the method and device further comprising: (3) suspending the lower portion together with the feed rod on an upper portion including a connecting element, the connecting element being connected to a pull shaft of a zone pull equipment such that the upper portion and the lower portion are radially connected to each other in a mating state, the upper portion including a radial alignment element, and three length-adjustable spacer elements are attached to the upper portion such that each of the spacer elements can exert a force on the gripping arm, the method and device further comprising: (4) moving the radial alignment element so that the axis of rotation of the feed rod at the end where the groove is located is aligned with the axis of rotation of the pull shaft; (5) setting the adjustable-length spacer element so that the axis of rotation of the feed rod at the end opposite the groove coincides with the axis of rotation of the pull shaft; (6) pulling the conical portion of the single crystal rod; (7) pulling up the cylindrical portion of the single crystal rod.

Description

[Technical Field]

[0001] The subject of the present invention is an apparatus and method for producing single crystal rods from silicon in a zone pulling facility using an orientation grooved feed rod. [Background technology]

[0002] On an industrial scale, zone pulling is used especially for producing single crystals from silicon, which involves obtaining single crystals from a polycrystalline feed rod, but optionally also using a feed rod of monocrystalline silicon.

[0003] For this purpose, a feed rod is first melted at one end using a high-frequency coil (inductor), and a single-crystal seed is attached to the resulting molten droplet. The gradually melted material from the feed rod serves as the source of the single crystal that subsequently grows on the seed. To bypass dislocations from the crystal lattice, a thin, longitudinal section called the neck is first crystallized. The growing single crystal is then grown until its diameter reaches the desired diameter in a longitudinal section called the initial cone (seed cone). A longitudinal section is then created in which the single crystal has the desired diameter. To complete the process, a longitudinal section called the terminal cone is created. Optionally, the process can be completed without a terminal cone; however, in that case, the end of the longitudinal section with the desired diameter contains dislocations and cannot be used for the intended subsequent processing.

[0004] In this case, the feed rod is attached at one end to a rotatable shaft (pulling shaft) so that it will not slip even if the direction of rotation suddenly changes. It is also necessary that the middle of the other end of the feed rod always lies on the rotation axis of the pulling shaft during crystal pulling. If the center of the other end moves away from the rotation axis of the pulling shaft, this can significantly affect the melting by the pulling coil, which can have a negative impact on the entire pulling process.

[0005] This effect can be observed very easily when the frequency of the high frequency coil (pulling coil) is measured as a function of time, as the frequency is dependent on the load and therefore a function of the distance of the feed rod from the coil.

[0006] Currently available commercially are single crystal silicon rods with nominal diameters of up to 200 mm produced by the zone pulling process, where the target diameter of the single crystal rod, in addition to the length of the rod to be pulled, naturally determines the weight of the feed rod required for this.

[0007] Therefore, the development of longer single crystal rods to increase yields and the development of larger diameter single crystal rods necessarily requires heavier feed rods to be fitted into the pulling equipment, and each of these feed rods must be held accurately and securely on the pulling shaft.

[0008] Japanese Patent Application No. 2019-167254A2, for example, discloses a device for holding a feed rod in a zone melting facility, which includes a connecting element between a lifting shaft and the feed rod, multiple locking portions, a horizontal positioning portion for setting the horizontal position of the feed rod, and a shielding portion for shielding the feed rod from radiant heat. Summary of the Invention [Problem to be solved by the invention]

[0009] The devices disclosed in the cited prior art are, in principle, suitable for positioning feed rods in zone-pulling fixtures. However, they have proven too unstable to fit, resulting in too many inaccuracies, especially when using very heavy and long feed rods. Furthermore, the devices are not easy to install, and therefore require the heavy feed rods to be inserted into the pulling fixture and fixed there in a complex and usually risky manner. A second drawback is that the angle of the feed rod in the pulling fixture cannot be set relative to its ideal line, or this can be very difficult to optimize, resulting in a low yield of pulled rods.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved version of the prior art device which does not suffer from the above-mentioned drawbacks.

[0011] It is also an object of the present invention to provide a method for fitting a feed rod that allows even very heavy feed rods to be fitted reliably and accurately into zone lifting equipment. [Means for solving the problem]

[0012] This object is achieved by the method and apparatus set out in the appended claims. The features specified with respect to the above-described embodiments of the method according to the invention may be correspondingly applied to the product according to the invention. Conversely, the features specified with respect to the above-described embodiments of the product according to the invention may be correspondingly applied to the method according to the invention. These and other features of the embodiments according to the invention are explained in the accompanying drawings and in the accompanying claims. The individual features may be realized separately or in combination in embodiments of the invention. Furthermore, these features may describe advantageous embodiments that are independently protectable. [Brief explanation of the drawings]

[0013] [Figure 1]FIG. 1 shows a particular embodiment according to the invention of an arrangement for holding a feed rod (101) in a crystal pulling installation for zone pulling. [Figure 2] 1 shows the upper part of the arrangement according to the invention of the device; FIG. [Figure 3] 1 shows the lower part of an arrangement according to the invention of a device; [Figure 4] FIG. 4 shows an example of how the lower part (401) can be suspended from the upper part (402). [Figure 5] 1 shows in detail a particular embodiment according to the invention of an element for radial positioning (linear guide) of a device in a pulling installation; DETAILED DESCRIPTION OF THE INVENTION

[0014] DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS IN ACCORDANCE WITH THE INVENTION 1 shows a particular embodiment of an arrangement according to the invention for holding a feed rod (101) in a crystal pulling installation for zone pulling. A connecting element (108) located on top in the form of an adapter attached to the pulling shaft holds a radial positioning element (107) of the device. The connecting element (108) is preferably designed so that it can be screwed onto the pulling shaft by means of a screw thread and at the same time fixed by a bolt, so that a sudden change in the direction of rotation of the entire arrangement does not allow the thread itself to loosen.

[0015] Next, the radial alignment elements (107) of the arrangement are attached, which may for example comprise linear guides that allow the radial alignment of the arrangement to be ensured.

[0016] Three grippers (103) hold the azimuth grooves (102) of the feed rod (101) by one end, said grooves being located near the ends of the feed rod.

[0017] In this case, a gripping arm or gripper (103) is attached to the lower part of the device by a bolt or splint (104) so ​​that it can rotate to grip the feed rod. By means of a screw (105) attached to the upper part so that it can exert a force on the gripper, the feed rod (101) can be fixed on the one hand and, on the other hand, aligned so that the distal end of the feed rod (101) is accurately centered.

[0018] Figure 2 shows the upper part of the arrangement according to the invention of the device. The upper part is screwed onto the lifting shaft by means of an adapter (206) and may be secured by a bolt. The bolting is appropriate as the rotation of the whole arrangement may change suddenly, which prevents the arrangement from loosening.

[0019] Next, the radial alignment element (205) of the arrangement is attached, which comprises, for example, a linear guide that ensures the radial alignment of the arrangement, and which can be operated by a screw (204).

[0020] The upper part also includes bearings (203) that serve to easily suspend the lower part. To be able to suspend the lower part, corresponding openings (202) are necessary in the upper part. The upper part also includes length-adjustable spacer elements (201) that are attached so that they can exert a force on the gripping arms that are fastened to the lower part. A simple concrete embodiment of the spacer element is a screw with a counter nut.

[0021] Figure 3 shows the lower part of the device in accordance with the present invention. Three gripping arms or grippers (301) are attached by bolts or rivets (302) so that they can be rotated to engage the grooves in the feed rod. In this case, the rotation of the gripping arms can be set and fixed by a screw mechanism.

[0022] The lower part is provided with a counter bearing (303) so that it can be easily suspended on the upper part. Preferably, the gripper or grasping arm (301) is monolithically manufactured from one piece.

[0023] Figure 4 shows by way of example how a lower part (401) can be suspended from an upper part (402). In this case, the upper part comprises a connecting element (403) connectable to a lifting shaft and a radial alignment element (404) with linear guides that allows the device to be radially aligned. The lower part, suspended from the upper part, comprises a movable gripping arm (405) attached by a rivet or splint secured by a snap ring.

[0024] Figure 5 shows in detail a specific embodiment of the radial positioning element (linear guide) of the device in the lifting installation according to the invention. One or more leaf springs (503) supporting the connecting element (502) rest on a base plate (501). By means of a screw (504), the connecting element (502) can be precisely adjusted horizontally so that the position of the rod suspended in the device satisfies the specified requirements. In this case, a screw (505) is used to counter the linear guide to fix the set position.

[0025] After analyzing the above problems, the inventors have realized that a preferable solution to the above problems is to design a device for holding a feed rod in at least two parts, one part (hereinafter referred to as the lower part) capable of being attached to the rod while outside the crystal pulling equipment, and a second part (hereinafter referred to as the upper part) of the device which is securely attached to the pulling shaft in the crystal pulling equipment.

[0026] A pulling shaft is the term applied to a device that essentially performs two tasks in a pulling installation: (1) it ensures that the feed rod fastened to it is held while possibly changing the speed and / or direction of rotation, and (2) it allows the feed rod to move axially at a predetermined (or possibly varying) speed.

[0027] In this case, the feed rod supplies the material that is subsequently used to produce the single crystal. To pull a single crystal from silicon, for example, a silicon polycrystalline feed rod is used. Of course, a single crystal pulled by, for example, the Czochralski pulling method can also be used as the feed rod. It is also possible to use other semiconductor materials for the feed rod.

[0028] It is essential for the feed rod to have a cylindrical shape and to have a groove near one of its sides (the upper side) that is dimensioned so that the feed rod can be held without slipping out. Figure 1 shows, by way of example in this respect, a feed rod (101) with a correspondingly formed groove (102).

[0029] The weight of the feed rod can vary depending on the desired diameter and length of the single crystal rod. Typical weights for single crystal rods of silicon in this case can be well over 100 kg, and in some cases even well over 200 kg.

[0030] Securing such a heavy feed rod in a lifting fixture by means available in the prior art is difficult, time-consuming, and risky, as the weight of the feed rod must be held precisely upright in the lifting fixture for as long as necessary until it is mounted and aligned on the lifting shaft.

[0031] Improper alignment can cause oscillations in the emitter frequency during crystal pulling, which often leads to rod failure (breakage or dislocations).

[0032] The inventors have recognized that it is preferable for the lower part of the device according to the invention to be first attached to the feed rod while the feed rod is outside the lifting installation. Particularly preferably, in this case the feed rod is horizontal.

[0033] The lower part of the device according to the invention (as shown for example in Figure 3) preferably comprises three gripping arms or grippers (301) which in this case are rotatably attached to the device by bolts or rivets (302).

[0034] When the lower part is attached to the feed rod, the grippers (301, 103) engage in the grooves (102) of the feed rod (101) and are fixed thereto.

[0035] There is an adjustment screw in the center of the lower part that can be used to open or close all of the gripping arms simultaneously, and by using this adjustment screw the lower part is fastened to the feed rod by the gripping arms.

[0036] The feed rod is preferably fitted into a lifting fixture with the lower part of the device mounted thereon.

[0037] In this case, the counter-bearing 303 of the lower part is first suspended on the bearing of the upper part 203. This bearing is preferably configured so that the lower part can be easily suspended, for which purpose a corresponding opening (202) is required in the upper part, which in particular allows access from the side.

[0038] As a result, the lower part is radially connected to the upper part in a form-fitting manner, and the bearing used has the effect that these upper and lower parts are additionally connected to each other in a self-centering, removable manner.

[0039] The upper part preferably includes elements that serve to radially align the feed rod and preferably includes a linear guide by means of which the feed rod can be set so that the axis of rotation of the lifting shaft coincides with the axis of rotation of the feed rod, in which case the linear guide is preferably arranged so that its path of movement is perpendicular to the axis of rotation of the lifting shaft.

[0040] During setup, preferably, a linear guide is first used to set the feed rod so that the axis of rotation of the groove located in the feed rod coincides with the axis of rotation of the pull shaft. The desired position of the linear guide is then preferably fixed by a counterscrew (505) located in the device. Successful measurement can be confirmed, for example, by rotating the pull shaft while the feed rod is fixed to the pull shaft and simultaneously checking concentricity.

[0041] The upper part likewise preferably includes length-adjustable spacer elements (105), such as screws, mounted so as to be able to exert a force on gripping arms (103) fastened to the lower part.

[0042] The effect of setting these length-adjustable spacer elements (201) is that the feed rod can be aligned along its axis. In this case, the feed rod is preferably set so that the rotation axis of the pulling shaft coincides with the rotation axis of the feed rod. In particular, it is ensured that the rotation axis of the feed rod at the end opposite the groove coincides with the rotation axis of the pulling shaft. This can be checked by checking the concentricity.

[0043] FIG. 1 shows two views of a feed rod (101) clamped in a device according to the invention.

[0044] Once the feed rod is inserted, the equipment can be closed and pulling of the crystal can begin by first raising the initial cone, which reaches the target diameter and then rides over the cylindrical portion. After the desired length of the single crystal rod is reached, the terminal cone is raised. After crystal pulling is complete, the single crystal rod can be removed from the equipment and a new feed rod can be prepared.

[0045] Ideally, during crystal pulling of the first crystal, the feed rod is already attached to the lower part as defined by the present invention, which further significantly reduces the setup time of the equipment. [Explanation of symbols]

[0046] sign 101: Feed rod. The feed rod may be made of polycrystalline or single crystalline semiconductor material.

[0047] 102: Azimuthal groove on one side of the feed rod (101). In the example shown, the groove is formed asymmetrically, i.e. the diameter of the feed rod is different on the left and right sides of the groove.

[0048] 103: A gripping arm formed so that one end fits into the azimuth groove (102) of the feed rod and the other end is rotatably fastened to the lower part. 104: Rivet to which one end of the gripping arm is attached so that the orientation of the gripping arm can be changed 105: Screw (length adjustable spacer element attached to the upper part so that it can exert force on the gripping arm) 106: Parts that are connected to each other in a self-aligning and detachable manner 107: Radial alignment element 108: Top-located connecting element 201: Screw (length adjustable spacer element attached to upper part so as to be able to exert force on gripping arm) 202: Opening to allow the lower part to be suspended 203: Bearing for lower part 204: Leveling screw for linear guide 205: Radial alignment element with linear guides 206: Top-located connecting element 301: Grasping arm 302: Rivet or splint secured by a snap ring 303: Counter bearing for suspending the lower part to the upper part 401: Lower part 402: Upper part 403: Top-located connecting element 404: Radial alignment element with linear guides 405: Movable gripping arm 406: Rivet or splint secured by a snap ring 501: Base plate 502: Connection element 503: Leaf spring 504: Leveling screw for linear guide 505: Screw for countering linear guide 506: Cover

Claims

1. 1. A device for holding a feed rod (101) in a pulling installation for zone melting, comprising: An upper portion (402), said upper portion (402) comprising: a connecting element (107) serving to fit onto a lifting shaft of the lifting installation, and an element (107) for radial positioning of the upper part (402) of the lifting installation, said device further comprising: A lower portion (401) comprising: Three gripping arms (103) are provided, one end of each of which is fitted into a groove (102) on the side surface of the supply rod (101) and the other end of each of which is rotatably attached; Three length-adjustable spacer elements (105) are attached to said upper portion (402) so that each can exert a force on the gripping arm (301); The device, wherein the upper part (402) and the lower part (401) are connected by bearings, the bearings radially connecting to each other in a self-centering, removable fit.

2. 2. The apparatus of claim 1, wherein the radial alignment element (107) comprises linear guides (404), the linear guides (404) being arranged so that they can provide linear guidance perpendicular to the lifting shaft.

3. 2. The device according to claim 1, wherein the three gripping arms (103) are each monolithically manufactured from one piece.

4. 1. A method for pulling a single crystal rod from silicon in a zone melt pulling facility, comprising: (1) providing a silicon feed rod (101) with a groove (102) on the side at one end; (2) attaching to the supply rod (101) a lower part (401) of a device for holding the supply rod, the device comprising three gripping arms (301), the three gripping arms (301) being configured such that one end fits into the groove (102) of the supply rod (101) and the other end is rotatably attached to the lower part (401), the method further comprising: (3) suspending the lower part (401) together with the supply rod (101) on an upper part (401) of the device including a connecting element (502), the connecting element (502) being connected to a lifting shaft of the lifting equipment such that the upper part (402) and the lower part (401) are connected to each other by radially connectable bearings in a self-aligning fit, the upper part (402) including a radial alignment element (404), and three length-adjustable spacer elements attached to the upper part so as to be able to exert a force on the gripping arm (301), the method further comprising: (4) moving the radial alignment element (107) so that the axis of rotation of the supply rod at the end where the groove (102) is located coincides with the axis of rotation of the lift shaft; (5) setting the length-adjustable spacer element so that the axis of rotation of the supply rod (101) at the end opposite the groove (102) coincides with the axis of rotation of the lift shaft; (6) pulling up the conical portion of the single crystal rod; (7) pulling up the cylindrical portion of the single crystal rod.

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