CN116096946A - System and method for reducing shaking and dropping of silicon crystals during silicon production - Google Patents

Abstract

A method for producing a silicon ingot by the Czochralski method comprises rotating a crucible containing a silicon melt, bringing the silicon melt into contact with a seed crystal, while the crucible is rotating about an axis of symmetry Simultaneously withdrawing the seed crystal from the silicon melt along the axis of symmetry to form a silicon ingot, and inducing a current in the ingot to resist movement of the ingot away from the axis of symmetry.

Description

System and method for reducing shaking and dropping of silicon crystals during silicon production

Cross References to Related Applications

This application claims priority to U.S. Provisional Patent Application No. 63/055,426, filed July 23, 2020, which is hereby incorporated by reference in its entirety.

technical field

The present disclosure relates generally to the production of silicon ingots, and more particularly, the present disclosure relates to systems and methods for reducing shaking and falling of silicon crystals during silicon production (eg, due to earthquakes).

Background technique

During Czochralski crystal growth, due to vibration, misalignment, turbulent gas flow, and the like, orbiting or shaking of the silicon crystal, which is detrimental to high quality crystal growth, occurs. Furthermore, in the event of an earthquake, crystal shaking can be so severe that the crystal strikes parts of the growth chamber or crystal puller. When a crystal hits a chamber or part, the crystal and part are usually damaged. In some cases, contact can cause the neck of the crystal to break and the crystal to fall. Any crystal drop can cause serious damage to the component and possibly the crystal puller itself, as well as negative impact on tool time, material and revenue and the like. Falling crystals themselves are usually damaged and unusable.

At least some known systems utilize damping devices that rely on active counter-movement to reduce or eliminate movement in the crystal caused by orbiting or earthquakes. Such systems may negatively affect normal crystal growth due to false positive signal processing or missing anomalous events (such as real earthquakes) due to lack of signal or signal sensitivity or both.

Accordingly, a need exists for methods and systems that automatically and reliably reduce shaking and dropping of crystals during silicon production without negatively impacting crystal growth through false detection.

The "Background" section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. It is believed that this discussion helps to provide the reader with background information to facilitate a better understanding of various aspects of the disclosure. Accordingly, it should be understood that these statements are to be read in this sense and not as admissions of background art.

Contents of the invention

One aspect of the invention is a crystal growth system for producing silicon ingots. The system includes a vacuum chamber, a crucible disposed within the vacuum chamber, a pull shaft, a control unit, and at least one magnet. The crucible is rotatable about an axis of symmetry and configured to hold a melt comprising molten silicon. The pulling shaft is movable along and rotatable about the axis of symmetry and is configured to hold a seed. The control unit includes a processor and a memory. The memory stores instructions that, when executed by the processor, cause the processor to withdraw the seed crystal from the melt in the crucible to form the silicon ingot. The at least one magnet induces a current in the silicon ingot to resist movement of the silicon ingot away from the axis of symmetry. The at least one magnet is configured to generate a horizontal magnetic field above the surface of the melt having a non-zero magnetic flux gradient that reaches a maximum around the axis of symmetry.

Another aspect of the invention is a method for producing silicon ingots by the Chowklassky method. The method comprises rotating a crucible containing a silicon melt, contacting the silicon melt with a seed crystal, withdrawing the seed crystal from the silicon melt along the axis of symmetry while the crucible is rotating about the axis of symmetry. forming a silicon ingot, and inducing a current in the silicon ingot to resist movement of the silicon ingot away from the axis of symmetry.

There are various subdivisions of the features noted with respect to the aspects mentioned above. Further features may also be incorporated into the aspects mentioned above. These refinements and additional features may exist individually or in any combination. For example, various features discussed below with respect to any of the illustrated embodiments may be incorporated into the above-described aspects alone or in any combination.

Description of drawings

Figure 1 is a top view of a crucible of one embodiment.

FIG. 2 is a side view of the crucible shown in FIG. 1 .

Fig. 3 is a schematic diagram illustrating a horizontal magnetic field applied to a crucible containing a melt in a crystal growth apparatus.

Figure 4 is a block diagram of a crystal growth system.

FIG. 5 is an example coil of a magnet of the crystal growth system shown in FIG. 4 .

FIG. 6 is a magnetic assembly including the coil shown in FIG. 5 .

Figure 7 is a graph comparing the magnetic flux density within the melt with the magnetic flux density above the melt as a function of distance from the axis of symmetry.

The same reference numerals in the various drawings refer to the same elements.

Detailed ways

Referring first to FIGS. 1 and 2 , a crucible of an embodiment is indicated generally at 10 . The cylindrical coordinates of the crucible 10 include the radial direction R12, the angular direction θ14 and the axial direction Z16. Crucible 10 contains melt 25 with melt surface 36 . Crystal 27 (also sometimes referred to as boule 27 or silicon boule 27 ) grows from melt 25 . Melt 25 may contain one or more convective flow cells 17, 18 induced by heating crucible 10 and rotating crucible 10 and/or crystal 27 in angular direction Θ14. The structure and interaction of these one or more convective flow cells 17, 18 are modulated by adjusting one or more process parameters and/or applying a magnetic field, as will be described in detail below.

FIG. 3 is a diagram illustrating a horizontal magnetic field applied to crucible 10 containing melt 25 in a crystal growth apparatus. As shown in the figure, crucible 10 contains silicon melt 25 from which crystal 27 grows. The transition between the melt and the crystal is often called the crystal-melt interface (alternatively called the melt-crystal, solid-melt, or melt-solid interface) and is usually non-linear, eg concave with respect to the melt surface , convex or gull-wing. Two magnetic poles 29 are placed opposite to generate a magnetic field approximately perpendicular to the crystal growth direction and approximately parallel to the melt surface 36 . Pole 29 may be a conventional electromagnet, a superconducting electromagnet, or any other suitable magnet for generating a horizontal magnetic field of desired strength and flux gradient. The application of a horizontal magnetic field generates a Lorentz force in the axial direction, in the opposite direction to the fluid motion, the opposite force that drives the convection of the melt. Convection in the melt is thus suppressed and the axial temperature gradient in the crystal near the interface increases. The melt-crystal interface then moves up to the crystal side to accommodate the increased axial temperature gradient in the crystal near the interface and the contribution of melt convection in the crucible decreases. The horizontal configuration has the advantage of effectively suppressing convection at the melt surface 36 . In addition, the magnetic pole 29 is used to reduce the shaking and falling of the crystal 27, as will be described below.

FIG. 4 is a block diagram of a crystal growth system 100 . System 100 employs the Chowklassky crystal growth method to produce silicon semiconductor boules. In the depicted embodiment, system 100 is configured to produce boules having diameters of one hundred and fifty millimeters (150 mm), greater than one hundred and fifty millimeters (150 mm), more specifically in the range of about 150 mm to 460 mm and Even more specifically a cylindrical semiconductor boule about three hundred millimeters (300 mm) in diameter. In other embodiments, the system 100 is configured to produce semiconductor boules having a two hundred millimeter (200 mm) boule diameter or a four hundred and fifty millimeter (450 mm) boule diameter. Additionally, in an embodiment, the system 100 is configured to produce a semiconductor ingot having a total ingot length of at least nine hundred millimeters (900 mm). In some embodiments, the system is configured to produce the Semiconductor boules. In other embodiments, the system 100 is configured to produce materials having a diameter in the range of about nine hundred millimeters (900 mm) to one thousand two hundred millimeters (1200 mm), between about 900 millimeters to about two thousand millimeters (2000 mm), or at about Semiconductor boules with a total boule length between 900 millimeters and about 2,500 millimeters (2,500 mm). In some embodiments, the system is configured to produce semiconductor ingots having a total ingot length greater than 2000 mm.

Crystal growth system 100 includes a vacuum chamber 101 enclosing crucible 10 . Side heaters 105 , such as resistive heaters, surround the crucible 10 . A bottom heater 106 , such as a resistive heater, is positioned below the crucible 10 . During heating and crystal pulling, a crucible drive unit 107 , such as a motor, rotates the crucible 10 , for example in a clockwise direction as indicated by arrow 108 . The crucible drive unit 107 can also raise and/or lower the crucible 10 as needed during the growth process. Inside the crucible 10 is a silicon melt 25 having a melt level or melt surface 36 . In operation, system 100 pulls single crystal 27 from melt 25 starting from seed crystal 115 attached to pull shaft or cable 117 . One end of the pull shaft or cable 117 is connected by a pulley (not shown) to a drum (not shown) or any other suitable type of lifting mechanism, such as a shaft, and the other end is connected to the holding seed 115 and from A chuck (not shown) for the crystal 27 grown from the seed crystal 115.

Crucible 10 and single crystal 27 have a common axis of symmetry 38 . As melt 25 is depleted, crucible drive unit 107 may raise crucible 10 along axis 38 to maintain melt level 36 at a desired height. Crystal drive unit 121 similarly rotates pull shaft or cable 117 in the opposite direction 110 (eg, counter-rotation) to the direction in which crucible drive unit 107 rotates crucible 10 . In embodiments using co-rotation, crystal drive unit 121 may rotate pull shaft or cable 117 in the same direction in which crucible drive unit 107 rotates crucible 10 (eg, in a clockwise direction). Co-rotation may also be referred to as co-rotation. In addition, the crystal driving unit 121 raises and lowers the crystal 27 relative to the melt level 36 as needed during the growth process.

A certain amount of polycrystalline silicon (polycrystalline silicon or polysilicon) is filled into the crucible 10 according to the Chowklarski single crystal growth process. A heater power supply 123 powers the resistive heaters 105 and 106 , and an insulator 125 lines the inner walls of the vacuum chamber 101 . When the vacuum pump 131 removes gas from the vacuum chamber 101 , the gas supplier 127 (eg, a bottle) supplies argon gas to the vacuum chamber 101 via the gas flow controller 129 . An outer chamber 133 supplied with cooling water from a reservoir 135 surrounds the vacuum chamber 101 .

The cooling water is then discharged to the cooling water return manifold 137 . Typically, a temperature sensor such as a photocell 139 (or pyrometer) measures the temperature at the surface of the melt 25 and a diameter sensor 141 measures the diameter of the crystal 27 . In the depicted embodiment, system 100 does not include an upper heater. The presence or absence of the upper heater alters the cooling characteristics of crystal 27 .

Magnetic poles 29 are positioned outside the vacuum chamber 101 to generate a horizontal magnetic field (as shown in FIG. 3 ). Although illustrated as being generally centered on the melt surface 36 , the position of the pole 29 relative to the melt surface 36 may be varied to adjust the position of the maximum Gaussian plane (MGP) relative to the melt surface 36 . Reservoir 153 provides cooling water to pole 29 prior to discharge via cooling water return manifold 137 . Iron shields 155 surround the poles 29 to reduce stray magnetic fields and enhance the strength of the generated fields.

The control unit 143 is used to adjust a plurality of process parameters, including (but not limited to) at least one of crystal rotation rate, crucible rotation rate and magnetic field strength. In various embodiments, control unit 143 may include memory 173 and processor 144 that processes signals received from various sensors of system 100 (including but not limited to photocell 139 and diameter sensor 141 ), and controls One or more devices of system 100, including (but not limited to): crucible drive unit 107, crystal drive unit 121, heater power supply 123, vacuum pump 131, gas flow controller 129 (e.g., argon flow controller), pole power supply 149, and 151 and any combination thereof. Memory 173 may store instructions that, when executed by processor 144, cause the processor to perform one or more of the methods described herein. That is, the instructions configure the control unit 143 to perform one or more methods, processes, procedures, and the like described herein.

The control unit 143 may be a computer system. As described herein, a computer system refers to any known computing device and computer system. As described herein, all such computer systems include a processor and memory. However, any processor reference herein to a computer system may also refer to one or more processors, where a processor may be located on one computing device or multiple computing devices acting in parallel. Additionally, any memory in a computing device referred to herein may also refer to one or more memories, where the memories may be located in one computing device or in multiple computing devices acting in parallel. Furthermore, the computer system may be located near the system 100 (eg, in the same room, or in an adjacent room), or may be remotely located and coupled to the remainder of the system via a network (eg, Ethernet, Internet, or the like).

The term processor as used herein refers to a central processing unit, microprocessor, microcontroller, reduced instruction set circuit (RISC), application specific integrated circuit (ASIC), logic circuit, and any other processor capable of performing the functions described herein. other circuits or processors. The above are examples only, and thus are in no way intended to limit the definition and/or meaning of the term "processor." Memory may include, but is not limited to, random access memory (RAM) such as dynamic RAM (DRAM) or static RAM (SRAM), read only memory (ROM), erasable programmable read only memory (EPROM), electronic Erasable Programmable Read-Only Memory (EEPROM) and Non-Volatile RAM (NVRAM).

In one embodiment, computer programming to enable control unit 143 is provided and embodied on a computer readable medium. The computer readable medium may include the memory 173 of the control unit 143 . In an example embodiment, the computer systems execute on a single computer system. Alternatively, a computer system may include multiple computer systems, a connection to a server computer, a cloud computing environment, or the like. In some embodiments, a computer system includes multiple components distributed among multiple computing devices. One or more components may be in the form of computer-executable instructions embodied on a computer-readable medium.

Computer systems and processes are not limited to the specific embodiments described herein. In addition, each computer system component and each process can be practiced independently of and separately from other components and processes described herein. Each component and process may also be used in conjunction with other assembly packages and processes.

In one embodiment, the computer system may be configured to receive measurements from one or more sensors (including but not limited to: temperature sensor 139 , diameter sensor 141 , and any combination thereof), and to control one or more of the system 100 a device, including (but not limited to): crucible drive unit 107, crystal drive unit 121, heater power supply 123, vacuum pump 131, gas flow controller 129 (such as an argon flow controller), magnetic pole power supplies 149 and 151, and any combination thereof, As described herein and illustrated in FIG. 4 in one embodiment. The computer system performs all of the steps for controlling one or more devices of system 100, as described herein.

The poles 29 additionally serve to reduce and prevent shaking and falling of the crystal 27 eg due to earthquakes.

When a silicon crystal, such as crystal 27, moves through a magnetic field, eddy currents induced within the crystal cause electromagnetic forces opposing this movement. Although this damping or braking force is very complex due to the complexity of the typical magnetic field distribution and the conductivity distribution when the crystal is pulled during growth, the force is always proportional to the magnetic field flux density B through the crystal, The spatial gradient dB/dx of the magnetic flux in the direction of motion, the conductivity of the crystal, the velocity of motion v and the like. Silicon crystals are good conductors at or near the growth temperature, where the conductivity σ is about 10 ⁵ S/m. By using poles 29 with a magnetic flux density B from 1000 Gauss to 5000 Gauss (0.1T to 0.5T) and a high conductance transistor, the crystal produces a considerable damping force during significant eccentric motion of the crystal. Increasing the magnetic flux gradient further increases the force against crystal movement.

Therefore, to reduce shaking and falling of the ingot 27 , the system 100 includes and uses magnets (eg, poles 29 ) to induce a current in the ingot 27 to resist movement of the ingot 27 away from the axis of symmetry 38 . The poles 29 are configured (ie, designed, constructed, composed, oriented, positioned, and the like) to produce a horizontal magnetic field with a non-zero magnetic flux gradient above the surface 36 of the melt. The magnetic flux gradient reaches a maximum around the axis of symmetry 38 .

Pole 29 transmits a strong and uniform horizontal magnetic field near or around crystal 27 to melt the interface and within silicon melt 25 and is centered and positioned on axis of symmetry 38 . However, in regions where normal crystal growth is not affected (for example, above the melt surface 36), the coils of the poles 29 are configured to produce large magnetic flux gradients. With the strong magnetic field at the crystal 27 and the large magnetic flux gradient at the crystal 27 well above the melt 25, whenever the crystal moves away from the axis of symmetry 38, the eddy currents induced in the conduction transistor 27 are strong enough to counteract this unwanted movement . This causes the crystal 27 to self-center along the axis of symmetry 38 in response to any movement away from the axis of symmetry 38 without the need for any sensors. The greater and/or faster the undesired movement away from the axis of symmetry 38, the greater the reaction force that returns the crystal 27 along the axis of symmetry 38 to its central axis. When the crystal 27 is centered on the axis of symmetry 38, there is no reaction force, and thus no risk of false positive effects and corresponding negative effects on normal crystal growth.

FIG. 5 is an example coil 500 for a magnetic assembly of the crystal growth system 100 . FIG. 6 is a magnetic assembly 600 including the two coils shown in FIG. 5 used to form pole 29 . The resulting magnetic flux gradient depends on the configuration, shape, size and number of turns of the coil 500 . The magnet assembly 600 utilizes a pair of saddle coils 500 aligned in the same direction and wrapped within a magnet housing 602 . In an example embodiment, the cylindrical magnet housing 602 has an ID of 1194 mm, an OD of 1556 mm, and a height of 1088 mm. Each coil 500 has 240 turns and carries up to 718 amps. Other embodiments may use coils and/or magnetic assemblies including different coil shapes, different numbers of turns, different pitches, and the like.

In an example embodiment, poles 29 produce a maximum magnetic flux density of approximately 1500 Gauss. In some embodiments, the poles produce a maximum magnetic flux density of at least 1500 Gauss. In other embodiments, poles 29 produce a maximum magnetic flux density of 2200 Gauss or at least 2200 Gauss. In other embodiments, the poles produce a maximum magnetic flux density between 1500 Gauss and 5000 Gauss. In an example embodiment, the coils (not shown) of the poles 29 are superconducting coils. Alternatively, the coils can be made from conventional conductors.

As noted above, poles 29 produce a relatively uniform magnetic flux density (ie, have a very low magnetic flux density gradient) within melt 25 and at the interface between crystal 27 and melt surface 36 . Above the melt 25 , the magnetic poles 29 generate a magnetic field that varies in the horizontal direction and has a maximum around the axis of symmetry 38 . 7 is a simulated graph 700 comparing magnetic flux density 702 within melt 25 to magnetic flux density 704 above melt 25 as a function of distance from axis of symmetry 38 (indicated by radius 0 in the graph). Both the magnetic flux density 702 within the melt and the magnetic flux density 704 above the melt have a maximum value of approximately 2200 Gauss. The gradient of the magnetic flux density 702 within the melt 25 is almost zero, with very little variation with increasing distance from the axis of symmetry. However, we can see that for the magnetic flux density 704 above the melt 25 the variation and thus the gradient is significantly greater off-axis center (r=0). In fact, the magnetic flux density 704 above the melt 25 exhibits a decrease in magnetic flux of about 250 Gauss (or at least ten percent of the maximum value) within about 200 millimeters of the axis of symmetry 38 . With such a strong magnetic field at the crystal 27, much higher than the large gradients in the crystal of the melt 25, the eddy currents generated within the conduction transistor 27 and therefore the forces resisting movement whenever the crystal moves away from the axis of symmetry 38 are strong enough to suppress this to move.

The pointed magnetic system provides no damping of movement of the crystal away from the axis of symmetry. Data on a similar crystal growth system using pointed magnets and no vibration damping had a 24.2% discard rate across 33 earthquakes. That is, of the 33 earthquakes experienced by the system, crystals dislodged from the crystal pullers and fell in 24.2%. Based on data and experimentation, an exemplary system of the present invention is expected to have a discard rate of 6.7% or higher. The 6.7% drop rate assumes a system using a lower Gauss (eg 1500 Gauss) magnet. When using a 2200 Gauss magnet, the expected discard rate is about 0%.

Embodiments of the methods described herein achieve superior results compared to previous methods and systems. For example, the methods and systems described herein do not contact and do not invade normal crystal growth. The system is always active. There is no need for any sensors for cable or crystal movement, or any seismometers for detecting seismic events. There is no risk of missing a true anomaly, even because the reverse movement or damping mechanism is always in effect. In addition, specially designed magnets induce a force strong enough to inhibit undesired movement of the crystal.

When introducing elements of the invention or its embodiment(s), the articles "a/an", "the", "the and said" are intended to mean that there are one or more of the elements By. The terms "comprising", "comprising" and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

As used herein throughout the specification and claims, approximating language may be used to modify any quantitative expression that may be permissively varied without resulting in a change in the basic function to which it is associated. Accordingly, a value modified by a term or terms such as "about," "approximately," and "substantially" is not to be limited to the precise value specified. In at least some examples, the approximate language may correspond to the precision of the instrument used to measure the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged; such ranges are identified and include all the subranges subsumed therein unless context or language indicates otherwise.

As various changes could be made in the above without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims (23)

CLAIMS 1. A crystal growth system for producing an ingot of crystalline material, said system comprising: Chamber; a crucible disposed within the chamber, the crucible rotatable about an axis of symmetry and shaped to hold the melt; a pull shaft movable along and rotatable about the axis of symmetry and configured to hold a seed; a control unit comprising a processor and memory storing instructions that, when executed by the processor, cause the processor to withdraw the seed from the melt in the crucible to form the ingot ,and a magnet for inducing a current in the ingot to resist movement of the ingot away from the axis of symmetry, the magnet positioned to produce a horizontal magnetic field with a non-zero magnetic flux gradient above the surface of the melt , the magnetic flux gradient reaches a maximum around the axis of symmetry. 2. The system of claim 1, wherein the magnet is positioned to generate the horizontal magnetic field at the surface of the melt with a lower magnetic flux gradient. 3. The system of claim 2, wherein the lower magnetic flux gradient at the surface of the melt is substantially zero. 4. The system of any preceding claim, wherein the magnet is configured to produce the non-zero magnetic flux gradient, wherein magnetic flux decreases by at least ten percent of the maximum value within about 200 millimeters of the axis of symmetry . 5. The system of any preceding claim, wherein the at least one magnet comprises an electromagnet having a conductive coil. 6. The system of claim 5, wherein the conductive coil comprises a superconducting coil. 7. The system of any preceding claim, wherein the magnet is configured to generate the horizontal magnetic field having a maximum magnetic flux density of at least 1500 Gauss. 8. The system of claim 7, wherein the magnet is configured to generate the horizontal magnetic field having a maximum magnetic flux density of at least 2200 Gauss. 9. A silicon ingot produced using a system according to any preceding claim. 10. The silicon crystal ingot of claim 9, wherein the silicon crystal ingot is produced during an earthquake using the system of claim 1 without fracture. 11. A wafer produced from a silicon ingot according to any one of claims 9 and 10. 12. A method for producing a silicon ingot by the Chowklarski process, the method comprising: Rotate the crucible containing the silicon melt; contacting the silicon melt with a seed crystal; withdrawing the seed crystal from the silicon melt along the axis of symmetry while rotating the crucible about the axis of symmetry to form a silicon ingot; and A current is induced in the silicon ingot to resist movement of the silicon ingot away from the axis of symmetry. 13. The method of claim 12, wherein inducing an electric current in the silicon ingot to resist movement of the silicon ingot away from the axis of symmetry comprises using a magnet to create an electric current above the surface of the silicon melt with A horizontal magnetic field with a non-zero magnetic flux gradient that reaches a maximum around the axis of symmetry. 14. The method of claim 13, further comprising using the magnet to generate the horizontal magnetic field at the surface of the melt with a lower magnetic flux gradient. 15. The method of claim 14, wherein the lower magnetic flux gradient at the surface of the melt is substantially zero. 16. The method of any one of claims 13 to 15, wherein using the magnet to generate the horizontal magnetic field comprises using the magnet to generate the non-zero magnetic flux gradient, wherein the magnetic flux is at the axis of symmetry reduce by at least ten percent of the maximum value within about 200 mm. 17. The method of any one of claims 13 to 16, wherein using a magnet to generate the horizontal magnetic field includes using an electromagnet with a conductive coil. 18. The method of claim 17, wherein using at least one electromagnet with a conductive coil includes using a magnet with a superconducting coil. 19. The method of any one of claims 13-18, wherein using a magnet to generate the horizontal magnetic field includes using a magnet to generate the horizontal magnetic field having a maximum magnetic flux density of at least 1500 Gauss. 20. The method of claim 19, wherein using a magnet to generate the horizontal magnetic field comprises using a magnet to generate the horizontal magnetic field having a maximum magnetic flux density of at least 2200 Gauss. 21. A silicon crystal ingot produced using the method of any one of claims 13 to 20. 22. The silicon crystal ingot of claim 21, wherein the silicon crystal ingot was created during an earthquake without fracture. 23. A wafer produced from a silicon ingot according to any one of claims 21 and 22.

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