TW202409363A - Axial positioning of magnetic poles while producing a silicon ingot - Google Patents

Abstract

Method for producing a silicon ingot in which a horizontal magnetic field is generated are disclosed. The magnet position is controlled in at least two stages of ingot growth. The magnetic poles may be at a first position during a first stage of ingot growth and lowered to a second position in a second stage of ingot growth. By controlling the magnet position, the crystal-melt interface shape may be relatively more consistent.

Description

Axial positioning of magnetic poles during silicon ingot production

The field of the invention relates to methods for producing single crystal silicon ingots in a horizontal magnetic field Czochralski process and related ingot puller equipment for producing single crystal silicon ingots.

Monocrystalline silicon is a starting material used in many processes for manufacturing semiconductor electronic components and solar materials. For example, semiconductor wafers produced from silicon ingots are often used to produce integrated circuit chips with printed circuit systems on them. In the solar industry, monocrystalline silicon can be used instead of polycrystalline silicon due to the absence of grain boundaries and dislocations.

To produce semiconductor or solar wafers, a single crystal silicon ingot can be produced by dipping a seed crystal into molten silicon held in a crucible in a Czochralski process. The seed crystal is extracted in a manner sufficient to achieve the desired diameter of the ingot. After the ingot is formed, the silicon ingot is processed into the desired shape from which semiconductor or solar wafers can be produced.

Polished silicon wafers that meet manufacturer requirements that lack condensed point defects, such as crystal-origin pits (COP), may be referred to as "neutral silicon" or "perfect silicon." Perfect silicon wafers are preferred for many semiconductor applications as a lower cost polished wafer in place of, for example, epitaxially deposited wafers. During the growth of perfect silicon ingots in the Chuklaski process with a horizontal magnetic field, the shape of the crystal-melt interface is usually concave. To produce perfect silicon, the thermal conditions of the ingot or crystal-melt interface shape are controlled, while the pulling speed is adjusted. Pull speed and thermal conditions (such as by adjusting the gap between the melt surface and the reflector and controlling the bottom heater) can be continuously adjusted to control the shape of the crystal-melt interface. Thermal conditions change during ingot growth to complicate control of the crystal-melt interface, allowing perfect silicon to be produced only in one axial window of ingot growth.

What is needed are methods for controlling a horizontal magnetic field to maintain a relatively constant crystal-melt interface and puller apparatus in which such methods can be implemented to produce single crystal silicon ingots (e.g., perfect silicon).

This section is intended to introduce the reader to various aspects of technology that may be related to various aspects of the invention that are described and/or claimed below. We believe that this discussion is helpful in providing the reader with background information to facilitate a better understanding of various aspects of the invention. Therefore, it should be understood that these statements should be read in this light and should not be read as an endorsement of prior art.

One aspect of the invention is directed to a method for producing a silicon ingot. Polycrystalline silicon is melted in a crucible enclosed in a growth chamber to form a melt. The melt has a melt free surface. A horizontal magnetic field is generated in the growth chamber. A seed crystal is brought into contact with the melt. The seed crystal is extracted from the melt to form the silicon ingot. The position of a maximum gauss plane during the formation of a constant diameter portion of the silicon ingot is adjusted during at least two stages of ingot growth. The at least two stages include a first stage and a second stage. The first stage corresponds to the formation of the silicon ingot starting from the formation of the constant diameter portion of the silicon ingot up to an intermediate ingot length. The second stage corresponds to the formation of the silicon ingot from at least the intermediate ingot length to a total length of the constant diameter portion. Adjusting the position of the maximum Gaussian plane includes maintaining the position of the maximum Gaussian plane in the second phase at a position lower than the position of the maximum Gaussian plane during the first phase.

Another aspect of the invention is directed to an ingot puller apparatus for manufacturing a single crystal silicon ingot. The ingot puller apparatus contains a crucible for holding a silicon melt. An ingot puller housing defines a growth chamber for pulling a silicon ingot from the silicon melt. The crucible is placed in the growth chamber. A pair of magnetic poles are disposed radially outward from the crucible. The apparatus includes translation means for axially moving the magnetic poles relative to the crucible.

There are various improvements to the features mentioned above with respect to the above aspects of the invention. Further features may also be incorporated into the above aspects of the invention. Such improvements and additional features may exist independently or in any combination. For example, various features discussed below with respect to any illustrated embodiment of the invention may be incorporated into any of the above aspects of the invention alone or in any combination.

This application claims priority to U.S. Nonprovisional Patent Application No. 17/897,682 filed on August 29, 2022 and U.S. Nonprovisional Patent Application No. 17/897,685 filed on August 29, 2022. The entire text of both applications is incorporated herein by reference.

The present invention is directed to methods for manipulating the shape of the ingot-melt interface during ingot growth (ie, changing the shape of the solidification front). The methods and apparatus of the present invention may involve changing the position of the maximum Gaussian plane during ingot growth to change the shape of the ingot-melt interface as the ingot grows.

The methods of the present invention may generally be implemented in any puller apparatus configured to pull a single crystal silicon ingot and in which a horizontal magnetic field is applied to the melt. An exemplary puller apparatus (or more simply, "puller") is generally indicated by "100" in FIG. 1. The puller apparatus 100 includes a crucible 102 for holding a melt 104 of a semiconductor or solar grade material (such as silicon), which is supported by a susceptor 106. The puller apparatus 100 includes a crystal puller housing 109 that defines a growth chamber 152 for pulling a silicon ingot 113 (FIG. 2) from the melt 104 along a pulling axis A.

The crucible 102 includes a bottom surface 128 and a side wall 131 extending upward from the bottom surface 128 . The side walls 131 are generally vertical. Bottom 128 includes a curved portion of crucible 102 that extends below side wall 131 . A silicon melt 104 having a melt surface 111 is in the crucible 102 .

In some embodiments, crucible 102 is layered. For example, crucible 102 may be made from a quartz base layer and a synthetic quartz lining disposed on the quartz base layer.

The bearing 106 is supported by a shaft 105 . The holder 106, the crucible 102, the shaft 105 and the spindle 113 (Fig. 2) have a common longitudinal axis A or "pull axis" A.

A lifting mechanism 114 is provided in the ingot pulling device 100 for growing the self-melting body 104 and pulling an ingot 113 . The pull mechanism 114 includes a pull cable 118, a seed holder or chuck 120 coupled to one end of the pull cable 118, and a device coupled to the seed holder or chuck 120 for initiating crystal growth. A silicon seed crystal 122. One end of the lifting cable 118 is connected to a pulley (not shown) or a roller (not shown) or any other suitable type of lifting mechanism (such as a shaft) and the other end is connected to the chuck 120 holding the seed crystal 122 . In operation, seed 122 is lowered into contact with melt 104 . The lifting mechanism 114 is operated to cause the seed crystal 122 to rise. This causes a single crystal ingot 113 to be extracted from the melt 104 (Fig. 2).

During heating and crystal pulling, a crucible drive unit 107 (eg, a motor) rotates the crucible 102 and holder 106. A lifting mechanism 112 raises and lowers the crucible 102 along the lifting axis A during the growth process. For example, crucible 102 may be in a lowest position (near bottom heater 126) where an initial charge of solid polycrystalline silicon previously added to crucible 102 is melted. Crystal growth is initiated by bringing the melt 104 into contact with the seed crystal 122 and lifting the seed crystal 122 by the pulling mechanism 114 . As the ingot grows, the silicon melt 104 is consumed and the height of the melt in the crucible 102 decreases. The crucible 102 and holder 106 can be raised so that the melt surface 111 is maintained at or near the same position relative to the spindle puller apparatus 100 (Fig. 2).

A crystal drive unit (not shown) can also rotate the pull cable 118 and ingot 113 ( FIG. 2 ) in a direction opposite to the direction in which the crucible drive unit 107 rotates the crucible 102 (e.g., counter-rotate). In embodiments using co-rotation, the crystal drive unit can rotate the pull cable 118 in the same direction in which the crucible drive unit 107 rotates the crucible 102. Additionally, the crystal drive unit raises and lowers the ingot 113 relative to the melt surface 111 as needed during the growth process.

The puller apparatus 100 may include an inert gas system for introducing and extracting an inert gas, such as argon, from the growth chamber 152. The puller apparatus 100 may also include a dopant feed system (not shown) for introducing dopant into the melt 104.

According to the Chuklaski single crystal growth procedure, a quantity of polycrystalline silicon or polysilicon is fed into the crucible 102 . The initial semiconductor or solar grade material introduced into the crucible is melted by heat provided from one or more heating elements to form a silicon melt in the crucible. The spindle puller apparatus 100 includes bottom insulation 110 and side insulation 124 to retain heat within the puller apparatus. In the illustrated embodiment, the spindle puller apparatus 100 includes a bottom heater 126 disposed below the crucible floor 128 . The crucible 102 can be moved relatively close to the bottom heater 126 to melt the polycrystalline silicon fed into the crucible 102 .

To form an ingot, a seed crystal 122 is brought into contact with a surface 111 of the melt 104. A pulling mechanism 114 is operated to pull the seed crystal 122 from the melt 104. Referring now to FIG. 2 , ingot 113 includes a crown portion 142 wherein the ingot transitions outwardly from the seed crystal 122 and tapers to achieve a target diameter. Ingot 113 includes a constant diameter portion 145 or cylindrical “body” of the crystal that grows by increasing the pull rate. The body 145 of ingot 113 has a relatively constant diameter. Ingot 113 includes a tail or taper (not shown) wherein the diameter of the ingot tapers after the body 145. When the diameter becomes small enough, the ingot 113 is then separated from the melt 104.

The ingot puller apparatus 100 is configured to produce a cylindrical semiconductor ingot having an ingot diameter of 150 mm, greater than 150 mm, and more specifically in a range from about 150 mm to about 450 mm, and more specifically In other words, about 300 mm in diameter. In other embodiments, the ingot puller apparatus 100 is configured to produce a semiconductor ingot having a 200 mm ingot diameter or a 450 mm ingot diameter. Additionally, in one embodiment, the apparatus 100 is configured to produce a semiconductor ingot having an overall ingot length of at least 900 mm. In some embodiments, the system is configured to produce a semiconductor ingot having a length of 1950 mm, 2250 mm, 2350 mm, or longer than 2350 mm. In other embodiments, the spindle puller apparatus 100 is configured to produce a product having an overall diameter in the range of about 900 mm to about 1200 mm, between about 900 mm to about 2000 mm, or between about 900 mm to about 2500 mm. One of the ingot lengths is a semiconductor ingot. In some embodiments, the system is configured to produce a semiconductor ingot having an overall ingot length greater than 2000 mm.

The puller apparatus 100 includes a side heater 135 and a susceptor 106 surrounding the crucible 102 to maintain the temperature of the melt 104 during crystal growth. The side heater 135 is radially disposed outwardly to the crucible side wall 131 as the crucible 102 moves upward and downward along the pulling axis A. The side heater 135 and the bottom heater 126 can be any type of heater that allows the side heater 135 and the bottom heater 126 to operate as described herein. In some embodiments, the heaters 135, 126 are resistive heaters. The side heater 135 and the bottom heater 126 can be controlled by a control system (not shown) so that the temperature of the melt 104 is controlled during the entire pulling process.

The spindle puller device 100 may include a heat shield 151 . Thermal shield 151 may cover ingot 113 and may be positioned within crucible 102 during crystal growth (Fig. 2). The spindle puller apparatus 100 may be cooled, such as by circulating cooling fluid through an outer chamber of the apparatus. A cooling jacket 154 is placed within the growth chamber 152 for cooling the ingot 113 .

The crystal growth process of the present invention may be a batch process in which solid silicon is initially added to the crucible 102 to form a silicon melt without additional solid silicon being added to the crucible 102 during crystal growth.

The ingot puller apparatus 100 of the present invention includes a pair of magnetic poles 129, 130 (Fig. 1) that generates a horizontal magnetic field during ingot growth. Magnetic poles 129, 130 are disposed radially outward from the crucible 102.

FIG. 3 is a diagram showing a horizontal magnetic field applied to a crucible 102 containing a melt 104 from which an ingot 113 is grown. The transition between the melt and the ingot is generally referred to as the crystal-melt interface 125 (alternatively, the "ingot-melt" or "solid-melt" interface) and is typically nonlinear, e.g., concave, convex, or seagull-wing relative to the melt surface 111. Two magnetic poles 129, 130 are opposedly positioned to produce a magnetic field generally perpendicular to the ingot growth direction and generally parallel to the melt surface 111. The magnetic poles 129, 130 may be a conventional electromagnetic magnet, a superconducting electromagnetic magnet, or any other suitable magnet for producing a horizontal magnetic field of the desired strength. Applying a horizontal magnetic field results in a Lorentz force in the axial direction, in a direction opposite to the fluid motion, opposing the force driving the melt convection. Convection in the melt is thus suppressed and the axial temperature gradient in the ingot near the interface increases. The melt-ingot interface then moves upward to the side of the ingot to accommodate the increased axial temperature gradient in the ingot near the interface and the contribution from the melt convection in the crucible decreases. The horizontal configuration has the efficiency advantage of weakening a convective flow at the melt surface 111.

Magnetic poles 129, 130 may be cooled by circulating cooling fluid through them. An iron shield 155 (Fig. 1) may surround the magnetic poles 129, 130 to reduce stray magnetic fields and enhance the strength of the generated magnetic field.

According to an embodiment of the present invention, a position of a Maximum Gaussian Plane ("MGP") during the formation of a constant diameter portion of a silicon ingot is adjusted during at least two stages of ingot growth. The MGP is characterized by a maximum magnitude of the horizontal component of the magnetic field and a zero vertical component along the MGP. The position of the magnetic poles 129, 130 relative to the melt free surface 111 (or more simply, the "melt surface") is changed during ingot growth by moving the magnetic poles 129, 130.

Referring now to Figure 4, there is shown an example distribution of MGP positions during ingot growth. The position of MGP is adjusted in a first stage _S1 and a second stage _S2 . The first stage _S1 corresponds to the growth of the silicon ingot. The formation of the constant diameter portion begins until an intermediate ingot length is formed, and the second stage _S2 corresponds to the formation of the ingot from at least the intermediate ingot length to the total length of the constant diameter portion. As shown in Figure 4, adjusting the position of the maximum Gaussian plane includes maintaining the position of the maximum Gaussian plane in the second stage _S2 at a position lower than the position of the maximum Gaussian plane during the first stage _S1 . For example, the position of the maximum Gaussian plane during the first stage S ₁ is maintained higher than the free surface of the melt. The position of the maximum Gaussian plane during the second stage _S2 is maintained lower than the free surface of the melt.

In the embodiment of FIG. 4 , the MGP distribution includes an intermediate stage S ₃ , which corresponds to the silicon ingot formation between the first stage S ₁ and the second stage S ₂ . Adjusting the position of the maximum Gaussian plane may include lowering the position of the maximum Gaussian plane from the position in the first stage S ₁ to the position in the second stage S ₂ during the intermediate stage S ₃ .

In some embodiments, the position of the maximum Gaussian plane (corresponding to the normalized position "1" in Figure 4) is maintained during the first stage at a position at least 20 mm above the free surface of the melt, or as in In other embodiments, during the first stage at least 40 mm above the free surface of the melt, at least 60 mm above the free surface of the melt, from the free surface of the melt to 150 mm above the free surface of the melt, from 20 mm above the surface to 150 mm above the free surface of the melt or from 40 mm above the free surface of the melt to 150 mm above the free surface of the melt.

Alternatively or additionally, the position of the maximum Gaussian plane may be maintained below the melt free surface during the second phase or at a position at least 20 mm below the melt free surface during the second phase. In some embodiments, the position of the maximum Gaussian plane is maintained at a position at least 40 mm below the melt free surface, at least 60 mm below the melt free surface, at least 80 mm below the melt free surface, at least 100 mm below the melt free surface, from the melt free surface to 200 mm below the melt free surface, from 20 mm below the melt free surface to 200 mm below the melt free surface, or from 20 mm below the melt free surface to 150 mm below the melt free surface during the second phase.

In some embodiments and as shown in Figure 4, the MGP may be further from the melt free surface in the second stage _S2 than in the first stage _S1 (i.e., the absolute distance is greater in the second stage) . The ratio of (1) the distance from MGP to the free surface of the melt in the second stage S ₂ to (2) the distance from the MGP to the free surface of the melt in the first stage S ₁ may be at least 1.0, at least 1.25, at least 1.4, or At least 1.5.

In the embodiment of Figure 4, the position of the maximum Gaussian plane is lowered below the free surface of the melt during the intermediate stage _S3 . The position of the maximum Gaussian plane can be lowered by at least 40 mm (or at least 75 mm, at least 100 mm, or at least 150 mm) in the intermediate stage _S3 (i.e., between the end of _S1 and the beginning of _S2 ) over no more than 60% of the constant diameter portion or no more than 50% or no more than 40% of the constant diameter portion in other embodiments.

The crucible 102 may be moved as the melt 104 is consumed to maintain a relatively constant position of the melt interface. In some embodiments, the position of the poles 129, 130 relative to the melt free surface 111 may be adjusted by moving both the poles 129, 130 and the position of the melt free surface 111 (e.g., allowing the melt to be consumed or by moving the crucible 102). In other embodiments, the position of the poles 129, 130 relative to the melt free surface 111 is adjusted only by moving the poles 129, 130 (i.e., the melt free surface 111 is maintained in a relatively constant position by moving the crucible 102 as the melt 104 is consumed).

The length of the first stage S ₁ may be at least 10% of the constant diameter portion, or as in other embodiments, at least 20% of the constant diameter portion, at least 10% and less than 50% of the constant diameter portion, or at least 20% of the constant diameter portion. 10% and less than 40%. The first stage _S1 may start at the beginning of the constant diameter portion of the ingot. The position of the maximum Gaussian plane may remain constant during the first phase S ₁ or may vary during the first phase.

The length of the second stage _S2 may be at least 10% of the length of the constant diameter portion, or as in other embodiments, at least 20% of the constant diameter portion, at least 30% of the constant diameter portion, at least 10% and less than 50% of the constant diameter portion, or at least 20% and less than 50% of the constant diameter portion. The second stage _S2 may extend from the end of the first stage _S1 (or in an embodiment with an intermediate stage, the end of the intermediate stage _S3 ) to the end of the constant diameter portion of the tablet. The position of the maximum Gaussian plane may remain constant during the second stage _S2 or may vary during the second stage.

The poles 129, 130 may be operated at any power(s) that enables consistent ingot growth as described herein. For example, during the first, second and intermediate stages of ingot growth, the horizontal magnetic field may be less than 0.4 Tesla or, in other embodiments, less than 0.35 Tesla, less than 0.3 Tesla, less than 0.25 Tesla. Tesla may be produced from a magnetic flux intensity of about 0.2 Tesla to about 0.4 Tesla. Generally speaking, the strength of a magnetic field is its magnitude at the center of the maximum Gaussian plane 52.

The crucible 102 may rotate in a direction opposite to the direction in which the ingot 113 rotates, wherein the crucible 102 rotates at a rate in a range from 0.1 RPM to 5.0 RPM (i.e., -0.1 RPM to -5.0 RPM), or even from 0.1 RPM to 1.6 RPM (i.e., -0.1 RPM to -1.6 RPM), or from 0.1 RPM to 1.2 RPM (i.e., -0.1 RPM to -1.2 RPM). In other embodiments, the crucible 102 rotates in the same direction in which the ingot 113 rotates, wherein the crucible 102 rotates at a rate in a range from 0.1 RPM to 5.0 RPM, from 0.7 RPM to 5 RPM, or from 1.2 RPM to 5.0 RPM.

The spindle puller apparatus 100 includes a translation device 160 for axial movement of the magnetic poles 129, 130 relative to the crucible 102 and the melt free surface 111 (Fig. 1). Any translation device 160 for moving the magnetic poles 129, 130 that allows the spindle puller device 100 to operate as described herein may be used. For example, the translation device 160 may include a guide 163 and a mounting base 170 that moves each magnetic pole 129 , 130 relative to the guide 163 . The guide 163 may include one or more rails, with the mounting 170 connecting each pole 129, 130 to the one or more rails. The spindle puller device 100 includes an actuator 175 that moves the magnetic poles 129 , 130 relative to the guide 163 . For example, actuator 175 may be a pneumatic or hydraulic cylinder, a rack and pinion, a pulley, or a gear train with a ball screw. A motor 178 can power actuator 175 . Motor 178 may be controlled by a controller 108 . Alternatively, the translation device 160 may include other devices or devices that regulate the movement of the poles 129, 130.

5 is a block diagram of an exemplary computing device 200 that may be used as or included as part of the controller 108 for adjusting the position of the magnetic poles 129, 130. The computing device 200 includes a processor 201, a memory 202, a media output component 204, an input device 206, and a communication interface 208. Other embodiments include different components, additional components, and/or do not include all of the components shown in FIG. 5 .

Processor 201 is configured to execute instructions. In some embodiments, executable instructions are stored in memory 202 . Processor 201 may include one or more processing units (eg, in a multi-core configuration). As used herein, the term "processor" refers to a central processing unit, a microprocessor, a microcontroller, a reduced instruction set circuit (RISC), an application specific integrated circuit (ASIC), a programmable logic circuit (PLC) and any other circuit or processor capable of performing the functions described herein. The above are examples only and are therefore in no way intended to limit the definition and/or meaning of the term "processor".

The memory 202 stores non-transitory computer-readable instructions for executing the techniques described herein. These instructions, when executed by the processor 201, cause the processor 201 to execute at least a portion of the methods described herein. That is, the instructions stored in the memory 202 configure the controller 108 to execute the methods described herein. In some embodiments, the memory 202 stores computer-readable instructions for providing a user interface to a user via the media output component 204 and receiving and processing input from the input device 206. Memory 202 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), electrically erasable programmable read-only memory (EEPROM), and non-volatile RAM (NVRAM). Although shown as being separate from processor 201, in some embodiments, memory 202 is combined with processor 201, such as in a microcontroller or microprocessor, but may still be mentioned separately. The above memory types are examples only and are therefore not limited to the types of memory that can be used to store a computer program.

The media output component 204 is configured to present information to a user (e.g., an operator of the system). The media output component 204 is any component capable of conveying information to a user. In some embodiments, the media output component 204 includes an output adapter, such as a video adapter and/or an audio adapter. The output adapter is operatively connected to the processor 201 and operatively connected to an output device, such as a display device (e.g., a liquid crystal display (LCD), a light emitting diode (LED) display, an organic light emitting diode (OLED) display, a cathode ray tube (CRT), an "electronic ink" display, one or more light emitting diodes (LEDs)) or an audio output device (e.g., a speaker or headphones).

The computing device 200 includes or is connected to an input device 206 for receiving input from a user. The input device 206 is any device that allows the computing device 200 to receive analog and/or digital commands, instructions, or other input from a user (including visual, auditory, tactile, button presses, stylus taps, etc.). The input device 206 may include, for example, a variable resistor, an input dial, a keyboard/keypad, a pointing device, a mouse, a stylus, a touch-sensitive panel (such as a touchpad or a touch screen), a gyro, an accelerometer, a position detector, an audio input device, or any combination thereof. A single component, such as a touch screen, can serve as both an output device and an input device 206 for the media output component 204 .

The communication interface 208 enables the computing device 200 to communicate with remote devices and systems (such as the motor 178 or the actuator 175, remote sensors, remote databases, remote computing devices, and the like) and may include one or more communication interfaces for interacting with one or more remote devices or systems. The communication interface may be a wired or wireless communication interface that allows the computing device 200 to communicate with remote devices and systems directly or via a network. The wireless communication interface may include a radio frequency (RF) transceiver, a Bluetooth® adapter, a Wi-Fi transceiver, a ZigBee® transceiver, a near field communication (NFC) transceiver, an infrared (IR) transceiver, and/or any other device and communication protocol for wireless communication. (Bluetooth is a registered trademark of the Bluetooth Special Interest Group of Kirkland, Washington; ZigBee is a registered trademark of the ZigBee Alliance of San Ramon, California). The wired communication interface may use any suitable wired communication protocol for direct communication, including but not limited to USB, RS232, I2C, SPI, analog, and proprietary I/O protocols. In some embodiments, the wired communication interface includes a wired network adapter that allows the computing device 200 to be coupled to a network (such as the Internet, a local area network (LAN), a wide area network (WAN), a mesh network, and/or any other network) to communicate with remote devices and systems via the network.

The computer systems discussed herein may include additional, fewer, or alternative functionality, including functionality discussed elsewhere herein. The computer systems discussed herein may include or be implemented by computer-executable instructions stored on a non-transitory computer-readable medium.

Non-transitory memory 202 stores instructions executed by processor 201 to configure controller 108 . According to an embodiment of the present invention, the controller 108 is configured to cause the translation device 160 to move the pole pair 129, 130 to adjust the position of one of the maximum Gaussian planes during the formation of a constant diameter portion of the silicon ingot according to the embodiments described above. . For example, the position of the maximum Gaussian plane can be adjusted in at least two stages of ingot growth, wherein the position of the maximum Gaussian plane in the second stage is a position lower than the position of the maximum Gaussian plane during the first stage. The controller 108 may be configured to maintain the position of the maximum Gaussian plane at the distance from the melt free surface in the embodiments described above in at least two stages (and optionally an intermediate stage). The controller 108 can be configured to maintain the position of the maximum Gaussian plane such that various lengths of the first and second stages described above can be achieved and the velocity of the magnet reduced in intermediate stages.

The controller 108 can be triggered to change the position of the magnetic poles during various stages of ingot growth (e.g., terminate the first stage and move to the intermediate stage or terminate the intermediate stage and move to the second stage) by the weight of the melt, the length of the ingot, or by timing control.

Compared with conventional methods and equipment for producing single crystal silicon, the methods and equipment of embodiments of the present invention have several advantages. The shape of the crystal-melt interface can be maintained relatively constant by moving the magnetic poles during growth of the HMCZ ingot. The magnet position can be controlled to reduce the crystal-melt interface height, which reduces changes in the axial gradient of v/G control during perfect silicon production, thereby increasing the perfect silicon window. The magnet position can be controlled to reduce seed-side oxygen. The crystal-melt interface can be maintained relatively constant regardless of the melt volume and the position of the crucible. Using higher MGP at the seed end can reduce seed end oxygen due to less oxygen being incorporated into the bulk. The ramp-down magnet position in the intermediate to late bulk drives the crystal-melt interface similar to the seed end portion of the crystal without affecting O _i . Therefore, the critical v/G increases at the intermediate to late bulk and a higher pull rate is used to produce perfect silicon, which increases productivity. Constant or less variation in axial v/G results in less quality loss and improved yield. Increasing the crystal-melt interface height (i.e., being more concave) results in increased pull speed and improved productivity. Oxygen control at the seed end results in flexible oxygen control at the seed end (higher O _i (negative MGP) or lower O _i (positive MGP) selected by the customer). Example

The procedure of the present invention is further illustrated by the following examples. These examples should not be considered limiting. Example 1 : Effect of MGP position on interface shape and ingot growth

As shown in Figure 6, in the case of short crystal growth length (i.e., larger melt volume), a positive MGP has a greater effect on the melt flow just below the melt free surface, while in the case of a negative MGP, the effect on the melt flow is toward the bottom of the crucible. This causes the flow velocity of the positive MGP to be relatively slower than that of the negative MGP, which means higher oxygen evaporation at the melt free surface. Since the strength of the magnetic field is similar at the crystal-melt interface, the crystal-melt interface will be similar.

With increasing crystal length, the flow velocity at the free surface of the melt is similar for both MGP conditions, and thus the dissolution and evaporation of oxygen are similar. However, the shape of the crystal-melt interface is different due to the different magnetic field directions and lines in the melt below the center.

The typical height of the crystal-melt interface varies with melt depth for both positive and negative MGPs, as shown in Figure 7. In the case of positive MGPs (i.e., the maximum Gaussian plane is located above the melt free surface), the crystal-melt interface is pushed into the growing crystal front at larger melt depths and the force used to push the interface gradually decreases as the melt volume decreases. Meanwhile, negative MGPs maintain a force used to push the crystal-melt interface regardless of melt volume, which achieves a relatively constant axial crystal-melt interface height regardless of melt depth.

Figure 8 shows a vertical slab and a lifetime contour plot of the measured crystal-melt interface. A short slab was taken at a specific crystal location and given a heat treatment to delineate the stripes of its solidification history. Next, the x-y coordinates of the image from the lifetime contour plot were generated. The height of the interface was directly inferred from the difference from the center to the edge of the contour plot.

The height of the crystal-melt interface as a function of MGP is plotted in Figure 9. As shown in Figure 9, in the case of negative MGP, the height of the crystal-melt interface is similar at both the seed end and the opposite end, thereby fixing one parameter for axial v/G perfect silicon control.

FIG10 shows an example of axial oxygen distribution at different MGP locations. The O _i difference between positive and negative MGPs is due to the magnetic field in the melt region and gradually decreases as the melt volume decreases. The low O _i of the positive MGP from the early body is caused by the magnetic field approaching the free surface of the melt, thereby enhancing evaporation. As shown in FIG10 , increasing the area ratio between the free melt surface and the wet surface of the crucible mitigates the effect of the MGP difference.

Figure 11 is a box plot of normalized _Oi at three different normalized MGP values. Figure 11 shows the increase of _Oi by decreasing the magnet position at three different conditions of melt volume. Group A contains _Oi data less than 9% from the solidified ingot, Group B contains _Oi data from 9% to 22% from the solidified ingot, and Group C contains _Oi data from 22% to 33.6% from the solidified ingot.

To achieve a lower O _i specification, a higher magnet position can be used for both O _i and interface height. However, as explained above, a lower magnet position can be used for better interface control. As shown in Figure 10, O _i in late bulk growth is insensitive to magnet position.

Figure 12 shows the effect of lowering the magnet position on defect distribution. Crystal defects change from vacancy-rich perfect silicon (Pv) to dislocation clusters (I defects). In addition, the radial defect pattern changes. The crystal center becomes vacancy dominated at the positive MGP. By lowering the magnet position, the dominant point defects at the crystal center change to interstitial dominated. This transition is caused by interface changes at a constant temperature at the crystal surface. The v/G at the crystal center increases and the crystal edge keeps the v/G the same as at the high MGP, so at the same pull rate under different MGP conditions, the defects in the crystal center are transformed to I defects.

As used herein, the terms "about," "substantially," "substantially," and "approximately" when used in conjunction with a range of size, concentration, temperature, or other physical or chemical property or characteristic, are meant to encompass variations that may exist in the upper and/or lower limits of the range of the property or characteristic, including variations resulting, for example, from rounding, measurement methods, or other statistical variations.

When introducing elements of the present invention or (several) embodiments thereof, the articles "a," "an," and "the" are intended to mean that there is one or more of the elements. The terms "comprising," "including," "containing," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms indicating a particular orientation (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require any particular orientation of the items being described.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matters contained in the above description and shown in the accompanying drawing(s) shall be interpreted as illustrative and not limiting. .

52: Maximum Gaussian plane 100: Ingot puller equipment 102: Crucible 104: Melt 105: Shaft 106: Support 107: Crucible drive unit 108: Controller 109: Crystal puller housing 110: Bottom insulation 111: Melt surface 112: Lifting mechanism 113: Silicon ingot 114: Pulling mechanism 118: Pulling cable 120: Seed holder/chuck 122: Silicon seed 124: Side insulation 125: Crystal-melt interface 126: Bottom heater 128: Bottom surface 129: Magnetic pole 130: Magnetic pole 131: Side wall 135: Side heater 142: Crown section 145: Constant diameter section/main body 151: Heat shield 152: Growth chamber 154: Cooling jacket 155: Iron shield 160: Translation device 163: Guide 170: Mounting seat 175: Actuator 178: Motor 200: Computing device 201: Processor 202: Memory 204: Media output unit 206: Input device 208: Communication interface A: Lifting axis/longitudinal axis

Figure 1 is a cross-section of a HMCZ ingot puller equipment before silicon ingot growth;

Figure 2 is a cross-section of the HMCZ ingot puller equipment in Figure 1 during the growth of silicon ingots;

FIG3 is a schematic diagram showing a magnetic field applied to a crucible containing a melt in a crystal growth apparatus;

FIG4 is an example of the MGP position distribution during the growth of HMCZ tablets;

FIG. 5 is a block diagram of an exemplary controller for use in the puller apparatus shown in FIG. 1 ;

FIG6 is a schematic diagram of a magnet and a silicon melt at two different crystal lengths and magnet positions;

Figure 7 is a graph showing normalized interface height as a function of percent solidification of the ingot;

FIG8 shows a vertical plate and a life contour plot of the measured crystal-melt interface;

Figure 9 shows the normalized height of the crystal-melt interface as a function of MGP at different crystal positions;

FIG. 10 shows the axial O _i distribution with two different MGP positions (normalized O _i = [O _i / lowest O _i ]);

Figure 11 is a box plot of normalized O _i at three different normalized MGP values; and

FIG. 12 is an example of a crystal defect pattern at three different magnet positions.

Corresponding element symbols indicate corresponding parts throughout the drawings.

100: Puller equipment

102:Crucible

104:Melt

105: Shafts

106: Seat

107: Crucible drive unit

108: Controller

109: Crystal puller housing

110: Bottom insulation

111: Melt surface

112:Improvement mechanism

114: Lifting mechanism

118: Pulling the cable

120: Seed holder/chuck

122:Silicon seed

124: Side insulation

126: Bottom heater

128: Bottom

129:Magnetic pole

130: Magnetic poles

131:Side wall

135: Side heater

151:Heat shielding

152: Growth Room

154: Cooling set

155: Iron shield

160: Translation device

163: Guide

170:Mounting base

175:Actuator

178:Motor

A: Lifting axis/longitudinal axis

Claims (36)

A method for producing a silicon ingot, the method comprising: melting polycrystalline silicon in a crucible enclosed in a growth chamber to form a melt having a melt free surface; generating a horizontal magnetic field in the growth chamber; bringing a seed crystal into contact with the melt; extracting the seed crystal from the melt to form the silicon ingot; and adjusting a position of a maximum Gaussian plane during formation of a constant diameter portion of the silicon ingot in at least two stages of ingot growth, the at least two stages comprising: a first stage corresponding to formation of the silicon ingot from formation of a constant diameter portion of the silicon ingot to an intermediate ingot length; and a second stage corresponding to the formation of the silicon ingot of a total length from at least the intermediate ingot length to the constant diameter portion; and wherein adjusting the position of the maximum Gaussian plane includes maintaining the position of the maximum Gaussian plane in the second stage at a position lower than the position of the maximum Gaussian plane during the first stage. The method of claim 1, wherein the at least two stages include an intermediate stage corresponding to the formation of the silicon ingot between the first stage and the second stage, wherein adjusting the position of the maximum Gaussian plane includes in the intermediate stage The position of the maximum Gaussian plane is reduced from the position in the first phase to the position in the second phase during the phase. As in the method of claim 1, the position of the maximum Gaussian plane is maintained above the free surface of the melt during the first stage. A method as claimed in claim 3, wherein the position of the maximum Gaussian plane is maintained below the free surface of the melt during the second stage. The method of claim 1, wherein during the first stage the position of the maximum Gaussian plane is maintained at a position at least 20 mm above the free surface of the melt. The method of claim 1, wherein during the second stage the position of the maximum Gaussian plane is maintained at a position at least 20 mm below the free surface of the melt. The method of claim 1, wherein the at least two stages include an intermediate stage corresponding to the formation of the silicon ingot between the first stage and the second stage, wherein adjusting the position of the maximum Gaussian plane includes in the intermediate stage The position of the maximum Gaussian plane is lowered from the position in the first stage to the position in the second stage during the phase, wherein the position of the maximum Gaussian plane is lowered below the melt during the intermediate phase. body free surface. The method of claim 1, wherein the at least two stages include an intermediate stage corresponding to the formation of the silicon ingot between the first stage and the second stage, wherein adjusting the position of the maximum Gaussian plane includes in the intermediate stage reducing the position of the maximum Gaussian plane from the position in the first stage to the position in the second stage during the stage, wherein the position of the maximum Gaussian plane is at no more than 50% of the constant diameter portion Lower by at least 40 mm. A method as claimed in claim 1, wherein the at least two stages include an intermediate stage corresponding to the formation of the silicon ingot between the first stage and the second stage, wherein adjusting the position of the maximum Gaussian plane includes lowering the position of the maximum Gaussian plane from the position in the first stage to the position in the second stage during the intermediate stage, wherein the position of the maximum Gaussian plane is lowered by at least 75 mm over no more than 50% of the constant diameter portion. A method as claimed in claim 1, wherein the at least two stages include an intermediate stage corresponding to the formation of the silicon ingot between the first stage and the second stage, wherein adjusting the position of the maximum Gaussian plane includes lowering the position of the maximum Gaussian plane from the position in the first stage to the position in the second stage during the intermediate stage, wherein the position of the maximum Gaussian plane is lowered by at least 100 mm over no more than 50% of the constant diameter portion. The method of claim 1, wherein the at least two stages include an intermediate stage corresponding to the formation of the silicon ingot between the first stage and the second stage, wherein adjusting the position of the maximum Gaussian plane includes in the intermediate stage reducing the position of the maximum Gaussian plane from the position in the first stage to the position in the second stage during the stage, wherein the position of the maximum Gaussian plane is at no more than 50% of the constant diameter portion Lower at least 150 mm. The method of claim 1, wherein a length of the first stage is at least 10% and less than 40% of the constant diameter portion. The method of claim 12, wherein the first stage begins at one of the constant diameter portions of the tablet. The method of claim 1, wherein a length of the second stage is at least 20% and less than 50% of the constant diameter portion. The method of claim 14, wherein the second stage extends to a total length of the constant diameter portion of the tablet. The method of claim 1, wherein the position of the maximum Gaussian plane is constant during the first phase. The method of claim 1, wherein the position of the maximum Gaussian plane changes during the first phase. The method of claim 1, wherein the position of the maximum Gaussian plane is constant during the second phase. A method as claimed in claim 1, wherein the position of the maximum Gaussian plane changes during the second phase. An ingot pulling device for manufacturing a single crystal silicon ingot. The ingot pulling device includes: a crucible for holding a silicon melt; an ingot puller housing defining a growth chamber for pulling a silicon ingot from the silicon melt, the crucible being disposed in the growth chamber; a pair of magnetic poles disposed radially outward from the crucible; and A translation device that moves the magnetic poles axially relative to the crucible. A puller device as claimed in claim 20, wherein the translation device includes: a guide member; and a mounting seat that enables each magnetic pole to move relative to the guide member. A puller apparatus as claimed in claim 21, wherein the guide member includes a rail and the mounting base connects each magnetic pole to the rail. The spindle pulling device of claim 21, which includes an actuator that moves the magnetic poles relative to the guide. The spindle pulling device of claim 23, wherein the actuator includes a pneumatic or hydraulic cylinder, a rack and pinion, a pulley or a gear train with a ball screw. A puller device as claimed in claim 23, which includes a motor for providing power to the actuator. The spindle pulling device of claim 20, which includes a controller including a processor and non-transitory memory storing instructions, the instructions being executed by the processor to configure the controller, the controller Configured to cause the translation device to move the magnetic pole pair to adjust a position of a maximum Gaussian plane during formation of a constant diameter portion of the silicon ingot during at least two stages of ingot growth, the at least two stages including: a first stage corresponding to the formation of the silicon ingot starting from the formation of the constant diameter portion of the silicon ingot up to an intermediate ingot length; and A second stage corresponding to the formation of the silicon ingot from at least the intermediate ingot length to a total ingot length. The spindle puller device of claim 26, wherein the controller is configured to maintain the position of the maximum Gaussian plane in the second phase at a position lower than the position of the maximum Gaussian plane during the first phase. . The puller apparatus of claim 27, wherein the controller is configured to maintain the position of the maximum Gaussian plane at least 20 mm above a melt free surface during the first stage. The puller apparatus of claim 27, wherein the controller is configured to maintain the position of the maximum Gaussian plane at least 20 mm below the melt free surface during the second stage. The ingot puller apparatus of claim 26, wherein the at least two stages include an intermediate stage corresponding to the formation of the silicon ingot between the first stage and the second stage, and wherein the controller is configured to The position of the maximum Gaussian plane is reduced from the position in the first phase to the position in the second phase during an intermediate phase, and wherein the controller is configured to reduce the maximum Gaussian plane during the intermediate phase lowered below the free surface of the melt. A puller apparatus as claimed in claim 26, wherein the at least two stages include an intermediate stage corresponding to the formation of the silicon ingot between the first stage and the second stage, wherein the controller is configured to lower the position of the maximum Gaussian plane from the position in the first stage to the position in the second stage during the intermediate stage, and wherein the controller is configured to lower the maximum Gaussian plane by at least 40 mm over no more than 60% of the constant diameter portion. The ingot puller apparatus of claim 26, wherein the at least two stages include an intermediate stage corresponding to the formation of the silicon ingot between the first stage and the second stage, and wherein the controller is configured to lowering the position of the maximum Gaussian plane from the position in the first phase to the position in the second phase during an intermediate phase, and wherein the controller is configured such that the maximum Gaussian plane is in the constant diameter portion It should be lowered by at least 75 mm by no more than 40%. The ingot puller apparatus of claim 26, wherein the at least two stages include an intermediate stage corresponding to the formation of the silicon ingot between the first stage and the second stage, and wherein the controller is configured to lowering the position of the maximum Gaussian plane from the position in the first phase to the position in the second phase during an intermediate phase, and wherein the controller is configured such that the maximum Gaussian plane is in the constant diameter portion It should be lowered by at least 100 mm by no more than 40%. The ingot puller apparatus of claim 26, wherein the at least two stages include an intermediate stage corresponding to the formation of the silicon ingot between the first stage and the second stage, and wherein the controller is configured to lowering the position of the maximum Gaussian plane from the position in the first phase to the position in the second phase during an intermediate phase, and wherein the controller is configured such that the maximum Gaussian plane is in the constant diameter portion It should be lowered by at least 150 mm by no more than 40%. The spindle puller device of claim 26, wherein the controller is configured to maintain a length of the first stage at least 10% and less than 50% of the constant diameter portion. A puller apparatus as claimed in claim 26, wherein the controller is configured so that a length of the second stage is maintained at least 20% and less than 50% of the constant diameter portion.