System and method for producing silicon using horizontal magnetic field

Abstract

A method for producing silicon ingot by a horizontal magnetic field Czochralski method comprises: rotating a crucible containing silicon melt; applying a horizontal magnetic field to the crucible; contacting the silicon melt with a seed crystal; and extracting the seed crystal from the silicon melt while rotating the crucible to form a silicon ingot. The crucible has a wettable surface and a cristobalite layer formed thereon.

Description

[0001] CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 947,785, filed on December 13, 2019, the entire disclosure of which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present disclosure relates generally to the production of silicon ingots, and more particularly, to methods and systems for achieving a high success rate in producing silicon ingots in a Czochralski process using a horizontal magnetic field. Background Art

[0004] During the 1990s, at least some high quality silicon growth was controlled primarily by the thermal conditions of the puller and more specifically the hot zone (HZ) design itself, as the ratio of pull rate to thermal gradient (v / G) was seen as the dominant factor. In the late 1990s, further consideration of the crystal / melt interface at the same v / G was included in the growth of at least some high quality silicon. At that time, high quality silicon did expand into memory devices as more customers transitioned from epitaxial silicon to polished silicon and from 200 mm silicon to 300 mm silicon. Soon after, it was determined that high quality silicon growth required very stable process growth conditions and controlled melt flow to achieve the specific crystal / melt needed to achieve the desired low crystal defectivity during growth.

[0005] At the periphery, the need for magnetic field application to stabilize the melt flow in the increasing melt volume was identified as a dominant feature as silicon crystal growth transitioned from 200 to 300 mm and the corresponding charge size increased to maintain productivity.

[0006] In the early 2000s, when high-quality 300mm silicon production began, several silicon manufacturers transitioned to the horizontal magnetic field Czochralski process (HMCZ) in order to effectively control the crystal / melt interface. Other silicon manufacturers use cusp magnetic fields for 300mm production of high-quality silicon. In both cases, the magnetic field in the silicon melt has a significant impact on crystal quality and performance, and each manufacturer develops its own technology to optimize performance and quality from the beginning.

[0007] During the process of producing single crystal silicon ingots using a CZ process and a magnetic field, oxygen can be introduced into the silicon crystal ingot through the melt-solid or melt-crystal interface. Oxygen can cause various defects in the wafers produced from the ingot, thereby reducing the yield of semiconductor devices manufactured using the ingot. For example, memory devices, insulated gate bipolar transistors (IGBTs), high quality radio frequency (RF), high resistivity silicon-on-insulator (HR-SOI), and charge trapping layer SOI (CTL-SOI) applications generally require low interstitial oxygen concentration (Oi) in order to achieve high resistivity. In the case of the HMCZ process, it is believed that the process generally requires very low crucible rotation (C / R) to control the oxygen in the growing crystal, especially to control the oxygen inclusion to the desired range suitable for memory devices. In addition, a higher incidence of missing zero dislocations (LZD) from the crown to the end of the body is found in the HMCZ compared to the process using a cusp magnetic field.

[0008]

[0006] Therefore, there is a need for methods and systems that reduce LZD losses using HMCZ growth and provide improved ZD success rates for high quality silicon growth from crown to body.

[0009] This background section is intended to introduce the reader to various aspects of the art that may be relevant to the various aspects of the present disclosure described and / or claimed below. It is believed that this discussion is helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Therefore, it should be understood that these statements should be read in this sense and not as an admission of prior art. Summary of the invention

[0010] In one aspect of the present disclosure, a method for producing a silicon ingot by a horizontal magnetic field Czochralski method includes: rotating a crucible containing a silicon melt; applying a horizontal magnetic field to the crucible; contacting the silicon melt with a seed crystal; and extracting the seed crystal from the silicon melt while rotating the crucible to form a silicon ingot. The crucible has a wettable surface and a cristobalite layer formed thereon.

[0011] Another aspect is a wafer produced from a silicon ingot produced using the method described above.

[0012] Another aspect is a system for producing silicon ingots. The system includes a controller configured to produce silicon ingots according to the method described above.

[0013] There are various improvements to the features mentioned with respect to the above aspects. Further features may also be incorporated into the above aspects. These improvements 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 aspects independently or in any combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1is a top view of a crucible according to an embodiment.

[0015] Figure 2 yes Figure 1 Side view of the crucible shown in .

[0016] Figure 3 is a schematic diagram illustrating a horizontal magnetic field applied to a crucible containing a melt in a crystal growing apparatus.

[0017] Figure 4 is a block diagram of a crystal growth system.

[0018] Figure 5 The temperature field in the melt-free surface through the MGP in mm and the crucible rotation in RPM are presented.

[0019] Figure 6 is a graph showing the crystallization rate as a function of time.

[0020] Figure 7 It is a graph showing the thickness of the formed layer as a function of time at a temperature of 1360°C.

[0021] Figure 8 It is a contour plot of the ZD success rate by crucible rotation and the amount of melt modifier in the natural sand crucible.

[0022] Like reference symbols in the various drawings indicate like elements. DETAILED DESCRIPTION

[0023] First reference Figure 1 and 2 , a crucible of one embodiment is generally indicated at 10. A cylindrical coordinate system for the crucible 10 includes a radial direction R12, an angular direction θ14, and an axial direction Z16. The crucible 10 contains a melt 25 having a melt surface 36. A crystal 27 is grown from the melt 25. The melt 25 may contain one or more convection cells 17, 18 induced by heating of the crucible 10 and rotation of the crucible 10 and / or the crystal 27 in the angular direction θ14. The structure and interaction of the one or more convection cells 17, 18 are modulated via adjustment of one or more process parameters and / or application of a magnetic field, as described in detail herein below.

[0024] Figure 31 is a diagram illustrating a horizontal magnetic field applied to a crucible 10 containing a melt 25 in a crystal growth apparatus. As shown, the crucible 10 contains a silicon melt 25 from which a crystal 27 is grown. The transition between the melt and the crystal is generally referred to as a crystal-melt interface (alternatively, a melt-crystal, solid-melt or melt-solid interface) and is generally nonlinear, for example, concave, convex or gull-wing relative to the melt surface. Two magnetic poles 29 are placed opposite to each other to produce a magnetic field that is generally perpendicular to the crystal growth direction and generally parallel to the melt surface 36. The magnetic poles 29 can be conventional electromagnets, superconductor electromagnets, or any other suitable magnets for producing a horizontal magnetic field with a desired strength. The application of a horizontal magnetic field results in a Lorentz force in the axial direction (in the direction opposite to the fluid motion), which is a reaction force that drives the convection of the melt. Therefore, convection in the melt is 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 from melt convection in the crucible decreases.The horizontal configuration has the advantage of effectively suppressing convection at the melt surface 36.

[0025] Figure 4 1 is a block diagram of a crystal growth system 100. The system 100 employs the Czakowski crystal growth method to produce semiconductor ingots. In this embodiment, the system 100 is configured to produce cylindrical semiconductor ingots having an ingot diameter of one hundred fifty millimeters (150 mm), greater than one hundred fifty millimeters (150 mm), more specifically in the range from approximately 150 mm to 460 mm, and even more specifically, approximately three hundred millimeters (300 mm). In other embodiments, the system 100 is configured to produce semiconductor ingots having a two hundred millimeter (200 mm) ingot diameter or a four hundred fifty millimeter (450 mm) ingot diameter. Additionally, in one embodiment, the system 100 is configured to produce semiconductor ingots having a total ingot length of at least nine hundred millimeters (900 mm). In some embodiments, the system is configured to produce semiconductor ingots having a length of one thousand nine hundred fifty millimeters (1950 mm), two thousand two hundred fifty millimeters (2250 mm), two thousand three hundred fifty millimeters (2350 mm), or longer than 2350 mm. In other embodiments, the system 100 is configured to produce semiconductor ingots having a total ingot length in a range from approximately nine hundred millimeters (900 mm) to one thousand two hundred millimeters (1200 mm), between approximately 900 mm to approximately two thousand millimeters (2000 mm), or between approximately 900 mm to approximately two thousand five hundred millimeters (2500 mm). In some embodiments, the system is configured to produce semiconductor ingots having a total ingot length greater than 2000 mm.

[0026] The crystal growth system 100 includes a vacuum chamber 101 enclosing a crucible 10. Side heaters 105 (e.g., resistive heaters) surround the crucible 10. A bottom heater 106 (e.g., resistive heater) is positioned below the crucible 10. During heating and crystal pulling, a crucible drive unit 107 (e.g., 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. Within the crucible 10 is a silicon melt 25 having a melt level or melt surface 36. In operation, the system 100 pulls a single crystal 27 from the melt 25 starting with a seed crystal 115 attached to a pulling shaft or cable 117. One end of the pulling shaft or cable 117 is connected by a pulley (not shown) or a drum (not shown) or any other suitable type of lifting mechanism (e.g., a shaft), and the other end is connected to a chuck (not shown) that holds the seed crystal 115 and the crystal 27 grown from the seed crystal 115.

[0027] The crucible 10 and the single crystal 27 have a common axis of symmetry 38. The crucible drive unit 107 can raise the crucible 10 along the axis 38 to maintain the melt level 36 at a desired height when the melt 25 is depleted. The crystal drive unit 121 similarly rotates the pull shaft or cable 117 in a direction 110 opposite to the direction in which the crucible drive unit 107 rotates the crucible 10 (e.g., counter-rotation). In an embodiment using isotropic rotation, the crystal drive unit 121 can rotate the pull shaft or cable 117 in the same direction in which the crucible drive unit 107 rotates the crucible 10 (e.g., in a clockwise direction). Isotropic rotation can also be referred to as co-rotation. In addition, the crystal drive unit 121 raises and lowers the crystal 27 relative to the melt level 36 as needed during the growth process.

[0028] According to the Czakowski single crystal growth process, a certain amount of polycrystalline silicon (polysilicon) is loaded into the crucible 10. The heater power supply 123 supplies power to the resistance heaters 105 and 106, and the insulation 125 lines the inner wall of the vacuum chamber 101. When the vacuum pump 131 removes the gas from the vacuum chamber 101, the gas supply 127 (e.g., a bottle) feeds argon gas to the vacuum chamber 101 via the gas flow controller 129. The outer chamber 133, which is fed with cold water from the water tank 135, surrounds the vacuum chamber 101.

[0029] Then, the cold water is drawn to the cold water return manifold 137. Generally, a temperature sensor such as a photoelectric tube 139 (or pyrometer) measures the temperature of the melt 25 at its surface, and a diameter sensor 141 measures the diameter of the single crystal 27. In this embodiment, the system 100 does not include an upper heater. The presence or absence of an upper heater alters the cooling characteristics of the crystal 27.

[0030] The magnetic pole 29 is positioned outside the vacuum chamber 101 to generate a horizontal magnetic field ( Figure 3 15). Although illustrated as being approximately centered on the melt surface 36, the position of the pole 29 relative to the melt surface 36 can be varied to adjust the position of the maximum Gauss plane (MGP) relative to the melt surface 36. A water trough 153 provides cold water to the pole 29 before being drawn through the cold water return manifold 137. A ferrous shield 155 surrounds the pole 29 to reduce stray magnetic fields and enhance the strength of the generated field.

[0031] The control unit 143 is used to adjust a plurality of process parameters, including but not limited to at least one of the crystal rotation rate, the crucible rotation rate, and the magnetic field strength. In various embodiments, the control unit 143 may include a memory 173 and a processor 144 that processes signals received from various sensors of the system 100 (including but not limited to the photoelectric tube 139 and the diameter sensor 141) and controls one or more devices of the system 100 (including but not limited to the crucible drive unit 107, the crystal drive unit 121, the heater power supply 123, the vacuum pump 131, the gas flow controller 129 (e.g., an argon gas flow controller), the pole power supply 149, and any combination thereof). The memory 173 may store instructions that, when executed by the processor 144, cause the processor to perform one or more 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.

[0032] 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 a memory. However, any processor in a computer system mentioned herein may also refer to one or more processors, wherein the processor may be in one computing device or multiple computing devices acting in parallel. In addition, any memory in a computer device mentioned herein may also refer to one or more memories, wherein the memory may be in one computing device or multiple computing devices acting in parallel. In addition, the computer system may be located near the system 100 (e.g., in the same room, or in an adjacent room), or may be remotely located and coupled to the rest of the system via a network (e.g., Ethernet, the Internet, or the like).

[0033] 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 logic circuit, and any other circuit or processor capable of performing the functions described herein. The above are merely examples, and thus, it is not intended to limit the definition and / or meaning of the term "processor" in any way. The memory may include, but is not limited to, a random access memory (RAM) such as a dynamic RAM (DRAM) or a static RAM (SRAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), and a non-volatile RAM (NVRAM).

[0034] In one embodiment, a computer program is provided to enable the control unit 143, and this program is 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 system is executed on a single computer system. Alternatively, the computer system may include multiple computer systems, a connection to a server computer, a cloud computing environment, or the like. In some embodiments, the computer system includes multiple components distributed among multiple computing devices. One or more components may be in the form of computer executable instructions embodied in a computer readable medium.

[0035] The computer systems and processes are not limited to the specific embodiments described herein. In addition, each component of the computer system and each process can be practiced independently and separately from other components and processes described herein. Each component and process can also be used in combination with other assembly packages and processes.

[0036] 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 control 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 gas flow controller), pole power supply 149, and any combination thereof, as described herein and in Figure 4 A computer system performs all steps for controlling one or more devices of system 100 as described herein.

[0037] Typically, the losses (quantified by the LZD rate) of the zero dislocation (ZD) structure during Cz growth (HMCZ) of silicon crystals in a horizontal magnetic field are higher than those in growth in a cusp (or vertical) magnetic field. However, if the crystal is grown in a synthetic lined crucible, the LZD rate in the HMCZ can be significantly reduced compared to a natural sand lined crucible. But while the ZD rate is better, the cost of synthetic lined crucibles is higher than that of natural sand. In addition, the thin (approximately 2 mm thickness) synthetic liners dissolve in a relatively short process time, leaving the back sand layer exposed to the melt, which allows quartz particles to enter the melt and impact the growing crystal. Therefore, the exposure of bubbles in the liner or even from the back sand into the melt is higher. In order to avoid bubble exposure and / or dissolution contamination of the back sand when using synthetic lined crucibles, the process thermal hours are typically limited to less than about 250 hours, which is much shorter than the process time achievable with natural sand crucibles (approximately 400 to 500 hours or more). Since the thermal time of crystal growth depends on process conditions, HZ configuration and attempts, the use of synthetic lined crucibles can affect the rechargeability of each batch and multi-rod growth. Therefore, silicon growth in synthetic lined crucibles using HMCZ generally requires optimization of crucible conditions to ensure the best ZD rate and minimum attempts so that maximum rechargeability can be achieved.

[0038] In addition, horizontal magnets in Cz growth enhance melt flow using irregular velocity melt waves that continuously strike the crucible wall surface with strong force in an instantaneous manner. In this case, the crucible surface conditions are very critical for quartz piece production, which is directly related to ZD success. Figure 5 It is shown in Figure 1 that the melt flow and the temperature field of the melt are significantly affected by the magnetic field strength and the MGP position. As shown in the figure, the temperature change in the circumferential direction at the melt surface changes significantly with the magnetic field direction.

[0039] These and other difficulties can be overcome or alleviated in embodiments of the present disclosure by using one or both of the two techniques described in detail below. Generally speaking, in a first aspect, a cristobalite layer is formed on a wettable surface on the interior of a crucible. A wettable surface generally refers to a surface of a crucible that can come into contact with the melt during silicon production. The wettable surface generally includes an inner bottom of the crucible, at least a portion of an inner sidewall of the crucible, and an inner portion connecting the inner sidewall to the bottom of the crucible. Figure 2 In , the wettable surface is the entire interior surface of the crucible 10 below and including the melt surface 36. The wettable surface may also extend above the melt surface 36. A second technique described in this disclosure is to increase the rotation speed of the crucible.

[0040] In general, strong and unstable melt flow is induced by the HMCZ magnetic field and this can generate strong thermo-mechanical stresses and mechanical shocks on the crucible wall, causing quartz particle generation. However, high crucible rotation (C / R) will generate faster convection near the crucible wall surface (which can interface with the melt flow driven by the magnetic field). This will reduce the stress and shocks on the wall surface. Therefore, the generation of quartz particles at the wall surface is reduced, which in turn reduces LZD during crystal growth.

[0041] It is also possible to form a substantially uniform crystalline SiO 2 The LZD is reduced by forming a layer of amorphous quartz (called the cristobalite layer). This layer is more stable and stronger than amorphous quartz itself, and thereby it is more resistant to attack by the melt through stress or mechanical shock. Thus, the cristobalite layer reduces quartz grain generation.

[0042] There are at least two methods for promoting the growth of crystalline layers on a quartz crucible. The first method is to use a pre-coated crucible pre-coated with a compound such as BaOH, which will promote cristobalite growth, and the other method is to add a suitable melt modifier (MM) to the melt prior to crystal growth. Non-limiting examples of suitable MMs include barium (Ba) and strontium (Sr). More specifically, non-limiting examples of suitable MMs include barium carbonate (BaCO 3 ), barium oxide (BaO) and strontium carbonate (SrCO 3 ).

[0043] The formation of quartz on the wall of amorphous quartz lining is affected by pressure, Oi concentration, H 2 O and hydrogen content and similar controls. Figure 6 and 7 It is shown in Figure 5 that the formation and growth of the crystalline layer on the crucible wall is controlled by the temperature of the crucible wall and the concentration of MM consumed by the crucible. Figure 6 Comparison of No MM and 8% Al 2 O 3 Time-dependent crystallization rate of MM. Figure 7 Comparison No MM, 8% Al 2 O 3Thickness of the formed layer of MM and barium-based MM as a function of time at a temperature of 1360°C. These graphs indicate that appropriate MM addition (e.g., barium-based MM) or pre-coating of barium compounds into the melt produces a uniform and thick crystalline (i.e., cristobalite) layer on the wall of a natural sand crucible, giving similar behavior and performance to a synthetic lined crucible. Since the cristobalite layer has a slower dissolution rate than fused quartz, the generation of quartz pieces by thermal or mechanical stresses is reduced, and thus the subsequent reduction of crystalline LZD occurrence. In addition, due to the difference in material properties, the generation of secondary bubbles in the bubble-free layer (BFL) of a natural sand crucible and their propagation into the melt are generally much less than those of a synthetic lined crucible.

[0044] A uniform cristobalite layer is formed and grown during the stabilization mode, starting before crystal growth (i.e., after or during melting of the polysilicon) by pre-coating on the crucible or by post-addition of the melt modifier to the melt. In the case of post-MM addition, the MM is introduced after meltdown, so the rate of formation of cristobalite is slower than with pre-coating in other ways. However, post-MM addition can produce lower cavitation (APK) losses because bubbles formed and trapped at the crucible wall can be released to the surface before a stable cristobalite layer is formed. Since it usually takes 3 to 7 hours from the start of the stabilization step to the start of bulk growth, it is estimated that the cristobalite thickness is greater than about 2 mm, with an appropriate amount of MM added to increase the rate of formation of cristobalite. In practice, a cristobalite layer of less than about 1.0 mm is usually formed on the surface of the crucible (natural sand or synthetic). A special case (such as a heavily doped process for P++ or N++) produces a thicker cristobalite layer by adding a large amount of MM. In such cases, a cristobalite layer of approximately 1.0 mm (+ / -) is formed. These thicknesses differ from 2.0 mm because, although the cristobalite layer grows with thermal time, e.g. Figure 7 , but the wet cristobalite layer is continuously dissolved into the melt. Other embodiments include a cristobalite layer of approximately 2.0 mm, greater than 1.5 mm, greater than 1.0 mm, greater than 0.75 mm, greater than 0.5 mm, or greater than 0.25 mm formed on the wettable surface of the crucible. In some embodiments, the cristobalite layer is less than 3.0 mm thick, less than 2.0 mm thick, less than 1.25 mm thick, or less than 1.0 mm thick. In some embodiments, the cristobalite layer falls within the range defined by the minimum and maximum values ​​above, such as between 0.25 mm and 1.25 mm. In general, a cristobalite layer that is too thin may not be sufficient to provide the benefits described herein, while a cristobalite layer that is too thick may be more likely to break during silicon production and enter the melt (potentially contributing to LZD).

[0045] The addition of the melt modifier described above forms a uniform crystalline layer at the wettable surface of the crucible and this crystalline structure has a strong resistance to the thermomechanical stress induced by the irregular (transient) melt flow generated during HMCZ. The formation of thick and uniform cristobalite can resist the stress and impact from the melt flow, thereby reducing the crucible surface damage (i.e., resistance to damage that produces quartz particles in the melt), which will increase ZD success.

[0046] As mentioned previously, the strong convection caused by the higher quartz rotation will reduce the temperature variation in the melt-free surface and reduce the melt flow induced by the horizontal magnet, as in Figure 5 6 in . In case 6, the C / R is 1.6 RPM compared to 0.6 RPM in cases 1 to 5 and 7. In other words, the force generated by the magnetic field from the melt to the crucible wall surface is reduced or blocked by the convection associated with the higher crucible rotation. Thereby, the possibility of quartz pieces being generated due to damage to the crucible wall surface is reduced, thereby also improving the potential for ZD success.

[0047] To understand ZD success, test conditions varying in crucible rotation speed and melt modifier addition were performed in a horizontal magnet for both synthetic lined crucibles and natural sand crucibles. Synthetic crucibles showed high ZD success rates across a wide range of crucible rotation and MM. For natural sand lined crucibles, a total of 96 experiments using 19 different conditions were completed and the results were compared using the 96 experiments. Figure 8 The contour plot in summarizes the results. Figure 8 The data is from approximately 200mm body length to the approximate OE of the crystal. Figure 8 In , CR is the crucible rotation in RPM, 0.0% success_3 is a ZD failure (LZD), and 1.0% success_3 is 100% ZD success. The sign of the crucible rotation indicates the direction of rotation of the crucible. For some pulls, the crucible rotation was tilted between speeds during part of the pull, an arbitrary value of the crucible rotation was chosen for plotting, and data was collected from a body length of greater than 1000 mm to the approximate OE of the crystal. The results clearly show that as the absolute value of the speed of the crucible rotation and the amount of melt modifier (in this case, Ba-based) increase, higher ZD success rates are achieved.

[0048] The use of increased speed of crucible rotation and the generation of a cristobalite layer are shown to individually and in combination lead to improved ZD results. At lower C / Rs (e.g., between about 0 to about 2 RPM), it is necessary to add suitable MMs (or use a pre-coated crucible) to increase the ZD success rate. When the C / R is increased to between about 2 RPM to about 5 RPM, the amount of MMs required to obtain an equivalent success rate is reduced and may even be zero MMs. Within this range, additional gains in ZD success rate can be obtained by using at least some MMs. When the C / R exceeds about 5 RPM, there are generally no ZD issues from the crucible and MMs may not be needed. However, at such speeds, additional process conditions may be required to control the quality of the product because it may have other problems, such as oxygen control due to melt flow rate, melt level control caused by centrifugal forces, and the like.

[0049] Therefore, some embodiments of the present disclosure use more than 1.7 grams of MM per square meter of wettable surface area of ​​the crucible at any C / R rate during the HMCZ process to improve the ZD success rate. In some embodiments, 1.7 grams / m2 of wettable surface area of ​​the crucible is used. 2 To 2.0 g / m 2 In yet other embodiments, 1.7 g / m 2 of the wettable surface of the crucible is used. 2 To 5.4 g / m 2 In yet other embodiments, a crucible wettable surface of greater than 5.4 g / m 2 MM, but a large amount of MM can cause LZD during multiple recharge processes. 2 ) is based on BaCO 3 As MM, BaO or SrCO 3 A similar embodiment comprises a functionally equivalent BaCO 3 A certain amount of a specific MM.

[0050] Some embodiments use a range of about 0 to 0.5 g / m 2 MM between 0.1% and crucible rotation greater than about 2.0RPM. In some such embodiments, the crucible is a natural sand crucible. Alternatively, the crucible may be a synthetic crucible.

[0051] Embodiments of the methods described herein achieve superior results compared to previous methods and systems.For example, the methods described herein facilitate the production of silicon with a higher ZD success rate than some other methods.

[0052] When introducing elements of the present invention or embodiments of the present invention, the articles "a," "an," and "the," are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0053] Approximate language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that may be permissibly varied without resulting in a change in the basic function to which it is related. Thus, a value modified by a term or terms such as "about," "approximately," and "substantially" is not limited to the precise value specified. In at least some examples, approximate language may correspond to the precision of an instrument used to measure a value. Here and throughout the specification and claims, range limitations may be combined and / or interchanged; such ranges are identified and include all subranges contained therein unless context or language indicates otherwise.

[0054] 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

1. A method for producing silicon ingot, the method comprising: A natural sand crucible for rotating a silicon melt, the crucible having an inner wall and a cristobalite layer formed thereon at more than two revolutions per minute, the cristobalite layer having a thickness between 0.25 mm and 1.25 mm; applying a horizontal magnetic field to the crucible; contacting the silicon melt with a seed crystal; and The seed crystal is extracted from the silicon melt while rotating the crucible between two revolutions per minute and five revolutions per minute to form the silicon ingot.

2. The method according to claim 1, wherein the method further comprises: adding solid polycrystalline silicon to the natural sand crucible; and The polycrystalline silicon is heated to form the silicon melt.

3. The method of claim 2, further comprising adding a melt modifier to the natural sand crucible to form the cristobalite layer on the inner wall of the natural sand crucible.

4. The method of claim 3, wherein adding the melt modifier comprises: The melt modifier is added while the polycrystalline silicon is heated to form the silicon melt.

5. The method of claim 3, wherein adding the melt modifier comprises: The melt modifier is added after the silicon melt is formed.

6. The method of claim 3, wherein adding the melt modifier comprises adding barium carbonate (BaCO3).

7. The method of claim 6, wherein adding barium carbonate comprises adding more than 1.7 grams per square meter of the inner wall of the natural sand crucible.

8. The method of claim 3, wherein adding the melt modifier comprises: Strontium carbonate (SrCO3) was added.

9. The method of claim 8, wherein adding strontium carbonate comprises: Strontium carbonate was added in an amount functionally equivalent to 1.7 grams of barium carbonate per square meter of the inner wall of the natural sand crucible.

10. The method of claim 2, wherein adding solid phase polycrystalline silicon to the natural sand crucible comprises: Solid-phase polycrystalline silicon is added to the natural sand crucible having the barium-based coating layer formed on the inner wall of the natural sand crucible.

11. A wafer from a silicon ingot produced according to the method of any one of the preceding claims.

12. A system for producing silicon ingots, the system comprising a controller configured to produce silicon ingots according to the method of any one of claims 1 to 10.

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