System and method for forming single crystal silicon ingot with crucible having synthetic liner

Abstract

A method for producing a single crystal silicon ingot from a silicon melt includes disposing a crucible within an interior chamber of an ingot lifter, the crucible including an interior surface and a synthetic liner on the interior surface. The method further includes adding an initial feed of polycrystalline silicon to the crucible, melting the initial feed of polycrystalline silicon to form the silicon melt in the crucible, and dissolving a melt modifier into the silicon melt to devitrify the synthetic liner and to form a crystalline layer on the crucible. The crystalline layer has a thickness of less than 700 microns. The method further includes pulling a monocrystalline silicon ingot from the silicon melt.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 369,786, filed on July 29, 2022, the entire disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The art relates to systems and methods for forming single crystal ingots with crucibles having synthetic linings, and in particular, the art relates to systems and methods for forming single crystal silicon ingots by a Czochralski or continuous Czochralski process, wherein the synthetic liner is combined with a melt modifier to promote devitrification of the liner. Background Art

[0004] Single crystal silicon, which is the starting material for most manufacturing processes of many electronic components, such as semiconductor devices and solar cells, is typically prepared by the Czochralski (CZ) or continuous Czochralski (CCZ) methods. In these methods, polycrystalline source material, such as polycrystalline silicon ("polysilicon"), in the form of a solid feedstock material is fed into a quartz crucible and melted, a single seed crystal is contacted or melted with the molten silicon, and a single crystal silicon ingot is grown by slow extraction.

[0005] A quartz crucible includes an inner surface defining a cavity for receiving a melt. Some crucibles include a glass silicon liner having a coating applied to the inner surface. Such a liner may be designed to undergo a devitrification process at high temperatures, which causes the liner to crystallize, becoming cristobalite rather than glass silica and causing a crystalline layer to form on the crucible. Devitrification of the liner provides enhanced hardness to the heated crucible sidewalls and reduces reactions between the melt and the crucible that can induce vibrations in the silicon melt and negatively affect the resulting ingot. Synthetic silica or natural silica liners may be used.

[0006] Synthetic silica linings have the advantage of containing lower impurities than natural silica linings, thereby reducing the possibility of contaminating the melt. However, one problem with synthetic linings in crucibles is that the devitrification process results in random nucleation on the synthetic lining, and as these nuclei grow, the resulting devitrification is also random. This causes the surface presented to the melt to be a mixed structure with glassy and crystalline properties. Due to the mixed surface, synthetic lined crucibles without other modifications must be operated in short time intervals to limit the length of exposure to the melt, also known as "hot time". In addition, without modification, the resulting crystalline layer has an increased surface roughness, which causes increased bubble nucleation in the melt, which may damage the ingot.

[0007] Devitrification agents or nucleating agents (terms used interchangeably herein) such as palladium (Ba), calcium (Ca) or strontium (Sr) may be applied to the synthetic liner to promote devitrification of the synthetic liner. However, once nucleated by such agents, devitrification of the liner proceeds much faster relative to the natural liner and results in an increase in the thickness of the crystalline layer. For example, for the same concentration of nucleating agent, some such crystalline layers produced from synthetic liners coated with nucleating agents have a thickness increased by 5 times or more relative to the natural liner. As an example, a typical devitrified synthetic liner on a crucible has a thickness of about 2 millimeters (mm).

[0008] The increased thickness of the synthetic devitrified liner relative to the natural liner reduces the structural stability of the devitrified layer during use. For example, during ingot growth, the devitrified layer is thermally cycled over a large temperature range from about 1100°C to about 1500°C to produce temperature differences at different sections along the thickness of the liner and induce strain in the liner. If the strain becomes large enough, thermal spalling occurs and portions of the liner break into the melt to provide a potential source of particles in the melt and may cause defects in the ingot. In addition, because the synthetic liner is thicker than the natural liner, it will drift toward and contact the meniscus of the growing ingot before melting. If the unmelted portion of the liner contacts the meniscus, the loss of the zero dislocation structure and the single crystal dislocation and resulting in polycrystalline material will result, making the crystal inoperable for device applications.

[0009] This section is intended to introduce the reader to various aspects of the technology that may be related to the various aspects of the present disclosure that will be 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 the various aspects of the present disclosure. Therefore, it should be understood that these statements should be interpreted in this light and should not be interpreted as any admission of prior art. Summary of the invention

[0010] One aspect of the present disclosure relates to a method for producing a single crystal silicon ingot from a silicon melt held in a crucible positioned within an ingot puller apparatus. The method includes positioning a crucible within an inner chamber of an ingot puller, the crucible including an inner surface and a synthetic lining on the inner surface. The method further includes adding an initial charge of polycrystalline silicon to the crucible, melting the initial charge of polycrystalline silicon so that the silicon melt is formed in the crucible, and dissolving a melt modifier into the silicon melt so that the synthetic lining is devitrified and a crystalline layer is formed on the crucible. The crystalline layer has a thickness of less than 700 microns. The method further includes pulling a single crystal silicon ingot from the silicon melt.

[0011] Another aspect of the present disclosure relates to a crucible for use with an ingot puller apparatus. The crucible includes a body having an inner surface and an opposite outer surface and a synthetic lining disposed on the inner surface of the body. The synthetic lining has a composition that devitrifies when exposed to a silicon melt to cause a crystalline layer to form on the crucible during a crystal growth operation. The crystalline layer has a thickness of less than 700 microns.

[0012] Another aspect of the present disclosure relates to a method for producing a single crystal silicon ingot from a silicon melt held in a crucible positioned within an ingot puller apparatus. The method includes disposing the crucible within an inner chamber of the ingot puller, the crucible including an inner surface and a synthetic lining on the inner surface. The method further includes adding an initial charge of polycrystalline silicon to the crucible and adding a melt modifier precursor to the crucible. The method further includes melting the initial charge of polycrystalline silicon so that the silicon melt is formed in the crucible and dissolving the melt modifier precursor in the silicon melt to release a concentration of melt modifier into the silicon melt. The concentration of melt modifier causes the synthetic lining to devitrify and a crystalline layer to form on the crucible. The crystalline layer has a thickness of less than 700 microns.

[0013] There are various improvements with respect to the features mentioned in the above aspects. Further features may also be incorporated into the above aspects. These improvements and additional features may exist independently or in any combination. For example, various features discussed below with respect to any of the illustrated embodiments may be incorporated into any of the above aspects independently or in any combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic diagram of a pulling apparatus for forming a single crystal silicon ingot;

[0015] Figure 2 It has a melt inside Figure 1 A schematic cross-sectional view of the crucible of the pulling apparatus shown in FIG.

[0016] Figure 3 yes Figure 2 Schematic cross-sectional view of region A of the crucible shown in , which shows the lining of the crucible before devitrification;

[0017] Figure 4 yes Figure 3 A schematic cross-sectional view of the region of the crucible shown in FIG. Figure 3 The crystalline layer formed on the crucible due to the devitrification of the lining shown in FIG.

[0018] Figure 5 The results of surface roughness tests of a first lined crucible sample immersed in a controlled silicon melt and a second lined crucible sample immersed in a doped silicon melt are shown;

[0019] Figure 6 showing microscope images taken of the first and second lined crucible samples after immersion in respective melts; and

[0020] Figure 7 is a flow chart of a method for producing a single crystal silicon ingot from a silicon melt held within a crucible positioned within an ingot puller apparatus.

[0021] Corresponding reference characters indicate corresponding parts throughout the several views. DETAILED DESCRIPTION

[0022] refer to Figure 1 , an ingot pulling apparatus or ingot puller is schematically shown and generally indicated by reference numeral 100. The ingot puller 100 is used to produce a monocrystalline (i.e., single crystal) ingot of semiconductor or solar grade material, such as, for example, a monocrystalline silicon ingot. An example ingot is grown by a so-called Czochralski (CZ) process, in which the ingot is removed from a silicon melt 102 held within a crucible 104 of the crystal puller 100. The ingot may also be grown by a batch CZ process, in which polycrystalline silicon is fed to the crucible 104 in an amount sufficient to grow one ingot, such that the crucible 104 is substantially depleted of the silicon melt 102 after growing one ingot. In other embodiments, the ingot may be grown by a continuous CZ (CCZ) process, in which polycrystalline silicon is continuously or periodically added to the crucible 104 to replenish the silicon melt 102 during the growth process. The CCZ process facilitates the growth of multiple ingots pulled from a single crucible 104.

[0023] The ingot puller 100 includes a housing 106 defining a crystal growth chamber 108 and a pulling chamber 110 having a smaller lateral dimension than the growth chamber 108. The growth chamber 108 has a generally dome-shaped upper wall 112 that transitions from the growth chamber 108 to the narrow pulling chamber 110. The ingot puller 100 includes an inlet port 114 and an outlet port 116 that can be used to introduce process gases into and remove process gases from the housing 106 during crystal growth.

[0024] A crucible 104 within the ingot puller 100 contains a silicon melt 102 from which a silicon ingot is drawn. The crucible 104 is suitably made of quartz or fused silica, which has a high degree of thermal stability and is substantially non-reactive with the molten silicon in the melt 102, although some slow dissolution of the crucible into the melt may occur. The crucible 104 may alternatively be made of other materials besides quartz. For example, the quartz crucible 104 may be made of a composite material including silica and an additional material such as silicon nitride or silicon carbide. For example, in some applications such as solar grade wafers or multicrystalline ingots, a crucible formed of such a composite material may be used.

[0025] The silicon melt 102 is obtained by melting polycrystalline silicon fed into the crucible 104. A feeding system (not shown) is used to feed solid feedstock material into the crucible assembly 104 and / or the melt 102. The crucible 104 is positioned within and supported by a susceptor 118, which in turn is supported by a rotatable shaft 120. The susceptor 118 and the rotatable shaft 120 facilitate rotation of the crucible 104 about the central longitudinal axis X of the ingot puller 100.

[0026] A heating system 122 (e.g., a resistive heater 122) surrounds the susceptor 118 and the crucible 104 and supplies heat for melting the silicon feed material to produce the melt 102 and / or maintaining the melt 102 in a molten state by conduction through the susceptor 118 and the crucible 104. The heater 122 may also extend below the susceptor 118 and the crucible 104. The heater 122 is controlled by a control system (not shown) so that the temperature of the melt 102 is precisely controlled during the entire pulling process. For example, the controller may control the current provided to the heater 122 to control the amount of thermal energy supplied by the heater 122. The controller may control the heater 122 so that the temperature of the melt 102 is maintained above about the melting temperature of silicon (e.g., about 1412° C.). For example, the melt 102 may be heated to a temperature of at least about 1425° C., at least about 1450° C., or even at least about 1500° C. Insulation (not shown) surrounding the heater 122 may reduce the amount of heat lost through the housing 106. The ingot puller 100 may also include a heat shield assembly (not shown) above the surface of the melt 102 for shielding the ingot from the heat of the crucible 104 to increase the axial temperature gradient at the solid-melt interface.

[0027] A pulling mechanism (not shown) is attached to a pulling wire 124 extending downward from the mechanism. The mechanism is capable of raising and lowering the pulling wire 124 and rotating the pulling wire 124. The ingot puller 100 may have a pulling shaft instead of a wire, depending on the type of puller. The pulling wire 124 terminates in a pulling assembly 126 of a seed chuck 128 that holds a seed 130 for growing a silicon ingot. When growing the ingot, the pulling mechanism lowers the seed 130 until it contacts the surface of the silicon melt 102. After the seed 130 begins to melt, the pulling mechanism slowly lifts the seed upward through the growth chamber 108 and the pulling chamber 110 to grow a single crystal ingot. The speed at which the pulling mechanism rotates the seed 130 and the speed at which the pulling mechanism lifts the seed (i.e., the pulling rate v) are controlled by the control system. As the seed crystal 130 is slowly lifted from the melt 102 , silicon atoms from the melt 102 align themselves with and attach to the seed crystal 130 to form an ingot.

[0028] Process gas is introduced into the housing 106 through the inlet port 114 and withdrawn from the outlet port 116. The process gas creates an atmosphere within the housing and the melt and the atmosphere form a melt-gas interface. The outlet port 116 is in fluid communication with an exhaust system (not shown) of the ingot puller.

[0029] refer to Figure 2 , schematically shows a crucible 104 containing a silicon melt 102 therein. The crucible 104 includes a body 140 including a bottom wall 142 and a side wall 144 extending upwardly from the bottom wall 142. The bottom wall 142 and the side wall 144 define a cavity 146 in which the melt 102 is received. The body 140 further includes an inner surface 148 and an outer surface 150 extending along opposite sides of the bottom wall 142 and the side wall 144. The side wall 144 forms an edge 152 at the top of the open crucible 104. The body 140 is formed of a natural silica material or quartz (used interchangeably herein).

[0030] The crucible 104 further includes a crystalline layer 154 disposed on the inner surface 148 of the body 140 and facing the melt 102. The crystalline layer 154 includes an unwetted portion 157 extending from the edge 152 to the surface of the melt 102 and a wetted portion 157 extending below the unwetted portion 157 and below the surface of the melt 102. The wetted portion 157 contacts the melt 102 during at least a portion of the ingot growth process, while the unwetted portion 157 does not contact the melt 102. The crystalline layer 154 on the crucible 104 is formed by a devitrified synthetic lining 158 ( Figure 3 The liner 158 is immersed in the melt 102 in the wetted portion 157 to crystallize the wetted portion 157 of the layer, while the unwetted portion 157 of the layer 154 does not crystallize during the ingot growth process.

[0031] Figure 3 and 4 Region A showing the crucible 104 ( Figure 2 ). Figure 3 Region A of the crucible 104 with the synthetic lining 158 is shown before the liner is immersed in the melt 102 . Figure 4 Region A of crucible 104 is shown after the liner has been immersed in melt 102 and devitrified to form crystalline layer 154. The schematic proportions of liner, crystalline layer 154 and crucible 104 are not shown to scale in the figures. In particular, the thickness of liner and crystalline layer 154 are exaggerated in the figures.

[0032] refer to Figure 3, the liner 158 is formed of synthetic silica and is also referred to herein as a "synthetic liner." Table 1 below shows the chemical composition of the synthetic liner 158 in parts per million ("ppm") compared to a natural quartz or "natural sand" liner. As shown in Table 1, the synthetic liner 158 includes a significantly reduced concentration of impurities relative to a natural liner.

[0033]

[0034]

[0035] Table 1: Example impurity composition of natural liner and synthetic liner 158

[0036] The liner 158 extends continuously from the edge 152 along the inner surface 148 of the crucible 104 and along the bottom wall 142 to substantially cover the inner surface 148. In other embodiments, at least some portions of the surface of the body 140 (e.g., portions of the body 140 proximate the non-wetted portion 157) may not be covered by the liner. The crucible 104 is manufactured with the liner by an arc fusion process, but other manufacturing processes suitable for the crucible 104 may be used, such as plasma jetting, slurry casting, or 3D printing.

[0037] The liner 158 is designed and adapted for the devitrification process at high temperatures, so that when the liner 158 is exposed to the high temperature melt 102, the melt 102 causes the liner 158 to crystallize, such as Figure 4 To form the crystalline layer 154 (eg Figure 2 ), an initial charge of polycrystalline silicon is added to the crucible 104 and melted to form the melt 102. In addition, a melt modifier precursor is introduced into the crucible 104 before or after the polycrystalline silicon is melted. As the crucible 104 is heated, the polycrystalline silicon melts to form the silicon melt 102. The melt modifier precursor reacts with the melt 102 to release exhaust gas and dissolve the melt modifier within the melt 102. Exhaust gas (e.g., carbon dioxide) is exhausted from the crucible 104.

[0038] By using a device that at least partially extends from the housing 106 ( Figure 1 ) and can be positioned to allow the precursor to flow into the melt 102. In other embodiments, the melt modifier precursor and / or the melt modifier itself can be introduced into the melt 102 by a variety of different equipment and methods, such as (without limitation) by implanting the precursor into the cavity 146 of a seed crystal immersed in the melt 102, by placing the precursor into a silicon holder (not shown) which is then placed in the melt 102, by positioning a quartz trap door container containing the precursor therein over the melt 102 and opening the door to release the precursor into the melt 102.

[0039] The melt modifier reacts with the melt 102 such that the modified melt 102 (also referred to as "doped melt 102") acts as a nucleating agent on the liner that promotes devitrification of the composite liner 158 to form a crystalline layer 154. The silicon melt 102 is doped to a concentration of about 0.013 mg modifier / kg silicon.

[0040] The melt 102 may be doped before each crystal growth operation or may be doped generally depending on the Cz process used and whether the doping affects the crystal yield of the corresponding Cz process. For example, some Cz processes are less thermally aggressive and doping is not necessarily performed every time between the initial crystal and subsequent crystals. For other Cz processes, doping may be beneficial between the initial crystal and subsequent crystals.

[0041] A suitable melt modifier is barium oxide (BaO). However, barium oxide is unstable at normal atmospheric temperature and pressure. Specifically, at normal atmospheric temperature and pressure, barium oxide reacts with water (H2O) and carbon dioxide (CO2) in the atmosphere to form barium carbonate (BaCO3). Applying heat from the melt 102 to the barium carbonate decomposes the barium carbonate back into barium oxide and carbon dioxide. Therefore, barium carbonate (also referred to as a "melt modifier precursor") is introduced into the melt 102 and decomposes into the melt 102 to release carbon dioxide (CO2) and provide a concentration of barium oxide (BaO) melt modifier within the melt 102.

[0042] The barium oxide may alternatively be maintained in an unreacted pure state. For example, the barium oxide may be stored and maintained in a bottle that also contains an inert gas to minimize exposure to moisture, and steps may be taken to minimize contact of air with the barium oxide when the barium oxide is transferred to the silicon melt 102. In further embodiments, other suitable melt modifier precursors may be used. Suitable melt modifier precursors may include any compound containing suitable ions (e.g., barium, calcium, strontium, magnesium) and suitable counter molecules that decompose and transport the ions into the melt 102 to allow the ions to react with the glass lining surface 149 ( Figure 3 ) reacts and mediates the nucleation of cristobalite on the lining surface 149. Suitable auxiliary molecules include, for example, and without limitation, oxygen, carbonates, oxalates, fluorine, etc. Example suitable precursors include, without limitation, strontium carbonate (SrCO3), calcium carbonate (CaCO3), and / or magnesium carbonate (MgCO3).

[0043] The liner has a starting thickness T1 extending from an inner surface 148 of the quartz body 140 of the crucible 104 to a liner surface 149 positioned to contact the melt 102. Based on the crystallized layer 154 ( Figure 4The starting thickness T1 of the liner is selected based on the desired resulting crystal thickness T2 (shown in FIG. 1 ). For example, in the present embodiment, the starting thickness T1 is less than 500 micrometers (um) to produce a resulting crystal thickness T2 of less than 700 micrometers (um). The concentration of the melt modifier in the doped melt 102 reacts with the synthetic liner 158 to promote devitrification of the synthetic liner 158 and produce a thin devitrified layer, such as Figure 4 As shown in .

[0044] refer to Figure 4 , the liner is shown as a crystallized or "devitrified" layer (terms used interchangeably herein) after exposure to the doped melt 102. Specifically, in the example embodiment, the silica liner devitrifies to cristobalite due to exposure to the modified melt 102. The crystallized layer 154 alters the equilibrium at the melt 102 / crucible 104 boundary (i.e., the "cristobalite / silicon / glass phase boundary") such that bubble nucleation is avoided, silicon melt 102 vibrations are reduced, and the resulting structure of the ingot is improved.

[0045] The crystalline layer 154 extends radially inward from the inner surface 148 of the body 140 of the quartz crucible 104 to a crystalline surface 162 that contacts the melt 102. In addition to promoting devitrification of the liner 158, the doped melt 102 also provides a reduced surface roughness than an unmodified or "undoped" melt 102, such as relative to Figure 5 and 6 14. The crystalline layer 154 defines a crystalline thickness T2 between the inner surface 148 of the body 140 and the liner surface 149. Due to the devitrification of the liner, the crystalline thickness T2 increases relative to the starting thickness T1 of the liner. The crystalline thickness T2 is less than or equal to 700 micrometers (um), less than or equal to 500 micrometers (um), or less than or equal to 100 micrometers (um). The crystalline thickness T2 is preferably thick enough to allow the starting synthetic liner 158 to be continuous during the arc fusion process. In some embodiments, the crystalline thickness T2 may be 50 micrometers (um).

[0046] The crystal thickness T2 is less than or equal to 700 microns to at least partially improve the resistance of the crystal layer 154 to thermal spalling compared to a crystal liner having a thickness greater than or equal to 700 microns. For example, experimental testing indicates that keeping the crystal layer 154 thickness T2 below 700 microns produces a full bottom crystal, where using a crucible with a crystal thickness T2 exceeding 700 microns increases the likelihood of thermal spalling and results in the loss of dislocation structures between crystals of about 65% of the desired crystal body 140 length.

[0047] Figure 5 and 6Results from example experiments are presented that demonstrate that the crystallized layer 154 using the doped melt 102 reduces surface roughness compared to the undoped melt 102. Smoother surface roughness of the crystallized layer 154 is desirable because increased roughness of the crystallized layer 154 causes increased instability at the melt 102 / crucible 104 boundary, which can cause damage to the resulting ingot.

[0048] For example, the surface roughness of the crystallization surface 162 is related to the heat transfer coefficient of the crystallization layer 154. In addition, the heat transfer coefficient of the crystallization layer 154 is related to the bubble nucleation at the melt 102 / crucible 104 boundary. In other words, as the surface roughness of the crystallization layer 154 increases, the bubble nucleation at the melt 102 / crucible 104 boundary also increases. Therefore, the surface roughness of the crystallization layer 154 can be understood to directly affect the nucleation probability of the crystallization surface 162, wherein a smoother or less rough surface has a reduced nucleation probability due to gas nucleation at the melt 102 / crucible 104 boundary.

[0049] Bubble nucleation releases bubbles into the melt 102 causing the melt 102 to vibrate and potentially damage the structure of the ingot. Additionally, bubble nucleation at the melt 102 / crucible 104 boundary can also create microscopic voids in the silicon melt 102 that can persist into the growing ingot as the crystal ingot forms. If present in the growing ingot, these voids (also collectively referred to as "air pockets" or "pinholes") weaken the resulting ingot structure and may even render the ingot unsuitable for use in electronic devices.

[0050] In the experiment, quartz samples having a synthetic silica lined surface having a thickness greater than or equal to 2 millimeters (mm) were each immersed in a silicon melt 102 at a temperature of 1525° C. for a 2 hour immersion time. In a control test, the melt 102 was undoped, meaning that the melt 102 contained silicon and no nucleating agent melt modifier was used. In a second test, the melt 102 was doped to about 0.013 milligrams of BaO / kilogram of silicon. The control test produced an undoped quartz sample and the second test produced a doped quartz sample. The samples were each removed from the melt 102 after the 2 hour immersion and photographed and measured to compare the resulting surface roughness between the melts.

[0051] refer to Figure 5 , the first graph indicated at 502 shows a comparison of the root mean square (RMS) deviation in microns between a doped sample (indicated by BaCO3) and an undoped sample. The second graph indicated at 504 shows a comparison of the area ratio between the doped and undoped samples. The area ratio is determined by measuring the area on the peaks and valleys on the crystal surface and normalizing the measurement to the area of ​​the plan view.

[0052] As shown in the first graph, the doped sample has a reduced RMS deviation compared to the doped sample. Specifically, the doped sample has an RMS deviation of about 1 micron, where the detected deviation spans between 0.8 microns and 1.2 microns. In contrast, the undoped sample has an RMS deviation of about 1.24 microns, where the range of deviation is between about 1.15 and about 1.35. In addition, as shown in the second graph, the doped sample also has an area ratio that is reduced relative to the undoped sample. Specifically, the doped sample has an area ratio of about 1.0575, while the undoped sample has an area ratio of about 1.08. Therefore, it is found that the undoped sample has a greater difference between surface peaks and valleys than the doped sample.

[0053] Figure 6 Microscope photographs taken of an undoped sample (indicated at 602) and a doped sample (indicated at 604) after they are removed from the melt 102 are shown. The doped sample 602 has a significantly reduced roughness relative to the undoped sample 604. As shown in the photograph, the undoped sample photograph shows more intense vortex features, such as shown at 603a and 603b on the crystallized surface 162, which coincide with more dramatic peaks and valleys. In contrast, the imaging of the doped sample shows a much more monotonous and consistent crystallized surface 162 to indicate reduced surface roughness.

[0054] Figure 7 700 is a flow chart of a method 700 for producing a single crystal silicon ingot from a silicon melt 102 held in a crucible 104 positioned in an ingot puller apparatus. The method includes providing 702 a crucible 104 within an inner chamber of the ingot puller, the crucible 104 including an inner surface 148 and a synthetic lining 158 on the inner surface 148. The method further includes adding 704 an initial charge of polycrystalline silicon to the crucible 104. The method also includes melting 706 the initial charge of polycrystalline silicon to form a silicon melt 102 in the crucible 104. The method further includes dissolving 708 a melt modifier into the silicon melt 102 to devitrify the synthetic lining 158 and form a crystalline layer 154 on the crucible 104, the crystalline layer 154 having a thickness T2 of less than 700 microns. The method also includes pulling 710 a single crystal silicon ingot from the silicon melt 102.

[0055] As described herein, advantages of using a synthetic liner 158 having a reduced thickness in conjunction with a melt 102 spiked with a high concentration of nucleating agent include increased resistance of the crystallized layer 154 to thermal spalling. Thus, the crucible 104 can be exposed to the silicon melt 102 for longer continuous periods or added high temperature times, which achieves cost reductions and increased throughput and yield. Because throughput and yield are increased, ingots are produced more efficiently and at a lower cost. Additional advantages include reduced surface roughness of the crystallized surface 162, which reduces bubble nucleation in the melt 102, thereby improving the resulting structure and reducing defects in the growing ingot.

[0056] 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 method, or other statistical variations.

[0057] When introducing elements of the present disclosure or embodiments thereof, the articles "a," "an," and "the" are intended to mean that there are 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.

[0058] As various changes could be made in the above constructions and methods without departing from the scope of the present disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative rather than limiting.

Claims

1. A method for producing a single crystal silicon ingot from a silicon melt held in a crucible positioned in an ingot puller apparatus, the method comprising: placing the crucible within an inner chamber of the ingot puller, the crucible comprising an inner surface and a synthetic lining on the inner surface; adding an initial charge of polycrystalline silicon to the crucible; melting the initial charge of polycrystalline silicon so that the silicon melt is formed in the crucible; dissolving a melt modifier into the silicon melt to devitrify the synthetic lining and form a crystalline layer on the crucible, the crystalline layer having a thickness of less than 700 microns; and A single crystal silicon ingot is pulled from the silicon melt. 2 . The method of claim 1 , wherein the synthetic liner has a first thickness and wherein the thickness of the crystallized layer is greater than the first thickness.

3. The method of claim 1 or 2, wherein the crucible comprises a body having a bottom wall and side walls extending from the bottom wall to define a cavity within the body of the crucible, the inner surface extending along the bottom wall and the side walls, wherein the synthetic lining extends continuously across the side walls and bottom wall to substantially cover the inner surface of the body.

4. The method of any one of claims 1 to 3, wherein the synthetic liner comprises a synthetic silica material.

5. The method of any one of claims 1 to 4, further comprising forming the crucible with the composite lining by an arc fusion process.

6. The method of any one of claims 1 to 5, wherein dissolving the melt modifier dopes the melt to comprise a concentration of about 0.013 mg melt modifier / kg silicon.

7. The method of any one of claims 1 to 6, wherein the method further comprises: adding a melt modifier precursor to the crucible; forming the melt modifier by decomposing the melt modifier precursor in the melt; and Exhaust gas released due to the decomposition is discharged from the crucible.

8. The method of claim 7, wherein the melt modifier precursor is barium carbonate and wherein the melt modifier is barium oxide.

9. The method of any one of claims 1 to 6, further comprising adding the melt modifier to the melt through a feed tube.

10. The method according to any one of claims 1 to 9, further comprising: selecting a starting thickness of the synthetic liner based on a desired final thickness of the crystallized layer; and The synthetic lining is formed on the crucible to have the starting thickness. The method of claim 10 , wherein the starting thickness is less than 500 microns.

12. A crucible for use with an ingot puller apparatus, the crucible comprising: a body having an inner surface and an opposing outer surface; and A synthetic liner is disposed on the inner surface of the body, the synthetic liner having a composition that devitrifies when exposed to a silicon melt to cause a crystalline layer to form on the crucible during a crystal growing operation, the crystalline layer having a thickness of less than 700 microns.

13. The crucible of claim 12, wherein the synthetic lining has a first thickness and wherein the thickness of the crystalline layer is greater than the first thickness.

14. The crucible of claim 12 or 13, wherein the crucible comprises a body having a bottom wall and side walls extending from the bottom wall to define a cavity within the body of the crucible, the inner surface extending along the bottom wall and the side walls, wherein the synthetic lining extends continuously across the side walls and bottom wall to substantially cover the inner surface of the body.

15. The crucible of any one of claims 12 to 14, wherein the synthetic lining comprises a synthetic silica material.

16. The crucible of any one of claims 12 to 15, wherein the synthetic lining has a thickness of less than 500 microns.

17. A method for producing a single crystal silicon ingot from a silicon melt held in a crucible, the method comprising: placing the crucible in an inner chamber of an ingot puller, the crucible comprising an inner surface and a synthetic lining on the inner surface; adding an initial charge of polycrystalline silicon to the crucible; adding a melt modifier precursor to the crucible; melting the initial charge of polycrystalline silicon so that the silicon melt is formed in the crucible; and The melt modifier precursor is dissolved in the silicon melt to release a concentration of melt modifier into the silicon melt that devitrifies the synthetic liner and forms a crystalline layer on the crucible, the crystalline layer having a thickness of less than 700 microns.

18. The method of claim 17, wherein the synthetic liner has a first thickness and wherein the thickness of the crystallized layer is greater than the first thickness.

19. The method of claim 17 or 18, wherein the crucible comprises a body having a bottom wall and side walls extending from the bottom wall to define a cavity within the body of the crucible, the inner surface extending along the bottom wall and the side walls, wherein the synthetic lining extends continuously across the side walls and bottom wall to substantially cover the inner surface of the body.

20. The crucible of any one of claims 17 to 19, wherein the synthetic lining comprises a synthetic silica material.

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