Systems and methods for controlling gas dopant vaporization rates during crystal growth processes

Abstract

A method for growing a single crystal ingot includes growing a single crystal silicon ingot from a silicon melt in a crucible in an inner chamber, adding a volatile dopant to a feed tube, positioning the feed tube in the inner chamber at a first height relative to a surface of the melt, adjusting the feed tube in the inner chamber to a second height at a rate, and heating the volatile dopant to form a gaseous dopant as the feed tube moves from the first height to the second height at the rate. The second height and the rate are each selected to control a vaporization rate of the volatile dopant. The method also includes introducing a dopant species into the melt while growing the ingot by contacting a surface of the melt with the gaseous dopant.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 18 / 046,314, filed October 13, 2022, and U.S. Patent Application No. 18 / 046,319, filed October 13, 2022, the disclosures of which are incorporated herein by reference in their entireties.

[0002] The field relates generally to the preparation of single crystals of semiconductor materials, and more particularly to systems and methods for controlling gas dopant vaporization rates during crystal growth processes. [Background technology]

[0003] Single-crystal silicon, the starting material for most processes for the manufacture of semiconductor electronic components, is commonly prepared by the so-called Czochralski ("Cz") method, in which polycrystalline silicon ("polysilicon") is charged into a crucible and melted, and a seed crystal is brought into contact with the molten silicon or silicon melt and slowly withdrawn to grow a single-crystal ingot.

[0004] To achieve a desired resistivity in the silicon crystal, a certain amount of dopant is added to the melt. Traditionally, the dopant is fed into the melt from a feed hopper positioned several feet above the silicon melt level. However, this approach is undesirable for volatile dopants, as such dopants tend to evaporate uncontrolled into the ambient environment, resulting in the formation of oxide particles (i.e., suboxides) that can fall into the melt and become incorporated into the growing crystal. These particles act as heterogeneous nucleation sites, ultimately leading to failure of the crystal pulling process.

[0005] Furthermore, in conventional systems, sublimation of dopant granules at the melt surface often causes a localized temperature drop in the surrounding silicon melt, resulting in the formation of "silicon boats" adjacent to the dopant granules. These silicon boats, along with the surface tension of the melt, prevent many of the dopant granules that reach the melt surface from sinking into the melt, thus increasing the time available for sublimation to the atmosphere. This phenomenon results in significant loss of dopant to the gaseous environment and further increases the concentration of contaminant particles in the growth chamber.

[0006] Some known dopant systems introduce volatile dopants into the growth chamber as gases. The gas dopant can be formed by vaporizing the volatile dopant in a feed hopper. The gas dopant thus formed exits the feed hopper, subsequently contacts the surface of the melt, and flows into the melt. The dopant species in the melt are then transported by diffusion and convection from the surface of the melt toward the solid-liquid interface formed by the growing single crystal ingot. However, such systems tend to supply dopants non-uniformly during the growth process, thereby increasing radial and / or axial dopant concentration variations in the grown ingot.

[0007] Some doping systems use inert gases to deliver volatile dopants into the growth chamber and / or to transport gaseous dopants from a feed hopper to the surface of the silicon melt. However, the use of inert gases tends to dilute the gaseous dopant, thereby reducing the dopant concentration, and to purge evaporated dopants from the growth chamber too quickly. For example, dopants with low segregation coefficients, such as arsenic (0.3) and phosphorus (0.35), require a dopant concentration in the melt that is approximately three times higher than the desired dopant concentration in the grown crystal. As a result, the evaporated dopant does not have enough time to flow into the silicon melt, requiring more dopant to achieve the desired dopant concentration in the silicon melt.

[0008] Therefore, there is a need for a simple, cost-effective technique for producing doped single crystal silicon by a crystal pulling process. There is also a need for a doping method that facilitates controlled introduction of gas dopant species into a silicon melt during a crystal pulling process. Furthermore, there is a need for a gas doping method that allows for the use of dopant source materials that are readily available and / or relatively inexpensive, and that allows for relatively easy doping of the melt.

[0009] This Background section is intended to introduce the reader to various aspects of technology that may be related to various aspects of the present disclosure, which are described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. Summary of the Invention

[0010] In one aspect, a method for growing a doped single crystalline silicon ingot using an ingot puller is disclosed. The ingot puller includes an inner chamber, a crucible disposed within the inner chamber, a heat source, and a feed tube having an open end. The feed tube includes a capsule proximate the open end. The method includes adding polycrystalline silicon to the crucible, heating the crucible with a heat source to form a silicon melt from the polycrystalline silicon in the crucible, and growing a single crystalline silicon ingot from the melt by contacting the melt with a seed crystal and withdrawing the seed crystal from the melt to grow the single crystalline silicon ingot. The single crystalline silicon ingot has a neck region, a shoulder region, and a body region. The method also includes adding a charge of a volatile dopant to the feed tube, where the charge of the volatile dopant is received by the capsule. The method further includes positioning the feed tube within the inner chamber such that the open end of the feed tube has a first height relative to a surface of the melt. The method also includes adjusting the feed tube within the inner chamber to move the open end of the feed tube from a first height to a second height relative to the surface of the melt. The second height is smaller than the first height, and the open end of the feed tube is moved from the first height to the second height at a rate. The method also includes heating a capsule containing a volatile dopant by radiant heat from a heat source and the surface of the melt as the open end moves from the first height to the second height at the rate to form a gaseous dopant. The second height and the rate are each selected to control a vaporization rate of the volatile dopant. The method also includes introducing a dopant species into the melt while growing a body region of the single crystal silicon ingot by contacting the surface of the melt with the gaseous dopant. The vaporization rate is controlled so that the dopant species is introduced at a rate sufficient to maintain the resistivity of the body region along the axial length of the body region.

[0011] In another aspect, an ingot pulling apparatus for growing doped single crystal silicon ingots is disclosed. The apparatus includes an outer housing defining an inner chamber and a crucible disposed within the inner chamber for holding a silicon melt. The apparatus also includes a gas doping system for introducing a dopant species into the melt. The gas doping system includes a feed tube extending between a first end and a second end, the second end being positioned within the inner chamber. The feed tube also includes a capsule disposed proximate the second end. The gas doping system also includes a dopant feed source coupled in flow communication with the first end of the feed tube, the dopant feed source configured to add a volatile dopant to the feed tube. The gas doping system also includes a positioning system configured to adjust the position of the feed tube between a first position, where the second end of the feed tube is at a first height above the surface of the melt, and a second position, where the second end of the feed tube is at a second height above the surface of the melt that is less than the first height. The gas doping system also includes a controller communicatively coupled to the dopant feed source and the positioning system. The controller is configured to cause the dopant feed source to add a targeted amount of volatile dopant to the feed tube and to cause the positioning system to move the feed tube to the second position at a rate. The second height and the rate are each selected to control a vaporization rate of the volatile dopant in the feed tube during the ingot pulling process.

[0012] In another aspect, an ingot pulling apparatus for growing doped single crystal silicon ingots is disclosed. The apparatus includes an outer housing defining an inner chamber and a crucible disposed within the inner chamber for holding a silicon melt. The apparatus also includes a first gas doping system and a second gas doping system for introducing a dopant species into the melt. Each of the first gas doping system and the second gas doping system includes a feed tube extending between a first end and a second end, the second end being positioned within the inner chamber. The feed tube also includes a capsule disposed proximate the second end. Each of the first gas doping system and the second gas doping system also includes a dopant feed source coupled in flow communication with the first end of the feed tube, the dopant feed source configured to add a volatile dopant to the feed tube. Each of the first and second gas doping systems also includes a positioning system configured to adjust the position of the feed tube between a first position, where the second end of the feed tube is at a first height above the surface of the melt, and a second position, where the second end of the feed tube is at a second height above the surface of the melt that is less than the first height. The gas doping system also includes a controller communicatively coupled to the dopant feed source and the positioning system. The controller is configured to cause the dopant feed source to add a targeted amount of volatile dopant to the feed tube and cause the positioning system to move the feed tube to the second position. The second height is selected to control the evaporation rate of the volatile dopant in the feed tube during the ingot pulling process.

[0013] Various refinements of the features described in connection with the foregoing aspects of the present disclosure exist. Additional features may also be incorporated into the foregoing aspects of the present disclosure. These refinements and additional features may exist individually or in any combination. For example, the various features discussed below in connection with any of the illustrated embodiments of the present disclosure may be incorporated, alone or in any combination, into any of the foregoing aspects of the present disclosure. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional view of an exemplary ingot pulling apparatus including a gas doping system. [Figure 2] 2 is an enlarged cross-sectional view of a portion of the gas doping delivery tube of FIG. 1. [Figure 3] FIG. 1 shows simulated convection (left) and diffusion (right) patterns of dopant species in a silicon melt during a crystal growth process. [Figure 4] FIG. 1 shows simulated profiles of velocity distribution (left) and gaseous dopant concentration (right) within the inner chamber of an ingot puller. [Figure 5] 10 is a plot showing an estimated temperature profile at the second end of the feed tube versus height above the melt-gas interface during a crystal growth process. [Figure 6] 1 is a plot showing doping efficiency versus height of the feed tube above the melt-gas interface during a crystal growth process. [Figure 7] 1A-1D illustrate an exemplary method for growing a doped single crystal silicon ingot. [Figure 8] 1 is a plot illustrating gaseous dopant control over time during a gas doping process. [Figure 9] 1 is a plot showing the average dopant concentration in the silicon melt and the radial resistivity change in the growing ingot during the gas doping process. [Figure 10] 1 is a plot showing the axial resistivity change along the growing ingot during a crystal growth process with and without a gas doping process. [Figure 11] 10 is a plot showing axial resistivity control along the growing ingot during a crystal growth process using a multiple loading gas doping process. [Figure 12] FIG. 2 is a schematic cross-sectional view of another exemplary ingot pulling apparatus including two gas doping systems. DETAILED DESCRIPTION OF THE INVENTION

[0015] Like reference numbers used in the various drawings indicate like elements.

[0016] An exemplary ingot pulling apparatus, or ingot puller, is shown generally at 100 in FIG. 1 . The ingot puller 100 is used to produce single crystalline (i.e., monocrystalline) ingots 102 of semiconductor or solar-grade material, such as, for example, single crystalline silicon ingots 102. In some embodiments, the ingots 102 are grown by the so-called Czochralski (CZ) process, in which the ingots 102 are pulled from a silicon melt 104 held in a crucible 106 of the ingot puller 100. In some embodiments, the ingots 102 are grown by a batch CZ process, in which polycrystalline silicon is charged to the crucible 106 in an amount sufficient to grow one ingot 102, such that the silicon melt 104 is essentially depleted from the crucible 106 after the growth of one ingot 102. In other embodiments, the ingots 102 are grown by a continuous CZ (CCZ) process, in which polycrystalline silicon is continuously or periodically added to the crucible 106 to replenish the silicon melt 104 during the growth process. The CCZ process facilitates the growth of multiple ingots 102 drawn from a single melt 104. Unless otherwise specified, embodiments of the subject matter described herein are not limited to a particular crystal growth process. For example, in other embodiments, polycrystalline silicon ingots may be grown using a directional solidification process for solar applications.

[0017] 1 , the ingot puller 100 includes an outer housing 108 that defines an inner chamber 110 therein. A crucible 106 is disposed within the inner chamber 110. The crucible 106 contains a silicon melt 104 from which a silicon ingot 102 is drawn. The crucible 106 may be supported by a susceptor (not shown). The ingot puller 100 may be configured to rotate the crucible 106 and / or move the crucible 106 vertically within the inner chamber 110.

[0018] To prepare the silicon melt 104, polycrystalline silicon is added to the crucible 106. The polycrystalline silicon is heated above the melting temperature of silicon (approximately 1414° C.) to liquefy the polycrystalline silicon into the silicon melt 104. A heat source 112 operates to melt the polycrystalline silicon. For example, the heat source 112 includes one or more heaters 114 mounted within an inner chamber 110 below or to the side of (i.e., radially outward from) the crucible 106 that are operated to melt the polycrystalline silicon to prepare the silicon melt 104.

[0019] Before or after the melt 104 is generated, the melt 104 can be doped with a dopant, typically an n-type dopant, to compensate for p-type impurities (e.g., boron) in the melt. The n-type dopant may be added before the growth of the ingot 102. By supplementing the melt 104, the resistivity of the resulting ingot 102 can be controlled (e.g., increased) to a target resistivity. For example, the seed end of the ingot 102 (i.e., the portion of the ingot closest to the ingot crown) can have a resistivity of at least about 30 Ω-cm, or, in other embodiments, at least about 35 Ω-cm, at least about 40 Ω-cm, at least about 45 Ω-cm, at least about 50 Ω-cm, at least about 55 Ω-cm, at least about 60 Ω-cm, or between about 30 Ω-cm and about 100 Ω-cm, or between about 60 Ω-cm and about 80 Ω-cm. Suitable n-type dopants include phosphorus and arsenic.

[0020] Once the melt 104 is prepared, the single crystal silicon ingot 102 is pulled from the melt 104 using a pulling system 116. The pulling system 116 includes a pulling mechanism (not shown) attached to a pulling wire 122 extending downward from the mechanism. The mechanism raises and lowers the pulling wire 122 along a pulling axis X1 and can rotate the pulling wire 122 about the pulling axis X1. Depending on the type of puller, the ingot puller 100 may have a pulling shaft rather than a wire. The pulling wire 122 terminates in a seed chuck 120 that holds and / or is secured to a seed crystal 118. The pulling mechanism lowers the seed chuck 120 and seed crystal 118 along the pulling axis X1 until the seed crystal 118 contacts the surface of the silicon melt 104. Once the seed crystal 118 begins to melt, the pulling mechanism slowly raises the seed crystal 118 along the pulling axis X1, growing the single crystal ingot 102. Alternatively, the pulling mechanism may rotate the seed crystal 118 about the pulling axis X1 by raising the seed crystal 118. As the seed crystal 118 slowly rises along the pulling axis X1 out of the melt 104, the silicon ingot 102 begins to solidify and is pulled out of the melt 104.

[0021] A process gas (e.g., argon) is introduced into the inner chamber 110 through a gas inlet port 128 and withdrawn through an outlet port (not shown), which is in fluid communication with the ingot puller 100's exhaust system (not shown). The process gas creates an inert atmosphere within the housing. The surface of the melt 104 and the inert atmosphere form a melt-gas interface 126. The melt-gas interface 126 is located radially outward from the solid-melt interface 124 along which the ingot 102 grows. For purposes of discussion, the melt-gas interface 126 and the surface of the melt 104 may be used interchangeably.

[0022] The ingot 102 is covered by an annular heat shield 130 and a cooling jacket 132. The annular heat shield 130 and the cooling jacket 132 are each mounted within the inner chamber 110 above the melt 104. The heat shield 130 is mounted radially outward from the cooling jacket 132 and defines an elongated passage 134 sized and shaped to receive the ingot 102 as it is pulled from the melt 104 along the pulling axis X1. The heat shield 130 is mounted above the melt-gas interface 126 such that a gap 136 is defined therebetween. The cooling jacket 132 is positioned radially inward from the heat shield 130 and within the elongated passage 134. The cooling jacket 132 is disposed concentrically with the heat shield 130 along the pulling axis X1 and defines a central passageway 140 for receiving the ingot 102 as it is pulled along the pulling axis X1 by the pulling system 116. A portion 138 of the passageway 134 defined by the heat shield 130 is positioned below the cooling jacket 132. The heat shield 130 insulates and / or reflects radiant heat from the ingot 102 as it is pulled through the passageway 134. The cooling jacket 132 may be in the form of a cylindrical, fluid-cooled heat exchanger that facilitates cooling of the ingot 102 as it is pulled through the passageway 140. The heat shield 130 and the cooling jacket 132 can facilitate control of axial and radial temperature gradients, thereby promoting solidification and crystallization of molten silicon in the melt 104 into the growing ingot 102. The configuration of the heat shield 130 and cooling jacket 132 may be varied to enhance the temperature effects within the passages 134, 140 as the ingot 102 is pulled through them.

[0023] The ingot puller 100 also includes a gas doping system 200 for introducing a gaseous dopant (represented by arrow 202) into the melt 104. The doping system 200 includes a dopant feed source 204, a feed tube 206, and an evaporation capsule 208. Generally, the gas doping system 200 flows the gaseous dopant 202 across the melt-gas interface 126 during growth of the ingot 102. The gaseous dopant 202 flows through the melt-gas interface 126 into the melt 104. The dopant species is then transported by diffusion and convection toward the solid-melt interface 124, thereby doping the ingot 102 to control resistivity variations that occur during growth of the ingot 102.

[0024] The feed tube 206 extends along a feed tube axis X2 between a first end 210 and a second end 212 (FIG. 2). The first end 210 is positioned adjacent to the dopant feed source 204, which may be positioned outside the outer housing 108. The second end 212 is positioned within the inner chamber 110 and oriented toward the surface of the melt 104. The feed tube 206 may extend through a valve assembly (not shown) that provides an entry point for the feed tube 206 through the outer housing 108 and seals the entry point when the feed tube 206 is removed from the ingot puller 100. The feed tube 206 is open at a first end 210 to receive a volatile dopant (indicated by arrow 216 in FIG. 2 ) from a dopant feed source 204 and is open at a second end 212 to allow gaseous dopant 202 to flow out of the second end 212 of the feed tube 206 toward the surface of the melt 104, particularly toward the melt-gas interface 126.

[0025] As shown in FIG. 1 , the feed tube 206 may be angled relative to the pull axis X1 and the surface of the melt 104 to facilitate distribution of the gaseous dopant 202 across the melt-gas interface 126. For example, the feed tube 206 may be angled so that the feed tube axis X2 forms an angle with the pull axis X1 of about 10 degrees to about 80 degrees, e.g., about 15 degrees to about 45 degrees. The orientation of the feed tube 206 can translate into the orientation of the open end 212. In some embodiments, the open end 212 may be angled relative to the feed tube axis X2. For example, the open end 212 may be angled relative to the feed tube axis X2 so that the opening formed by the open end 212 is substantially parallel to the melt-gas interface 126. In other embodiments, the feed tube 206 may be positioned substantially perpendicular to the melt-gas interface 126 such that the feed tube axis X2 is parallel to the pull axis X1. In still other embodiments, the feed tube 206 and / or the open end 212 of the feed tube 206 may have any other suitable configuration or orientation that enables the gas doping system 200 to function as described herein.

[0026] The doping system 200 may also include an inert gas supply 214 coupled in fluid communication with the feed tube 206 to direct the gaseous dopant 202 from the feed tube 206 through the second end 212 to reduce backflow of the gaseous dopant 202. The inert gas (indicated by arrows 218 in FIG. 2 ) introduced into the feed tube 206 by the inert gas supply 214 and / or the process gas introduced through the gas inlet port 128 may direct the gaseous dopant 202 to flow across the melt-gas interface 126 and into the melt 104. The inert gas 218 and / or the process gas introduced through the gas inlet port 128 may also be used to generate an inert atmosphere above the melt-gas interface 126. The inert gas 218 may be introduced into the feed tube 206 from the inert gas supply 214 at a suitable flow rate such that the inert gas 218 flows downward toward the second end 212. The inert gas 218 may be argon, although any other suitable inert gas may be used that enables the gas doping system 200 to function as described herein. The flow rate of the inert gas 218 is suitably sufficient to direct the gaseous dopant 202 from the second end 212 toward the melt-gas interface 126 without substantially causing undesired dilution of the gaseous dopant 202 and / or without causing the gaseous dopant 202 to substantially exit the inner chamber 110 without flowing into the melt 104. For example, the inert gas flow rate may be less than about 10 normal liters per minute, less than about 5 normal liters per minute, or less than about 2 normal liters per minute.

[0027] A first end 210 of the feed tube 206 is coupled in flow communication with a dopant feed source 204. The dopant feed source 204 delivers a volatile dopant 216, which may be in the form of a solid-phase dopant or a liquid-phase dopant, to the first end 210 of the feed tube 206. As used herein, the term "volatile dopant" generally refers to a dopant that has a sublimation or evaporation temperature below the melting temperature of silicon (approximately 1414°C) such that the volatile dopant 216 can vaporize into gaseous dopant 202 under the thermal conditions within the inner chamber 110 during the crystal growth process.

[0028] The dopant delivery source 204 may be automated, partially automated, or manually operated. Automatic control of the dopant delivery source 204 may be facilitated by a controller 220 communicatively coupled to the dopant delivery source 204. The dopant delivery source 204 may automatically deliver the volatile dopant 216 into the feed tube 206 based on one or more user-defined and / or environment-specific parameters. For example, the dopant feed source 204 may deliver the volatile dopant 216 to the feed tube 206 based on any one or more of the following parameters: a preset time during the growth process, a user-defined interval, a target resistivity of the ingot 102 during the growth process, the mass of the volatile dopant 216 in the feed tube 206 and / or the evaporation capsule 208, the concentration of the gaseous dopant 202 in the feed tube 206, the evaporation capsule 208, and / or the inner chamber 110, the vaporization rate of the volatile dopant 216, and the volumetric or mass flow rate of the gaseous dopant 202 and / or the inert gas 218. Continuous and / or intermittent delivery of the volatile dopant 216 may facilitate maintaining a relatively constant gaseous dopant concentration in the inner chamber 110 and in the melt 104 during the crystal growth process, resulting in a more uniform dopant concentration profile in the grown ingot.

[0029] The controller 220 can be programmed to control the frequency and / or amount of volatile dopant 216 delivered by the dopant delivery source 204 into the feed tube 206. The controller 220 includes a processor 222 that sends and receives signals to and from the controller 220 and / or the dopant delivery source 204 based on one or more user-defined and / or environment-specific parameters. The controller 220 also includes a user interface 224 communicatively coupled to the processor 222 and a sensor 226 communicatively coupled to the processor 222. The user interface 224 receives the user-defined parameters and communicates the user-defined parameters to the processor 222 and / or the controller 220. The sensor 226 receives and / or measures the environment-specific parameters and communicates such environment-specific parameters to the processor 222 and / or the controller 220. For example, the sensor 226 may be a pyrometer that measures the temperature of the melt 104 and / or the temperature of the growing ingot 102. The environment-specific parameters communicated by the sensor 226 may be used by the processor 222 and / or controller to cause the dopant delivery source 204 to deliver the volatile dopant 216 to the feed 206 .

[0030] The evaporation capsule 208 is disposed within the feed tube 206 proximate the second end 212 and within the inner chamber 110. Still referring to FIG. 2 , volatile dopant 216 delivered to the feed tube 206 flows downward through a channel 228 defined by an annular sidewall 230 of the feed tube 206 and is received by the evaporation capsule 208, which forms a receptacle within the feed tube proximate the second end 212. The evaporation capsule 208 includes a base 232 extending inwardly from the sidewall 230 and a capsule sidewall 234 joined to the base 232 and extending upwardly from the base 232 along the feed tube axis X2. In other embodiments, the evaporation capsule 208 may have any other suitable configuration that enables the gas doping system 200 to function as described herein. For example, in some embodiments, the capsule 208 may be removably connected to the tube, allowing the capsule to be separated from the tube for dopant loading.

[0031] A portion 236 of the channel 228 through which the gaseous dopant 202 flows is partially defined by the capsule sidewall 234 and the feed tube sidewall 230. The portion 236 of the channel 228 facilitates fluid communication between the evaporation capsule 208 and the open end 212 of the feed tube 206. This allows the gaseous dopant 202, formed by vaporizing the volatile dopant 216 received by the evaporation capsule 208, to flow from the evaporation capsule 208 to the second end 212 and out the feed tube 206. The cross-sectional area of ​​the portion 236 of the channel 228, as viewed perpendicular to the feed tube axis X2, can be adjusted to increase or decrease the flow rate of the gaseous dopant 202 passing therethrough. For example, the cross-sectional area of ​​the portion 236 of the channel 228 can be decreased by increasing the length of the base 232 of the evaporation capsule 208. Similarly, the length of the portion 236 of the channel 228 can be increased or decreased by changing the height of the capsule sidewall 234.

[0032] The feed tube 206 may also include a guide 238 disposed within the channel 228 above the evaporation capsule 208 to facilitate the flow of the volatile dopant 216 into the evaporation capsule 208. The guide 238 may also act as a fluid flow restrictor, allowing the passage of the volatile dopant 216 while restricting the backflow of the gaseous dopant 202. Alternatively, the guide 238 may act as a one-way valve for the dopant supplied to the inner chamber 110 via the gas doping system 200.

[0033] The guide 238 may be conical and extend inward from the feed tube sidewall 230 and downward toward the second end 212. In alternative embodiments, the guide 238 may have any suitable configuration that enables the gas doping system 200 to function as described herein. The guide 238 funnels the volatile dopant 216 through the opening 240 into the evaporation receptacle. Once the volatile dopant 216 is vaporized within the evaporation capsule 208, the guide 238 redirects the gaseous dopant 202 flowing upward and away from the opening 240, thereby limiting backflow of the gaseous dopant 202. Additionally, the guide 238 directs the inert gas 218 through the opening 240 (which has a smaller diameter than the channel 228), creating a localized high-pressure region of the inert gas 218 near the opening 240, thereby limiting backflow of the gaseous dopant 202.

[0034] The feed tube 206 may also include a fluid distribution plate (not shown) that facilitates distributing the gaseous dopant 202 across the melt-gas interface 126. The fluid distribution plate may be coupled to the feed tube 206 at the second end 212. The fluid distribution plate may have a hemispherical, conical, rectangular, or square shape, or any other suitable shape that enables the gas doping system 200 to function as described herein.

[0035] The evaporation capsule 208 and the feed tube 206, as well as the guide 238 and the fluid distribution plate (if included), can be made of any suitable material that enables the gas doping system 200 to function as described herein. In some embodiments, these components are each suitably made from fused silica (e.g., a single piece of fused silica). In yet other embodiments, the evaporation capsule 208 and the feed tube 206, as well as the guide 238 and the fluid distribution plate, may be manufactured as separate components. Integrating the evaporation capsule 208 within the feed tube 206 can provide a relatively simple construction of the gas doping system 200 and can reduce the overall size of the gas doping system 200. As a result, it is easy to position the feed tube 206 and the evaporation capsule 208 within the furnace using a positioning system such as the positioning system 242.

[0036] The feed tube 206 is slidably coupled to a positioning system 242 that raises and / or lowers the feed tube 206 along the feed tube axis X2. The positioning system 242 includes a rail 244, a coupling member 246, and a motor (e.g., a stepper motor) (not shown). The coupling member 246 slidably couples the feed tube 206 to the rail 244. The motor moves the coupling member 246 and the feed tube 206 along the rail 244. The rail 244 extends in a direction generally parallel to the feed tube axis X2. Using the positioning system 242, the second end 212 of the feed tube 206 and the evaporation capsule 208 are raised and lowered in and out of the inner chamber 110. Additionally, the positioning system 242 facilitates adjustment of the height H of the second end 212 above the melt-gas interface 126.

[0037] The positioning system 242 is communicatively coupled to the controller 220. The controller 220 can be programmed to control the positioning system 242 to dynamically adjust the height H of the second end 212 of the feed tube 206 above the melt-gas interface 126 during the crystal growth process, as well as the speed at which the feed tube 206 moves along the rails 244 to adjust the height H of the second end 212. For example, the processor 222 can send and receive signals to and from the controller 220 and / or the positioning system 242 based on one or more user-defined and / or environment-specific parameters. The user-defined parameters for controlling the positioning system 242 can be received by a user interface 224, which communicates the user-defined parameters to the processor 222 and / or the controller 220. As described above, the sensor 226 receives and / or measures the environment-specific parameters and communicates such environment-specific parameters to the processor 222 and / or the controller 220. The user-defined parameters and environment-specific parameters may be used by the processor 222 and / or the controller 220 to cause the positioning system 242 to adjust the height H of the second end 212 of the feed tube 206 and / or to control the rate at which the height H of the second end 212 changes with movement of the feed tube 206 along the rail 244.

[0038] In operation, the Czochralski process (batch or continuous) begins by loading polycrystalline silicon (or "polysilicon") into the crucible 106. The solid polysilicon added to the crucible 106 is typically granular polysilicon, although chunk polysilicon may also be used and is fed into the crucible 106 using a polysilicon feeder (not shown) optimized for use with granular polysilicon. Chunk polysilicon typically has a size of 3 to 45 millimeters (e.g., largest dimension), while granular polysilicon typically has a size of 400 to 1400 microns. Granular polysilicon has several advantages, including providing easy and precise control of the feed rate due to its smaller size. However, the cost of granular polysilicon is typically higher than that of chunk polysilicon due to the chemical vapor deposition process or other fabrication methods used in its production. Chunk polysilicon has the advantage of being cheaper and capable of higher feed rates, given its larger size.

[0039] Generally, the melt 104 from which the ingot 102 is drawn is formed by loading polycrystalline silicon into a crucible 106 to form an initial silicon charge. Typically, the initial charge is about 100 kilograms to about 1000 kilograms of polycrystalline silicon, which may be granular, chunk, or a combination of granular and chunk. The mass of the initial charge depends on the desired crystal diameter and the configuration of the ingot puller 100. In some embodiments, the initial polycrystalline silicon charge is sufficient to grow one single crystal silicon ingot, i.e., in a batch Czochralski process. Typically, the total axial length (measured in the direction of the pulling axis X1) of the solid body of the single crystal silicon ingot 102 is at least about 1100 millimeters (mm). In a continuous Czochralski process, the polycrystalline silicon is continuously fed during crystal growth, so the initial charge does not reflect the length of the crystal. Therefore, the initial charge may be smaller, such as about 100 kg to about 200 kg. If the polycrystalline silicon is continuously fed and the height of the inner chamber 110 is sufficiently high, the axial length of the ingot 102 can extend to a length such as 4000 mm. Various sources of polycrystalline silicon can be used, including, for example, granular polycrystalline silicon produced by the thermal decomposition of silane or halosilane in a fluidized-bed reactor or polycrystalline silicon produced in a Siemens reactor. Once the polycrystalline silicon is added to the crucible to form a charge, the charge is heated to a temperature above the melting temperature of silicon (e.g., about 1414°C) to melt the charge and thereby form a silicon melt 104 containing molten silicon. The silicon melt 104 has an initial volume of molten silicon and an initial melt height level, with these parameters being determined by the size of the initial charge. In some embodiments, the crucible 106 containing the silicon melt is heated to a temperature of at least about 1425°C, at least about 1450°C, or even at least about 1500°C. The initial polycrystalline silicon charge is heated by supplying power to heater 114 .

[0040] Once the solid polycrystalline silicon charge liquefies to form the silicon melt 104, the seed crystal 118 is lowered into contact with the melt 104. The seed crystal 118, with the silicon attached, is then withdrawn from the melt 104, thereby forming a solid-melt interface 124 near or at the surface of the melt 104. Generally, the initial pull rate of the seed crystal 118 is fast to form a neck portion of the ingot having a diameter relatively small relative to the diameter of the body of the subsequently grown ingot 102. In some embodiments, the seed crystal 118 is withdrawn at a neck pull rate of at least about 1.0 mm / min, e.g., from about 1.5 mm / min to about 6 mm / min. In some embodiments, the seed crystal 118 and the crucible 106 are rotated in opposite directions, i.e., counter-rotation. The counter-rotation achieves convection in the silicon melt 104. Rotation of the seed crystal 118 is primarily used to provide a symmetrical temperature profile, reduce angular fluctuations in impurities, and control the shape of the solid-melt interface 124. In some embodiments, the seed crystal 118 is rotated at a speed of about 5 rpm to about 30 rpm. In some embodiments, the seed crystal rotation speed may vary during growth of the main body of the single crystal silicon ingot 102. In some embodiments, the crucible 106 is rotated at a speed of about 0.5 rpm to about 10 rpm. In some embodiments, the seed crystal 118 is rotated at a faster speed than the crucible 106. Typically, the neck portion has a length of about 300 millimeters to about 700 millimeters, although the length of the neck portion may vary outside these ranges.

[0041] After the neck is formed, an outwardly flaring seed-cone portion of the ingot 102 adjacent the neck is grown. Typically, the pull rate of the seed crystal 118 is reduced from the neck pull rate to a rate suitable for growing the outwardly flaring seed-cone portion. For example, the seed-cone pull rate during growth of the outwardly flaring seed-cone portion is between about 0.5 mm / min and about 2.0 mm / min. In some embodiments, the outwardly flaring seed-cone portion has a length between about 100 mm and about 400 mm. The length of the outwardly flaring seed-cone portion may vary outside of these ranges. In some embodiments, the outwardly flaring seed-cone portion is grown to a terminal diameter between about 150 mm and about 450 mm. The terminal diameter of the outwardly flaring seed-cone portion is generally equivalent to the constant diameter of the main ingot body of the single crystal silicon ingot 102.

[0042] After formation of the neck and the outwardly flaring seed-cone portion adjacent the neck portion, a main ingot body of the ingot 102 is grown having a constant diameter adjacent the outwardly flaring seed-cone portion. The constant diameter portion of the main ingot body has a periphery, a central axis parallel to the periphery and the pull axis X1, and a radius extending from the central axis to the periphery. The central axis also passes through the cone portion and the neck. The diameter of the main ingot body may vary; in some embodiments, the diameter may be about 150 mm, at least about 150 mm, about 200 mm, at least about 200 mm, about 300 mm, at least about 300 mm, about 450 mm, or even at least about 450 mm. Alternatively, the radial length of the solid main ingot body of the single crystal silicon ingot 102 is about 75 mm, at least about 75 mm, about 100 mm, at least about 100 mm, about 150 mm, at least about 150 mm, about 225 mm, or even at least about 225 mm. The main ingot body of the single crystal silicon ingot 102 is ultimately grown to an axial length (measured along the pulling axis X1) of at least about 1000 mm, such as at least 1200 mm, such as at least 1250 mm, such as at least 1400 mm, such as at least 1500 mm, or at least 2000 mm, or at least 2200 mm, such as 2200 mm, or at least about 3000 mm, or at least about 4000 mm. In some preferred embodiments, the total axial length of the solid main ingot body of the single crystal silicon ingot 102 is at least about 1100 mm, such as from about 1200 mm to about 1300 mm, for example from about 1200 mm to about 1250 mm.

[0043] In the continuous Czochralski process, polycrystalline silicon, i.e., granules, chunks, or a combination of granules and chunks, is added to the melt 104 during growth of the main ingot body of the single crystal silicon ingot 102, thereby achieving a constant volume of molten silicon in the melt 104 and a constant melt height level. Maintaining a substantially constant melt volume during growth of most of the axial length of the body of the single crystal silicon ingot 102 makes it possible to achieve high ingot quality over most of the axial length of the body of the single crystal silicon ingot 102 at a constant pulling rate. A constant melt volume regardless of crystal length makes it possible to maintain a constant solid-melt interface 124 and therefore uniform crystal quality over most of the body of the ingot 102. Thus, in some embodiments, the volume of the melt 104 changes by no more than about 1.0% by volume during the growth of at least about 90% of the body of the single crystal silicon ingot 102, or by no more than about 0.5% by volume during the growth of at least about 90% of the body of the single crystal silicon ingot 102, or even by no more than about 0.1% by volume during the growth of at least about 90% of the body of the single crystal silicon ingot 102. Alternatively, in some embodiments, the melt height level changes by less than about + / - 0.5 millimeters during the growth of at least about 90% of the body of the single crystal silicon ingot 102.

[0044] In the batch Czochralski process, the initial charge of polycrystalline silicon is sufficient to grow the entire length of the ingot 102. Rather than maintaining a constant melt height level, the volume of the melt 104 is depleted as the ingot 102 grows. In some embodiments, growing the ingot 102 in the batch Czochralski process may require vertical movement of the crucible 106 in the same direction as the ingot is pulled, i.e., along the pull axis X1.

[0045] During growth of the ingot 102, gaseous dopants 202 are introduced into the melt 104 using a gas doping system 200 to modify and / or control the base resistivity of the ingot 102. Preferably, the gas doping process can begin once a predetermined axial length of the body of the ingot 102 has been grown. In a batch Czochralski growth process, for example, significant resistivity variations in the body of the ingot 102 and / or changes in the type of the ingot 102 can occur as the melt 104 is depleted during the growth of a single ingot 102. As the melt 104 is depleted, dopants previously introduced into the melt 104 and having low segregation coefficients (e.g., n-type dopants, such as arsenic or phosphorus) accumulate in the melt 104, changing the resistivity of the growing ingot 102. Thus, a gas doping process can be initiated to dope or counter-dope the ingot 102 with a gaseous dopant 202 suitable for correcting and / or controlling resistivity variations at later stages of the growth process. The time at which the gas doping process is initiated can be manually or automatically controlled by the controller 220 based on user-defined or environment-specific parameters. In some examples, once a particular axial length of the body of the ingot 102 has been grown, the gas doping process is initiated at a suitable time based on empirical data and a predicted resistivity drop.

[0046] To begin the doping process, an initial charge of solid or liquid phase volatile dopant 216, such as a volatile p-type dopant (e.g., boron) or a volatile n-type dopant (e.g., arsenic, phosphorus), or any other element or compound having a suitably low sublimation or evaporation temperature that enables the gas doping system 200 to function as described herein, is introduced from dopant feed source 204 into feed tube 206. The amount and type of initial charge of volatile dopant 216 is selected to achieve a targeted modification of the base resistivity of the ingot 102. The solid dopant falls downward through channel 228 in feed tube 206 and is funneled by guide 238 through opening 240 into evaporation capsule 208.

[0047] At this stage, the second end 212 of the feed tube 206 may be at an initial height (not shown in FIG. 1 ) above the melt-gas interface 126. The initial height may also be referred to herein as a first height. Heat is supplied to the evaporation capsule 208 to vaporize the volatile dopant 216. In the example shown in FIG. 1 , heat is supplied to the evaporation capsule 208 in the form of radiant heat from the melt 104 and the heat source 112, which may include a heater 114. When the second end 212 of the feed tube 206 is at an initial height above the melt-gas interface 126, the evaporation capsule 208 positioned proximate the second end 212 may not receive enough radiant heat from the melt 104 and the heat source 112 to raise the temperature of the evaporation capsule 208 to a temperature sufficient to vaporize the volatile dopant 216. The positioning system 242 is used to lower the feed tube 206 along the feed tube axis X2 so that the second end 212 is positioned at a height H (shown in FIG. 1 ) above the melt-gas interface 126. When the second end 212 is at height H, the evaporation capsule 208 is positioned sufficiently close to the melt 104 so that radiant heat from the melt 104 and the heater 114 is sufficient to vaporize the volatile dopant 216 in the evaporation capsule 208 into the gaseous dopant 202. For example, the height H may be about 1 centimeter and about 15 centimeters above the melt-gas interface 126. In other embodiments, a separate heating element (not shown) may be used to supply heat to the evaporation capsule 208 to vaporize the volatile dopant 216 therein into the gaseous dopant 202.

[0048] 1 , the second end 212 at height H can be positioned in a portion 138 of the passage 134 defined by the heat shield 130 located below the cooling jacket 132. Alternatively, the second end 212 at height H can be positioned within the gap 136 defined between the melt-gas interface 126 and the heat shield 130. Movement of the feed tube 206 to position the second end 212 at height H may require the feed tube 206 to pass through the heat shield 130. The heat shield 130 may include a conduit (not shown) therein sized and shaped to receive the feed tube 206 and allow movement of the feed tube 206 therethrough.

[0049] The gaseous dopant 202, formed by heating an initial charge of volatile dopant 216 within the evaporation capsule 208, then flows out the second end 212 toward the melt-gas interface 126. The gaseous dopant 202 contacts the surface of the melt 104 at the melt-gas interface 126 and flows into the melt 104. The dopant species introduced into the melt 104 are transported by diffusion and convection toward the solid-melt interface 124 and are taken up by the growing ingot 102.

[0050] Doping the melt 104 with a gaseous dopant 202 can present several challenges for producing a growing ingot 102 with a target resistivity. First, a target dopant concentration in the melt 104 must be determined to achieve the target resistivity of the ingot 102. The target dopant concentration is determined based on a number of transport mechanisms that affect the amount of dopant in the melt 104 that is taken up by the ingot 102, including, for example, convective mass transport, diffusion resulting from dopant concentration gradients, and dopant segregation from the ingot 102. Also, in the case of a continuous Czochralski growth process, additional dopant and melt material added to the melt 104 throughout the growth process affect the dopant concentration in the ingot 102.

[0051] These transport mechanisms can be simulated to study thermal heat flow and dopant concentration distribution and to estimate the path of dopant species from the melt-gas interface 126 through the melt 104 to the solid-melt interface 124. Transport mechanism studies can be used to control for variations in dopant concentration at the solid-melt interface 124, which could otherwise result in non-uniform axial and radial resistivity profiles of the growing ingot 102. For example, FIG. 3 shows melt convection patterns (left) and dopant diffusion patterns (right) in the melt 104, depicted by the arrows in FIG. 3 indicating the direction of dopant transport. In the illustrated example, the melt convection pattern includes two vortices, and the average melt velocity is approximately 2 mm / sec. From the point where the gaseous dopant 202 enters the melt 104, the dopant species may require more than 16 minutes to reach the solid-melt interface 124. These transport patterns are shown by way of example only. The transport mechanisms depend on the environmental conditions and operating parameters within the ingot puller 100, including, for example, the pull rate of the seed crystal 118, the pressure within the inner chamber 110, the rotation rate of the crucible 106, the rotation rate of the seed crystal 118, the gas flow rate across the surface of the melt 104, and the size of the gap 136 between the heat shield 130 and the melt-gas interface 126. Transport properties, such as the diffusion coefficients of various volatile dopants 216, can be empirically determined for a particular configuration of the ingot puller 100 and growth process based on another Czochralski growth procedure performed using the ingot puller 100 and can be used to generate simulations, such as that shown in FIG. 3, to study the transport mechanisms. For example, for a boron dopant species, the boron dopant diffusion coefficient in the silicon melt 104 is 6×10 -5 It may also be kg / m / s.

[0052] The shape of the solid-melt interface 124 may also be controlled by adjusting the parameters described above, and the shape of the solid-melt interface 124 can affect the axial and radial resistivity gradients of the growing ingot 102. As shown in FIG. 3 , the solid-melt interface 124 has an M-curve shape, with the center of the concave portion of the solid-melt interface 124 extending approximately 8.5 mm into the melt 104. The ingot 102 solidifies from the crystal edge at the intersection of the solid-melt interface 124 and the melt-gas interface 126. As dopant species enter the melt 104 and are transported to the solid-melt interface 124, the resistivity of the ingot 102 is modified starting from the crystal edge.

[0053] By simulating the transport mechanism of the dopant species in the melt 104, the dopant concentration at the solid-melt interface 124 can be estimated based on the concentration of the dopant species flowing into the melt from the gaseous dopant 202. The concentration of the dopant taken up by the crystalline ingot 102 can be determined from the dopant concentration in the melt, taking into account the dopant segregation coefficient and solidification rate. For a batch Czochralski growth process, the following equation can be used: TIFF2025534705000002.tif1481 ​​formula 1 where C c represents the dopant concentration in the crystal ingot, and k i represents the effective segregation coefficient of the dopant (which may be known or empirically determined), η represents the fraction of the grown ingot 102, and C c ,0 represents the dopant concentration of the melt 104 from which the crystalline ingot 102 was grown. The resistivity of the crystalline ingot 102 can be determined based on the dopant concentration in the ingot 102 using standard conversion tables and / or formulas known in the art, such as standards SEMI MF723-0307 and SEMI F723-99 published by SEMI International Standards, which are incorporated herein by reference for all relevant consistent purposes.

[0054] Thus, the above simulations and calculations can be used to predict the resistivity, as well as the axial and radial resistivity gradients, within the ingot 102 pulled from the melt 104 during the Czochralski growth process. These can be used as a basis for setting target dopant concentrations in the melt 104 at various stages of the growth process. However, the use of gaseous dopants 202 presents the additional challenge of controlling the amount of dopant added to the melt 104 to meet the target dopant concentration and, consequently, control the axial and radial resistivity profiles of the ingot grown from the melt 104. In addition to the above-mentioned parameters related to the transport of dopant species in the melt 104, many factors affect the doping efficiency of the volatile dopant 216 contained in the evaporation capsule 208. "Doping efficiency" refers to the amount of dopant species taken up by the growing ingot 102 versus the amount of volatile dopant 216 added to the feed tube 206 in a single charge. For example, the gas transport characteristics of the gaseous dopant 202 traveling from the second end 212 of the feed tube 206 to the melt-gas interface 126 affect the amount of gaseous dopant 202 that enters the melt 104. The path of the gaseous dopant 202 is guided by diffusion of the gaseous dopant 202 and forced convection by the inert gas 218 and / or process gas supplied by the gas inlet port 128. Similar to the transport of dopant species in the melt 104 (shown in FIG. 3 ), the gas transport of the gaseous dopant 202 toward the melt-gas interface 126 can be simulated as shown in FIG. 4 . Specifically, FIG. 4 shows simulated profiles of velocity distribution (left) and gaseous dopant 202 concentration (right) within the inner chamber 110 of the ingot puller 100.

[0055] Additionally, the amount of gaseous dopant 202 produced depends on both the amount of volatile dopant 216 delivered to the evaporation capsule 208 as well as the thermal conditions used to vaporize the volatile dopant 216 within the evaporation capsule 208. As discussed above, the evaporation capsule 208 must reach a suitable temperature to vaporize the volatile dopant 216 and form a suitable amount of gaseous dopant 202 that can flow to the melt-gas interface 126. Otherwise, the volatile dopant 216 will remain within the evaporation capsule 208 and will not be introduced to the melt 104 as gaseous dopant 202. The temperature conditions required to vaporize the volatile dopant 216 depend on the phase changes the volatile dopant 216 undergoes and the temperatures at which these changes occur. For example, in the example of delivering solid boric acid powder to the evaporation capsule 208 to introduce boron as a dopant species into the melt 104, the following phase changes and reactions occur: 1.H3BO3(s)-->HBO3(s)+H2O(g), T>170℃(443K), 2.4HBO2(s)-->H2B4O7(l)+H2O(g), T>300℃(573K), 3.H2B4O7(l)-->2B2O3(l)+H2O(g), T>330℃(600K), 4.B2O3(l)-->B2O3(g), T>510℃(783K) See High-Temperature Vaporization of B2O3(l) under Reducing Conditions, J.Phys.Chem.B 2011, 115, 45, 13253-13260. The temperature in the inner chamber near the melt 104 can reach 1200-1400 K. Thus, at the operating temperatures experienced by the capsule 208 when the second end 212 is at height H, the concomitant vaporization of B2O3(l) occurs according to equilibrium conditions.

[0056] The phase change and reaction properties of the volatile dopant 216 can be used to set a target temperature for the evaporation capsule 208 such that sufficient vaporization of the volatile dopant 216 occurs.

[0057] As discussed above, the heat supplied to the evaporation capsule 208 depends on the height of the second end 212 of the feed tube 206 above the melt-gas interface 126. Accordingly, the vaporization of the volatile dopant 216 to produce the gaseous dopant 202 can be controlled by controlling the height H of the second end 212 and the rate at which the positioning system 242 lowers the feed tube 206 to move the second end 212 from an initial height to height H (also referred to as second height H). Specifically, the rate at which the second end 212 is moved from the initial height to the second height H controls the rate at which the temperature of the evaporation capsule 208 increases, which in turn controls the rate at which the volatile dopant 216 vaporizes. Therefore, by controlling the height H and the rate at which the second end 212 moves from the initial height to height H, the amount of gaseous dopant 202 flowing into the melt 104 can be controlled, taking into account the above-described considerations regarding gas transport properties.

[0058] However, a further challenge is the difficulty of directly measuring the evaporation rate of the volatile dopant 216 and the temperature of the evaporation capsule 208 during the crystal growth process. For example, a temperature sensor measuring the temperature of the evaporation capsule 208 during the growth process may undesirably affect or influence the gas dopant process and therefore may not be used. Therefore, it is difficult to determine a suitable height H and travel speed of the feed tube 206 to achieve a targeted evaporation of the volatile dopant 216 and, therefore, a targeted dopant concentration in the melt 104. The temperature profile of the second end 212 of the feed tube 206 relative to the height above the melt-gas interface 126 can be generated by two or more thermal simulations, in which the height H is varied during the thermal simulations (see FIG. 5 ). The targeted height H of the second end 212 may be set based on the simulated temperature profile. Thermal simulations were performed using commercially available tools and other software codes that model heat transfer within a puller (e.g., ingot puller 100) during the growth of a crystalline ingot (e.g., ingot 102). The temperature of second end 212 may also be measured experimentally using a temperature sensor (e.g., sensor 226) during a sample run of the puller.

[0059] In addition to the simulated temperature profile, the doping efficiency of the volatile dopant 216 can be estimated based on the height H and used to control the height H of the second end 212 of the feed tube and the speed at which the second end 212 moves from its initial height to the height H. The doping efficiency is the ratio of the amount of volatile dopant 216 fed into the evaporation capsule 208 to the amount of dopant species incorporated into the ingot 102. The doping efficiency profile (shown in FIG. 6) can be generated based on simulation or experimentally. To experimentally determine the doping efficiency, a test run can be performed, and the resistivity of the resulting ingot 102 can be measured versus the amount of volatile dopant 216 added. As shown in FIG. 6, the doping efficiency increases as the height H decreases. The doping efficiency affects the amount of volatile dopant 216 charged to achieve a target resistivity in the ingot 102. The doping efficiency remains below 1% even in the higher range of doping efficiencies (0.3% to 0.35%). This may indicate that a longer retention time of the second end 212 of the feed tube 206 at height H should be used. The low doping efficiency may be due to a significant portion of the volatile material 216 remaining in the capsule 208 or being carried out with the process gas and / or inert gas 218 through the exhaust of the puller 100.

[0060] 7, an exemplary method 300 for growing a doped single crystal silicon ingot (e.g., ingot 102) using an ingot puller (e.g., ingot puller 100) and a gas doping system (e.g., gas doping system 200) is shown. In a first step 302, the single crystal silicon ingot 102 is grown by contacting a silicon melt 104 with a seed crystal 118 and pulling the seed crystal 118 from the melt 104 at a pull rate sufficient to grow an ingot 102 having a neck region, an outwardly flaring seed-cone or shoulder region adjacent the neck region, and a body region adjacent the shoulder region. The melt 104 is prepared by adding polycrystalline silicon to a crucible 106 and heating the crucible 106 with a heater 114 to form the melt 104.

[0061] The single crystal silicon ingot 102 grown in the first step 302 may suitably be a low resistivity ingot, i.e., the ingot 102, a segment of the ingot (e.g., the neck region, the outwardly flaring seed-cone, and / or the body region), and / or any single crystal silicon wafers sliced ​​from the ingot 102, have a relatively low minimum bulk resistivity, such as less than about 200 ohm-cm, less than about 150 ohm-cm, less than about 100 ohm-cm, less than about 50 ohm-cm, less than about 20 ohm-cm, less than about 1 ohm-cm, less than about 0.1 ohm-cm, or even less than about 0.01 ohm-cm. In some embodiments, the ingot, segment, or any single crystal silicon wafer sliced ​​therefrom has a relatively low minimum bulk resistivity, such as less than about 200 ohm-cm, or between about 0.01 ohm-cm and about 200 ohm-cm, e.g., between about 1 ohm-cm and about 200 ohm-cm, between about 20 ohm-cm and about 200 ohm-cm, between about 40 ohm-cm and about 100 ohm-cm, or between about 60 ohm-cm and about 80 ohm-cm. Low resistivity ingots and wafers sliced ​​therefrom can include electrically active dopants, such as p-type dopants such as boron, aluminum, gallium, and indium, and / or n-type dopants such as phosphorus, arsenic, and antimony.

[0062] In a second step 304, during growth of the ingot 102 in the first step 302, a charge of volatile dopant 216 is added into the feed tube 206 and received by an evaporation capsule 208 disposed within the feed tube 206 proximate the second end 212. The charge of volatile dopant 216 is added into the feed tube 206 by a dopant feed source 204. The amount of volatile dopant 216 added in the first step 302 is selected to achieve a suitable modification of the base resistivity of the ingot 102 being grown. The amount of charge added by the feed source 204 may be controlled automatically by a controller 220 or manually. Before, during, and / or after adding the charge of volatile dopant 216 into capsule 208 in first step 302, in step 306, feed tube 206 is positioned within inner chamber 110 of ingot puller 100 so that open second end 212 of feed tube 206 has an initial height relative to the surface of melt 104. The initial height is a suitable distance from melt 104 so that radiant heat does not substantially raise capsule 208 to the vaporization temperature of volatile dopant 216. Positioning system 242 is used to position feed tube 206 at the appropriate initial height, which may be automatically controlled by controller 220 or manually controlled.

[0063] In step 308, the feed tube 206 is adjusted within the inner chamber 110 to move the open second end 212 of the feed tube 206 from an initial height to a height H relative to the surface of the melt 104. The height H is less than the initial height and is a suitable distance to allow radiant heat from the melt 104 and the heater 114 to raise the capsule 208 to the vaporization temperature of the volatile dopant 216. The open second end 212 of the feed tube 206 is moved from the initial height to the height H at a certain rate. A positioning system 242 is used to adjust the feed tube 206 to move the open second end 212 to the appropriate height H, which may be automatically controlled by the controller 220 or manually controlled. In step 310, capsule 208 containing volatile dopant 216 is heated by radiant heat from melt 104 and heater 114 as open second end 212 is moved at a velocity rate from an initial height to height H. As capsule 208 moves toward the surface of melt 104, the temperature of capsule 208 increases to a temperature suitable for vaporizing volatile dopant 216, thereby producing gaseous dopant 202. Thus, both height H and velocity rate affect the rate at which volatile dopant 216 vaporizes to form gaseous dopant 202, also referred to herein as the vaporization rate.

[0064] The height H and velocity rate are each selected to control the vaporization rate of the volatile dopant 216 within the capsule 208. For example, the height H and velocity rate can be selected based on the temperature profile (shown in FIG. 5) generated for the second end 212 at various heights above the surface of the melt 104, as well as the phase change and reaction characteristics of the particular volatile dopant 216 being used. Additionally or alternatively, the height H and velocity rate are selected based on the doping efficiency profile (shown in FIG. 6) generated for the volatile dopant 216 at various heights above the surface of the melt 104. The doping efficiency may also be used to select the amount of volatile dopant 216 to include in the charge during step 304.

[0065] In step 312, dopant species are introduced into the melt 104 while growing the body region of the single crystal silicon ingot 102 by contacting the surface of the melt 104 (i.e., at the melt-gas interface 126) with a gaseous dopant 202. By simulating the transport mechanism of the dopant species in the melt 104 as described herein, the dopant concentration at the solid-melt interface 124 can be estimated based on the concentration of the dopant species flowing into the melt from the gaseous dopant 202. The concentration of the dopant taken up by the crystalline ingot 102 can be determined from the dopant concentration in the melt, taking into account the dopant's segregation coefficient and solidification rate, and the resistivity of the growing ingot 102 can thereby be determined. In this regard, the vaporization rate is controlled to introduce a suitable amount of dopant species into the melt 104 for uptake by the ingot 102 and to control the rate at which the dopant species is uptaken by the ingot 102 to maintain the resistivity of the body region over the axial length of the body region. Based on this, the height H and the rate at which the second end 212 moves to height H may be selected, as described above.

[0066] For example, the evaporation rate can be controlled so that the dopant species is introduced at a rate sufficient to maintain the resistivity of the body region within a predetermined range (e.g., about 0.01 ohm-cm to about 200 ohm-cm, about 20 ohm-cm to about 200 ohm-cm, about 30 ohm-cm to about 100 ohm-cm, or about 60 ohm-cm to about 80 ohm-cm) and to control the variation in resistivity of the body region to within + / −15% over an axial length of at least 300 mm (or more), at least 500 mm, or even at least 800 mm. In some examples, the evaporation rate can be controlled so that the dopant species is introduced at a rate sufficient to maintain the resistivity of the body region within a predetermined range (e.g., from about 30 ohm-cm to about 100 ohm-cm, or from about 60 ohm-cm to about 80 ohm-cm) and to control the variation in resistivity of the body region to within + / - 10% over an axial length of at least 300 mm, at least 500 mm, or even at least 800 mm.

[0067] In step 312, the feed tube 206 remains in a position where the open second end 212 has a height H above the surface of the melt 104 for a period of time suitable to allow the gaseous dopant 202 to exit the feed tube 206 at a vaporization rate. The residence time of the feed tube 206 in this position during step 312 may be an additional control variable determined by the considerations discussed above. After step 312, the positioning system 242 may raise the feed tube 206 so that the second end 212 is at the initial height. The positioning system 242 is used to adjust the feed tube 206 to move the open second end 212 to the initial height, which may be automatically or manually controlled by the controller 220 once the controller 220 determines that the residence time of the second end 212 at height H has elapsed.

[0068] In some embodiments, method 300 can repeat at step 304, where one or more subsequent charges of volatile dopant 216 are successively added to feed tube 206 and vaporized into gaseous dopant 202, and dopant species from the subsequent batch of gaseous dopant 202 are introduced into melt 104 at step 312. Each of the multiple charges of volatile dopant 216 is added after dopant species from a previous charge of volatile dopant 216 have been introduced into melt 104. Each of the multiple charges can include the same type of volatile dopant 216 as the previous charge or a different volatile dopant 216. Feed tube 206 can be repositioned so that second end 212 is at an initial height for each subsequent charge of volatile dopant 216.

[0069] 8-11, gas dopant control and resulting resistivity in an ingot 102 grown according to method 300 are shown. FIG. 8 is a plot illustrating gaseous dopant control over time during a gas doping process. As shown in FIG. 8, the evaporation rate of the volatile dopant 216 can be controlled so that the amount of gaseous dopant 202 generated increases and then decreases at a controlled linear rate based on the selected height H and the velocity rate of the second end 212 moving to the second height H. FIG. 9 is a plot illustrating the average dopant concentration (at the solid-melt interface 124) in the silicon melt 104 during the gas doping process shown in FIG. 8 and the radial resistivity change of the ingot 102 during growth. As shown in FIG. 9, the amount of dopant at the solid-melt interface 124 increases at a constant rate to a maximum dopant concentration and then decreases at a constant rate under the control region (gas dopant process time), consistent with the gaseous dopant 202 generation rate shown in FIG. 8. FIG. 9 also shows that the radial resistivity gradient across the diameter of the ingot 102, calculated as the difference in resistivity at the axial center of the ingot 102 and the edge of the ingot 102 divided by the average resistivity, (res_cent-res_edge) / average, decreases at a controlled rate under the controlled regime and then decreases. Thus, control of the vaporization rate translates into control of the dopant species at the solid-melt interface 124 and control of the radial resistivity of the growing ingot 102. FIG. 10 is a plot showing the axial resistivity change along the growing ingot during the crystal growth process with and without a gas doping process. As shown in FIG. 10, without the gas doping process, the axial resistivity of the main body portion of the ingot 102 gradually decreases and falls below the lower resistivity limit (LRL) when the main body portion reaches a certain axial length (e.g., approximately 500 mm). When a controlled gas doping process according to the present disclosure is used, which may be initiated at a point where the resistivity may fall below the LRL, the axial resistivity is maintained within the range between the LRL and the upper resistivity limit (URL) over a significant portion of the axial length of the main ingot body (e.g., about 1000 mm).The axial resistivity can be further improved and maintained within the range between the LRL and the URL using multiple loadings of volatile dopant 216 at suitable intervals (as shown in FIG. 11 ). The range defined by the URL and the LRL can be, for example, + / −15% of the target resistivity, + / −13% of the target resistivity, or + / −10% of the target resistivity. The axial resistivity of the body ingot can be maintained within the range defined by the URL and the LRL over an axial length of at least 300 mm, at least 500 mm, or even at least 800 mm.

[0070] 12 , another exemplary ingot puller is generally designated 150. Ingot puller 150 includes the same features and elements as ingot puller 100 shown in FIG. 1 and described herein. In addition, ingot puller 150 includes a second gas doping system 400 for introducing gaseous dopant 202 into melt 104. Doping system 400 includes similar features and elements as those included in gas doping system 200 shown in FIG. 1 and described herein. Ingot puller 150 including both gas doping system 200 and gas doping system 400 can facilitate improved control of the base resistivity of ingots 102 grown by ingot puller 150.

[0071] As described above for gas doping system 200 (which may be referred to as “first gas doping system 200”), gas doping system 400 (which may be referred to as “second gas doping system 400”) includes a dopant feed source 404, a feed tube 406, and an evaporation capsule 408. The feed tube 406 extends along a feed tube axis X3 between a first end 410 and a second end 412. The first end 410 is located adjacent to the dopant feed source 404, and the second end 412 is positioned within the inner chamber 110 and oriented toward the surface of the melt 104. The feed tube 406 may extend between the first end 410 and the second end 412 through a valve assembly (not shown) that provides an entry point for the feed tube 406 through the outer housing 108 and seals the entry point when the feed tube 406 is removed from the ingot puller 150. The feed tube 406 is open at a first end 410 to receive a volatile dopant (e.g., volatile dopant 216 shown in FIG. 2 ) from a dopant feed source 404 and is open at a second end 412 to allow gaseous dopant 202 to flow out of the feed tube 406 toward the surface of the melt 104, particularly toward the melt-gas interface 126. The feed tube 406 may be angled relative to the pull axis X2 or may have a configuration or orientation similar to that described above for the feed tube 206.

[0072] The doping system 400 may also include an inert gas supply 414 coupled in fluid communication with the feed tube 406, as described above for the inert gas supply 214 in the doping system 200, to direct the gaseous dopant 202 from the feed tube 406 through the second end 412 to reduce backflow of the gaseous dopant 202.

[0073] A first end 410 of the feed tube 406 is coupled in flow communication with a dopant feed source 404. The dopant feed source 404 delivers a volatile dopant 216, which may be in the form of a solid-phase dopant or a liquid-phase dopant, to the first end 410 of the feed tube 406, as described above for the dopant feed source 204 of the doping system 200. The dopant feed source 404 may be automated, partially automated, or manually operated. Automatic control of the dopant feed source 404 may be facilitated by a controller 220 communicatively coupled to the dopant feed source 404. The controller 220 may be programmed to control the frequency and / or amount of the volatile dopant 416 delivered by the dopant feed source 404 into the feed tube 406.

[0074] The evaporation capsule 408 is disposed within the feed tube 406 proximate the second end 412 and within the inner chamber 110, as described above for the evaporation capsule 208 shown in Figure 2. The feed tube 406 and evaporation capsule 408 may have the same configuration as the feed tube 206 and evaporation capsule 208 shown and described above in Figures 1 and 2. The feed tube 406 may include guides (e.g., guide 238) and a fluid distribution plate, as described above for the feed tube 206.

[0075] The feed tube 406 is slidably coupled to a positioning system 442 that raises and / or lowers the feed tube 406 along the feed tube axis X3. The positioning system 442 includes a rail 444, a coupling member 446, and a motor (not shown). The coupling member 446 slidably couples the feed tube 406 to the rail 444. The motor moves the coupling member 446 and the feed tube 406 along the rail 444. The rail 444 extends in a direction generally parallel to the feed tube axis X3. Using the positioning system 442, the second end 412 of the feed tube 406 and the evaporation capsule 408 are raised and lowered in and out of the inner chamber 110. Additionally, the positioning system 442 facilitates adjustment of the height of the second end 412 above the melt-gas interface 126 (which may be similar to the height H of the second end 212 of the feed tube 206 described above). The positioning system 442 is communicatively coupled to the controller 220, which can be programmed to control the positioning system 442 to dynamically adjust the height of the second end 412 of the feed tube 406 above the melt-gas interface 126 during the crystal growth process, as described above with respect to the positioning system 242, and the rate at which the feed tube 406 moves along the rail 444 to adjust the height of the second end 412. The height to which the second end 412 of the feed tube 406 moves may be the same as the height H of the second end 212 of the feed tube 206 described above, and the rate at which the feed tube 406 moves to adjust the height of the second end 412 may be the same as the rate at which the feed tube 206 moves to adjust the height of the second end 412. Alternatively, second end 212 of feed tube 206 may be moved to height H at a first speed rate, and second end 412 of feed tube 406 may be moved to a second height different from height H and / or may be moved at a second speed rate different from the first speed rate.

[0076] The disclosed ingot puller and related gas doping system and method provide improvements over known ingot pullers that facilitate doping of ingots using gaseous dopants. By controlling the height of the feed tube above the silicon melt surface, the speed of movement of the feed tube, and the residence time of the feed tube at the controlled height during the doping process, the vaporization rate of volatile dopants within the feed tube can be fine-tuned and controlled. As a result, the amount of dopant species introduced into the melt and the rate at which the dopant species is introduced are controlled to achieve and maintain the base resistivity of the growing ingot.

[0077] When introducing elements of the invention or embodiments thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more 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.

[0078] Unless otherwise specified, terms expressing approximation, such as "approximately," "substantially," and "about" used herein indicate that the modified term may apply only to an approximate degree, as recognized by those skilled in the art, rather than to an absolute or complete degree. Thus, values ​​modified with terms such as "about," "approximately," and "substantially" are not limited to the exact value specified. In at least some instances, terms expressing approximation may correspond to the precision of an instrument for measuring the value. Additionally, unless otherwise specified, terms such as "first," "second," and the like are used herein merely as labels and are not intended to impose any order, position, or hierarchy on the items to which they refer. Furthermore, for example, a reference to a "second" item does not require or exclude the presence of, for example, a "first" or lower-numbered item or a "third" or higher-numbered item.

[0079] Since various changes can be made in the above described structures and methods 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. 1. A method for growing a doped single crystalline silicon ingot using an ingot pulling apparatus including an inner chamber, a crucible disposed within the inner chamber, a heat source, and a feed tube having an open end, the feed tube including a capsule proximate the open end, the method comprising: adding polycrystalline silicon to the crucible; heating the crucible with the heat source to form a silicon melt from the polycrystalline silicon in the crucible; growing the single crystal silicon ingot from the melt by contacting the melt with a seed crystal and withdrawing the seed crystal from the melt to grow the single crystal silicon ingot, the single crystal silicon ingot having a neck region, a shoulder region, and a body region; adding a charge of a volatile dopant to the feed tube, the charge of the volatile dopant being received by the capsule; positioning the feed tube within the inner chamber such that the open end of the feed tube has a first height relative to a surface of the melt; adjusting the feed tube within the inner chamber to move the open end of the feed tube from the first height to a second height relative to the surface of the melt, the second height being less than the first height, and the open end of the feed tube being moved from the first height to the second height at a rate of speed; heating the capsule containing the volatile dopant with radiant heat from the heat source and the surface of the melt as the open end moves from the first height to the second height at the rate of velocity to form a gaseous dopant, wherein the second height and the rate of velocity are each selected to control a vaporization rate of the volatile dopant; introducing a dopant species into the melt while growing the body region of the single crystal silicon ingot by contacting the surface of the melt with the gaseous dopant, wherein the vaporization rate is controlled such that the dopant species is introduced at a rate sufficient to maintain the resistivity of the body region over an axial length of the body region; A method comprising:

2. 10. The method of claim 1, wherein the evaporation rate is controlled to introduce the dopant species at a rate sufficient to maintain the resistivity of the body region within a predetermined range and to control the variation in the resistivity of the body region to within + / - 15% over an axial length of at least 300 mm.

3. 10. The method of claim 1, wherein the evaporation rate is controlled to introduce the dopant species at a rate sufficient to maintain a resistivity of the body region within a predetermined range and to control the variation in the resistivity of the body region to within + / - 15% over an axial length of at least 500 mm.

4. 10. The method of claim 1, wherein the evaporation rate is controlled to introduce the dopant species at a rate sufficient to maintain the resistivity of the body region within a predetermined range and to control the variation in the resistivity of the body region to within + / - 15% over an axial length of at least 800 mm.

5. 10. The method of claim 1, wherein the evaporation rate is controlled to introduce the dopant species at a rate sufficient to maintain a resistivity of the body region within a predetermined range and to control the variation in the resistivity of the body region to within + / - 10% over an axial length of at least 300 mm.

6. 10. The method of claim 1, wherein the evaporation rate is controlled such that the dopant species is introduced at a rate sufficient to maintain the resistivity of the body region within a predetermined range and to control the variation in the resistivity of the body region to within + / - 10% over an axial length of at least 500 mm.

7. 2. The method of claim 1, wherein the evaporation rate is controlled such that the dopant species is introduced at a rate sufficient to maintain a resistivity of the body region within a predetermined range and to control the variation in the resistivity of the body region to within + / - 10% over an axial length of at least 800 mm.

8. 8. The method of any one of claims 1 to 7, further comprising adding multiple charges of the volatile dopant to the feed tube, each of the multiple charges being added after dopant species from a previous volatile dopant charge have been introduced into the melt.

9. 9. The method of claim 1, wherein the vaporization rate is controlled such that introducing the dopant species comprises increasing the amount of the dopant species at a constant rate up to a maximum dopant concentration, followed by decreasing the amount of the dopant species at a constant rate.

10. 10. The method of any one of claims 1 to 9, further comprising introducing a flow of inert gas into at least one of the inner chamber and the feed tube to create an inert atmosphere, and using the flow of inert gas to direct the gaseous dopant to the surface of the melt.

11. The method of any one of claims 1 to 10, wherein adding the charge of the volatile dopant to the feed tube comprises adding a charge of a solid dopant to the feed tube.

12. The method of claim 11 , wherein the solid dopant is a solid n-type dopant.

13. The method of claim 11 , wherein the solid dopant is a solid p-type dopant.

14. The method of claim 13 , wherein the solid dopant is boric acid.

15. The ingot pulling system includes at least two feed tubes, each feed tube having an open end and a capsule adjacent the open end, and the method includes: adding a charge of the volatile dopant to each feed tube, the charge of the volatile dopant being received by the capsule of each of the feed tubes; positioning each feed tube within the inner chamber such that the open end of each feed tube has the first height; adjusting each feed tube within the inner chamber to move the open end of the feed tube from the first elevation to the second elevation at a rate of velocity; heating the capsules of each feed tube containing the volatile dopant by radiant heat from the heat source and the surface of the melt to form gaseous dopant as the open end of each feed tube moves from the first height to the second height at the velocity rate, wherein the second height and the velocity rate are each selected to control a vaporization rate of the volatile dopant in each capsule; introducing dopant species into the melt while growing the body region of the single crystal silicon ingot by contacting the surface of the melt with the gaseous dopant from each capsule, wherein the vaporization rate is controlled such that the dopant species is introduced at a rate sufficient to maintain the resistivity of the body region over an axial length of the body region; The method of any one of claims 1 to 14, further comprising:

16. 16. The method of any one of claims 1 to 15, wherein the ingot pulling system includes a heat shield surrounding the single crystal silicon ingot during growth, and wherein positioning the feed tube within the inner chamber includes positioning the open end of the feed tube within a channel defined between the heat shield and the body region of the single crystal silicon ingot.

17. 16. The method of any one of claims 1 to 15, wherein the ingot pulling system includes a heat shield surrounding the single crystal silicon ingot being grown, the heat shield defining a gap above the surface of the melt, and positioning the feed tube within the inner chamber includes positioning the open end of the feed tube within the gap.

18. The method of any one of claims 1 to 17, wherein adjusting the feed tube is performed after a predetermined axial length of the body region of the single crystal silicon ingot has been grown.

19. 19. The method of any one of claims 1 to 18, wherein the second height and the velocity rate selected to control the evaporation rate are determined at least in part on a simulated temperature profile of the open end of the feed tube as a function of height of the open end relative to the surface of the melt.

20. 20. The method of any one of claims 1 to 19, wherein the second height and the rate selected to control the evaporation rate are determined, at least in part, on a doping efficiency profile of the volatile dopant as a function of the height of the open end relative to the surface of the melt.

21. 21. The method of any one of claims 1 to 20, wherein the evaporation rate is controlled such that the dopant species is introduced at a rate sufficient to maintain a resistivity of the body region within a predetermined range of about 0.01 ohm-cm to about 200 ohm-cm over an axial length of the body region.

22. 1. An ingot pulling apparatus for growing a doped single crystal silicon ingot, comprising: an outer housing defining an inner chamber; a crucible disposed within the inner chamber for holding a silicon melt; a gas doping system for introducing dopant species into the melt, comprising: a feed tube extending between a first end and a second end, the second end being positioned within the interior chamber, the feed tube including a capsule disposed proximate the second end; a dopant feed source coupled in flow communication with the first end of the feed, the dopant source configured to add a volatile dopant to the feed; a positioning system configured to adjust a position of the feed tube between a first position where the second end of the feed tube is at a first height above a surface of the melt and a second position where the second end of the feed tube is at a second height above the surface of the melt that is less than the first height; a controller communicatively coupled to the dopant feed source and the positioning system, the controller configured to cause the dopant feed source to add a target amount of volatile dopant to the feed tube and to cause the positioning system to move the feed tube to the second position at a rate, the second height and the rate each selected to control a vaporization rate of the volatile dopant in the feed tube during an ingot pulling process; a gas doping system comprising: An ingot pulling apparatus comprising:

23. a second gas doping system for introducing dopant species into the melt, a second feed tube extending between a first end and a second end, the second end of the second feed tube being positioned within the inner chamber, the second feed tube including a second capsule disposed proximate the second end; a second dopant source coupled in flow communication with the first end of the second feed conduit, the second dopant source configured to add a volatile dopant to the second feed conduit; a second positioning system configured to adjust a position of the second feed pipe between a first position where the second end of the second feed pipe is at a first height above a surface of the melt and a second position where the second end of the second feed pipe is at a second height above the surface of the melt that is less than the first height; a second gas doping system comprising:

23. The apparatus of claim 22, wherein the controller is communicatively coupled to the second dopant feed source and the second positioning system and configured to cause the second dopant feed source to add a target amount of the volatile dopant to the second feed tube and the second positioning system to move the second feed tube to the second position at a speed rate, wherein each of the second height of the second feed tube and the speed rate is selected to control a vaporization rate of the volatile dopant in the second feed tube during the ingot pulling process.

24. 24. The apparatus of claim 23, wherein the second height of the second feed tube is different from the second height of the feed tube.

25. 25. Apparatus according to claim 23 or 24, wherein the velocity rate of the second feed is different from the velocity rate of the feed.

26. 26. The apparatus of claim 22, further comprising a heat shield surrounding a growth chamber within the inner chamber in which a single crystal silicon ingot is grown, wherein the second end of the feed tube in the second position is positioned within a channel within the growth chamber defined by the heat shield.

27. 26. The apparatus of claim 22, further comprising a heat shield surrounding a growth chamber within the inner chamber in which a single crystal silicon ingot is grown, the heat shield defining a gap above the surface of the melt, the second end of the feed pipe in the second position being positioned within the gap.

28. 28. The apparatus of any one of claims 22 to 27, wherein the controller is configured to determine the second height and the velocity rate based on a simulated temperature profile of the second end of the feed pipe as a function of height of the second end relative to the surface of the melt.

29. 29. The apparatus of any one of claims 22 to 28, wherein the controller is configured to determine the second height and the velocity rate based on a doping efficiency profile of the volatile dopant as a function of height of the second end relative to the surface of the melt.

30. 30. Apparatus according to any one of claims 22 to 29, wherein the dopant delivery source is configured to add a charge of solid dopant to the delivery tube.

31. 31. The device of claim 30, wherein the solid dopant is a solid n-type dopant.

32. 32. The device of claim 31 , wherein the solid dopant is a solid p-type dopant.

33. 33. The apparatus of claim 32, wherein the solid dopant is boric acid.

34. 1. An ingot pulling apparatus for growing a doped single crystal silicon ingot, comprising: an outer housing defining an inner chamber; a crucible disposed within the inner chamber for holding a silicon melt; a first gas doping system and a second gas doping system for introducing a dopant species into the melt, the first gas doping system and the second gas doping system each comprising: a feed tube extending between a first end and a second end, the second end being positioned within the interior chamber, the feed tube including a capsule disposed proximate the second end; a dopant feed source coupled in flow communication with the first end of the feed, the dopant source configured to add a volatile dopant to the feed; a positioning system configured to adjust a position of the feed tube between a first position where the second end of the feed tube is at a first height above a surface of the melt and a second position where the second end of the feed tube is at a second height above the surface of the melt that is less than the first height; a controller communicatively coupled to the dopant feed source and the positioning system, the controller configured to cause the dopant feed source to add a target amount of the volatile dopant to the feed tube and the positioning system to move the feed tube to the second position, the second height selected to control a vaporization rate of the volatile dopant in the feed tube during an ingot pulling process; a first gas doping system and a second gas doping system, An ingot pulling apparatus comprising:

35. 35. The apparatus of claim 34, wherein the second height of the feed conduit of the second gas doping system is different from the second height of the feed conduit of the first gas doping system.

36. 36. The apparatus of claim 34 or 35, wherein the controller of each of the first gas doping system and the second gas doping system is configured to cause the respective positioning system to move the respective feed tube at a speed rate selected to control the evaporation rate of the volatile dopant in the respective feed tube.

37. 37. The apparatus of claim 36, wherein the velocity rate of the feed pipe of the second gas doping system is different from the velocity rate of the feed pipe of the first gas doping system.

38. 38. The apparatus of any one of claims 34 to 37, further comprising a heat shield surrounding a growth chamber within the inner chamber in which a single crystal silicon ingot is grown, the second end of each feed tube in the second position being positioned within a channel within the growth chamber defined by the heat shield.

39. 38. The apparatus of any one of claims 34 to 37, further comprising a heat shield surrounding a growth chamber within the inner chamber in which a single crystal silicon ingot is grown, the heat shield defining a gap above the surface of the melt, the second end of each feed pipe in the second position being positioned within the gap.

40. 40. The apparatus of any one of claims 34 to 39, wherein the controller of each of the first gas doping system and the second gas doping system is configured to determine the second height of the second end of the respective feed pipe based on a simulated temperature profile of the second end of the respective feed pipe as a function of height of the second end relative to the surface of the melt.

41. 41. The apparatus of any one of claims 34 to 40, wherein the controller of each of the first gas doping system and the second gas doping system is configured to determine the second height of the second end of the respective feed tube based on a doping efficiency profile of the volatile dopant as a function of height of the second end relative to the surface of the melt.

42. 42. The apparatus of any one of claims 34 to 41, wherein the dopant delivery source of each of the first gas doping system and the second gas doping system is configured to add a charge of solid dopant to the delivery tube.

43. 43. The device of claim 42, wherein the solid dopant is a solid n-type dopant.

44. 43. The device of claim 42, wherein the solid dopant is a solid p-type dopant.

45. 45. The apparatus of claim 44, wherein the solid dopant is boric acid.

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