Patent Description:
In high resistivity silicon wafer applications, the resistivity of the single crystal silicon ingot from which the wafers are sliced may be controlled by addition of various dopants to the melt. The dopants may be used to compensate for various impurities (e.g., boron or phosphorous) in the source of polycrystalline silicon used to form a melt from which the silicon ingot is withdrawn.

When one or more dopants are added to achieve a target resistivity in the ingot, certain dopants and/or impurities may accumulate in the melt due to differences in the segregation coefficients of the compounds. For example, boron has a segregation coefficient of about <NUM> which allows boron to be readily taken up into the growing ingot. Phosphorous has a segregation coefficient of about <NUM> which causes phosphorous to accumulate in the melt relative to boron which is taken up more readily. Accordingly, as the ingot grows and the melt is depleted, phosphorous accumulates in the melt altering the resistivity of the growing ingot. This can cause the resistivity to decrease and fall out of customer specifications and/or for a type-change to occur in the ingot.

A need exists for methods for counter-doping a silicon melt during ingot growth to increase the length of the ingot that remains within customer specifications. A need also exists for doping methods that allow for use of dopant source materials that are readily available and/or relatively inexpensive and that allow the melt to be doped with relative ease. Further, an ingot puller apparatus that allows a liquid-phase dopant to be used as the source of dopant is needed.

<CIT> describes methods for producing a silicon crystal silicon ingot. The ingot is doped with boron using solid-phase boric acid as the source of boron. Ingot puller apparatus that use a solid-phase dopant are also disclosed. The solid-phase dopant may be disposed in a receptacle that is moved closer to the surface of the melt or a vaporization unit may be used to produce a dopant gas from the solid-phase dopant.

<CIT> describes a silicon single crystal pulling device and a method for producing a silicon single crystal using the pulling device, using sublimation of the dopant during addition or flipping on a liquid surface of a silicon melt.

In one aspect of the present invention, an ingot puller apparatus for producing a doped single crystal silicon ingot includes a housing defining a chamber, a crucible disposed within the chamber, and a dopant injector extending into the housing. The dopant injector includes a delivery module attached to and extending through the housing into the chamber. The delivery module includes a dopant injection tube positioned within the chamber and a vaporization cup positioned within the dopant injection tube and the chamber. A valve selectively channels the liquid dopant into the vaporization cup and the vaporization cup vaporizes the liquid dopant into a vaporized dopant.

In another aspect of the present invention, an ingot puller apparatus for producing a doped single crystal silicon ingot includes a housing defining a chamber, a crucible disposed within the chamber, and a dopant injector extending into the housing. The dopant injector includes an injection module attached to an outer surface of the housing. The injection module includes a first reservoir for containing a liquid dopant, a second reservoir for containing the liquid dopant, a first valve for selectively channeling the liquid dopant from the first reservoir to the second reservoir, and a second valve for selectively channeling the liquid dopant from the second reservoir to the chamber. The dopant injector also includes a delivery module attached to the injection module and extending through the housing into the chamber. The second valve selectively channels the liquid dopant into the delivery module and the delivery module vaporizes the liquid dopant into a vaporized dopant.

In another aspect of the present invention, a method for producing a single crystal silicon ingot from a silicon melt held within a crucible positioned within an ingot puller apparatus is provided. The ingot puller apparatus includes a dopant injector extending into a housing of the ingot puller apparatus, the dopant injector including a first reservoir, a first valve, a second reservoir, a second valve, a dopant injection tube positioned within the housing, and a vaporization cup positioned within the dopant injection tube and the housing. The method includes adding polycrystalline silicon to the crucible. The crucible is disposed within an ingot puller inner chamber. The method also includes heating the polycrystalline silicon to cause a silicon melt to form in the crucible. The method further includes pulling a single crystal silicon ingot from the silicon melt. The method also includes injecting a liquid dopant into the ingot puller apparatus by channeling the liquid dopant from the first reservoir to the second reservoir by opening the first valve and channeling the liquid dopant from the second reservoir to the housing by opening the second valve. The method further includes vaporizing the liquid dopant into a vaporized dopant within the ingot puller apparatus by heating the liquid dopant using the vaporization cup and reducing a pressure of the liquid dopant by injecting the liquid dopant into the housing, wherein the housing is maintained at a pressure below atmospheric pressure. The method also includes contacting the vaporized dopant with a surface of the melt to cause the vaporized dopant to enter the melt as a dopant while pulling the single crystal silicon ingot from the melt.

In another aspect, a method for doping a single crystal silicon ingot pulled from a silicon melt held within a crucible positioned within an ingot puller apparatus. The ingot puller apparatus includes a housing, a dopant injector extending into the housing, and a heating system positioned with the housing. The dopant injector including a dopant injection tube positioned within the housing and a vaporization cup positioned within the dopant injection tube and the housing. The method includes heating the vaporization cup using the heating system. The method also includes injecting liquid dopant into the dopant injection tube and the vaporization cup. The method further includes vaporizing the liquid dopant into vaporized dopant within the housing. The liquid dopant is vaporized by flash evaporation by heating the liquid dopant with the vaporization cup. The method also includes channeling the vaporized dopant into the housing using the dopant injection tube.

Various refinements exist of the features noted in relation to the above-mentioned aspects of the present invention. Further features may also be incorporated in the above-mentioned aspects of the present invention as well.

An example ingot puller apparatus <NUM> is generally shown in <FIG>. The apparatus <NUM> of <FIG> may be used to counter-dope or dope the ingot with a vaporized boron dopant as in the method described herein or may be used with other liquid-phase dopants that may be vaporized below the melting point of silicon (about <NUM>) in either the native form, or a hydrated form, or in a compound that is non-contaminating to the crystal growth process.

Referring now to <FIG>, the ingot puller apparatus <NUM> includes an ingot puller outer housing <NUM> that defines an ingot puller inner chamber <NUM> within the housing <NUM>. A crucible <NUM> is disposed within the ingot puller inner chamber <NUM>. The crucible <NUM> contains the silicon melt <NUM> from which a silicon ingot <NUM> is pulled. The ingot <NUM> is shrouded by a heat shield <NUM>.

The ingot puller apparatus <NUM> includes a dopant injector <NUM> for injecting liquid dopant into the ingot puller apparatus as the ingot <NUM> is pulled from the silicon melt <NUM>. The dopant injector <NUM> enables the silicon melt <NUM> to be counter-doped with a liquid dopant multiple times as the ingot <NUM> is pulled from the melt, increasing the resistivity of the ingot, increasing the portion of the ingot that is within customer specifications (e.g., high resistivity), and increasing the efficiency of the ingot puller apparatus.

The dopant injector <NUM> includes an injection module <NUM>, a delivery module <NUM>, and a first flange <NUM>. The injection module <NUM> and the delivery module <NUM> are each attached to the first flange <NUM>, and the flange attaches the injection module and the delivery module to the housing <NUM>. Specifically, the housing <NUM> defines a dopant injector opening <NUM>, and the first flange <NUM> is attached to the housing such that the flange covers the dopant injector opening.

The injection module <NUM> is attached to a first side <NUM> of the first flange <NUM> such that the injection module is positioned outside the chamber <NUM>. The delivery module <NUM> is attached to a second side <NUM> of the first flange <NUM> such that the delivery module is positioned within the chamber <NUM>. The injection module <NUM> receives dopant and channels the dopant to the delivery module <NUM>, and the delivery module receives dopant from the injection module and injects the dopant into the chamber <NUM> as described herein. The injection module <NUM> receives a liquid dopant, and the delivery module <NUM> vaporizes the liquid dopant within the chamber <NUM> as described herein.

As shown in <FIG>, the injection module <NUM> includes a second flange <NUM>, a doping chamber <NUM> attached to the second flange <NUM>, an actuation mechanism <NUM> positioned on top of the doping chamber, cooling fluid conduits <NUM> and <NUM> for channeling cooling fluid to the dopant injector <NUM>, a bellows <NUM> attached to the first flange <NUM> and the second flange <NUM>, and ports <NUM>, <NUM>, and <NUM> for channeling material into and out of the dopant injector. The doping chamber <NUM> is attached to a first side <NUM> of the second flange <NUM>, the bellows <NUM> is attached to a second side <NUM> of the second flange <NUM> and the first side <NUM> of the first flange <NUM>, and the ports <NUM>, <NUM>, and <NUM> are attached to and extend from the doping chamber. The bellows <NUM> enables the injection module <NUM> to be positioned within the ingot puller inner chamber <NUM> proximate the silicon melt <NUM>. Specifically, the bellows <NUM> enables the injection module <NUM> to be moved vertically relative to the silicon melt <NUM>.

The cooling fluid conduits <NUM> and <NUM> include a cooling fluid supply <NUM> and a cooling fluid return <NUM>. The cooling fluid conduits <NUM> and <NUM> extend through the actuation mechanism <NUM> and into the doping chamber <NUM>. The actuation mechanism <NUM> includes air cylinders <NUM> for actuating valves within the dopant injector <NUM> as described herein. The ports <NUM>, <NUM>, and <NUM> include an inert gas port <NUM> for supplying an inert gas to the dopant injector <NUM>, a pressure sensor port <NUM> for measuring a pressure of the doping chamber <NUM>, and a vacuum port <NUM> for generating a vacuum within the doping chamber.

As shown in <FIG>, the injection module <NUM> also includes a dopant addition tube <NUM>, a first reservoir tube <NUM> defining a first reservoir <NUM>, a second reservoir tube <NUM> partially defining a second reservoir <NUM>, a first valve <NUM>, a second valve <NUM>, an actuator <NUM>, an actuation shaft <NUM>, and a cooling jacket <NUM>. The dopant addition tube <NUM>, the first reservoir tube <NUM>, the first reservoir <NUM>, and the first valve <NUM> are all positioned within the doping chamber <NUM>. The second reservoir tube <NUM>, the second reservoir <NUM>, the actuation shaft <NUM>, and the cooling jacket <NUM> all extend from the doping chamber <NUM>. The second reservoir tube <NUM> circumscribes the actuation shaft <NUM> to define the second reservoir <NUM> therebetween, and the cooling jacket <NUM> circumscribes the second reservoir tube <NUM>.

The dopant addition tube <NUM> is coupled to the first reservoir <NUM>, and the first valve <NUM> is selectively actuated by the actuation shaft <NUM> to maintain or release liquid dopant within the first reservoir. The dopant addition tube <NUM> receives liquid dopant and channels the liquid dopant to the first reservoir <NUM>. The first valve <NUM> is closed and maintains the liquid dopant within the first reservoir <NUM>. Upon actuation by the actuation shaft <NUM>, the first valve <NUM> opens and channels the liquid dopant into the second reservoir <NUM> as described herein.

The first reservoir <NUM> is coupled to the second reservoir <NUM>, and the first valve <NUM> is selectively actuated by the actuation shaft <NUM> to release liquid dopant within the first reservoir to the second reservoir. The second reservoir <NUM> receives liquid dopant and channels the liquid dopant to the delivery module <NUM>. The second valve <NUM> is closed and maintains the liquid dopant within the second reservoir <NUM>. Upon actuation by the actuation shaft <NUM>, the second valve <NUM> opens and channels the liquid dopant into the delivery module <NUM> as described herein. The cooling jacket <NUM> receives a cooling fluid from the cooling fluid supply <NUM> and returns the cooling fluid to the cooling fluid return <NUM>. The cooling fluid cools the injection module <NUM> to prevent the injection module from overheating.

The ingot puller inner chamber <NUM> is maintained at a first pressure, and the doping chamber <NUM> is maintained at a second pressure greater than the first pressure. Specifically, the first pressure of the ingot puller inner chamber <NUM> is maintained at a vacuum, and the second pressure of the doping chamber <NUM> is maintained at atmospheric pressure such that the liquid dopant is also maintained at atmospheric pressure. In alternative embodiments, the first pressure of the ingot puller inner chamber <NUM> is maintained at a pressure below atmospheric pressure, and the second pressure of the doping chamber <NUM> is maintained at a pressure above the first pressure. Accordingly, the liquid dopant is maintained at the second pressure (atmospheric pressure) until the liquid dopant is injected into the ingot puller inner chamber <NUM> where the pressure of the liquid dopant is reduced to the first pressure (a vacuum).

The actuator <NUM> is positioned within the doping chamber <NUM> and is coupled to the air cylinders <NUM> and the actuation shaft <NUM>. The air cylinders <NUM> actuate the actuator <NUM>, and the actuator actuates the first valve <NUM> and the actuation shaft <NUM>. The actuation shaft <NUM> actuates the second valve <NUM>. More specifically, in the illustrated embodiment, the actuator <NUM> is a liner actuator that translates the first valve <NUM> and the shaft <NUM> linearly to translate open the first valve and to translate the second valve <NUM> linearly to open the second valve. In alternative embodiments, the actuation shaft <NUM> is coupled to both the first valve <NUM> and the second valve <NUM> and actuates both the first valve and the second valve. In some embodiments, the actuation shaft <NUM> independently actuates the first valve <NUM> and the second valve <NUM>. In alternative embodiments, the actuation shaft <NUM> actuates the first valve <NUM> and the second valve <NUM> simultaneously. For example, the actuation shaft <NUM> may actuate the first valve <NUM> and the second valve <NUM> simultaneously such that the first valve <NUM> is closed when the second valve <NUM> is open and the first valve <NUM> is open when the second valve <NUM> is closed in order to maintain the first pressure within the ingot puller inner chamber <NUM>.

The delivery module <NUM> includes a feed tube <NUM> and a vaporization cup <NUM> positioned within the feed tube. The feed tube <NUM> is positioned within the ingot puller inner chamber <NUM> and channels vaporized dopant to the silicon melt <NUM>. Specifically, the vaporization tube <NUM> is heated by radiant heat from within the ingot puller inner chamber <NUM> and receives the liquid dopant from the second reservoir <NUM>. The ingot puller apparatus <NUM> includes a heating system <NUM> that melts the silicon melt <NUM> and radiates heat into the ingot puller inner chamber <NUM>. The liquid dopant is vaporized into a vaporized dopant within the ingot puller inner chamber <NUM> where the liquid dopant is vaporized by flash evaporation by heating the liquid dopant with the vaporization cup <NUM> and reducing the pressure of the liquid dopant from the second pressure to the first pressure by injecting the liquid dopant into the ingot puller inner chamber <NUM>.

The feed tube <NUM> has a distal end <NUM> furthest from the ingot puller outer housing <NUM> and a proximal end <NUM> nearest the ingot puller outer housing. A feed tube axis A extends through the distal end <NUM> and the proximal end <NUM> of the feed tube <NUM>. The feed tube <NUM> may be made of quartz or other suitable materials.

The feed tube <NUM> is moveable within the ingot puller inner chamber <NUM> along the feed tube axis A. The feed tube <NUM> may be lowered into the ingot puller inner chamber <NUM> toward the silicon melt <NUM>. Specifically, the feed tube <NUM> is attached to the cooling jacket <NUM>, and the cooling jacket is attached to the doping chamber <NUM>. The bellows <NUM> enables the doping chamber <NUM>, the cooling jacket <NUM>, and the feed tube <NUM> to move along the feed tube axis A toward and away from the silicon melt <NUM>. By moving the doping chamber <NUM>, the cooling jacket <NUM>, and the feed tube <NUM>, the distal end <NUM> of the feed tube <NUM> moves between a raised position in which the distal end positioned away from the silicon melt <NUM> and a lowered position in which the distal end is positioned proximate the surface of the silicon melt <NUM>. The heat shield <NUM> may include a channel <NUM> formed therein to provide a pathway for the feed tube <NUM> to approach the silicon melt <NUM>.

In the lowered position of the feed tube <NUM>, the vaporized dopant travels down the feed tube where it is directed to the surface of the silicon melt <NUM>. The vaporized dopant passes through the distal end <NUM> of the feed tube <NUM> to contact the silicon melt <NUM> to cause the silicon melt to be doped and/or counter doped. As the doping chamber <NUM>, the cooling jacket <NUM>, and the feed tube <NUM> are moved from the raised position to the lower position, the distance between the vaporization cup <NUM> and the silicon melt <NUM> and the heating system <NUM> may be changed (e.g., by an operator).

The vaporization cup <NUM> includes a receiver <NUM> and a vaporization plug <NUM> positioned within the receiver and divides the receiver into a liquid reception portion <NUM> and a vapor channel portion <NUM>. The receiver <NUM> and the vaporization plug <NUM> define the liquid reception portion <NUM>, and the receiver <NUM> defines channels <NUM> that channel vaporized dopant from the liquid reception portion to the feed tube <NUM>. The vaporization plug <NUM> has a first end <NUM> and a second end <NUM> and defines vaporization channels <NUM> extending from the first end to the second end that channel vaporized dopant from the liquid reception portion <NUM> to the vapor channel portion <NUM>.

Excess heat from the heating system <NUM> heats the vaporization plug <NUM>, and the second valve <NUM> channels the liquid dopant from the second reservoir <NUM> into the liquid reception portion <NUM> and onto the vaporization plug. The vaporization plug <NUM> vaporizes the liquid dopant into vaporized dopant by flash evaporation by heating the liquid dopant with the vaporization plug <NUM> and reducing the pressure of the liquid dopant from the second pressure to the first pressure by injecting the liquid dopant into the liquid reception portion <NUM>. The vaporization channels <NUM> channel the vaporized dopant into the channels <NUM> of the vapor channel portion <NUM> which channel the vaporized dopant into the feed tube <NUM> and to the silicon melt <NUM>. Additionally, a process gas (e.g., argon) may be circulated through the doping chamber <NUM> through the inert gas port <NUM> for channeling the vaporized dopant through the vaporization cup <NUM> and the feed tube <NUM>.

The pressure sensor port <NUM> enables measurement of the pressure within the ingot puller inner chamber <NUM>. The vacuum port <NUM> enables pump-down and leak testing. The cooling jacket <NUM> cools the injection module <NUM> to prevent the injection module from overheating.

Example methods of the present invention are shown in <FIG> and <FIG>. The method may be carried out by use of the ingot puller apparatus <NUM> that is configured to produce a boron-containing gas from liquid-phase boric acid.

In accordance with embodiments of the method for preparing a silicon ingot, a silicon melt is prepared in the crucible <NUM> disposed within the ingot puller inner chamber <NUM> of the ingot puller apparatus <NUM>. The crucible <NUM> may be supported by a susceptor (not shown). The ingot puller apparatus <NUM> may be configured to rotate the crucible <NUM> and/or move the crucible <NUM> vertically within the ingot puller apparatus <NUM>.

To prepare the silicon melt, polycrystalline silicon is added to the crucible <NUM>. The polycrystalline silicon is heated to above the melting temperature of silicon (about <NUM>) to cause the polycrystalline silicon to liquefy into the silicon melt <NUM>. The heating system <NUM> is operated to melt-down the polycrystalline silicon. For example, one or more heaters <NUM> below or to the side of the crucible <NUM> are operated to melt-down the silicon.

Before or after the melt <NUM> is produced, the melt may 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 growth of the ingot <NUM> commences. By compensating the melt, the resistivity of the resulting ingot <NUM> may be increased. For example, the seed end of the ingot (i.e., the portion of the ingot nearest the ingot crown) may have a resistivity of at least about <NUM>Ω-cm or, as in other embodiments, at least about <NUM>Ω-cm, at least about <NUM>Ω-cm, at least about <NUM>Ω-cm, at least about <NUM>Ω-cm, at least about <NUM>Ω-cm, at least about <NUM>Ω-cm or from about <NUM>Ω-cm to about <NUM> ohm-cm. Suitable n-type dopants include phosphorous and arsenic.

Once the melt <NUM> is prepared, the single crystal silicon ingot <NUM> is pulled from the melt <NUM>. A seed crystal <NUM> is secured to a seed chuck <NUM>. The seed chuck <NUM> and seed crystal <NUM> are lowered until the seed crystal <NUM> contacts the surface of the silicon melt <NUM>. Once the seed crystal <NUM> begins to melt, a pulling mechanism slowly raises the seed crystal <NUM> up to grow the monocrystalline ingot <NUM>. A process gas (e.g., argon) is circulated through the ingot puller inner chamber <NUM> of the ingot puller apparatus <NUM>. The process gas creates an atmosphere within the ingot puller inner chamber <NUM>.

Embodiments of methods of the present invention include providing a source of liquid-phase boric acid (H<NUM>BO<NUM>). The boric acid may be relatively pure such as about <NUM>% pure or more, <NUM>% pure or more, or <NUM>% pure or more. In some embodiments, the boric acid may be relatively isotopically pure (i.e., boron-<NUM>).

A boron-containing gas is produced from the liquid-phase boric acid. The gas that is produced is generally in the form of boric acid (H<NUM>BO<NUM>) or derivatives thereof (BxOyHz+ complexes) and not other compounds (e.g., diborane (B<NUM>H<NUM>) or boron dihydride (BH<NUM>)). However, it should be understood that other boron compounds may be added to the boron-containing gas.

The liquid-phase boric acid may be heated to above its vaporization temperature (about <NUM>) to produce a boron-containing gas. For example, the liquid-phase boric acid may be heated by heat radiated from the silicon melt <NUM> in the ingot puller apparatus <NUM> or by the heating system <NUM>.

Once the boron-containing gas is produced, the boron-containing gas contacts the surface of the silicon melt <NUM> to allow boron to diffuse into the melt. Once boron enters the melt, boron compensates for phosphorous which has concentrated in the melt due to the relatively low segregation coefficient of phosphorous, thereby increasing the resistivity of the remaining portion of the ingot <NUM> that forms in the ingot puller apparatus <NUM>.

<FIG> is a graph <NUM> of ingot resistivity as a function of ingot length. As shown in <FIG>, the silicon melt <NUM> may be counter-doped as described herein multiple times as the ingot <NUM> is pulled from the silicon melt. Specifically, the resistivity of the ingot <NUM> may decrease as the ingot is pulled from the silicon melt <NUM> because of the concentration of phosphorous. The silicon melt <NUM> may be counter-doped with the dopant injector <NUM> as described herein multiple times as the ingot <NUM> is pulled from the silicon melt <NUM> to increase the resistivity of the ingot during production such that a larger portion of the ingot is within customer specifications (e.g., high resistivity). More specifically, as shown in <FIG>, the silicon melt <NUM> is counter-doped twice as the ingot <NUM> is pulled from the silicon melt <NUM>. Accordingly, the dopant injector <NUM> increases the efficiency of the ingot puller apparatus <NUM> by counter-doping the silicon melt <NUM> multiple times during production of the ingot <NUM> and maintaining the resistivity of a larger portion of the ingot within customer specifications (e.g., high resistivity).

<FIG> is a flow diagram of a method <NUM> for producing a single crystal silicon ingot from a silicon melt held within a crucible positioned within an ingot puller apparatus. The method <NUM> includes adding <NUM> polycrystalline silicon to the crucible, and the crucible is disposed within an ingot puller inner chamber. The method <NUM> also includes heating <NUM> the polycrystalline silicon to cause a silicon melt to form in the crucible. The method <NUM> further includes pulling <NUM> a single crystal silicon ingot from the silicon melt. The method <NUM> also includes injecting <NUM> a liquid dopant into the ingot puller apparatus. The method <NUM> further includes vaporizing <NUM> the liquid dopant into a vaporized dopant within the ingot puller apparatus. The method <NUM> also includes contacting <NUM> the vaporized dopant with a surface of the melt to cause the vaporized dopant to enter the melt as a dopant while pulling the single crystal silicon ingot from the melt.

<FIG> is a flow diagram of a method <NUM> for doping a single crystal silicon ingot pulled from a silicon melt held within a crucible positioned within an ingot puller apparatus. The ingot puller apparatus includes a housing, a dopant injector extending into the housing, and a heating system positioned with the housing. The dopant injector includes a dopant injection tube positioned within the housing and a vaporization cup positioned within the dopant injection tube and the housing. The method <NUM> includes heating <NUM> the vaporization cup using the heating system. The method <NUM> also includes maintaining <NUM> a pressure of an interior of the housing at a first pressure. The method <NUM> further includes injecting <NUM> liquid dopant into the dopant injection tube and the vaporization cup. A pressure of the liquid dopant is maintained at a second pressure greater than the first pressure prior to injection into the dopant injection tube and the vaporization cup. The method <NUM> also includes vaporizing <NUM> the liquid dopant into vaporized dopant within the housing. The liquid dopant is vaporized by flash evaporation by heating the liquid dopant with the vaporization cup and reducing the pressure of the liquid dopant from the second pressure to the first pressure by injecting the liquid dopant into the housing. The method <NUM> further includes channeling <NUM> the vaporized dopant into the housing using the dopant injection tube.

Compared to conventional methods for producing a single crystal silicon ingot from a silicon melt, the systems and methods of the present invention have several advantages. Specifically, a larger portion of the ingot may be within customer specifications (e.g., high resistivity) and/or a type-change in the ingot may be prevented. More specifically, the systems and methods of the present invention control the rate of doping such that compensating boron is incorporated into the ingot to neutralize the effect of segregation by phosphorous. Thus, the net free charge carriers may be maintained between limits over the length of the ingot. Depending on the target resistivity of the ingot, controlling the rate of doping may prevent a type change of the ingot from n-type to p-type or in other examples, from p-type to n-type. Liquid-phase boric acid has a relatively low vaporization temperature which allows a dopant gas to be produced with relative ease. Additionally, the vaporization cup may be placed within ingot puller housing which allows the heat of the melt and the heating system to vaporize the dopant. The feed tube is moveable within the ingot puller apparatus such that the distance from the melt may be controlled which allows the rate of dopant addition to the melt to be controlled. Accordingly, the systems and methods described herein increases the efficiency of the ingot puller apparatus by counter-doping the silicon melt multiple times during production of the ingot and maintaining the resistivity of a larger portion of the ingot within customer specifications (e.g., high resistivity).

As used herein, the term "about" when used in conjunction with ranges of dimensions, concentrations, temperatures or other physical or chemical properties or characteristics is meant to cover variations that may exist in the upper and/or lower limits of the ranges of the properties or characteristics, including, for example, variations resulting from rounding, measurement methodology or other statistical variation.

Claim 1:
An ingot puller apparatus (<NUM>) for producing a doped single crystal silicon ingot, the ingot puller apparatus comprising:
a housing (<NUM>) defining a chamber (<NUM>);
a crucible (<NUM>) disposed within the chamber; and
a dopant injector (<NUM>) extending into the housing, the dopant injector comprising:
a delivery module (<NUM>) attached to and extending through the housing into the chamber, the delivery module comprising:
a dopant injection tube (<NUM>) positioned within the chamber; and
a vaporization cup (<NUM>) positioned within the dopant injection tube and the chamber, wherein a valve (<NUM>) selectively channels the liquid dopant into the vaporization cup and the vaporization cup vaporizes the liquid dopant into a vaporized dopant.