Use of a buffer during growth of single crystal silicon ingots

Abstract

Continuous Czochralski (CCz) discloses a method for producing a single crystal silicon ingot. A batch of buffer material (e.g., quartz cullet) is added to the outer melt zone of a crucible assembly before the main body of the ingot is grown. In some embodiments, the ratio of the mass M of the batch of buffer material added to the melt and the time between adding the batch of buffer material to the melt and the time when the main body of the ingot begins to grow is controlled such that the ratio M / T is greater than a threshold value M / T.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 132,712, filed December 31, 2020, and U.S. Provisional Patent Application No. 63 / 132,713, filed December 31, 2020. Both applications are incorporated herein by reference in their entireties.

[0002] The field of the disclosure relates to methods for producing single crystal silicon ingots by the Continuous Czochralski (CCz) process, and more particularly, to adding a buffer member to the outer melting zone of a crucible assembly. [Background technology]

[0003] The Continuous Czochralski (CCz) process is well suited for forming 300 mm or 200 mm diameter ingots, such as ingots that are relatively heavily doped with arsenic or phosphorus. The Continuous Czochralski (CCz) process involves forming a single crystal silicon ingot from a silicon melt while continuously or intermittently adding solid polycrystalline silicon to the melt to replenish the melt while the ingot is growing. The process may involve forming multiple ingots from the same melt while the hot zone is held at temperature (i.e., the melt is continuously present in the crucible assembly while multiple ingots are growing).

[0004] Customers increasingly specify that wafers sliced ​​from ingots grown by the continuous Czochralski process have low void counts (e.g., less than 30 defects per wafer) for both 200 mm and 300 mm ingots. The continuous Czochralski process can involve a crucible assembly that includes at least two, and often three, melt zones separated by physical barriers: an outer melt zone where solid polycrystalline silicon is fed, a middle melt zone where the melt stabilizes, and an inner melt zone where the silicon ingot is pulled. The addition of solid polycrystalline silicon to the melt causes the formation of inert gas bubbles (e.g., argon bubbles) in the melt, which affects the void count.

[0005] A need exists for a method of forming a silicon ingot that reduces the number of defects in silicon wafers sliced ​​from the ingot and / or reduces the formation of inert gas bubbles in the melt or promotes the disappearance of inert gas bubbles.

[0006] This 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 disclosed below. This description 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. As such, 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

[0007] One aspect of the invention is directed to a method of growing a single crystal silicon ingot in a continuous Czochralski process. A melt of silicon is formed in a crucible assembly. A batch of buffer material is added to the melt. The mass of the batch is M. A surface of the melt contacts a seed crystal. A single crystal silicon ingot is withdrawn from the melt. The single crystal silicon ingot includes a body. There is a time T between adding the batch of buffer material to the melt and the start of growth of the body. The ratio of M / T is controlled to be greater than a threshold M / T to reduce the number of voids in wafers sliced ​​from the single crystal silicon ingot. Solid polycrystalline silicon feedstock is added to the crucible to replenish the melt while the single crystal silicon ingot is being withdrawn.

[0008] One aspect of the present invention is directed to a method for determining a threshold M / T ratio for growing a monocrystalline silicon ingot in a continuous Czochralski process, which includes forming a melt of silicon in a crucible assembly, adding a batch of buffer material of mass M to the melt, contacting the melt with a seed crystal, withdrawing a monocrystalline silicon ingot from the melt, where the monocrystalline silicon ingot has a body, there being a time T between adding the batch of buffer material to the melt and the start of growth of the body, and adding solid polycrystalline silicon feedstock to the crucible assembly to replenish the melt while withdrawing the monocrystalline silicon ingot. The method for determining the threshold M / T ratio includes growing a plurality of monocrystalline silicon ingots, where two of the plurality of ingots are grown with different M / T ratios. A number of defects is measured for a plurality of wafers sliced ​​from the plurality of monocrystalline silicon ingots. The M / T ratio of the monocrystalline silicon ingot from which the wafers having a number of defects less than the threshold number of defects are determined.

[0009] There are various refinements of the features mentioned in relation to the above aspects of the disclosure. Further features may also be incorporated into the above aspects of the disclosure as well. These refinements and additional features may exist individually or in any combination. For example, the various features described below in relation to any of the illustrated embodiments of the disclosure may be incorporated alone or in any combination into any of the above aspects of the disclosure. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view of an embodiment of an ingot pulling apparatus having a solid polycrystalline silicon charge disposed therein.

[0011] [Diagram 2] FIG. 1 is a cross-sectional view of an ingot pulling apparatus having a melt including a buffer member within the melt.

[0012] [Diagram 3] FIG. 2 is a cross-sectional view of an ingot puller showing a silicon ingot being pulled from a silicon melt.

[0013] [Figure 4] 1 is a box plot showing the number of voids in wafers sliced ​​from ingots where the M / T was below a threshold M / T.

[0014] [Diagram 5] 1 is a box plot showing the number of voids in wafers sliced ​​from ingots where M / T was greater than a threshold M / T.

[0015] [Figure 6] FIG. 1 is a scatter plot showing the number of defects as a function of M / T.

[0016] [Figure 7] 1 is a box plot of wafers sliced ​​from ingots where the M / T was below a threshold M / T.

[0017] [Figure 8] 1 is a box plot of wafers sliced ​​from ingots where M / T was greater than a threshold M / T.

[0018] [Figure 9] FIG. 13 is a scatter plot showing defect counts as a function of M / T for other ingot pulling equipment.

[0019] Corresponding reference characters indicate corresponding elements throughout the drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present disclosure provides a method for growing single crystal silicon ingots in a continuous Czochralski (CCz) process. A buffer material (e.g., quartz cullet) is added to a silicon melt prior to the formation of the main body of the ingot. The ratio of the mass M of the buffer material added to the time T from the addition of the buffer material to the start of the growth of the main body of the ingot is controlled to be greater than a threshold value M / T. By controlling the ratio (M / T) of the mass of the buffer material to the time until the ingot body starts to grow to be greater than a threshold value M / T, the amount of defects obtained in the silicon wafer can be reduced.

[0021] An example of an ingot pulling apparatus 5 for producing an ingot 60 by the continuous Czochralski process is shown in FIG. 3. The ingot pulling apparatus 5 includes a crucible assembly 10 containing a melt 6 of semiconductor or solar grade silicon material. A susceptor 13 supports the crucible assembly 10. The crucible assembly 10 has a sidewall 40 and one or more fluid barriers 20, 30 or "weirs" that separate the melt into different melt zones. In the embodiment shown, the crucible assembly 10 includes a first weir 20. The first weir 20 and the sidewall 40 define an outer melt zone 42 of the silicon melt. The crucible assembly 10 includes a second weir 30 on the inner diameter side of the first weir 20, which defines an inner melt zone 22 of the silicon melt. The inner melt zone 22 is a growth region in which a single crystal silicon ingot 60 grows. The first and second weirs 20 and 30 define an intermediate melt zone 32 of the silicon melt in which the melt 6 may stabilize as it moves toward the inner melt zone 22. The first and second weirs 20, 30 each have at least one opening defined therein for allowing molten silicon to flow to the inner diameter side toward the growth region of the inner melt zone 22.

[0022] In the embodiment shown, the first weir 20, the second weir 30, and the sidewall 40 each have a generally annular shape. The first weir 20, the second weir 30, and the sidewall 40 may be part of a trio of nests joined at the bottom or floor 45 of the crucible assembly 10 (i.e., the first and second weirs 20, 30 are sidewalls of two nested crucibles within a larger crucible). The crucible assembly configuration depicted in Figures 1-3 is exemplary. In other embodiments, the crucible assembly 10 has a single floor (i.e., no nested crucibles) with the weirs extending upward from the floor 45. Optionally, the floor 45 may be flat rather than curved, and / or the weirs 20, 30 and / or the sidewall 40 may have straight faces. Additionally, although the illustrated crucible assembly 10 is shown with two dams, other embodiment crucible assemblies 10 may have a single dam or even no dams.

[0023] The supply pipe 46 supplies polycrystalline silicon, which may be, for example, granular, chunk, or a combination of granular and chunk, to the outer melt zone 42 at a rate sufficient to maintain a substantially constant melt height level and volume during growth of the ingot 60.

[0024] Generally, the melt 6 from which the ingot 60 is drawn is formed by loading polycrystalline silicon into a crucible to form an initial silicon charge 27 (FIG. 1). Generally, the initial charge is about 10 kg to about 200 kg of polycrystalline silicon and can be granular, chunk, or a combination of granular and chunk. The mass of the initial charge depends on the diameter of the desired crystal and the hot zone design. Since polycrystalline silicon is continuously fed during crystal growth, the initial charge does not translate to the length of the ingot crystal.

[0025] Various sources of polycrystalline silicon may be used, including, for example, granular polycrystalline silicon produced by the pyrolysis of silane or halosilane in a fluidized bed reactor, or polycrystalline silicon produced in a Siemens reactor. As described below, an amount of buffer material may be added to the initial charge of polycrystalline silicon 27 in the outer melting zone 42 of the crucible assembly 10 before or during melting of the initial charge of polycrystalline silicon 27.

[0026] Once polycrystalline silicon (and optionally a buffer member) is added to crucible assembly 10 to form charge 27, charge 27 is heated to a temperature above the melting temperature of the silicon at which the charge melts (e.g., about 1412°C), thereby forming silicon melt 6 (FIG. 2) having molten silicon. Silicon melt 6 has an initial volume of molten silicon and an initial melt height level, with these parameters being determined by the size of initial charge 27. In some embodiments, crucible assembly 10 with silicon melt 6 is heated to a temperature of at least about 1425°C, at least about 1450°C, or even at least about 1500°C.

[0027] The ingot pulling apparatus 5 includes a pulling mechanism 114 (FIG. 3) for growing and pulling an ingot 60 from the melt in the inner melt zone 22. The pulling mechanism 114 includes a pulling cable 118, a seed holder or chuck 120 coupled to one end of the pulling cable 118, and a seed crystal 122 coupled to the seed holder or chuck 120 for initiating crystal growth. One end of the pulling cable 118 is connected to a lifting mechanism (e.g., a drive pulley or drum, or any other suitable type of lifting mechanism) and the other end is connected to the chuck 120 which holds the seed crystal 122. In operation, the seed crystal 122 is lowered into the inner melt zone 22 to contact the melt 6. The pulling mechanism 114 is operated to raise the seed crystal 122 along a pulling axis A. This causes a single crystal ingot 60 to be pulled from the melt 6.

[0028] As the charge of polycrystalline silicon 27 (FIG. 1) liquefies to form a silicon melt 6 (FIG. 2) having molten silicon, a silicon seed crystal 122 (FIG. 3) is lowered into the inner melt zone 22 to contact the melt 6. The silicon seed crystal 122 is then pulled out of the melt 6 with the silicon attached thereto, where it forms a neck 52, thereby forming a molten-solid interface near or at the surface of the melt 6.

[0029] The pulling mechanism 114 can rotate the seed crystal 122 and the ingot 60 connected thereto. The crucible drive unit 44 can rotate the susceptor 13 and the crucible assembly 10. In some embodiments, the silicon seed crystal 122 and the crucible assembly 10 rotate in opposite directions, i.e., counter-rotate. The counter-rotation creates convection in the silicon melt 6. The rotation of the seed crystal 122 is primarily used to provide a symmetrical temperature profile, reduce angular variation of impurities, and control the crystal melt surface shape.

[0030] After the neck 52 is formed, an outwardly flaring seed cone portion 54 (or "crown") adjacent the neck 52 is grown. Typically, the pull rate is reduced from that of the neck to a rate suitable for growing the outwardly flaring seed cone portion 54. Once the seed cone reaches a target diameter, the body 56 or "constant diameter portion" of the ingot 60 is grown. In some embodiments, the diameter of the body 56 of the ingot 60 is 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.

[0031] While the ingot 60 is being pulled from the melt 6, solid polysilicon feedstock is added to the outer melt zone 42 through a pipe 46 or other flow path to replenish the melt 6 in the ingot growth apparatus 5. Solid polycrystalline silicon may be added from a polycrystalline silicon supply system 66 and may be added continuously or intermittently to the ingot puller 5 to maintain the melt level. Generally, polycrystalline silicon may be metered into the ingot puller 5 by any method available to one of ordinary skill in the art.

[0032] In some embodiments, dopants are also added to the melt 6 during ingot growth. The dopants may be introduced from a dopant supply system 72. The dopants may be added as a gas or a solid and may be added to the outer melt zone 42.

[0033] The apparatus 5 may include a heat shield 116 disposed around the growing ingot 60 to allow the ingot 60 to radiate latent heat of solidification and heat flux from the melt 6. The heat shield 116 may be at least partially conical in shape, sloping downwardly at an angle to form an annular opening in which the ingot 60 is disposed. A flow of inert gas, such as argon, is typically provided along the length of the growing crystal. The ingot 60 is pulled through a growth chamber 78 that is sealed from the surrounding air.

[0034] A plurality of independently controlled annular bottom heaters 70 may be radially positioned below the crucible assembly 10. The annular bottom heaters 70 apply heat in a relatively controlled distribution across the base surface area of ​​the crucible assembly 10. The annular bottom heaters 70 may be individually controlled planar resistive heating elements as described in U.S. Pat. No. 7,635,414, incorporated herein by reference for all relevant and consistent purposes. The apparatus 5 may include one or more side heaters 74 positioned on the outer diameter side of the crucible assembly 10 to control the temperature distribution through the melt 6.

[0035] The ingot growth apparatus 5 shown in FIGS. 1-3 and described herein is exemplary, and generally any system in which crystalline ingots are produced by the continuous Czochralski process may be used unless otherwise specified.

[0036] According to an embodiment of the present disclosure, before the ingot 60 is grown, a batch 31 ( FIG. 2 ) of buffer members 35 (e.g., quartz cullet) is added to the silicon melt 6, specifically to the outer melt zone 42. The buffer members 35 may be less dense than the silicon melt 6 so that they float within the melt 6 (i.e., a portion is disposed on the surface of the melt 6). Suitable buffer members 35 that may be added to the outer melt zone 42 include, for example, solid materials that prevent polysilicon added through the feed tube 46 from directly entering the melt 6 and / or provide a surface area where inert gas bubbles can dissipate. The buffer members 35 may form gaps between the buffer members 35. The buffer members 35 may be free to move (e.g., when impacted by a falling polycrystalline feedstock). In some embodiments, the buffer members 35 include quartz, such as quartz cullet. If quartz cullets are used, the cullets may have any suitable shape (e.g., cylindrical) and any suitable size (e.g., if cylindrical cullets are used, diameter of about 1 mm to about 10 mm and / or length of about 1 mm to about 10 mm).

[0037] After the batch 31 of buffer members 35 is added to the melt 6, the ingot 60 is pulled from the melt 6. According to an embodiment of the present disclosure, the ratio of the mass M of the batch 31 of buffer members 35 added to the melt 6 to the time T between adding the batch 31 of buffer members 35 to the melt 6 and when the ingot body 56 ( FIG. 3 ) begins to grow is controlled such that the ratio of M / T is greater than a threshold ratio of M / T to reduce the number of voids in wafers sliced ​​from the single crystal silicon ingot. Generally, the time T corresponds to the time from when the batch 31 of buffer members 35 is fully added to when the ingot body 56 begins to grow.

[0038] In some embodiments, the ratio of M / T is controlled to be greater than a threshold M / T such that the wafer sliced ​​from the single crystal silicon ingot has less than 30 voids with a size of 0.2 μm or more, or even less than 20 voids with a size of 0.2 μm or more. The threshold M / T may vary depending on the hot zone design of the ingot puller. To determine the threshold M / T, a threshold defect count (e.g., less than 30 defects, less than 20 defects, or less than 10 defects with a size of 0.2 μm or more, a maximum defect count desired by the manufacturer and / or customer, etc.) is set. A plurality of single crystal silicon ingots are grown, of which at least two ingots (e.g., 2, 3, 5, 10, 25, 100 ingots) are grown with different M / T ratios. The defect counts of one or more wafers sliced ​​from the plurality of single crystal silicon ingots are measured (e.g., with an SP1 inspection tool). The M / T ratio of the single crystal silicon from which the wafer having a defect count less than the threshold defect count is sliced ​​is determined based on the measured defect count (i.e., the threshold M / T is determined based on the value of M / T at which the defect count was less than or equal to the threshold defect count).

[0039] In some embodiments, the threshold M / T at which M / T is controlled to be greater is 40 g / h. In other embodiments, the threshold M / T is 50 g / h or even 55 g / h. In some embodiments, the threshold M / T at which M / T is controlled to be greater is 60 g / h. In yet other embodiments, the threshold M / T at which M / T is controlled to be greater is 70 g / h. The threshold M / T (and the actual M / T used in the ingot puller for growing the ingot) may be constrained by practical limitations of the ingot growth process (e.g., when the solid polysilicon ingot begins to mound on the buffer member, and the flow of the solid polysilicon ingot into the melt is not impeded). For example, M / T may be controlled to be above the threshold M / T and less than 500 g / h or even less than 250 g / h.

[0040] As shown in FIG. 2, according to some embodiments of the present disclosure, the batch 31 of buffer members 35 may be large enough such that the buffer members 35 extend continuously from the side wall 40 of the crucible assembly 10 to the first dam 20.

[0041] In this regard, the mass M of the batch 31 of buffer material 35 (e.g., quartz cullet) generally excludes any buffer material added before the initial charge 27 (FIG. 1) was melted (i.e., excludes the initial charge of buffer material added to the solid single crystal charge).

[0042] To control the ratio of M / T such that it is greater than a threshold M / T, the mass M of the batch 31 of buffer material 35 added to the outer melt zone 42 may be increased, or the time T between the addition of the buffer material and the growth of the body 56 of the ingot 60 may be decreased (e.g., by adding the buffer material later, i.e., closer to when the ingot body 56 begins to grow). It should be noted that controlling M / T to be "greater than" a threshold M / T generally includes any manner in which a minimum M / T is selected or set for use in the ingot growth process (i.e., including embodiments in which M / T in the ingot growth process is "equal to" or greater than a minimum value, in other words the threshold M / T is units smaller than the minimum M / T selected such that M / T is greater than the threshold).

[0043] As the ingot 60 is withdrawn from the melt 6, solid single crystal silicon feedstock is added to the crucible assembly 10 during withdrawal of the single crystal silicon ingot 60 to replenish the melt 6. In some embodiments, buffer material 35 is not added to the melt while the ingot is growing (e.g., neck, crown and / or body). When buffer material is added during growth of the neck 52 and / or crown 54 as in other embodiments of the present disclosure, the mass M of the batch 31 of buffer material 35 may include any buffer material added while the seed crystal 122 ( FIG. 3 ) is lowered and / or any buffer material added during growth of the neck 52 and crown 54 of the ingot 60, as well as any buffer material added before the lowering of the seed crystal 122 (and after melting of the solid single crystal silicon charge and / or after completion of growth of the previous ingot, if any). In some embodiments of the present disclosure, buffer material 35 is not added while the ingot body 56 is being pulled from the melt 6. If buffer material 35 is added during growth of ingot body 56, such buffer material 35 is not considered part of batch 31 (i.e., is not part of mass M of batch 31) added before growth of body 56 of ingot 60.

[0044] In some continuous Czochralski processes, one or more ingots are grown while the hot zone (i.e., the lower portion of the apparatus 5, such as the crucible assembly 10 and the susceptor 13) is heated with the silicon melt 6 continuously present in the crucible assembly 10. In such methods, a first ingot is grown to a target length, growth is terminated, the ingot is removed from the ingot puller, and a seed crystal is lowered into the melt to begin growing a second single crystal silicon ingot (i.e., using the same melt from which the first ingot was pulled). The next ingot may be grown with the hot zone intact and at a temperature where the continuous silicon melt in the crucible assembly 10 is present (until one or more components of the hot zone degrade, e.g., necessitating cooling of the crucible assembly and replacement of the degraded components). For example, at least 1, 2, 3, 4, 5, 6, 10, or 20 or more ingots may be grown.

[0045] After growth of the first ingot 60 is completed and the ingot is removed (e.g., removed from the pulling chamber 10 of the ingot puller), a second batch of buffer material may be added to the melt remaining after the first ingot is removed. A seed crystal 122 (i.e., the same seed crystal used to pull the first ingot or a different seed crystal) is lowered to contact the melt. According to an embodiment of the present disclosure, the mass M of the second batch of buffer material added to the melt is 2 and the time T from adding the second batch of buffer material until the growth of the main body of the ingot begins. 2 The ratio of M to M is controlled to be greater than a threshold M / T (i.e., the threshold M / T referenced above) to reduce the number of voids in wafers sliced ​​from the second single crystal silicon ingot. In this regard, there may be an amount of the first batch of buffer material still remaining in the melt when the second batch is added. The amount (or the entire amount) of the first batch may be depleted by melting in the silicon melt. The first batch remaining in the melt is generally less than the mass M of the second batch. 2 is not part of.

[0046] The ingot puller 5 may include a buffer material feed system 55 (FIG. 2) for adding batches of buffer material 35 to the outer melt zone 42. The buffer material feed system 55 may be configured for automatic or manual addition of the buffer material. For example, the buffer material feed system 55 may include a storage container for containing the buffer material (e.g., quartz cullet) and a weighing device (e.g., a weigh hopper, survey wheel, or the like). The buffer material feed system 55 may include a buffer material feed pipe that is the same as or separate from the pipe 46 where the polysilicon is added. The buffer material 35 may be weighed out by an operator or may be automatically fed into the pipe by the buffer material feed system 55.

[0047] Compared with the conventional method of growing a monocrystalline silicon ingot with a continuous Czochralski process, the method of the present disclosure has several advantages. By controlling the ratio of the mass M of the batch of buffer material added to the melt to the time T between the batch of buffer material being added to the melt and the time when the main body of the monocrystalline silicon ingot begins to grow to be greater than a threshold value of M / T, the number of voids in wafers sliced ​​from such an ingot grown with a continuous Czochralski process can be reduced. For example, such wafers can have less than 30 defects (measured with an SP1 inspection tool with a size of 0.2 μm or more) per wafer. Without being bound to any particular theory, it is believed that the addition of polycrystalline silicon into the outer melt zone of the crucible assembly creates relatively small bubbles (e.g., less than 10 pm) of inert gas (e.g., argon) that can be carried by the melt through openings in the respective weirs that allow the bubbles to reach the solid-melt interface. The buffer material may act to prevent inert gas entrapment in the melt by preventing the polycrystalline feedstock from dumping directly into the melt. The buffer material may also provide surface area and nucleation points for inert gas bubbles to collect, thereby allowing the bubbles to increase in size and become buoyant. Increasing the ratio of the mass M of the batch of buffer material added to the melt to the time T between adding the batch of buffer material to the melt and the onset of ingot body growth to at least 60 g / h increases the efficiency with which the buffer material reduces inert gas impingement and / or dissipates inert gas bubbles. EXAMPLES

[0048] The processes of the present disclosure are further illustrated by the following examples, which should not be construed in a limiting sense. Example 1: Number of voids in wafers grown from ingots with M / T less than the M / T threshold

[0049] Single crystal silicon ingots were grown in a continuous Czochralski process in an ingot puller similar to that shown in FIG. 3. The silicon ingots were grown with a body section of 300 mm and were doped with red phosphorus. An initial charge of polycrystalline silicon was added to the outer melt zone, the middle melt zone, and the inner melt zone. Quartz cullet (4 kg) was added to the top of the polycrystalline feedstock in the outer melt zone. After the charge melted, additional polycrystalline silicon was added through the polycrystalline silicon feed system until the initial charge was fully formed. A batch of quartz cullet (1 kg) was added to the melt. A seed crystal was lowered and a single crystal silicon ingot was grown from the melt. The ingots were then grown while the hot zone maintained temperature (i.e., from the same melt without allowing the hot zone to cool). Before the growth of each subsequent ingot, a batch of buffer material (quartz cullet) (1.5 kg) was added to the outer melt zone. The first ingot was grown with the ratio of the mass M of the batch of buffer material added to the melt to the time T between adding the batch of buffer material to the melt and the start of growth of the ingot body being below a threshold M / T (in this case below 60 g / h). The second ingot was grown after the first ingot with a ratio of M / T above the threshold M / T (i.e. above 60 g / h). As shown, one ingot in the second run was grown below the threshold M / T to confirm the effect.

[0050] The defect counts for wafers sliced ​​from ingots from the first test (M / T less than the threshold M / T) and the second test (M / T greater than the threshold M / T) are shown in Figures 4 and 5, respectively. As can be seen from the comparison of the figures, increasing M / T to the threshold M / T reduced the defect growth in the wafers to less than 30 defects / wafer, thereby increasing the amount of wafers that were within the customer-specified range. Figure 6 is a scatter plot showing the defect counts as a function of M / T ratio (for both red phosphorus ingots and other ingots doped with arsenic). As shown in Figure 6, the defect counts were less than 30 defects / wafer in all tests where M / T was greater than the threshold M / T. Example 2: Axial trend of defect count

[0051] FIG. 7 shows the defect counts of wafers sliced ​​along the axis of an ingot grown by the process of Example 1, where the M / T was about 27 g / h. As shown in FIG. 7, the defect counts across the axis of the ingot were greater than 30 defects / wafer. FIG. 8 shows the defect counts of wafers sliced ​​along the axis of an ingot grown by the process of Example 1, where the M / T was about 70 g / h. As shown in FIG. 8, the defect counts across the axis of the ingot were less than 30. Ingots grown under both conditions showed axial uniformity of defects, indicating that no buffer material needs to be added during the growth of the ingot body. Example 3: Determination of the threshold M / T of an ingot pulling device

[0052] FIG. 9 is a scatter plot showing defect counts as a function of M / T ratio for wafers sliced ​​from a single crystal silicon ingot similar to the apparatus shown in FIG. 3. The ingot puller was a different apparatus than that used in Example 1-2. As shown in FIG. 9, a minimum threshold M / T of 70 g / h resulted in defect counts below 30 defects / wafer in all tests where M / T was greater than the threshold M / T. The threshold M / T (i.e., minimum) for the ingot puller was determined to be about 70 g / h.

[0053] As used herein, when used in connection with a range of dimensions, concentrations, temperatures, or other physical or chemical properties or characteristics, the terms "about," "substantially," "essentially," and "approximately" are meant to encompass the variation that may exist at the upper and / or lower limits of the range of the property or characteristic, including, for example, the variation that results from rounding, measurement methodology, or other statistical variations.

[0054] When introducing elements of the disclosure or embodiments thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more elements. The terms "have," "include," "including," and "having" are intended to be inclusive and mean that there may be additional elements beyond the listed elements. Use of specific orientation terms (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require any particular orientation of the items described.

[0055] Since various changes may be made in the structure and methods described above without departing from the scope of the present disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted in an illustrative and not a limiting sense.

Claims

1. 1. A method for growing a single crystal silicon ingot in a continuous Czochralski process, the method comprising: forming a melt of silicon in a crucible assembly; adding a batch of quartz cullet of mass M to said melt; contacting a surface of the melt with a seed crystal; extracting the single crystal silicon ingot from the melt, wherein the single crystal silicon ingot has a body, and there is a time T between adding the batch of quartz cullet to the melt and the initiation of growth of the body; controlling a ratio of M / T to be greater than a threshold M / T so as to reduce a number of voids in wafers sliced ​​from the single crystal silicon ingot; adding solid polycrystalline silicon feedstock to the crucible assembly to replenish the melt while withdrawing the single crystal silicon ingot; A method comprising:

2. The method further comprises slicing a plurality of wafers from the single crystal silicon ingot, wherein the M / T ratio is controlled to be greater than the threshold M / T such that the wafers sliced ​​from the single crystal silicon ingot have a void count of less than 30 voids with a void count of 0.2 μm or greater. The method of claim 1.

3. The method further comprises slicing a plurality of wafers from the single crystal silicon ingot, wherein the M / T ratio is controlled to be greater than the threshold M / T such that the wafers sliced ​​from the single crystal silicon ingot have a void count of less than 20 voids with a size of 0.2 μm or more. The method of claim 1.

4. The method comprises: growing a plurality of single crystal silicon ingots, where at least two of the plurality of ingots are grown with different M / T ratios; measuring the number of voids in one or more wafers sliced ​​from said plurality of single crystal silicon ingots; determining an M / T ratio of the single crystal silicon ingot from which the wafers having a void count below the threshold void count are sliced; determining the threshold M / T by The method of claim 1.

5. The threshold void count is 30 voids with a size of 0.2 μm or more. The method according to claim 4.

6. The threshold M / T is 40 g / h. The method of claim 1.

7. The threshold M / T is 60 g / h. The method of claim 1.

8. the batch of quartz cullet is a first batch, the single crystal silicon ingot is a first silicon ingot, and the method further comprises: Terminating the growth of the first single crystal silicon ingot; Mass M of the second quartz cullet ２ to said melt; contacting a surface of the melt with a seed crystal; withdrawing a second single crystal silicon ingot from the melt, the second single crystal silicon ingot having a body, and determining a time T between adding the second batch of quartz cullet to the melt and initiation of growth of the body. ２ to reduce the number of voids in wafers sliced ​​from the second single crystal silicon ingot, ２ / T ２ is controlled so that the ratio is greater than the threshold value M / T. The method of claim 1 , comprising:

9. the crucible assembly having a weir and a sidewall, the weir and the sidewall defining an outer melting zone between the weir and the sidewall, and the batch of quartz cullet is added to the outer melting zone. The method of claim 1.

10. the weir is a first weir and the crucible assembly has a second weir on an inner diameter side of the first weir, the first weir and the second weir defining an intermediate melt zone between the first weir and the second weir, and the second weir defining an inner melt zone within the second weir.

10. The method of claim 9.

11. The silicon melt in the crucible assembly is formed by adding an initial charge of solid polycrystalline silicon to the crucible assembly, and the method includes: adding said batch of quartz cullet to said initial charge of solid polycrystalline silicon; melting said initial charge of solid polycrystalline silicon with said quartz cullet disposed therein; The method of claim 1 , comprising:

12. the quartz cullet has a lower density than the silicon melt such that the quartz cullet floats in the melt; The method of claim 1.

13. the single crystal silicon ingot is the first ingot withdrawn from the silicon melt in the crucible assembly after the melt is formed; The method of claim 1.

14. The single crystal silicon ingot is a single crystal silicon ingot that grows after an initial single crystal silicon ingot is pulled from the melt. The method of claim 1.

15. the batch of quartz cullet is not added to the melt while the body of the single crystal silicon ingot is being withdrawn from the melt. The method of claim 1.

16. While the neck and / or crown of the single crystal silicon ingot is being withdrawn from the melt, the batch of quartz cullet is not added to the melt. The method of claim 1.

17. 1. A method for determining a threshold ratio M / T for growing a single crystal silicon ingot in a continuous Czochralski process comprising forming a melt of silicon in a crucible assembly; adding a batch of quartz cullet of mass M to the melt; contacting the melt with a seed crystal; withdrawing a single crystal silicon ingot from the melt, wherein the single crystal silicon ingot has a body, there being a time T between adding the batch of quartz cullet to the melt and initiation of growth of the body, and adding solid polycrystalline silicon feedstock to the crucible assembly to replenish the melt while withdrawing the single crystal silicon ingot, the method comprising: growing a plurality of said single crystal silicon ingots, wherein at least two of said plurality of ingots are grown with different M / T ratios; measuring a defect count in one or more wafers sliced ​​from the plurality of single crystal silicon ingots; determining an M / T ratio of a single crystal silicon ingot from which wafers having a defect count below a threshold defect count are sliced; A method comprising:

18. measuring the number of defects in one or more wafers sliced ​​from the plurality of single crystal silicon ingots includes directing light onto a surface of the wafer and detecting reflected light from the surface; 20. The method of claim 17.

19. The threshold defect number is 30 defects having a size of 0.2 μm or more.

20. The method of claim 17.

20. The crucible assembly having a weir and a sidewall, the weir and the sidewall defining an outer melt zone between the weir and the sidewall, and the batch of quartz cullet is added to the outer melt zone.

20. The method of claim 17.

21. The weir is a first weir, and the crucible assembly has a second weir on an inner diameter side of the first weir, the first weir and the second weir defining an intermediate melting zone between the first weir and the second weir, and the second weir defining an inner melting zone within the second weir.

21. The method of claim 20.

22. The silicon melt in the crucible assembly is formed by the addition of an initial charge of solid polycrystalline silicon to the crucible assembly, the method comprising: adding quartz cullet to said initial charge of solid polycrystalline silicon; melting said initial charge of solid polycrystalline silicon with said quartz cullet disposed therein; 20. The method of claim 17 comprising:

23. The quartz cullet has a density lower than that of the silicon melt such that the quartz cullet floats in the melt.

20. The method of claim 17.

24. The method of claim 23, wherein quartz cullet is not added while the body of the single crystal silicon ingot is being extracted from the melt.

20. The method of claim 17.

25. The method of claim 24, wherein quartz cullet is not added while the neck and / or crown of the single crystal silicon ingot is being pulled from the melt.

20. The method of claim 17.

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