Method for growing single crystal silicon ingot by continuous Czochralski method

Abstract

The present invention discloses a method for growing a single crystal ingot by the continuous Czochralski method. Before the growth of the main body of the ingot, a batch of buffer (such as quartz cullet) is added to the outer melt region of the crucible assembly. In some embodiments, the ratio of the mass M of the batch of buffer added to the melt to the time between adding the batch of buffer to the melt and the start of growth of the main body of the ingot is controlled such that the M / T ratio is greater than a threshold M / T.

Description

[0001] Relevant information of divisional application

[0002] This application is a divisional application of a Chinese patent application with the invention title "Method for Growing Single Crystal Silicon Ingot by Continuous Czochralski Method", application number 202180092003.0, and filing date December 29, 2021.

[0003] Cross-reference of related applications

[0004] 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. The entire contents of both applications are incorporated herein by reference. Technical Field

[0005] The field of the present disclosure relates to methods for producing single crystal silicon ingots by the continuous Czochralski method (CCz), and more particularly to methods of adding a buffer to the outer melt zone of a crucible assembly. Background Art

[0006] The continuous Czochralski method (CCz) is well suited for forming single crystal silicon ingots with diameters of 300 mm or 200 mm, such as relatively heavily doped arsenic or phosphorus ingots. The continuous Czochralski method involves forming a single crystal silicon ingot from a silicon melt while continuously or intermittently adding solid polysilicon to the melt to replenish the melt as the ingot grows. The method may involve forming multiple ingots from the same melt while the hot zone is maintained at a temperature (i.e., the melt continuously exists in the crucible assembly during the growth of multiple ingots).

[0007] Customers are increasingly specifying that for both 200 mm and 300 mm ingots, wafers cut from ingots grown by the continuous Czochralski method have a low void count (e.g., less than 30 defects per wafer). The continuous Czochralski method may involve a crucible assembly that includes at least two and typically three melt zones separated by physical barriers - an outer melt zone into which solid polysilicon is fed, an intermediate melt zone in which the melt is stabilized, and an inner melt zone from which the silicon ingot is pulled. Adding solid polysilicon to the melt causes inert gas bubbles (e.g., argon bubbles) to form in the melt, which affects the void count.

[0008] There is a need for methods of forming silicon ingots that reduce the defect count in silicon wafers cut from the ingots and / or that reduce the formation of inert gas bubbles in the melt or promote the dissipation of inert gas bubbles.

[0009] This section is intended to introduce to the reader various aspects of technologies that may be related to various aspects of the present disclosure, which are described and / or claimed below. This discussion is considered to be helpful in providing background information to the reader 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 from this perspective and not as an admission of prior art. Summary of the Invention

[0010] One aspect of the present disclosure refers to a method for growing a single crystal silicon ingot by the continuous Czochralski method. A silicon melt is formed in a crucible assembly. A batch of buffer is added to the melt. The batch has a mass M. The surface of the melt is brought into contact with a seed. 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 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 void count in wafers cut from the single crystal silicon ingot. While withdrawing the single crystal silicon ingot, solid polysilicon raw material is added to the crucible to replenish the melt.

[0011] One aspect of the present disclosure refers to a method for determining a threshold ratio of M / T for growing a single crystal silicon ingot by the continuous Czochralski method. The continuous Czochralski method includes: forming a silicon melt in a crucible assembly; adding a batch of buffer to the melt, where the batch has a mass M; bringing the surface of the melt into contact with a seed; withdrawing a single crystal silicon ingot from the melt, the single crystal silicon ingot including a body, there is a time T between adding the batch of buffer to the melt and the start of growth of the body; and adding solid polysilicon raw material to the crucible assembly to replenish the melt while withdrawing the single crystal silicon ingot. The method for determining the threshold ratio of M / T includes growing a plurality of single crystal silicon ingots, where at least two of the ingots are grown at different M / T ratios. Measuring the defect count in one or more wafers cut from the plurality of single crystal silicon ingots. Determining the M / T ratio of the single crystal silicon ingot from which the wafer having a defect count below the threshold defect count is cut.

[0012] There are various improvements to the features mentioned in the above aspects of the present disclosure. Further features may also be incorporated into the above aspects of the present disclosure. These improvements and additional features may exist individually or in any combination. For example, the various features related to any of the illustrated embodiments of the present disclosure discussed below may be incorporated into any of the above aspects of the present disclosure individually or in any combination. Brief Description of the Drawings

[0013] Figure 1 is a cross-sectional view of an exemplary ingot pulling apparatus in which solid polysilicon feed is disposed;

[0014] Figure 2 is a cross-sectional view of an ingot pulling apparatus having a melt and a buffer in the melt;

[0015] Figure 3 is a cross-sectional view of a crystal pulling device that shows pulling a silicon ingot from a silicon melt;

[0016] Figure 4 is a box plot that shows the void count in wafers cut from an ingot where M / T is less than a threshold M / T;

[0017] Figure 5 is a box plot that shows the void count in wafers cut from an ingot where M / T is greater than a threshold M / T;

[0018] Figure 6 is a scatter plot that shows the defect count varying according to M / T;

[0019] Figure 7 is a box plot of wafers cut from an ingot where M / T is less than a threshold M / T;

[0020] Figure 8 is a box plot of wafers cut from an ingot where M / T is greater than a threshold M / T; and

[0021] Figure 9 is a scatter plot that shows the defect count varying according to M / T for another crystal pulling device.

[0022] Throughout the drawings, corresponding reference numerals indicate corresponding parts. Detailed Description

[0023] The present disclosure provides a method for growing a single crystal silicon ingot by the continuous Czochralski method (CCz). Before forming the body of the ingot, a buffer (such as quartz cullet) is added to the silicon melt. The ratio of the mass M of the added buffer to the time T between adding the buffer and the start of growth of the body of the ingot is controlled to be greater than a threshold M / T. By controlling the ratio of the mass of the buffer to the time until the start of growth of the ingot body (M / T) to be greater than the threshold M / T, the amount of defects in the resulting silicon wafers can be reduced.

[0024] An exemplary crystal pulling device 5 for producing an ingot 60 by the continuous Czochralski method is shown in Figure 3Shown in. The ingot puller device 5 includes a crucible assembly 10, and the crucible assembly 10 includes a melt 6 of semiconductor or solar-grade silicon material. The base 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 divide the melt into different melt zones. In the illustrated embodiment, 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 radially inward of the first weir 20, which defines an inner melt zone 22 of the silicon melt. The inner melt zone 22 is the growth zone from which the single-crystal ingot 60 grows. The first weir 20 and the second weir 30 define an intermediate melt zone 32 of the silicon melt, where the melt 6 can be stabilized as it moves toward the inner melt zone 22. Each of the first and second weirs 20, 30 has at least one opening defined therein to allow the molten silicon to flow radially inward toward the growth zone of the inner melt zone 22.

[0025] In the illustrated embodiment, each of the first weir 20, the second weir 30, and the sidewall 40 has a generally annular shape. The first weir 20, the second weir 30, and the sidewall 40 can be part of three nested crucibles joined at the bottom or bottom plate 45 of the crucible assembly 10 (i.e., the first and second weirs 20, 30 are the sidewalls of two crucibles nested within a larger crucible). Figures 1 to 3 The crucible assembly configuration depicted is exemplary. In other embodiments, the crucible assembly 10 has a single-layer bottom plate (i.e., without nested crucibles), where the weirs extend upward from the bottom plate 45. Optionally, the bottom plate 45 can be flat rather than curved and / or the weirs 20, 30 and / or the sidewall 40 can be straight-edged. Further, although the illustrated crucible assembly 10 shows two weirs, in other embodiments, the crucible assembly can have a single weir or even no weirs.

[0026] The feed tube 46 feeds polysilicon, which can be (for example) granular, lump, or a combination of granular and lump, into the outer melt zone 42 at a rate sufficient to maintain a generally constant melt height level and volume during the growth of the ingot 60.

[0027] Typically, the melt 6 from which the ingot 60 is drawn is formed by loading polysilicon into the crucible to form an initial silicon feed 27 ( Figure 1 ). Generally, the initial feed is between about 10 kilograms and about 200 kilograms of polysilicon, which can be granular, lump, or a combination of granular and lump. The mass of the initial feed depends on the desired crystal diameter and the hot zone design. The initial feed does not reflect the length of the ingot crystal, since polysilicon is continuously fed during crystal growth.

[0028] A variety of polysilicon sources can be used, including (for example) granular polysilicon produced by thermal decomposition of silane or halosilane in a fluidized bed reactor or polysilicon produced in a Siemens reactor. As described below, a quantity of buffer can be added to the initial feed 27 of polysilicon in the outer melt zone 42 of the crucible assembly 10 before or during the initial feed 27 of molten polysilicon.

[0029] Once the polysilicon (and optionally the buffer) is added to the crucible assembly 10 to form the feed 27, the feed 27 is heated to a temperature above the approximate melting temperature of silicon (e.g., about 1412 °C) to melt the feed, and thereby form a silicon melt 6 comprising molten silicon ( Figure 2 ). The silicon melt 6 has an initial volume of molten silicon and an initial melt height level, and these parameters are determined by the size of the initial feed 27. In some embodiments, the crucible assembly 10 comprising the 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.

[0030] The ingot pulling device 5 includes a pulling mechanism 114 ( Figure 3 ) for growing and pulling an ingot 60 from the melt within 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 122 coupled to the seed holder or chuck 120 for initializing crystal growth. One end of the pulling cable 118 is connected to a lifting mechanism (such as a driven pulley or drum or any other suitable type of lifting mechanism), and the other end is connected to the chuck 120 holding the seed 122. In operation, the seed 122 is lowered to contact the melt 6 in the inner melt zone 22. The pulling mechanism 114 is operated to raise the seed 122 along the pulling axis A. This causes a single crystal ingot 60 to be pulled from the melt 6.

[0031] Once the feed 27 of polysilicon ( Figure 1 ) is liquefied to form a silicon melt 6 comprising molten silicon ( Figure 2 ), the silicon seed 122 ( Figure 3 ) is lowered to contact the melt 6 within the inner melt zone 22. The silicon seed 122 is then withdrawn from the melt 6, with silicon attached thereto to form a neck 52, thereby forming a melt-solid interface near or at the surface of the melt 6.

[0032] The pulling mechanism 114 can rotate the seed 122 and the ingot 60 connected thereto. The crucible drive unit 44 can rotate the base 13 and the crucible assembly 10. In some embodiments, the silicon seed 122 and the crucible assembly 10 rotate in opposite directions (i.e., counter-rotate). Counter-rotation achieves convection in the silicon melt 6. Rotation of the seed 122 is mainly used to provide a symmetric temperature distribution, suppress angular variations of impurities, and also control the crystal melt interface shape.

[0033] After the neck 52 is formed, an outwardly flaring seed cone portion 54 (or "crown") adjacent to the neck 52 grows. Generally, the pulling rate is reduced from the neck pulling rate to a rate suitable for the growth of the outwardly flaring seed cone portion 54. Once the seed cone portion reaches the target diameter, the "constant diameter portion" of many bodies 56 or ingots 60 grows. In some embodiments, the body 56 of the ingot 60 has a diameter of 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.

[0034] When the ingot 60 is pulled from the melt 6, solid polysilicon feedstock is added to the outer melt zone 42 through the tube 46 or other channels to replenish the melt 6 in the ingot growth apparatus 5. The solid polysilicon can be added from a polysilicon feed system 66 and can be added continuously or intermittently to the ingot puller apparatus 5 to maintain the melt level. Generally, the polysilicon can be metered into the ingot puller apparatus 5 by any method available to those skilled in the art.

[0035] In some embodiments, dopants are also added to the melt 6 during ingot growth. The dopants can be introduced from a dopant feed system 72. The dopants can be added as a gas or a solid and can be added to the outer melt zone 42.

[0036] The apparatus 5 can include a thermal shield 116 disposed around the ingot 60 to allow the growing ingot 60 to radiate its latent heat of solidification and the heat flux from the melt 6. The thermal shield 116 can be at least partially conical and slope downward at an angle to create an annular opening in which the ingot 60 is disposed. Generally, a flow of an inert gas (such as argon) is provided along the length of the growing crystal. The ingot 60 is pulled through a growth chamber 78 sealed from the surrounding atmosphere.

[0037] A plurality of independently controlled annular bottom heaters 70 can be disposed in a radial pattern below the crucible assembly 10. The annular bottom heaters 70 apply heat in a relatively controlled distribution across the entire base surface area of the crucible assembly 10. The annular bottom heaters 70 can be individually controlled flat resistance heating elements as described in U.S. Patent No. 7,635,414, which is incorporated herein by reference for all relevant and consistent purposes. The apparatus 5 can include one or more side heaters 74 disposed radially outward of the crucible assembly 10 to control the temperature distribution through the melt 6.

[0038] Figures 1 to 3 The ingot growth apparatus 5 shown and described herein is exemplary and generally any system in which an ingot is prepared by the continuous Czochralski method can be used, unless otherwise specified.

[0039] According to an embodiment of the present disclosure, prior to the growth of the ingot 60, a batch 31 (Figure 2 ) A buffer 35 (such as quartz cullet) is added to the silicon melt 6, and particularly to the outer melt zone 42. The density of the buffer 35 can be less than that of the silicon melt 6, such that the buffer 35 floats within the melt 6 (i.e., a portion is disposed on the surface of the melt 6). Suitable buffers 35 that can be added to the outer melt zone 42 include (for example) solid materials that prevent the direct entry of polysilicon added through the feed tube 46 into the melt 6 and / or provide a surface area for the dissipation of inert gas bubbles. The buffers 35 can form gaps between the buffers 35. The buffers 35 can move freely (such as when impacted by falling polycrystalline feedstock). In some embodiments, the buffer 35 comprises quartz (such as quartz cullet). When using quartz cullet, the cullet can have any suitable shape (such as cylindrical) and any suitable size (for example, when using cylindrical cullet, a diameter of about 1 mm to 10 mm and / or a length of about 1 mm to about 10 mm).

[0040] After adding the batch 31 of the buffer 35 to the melt 6, the ingot 60 is lifted from the melt 6. According to an embodiment of the present disclosure, the ratio of the mass M of the batch 31 of the buffer 35 added to the melt 6 to the time T between adding the batch 31 of the buffer 35 to the melt 6 and when the ingot body 56 ( Figure 3 ) starts to grow is controlled such that the ratio of M / T is greater than a threshold ratio of M / T to reduce the void count in the wafers cut from the single-crystalline silicon ingot. Generally, the time T corresponds to the time when the batch 31 of the buffer 35 has been completely added and when the ingot body 56 starts to grow.

[0041] In some embodiments, the ratio of M / T is controlled to be greater than the threshold M / T such that the wafers cut from the single-crystalline silicon ingot have a void count with fewer than 30 defects of a size of 0.2 μm or greater or even have a void count with fewer than 20 defects of a size of 0.2 μm or greater. The threshold M / T can vary depending on the hot zone design of the ingot pulling device. To determine the threshold M / T, a threshold defect count is established (for example, the maximum defect count desired by the manufacturer and / or customer, such as fewer than 30 defects, fewer than 20 defects, or fewer than 10 defects of a size of 0.2 μm or greater). Multiple single-crystalline silicon ingots are grown, where at least two of the ingots (such as 2, 3, 5, 10, 25, 100 ingots) are grown at different M / T ratios. The defect count in one or more wafers cut from the multiple single-crystalline silicon ingots is measured (such as using an SP1 inspection tool). The M / T ratio of the single-crystalline silicon ingot from which the wafer having a defect count below the threshold defect count is cut is determined based on the measured defect count (i.e., the threshold M / T is determined based on the M / T value where the defect count is equal to or below the defect threshold count).

[0042] In some embodiments, the M / T is controlled to be greater than a threshold M / T thereof, which is 40 grams per hour. In other embodiments, the threshold M / T is 50 grams per hour or even 55 grams per hour. In some embodiments, the M / T is controlled to be greater than a threshold M / T thereof, which is 60 grams per hour. In other embodiments, the M / T is controlled to be greater than a threshold M / T thereof, which is 70 grams per hour. The threshold M / T (and the actual M / T used to grow the ingot in the ingot puller device) can be constrained by the actual limitations of the ingot growth process (e.g., not inhibiting the flow of solid polysilicon into the melt, such as when solid polysilicon starts to pile up on top of the buffer). For example, the M / T can be controlled to be higher than the threshold M / Ts listed above and less than 500 grams per hour or even less than 250 grams per hour.

[0043] As Figure 2 shown in and according to some embodiments of the present disclosure, the buffer 35 of the batch 31 can be large enough such that the buffer 35 extends continuously from the sidewall 40 of the crucible assembly 10 to the first weir 20.

[0044] In this regard, the mass M of the buffer 35 (e.g., quartz cullet) of the batch 31 generally excludes any buffer added before the initial feed 27 ( Figure 1 ) is melted (i.e., excludes the initial feed of the buffer added to the solid polycrystalline feed).

[0045] To control the ratio of M / T such that the ratio of M / T is greater than the threshold M / T, the mass M of the buffer 35 of the batch 31 added to the outer melt zone 42 can be increased, or the time T between adding the buffer and the growth of the body 56 of the ingot 60 can be reduced (e.g., by adding the buffer later, i.e., closer to the time when the ingot body 56 starts to grow). It should be noted that controlling the M / T to be "greater than" the threshold M / T generally encompasses any method of selecting or establishing a minimum M / T for the ingot growth process (i.e., includes embodiments in which the M / T during the ingot growth process "equals" or is greater than the minimum value, or in other words, the threshold M / T is a unit lower than the minimum M / T selected such that the M / T is greater than the threshold).

[0046] When the ingot 60 is extracted from the melt 6, solid polysilicon raw material is added to the crucible assembly 10 while the single-crystal silicon ingot 60 is being pulled to replenish the melt 6. In some embodiments, no buffer 35 is added to the melt during ingot growth (e.g., the neck, crown, and / or body). If a buffer is added during the growth of the neck 52 and / or the crown 54 as in other embodiments of the present disclosure, then the mass M of the buffer 35 of the batch 31 can include the seed 122 ( Figure 3)Any buffer 35 added during the growth of the neck 52 and crown 54 of the ingot 60 while decreasing and / or adding, and any buffer added before decreasing the seed 122 (and after feeding the molten solid polysilicon and / or after termination of the growth of the previous ingot (if any)). In some embodiments of the present disclosure, no buffer 35 is added while the ingot body 56 is being lifted from the melt 6. If buffer 35 is added during the growth of the ingot body 56, then such buffer 35 is not considered part of batch 31 added before the growth of the body 56 of the ingot 60 (i.e., not part of the mass M of batch 31).

[0047] In some continuous Czochralski methods, while the hot zone (i.e., the lower part of the apparatus 5, such as the crucible assembly 10 and the susceptor 13) is kept heated, more than one ingot is grown, where the silicon melt 6 is continuous within the crucible assembly 10. In such methods, a first ingot is grown to a target length and growth is terminated, the ingot is removed from the puller, and then the seed is lowered into the melt to initiate the growth of a second single crystal silicon ingot (i.e., using the same melt from which the first ingot was extracted). Subsequently, the ingot can be grown with the hot zone intact and at the temperature of the continuously molten silicon within the crucible assembly 10 (e.g., until one or more components of the hot zone have degraded, such as the crucible assembly needs to be cooled and the degraded components replaced). For example, at least 1, 2, 3, 4, 5, 6, 10, or 20 or more ingots can be grown.

[0048] After the growth of the first ingot 60 is terminated and the ingot is removed (e.g., removed from the pull chamber of the puller apparatus 10), a second batch of buffer can be added to the melt remaining after the first ingot has been removed. The seed 122 (i.e., the same seed or a different seed used to pull the first ingot) is lowered to contact the melt. According to an embodiment of the present disclosure, the ratio of the mass M2 of the second batch of buffer added to the melt to the time T2 between adding the second batch of buffer and the start of growth of the ingot body is controlled to be greater than a threshold M / T (i.e., the threshold M / T mentioned above) to reduce the void count in the wafers cut from the second single crystal silicon ingot. In this regard, when the second batch is added, there may be a certain amount of the first batch of buffer still remaining in the melt. Due to dissolution in the silicon melt, the amount (or all of the amount) of the first batch may be depleted. The first batch remaining in the melt is generally not part of the mass M2 of the second batch.

[0049] The puller apparatus 5 can include a buffer feed system 55( Figure 2)For adding a plurality of batches of batch buffer 35 to the outer melt zone 42. The buffer system 55 can be configured for autonomous addition of buffer 35 or for manual addition. For example, the buffer feed system 55 can include a storage container for containing the buffer (such as quartz cullet) and metering means (such as a weighing hopper, metering wheel or the like). The buffer feed system 55 can include a buffer feed pipe, which can be the same pipe 46 as the pipe for adding polysilicon or can be a separate pipe. The buffer 35 can be weighed by an operator or automatically fed into the pipe by the buffer feed system 55.

[0050] Compared with the conventional method for growing a single crystal ingot by the continuous casting method (CCz), the method of the present disclosure has several advantages. By controlling the ratio of the mass M of the batch of buffer added to the melt to the time T between adding the batch of buffer to the melt and the start of growth of the main body of the single crystal ingot to be greater than the threshold of M / T, the void count of the wafers cut from the ingots grown by such continuous casting methods can be reduced. For example, such wafers can have less than 30 defects per wafer (having a size of 0.2 μm or larger and measured by an SP1 inspection tool). Without being bound by any particular theory, it is believed that adding polysilicon to the outer melt zone of the crucible assembly produces relatively small bubbles (such as less than 10 μm) of an inert gas (such as argon) that can be carried by the melt through the openings in each weir that allow the bubbles to reach the solid-melt interface. The buffer can prevent the inert gas from being trapped in the melt by preventing the polycrystalline raw material from being directly poured into the melt. The buffer can also provide a surface area and nucleation sites for the aggregation of inert gas bubbles, thereby increasing the size of the bubbles to allow them to become buoyant. By increasing the ratio of the mass M of the batch of buffer added to the melt to the time T between adding the batch of buffer to the melt and the start of ingot body growth to at least 60 grams per hour, the efficiency of the buffer in reducing inert gas shock and / or inert gas bubble dissipation is increased.

[0051] Examples

[0052] The process of the present disclosure is further illustrated by the following examples. These examples should not be construed as limiting.

[0053] Example 1: Number of voids in a wafer grown from an ingot with M / T less than the threshold of M / T

[0054] A single crystal ingot is similar to Figure 3The ingot puller device of the apparatus shown is grown by the continuous Czochralski method. The silicon ingot is grown with a 300 mm body portion and doped with red phosphorus. The initial feed of polysilicon is added to the outer melt zone, the intermediate melt zone, and the inner melt zone. Crushed quartz glass (4 kg) is added to the top of the polysilicon raw material in the outer melt zone. After the feed is melted, additional polysilicon is added through the polysilicon feed system until the initial feed is completely formed. A batch of crushed quartz glass (1 kg) is added to the melt. The seed is lowered and a single crystal silicon ingot is grown from the melt. Subsequently, the ingot is grown while maintaining the hot zone at a temperature (i.e., from the same melt without cooling the hot zone). Before the growth of each subsequent ingot, a batch (1.5 kg) of buffer (crushed quartz glass) is added to the outer melt zone. The first round of ingots is grown with a ratio of the mass M of the batch of buffer added to the melt to the time T between adding the batch of buffer to the melt and the start of ingot body growth less than a threshold M / T (less than 60 g / h in this case). The second round of ingots is grown after the first round with a ratio of M / T greater than the threshold M / T (i.e., 60 g / h or more). As indicated, one ingot in the second round is grown with an M / T below the threshold M / T to confirm the effect.

[0055] The defect counts in wafers cut from ingots of the first round (M / T less than the threshold M / T) and the second round (M / T greater than the threshold M / T) are shown respectively in Figure 4 and 5 As can be seen from comparing the figures, increasing M / T to the threshold M / T reduces the defect growth in the wafers to less than 30 defects / wafer, thus increasing the amount of wafers within customer specifications. Figure 6 is a scatter plot showing the defect counts varying according to the M / T ratio (for both red phosphorus ingots and other ingot wheels doped with arsenic). As Figure 6 shown, for all runs with M / T greater than the threshold M / T, the defect counts are below 30 defects / wafer.

[0056] Example 2: Axial trend of defect count

[0057] Figure 7 shows the defect counts in wafers cut along the axis of an ingot grown by the process of Example 1, where M / T is approximately 27 g / h. As Figure 7 shown, the defect counts across the entire axis of the ingot are greater than 30 defects / wafer. Figure 8 shows the defect counts in wafers cut along the axis of an ingot grown by the process of Example 1, where M / T is approximately 70 g / h. As Figure 8 shown, the defect counts across the entire axis of the ingot are less than 30. The ingots grown under both conditions exhibit axial uniformity of defects. This indicates that no buffer addition is required during the growth of the ingot body.

[0058] Example 3: Ingot pulling device Determination of the threshold M / T of the equipment

[0059] Figure 9 is a scatter plot showing that the defect count of wafers cut from a single crystal ingot of a device similar to that shown in Figure 3 varies according to the M / T ratio. The ingot puller device is a device different from those used in Examples 1 to 2. As shown in Figure 9 for all runs in which the M / T is greater than the threshold M / T, a minimum threshold of M / T of 70 grams per hour results in a defect count of less than 30 defects per wafer. The threshold M / T (i.e., the minimum value) of the ingot puller device was determined to be approximately 70 grams per hour.

[0060] As used herein, when used in conjunction with ranges of dimensions, concentrations, temperatures, or other physical or chemical properties or characteristics, the terms “about,” “substantially,” “essentially,” and “approximately” are intended to cover variations that may exist in the upper and / or lower limits of the range of the property or characteristic, including (for example) variations caused by rounding, measurement methods, or other statistical variations.

[0061] When introducing elements of the present disclosure or embodiments thereof, the articles “a / an” and “the / said” are intended to mean that there is one or more of the elements. The terms “comprising,” “including,” “containing,” and “having” are intended to be inclusive and mean that additional elements may exist in addition to the listed elements. The use of terms indicating a particular orientation (e.g., “top,” “bottom,” “side,” etc.) is for ease of description and does not require any particular orientation of the object being described.

[0062] Since various changes may be made to the above-described construction and method 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 as illustrative and not in a limiting sense.

Claims

1. A method for determining a threshold ratio of M / T for growing a single crystal silicon ingot by the continuous Czochralski method, the continuous Czochralski method including forming a silicon melt in a crucible assembly, adding a batch of quartz cullet to the melt, wherein the batch has a mass M, bringing the surface of the melt into contact with a seed, pulling a single crystal silicon ingot from the melt, the single crystal silicon ingot including a body, there being a time T between adding the batch of quartz cullet to the melt and the start of growth of the body, and adding solid polysilicon feedstock to the crucible assembly while pulling the single crystal silicon ingot to replenish the melt, the method including: Growing a plurality of single crystal silicon ingots, wherein at least two of the ingots are grown at different M / T ratios; Measuring a defect count in one or more wafers cut from the plurality of single crystal silicon ingots; and Determining the M / T ratio of the single crystal silicon ingot from which the wafer having a defect count below a threshold defect count is cut.

2. The method according to claim 1, wherein measuring the defect count in one or more wafers cut from the plurality of single crystal silicon ingots includes directing light to the surface of the wafer and detecting reflected light from the surface.

3. The method according to claim 1, wherein the threshold defect count is 30 defects of a size of 0.2 μm or greater.

4. The method according to claim 1, wherein the crucible assembly includes 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.

5. The method according to claim 4, wherein the weir is a first weir, the crucible assembly includes a second weir radially inward 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.

6. The method according to claim 1, wherein the silicon melt in the crucible assembly is formed by adding an initial feed of solid polysilicon to the crucible assembly, the method including: Adding quartz cullet to the initial feed of solid polysilicon; And Melting the initial feed of solid polysilicon in which the quartz cullet is disposed.

7. The method according to claim 1, wherein the density of the quartz cullet is less than that of the silicon melt such that the quartz cullet floats in the melt.

8. The method according to claim 1, wherein no quartz cullet is added while pulling the body of the single crystal silicon ingot from the melt.

9. The method according to claim 1, wherein no quartz cullet is added while pulling the neck and / or crown of the single crystal silicon ingot from the melt.

Images