Use of buffer materials during single-crystal silicon ingot growth
By adding a buffer member to the outer molten zone and controlling the M/T ratio in the CCz method, the method effectively reduces defects and inert gas bubbles in silicon ingots, improving the quality of silicon wafers.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- GLOBALWAFERS CO LTD
- Filing Date
- 2026-03-17
- Publication Date
- 2026-06-23
AI Technical Summary
The continuous Czochralski (CCz) method for growing silicon ingots faces challenges in reducing the number of defects and inert gas bubbles in wafers sliced from the ingots, particularly for 200mm and 300mm ingots, due to the formation of inert gas bubbles during the addition of solid polycrystalline silicon to the molten material.
A buffer member, such as quartz cullet, is added to the outer molten zone of the crucible assembly, and the M/T ratio (mass of buffer material to time between addition and ingot growth start) is controlled to be greater than a threshold to reduce voids and inert gas bubbles, using a controlled crucible assembly with weirs to manage bubble formation.
The method significantly reduces the number of defects in silicon wafers to fewer than 30 per wafer, with voids of 0.2 μm or larger, by effectively managing inert gas bubbles through controlled buffer material addition, enhancing the quality of silicon ingots.
Smart Images
Figure 2026102783000001_ABST
Abstract
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 on December 31, 2020, and U.S. Provisional Patent Application No. 63 / 132,713, filed on December 31, 2020. Both applications are hereby incorporated by reference in their entirety.
[0002] The field of the present disclosure relates to a method for manufacturing a single - crystal silicon ingot by the continuous Czochralski (CCz) method, and more particularly, to a method of adding a buffer member to the outer molten zone of a crucible assembly.
Background Art
[0003] The continuous Czochralski (CCz) method is well - suited for forming ingots with a diameter of 300 mm or 200 mm, such as ingots doped with a relatively large amount of arsenic or phosphorus. The continuous Czochralski (CCz) method 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 as the ingot grows. The method may involve forming multiple ingots from the same melt while the hot zone maintains the temperature (i.e., while multiple ingots are growing and the melt continuously exists in the crucible assembly).
[0004] The customer further specifies that for both 200mm and 300mm ingots, wafers sliced from ingots grown by the continuous Czochralski process must have a low void count (e.g., fewer than 30 defects per wafer). The continuous Czochralski process may involve a crucible assembly containing at least two, often three, melting zones separated by a physical barrier: an outer melting zone where solid polycrystalline silicon is supplied, an intermediate melting zone where the molten material stabilizes, and an inner melting zone where the silicon ingot is pulled up. The addition of solid polycrystalline silicon to the molten material causes the formation of inert gas bubbles (e.g., argon bubbles) in the molten material, which affects the void count.
[0005] There is a need for a method of forming silicon ingots that reduces the number of defects in silicon wafers sliced from the ingot, and / or reduces the formation of inert gas bubbles in the molten material, or promotes the disappearance of inert gas bubbles.
[0006] This section is intended to introduce to the reader various technical aspects relating to various aspects of this disclosure, which are described and disclosed below. This description is intended to help provide the reader with background information to facilitate a better understanding of the various aspects of this disclosure. Accordingly, these descriptions should be read in this context and understood not as prior art acknowledgments. [Overview of the project]
[0007] One aspect of the present invention relates to a method for growing a single-crystal silicon ingot in a continuous Czochralski process. A silicon molten mass is formed in a crucible assembly. A batch of buffer material is added to the molten mass. The mass of the batch is M. The surface of the molten mass is in contact with a seed crystal. A single-crystal silicon ingot is drawn from the molten mass. The single-crystal silicon ingot contains a body. There is a time T between the addition of the batch of buffer material to the molten mass and the start of body growth. The M / T ratio is controlled to be greater than a threshold M / T to reduce the number of voids in the wafer sliced from the single-crystal silicon ingot. A solid polycrystalline silicon feedstock is added to the crucible to replenish the molten mass while the single-crystal silicon ingot is being drawn.
[0008] One aspect of the present invention is directed toward a method for determining a threshold M / T ratio for growing single-crystal silicon ingots in a continuous Czochralski process. The continuous Czochralski process includes forming a silicon molten mass in a crucible assembly, adding a batch of buffer material of mass M to the molten mass, contacting the molten mass with a seed crystal, drawing a single-crystal silicon ingot from the molten mass, where the single-crystal silicon ingot has a body, there is a time T between the addition of the batch of buffer material to the molten mass and the start of body growth, and adding solid polycrystalline silicon feedstock to the crucible assembly to replenish the molten mass while the single-crystal silicon ingot is being drawn. The method for determining the threshold M / T ratio includes growing a plurality of single-crystal silicon ingots, where two of the plurality of ingots are grown at different M / T ratios. The number of defects in a plurality of wafers sliced from the plurality of single-crystal silicon ingots is measured. The M / T ratio of the sliced single-crystal silicon ingot is determined for wafers with fewer defects than a threshold defect number.
[0009] Various improvements to the features referred to in relation to the above aspects of this disclosure exist. Further features may also be incorporated into the above aspects of this disclosure. These improvements and additional features may exist individually or in any combination. For example, the various features described below in relation to any of the embodiments of this disclosure shown may be incorporated individually or in any combination into any of the above aspects of this disclosure. [Brief explanation of the drawing]
[0010] [Figure 1] This is a cross-sectional view of an embodiment of an ingot pulling device having a solid polycrystalline silicon charge placed therein.
[0011] [Figure 2] This is a cross-sectional view of an ingot lifting device having a molten material containing a buffering member.
[0012] [Figure 3] This is a cross-sectional view of an ingot pulling device showing a silicon ingot being pulled up from molten silicon.
[0013] [Figure 4] This is a box plot showing the number of voids in wafers sliced from ingots where the M / T ratio was below the threshold M / T.
[0014] [Figure 5] This is a box plot showing the number of voids in wafers sliced from ingots where the M / T ratio was greater than the threshold M / T.
[0015] [Figure 6] This is a scatter plot showing the number of defects as a function of M / T.
[0016] [Figure 7] This is a box plot of wafers sliced from ingots where the M / T ratio was below the threshold M / T.
[0017] [Figure 8] A box plot of wafers sliced from an ingot where M / T was greater than the threshold M / T.
[0018] [Figure 9] A scatter diagram showing the number of defects of other ingot lifting devices as a function of M / T.
[0019] Corresponding reference numerals indicate corresponding elements throughout the drawings.
BEST MODE FOR CARRYING OUT THE INVENTION
[0020] The present disclosure provides a method for growing a single crystal silicon ingot in a continuous Czochralski (CCz) process. A buffer member (e.g., a quartz crucible) is added to the silicon melt before formation of the body of the ingot. The ratio of the mass M of the buffer member added and the time T from addition of the buffer member to the start of growth of the body of the ingot is controlled to be greater than a threshold M / T. By controlling the ratio (M / T) of the mass of the buffer member and the time until the ingot body begins to grow to be greater than the threshold M / T, the amount of defects obtained in the silicon wafer can be reduced.
[0021] An embodiment of an ingot lifting device 5 for manufacturing an ingot 60 by a continuous Chokralski process is shown in FIG. 3. The ingot lifting device 5 includes a crucible assembly 10 containing a melt 6 of a semiconductor or solar grade silicon material. A susceptor 13 supports the crucible assembly 10. The crucible assembly 10 has a side wall 40 and one or more fluid barriers 20, 30, i.e., "weirs", that separate 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 side wall 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, and the second weir 30 defines an inner melt zone 22 of the silicon melt. The inner melt zone 22 is a growth region where a single crystal silicon ingot 60 grows. The first weir 20 and the second weir 30 define an intermediate melt zone 32 of the silicon melt that can be stabilized as the melt 6 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 molten silicon to flow toward the inner diameter side toward the growth region of the inner melt zone 22.
[0022] In the illustrated embodiment, each of the first weir 20, the second weir 30, and the side wall 40 generally has an annular shape. The first weir 20, the second weir 30, and the side wall 40 can be part of three nested parts joined at the bottom, or floor 45, of the crucible assembly 10 (i.e., the first and second weirs 20, 30 are the side walls of two nested crucibles within a larger crucible). The crucible assembly configuration depicted in FIGS. 1 - 3 is exemplary. In other embodiments, the crucible assembly 10 has a single layer floor (i.e., no nested crucibles) where the weirs extend upward from the floor 45. Optionally, the floor 45 may be flat rather than curved, and / or the weirs 20, 30 and / or the side wall 40 may have straight surfaces. Further, although the illustrated crucible assembly 10 is shown with two weirs, other embodiments of the crucible assembly 10 may have a single weir or even no weirs.
[0023] The supply pipe 46 supplies polycrystalline silicon, which may be granular, lumpy, or a combination of granular and lumpy, to the outer melting zone 42 at a sufficient rate to maintain a substantially constant molten height level and volume during the growth of the ingot 60.
[0024] Generally, the molten material 6 from which the ingot 60 is drawn is formed by loading polycrystalline silicon into the crucible to form an initial silicon charge 27 (Figure 1). Generally, the initial charge is about 10 kg to 200 kg of polycrystalline silicon and can be granular, lumpy, or a combination of granular and lumpy. The mass of the initial charge depends on the desired crystal diameter and the design of the hot zone. Since polycrystalline silicon is supplied continuously during crystal growth, the initial charge does not reflect the length of the ingot crystal.
[0025] For example, polycrystalline silicon from various sources can be used, including granular polycrystalline silicon produced by the thermal decomposition of silane or halosilane in a fluidized bed reactor, or polycrystalline silicon produced in a Siemens reactor. As described below, the amount of buffer material can be added to the initial charge of polycrystalline silicon 27 in the outer melting zone 42 of the crucible assembly 10 before or during the melting of the initial charge of polycrystalline silicon 27.
[0026] When polycrystalline silicon (and optionally a buffer) is added to the crucible assembly 10 to form a charge 27, the charge 27 is heated to a temperature above the melting temperature of silicon at which the charge melts (e.g., about 1412°C), thereby forming a silicon molten mass 6 (Figure 2) containing molten silicon. The silicon molten mass 6 has an initial volume of molten silicon and an initial melt height level, these parameters being determined by the size of the initial charge 27. In some embodiments, the crucible assembly 10 containing the silicon molten mass 6 is heated to a temperature of at least about 1425°C, at least about 1450°C, or even further at least about 1500°C.
[0027] The ingot pulling device 5 includes a pulling mechanism 114 (Figure 3) for growing and pulling up an ingot 60 from the molten material in the inner molten 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 that holds the seed crystal 122. In operation, the seed crystal 122 descends into the inner molten zone 22 to contact the molten material 6. The pulling mechanism 114 is operated to raise the seed crystal 122 along the pulling axis A. This pulls the single-crystal ingot 60 from the molten material 6.
[0028] When the polycrystalline silicon charge 27 (Figure 1) liquefies to form a silicon molten material 6 (Figure 2) containing molten silicon, the silicon seed crystal 122 (Figure 3) descends into the inner molten zone 22 to come into contact with the molten material 6. The silicon seed crystal 122 is then withdrawn from the molten material 6 with the silicon still attached, forming a neck 52 therein, which in turn forms a molten solid interface near or on the surface of the molten material 6.
[0029] The pulling mechanism 114 can rotate the seed crystal 122 and the ingot 60 connected to it. 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., in reverse. The reverse rotation creates convection in the silicon molten material 6. The rotation of the seed crystal 122 is primarily used to provide a symmetrical temperature profile, suppress angular changes in impurities, and further control the crystalline molten surface shape.
[0030] After the formation of the neck 52, a seed cone portion 54 (i.e., the "crown") adjacent to the neck 52 and flaring outward grows. Generally, the pull rate decreases from the pull rate of the neck portion to a rate suitable for growing the outwardly flared seed cone portion 54. Once the seed cone portion reaches the target diameter, the body 56, i.e., the "constant diameter portion" of the ingot 60, grows. 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 more than about 450 mm.
[0031] While the ingot 60 is being pulled from the molten material 6, solid polysilicon feed material is added to the outer molten zone 42 through tubes 46 or other channels to replenish the molten material 6 in the ingot growth apparatus 5. Solid polycrystalline silicon may also be added from the polycrystalline silicon supply system 66 and may be added to the ingot pull-up apparatus 5 continuously or intermittently to maintain the molten level. Generally, polycrystalline silicon may be metered in the ingot pull-up apparatus 5 by any method possible to those skilled in the art.
[0032] In some embodiments, a dopant is also added to the molten material 6 during ingot growth. The dopant may be introduced from a dopant supply system 72. The dopant may be added as a gas or a solid, and may be added to the outer molten zone 42.
[0033] The apparatus 5 may include a heat shield 116 positioned around the growing ingot 60 to allow the growing ingot 60 to radiate the latent heat of solidification and the heat flow rate from the molten material 6. The heat shield 116 may be at least partially conical in shape and inclined downward at an angle that forms an annular opening in which the ingot 60 is placed. A flow of an inert gas, such as argon, is typically supplied along the length of the growing crystal. The ingot 60 is pulled up through a growth chamber 78 sealed from the ambient air.
[0034] Multiple independently controlled annular bottom heaters 70 may be arranged radially beneath 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 may also be individually controlled planar resistance heating elements, as described in U.S. Patent No. 7,635,414, which are incorporated hereby by reference to 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 molten material 6.
[0035] The ingot growth apparatus 5 shown and described herein is illustrative and is a general, arbitrary system in which crystalline ingots are produced by a continuous Czochralski method, which can be used unless otherwise specified.
[0036] According to embodiments of the present disclosure, before the ingot 60 grows, a batch 31 (Figure 2) of buffer material 35 (e.g., quartz cullet) is added to the silicon molten 6, specifically to the outer molten zone 42. The buffer material 35 may be less dense than the silicon molten 6 so that it floats in the molten 6 (i.e., a portion of it is placed on the surface of the molten 6). Buffer material 35 suitable for being added to the outer molten zone 42 includes, for example, a solid material that prevents polysilicon added through a feed pipe 46 from directly entering the molten 6 and / or provides a surface area where inert gas bubbles have disappeared. The buffer material 35 may form gaps between them. The buffer material 35 may be freely movable (e.g., when impacted by falling polycrystalline feed material). In some embodiments, the buffer material 35 includes quartz, such as quartz cullet. When quartz cullet is used, the cullet may have any suitable shape (e.g., cylindrical) and any suitable size (e.g., when cylindrical cullet is used, a diameter of approximately 1 mm to 10 mm and / or a length of approximately 1 mm to 10 mm).
[0037] After a batch 31 of the buffer member 35 is added to the molten material 6, the ingot 60 is withdrawn from the molten material 6. According to embodiments of the present disclosure, the ratio of the mass M of the batch 31 of the buffer member 35 added to the molten material 6 to the time T from the time the batch 31 of the buffer member 35 is added to the molten material 6 until the ingot body 56 (Figure 3) begins to grow is controlled such that the M / T ratio is greater than a threshold ratio of M / T to reduce the number of voids in the wafer sliced from the single-crystal silicon ingot. Generally, time T corresponds to the time from when the batch 31 of the buffer member 35 is fully added until the ingot body 56 begins to grow.
[0038] In some embodiments, the M / T ratio is controlled to be greater than a threshold M / T such that wafers sliced from a single-crystal silicon ingot have fewer than 30 voids with a size of 0.2 μm or larger, or fewer than 20 voids with a size of 0.2 μm or larger. The threshold M / T may vary depending on the hot zone design of the ingot pulling apparatus. To determine the threshold M / T, a threshold defect number is set (e.g., fewer than 30 defects, fewer than 20 defects, or fewer than 10 defects with a size of 0.2 μm or larger, or the maximum number of defects desirable to the manufacturer and / or customer). Multiple 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 count of one or more wafers sliced from the multiple single-crystal silicon ingots is measured (e.g., with an SP1 inspection tool). The M / T ratio of single-crystal silicon sliced from a wafer with fewer defects than the threshold defect count is determined based on the measured defect count (i.e., the threshold M / T is determined based on the M / T value where the number of defects was less than or equal to the threshold defect count).
[0039] In some embodiments, the threshold M / T 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 controlled to be greater is 60 g / h. In yet another embodiment, the threshold M / T controlled to be greater is 70 g / h. The threshold M / T (and the actual M / T used in the ingot pulling device for growing the ingot) may be constrained by practical limits of the ingot growth process (e.g., when the flow of the solid polysilicon ingot into the molten material is not obstructed, such as when the solid polysilicon begins to mount on the buffer material). For example, the M / T may be controlled to be greater than the above threshold M / T and less than 500 g / h or even less than 250 g / h.
[0040] As shown in Figure 2, according to some embodiments of the present disclosure, the batch 31 of the buffer members 35 may be sufficiently large so that the buffer members 35 extend continuously from the side wall 40 of the crucible assembly 10 to the first weir 20.
[0041] In this case, the mass M of batch 31 of buffer material 35 (e.g., quartz cullet) generally excludes any buffer material added before the initial charge 27 (Figure 1) was melted (i.e., excludes the initial charge of buffer material added to the solid single crystal charge).
[0042] To control the M / T ratio so that it is greater than a threshold M / T, the mass M of the batch 31 of buffer material 35 added to the outer molten zone 42 may be increased, or the time T between the addition of the buffer material and the growth of the ingot body 56 may be decreased (for example, 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 method by which a minimum M / T is selected or set for use in the ingot growth process (i.e., 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 a unit smaller than the minimum M / T selected so that M / T is greater than a threshold).
[0043] As the ingot 60 is drawn from the molten material 6, solid single-crystal silicon feed material is added to the crucible assembly 10 while the single-crystal silicon ingot 60 is being drawn to replenish the molten material 6. In some embodiments, the buffer material 35 is not added to the molten material while the ingot is growing (e.g., neck, crown and / or body). If the buffer material is added during the 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 (Figure 3) is descending, and / or any buffer material added during the growth of the neck 52 and crown 54 of the ingot 60, as well as any buffer material added before the descending of the seed crystal 122 (and after the melting of the solid single-crystal silicon charge and / or after the completion of the growth of the previous ingot, if any). In some embodiments of the present disclosure, the buffer material 35 is not added while the ingot body 56 is being drawn from the molten material 6. If the buffer member 35 is added during the growth of the ingot body 56, such buffer member 35 is not considered part of the batch 31 to which it was added before the growth of the ingot body 56 (i.e., it is not part of the mass M of batch 31).
[0044] In some continuous Czochralski processes, one or more ingots are grown while the hot zone (i.e., the lower part of the apparatus 5, such as the crucible assembly 10 and susceptor 13) is heated together with the silicon molten 6 continuously present in the crucible assembly 10. In such a manner, the first ingot grows to a target length, the growth is completed, the ingot is removed from the ingot puller, and the seed crystal descends into the molten material to begin the growth of a second single-crystal silicon ingot (i.e., using the same molten material from which the first ingot was pulled). Subsequent ingots may be grown while the hot zone remains unchanged and at the temperature at which the continuous silicon molten material in the crucible assembly 10 is present (until one or more components of the hot zone degrade, e.g., requiring cooling of the crucible assembly and replacement of degraded components). For example, at least 1, 2, 3, 4, 5, 6, 10, or 20 or more ingots may be grown.
[0045] After the growth of the first ingot 60 is complete and the ingot has been removed (e.g., removed from the lifting chamber 10 of the ingot lifting device), a batch of second buffer material may be added to the molten material remaining after the removal of the first ingot. A seed crystal 122 (i.e., the same or a different seed crystal used to lift the first ingot) descends to contact the molten material. According to embodiments of the present disclosure, the ratio of the mass M2 of the batch of second buffer material added to the molten material to the time T2 from the addition of the batch of second buffer material until the growth of the ingot body begins 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 the wafer sliced from the second single-crystal silicon ingot. In this case, there may still be an amount of the batch of first buffer material remaining in the molten material when the second batch is added. The amount (or all) of the first batch may be depleted by melting in the silicon molten material. The first batch remaining in the molten material is generally not part of the mass M2 of the second batch.
[0046] The ingot lifting device 5 may include a buffer material supply system 55 (Figure 2) for adding batches of buffer material 35 to the outer melting zone 42. The buffer system 55 may be configured to automatically or manually add the buffer material. For example, the buffer material supply system 55 may include a storage container for holding the buffer material (e.g., quartz cullet) and a weighing device (e.g., a weighing hopper, a weighing wheel, or the like). The buffer material supply system 55 may include a buffer material supply pipe, which is the same as or separate from the pipe 46 into which the polysilicon is added. The buffer material 35 may be weighed out by an operator or automatically supplied to the pipe by the buffer material supply system 55.
[0047] Compared to conventional methods for growing single-crystal silicon ingots using a continuous Czochralski process, the method of this disclosure offers several advantages. By controlling the ratio of the mass M of a batch of buffer material added to the molten material to the time T between the addition of the batch of buffer material to the molten material and the start of growth of the single-crystal silicon ingot body, the number of voids in wafers sliced from ingots grown using such a continuous Czochralski method can be reduced. For example, such wafers may have fewer than 30 defects per wafer (size 0.2 μm or larger, measured with an SP1 inspection tool). Without being bound by any particular theory, it is conceivable that the addition of polycrystalline silicon into the outer molten zone of the crucible assembly generates relatively small bubbles (e.g., less than 10 pm) of an inert gas (e.g., argon), which can be carried by the molten material through openings in each weir, allowing the bubbles to reach the solid-molten interface. The buffering material may act to prevent the inert gas from being trapped in the molten material by preventing the polycrystalline feed material from being directly dumped into the molten material. The buffering material may also provide a surface area and nucleation points for inert gas bubbles to aggregate, thereby increasing the size of the bubbles and allowing them to have buoyancy. By increasing the ratio of the mass M of the batch of buffering material added to the molten material to the time T between the addition of the batch of buffering material to the molten material and the start of ingot body growth to at least 60 g / h, the efficiency of the buffering material in reducing inert gas collisions and / or eliminating inert gas bubbles is increased. [Examples]
[0048] The processes described herein are further illustrated by the following embodiments, which should not be considered limiting. Example 1: Number of voids in a wafer grown from an ingot with an M / T smaller than the M / T threshold.
[0049] Single-crystal silicon ingots were grown using the continuous Czochralski method in an ingot pulling apparatus similar to the one shown in Figure 3. The silicon ingots grew with a 300 mm body and were doped with red phosphorus. An initial charge of polycrystalline silicon was added to the outer molten zone, the intermediate molten zone, and the inner molten zone. Quartz cullet (4 kg) was added to the top of the polycrystalline feed material in the outer molten zone. After the charge melted, additional polycrystalline silicon was added through the polycrystalline silicon feed system until the initial charge was completely formed. A batch of quartz cullet (1 kg) was added to the molten material. The seed crystal descended, and the single-crystal silicon ingot grew from the molten material. The ingots were then grown while the hot zone maintained its temperature (i.e., from the same molten material without cooling the hot zone). Before the growth of each subsequent ingot, a batch of buffer material (quartz cullet) (1.5 kg) was added to the outer molten zone. The first ingot was grown under conditions where the ratio of the mass M of the batch of buffer material added to the molten material to the time T between the addition of the batch of buffer material to the molten material and the start of ingot growth was less than the threshold M / T (less than 60 g / h in this case). The second ingot was grown so that the M / T ratio was greater than the threshold M / T after the first ingot (i.e., greater than 60 g / h). As shown, one of the second ingots was grown at an M / T smaller than the threshold M / T to confirm the effect.
[0050] Figures 4 and 5 show the defect counts of wafers sliced from ingots from the first test (M / T less than the threshold M / T) and from the second test (M / T greater than the threshold M / T), respectively. As can be seen from the comparison of the figures, increasing the M / T to the threshold M / T reduced the wafer defect growth to less than 30 defects / wafer, thereby increasing the amount of wafers within the customer-specified range. Figure 6 is a scatter plot showing the defect count as a function of the M / T ratio (for both red phosphorus ingots and other arsenic-doped ingots). As shown in Figure 6, the defect count was less than 30 defects / wafer in all tests where the M / T was greater than the threshold M / T. Example 2: Axis trend of the number of defects
[0051] Figure 7 shows the defect count of a wafer sliced along the axial direction of an ingot grown using the process of Example 1, where the M / T was approximately 27 g / h. As shown in Figure 7, the defect count across the entire axis of the ingot was greater than 30 defects / wafer. Figure 8 shows the defect count of a wafer sliced along the axial direction of an ingot grown using the process of Example 1, where the M / T was approximately 70 g / h. As shown in Figure 8, the defect count across the entire axis of the ingot was less than 30. Ingots grown under both conditions showed axial uniformity of defects. This indicates that a buffer material does not need to be added during the growth of the ingot body. Example 3: Determination of the threshold M / T of the ingot lifting device
[0052] Figure 9 is a scatter plot showing the number of defects in wafers sliced from a single-crystal silicon ingot similar to that of the apparatus shown in Figure 3, as a function of the M / T ratio. The ingot pulling apparatus was different from the one used in Examples 1-2. As shown in Figure 9, when the minimum threshold M / T was set to 70 g / h, the number of defects was less than 30 defects / wafer in all tests where the M / T was greater than the threshold M / T. The threshold M / T (i.e., minimum value) of the ingot pulling apparatus was determined to be approximately 70 g / h.
[0053] When used in connection with ranges of dimensions, concentrations, temperatures, or other physical or chemical properties or characteristics, the terms “about,” “substantially,” “essentially,” and “approximately” as used herein mean encompassing any variations that may exist at the upper and / or lower limits of the range of the property or characteristic, including variations resulting from, for example, rounding, measurement methodology, or other statistical variations.
[0054] When introducing elements or embodiments of this disclosure, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more elements. The terms “have,” “include,” and “contain,” are intended to be inclusive and mean that there may be additional elements beyond those listed. Terms indicating a particular orientation (e.g., “top,” “bottom,” “side,” etc.) are for explanatory convenience and do not require any particular orientation of the described item.
[0055] Various modifications can be made to the above-described structures and methods without departing from the scope of this disclosure. Therefore, all matters included in the above description and shown in the accompanying drawings are intended to be interpreted as illustrative, not restrictive.
Claims
1. A method for growing a single-crystal silicon ingot in a continuous Czochralski process, wherein the method is: Forming a molten silicon in a crucible assembly, Adding a batch of buffer material with mass M to the molten material, The surface of the molten material is brought into contact with a seed crystal. The process involves withdrawing a single-crystal silicon ingot from the molten material, where the single-crystal silicon ingot has a body, and there is a time T between adding a batch of the buffer material to the molten material and the start of growth of the body. Controlling the M / T ratio to be greater than a threshold M / T in order to reduce the number of voids in the wafer sliced from the single-crystal silicon ingot, While the single-crystal silicon ingot is being drawn, solid polycrystalline silicon supply material is added to the crucible assembly to replenish the molten material. A method that includes [a certain feature].
2. The M / T ratio is controlled to be greater than a threshold M / T such that the wafer sliced from the single-crystal silicon ingot has fewer than 30 defects with a void size of 0.2 μm or larger. The method according to claim 1.
3. The M / T ratio is controlled to be greater than a threshold M / T such that the wafer sliced from the single-crystal silicon ingot has fewer than 20 defects with a void size of 0.2 μm or larger. The method according to claim 1.
4. The aforementioned method, Growing multiple single-crystal silicon ingots, wherein at least two of the multiple ingots are grown with different M / T ratios. To measure the number of defects in one or more wafers sliced from the aforementioned plurality of single-crystal silicon ingots, To determine the M / T ratio of a single-crystal silicon ingot sliced from a wafer with fewer defects than the threshold defect count. The method for determining the threshold M / T is to The method according to any one of claims 1 to 3.
5. The threshold defect count is 30 defects with a size of 0.2 μm or larger. The method according to claim 4.
6. The threshold M / T is 40 g / h, 50 g / h, or 55 g / h. The method according to any one of claims 1 to 5.
7. The threshold M / T is 60 g / h. The method according to any one of claims 1 to 5.
8. The aforementioned threshold M / T is less than 250 g / h. The method according to claim 6 or 7.
9. The diameter of the body of the single-crystal silicon ingot is approximately 150 mm, at least approximately 150 mm, approximately 200 mm, at least approximately 200 mm, approximately 300 mm, at least approximately 300 mm, approximately 450 mm, or even more than approximately 450 mm. The method according to any one of claims 1 to 8.
10. The aforementioned buffer member is made of quartz. The method according to any one of claims 1 to 9.
11. The aforementioned buffering member is quartz cullet. The method according to any one of claims 1 to 9.
12. The batch of the buffer member is the first batch, the single crystal silicon ingot is the first silicon ingot, and the method is To terminate the growth of the first single-crystal silicon ingot, Mass M of the second cushioning member ２ Adding a batch of the above to the molten material, The surface of the molten material is brought into contact with a seed crystal. The process involves withdrawing a second single-crystal silicon ingot from the molten material, where the second single-crystal silicon ingot has a body, and the time T from adding a batch of the second buffer member to the molten material until the start of growth of the body. ２ M exists to reduce the number of voids in the wafer sliced from the second single-crystal silicon ingot. ２ / T ２ The ratio is controlled to be greater than the threshold M / T. A method according to any one of claims 1 to 11, comprising:
13. The crucible assembly has a weir and a side wall, the weir and the side wall define an outer melting zone between the weir and the side wall, and the batch of the buffer member is added to the outer melting zone. The method according to any one of claims 1 to 12.
14. The weir is a first weir, and the crucible assembly has a second weir on the inner diameter side of the first weir, the first weir and the second weir define an intermediate melting zone between the first weir and the second weir, and the second weir defines an inner melting zone within the second weir. The method according to claim 13.
15. The silicon molten material of the crucible assembly is formed by adding an initial charge of solid polycrystalline silicon to the crucible assembly, and the method is Adding a batch of buffer material to the initial charge of the solid polycrystalline silicon, The initial charge of the solid polycrystalline silicon is melted together with the buffer member placed therein. A method according to any one of claims 1 to 14, comprising:
16. The density of the buffer member is lower than that of the silicon molten material so that the buffer member floats in the molten material. The method according to any one of claims 1 to 15.
17. The single-crystal silicon ingot is the first ingot to be drawn from the molten silicon in the crucible assembly after the molten silicon has been formed. The method according to any one of claims 1 to 16.
18. The single-crystal silicon ingot is a single-crystal silicon ingot that grows after the initial single-crystal silicon ingot has been drawn out of the molten material. The method according to any one of claims 1 to 16.
19. While the main body of the single-crystal silicon ingot is being drawn out of the molten material, no buffer material is added. The method according to any one of claims 1 to 18.
20. While the neck and / or crown of the single-crystal silicon ingot are being drawn out of the molten material, no buffer material is added. The method according to any one of claims 1 to 19.
21. A method for determining a threshold M / T ratio for growing a single-crystal silicon ingot in a continuous Czochralski process, comprising: forming a silicon molten mass in a crucible assembly; adding a batch of buffer material of mass M to the molten mass; contacting the molten mass with a seed crystal; withdrawing a single-crystal silicon ingot from the molten mass, wherein the single-crystal silicon ingot has a body, and there exists a time T between the addition of the batch of buffer material to the molten mass and the start of growth of the body, and adding solid polycrystalline silicon feed material to the crucible assembly to replenish the molten mass while the single-crystal silicon ingot is being withdrawn, wherein the method is: Growing multiple single-crystal silicon ingots, where at least two of the multiple ingots are grown with different M / T ratios. To measure the number of defects in one or more wafers sliced from the aforementioned plurality of single-crystal silicon ingots, To determine the M / T ratio of a single-crystal silicon ingot sliced from a wafer with fewer defects than the threshold defect count. A method that includes [a certain feature].
22. The threshold defect count is 20 defects with a size of 0.2 μm or larger. The method according to claim 21.
23. The threshold defect count is 30 defects with a size of 0.2 μm or larger. The method according to claim 21.
24. The aforementioned buffer member is made of quartz. The method according to any one of claims 21 to 23.
25. The aforementioned buffering member is quartz cullet. The method according to any one of claims 21 to 23.
26. Measuring the number of defects in one or more wafers sliced from the aforementioned plurality of single-crystal silicon ingots includes directing light onto the surface of the wafer and detecting the reflected light from the surface. The method according to any one of claims 21 to 23.