Preparation process of ingot with reduced deformation in rear section main body length

Abstract

The present invention discloses a method for growing a single crystal silicon ingot with reduced diameter deviation by a Czochralski method.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to U.S. Provisional Application No. 62 / 832,561, filed on April 11, 2019, the disclosure of which is incorporated by reference as if set forth in its entirety. Technical Field

[0003] The field of the present disclosure relates to a method of growing a single crystal silicon ingot using the Czochralski method. Background Art

[0004] Single crystal silicon, which is the starting material for most processes used to make semiconductor electronic components, is typically prepared by the Czochralski ("Cz") method. In this method, polycrystalline silicon ("polysilicon") is loaded into a crucible and melted, a seed crystal is brought into contact with the molten silicon, and a single crystal is grown by slow extraction. After the neck is formed, the diameter of the crystal is enlarged until the desired or target diameter is reached by, for example, reducing the pull rate and / or melt temperature. A cylindrical crystal body with an approximately constant diameter is then grown by controlling the pull rate and melt temperature while compensating for the reduced melt level. Towards the end of the growth process but before the crucible is exhausted of molten silicon, the crystal diameter typically decreases gradually to form a tail end in the form of an end cone. The end cone is typically formed by increasing the pull rate and the heat supplied to the crucible. When the diameter becomes sufficiently small, the crystal then separates from the melt.

[0005] Czochralski growth techniques include batch Czochralski methods and continuous Czochralski methods. In batch CZ, a single polycrystalline charge is loaded into a crucible, the single charge being sufficient to grow a single crystal silicon ingot, after which the crucible is substantially depleted of the silicon melt. In continuous Czochralski (CCZ) growth, polycrystalline silicon may be added to the molten silicon continuously or periodically during the growth process to replenish the melt, and thus multiple ingots may be pulled from a single crucible during the growth process.

[0006] To implement the CCZ process, conventional batch Czochralski growth chambers and apparatus are modified to include means for feeding additional polysilicon to the melt in a continuous or semi-continuous manner without adversely affecting the properties of the growing ingot. As the seed crystal is continuously grown from the melt, solid polysilicon (e.g., granular polysilicon) is added to the melt to replenish the melt. The feed rate at which additional solid polysilicon is added to the melt is typically controlled to maintain process parameters. To reduce the adverse effects of this replenishment activity on simultaneous crystal growth, conventional quartz crucibles are typically modified to provide an outer or annular melt zone into which the added material is delivered, along with an inner growth zone from which the silicon ingot is pulled. These zones are in fluid flow communication with each other.

[0007] The shrinking size of modern microelectronic devices places challenging limits on the quality of silicon substrates, which is essentially determined by the size and distribution of grown-in micro-defects. Most of the micro-defects formed in silicon crystals grown by the Czochralski (CZ) process and the floating zone (FZ) process are agglomerates with intrinsic point defects of silicon (vacancies and self-interstitials (or simply interstitials)).

[0008] A series of studies have confirmed that interstitial agglomerates exist in two forms: spherical interstitial clusters, called B vortex defects (or B defects); and dislocation rings, called A vortex defects (or A defects). Vacancy agglomerates discovered later (called D defects) have been identified as octahedral voids. Voronkov provided a widely accepted explanation for the distribution of microdefects observed in silicon crystals based on crystal growth conditions. According to Voronkov's model or theory, the temperature field near the melt / crystal interface drives the recombination of point defects, thereby providing a driving force for their diffusion from the melt / crystal interface (where they exist at their corresponding equilibrium concentrations) into the bulk of the crystal. The interaction between the transport of point defects (by both diffusion and convection) and their recombination establishes a point defect concentration beyond a short distance from the interface (called the recombination length). Typically, the difference between the vacancy concentration and the interstitial concentration beyond the recombination length (called the excess point defect concentration) remains essentially fixed away from the lateral surface of the crystal. In a rapidly pulled crystal, the spatial redistribution of point defects through their diffusion beyond the recombination length is generally unimportant, except for the region close to the lateral surface of the crystal that serves as a groove or source of point defects. Therefore, if the excess point defect concentration beyond the recombination length is positive, then vacancies remain in excess and agglomerate at lower temperatures to form D defects. If the excess point defect concentration is negative, then interstitials remain as dominant point defects and agglomerate to form A defects and B defects. If the excess point defect concentration is below a certain detection threshold, no detectable microdefects are formed. Therefore, generally, the type of primary microdefects is determined only by the excess point defect concentration established beyond the recombination length. The process of establishing the excess point defect concentration is called initial incorporation and the dominant point defect species is called the incorporation of dominant point defects. The type of incorporation of point defects is determined by the ratio of the crystal pulling rate (v) to the magnitude of the axial temperature gradient (G) near the interface. At higher v / G, the convection of point defects is dominant over their diffusion, and vacancies remain as incorporation of dominant point defects because the vacancy concentration at the interface is higher than the interstitial concentration. At lower v / G, diffusion is dominant over convection, allowing rapidly diffusing interstitials to be incorporated as dominant point defects. At v / G close to their critical values, the two point defects are incorporated at very low and comparable concentrations, annihilating each other and thus suppressing the potential formation of any microdefects at lower temperatures. The observed spatial microdefect distribution can generally be explained by the variation of v / G, which is caused by the radial inhomogeneity of G and by the axial variation of v. A notable feature of the radial microdefect distribution is the oxide particles formed by the interaction of oxygen with vacancies in regions with relatively low concentrations of incorporated vacancies (within a small range of v / G slightly above the critical v / G). These particles form narrow spatial bands that can be revealed as OSF (oxidation-induced stacking fault) rings by thermal oxidation. Typically, OSF rings mark the boundaries between adjacent crystal regions dominated by vacancies and interstitials (called V / I boundaries).

[0009] However, in many modern processes, the distribution of microdefects in CZ crystals grown at lower rates is affected by the diffusion of point defects in the bulk of the crystal (including diffusion caused by the lateral surfaces of the crystal). Therefore, accurate quantification of the distribution of microdefects in CZ crystals preferably incorporates the two-dimensional diffusion of point defects in both the axial and radial directions. Quantifying only the point defect concentration field can qualitatively capture the distribution of microdefects in CZ crystals because the type of microdefects formed is directly determined by it. However, for more accurate quantification of the distribution of microdefects, it is necessary to capture the agglomeration of point defects. Traditionally, the distribution of microdefects is quantified by decoupling the initial incorporation of point defects from the subsequent formation of microdefects. This method ignores the diffusion of the dominant point defects near the nucleation region from the region of higher temperature (where the microdefect density is negligible) to the region of lower temperature (where the microdefects exist at a higher density and consume the point defects). Alternatively, rigorous numerical simulations based on predicting the size distribution of microdefect populations at each position in the crystal are numerically expensive.

[0010] The transition between vacancy-dominated and interstitial-dominated materials occurs at a critical value of v / G, which currently appears to be about 2.5x10 -5 cm 2 / sK. If the value of v / G exceeds a critical value, then vacancies are the dominant intrinsic point defects, where their concentration increases as v / G increases. If the value of v / G is less than a critical value, then silicon self-interstitials are the dominant intrinsic point defects, where their concentration increases as v / G decreases. Thus, process conditions such as growth rate (which affects v) and hot zone configuration (which affects G) can be controlled to determine whether the intrinsic point defects within the single crystal silicon will be primarily vacancies (where v / G is typically greater than a critical value) or self-interstitials (where v / G is typically less than a critical value).

[0011] Agglomerated defect formation typically occurs in two steps. First, defect "nucleation" occurs, which is the result of supersaturation of intrinsic point defects at a given temperature; above this "nucleation threshold" temperature, the intrinsic point defects remain soluble in the silicon lattice. The nucleation temperature of agglomerated intrinsic point defects is greater than about 1000°C.

[0012] Once this "nucleation threshold" temperature is reached, the intrinsic point defects agglomerate; that is, they precipitate out of "solid solution" in the silicon lattice. The intrinsic point defects will continue to diffuse through the silicon lattice as long as the temperature of the portion of the ingot in which they exist remains above a second threshold temperature (i.e., the "diffusivity threshold"). Below this "diffusivity threshold" temperature, the intrinsic point defects will no longer move within a commercially useful time period.

[0013] As the ingot is held above the "diffusivity threshold" temperature, vacancy or interstitial intrinsic point defects diffuse through the silicon lattice to sites where agglomerated vacancy defects or interstitial defects, respectively, already exist, causing the size of a given agglomerated defect to grow. Growth occurs because these agglomerated defect sites essentially act as "sinks," attracting and collecting intrinsic point defects due to the more favorable energy state of agglomeration.

[0014] Vacancy-type defects are believed to be the origin of such observable crystal defects as D defects, flow pattern defects (FPDs), gate oxide integrity (GOI) defects, crystal origin particle (COP) defects, crystal origin light point defects (LPDs), and certain types of bulk defects observed by infrared light scattering techniques (such as scanning infrared microscopy and laser tomography). Clusters of oxygen or silicon dioxide are also present in regions with excess vacancies. Some of these clusters remain small and relatively strain-free, thereby causing essentially no damage to most devices made from this silicon. Some of these clusters are large enough to serve as nuclei for epoxide-induced stacking faults (OISFs). It is speculated that previously nucleated oxygen agglomerates catalyzed by the presence of excess vacancies promote this particular defect. In the presence of moderate vacancy concentrations, oxide clusters are primarily formed in CZ growth below 1000°C.

[0015] Defects related to self-interstitial are less studied. They are generally viewed as low-density interstitial dislocation loops or networks. Such defects are not responsible for gate oxide integrity failures (an important wafer performance criterion), but they are widely considered to be the cause of other types of device failures that are often associated with current leakage problems.

[0016] In this regard, it should be noted that, in general, oxygen in the form of interstitials in the silicon lattice is generally considered a point defect of silicon rather than an intrinsic point defect, while silicon lattice vacancies and silicon self-interstitials (or simply interstitials) are generally considered intrinsic point defects. Thus, substantially all microdefects may generally be described as agglomerated point defects, while D defects (or voids) and A defects and B defects (i.e., interstitial defects) may more specifically be described as agglomerated intrinsic point defects. Oxygen clusters are formed by the absorption of vacancies; therefore, oxygen clusters may be considered agglomerates of both vacancies and oxygen.

[0017] It should be further noted that the density of such vacancies and self-interstitial agglomeration point defects in Czochralski silicon has historically been around 1x10 3 / cm 3 To about 1x10 7 / cm 3 The density of oxygen clusters is about 1x10 8 / cm 3 to 1x10 10 / cm 3Thus, agglomerated intrinsic point defects are rapidly increasing in importance to device manufacturers, as such defects can severely impact the yield potential of single crystal silicon materials in the production of complex and highly integrated circuits.

[0018] In view of the foregoing, in many applications, it is preferred that a portion or all of the silicon crystal (which is subsequently cut into silicon wafers) is substantially free of these agglomerated intrinsic point defects. To date, several methods for growing substantially defect-free silicon crystals have been reported. In general, all of these methods involve controlling the ratio v / G so as to determine the initial type and concentration of intrinsic point defects present in the growing CZ single crystal silicon crystal. However, in addition, such methods may involve controlling the subsequent thermal history of the crystal to allow for extended diffusion time to suppress the concentration of intrinsic point defects therein, and thereby substantially limit or avoid the formation of agglomerated intrinsic point defects in a portion or all of the crystal. (See, e.g., U.S. Pat. Nos. 6,287,380, 6,254,672, 5,919,302, 6,312,516, and 6,328,795; the entire contents of which are hereby incorporated by reference herein.) Alternatively, however, such methods may involve a rapid cooling silicon (RCS) growth process, wherein the subsequent thermal history of the crystal is then controlled to rapidly cool at least a portion of the crystal through a target nucleation temperature so as to control the formation of agglomerated intrinsic point defects in that portion. One or both of these methods may also include allowing at least a portion of the grown crystal to remain above the nucleation temperature for an extended period of time to reduce the concentration of intrinsic point defects before rapidly cooling this portion of the crystal through the target nucleation temperature, thereby substantially limiting or avoiding the formation of agglomerated intrinsic point defects therein. (See, e.g., U.S. Patent Application Publication No. 2003 / 0196587, the entire disclosure of which is incorporated herein by reference.) Still further, methods have been developed to reduce or eliminate agglomerated point defects from the center to the edge of the ingot by simultaneously controlling the cooling rate of the solidified ingot and the radial variation of the axial temperature gradient (G) near the interface. (See, e.g., U.S. Patent No. 8,673,248, the entire disclosure of which is incorporated herein by reference.)

[0019] This section is intended to introduce the reader to various aspects of the technology that may be related to the various aspects of the present disclosure described and / or claimed below. It is believed that this discussion helps to provide the reader with background information to promote a better understanding of the various aspects of the present disclosure. Therefore, it should be understood that these statements should be read in this sense, and not as an admission of prior art. Summary of the invention

[0020] One aspect of the present disclosure relates to a method of preparing a single crystal silicon ingot by a Czochralski method. The method comprises: adding an initial charge of polycrystalline silicon to a crucible contained in a growth chamber, wherein the crucible comprises a bottom wall and side walls, and further wherein the growth chamber comprises a bottom heater positioned adjacent to the bottom wall of the crucible, a side heater positioned adjacent to the side walls, and a reflector; supplying power to the bottom heater, the side heater, or both the bottom heater and the side heater to thereby heat the crucible comprising the initial charge of polycrystalline silicon to cause a silicon melt to form in the crucible, wherein the power supplied to the side heater is greater than the power supplied to the bottom heater and further wherein the silicon melt has a free melt height level; contacting a silicon seed crystal with the silicon melt contained in the crucible; extracting the silicon seed crystal from the silicon melt at an initial pull rate in a direction perpendicular to the melt height level to thereby form a solid neck of the single crystal silicon ingot; extracting a silicon seed crystal adjacent to the silicon melt from the silicon melt by modifying the initial pull rate to thereby achieve an outwardly flaring seed-cone pull rate; a solid outward flaring seed cone of the solid neck of the single crystal silicon ingot; and extracting a solid body of the single crystal silicon ingot adjacent to the outward flaring seed cone from the silicon melt by modifying the outward flaring seed cone pull rate to thereby achieve a body pull rate, wherein the solid body of the single crystal silicon ingot has a radial diameter and an axial length, and surface tension generated when the solid body of the single crystal silicon ingot is extracted from the molten silicon results in a melt-solid interface positioned above the free melt height level, and further comprising a meniscus of molten silicon between the melt-solid interface and the free melt height level; wherein a cusp magnetic field is applied to the silicon melt during growth of the body of the single crystal silicon ingot; and wherein during growth of at least 40% of the total axial length of the solid body of the single crystal silicon ingot, a heat flux in the axial direction between the melt-solid interface and the free melt height level has at least about 20,000 W / m over at least about 85% of the radial length of the solid body of the single crystal silicon ingot. 2 The absolute value of .

[0021] There are various improvements to the features mentioned in the above aspects of the disclosure. Further features may also be incorporated into the above aspects of the disclosure. These improvements and additional features may exist individually or in any combination. For example, the various features discussed below with respect to any of the illustrated embodiments of the disclosure may be incorporated into any of the above aspects of the disclosure individually or in any combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 1A and 1B illustrate melt temperature profiles near the crystal / melt interface for a conventional hot zone (FIG. 1A) and a low-power hot zone (FIG. 1B).

[0023] Figure 2A and 2B Description of conventional hotspots ( Figure 2A ) and low power hotspots ( Figure 2B ). The temperatures were obtained after 400 mm growth and after 800 mm growth.

[0024] Figure 3 is a depiction of a hot zone suitable for practicing the method of the present invention.

[0025] Figure 4 is a series of diagrams depicting the movement of the crucible during the growth of an ingot during a batch Czochralski process.

[0026] Figure 5 is a simplified depiction of a hot zone configuration suitable for use with the method of the present invention.

[0027] Figure 6 is a diagram depicting the meniscus curve.

[0028] Fig. 7A and 7B is a graph depicting relative crucible relative height (HR) protocols during growth of an ingot according to some embodiments of the method of the present invention.

[0029] Fig. 8A and 8B is a graph depicting a seed rotation rate protocol during growth of an ingot according to some embodiments of the method of the present invention.

[0030] Fig. 9 Describe the location of magnetic coils suitable for producing a cusp magnetic field.

[0031] 10A, 10B and 10C illustrate magnetic field strength and cusp positions during Czochralski crystal growth during a conventional method (FIG. 10A) and during a method according to the present invention (FIGS. 10B and 10C).

[0032] Fig.11A and 11B Plotting the meniscus temperature profile according to an embodiment of the present invention ( Fig.11A ) and the heat flux on the melt side ( Fig. 11B ). Temperature and heat flux data were obtained after 400 mm growth and after 800 mm growth.

[0033] Fig. 12A and 12B Plotting the meniscus temperature profile according to an embodiment of the present invention ( Fig. 12A ) and the heat flux on the melt side ( Fig. 12B ). Temperature and heat flux data were obtained after 400 mm growth and after 800 mm growth.

[0034] Fig.13A and 13B Plotting the meniscus temperature profile according to an embodiment of the present invention ( Fig.13A ) and the heat flux on the melt side ( Fig. 13B ).

[0035] Fig.14A and 14B Depicted in the conventional low power hot zone process ( Fig.14A ) and in the process according to an embodiment of the present invention ( Fig. 14B ) during the main growth period.

[0036] Corresponding reference characters indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION

[0037] According to the method of the present invention, a single crystal silicon ingot is grown by the Czochralski (CZ) method under process conditions suitable for suppressing or preventing ingot deformation during the growth of the rear-stage main body length (after 600 mm) of the low-power hot zone type. It has been observed during the growth of the ingot in the low-power hot zone growth chamber that the cross-section of the crystal can change from the initial desired circular shape to a star-shaped shape during the rear-stage growth of the main body of the single crystal silicon ingot. Disadvantageously, the deformation can cause the camera monitoring the ingot growth conditions to be unable to track the shape of the growing ingot and the meniscus during the growth process. According to some embodiments, suitable growth conditions are selected during the growth of the ingot to suppress the drop in melt temperature near the crystal / melt interface and the meniscus, which in turn reduces the possibility of undercooling and thus deformation. That is, conditions are selected to minimize the temperature changes at the free melt surface level and the melt below the melt / crystal interface during the growth of the entire length of the ingot, which in turn minimizes or eliminates deformation so that the cross-section of the ingot maintains the desired circular shape along the entire length of the ingot.

[0038] The method of the present invention can be applied to a Czochralski puller with an applied magnetic field (e.g., a cusp magnetic field) and insulation added in the bottom of the hot zone, which is called a low power hot zone (LPHZ). Conventional hot zone pullers typically have high bottom heater power requirements during the growth process. The low power hot zone is a modification of a conventional hot zone where the bottom heater power requirements are reduced by installing additional insulation at the bottom to prevent heat from escaping from the bottom, which helps reduce power consumption and production costs.

[0039] Crystal growth in the low-power hot zone is more prone to ingot deformation at the rear body length (after 600 mm), and this problem is not usually observed in conventional hot zone pullers in which the bottom heater is set to high power. According to current understanding, the deformation at the rear body length is at least partially caused by the melt temperature near the melt / crystal interface. Figures 1A and 1B compare the thermal fields in the melt at the front body length (400 mm) and the rear body length (800 mm) in ingots grown in the conventional hot zone (Figure 1A) and the low-power hot zone (Figure 1B). The figure illustrates the temperature of the melt near the crystal / melt interface. As shown in Figure 1B, these temperatures are significantly reduced at the rear body length in the low-power hot zone, while the temperature difference in the conventional hot zone is much smaller, as shown in Figure 1A. For illustration, the contour line at T = 1690K is highlighted in each of the thermal fields in Figures 1A and 1B for comparison.

[0040] Figure 2A 2B (conventional hot zone) and 2B (low power hot zone) are temperature profiles depicting the meniscus curves along the main length of the front and rear sections of the two hot zone types. Figure 2A , in a conventional hot zone, the final meniscus temperature (i.e., at the melt free interface) at the rear body length (i.e., 800 mm) is about 1694 K (where no deformation is seen at this stage), which is very close to the meniscus temperature of the front body (i.e., 400 mm) at the melt free interface of 1694.4 K. See Figure 6 to obtain a depiction of the meniscus curve. Figure 2A The distance 0 mm in the figure corresponds to the solid-melt interface, while the distance 35 mm corresponds to the melt-free interface. These distances may vary depending on the hot zone design and the pulling conditions. Figure 2B As depicted in Figure 1, during crystal growth in the low power hot zone, the meniscus temperature at the 800 mm melt free interface has dropped to a value of 1689.9 K at 800 mm growth, and is significantly different from the temperature of 1691.4 K at the 400 mm main length. Figure 2A and 2B It is observed that the temperature gradient has also decreased from 400mm to 800mm body length at the interface of the low power hot zone and at the meniscus. These changes may be responsible for the increased deformation potential at 800mm body length in the low power hot zone configuration.

[0041] According to the method of the present invention, hot zone conditions are selected to increase the melt-side heat flux and the gradient along the meniscus during the growth of the entire main body length of the single crystal silicon ingot. Suitable process conditions selected according to some embodiments of the present invention include bottom heater power, relative crucible height, seed rotation rate, crucible rotation rate and magnetic field strength, and suitable conditions are found. Certain variables (including relative crucible height (RH), seed rotation rate, bottom heater power and magnetic field position) are found to increase the melt-side heat flux and thereby increase the temperature near the melt and the temperature gradient along the meniscus. Subsequently, the temperature profile achieved according to the method of the present invention causes the grown ingot to reduce or eliminate deformation throughout the main body length of the ingot.

[0042] Figure 3 is a depiction of a hot zone suitable for practicing the method of the present invention. The hot zone configuration includes a quartz crucible 10 of suitable diameter for holding silicon melt and for pulling ingots having a diameter of 450 mm or greater. A graphite crucible 20 encloses and supports the quartz crucible 10. Other configurations for holding the quartz crucible 10 are within the scope of the method of the present invention, such as a configuration lacking a graphite crucible 20. The hot zone configuration includes a side heater 30 positioned near the side wall of the quartz crucible 10 and a bottom heater 40 optionally positioned below the quartz crucible 10. The hot zone configuration includes insulation 50 configured to keep heat within the hot zone. A low power hot zone according to the present invention includes additional insulation 50 near the bottom of the quartz crucible 10. The growing crystal diameter and the shape and height of the meniscus are monitored by a camera 60 (e.g., a CCD camera) positioned at a top window 70. Data obtained from the camera can be fed back to the side heaters 30 and the bottom heater 40. During crystal growth, the power distribution can be adjusted between the heaters to achieve uniformity of the melt / solid interface, i.e., to maintain the desired shape and height of the meniscus. A heat shield or reflector 80 reflects heat flux from the hot portion of the furnace including the heaters 30, 40 and the crucible 10 to the melt 90. The reflector 80 reduces heat transfer from the hot portion to the cold portion of the furnace and thereby maintains separation between these two regions of the furnace. The reflector 80 helps control axial and radial temperature gradients, which drive the solidification and crystallization of the molten silicon 90 into a growing ingot 100.

[0043] The Czochralski method begins by loading polycrystalline silicon into a quartz crucible 10, referring to Figure 3. The solid polycrystalline silicon added to the quartz crucible 10 is typically granular polycrystalline silicon, but block polycrystalline silicon may be used and fed into the crucible using a polycrystalline silicon feeder optimized for use with granular polycrystalline silicon. Block polycrystalline silicon typically has a size (e.g., maximum dimension) between 3 mm and 45 mm, and granular polycrystalline silicon typically has a size between 400 microns and 1400 microns. Granular polycrystalline silicon has several advantages, including providing easy and precise control of the feed rate due to its smaller size. However, due to the chemical vapor deposition process or other manufacturing methods used in its production, the cost of granular polycrystalline silicon is typically higher than that of block polycrystalline silicon. Block polycrystalline silicon has the advantage of being cheaper and capable of a higher feed rate given its larger size.

[0044] In general, the melt 90 from which the ingot 100 is drawn is formed by loading polycrystalline silicon into the crucible 10 to form an initial silicon charge. In general, the initial charge is between about 100 kg and about 1000 kg, or between about 100 kg and about 800 kg, or between about 100 kg and about 500 kg of polycrystalline silicon, which may be granular, chunky, or a combination of granular and chunky. The mass of the initial charge depends on the desired crystal diameter and the HZ design. In some embodiments, the initial polycrystalline silicon charge is sufficient to grow one single crystal silicon ingot, i.e., in a batch process. In general, the total axial length of the solid body of the single crystal silicon ingot is at least about 1100 mm, such as between about 1200 mm and about 1300 mm, such as between about 1200 mm and about 1250 mm. In a continuous Czochralski process, the initial charge does not reflect the length of the crystal because polycrystalline silicon is continuously fed during crystal growth. Therefore, the initial charge can be smaller, for example, between about 100 kg and about 200 kg. If the polysilicon is fed continuously and the chamber height is high enough, the crystal length can be extended to 2000 mm, 3000 mm or even 4000 mm in length. Various sources of polysilicon 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. Once the polysilicon is added to the crucible to form the charge, the charge can be heated to a temperature above about the melting temperature of silicon (e.g., about 1412° C.) to melt the charge, and thereby form a silicon melt including molten silicon. The silicon melt has an initial molten silicon volume and has an initial melt height level, and these parameters are determined by the size of the initial charge. In some embodiments, the crucible including the silicon melt is heated to a temperature of at least about 1425° C., at least about 1450° C., or even at least about 1500° C. The initial polysilicon charge is heated by supplying power to the bottom heater 40, the side heater 30, or both the bottom heater 40 and the side heater 30. According to some embodiments, the power supplied to the side heater 30 is greater than the power supplied to the bottom heater 40. In some embodiments, the power of the bottom heater 40 is 2 kW or less, such as 1 kW or less. In some embodiments, the bottom heater 40 has no power supplied thereto, i.e., the supplied power is 0 kW, so that the hot zone configuration is a low-power hot zone configuration. The low-power hot zone according to the present invention includes additional insulation 50 near the bottom of the crucible 10.

[0045] refer to Figure 4Once the solid polycrystalline silicon charge 150 is liquefied to form a silicon melt 120 including molten silicon, a silicon seed 160 may be lowered to contact the melt. The silicon seed 160 is then extracted from the melt, with silicon attached to the silicon seed, thereby forming a melt-solid interface near or at the surface of the melt. Generally, the initial pull rate to form the neck is high. In some embodiments, the silicon seed and the neck are extracted at a neck pull rate of at least about 1.0 mm / minute (e.g., between about 1.5 mm / minute and about 6 mm / minute, such as between about 3 mm / minute and about 5 mm / minute). In some embodiments, the silicon seed and the crucible are rotated in opposite directions (i.e., counter-rotation). Counter-rotation enables convection in the silicon melt. The rotation of the crystal is primarily used to provide a symmetrical temperature profile, suppress angular variations of impurities, and also control the crystal-melt interface shape. In some embodiments, the silicon seed crystal is rotated at a rate between about 5 rpm and about 30 rpm, or between about 5 rpm and about 20 rpm, or between about 5 rpm and about 15 rpm (e.g., about 8 rpm, 9 rpm, or 10 rpm). In some embodiments, the seed crystal rotation rate may be changed during the growth of the main body of the single crystal silicon ingot. In some embodiments, the crucible is rotated at a rate between about 0.5 rpm and about 10 rpm, or between about 1 rpm and about 10 rpm, or between about 4 rpm and about 10 rpm, or between about 5 rpm and about 10 rpm. In some embodiments, the seed crystal is rotated at a faster rate than the crucible. In some embodiments, the seed crystal is rotated at a rate that is at least 1 rpm higher than the crucible rotation rate (e.g., at least about 3 rpm higher or at least about 5 rpm higher). In general, the neck has a length between about 300 mm and about 700 mm (e.g., between about 450 mm and about 550 mm). However, the length of the neck may vary outside these ranges.

[0046] After the neck is formed, an outwardly flared seed cone 170 is grown adjacent to the neck, as shown in FIG. Figure 4. Generally, the pull rate decreases from the neck pull rate to a rate suitable for growing the outward flared seed cone portion. For example, the seed cone pull rate during the growth of the outward flared seed cone 170 is between about 0.5 mm / min and about 2.0 mm / min, such as about 1.0 mm / min. In some embodiments, the outward flared seed cone 170 has a length between about 100 mm and about 400 mm, such as between about 150 mm and about 250 mm. The length of the outward flared seed cone 170 may vary outside these ranges. In some embodiments, the outward flared seed cone 170 grows to a terminal 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. The terminal diameter of the outward flared seed cone 170 is typically equal to the diameter of the constant diameter of the ingot body 180 of the single crystal silicon ingot.

[0047] After forming the neck and the outwardly flared seed cone 170 adjacent to the neck, an ingot body 180 having a constant diameter adjacent to the outwardly flared seed cone 170 is then grown. The constant diameter portion of the ingot body 180 has a circumferential edge, a central axis parallel to the circumferential edge, and a radius extending from the central axis to the circumferential edge. The central axis also passes through the cone and the neck. The diameter of the ingot body 180 can vary and in some embodiments, the diameter can be about 150 mm, at least about 150 mm, about 200 mm, at least about 200 mm, about 300 mm, at least about 300 mm, about 450 mm, or even at least about 450 mm. In other words, the radial length of the solid ingot body 180 of the single crystal silicon ingot is about 75 mm, at least about 75 mm, about 100 mm, at least about 100 mm, about 150 mm, at least about 150 mm, about 225 mm, or even at least about 225 mm. The ingot body 180 of the single crystal silicon ingot is ultimately grown to be at least about 1000 mm long, such as at least 1200 mm long, such as at least 1250 mm long, such as at least 1400 mm long, such as at least 1500 mm long, or at least 2000 mm long, or at least 2200 mm, such as 2200 mm, or at least about 3000 mm long, or at least about 4000 mm long. In some preferred embodiments, the total axial length of the solid ingot body 180 of the single crystal silicon ingot is at least about 1100 mm, such as between about 1200 mm and about 1300 mm, such as between about 1200 mm and about 1250 mm.

[0048] In some embodiments, the ingot body 180 may be pulled according to a pull rate protocol. For the majority of the growth of the main body of the single crystal silicon ingot, the pull rate is decreased from a relatively high pull rate to a minimum pull rate, and then increased to a constant pull rate. The initial high pull rate may be between about 0.5 mm / min and about 2.0 mm / min, such as about 1.0 mm / min, then decreased to a pull rate that may be as low as about 0.4 mm / min or even as low as about 0.3 mm / min, and thereafter increased to a constant pull rate between about 0.4 mm / min and about 0.8 mm / min, between about 0.4 mm / min and about 0.7 mm / min, or between about 0.4 mm / min and about 0.65 mm / min.

[0049] In the continuous Czochralski method, polycrystalline silicon (i.e., granular, block, or a combination of granular and block) is added to molten silicon during the growth of the ingot body 180 of the single crystal silicon ingot to thereby achieve a constant molten silicon volume and a constant melt height level. According to the method of the present invention, maintaining a substantially constant melt volume during the growth of a majority of the axial length of the body of the single crystal silicon ingot can achieve high ingot quality over a majority of the axial length of the body of the single crystal silicon ingot at a constant pull rate. The constant melt volume, regardless of the crystal length, can maintain a constant crystal / melt interface and thus a uniform crystal quality over a majority of the body of the ingot. Therefore, in some embodiments, the volume of molten silicon varies by no more than about 1.0 volume % during at least about 90% of the growth of the body of the single crystal silicon ingot, or varies by no more than about 0.5 volume % during at least about 90% of the growth of the body of the single crystal silicon ingot, or even varies by no more than about 0.1 volume % during at least about 90% of the growth of the body of the single crystal silicon ingot. In other words, in some embodiments, the melt height level varies by less than about + / - 0.5 millimeters during at least about 90% of the growth of the main body of the single crystal silicon ingot.

[0050] In the batch Czochralski process, the initial charge of polycrystalline silicon is sufficient to grow the entire length of the ingot. Rather than maintaining a constant melt height level, the volume of the silicon melt decreases as the ingot grows. Therefore, reference Figure 4 (Inset), the crucible 110 holds molten silicon 120, from which the ingot 140 is extracted. Figure 4 Sections a) to j) illustrate that an initial charge of solid polycrystalline silicon 150 is melted by applying heat from a heater 130 to form a melt 120. A silicon seed crystal 160 is brought into contact with the molten silicon 120, and a single crystal silicon ingot 140 is grown by slow extraction. As can be seen in the illustration, as the length of the single crystal silicon ingot 140 increases, the volume of the molten silicon 120 is depleted, making it necessary to vertically move the crucible 110 in the same direction as the ingot is pulled.

[0051] Regardless of whether the process is batch or continuous, growth conditions are selected to achieve optimized melt-side heat flux, temperature near the melt, and temperature gradient near the meniscus in order to grow an ingot that reduces or eliminates deformation along the entire length of the body of the ingot. In these growth conditions, the relative height of the bottom of the reflector 200 above the surface of the melt 210 is monitored, with reference to Figure 5 The relative height "HR" can be directly measured as the distance between the bottom of the reflector 200 and the melt level 210, as Figure 3 , the vector is labeled "HR". If the configuration of the hot zone does not allow direct measurement, i.e., the camera 220 cannot locate the bottom of the reflector 200, then the relative height "HR" can be measured indirectly using a reference point located, for example, below the crucible. The distance between the melt level and the reference point 230 is measured, and the distance between the bottom of the reflector 200 and the reference point 230 is measured (which is labeled "RZ"). The relative height "HR" is calculated by subtracting the distance between the melt level 210 and the reference point 230 from "RZ". In a batch process, the melt level changes as the ingot grows. Therefore, the crucible must be moved (i.e., raised) in order to maintain the desired "HR".

[0052] According to some embodiments, "HR" starts at a relatively high value, such as between about 60 mm and 120 mm or between about 70 mm and 100 mm. In some embodiments, the relatively high value of HR occurs during the growth of the neck and crown (i.e., the outward flaring seed cone) of the single crystal silicon ingot. The HR distance is initially large to allow the camera to capture the meniscus during the necking and crowning stages. The HR value is initially large to keep the meniscus in the observation window of the camera tracking it. In some embodiments, the relatively high value of HR may continue during the growth of the initial portion of the ingot body (e.g., during the growth of the first 200 mm to 400 mm of the ingot body). In some embodiments, after growing the neck and crown, the distance between the bottom of the reflector and the melt level is rapidly reduced by bringing the crucible close to the bottom of the reflector. In some embodiments, the distance between the bottom of the reflector and the melt level can be reduced at a rate of at least -0.05 mm per mm of ingot growth, or at least about -0.06 mm per mm of ingot growth, such as about -0.065 mm per mm of ingot growth, preferably less than about -0.1 mm per mm of ingot growth or less than about -0.08 mm per mm of ingot growth. Since the relative height decreases from a higher value to a lower value, the values ​​are stated as negative. In some embodiments, the HR is changed to a distance between 40 mm and 50 mm, such as between 45 mm and 50 mm, or between 45 mm and 48 mm, during the growth of most of the body of the ingot. In some embodiments, the HR is changed to a distance of 45 mm during the growth of most of the body of the ingot. In some embodiments, the HR is changed to a distance of 47 mm during the growth of most of the body of the ingot. These HR distances apply to the growth of at least about 50%, at least about 60%, at least about 70% of the length of the body of the ingot. Fig. 7A and 7B The "HR" profile according to an exemplary embodiment of the present invention is shown in . The crystal edge gradient is altered by the HR value according to the present invention, and the defect profile in the crystal is controlled by this crystal edge gradient. So basically, the defect profile determines to what value the HR is ramped and when the ramping should start. For example, in the front body, the crystal is heated a lot from the side and is therefore initially pulled at a low rate to obtain the desired diameter and then the seed lift force is ramped. Since this seed lift force changes with the length of the body, it is also necessary to change the temperature gradient to control defects, which in turn is controlled by changing the HR during crystal growth. As shown herein, for most of the growth of the body of the ingot, the "HR" is maintained at a constant low value, which increases rapidly when the ingot is completed and pulled from the remaining melt.

[0053] In some embodiments, a lower HR is combined with a lower seed rotation rate during the growth of most of the length of the main body of the single crystal silicon ingot. In some embodiments, the seed rotation rate can start with an initial high rate. A high seed rotation rate is suitable for the initial portion of the growing ingot because the melt temperature and heat flux are typically high during the growth of the first 200 mm to 600 mm of the length of the main body. In some embodiments, the initial seed rotation rate may be at least about 10 rpm, such as at least about 11 rpm or even at least about 12 rpm. In some preferred embodiments, the initial seed rotation rate may be at least about 11 rpm. After the growth of the initial portion of the ingot, the seed rotation rate decreases. In some embodiments, the seed rotation rate may decrease at a rate from about -0.005 rpm per millimeter of ingot growth to about -0.020 rpm per millimeter of ingot growth, such as from about -0.005 rpm per millimeter of ingot growth to about -0.014 rpm per millimeter of ingot growth. Since the seed rotation rate decreases from a higher value to a lower value, the value is stated as negative. Between about 600 mm and about 900 mm of the ingot body length, decreasing the seed rotation rate within this range may cause the seed rotation rate to be between about 5 rpm and about 10 rpm, such as about 8 rpm, about 9 rpm, or about 10 rpm. In some preferred embodiments, between about 600 mm and about 900 mm of the ingot body length, the seed rotation rate may be about 9 rpm. In some embodiments, at the rear section body growth (e.g., after about 1200 mm of growth), the rotation rate may be further decreased, such as between about 5 rpm and about 8 rpm, such as about 7 rpm or about 8 rpm. In some preferred embodiments, at the rear section body growth (e.g., after about 1200 mm of growth), the rotation rate may be about 7 rpm. In some preferred embodiments, at the rear section body growth (e.g., after about 1200 mm of growth), the rotation rate may be about 8 rpm. Selecting these seed rotation values ​​results in higher temperature gradients in the melt region near the solid-liquid interface and may also increase the meniscus temperature. Very low seed rotation values ​​may result in degradation of the oxygen radial gradient. At Fig. 8A and 8B A seed crystal rotation rate profile according to an exemplary embodiment of the present invention is shown in FIG.

[0054] In addition, according to the process of the present invention, a magnetic field can be applied to the crucible including the silicon melt. A sharp point or horizontal magnetic field can be applied to set the appropriate crystal / melt interface, that is, the shape and height of the meniscus. The magnetic field is mainly used to fix the desired crystal / melt interface shape and height, and the control of the oxygen content Qi is a secondary purpose.

[0055] Control of melt flow and the shape of the melt / solid interface, and thus the quality of the ingot, can be enhanced by applying a magnetic field to the silicon melt during the growth of the main body of the single crystal silicon ingot. In some embodiments, the applied magnetic field maintains a substantially constant melt / solid interface profile during at least about 70% of the growth of the main body of the single crystal silicon ingot or between about 70% and about 90% of the growth of the main body of the single crystal silicon ingot. The magnetic field applies an electromagnetic force that affects the flow of the silicon melt, and thus heat transfer in the melt is affected. It changes the profile of the crystal / melt interface and the temperature of the growing crystal.

[0056] The magnetic field affects the oxygen content and uniformity in the ingot. The sources of oxygen in the ingot are dissolution from the quartz crucible wall, SiOx(g) evaporation at the free surface of the melt (controlled by the melt flow dynamics), and incorporation into the growing crystal front. The magnetic field affects the convective melt flow during growth, which can affect oxygen evaporation and incorporation. The change in oxygen incorporation into a single crystal silicon ingot with time increments is controlled by diffusion and convection of oxygen in the melt according to the following equation:

[0057]

[0058] C is the oxygen concentration in the solidified silicon, t is the time, v is the convection velocity (melt flow velocity), rho (ρ) is the density of the silicon melt, is the gradient (d / dx). The applied magnetic field affects the melt velocity (v) and the oxygen concentration gradient in the melt Since the magnetic field causes steady-state melt flow, the incorporation of oxygen Oi into the ingot is time-constant, which enhances radial and axial oxygen concentration uniformity. The SOURCE term is derived from two parameters: dissolution of the quartz (SiO2) crucible, which is the production of oxygen (Si(l) + SiO2(s) → SiOx(g)); and evaporation, which is the removal (disappearance) of oxygen (SiOx(g)) from the melt. In a batch Cz process, this SOURCE term is not constant. Instead, it depends on the crystal length because the melt mass decreases as the crystal grows. When the ingot has grown most of its main length, the remaining melt volume is low, so that the amount of silicon melt in contact with the crucible is reduced, which therefore results in a lower concentration of oxygen incorporated into the melt from the crucible. Therefore, if the other terms (diffusion, convection, evaporation) are constant, then the oxygen incorporated into the solidifying silicon crystal is reduced. The melt free surface (contact surface between the melt and the gas) area affects the evaporation rate of SiOx(g). Less evaporation of SiOx(g) means more oxygen is incorporated into the solidified silicon crystal. According to the method of the present invention, the melt quality is maintained constant due to the addition of polysilicon as the ingot grows. Therefore, all source terms (oxygen produced by dissolving SiO2 crucible into the melt and evaporating SiOx(g) gas by the free surface of the melt) are constant. Therefore, diffusion and convection terms affect the oxygen of the solidified silicon crystal. The applied magnetic field makes the melt flow more stable (i.e., the melt flow is constant, like a time-independent stable condition), so the incorporation of oxygen is uniform and stable in the axial and radial directions during the growth of the entire length of the ingot. In some embodiments, interstitial oxygen can be incorporated into the ingot at a concentration between about 4PPMA and about 18PPMA. In some embodiments, interstitial oxygen can be incorporated into the ingot at a concentration between about 10PPMA and about 35PPMA. In some embodiments, the ingot includes oxygen having a concentration of not more than about 15PPMA or not more than about 10PPMA. Interstitial oxygen can be measured according to SEMI MF 1188-1105.

[0059] In some embodiments, a horizontal magnetic field is applied to the silicon melt during the growth of the main body of the single crystal silicon ingot. In the presence of a horizontal magnetic field, crystal growth is achieved by placing a crucible holding the silicon melt between the poles of a conventional electromagnet. In some embodiments, the horizontal magnetic field may have a magnetic flux density between about 0.2 Tesla and about 0.4 Tesla in the melt region. At a given intensity, the magnetic field in the melt varies by less than + / - about 0.03 Tesla. The application of a horizontal magnetic field generates a Lorentz force in the axial direction (in the direction opposite to the fluid motion), which is opposite to the force driving the melt convection. Therefore, convection in the melt is suppressed, and the axial temperature gradient near the interface in the crystal is increased. The melt-crystal interface then moves upward to the crystal side to accommodate the increased axial temperature gradient near the interface in the crystal and the contribution of the melt convection from the crucible is reduced.

[0060] In some embodiments, a cusp magnetic field is applied to the silicon melt during growth of the bulk of the single crystal silicon ingot. Fig. 9 Magnetic coil positions suitable for achieving a cusp magnetic field are described in . The cusp magnetic field has two control parameters, namely, magnetic flux density and magnetic field shape. The cusp magnetic field applies a horizontal (radial) magnetic field component at the nearest surface of the melt, combined with a vertical (axial) magnetic field applied deeper into the melt near the axis of the ingot. The cusp magnetic field is generated using a pair of Helmholtz coils 300, 310 carrying current in opposite directions. Therefore, at a position in the middle of the two magnetic fields, vertically along the ingot axis, the magnetic fields cancel each other so that the vertical magnetic field component is zero or close to zero. For example, the cusp magnetic flux density is typically about zero to about 0.2 Tesla in the axial direction. The magnetic flux density in the radial direction is typically higher than the magnetic flux density in the vertical direction. For example, the cusp magnetic flux density is typically between about 0 T and about 0.6 T in a radial position, such as between about 0.2 T and about 0.5 T, depending on the radial position. The radial cusp magnetic field constrains the flow of the melt, thereby stabilizing the melt. In other words, applying a radial cusp magnetic field causes convection adjacent to a portion of the solid-liquid interface where crystal growth occurs, and inhibits convection at the rest of the melt, thereby serving as an effective method for achieving uniform oxygen distribution. Hot melt convection can be controlled locally and independently by cusp magnetic fields at both the melt free surface and the melt-crucible interface. This enables control of oxygen concentration in the growing crystal by magnetic flux density alone, regardless of crystal rotation speed. Control of oxygen concentration is achieved via control of crystal rotation speed in the presence of an axial or radial magnetic field. Applying a cusp magnetic field can achieve growth on an ingot including less oxygen content than an ingot grown without an applied magnetic field, for example, not more than about 15 PPMA or not more than about 10 PPMA. Interstitial oxygen can be measured according to SEMI MF 1188-1105.

[0061] According to the method of the present invention, the cusp magnetic field applied to the silicon melt during the growth of the main body of the single crystal silicon ingot is derived from the upper magnetic coil 300 and the lower magnetic coil 310, wherein the upper magnetic field strength derived from the upper magnetic coil 300 is greater than the lower magnetic field strength derived from the lower magnetic coil 310. In some embodiments, the upper magnetic field strength derived from the upper magnetic coil 300 exceeds the lower magnetic field strength derived from the lower magnetic coil 310 by at least 10% or at least 15%. As illustrated in FIGS. 10B and 10C , by applying a greater magnetic field strength to the upper magnetic coil than to the lower magnetic coil, the cusp position can be moved downward into the melt compared to the conventional method illustrated in FIG. 10A . It has been found that lowering the cusp position increases the temperature in the meniscus region.

[0062] According to the method of the present invention, the conditions disclosed herein minimize the temperature changes at the free melt surface level and at the melt below the melt / crystal interface in the body of the back stage, because no deformation is seen in the body of the front stage. The conditions according to the method of the present invention help prevent the melt temperature from dropping near the crystal / melt interface and the meniscus, which in turn reduces the possibility of undercooling and thus deformation. Contributing factors to achieving the desired results are melt-side heat flux, temperature near the melt, and temperature gradient near the meniscus, which can be increased by selecting HR, seed rotation, and magnetic cusp conditions.

[0063] The melt side heat flux is determined according to the following equation:

[0064]

[0065] where k m is the thermal conductivity of the melt and is the axial temperature gradient. The heat flux depends on the axial temperature gradient in the melt. Therefore, a larger heat flux results in a larger axial temperature gradient, which means a higher temperature of the melt below the melt / crystal interface and a higher temperature gradient near the meniscus, which results in reduced ingot deformation along the axial length of the ingot. According to some embodiments, during the growth of at least 40% of the total axial length of the solid body of the single crystal silicon ingot, the heat flux in the axial direction between the melt-solid interface and the free melt height level has at least about 20,000 W / m over at least about 85% of the radial length of the solid body of the single crystal silicon ingot. 2 , at least about 21,000W / m 2 , at least about 22,000W / m 2 , at least about 23,000W / m 2 or at least about 24,000W / m 2 According to some embodiments, during the growth of at least 60% of the axial length of the solid body of the single crystal silicon ingot, the heat flux in the axial direction between the melt-solid interface and the free melt height level has at least about 20,000 W / m over at least about 85% of the radial length of the solid body of the single crystal silicon ingot. 2 , at least about 21,000W / m 2 , at least about 22,000W / m 2 , at least about 23,000W / m 2 or at least about 24,000W / m 2 According to some embodiments, during growth of at least 80% of the axial length of the solid body of the single crystal silicon ingot, the heat flux in the axial direction between the melt-solid interface and the free melt height level has at least about 20,000 W / m over at least about 80% of the diameter of the solid body of the single crystal silicon ingot. 2 , at least about 21,000W / m2 , at least about 22,000W / m 2 , at least about 23,000W / m 2 or at least about 24,000W / m 2 According to some embodiments, during growth of at least 90% of the total length of the solid body of the single crystal silicon ingot, the heat flux in the axial direction between the melt-solid interface and the free melt height level has at least about 20,000 W / m over at least about 85% of the radial length of the solid body of the single crystal silicon ingot. 2 , at least about 21,000W / m 2 , at least about 22,000W / m 2 , at least about 23,000W / m 2 or at least about 24,000W / m 2 According to some embodiments, during growth of at least 95% of the total length of the solid body of the single crystal silicon ingot, the heat flux in the axial direction between the melt-solid interface and the free melt height level has at least about 20,000 W / m over at least about 85% of the radial length of the solid body of the single crystal silicon ingot. 2 , at least about 21,000W / m 2 , at least about 22,000W / m 2 , at least about 23,000W / m 2 or at least about 24,000W / m 2 The absolute value of .

[0066] Still further, conditions are selected to achieve a temperature gradient along the meniscus curve. Figure 6 . According to some embodiments, during the growth of at least 40% of the total length of the solid body of the single crystal silicon ingot, the temperature gradient along the meniscus curve between the melt-solid interface and the free melt height level has an average value of at least about 0.16° / mm or at least about 0.18° / mm. According to some embodiments, during the growth of at least 60% of the total length of the solid body of the single crystal silicon ingot, the temperature gradient along the meniscus curve between the melt-solid interface and the free melt height level has an average value of at least about 0.16° / mm or at least about 0.18° / mm. According to some embodiments, during the growth of at least 80% of the total length of the solid body of the single crystal silicon ingot, the temperature gradient along the meniscus curve between the melt-solid interface and the free melt height level has an average value of at least about 0.16° / mm or at least about 0.18° / mm. According to some embodiments, during growth of at least 90% of the total length of the solid body of the single crystal silicon ingot, the temperature gradient along the meniscus curve between the melt-solid interface and the free melt height level has an average value of at least about 0.16° / mm or at least about 0.18° / mm.

[0067] By achieving these melt fluxes and temperature gradients, the temperature of the molten silicon at the meniscus is higher than what can conventionally be achieved in a low power hot zone. According to some embodiments, during the growth of at least 40% of the total length of the solid body of the single crystal silicon ingot, the temperature of the molten silicon in the meniscus is at least 1691K or at least 1692K, as measured at the free melt height level. According to some embodiments, during the growth of at least 60% of the total length of the solid body of the single crystal silicon ingot, the temperature of the molten silicon in the meniscus is at least 1691K or at least 1692K, as measured at the free melt height level. According to some embodiments, during the growth of at least 80% of the total length of the solid body of the single crystal silicon ingot, the temperature of the molten silicon in the meniscus is at least 1691K or at least 1692K, as measured at the free melt height level. According to some embodiments, during at least 85% of the growth of the total length of the solid body of the single crystal silicon ingot, the temperature of the molten silicon in the meniscus is at least 1691 K or at least 1692 K, as measured at the free melt height level. According to some embodiments, during at least 90% of the growth of the total length of the solid body of the single crystal silicon ingot, the temperature of the molten silicon in the meniscus is at least 1691 K or at least 1692 K, as measured at the free melt height level.

[0068] In some embodiments, Fig.11A and 11B The process conditions suitable for achieving the meniscus temperature profile and melt flux on the melt side are depicted in Figure 1, including bottom heater power (BH) = 0 KW, seed rotation rate (SR) = 9 rpm, and relative height (HR) = 47 mm (Test Condition 1). The heat flux (Qmelt) value is a measure of the heat flux into the melt across the crystallization front. Negative values ​​represent heat transfer from the melt across the melt / solid interface to the crystal. Fig.11A It is shown in Figure 1 that at 400 mm and 800 mm axial growth, the meniscus temperature along the meniscus curve is at least 1692 K. In addition, at both 400 mm and 800 mm axial growth, the heat flux has a radial length of greater than 20,000 W / m 2 The absolute value of Fig. 11B Displayed in.

[0069] In some embodiments, Fig. 12A and 12B The process conditions suitable for achieving the meniscus temperature profile and melt flux on the melt side are depicted in Figure 1, including bottom heater power (BH) = 0 KW, seed rotation rate (SR) = 9 rpm, and relative height (HR) = 45 mm (Test Condition 1). The heat flux (Qmelt) value is a measure of the heat flux into the melt across the crystallization front. Negative values ​​represent heat transfer from the melt across the melt / solid interface to the crystal. Fig. 12AIt is shown in Figure 1 that at 400 mm and 800 mm axial growth, the meniscus temperature along the meniscus curve is at least 1692 K. In addition, at both 400 mm and 800 mm axial growth, the heat flux has a radial length of greater than 20,000 W / m 2 The absolute value of Fig. 12B Displayed in.

[0070] In some embodiments, it was found that the temperature in the meniscus region increased as the magnetic cusp position was reduced. To reduce the magnetic cusp position, a 15% gap was provided between the upper and lower magnets, with the upper magnet having a higher strength. A comparison between the temperature profile in the meniscus region and the heat flux on the melt side was made, as described below. Fig.13A and 13B Displayed in. Fig.13A The lower temperatures and gradients shown in relate to a conventional low power hot zone (conventional LPHZ) with the magnetic cusp location illustrated in FIG. 10A . Fig.13A The higher temperatures and gradients shown in relate to the hot zones with the cusp positions illustrated in FIGS. 10B and 10C (Test Conditions 1 and 2) according to embodiments of the invention. Thus, the cusp magnetic field position along with the seed rotation rate and relative height can be combined to increase the meniscus temperature profile.

[0071] The process of the present invention enables the growth of a single crystal silicon ingot in which the deviation from the set point diameter is minimized. Minimizing / reducing deformation results in the actual diameter profile of the grown crystal being close to the set point value. Fig.14A , conventional low power hot zone processes can result in significant deviations from the desired crystal diameter. The set point diameter is represented by the solid line, and Fig.14A It is demonstrated that the actual diameter can deviate significantly from the set point diameter. Fig. 14B , some vibrations and deviations may still occur, however, the process of the present invention achieves crystal growth in which the diameter value remains close to the set point value. In view of this, the process of the present invention results in crystals with diameters that vary little around the set point value, thereby reducing ingot deformation over the entire length of the body of the ingot.

[0072] As used herein, the terms "about," "substantially," "substantially," and "approximately" when used in conjunction with ranges of size, concentration, temperature, or other physical or chemical properties or characteristics are meant to encompass variations that may exist in the upper and / or lower limits of the ranges for that property or characteristic, including variations resulting, for example, from rounding, measurement method, or other statistical variations.

[0073] When introducing elements of the present disclosure and its embodiment(s), the articles "a," "an," "the," and "said" are intended to mean that there are one or more of these elements. The terms "comprising," "including," "containing," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms indicating a particular orientation (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require any particular orientation of the items described.

[0074] As various changes could be made in the above constructions and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description and shown in the [several] accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

1. A method for preparing a single crystal silicon ingot by a Czochralski method, the method comprising: adding an initial charge of polycrystalline silicon to a crucible contained within a growth chamber, wherein the crucible includes a bottom wall and side walls, and further wherein the growth chamber includes a bottom heater positioned beside the bottom wall of the crucible, side heaters positioned beside the side walls, and a reflector; supplying power to the bottom heater, the side heater, or both the bottom heater and the side heater to thereby heat the crucible including an initial charge of the polycrystalline silicon to cause a silicon melt to form in the crucible, wherein the power supplied to the side heater is greater than the power supplied to the bottom heater, wherein the power supplied to the bottom heater is 2 kW or less, wherein the crucible rotates at a rate between 0.5 rpm and 10 rpm, and further wherein the silicon melt has a free melt height level; contacting a silicon seed crystal with the silicon melt contained in the crucible; extracting the silicon seed crystal from the silicon melt in a direction perpendicular to the free melt height level at an initial pull rate between 1.5 mm / min and 6 mm / min to thereby form a solid neck of the single crystal silicon ingot, wherein during the growth of the solid neck, the relative height between the free melt height level and the bottom of the reflector is between 60 mm and 120 mm, and wherein during the growth of the solid neck, the silicon seed crystal rotates at a rate between 5 rpm and 30 rpm; extracting a solid flared seed cone adjacent to the solid neck of the single crystal silicon ingot from the silicon melt by modifying the initial pull rate to between 0.5 mm / minute and 2.0 mm / minute to thereby achieve a flared seed cone pull rate, wherein during growth of the solid flared seed cone, the relative height between the free melt head level and the bottom of the reflector is between 60 mm and 120 mm; and A solid body of the single crystal silicon ingot adjacent to the solid outward flared seed cone is extracted from the silicon melt by modifying the outward flared seed cone pull rate to thereby achieve a body pull rate, wherein the solid body of the single crystal silicon ingot is pulled according to a pull rate protocol, wherein the pull rate decreases from an initial pull rate between 0.5 mm / min and 2.0 mm / min to a pull rate as low as about 0.4 mm / min or as low as about 0.3 mm / min, and then increases to a constant pull rate between 0.4 mm / min and 0.8 mm / min, wherein the solid body of the single crystal silicon ingot has a radius and an axial length, and surface tension generated when the solid body of the single crystal silicon ingot is withdrawn from the silicon melt results in a melt-solid interface positioned above the free melt height level, and further comprising a meniscus of the silicon melt between the melt-solid interface and the free melt height level, wherein during the growth of at least 50% of the solid body of the single crystal silicon ingot, the relative height between the free melt height level and the bottom of the reflector is between 40 mm and 50 mm, and wherein during the growth of the solid body of the single crystal silicon ingot, the silicon seed crystal is rotated at a rate between 5 rpm and 10 rpm; wherein a cusp magnetic field is applied to the silicon melt during growth of the solid body of the single crystal silicon ingot; wherein the cusp magnetic field applied to the silicon melt during growth of the solid body of the single crystal silicon ingot is derived from an upper magnetic coil and a lower magnetic coil, and wherein the upper magnetic field strength derived from the upper magnetic coil is greater than the lower magnetic field strength derived from the lower magnetic coil; and wherein during growth of at least 40% of the total axial length of the solid body of the single crystal silicon ingot, a heat flux in the axial direction between the melt-solid interface and the free melt height level is at least 20,000 W / m over at least 85% of the radius of the solid body of the single crystal silicon ingot 2 The absolute value of . The method according to claim 1 , wherein the bottom wall of the crucible is insulated.

3. A method according to claim 1 or claim 2, wherein the total axial length of the solid body of the single crystal silicon ingot is at least 1100 mm.

4. The method of claim 1 or claim 2, wherein the total axial length of the solid body of the single crystal silicon ingot is between 1200 mm and 1300 mm.

5. The method of claim 1 or claim 2, wherein the radius of the solid body of the single crystal silicon ingot is at least 75 mm or at least 100 mm.

6. The method of claim 1 or claim 2, wherein the radius of the solid body of the single crystal silicon ingot is at least 150 mm.

7. The method of claim 1 or claim 2, wherein the radius of the solid body of the single crystal silicon ingot is about 75 mm, about 100 mm, or about 150 mm.

8. The method of claim 1 or claim 2, wherein during growth of at least 60% of the axial length of the solid body of the single crystal silicon ingot, the heat flux in the axial direction between the melt-solid interface and the free melt height level has a value of at least 20,000 W / m over at least 85% of the radius of the solid body of the single crystal silicon ingot. 2 The absolute value of .

9. The method of claim 1 or claim 2, wherein during growth of at least 80% of the axial length of the solid body of the single crystal silicon ingot, the heat flux in the axial direction between the melt-solid interface and the free melt height level has a value of at least 20,000 W / m over at least 80% of the radius of the solid body of the single crystal silicon ingot. 2 The absolute value of .

10. The method of claim 1 or claim 2, wherein during growth of at least 90% of the total length of the solid body of the single crystal silicon ingot, the heat flux in the axial direction between the melt-solid interface and the free melt height level has a value of at least 20,000 W / m over at least 85% of the radius of the solid body of the single crystal silicon ingot. 2 The absolute value of .

11. A method according to claim 1 or claim 2, wherein during the growth of at least 40% of the total length of the solid body of the single crystal silicon ingot, the temperature gradient along the meniscus curve between the melt-solid interface and the free melt height level has an average value of at least 0.16°C / mm.

12. A method according to claim 1 or claim 2, wherein during the growth of at least 40% of the total length of the solid body of the single crystal silicon ingot, the temperature gradient along the meniscus curve between the melt-solid interface and the free melt height level has an average value of at least 0.18°C / mm.

13. A method according to claim 1 or claim 2, wherein during the growth of at least 60% of the total length of the solid body of the single crystal silicon ingot, the temperature gradient along the meniscus curve between the melt-solid interface and the free melt height level has an average value of at least 0.16°C / mm.

14. A method according to claim 1 or claim 2, wherein during the growth of at least 60% of the total length of the solid body of the single crystal silicon ingot, the temperature gradient along the meniscus curve between the melt-solid interface and the free melt height level has an average value of at least 0.18°C / mm.

15. A method according to claim 1 or claim 2, wherein during the growth of at least 80% of the total length of the solid body of the single crystal silicon ingot, the temperature gradient along the meniscus curve between the melt-solid interface and the free melt height level has an average value of at least 0.16°C / mm.

16. A method according to claim 1 or claim 2, wherein during the growth of at least 80% of the total length of the solid body of the single crystal silicon ingot, the temperature gradient along the meniscus curve between the melt-solid interface and the free melt height level has an average value of at least 0.18°C / mm.

17. The method of claim 1 or claim 2, wherein during growth of at least 40% of the total length of the solid body of the single crystal silicon ingot, the temperature of the silicon melt in the meniscus measured at the free melt height level is at least 1691K.

18. The method of claim 1 or claim 2, wherein during growth of at least 40% of the total length of the solid body of the single crystal silicon ingot, the temperature of the silicon melt in the meniscus measured at the free melt height level is at least 1692K.

19. The method of claim 1 or claim 2, wherein during growth of at least 60% of the total length of the solid body of the single crystal silicon ingot, the temperature of the silicon melt in the meniscus measured at the free melt height level is at least 1691K.

20. The method of claim 1 or claim 2, wherein during growth of at least 60% of the total length of the solid body of the single crystal silicon ingot, the temperature of the silicon melt in the meniscus measured at the free melt height level is at least 1692K.

21. The method of claim 1 or claim 2, wherein during growth of at least 85% of the total length of the solid body of the single crystal silicon ingot, the temperature of the silicon melt in the meniscus measured at the free melt height level is at least 1691K.

22. The method of claim 1 or claim 2, wherein during growth of at least 85% of the axial length of the solid body of the single crystal silicon ingot, the temperature of the silicon melt in the meniscus measured at the free melt height level is at least 1692K.

23. The method of claim 1 or claim 2, wherein the upper magnetic field strength derived from the upper magnetic coil exceeds the lower magnetic field strength derived from the lower magnetic coil by at least 10%.

24. The method of claim 1 or claim 2, wherein the upper magnetic field strength derived from the upper magnetic coil exceeds the lower magnetic field strength derived from the lower magnetic coil by at least 15%.

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