Method for producing single crystal silicon ingots by horizontal magnetic field Czochralski

Abstract

A method for producing a single crystal silicon ingot using a horizontal magnetic Czochralski method is disclosed. During the growth of the neck and / or at least a portion of the crown, no magnetic field or a relatively weak magnetic field of 1500 Gauss or less is applied to the neck and / or crown. During the growth of the ingot body, a horizontal magnetic field (e.g., 1500 Gauss or more) is applied.

Description

Cross-Reference to Related Applications

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 056,056, filed July 24, 2020, which is incorporated herein by reference in its entirety. [Technical Field]

[0002] The present disclosure relates to horizontal field Czochralski single crystal silicon ingot production. [Background technology]

[0003] The horizontal magnetic field Czochralski (HMCZ) method is sometimes used to produce relatively high-quality silicon wafers. Strong convection control under a horizontal magnetic field results in a relatively smooth axial diameter profile and improved nanotopology due to reduced dopant striations. The magnetic field can alter the ingot-melt interface due to the relatively fast and complex melt flow. To ensure crystals grow with a high zero-dislocation (ZD) success rate, the ingot crown is grown under controlled conditions by applying a horizontal magnetic field. The controlled growth conditions include long process times to increase the crown height (e.g., 250 mm to 450 mm for a 300 mm crystal), and in some cases, special crown shapes are used. Neck growth is traditionally performed under a horizontal magnetic field to stabilize the melt temperature near the meniscus. Traditional horizontal magnetic field methods result in longer process times.

[0004] In the production of single crystal silicon ingots by the horizontal magnetic field Czochralski (HMCZ) method, there is a need for a method that can reduce the process time required to form the ingot.

[0005] This section is intended to introduce various aspects of art that may be related to various aspects of the present disclosure, which are described and / or claimed below. This discussion is believed to be helpful in providing background information to facilitate an understanding of the various aspects of the present disclosure. As such, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

[0006] One aspect of the present disclosure is directed to a method for producing a single crystal silicon ingot having a neck and a body suspended from the neck by a horizontal magnetic field Czochralski process. A seed crystal is brought into contact with a silicon melt held in a crucible. The neck is withdrawn from the silicon melt. No horizontal magnetic field is applied to the melt while the neck is withdrawn from the melt. The ingot body is withdrawn from the melt. The body is suspended from the neck. A horizontal magnetic field is applied to the melt while the ingot body is withdrawn from the melt.

[0007] Another aspect of the present disclosure is directed to a method for producing a single crystal silicon ingot having a neck and a body suspended from the neck by a horizontal magnetic field Czochralski process. A seed crystal is brought into contact with a silicon melt held in a crucible. The neck is withdrawn from the silicon melt. A horizontal magnetic field is applied to the melt while the neck is withdrawn from the melt. The horizontal magnetic field is generated at a magnetic flux density of 1500 Gauss or less. An ingot body is withdrawn from the melt. The body is suspended from the neck. A horizontal magnetic field is applied to the melt while the ingot body is withdrawn from the melt.

[0008] Various refinements exist in the features noted in connection with the above-described aspects of the present disclosure. Additionally, additional features may likewise be incorporated into the above-described aspects of the present disclosure. These refinements and additional features may exist individually or in any combination. For example, the various features described below in connection with any of the illustrated embodiments of the present disclosure may be incorporated, alone or in any combination, into any of the above-described aspects of the present disclosure. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of an ingot puller apparatus used to pull a single crystal silicon ingot from a silicon melt.

[0010] [Figure 2] FIG. 2 is a cross-sectional view of an ingot puller device.

[0011] [Figure 3] FIG. 3 is a partial front view of a single crystal silicon ingot grown by the Czochralski method.

[0012] [Figure 4] FIG. 4 is a plan view of the crucible of the ingot puller apparatus.

[0013] [Figure 5] FIG. 5 is a side view of the crucible.

[0014] [Figure 6] FIG. 6 is a schematic diagram showing a horizontal magnetic field applied to a crucible containing a melt.

[0015] [Figure 7] FIG. 7 is a graph showing crown times for a group of wafers grown while a horizontal magnetic field was applied to the crown and a group of wafers grown while no horizontal magnetic field was applied to the crown.

[0016] [Figure 8] FIG. 8 is a graph showing neck pull-out rates for zero-dislocation neck growth for various reflector heights for necks grown with a cusp magnetic field and for necks with no magnetic field applied during neck growth.

[0017] [Figure 9] FIG. 9 is a graph showing the crown-zero dislocation loss failure rate for various reflector heights during HMCZ with no applied magnetic field during neck growth.

[0018] Corresponding reference numbers indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present disclosure relates to a method for producing single crystalline silicon ingots by the horizontal magnetic field Czochralski (HMCZ) process. In Figure 1, an ingot puller apparatus (or more simply "ingot puller") for growing single crystalline silicon ingots is shown generally at 100. The ingot puller apparatus 100 includes a crystal puller housing 108 that forms a growth chamber 152 for pulling a silicon ingot 113 from a silicon melt 104. The ingot puller apparatus 100 includes a crucible 102 disposed within the growth chamber 152 for holding the silicon melt 104. The crucible 102 is supported by a susceptor 106.

[0020] The crucible 102 includes a floor 129 and a sidewall 131 extending upwardly from the floor 129. The sidewall 131 is generally vertical. The floor 129 includes a curved portion that extends below the sidewall 131 of the crucible 102. Within the crucible 102 is a silicon melt 104 having a melt surface 111 (i.e., the melt-ingot interface). A susceptor 106 is supported by a shaft 105. The susceptor 106, crucible 102, shaft 105, and ingot 113 share a common longitudinal axis A or "pull axis" A.

[0021] A pulling mechanism 114 is provided within the ingot puller apparatus 100 for growing and pulling an ingot 113 from the melt 104. 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 pulley (not shown), a drum (not shown), or other suitable type of lifting mechanism, such as a shaft, and the other end is connected to the chuck 120, which holds the seed crystal 122. In operation, the seed crystal 122 is lowered into contact with the melt 104. The pulling mechanism 114 operates to raise the seed crystal 122, thereby pulling the single crystal ingot 113 from the melt 104.

[0022] A crucible drive 107 (e.g., a motor) rotates the crucible 102 and susceptor 106 during heating and crystal pulling. A lift mechanism 112 raises and lowers the crucible 102 along the pull axis A during the growth process. As the ingot grows, the silicon melt 104 is consumed and the melt height within the crucible 102 decreases. The crucible 102 and susceptor 106 can be raised to keep the melt level 111 at or near the same position relative to the ingot puller apparatus 100.

[0023] Additionally, a crystal drive (not shown) may rotate the pull cable 118 and ingot 113 in a direction opposite (e.g., counter-rotation) to the direction that the crucible drive 107 rotates the crucible 102. In embodiments using homogeneous rotation, the crystal drive may rotate the pull cable 118 in the same direction that the crucible drive unit 107 rotates the crucible 102. Additionally, the crystal drive may raise and lower the ingot 113 relative to the melt surface 111 as required during the growth process.

[0024] The ingot puller apparatus 100 may include an inert gas system for introducing and withdrawing an inert gas, such as argon, from the growth chamber 152. The ingot puller apparatus 100 may also include a dopant delivery system (not shown) for introducing dopants into the melt 104.

[0025] According to the Czochralski single crystal growth process, large quantities of polycrystalline silicon or polysilicon are deposited in a crucible 102 (e.g., a 250 kg or greater deposit). Various sources of polycrystalline silicon can be used, including, for example, granular polycrystalline silicon produced by the pyrolysis of silane or halosilane in a fluidized bed reactor, or polycrystalline silicon produced in a Siemens reactor. When polycrystalline silicon is added to the crucible to form a deposit, the deposit is heated to a temperature above the melting point of silicon (e.g., about 1412°C) to melt the deposit. In some embodiments, the deposit (i.e., the resulting melt) is heated to a temperature of at least about 1425°C, at least about 1450°C, or at least about 1500°C. The ingot puller apparatus 100 includes bottom insulation 110 and side insulation 124 to retain heat within the puller apparatus 100. In the illustrated embodiment, the ingot puller apparatus 100 includes a bottom heater 126 disposed below the crucible floor 129. The crucible 102 is heated to a temperature of 1000.5° C. for 10 minutes. silicon The bottom heater 126 may be moved relatively close to the bottom heater 126 to melt the

[0026] To form an ingot, the seed crystal 122 contacts the surface 111 of the melt 104. A withdrawal mechanism 114 operates to withdraw the seed crystal 122 from the melt 104. The ingot 113 includes a crown portion 142 where the ingot transitions from the seed crystal 122 and tapers outward as it reaches a target diameter. The ingot 113 includes a constant diameter portion 145, or cylindrical "body," of the crystal that is grown by increasing the withdrawal rate. The body 145 of the ingot 113 has a relatively constant diameter. After the body 145, the ingot 113 includes a tail or end cone (not shown) where the ingot tapers in diameter. When the diameter is sufficiently small, the ingot 113 is separated from the melt 104. The ingot 113 has a central longitudinal axis A that extends through the crown portion 142 and the terminal end of the ingot 113.

[0027] The ingot puller apparatus 100 includes a side heater 135 and a susceptor 106 surrounding the crucible 102 to maintain the temperature of the melt 104 during crystal growth. The side heater 135 is positioned radially outward relative to the crucible sidewall 131 as the crucible 102 moves up and down the pull axis A. The side heater 135 and the bottom heater 126 may be any type of heater capable of operating as described herein. In some embodiments, the heaters 135, 126 are resistance heaters. The side heater 135 and the bottom heater 126 may be controlled by a control system (not shown) so that the temperature of the melt 104 is controlled throughout the pulling process.

[0028] According to an embodiment of the present disclosure, the ingot puller apparatus 100 includes a reflector assembly 151 (or simply a "reflector" or "heat shield") that is positioned above the melt 104 in the growth chamber 152 and covers the ingot 113 during ingot growth. The heat shield 151 may be positioned partially within the crucible 102 during crystal growth. The heat shield 151 forms a central passageway 160 for receiving the ingot 113 as it is withdrawn by the withdrawal mechanism 114.

[0029] The reflector 151 is generally a heat shield configured to retain heat beneath it and above the melt 104. In this regard, any reflector shape and construction material known to those skilled in the art (e.g., graphite or quartz) may be used without limitation. The reflector 151 has a bottom 138 (FIG. 2). The bottom 138 of the reflector 151 is spaced from the surface of the melt by a distance Hr during ingot growth.

[0030] 3 shows a single crystal silicon ingot 113 produced in accordance with an embodiment of the present disclosure, and generally in accordance with the Czochralski process. The ingot 113 includes a neck 116, an outwardly flared portion 142 (synonymously "crown" or "cone"), a shoulder 119, and a constant diameter body 145. The neck 116 is attached to a seed crystal 122 that is drawn into contact with the melt to form the ingot 113. The body 145 is suspended from the neck 116. The neck 116 terminates when the cone portion 142 of the ingot 113 begins to form.

[0031] The constant diameter portion 145 of the ingot 113 has a periphery 150, a central axis A parallel to the periphery 150, and a portion extending from the central axis A to the periphery 150 and a central axis A passing through the cone 142 and the neck 116. The diameter of the main ingot body 145 can vary. In some embodiments, the diameter can be about 150 mm, about 200 mm, about 300 mm, greater than about 300 mm, about 450 mm, or greater than about 450 mm.

[0032] The single crystal silicon ingot 113 may generally have any resistivity. The single crystal silicon ingot 113 may be doped or undoped.

[0033] According to an embodiment of the present disclosure, the ingot body 145 is grown according to the known horizontal magnetic field Czochralski (HMCZ) technique while applying a horizontal magnetic field to the crucible 102 and melt 104. Figures 4-5 illustrate the horizontal magnetic field applied to the crucible 102 and melt 104 during ingot growth. The cylindrical coordinate system of the crucible 102 includes a radial direction R, an angular direction θ, and an axial direction Z. The melt 104 may include one or more convection cells 132, 134 induced by heating the crucible 102 and rotating the crucible 102 and / or ingot 113 about the angular direction θ. The structure and interaction of these one or more convection cells 132, 134 may be adjusted by adjusting one or more process parameters and / or applying a horizontal magnetic field, as described in more detail below.

[0034] 6 is a diagram illustrating a horizontal magnetic field applied to the crucible 102 and melt 104 in the ingot puller apparatus 100. As shown, the crucible 102 contains a silicon melt 104 from which an ingot 113 is grown. The transition between the melt and the crystal is commonly referred to as the crystal-melt interface (alternatively, melt-crystal, solid-melt, or melt-solid interface) and is typically nonlinear, e.g., concave, convex, or gull-wing shaped relative to the melt surface. Two magnetic poles 157 are opposed to generate a magnetic field that is generally perpendicular to the crystal growth direction and generally parallel to the melt surface 111.

[0035] The magnetic pole 157 may be a conventional electromagnet, a superconducting electromagnet, or any other suitable magnet for generating a horizontal magnetic field of the desired strength. Application of the horizontal magnetic field creates a Lorentz force along the axial direction opposite to the fluid motion, which acts as an opposing force to drive the convection of the melt. Therefore, the convection of the melt is suppressed. The axial temperature gradient of the crystal near the interface also increases. The melt-crystal interface then moves upward toward the crystal, corresponding to the increase in the axial temperature gradient in the crystal near the interface. The contribution from the convection of the melt within the crucible also decreases. The horizontal arrangement has the advantage of being more efficient in damping the convection at the melt surface 111.

[0036] The position of the magnetic poles 157 relative to the melt surface 111 can be varied to adjust the position of the maximum Gauss plane (MGP) relative to the melt surface 111. The magnetic poles 157 can be cooled (e.g., water-cooled) and / or include iron shielding to reduce stray magnetic fields and increase the strength of the generated magnetic field.

[0037] The loss of the zero-dislocation (ZD) structure (as quantified by the LZD ratio) is greater during growth of silicon crystal Cz in a horizontal magnetic field (HMCZ) relative to growth in a cusp (or vertical) magnetic field. The LZD ratio in the HMCZ, on the other hand, can be reduced in shorter process times by applying no magnetic field (e.g., a horizontal magnetic field or any type of magnetic field) during growth of neck 116 and / or during growth of at least a portion of crown 142, or by applying a relatively weak horizontal magnetic field (e.g., less than 1500 Gauss) during growth of neck 116 and / or during growth of at least a portion of crown 142.

[0038] According to embodiments of the present disclosure, when the seed crystal 122 contacts the silicon melt 104 and the neck 116 begins to grow, no magnetic field is applied to the melt 104 (i.e., the magnetic pole 157 is not powered), or a relatively weak magnetic field such as 1500 Gauss is applied. As the neck 116 forms, the outwardly flaring crown 142 begins to be pulled out of the melt 104. In some embodiments, the entire crown 142 is formed without a magnetic field being applied to the melt. Alternatively, a relatively weak magnetic field such as 1500 Gauss is applied. In some embodiments, when the crown diameter is less than 120 mm, no magnetic field is applied to the melt, or a magnetic field with a magnetic flux density less than 1500 Gauss is applied. In such embodiments, when the crown 142 reaches a diameter of 120 mm, the magnetic flux density of the horizontal magnetic field can exceed 1500 Gauss (e.g., 0 Gauss to 4000 Gauss). In some embodiments, the magnetic flux increases during crown growth.

[0039] When the desired ingot diameter is reached, a shoulder 119 forms to transition towards the formation of a constant diameter portion 145 of the ingot 113. During the growth of the constant diameter portion 145, a horizontal magnetic field is applied to the melt 104. For example, the horizontal magnetic field has a magnetic flux density of at least 1500 Gauss (e.g., 1500 Gauss to 4000 Gauss, or 2000 Gauss to 4000 Gauss).

[0040] During neck growth, one or more growth conditions may be controlled to reduce the incidence of dislocations in the neck 116. For example, in some embodiments, the crucible 102 rotates at a crucible rotation rate of 8 rpm or greater while the neck 116 is being withdrawn from the melt 104. Alternatively or additionally, the distance (Hr) between the bottom 138 of the reflector 151 and the surface 111 of the melt 104 may be at least 40 mm, or at least 60 mm, while the neck 116 is being withdrawn from the melt 104. Alternatively or additionally, the neck withdrawal rate may be at least 1.5 mm / min, or between 1.5 mm / min and 4.5 mm / min. Also, a relatively long crown may be used, such as a crown having a height of at least 220 mm.

[0041] Compared to conventional methods for growing single crystal ingots by the horizontal magnetic field Czochralski method, the disclosed method has several advantages. By applying no horizontal magnetic field or a relatively weak field (e.g., less than 1500 Gauss) during at least a portion of neck growth and / or crown growth, the process time for producing the ingot can be reduced. By increasing the crucible rotation speed (e.g., 8 rpm or more), melt convection can be increased. By increasing the distance (Hr) between the reflector and the melt during neck growth (e.g., 40 mm or more), the neck temperature can be increased, reducing dislocations in the neck, and the process time can be reduced.

[0042] [Example] The processes of the present disclosure are further illustrated by the following examples, which should not be construed in a limiting sense.

[0043] [First Example: Comparison of Crown Treatment Time with and without Horizontal Magnetic Field Application] The ingots were grown by the horizontal magnetic field Czochralski process (HMCZ). One group of ingots ("Group A") was grown with a horizontal magnetic field applied during crown growth. A second group of ingots ("Group B") was grown with a horizontal magnetic field applied during crown growth at a faster withdrawal rate. A third group of ingots ("Group C") was grown without a magnetic field applied during crown growth (but with a magnetic field applied during the growth of the main body of the ingot).

[0044] The time for growing the crown of each batch of ingots is shown in Figure 7. As shown in Figure 7, the ingots to which a horizontal magnetic field was applied during crown growth took 1.5 times longer to grow than the ingots to which a horizontal magnetic field was not applied during crown growth. The longer run time can be attributed to the increased crown height in the ingots to which a horizontal magnetic field was applied during crown growth.

[0045] [Second Example: Drawing Speed ​​for Zero-Dislocation Ingot Growth] Figure 8 shows the range of neck drawing speeds at which zero dislocations are obtained for various reflector distances ("Hr Group 1") and various magnet conditions (applied cusp field ("cusp on") or no applied field ("HMCZ off") during neck growth). As shown in Figure 8, for conditions with no applied horizontal magnetic field, a faster neck drawing speed is used to ensure zero dislocation growth.

[0046] [Third Example: Effect of Reflector Distance on Zero Transposition Rate] Ingots were grown by HMCZ with no applied magnetic field during neck growth. The ingots were grown over various reflector-to-melt distances ("neck Hr"). As shown in Figure 9, as Hr becomes shallower, it becomes more difficult for the melt flow near the neck-melt interface to remove dislocations. Wider Hr and higher temperature conditions favor the movement of dislocations in the neck.

[0047] As used herein, when used in connection with a range of dimensions, concentrations, temperatures, or other physical or chemical properties or characteristics, the terms "about," "substantially," "essentially," and "approximately" are meant to encompass variation that may exist at the upper and / or lower limits of the range of the property or characteristic, including, for example, variation that results from rounding, measurement methodology, or other statistical variation.

[0048] When describing elements of the present disclosure or embodiments thereof, the articles are intended to mean that there are one or more of the elements. The terms "comprises," "includes," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of specific directional terms (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require a specific orientation of the elements being described.

[0049] Since various changes may be made in the structure and methods described above without departing from the scope of the present disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

Claims

1. 1. A method for producing a single crystal silicon ingot by a horizontal magnetic field Czochralski process, the single crystal silicon ingot having a neck, a body suspended from the neck, and an outwardly flared portion disposed between the neck and the ingot body, wherein the single crystal silicon ingot is grown in an ingot puller apparatus having a heat shield; contacting a seed crystal with a silicon melt held in a crucible; withdrawing the neck from the silicon melt; wherein no horizontal magnetic field is applied to the melt while the neck is being withdrawn from the melt; the crucible is rotated at a crucible rotation speed of 8 rpm or more while the neck is being withdrawn from the melt; the distance between the melt and the bottom of the heat shield is at least 60 mm while the neck is being withdrawn from the melt; withdrawing the outwardly flared portion from the melt, wherein no horizontal magnetic field is applied to the melt during withdrawal of the outwardly flared portion from the melt; withdrawing the ingot body from the melt, the body suspended from the neck and the outwardly flared portion disposed between the neck and the ingot body, wherein a horizontal magnetic field is applied to the melt while the ingot body is withdrawn from the melt.

2. The method of claim 1 , wherein no magnetic field is applied to the silicon melt while withdrawing the outwardly flared portion.

3. The method of claim 1 , wherein a magnetic field is not applied to the silicon melt while the neck is being withdrawn from the silicon melt.

4. The method described in claim 1, wherein the distance between the molten material and the bottom of the heat shield is at least 40 mm while pulling the outward flared portion from the molten material.

5. The method described in claim 1, wherein the distance between the molten material and the bottom of the heat shield is at least 60 mm while pulling the outward flared portion from the molten material.

6. 10. The method of claim 1, wherein the neck grows at a drawing rate of at least 1.5 mm / min and less than 4.5 mm / min.

7. The method described in claim 1, wherein the outward flared portion has a height that is at least 220 mm.

8. 1. A method for producing a single crystal silicon ingot by a horizontal magnetic field Czochralski process, the single crystal silicon ingot having a neck, a body suspended from the neck, and an outwardly flared portion disposed between the neck and the ingot body, wherein the single crystal silicon ingot is grown in an ingot puller apparatus having a heat shield; contacting a seed crystal with a silicon melt held in a crucible; withdrawing the neck from the silicon melt; wherein a horizontal magnetic field is applied to the melt while the neck is being withdrawn from the melt, the horizontal magnetic field having a magnetic flux density of 1500 Gauss or less; the crucible is rotated at a crucible rotation speed of 8 rpm or more while the neck is being withdrawn from the melt; the distance between the melt and the bottom of the heat shield is at least 60 mm while the neck is being withdrawn from the melt; withdrawing the outwardly flared portion from the melt, wherein a horizontal magnetic field is not applied to the melt while withdrawing the outwardly flared portion from the melt; and withdrawing the ingot body from the melt, wherein the body is suspended from the neck and the outwardly flared portion is disposed between the neck and the ingot body, wherein a horizontal magnetic field is applied to the melt while the ingot body is withdrawn from the melt.

9. 9. The method of claim 8, wherein the neck grows at a drawing rate of at least 1.5 mm / min and less than 4.5 mm / min.

10. The method described in claim 8, wherein the outward flared portion has a height that is at least 220 mm.

11. 10. The method of claim 1, wherein the ingot body has a diameter of 300 mm.

12. 9. The method of claim 8, wherein the ingot body has a diameter of 300 mm.

Images