Ingot lifting device having a heat shield disposed below a side heater and a method of manufacturing an ingot with such a device

Abstract

An ingot pulling apparatus and a method for producing an ingot in such an ingot pulling apparatus are disclosed that have a heat shield positioned below a side heater. In some embodiments, the side heater is relatively short. The side heater can be completely above the floor of the crucible when the crucible is in its lowest position during ingot pulling.

Description

Technical Field

[0001] The field of the present disclosure relates to an ingot pulling apparatus, and more particularly to an ingot pulling apparatus having a heat shield disposed below a side heater.

Background Art

[0002] Some conventional ingot pulling apparatuses include relatively long side heaters in the ingot pulling hot zone. To achieve the desired temperature profile of the melt, the insulation material at the bottom of the hot zone is removed. Removal of the insulation material increases the energy input to the side heater, thereby reducing the thermal efficiency. Further, when raising the crucible during crystal growth, the relatively long heater can heat the bottom of the crucible and the shaft used to raise the crucible, further reducing the energy efficiency of the process.

[0003] There is a need for an ingot pulling apparatus having a hot zone that allows the desired temperature profile to be achieved while increasing the efficiency of the hot zone and the heating system.

[0004] This section is intended to introduce the reader to various technical aspects that may relate to various aspects of the present disclosure, which are described and disclosed below. This description is believed to be useful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, these descriptions should be read in this light and should not be construed as an admission of prior art.

Summary of the Invention

[0005] One aspect of the present invention is directed to an ingot pulling apparatus for manufacturing a silicon ingot. The ingot pulling apparatus includes a crucible for holding a silicon melt. The crucible has a floor and sidewalls extending from the floor. The ingot pulling apparatus includes a growth chamber for pulling a silicon ingot from the melt along a pulling axis. The ingot pulling apparatus includes a lifting mechanism for raising and lowering the crucible relative to the pulling axis during crystal growth. The crucible moves axially between a lowest position where the silicon charge melts to produce the silicon melt, a seed dip position where a seed crystal first contacts the melt to pull the silicon ingot from the melt, and a terminal position where the melt in the crucible is depleted. When the crucible moves from the lowest position to the terminal position, a side heater is disposed radially outward of the radius of the crucible sidewall. A bottom heater is disposed below the floor of the crucible. A heat shield is disposed directly below the side heater.

[0006] Still another aspect of the present disclosure is directed to a method of manufacturing an ingot in an ingot pulling apparatus comprising a crucible having a floor and sidewalls extending from the floor, a side heater disposed radially outward of the radius of the crucible sidewall, and a heat shield disposed directly below the side heater. When the crucible is in the lowest position, a silicon melt is formed in the crucible and the side heater is completely above the floor of the crucible. The melt contacts a seed crystal. The ingot is removed from the silicon melt. The crucible rises as the ingot is removed from the silicon melt and when the ingot is separated from the melt, the crucible is in the terminal position.

[0007] There are various improvements to the features mentioned with respect to the above aspects of the present disclosure. Further features may also be incorporated into the above aspects of the present disclosure as well. These improvements 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 into any of the above aspects of the present disclosure, alone or in any combination.

Brief Description of the Drawings

[0008]

Figure 1

[0009]

Figure 2

[0010]

Figure 3

[0011]

Figure 4

[0012]

Figure 5

[0013]

Figure 6

[0014] Corresponding reference numerals indicate corresponding elements throughout the drawings.

Embodiments for Carrying Out the Invention

[0015] The ingot pulling device (or more simply, the "ingot puller") is generally indicated by "100" in FIG. 1. The ingot pulling device 100 includes a crucible 102 supported by a susceptor 106 for holding a melt 104 of a semiconductor such as silicon or a solar grade material. The ingot pulling device 100 includes a crystal pulling housing 108 that defines a growth chamber 152 for pulling a silicon ingot 113 (FIG. 2) from the melt 104 along a pulling axis A.

[0016] The crucible 102 includes a floor 129 and side walls 131 extending upward from the floor 129. The side walls 131 are generally vertical. The floor 129 includes a curved portion of the crucible 102 that extends below the side walls 131. The crucible 102 includes a bottom 116 that is the lowest position of the crucible 102 with respect to the pulling axis A. There is a silicon melt 104 having a melt surface 111 (i.e., the melt-ingot interface) within the crucible 102.

[0017] The susceptor 106 is supported by a shaft 105. The susceptor 106, crucible 102, shaft 105, and ingot 113 (FIG. 2) have a common longitudinal axis A, i.e., the "pulling axis" A.

[0018] A pulling mechanism 114 is provided within the ingot pulling device 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), or a drum (not shown), or some other suitable type of lifting mechanism, such as a shaft, and the other end is connected to a chuck 120 that holds the seed crystal 122. During operation, the seed crystal 122 descends and contacts the melt 104. The pulling mechanism 114 is operated to raise the seed crystal 122. Thereby, a single crystal ingot 113 (FIG. 2) is pulled from the melt 104.

[0019] During heating and crystal pulling, the crucible drive unit 107 (e.g., a motor) rotates the crucible 102 and the susceptor 106. The lifting mechanism 112 raises and lowers the crucible 102 along the pulling axis A during the growth process. For example, as shown in FIG. 1, the crucible can be at the lowest position (near the bottom heater 126) where the charge of solid polycrystalline silicon pre-added to the crucible 102 is melted. Crystal growth is initiated by bringing the melt 104 into contact with the seed crystal 122 and raising the seed crystal 122 by the pulling mechanism 114. The crucible 102 can be raised a distance from its lowest position before the melt 104 contacts the seed crystal 122 (i.e., raised to the "seed dip position").

[0020] As the ingot grows, the silicon melt 104 is consumed and the height of the melt in the crucible 102 decreases. The crucible 102 and the susceptor 106 can be raised to maintain the melt surface 111 at the same position or near to the ingot pulling device 100. The crucible 102 can move axially between its lowest position (e.g., the melting position) shown in FIG. 1, the seed dip position where the seed crystal first contacts the melt to pull the silicon ingot from the melt, and the end position (FIG. 3) where the melt in the crucible is depleted. The end position of the crucible 102 is above the seed dip position (and the lowest position) of the crucible 102.

[0021] A crystal drive unit (not shown) may also rotate the pulling cable 118 and the ingot 113 (FIG. 2) in a direction opposite to the direction in which the crucible drive unit 107 rotates the crucible 102 (e.g., counter-rotation). In embodiments using co-directional rotation, the crystal drive unit may rotate the pulling cable 118 in the same direction as the direction in which the crucible drive unit 107 rotates the crucible 102. Further, the crystal drive unit raises and lowers the ingot 113 as desired with respect to the melt surface 111 during the growth process.

[0022] The ingot lifting device 100 may include an inert gas system for introducing and recovering an inert gas such as argon from the growth chamber 152. The ingot lifting device 100 may also include a dopant supply system (not shown) for introducing a dopant into the melt 104.

[0023] According to the Czocharalski single crystal growth process, an amount of polycrystalline silicon or polysilicon is charged into the crucible 102. The semiconductor or solar grade material introduced into the crucible is melted by heat supplied from one or more heating elements. The ingot lifting device 100 includes a bottom heat insulator 110 and side heat insulators 124 for maintaining heat within the lifting device. In the illustrated embodiment, the ingot lifting device 100 includes a bottom heater 126 disposed below the floor 129 of the crucible. The crucible 102 can move so as to approach relatively close to the vicinity of the bottom heater 126 to melt the polycrystalline charged into the crucible 102.

[0024] To form an ingot, the seed crystal 122 contacts the surface 111 of the melt 104. The lifting mechanism 114 is operated to lift the seed crystal 122 from the melt 104. Referring now to FIG. 2, the ingot 113 includes a crown portion 142 that tapers outwardly as it transitions from the seed crystal 122 such that the ingot reaches a target diameter. The ingot 113 includes a constant diameter portion 145 of the crystal, i.e., the "body portion" of the cylinder, and grows by increasing the lifting rate. The body portion 145 of the ingot 113 has a relatively constant diameter. The ingot 113 includes a tail or end cone 149 (FIG. 3) where the ingot tapers in diameter after the body portion 145. When the diameter becomes small enough, the ingot 113 separates from the melt 104. The ingot 113 has a central longitudinal axis A that extends through the crown portion 142 and the terminus 150 of the ingot 113.

[0025] The ingot lifting device 100 includes a side heater 135 and a susceptor 106 that surrounds the crucible 102 to maintain the temperature of the melt 104 during crystal growth. The side heater 135 is disposed radially outward of the crucible sidewall 131 when the crucible 102 moves up and down along the lifting axis A (e.g., from the lowest position to the end position). The side heater 135 and the bottom heater 126 may be any type of heater that enables the side heater 135 and the bottom heater 126 to be operated 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) such that the temperature of the melt 104 is controlled throughout the lifting process.

[0026] According to an embodiment of the present disclosure, the side heater 135 may have a relatively short length L 135 (i.e., height) compared to conventional ingot lifting, and may reduce the amount of oxygen incorporated into the ingot 113. In some embodiments, the length L of the side heater 135 135 may be 500 mm or less, 450 mm or less, 400 mm or less, or 350 mm or less. At least a portion of the side heater 135 is horizontally aligned with the sidewall 131 of the crucible 102 when the crucible 102 moves between the lowest position of the crucible, the seed dip position, and the end position (e.g., a radius extending perpendicularly outward from the lifting axis A can intersect the sidewall 131 and the crucible 102).

[0027] The ingot lifting device 100 also includes a heat shield 140 that surrounds the crucible 102 and the susceptor 106 to maintain the temperature of the melt 104 during crystal growth. The heat shield 140 is disposed below the side heater 135 and may be spaced from the side heater 135 by a gap 155. In some embodiments, the heat shield 140 is spaced from the side heater 135 by about 50 mm or less, or 40 mm or less (e.g., 30 mm to about 50 mm). In other embodiments, the heat shield 140 is not spaced from the side heater 135 (i.e., the heat shield 140 and the side heater 135 are continuous).

[0028] In the illustrated embodiment, the heat shield 140 is disposed directly below the side heater 135 (i.e., the side heater 135 and the heat shield 140 are aligned when viewed from below, i.e., "vertically aligned"). In some embodiments, the length L 140 (FIG. 2) of the heat shield 140 is greater than the thickness T 140 of the heat shield 140. The thickness T 140 of the heat shield 140 is at least the thickness T 135 of the side heater 135, and in other embodiments, at least 1.1 times the thickness T 135 of the side heater 135, at least 1.25 times the thickness T 135 of the side heater 135, or at least 1.5 times the thickness T 135 of the side heater 135 (e.g., 1.0 to 2.0 times the thickness T 135 of the side heater 135). The heat shield 140 can be disposed radially with respect to the side heater 135 such that a portion of the heat shield 140 overlaps each side surface of the side heater 135 (i.e., when viewed from above, a first portion of the heat shield 140 is radially inward with respect to the side heater 135 and a second portion of the heat shield 140 is radially outward with respect to the side heater 135).

[0029] The heat shield 140 may generally be made of any material that reduces the cooling of the bottom of the side heater 135. The heat shield may include a heat insulating material or a reflective material. The heat shield may be layered. In embodiments where the heat shield is made of a heat insulating material, the heat insulating material may be covered with graphite to reduce the risk of dislocation (zero dislocation) of the ingot. In some embodiments, the heat shield may include a graphite shell with a molybdenum sheet disposed within the shell to block radiation.

[0030] The ingot lifting device 100 may include a second heat shield 151 (e.g., including a first heat shield 140 which is a "lower" heat shield and a second heat shield 151 which is an "upper heat shield"). The second heat shield 151 may surround the ingot 113 such that the ingot passes through an opening 160 formed by the heat shield 151. The heat shield 151 may be disposed inside the crucible 102 during crystal growth (e.g., as shown at the end position of the crucible 102 as shown in FIG. 3).

[0031] The crucible 102 is shown in its lowest position in FIG. 1. In the illustrated embodiment, when the crucible 102 is in its lowest position, the side heater 135 is completely above the floor 129 of the crucible 102. For example, the distance between the bottom 116 of the crucible 102 and the side heater 135 (i.e., the distance to the bottom of the side heater 135) may be at least about 25 mm, or at least about 50 mm. The distance between the bottom 116 of the crucible 102 and the upper part of the side heater 135 may be at least about 75 mm, or at least about 100 mm. At least a part of the heat shield 140 is above the bottom 116 of the crucible 102. At least a part of the heat shield 140 is also below at least a part of the floor 129 of the crucible 102.

[0032] The crucible 102 is shown at its end position in FIG. 3. In the illustrated embodiment, when the crucible 102 is in the end position, the heat shield 140 is completely below the floor 129 of the crucible 102. The heat shield 140 is also completely below the susceptor 106 when the crucible 102 is in the end position.

[0033] The ingot lifting device of the present disclosure has several advantages over conventional ingot lifting devices. In embodiments where the ingot lifting device has a relatively short side heater (e.g., the side heater length is 500 mm or less, 450 mm or less, 400 mm or less, or 350 mm or less, and / or when the crucible is in its lowest position, the side heater is completely above the floor of the crucible), the heating from the side heater is directed directly at the crucible and susceptor rather than having some energy directed towards the shaft and bottom insulation as the crucible rises during crystal growth. This results in more efficient use of energy and the melting high point moving upward from the interface between the melt and the crucible. This improves efficiency as more added insulation can move the high point downward and maintain the same temperature profile with less energy and less leakage to the bottom of the hot zone. During the growth of the rear body portion of the ingot (i.e., the portion of the constant diameter section towards the end cone that grows when the crucible is relatively high in the lifting device), the temperature range of the crucible wall can be wider compared to the use of a long heater, enabling reduction of the inter-lattice oxygen in the rear body portion.

[0034] In embodiments where the heat shield is disposed below the side heater, the heat shield reduces the exposure of relatively low temperature elements below the bottom of the hot zone, so the heat shield reduces the cooling of the lower part of the side heater. This reduces the energy required for the heater to reach the desired temperature and increases the energy efficiency of the hot zone.

Examples

[0035] The process of the present disclosure is further illustrated by the following examples. These examples should not be considered in a limiting sense. Example 1: Use of a hot zone with a 525 mm heater vs. use of a hot zone with a 325 mm heater and a heat shield disposed below the heater

[0036] Figure 5 shows the temperature profile of the hot zone configuration of the ingot pulling apparatus of FIG. 4 (in FIGS. 5 and 6, the low temperature portions of the melt and the heater are shown by darker dotted lines). The hot zone of FIG. 4 included a side heater 135 that was 525 mm in length and did not include a heat shield below the side heater. The hot zone also included some insulation that had been moved downward to the bottom of the hot zone to achieve the desired temperature profile. The side heater of FIG. 4 was operated at 103 kW and the bottom heater was operated at 5 kW (total heat input 108 kW). The temperature profile of FIG. 5 is desirable such that the melting high temperature point is at the interface between the melt and the crucible. As shown in the temperature profile of the side heater on the right in FIG. 5, the side heater was relatively cooler towards the bottom of the heater due to the reduction of the insulation.

[0037] Figure 6 shows the temperature profile of the hot zone configuration of the ingot pulling apparatus of FIGS. 1 - 3 in which a relatively short side heater 135 that was 325 mm in length (i.e., 200 mm shorter than the side heater of FIG. 4) was used. The hot zone included a heat shield 140 disposed below the side heater 135. The hot zone included a large amount of insulation (about 1 inch) that had been moved downward to the bottom of the ingot pulling apparatus compared to the hot zone of FIG. 4. The side heater 135 was operated at 59 kW and the bottom heater was operated at 5 kW (total heat input 64 kW).

[0038] As shown in FIG. 6, the melt had substantially the same desired temperature profile as the hot zone of FIG. 4 (shown in FIG. 5), but the ingot pulling apparatus was operated at 44 kW less power (i.e., 41% less).

[0039] 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" herein are intended to cover variations that may exist at the upper and / or lower limits of the range of the property or characteristic, including, for example, variations resulting from rounding, measurement methodology, or other statistical variations.

[0040] When introducing elements of the present disclosure or embodiments thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "having," "including," "comprising," and "containing" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Terms indicating a particular orientation (e.g., "top," "bottom," "side," etc.) are for convenience of explanation and do not require any particular orientation of the item being described.

[0041] Since various changes can be made in the above structures and methods without departing from the scope of the present disclosure, all matters included in the above description and shown in the accompanying drawings are intended to be construed in an illustrative, and not a limiting, sense.

Claims

1. An ingot pulling apparatus for manufacturing a silicon ingot, comprising: a floor and side walls extending from the floor, a crucible for holding a silicon melt, a growth chamber for pulling a silicon ingot from the melt along a pulling axis, a lifting mechanism for raising and lowering the crucible during crystal growth, wherein the crucible moves along the pulling axis between a lowest position where a silicon charge is melted to produce the silicon ingot, a seed dip position where a seed crystal first contacts the melt to pull the silicon ingot from the melt, and a terminal position where the melt in the crucible is depleted, a side heater disposed radially outward of the crucible side wall when the crucible moves from the lowest position to the terminal position, a bottom heater disposed below the floor of the crucible, and a heat shield disposed directly below the side heater. The ingot pulling apparatus as claimed.

2. The side heater is completely above the floor of the crucible when the crucible is in the lowest position. The ingot pulling apparatus according to claim 1.

3. At least a part of the heat shield is above the bottom of the crucible when the crucible is in the lowest position. The ingot pulling apparatus according to claim 1.

4. At least a part of the heat shield is below at least a part of the floor of the crucible when the crucible is in the lowest position. The ingot pulling apparatus according to claim 1.

5. The heat shield is completely below the floor of the crucible when the crucible is in the terminal position. The ingot pulling apparatus according to claim 1.

6. The length of the side heater is 350 mm or less. The ingot pulling apparatus according to claim 1.

7. The length of the heat shield with respect to the pulling axis is greater than the thickness of the heat shield. The ingot pulling apparatus according to claim 1.

8. At least a part of the side heater is horizontally aligned with the side wall of the crucible when the crucible moves between the lowest position and the terminal position. The ingot pulling apparatus according to claim 1.

9. The side heater and the heat shield are spaced apart by a gap. The ingot pulling apparatus according to claim 1.

10. The side heater is spaced 50 mm or less, 40 mm or less from the heat shield, or the side heater is not spaced from the heat shield by a gap. The ingot lifting device according to claim 1.

11. The ingot lifting device further includes a susceptor that supports the crucible, and the heat shield is completely below the susceptor when the crucible is in the terminal position. The ingot lifting device according to claim 1.

12. The distance between the bottom of the crucible and the bottom of the side heater is at least 25 mm when the crucible is in the lowest position. The ingot lifting device according to claim 1.

13. The side heater has a thickness, the heat shield has a thickness, and the thickness of the heat shield is at least the thickness of the side heater, or at least 1.5 times the thickness of the side heater. The ingot lifting device according to claim 1.

14. The first part of the heat shield is radially inward of the side heater, and the second part of the heat shield is radially outward of the side heater. The ingot lifting device according to claim 13.

15. Comprising a bottom heat insulating material, The bottom heat insulating material and the heat shield are spaced apart by a gap. The ingot lifting device according to claim 1.

16. A method of manufacturing an ingot in an ingot lifting device including a crucible having a floor and side walls extending from the floor, a side heater disposed radially outward of the crucible side walls, and a heat shield disposed directly below the side heater, the method comprising: Forming a silicon melt in the crucible when the crucible is in the lowest position, wherein the side heater is completely above the floor of the crucible when the crucible is in the lowest position. Bringing the melt into contact with a seed crystal. Removing an ingot from the silicon melt. Raising the crucible as the ingot is removed from the silicon melt, and the crucible is in the terminal position when the ingot is separated from the melt, wherein the side heater is disposed radially outward of the crucible side walls as the crucible moves from the lowest position to the terminal position. A method comprising.

17. The heat shield is disposed directly below the side heater. The method according to claim 16. **Claim 18** At least a part of the heat shield is above the bottom of the crucible when the crucible is in the lowest position. The method according to claim 16. **Claim 19** At least a part of the heat shield is below at least a part of the floor of the crucible when the crucible is in the lowest position. The method according to claim 16. **Claim 20** The heat shield is completely below the floor of the crucible when the crucible rises to the end position. The method according to claim 16. **Claim 21** The length of the side heater is 350 mm or less. The method according to claim 16. **Claim 22** The ingot lifting device is provided with a bottom heat insulating material. The bottom heat insulating material and the heat shield are separated by a gap. The method according to claim 16.

Images