Apparatus for manufacturing single crystals and method of using same

Abstract

Disclosed herein is an apparatus for producing a single crystal, the apparatus comprising: a furnace wherein the furnace comprises a furnace wall, a furnace substrate, and a furnace lid; the furnace wall is arranged between the furnace base plate and the furnace cover; the growth chamber comprises an outer pipe, a growth chamber bottom plate and a growth chamber top plate; wherein the furnace lid has an opening through which the growth chamber protrudes, and wherein the growth chamber operates to contain a crucible containing a melt for producing a single crystal; a pull rod contacting the melt to produce an ingot; and a conduit disposed between the furnace wall and the outer tube of the growth chamber; wherein the conduit is operative to transport an inert gas through the furnace to heat the inert gas and deposit the heated inert gas into the growth chamber.

Description

Technical Field

[0001] This disclosure relates to an apparatus for manufacturing single crystals and a method of using the same. In particular, this disclosure relates to an apparatus for recovering heat generated in a furnace during the manufacturing of single crystals. Background Technology

[0002] During the fabrication of a crystal boule in a furnace, an induction coil located outside a quartz tube (field temperature device) heats the crucible via induction heating. During this process, the raw material, in powder form, is located in the crucible and melts in a process atmosphere (typically an inert gas) to prevent oxidation during the growth and cooling stages.

[0003] Figure 1 A prior art method is described in which an inert gas is introduced into apparatus 100 to reduce the possibility of oxidation of crystalline boules. Apparatus 100 includes a furnace 102 containing cooling pipes 103 disposed in its walls. Fluid flowing through the cooling pipes 103 can be used to cool the furnace and control the temperature within the furnace. The furnace 102 is mounted on a substrate 104 and has a furnace cover 106 disposed at one end opposite to the substrate 104. A growth chamber 108 is disposed in the furnace, in which a crucible 110 is disposed. The growth chamber 108 protrudes through an opening in the furnace cover 106. The crucible 100 contains a melt 112 obtained from molten raw materials. A pull rod 114 having a seed crystal 116 disposed at its lower end is immersed in the melt 112 and then slowly removed from the melt (moving vertically) while undergoing a rotational motion. The vertical and rotational motion of the pull rod is used to produce a crystalline boule 118.

[0004] A crystal ingot is a single-crystal ingot produced by using a seed crystal to create a larger crystal or ingot. The seed crystal is immersed in molten raw material and slowly removed. The melt grows crystalline on the seed crystal. As the seed crystal is removed, the melt solidifies and eventually produces a large cylindrical crystal ingot.

[0005] Growth chamber 108 includes an outer tube 107, an inner tube 109, a growth chamber bottom plate 128, and a growth chamber top plate 129. The outer tube 107 and inner tube 109 are disposed between the growth chamber bottom plate 128 and the growth chamber top plate 129. The outer tube 107 is typically made of quartz, while the inner tube 109 is typically made of zirconium oxide. A packing 126 is disposed between the growth chamber bottom plate 128 and the crucible 110. The packing serves as a first porous molten ingot through which a first inert gas flow can travel to surround the ingot and the melt contained in the crucible 110.

[0006] Located beneath the bottom plate 128 of the growth chamber and the base plate 104 of the furnace is a second porous frit 130 comprising particles or clumps of heat-resistant material. The porous frit 130 also allows inert gases to pass through it.

[0007] The upper plate 129 includes two ports (also called eyepieces) 120 through which a second inert gas flow can be introduced to surround the melt in the ingot and crucible 110. The ports 120 may include lenses (not shown) through which the activity in the growth chamber 108 can be observed.

[0008] An induction coil 124 is disposed between the furnace 102 and the growth chamber 108. The induction coil 124 is used to heat the crucible and its contents to generate a melt for manufacturing ingots.

[0009] The inert atmosphere surrounding the ingot is heated in a separate external heater (not shown) before entering the quartz tube. This is done to minimize the thermal gradient experienced by the ingot when it comes into contact with an atmosphere at a temperature drastically different from that of the crucible or ingot. Using a separate heater to heat the process gas is expensive. While preventing cracking is desirable, it is also desirable to produce single crystals in a cost-effective manner. Summary of the Invention

[0010] This document discloses an apparatus for producing single crystals, comprising: a furnace, wherein the furnace includes a furnace wall, a furnace substrate, and a furnace cover; the furnace wall is disposed between the furnace substrate and the furnace cover; a growth chamber, comprising an outer tube, a growth chamber bottom plate, and a growth chamber top plate; wherein the furnace cover has an opening through which the growth chamber protrudes, and wherein the growth chamber is operable to contain a crucible containing a melt for producing single crystals; a pull rod that contacts the melt to produce an ingot; wherein the pull rod contacts the melt via a seed crystal through an opening in the furnace cover and through an opening in the growth chamber top plate; and a conduit disposed between the furnace wall and the outer tube of the growth chamber; wherein the conduit is operable to transport inert gas through the furnace to heat the inert gas and deposit the heated inert gas into the growth chamber.

[0011] This paper also discloses a method for producing single crystals, the method comprising: placing a crucible in a growth chamber; wherein the crucible contains powder for producing single crystals; wherein the growth chamber includes an outer tube, a growth chamber bottom plate, and a growth chamber top plate; wherein the growth chamber top plate includes an opening; placing the growth chamber in a furnace; wherein the furnace is heated to melt the powder, thereby producing a single crystal melt; contacting the melt with a single crystal seed crystal of a contact pull rod; removing the pull rod from the melt to produce an ingot; introducing an inert gas into a conduit located in the furnace; wherein the conduit is located between the furnace wall and the outer tube of the growth chamber; heating the inert gas as it travels through the conduit; and discharging the heated inert gas into the growth chamber to contact the ingot. Attached Figure Description

[0012] Figure 1 It is a depiction of existing furnaces and growth chambers used for crystal growth.

[0013] Figure 2 This is a schematic depiction of an exemplary furnace that uses the recovered heat to heat an inert gas; Figure 3A A schematic depiction of one embodiment of a conduit that can be deployed in a furnace to heat an inert gas; and Figure 3B This is another schematic depiction of an embodiment of a conduit that can be deployed in a furnace to heat an inert gas. Detailed Implementation

[0014] This document discloses an apparatus for producing and growing single crystals while using an inert gas (to promote uniform crystal growth) that utilizes recovered heat. The apparatus uses heat generated in a furnace to heat the inert gas in contact with the crystal ingot. In an embodiment, during the heating and production of the crystal ingot, heat generated by an induction coil is used to heat the inert gas.

[0015] This paper also discloses a method for heating an inert gas using heat already present in the furnace to provide a heated inert atmosphere for single crystal growth. This method of heating the inert gas recovers some of the heat generated by the induction coils in the furnace and results in cost savings. It also avoids the potential use of an external heater to heat the inert gas, thus saving space and reducing equipment size.

[0016] Figure 2 An apparatus 1000 for growing single crystals is depicted. The apparatus 1000 includes a furnace 1102, which contains cooling pipes 1103 disposed in its wall 1105 (hereinafter referred to as furnace wall 1105). Although Figure 2The furnace includes cooling pipes located on the inner side of the wall, but cooling pipes can also be placed on the outer surface of the wall 1105. The fluid flowing through the cooling pipes 1103 can be used to cool the furnace and control the temperature within the furnace. The furnace 1102 is mounted on a substrate 1104 and has a furnace cover 1106 disposed on the end of the furnace wall 1105 opposite to the substrate 1104. A growth chamber 1108 is disposed in the furnace, in which a crucible 1110 is disposed. The growth chamber 1108 protrudes through an opening in the furnace cover 1106. The crucible 1100 contains a melt 1112 obtained from molten raw materials used to produce crystal ingots. A pull rod 1114 having a seed crystal 1116 disposed at its lower end is immersed in the melt 1112 and then slowly removed from the melt (moving vertically) while undergoing a rotational motion. The vertical and rotational motion of the pull rod is used to produce an ingot 1118. The pull rod 1114 is connected to a controller (not shown) and a motor (not shown), which can be used to drive the pull rod away from the melt (removing the pull rod from the melt) while simultaneously rotating the pull rod or facilitating a back-and-forth rotational motion.

[0017] A crystal ingot is a monocrystalline ingot produced by using a seed crystal to create a larger crystal or ingot. The seed crystal is immersed in molten raw material and slowly removed. The melt grows crystalline on the seed crystal. As the seed crystal is removed, the melt solidifies and eventually produces a large cylindrical crystal ingot.

[0018] Growth chamber 1108 includes an outer tube 1107, an inner tube 1109, a growth chamber bottom plate 1128, and a growth chamber top plate 1129. The outer tube 1107 and inner tube 1109 are disposed between the growth chamber bottom plate 1128 and the growth chamber top plate 1129. The outer tube 1107 is typically made of quartz, while the inner tube 1109 is typically made of zirconium oxide. A packing 1126 is disposed between the growth chamber bottom plate 1128 and the crucible 1110. The packing serves as a first porous molten ingot through which a heated inert gas flow can travel to surround the ingot and the melt contained in the crucible 1110.

[0019] Located beneath the bottom plate 1128 of the growth chamber and the base plate 1104 of the furnace is a second porous frit 1130 comprising particles or clumps of heat-resistant material. The second porous frit 1130 also allows inert gas to pass through it.

[0020] The upper plate 1129 includes two ports (also called eyepieces) 1120 through which a second inert gas flow is introduced to surround the melt in the ingot and crucible 1110. The ports 1120 may include lenses (not shown) through which the activity in the growth chamber 1108 can be observed.

[0021] An induction coil 1124 is positioned between the furnace 1102 and the growth chamber 1108. The induction coil 1124 is used to heat the crucible and its contents to generate a melt for manufacturing the ingot. The heat generated during the manufacturing process is typically not recovered and is often lost.

[0022] In this embodiment, the heat generated in the furnace is used to heat an inert gas that surrounds and covers the grown ingot to protect it from any potential oxidation during the manufacturing process. Contacting the grown ingot with the heated inert gas prevents cracking within the ingot due to thermal shock. Recovering the heat generated in the furnace during crystal growth is environmentally friendly because it reduces heat loss during the process. It also reduces costs and space utilization by eliminating the need to purchase and use external heaters. The inert gas may include nitrogen, helium, neon, argon, krypton, xenon, radon, or combinations thereof. Nitrogen is a preferred inert gas.

[0023] In the embodiment, reference Figure 2 The apparatus 1000 includes an inert gas inlet port 2002 located in a substrate 1104 at the bottom of the furnace 1102. The inert gas inlet port 2002 does not need to be located at the bottom of the furnace 1102, but can be located at any point in the furnace 1102. For example, it can be located at the top of the furnace (not shown) or at the furnace wall 1105 (not shown). In embodiments, the inert gas inlet port 2002 may preferably be located in the substrate 1104 or at the furnace cover 1106.

[0024] The inert gas inlet port 2002 is in fluid communication with a series of spirally arranged conduits 2004 located on the inner surface of the furnace wall 1105. These conduits are located between the furnace wall 1105 and the outer tube 1107 of the growth chamber. These conduits may be made of a material capable of withstanding the temperatures utilized in the furnace 1102. Exemplary materials are copper, copper alloys, steel, or other iron-based alloys. The length of the conduits deployed in a spiral arrangement should be sufficient to accommodate temperature variations of the inert gas from the supply temperature (which is typically room temperature (23°C)) to at least the melting temperature of the ingot (typically 2200°C for lutetium silicate (LSO) or yttrium lutetium silicate (LYSO), or typically 1850°C for gadolinium gallium garnet (GGG)).

[0025] Conduit 2004 has one or more outlet points for the heated inert gas. These are shown in square section 2010. In section 2010, conduit 2004 branches into one or more additional conduits that transport the heated inert gas to the growth chamber to shroud the grown ingot. Now refer again Figure 2The conduit 2004 branches into two auxiliary conduits 2006 and 2008, each traveling in opposite directions. Conduit 2006 travels to the top of the furnace, while the other conduit travels to the bottom. An optional two-way valve (not shown) may be used to allow heated inert gas to be delivered to either conduit 2006 or 2008. Conduit 2006 communicates with conduit 2004 and eyepiece 1120. The heated inert gas traveling through conduit 2006 travels to eyepiece 1120 and enters the growth chamber, where the heated inert gas envelops the ingot 1118 to prevent oxidation and cracking.

[0026] The conduit 2008 travels downwards to the bottom of the furnace 1102, where it contacts the second porous molten ingot and discharges the heated inert gas to the bottom of the crucible. The heated inert gas travels upwards through the first porous molten ingot, surrounds the crucible, and envelops the ingot 1118 to prevent oxidation and cracking. As described above, the heated inert gas can be transported in a single direction (through conduit 2006 or through conduit 2008) or in more than one direction (through both conduits 2006 and 2008 simultaneously).

[0027] Although the catheter was in 2004 Figure 2 The ducts are depicted as being arranged in a spiral within the furnace, but other configurations and designs of the ducts may be used. Figures 3A-3B Other possible arrangements that can be used to heat inert gases are described. Figure 3A and Figure 3B Only described ( Figure 2 The furnace wall 1105 and the duct 2004 for conveying inert gas through the furnace are arranged in the furnace 1102. Figure 3A and Figure 3B The growth chamber and its attachments are not shown.

[0028] Figure 3A Side and top views depict an alternative arrangement of a conduit 2004 for transporting inert gases, wherein the conduit is arranged with alternating "U"-shaped and "inverted U"-shaped sections connected by vertically aligned conduits. Figure 3A As seen in the extended side view of section AA', the ducts are arranged to run up and down along the furnace wall, with the vertical sections connected by U-shaped sections and inverted U-shaped sections.

[0029] Figure 3B Side and top views depict an alternative arrangement of the duct 2004 for transporting inert gases. Figure 3B In the middle, the conduits are arranged in a spiral pattern (see side view), except that the conduits may include inward-facing and outward-facing "U"-shaped sections connected by linear portions (see top view). The conduits are arranged in such a way that they do not interfere with the entry and exit of the growth chamber.

[0030] In one embodiment, in a method of growing a crystal ingot, an inert gas can be conveyed from an inlet port 2002 through a conduit 2004 (located in the furnace between the furnace wall and the growth chamber). The inert gas is heated during its journey through the conduit and released over the melt in the crucible within the growth chamber. The gas is preheated in the furnace as it travels through the conduit and then released over the crucible within the growth chamber. The gas enters the growth chamber from the top and travels downwards to surround the growing crystal ingot and the melt (contained in the crucible), thus preventing the ingot and melt from undergoing thermal shock or oxidation. The inert gas is heated to a temperature between the temperature of the ingot and the temperature of the furnace.

[0031] In another embodiment, in a different method of growing a crystal ingot, heated inert gas may be introduced into the growth chamber from a second porous molten core and a first porous molten core located at the bottom of the growth chamber. The inert gas initially travels upward and then around the crucible, surrounding the grown ingot and the melt within the crucible. In yet another embodiment, the heated inert gas travels both upward and downward in the growth chamber simultaneously, contacting both the ingot and the melt, thus preventing oxidation and cracking.

[0032] This method is advantageous because it recovers the heat generated in the furnace during the crystal growth process. Therefore, it reduces waste heat. This method improves the cost structure for producing scintillators used in processes such as positron emission tomography. Furthermore, it improves space utilization by eliminating the need for external heaters (located outside the furnace).

[0033] The apparatus disclosed herein can be advantageously used to produce single crystals from lutetium silicate, yttrium lutetium silicate, gadolinium gallium garnet, gadolinium aluminum gallium garnet, and combinations thereof.

[0034] While the invention has been described with reference to some embodiments, those skilled in the art will understand that various changes can be made without departing from the scope of the invention and that equivalents can be substituted for its elements. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of the invention without departing from its basic scope. Therefore, the invention is not intended to be limited to the specific embodiments disclosed as the best mode contemplated for carrying out the invention, but rather the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. An apparatus for producing single crystals, the apparatus comprising: A furnace, wherein the furnace includes a furnace wall, a furnace base plate, and a furnace cover; the furnace wall is disposed between the furnace base plate and the furnace cover; A growth chamber includes an outer tube, a growth chamber bottom plate, and a growth chamber top plate; wherein the furnace cover has an opening, the growth chamber protrudes through the opening, and wherein the growth chamber is operable to contain a crucible containing melt for manufacturing the single crystal; A pull rod that contacts the melt to produce an ingot; wherein the pull rod contacts the melt via a seed crystal through an opening in the furnace cover and through an opening in the top plate of the growth chamber. as well as A conduit is disposed between the furnace wall and the outer tube of the growth chamber; wherein the conduit operates to transport inert gas through the furnace to heat the inert gas and deposit the heated inert gas into the growth chamber.

2. The apparatus of claim 1, further comprising an inlet port for the inert gas, wherein the inlet port is in fluid communication with the conduit.

3. The apparatus of claim 1, wherein the conduit is in fluid communication with an eyepiece located in the top plate of the growth chamber, and wherein the heated inert gas is discharged into the growth chamber through the eyepiece opening to envelop the melt.

4. The apparatus of claim 1, wherein the conduit is in fluid communication with a porous molten metal located at the bottom of the growth chamber, and wherein the heated inert gas is discharged into the growth chamber through the porous molten metal to envelop the melt.

5. The apparatus of claim 1, wherein the conduit is in fluid communication with both an eyepiece located in the top plate of the growth chamber and a porous molten block located at the bottom of the growth chamber, and wherein the heated inert gas is simultaneously discharged from both the eyepiece and the porous molten block into the growth chamber to envelop the melt.

6. The apparatus of claim 1, wherein the pull rod contacts the melt via a seed crystal.

7. The apparatus of claim 1, wherein the conduit comprises a coil arranged in a spiral manner along the furnace wall.

8. The apparatus of claim 1, wherein the conduit is arranged along the furnace wall and includes a linear vertical section connected by alternating U-shaped sections and inverted U-shaped regions.

9. The apparatus of claim 1, wherein the conduit is arranged along the furnace wall and includes linear horizontal sections connected by U-shaped sections.

10. The apparatus of claim 1, wherein the conduit includes a valve that directs the heated inert gas to an eyepiece located in the top plate of the growth chamber or to a porous fused block located at the bottom of the growth chamber.

11. The device according to claim 1, wherein the conduit comprises copper or stainless steel.

12. The apparatus of claim 1, wherein the inert gas comprises nitrogen, helium, argon, neon, xenon, krypton, radon, or a combination thereof.

13. The apparatus of claim 1, wherein the inert gas is nitrogen.

14. The apparatus of claim 1, wherein the melt comprises lutetium silicate, yttrium lutetium silicate, gadolinium gallium garnet, or gadolinium aluminum gallium garnet.

15. The apparatus of claim 1, wherein the melt comprises lutetium silicate.

16. A method for producing single crystals, the method comprising: The crucible is placed in the growth chamber; The crucible contains powder for manufacturing single crystals; the growth chamber includes an outer tube, a growth chamber bottom plate, and a growth chamber top plate; the growth chamber top plate includes an opening. The growth chamber is placed in a furnace; wherein the furnace is heated to melt the powder, thereby producing a single crystal melt; The melt is brought into contact with the single crystal seed of the contact pull rod; The pull rod is removed from the melt to produce an ingot; An inert gas is introduced into a conduit located in the furnace; wherein the conduit is located between the furnace wall and the outer tube of the growth chamber; The inert gas is heated during its journey through the duct; and The heated inert gas is released into the growth chamber to contact the ingot.

17. The method of claim 16, wherein the inert gas is discharged from an eyepiece located in the top plate of the growth chamber and travels downward to envelop the ingot.

18. The method of claim 16, wherein the inert gas is discharged through a porous molten block located at the bottom of the growth chamber and travels upward and around the crucible to envelop the ingot.

19. The method of claim 16, wherein the inert gas is simultaneously discharged from an eyepiece opening located in the top plate of the growth chamber and through a porous molten block located in the bottom of the growth chamber to envelop the ingot.

20. The method of claim 16, wherein the single crystal comprises lutetium silicate, yttrium lutetium silicate, gadolinium gallium garnet, or gadolinium aluminum gallium garnet.

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