Single crystal manufacturing apparatus and method of use thereof

Abstract

Disclosed herein is an apparatus for producing a single crystal, comprising a furnace, a growth chamber, a pull rod, and a conduit. The furnace includes a furnace wall, a furnace base plate, and a furnace cover. The furnace wall is positioned between the furnace base plate and the furnace cover. The growth chamber includes an outer cylinder, a growth chamber bottom plate, and a growth chamber top plate. The furnace cover has an opening through which the growth chamber protrudes. The growth chamber functions to house a crucible containing a molten material for producing a single crystal. The pull rod comes into contact with the molten material to generate a crystal boule. The conduit is arranged between the furnace wall and the outer cylinder of the growth chamber, and functions to deliver an inert gas through the furnace, heat the inert gas, and supply the heated inert gas into the growth chamber.

Description

Technical Field

[0001] Disclosed herein are an apparatus for manufacturing a single crystal and a method of using the same. In particular, the present disclosure relates to an apparatus for reusing heat generated in a furnace during the production of a single crystal.

Background Art

[0002] When producing a crystal boule in a furnace, the crucible is heated by induction heating using an induction coil disposed outside a quartz tube (magnetic field temperature device). During this process, the raw material in powder form is placed in the crucible and melted in a processing atmosphere (typically an inert gas) to prevent oxidation during the growth and cooling stages.

[0003] FIG. 1 shows a prior art method of introducing an inert gas into apparatus 100 to reduce the possibility of oxidation of the crystal boule. Apparatus 100 includes a furnace 102 including cooling pipes 103 piped in the wall. By using a fluid flowing through the cooling pipes 103, the furnace can be cooled and the temperature inside the furnace can be controlled. The furnace 102 is attached to a base plate 104 and has a furnace cover 106 disposed at an end opposite to the base plate 104. Inside the furnace, a growth chamber 108 in which a crucible 110 is placed is disposed. The growth chamber 108 protrudes from an opening of the furnace cover 106. The crucible 100 contains a melt 112 obtained from the molten raw material. A pull rod 114 has a seed crystal 116 disposed at its lower end, is immersed in the melt 112, and is slowly pulled up (moved vertically) from the melt while rotating. The vertical and rotational movements of the pull rod are used to generate a crystal boule 118.

[0004] The crystal boule is a single crystal ingot made by generating a larger crystal (ingot) using a seed crystal. This seed crystal is immersed in the molten raw material and slowly withdrawn. The melt grows with a crystal structure on the seed crystal. When the seed crystal is withdrawn, the melt solidifies and finally a large cylindrical crystal boule is generated.

[0005] The growth chamber 108 includes an outer cylinder 107, an inner cylinder 109, a growth chamber bottom plate 128, and a growth chamber top plate 129. The outer cylinder 107 and inner cylinder 109 are positioned between the growth chamber bottom plate 128 and the growth chamber top plate 129. The outer cylinder 107 is typically made from quartz, and the inner cylinder 109 is typically made from zirconia. A packing material 126 is positioned between the growth chamber bottom plate 128 and the crucible 110. This packing material acts as a first porous frit through which a first flow of inert gas can pass, surrounding the crystalline boule and molten material contained in the crucible 110.

[0006] A second porous frit 130, consisting of granules or briquettes of a heat-resistant material, is placed beneath the bottom plate 128 and base plate 104 of the furnace growth chamber. The porous frit 130 can also be passed through with an inert gas.

[0007] The upper plate 129 includes two ports (also called observation windows) 120 through which a second flow of inert gas can be introduced to surround the crystal boule and molten material in the 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 positioned 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 molten material from which crystalline boules are produced.

[0009] The inert atmosphere surrounding the crystal boule 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 boule when it comes into contact with an atmosphere at a temperature significantly different from that of the crucible or boule. The use of a separate heater to heat the processing gas is expensive. While it is desirable to prevent crack formation, it is also desirable to produce single crystals in a cost-effective manner. [Overview of the project]

[0010] Disclosed here is an apparatus for producing a single crystal, comprising a furnace, a growth chamber, a pull rod, and a conduit. The furnace comprises a furnace wall, a furnace base plate, and a furnace cover, the furnace wall being positioned between the furnace base plate and the furnace cover. The growth chamber comprises an outer cylinder, a growth chamber bottom plate, and a growth chamber top plate, the furnace cover having an opening through which the growth chamber protrudes, and the growth chamber functions to house a crucible for containing a molten material for producing a single crystal. A pull rod, which contacts the molten material to produce a crystal boule, contacts the molten material via a seed crystal through an opening in the furnace cover and an opening in the growth chamber top plate. A conduit is positioned between the furnace wall and the outer cylinder of the growth chamber and functions to transport an inert gas through the furnace, heating the inert gas and introducing the heated inert gas into the growth chamber.

[0011] A method for producing a single crystal is also disclosed here. The method includes placing a crucible into a growth chamber, the crucible containing powder for producing a single crystal, the growth chamber comprising an outer cylinder, a growth chamber bottom plate, and a growth chamber top plate, the growth chamber top plate comprising an opening, placing the growth chamber into a furnace, the furnace being heated to melt the powder to produce a single crystal molten material, bringing the single crystal species attached to a pull rod into contact with the molten material, pulling the pull rod out of the molten material to produce a crystal boule, introducing an inert gas into a conduit located inside the furnace, the conduit being located between the furnace wall and the outer cylinder of the growth chamber, heating the inert gas as it passes through the conduit, and releasing the heated inert gas into the growth chamber to bring it into contact with the crystal boule. [Brief explanation of the drawing]

[0012] [Figure 1] A diagram showing prior art for a furnace and growth chamber used to grow crystals. [Figure 2] A schematic diagram illustrating an example of a furnace that uses recycled heat to heat an inert gas. [Figure 3A] A schematic diagram of one embodiment of a conduit that can be placed inside a furnace to heat an inert gas. [Figure 3B]A schematic diagram of another embodiment of a conduit that can be placed inside a furnace to heat an inert gas. [Modes for carrying out the invention]

[0013] Disclosed here is an apparatus used to generate and grow single crystals using an inert gas that utilizes recycled heat (to promote uniform crystal growth). This apparatus uses the heat generated in the furnace to heat the inert gas that comes into contact with the crystal boule. In one embodiment, the inert gas is heated using the heat generated by an induction coil during the heating and production of the crystal boule.

[0014] This document 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 reuses some of the heat generated by the induction coils in the furnace, resulting in cost savings. It also avoids the need for an external heater to heat the inert gas, thereby saving space and reducing the size of the apparatus.

[0015] Figure 2 shows an apparatus 1000 that can be used to grow a single crystal. The apparatus 1000 includes a furnace 1102 which includes cooling tubes 1103 arranged in its wall 1105 (hereinafter referred to as the furnace wall 1105). Although Figure 2 shows the cooling tubes inside the wall, the cooling tubes can also be arranged on the outer surface of the furnace wall 1105. The furnace can be cooled and the temperature inside the furnace can be controlled using the fluid flowing through the cooling tubes 1103. The furnace 1102 has a furnace cover 1106 mounted on a base plate 1104 and positioned on the end of the furnace wall 1105 opposite to the base plate 1104. Inside the furnace is a growth chamber 1108 which contains a crucible 1110. The growth chamber 1108 protrudes from an opening in the furnace cover 1106. The crucible 1100 contains a molten material 1112 obtained from the molten raw material used to produce a crystal boule. The pull rod 1114 has a seed crystal 1116 attached to its lower end and, after being immersed in the molten material 1112, is slowly pulled out of the molten material while rotating (moving vertically). The vertical and rotational motion of the pull rod is used to generate the crystal boule 1118. The pull rod 1114 is connected to a controller (not shown) and a motor (not shown), which may be used to drive the pull rod away from the molten material (pulling the pull rod out of the molten material) while rotating the pull rod or causing a reciprocating rotational motion.

[0016] A crystalline boule is a single-crystal ingot produced by generating a larger crystal (ingot) using a seed crystal. This seed crystal is immersed in molten material and slowly withdrawn. The molten material grows on the seed crystal with a crystalline structure. Once the seed crystal is withdrawn, the molten material solidifies, ultimately producing a large cylindrical crystalline boule.

[0017] The growth chamber 1108 includes an outer cylinder 1107, an inner cylinder 1109, a growth chamber bottom plate 1128, and a growth chamber top plate 1129. The outer cylinder 1107 and the inner cylinder 1109 are positioned between the growth chamber bottom plate 1128 and the growth chamber top plate 1129. The outer cylinder 1107 is typically made from quartz, and the inner cylinder 1109 is typically made from zirconia. A packing material 1126 is positioned between the growth chamber bottom plate 1128 and the crucible 1110. The packing material acts as a first porous frit through which a flow of heated inert gas can proceed to surround the crystalline boule and molten material contained within the crucible 1110.

[0018] A second porous frit 1130 containing granules or briquettes of heat-resistant material is placed beneath the bottom plate 1128 and base plate 1104 of the furnace growth chamber. The second porous frit 1130 can also be passed through with an inert gas.

[0019] The upper plate 1129 includes two ports (also called observation windows) 1120 through which a second flow of inert gas can be introduced to surround the crystal boule and molten material in the crucible 1110. The ports 1120 may include lenses (not shown) through which the activity in the growth chamber 1108 can be viewed and observed.

[0020] 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, generating the molten material used to produce crystalline boules. The heat generated in this manufacturing process is generally not reused and is lost in most cases.

[0021] In one embodiment, the heat generated in the furnace is used to heat an inert gas that surrounds and covers the growing crystal boules in the manufacturing process, protecting them from any potential oxidizing components. Contacting the heated inert gas prevents the formation of cracks within the growing crystal boules due to thermal shock. Reusing the heat generated in the furnace during crystal growth is environmentally friendly as it reduces heat loss during processing. Furthermore, it eliminates the need for external heaters, reducing costs and space requirements. The inert gas may include nitrogen, helium, neon, argon, krypton, xenon, radon, or combinations thereof. Nitrogen is a preferred inert gas.

[0022] In one embodiment, referring to Figure 2, the apparatus 1000 includes an inert gas inlet port 2002 located on a base plate 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 on the furnace 1102. For example, it can be located on the top of the furnace (not shown) or on the furnace wall 1105 (not shown). In one embodiment, the inert gas inlet port 2002 may preferably be located on the base plate 1104 or on the furnace cover 1106.

[0023] The inert gas inlet port 2002 is in fluid communication with a conduit 2004 arranged in a continuous helical configuration on the inner surface of the furnace wall 1105. This conduit is positioned between the furnace wall 1105 and the outer cylinder 1107 of the growth chamber. The conduit may be manufactured from a material capable of withstanding the temperatures used in the furnace 1102. Exemplary materials include copper, copper alloys, steel, or other iron-based alloys. The length of the conduit arranged in the helical configuration should preferably be sufficient to accommodate the temperature change of the inert gas from the supply temperature (generally room temperature (23°C)) to at least the melting temperature of the crystalline boule (typically 2200°C for lutetium orthosilicate (LSO's) or lutetium orthosilicate (LYSO's), and 1850°C for gadolinium gallium gallette (GGG's)).

[0024] The conduit 2004 has one or more outlet points for the heated inert gas. These are shown within the square section 2010. In section 2010, the conduit 2004 is divided into one or more additional conduits that transport the heated inert gas to the growth chamber to cover the growing crystal boule. Referring again to FIG. 2, the conduit 2004 branches into two additional conduits 2006, 2008 that each go in an opposite direction. The additional conduit 2006 goes towards the top of the furnace and the additional conduit 2008 goes towards the bottom of the furnace. An optional two-way valve (not shown) can be used to transport the heated inert gas to either the additional conduit 2006 or the additional conduit 2008. The additional conduit 2006 is in communication with the conduit 2004 and the observation window 1120. The heated inert gas traveling through the additional conduit 2006 goes into the observation window 1120 and enters the growth chamber where it covers the crystal boule 1118 and prevents oxidation and cracking.

[0025] The additional conduit 2008 goes downward to the bottom of the furnace 1102 where it contacts the second porous frit and discharges the heated inert gas to the bottom of the crucible. The heated inert gas passes through the second porous frit and travels upward around the crucible, enveloping the crystal boule 1118 and preventing oxidation and cracking. As described above, the heated inert gas can be transported in one direction (through the additional conduit 2006 or through the additional conduit 2008) or in two or more directions (through the additional conduit 2006 and the additional conduit 2008 simultaneously).

[0026] The conduit 2004 is shown in FIG. 2 as being helically woven within the furnace, but other configurations and designs may be used for the conduit. FIGS. 3A and 3B show other possible weavings that can be used to heat the inert gas. FIGS. 3A and 3B show only the furnace wall 1105 (of the furnace 1102 in FIG. 2) and the configuration of the conduit 2004 used to transport the inert gas through the furnace. The growth chamber and its attachment to the chamber are not shown in FIGS. 3A and 3B.

[0027] Figure 3A includes side and top views showing an alternative configuration of the inert gas supply conduit 2004. This conduit is configured to have alternating "U" sections and "inverted U" sections connected by vertical straight conduits. As seen in the enlarged side view of area A-A' in Figure 3A, the conduit is organized to meander vertically along the furnace wall, with the vertical sections connected by U-shaped and inverted U-shaped sections.

[0028] Figure 3B shows side and top views of another configuration of the conduit 2004 for supplying inert gas. In Figure 3B, this conduit is configured in a spiral shape (see side view), but may include inward and outward "U" sections connected by straight sections (see top view). This conduit is positioned so as not to obstruct the inlet and outlet of the growth chamber.

[0029] In one method for growing a crystalline boule according to one embodiment, an inert gas is transported from an inlet port 2002 through a conduit 2004 (located inside the furnace between the furnace wall and the growth chamber). The inert gas is heated as it travels through this conduit and released into the growth chamber above the molten material in the crucible. The gas is preheated in the furnace as it travels through the conduit and released above the crucible in the growth chamber. The gas enters the growth chamber from above and moves downward, surrounding the growing crystalline boule and the molten material (in the crucible), thus preventing the boule and molten material from being subjected to thermal shock or thermal oxidation. The inert gas is heated to a temperature between the temperature of the boule and the temperature of the furnace.

[0030] In another embodiment of a method for growing a crystalline boule, a heated inert gas is introduced into the growth chamber from second and first porous frits located at the bottom of the growth chamber. This inert gas initially moves upward and then around the crucible, surrounding the growing crystalline boule and the molten material in the crucible. In yet another embodiment, the heated inert gas moves simultaneously up and down within the growth chamber, coming into contact with the crystalline boule and the molten material, thus preventing oxidation and crack formation.

[0031] This method is beneficial because it reuses the heat generated in the furnace during the crystal growth process, thus reducing waste heat. It improves the cost structure for manufacturing scintillators for processes such as positron emission tomography. It improves usable space by avoiding the use of external heaters (outside the furnace).

[0032] The apparatus disclosed herein is useful for producing single crystals from lutetium orthosilicate, lutetium yttrium orthosilicate, gadolinium gallium garnet, gadolinium aluminum gallium garnet, or combinations thereof.

[0033] While the present invention has been described with reference to several embodiments, it will be understood by those ordinary in the art that various modifications can be made without departing from the scope of the invention, and that equivalents can be used instead of each element. In addition, many modifications can be made without departing from the essential scope of the invention to adapt specific situations or materials to the implications of the invention. Thus, the present invention is not limited to the specific embodiments disclosed as the best mode intended to carry out the invention, but is intended to include all embodiments within the claims.

Claims

1. A single crystal manufacturing apparatus comprising a furnace, a growth chamber, a pull rod, and a conduit, The furnace includes a furnace wall, a furnace base plate, and a furnace cover. The furnace wall is positioned between the furnace base plate and the furnace cover. The growth chamber includes an outer cylinder, a growth chamber bottom plate, and a growth chamber top plate. The furnace cover has an opening that allows the growth chamber to protrude, The growth chamber functions to house a crucible for holding the molten material for producing single crystals. The pull rod comes into contact with the molten material to produce a crystalline boule, The pull rod, which has a seed crystal, passes through the opening in the furnace cover and then through the opening in the upper plate of the growth chamber and comes into contact with the molten material. The conduit is positioned between the furnace wall and the outer cylinder of the growth chamber. A single crystal manufacturing apparatus, wherein the conduit functions to transport an inert gas through the furnace, heat the inert gas, and introduce the heated inert gas into the growth chamber.

2. The inlet port for the inert gas further includes, The single crystal manufacturing apparatus according to claim 1, wherein the inlet port is in fluid communication with the conduit.

3. The conduit is in fluid communication with an observation window provided on the upper plate of the growth chamber. The single crystal manufacturing apparatus according to claim 1, wherein the heated inert gas is released into the growth chamber through the opening of the observation window and surrounds the molten material.

4. The conduit is in fluid communication with the porous frit located at the bottom of the growth chamber. The single crystal manufacturing apparatus according to claim 1, wherein the heated inert gas is released into the growth chamber through the porous frit to surround the molten material.

5. The conduit is in fluid communication with both the observation window provided on the upper plate of the growth chamber and the porous frit located at the bottom of the growth chamber. The single crystal manufacturing apparatus according to claim 1, wherein the heated inert gas is released into the growth chamber from both the observation window and the porous frit to surround the molten material.

6. The single crystal manufacturing apparatus according to claim 1, wherein the pull rod contacts the molten material through the seed crystal.

7. The single crystal manufacturing apparatus according to claim 1, wherein the conduit is configured in the form of a coil that is spirally arranged along the furnace wall.

8. The single crystal manufacturing apparatus according to claim 1, wherein the conduit is routed along the furnace wall and includes vertically linear sections connected by alternating U-shaped sections and inverted U-shaped sections.

9. The single crystal manufacturing apparatus according to claim 1, wherein the conduit is routed along the furnace wall and includes lateral straight sections connected by U-shaped sections.

10. The conduit includes a valve, The single crystal manufacturing apparatus according to claim 1, wherein the valve directs the heated inert gas toward an observation window located on the upper plate of the growth chamber or a porous frit located at the bottom of the growth chamber.

11. The single crystal manufacturing apparatus according to claim 1, wherein the conduit is made of copper or stainless steel.

12. The single crystal manufacturing apparatus according to claim 1, wherein the inert gas consists of nitrogen, helium, argon, neon, xenon, krypton, radon, or a combination thereof.

13. The single crystal manufacturing apparatus according to claim 1, wherein the inert gas is nitrogen.

14. The single crystal manufacturing apparatus according to claim 1, wherein the molten material consists of lutetium orthosilicate, lutetium yttrium orthosilicate, gadolinium gallium garnet, or gadolinium aluminum gallium garnet.

15. The single crystal manufacturing apparatus according to claim 1, wherein the molten material consists of lutetium orthosilicate.

16. A method for producing single crystals, Place the crucible inside the growth chamber. The crucible contains powder for manufacturing single crystals, The growth chamber includes an outer cylinder, a growth chamber bottom plate, and a growth chamber top plate. The upper plate of the growth chamber includes an opening, The growth chamber is placed inside the furnace. The furnace is heated to melt the powder and produce a single-crystal molten material. Bringing the single crystal species attached to the pull rod into contact with the molten material, The pull rod is used to pull out the molten material and generate a crystalline boule. Introducing an inert gas into a conduit located inside the furnace, The conduit is located between the furnace wall and the outer cylinder of the growth chamber. Heating the inert gas as it passes through the conduit, A method comprising releasing the heated inert gas into the growth chamber and bringing it into contact with the crystal boule.

17. The method according to claim 16, wherein the inert gas is released from an observation window on the upper plate of the growth chamber and moves downward to surround the crystal boule.

18. The method according to claim 16, wherein the inert gas is released through porous frit at the bottom of the growth chamber, travels upward and around the crucible, and surrounds the crystalline boule.

19. The method according to claim 16, wherein the inert gas is released from an opening in an observation window on the upper plate of the growth chamber and through porous frit at the bottom of the growth chamber, surrounding the crystal boule.

20. The method according to claim 16, wherein the single crystal is made of lutetium orthosilicate, lutetium yttrium orthosilicate, gadolinium gallium garnet, or gadolinium aluminum gallium garnet.

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