Device for manufacturing single crystals and method of use thereof

Abstract

Disclosed herein is a device for producing a single crystal comprising a furnace, where the furnace comprises a furnace wall, a furnace base plate and a furnace cover; the furnace wall being disposed between the furnace base plate and the furnace cover; a growth chamber comprising an outer tube, a growth chamber bottom plate and a growth chamber top plate; where the furnace cover has an opening through which the growth chamber protrudes and where the growth chamber is operative to contain a crucible that contains a melt for manufacturing the single crystal; a pull rod that contacts the melt to produce a crystal boule; and a conduit disposed between the furnace wall and the outer tube of the growth chamber; where the conduit is operative to transport an inert gas through the furnace to heat the inert gas and to deposit the heated inert gas into the growth chamber.

Description

DEVICE FOR MANUFACTURING SINGLE CRYSTALS AND METHOD OF USETHEREOFBACKGROUND

[0001] This disclosure relates to a device for manufacturing single crystals and method of use thereof. In particular, this disclosure relates to a device that recycles heat generated in the furnace during the manufacture of a single crystals.

[0002] During the manufacturing of the crystal boule in a furnace, the crucible is heated by inductive heating using inductive coils that are located outside the quartz tube (the field temperature device). During this process, the raw materials in powder form are located in the crucible and are melted in a processing atmosphere (typically an inert gas) to prevent oxidation during the growth and cooling stages.

[0003] FIG. 1 depicts a prior art method of introducing an inert gas into a device 100 to reduce the possibility of oxidation of the crystalline boule. The device 100 comprises a furnace 102 that contains cooling tubes 103 disposed in its walls. Fluid flowing through the cooling tubes 103 can be used to cool the furnace and to control temperature in the furnace. The furnace 102 is mounted on a base plate 104 and has a furnace cover 106 disposed on an end opposite the base plate 104. Disposed in the furnace is a growth chamber 108 in which is disposed a crucible 110. The growth chamber 108 protrudes through an opening in the furnace cover 106. The crucible 100 contains a melt 112 that is obtained from melting raw materials. A pull rod 114 having a seed crystal 116 disposed at its lower end is dipped into the melt 112 and then slowly moved away from the melt (moved vertically) while undergoing rotary motion. The vertical and rotary motion of the pull rod is used to produce a crystal boule 118.

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

[0005] The growth chamber 108 contains an outer tube 107, an inner tube 109, a growth chamber bottom plate 128 and a growth chamber upper plate 129. The outer tube 107 and inner tube 109 are disposed between the growth chamber bottom plate 128 andthe growth chamber top plate 129. The outer tube 107 is typically manufactured from quartz, while the inner tube 109 is typically manufactured from zirconia. Disposed between the growth chamber bottom plate 128 and the crucible 110 is a fdler 126. The filler serves as a first porous frit through which a first stream of inert gases may travel to surround the crystal boule and the melt contained in the crucible 110.

[0006] Disposed beneath the growth chamber bottom plate 128 and the base plate 104 of the furnace is a second porous frit 130 that comprises granules or briquettes of a heat resistant material. The porous frit 130 can also permit an inert gas to pass through it.

[0007] The upper plate 129 contain two ports (also termed eyepieces) 120 through which a second stream of inert gases may be introduced to surround the crystal boule and the melt in the crucible 1 10. The ports 120 may contain lenses (not shown) through which the activity in the growth chamber 108 may be viewed.

[0008] Disposed between the furnace 102 and the growth chamber 108 are induction coils 124. The induction coils 124 are used to heat the crucible and its contents and to produce the melt from which the crystal boule is manufactured.

[0009] The inert atmosphere that surrounds the crystal boule is heated in a separate external heater (not shown) prior to entering the quartz tube. This is done to minimize the thermal gradient that the boule experiences upon contacting an atmosphere that is at a vastly different temperature 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 the cracking from occurring, it is also desirable to produce the single crystals in a cost effective manner.SUMMARY

[0010] Disclosed herein is a device for producing a single crystal comprising a furnace, where the furnace comprises a furnace wall, a furnace base plate and a furnace cover; the furnace wall being disposed between the furnace base plate and the furnace cover; a growth chamber comprising an outer tube, a growth chamber bottom plate and a growth chamber top plate; where the furnace cover has an opening through which the growth chamber protrudes and where the growth chamber is operative to contain a crucible that contains a melt for manufacturing the single crystal; a pull rod that contacts the melt to produce a crystal boule; where the pull rod via a seed crystal contacts the meltthrough the opening in the furnace cover and through an opening the growth chamber top plate; and a conduit disposed between the furnace wall and the outer tube of the growth chamber; where the conduit is operative to transport an inert gas through the furnace to heat the inert gas and to deposit the heated inert gas into the growth chamber.

[0011] Disclosed herein too is a method for producing a single crystal comprising disposing the crucible in a growth chamber; where the crucible contains a powder for manufacturing a single crystal; where the growth chamber comprises an outer tube, a growth chamber bottom plate and a growth chamber top plate; where the growth chamber top plate contains an opening; disposing the growth chamber in a furnace; where the furnace is heated to melt the powder to produce a single crystal melt; contacting the melt with a single crystal seed that contacts a pull rod; extracting the pull rod from the melt to produce a crystal boule, introducing an inert gas into a conduit located in the furnace, where the conduit is located between a furnace wall and the outer tube of the growth chamber; heating the inert gas during its travel through the conduit; and discharging the heated inert gas into the growth chamber to contact the crystal boule.BRIEF DESCRIPTION OF THE FIGURES

[0012] FIG. 1 is a depiction of a prior art furnace and growth chamber for growing crystals.

[0013] FIG. 2 is a schematic depiction of an exemplary furnace that uses recycled heat to heat the inert gases;

[0014] FIG. 3A is a schematic depiction of one embodiment of a conduit that can be deployed in a furnace to heat the inert gas, and

[0015] FIG. 3B is another schematic depiction of an embodiment of a conduit that can be deployed in a furnace to heat the inert gas.DETAILED DESCRIPTION

[0016] Disclosed herein is a device that is used to produce and grow single crystals while using an inert gas (to facilitate uniform crystal growth) that uses recycled heat. The device uses heat generated in the furnace to heat inert gases that contact the crystal boule. In an embodiment, the inert gas is heated using heat generated by the induction coils during the heating and production of the crystal boule.

[0017] Disclosed herein too is a method for heating an inert gas using heat already present in the furnace to provide a heated inert atmosphere for the growth of single crystals. This method of heating the inert gas recycles 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 gases thus saving space and reducing equipment size.

[0018] FIG. 2 depicts a device 1000 that can be used for growing single crystals. The device 1000 comprises a furnace 1102 that contains cooling tubes 1103 disposed in its walls 1105 (hereinafter furnace walls 1105). While the FIG. 2 includes the cooling tubes on an inside of the walls, the cooling tubes can be placed on an external surface of the walls 1 105 as well. Fluid flowing through the cooling tubes 1 103 can be used to cool the lurnace and to control temperature in the furnace. The furnace 1102 is mounted on a base plate 1104 and has a furnace cover 1106 disposed on an end of the furnace wall 1105 opposite the base plate 1104. Disposed in the furnace is a growth chamber 1108 in which is disposed a crucible 1110. The growth chamber 1108 protrudes through an opening in the furnace cover 1106. The crucible 1100 contains a melt 1112 that is obtained from melting raw materials used to produce the crystalline boule. A pull rod 1114 having a seed crystal 1116 disposed at its lower end is dipped into the melt 1112 and then slowly moved away from the melt (moved vertically) while undergoing rotary motion. The vertical and rotary motion of the pull rod is used to produce a crystal boule 1118. The pull rod 1114 is in communication with a controller (not shown) and motors (not shown) that may be used to drive the pull rod away from the melt (extracting the pull rod from the melt) while simultaneously rotating it or promoting to- and fro- rotary motion.

[0019] A crystal boule is a single-crystal ingot produced by using a seed crystal to create a larger crystal, or ingot. This seed crystal is dipped into the molten raw material and slowly extracted. The melt grows on the seed crystal in a crystalline fashion. As the seed is extracted, the melt solidifies and eventually a large, cylindrical crystal boule is produced.

[0020] The growth chamber 1 108 contains an outer tube 1 107, an inner tube 1109, a growth chamber bottom plate 1128 and a growth chamber upper plate 1129. The outer tube 1107 and inner tube 1109 are disposed between the growth chamber bottomplate 1 128 and the growth chamber top plate 1 129 The outer tube I 107 is typically manufactured from quartz, while the inner tube 1109 is typically manufactured from zirconia. Disposed between the growth chamber bottom plate 1128 and the crucible 1110 is a filler 1126. The filler serves as a first porous frit through which a stream of heated inert gases may travel to surround the crystal boule and the melt contained in the crucible 1 1 10.

[0021] Disposed beneath the growth chamber bottom plate 1128 and the base plate 1104 of the furnace is a second porous frit 1130 that comprises granules or briquettes of a heat resistant material. The second porous frit 1130 can also permit an inert gas to pass through it.

[0022] The upper plate 1 129 contain two ports (also termed eyepieces) 1 120 through which a second stream of inert gases may be introduced to surround the crystal boule and the melt in the crucible 1110. The ports 1120 may contain lenses (not shown) through which the activity in the growth chamber 1108 may be viewed and observed.

[0023] Disposed between the furnace 1102 and the growth chamber 1108 are induction coils 1124. The induction coils 1124 are used to heat the crucible and its contents and to produce the melt from which the crystal boule is manufactured. The heat generated during the manufacturing process is generally not recycled and is often lost.

[0024] In an embodiment, the heat generated in the furnace is used to heat an inert gas that surrounds and shrouds the growing crystal boule from any potential oxidative moieties during the manufacturing process. Having a heated inert gas contact the growing crystal boule prevents the formation of cracks in the boule due to thermal shock. Recycling the heat generated in the furnace during crystal growth is environmentally friendly because it reduces the heat lost during the process. It also reduces costs and space utilization because the procurement and use of an external heater may be avoided. The inert gas may include nitrogen, helium, neon, argon, krypton, xenon, radon, or a combination thereof. A preferred inert gas is nitrogen.

[0025] In an embodiment, with reference to the FIG. 2, the device 1000 comprises an inert gas entry port 2002 located in the base plate 1104 at the bottom of the furnace 1 102. The inert gas entry port 2002 does not need to be located at the bottom of the furnace 1102 but may be located at any point in the furnace 1102. For example, it may located at the top of the furnace (not shown) or at the furnace wall 1105 (not shown).Tn an embodiment, the inert gas entry port 2002 may be preferably located in the base plate 1104 or at the furnace cover 1106.

[0026] The inert gas entry port 2002 is in fluid communication with a series of helically arranged conduits 2004 located at an inner surface of the furnace wall 1105. The conduits are located between the furnace wall 1105 and the outer tube 1107 of the growth chamber. The conduits may be manufactured from a material that can withstand temperatures utilized in the furnace 1102. Exemplary materials are copper, copper alloys, steel or other iron based alloys. The length of conduit deployed in a helically arranged fashion should be sufficient to accommodate a temperature change in the inert gas from the supply temperature (which is commonly room temperature (23°C)) to at least the melt temperature of the crystal boule (typically 2200°C for lutetium orthosilicates (LSO’s) or lutetium yttrium orthosilicates (LYSO’s) or 1850°C for gadolinium gallium garnets (GGG’s)).

[0027] The conduit 2004 has one or more exit points for the heated inert gas. These are shown in the square section 2010. In the section 2010, the conduit 2004 is split into one or more additional conduits that transport the heated inert gas to the growth chamber to enshroud the growing crystal boule. With reference now again to the FIG. 2, the conduit 2004 is split into two additional conduits 2006 and 2008, each of which travel in opposite directions. Conduit 2006 travels to the top of the furnace, while conduit travels to the bottom of the furnace. An optional two-way valve (not shown) may be used to permit the heated inert gas to be transported to either one of the conduits 2006 or 2008. Conduit 2006 is in communication with the conduit 2004 and the eyepiece 1120. The heated inert gas traveling through conduit 2006 travels to the eyepieces 1120 and into the growth chamber where it enshrouds the crystal boule 1118 to prevent it from oxidation and from cracking.

[0028] Conduit 2008 travels downwards to the bottom of the furnace 1102, where it contacts the second porous frit and discharges heated inert gas to bottom of the crucible. The heated inert gas travels upwards through the first porous frit, around the crucible and enshrouds the crystal boule 1118 to prevent it from oxidation and cracking. As noted above, the heated inert gas may be transported in a single direction (through conduit 2006 or through conduit 2008) or in more than one direction (through conduits 2006 and 2008 simultaneously).

[0029] While the conduit 2004 is depicted as being in a helical arrangement in the furnace in FIG. 2, other configurations and designs for the conduit may be used. FIGs. 3A - 3B depicts other possible arrangements that may be used to heat the inert gas. The FIGs. 3A and 3B depict only the furnace wall 1105 (of the furnace 1102 in FIG. 2) and the conduit 2004 arrangement that is used to transport the inert gas through the furnace. The growth chamber and the attachments to it are not shown in the FIGs. 3 A and 3B.

[0030] The FIG. 3A has a side view and a top view that depicts an alternative arrangement of the inert gas carrying conduit 2004 where the conduit is arranged to have alternating “U” and “inverted U” sections that are connected by vertical linear conduits. As may be seen in the expanded side view of section AA' of the FIG. 3 A, the conduits are arranged to travel up and down along the furnace wall, with the vertical sections connected by U and inverted U sections.

[0031] FIG. 3B depicts a side view and top view of another arrangement of the conduit 2004 that carries an inert gas. In the FIG. 3B, the conduit is arranged in a helical fashion (see side view) except that the conduit may contain inward and outward facing “U” sections that are connected by linear portions (see top view). The conduit is arranged in such a manner so as to not interfere with the ingress and egress of the growth chamber into and out of the furnace.

[0032] In one embodiment, in one method of growing the crystalline boule, the inert gas can be transported through the conduit 2004 (located in the furnace between the furnace wall and the growth chamber) from entry port 2002. The inert gas heats up during its travel through the conduit and is released into growth chamber above the melt located in the crucible. The gas is preheated in the furnace while travelling through the conduit and is then released over the crucible within the growth chamber. The gas enters the growth chamber from the top and travels downward to surround the growing crystalline boule and the melt (contained in the crucible) thus preventing the boule and the melt from undergoing thermal shock or oxidation. The inert gas heats up to a temperature that lies between the temperature of the boule and the temperature of the furnace.

[0033] In another embodiment, in another method of growing the crystalline boule, the heated inert gas may be introduced into the growth chamber from the second and first porous frits located at the bottom of the growth chamber. The inert gas travelsupwards initially and then travels around the crucible and surrounds the growing crystal boule and the melt in the crucible. In yet another embodiment, the heated inert gas travels upwards and downwards in the growth chamber simultaneously and contacts the crystal boule and the melt, thus preventing oxidation and cracking from occurring.

[0034] This method is advantageous because it recycles the heat generated in the furnace during the crystal growth process. It therefore reduces the waste heat. It improves the cost structure for producing scintillators for processes such as positron emission tomography. It improves space utilization because the use of an external heater (located outside the furnace) may be avoided.

[0035] The device disclosed herein may be advantageously used for producing single crystals from lutetium orthosilicates, lutetium yttrium orthosilicates, gadolinum gallium garnets, gadolinum aluminum gallium garnets, and the like, or a combination thereof.

[0036] While the invention has been described with reference to some embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

What is claimed is:

1. A device for producing a single crystal comprising: a furnace, where the furnace comprises a furnace wall, a furnace base plate and a furnace cover; the furnace wall being disposed between the furnace base plate and the furnace cover; a growth chamber comprising an outer tube, a growth chamber bottom plate and a growth chamber top plate; where the furnace cover has an opening through which the growth chamber protrudes and where the growth chamber is operative to contain a crucible that contains a melt for manufacturing the single crystal; a pull rod that contacts the melt to produce a crystal boule; where the pull rod via a seed crystal contacts the melt through the 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; where the conduit is operative to transport an inert gas through the furnace to heat the inert gas and to deposit the heated inert gas into the growth chamber.

2. The device of Claim 1, further comprising an entry port for the inert gas, where the entry port is in fluid communication with the conduit.

3. The device of Claim 1, where the conduit is in fluid communication with an eyepiece located in the growth chamber top plate and where the heated inert gas is discharged through the eyepiece opening into the growth chamber to enshroud the melt.

4. The device of Claim 1, where the conduit is in fluid communication with a porous frit located at the bottom of the growth chamber and where the heated inert gas is discharged through the porous frit into the growth chamber to enshroud the melt.

5. The device of Claim 1, where the conduit is simultaneously in fluid communication with an eyepiece located in the growth chamber top plate and with a porous frit located at the bottom of the growth chamber and where the heated inert gas issimultaneously discharged from both the eyepiece and through the porous frit into the growth chamber to enshroud the melt.

6. The device of Claim 1, where the pull rod contacts the melt through a seed crystal.

7. The device of Claim 1, where the conduit comprises coils arranged in a helical fashion along the furnace wall.

8. The device of Claim 1, where the conduit is arranged along the furnace wall and comprises linear vertical sections connected by alternating U and inverted U shaped sections.

9. The device of Claim 1, where the conduit is arranged along the furnace wall and comprises linear horizontal sections connected by U shaped sections.

10. The device of Claim 1, where the conduit contains a valve, which directs the heated inert gas to an eyepiece located in the growth chamber top plate or to a porous frit located at a bottom of the growth chamber.

11. The device of Claim 1, where the conduit comprises copper or stainless steel.

12. The device of Claim 1, where the inert gas comprises nitrogen, helium, argon, neon, xenon, krypton, radon, or a combination thereof.

13. The device of Claim 1, where the inert gas is nitrogen.

14. The device of Claim 1, where the melt comprises lutetium orthosilicate, lutetium yttria orthosilicate, gadolinum gallium garnet or gadolinium aluminum gallium garnet.

15. The device of Claim 1, where the melt comprises lutetium orthosilicate.

16. A method for producing a single crystal comprising: disposing the crucible in a growth chamber; where the crucible contains a powder for manufacturing a single crystal; where the growth chamber comprises an outer tube, a growth chamber bottom plate and a growth chamber top plate; where the growth chamber top plate contains an opening; disposing the growth chamber in a furnace; where the furnace is heated to melt the powder to produce a single crystal melt; contacting the melt with a single crystal seed that contacts a pull rod, extracting the pull rod from the melt to produce a crystal boule; introducing an inert gas into a conduit located in the furnace; where the conduit is located between a furnace wall and the outer tube of the growth chamber; heating the inert gas during its travel through the conduit; and discharging the heated inert gas into the growth chamber to contact the crystal boule.

17. The method of Claim 16, where the inert gas is discharged from an eyepiece located in the growth chamber top plate and travels downwards to enshroud the crystal boule.

18. The method of Claim 16, where the inert gas is discharged through a porous frit located in a bottom of the growth chamber and travel s upwards and around the crucible to enshroud the crystal boule.

19. The method of Claim 16, where the inert gas is simultaneously discharged from an eyepiece opening located in the growth chamber top plate and through a porous frit located in a bottom of the growth chamber to enshroud the crystal boule.

20. The method of Claim 16, where the single crystal comprises lutetium orthosilicate, lutetium yttria orthosilicate, gadolinum gallium garnet or gadolinium aluminum gallium garnet.

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