Patent Publication Number: US-2020283887-A1

Title: Effusion cell

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is the U.S. National Phase application of PCT/KR2017/012598, filed Nov. 8, 2017, the contents of such application being incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an effusion cell used to form a thin film on a wafer or substrate, and more particularly, relates to an effusion cell capable of preventing a thin film forming material from condensing on an outlet portion of a nozzle when it evaporates. 
     BACKGROUND ART 
     Generally, an effusion cell heats and evaporates a thin film forming material to form a predetermined thin film on a substrate disposed in a high vacuum chamber. It is used to form a thin film made of a specific material on a wafer surface in a semiconductor manufacturing process or to form a thin film of a desired material on a surface of a glass substrate or the like in a manufacturing process of a large flat panel display device. 
       FIG. 1  is a view schematically showing a conventional effusion cell. 
     As shown in  FIG. 1 , the conventional effusion cell includes a case  10  having an inner space  11 , a crucible  20  provided in the inner space  11  and containing a thin film forming material, a heater  30  positioned between a side of the inner space  11  and an outer side of the crucible  20  to heat a side of the crucible  20 , and a reflective plate  40  provided between the side of the inner space  11  and the heater  30  to reflect the heat of the heater  30  to the crucible  20 . In addition, the crucible  20  is provided with a nozzle  50 , and an outlet  51  of the nozzle  50  through which the thin film forming material is discharged is positioned at an end of an upper end of the crucible  10 . 
     The thin film forming material contained in the crucible  20  is evaporated while being heated by the heater  30  and the reflective plate  40 , in which the evaporated thin film forming material is discharged to the outside via the outlet  51  of the nozzle  50  so as to be deposited on a substrate (not shown) placed on an outside of the crucible  20 . 
     However, since an upper end portion of the crucible  20 , i.e., the outlet  51  portion of the nozzle  50  is relatively low in temperature, the thin film forming material contained in the crucible  20  is condensed around the outlet  51  of the nozzle  50  when the thin film forming material is evaporated through the nozzle  50 . 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     To solve the problems as described above, an aspect of the present invention is an effusion cell capable of preventing a thin film forming material from condensing on an outlet portion of a nozzle. 
     In particular, an aspect of the present invention is an effusion cell capable of preventing a thin film forming material from condensing on an outlet portion of a nozzle by bending an inside of the nozzle such that a point where the thin film forming material is released to the outside is positioned below an upper end of the crucible. 
     In addition, another aspect of the present invention is an effusion cell capable of forming a relatively high temperature of a nozzle portion to prevent condensation of a thin film forming material on an outlet portion of a nozzle, by doubling a structure of a crucible to form a heat outlet in a top of an outer crucible so that radiant heat of a heater flows in a top direction of an inner crucible. 
     Solution to Problem 
     Aspects of the present invention provide an effusion cell for evaporating a thin film forming material, including: a case with an inner space; a crucible provided in the inner space and containing the thin film forming material; and a nozzle provided on a top of the crucible so that the thin film forming material is discharged to the outside of the crucible therethrough, in which the nozzle includes an upwardly reduced inclination formed to be inclined toward an inside of the crucible from one end of a lower of the nozzle; a first upwardly enlarged inclination formed to be inclined toward an edge of the crucible from an upper end portion of the upwardly reduced inclination; and a second upwardly enlarged inclination formed to be inclined toward the edge of the crucible at an upper end portion of the first upwardly enlarged inclination. 
     Here, when an angle formed by a first virtual line L 1  with a central axis C is called a first inclination angle θ 1 , with the first virtual line L 1  extending from a lower of the first upwardly enlarged inclination toward the central axis C in a longitudinal direction of the nozzle along an inclined surface of the first upwardly enlarged inclination, and an angle formed by a second virtual line L 2  with the central axis C is called a second inclination angle θ 2 , with the second virtual line L 2  extending toward the central axis C from a lower of the second upwardly enlarged inclination along an inclined surface of the second upwardly enlarged inclination, the second inclination angle θ 2  is preferably greater than the first inclination angle θ 1 . 
     In addition, when an angle formed by a third virtual line L 3  with the central axis C is called a third inclination angle θ 3 , with the third virtual line L 3  extending toward the central axis C from an upper end portion of the upwardly reduced inclination along the inclined surface of the upwardly reduced inclination, the second inclination angle θ 2  is preferably greater than the third inclination angle θ 3 . 
     In addition, the nozzle may further include a horizontal supporter provided on an upper end of the second upwardly enlarged inclination and supported on an upper end of the edge of the crucible; and a vertical supporter provided at a lower end of the upwardly reduced inclination to be in contact with and supported by the inner surface of the crucible. 
     In addition, the upwardly reduced inclination, the first upwardly enlarged inclination, the second upwardly enlarged inclination, the horizontal supporter, and the vertical supporter may be formed of one body. 
     In addition, the effusion cell may further include a thermal insulating cap to close a gap between a top corner of the crucible and the case. 
     Aspects of the present invention also provide an effusion cell for evaporating a thin film forming material, including: a case having an inner space; and a crucible provided in the inner space and containing the thin film forming material, in which the crucible has an inner crucible and an outer crucible disposed outside the inner crucible, and in which a heat outlet for allowing radiant heat of the heater to flow in is formed at a top of the outer crucible. 
     Here, it includes a nozzle provided on a top of the crucible so that the thin film forming material is discharged to the outside of the crucible therethrough, in which the nozzle includes an upwardly reduced inclination formed to be inclined toward an inside of the crucible from one end of a lower of the nozzle; a first upwardly enlarged inclination formed to be inclined toward an edge of the crucible from an upper end portion of the upwardly reduced inclination; and a second upwardly enlarged inclination formed to be inclined toward the edge of the crucible at an upper end portion of the first upwardly enlarged inclination. 
     In addition, the outer crucible is preferably formed of a metal material, and the inner crucible is preferably formed of a ceramic material. 
     Advantageous Effects of Invention 
     According to an aspect of the present invention, it is possible to provide an effusion cell capable of preventing condensation of a thin film forming material on an outlet portion of a nozzle. 
     In particular, an aspect of the present invention may provide an effusion cell capable of preventing a thin film forming material from condensing on an outlet portion of a nozzle by bending an inside of the nozzle such that a position where the thin film forming material is released to the outside is positioned below an upper end of the crucible. 
     In addition, an aspect of the present invention may provide an effusion cell capable of forming a relatively high temperature of a top of a crucible and a nozzle to prevent condensation of a thin film forming material on an outlet portion of a nozzle, by doubling a structure of a crucible to form a heat outlet in a top of an outer crucible so that radiant heat of a heater flows in a top direction of an inner crucible. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other aspects and features of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which: 
         FIG. 1  is a view schematically showing a conventional effusion cell; 
         FIG. 2  is a view schematically showing an effusion cell according to an embodiment of the present invention; 
         FIG. 3  is an enlarged view of a nozzle of  FIG. 2 ; 
         FIG. 4  is a view schematically showing a process of flowing a thin film forming material through the nozzle of  FIG. 2 ; 
         FIG. 5  is an enlarged view of a top of an effusion cell of  FIG. 2 ; and 
         FIG. 6  shows an effusion cell according to another embodiment of the present invention. 
     
    
    
     MODE FOR THE INVENTION 
     Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. 
       FIGS. 2 to 5  are views for explaining a first embodiment according to the present invention, in which  FIG. 2  is a view schematically showing an effusion cell according to an embodiment of the present invention,  FIG. 3  is an enlarged view of a nozzle of  FIG. 2 ,  FIG. 4  is a view schematically showing a process of flowing a thin film forming material through the nozzle of  FIG. 2 , and  FIG. 5  is an enlarged view of a top of an effusion cell of  FIG. 2 . 
     Referring to  FIGS. 2 to 5 , an effusion cell  100  according to the first embodiment of the present invention includes a case  110  having an inner space  11 , a crucible  120  provided in the inner space  11  and containing a thin film forming material, a heater  30  positioned between a side of the inner space  11  and an outer side of the crucible  120  to heat a side of the crucible  120 , and a reflective plate  40  provided between the side of the inner space  11  and the heater  30  to reflect the heat of the heater  30  to the crucible  120 . In addition, the nozzle  130  is provided a top of the crucible  120  to allow the thin film forming material to be discharged to the outside of the crucible  120  through the nozzle  130 . 
     As is well known, when the thin film forming material contained in the crucible  120  is heated by the heater  30 , the effusion cell  100  allows it to be discharged the outside of the crucible  120  through the nozzle  130  formed at an upper end of the crucible  120  to form a thin film on a substrate disposed in a chamber. 
     Here, since the case  110 , the crucible  120 , the heater  30 , and the reflective plate  40  are not significantly different from those known in the prior art, detailed descriptions thereof will be omitted. Hereinafter, the configuration of the nozzle  130  will be described in detail. 
     The nozzle  130  in the embodiment has a structure in which an inside of the nozzle  130  is bent a number of times in order to minimize the contact of an evaporation material to the upper end of the crucible  120 , i.e., the nozzle portion which has a relatively low temperature, when the thin film forming material contained in the crucible  120  is heated by the heater  30  and is discharged while being evaporated the outside of the crucible  120 . 
     By such a configuration, a position when the evaporated thin film forming material is discharged to the outside of the crucible  120  may be positioned below the upper end of the crucible  120 , so that it may be discharged the outside of the crucible  120  while maintaining a relatively high temperature. Therefore, compared to the prior art, it is possible to prevent the thin film forming material from condensing on the upper end portion of the crucible  120 . 
     Specifically, as shown in  FIGS. 2 to 4 , an inside of the nozzle  130  has a plurality of bent structures. To this end, the nozzle  130  includes an upwardly reduced inclination  131 , a first upwardly enlarged inclination  132 , and a second upwardly enlarged inclination  133 . 
     First, the upwardly reduced inclination  131  has a shape inclined from one end of a lower of the nozzle  130  toward the inside of the crucible  120 . An upper end of the upwardly reduced inclination  131  is positioned approximately in the middle of the nozzle  130  and has a passage to allow an evaporation material to pass therethrough. 
     The first upwardly enlarged inclination  132  has a shape inclined from the upper end of the upwardly reduced inclination  131  toward an edge of the crucible  120 . In other words, the first upwardly enlarged inclination  132  is bent and extended toward the edge of the crucible  120  at the upper end of the upwardly reduced inclination  131 . The first upwardly enlarged inclination  132  is formed to extend to a point that is about ½ of a distance from an approximately middle portion (upper end of the upwardly reduced inclination  131 ) in a longitudinal direction of the nozzle  130  to an upper end portion of the nozzle  130 . 
     The second upwardly enlarged inclination  133  has a shape inclined from the upper end of the first upwardly enlarged inclination  132  toward the edge of the crucible  120 . In other words, the second upwardly enlarged inclination  133  is bent again and extended toward the edge of the crucible  120  at the upper end of the first upwardly enlarged inclination  132 . The second upwardly enlarged inclination  133  extends to a point positioned slightly inward in the horizontal direction than the edge of the upper end of the nozzle  130 . 
     Here, an inclination angle with respect to a horizontal axis of the nozzle  130  of the second upwardly enlarged inclination  133  is smaller than an inclination angle with respect to ta horizontal axis of the nozzle  130  of the first upwardly enlarged inclination  132 . 
     In other words, as shown in  FIG. 3 , when an angle formed by a first virtual line L 1  with a central axis C is called a first inclination angle θ 1 , with the first virtual line L 1  extending from a lower of the first upwardly enlarged inclination  132  toward the central axis C in a longitudinal direction of the nozzle along an inclined surface of the first upwardly enlarged inclination  132 , and an angle formed by a second virtual line L 2  with the central axis C is called a second inclination angle θ 2 , with the second virtual line L 2  extending toward the central axis C from a lower of the second upwardly enlarged inclination  133  along an inclined surface of the second upwardly enlarged inclination  133 , the second inclination angle θ 2  is greater than the first inclination angle θ 1 . 
     By such a configuration, the maximum height at which the material for evaporating the thin film to be finally contacted with the nozzle  130  is a boundary point (bent portion) where the first upwardly enlarged inclination  132  and the second upwardly enlarged inclination  133  meet each other. Since a temperature of the first upwardly enlarged inclination  132  is relatively higher than a temperature of the second upwardly enlarged inclination  133 , compared to the prior art, the evaporation material may maintain a high temperature so that it may be discharged mostly without condensation on a top side of the crucible  120 . 
     This will be described with reference to  FIG. 4  as follows.  FIG. 4  shows an advancing direction of the evaporation material. As shown in  FIG. 4 , the evaporation material mostly travels straight in vacuum when evaporated. Therefore, when the thin film forming material contained in the crucible  120  is evaporated, a position of the maximum height at which the thin film forming material passing through the nozzle  130  may finally come into contact with the nozzle  130  is the first upwardly enlarged inclination  132  and the second upwardly enlarged inclination  133  is hardly touched. Therefore, the evaporation material is in contact with only the first upwardly enlarged inclination  132  having a relatively higher temperature than the second upwardly enlarged inclination  133 , and thus maintains a relatively high temperature, thereby preventing condensation of the evaporation material. 
     As shown in  FIG. 3 , when an angle formed by a third virtual line L 3  with the central axis C is called a third inclination angle θ 3 , with the third virtual line L 3  extending toward the central axis C from an upper end portion of the upwardly reduced inclination  131  along the inclined surface of the upwardly reduced inclination  131 , the second inclination angle θ 2  may be greater than the third inclination angle θ 3 . Therefore, as shown in  FIG. 4 , the thin film forming material ejected along the upwardly reduced inclination  131  may be ejected as it is without contacting the second upwardly enlarged inclination  133  due to the difference in inclination angle difference as described above. 
     The nozzle  130  may further include a horizontal supporter  134  and a vertical supporter  135 , as shown in  FIGS. 2 to 4 . The horizontal supporter  134  is provided on an upper end portion of the second upwardly enlarged inclination  133  and is supported on an upper end of an edge of the crucible  120 . The vertical supporter  135  is provided at a lower end portion of the upwardly reduced inclination  131  and is supported by being in contact with an inner surface of the crucible  120 . Therefore, it is possible to prevent the thin film forming material from leaking between the nozzle  130  and the crucible  120  by the horizontal supporter  134  and the vertical supporter  135 . 
     The upward reduction inclination portion  131 , the first upwardly enlarged inclination  132 , the second upwardly enlarged inclination  133 , the horizontal supporter  134 , and the vertical supporter  135  may be formed of one body. 
     In addition, the effusion cell  100  according to the embodiment of the present invention described above may further include a thermal insulating cap  140  as shown in  FIGS. 2 and 5 . 
     The thermal insulating cap  140  serves to slow the cooling rate of the top of the crucible  120  by blocking a gap between a top corner of the crucible  120  and the case  110 . In particular, as shown in  FIG. 5 , when the horizontal supporter  134  of the nozzle  130  is placed on the top of the edge of the crucible  120 , the thermal insulating cap  140  may be installed between the horizontal supporter  134  of the nozzle  130  and the case  110 . The thermal insulating cap  140  may have a double overlapping structure to further slow the cooling rate. 
     Next, the effusion cell  200  according to a second embodiment of the present invention will be described with reference to  FIG. 6 . 
       FIG. 6  shows an effusion cell  200  to which a crucible  220  having a double structure is applied. 
     The effusion cell  200  according to the embodiment of  FIG. 6  is the same as the first embodiment described above, except that the crucible  220  having the dual structure is formed and a heat outlet  222   a  is formed in the crucible  220 . Therefore, only the crucible  220  and the heat outlet  222   a  will be described. 
     The crucible  220  of  FIG. 6  is formed in a double structure of an inner crucible  221  and an outer crucible  222  disposed outside the inner crucible  221 , and the heat outlet  222   a  is formed at a top of the outer crucible  222  to allow radiant heat of the heater  30  to flow therein. 
     Since the radiant heat of the heater  30  is flowed into atop of the inner crucible  221  in which the nozzle  130  is disposed through the heat outlet  222   a , a temperature of the top of the crucible  220 , i.e., a temperature of the nozzle  130  may be maintained relatively high. Therefore, it is possible to prevent the thin film forming material from condensing on the top of the crucible  220 . 
     In other words, the heat outlet  222   a  formed in the outer crucible  222  is to further increase the temperature of the top of the inner crucible  221  positioned in a portion where the heat outlet  222   a  is formed by directly passing infrared rays emitted from the heater  30  than a lower. Due to the nature of the evaporation material and a deposition process, the temperature of the top of the inner crucible  221  where the nozzle  130  is positioned should be higher than the lower by such a configuration in order to ensure the nozzle is not clogged and the quality of the deposited film is improved. 
     When there is no heat outlet  222   a , the heat of the heater  30  is primarily transferred to the outer crucible  222  and then to the inner crucible  221  secondarily (indirectly). Therefore, it is not efficient to further raise the temperature of the top of the inner crucible  221  more than the lower. 
     In  FIG. 6 , the heat outlet  222   a  is shown to be formed of a plurality of small circular holes on the top of the outer crucible  222 . However, it is exemplary, and it may be formed in other shapes, such as a square, not circular. 
     In addition, instead of forming a multiple small circular holes, the heat outlets  222   a  may be formed in a number of about 1 to 3 having a relatively large size. In addition, when a plurality of heat outlets  222   a  are formed, a shape or size of each heat outlet  222   a  may vary. 
     In addition, the effusion cell  200  of  FIG. 6  is shown with the nozzle  130  of the first embodiment described with reference to  FIGS. 1 to 5 . However, it is not always necessary to carry out in parallel with the nozzle  130  described in the first embodiment. In other words, naturally, it may be carried out only the heat outlet  222   a  in the crucible  220  having the double structure with the inner crucible  221  and the outer crucible  222  without the nozzle, or it may be carried out in combination with a nozzle of another type other than the nozzle of the first embodiment. 
     Naturally, since combining the configuration of the second embodiment with the configuration of the first embodiment may keep the temperature of the top of the crucible and a temperature when the evaporation material are discharged higher, the effect of condensation of the evaporation material on the top of the crucible may be further enhanced. 
     The outer crucible  222  should serve to protect the heater  30  by confining a material flowing or falling off when the inner crucible  221  is broken. Therefore, it is preferable to form the outer crucible  222  with a metal material with good thermal and structural durability. 
     The inner crucible  221  should not chemically react with a material. Therefore, in general, it is preferable to use ceramic materials such as Al2O3, Pyrolitic Boron Nitride (PBN), Aluminum Nitride (AlN), or the like, which are not reactive with metallic materials. 
     Although the configuration and operation of the present invention have been described above with reference to the preferred embodiment of the present invention, naturally, the scope of the present invention is not limited thereto.