Abstract:
The present invention relates to an evaporation source for evaporating an organic electroluminescent layer. In particular, the present invention relates to the evaporation source preventing an aperture, through which a vaporized evaporation material is emitted, from being clogged by restricting heat transfer to outward. The evaporation source according to the present invention includes a cell retaining an evaporation material therein; a cell cap installed on the upper part of the cell and having a cell cap aperture for emitting a vaporized evaporation material; an external wall placed in the outside of the cell to support a heating means set up at the outside of the cell; a cover placed above the cell cap, fixed to the upper end of the external wall, and having a cover aperture corresponding to the cell cap aperture; and a shut-off plate placed between the cover and the cell cap and having a shut-off plate aperture corresponding to the cell cap aperture and the cover aperture in the center of the shut-off plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a Divisional of co-pending application Ser. No. 10/909,353 filed on Aug. 3, 2004, for which priority is claimed under 35 U.S.C. § 120. This application also claims priority from Korean Patent Application Nos. 2003-53761, filed on Aug. 4, 2003, 2003-56606, filed on Aug. 14, 2003, 2003-61351, filed on Sep. 3, 2003 and 2003-61352, filed on Sep. 3, 2003. The contents of each of these applications are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an evaporation source for evaporating an organic electroluminescent layer. In particular, the present invention relates to the evaporation source preventing an aperture, through which a vaporized evaporation material is emitted, from being clogged by restricting heat transfer to outward.  
         [0004]     2. Description of the Related Art  
         [0005]     Thermal, physical vacuum evaporation is a technique for forming an organic electroluminescent layer on a substrate by emitting a vaporized evaporation material (organic material). In this evaporation process, an evaporation material retained in a vessel is heated to evaporation temperature, and after emitted from the vessel, the vaporized evaporation material is coated on the substrate. This process is carried out in a chamber whose pressure is maintained between 10 −7  and 10 −2  Torr, wherein the vessel retaining the evaporation material and the substrate is installed in the chamber.  
         [0006]     Generally, the evaporation source, which is the vessel retaining the evaporation material, is made of an electrical resistance material, wherein the temperature of the electrical resistance material increases when the electric current flows through the walls of the evaporation source. When the electric current is applied to the evaporation source, the evaporation material retained therein is heated by radiation heat and conduction heat transferred from the walls of the evaporation source. An aperture for emitting the vaporized evaporation material to outward is formed on the upper surface of the evaporation source.  
         [0007]      FIG. 1  is a sectional view showing the inner configuration of the vacuum evaporation apparatus equipped with a conventional evaporation source. The evaporation source  1  is installed in the chamber  3  of the evaporation apparatus, and the substrate  2  is placed above the evaporation source  1 .  
         [0008]     The substrate  2  on which the organic electroluminescent layer is evaporated is mounted on an upper plate  3 - 1  of the chamber  3 , wherein the substrate  2  can be fixed or installed to move widthwise. A general configuration of the vacuum evaporation apparatus is to mount the substrate  2  on the upper plate  3 - 1  to move horizontally, and thus the explanation about this configuration is omitted.  
         [0009]     The evaporation source  1  is installed on an insulated structure  4  fixed to a base  3 - 2  of the chamber  3 , and connected to a cable for supplying electric power. The evaporation source  1  is capable of moving horizontally widthwise as well as being fixed to the insulated structure  4 . Another general configuration of the vacuum evaporation apparatus is to install the evaporation source  1  on the insulated structure  4  to move horizontally, and thus the explanation about this configuration is also omitted.  
         [0010]     The aperture  1 A- 1  formed on the upper surface of the evaporation source  1  is shown in  FIG. 1 , wherein the evaporation material vaporized in the evaporation source  1  is emitted through the aperture  1 A- 1  to outward in the direction of the substrate  2 . Generally, the evaporation sources are classified into point evaporation source and linear evaporation source depending on the shape of evaporation source and aperture.  
         [0011]     The entire shape of the point evaporation source is cylindrical, and the shape of its aperture is circular. The entire shape of the linear evaporation source is hexahedral, and the shape of its aperture is rectangular.  
         [0012]     The selection of evaporation source is determined by considering the conditions of evaporation process and substrate, and the shape of evaporation layer to be formed. For convenience&#39;s sake, the point evaporation source will be explained below.  
         [0013]      FIG. 2  is a sectional view showing a conventional point evaporation source. The point evaporation source  1  comprises a cell  1 C, a base  1 D and a cell cap  1 A. The evaporation material, which is an organic material, is retained in the inner space formed by the cell  1 C, the base  1 D and the cell cap  1 A.  
         [0014]     A heating means  1 B- 1 , for example, an electric resistance coil connected to electric power, is placed between the cell  1 C and an external wall  1 B to heat the evaporation material M retained in the inner space. The heating means  1 B- 1  is installed for the cell  1 C of the entire height to heat the entire evaporation material M.  
         [0015]     A cell cap aperture  1 A- 1  is formed in the center of the cell cap  1 A, wherein the vaporized evaporation material M heated by the heating means  1 B- 1  is emitted through the cell cap aperture  1 A- 1  to outward, that is, to the direction of the substrate  2 .  
         [0016]     The temperature around the cell cap aperture  1 A- 1  is lower than the temperature of the inner space in which the vaporized evaporation material is generated because the cell cap  1 A has no additional heating means installed thereon, and is exposed to the outside. Therefore, a part of the vaporized evaporation material emitted through the cell cap aperture  1 A- 1  is deposited around the cell cap aperture  1 A- 1  due to lower temperature thereabout.  
         [0017]     As the evaporation process continues, the amount of the deposited evaporation material increases. Therefore, fluent emission of the vaporized evaporation material is not carried out, and in the end, the cell cap aperture  1 A- 1  is clogged by increase of the deposited evaporation material.  
         [0018]     In order to prevent the vaporized evaporation material from being deposited around the cell cap aperture  1 A- 1 , it is necessary that the temperature of the cell cap aperture  1 A- 1  or the cell cap  1 A should keep above a predetermined temperature. Therefore, in order to do so, a cover  1 E, made of metallic material, is mounted on the upper end of the external wall  1 B as shown in  FIG. 2 , wherein the shape of the cover  1 E is of a circular plate.  
         [0019]     The cover  1 E mounted on the upper end of the external wall  1 B is placed on the cell cap  1 A, and maintains a predetermined space from the cell cap  1 A. A cover aperture  1 E- 1  for emitting the vaporized evaporation material is formed on the cover  1 E to correspond to the cell cap aperture  1 A- 1 . Therefore, the cell cap  1 A may maintain a predetermined temperature because the cover  1 E prevents the heat transferred from the cell cap  1 A from being emitted to outward.  
         [0020]     However, the heat transferred from the cell cap  1 A is emitted to outward because the cover  1 E is metallic. Therefore, the cell cap  1 A cannot maintain a predetermined temperature, and so the deposition of the vaporized evaporation material around the cell cap aperture  1 A- 1  cannot be completely prevented.  
       SUMMARY OF THE INVENTION  
       [0021]     The object of the present invention is to provide an evaporation source for preventing a vaporized evaporation material from being deposited around an aperture formed on a cell cap by inhibiting heat transferred to the cell cap having the aperture from heating means from being emitted to outward, and thus enabling the cell cap to maintain a predetermined temperature.  
         [0022]     The evaporation source according to one embodiment of the present invention includes a cell retaining an evaporation material therein; a cell cap installed on the upper part of the cell, and having a cell cap aperture for emitting a vaporized evaporation material; an external wall placed in the outside of the cell to support a heating means set up at the outside of the cell; a cover placed above the cell cap, fixed to the upper end of the external wall, and having a cover aperture corresponding to the cell cap aperture; and a shut-off plate placed between the cover and the cell cap and having a shut-off plate aperture corresponding to the cell cap aperture and the cover aperture in the center of the shut-off plate.  
         [0023]     The evaporation source according to another embodiment of the present invention includes a cell retaining an evaporation material therein; a cell cap installed on the upper part of the cell, and having a cell cap aperture for emitting a vaporized evaporation material; an external wall placed in the outside of the cell to support a heating means set up at the outside of the cell; a cover placed on the cell cap, fixed to the upper end of the external wall, and having a cover aperture corresponding to the cell cap aperture; and an upper reflector and a lower reflector having an upper aperture and a lower aperture corresponding to the cover aperture in the center thereof respectively and placed above the cover to prevent heat from being emitted to the outside of the cover, wherein the upper reflector is placed above the lower reflector.  
         [0024]     The evaporation source according to another embodiment of the present invention includes a cell retaining an evaporation material therein; a cell cap installed on the upper part of the cell and having a cell cap aperture for emitting a vaporized evaporation material; an external wall placed in the outside of the cell to support a heating means set up at the outside of the cell; and a reflector comprising a body placed above the cell cap, a metal layer placed on the lower surface of the body and a supporting member mounted on the body to contact the surface of the cell cap, wherein the body, made of a low conductivity material, has an reflector aperture corresponding to the cell cap aperture in the center thereof, and the metal layer has a low emissivity value.  
         [0025]     The evaporation source according to another embodiment of the present invention includes a cell retaining an evaporation material therein; a cell cap installed on the upper part of the cell and having a cell cap aperture for emitting a vaporized evaporation material; an external wall placed in the outside of the cell to support a heating means set up at the outside of the cell; and a cover contacting the upper surface of the cell cap, fixed to the upper end of the external wall, and having a cover aperture corresponding to the cell cap aperture.  
         [0026]     Therefore, the vaporized evaporation material is not deposited around the cell cap aperture because the temperature of the cell cap remains at a predetermined temperature while the vaporized evaporation material is emitted to outward, and the evaporation layer is formed on the substrate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The above and other features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.  
         [0028]      FIG. 1  is a sectional view showing the inner configuration of the vacuum evaporation apparatus equipped with a conventional evaporation source.  
         [0029]      FIG. 2  is a sectional view showing a conventional point evaporation source.  
         [0030]      FIG. 3  is a sectional view showing the point evaporation source according to the first embodiment of the present invention.  
         [0031]      FIG. 4  is a sectional view showing the point evaporation source according to the second embodiment of the present invention.  
         [0032]      FIG. 5  is a bottom view showing the upper reflector of the point evaporation source according to the second embodiment of the present invention.  
         [0033]      FIG. 6  is a detailed view showing part “A” of  FIG. 4 .  
         [0034]      FIG. 7  is a sectional view showing the point evaporation source according to the third embodiment of the present invention.  
         [0035]      FIG. 8  is a detailed view showing part “B” of  FIG. 7 .  
         [0036]      FIG. 9  is a sectional view showing the point evaporation source according to the fourth embodiment of the present invention.  
         [0037]      FIG. 10  is a detailed view showing part “C” of  FIG. 9 .  
         [0038]      FIG. 11  is a sectional view showing another point evaporation source according to the fourth embodiment of the present invention.  
         [0039]      FIG. 12  is a detailed view showing part “D” of  FIG. 11 . 
     
    
     DESCRIPTION OF EMBODIMENTS  
       [0040]     Hereinafter, preferred embodiments of the present invention will be explained in more detail with reference to the accompanying drawings.  
       The First Embodiment  
       [0041]      FIG. 3  is a sectional view showing the point evaporation source according to the first embodiment of the present invention. The point evaporation source  10  according to the first embodiment of the present invention comprises a cell  11  which is cylindrical, a cell cap  12  on which a cell cap aperture  12 A for emitting the vaporized evaporation material is formed, an external wall  13  which is cylindrical, and base  14 . A heating means  13 A is placed between the cell  11  and the external wall  13 .  
         [0042]     A cover  15  fixed to the upper end of the external wall  13  is placed on the cell cap  12  with maintaining a predetermined distance from the cell cap, wherein the shape of the cover  15  is of a circular plate. A cover aperture  15 A formed on the cover  15  corresponds to the cell cap aperture  12 A.  
         [0043]     In order to prevent the heat of the cell cap  12  from being transferred to outward, a shut-off plate  16  is placed between the cover  15  and the cell cap  12 , and is level with the cover  15  and the cell cap  12 , wherein the outer circumferential surface of the shut-off plate  16  is fixed to the inner circumferential surface of the cover  15 . Also, the shut-off plate  16  may be placed between the cover  15  and the cell cap  12  by fixing each end of a plurality of supporting rods (not shown) to the upper surface of the shut-off plate  16  and the lower surface of the cover  15  together.  
         [0044]     The shut-off plate  16  has a shut-off plate aperture corresponding to the cell cap aperture  12 A and the cover aperture  15 A in the center of the shut-off plate  16 . Therefore, the vaporized evaporation material emitted from the cell cap aperture  12 A is emitted through the shut-off plate aperture and the cover aperture  15 A to outward in the direction of the substrate.  
         [0045]     In the evaporation source according to the first embodiment of the present invention, heat is transferred from the inner space of the cell  11 , in which the vaporized evaporation material is generated, to the cell cap  12 , and then the heat transferred from the cell cap  12  to the cover  15  is shut off by the shut-off plate  16  placed above the cell cap  12 . Therefore, the temperature between the cell cap  12  and the shut-off plate  16  remains higher than the temperature between the shut-off plate  16  and the cover  15 .  
         [0046]     Also, the temperatures of the cell cap  12  and the cell cap aperture  12 A remains in a predetermined temperature, and thus the deposition of the vaporized evaporation material around the cell cap aperture  12 A is prevented because the temperature of the cell cap aperture  12 A is not decreased.  
         [0047]     It is desirable for the shut-off plate  16  to be made of low conductivity material, for example, SUS material or tantalum.  
         [0048]     The above constitution for the point evaporation source according to the first embodiment of the present invention is applicable to the linear evaporation source.  
         [0049]     As described above, the evaporation source according to the first embodiment of the present invention can properly maintain the temperature around the cell cap aperture through shutting off the transfer of heat from the cell cap to outward, and transferring heat to the cell cap, by placing the shut-off plate, which is made of low conductivity material, between the cell cap and the cover. Therefore, such problem that the vaporized evaporation material emitted through the cell cap aperture to outward is deposited around the cell cap aperture due to the decreased temperature is efficiently prevented.  
       The Second Embodiment  
       [0050]      FIG. 4  is a sectional view showing the point evaporation source according to the second embodiment of the present invention. The point evaporation source  20  according to the first embodiment of the present invention comprises a cell  21  which is cylindrical, a cell cap  22  on which a cell cap aperture  22 A for emitting the vaporized evaporation material M is formed, an external wall  23  which is cylindrical, and base  24 . A heating means  23 A is placed between the cell  21  and the external wall  23 .  
         [0051]     The cover  25  of a circular plate shape fixed to the upper end of the external wall  23  is mounted on the cell cap  22  to contact the surface thereof. A lower reflector  26  and an upper reflector  27  are placed above the cover  25  in sequence. The lower reflector  26  contacts the upper surface of the cover  25 , and the upper reflector  27  is placed above the lower reflector  26  with maintaining a predetermined distance.  
         [0052]      FIG. 5  is a bottom view showing the upper reflector of the point evaporation source according to the second embodiment of the present invention.  FIG. 6  is a detailed view showing part “A” of  FIG. 4 .  FIG. 5  and  FIG. 6  show the correlation between the lower reflector  26  and the upper reflector  27 .  
         [0053]     The lower reflector  26  and the upper reflector  27 , which are of circular plate shapes, have a lower aperture and an upper aperture corresponding to the cover aperture  25 A and the cell cap aperture  22 A, respectively, in their centers. Therefore, the lower reflector  26  and the upper reflector  27  have no effect to the function to emit the vaporized evaporation material.  
         [0054]     A plurality of projections  27 B are formed on the lower surface of the upper reflector  27 , wherein each projection  27 B is pointed at the end. Also, a plurality of recesses  26 B are formed on the upper surface of the lower reflector  26 , wherein each recess  26 B corresponds to each projection  27 B. Each projection  27 B of the upper reflector  27  is retained in each recess  26 B of the lower reflector  26  contacting at a point.  
         [0055]     Each recess  26 B formed on the upper surface of the lower reflector  26  has an elliptical shape in which a long principal axis is circumferentially oriented and a short principal axis is radially oriented. A plurality of the evaporation sources are circularly arranged in the vacuum evaporation apparatus, and emit the vaporized evaporation material with moving along a circular course. Under this condition, to compensate the relative motion of the upper reflector  27  to the lower reflector  26 , which moves circularly with the cover  25 , that is, to prevent the projection  27 B contacting the recess  26 B at a point from being separated from the recess  26 B, each recess  26 B is elliptically made.  
         [0056]     Hereinafter, the function of the evaporation source according to the second embodiment of the present invention will be described.  
         [0057]     The cell cap  22  remains at a predetermined temperature by the lower reflector  26  with preventing the heat transferred from the inner space of the evaporation source to the cell cap  22  and the cover  25  from being emitted to outward. The heat transferred to the lower reflector  26  is not transferred to the upper reflector  27  because the upper reflector  27  maintains a predetermined distance from the lower reflector  26  by the projections  27 B. In addition, the amount of the heat transferred to the upper reflector  27  through the projections  27 B is extremely little because the projection  27 B contacts the recess  26 B at a point.  
         [0058]     It is desirable for the pairs of the recess  26 B and the projections  27 B to be at least more than three so that the upper reflector  27  is balanced on the lower reflector  26 .  
         [0059]     As described above, the evaporation source according to the second embodiment of the present invention can prevent the phenomenon that the vaporized evaporation material is deposited around the cell cap aperture, by minimizing the heat emission to outward of the evaporation source by the lower reflector and the upper reflector, and by making the cell cap and the cover placed below the lower reflector and the upper reflector maintain a predetermined temperature at any time.  
       The Third Embodiment  
       [0060]      FIG. 7  is a sectional view showing the point evaporation source according to the third embodiment of the present invention.  FIG. 8  is a detailed view showing part “B” of FIG.  7 . The point evaporation source  30  according to the third embodiment of the present invention comprises a cell  31  which is cylindrical, a cell cap  32  on which a cell cap aperture  32 A for emitting the vaporized evaporation material is formed, an external wall  33  which is cylindrical, and base  34 . A heating means  33 A is placed between the cell  31  and the external wall  33 .  
         [0061]     A reflector  35  fixed to the upper end of the inner circumferential surface of the external wall  33  is mounted on the cell cap  32 , and level with the cell cap  32 . The reflector  35  has a reflector aperture  35 A corresponding to the cell cap aperture  32 A in the center of the reflector  35 .  
         [0062]     The reflector  35  comprises a body  35 B, a metal layer  35 D placed on the lower surface of the body  35 B, and a supporting member  35 C mounted on the body  35 B to contact the surface of the cell cap  32 , wherein the body  35 B is made of low conductivity metal or ceramic material.  
         [0063]     The body  35 B with low conductivity prevents the heat transfer from the cell cap  32  to outward. Also, the metal layer  35 D with low emissivity value is formed on the lower surface of the body  35 B to transfer the heat to the cell cap  32  again. Therefore, the cell cap  32  maintains a predetermined temperature.  
         [0064]     The heat from the cell cap  32  is also transferred to the supporting member  35 C. Therefore, in order to inhibit the heat transfer, the supporting member  35 C is made of low conductivity metal or ceramic material.  
         [0065]     The supporting member  35 C and the body  35 B can be integrally formed. However, in case of ceramic material, it is desirable for the supporting member  35 C and the body  35 B to be made separately because it is difficult to form the supporting member  35 C and the body  35 B integrally, wherein a bolt type or a close fit type is desirable.  
         [0066]     It is desirable for the supporting member  35 C to be at least more than four so that the supporting member  35 C supports the body  35 B because the supporting member  35 C contacts the cell cap  32  at a point. Also, it is desirable for the supporting member  35 C to be a pin type in order to minimize the contact area with the cell cap  32 , but not limited thereto.  
         [0067]     It is desirable for the body  35 B and the supporting member  35 C to be made of ceramic material, for example ZrO 2 , Al 2 O 3 , TiO 2 , and/or metal with low conductivity, for example Mn or Ti. And, it is desirable for the metal layer  35 D to be made of Au, Ag, or Al.  
         [0068]     The metal layer  35 D can be formed on the lower surface of the body  35 B by the thermal spray method, ECM (Electro Chemical Metalizing) method, or the electro plating method, wherein the thermal spray method comprises the flame spray method, the plasma spray method, or HVOF (High Velocity Oxigen-Fuel).  
         [0069]     As described above, the evaporation source according to the third embodiment of the present invention can maintain the temperature of the cell cap aperture at a predetermined level by the reflector made of the different materials, preventing the heat from being emitted to outward. Therefore, the problem that the vaporized evaporation material emitted through the cell cap aperture to outward is deposited around the cell cap aperture due to the decreased temperature can be efficiently resolved.  
       The Fourth Embodiment  
       [0070]      FIG. 9  is a sectional view showing the point evaporation source according to the fourth embodiment of the present invention. The point evaporation source  40  according to the fourth embodiment of the present invention comprises a cell  41  which is cylindrical, a cell cap  42  on which a cell cap aperture  42 A for emitting the vaporized evaporation material is formed, an external wall  43  which is cylindrical, and base  44 . A heating means  43 A is placed between the cell  41  and the external wall  43 , and the cell cap  42  is mounted on the upper end of the cell  41 .  
         [0071]     A cover  45  fixed to the upper end of the external wall  43  is mounted on the cell cap  42  contacting the upper surface thereof to smoothly transfer the heat to the cell cap  42 . The cover  45  has a cover aperture  45 A corresponding to the cell cap aperture  42 A.  
         [0072]     The heat generated from the heating means  43 A is transferred to the cover  45 . The heat transferred to the cover  45  is transferred to the cell cap  42  contacting the cover  45 . Therefore, the temperature of the cell cap aperture  42 A, which is formed in the center of the cell cap  42 , is not decreased due to the heat transferred from the cover  45 .  
         [0073]     It is desirable for the cover aperture  45 A and the cell cap aperture  42 A to have the same size. The heat generated by the heating means  43 A is transferred to the cell cap aperture  42 A through the cover  45  as well as the cell cap  42 , thereby more efficiently maintaining the temperature of the cell cap aperture  42 A at a predetermined level.  
         [0074]      FIG. 10  is a detailed view showing part “C” of  FIG. 9 . In case that the cover aperture . 45 A and the cell cap aperture  42 A have the same size, it is desirable for the thickness of the cover  45  to be decreased in the direction of the cover aperture  45 A to prevent the vaporized evaporation material from being deposited on the cover  45  during the evaporation process. Therefore, the inner circumferential surface of the cover aperture  45 A is sharply edged.  
         [0075]      FIG. 11  is a sectional view showing another point evaporation source according to the fourth embodiment of the present invention. A shut-off layer  46  is formed on the upper surface of the cover  45  fixed to the upper end of the external wall  43 , wherein the shut-off layer  46  is made of low conductivity material. The shut-off layer  46  has a shut-off layer aperture  46 A for emitting the vaporized evaporation material at a corresponding position to the cover aperture  45 A.  
         [0076]     The heat generated from the heating means  43 A is transferred to the cover  45  made of metallic material. The heat transferred to the cover  45  is transferred to the cell cap  42  contacting the cover  45 . The shut-off layer  46  formed on the upper surface of the cover  45  prevents the heat from being emitted from the cover  45  to outward. Therefore, most of the heat is transferred to the cell cap  42 .  
         [0077]     The shut-off layer  46  is made of low conductive material, for example ceramic material or metal material, wherein the ceramic material could be Al 2 O 3 , TiO 2 , SiC, or ZrO 2 , and the metal material could be Mn or Ti. It is desirable for the shut-off layer  46  to be formed on the cover  45  by the electro plating method.  
         [0078]      FIG. 12  is a detailed view showing part “D” of  FIG. 11 . In case that the shut-off layer aperture  46 A is smaller than the cover aperture  45 A, the vaporized evaporation material emitted through the cell cap aperture  42 A to outward is deposited on the shut-off layer aperture  46 A. Therefore, the shut-off layer aperture  46 A is larger than the cover aperture  45 A so that the vaporized evaporation material is not deposited on the shut-off layer aperture  46 A.  
         [0079]     In case that the shut-off layer aperture  46 A and the cover aperture  45 A have the same size, it is desirable for the thickness of the shut-off layer  46  to be decreased in the direction of the shut-off layer aperture  46 A to prevent the vaporized evaporation material from being deposited on the shut-off layer  46  during the evaporation process. Therefore, the inner circumferential surface of the shut-off layer aperture  46 A is sharply edged.  
         [0080]     As described above, the evaporation source according to the fourth embodiment of the present invention can maintain the cell cap aperture at a predetermined temperature by placing the cover to contact the cell cap, thereby transferring the heat generated in the heating means to the cell cap aperture through the cover. Also, the shut-off layer formed on the upper surface of the cover prevents the heat from being emitted to outward. Therefore, the problem that the vaporized evaporation material emitted through the cell cap aperture to outward is deposited around the cell cap aperture due to the decreased temperature can be efficiently resolved.  
         [0081]     From the above preferred embodiments for an evaporation source for evaporating an organic electroluminescent layer, it is noted that modifications and variations can be made by a person skilled in the art in light of the above teachings. Therefore, it should be understood that changes may be made for a particular embodiment of the present invention within the scope and spirit of the present invention outlined by the appended claims.