Abstract:
The present invention disclosed the deposition source installed in a chamber, heated by applied electric power to transfer heat to a vapor deposition material received therein and applying a vaporized deposition material generated therein to a substrate to form deposition organic electroluminescent layers onto the substrate, and comprising a vessel consisted of a top plate on which a vapor efflux aperture is formed, a side wall, and a bottom wall; a heating means for supplying heat to the deposition material received in the vessel, the heating means being capable of moving vertically; and a means for moving the heating means (or the bottom wall), the moving means (or the bottom wall) being operated in response to the signal of a sensing means on varied distances between the heating means and the surface of said deposition material. Thus, the heating means is moved downward (or the bottom wall) is moved upward by the moving means to maintain the distance between the heating means (or the substrate to be coated) and the surface of the deposition material at an initially-set value when the thickness of the deposition material is decreased.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a deposition source for thermal physical vapor deposition of organic electroluminescent layers, and particularly to a deposition source capable of forming a uniform electroluminescent layer on the entire surface of a substrate by compensating increase of the distance between a deposition material and a heating means (or the substrate ) from change of the thickness of the deposition material.  
         BACKGROUND OF THE INVENTION  
         [0002]    Thermal physical vapor deposition process, which is one of the processes for depositing an organic electroluminescent device, is a technique to coat an electroluminescent layer on a substrate in a housing with vaporized deposition material. In the deposition process, the deposition material is heated to the point of vaporization and the vapor of the deposition material is condensed on the substrate to be coated after the deposition material is moved out of the deposition source. This process is carried out with both deposition source holding the material to be vaporized and substrate to be coated in a vessel with the pressure range of 10 −7  to 10 −2  Torr.  
           [0003]    Generally speaking, the deposition source to hold the deposition material is made from electrically resistant materials whose temperature is increased when electrical current is passed through walls (member). When the electrical current is applied to the deposition source, the deposition material inside is heated by radiation heat from the walls and conduction heat from contact with the walls. Typically, the deposition source is in the shape of box with aperture to allow vapor efflux toward the direction of the substrate.  
           [0004]    Thermal physical vapor deposition source has been used to vaporize and deposit onto the substrate layers comprised of a wide range of materials, for example, organics of low temperature, metals, or inorganic compounds of high temperature. In the case of organic layer deposition, the starting material is generally powder. Organic powder has been recognized as giving a number of disadvantages for this type of thermal vaporization coating. First, many organics are relatively complex compounds (high molecular weight) with relatively weak bonding, and so intensive care must be taken to avoid decomposition during the vaporization process. Second, the powder form can give rise to particles of non-vaporized electroluminescent materials. The particles leave the deposition source with vapor and are deposited as undesirable lumps on the substrate. Such lumps are also commonly referred to as particulate or particulate inclusion in the layers formed on the substrate.  
           [0005]    Further exacerbation is found in that the powder form has a very large surface area enough to support water sucked in or absorbed or volatile organics, and the volatile organics can be released during heating and can cause gas and particulates to be thrown outward from the deposition source toward the substrate. Similar considerations pertain to materials which are melted before vaporization and form droplets erupted to the substrate surface.  
           [0006]    These unwanted particulates or droplets may result in unacceptable defects in products, particularly in electronic or optical products, dark spots may appear in images, or shorts or opens may result in failures within electronic devices.  
           [0007]    Organic deposition apparatuses have been proposed to heat the organic powder more uniformly and to prevent the bursts of particulates or droplets from reaching the substrate. Many designs for complicated baffling structures between the source material and the vapor efflux aperture have been suggested to ensure vapor exits.  
           [0008]    [0008]FIG. 1 is a schematic sectional view showing the inner structure of a conventional apparatus for depositing an organic electroluminescent layer, and shows a deposition source  10  mounted in a vacuum chamber  13  of the deposition apparatus and a substrate  12  located above the deposition source  10 . The substrate  12  to be coated with the organic electroluminescent layers is mounted to an upper plate  13 - 1  of the chamber  13 , and the deposition source  10  to have a deposition material  20  (organic material) is mounted on a thermally insulating structure  14  fixed to a bottom wall  13 - 2  of the chamber  13 .  
           [0009]    [0009]FIG. 2 a  is a sectional view showing the inner structure of the deposition source shown in FIG. 1, and shows that a baffle  11 B is provided in the deposition source  10  to prevent particulates or droplets contained in the vapor of the deposition material  20  from directly exiting through a vapor efflux aperture  11 C formed on the top plate  11 A of the deposition source  10 . The baffle  11 B corresponds to the vapor efflux aperture  11 C and is fixed to a number of support rods  11 B- 1  fixed to the top plate  11 A of the deposition source  10  to maintain certain space from the top plate  11 A.  
           [0010]    The deposition apparatus using the deposition source  10  with the above structure has a heater or a heating means on (or under) the top plate  11 A, or is constructed for the top plate  11 A to have a heater in order to transfer heat to the deposition material  20  located around the center away from the side wall  11 D. Thus, the heat generated at the side wall  11 D as well as from the top plate  11 A is transferred directly to the deposition material  20  so that the deposition material  20  is heated and vaporized. The vapor of vaporized deposition material  20  is moved along the surface of the baffle  11 B and deposited on the substrate  12  (in FIG. 1) after exit through the vapor efflux aperture  11 C.  
           [0011]    [0011]FIG. 2 b  is a sectional view showing the change of distance between the top plate of the deposition source in FIG. 1 and the deposition material after the deposition is processed for a certain amount of time. Thus, FIG. 2 b  shows a state that the distance between the top plate  11 A and the surface of the deposition material  20  is increased.  
           [0012]    As explained above, the quantity of the deposition material  20  received in the deposition source  10  is decreased gradually by heating and vaporizing reactions in progressing the deposition process also the thickness of the deposition material  20  is decreased. Thus, in a certain amount of time, the initial distance (A in FIG. 2 a ) between the top plate  11 A and the surface of the deposition material  20  in the deposition source is remarkably increased (a in FIG. 2 b ).  
           [0013]    Due to increase of the distance between the top plate  11 A and the surface of the deposition material  20 , the heat transfer path is increased so that the deposition rate (that is, vaporization rate of the deposition material) set at the initial stage is decreased. Thus, in order to maintain the initially-set deposition rate, the temperature of the top plate  11 A acting as the heater heating the deposition material  20  is needed.  
           [0014]    In particular, while the deposition process is progressed, the distance between the top plate  11 A and the surface of the deposition material  20  is increased. Under this situation, the sufficient heat generated at the top plate  11 A cannot reach the deposition material  20 , and so the deposition material located on the center is not vaporized though the heat generated from the side wall  11 D is supplied. Consequently, if the input amount of the deposition material  20  is high (that is, the thickness of the deposition material  20  is high), it is difficult to expect that all the deposition material is vaporized.  
           [0015]    Also, the distance between the substrate  12  and the deposition material  20 , which is directly related to the uniformity of deposition layer, is increased to result in change of the deposition characteristics in time.  
           [0016]    Low molecule organic electroluminescent material contains a large amount of organic material unstable to heat, and causes a problem of lowering the characteristics of the organic electroluminescent material by inducing resolution or change of the material characteristics due to excessive radiant heat in the deposition process. In addition, additional processes for cooling the chamber, exhausting the vacuum pressure, and re-vacuumizing are required to supply new deposition material to replenish the exhausted deposition material because the deposition process is conducted under high vacuum condition. Such additional processes cause loss of the process time.  
           [0017]    In order to solve these problems, it is desirable to maintain uniformly the initial deposition characteristics (for example, vaporization rate of the deposition material) in supplying more deposition material in the deposition source at a time.  
           [0018]    On the other hand, in the deposition source  10  with the structure shown in FIG. 2 a  and FIG. 2 b,  the side wall  11 D acts as a heating unit (for example, structure which coils are wound around the side wall  11 D). As shown in FIG. 1, however, since the sidewall  11 D is exposed to the exterior, the thermal efficiency is lowered because all heat generated at the side wall  11 D is not transferred to the deposition material  20  and some heat is radiated to the exterior.  
           [0019]    In addition, as describe above, in progressing the deposition process, the deposition material  20  supplied in the deposition source  10  is consumed, and so the thickness of the deposition material  20  is decreased. Thus, heat is generated at the sidewall  11 D corresponding to the portions without the deposition material and is not transferred directly to the deposition material, which contributes to energy waste.  
           [0020]    Another drawback of the deposition source  10  is that the heat generated at the top plate  11 A and the side wall  11 D is not sufficiently transferred to the deposition material  20  located at the lower portion of the deposition source  10 , that is, the deposition material  20  adjoining the surface of the bottom wall  11 E. As a result, all of the deposition material  20  is not heated and vaporized. Particularly, depending on positions within the deposition source  10 , the temperature of each deposition material  20  becomes different, that is, thermal gradient within the deposition source. Therefore, it is difficult to form a uniform deposition layer on the substrate.  
         SUMMARY OF THE INVENTION  
         [0021]    An object of the present invention is to provide the deposition source which can compensate change of the distance between the heating means and the surface of the deposition material caused by decrease of the thickness of the deposition material according to consumption of the deposition material in the deposition process for the purpose of solving problems caused by increase of the distance between the top plate (heating means) of the deposition source and the surface of the deposition material supplied into the deposition source from the deposition process.  
           [0022]    Another object of the present invention is to provide the deposition source which can enhance thermal efficiency through preventing heat generated at the heating means from exiting to the exterior by adding a heat-cutting function.  
           [0023]    Further, another object of the present invention is to provide the deposition source for forming organic electroluminescent layers which can obtain a uniform deposition layer by minimizing factors of temperature change and by efficiently using all the deposition material through supplying heat to the deposition source adjoining the surface of the bottom wall.  
           [0024]    The deposition source according to the present invention is installed in a chamber, heated by applied electric power to transfer heat to a vapor deposition material received therein and applying a vaporized deposition material generated therein to a substrate to form deposition organic electroluminescent layers onto the substrate, and comprises a vessel consisted of a top plate on which a vapor efflux aperture is formed, a side wall, and a bottom wall; a heating means for supplying heat to the deposition material received in the vessel, the heating means being capable of moving vertically; and a means for moving said heating means, the moving means being operated in response to the signal of a sensing means on varied distances between the heating means and the surface of said deposition material. Thus, the heating means is moved downward by the moving means to maintain the distance between the heating means and the surface of the deposition material at an initially-set value when the thickness of the deposition material is decreased.  
           [0025]    Another deposition source according to the present invention is installed in a chamber, to form deposition organic electroluminescent layers onto the substrate, by applying a vaporized deposition material generated therein to a substrate, by transferring heat to a vapor deposition material received therein, heated by applied electric power, and comprises a vessel consisted of a top plate on which a vapor efflux aperture is formed, a side wall, and a bottom plate, the bottom plate being capable of moving vertically; a heating means for supplying heat to the deposition material received in the vessel; and a means for moving said bottom plate, the moving means being operated in response to the signal of a sensing means on varied distances between the heating means and the surface of the deposition material. Thus, the bottom plate is moved upward by the moving means to maintain the distance between the heating means and the surface of the deposition material and the distance between the substrate to be coated and the surface of the deposition material at an initially-set value when the thickness of the deposition material is decreased. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    The present invention will be more clearly understood from the detailed description in conjunction with the following drawings.  
         [0027]    [0027]FIG. 1 is a schematic sectional view of a conventional apparatus for depositing an organic electroluminescent layer.  
         [0028]    [0028]FIG. 2 a  is a sectional view showing the structure of the deposition source shown in FIG. 1 prior to performing the deposition process;  
         [0029]    [0029]FIG. 2 b  is a sectional view showing change of the distance between the top plate of the deposition source and the deposition material in FIG. 1 after the deposition process is performed for a certain period of time.  
         [0030]    [0030]FIG. 3 a  is a sectional view of the deposition source according to the first embodiment of the present invention.  
         [0031]    [0031]FIG. 3 b  is a detailed view of part  3   b  in FIG. 3 a.    
         [0032]    [0032]FIG. 3 c  is a view showing relationship between the top plate of the deposition source and the deposition material after the deposition process is completed.  
         [0033]    [0033]FIG. 4 is a sectional view of the deposition source according to the second embodiment of the present invention.  
         [0034]    [0034]FIG. 5 is a sectional view of the deposition source according to the third embodiment of the present invention.  
         [0035]    [0035]FIG. 6 is a sectional view taken along line  6 - 6  in FIG. 5.  
         [0036]    [0036]FIG. 7 is a schematic perspective view showing relationship between the substrate and the deposition source according to the fourth embodiment.  
         [0037]    [0037]FIG. 8 a  is a plane view of the substrate showing the initial state which the electroluminescent layer is deposited on the surface using the deposition source shown in FIG. 7.  
         [0038]    [0038]FIG. 8 b  is a plane view of the substrate showing the state that deposition of the electroluminescent layer has been completed under the state that the deposition source (or substrate) shown in FIG. 7 has been moved.  
         [0039]    [0039]FIG. 9 a  and FIG. 9 b  are schematic sectional views showing various shapes of the deposition source according to the fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]    Reference should be made to the drawings. The same reference numerals are used throughout the drawings to designate same or similar elements.  
         [0041]    First Embodiment  
         [0042]    [0042]FIG. 3 a  is a sectional view of the deposition source according to the first embodiment of the present invention. A deposition source  100  according to the first embodiment is a vessel consisted of a top plate  101 , a side wall  102 , and a bottom wall  103 . The deposition source  100  contains solid organic electroluminescent vapor deposition material  20  (hereinafter, referred to as “deposition material”). A vapor efflux aperture  11 A is formed on the top plate  101 . The function of the vapor efflux aperture  101 A is to discharge vapor of vaporized deposition material from the deposition source  100 . A baffle member  104  fixed to a lower surface of the top plate  101  corresponds to the efflux aperture  101 A.  
         [0043]    The top plate  101  can act as a heating means (heater) for supplying heat to the deposition material  20  or a separate heating means can be placed on (or below) the top plate  101 . In the description below, a case where the top plate  101  acts as a heating means will be explained as an example.  
         [0044]    The most important feature of the first embodiment as shown in FIG. 3 a  is that the top plate  101  of the deposition source  100  can be vertically moved. A movement means  151  to move the top plate  101  is mounted to the top plate  101 .  
         [0045]    The movement means  151  used in the deposition source  100  according to the first embodiment is a hydraulic or pneumatic cylinder. Two support brackets  154  fixed a the side wall of the chamber ( 13  in FIG. 1) are extended above the deposition source  100 , and the cylinders  151  are mounted to each end portion of the brackets  154 . Rods  152  of each cylinder  151  are fixed to both sides of the top plates  101 , and therefore, each cylinder  151  does not have any effect on vapor efflux of the deposition material  20  through the aperture  101 A of the top plate  101 .  
         [0046]    On the other hand, each cylinder  151  is controlled by a control means which is not shown in FIG. 3 a,  and the control means is connected to a sensing means  153  (for example, optical sensor) installed on the lower surface of the baffle  104  so that the control means can control each cylinder  151  according to a signal from the sensing means  153 .  
         [0047]    [0047]FIG. 3 b  is a detailed view showing part  3   b  in FIG. 3 a.  FIG. 3 b  shows partially the structure of the side wall  102  and the top plate  101  which can be vertically moved along the side wall  102  of the deposition source  100 .  
         [0048]    A number of vertical grooves  102 - 1  are formed on the inner surface of the side wall  102 , and protrusions  101 - 1  are formed on the outer circumference surface of the top plate  101 . Each protrusion  101 - 1  corresponds to each groove  102 - 1  and can be received in the corresponding groove  102 - 1  when the top plate  101  and the side wall  102  are assembled. Thus, when the top plate  101  is moved vertically, each protrusion  101 - 1  is moved along the corresponding groove  102 - 1 . Consequently, the top plate  101  can be moved smoothly in the vertical direction without any deviation to the side wall  102  from the initial location.  
         [0049]    [0049]FIG. 3 c  is a view showing relationship between the top plate of the deposition source and the deposition material after the deposition process is completed. The function of the deposition source constructed as described above will be explained in reference to FIG. 3 a  and FIG. 3 c.    
         [0050]    As explained above, in the depositing process, the quantity of the deposition material  20  received in the deposition source  100  is decreased gradually by the heating and vaporizing action. Thus, the distance between the surface of the deposition material  20  and the top plate  101  is changed (increased). The sensing means  153  mounted on the lower surface of the baffle  104  senses this change of the distance between the surface of the deposition material  20  and the top plate  101 , and then transmits the sensed signal to the control means.  
         [0051]    The control means calculates the distance between the surface of the deposition material  20  and the top plate  101  (that is, sum of the distance between the surface of the deposition material  20  and the sensing means  153 , and the distance between the lower surface of the baffle  104  and the top plate  101 ) on the basis of the signals transmitted from the sensing means  153 , and then compares the calculated distance with the initially-set distance (value).  
         [0052]    As a result of the above comparison, if the distance between the surface of the deposition material  20  and the top plate  101  is changed, the control means operates each cylinder  151 . By operating each cylinder  151 , the rods  152  of each cylinder  151  are extended downward so that the top plate  101  fixed to the ends of the rods  152  is moved downward along the side wall  102 .  
         [0053]    If the distance between the surface of the deposition material  20  and the top plate  101  becomes the same as the initially-set distance (A in FIG. 3 a ) by downward movement of the top plate  101 , that is, when the distance between the surface of the deposition material  20  and the top plate  101  calculated by the control means on the basis of the signals transmitted from the sensing means  153  becomes the same as the initially-set distance, the control means halts the operation of each cylinder  151 .  
         [0054]    The downward movement of the top plate  101  caused by the control means and each cylinder  151  is continued during the deposition process. After vaporizing all of the deposition material  20 , the control means makes the rods  152  of each cylinder  151  return to the initial state as shown in FIG. 3 a.  Then, the top plate  101  of the deposition source  100  returns to its initial position, and thereafter, new deposition material is supplied to the deposition source  100 .  
         [0055]    On the other hand, FIG. 3 a  and FIG. 3 c  show that the optical sensor  153  acting as the sensing means is installed on the lower surface of the baffle  104 , but the optical sensor  153  can be installed at any position including the lower surface of the top plate  101  as long as the optical sensor  153  does not hinder the deposition process and can sense the distance between the surface of the deposition material  20  and the top plate  101 .  
         [0056]    Second Embodiment  
         [0057]    [0057]FIG. 4 is a sectional view of the deposition source according to the second embodiment of the present invention. The entire structure of a deposition source  200  according to this embodiment is the same as that of the deposition source  100  shown in FIG. 3 a  and FIG. 3 c.  In this embodiment, a top plate  201  can act as a heating means (heater) for supplying heat to the deposition material  20  or a separate heating means can be placed on (or below) the top plate  201 . In the description below, a case where the top plate  201  acts as a heating means will be explained as an example.  
         [0058]    The most important feature of the deposition source  200  according to the second embodiment is that a bottom plate  203  can be moved vertically in response to change of the distance between the surface of the deposition material  20  and the top plate  201 .  
         [0059]    As described above, the uniformity of the deposition layer to be formed on the surface of the substrate ( 12  in FIG. 1) depends on change of the distance between the substrate  12  and the deposition material  20 . In the deposition source  100  shown in FIG. 3a, change of the distance between the top plate  101  and the deposition material  20  can be compensated by the vertical movement of the top plate  101 , but a means to adjust change of the distance between the substrate  12  and the deposition material  20  is not disclosed.  
         [0060]    In order to compensate change of the distance between the substrate  12  and the deposition material  20 , the deposition source  200  according to this embodiment has the stricture which the bottom plate  203  can be moved vertically along a side wall  202 .  
         [0061]    A movement means  251  for moving the bottom plate  203  is mounted under the bottom plate  203  on which the deposition material  20  is located. The movement means used in the deposition source  200  according to the second embodiment is a hydraulic or pneumatic cylinder. The cylinder  251  is installed on a bottom wall  13 - 2  of the chamber  13  shown in FIG. 1, a rod  252  of the cylinder  251  is passed through the bottom wall  13 - 2 , and the end of the rod  252  is fixed to the lower surface of the bottom plate  203 . However, the structure shown in FIG. 4 is merely an example, and so the cylinder having another structure can be installed.  
         [0062]    In the this embodiment, the cylinder  251  is controlled by a control means which is not shown in FIG. 4, the control means is connected to a sensing means  253  (for example, optical sensor) so that the control means controls the cylinder  251  according to the signal transmitted from the sensing means  253 .  
         [0063]    On the other hand, a number of vertical grooves are formed on the inner surface of the side wall  202 , and a number of protrusions are formed on the outer circumference surface of the bottom plate  203 . Each protrusion corresponds to each groove and can be received in the corresponding groove. Therefore, the bottom plate  203  can be moved smoothly in the vertical direction without any deviation to the side wall  202  from the initial location. This structure of the second embodiment is the same as that of the first embodiment as shown in FIG. 3 c  except difference of the member on which the protrusions are formed. Therefore, a further detailed description on the protrusions and grooves is omitted.  
         [0064]    In the depositing process, the quantity of the deposition material  20  received in the deposition source  200  is decreased gradually by the heating and vaporizing actions. Thus, the distance between the substrate ( 12  in FIG. 1) and the deposition material  20  is increased (surely, the distance between the surface of the deposition material  20  and the top plate  201  is also increased, and the increased distance between the surface of the deposition material  20  and the top plate  201  is the same as the increased distance between the substrate  12  and the surface of the deposition material  20 ).  
         [0065]    The sensing means  253  mounted to a lower surface of a baffle  204  senses change of the distance between the surface of the deposition material  20  and the top plate  201 , and then transmits the sensed signal to the control means. The control means calculates the distance between the surface of the deposition material  20  and the top plate  201  on the basis of the signals transmitted from the sensing means  253 , and then compares the calculated distance with the initially-set distance.  
         [0066]    As a result of the above comparison, if the distance between the surface of the deposition material  20  and the top plate  201  is changed, the control means operates the cylinder  251  installed under the bottom plate  203 . By operating of the cylinder  251 , the rod  252  of the cylinder  251  is extended upward so that the bottom plate  203  fixed to the end of the rod  252  is moved upward along the side wall  202 .  
         [0067]    If the distance between the surface of the deposition material  20  and the top plate  201  becomes the same as the initially-set distance (A in FIG. 3 a ) by the upward movement of the bottom plate  203 , that is, when the distance between the surface of the deposition material  20  and the top plate  201  calculated by the control means on the basis of the signals transmitted from the sensing means  253  becomes the same as the initially-set distance, the control means halts the operation of the cylinder  251 .  
         [0068]    The upward movement of the bottom plate  203  caused by the control means and the cylinder  251  is continued during the deposition process. After vaporizing all of the deposition material  20 , the control means makes the rod  252  of the cylinder  251  return to the initial state. Then, the bottom plate  203  of the deposition source  200  returns to its initial position, and thereafter, new deposition material is supplied to the deposition source  200 .  
         [0069]    On the other hand, FIG. 4 shows that the optical sensor  253  acting as the sensing means is installed at the lower surface of the baffle  204 , but the optical sensor can be installed at any positions including the lower surface of the top plate  201  as long as the optical sensor  253  does not hinder the deposition process and can sense the distance between the surface of the deposition material  20  and the top plate  201 .  
         [0070]    In the deposition sources  100  and  200  according to the first and second embodiments as described above, when the thickness of the deposition material  20  caused by consumption thereof during the deposition process is changed, the distance between the surface of the deposition material  20  and the top plate  101  (the first embodiment) or the distance between the surface of the deposition material  20  and the substrate  12  (the second embodiment) can be maintained at the initially-set distance by the movement of the top plate  101  (the first embodiment) or the bottom plate  203  (the second embodiment). Thus, an appropriate amount of heat is transferred to the deposition material  20  during the deposition process so that the deposition temperature of the deposition material  20  can be maintained uniformly and the optimum deposition rate can be maintained.  
         [0071]    In the second embodiment, especially, the distance between the top plate  201  and the deposition material  20  as well as the optimum distance between the substrate and the deposition material are always maintained, and so it is possible to form a uniform deposition layer. Also, the deposition material adjoining the surface of the bottom plate  203  can be vaporized so that it is possible to minimize the residual of the deposition material.  
         [0072]    In particular, in a case where the deposition material is supplied to the maximum, all of the deposition material can be vaporized, and the time loss caused by vacuuming, heating, and cooling processes to be performed in the deposition chamber after replenishing the deposition material can be minimized. Therefore, the second embodiment enables the depth of the deposition source to make deeper than the conventional depositional source, and so the quantity of the deposition material supplied to the deposition source can be maximized.  
       Third Embodiment  
       [0073]    [0073]FIG. 5 is a sectional view of the deposition source according to the third embodiment of the present invention. The deposition source  300  according to this embodiment has a vessel consisted of a top plate  301  acting as the heating means, a side wall  302 , and a bottom wall  303 . The structure of the top plate  301 , on which a vapor efflux aperture  301 A is formed and to which a baffle member  304  is fixed, is the same as the top plates  101  and  201  of the deposition sources  100  and  200  of the first and second embodiments, respectively. Therefore, a further detailed description thereon is omitted.  
         [0074]    The important aspect of the deposition source  300  shown in FIG. 5 is that a number of coils C 1 , C 2 , . . . Cn as a heating means for transferring heat to the deposition material  20  are wound around the side wall  302 , and a casing  350  is located at the outer side of the side wall  302 .  
         [0075]    A number of coils C 1 , C 2 , . . . Cn are wound on the outer circumference surface of the side wall  302 . The uppermost coil C 1  coincides with the surface of the deposition material  20  received in the deposition source with the maximum height (thickness), and the lowermost coil Cn coincides with the surface of the bottom wall  303 .  
         [0076]    The coils C 1 , C 2 , . . . Cn are arranged for electric power to be individually applied thereto. A control means (not shown) controls the electric power applied to each coil C 1 , C 2 , . . . Cn, and the control means is connected to a sensing means  353  (for example, optical sensor) which is mounted to the interior of the deposition source.  
         [0077]    The function of the coils C 1 , C 2 , . . . Cn arranged and described as above is as follows.  
         [0078]    In the early stage of the deposition process, the surface of the deposition material  20 , which is supplied into the deposition source  20  with the maximum height, coincides with the uppermost coil C 1 . At this time, electric power is applied to only the uppermost coil C 1 , not the other coils C 2 , . . . Cn, by the control means. The upper side of the deposition material  20  is heated and vaporized by the heat generated at the top plate  301  acting as a heating means and by the heat generated at the uppermost coil C 1 .  
         [0079]    In the depositing process, the quantity of the deposition material  20  received in the deposition source  200  is decreased gradually by the heating and vaporizing action (that is, decrease of the height of the deposition material  20 ).  
         [0080]    The sensing means  353  mounted on the lower surface of the baffle  304  senses change of the height of the deposition material  20 , and transmits the sensed signal to the control means. Then, the control means calculates the height of the deposition material  20  on the basis of the signals transmitted from the sensing means  353 . According to the calculated height of the deposition material  20 , the control means controls the electric power applied to the other coils C 1 , C 2 , . . . Cn.  
         [0081]    That is, when the height of the deposition material  20  is reduced and the surface of the deposition material  20  corresponds to the second coil C 2  positioned below the uppermost coil C 1 , the control means blocks the electric power applied to the uppermost coil C 1  and applies the electric power to the second coil C 2 .  
         [0082]    In succession, if the surface of the deposition material  20  corresponds to the lowermost coil Cn, the control means applies the electric power to the lowermost coil Cn and blocks the electric power applied to the other coils C 1 , C 2  . . .  
         [0083]    As described above, in the depositing process, even though the height of the deposition material  20  is changed, any one coil to which the electric power is applied always corresponds to a portion of the deposition material  20  to which the heat generated by the top plate  301  is transferred. Therefore, it is possible to prevent the heat generated by the coils C 1 , C 2 , . . . Cn from transferring unnecessarily to the portion of the deposition material which heating and vaporizing do not take place and the deposition material is not present.  
         [0084]    On the other hand, the casing  350  located at the outer side of the side wall  302  prevents the heat generated at each coil C 1 , C 2 , . . . Cn from radiating outward. Thus, most of the heat generated at each coil C 1 , C 2 , . . . Cn is transferred to the deposition material  20  through the side wall  302  so that it is possible to minimize heat loss. Particularly, if the space formed between the side wall  302  and the outer casing  350  is filled with a thermal insulation material, the heat radiation is prevented more effectively to minimize thermal gradient in the entire system. The reference numeral  350 A indicates the opening formed on the casing  350  for connecting power lines to the coils C 1 , C 2 , . . . Cn.  
         [0085]    More excellent adiabatic property can be obtained by forming the casing  350  with oxide or nitride of aluminum (Al), zirconium (Zr), silicon (Si), yttrium (Y), etc., having high thermal capacity.  
         [0086]    Another feature of the deposition source according to this embodiment is shown in FIG. 6. FIG. 6 is a sectional view taken along the line  6 - 6  in FIG. 5 and shows a recess  303 A formed at the lower surface of the bottom wall  303  and a coil C received in the recess  303 A.  
         [0087]    The recess  303 A is formed to the longitudinal (or widthwise) direction on the bottom wall  303 , and consists of many linear portions and connection portions connecting two neighboring linear portions. Thus, the single coil C is spread on the entire surface of the bottom wall  303 . Both ends of the coil C are connected to the power supply (not shown).  
         [0088]    When the deposition process is performed, the electric power is applied to any one of the coils C 1 , C 2 , . . . Cn wound around the side wall  302  as well as the coil C received in the recess  303 A of the bottom wall  303  (surely, the electric power is applied to the top plate  301  acting as a heating means). Therefore, the heat generated at the coil C received in the recess  303 A of the bottom wall  303  is transferred to the deposition material adjoining the surface of the bottom wall  303 .  
         [0089]    In the deposition source according to third embodiment as described above, in the processing the depositing process, even though a height of the deposition material is changed, the coil to which the electric power is applied is always corresponded to a portion of the deposition material to which heat generated by the top plate is transferred. Therefore, it is possible to prevent heat generated by the coils from transferring unnecessarily to a portion of the deposition material which is not heated and vaporized and a portion of the deposition source in which the deposition material is not present.  
         [0090]    Also, the casing provided at the exterior of the side wall prevents the heat generated at the coils mounted to the side wall from radiating outward, and so most generated heat is transferred to the deposition material through the side wall to minimize thermal gradient in the entire system.  
         [0091]    In addition, when an additional coil is provided at the bottom wall of the deposition source, sufficient heat can be transferred to the deposition material which is remotely located from the heating means (that is, the deposition material adjoining the surface of the bottom wall), and so all of the deposition material can be used effectively and a uniform deposition layer can be obtained.  
         [0092]    Fourth Embodiment  
         [0093]    [0093]FIG. 7 is a schematic perspective view showing relationship between the deposition source according to the fourth embodiment and the substrate. An inner structure of the deposition source  400  is not shown in FIG. 7.  
         [0094]    The deposition source  400  according to this embodiment is consisted of a top plate  401  with certain length and width, a side wall  402 , and a bottom wall. A vapor efflux aperture  401 A is formed on the top plate  401 . An organic electroluminescent vapor deposition material is received in the space formed by the top plate  401 , the side wall  402 , and the bottom wall.  
         [0095]    A feature of this embodiment is to constitute the deposition source  400  whose effective deposition length (that is, length A of the vapor efflux aperture  401 A of the top plate  401  actually contributing to the deposition process) is longer than, or the same as, the width b of the substrate  12  on which the electroluminescent layer is formed.  
         [0096]    [0096]FIG. 8 a  is a plane view of the substrate showing the initial state that the electroluminescent layer is formed on the surface of the substrate by means of the deposition source  400  shown in FIG. 7. If the deposition source  400  as described above is used for forming the electroluminescent layer on the surface of the substrate  12 , the deposition material&#39;s vapor is diffused through the aperture  400 A of the top plate  401 , and then dispersed and deposited uniformly on the surface of the substrate  12  over the entire width.  
         [0097]    The more effective deposition process can be performed by moving the deposition source  400  constructed as described above or the substrate  20  to the longitudinal direction of the substrate. That is, when the deposition source  400  or the substrate  20  is moved horizontally (linearly) to the arrow direction shown in FIG. 8, the electroluminescent layer as shown in FIG. 8 a  is continuously deposited on the surface of the substrate  12  over the entire length. Ultimately, as shown in FIG. 8 b  showing the surface of the substrate on which the deposition of the electroluminescent layer is completed after moving horizontally the deposition source  400  or the substrate  12 , the uniform electroluminescent layer is formed on the entire surface of the substrate  12 .  
         [0098]    On the other hand, each respective deposition source  100 ,  200 ,  300  and  400  described in the first to fourth embodiments has the inner space divided into the lower and upper portion, and the cross sectional surface of the lower portion is the same as that of the upper portion. Therefore, the flow rate of vapor of the deposition material at the lower portion is practically equal to the flow rate at the upper portion. Also, due to the large surface area of the upper portion of the deposition source, heat loss of the deposition material in the inner space is increased. In order to eliminate the above drawbacks, the present invention modified the shape of the deposition source.  
         [0099]    [0099]FIG. 9 a  to FIG. 9 d  are sectional views of the deposition sources, and show various shapes of the deposition source according to the present invention. Another feature of the deposition sources  500 A,  500 B,  500 C, and  500 D according to the present invention is that the sectional surface area of the upper portion at which the aperture is formed is smaller than that of the lower portion.  
         [0100]    Though the sectional surface areas in a tube can be different in different positions, the quantity of flow is same anywhere in the tube, and therefore, the flow rate of a portion having smaller sectional surface area is higher than that of another portion having larger sectional surface area.  
         [0101]    Consequently, just before diffusing vapor of the deposition material through the aperture, the flow rate of vapor at the upper portion having smaller sectional surface area is higher than that of vapor at the lower portion of the deposition source. Higher flow rate induces increase of the vapor&#39;s kinetic energy (molecules of the vaporized deposition material), and so the density and uniformity of the deposition layer formed on the substrate can be enhanced. Also, since the sectional surface area of the upper portion through which the vapor of the deposition material is diffused is small, heat loss outward can be minimized and the deposition source is not influenced by such exterior interference as change of ambient temperature.  
         [0102]    In the present invention, on the other hand, a material having higher thermal capacity than quartz, for example, oxide or nitride of aluminum (Al), zirconium (Zr), silicon (Si), or yttrium (Y), or composite material of at least two above, is used as the deposition source&#39;s material. The thermal capacity of these metal oxide or nitride is larger than organic material used as the deposition material (about 3:1), and therefore, the adiabatic property of the deposition source can be improved.  
         [0103]    The preferred embodiments of the present invention have been described for illustrative purposes, and those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the present invention as disclosed in the accompanying claims.