Abstract:
An apparatus for coating an areal substrate, for example a rectangular plate comprises a vaporizer source and a distributor system for the supply of vaporized material onto the substrate. The distributor system comprises a line source, with this line source and the substrate is movable relative to one another. The apparatus serves preferably for the production of flat screens with organic light-emitting diodes.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to an apparatus for coating an areal substrate, and to methods of using the apparatus to coat substrates. 
     For over one hundred years the cathode ray tube has been the means of choice for the optical representation of still and/or moving pictures by means of raster-form spot representation. One disadvantage of the cathode ray tube, however, is that it has considerable depth such that, for example, flat television screens cannot be produced with it. 
     Therefore, for some time attempts have been to produce a flat screen or a flat display. Some of the best known of the structural elements developed over the last years and decades with which flat screens can be produced are light-emitting diodes (LEDs), liquid crystal elements (LCDs) and plasma elements. These modern structural elements, however, still have also specific disadvantages. Thus, conventional LEDs consume relatively significant levels of energy, while plasma elements, which are small fluorescent tubes, cannot be reduced to any desired size. The pixel raster of the plasma elements is limited to approximately 0.5 mm. More recent developments in the production of flat screens are directed toward so-called organic light-emitting diodes (OLEDs). The advantages of these organic light-emitting diodes comprises that at voltages of less than 5 volts they have low energy consumption, are strongly luminous, have a wide radiative angle, can be applied in temperature ranges from −40° C. to +85° C., and are of low weight. In addition, their quantum efficiency, i.e. the number of generated photons per injected electron or hole, has risen to more than 16% (Helmut Lemme: OLEDs—Senkrechtstarter aus Kunststoff, Elektronik 2/2000, p. 98, right column, paragraph 2, No. [5]: Yi He; Janicky, J.: High Efficiency Organic Polymer Light-Emitting Heterostructure Apparatuss, Eurodisplay &#39;99, VDE-Verlag Berlin, Offenbach) and thus above the quantum efficiency of inorganic LEDs from III-V semiconductors. OLEDs thus are choices for applications in battery-operated apparatus. OLEDs are comprised of one or more semiconducting organic layers disposed between two electrodes with at least one of these electrodes, as a rule, being transparent. If an electric field is applied, electrons or holes are injected through the cathode or anode into the transport bands of the organic layer. Both charge carriers migrate toward one another and a certain portion of them recombines, whereby light quanta are generated through spontaneous emission (Helmuth Lemme: OLEDs—Senkrechtstarter aus Kunststoff, Elektronik 2/2000, pp. 97 to 103; E. Becker et al: Organische Lumineszenz: Neue Technologie für flache Bildschirme, Fernseh- und Kino-Technik, 8-9/2000, pp. 1 to 5). 
     The production of OLEDs can be accomplished by means of an OVPD (Organic Vapor Phase Deposition, U.S. Pat. No. 5,554,220) technology, in which a carrier gas stream at very low pressure in a heated reactor takes up materials and deposits these as thin layers on a substrate. This substrate can be, for example, an ITO (Indium Zinc Oxide) electrode which previously had been vapor-deposited onto glass. Onto the organic luminescent layer subsequently a further electrode is vapor-deposited and the electrodes with the active luminescent layer have approximately a thickness of 400 nanometers. 
     In a further method for the coating of a substrate with a thin organic layer, a substrate holder with a heater is provided, which holds on its underside a substrate, for example glass (EP 0 962 260 A1=U.S. Pat. No. 6,101,316). Beneath this substrate, two vaporizer sources are provided, which vaporize organic material which becomes deposited on the substrate if a diaphragm disposed between the substrate and the vaporizer is opened. With this method the uniform coating of substrates over large areas is not possible. Employing two separate vaporizers leads to superpositions of the vaporized materials on the substrate causing nonuniformity of the coating. 
     A vacuum vaporization installation is furthermore known, which comprises a vaporizer tank in which the material to be vaporized is vaporized. The topside of this vaporizer tank is provided with a hood extending outwardly in the horizontal direction (EP 0 477 474 A1). Linear distribution of the vaporized material is not attainable with this installation. 
     An apparatus is also known for coating a steel band, which comprises at least one vacuum vaporization container heated by induction. The apparatus is wherein each of the containers has an opening for the outlet of metal vapors and that the outlet opening for the metal vapors has the form of a narrow slot, disposed at a small spacing from the substrate to be coated (WO 96/35822). With this apparatus the linear distribution of vapor is also not possible. 
     A vaporizer source for the production of organic electroluminescence diodes is described in EP 0 982 411 A1. This source comprises a container of an insulating material, which receives the organic material. Closely around the container is placed a heater, which vaporizes the organic material. The container has a heating zone, which is heated directly by the heater and which is in contact with the organic material via a contact zone. The way in which the coating of substrates takes place is not described in detail. 
     In order to complete coatings over a large area, it is in principle possible to employ dot-form, line-form or areal vaporizers. While dot-form vaporizers are known for example through EP 0 982 411 A2 and EP 0 962 260 A1, a line-form vaporizer is already known from DE 42 04 938 C1. In the case of this line-form vaporizer, the vaporative deposition onto the substrate takes place from below. The same applies to a line-form vaporizer disclosed in DE 199 21 744 A1. 
     The disadvantage of dot-form vaporizers consists therein that with them a homogeneous coating on large areas can only be realized if the distance between vaporizer and substrate is large. This requires a coating installation to be very large in order for the distance between vaporizer and substrate to be large. In addition, only a small portion of the vaporizer material is utilized. 
     Moreover, the vaporizer source must be disposed beneath the substrate which can lead to problems with masks positioned between vaporizer source and substrate, and specifically not before the substrate reaches a size of approximately 300 mm×400 mm and with small structures in the masks. 
     If linear vaporizer sources are disposed horizontally and underneath a substrate to be coated, problems are encountered with masks starting at approximately 300 mm×400 mm and small structures within the masks, for example with pixel sizes from 0.4 mm×0.4 mm, since in this case the masks are sagging: which leads to inhomogeneous coating. In order to attain a high level of homogeneity with relatively thick layers, the vaporizer sources or the substrate must furthermore be moved slowly relative to one another. 
     The present invention provides an apparatus for the coating of substrates, which has a reduced space requirement, with which uniform coating can be achieved and with which it is also possible to apply large masks. Methods of using the apparatus to coat substrates are also a part of the invention. 
     The invention relates to an apparatus for coating an areal substrate, for example a rectangular plate. This apparatus comprises a vaporizer source and a distributor system for conveying vaporized material onto the substrate. The distributor system comprises a line source, with this line source and the substrate being movable relative to one another. The apparatus serves preferably for the production of flat screens with organic light-emitting diodes. 
     An advantage provided by the invention is that large quantities of areal material can be coated since the substrates are guided past a linear vaporizer source. Masks, disposed between vaporizer source and substrate, do not sag since they are disposed parallel to the areal substrate. In addition, efficient utilization of the vaporized material is made possible, and chemical reactions of vaporized organic materials with the surrounding parts do not take place. Furthermore, thereby that the entire distributor region beyond the crucible and before the final outlet opening is at a defined high temperature, condensation of the vaporized material is prevented without leading to a chemical decomposition of the organic molecules. 
     An embodiment example of the invention is depicted in the drawings and is described in further detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective overall view of a coating chamber according to the invention. 
         FIG. 2  is a front view of the coating chamber according to  FIG. 1 . 
         FIG. 3  is a section A-A through the chamber according to  FIG. 2 . 
         FIG. 4  is a section B-B through the chamber according to  FIG. 2 . 
         FIG. 5  is an enlarged sectional representation of the crucible according to  FIG. 3 . 
         FIG. 6  is an enlarged partial representation from  FIG. 4 . 
         FIG. 7  is a perspective exploded drawing of a distributor for distributing the vaporized material. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a perspective overall view of coating boiler  1  according to the invention having a vaporizer. Coating boiler  1  has a front side  2  and rear side  3 . Front side  2  is provided with front opening  4  and rear side  3  is provided with rear opening  5  for the introduction of a drive. Front and rear openings  4  and  5  can be closed again after the introduction of a drive. Disposed above front opening  4  is front plate  6 , which supports front carrier plate  7  and rear carrier frame  8 . 
     Parts (housing parts)  10 ,  11 ,  12  of coating boiler  1  form a housing, which forms a working region with its own housings disposed next to one another, which are not depicted in  FIG. 1 . 
     A substrate  9 , for example a glass plate, can be moved through the working regions disposed one next to the other and be worked in a manner which is different in each case. The overall installation, not shown here, is thus structured modularly, with the coating boiler  1  representing one of several modules. The chamber, in which the substrate  9  is coated, without a process has a base pressure of less than 10 −4  Pa and with a process of less than 10 −2  Pa, with this pressure being a function of the vaporization rates. 
     Carrier plate  7  and carrier frame  8  are connected with one another, with several flanged measuring tubes  13  to  23  each projecting from front carrier plate  7 . For example, the flanged measuring tube  13  may be observation tube having a glass covering, through which substrate  9  may be viewed. In the flanged measuring tube  14 , a thermocouple can be disposed, while in flanged measuring tube  15  a quartz oscillator can be disposed, with which the vaporizer rate of the vaporizer source may be measured. Handle  24  may be provided to make it possible to lift carrier plate  7  and carrier frame  8  like a door from the rest of coating boiler  1 . Cooling tubing  25  for cooling carrier plate  7  and carrier frame  8  is wound about the flanged measuring tubes)  13  to  23 , and specifically such that the cooling tubing extends from connection pipe  26  for cooling fluid above flanged measuring tubes  13  to  16 , combined into a first group, and is subsequently guided beneath these flanged measuring tubes  13  to  16  and thus above additional flanged measuring tubes  17  to  19 , combined into a second group, and, lastly, beneath a third group of flanged measuring tubes  20  to  23  is connected with a further connection pipe  27  for the cooling fluid. 
     Disposed between the flanged measuring tubes  13  to  23  and opening  4  is a vaporizer source  28  which includes front tube  29  and rear tube  30 . Both front and rear tubes  29 ,  30  are held together by connection clamps  37 ,  38 , which are provided for receiving connection bolts. At the lower end of rear tube  30  are disposed two ports  32 ,  33 , to which for example a power source can be connected. A cooling tube  36  is guided about rear tube  30 , which is connected with cooling means port  39 . Suspension hooks  34 ,  35  are provided, with which carrier plate  7  forming a door or carrier frame  8  can be raised. 
     Not shown in  FIG. 1  is a mask, which is conventionally disposed parallel to the substrate  9 , and specifically between substrate  9  and front plate  6 . Since the mask is oriented vertically, the sagging due to gravity is excluded. 
     Substrate  9  is oriented vertically, i.e. parallel to the direction of the gravitational force of the earth. However, minor deviations from parallelity are permitted, i.e., the substrate is substantially parallel with the earth&#39;s gravity. The entire coating boiler  1  can, for example, for reasons not further explained here, be inclined by approximately 7° with respect to the vertical. The invention prevents or minimizes sagging of potential masks. If the mask, due to an oblique position of the substrate  9  rests on the top side of this substrate  9 , it cannot sag. 
     In  FIG. 2  the same configuration as in  FIG. 1  is once again depicted in front view. Evident here are vaporizer source  28 , flanged obliquely onto front carrier plate  7 , flanged measuring tubes  13  to  23 , cooling tubing  25 , and handle  24 . In addition, sectional lines A-B or B-B are shown, which characterize the sections depicted in  FIGS. 3 and 4 . 
     The sectional representation depicted in  FIG. 3  shows carrier plate  7  with the measuring tubes and their flanges  14 ,  18 ,  21  as well as the substrate  9  and the tubes  29 ,  30  of the vaporizer source  28 . Substrate  9  is for example a glass plate, which can be moved into the plane of drawing and out of it. The retention and the drive for this substrate  9  are not shown in FIG.  3 . The same applies to the retention and the drive of a mask, potentially on the left next to the substrate  9 , which can cover the entire surface of substrate  9 . 
     Within tube  29  is disposed a ceramic tube  43 , which is encompassed by a metal shielding tube  42 . At the lower end of the ceramic tube  43  is provided a crucible  44 , whose front portion connects to a quartz tube  46 . In the representation of  FIG. 3 , this quartz tube  46  is pulled out such that the distance between its lower end and the crucible  44  is relatively large. The obliquely disposed quartz tube  46  transitions at its front end into the rear wall  47  of a vertically oriented quartz tube  40 , which, on its side  48  facing away from the quartz tube  46 , is provided with several holes disposed on a vertical line. These holes are depicted in further detail in  FIG. 7 . 
     The vertically disposed quartz tube  40  is encompassed by two halves  52 ,  58  of a ceramic tube, which, in the representation of  FIG. 3 , are pulled apart to the left and the right. In the assembled state and during operation, the two halves  52 ,  58  are brought together such that they form a tubular unit which encompasses the quartz tube  40 . It is particularly preferred that quartz tube  40  is arranged in a plane parallel to the surface of the substrate. 
     The two halves  52 ,  58  of the ceramic tube are, in turn, encompassed by metal tube halves  53 ,  57 . The halves  52 ,  53  of the ceramic tube or of the metal tube provided on the right side have holes at the same site as the vertical quartz tube  40 . The holes of the three tubes are thus positioned one beyond the other and form a line source. 
     During operation, the lower end of quartz tube  46  is connected with crucible  44  such that the material vaporized from crucible  44  is conducted through the oblique quartz tube  46  into the vertical quartz tube  40 , which is encompassed by ceramic halves  52 ,  58  and metal tube halves  53 ,  57 . The vaporized material now is conducted through the vertically disposed holes of quartz tube  40  and through the holes of halves  52 ,  53  of the ceramic or the metal tube into the chamber in which the substrate  9  is disposed. Since these holes—in contrast to the representation of FIG.  3 —during operation are disposed on the left of substrate  9 , substrate  9  is acted upon with the vaporized material. 
     If a mask is disposed between the metal tube  53  and substrate  9 , the vaporized material first reaches this mask before it arrives on substrate  9 . 
     Past the line source, formed by the vertically disposed holes of quartz tube  40 , of ceramic tube  52 ,  58  and of metal tube  53 ,  57  the substrate  9  is guided out of the plane of drawing or into the plane of drawing. In this way, the continuous coating of a large substrate area is possible. 
     The temperature of crucible  44  and the temperature of the distributor system containing tube  40  and  46 , are regulated separately, and the precise regulation of the temperature for the range between 100° and 800° C. must be ensured. The entire distributor system succeeding the crucible  44  must be at a defined high temperature, which prevents condensation on surfaces exposed to the vapor, e.g., the walls of the coating boiler  1 , walls of the distributor system, including tubes  40  and  46  bores or slots therein and corresponding bores or slots, but does not thermally decompose organic molecules. As explained in conjunction with  FIG. 6 , the uniformity of the temperature is best achieved through indirect heating by means of radiation. The homogeneity of the coating of substrate  9  is attained through a ratio, adapted to the vaporization rate, of the diameters of tubes  40 ,  46  to the area of the outlet opening comprised of many small holes or a slot. The outlet opening can advantageously be kept free of coating through specific tempering. 
     The distance between the front side  48  of tube  40  and substrate  9  during operation should be kept as small as feasible. With the apparatus depicted in  FIGS. 1 to 3  it is feasible to replenish coating material with only the crucible region needing to be ventilated. It is furthermore possible to bring the crucible  44  maintained under vacuum or protective gas to the distributor system without ventilating the crucible, the entire source or the installation. It is also possible to provide two vaporizer crucibles, which vaporize different materials, and the two material vapors are homogeneously mixed in the distributor system. 
     In  FIG. 4  is shown a section B-B through the coating boiler  1 . Evident are again the two tubes  29 ,  30 , the cooling tubing  36 , and the plate  7  or the frame  8 . 
     Tube  29  is sectioned through such that in it the metal tube  42  and in it the ceramic tube  43  and in it the quartz tube  46  are evident. The vertical quartz tube  40  with its front side  48  and its rear side  47  can be seen approximately at the level of substrate  9 . In front of it is disposed the one half  52  of the ceramic tube and the one half  53  of the metal tube. Behind the quartz tube  40  is evident the other half  58  of the ceramic tube and the other half  57  of the metal tube. On the metal tube  42  flanged on obliquely with respect to the carrier plate  7  are disposed two adjusting aids  62 ,  63  which serve for the purpose of orienting the metal tube  42  such that the vertical holes of the line source are directed perpendicularly onto the substrate  9 . 
       FIG. 5  shows the lower region of vaporizer  28  according to  FIG. 3  at an enlarged scale. 
     Crucible  44  is divided by a partition wall  69  into an upper chamber  73  and into a lower chamber  45 . In the upper chamber  73  is located the organic substance, which is to be vaporized. Which substance is involved here is shown, for example, in Illustration 4 of the above cited paper by E. Becker et al. Possible materials for the electron transport are in particular (Alq 3 , PBD), for the light emission (Alq 3 , 1-AZM-Hex, OXD-8, doping substances: Ph-Qd, DCM, Eu(TTFA) 3 Phen) as well as for the hole transport (CuPc, TNATA, TAD, NPD). Other substances are also possible (cf. WO 99/25894, Claim 6). 
     The crucible  44  is comprised of quartz glass. However, it is also possible to employ crucibles of tantalum, molybdenum or tungsten. It must be ensured in every case that the crucible  44  does not react chemically with the material disposed in it. 
     The oblique bottom  69  of the upper chamber  73  of crucible  44  ensures that this bottom  69  is oriented parallel to the earth&#39;s surface. Opposite the bottom  66  of the empty chamber  45  of crucible  44  is provided a support  82  with staying springs  83 ,  65 ,  81 . A heat sensor  78 ,  84 , which is disposed with its upper portion  84  in the proximity of the bottom  66  or also introduced into chamber  45 , is encompassed in its lower region by a coil spring  79 . A cooling means inlet  39  is connected with a cooling fluid line  71 . By  85  is denoted a short steel tube, which is provided with a hole  86 , through which the feed lines or the like can be introduced. 
       FIG. 6  shows once again an enlarged detail from  FIG. 4 . Herein several heating wires  88  to  90  or  92 ,  93  can be seen, which are disposed on the outside of the ceramic tube  43  or  58 , in order to heat it such that the ceramic tube  43  or  58  can indirectly heat the quartz tube  46  or  40 . Instead of heating rods  88  to  90 ,  92 ,  93 , it is also possible to provide numerous small heating coils or other heating elements. By  96 ,  95  are denoted portions of a cover disposed at the lower end of metal tube  53 ,  57 . 
     In  FIG. 7  are represented once again in perspective view essential components of the distributor system, which distributes the material vaporized in crucible  44  onto the substrate. The one end of quartz tube  46  is connected with crucible  44 , not shown here, while the other end of this quartz tube  46  terminates obliquely, i.e. approximately at an angle of 45°, in the quartz tube  40 . About the quartz tube  46  is placed the ceramic tube  43 , which in turn is encompassed by the metal tube  42 . The ceramic or the metal of tubes  43  or  42  are selected such that they do not enter into reaction with the vaporized material. 
     All three tubes  42 ,  43 ,  46 , flanged on at an angle of approximately 45°, are partially shown in section. Tubes  42 ,  43  terminate in semitubes  57 ,  58 , which are comprised of the same material as they themselves are. 
     These semitubes  57 ,  58 , shown in exploded view, are opposed by the ceramic semitube  52  and the metal semitube  53 . 
     Semitubes  58  and  52  or  57  and  53 , respectively, are connected with the aid of clamps or other connecting means, such that in the operating state the two quartz tubes  46  and  40  are each encompassed by one ceramic tube, which, in turn, is encompassed by a metal tube. 
     In order for the substrates, which are moved perpendicularly to the longitudinal axis of quartz tube  40  in the direction of arrow  100 , to be acted upon by a line-form vaporizer source, in the quartz rube  40  as well as also in the ceramic semitube  52  and the metal semitube  53  numerous opposing bores  101 ,  102 ,  103  are provided, which together form a line source. By employing several bores disposed in a line, a better distribution of the vaporized material takes place in comparison to a longitudinal slot. This applies in particular to the quartz tube  40 , where the initial distribution of the vaporized material takes place. It would be possible, however, for a continuous slot to be provided in the metal semitube  53 , without the uniform distribution of the vaporized material being hereby significantly affected. However, also pure slots in the ceramic semitube  52  and/or the quartz tube  40  is in principle possible. 
     As already emphasized, the orientation of the substrate and its direction of movement parallel or perpendicularly to the gravitational force of the earth is to be understood as meaning that sagging of a potentially present mask is prevented. This would also be case if the mask were to rest on the top side of a substrate oriented transversely to the direction of the earth&#39;s gravitational force and a coating “from above” were to take place. 
     It is further understood that, instead of a stationary vaporizer source toward which a substrate is moved, a stationary substrate could also be provided, past which a vaporizer source is guided.