Coating apparatus – Gas or vapor deposition – Crucible or evaporator structure
Reexamination Certificate
2000-03-03
2001-05-29
Lund, Jeffrie R. (Department: 1763)
Coating apparatus
Gas or vapor deposition
Crucible or evaporator structure
C219S121500, C392S452000, C118S7230VE
Reexamination Certificate
active
06237529
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the thermal, physical vapor deposition of organic electroluminescent layers.
BACKGROUND OF THE INVENTION
Thermal, physical vapor deposition is a well known technique for the coating of a substrate with a material which is held in a container or in a housing, the deposition source, and heated to the point of vaporization, the vapor moving out of the deposition source and condensing on a substrate to be coated. Most often this process is carried out with both the deposition source holding the material to be vaporized and the substrate to be coated contained in a vessel which is evacuated to a level of pressure in a range of from 10
−7
to 10
−2
Torr. Such reduced pressure is useful in avoiding unwanted reactions between either the materials of which the source is constructed or the deposition materials contained in the deposition source with the atmosphere in the vessel as the temperature of the deposition source is increased to the point where the deposition materials vaporize.
Typically, the deposition source is made from an electrically resistive material whose temperature will increase when an electrical current is passed through the container walls. The deposition material inside is then heated by radiation from the walls and by conduction from contact with the walls. Typically, the container is shaped like a box, with an aperture to allow escape (efflux) of the vapor in the direction of the substrate. However, other methods of heating the walls have been used, including radiation from coils surrounding the container, induction heating of the container with suitable coils, electron impact, and irradiation from an optical source.
If the container or housing is fabricated from a material in such a way as to be liquid-tight, then there is no concern whether vaporization is by sublimation from the solid or evaporation from a liquid formed as the solid first melts. In any case, it is well known that the container can be lined with a high-temperature-compatible, liquid-tight material, such as quartz, a ceramic, a shaped carbon material, or the like and that such liner be heated by a surrounding resistive heater.
Thermal, physical vapor deposition sources have been used to vaporize and deposit onto a substrate layers comprised of a wide range of materials, for example low temperature organics, metals, or fairly high temperature inorganic compounds. In the case of organic layer deposition, the starting material is typically a powder. It has been recognized that such organic powders present a number of challenges to this type of thermal vaporization coating. First, many of the organics are relatively complex compounds (high molecular weight), with relatively weak bonding, so that care must be taken to avoid decomposition during the vaporization process. Next, the powder form can give rise to particles of unvaporized electroluminescent material leaving the deposition source with the vapor and being deposited as undesirable lumps on the substrate. Such lumps are also commonly referred to as particulates or particulate inclusions in a layer formed on a substrate. This is additionally exacerbated in that the powder form also has a very large surface area which may hold absorbed or adsorbed water or volatile organics which can be released during heating and can cause eruptions of gas and particulates to be thrown outward from the deposition source toward the substrate. Similar considerations pertain to materials which melt before vaporization (evaporation) and can result in droplets being ejected to the substrate surface.
There are many applications where these unwanted particulates or droplets will result in unacceptable defects in a product, particularly in electronic or optical applications where dark spots may result in images or shorts or opens may result in electronic device failures.
There has been much effort spent in devising organic deposition sources designed to more uniformly heat such an organic powder charge and to also prevent the bursts of particulates or droplets from reaching the substrate. Numerous designs of complicated baffling structures between the source material and the exit opening have been suggested to try to assure only vapor exits. See for examples U.S. Pat. Nos. 3,466,424 and 4,401,052. There are also various elaborate container features added interior to the source material container seeking to achieve maximum contact area between the organic vapor deposition material and hot members of the container. See for examples U.S. Pat. Nos. 2,447,789 and 3,271,562.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thermal, physical vapor deposition source for organic electroluminescent material which eliminates the problems of the prior art deposition sources discussed above.
It is another object of the present invention to provide a thermal physical vapor deposition source having a simplified baffle structure which allows maximum passage of vapor while eliminating the direct exit of particulate electroluminescent materials.
It is yet another object of the present invention to provide a thermal physical vapor deposition source with lower thermal inertia or more rapid temperature response to changes in power input to the source.
These and other objects are achieved by a thermal physical vapor deposition source for vaporizing solid organic electroluminescent materials and applying a vaporized electroluminescent material as a layer onto a surface of a substrate in forming a display device, comprising:
a) a housing defining an enclosure having side walls and a bottom wall, the enclosure receiving solid organic electroluminescent material which can be vaporized, and the width of the housing having a dimension w
h
;
b) the housing is further defined by a top plate having a conductive portion and defining a vapor efflux aperture slit having a width w
s
for permitting vaporized electroluminescent materials to pass through the slit onto a surface of a substrate;
c) a conductive baffle member having a width b, the baffle member being centered on the slit and spaced from the side walls and spaced from the top plate by a distance m, the baffle member substantially providing a line-of-sight covering of the slit preventing direct access of vaporized electroluminescent materials to the slit, and preventing particulate electroluminescent materials from passing through the slit;
d) a straight-line projection from an edge of the slit to an edge of the baffle member onto a side wall defining a position on the side wall such that such position is spaced from the top plate by a dimension L;
e) the ratios of the dimensions: w
h
to w
s
being in a range of from 1.5 to 6.0; L to w
s
being in a range of from 2 to 6; and m to L being in a range of from 0.15 to 0.40; and
f) means for applying an electrical potential to different parts of the housing to cause heat to be applied to the solid organic electroluminescent material in the enclosure causing the solid organic electroluminescent material to vaporize so that vaporized electroluminescent material is projected off of the side walls and the top plate of the housing and the top surface of the baffle member through the slit onto the substrate while particulate electroluminescent materials are prevented from passing through the slit by the baffle member.
Advantages
A feature of the present invention is that lower heating levels can be applied to solid organic electroluminescent materials to achieve a desired rate of vapor exit from the source through the efflux aperture, providing an effective way of applying vaporized electroluminescent material as a layer to a substrate at the highest rate with the least chance of decomposition.
Another feature of the present invention is that the placement of the baffle member with respect to the slit substantially prevents particulate electroluminescent material from passing through the slit.
Another feature of the present invention is that in the cases where rapid thermal response is desired, this can
Eastman Kodak Company
Lund Jeffrie R.
MacArthur Sylvia R.
Owens Raymond L.
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