Patent Application
20070028629
This application claims priority from European Patent Application No: 050 16 832 filed Aug. 3, 2005, incorporated herein by reference in its entirety.
The invention relates to an evaporator arrangement for the coating of substrates with at least one material.
Apart from the electrolytic method, the coating of a substrate with a material can also take place by sputtering or by vapor deposition. The layer generated in this manner often serves for protecting the coated material; however, it may also have purely decorative or functional relevance.
Applying a layer by vapor deposition is of great importance especially in the coating of substrates with metals. In this method a metal is melted in a crucible with the temperature being selected such that the metal changes to the gaseous state and migrates in the direction of the substrate to be coated, where it condenses.
For coating substrates evaporator units are known in which several evaporator boats are disposed in an evacuated space. Into these evaporator boats is introduced, frequently in a continuous process, material in the form of a wire which is evaporated. This vapor rises and condenses on the substrate to be coated, and the substrate, often in the form of a band, is guided over the evaporator boats. Of disadvantage in this evaporator unit is that splatters are generated during the direct evaporation, since irregular vapor pressures are formed due to impurities and gaseous components. The splatters are moreover formed by rapid movement of the melt in hot zones of the evaporator boats. In addition, the melting off of the wire, which to some extent is discontinuous, leads to different evaporation rates since these are dependent on the target site of the wire.
DE 40 27 034 C1 discloses an evaporator arrangement for coating band-shaped substrates in a vacuum coating chamber. The evaporator boats utilized in this case form an evaporator bank, the boats being disposed longitudinally with respect to the running direction of the band and parallel and approximately equidistantly with respect to one another.
Furthermore is known from DE 44 04 550 C2 an arrangement for the regulation of the evaporation rate from crucibles heated by current throughflow, wherein metal is evaporated in these crucibles. In this case the regulation of the evaporation rate takes place via an electrical resistance heating system, the total resistance resulting from the electrical resistance of the crucible and from the electrical resistance of the material in the crucible.
An arrangement for the evaporation of metal is furthermore known, wherein a wire is inserted into a groove which is in flow connection with an evaporator crucible (DE 34 28 651 A1). Due to the different vapor pressures, impurities and gaseous components can lead during the melting of the wire to the generation of splatters, which reach the substrate. To avoid this, above the groove a cooled screening or cover is disposed. This ensures that the substrate is only coated by the material rising from the evaporator crucible.
Furthermore, other evaporator boats are also known, in which between a first zone and a second zone a screening in the form of a wall is located. This wall is intended to prevent splatters generated during the melting of the metal from reaching the substrate to be coated (U.S. Pat. No. 3,467,058, EP0 430 210 B1).
Lastly is also known another evaporator arrangement which comprises a melt-down zone, an evaporator zone and a connection between the two zones (U.S. Pat. No. 3,020,177 A; EP 1 327 699 A).
The problem underlying the invention comprises providing an evaporator arrangement for coating substrates with materials, in particular with metals, which is conceptualized such that no splatters can reach the substrate, wherein the installation of walls or other screenings is not necessary.
This problem is resolved according to the present invention.
The invention therewith relates to an evaporator arrangement with a crucible, wherein the crucible is divided into at least three zones, each of which is heated to different temperatures. The first zone is a melt-down zone and the second zone the heating zone and the third zone the evaporator zone. The evaporator arrangement is preferably suitable for the evaporation of metals. If metals are evaporated, a metal wire is preferably guided into the melt-down zone. However, metal alloys can also be evaporated thereby that one or several metal wires comprised of different materials are introduced into the melt-down zone.
The advantage attained with the invention consists in particular therein that a splatter-free and highly uniform evaporation rate is achieved for qualitatively high-grade layers on organic substrates, for example OLEDs, and synthetic films. This is of importance for example in the production of capacitors, where splatter-free layers must be applied onto extremely thin films with good uniformity and under low radiative loading. It is also advantageous that no high demands must be made of the precision of the wire guidance, since the target point of the wire on the heated crucible is unimportant to the evaporation rate. Since in the melt-down zone lower temperatures obtain than in the evaporator zone, the wire guidance is also under low thermal loading and low vapor deposits. Through the division into melt-down and evaporator zone, impurities such as grime or oxide layers can largely be kept away from the evaporator zone. The service life of the crucible is also increased since the liquid material to be evaporated only moves slowly.
Embodiments of the invention are shown in the drawing and will be explained in further detail in the following.
The wire 3 can be, as for example in U.S. Pat. No. 3,467,058, on a spool, from which it is continuously introduced into the melt-down zone 2. If an alloy is to be applied onto the substrate, the wire 3 can already be comprised of this alloy or the alloy can be produced by the simultaneous melting of several wires of the desired metals which are to form the alloy.
The manner in which the wire 3 is introduced into the melt-down zone 2 is insignificant, since no high demands are made of the precision of the wire guidance.
With this evaporator arrangement 1 such metals, or their alloys, are preferably to be evaporated which comprise Ag, Cu or Al.
The melt-down zone 2 of the crucible 6 is followed by a so-called heating zone 4, where a temperature obtains which must not reach the boiling temperature of the metal having the lowest boiling point, but which is higher than the temperature of the melt-down zone 2. In this heating zone 4 low boiling impurities are removed such that metals are obtained which have a very high degree of purity.
The heating zone 4 of crucible 6 has a form adapted to the material of the melt 25 and the particular temperature-dependent surface tensions. It often has the form of a channel, as shown here, which connects the melt-down zone 2 with an evaporator zone 5. The heating zone 4 is smaller than the zones 2 and 5 and prevents the interchange of the melt 25 in zones 2 and 5, since it is important that the colder region 2 is separated from the hotter region 5, for it is to be avoided that evaporation occurs already in the melt-down zone 2. The size of the heating zone 4 is a function of the material; it may in practice have a length of, for example, 10 mm. The temperature of the melt 25 increases continuously from zone 2 to zone 5.
When the melt 25 has passed through the heating zone 4 of the crucible 6, it reaches the evaporator zone 5, where the material is lastly vapor deposited onto the substrate, which is disposed over the evaporator zone 5.
The melting point of the material of the crucible 6 must be far above the evaporation temperature of the metals which are to be evaporated. Possible materials for the crucible 6 are high-melting compounds, and the crucible 6 can also be comprised of several compounds of this type. Apart from graphite, compounds of the metallic borides, nitrides or carbides for example can be utilized as well as compounds of the non-metallic borides, nitrides or carbides. TiB2 together with BN are suitable as materials of the crucible 6.
The crucible 6 is heated in such manner that the temperature in region 2 is lowest and in region 5 highest, wherein the heating can take place via only one or via several heaters operated separately of one another.
In the embodiment example shown in
For aluminum applies for example that the temperature in the melt-down zone 2 is higher by approximately 300 to 500° C. than the melting point and in the evaporator zone 5 higher by approximately 900° C. The temperatures in zones 2 to 4 are selected such that in them no evaporation of the material occurs. It would theoretically be sufficient for the temperature in the melt-down zone to be only marginally above the melting temperature. However, since the introduced metal wire leads to a cooling down, the temperature in the melt-down zone is selected higher.
It is understood that the resistance relationships can be obtained not only through lateral indentations but also through different thicknesses of the crucible material in the vertical direction. Significant is the particular total cross section which is accountable for the electrical resistance.
The rising vapor lobe of the metal to be evaporated remains nearly constant during the evaporation, whereby the coating becomes highly uniform. If several evaporator boats form an evaporator bank, the evaporator boats are oriented such that the substrate is uniformly coated. This can be achieved not only through the disposition of the evaporator boats with respect to one another, but also thereby that the substrate is guided over the evaporator bank at such distance that uniform coating results.
By separating the evaporator zone 5 from the melt-down zone 2 the movement of liquid metal in the evaporator zone 5 itself is very low whereby the service life of the evaporator arrangement 1 is also increased.
The evaporation rate can be controlled via the speed of the melting-down of the wire and the geometry of the crucible 6. For continuous operation of the evaporator arrangement 1 regulation of the level of fill of the melt 25, of the wire advance and of the evaporator output can be provided.
Since the evaporation rate is highly uniform and no splattering occurs which may reach the substrate, such an evaporator arrangement 1 is suitable for the coating of, for example, synthetic films with metal. The evaporation rate is therein determined via the surface of the evaporator zone 5, the temperature of the evaporator crucible as well as the wire feed, i.e. the quantity of molten wire 3 per unit time. Such an arrangement can for example be utilized for the fabrication of capacitors, since here splatter-free layers are applied onto extremely thin films and the layers, moreover, must be highly uniform.
A further application field is also the production of metallic yarn, since here the requirements made of the evaporator arrangement 1 are also very high.
Instead of three separate voltage sources 18, it is also feasible to provide only one voltage source, parallel with which the three zones 2, 4, 5 are connected. In order to generate here different temperatures in different zones, the zones may be comprised of different materials or have different current flow cross sections.
The basins of the different zones can however all be at the same level or only the basins of zones 4 and 5 can lie at the same level. A flow of the material from the melt-down zone 2 to the evaporator zone 5 takes place in this case also since the level of the material in the evaporator zone 5 decreases due to the evaporation and therewith draws material from the melt-down zone 2.
In
The evaporator boats 45 to 54 are disposed on an evaporator bank 67, which can be slid under the coating roller 66. However, it is also conceivable that the evaporator boats 45 to 54 are disposed on a slide-in cart, which can also be slid under a coating roller.
In
However, it is also feasible to dispose above the evaporator zone 5 of the crucible according to
Instead of electrical resistance heaters, inductive heaters can also be provided, which are so laid out such that they generate different temperatures in different zones of an evaporator boat.
| Number | Date | Country | Kind |
|---|---|---|---|
| 050 16 832 | Aug 2005 | EP | regional |
