Abstract:
A reactor for simultaneous coating of eyeglasses on both sides thereof. Two partial devices are provided, each with a microwave energy waveguide, a gas supply and an apparatus for evacuating the coating chamber where the first and second devices can be moved relative to each other to open and close the coating chamber. The coating chamber itself is removable from the device and includes two gas supply connections and two connections for evacuating the coating chamber as well as microwave windows for coupling in microwave energy.

Description:
BACKGROUND OF THE INVENTION 
     Coating reactors are being used for the coating of substrates, having a bottom part, a top part and side walls, a supply line for gaseous media into the interior of the coating reactor and microwave windows for coupling in high-frequency energy or microwave energy by means of which a plasma is ignited in the interior of the reactor. The microwave energy is preferably pulsed microwave energy. A device and a method for coating a substrate by means of pulsed microwave energy is disclosed in DE 38 30 249 C2, for example. 
     DE 44 14 0831 A1 describes a device for producing thin films on plastic substrates by means of gas phase deposition via low pressure plasma with two diametrically opposed sources and a coating chamber in which the substrates are held between the range of action of both sources. 
     U.S. Pat. No. 6,010,755 describes a coating apparatus for applying protective layers on a magnetic memory device, where an ECR plasma is generated in a vacuum chamber and where the ECR plasma is coupled in from opposite sides. 
     All of the devices according to prior art are disadvantageous in that inhomogeneous coatings are deposited, especially in the edge areas, the coating conditions vary from one substrate to be coated to the next and therefore they are difficult to reproduce, and the volume of such reactors is relatively large, so that the gas exchange times, and thus the process times are relatively long. Another disadvantage of the devices according to prior art is that variations in the coating thickness cannot be prevented. 
     Therefore, the aim of the invention is to provide a device for coating substrates with which the above mentioned disadvantages are prevented. 
     SUMMARY OF THE INVENTION 
     According to the invention, the problem is solved by means of a device characterized in that the waveguides for coupling in microwave energy, the gas supply apparatus and the apparatus for evacuating the coating chamber are disposed coaxial relative to each other. Problems of uniformity in coating can be prevented with such a coaxial arrangement in a type of tubular reactor with coaxial microwave, gas and vacuum coupling. Another advantage of such an arrangement is that it is able to operate with a relatively small reactor volume preventing unnecessarily long gas exchange times and thus process times. 
     The coating reactor or coating chamber can be especially easily loaded with a substrate to be coated when the device for the coating of substrates comprises two partial devices, each with a waveguide for coupling in microwave energy, a gas supply apparatus and a apparatus for evacuating the coating chamber, where the first and second partial devices can be moved relative to each other, and where by means of such moving a coating chamber can be opened or closed. The coating chamber itself is an apparatus which is removable from the device for the coating of substrates, preferably comprising two gas supply connections and two connections for evacuating the coating chamber and microwave windows for coupling in microwave energy. When the two partial devices are moved apart, the coating chamber can be removed, loaded outside the device for the coating of substrates and then placed in the device for the coating of substrates. Then, the two partial devices are closed, the coating chamber is evacuated, the gas and precursor gas are introduced and the plasma can be ignited in the coating chamber so as to coat the substrate loaded outside the coating device. When the coating process is completed, the two partial devices can be moved apart again, the coating chamber can be removed and the coating reactor can be unloaded outside the coating device. 
     Such an exchangeable coating chamber is advantageous in that the coating conditions are reproducible for any substrate to be coated. 
     For example, with such a coating chamber, the microwave windows, which are preferably part of the coating chamber itself, can be replaced before each new coating so as to prevent that the microwave windows are also coated by each coating, as they are according to prior art, which causes the dielectric constant and thus the coating conditions to change from one coating to the next. Therefore, the invention achieves that the coating conditions can be set so as to be reproducible for any coating process of an eyeglass. The coating chamber of the invention can be made as a disposable chamber, which means a coating chamber which is discarded every time a coating is completed. Alternatively, the coating chamber could be cleaned after each coating so that a coating deposited on the microwave windows is removed every time a coating is completed. 
     It is especially preferable that the coating chamber is configured in a tubular form where the first and the second gas supply apparatus and the first and the second apparatus for evacuating the coating chamber are disposed opposite each other, and with a tubular coating chamber that they are predominantly disposed coaxial relative to the tube axis. A tubular coating chamber is advantageous in that it is rotational and that it has the same symmetry as the object to be coated, thereby achieving an especially uniform coating. 
     However, the invention is not limited to tubular or rotation-symmetrical coating chambers. Other geometries are also conceivable. 
     Preferably, the substrate to be coated is a planar or curved substrate with a maximum diameter or a maximum edge length of the substrate of 15 cm. The substrate to be coated is usually an eyeglass substrate or a lens substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An example of the invention will be described below by means of the drawings, as follows: 
         FIG. 1  is a device in one form of the invention pulled apart for loading, 
         FIG. 2  is a device in one form of the invention in loaded state for coating a substrate. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a device  1  of the invention for coating a substrate  2 , which in the present case is a curved substrate  2 , for example a lens substrate or an eyeglass substrate. The device  1  consists of two partial devices  3 ,  5  which can be moved in the direction of the tube axis A. 
     Each of the two partial devices  3 ,  5  comprises a waveguide  6  with apertures  7 . 1 ,  7 . 2  for coupling in microwave or high-frequency energy from a microwave or high-frequency generator, which is not shown. Moreover, each of the two partial devices is provided with a tubular vacuum connection  9 . 1 ,  9 . 2 . The coating reactor  10 , in which the substrate  2  to be coated is placed, as well as a pump for evacuating the coating chamber  10  are connected to the vacuum connection. In the present case, the pump for evacuating the coating chamber  10  is not shown. A gas supply line  12 . 1  runs coaxial to the tube axis inside each tubular vacuum connection. The coating reactor  10 , in which the substrate  3  to be coated is placed, as well as a pump for evacuating the coating chamber  10  are connected to the vacuum connection. In the present case, the pump for evacuating the costing chamber  10  is not shown. A gas supply line  12 . 1  runs coaxial to the tube axis inside each tubular vacuum connection. 
     Similar to the vacuum connection  9 . 1 ,  9 . 2 , the coating chamber  10  is substantially tubular. When the partial devices are pulled apart, as shown in  FIG. 1 , the coating chamber  10  can be placed in the coating device through the opening  14 . The coating chamber  10  comprises the connections  9 . 3  and  9 . 4  forming a vacuum-tight connection with the vacuum connections  9 . 1  and  9 . 2 . The coating chamber  10  also comprises two gas supply connections  12 . 3  and  12 . 4  which also form a vacuum-tight connection with the gas supply lines  12 . 1  and  12 . 2  when the coating chamber  10  is installed. 
     The microwave energy is coupled into the coating chamber  10  via the microwave windows  16 . 1  and  16 . 2 , for example. 
     The advantage of the present coating system is that the coating chamber  10  can be removed allowing that the microwave windows which are also coated after every coating process can be cleaned, for example. Alternatively, a new coating chamber can be used for every eyeglass to be coated. Such a method ensures that the coating conditions are always the same. 
       FIG. 2  shows the device of the invention in loaded state, i.e. where the coating chamber  10  is installed. Identical components in  FIG. 1  have the same reference numbers.  FIG. 2  clearly shows that when the two partial devices are moved together in coaxial direction, the vacuum connections  9 . 3  and  9 . 4  of the coating chamber  10  form a tight connection with the vacuum connections  9 . 1  and  9 . 2  of the first and the second partial device, similar to the gas supply lines  12 . 3  and  12 . 4  and the gas supply lines  12 . 1  and  12 . 2  of the first and second partial device.  FIG. 2  also clearly shows the coaxial arrangement of the gas supply line relative to the vacuum connection.  FIG. 2  also shows that the gas supply lines end on opposite sides of the substrate so as to ensure a highly uniform gas supply into the reactor chamber and thus ensuring a more homogeneous coating of the substrate compared to the prior art. 
     The microwave energy is coupled in via the waveguide  6  with apertures  7 . 1 ,  7 . 2  from a microwave source located outside the device  1 . The waveguide  6  is disposed coaxial to the substantially tubular vacuum connection  9 . 1 ,  9 . 2  and to the coating chamber. The waveguide  6  into which the microwave energy is coupled via the apertures  7 . 1 ,  7 . 2  can also be configured rotation-symmetrical, for example as a tube encompassing the coating chamber, similar to the tubular coating chamber  10 , which is also called the coating reactor. In the illustrated and above-described embodiment, the tubular waveguide  6 , the tubular vacuum connections  9 . 1 ,  9 . 2  and the supply lines  12 . 1  and  12 . 2  are concentric and waveguide  6  is concentric with coating chamber  10 . Other configurations are also possible without deviating from the invention. The microwave energy supplied by means of the waveguide  6  into the coating reactor or the coating chamber is coupled into the coating chamber  10  in which the substrate  2  is located via microwave windows  16 . 1 ,  16 . 2 . The coating is preferably achieved by means of the PICVD method, such as disclosed in DE 38 30 249 C2, for example. According to said method, the gas of a gas atmosphere and a precursor gas are first supplied via the gas supply lines  12 . 1 ,  12 . 2 ,  12 . 3  and  12 . 4  into the interior of the coating reactor  10 . Then, by means of the coupled energy, for example high-frequency energy or microwave energy, a plasma is ignited in the interior of the coating reactor  10 . In the present embodiment, the plasma is ignited by means of the microwave energy supplied via the waveguide structure  6 . The microwave energy supplied by means of the waveguide  6  is coupled into the reactor interior via the electric windows  16 . 1 ,  16 . 2 . As described above, the microwave energy is pulsed microwave energy. The advantage of a pulsed plasma is the substantially lower heat load on the substrate to be coated, which is preferably a plastic material. In addition, the activation of the plasma by means of pulsed microwave radiation allows a coating with alternating layers or gradient layers, such as disclosed in U.S. Pat. No. 5,736,207. The precursor gases introduced into the interior of the three-dimensional hollow space or the reactor can comprise HMDSN, HMDSO or TICI 4 , for example. Conceivable gas atmospheres are a 0 2  atmosphere, a N 2  atmosphere or a N 2 +NH 3  atmosphere. By means of the pulsed plasma the substrate can be provided on all sides with a coating, for example a SiO x , Ti0 x  or Si0 x  or Si x N y  coating, preferably having a thickness ranging between 10 and 10000 nm. The device of the invention is the first to allow that a substrate is coated as homogeneously as possible with an optimized volume which is to be filled with gas.