Patent Application
20160299262
This invention relates to a process and according vacuum chamber design for the in-situ annealing of anti-fingerprint coatings directly after deposition of such coatings. Typically, such anti-fingerprint coatings are applied to the touch-sensitive cover glasses of electronic devices (smartphones, tablet PCs).
A chemical binding reaction between such anti-fingerprint coating and glass surface has to be accomplished to ensure good adhesion. This binding reaction typically requires water.
The content of EP 2 409 317, EP 2 409 339 and WO 2013/057228 is incorporated by reference herein in its entirety, especially with a view on the basic deposition process of anti-fingerprint coatings and functionality of an inline vacuum deposition system.
Anti-fingerprint coatings provide an easy-to-clean, non-sticking surface finish for touch-sensitive surfaces such as smartphone or tablet PC cover glasses. The surface becomes oleophobic and hydrophobic which allows easy removal of particles and grease and also allows for a comfortable feeling when actually using such a touch panel device. Typically, chemical solutions of alkoxy silane molecules are used for this application, because the silane group of these molecules provides hydrophobic and oleophobic functionality whereas the alkoxy group forms a strong covalent bond to glass.
Several coating techniques are used in the industry: Dip coating, spray coating, or physical vapour coating. WO 2013/057228 describes equipment for physical vapour deposition from liquid precursors (alkoxy silane molecules dissolved in a solvent).
All of these coating techniques require a subsequent curing step, because the chemical bonding reaction between the alkoxy group and the glass surface has to be initiated. This reaction consumes water; therefore the curing is typically performed by placing the substrates in a hot, humid environment for several hours. Alternatively, curing can also be accomplished by exposing such coated substrates to humidity from the ambient air for several days.
The chemical precursor materials as well as instructions for processing and curing are commercially available from manufacturers like Daikin or Dow Corning (see e.g. Dow Corning 2634 product information, Daikin Optool DSX product information). In this disclosure the term anti-smudge or anti-fingerprint material is being used interchangeably for materials of this kind.
As mentioned above the proposed curing processes to date typically take several hours and can therefore only be applied reasonably in batch processes where a large number of substrates are treated simultaneously. In industrial scale this requires voluminous conditioning cabinets with respective load, heat, cool down and unload processes.
In summary, the established ex-situ curing methods have two main disadvantages:
1. They typically require controlled humidity (>50%) and temperature (>50° C.) simultaneously. Therefore, process control is quite sophisticated.
2. Typical curing processes take several hours. Therefore, curing has to be separated from the coating process (done in another tool), which increases the overall costs. High throughput in industrial scale necessitates large tools, which increases investment costs.
The goal of this application is therefore a significant reduction or elimination of the curing time period by introducing an in-situ treatment in water vapour atmosphere immediately after coating without breaking vacuum.
a: Photograph of an annealing station according to the invention
b: An inventive annealing apparatus in a schematic overview
This present invention addresses an in-situ annealing station construed to adjust and control a water vapour pressure and a defined process temperature; said station can be integrated as a process chamber into a multi chamber processing tool in which an anti-fingerprint coating process is being performed. The substrate is always under vacuum conditions until the annealing process has finished. Experimental data show that a significant reduction of the ex-situ curing duration can be achieved by introducing this in-situ treatment in water vapour immediately after the coating step. This can even eliminate the need for slow batch-type curing processes and allows for a fast in-line coating and curing sequence with the substrates being continuously processed. The invention therefore has the potential to lower production costs.
A radiative heating station has been used to facilitate an in-situ post-deposition annealing process with adjustable water vapour pressure. A suitable multi-chamber tool has been described e.g. in EP 2 409 317 and EP 2 409 339 and such a basic coating process has been described in WO 2013/057228.
The annealing station is technically based on a radiative heater station as it is known in the art. It is widely known to use quartz lamps positioned in a close spatial relationship to a substrate to be heated up. In the present invention said annealing station has been additionally equipped with an adjustable water supply to allow for a dosing of water into the heater station, such that the heating step can be performed in the presence of water vapour. In consequence, a rapid thermal anneal with adjustable water vapour pressure can be performed. Placed in the same tool as the DLD (Direct Liquid Deposition) station described in WO 2013/057228 this allows the deposition and in-situ water vapour treatment in one and the same machine in one and the same process cycle.
When the connection between water reservoir and vacuum chamber is being opened, the water in the reservoir will boil due to the reduced pressure. A needle valve between said water reservoir and the vacuum (annealing) chamber allows thus adjusting the water vapour pressure. The substrate (inside the chamber, not shown) is heated by an array of halogen lamps.
Evacuating means such as pumps as well as measuring units (pressure and temperature control means) have been omitted in this scheme. It goes without saying that the resulting water vapour pressure in chamber 15 will be the result of water vapour supply (controlled via valve 14), the pumping power installed and the volume of chamber 15.
In an inventive process a substrate (preferable one or at least one, if e.g. a substrate carrier is being used) is being placed in an annealing chamber 15 by means of a robot or other transport means. The chamber will be separated from ambient during the annealing step. Via valve 14 a defined amount of water is being dosed into chamber 15 to develop water vapour to take effect on the coating which had been deposited in a previous vacuum deposition step. The dosing can be done in one step, i.e. a defined portion of water for the curing to be inserted once per annealing step, in a discontinuous way (pulsed) or in a continuous dosing. Depending on the volume of the annealing chamber and the pump power the necessary water volume to be dosed will vary, therefore the respective parameter named below is the resulting vapour pressure (target pressure) in the chamber.
Heater 18 acts in parallel to the dosing on the substrate and is elevating its temperature to the desired and defined level. Pressure and temperature control means allow for dynamically controlling this process; alternatively fixed settings for heater and water dosing can be used which may be derived from earlier experiments. After a predetermined treatment time in the annealing chamber, the water inflow may be stopped, the residuals pumped away and the substrate can be removed from the chamber. Depending on the level of dosage it is also possible to simply allow said defined dose of water passing constantly into chamber 15, if the pump capacity allows for it and if cross-contamination is no issue in the respective system.
It has been found to be especially advantageously that after said earlier deposition step the annealing step takes place immediately without breaking vacuum. This way any contamination from ambient air which may have negative effect on the molecular reactions described above, can be avoided.
The following parameters have found to be useful:
Annealing time: 5 s
Annealing temperature: 130° C.
Resulting water vapour pressure in annealing chamber: 1×10−3 to 1×10−2 mbar (hPa)
Advantageously, the annealing step is integrated as a process step in an inline substrate treatment tool. This allows integrating the annealing into the sequence of process steps which is necessary to deposit the anti-fingerprint layer.
In this case the process stations are arranged in a circle and a respective handler provides for a sequential access of the process stations PC1-PC4. The substrate surface is pretreated and coated in analogy to patent application WO2013/057228A1 in chamber PC1-PC4. Chamber 5 is the inventive annealing station. There is no vacuum break between coating and annealing.
In such kind of deposition tool the substrates are being fed from a waiting position via a Load Lock into a vacuum section (the upper part with process stations). They sequentially have access to PC1 to PC5 before being brought back to atmosphere. In more detail such a system has been described in EP 2 409 317 and EP 2 409 339. In PC2 and PC3 an adhesion layer is being deposited. In order to match the cycle time of about 5 s, two stations are being used so the overall treatment time for the SiO2 coating can be distributed on two stations. This way, the limitations of a sequential deposition tool, where the “slowest” process station limits the tact time, can be remedied.
A typical process in industrial environment uses, after a regular cleaning of the substrate with a detergent the following process steps in a vacuum environment:
A standard steel wool abrasion test was performed to assess the durability of anti-fingerprint coatings after curing. In this test, a steel-wool pad (grade “0000”) of 1 cm2 size is being charged with 1 kg and a series of strokes with this pad being performed over the coated and annealed surface at a speed of about 5 cm/s.
The wear resistance of the coating is determined by the water contact angle test, in which a drop of water is placed on the surface of the substrate and the contact angle between the water droplet and the surface is measured. The water contact angle measured vs. certain numbers of strokes of the steel wool pad is shown in
The results of various curing processes in
Comparing samples no. 2 and 4 of
Furthermore, comparison of samples no. 1 and 3 shows that the short in-situ anneal in water vapour drastically reduces the duration of, and also eliminates the need for high humidity in, the subsequent ex-situ curing process when aiming at very high film quality.
These experimental data show that the hardware and corresponding process flow according to the invention has the potential to significantly reduce process time in the production of anti-fingerprint coated devices. Reduced process duration translates into reduced production costs, which is beneficial for our customers.
In summary, a processing station for simultaneously heating a substrate and charging it with water vapour comprises at least an evacuable enclosure or chamber with an adjustable and controllable supply for water into said chamber and a heating means allowing for elevating the temperature of a substrate arranged in said chamber and means for evacuating said chamber to a predefined pressure level. Said processing chamber may include a substrate support, temperature and pressure control means, handling means for arranging, loading and unloading a substrate. Said adjustable and controllable supply for water into said chamber comprises control means for dosing water, such as valves, throttle valves, preset valve, needle valves or alike which may be actuated manually or via a drive.
Consequently, a deposition process for an anti-fingerprint coating on glass, comprises a process sequence including (a) deposition of the anti-fingerprint coating and (b) in-situ curing with water vapour without vacuum break in between. A curing process for a surface of a substrate coated with an anti-fingerprint coating of the kind described herein, will include the features
Said curing process as described above will preferably last for a few seconds, preferably 5 s, and/or is adjusted to the tact time of an inline substrate treatment system performing said curing process and other treatment steps.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CH2014/000162 | 11/13/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61904159 | Nov 2013 | US |
