Abstract:
A physical vapor deposition (PVD) chamber for depositing a transparent and clear hydrogenated carbon, e.g., hydrogenated diamond-like carbon, film. A chamber body is configured for maintaining vacuum condition therein, the chamber body having an aperture on its sidewall. A plasma cage having an orifice is attached to the sidewall, such that the orifice overlaps the aperture. Two sputtering targets are situated on cathodes inside the plasma cage and are oriented opposite each other and configured to sustain plasma there-between and confined inside the plasma cage. The plasma inside the cage sputters material from the targets, which then passes through the orifice and aperture and lands on the substrate. The substrate is moved continuously in a pass-by fashion during the process.

Description:
RELATED CASES 
     This Application claims priority benefit from U.S. Provisional Application, Ser. No. 61/668,402, filed on Jul. 5, 2012. 
    
    
     BACKGROUND 
     1. Field 
     This disclosure relates to fabrication of transparent substrates, such as, for example, substrates for flat panel displays and touch screens, and, more specifically, for fabrication of highly transparent protective coatings for such panels. 
     2. Related Art 
     With the proliferation of mobile devices having flat screen display and/or touchscreens, the problem of screen scratching becomes problematic. This is especially the case with mobile phones and tablets, which employ touchscreens and are susceptible to scratching. Accordingly, a strong scratch-resistant coating is needed. 
     Diamond-like coating (DLC) has been suggested as scratch resistant coating for various applications; however, state of the art systems that generate such coating are unable to provide transparent and clear coating. Rather, current coating have slight tint and are not clear. However, users of such devices require clear screen to transmit vivid colors of the image on the screen. Therefore, the yellowing tint of the standard DLC is unacceptable for such applications. 
     SUMMARY 
     The following summary of the disclosure is included in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below. 
     Embodiments disclosed herein enable the fabrication of hydrogenated carbon coating, e.g., a diamond-like coating (DLC), which is transparent and clear, meaning it has no perceptible tint. The resulting coating is highly resistive to scratches and is highly transmissive to light, e.g., light emanating from a flat panel display or touchscreen. 
     According to one embodiment, system and method for providing hydrogenated carbon coating over glass are disclosed. The resulting coating is transparent and is clear without perceptible tint. The coating is generated using physical vapor deposition (PVD) wherein argon and hydrogen gas are injected into the plasma to generate hydrogenated carbon coating. 
     According to one embodiment, the PVD system is constructed such that there is no or minimal line-of-sight from the target to the coated substrate. The plasma is generated remotely from the substrate, and particles are sputtered from the targets into the plasma zone, without the ability to reach the substrate directly on a line-of-sight approach. Specifically, particles emanating in a trajectory perpendicular to the sputtering surface of the target travel in a direction that is parallel to the direction of travel of the substrate. 
     According to disclosed embodiments, the PVD is performed without applying any electrical bias to the substrate. In some embodiments only one side of the substrate is coated and in other embodiments both sides are coated simultaneously. The disclosed coating has good adhesion, good clear transmission with no perceptible tint, while providing high resistance to scratching. 
     According to one embodiment, a physical vapor deposition (PVD) chamber for depositing a transparent and clear hydrogenated carbon film is provided. A chamber body is configured for maintaining vacuum condition therein, the chamber body having an aperture on its sidewall. A plasma cage having an orifice is attached to the sidewall, such that the orifice overlaps the aperture. Two sputtering targets are situated on cathodes inside the plasma cage and are oriented opposite each other and configured to sustain plasma there-between and confined inside the plasma cage. The plasma inside the cage sputters material from the targets, which then passes through the orifice and aperture and lands on the substrate. The substrate is moved continuously in a pass-by fashion during the process. 
     According to another embodiment, a method of forming clear hydrogenated carbon film over a substrate is provided, comprising: providing a process chamber and a plasma cage positioned outside the process chamber; affixing amorphous carbon sputtering targets onto two cathodes inside the plasma cage, such that the two sputtering targets face each other; evacuating the process chamber; injecting into the plasma cage process gasses of argon and hydrogen; igniting and sustaining plasma by applying DC power to the two cathodes and confining the plasma inside the plasma cage; transporting the substrate inside the process chamber; providing a path for particles sputtered from the sputtering target to reach the substrate inside the process chamber. 
     According to yet another embodiment, a system for depositing a clear hydrogenated carbon on a substrate is provided, comprising: an entrance loadlock chamber; a pre-clean chamber attached to the entrance loadlock chamber via an isolation valve; an isolation chamber coupled to the pre-clean chamber; a static sputtering chamber coupled to the isolation chamber and configured for depositing SiO2 film over the substrate; a second isolation chamber coupled to the static sputtering chamber; a pass-by sputtering chamber coupled to the second isolation chamber and configured for depositing hydrogenated carbon film over the SiO2 film; and, an exit loadlock chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other aspects and features of the invention would be apparent from the detailed description, which is made with reference to the following drawings. It should be mentioned that the detailed description and the drawings provide various non-limiting examples of various embodiments of the invention, which is defined by the appended claims. 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the invention. The drawings are intended to illustrate major features of the exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale. 
         FIG. 1  is an overall schematic of a system for the application of hydrogenated carbon film on a substrate, according to one embodiment; 
         FIG. 2  is a top-view schematic of a sputtering chamber according to one embodiment; 
         FIG. 3  is a top view schematic of a sputtering chamber according to another embodiment; 
         FIG. 4  is a plot of clarity of the glass substrate with a DLC coating using various ratios of argon to hydrogen gas, according to disclosed embodiments; 
         FIG. 5  is a plot of a DLC film and DLC film over SiO2 film, according to disclosed embodiments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an embodiment of a system for depositing scratch resistant hydrogenated carbon, e.g., hydrogenated DLC coating over glass substrates. In this example, the system has two separate rows of chambers, which may be stacked vertically, e.g., upper and lower rows, or placed side by side horizontally. Employing a vertical architecture enables easy access to both sides of each chamber without increasing the overall footprint of the system. Easy access to both sides of each chamber allows for simultaneous sputtering of both sides of each substrate, if that&#39;s needed. If only one side needs to be coated, then horizontal side-by-side architecture can be employed. If the substrates are transported and processed while held in a vertical orientation, then the footprint of the system may not increase dramatically, even for a side-by-side architecture. 
     Regardless of the architecture, as shown in  FIG. 1 , the substrates are loaded and unloaded in atmospheric load/unload platform  100 . The substrates then enter loadlock vacuum chamber  105 . In  FIG. 1 , “x” marks a location of a vacuum isolation valve. Thus, for example, loadlock vacuum chamber  105  has an isolation valve on both sides, i.e., entrance and exit. When the substrate enters the loadlock, the valves are closed and the loadlock is evacuated, thus introducing the substrate to a vacuum environment. The substrates then exit the loadlock and enter station  1  of process module  1 , which is a pre-clean station  110 . Station  1  is an inductively coupled plasma chamber and it performs pre-clean of the substrate by generating plasma using argon and oxygen gas. In this chamber, a substrate is stopped in front of the inductively coupled plasma source and plasma cleaning on the substrate is performed. In this sense, this chamber may be referred to as static chamber, since the substrate is held static during processing. From there the substrates are moved in to station  2  of process module  1 , which is an isolation chamber  115 , isolating the pre-clean chamber from the processing of process module  2 . 
     The substrates are then moved to station  3  of process module  2 , which is a PVD chamber  120 . PVD chamber  120  is a pass-by PVD chamber, meaning that the substrates are continuously moved and scanned past the target as the deposition process is taking place. In station  3  the substrates are coated with a thin layer of SiO2, using silicon target in the presence of plasma sustained with oxygen and argon gas. The SiO2 layer is of thickness of 10-80 Å, and in some embodiments it is 40-60 ÅA, thus being totally clear and transparent without any tint. The substrates then move to station  4 , which is an isolation chamber  125 . Thus, in this embodiment, the PVD chamber  120  has an isolation chamber at its entrance and an isolation chamber at its exit, to ensure total isolation of the PVD chamber form the remaining parts of the system. 
     The substrates are then rotated in rear module  130  and moved into station  5 , which is isolation chamber  135 . Notably, when the system employs a vertically stacked architecture, station  5  would also incorporate an elevator to raise or lower the substrate to the next row of chambers. The substrate is then moved into station is, which is a PVD chamber for depositing the hydrogenated carbon or hydrogenated DLC film. PVD chamber  140  is a pass-by PVD chamber, meaning that the substrate is moved continuously and is scanned in front of the deposition source during the sputtering process. Thus, the system of  FIG. 1  is a mixed system, having a stop and go inductively coupled plasma pre-clean chamber and a pass-by PVD chamber in the same processing line. 
     At station  6 , which is a PVD chamber  140 , a hydrogenated DLC layer is deposited over the SiO2 layer, using remotely confined plasma, wherein the sputtering targets have no line of sight to the substrate, such that particles are prevented from flying directly from the target to the substrate. This process is performed at about 1-30 mTorr or, at 7-10 mTorr, using 25-70% hydrogen and 25-80% argon gas. The substrate may be at room temperature, i.e., 25° C., or may be heated due to the prior plasma clean and SiO2 deposition, or otherwise by a heater, up to about 250° C. The DLC coating is about 40-75 A and is completely transparent and clear to the visible spectrum, having no tint. The substrates are then moved to station  7 , which is an isolation chamber  145 , and from there exit to the load/unload platform via loadlock  150 . Thus, PVD chamber  140  also has an isolation chamber at its entrance and one at its exit. 
       FIGS. 2 and 3  illustrate a top cross-sectional view of embodiments for sputtering systems especially suitable for depositing the hydrogenated DLC coating in station  140 . Either one of these two embodiments may be used; however, if total lack of line of sight from target to substrate is sought, then the embodiment of  FIG. 3  should be employed. Also, the embodiments of  FIGS. 2 and 3  are illustrated with sputtering sources on either side of the processing chamber, enabling simultaneous deposition on both sides of the substrate. However, for substrates that require deposition on only one surface, one of the sources may be omitted, such that the chamber has one sputtering source attached to one sidewall only. 
     As can be seen in  FIG. 2 , a processing chamber  210  has an entrance opening with valve  212 , and exit opening with valve  214 , through which substrates  200  are introduced and removed from the chamber, respectively. The chamber also has opposing sidewall, at least one of which having an aperture  208 , to enable particulate to pass there-through and be deposited on the substrate  200  when the substrate is situated within the chamber. The substrate  200  may be stationary or moving, in the direction shown by the arrow, during the deposition process. The processing chamber  210  is configured for maintaining vacuum therein, and is evacuated by vacuum pump  217 . 
     A plasma cage  202  is attached to the sidewall of chamber  210  and has an aperture corresponding to the aperture in the chamber sidewall. The plasma cage  202  confines the plasma to an area remotely from the substrate  200 , such that no plasma reaches the substrate  200 . Targets  206  are attached to cathodes  203  and are situated inside the plasma cage  202 , such that particles sputtered from the targets  206  do not have a line of sight path to the substrate  200 , but rather must meander and reach the substrate  206  via window  208 , as shown by the dotted-line arrows. Note that the plasma cage  202  of  FIG. 2  has its targets  206  positioned in a direction parallel to the path of the substrate  200 . In the embodiment illustrated in  FIG. 2 , DC power is applied to the cathodes to sustain the plasma and sputter material from the targets so as to deposit the sputtered material onto the substrate  200 . In other embodiments, an AC or pulsed DC power may be applied to the cathodes. 
     The processing chamber shown in  FIG. 3  is very similar to that of  FIG. 2 , except that the plasma cage  302  of  FIG. 3  has its targets  306  and cathodes  303  positioned such that the sputtering surface of the targets is in a plane perpendicular to the path of the substrate  300 . Stated another way, a line that is perpendicular to the sputtering surface of either target, e.g., shown as the broken-line arrow in  FIG. 3 , would be parallel to the direction of travel of the target, shown as solid-line arrow. However, in the embodiment of  FIG. 3  as well, particles sputtered from the targets  306  do not have a line of sight path to the substrate, but must meander and reach the substrate via window  308 . 
     In both embodiments of  FIGS. 2 and 3 , the plasma is sustained with processing gas injected via injectors  201  and  301 , respectively, in this case a mixture of argon and hydrogen gas. The argon gas is used to generate ions that sputter particles from the targets, while the hydrogen is used for hydrogenating the sputtered film.  FIG. 4  is a plot of transmission vs DLC thickness at different Ar/H2 ratios. Very good results can be seen at 50% Ar 50% H2. 
     An optional feature illustrated in  FIG. 3  is providing magnet arrays  330  behind each of the opposing targets, and wherein the magnetic polarity on one side is opposite the polarity on the other side. Moreover, it has been found that in order to obtain a transparent and clear DLC film, the maximum magnet energy products for the individual magnets must be in the ranges between 200 kJ/m 3 &lt;BH max &lt;425 kJ/m 3  and preferably 300 kJ/m 3 &lt;BH max &lt;400 kJ/m 3 . Additionally, when the targets are arranged as shown in  FIG. 3 , the separation between the target pairs should be confined to between 30 and 300 mm and preferably between 40 and 200 mm. 
       FIG. 5  is a plot of transmission data for both 75 Å DLC and a film of 75 Å DLC deposited over a film of 50 Å SiO2. As can be seen, transmission for both cases is good over all visible frequencies and, is actually improved with the addition of thin SiO2 layer. 
     To achieve a highly transparent and clear DLC film, the DC power is applied to the target at a specific power density, i.e., power per target area, range. For best results, the power density is about 30-770 kW per square inch of the target. It was discovered that maintaining power density outside this range results in tint or coloration of the film, which is unacceptable for plat screen and touchscreen applications. For example, for a 13 inch target, about 1-4 kW of DC power can be applied to the target, which is 77-308 kW/inch. The DC voltage is 400-1000V, and may be continuous or pulsed. The target material is amorphous carbon, about 90-100% pure carbon. The sputtering gas is generally a H2/Ar mixture with flow of about 50% Ar:50% H2 to 85% Ar:15% H2, wherein a flow of 50% Ar:50% H2 provided the best results, and of 70% Ar:30% H2 provided acceptable, but less desirable results. Other gasses may be added. 
     In one embodiment, a coating of 75 Å of DLC is deposited using three passes of the substrate in front of a stationary target, each pass depositing 25 Å. The target is DC energized at 2 kW and the substrate is moved at 10 mm/sec during the sputtering process. 
     It should be understood that processes and techniques described herein are not inherently related to any particular apparatus and may be implemented by any suitable combination of components. Further, various types of general purpose devices may be used in accordance with the teachings described herein. It may also prove advantageous to construct specialized apparatus to perform the method steps described herein. 
     The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations of hardware, software, and firmware will be suitable for practicing the present invention. Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.