Patent Publication Number: US-2018037984-A1

Title: Endblock for rotatable target with electrical connection between collector and rotor at pressure less than atmospheric pressure

Description:
Example embodiments of this invention relate to an endblock for a rotatable sputtering target such as a rotatable magnetron sputtering target. A sputtering apparatus design, including an endblock design, includes locating the electrical contact(s) (e.g., brush(es)) between the collector and rotor in an area under vacuum (as opposed to in an area at atmospheric pressure) which has been found to provide for significant advantages. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Sputtering is known in the art as a technique for depositing layers or coatings onto substrates such as glass substrates. For example, a low-emissivity (low-E) coating can be deposited onto a glass substrate by successively sputter-depositing a plurality of different layers onto the substrate. As an example, a low-E coating may include the following layers in this order: glass substrate/SnO 2 /ZnO/Ag/ZnO, where the Ag layer is an IR reflecting layer and the metal oxide layers are dielectric layers. In this example, one or more tin (Sn) targets may be used to sputter-deposit the base layer of SnO 2 , one or more zinc (Zn) inclusive targets may be used to sputter-deposit the next layer of ZnO, an Ag target may be used to sputter-deposit the Ag layer, and so forth. The sputtering of each target is performed in a chamber housing a gaseous atmosphere (e.g., a mixture of Ar and O gases in the Sn and/or Zn target atmosphere(s)). Example references discussing sputtering and devices used therefore include U.S. Pat. Nos. 8,192,598, 6,736,948, 5,427,665, 5,725,746 and 2004/0163943, the entire disclosures of which are all hereby incorporated herein by reference. 
     A sputtering target (e.g., cylindrical rotatable magnetron sputtering target) typically includes a cathode tube within which is a magnet array. The cathode tube is often made of stainless steel. The target material is typically formed on the tube by spraying, casting or pressing it onto the outer surface of the stainless steel cathode tube. Often, a bonding or backing layer is provided between the tube and the target to improve bonding of the target material to the tube. Each sputtering chamber includes one or more targets, and thus includes one or more of these cathode tubes. The cathode tube(s) may be held at a negative potential (e.g., −200 to −1500 V), and may be sputtered when rotating. When a target is rotating, ions from the sputtering gas discharge are accelerated into the target and dislodge, or sputter off, atoms of the target material. These atoms, in turn, together with the gas form the appropriate compound (e.g., tin oxide) that is directed to the substrate in order to form a thin film or layer of the same on the substrate. 
     In addition to the quality of the coating the magnetron deposits upon the substrate, dependability and serviceability of the magnetron is an issue. This is not an easy task taking into account the constraints of the process that is involved. A cylindrical magnetron sputters material from a rotating target tube onto the substrate as it is transported past the target. In order to coat such a large piece of glass or the like the target tube can be up to 15 feet in length and up to 6 inches or more in diameter and can weigh up to 1700 pounds for example. Another complication is that the sputtering actually erodes the target tube during the sputtering process, so the target tube is constantly changing shape during its serviceable lifetime. And the sputtering process can require that an extremely high AC or DC power (e.g., 800 Amps DC, 150 kW AC) be supplied to the target in certain instances. This power transfer creates significant heat in the target tube and the surrounding components, which must be cooled in order to assure proper performance and to avoid failure of the magnetron. Thus, it is known to pump water through the center of the rotating target tube at high pressure and flow rate to cool the target. 
       FIG. 1  is a side plan view of a rotating sputtering target and conventional endblock.  FIG. 1  illustrates that the rotating target  1  is supported on one end by an endblock  3 . The endblock  3  may be supported by and/or attached to a wall or ceiling  5  of a sputtering chamber  8  in a sputtering apparatus  7 . Outside of the sputtering chamber(s)  8 , the sputtering apparatus is at atmospheric pressure  9 . In  FIG. 1 , reference numeral  9  indicates areas at atmospheric pressure. Efficient and effective sputtering requires that the sputtering process take place in a vacuum or a reduced pressure relative to atmosphere—in  FIG. 1  the chamber  8  (other than the endblock  3 ) is under vacuum and thus is at pressure less than atmospheric pressure. The rotating target system is designed to have a robust sealing system, including seals  11  and  12  to prevent pressure or vacuum leaks between the low pressure areas  8  and the atmospheric pressure areas  9 . 
     Electrically conductive brushes  15  provide for electrical contact and thus a power connection between the collector and the rotor. In the conventional system of  FIG. 1 , the brushes  15  that provide the electrical power connection between the collector and rotor are located in an area  9  at atmospheric pressure. 
     It has surprisingly been found that a new design that includes locating the electrical contact(s) (e.g., brushes) between the collector and rotor in an area under vacuum (as opposed to in an area at atmospheric pressure as in conventional  FIG. 1 ) provides for significant advantages over the conventional design. Moving the power connection between the rotor and collector to an area under vacuum (an area at a pressure less than atmospheric pressure), for example, allows for a structure where both the rotor and collector can be efficiently cooled (e.g., water cooled) which has surprisingly been found to allow the sputtering rate to be improved (e.g., up to a 20% improvement in sputtering rate has surprisingly been found compared to the conventional  FIG. 1  design). A rotating sputtering target, such as a magnetron sputtering target, is often supported by two endblocks—one at each end of the target. One or both of the endblocks for supporting a rotating target may be designed in accordance with example embodiments of this invention. 
     In example embodiments of this invention, there is provided a sputtering apparatus comprising: at least one endblock for supporting an end of a cylindrical rotatable sputtering target, the endblock including a fixed conductive collector, and a rotatable conductive rotor for rotating with the cylindrical sputtering target during sputtering operations; the endblock further including an electrical power transfer structure (e.g., conductive brush(es)) located between the fixed conductive collector and the rotatable rotor for allowing electrical power to be transferred from the collector to the rotor; a first cooling area through which liquid flows for cooling the fixed conductive collector, the first cooling area being located around at least a portion of the fixed conductive collector and being substantially concentric with the fixed conductive collector; a second cooling area, separate from the first cooling area, through which liquid flows for cooling the rotor and target, the second cooling area being at least partially surrounded by the rotor, and wherein the liquid in the second cooling area flows in at least a direction that is substantially parallel to an axis about which the target and rotor are to rotate; wherein the liquid in the first cooling area flows around the axis about which the target and rotor are to rotate; and wherein the electrical power transfer structure, the rotor, and the collector are each located (partially or fully) in an area under vacuum having pressure less than atmospheric pressure (e.g., so that there is no significant difference in pressure therebetween). 
     Unless otherwise stated or indicated, “fixed” as used herein when referring to an element being “fixed” means that the element at issue does not rotate together with the rotor or target tube during sputtering operations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side plan view of a rotating sputtering target and conventional endblock. 
         FIG. 2  is a side plan view of a rotating sputtering target and endblock according to an example embodiment of this invention. 
         FIG. 3  is a cross sectional view of the endblock of  FIG. 2  according to an example embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION 
     Referring now more particularly to the accompanying drawings in which like reference numerals indicate like parts throughout the figures. 
       FIG. 2  is a side plan view of a rotating sputtering target and endblock. The endblock  4  is for a cathode revolver that is to be placed in a sputtering apparatus prior to sputtering operations, and then utilized in the sputtering apparatus during sputtering operation.  FIG. 2  illustrates that the rotating cylindrical magnetron target  1  is supported at one end by an endblock  4  designed according to an example embodiment of this invention. And  FIG. 3  is a cross sectional view of the endblock  4  of  FIG. 2 . The endblock  4  may be supported by and/or attached to a wall and/or ceiling  5  of a sputtering chamber  8  in a sputtering apparatus  10  via an endblock support  16 . In other preferred embodiments, the endblock  4  may be mounted on and supported by a cathode revolver via support  16  for selective use in sputtering apparatus such as the cathode revolver disclosed in U.S. application Ser. No. 12/461,130, the disclosure of which is hereby incorporated herein by reference. Outside of the sputtering chamber(s)  8 , the sputtering apparatus is at atmospheric pressure  9 . In  FIGS. 2-3 , reference numeral  9  indicates areas at atmospheric pressure which are generally areas above the ceiling  5  and/or outside of the chamber  8 . Efficient and effective sputtering requires that the sputtering process take place in a vacuum or a reduced pressure relative to atmosphere—in  FIGS. 2-3  the sputtering chamber  8  (including the endblock  4 ) is under vacuum and thus is at pressure less than atmospheric pressure. The rotating target system is designed to have a robust sealing system, including seals to prevent pressure or vacuum leaks between the low pressure areas  8  and the atmospheric pressure areas  9 . 
     Electrically conductive brushes/contacts  18  provide for electrical contact and thus a power connection between the fixed conductive collector  20  and the rotating conductive rotor  22  in order to transfer large amounts of energy from the collector  20  to the rotor  22  and target tube/cathode  1  needed for the sputtering process. Power (current and/or voltage) is applied to or through the conductive endblock support  16  and travels through the conductive collector  20  which is in electrical communication (directly or indirectly) with the conductive support  16 . Thus, the fixed endblock support  16  is in electrical communication with the fixed collector  20  and power is provided to the collector  20  from exterior the chamber  8  via fixed endblock support  16 . The power is then transferred form the fixed conductive collector  20  to the rotating conductive rotor  22  via contact(s) such as contact brushes  18  or the like, with the power then being provided from the rotor  22  to the target tube assembly. 
     In contrast with  FIG. 1 , in  FIGS. 2-3  the contact brushes  18  that provide the electrical power connection between the collector  20  and rotor  22  are located in an area  8  under vacuum (in an area at pressure less than atmospheric pressure). The entire illustrated area  8  shown in  FIG. 3 , under the ceiling  5 , is under vacuum and is thus at pressure less than atmospheric pressure. The rotor  22  rotates along with the sputtering target  1  about longitudinal axis  24  which extends through the target  1  and the endblock  4 , whereas the collector  20  is fixed in place and does not rotate with the target  1 . The rotor  22  may be of a single piece design, or may be made up of multiple pieces. Inner bearings  52  and outer bearings  54 , each concentric with the rotor  22  and spindle tube  56  so as to all have a common axis  24 , allow the rotor  22  to rotate about axis  24  relative to fixed spindle tube  56  and fixed support  58  which at least partially surrounds the rotor  22 . The spindle tube  56  is fixed in place relative to the rotor, and the spindle tube  56  is preferably fixed (directly or indirectly) to the magnet bar structure (not shown) in the target tube. The target  1  is connected to and located at the inboard side  4   a  of the endblock  4 . Another similar or different endblock (not shown) may support the other end of the rotatable target  1 . In certain example embodiments, the endblock  4  shown in  FIGS. 2-3  may be considered the driving endblock for supporting one end of the rotatable target  1 , whereas a different endblock (e.g., without a collector) such as a cooling endblock supporting the opposite end of the target  1 . In certain example embodiment, the cooling liquid (e.g., water) input  30  and output  32  for the collector cooling area are located in the driving endblock  4  shown in  FIGS. 2-3 , whereas the cooling liquid (e.g., water) input and output for the cooling area  40  are located in the other endblock (not shown) at the opposite end of the target  1 . 
     It has surprisingly been found that the design of  FIGS. 2-3  that includes locating the electrical contact(s) (e.g., brushes)  18  between the collector  20  and rotor  22  in an area  8  entirely under vacuum (as opposed to in an area  9  at atmospheric pressure as in conventional  FIG. 1 ) provides for significant advantages over the conventional design of  FIG. 1 . Moving the power connection between the rotor  22  and collector  22  to an area  8  under vacuum (an area at a pressure less than atmospheric pressure), for example, allows for a structure where both the rotor  22  and collector  20  can be efficiently cooled (e.g., water cooled) which has surprisingly been found to allow the sputtering rate to be improved (e.g., up to a 20% improvement in sputtering rate has surprisingly been found compared to the conventional  FIG. 1  design). 
     A water inlet  30  and water outlet  32  are provided for allowing water to be input and output from an area for cooling the collector  20 . The cooling area  36  through which the cooling water flows and is circulated for cooling the collector  20  surrounds axis  24  and at least part of the rotor  22 , and is located within the collector and/or so as to surround the collector  20  as shown in  FIGS. 2-3 . The inlet  30 , outlet  32 , and cooling area  36  are fixed and do not rotate with the rotor. A separate cooling area  40  surrounded by the rotor  22  is provided for allowing water to flow in order to cool the rotor  22  and target  1 , this cooling area  40  including an inner portion  40   a  and an outer portion  40   b  that surrounds the inner portion  40   a . Cooling water flows in one direction in inner portion  40   a  and in the opposite direction in outer portion  40   b , as shown by arrows in  FIG. 3 . As shown in  FIG. 3 , a portion of the rotor  22  may be located between the cooling area  36  and the rotor cooling area  40 . The water in collector cooling area  36  generally flows in different directions than does the water in rotor cooling area  40  ( 40   a ,  40   b ). The target  1  is typically horizontally aligned relative to the ground and rotates about axis  24 , and the liquid in areas  40   a  and  40   b  preferably flows in respective directions that are substantially parallel to axis  24 . 
     In example embodiments of this invention, there is provided a sputtering apparatus comprising: at least one endblock  4  for supporting an end of a cylindrical rotatable sputtering target  1 , the endblock  4  including a fixed conductive collector  20 , and a rotatable conductive rotor  22  for rotating with the cylindrical sputtering target during sputtering operations; the endblock  4  further including an electrical power transfer structure (e.g., conductive brush(es))  18  located between the fixed conductive collector  20  and the rotatable rotor  22  for allowing electrical power to be transferred from the collector  20  to the rotor  22 ; a first cooling area  36  through which liquid flows for cooling the fixed conductive collector  20 , the first cooling area  36  being located around at least a portion of the fixed conductive collector  20  and being substantially concentric with the fixed conductive collector  20 ; a second cooling area  40 , separate from the first cooling area  36 , through which liquid flows for cooling the rotor  22  and target  1 , the second cooling area  40  being at least partially surrounded by the rotor  22 , and wherein the liquid in the second cooling area  40  flows in at least a direction(s) that is substantially parallel to an axis  24  about which the target  1  and rotor  22  are to rotate; wherein the liquid in the first cooling area  36  flows around the axis  24  about which the target  1  and rotor  22  are to rotate; and wherein the electrical power transfer structure  18 , the rotor  22 , and the collector  20  are each located (partially or fully) in an area  8  under vacuum having pressure less than atmospheric pressure (e.g., so that there is no significant difference in pressure therebetween) during sputtering operations. 
     In the sputtering apparatus of the immediately preceding paragraph, the electrical power transfer structure  18  may be made up of one or more conductive brush(es) or any other suitable conductive structure/material. 
     In the sputtering apparatus of any of the preceding two paragraphs, the entirety of the electrical power transfer structure  18  and the entirety of the rotor  22  may each be located in the area under vacuum having pressure less than atmospheric pressure. 
     In the sputtering apparatus of any of the preceding three paragraphs, the target  1  may be located entirely in the area under vacuum having pressure less than atmospheric pressure. 
     In the sputtering apparatus of any of the preceding four paragraphs, the entirety of the collector  20  may be located in the area under vacuum having pressure less than atmospheric pressure. 
     In the sputtering apparatus of any of the preceding five paragraphs, a cooling liquid inlet and a cooling liquid outlet for the first cooling area may be provided in or proximate said (first) endblock, and wherein a cooling liquid inlet and a cooling liquid outlet for the second cooling area may be provided in or proximate another (second) endblock that is provided at an end of the target opposite the end at which said (first) endblock including the collector is located. 
     In the sputtering apparatus of any of the preceding six paragraphs, the liquid in the first cooling area need not mix with the liquid in the second cooling area (the first and second cooling areas are not in fluid communication with each other). Alternatively, in other example embodiments, the liquid in the first and second cooling areas may mix and the first and second cooling areas may be in fluid communication with each other. 
     In the sputtering apparatus of any of the preceding seven paragraphs, the liquid in the first cooling area and/or the liquid in the second cooling area may comprise water. 
     In the sputtering apparatus of any of the preceding eight paragraphs, the endblock and target may be mounted on a cathode revolver for selective movement and use in sputtering operations in the sputtering apparatus. Alternatively, the endblock and target need not be mounted on such a cathode revolver, and may instead for example be mounted from a ceiling of a sputtering chamber without any intervening revolver. 
     In certain example embodiments of this invention, there is provided an endblock for supporting a rotatable sputtering target in a sputtering apparatus, the endblock comprising: a fixed conductive collector; a rotatable conductive rotor for rotating with the rotatable sputtering target during sputtering operations; an electrical power transfer structure located between the fixed conductive collector and the rotatable rotor at least for allowing electrical power to be transferred from the collector to the rotor; and wherein the electrical power transfer structure, the rotor, and the collector are each adapted to be located in an area under vacuum having pressure less than atmospheric pressure during sputtering operations. 
     The endblock of the immediately preceding paragraph may further include a first cooling area through which liquid flows for cooling the fixed conductive collector, the first cooling area being located around at least a portion of the fixed conductive collector and being substantially concentric with the fixed conductive collector. 
     The endblock of any of the immediately preceding two paragraphs may further include a second cooling area through which liquid flows for cooling the rotor and target, the second cooling area being at least partially surrounded by the rotor, and wherein the liquid in the second cooling area flows in at least a direction that is substantially parallel to an axis about which the target and rotor are to rotate. 
     In the endblock of any of the immediately preceding three paragraphs, the liquid in the first cooling area may flow around the axis about which the target and rotor are to rotate. 
     In the endblock of any of the preceding four paragraphs, the electrical power transfer structure may include or be made up of one or more conductive brush(es). 
     In the endblock of any of the preceding five paragraphs, the entirety of the electrical power transfer structure and the entirety of the rotor may be adapted to be located in the area under vacuum having pressure less than atmospheric pressure during sputtering operations. 
     In the endblock of any of the preceding six paragraphs, first and second cooling areas need not be in fluid communication with each other. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.