Patent Publication Number: US-8117878-B1

Title: Method and apparatus for forming and texturing process shields

Description:
REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/965,243, filed on Aug. 17, 2007, entitled “Method and Apparatus for Forming and Texturing Process Shields,” by Alan Popiolkowski and Shannon Hart, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to metal forming, and more particularly but not exclusively to methods and apparatus for forming and texturing process shields employed in semiconductor processing equipment. 
     2. Description of the Background Art 
     Various types of process shields are employed in semiconductor processing equipment. For example, in a physical vapor deposition (PVD) system, process shields are employed to collect materials that fail to deposit on a wafer being processed. 
     Conventional techniques for manufacturing process shields include metal spinning and use of twin wire arc spray. Deep drawing and hydroforming are two other processes capable of making tubular type parts, such as a process shields. However, deep drawing and hydroforming are not economically feasible with low volume production due to the high cost of associated tooling. Twin wire arc spray is also not desirable because it adds to the cost of manufacturing the shield, is inconsistent as it is predominantly a manual process, and is subject to separation and particle generation due to the sheet like film that builds up during wafer processing. 
     SUMMARY 
     A textured process shield and similar parts may be formed and textured in the same forming process using a mandrel. The mandrel may have movable portions that may be set into a forming die to form a workpiece into a process shield and collapsed to allow the process shield to be removed from the mandrel. 
     In one embodiment, the movable portions comprise several textured shoes supported by movable jaws. The jaws may be actuated to lock into forming die position to allow forming and texturing of the work piece and then collapsed to allow removal of the resulting process shield. 
     In another embodiment, the movable portions comprise movable tapered jaws. A tapered plug may be positioned within the mandrel to actuate the tapered jaws. The tapered jaws may have a contact surface comprising angled indentations that are at an angle relative to a normal plane of the contact surface. The tapered jaws may be locked into forming die position to allow forming and texturing of a workpiece and then collapsed to allow removal of the resulting process shield. 
     These and other features of the present invention will be readily apparent to persons of ordinary skill in the art upon reading the entirety of this disclosure, which includes the accompanying drawings and claims. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows a PVD system in accordance with an embodiment of the present invention. 
         FIG. 2  schematically shows a metal forming system in accordance with an embodiment of the present invention. 
         FIGS. 3A and 3B  schematically show a mandrel in accordance with an embodiment of the present invention. 
         FIG. 3C  shows a process shield formed using the mandrel of  FIGS. 3A and 3B , in accordance with an embodiment of the present invention. 
         FIG. 4  shows a flow diagram of a method of operating a mandrel to form a process shield, in accordance with an embodiment of the present invention. 
         FIGS. 5A ,  5 B,  5 C,  5 D,  5 E, and  5 F provide graphical illustrations for the method of  FIG. 4 , in accordance with an embodiment of the present invention. 
         FIG. 6  schematically shows a mandrel in accordance with an embodiment of the present invention. 
         FIGS. 7A and 7B  schematically show front and side cross-sectional views, respectively, of the mandrel of  FIG. 6  in accordance with an embodiment of the present invention. 
         FIG. 8  shows a jaw contact surface in accordance with an embodiment of the present invention. 
         FIGS. 9A ,  9 B, and  9 C show portions of process shields in accordance with embodiments of the present invention. 
         FIG. 10  shows a flow diagram of a method of operating a mandrel to form a process shield, in accordance with an embodiment of the present invention. 
     
    
    
     The use of the same reference label in different drawings indicates the same or like components. The drawings are not to scale. 
     DETAILED DESCRIPTION 
     In the present disclosure, numerous specific details are provided, such as examples of apparatus, components, and methods, to provide a thorough understanding of embodiments of the invention. Persons of ordinary skill in the art will recognize, however, that the invention can be practiced without one or more of the specific details. In other instances, well-known details are not shown or described to avoid obscuring aspects of the invention. 
       FIG. 1  schematically shows a PVD system  150  in accordance with an embodiment of the present invention. The PVD system  150  includes a pedestal  152  supporting a substrate  157  (e.g., semiconductor wafer) to be coated with target material from a target  154 . The PVD system  150  may comprise a hollow cathode magnetron, for example. In that example, the target  154  is a hollow cathode target. As can be appreciated, the process shield and methods and apparatus for fabricating same disclosed herein are applicable to other semiconductor processing equipment, including other types of PVD systems. 
     The PVD system  150  includes a textured process shield  153  inside the vacuum chamber  160 . The textured process shield  153  may have a tubular shape concentric with the pedestal  152 . The textured process shield  153  surrounds the substrate  157  to collect target materials that miss the substrate  157 . The textured process shield  153  is so named because of the texturing on its inner diameter surface, which faces towards the substrate  157 . The texturing advantageously prevents sheet-like build up of materials that may eventually crack and cause particle contamination inside the chamber  160 . 
       FIG. 2  schematically shows a metal forming system  200  in accordance with an embodiment of the present invention. In the example of  FIG. 2 , the system  200  includes a mandrel  202 , a tailstock  203 , and rollers  204 . Each roller  204  may have an outside diameter with a radius equal to approximately half it thickness Each roller  204  rolls about a centerline  205 . The work piece  201  may comprise a material to be formed into a process shield  153  (see  FIG. 1 ). The work piece  201  may comprise a circular die, water jet, plasma or laser cut pre-form made from sheet or plate stock. For example, the work piece  201  may comprise aluminum having a diameter of about 33 inches. Other materials may also be used. The material of work piece  201  preferably has enough ductility to allow the mandrel  202  to be expanded into the work piece  201  for removal, as later explained. The mandrel  202  may be hydraulically, pneumatically or mechanically actuated to expand and collapse. 
     In operation, the tailstock  203  clamps the work piece  201  to the mandrel  202 . Thereafter, the mandrel  202  and work piece  201  are rotated while the rollers  204  are moved to push the work piece  201  towards the mandrel  202  to conform the shape of the work piece  201  to that of the mandrel  202 . The dashed outlines  201 - 1  and  201 - 2  schematically illustrate the bending of the work piece  201  towards the mandrel  202  during this phase of the forming process. 
     The rollers  204  impinge on the rotating work piece  201  and traverse down the length of the mandrel  202 , causing the work piece  201  to lay in intimate contact with the textured shoes of the mandrel  202 . This causes the inside diameter of the work piece  201  to take on the male/female features that exist on the shoes of the mandrel  202 . Any subsequent outside diameter texturing on the resulting tubular part that is needed at this point may be applied with an appropriate textured roller. Once the forming and texturing of the work piece  201  is completed, the mandrel  202  is actuated to collapse, allowing the resulting formed tubular, bucket-shaped part to be stripped from the mandrel  202 , without having to take apart or cut away portions of the formed part. The formed part may be used as a single-piece textured process shield  153 . 
       FIGS. 3A and 3B  schematically show a mandrel  202 A in accordance with an embodiment of the present invention. The mandrel  202 A is a particular embodiment of the mandrel  202  of  FIG. 2 . 
       FIG. 3A  shows a side view of the mandrel  202 A. The mandrel  202 A may have a tubular shape that is symmetric about a centerline  250 . 
       FIG. 3B  shows a cross-section of the mandrel  202 A taken at section line A-A of  FIG. 3A . As shown in  FIG. 3B , the mandrel  202 A may comprise six textured shoes  221  (i.e.,  221 - 1 ,  221 - 2 ,  221 - 3 ,  221 - 4 ,  221 - 5 , and  221 - 6 ), three primary jaws  223  (i.e.,  223 - 1 ,  223 - 2 , and  223 - 3 ), and three secondary jaws  222  (i.e.,  222 - 1 ,  222 - 2 , and  222 - 3 ). Note the separate shoe  221  for each jaw. In the example of  FIG. 3A , shoe  221 - 1  is on the secondary jaw  222 - 1 , shoe  221 - 2  is on the primary jaw  223 - 1 , shoe  221 - 3  is on the secondary jaw  222 - 2 , shoe  221 - 4  is on the primary jaw  223 - 2 , shoe  221 - 5  is on the secondary jaw  222 - 3 , and shoe  221 - 6  is on the primary jaw  223 - 3 . 
     The textured shoes  221  may be detachable and interchangeable to allow different textures of different types to be used on the same mandrel  202 A. As will be more apparent below, the jaws  222  and  223  are so named because they can be moved to expand and collapse the mandrel  202 A. The mandrel  202 A may be made of a relatively hard material. The textured shoes  221  may be formed by any suitable means including embossing, chemical etching or machining. The textured shoes  221  may comprise adjacent indentations each having an aspect ratio in the range of 1:01 to 1:2 where 1 is the diameter of the indentation and the 0.01 to 2 is the depth of the indentation. 
       FIG. 3C  schematically shows a process shield  230  formed using the mandrel  202 A, in accordance with an embodiment of the present invention. The process shield  230  is a particular embodiment of the process shield  153 . The process shield  230  is tubular in this example, and symmetric about the centerline  250 . The process shield  230  includes a textured surface  231  on the inner surface of its wall  232 . The textured surface  231  faces a substrate in a processing chamber during normal operation. 
     FIGS.  4  and  5 A- 5 F illustrate the operation of the mandrel  202 A to form a process shield in accordance with an embodiment of the present invention.  FIG. 4  shows a flow diagram of a method  400  of operating the mandrel  202 A while  FIGS. 5A-5F  provide corresponding schematic illustrations.  FIGS. 5A-5F  only show textured shoes  221 - 1 ,  221 - 2 , and  221 - 6 , primary jaws  223 - 1  and  223 - 3 , and secondary jaw  222 - 1  for clarity of illustration. However, the illustrations apply to the rest of the mandrel  202 A. In general, the three primary jaws  223  with their attached shoes  221  move in unison, and the three secondary jaws  222  with their attached shoes  221  move in unison. The primary jaws  223  and the secondary jaws  222  as sets, move independently of each other. 
     In preparation for the forming process, the primary jaws  223  are expanded to allow the secondary jaws  222  to move freely ( FIG. 4 , step  402 ;  FIG. 5A , see arrows  501 ). The secondary jaws  222  are then moved up to a forming position with the primary jaws  223 , creating a forming die ( FIG. 4 , step  404 ;  FIG. 5B , see arrow  502 ). The primary jaws  223  are collapsed onto the secondary jaws  222  ( FIG. 4 , step  406 ;  FIG. 5C , see arrows  503 ), locking the mandrel  202 A to forming position. The work piece  201  (e.g., a pre-form) is then positioned with the mandrel  202 A and clamped with the tailstock  203  ( FIG. 4 , step  408 ; see also  FIG. 2 ). The work piece  201  is then formed and textured in the same forming process ( FIG. 4 , step  410 ) to create a tubular textured process shield (“formed part”). After the process shield is formed and textured, the primary jaws  223  are expanded to release the secondary jaws  222  while the process shield is in-situ ( FIG. 4 , step  412 ;  FIG. 5D , see arrows  504 ). The primary jaws  223  are expanded within the elastic limit of the material of the work piece  201 . This frees the secondary jaws  222 . The secondary jaws  222  are then collapsed by retracting them back towards the center of the mandrel  202 A into accommodating pockets ( FIG. 4 , step  414 ;  FIG. 5E , see arrow  505 ). This allows the primary jaws  223  to collapse by retracting over the secondary jaws  222  ( FIG. 4 , step  416 ;  FIG. 5F , see arrows  506 ), freeing the process shield. The process shield is then stripped from the mandrel  202 A ( FIG. 4 , step  418 ). 
     Note that because of the novel design of the mandrel  202 A, a single-piece process shield is formed and textured in the same forming process. The process shield can be removed from the mandrel after the forming process without having to take apart or otherwise cut away portions of the process shield. 
     As can be appreciated, the multiple shoes  221  of the mandrel  202 A may be smooth or textured depending on the part being manufactured. The shoes  221  are textured in these examples to form a textured process shield. The mandrel  202 A allows a process shield to be formed and textured in the same forming process, resulting in significant cost savings. Each shoe  221  may be actuated, e.g., pneumatically or hydraulically, using support shafts in the form of the primary jaws  223  and secondary jaws  222 . The actuator mechanism may be used not just to support the shaft and shoes, but also to provide movement to enable stripping of the formed part from the mechanism. 
     Referring now to  FIG. 6 , there is schematically shown a mandrel  202 B in accordance with an embodiment of the present invention. The mandrel  202 B is a particular embodiment of the mandrel  202  of  FIG. 2 . 
     In the example of  FIG. 6 , the mandrel  202 B includes a plurality of jaws  601  (i.e.,  601 - 1 , . . . ,  601 - 8 ) and a main barrel  702 . Note that the mandrel  202 B also includes a tapered plug  700  as shown in  FIG. 7B . There are eight jaws  601  in this example. The number of jaws  601  may vary depending on the application. The outer surface of the jaws  601  comprises a textured contact surface which pattern is transferred onto the workpiece during the forming process.  FIG. 6  also shows a finished part in the form of a process shield  701  and a tailstock  703 . In the example of  FIG. 6 , the tailstock  703  comprises a shaft  706  with a flanged clamp plate  705  that engages a spigot (see spigot  704  in  FIG. 7B ) during the forming process. 
     In one embodiment, the jaws  601  have tapered inside surfaces. Moving the tapered plug (see  700  in  FIG. 7B ) into the mandrel  202 B expands the jaws  601  into forming die position. A hard stop may be used to limit the expansion of the jaws  601  with the plug positioned into the mandrel  202 B. In preparation to the forming process, the mandrel  202 B is locked into forming die position by pressing the tailstock  703  against the mandrel  202 B with the workpiece in between. The mandrel  202 B is then rotated while the workpiece is impinged on its surface, forming the workpiece into a process shield  701  with a textured inner surface as before. After the forming process, the plug  700  moves forward to disengage the mating tapered surface on the jaws  601 , thereby collapsing the jaws  601  and allowing the process shield  701  to be stripped from the mandrel  202 B without having to take apart or otherwise cut away portions of the process shield  701 . This advantageously allows for a single-piece process shield made from a single piece of material, such as a pre-form comprising aluminum. 
       FIGS. 7A and 7B  schematically show front and side cross-sectional views, respectively, of the mandrel  202 B in accordance with an embodiment of the present invention. In the example of  FIG. 7A , the mandrel  202 B includes a set of primary jaws (labeled  601 - 2 ,  601 - 4 ,  601 - 6 , and  601 - 8 ) and a set of secondary jaws (labeled  601 - 1 ,  601 - 3 ,  601 - 5 , and  601 - 7 ). The primary jaws  601  are made bigger than the secondary jaws  601 . The primary jaws  601  are configured such that as the plug  700  is retracted into the mandrel  202 B, the primary jaws  601  expand to allow the secondary jaws  601  to move up. When the plug  700  is fully retracted into the mandrel  202 B, the primary jaws  601  locks into forming die position with the secondary jaws  601 . 
       FIG. 7B  shows the mandrel  202 B with the plug  700  retracted into the mandrel  202 B in forming die position.  FIG. 7B  also shows the main barrel  702 , the tapered inside surface of the jaws  601 , and the corresponding tapered outside surface of the plug  700 . A location spigot  704  engages the flanged clamp plate  705  of the tailstock  703 . The plug  700  may be positioned within the mandrel  202 B to a movement range of about 1.00 inch or less, for example. 
       FIG. 8  shows a jaw section contact surface  800  in accordance with an embodiment of the present invention. The surface  800  may be used as the outer surface of the jaws  601  that contacts the workpiece being formed into a process shield. 
     In the example of  FIG. 8 , the jaw contact surface  800  includes a pattern having indentations  801 . A workpiece contacting the indentations  801  will be imparted with an inverse pattern, which comprises angled dimples in this example. Only some of the indentations  801  have been labeled and shown for clarity of illustration. 
     In the example of  FIG. 8 , the indentations  801  are configured to impart angled dimples on the workpiece. That is, each indentation  801  comprises a hollow cavity formed at an angle (e.g., 45 degrees) relative to the axis of revolution of the mandrel. The indentations  801  are at an angle to allow for ease of removal of the resulting process shield. As can be appreciated, the angle of the indentations  801  relative to the normal plane may vary depending on where the indentations  801  are on the surface  800 . For example, a group of indentations  801  in one location of the surface  800  may be at a 45 degree angle, while another group of indentations  801  at another location may be at another degree angle. The angle of the indentations  801  relative to the normal plane of the surface  800  may be optimized for a particular process shield, as different PVD systems may impart different trajectories to sputtered target material. 
       FIG. 9A  shows a portion of a process shield  900  in accordance with an embodiment of the present invention.  FIG. 9A  shows the dimples  901  formed on the inner surface of the process shield  900 . Only some of the dimples  901  are labeled for clarify of illustration. 
     In the example of  FIG. 9A , each dimple  901  is at an angle of 90 degrees relative to the normal plane of the inner surface of the process shield  900 . The dimples  901  may be imparted by a mandrel  202 B having a textured pattern comprising indentations (e.g., indentations  801 ). The number and location of the dimples  901  may vary depending on the number and locations of corresponding indentations on the contact surface of the mandrel  202 B. 
       FIG. 9B  shows a portion of a process shield  920  in accordance with an embodiment of the present invention.  FIG. 9B  shows the dimples  921  formed on the inner surface of the process shield  920 . Only some of the dimples  921  are labeled for clarify of illustration. 
       FIG. 9B  is an example where each dimple  921  is at an angle less than 90 degrees relative to the normal plane of the inner surface of the process shield  920 . In the example of  FIG. 9B , each dimple  921  is at a 45 degree angle relative to the normal plane of the inner surface of the process shield  920 . The dimples  921  may be imparted by a mandrel  202 B having a textured pattern comprising indentations (e.g., indentations  801 ). The number and location of the dimples  921  may vary depending on the number and locations of corresponding indentations on the contact surface of the mandrel  202 B. 
       FIG. 9C  shows a magnified view of the process shield  920 , showing the dimples  921 . 
       FIG. 10  shows a flow diagram of a method  950  of operating the mandrel  202 B to form a process shield, in accordance with an embodiment of the present invention. 
     In preparation for the forming process, the tapered plug  700  is retracted into the mandrel  202 B to set and lock the mandrel into forming position (step  951 ). Retraction of the plug  700  into the mandrel  202 B expands the primary jaws  601  (i.e., jaws  601 - 2 ,  601 - 4 ,  601 - 6 , and  601 - 8 ) to allow the secondary jaws  601  (i.e., jaws  601 - 2 ,  601 - 4 ,  601 - 6 , and  601 - 8 ) to move up. Full retraction of the plug  700  into the mandrel  202 B collapses the primary jaws  601  onto the secondary jaws  601 , creating a forming die. The mandrel  202 B is then rotated (step  952 ). 
     A workpiece (e.g., see process shield  701  of  FIG. 6 ) is then impinged on the rotating mandrel (step  953 ). This may be performed by positioning the workpiece with the mandrel and clamped with a tailstock (e.g., tailstock  703  of  FIG. 6 ). Impinging the workpiece on the rotating mandrel  202 B in the same fashion as depicted by rollers  204  in  FIG. 2  forms and textures the inner surface of the resulting process shield in the same forming process. 
     After the forming process, the plug  700  moves forward away from the mandrel  202 B. This disengages the mating surface on the jaws  601 , thereby allowing the collapsing of the jaws  601  and freeing the process shield  701  from the mandrel  202 B without having to take apart or cut portions of the finished process shield. The process shield may be stripped from the mandrel  202 B at this point (step  955 ). 
     Methods and apparatus for forming and texturing process shields and similar parts for semiconductor processing equipment have been disclosed. While specific embodiments of the present invention have been provided, it is to be understood that these embodiments are for illustration purposes and not limiting. Many additional embodiments will be apparent to persons of ordinary skill in the art reading this disclosure.