Abstract:
A carrier provides the ability to perform wet chemical processing on substrates using low cost equipment inspired by the electroplating methods typically utilized in leadframe-based semiconductor packaging or printed circuit board industries. Two frame pieces are mated together to form the carrier which enables transport of at least one substrate through wet chemical processing and includes a non-conductive frame with an exposed conductive flange to allow electrical coupling with processing equipment. Electrical contacts within the non-conductive frame make contact with the at least one substrate and are coupled to the conductive flange allowing an electrical potential to develop across the substrate while undergoing processing within the electroplating equipment.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/256,308 filed on Oct. 30, 2009. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to the field of semiconductor device manufacturing and, in particular, to a carrier for use in wet chemical processing of a substrate. 
     BACKGROUND 
     Integrated circuits are formed through a process known as semiconductor device fabrication. The semiconductor device may be formed on a thin slice, or wafer, of semiconductor material, such as silicon crystal. The wafer serves as a substrate for microelectronic devices built on the wafer. During fabrication of these integrated circuits, the silicon wafer is put through a sequence of wet chemical processing steps. One wet chemical processing step in the sequence is electrochemical deposition, commonly known as electroplating. 
     In the electroplating process, electrical current is used to deposit metal ions from a solution onto a wafer, forming a film or patterned structure of metal on the wafer. Certain semiconductor packaging technologies, such as Wafer Level Chip Scale Packaging and Flip Chip, involve multiple electroplating steps. Many electroplating processes make use of semiconductor fabrication plant (fab) equipment. The fab equipment is designed to plate a single wafer at a time causing the electroplating process to be slow. The fab equipment is also typically very expensive. In addition, downtime is common due to high maintenance requirements and plating chemistries are expensive due to the small quantities used. These factors result in a high cost per wafer to perform electroplating. 
     Plating equipment used in other industries, including batch and continuous processing systems used in traditional semiconductor packaging are considerably less expensive and more efficient than the fab equipment. This plating equipment may include that used for printed circuit boards or leadframe plating lines. Such plating equipment provides typical throughputs which are approximately ten times greater than that of fab equipment at a cost that is typically half that of the fab equipment. Currently, however, there is no way to electroplate semiconductor wafers using printed circuit board or leadframe style plating equipment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings. 
         FIG. 1  is a diagram illustrating a carrier according to an embodiment. 
         FIG. 2  is a diagram illustrating a carrier according to an embodiment. 
         FIG. 3  is a diagram illustrating a carrier according to an embodiment. 
         FIG. 4  is a cross section diagram illustrating a carrier according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following description sets forth numerous specific details such as examples of specific systems, components, methods, and so forth, in order to provide a good understanding of several embodiments of the present invention. It will be apparent to one skilled in the art, however, that at least some embodiments of the present invention may be practiced without these specific details. In other instances, well-known components or methods are not described in detail or are presented in simple block diagram format in order to avoid unnecessarily obscuring the present invention. Thus, the specific details set forth are merely exemplary. Particular implementations may vary from these exemplary details and still be contemplated to be within the scope of the present invention. 
     Embodiments of an apparatus are described for a carrier that provides the ability to perform wet chemical processing on a substrate using low cost, printed circuit board or leadframe style plating equipment. The carrier allows the substrate to be suspended from a machine transport mechanism as the substrate is moved through the electroplating machine. In one embodiment, the carrier includes a conductive flange which couples the carrier to the machine transport mechanism of the plating equipment. A non-conductive frame formed from two frame pieces is coupled to the conductive flange and holds at least one substrate in place during electroplating. The frame can hold two device substrates or one device and one dummy structure if required to handle uneven batch sizes. Depending on the embodiment, the substrate held in the carrier may be any of a number of different substrate types. For example, the substrate may be a crystalline substrate, such as a semiconductor wafer, a composite material such as a laminate substrate or molded structure, a flex circuit or polymer based structure, a metallic substrate, or other type of substrate. As an example, further description herein will be in terms of a wafer and the carrier may be referred to as a wafer carrier, however, this description shall not be construed as limiting in any way. Electrical contact is coupled to the conductive flange enabling a plating electrical circuit to be selectively established when the carrier is suspended by the machine transport mechanism in a wet bath during processing. 
       FIG. 1  is a diagram illustrating a wafer carrier  100  according to an embodiment of the present invention. The wafer carrier  100  includes a conductive flange  110  which couples the wafer carrier  100  to a machine transport mechanism within a plating machine (not shown). In one embodiment, the processing equipment may include an in-line plating machine. The in-line plating machine may be similar to equipment used in leadframe strip plating lines. Leadframe strip plating lines are well established in the packaging industry and may generally suspend and traverse conductive copper leadframes on a metal belt through a sequence of steps in the plating process. In another embodiment, the wafer carrier may be used with rack style plating equipment such as that used in electroplating of printed circuit boards. In other embodiments, some other transport mechanism may be used. 
     Conductive flange  110  attaches to the transport mechanism of the plating equipment and allows the wafer carrier  100  to be advanced through the plating machine. In one embodiment conductive flange  110  is formed from stainless steel, although in other embodiments, conductive flange  110  may be formed from any conductive material, such as for example, copper, another metal, or a non-metal conductive material. In one embodiment, conductive flange  110  is thin enough to afford it some degree flexibility. In certain in-line plating machines, the belt is curved around drums as the belt changes direction. The conductive flange  110 , when attached to the belt, may also curve around the drums. In one embodiment, conductive flange  110  may be flexible enough to bend in an arc having a radius of approximately 24 inches. 
     Wafer carrier  100  also includes non-conductive frame  120 . Non-conductive frame  120  is coupled to conductive flange  110  so that non-conductive frame  120  is able to be suspended from the machine transport mechanism of the plating machine. In one embodiment, non-conductive frame  120  is formed from a ring of non-conductive material, such as for example chlorinated polyvinyl chloride (CPVC). In other embodiments, other non-conductive materials may be used. Non-conductive frame  120  may be formed into a ring of non-conductive material having an inside diameter slightly smaller than the diameter of the wafer to be electroplated. For example, non-conductive frame  120  may be sized appropriately to hold a 200 millimeter (mm) or a 300 mm silicon wafer. In other embodiments, non-conductive frame  120  may be sized to hold a wafer having some other size. 
     In one embodiment, non-conductive frame  120  may be formed from two separate frame pieces  121  and  122 . Frame pieces  121  and  122  may be identical or substantially identical having one or more built-in clamps  123  to hold the pieces  121  and  122  together. In one embodiment, each frame piece is identical and includes half of the total number of clamps. In other embodiments, the clamps  123  may all be included on one frame piece or arranged between the two frame pieces in some other proportion. In one embodiment, each frame piece  121  and  122  holds a wafer and the frame pieces  121  and  122  are secured together with the wafers being oriented parallel to one another and held together by clamps  123  to form non-conductive frame  120 . The frame pieces  121  and  122  may be oriented so that the wafers are back-to-back, with the front side of each wafer facing out. Optionally, a spacer may be placed in between the two wafers within the frame assembly to provide a compliant layer. 
       FIG. 2  is a diagram illustrating a wafer carrier  100  according to an embodiment of the present invention. In this embodiment clamps  123  are open and frame piece  121  has been removed. Remaining is frame piece  122 . A wafer may be placed into frame piece  122  which can be secured together with frame piece  121  by clamps  123 . Clamps  123  may also be formed from CPVC or other non-conductive material or material which is not subject to build-up or reduction during processing. 
       FIG. 3  is a diagram illustrating a wafer carrier  100  according to an embodiment of the present invention. In this embodiment, wafers  351  and  352  are placed into non-conductive frame  120 . When placed in non-conductive frame  120 , wafers  351  and  352  may be oriented back-to-back, with the front side of each wafer facing out. In one embodiment, wafer  351  and  352  may contact each other on the back side when compressed between the pieces of non-conductive frame  120 . The pieces of non-conductive frame  120  are secured together with clamp  123 . Alternatively, an insert material may be added between wafers  351  and  352  during the process of compressing and clamping frame pieces  121  and  122  together and securing with clamp  123 . 
       FIG. 4  is a cross-section diagram illustrating a wafer carrier  100  according to an embodiment of the present invention. The cross section A-A is taken from the view indicated by plane A-A shown in  FIG. 3 . The wafer carrier  100  includes a conductive flange  110  which serves to couple the wafer carrier  100  to a plating machine. Coupled to conductive flange  110  is non-conductive frame  120 . In one embodiment non-conductive frame  120  includes two frame pieces  121  and  122 . The pieces  121  and  122  of non-conductive frame  120  are secured together with one or more clamps  123 . Clamp  123  may be connected to one of the frame pieces, such as non-conductive frame piece  122 . Wafer carrier  100  holds two wafers  351  and  352  in place during a plating process, such as electroplating. The wafers  351  and  352  may be oriented back-to-back, so that the front side of each wafer is facing out. 
     Other than frame piece  122  having clamp  123  connected to it, non-conductive frame pieces  121  and  122  may be substantially identical in one embodiment. The various features of the non-conductive body  120  may be described with respect to either frame piece  121  or  122 ; however it should be understood that the description applies equally to both frame pieces. In alternative embodiments, there may be differences between frame pieces  121  and  122 . 
     In one embodiment, each non-conductive frame piece includes a seal  424  in an area where the wafer  352  contacts the frame piece  122 . Seal  424  may take the form of a ring that fits between the edge of wafer  352  around the interior circumference of frame piece  122 . During electroplating various chemicals may be applied to the front side of the wafer  352 . It would be undesirable to have these electroplating process chemicals contact the inner portions of the frame piece  122 . The seal  424  prevents the electroplating process chemicals from leaking into the frame piece  122 . In one embodiment seal  424  is made from chemically resistant rubber or rubber like materials such as Viton, however in other embodiments, some other material may be used. 
     In one embodiment, the wafer seal  424  is designed with features such that it will retain the wafer  352  within the frame piece  122  for the purposes of simplified loading and unloading of the wafer carrier and any other purpose when the wafer is retained in frame piece  122  prior to assembly with or after disassembly from the other frame piece  121 . 
     One embodiment of the retaining feature is illustrated, and includes a flexible lip that is slightly smaller in diameter than the wafer to be retained. In operation, the wafer is pushed into the seal axially causing the flexible lip to deform and allowing the wafer to pass the lip, after which the lip returns to its original shape, and rests on the back surface of the wafer, retaining it. Removal of the wafer is accomplished by reversing the procedure. Pulling the wafer out of the seal will deform the lip, allowing the wafer to be removed, after which the lip will return to its original shape. Pushing and pulling forces are minimal during the process so as not to harm the wafer. 
     During the electroplating process, an electric potential is developed in the plating system where the wafers being plated are the cathode. In one embodiment, the electrical potential causes ions to flow from the anode to the cathode, which is the wafer in the wafer carrier  120 . The current may flow from an electroplating solution through the wafer, through pogo pin  428 , through electrical contact  427 , through conductor  426 , and out to ground through flange  110 . In one embodiment, conductor  426  may be a copper wire connected between flange  110  and electrical contact  427 , however, in other embodiments, some other conductor may be used. Electrical contact  427  may be a copper ring that extends around the circumference of piece  121 . Electrical contact  427  may be embedded within frame piece  121 . In other embodiments, some other conductive metal may be used to form electrical contact  427 . 
     A connection is formed between electrical contact  427  and wafer  351  through one or more pogo pins  428 . Pogo pin  428  is a device used to establish an electrical connection between a conductive surface on the wafer to be plated and the electrical contact  427 . In one embodiment, pogo pin  428  takes the form of a slender cylinder containing a spring-loaded pin at least one end. Pogo pin  428  is securely press fit into frame pieces  121  and  122  enabling electrical contact between electrical contact  427  and wafer  351 . The sharp spring-loaded points at the end of pogo pin  428  make secure electrical contact with wafer  351  and thereby connect them together. Pogo pin  428  may be plated in gold or some other conductive precious metal. There may be a plurality of pogo pins spaced around electrical contact  427  to contact the edge of wafer  351 . In one embodiment, the plurality of pogo pins may be spaced evenly apart from one another. 
     Each of non-conductive frame pieces  121  and  122  includes a capture ring  430 . Capture ring  430  extends around the circumference of frame piece  122 . In one embodiment capture ring  430  is made from CPVC, however, in other embodiments, some other non-conductive material or material which is not subject to build-up or reduction during processing may be used. Capture ring  430  is held to frame piece  122  by a number of screws  431 . The screws  431  may be appropriately tightened to apply sufficient pressure to electrical contact  427  to ensure a solid connection electrical contact  427 , pogo pin  428  and wafer  352 . In one embodiment, screws  431  may be made from non-conductive plastic, however, in other embodiments, some other material may be used such as material which is not subject to build-up or reduction during processing. 
     In one embodiment, each of non-conductive frame pieces  121  and  122  includes a system to test the integrity of the seals therein. Conductor  426  may be run from conductive flange  110  to electrical contact  427  through vacuum cavity  432 . Vacuum cavity  432  may have an outlet secured by a stopper. In one embodiment, the stopper may include a titanium ball  433  pressed by a spring  434  against an o-ring  435 . The ball  433  may be depressed in order to test the vacuum in vacuum cavity  426 . If vacuum cavity  432  holds a vacuum for a predetermined length of time, it follows that seals are functioning properly. Titanium ball  433  seals off vacuum cavity  432  when not being tested. 
     In addition to the electrochemical deposition, the wafer carrier described herein may be used during other wet chemical processing steps. These processing steps may include for example, plating pattern resist strip, etching of the seed layer metal, or other processes. During electroplating, a template formed from a plating pattern resist, such as a photoresist, is applied to the surface of the wafer, covering a portion of the surface. The uncovered portion of the wafer surface is electroplated. In a subsequent processing step, the plating pattern resist is removed during plating pattern resist strip. A seed layer metal on the wafer, which may be formed from titanium-tungsten and copper, is removed through an etching process. Etchants are applied to the wafer to remove the exposed seed layer metal. In one embodiment, the wafer carrier may hold the wafers during these and other processes. 
     Although the operations of the methods herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operation may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be in an intermittent and/or alternating manner.