Abstract:
An electroplating apparatus has one or more membrane tube rings which act as electric field shields, to provide advantageous plating characteristics at the perimeter of a work piece. The membrane tube rings may be filled with fluids having different conductivity, to change the shielding effect as desired for electroplating different types of substrates. The membrane tube rings may optionally be provided in or on a diffuser plate in the vessel of the apparatus.

Description:
PRIORITY CLAIM 
       [0001]    This application is a Continuation of U.S. patent application Ser. No. 14/601,989, filed Jan. 21, 2015, and now pending. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Manufacture of microelectronic devices and other micro-scale devices typically requires formation of multiple metal layers on a wafer or other substrate. By electroplating metals layers in combination with other steps, patterned metal layers forming the micro-scale devices are created. 
         [0003]    The substrate is electroplated in a plating apparatus or chamber, with one side of the substrate in a bath of liquid electrolyte, and with electrical contacts touching a conductive layer on the substrate surface. Electrical current is passed through the electrolyte and the conductive layer. Metal ions in the electrolyte plate out onto the substrate, forming a metal film on the substrate. To better achieve uniform plated film thickness, the plating apparatus may have an annular dielectric shield, which shields or reduces the electric field in the electrolyte near the edge of the substrate. 
         [0004]    Achieving a uniformly thick plated metal film can be difficult, for various reasons. In Damascene plating, the sheet resistance of the film changes during the plating process, which alters the electric field within the plating apparatus and tends to cause the plated film at the wafer edge to be thicker. In wafer level packaging applications, the active plating area around the edge of the wafer can vary significantly, depending on the patterns on the wafer. The active plating area may also vary depending on the specified edge exclusion zone or dimension. Substrate diameters may also vary by up to several millimeters. This can cause variations in the plated metal film near the perimeter of the substrate, due to the varying geometries resulting from changing substrate diameters. 
         [0005]    In present electroplating apparatus, to achieve optimum plating results, the electric field shields must be changed to match the characteristics of the wafer. As changing the shields is time consuming, there is a need for plating apparatus that can adjust for a changing wafer active area without having to change the shields. 
       SUMMARY OF THE INVENTION 
       [0006]    An electroplating apparatus has one or more membrane tube rings which act as electric field shields, to provide advantageous plating characteristics at the perimeter of a substrate. The membrane tube rings may be filled with fluids having different conductivity, to change the shielding effect as desired for electroplating different types of substrates. The membrane tube rings may optionally be provided in or on a diffuser plate in the vessel of the apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic section view of an electroplating apparatus. 
           [0008]      FIG. 2  is a schematic section view of a vessel of an alternative electroplating apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    In  FIG. 1 , an electroplating apparatus  20  has a rotor  24  in a head  22 . The rotor  24  includes a backing plate  26  and a contact ring  30  having a seal ring  80 . Contact ring actuators  34  move the contact ring  30  vertically (in the direction T in  FIG. 1 ), to engage the contact ring  30  and the seal ring  80  onto the down facing surface of a wafer or substrate  50 . A bellows  32  may be used to seal internal components of the head. 
         [0010]    The contact ring typically has metal fingers  35  that contact a conductive layer on the substrate  50 . In  FIG. 1 , the head  22  is shown positioned to place the substrate  50  in a process position, where the substrate is in contact with the bath of liquid electrolyte held in a vessel  38 . For processing a 300 mm diameter substrate, the vessel may have a diameter of 305 to 380 mm. 
         [0011]      FIG. 1  shows a design having a center electrode  40  surrounded by a single outer electrode  42 , although multiple concentric outer electrodes may be used. A single electrode may also be used. In a typical electroplating process, for example with copper Damascene, the electrodes  40  and  42  are anodes, and the substrate is connected to a cathode. An electric field shaping unit  44  made of a di-electric material may be positioned in the vessel between the electrodes and the wafer. A membrane  60  may optionally be included, with anolyte in a lower chamber below the membrane and with catholyte in an upper chamber above the membrane  60 . If no membrane  60  is used, the vessel forms a single chamber holding a single electrolyte. Electric current passes from the electrodes through the electrolyte to a conductive surface on the wafer. A motor  28  in the head may be used to rotate the wafer during electroplating. 
         [0012]    A membrane tube  90  formed into a ring is provided in the vessel. The membrane tube  90  is positioned so that is adjacent to the outer edge of substrate  50 , and between the substrate  50  and the anodes  40  and/or  42 . Generally the membrane tube  90  may be within 1-3 mm of the substrate, to better control the electric field near the edge of the substrate  50 . The membrane tube  90  may be attached to and supported on the side wall of the vessel  38 , or on the field shaping unit  44 . Depending on the specific vessel used, the membrane tube  90  may be supported on dielectric standoffs or brackets. 
         [0013]    The membrane tube  90  has an inlet and an outlet to allow the membrane tube  90  to be filled with a fluid having an electrical conductance suitable for providing the shielding desired. For example, the inlet may be plumbed to a valve  96  connected to fluid sources  98  and  100 , such as air, nitrogen or other gas, and/or a source of an electrolyte or water. The outlet may be plumbed to a drain for use in purging the membrane tube  90 , or to a recirculation line. In use, the fluid in the membrane tube  90  may be flowing or static. 
         [0014]    The membrane tube may be a membrane material, such as Nafion sulfonated tetrafluoroethylene based fluoropolymer-copolymer. A Nafion tube has a conductance (e.g. typically about 20-100 mS/cm) sufficient to cause the membrane tube itself to act as a partial shield. Other membrane tube materials having greater conductivity may be used to reduce the minimum shielding effect provided. A typical membrane tube  90  may have an outer diameter of 2-6 mm, a wall thickness of about 0.5 mm, and an inner diameter of 2.5 to 6 mm, or 3 to 5 mm. Alternatively, a round, square or rectangular duct may be built into the cylindrical sidewall of the vessel to achieve the same effect. 
         [0015]    As shown in  FIG. 2 , membrane tubes  90  and  92  may be arranged on or within a diffuser plate  94  to compensate for a particular wafer pattern or a wafer scribe mark. The membrane tubes  90  and  92  are formed into rings, and are referred to here as ring membrane tubes. Using the ring membrane tubes with a diffuser plate allows a single electroplating apparatus  20  to more uniformly plate substrates having different sizes. The inner membrane tube  92  and an the outer membrane tube  90  may be plumbed together, so that both membrane tubes are supplied with the same fluid. Each membrane tube  90  and  92  may be formed into a ring or circle and secured in position in or on the vessel  38 . 
         [0016]    If the two membrane tubes  90  and  92  have the same fluid, they may be provided as a single tube formed into two rings, with a transition region where the tube moves from the inner ring to the outer ring. If the two tubes are separate, they may be supplied with different fluids from separate plumbing connections outside the chamber. This allows for added control of the shielding, i.e., the effective shield ID may vary based upon whether only the inner tube or both tubes were filled with a non-conducting fluid. 
         [0017]    Membrane tubes may be distributed across the entire face of a diffuser plate to achieve radial current density control (i.e. to replicate the functionality of concentric anodes). To make the shield inactive, membrane tubes may be imbedded within a 20% open area diffuser. The open area provides the diffuser with a resistance matched to the resistance of a 20 mS/cm Nafion membrane tube when filled with catholyte. In applications where the substrate does not rotate during processing, a diffuser plate specifically designed to work with a specific substrate pattern may be used. In this case, the membrane tubes are laid out within the diffuser plate in a way that compensates for electric field variations caused by a particular wafer pattern or a scribe area. Membrane tubes may alternatively be distributed across the whole diffuser plate to achieve radial current density control. Two or more rings of membrane tubes may be used in a diffuser plate, as shown in  FIG. 2 , or without a diffuser plate, as shown in  FIG. 1 . 
         [0018]    The dielectric material annular shield in a conventional plating apparatus may be replaced with a membrane tube  90  to create an adjustable chamber shield. With the membrane tube filled with catholyte (or a higher conductivity fluid), it is inactive as a shield, because it is immersed in or surrounded by the catholyte, or electrolyte, in the vessel  38  having the same conductivity. However, when filled with a gas, such as air or nitrogen, or a liquid such as deionized water, having a conductivity lower than the surrounding electrolyte, the membrane tube acts as shield to the electric field. One or more membrane tubes  90  may also be used in an electroplating apparatus set up as a bridge apparatus capable of processing different size wafers, with the membrane tube  90  altering the electric field in the vessel as needed for a selected wafer size. A wire electrode may be positioned within a membrane tube to better allow the membrane tube itself to act as an anode or a current thief. 
         [0019]    Liquids of varying conductivity may be used in the membrane tube  90  to achieve shielding matched to a specific substrate. Changing the conductivity of the fluid in the membrane tube may also be used to compensate for changing process conditions, such as the changing film resistance that may occur during plating. A higher conductivity fluid in the membrane tube may be used to increase current flow locally (as opposed to local shielding). 
         [0020]    As used here membrane tube or membrane tube ring means a tube of a material that allows ionic current to flow through the tube walls. One or both of the membrane tubes  90  and  92  may optionally be connected to an anode current source and operated as anodes, with or without simultaneous operation of the anodes  40  and/or  42 . In this use, an inert or an active anode conductor may be provided in the membrane tubes. It is also possible for the anode of the membrane tubes to be formed via a material different from the material of the vessel anodes  40  and  42  to allow multiple materials to be co-plated, for example as with plating solder. The conductor providing the anode current in the membrane tube may be a wire, with the wire pulled through the membrane tube to replenish the anode material, as needed. 
         [0021]    Thus, novel apparatus and methods have been shown and described. Various changes and substitutions may of course be made without departing from the spirit and scope of the invention. The invention, therefore, should not be limited except by the following claims and their equivalents.