Abstract:
Terminal pads and methods of fabricating terminal pads. The methods including forming a conductive diffusion barrier under a conductive pad in or overlapped by a passivation layer comprised of multiple dielectric layers including diffusion barrier layers. The methods including forming the terminal pads subtractively or by a damascene process.

Description:
RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 11/953,927 filed on Dec. 11, 2007 which is a division of U.S. Pat. No. 7,361,993 Ser. No. 10/908,346 filed on May 9, 2005 and issued Apr. 22, 2008. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of integrated circuits; more specifically, it relates to terminal pads for an integrated circuit and methods for fabricating the terminal pads. 
     BACKGROUND OF THE INVENTION 
     Integrated circuits include devices such as metal-oxide-silicon field effect transistors (MOSFETs) formed in a semiconductor substrate, interconnected into circuits by wires in interconnect layers formed on top of the substrate. At the highest or uppermost level of an integrated circuit chips, these wires must be connected to terminal pads which allow wirebond or solder bump connections to a next level of packaging, such as to a module or circuit board. Conventional terminal pads are complex structures because of the structural strength and contamination seal the terminal pad must provide. For integrated circuit chips for low cost or commodity products and such as used in wireless technology, conventional terminal pad structures and fabrication processes add significant costs to the fabrication process. Therefore, there is a need for cost performance terminal pad structures and fabrication processes having structural strength and contamination seal abilities. 
     SUMMARY OF THE INVENTION 
     A first aspect of the present invention is a method of forming a terminal pad, comprising: providing an electrically conductive wire formed in a dielectric layer on a substrate, a top surface of the wire coplanar with a top surface of the dielectric layer; forming a passivation layer on the top surface of the dielectric layer and the top surface of the wire, the passivation layer comprising a lower dielectric layer on the top surfaces of the dielectric layer and the wire, an intermediate dielectric layer on a top surface of the lower dielectric layer and an upper dielectric layer on a top surface of the intermediate dielectric layer; forming a trench in the passivation layer, the trench extending from a top surface of the passivation layer to a bottom surface of the passivation layer, the top surface of the wire exposed in the bottom of the trench; forming a conformal and electrically conductive liner directly on sidewalls of the trench and in direct physical and electrical contact with the top surface of the wire exposed in the bottom of the trench; and filling the trench with an electrical core conductor, a top surface of the core conductor, a top surface of the liner and a top surface of the passivation layer coplanar, the core conductor and the liner comprising the terminal pad. 
     A second aspect of the present invention is a structure, comprising: an electrically conductive wire formed in a dielectric layer on a substrate, a top surface of the wire coplanar with a top surface of the dielectric layer; a passivation layer on the top surface of the dielectric layer and the top surface of the wire, the passivation layer comprising a lower dielectric layer on the top surfaces of the dielectric layer and the wire, an intermediate dielectric layer on a top surface of the lower dielectric layer and an upper dielectric layer on a top surface of the intermediate dielectric layer; a conformal and electrically conductive liner on sidewalls of the trench and in direct physical and electrical contact with the top surface of the wire contained within the trench; and an electrical core conductor, a top surface of the core conductor, a top surface of the liner and a top surface of the passivation layer coplanar, the core conductor and the liner comprising a terminal pad. 
     A third aspect of the present invention is a method of forming a terminal pad, comprising: providing an electrically conductive wire formed in a dielectric layer on a substrate, a top surface of the wire coplanar with a top surface of the dielectric layer; forming an electrically conductive barrier layer on the top surface of the dielectric layer and the top surface of the wire; forming an electrically conductive layer on a top surface of the conductive barrier layer; subtractively removing regions of the conductive barrier layer and regions of the conductive layer to form the terminal pad; forming an electrically non-conductive passivation layer on the top surface of the dielectric layer and all exposed surfaces of the terminal pad, the passivation layer comprising a lower dielectric layer on the top surface of the dielectric layer and on the all exposed surfaces of the terminal pad and an intermediate dielectric layer on a top surface of the lower dielectric layer; and forming a via in the passivation layer, the via extending from a top surface of the passivation layer to a top surface of the terminal pad. 
     A fourth aspect of the present invention is a structure, comprising: an electrically conductive wire formed in a dielectric layer on a substrate, a top surface of the wire coplanar with a top surface of the dielectric layer; an electrically conductive barrier layer on the top surface of the dielectric layer and the top surface of the wire; a terminal pad comprising an electrically conductive layer on a top surface of an electrically conductive barrier layer, the terminal pad in physical and electrical contact with the wire; an electrically non-conductive passivation layer on the top surface of the dielectric layer and all exposed surfaces of the terminal pad, the passivation layer comprising a lower dielectric layer on the top surface of the dielectric layer and the all exposed surfaces of the terminal pad and an intermediate dielectric layer on a top surface of the lower dielectric layer; and a via in the passivation layer, the via extending from a top surface of the passivation layer to a top surface of the terminal pad. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
         FIGS. 1A through 1F  are cross-sectional views illustrating fabrication of a terminal pad structure according to a first embodiment of the present invention; 
         FIGS. 2A and 2B  are top views of terminal pads according the first embodiment of the present invention; 
         FIGS. 3A through 3F  are cross-sectional views illustrating fabrication of a terminal pad structure according to a second embodiment of the present invention; and 
         FIGS. 4A through 4B  are top views of terminal pads according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A through 1F  are cross-sectional views illustrating fabrication of a terminal pad structure according to a first embodiment of the present invention.  FIG. 1A  illustrates an exemplary integrated circuit chip prior to formation of a terminal pad according to the first embodiment of the present invention. In  FIG. 1A  formed on a substrate  100 , are wiring levels  105  and  110 . Wiring level  105  includes a dielectric layer  115 . Wiring level  110  includes a dielectric layer  120  and a dielectric layer  125 . Formed in dielectric layer  105  is a damascene wire  130  comprising an electrically conductive liner  135  and an electrically conductive core conductor  140 . Formed in interlevel dielectric layer  110  is a damascene wire  145  and integral via  150  comprising an electrically conductive liner  155  and an electrically conductive core conductor  160 . Top surface  165  of dielectric layer  125 , top surface  170  of conductive liner  155  and top surface  175  of core conductor  160  are coplanar. 
     In one example dielectric layers  115  and  125  independently comprise silicon dioxide (SiO 2 ), or a low K (dielectric constant) material, examples of which include but are not limited to hydrogen silsesquioxane polymer (HSQ), methyl silsesquioxane polymer (MSQ), polyphenylene oligomer, and SiO x (CH3) y . A low K dielectric material has a relative permittivity of 4 or less. 
     In one example, conductive liners  135  and  155  independently comprise Ti, TiN, Ta, TaN, W or combinations thereof. In one example, core conductors  140  and  160  comprise copper or copper alloys. Dielectric layer  120  may act as a diffusion barrier for materials of core conductors  140  and  160 . In the example of core conductor  160  being copper, dielectric layer  120  may be a diffusion barrier for copper and may comprise, for example, silicon nitride. Conductive liners  135  and  155  may act as a diffusion barriers for materials of core conductors  140  and  160  respectively. In the example of core conductor  160  being copper, conductive liners  135  and  155  may be diffusion barriers for copper. 
     While two levels of wiring are illustrated in  FIG. 1A , any number of wiring levels similar to wiring levels  105  and  100  may be employed. Wiring level  110 , should be considered the last wiring level before terminal pads are formed. The distinction between a wiring level and the terminal pad level of an integrated circuit is a wiring level interconnects an upper wiring level to a lower wiring level or to contacts to devices such as metal-oxide-silicon field effect transistors (MOSFETs) while terminal pads are connected to a lower wiring level only (there may be terminal pad to terminal pad connections) and there are no wiring levels above the terminal pad level. 
     In  FIG. 1B , a dielectric passivation layer  180  is formed in direct contact with top surface  165  of dielectric layer  125 , top surface  170  of conductive liner  155  and top surface  175  of core conductor  160 . Passivation layer  180  includes a lower dielectric layer  185  formed on top surface  165  of dielectric layer  125 , top surface  170  of conductive liner  155  and top surface  175  of core conductor  160 , an intermediate dielectric layer  190  formed on lower dielectric layer  185  and an upper dielectric layer  195  formed on intermediate dielectric layer  190 . In one example, lower dielectric layer  185  comprises silicon nitride (SiN) or silicon carbide nitride (SiCN) and is between about 0.05 micron to about 0.1 micron thick. In one example, intermediate dielectric layer  190  comprises silicon dioxide and is between about 0.5 micron to about 2 microns thick. In one example, upper dielectric layer  195  comprises silicon nitride and is between about 0.5 micron to about 2.0 microns thick. Passivation layer prevents contamination such as ionic contamination (e.g. chlorine, water vapor) from reaching core conductor  160 , which is particularly important when core conductor  160  comprises copper or aluminum. Formed on top of upper dielectric layer  195  is an optional chemical-mechanical-polish (CMP) polish stop layer  197 . 
     In  FIG. 1C , a trench  200  is etched through optional polish stop layer  197  (if present), upper dielectric layer  195 , intermediate dielectric layer  190  and lower dielectric lower dielectric layer  185  to expose top surface  175  of core conductor  160  but not expose any portion of liner  155  or any portion of dielectric layer  125 . Trench  200  is thus “fully landed” (see  FIGS. 2A and 2B ) on wire  145 . Trench  200  may be formed by any number of well-known photolithographic processes followed by any number of well-known directional etch processes such as reactive ion etch (RIE). 
     In  FIG. 1D , a conformal conductive liner  205  is formed on all exposed surfaces of core conductor  160 , lower dielectric layer  185 , intermediate dielectric layer  190 , upper dielectric layer  195  and optional polish stop layer  197  (if present). An electrically conductive fill  210  is formed on conductive liner completely filling trench  200 . 
     In  FIG. 1E , a CMP process is performed, to create a terminal pad  215  comprising an electrically conductive liner  220  and an electrically conductive core conductor  225 , a top surface  230  of upper dielectric layer  195 , a top surface  235  of conductive liner  220  and a top surface  240  of core conductor  225  being coplanar. In one example, conductive liner  220  comprises comprise Ti, TiN, Ta, TaN, W or combinations thereof. In one example, conductive core  225  comprises Al or AlCu (not more than about 1% Cu). The fact that terminal pad  215  is a damascene structure (recessed or inlayed into a supporting layer) adds strength to the overall terminal pad structure. The fact that pad  215  is “fully landed” on wire  145  and damascened into passivation layer  180  seals wiring level  110  and all lower wiring levels from contamination. 
     If optional polish stop layer  197  (see  FIG. 1B ) was formed in  FIG. 1A , it may be thinned by the CMP process as illustrated in  FIG. 1E . Alternatively, optional polish stop layer  197  may not be present in  FIG. 1E  (and subsequently in  FIG. 1F ) because of the possibility of the polish stop layer being entirely consumed by the CMP process. 
     At this point wirebond connections may be made to terminal pad  215 . Wirebonding is a process whereby, thin gold or aluminum wires are attached to the pads using pressure and heat energy or ultrasonic energy. Generally, an interfacial alloy is formed between the wirebond wire and terminal pad. 
     In  FIG. 1F , further processing is performed in order to make a solder bump connection to terminal pad  215 . Solder bump connections are also known controlled collapse chip connections (C 4 ). In  FIG. 1F  a ball limiting metal (BLM) pad  245  is formed on terminal pad  215 . BLM pad  245  completely overlaps terminal pad  215  (See  FIGS. 2A and 2B ). A solder bump  250  is then formed on BLM pad  245 . Solder bump  250  is illustrated after a thermal reflow process has been performed. In one example, BLM pad  245  and solder bump  250  are formed by evaporation through a metal mask. In a second example, BLM pad  245  is formed by evaporation through a metal mask and solder bump  250  is formed by electroplating through an organic mask after the BLM is formed. In one example BLM pad  245  is formed from multiple layers of metals, each layer selected from the group consisting of Cr, Cu, Au, Ni, Ti, TiN, Ta and TaN. In one example, BLM pad  245  comprises a layer of Cu over a layer of Cr in contact with terminal pad  215  and a layer of Au over the layer of Cu. In one example, BLM pad  245  comprises a layer of Ni over a layer of Cr in contact with terminal pad  215  and a layer of Au over the layer of Ni. In one example, solder bump  250  comprises a Pb/Sn alloy. 
       FIGS. 2A and 2B  are top views of terminal pads according the first embodiment of the present invention. In  FIG. 2A , wire  145  (see  FIG. 1E  or  1 F) is in itself a wiring pad  145 A having sides  260 A,  260 B,  260 C and  260 D. Terminal pad  215  has sides  265 A,  265 B,  265 C and  265 D. Sides  265 A,  265 B,  265 C and  265 D of terminal pad  215  are aligned within the perimeter formed by sides  260 A,  260 B,  260 C and  260 D of wiring pad  145 A. In  FIG. 2A , BLM pad  245  overlaps sides  260 A,  260 B,  260 C and  260 D of wire pad  145 A as well as sides  265 A,  265 B,  265 C and  265 D of terminal pad  215 . Alternatively, BLM pad  245  may overlap sides  265 A,  265 B,  265 C and  265 D of terminal pad  245  but not overlap sides  260 A,  260 B,  260 C and  260 D of wire pad  145 A. 
     In  FIG. 2B , wire  145  has sides  260 A,  260 C and an end  270 . Terminal pad  215  has sides  265 A,  265 B,  265 C and  265 D. Sides  265 A,  265 B,  265 C and  265 D of terminal pad  215  are aligned within respective sides  260 A,  260 C and end  270  of wire  145 . In  FIG. 2B , BLM pad  245  overlaps sides  260 A,  260 C and end  270  of wire  145  as well as sides  265 A,  265 B,  265 C and  265 D of terminal pad  245 . However, side  265 B of terminal pad  215  does not extend across any side of wire  145 . Alternatively, BLM pad  245  may overlap sides  265 A,  265 B,  265 C and  265 D of terminal pad  215  but not overlap sides  260 A,  260 C and end  270  of wire  145 . Again, side  265 B of terminal pad  215  would not extend across any side of wire  145 A. 
       FIGS. 3A through 3F  are cross-sectional views illustrating fabrication of a terminal pad structure according to a second embodiment of the present invention.  FIG. 3A  illustrates an exemplary integrated circuit chip prior to formation of a terminal pad according to the second embodiment of the present invention.  FIG. 3A  is identical to  FIG. 1A . In  FIG. 3B , an electrically conductive barrier layer  275  is formed on top surface  165  of dielectric layer  125 . An electrically conductive layer  280  is then formed on conductive barrier layer  275 . 
     In  FIG. 3C , a terminal pad  285  is formed from conductive barrier layer  275  and conductive layer  280  subtractively. Terminal pad  285  may be formed by any number of well known photolithographic processes followed by any number of etch processes such as RIE or wet etching. In one example, conductive barrier layer  275  is a diffusion barrier to a material contained within wire  145 . In one example, conductive barrier layer  275  comprises Ti, TiN, Ta, TaN, W or combinations thereof. In one example, conductive layer  280  comprises Al or AlCu (not more than about 1% Cu). In the example, of conductive layer  280  containing aluminum and a chlorine based RIE etch is used, a passivation step using chromic-phosphoric acid may be performed in order to passivation exposed aluminum. 
     In  FIG. 3D , a conformal lower dielectric layer  290  is formed in direct contact with top surface  165  of dielectric layer  125  and all exposed surfaces of terminal pad  285 . An intermediate dielectric layer  295  is formed on lower dielectric layer  290  and an optional electrically non-conductive upper layer  300  is formed on intermediate dielectric layer  295 . In one example, lower dielectric layer  290  comprises silicon dioxide and is between about 0.5 micron to about 2.0 microns thick. In one example, intermediate dielectric layer  295  comprises silicon nitride and is between about 0.5 micron to about 2.0 microns thick. In one example, optional upper layer  300  (if present) comprises polyimide or photosensitive polyimide and is between about 2 microns to about 10 microns thick. 
     In  FIG. 3E , a via  305  is etched through lower dielectric layer  290 , intermediate dielectric layer  295  and upper layer  300  to a expose top surface  310  of terminal pad  285 . Via  305  may be formed by any number of well-known photolithographic processes followed by any number of well-known etch processes such as RIE. Terminal pad  285  extends under all edges  315  of via  305 . Via  305  is “fully landed” on terminal pad  305 . The fact that terminal pad  285  is overlapped by lower dielectric layer  290 , intermediate dielectric layer  295  and upper layer  300  adds strength to the overall terminal pad structure. The fact that via  305  is “fully landed” on terminal pad  285  seals wiring level  110  and all lower wiring levels from contamination and adds strength to the overall terminal pad structure. At this point wirebond connections may be made to terminal pad  285  as described supra in reference to  FIG. 1E . 
     In  FIG. 3F , further processing is performed in order to make a solder bump connection to terminal pad  285 . In  FIG. 3F  a BLM pad  320  is formed on terminal pad  285 . A solder bump  325  is then formed on BLM pad  320 . Solder bump  325  is illustrated after a thermal reflow process has been performed. In one example, BLM pad  320  and solder bump  325  are formed by evaporation through a metal mask. In a second example, BLM pad  320  is formed by evaporation through a metal mask and solder bump  325  is formed by electroplating through an organic mask after the BLM is formed. In one example BLM pad  320  is formed from multiple layers of metals, each layer selected from the group consisting of Cr, Cu, Au, Ni, Ti, TiN, Ta and TaN. In one example, BLM pad  320  comprises a layer of Cu over a layer of Cr in contact with terminal pad  285  and a layer of Au over the layer of Cu. In one example, BLM pad  320  comprises a layer of Ni over a layer of Cr in contact with terminal pad  285  and a layer of Au over the layer of Ni. In one example, solder bump  325  comprises a Pb/Sn alloy. 
       FIGS. 4A through 4B  are top views of terminal pads according to the second embodiment of the present invention.  FIGS. 4A and 4B  are top views of terminal pads according the second embodiment of the present invention. In  FIG. 4A , wire  145  (see  FIG. 1E  or  1 F) is in itself a wiring pad  145 A having sides  260 A,  260 B,  260 C and  260 D. Via  305  has sides  330 A,  330 B,  330 C and  330 D. Terminal pad  285  has sides  335 A,  335 B,  335 C and  335 D. Sides  260 A,  260 B,  260 C and  260 D of wire pad  145 A are aligned within the perimeter formed by sides  330 A,  330 B,  330 C and  330 D of via  305 . Sides  330 A,  330 B,  330 C and  330 D of via  305  are aligned within the perimeter formed by sides  335 A,  335 B,  335 C and  335 D of terminal pad  285 . In  FIG. 4A , BLM  320  overlaps sides  335 A,  335 B,  335 C and  335 D of via  305 . 
     In  FIG. 4B , wire  145  has sides  260 A,  260 C and an end  270 . Terminal pad  285  has sides  335 A,  335 B,  335 C and  335 D. Sides  335 A,  335 B,  335 C and  335 D of terminal pas  285  are aligned within respective sides  260 A,  260 C and end  270  of wire  145 . In  FIG. 4B , BLM  320  overlaps sides  260 A,  260 C and end  270  of wire  145  as well as sides  330 A,  330 B,  330 C and  330 D of via  305  and sides  335 A,  335 B,  335 C and  335 D of terminal pad  285 . Alternatively, BLM  320  may overlaps sides  330 A,  330 B,  330 C and  330 D of via  305  but not overlap sides  335 A,  335 B,  335 C and  335 D of terminal pad  285 . 
     Thus the present invention provides cost performance terminal pad structures and fabrication processes having structural strength and contamination seal abilities. 
     The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.