Abstract:
A semiconductor chip having an exposed metal terminating pad thereover, and a separate substrate having a corresponding exposed metal bump thereover are provided. A conducting polymer plug is formed over the exposed metal terminating pad. A conforming interface layer is formed over the conducting polymer plug. The conducting polymer plug of the semiconductor chip is aligned with the corresponding metal bump. The conforming interface layer over the conducting polymer plug is mated with the corresponding metal bump. The conforming interface layer is thermally decomposed, adhering and permanently attaching the conducting polymer plug with the corresponding metal bump. Methods of forming and patterning a nickel carbonyl layer are also disclosed.

Description:
[0001]     This application is a Continuation-in-Part of application Ser. No. 09/612,576 filed on Jul. 7, 2000 and assigned to a common assignee. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to the packaging of semiconductor devices, and more specifically to copper interconnect processes between chips and substrates in packaging processes.  
       BACKGROUND OF THE INVENTION  
       [0003]     Recent integration of copper interconnect processes into IC (integrated circuit) manufacturing requires copper terminating chips to be bonded directly on the copper metal pad and circuit boards. The present invention allows the use of conducting polymers to bond copper terminating chips directly on copper substrate or printed circuit boards.  
         [0004]     U.S. Pat. No. 5,923,955 to Wong describes a process for creating a flip-chip bonded combination for a first and second integrated circuits using a Ni/Cu/TiN structure.  
         [0005]     U.S. Pat. No. 5,891,756 to Erickson describes a method for forming a solder bump pad, and specifically to converting a wire bond pad of a surface-mount IC device to a flip-chip solder bump pad such that the IC device can be flip-chip mounted to a substrate. The method uses a Ni layer over the pad.  
         [0006]     U.S. Pat. No. 5,795,818 to Marrs describes a method of forming an interconnection between bonding pads on an integrated circuit chip and corresponding bonding contacts on a substrate. The method uses coined ball bond bumps.  
         [0007]     U.S. Pat. No. 5,904,859 to Degani describes a method for applying under bump metallization (UBM) for solder bump interconnections on interconnection substrates. The UBM comprises a Cu, Cu/Cr, Cr multilayer structure.  
         [0008]     U.S. Pat. No. 5,767,009 to Yoshida et al. describes a method of reducing cross talk noise between stacked semiconductor chips by the use of a chip on chip mounting structure.  
         [0009]     U.S. Pat. No. 5,804,876 to Lake et al. describes a low contact resistance electrical bonding interconnect having a metal bond pad portion and conductive epoxy portion.  
       SUMMARY OF THE INVENTION  
       [0010]     Accordingly, it is an object of the present invention is to provide a method of bonding a chip to a substrate without the need for a bump metal, wetting agents, and barrier materials.  
         [0011]     Another object of the present invention is to provide a method of bonding a chip to a substrate avoiding the use of environmentally unfriendly solder and solder material.  
         [0012]     An additional object of the present invention is to provide a method of bonding a chip to a substrate in smaller micron scale metal pitch sizes.  
         [0013]     Other objects will appear hereinafter.  
         [0014]     It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a semiconductor chip having an exposed metal terminating pad thereover, and a separate substrate having a corresponding exposed metal bump thereover are provided. A conducting polymer plug is formed over the exposed metal terminating pad. A conforming interface layer is formed over the conducting polymer plug. The conducting polymer plug of the semiconductor chip is aligned with the corresponding metal bump. The conforming interface layer over the conducting polymer plug is mated with the corresponding metal bump. The conforming interface layer is thermally decomposed, adhering and permanently attaching the conducting polymer plug of the semiconductor chip with the corresponding metal bump of the separate substrate. Methods of forming and patterning a nickel carbonyl layer are also disclosed.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The features and advantages of the present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate similar or corresponding elements, regions and portions and in which:  
         [0016]     FIGS.  1  to  6  schematically illustrate in cross-sectional representation a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Unless otherwise specified, all structures, layers, etc. may be formed or accomplished by conventional methods known in the prior art.  
         [0018]     Accordingly, as shown in  FIG. 1 , semiconductor structure  200  includes an overlying final metal layer  212  connected to, for example, metal line  214  through metal via  216 . Metal terminating pad  218  overlies final metal layer  212  at a predetermined position within first passivation layer  220 .  
         [0019]     Semiconductor structure  200  is understood to possibly include a semiconductor wafer or substrate, active and passive devices formed within the wafer, conductive layers and dielectric layers (e.g., inter-poly oxide (IPO), intermetal dielectric (IMD), etc.) formed over the wafer surface. The term “semiconductor structure  200 ” is meant to include a semiconductor chip.  
         [0020]     Final metal layer  212  and metal terminating pad  218  are preferably comprised of copper as will be used for illustrative purposes hereafter.  
         [0021]     Additional metal vias  216 , metal lines  214 , metal terminating pads  218 , etc., may be formed within and over semiconductor structure  200  although for purposes of illustration, only single such structures are shown in  FIG. 11 . For purposes of simplicity, metal via  216 , metal line  214 , and final metal layer  212  are not explicitly illustrated in the following  FIGS. 2-6 .  
         [0022]     Final passivation layer  222  is formed over first passivation layer  220  and copper terminating pad  218  to a thickness of from about 1000 to 10,000 Å, and more preferably from about 2000 to 5000 Å.  
         [0023]     Opening  224  is formed within second passivation layer  222  exposing copper terminating pad  218 .  
         [0024]     As shown in  FIG. 2 , planarized conducting polymer plug  250  is formed within opening  224  by flowing or using a spin-on-technique on copper surfaces such a bonding pads  218  or copper tracks on printed circuit boards. Planarized conducting polymer plug  250  is preferably from about 1000 to 10,000 Å thick, and more preferably from about 3000 to 6000 Å thick.  
         [0025]     Conducting polymer plug  250  includes, but is not restricted to doped polyacetylene, poly (para-phenylene vinylene) (PPV), or polyaniline manufactured by DuPont, Ciba Geigy, and Sieman&#39;s and others.  
         [0026]     Conducting polymer plug  250  is used to achieve an effective copper/copper surface bonding in copper terminating IC chip pads  218 . The conducting polymer has good conductive properties, is highly doped to degeneracy (see below), has good adhesive properties and very useful thermal insulation properties.  
         [0027]     The main characteristics of the conducting polymer forming conducting polymer plug  250  is the presence of the so-called conjugated chain where the chemical bonding between the atoms in the mainly carbon “backbone” of the polymer chain alternates between single and double bonds.  
         [0028]     There are two types of bonds namely the omega-bond and the phi-bond. Electrons in the former (omega-bond) are strongly localized and form strong bonds, in contrast to the later (phi-bond) in which the electrons form weak bonds and are not localized.  
         [0029]     The electrons in phi-bonds can be thought of a cloud that extends along the entire length of the conjugated chain in which electrons are free to move in a similar fashion to conducting electrons in a metal. The conducting polymer is heavily doped to achieve a conduction which is comparable to a degenerate semiconductor and is sufficient enough not to perturb the device performance.  
         [0030]     As shown in  FIG. 3 , interface layer  260  is formed over second passivation layer  222  and conducting polymer plug  250 . Interface layer  260  is preferably comprised of nickel carbonyl (Ni(CO) 4 ) as will be used for illustrative purposes hereafter. The material for interface layer is selected to be subject to thermal decomposition be chemical combustible.  
         [0031]     Ni(CO) 4  has a freezing point of −19° C., between −19° C. and 40° C. nickel carbonyl exists as a liquid and, at temperatures above 40° C., the following reaction takes place:
 
Ni(CO) 4 →Ni+4 CO 
 
 Below 40° C., the reverse reaction takes place:
 
Ni+4 CO→Ni(CO) 4  
 
         [0032]     Two methods may be used to form Ni(CO) 4  interface layer  260 . In the first method, nickel is first deposited (through sputtering or electroplating) over second passivation layer  222  and conducting polymer plug  250 . Then, carbon monoxide (CO) is introduced into the reaction chamber and reacts with the deposited nickel layer to form Ni(CO) 4  interface layer  260 . The CO may be pressurized as necessary. The temperature of the chamber and/or the temperature of the wafer must be less than 40° C. to form the Ni(CO) 4  and then keep below −19° C. to maintain the Ni(CO) 4  interface layer  260  as a solid.  
         [0033]     In the second method, liquid Ni(CO) 4  (at a temperature between −19° C. and 40° C.) is flowed over second passivation layer  222  and conducting polymer plug  250  and then the temperature of the chamber and/or the temperature of the wafer is lowered to less than −19° C. so as to convert the liquid Ni(CO) 4  into solid Ni(CO) 4  interface layer  260 .  
         [0034]     Regardless of which method is used, the temperature of the chamber and/or the temperature of the wafer must be less than −19° C. to maintain the Ni(CO) 4  interface layer  260  as a solid.  
         [0035]     As shown in  FIG. 4 , the excess of Ni(CO) 4  interface layer  260  not over conducting polymer plug  250  is removed to form conforming Ni(CO) 4  interface layer  260 ′ over conducting polymer plug  250 . To remove the excess of Ni(CO) 4  interface layer  260  not over conducting polymer plug  250 , a partial chrome photomask (not shown) is formed over the wafer with the chrome portion of the photomask overlying that portion of the Ni(CO) 4  interface layer  260  overlying the conducting polymer plug  250 . The partial chrome photomask is then subjected to a radiation source such that radiation penetrates the photomask to the Ni(CO) 4  interface layer  260  not over conducting polymer plug  250  and raising the temperature of that portion of the Ni(CO) 4  interface layer  260  above 40° C. so that the reaction
 
Ni(CO) 4 →Ni+4 CO 
 
 takes place, removing the Ni(CO) 4  interface layer  260  not over conducting polymer plug  250 . No radiation may penetrate the chrome portion of the photomask overlying the Ni(CO) 4  interface layer  260  over conducting polymer plug  250  so that portion of the Ni(CO) 4  interface layer  260  remains as Ni(CO) 4 . 
 
         [0036]     Final passivation layer  222  is also then removed, exposing conducting polymer plug  250  with overlying conforming Ni(CO) 4  interface layer  260 ′. As shown in  FIG. 5 , pre-formed metal bump  300  (connected to metal track  310  within substrate  320 ) is aligned, mechanically pressed, and mated with, conducting polymer plug  250  with overlying conforming Ni(CO) 4  interface layer  260 ′. Substrate  320  may be a bond pad or a printed circuit board, for example.  
         [0037]     Metal bump  300  and metal track  310  are preferably comprised of copper as will be used for illustrative purposes hereafter. Cu metal bump  300  is formed by electroless plating, at about 200° C.  
         [0038]     As shown in  FIG. 6 , conforming Ni(CO) 4  interface layer  260 ′ thermally decomposes allowing copper bump  300  to adhere directly with conducting polymer plug  250  at temperature above about 40° C.:
 
Ni(CO) 4 →Ni+4 CO 
 
 With slight application of pressure, the thermal decomposition of Ni(CO) 4  interface layer  260 ′ facilitates Ni bonding of copper bump  300  to conducting poly plug  250 . 
 
         [0039]     The present invention may find wide application in flip-chip, chip-on-board, and micron metal bonding and provides for micron scale bonding.  
         [0040]     Thus, the present invention permits semiconductor chips with copper interconnect termination to be directly bonded by a flip-chip, chip-on-board, and micron metal bonding processes onto a copper substrate or printed circuit board, eliminating the need for a bump metal, wetting agent metals and barrier materials with the attendant costly process steps and materials involved. It further avoids the use of environmentally unfriendly solder and solder materials, and allows for use in smaller micron scale metal pitch sizes unlike most of the current bonding techniques.  
         [0041]     While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.