Abstract:
An apparatus and method for incorporating discrete passive components into an integrated circuit package. A first surface of a substrate is coated with a material to mechanically protect the first surface. A first metal layer and then an insulating layer are formed on a second surface of the substrate. Selected areas are removed from the insulating and a second metal layer is formed over the insulating layer and the exposed metal layer. Selected areas of the second metal layer are removed to form a plurality of structures, including at least one of a wirebonding pad, a solder-bonding pad, a device interconnect circuit, or an attach pad to which an electronic component may be attached. An electronic component may be attached to at least one of the structures. The resulting integrated circuit die may be incorporated into an electronic package.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 11/304,084, filed on Dec. 15, 2005, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention generally concerns fabrication of semiconductor devices, particularly semiconductor devices incorporated in integrated circuit packages. 
       BACKGROUND 
       [0003]    Miniaturization of integrated circuit (IC) packages which may be incorporated in portable consumer products such as cellular phones, and mobile or laptop computers, has become increasingly important. One approach to miniaturization is the use of multi-chip modules where multiple chips having related functions are incorporated in a single package. 
         [0004]    Single packages may also include stacked chips, in which chips are vertically stacked on top of each other. A potential drawback to using stacked die techniques is that no interconnection exists on the surfaces of the stacked die; the die interconnect is limited to die-to-die and die-to-substrate interconnections. Therefore, the IC die count is typically limited to one die per attach surface. It is not feasible to attach discrete electronic components to these surfaces since they typically require solderable attachment lands and interconnect circuitry or a noble metal surface for low contact resistance connections. 
         [0005]    As such, it would be desirable to improve the manner in which discrete electronic components are incorporated in IC packages, such as utilizing die surfaces not conventionally used for die interconnections. 
       SUMMARY 
       [0006]    In one embodiment, a method of fabrication comprises providing a substrate with a first surface having a passivation layer. At least one structure is built on a second surface of the substrate; an electronic component is to be attached to at least one structure. The structures that may be built include a wirebonding pad, a solder-bonding pad, a device interconnect circuit, or an attach pad to which an electronic component may be attached. 
         [0007]    Another embodiment is an electronic package. The electronic package comprises a substrate which is coupled to a first surface of an integrated circuit die. The first surface of the integrated circuit die has means for coupling to the first surface of the substrate and has at least one first electronic component attached to the first surface of the integrated circuit die. At least one structure is attached to a second surface of the integrated circuit die. 
         [0008]    Yet another embodiment is an electronic package comprising a substrate which is coupled to a flip chip. At least one first electronic component and means for coupling the flip chip to the substrate is attached to a first surface of the flip chip. At least one structure is attached to a second surface of the flip chip. 
         [0009]    In another embodiment, a semiconductor device comprises a substrate having a first surface and a second surface, a passivation layer on the first surface of the substrate, and at least one structure attached to the second surface of the substrate. The structure is configured to be coupled to an electronic component. 
         [0010]    In yet another embodiment, a method of integrated circuit device packaging comprises providing a substrate, coupling a first surface of an integrated circuit die to the substrate, and attaching at least one electronic component to at least one structure on a second surface of the integrated circuit die. The first surface of the integrated circuit die is coupled to at least one electronic component. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]      FIGS. 1   a - 1   b  are flowcharts of a fabrication process in an exemplary embodiment of the invention. 
           [0012]      FIGS. 2   a  - 2   j  are diagrams showing stages of fabrication in an exemplary embodiment of the invention. 
           [0013]      FIG. 3  is a view of a chip fabricated in accordance with steps shown in  FIGS. 2   a - 2   j  attached to a substrate. 
           [0014]      FIG. 4  is an overhead plan of a multi-chip module incorporating chips fabricated in accordance with steps shown in  FIGS. 2   a - 2   j.    
           [0015]      FIG. 5  is a side view of a multi-chip module incorporating chips fabricated in accordance with steps shown in  FIGS. 2   a - 2   j.    
       
    
    
     DETAILED DESCRIPTION  
       [0016]    In  FIG. 1   a,  an exemplary process for fabricating a semiconductor device with circuitry on both surfaces of the device (such that one surface connects the device to an electronic package&#39;s substrate (such as a printed circuit board (“PCB”) and another surface may be used to attach discrete electronic components) is shown. A wafer is provided with fabricated circuitry on a first surface of the wafer (block  100 ). The wafer may be made of any suitable semiconductor material, such as silicon or gallium arsenide, used in the art. It should also be appreciated that any substrate (such as silicon on an insulator), or semiconductor substrate, including the wafer, may be used in various embodiments. The device substrate should not be confused with the same substrate often used to generally label PCBs. The fabricated devices on the first surface are produced through conventional semiconductor manufacturing methods. 
         [0017]    A removable layer, for mechanical protection for the first surface of the semiconductor substrate, such as photoresist or dry film, is deposited over a top passivation layer on the first surface of the wafer (block  102 ), where the fabricated circuitry is located. In  FIG. 2   a,  the wafer  14  has a first surface  80  and a second surface  82 , with a passivation layer  12  and a layer of protective material  10  on a first surface  80  of the wafer  14 , which also contains the fabricated devices (not shown here). The layer of protective material  10  is typically 1 to 10 microns thick and provides mechanical protection to the passivation layer  12 , which in turn protects the active device circuitry. The layer of protective material is formed using methods well-known to those of skill in the art. 
         [0018]    The second surface of the wafer is then metallized ( FIG. 1   a,  block  104 ). In  FIG. 2   b,  the wafer  14  is turned “upside down” and a metal layer  16  is formed over the second surface  82  of the wafer  14 . In one embodiment, the second surface  82  of the wafer  14  is blanket metallized by standard metal deposition processes, such as evaporation or chemical vapor deposition (“CVD”), sputtering, and plating. The resulting metal layer  16  is typically about 0.1 micron to 10 microns thick. The metal layer  16  provides RF shielding and wirebonding functions. The metal layer  16  may be a single layer, for example, aluminum (Al), or may be formed of multiple layers, using metals such as titanium tungsten-gold (TiW—Au), titanium-gold (Ti—Au), chromium-gold (Cr—Au), titanium tungsten-nickel-gold (TiW—Ni—Au), titanium-nickel-gold (Ti—Ni—Au), titanium-copper-nickel-gold (Ti—Cu—Ni—Au), titanium-tungsten-copper-nickel-silver (TiW—Cu—Ni—Ag), etc. Metal layer  16  choices may be selected based on the mechanism used to attach components to the semiconductor device fabricated on the wafer. For example, the use of gold, silver, and/or palladium is suitable for wire-bonding and the use of nickel and copper is suitable for soldering. Nickel is a good diffusion barrier. Titanium, titanium tungsten, and chromium provide adhesion of the metal film stack to the wafer. 
         [0019]    An insulating layer is formed over the metal layer ( FIG. 1   a,  block  106 ). In  FIG. 2   c,  an insulating film  18 , such as polyimide, benzocyclobutene (BCB), etc., is formed over the metal layer  16 . The insulating film  18  is typically about 2 to 15 microns thick. The insulating film  18  is formed using methods well-known to those of skill in the art. This insulating film  18  may be either photo-definable or standard non-photo-sensitive film. 
         [0020]    In the case of using a non-photo-sensitive insulating film, a photosensitive material, such as photoresist, is deposited over the insulating film layer ( FIG. 1   a,  block  108 ). In  FIG. 2   d,  a layer of photosensitive film (typically 1 to 10 microns), such as photoresist  20 , is deposited over the insulating film  18 . This layer  20  of photoresist is patterned and developed using methods well-known to those of skill in the art. 
         [0021]    A mask is placed over the photosensitive material, such as photoresist, and then exposed and etched away ( FIG. 1   a,  block  110 ). The insulating film layer that is now exposed is removed using wet etch or dry etch techniques. The remaining photosensitive material is also removed using methods well-known to those of skill in the art ( FIG. 1   a,  block  110 ). In  FIG. 2   e,  the second surface  82  of the wafer  14  has a patterned insulating film layer  18  remaining on the metal layer  16  after the removal of the layer of photoresist. The method just described uses a negative acting photoresist. A positive acting photoresist can also be used to achieve the same goal. 
         [0022]    The remaining insulating film and exposed metal layer is covered with a second metal layer ( FIG. 1   a,  block  112 ). In one embodiment, the surface is blanket metalized employing processes such as sputtering or plating. Other deposition processes known in the art may also be employed. In  FIG. 2   f,  the second metal layer  22  covers the insulating film  18  and the exposed metal layer  16 . The second metal layer is typically about 0.1 to 10 microns thick. The second metal layer  22  may be a single layer, for example, aluminum (Al), or may be formed of multiple layers, using metals such as titanium tungsten-gold (TiW—Au), titanium-gold (Ti—Au), chromium-gold (Cr—Au), titanium tungsten-nickel-gold (TiW—Ni—Au), titanium-nickel-gold (Ti—Ni—Au), titanium-copper-nickel-gold (Ti—Cu—Ni—Au), titanium-tungsten-copper-nickel-silver (TiW—Cu—Ni—Ag), etc. In other embodiments, the metal layer  22  may be formed of metal which are wirebondable or solderable (such as copper, silver, etc.) or serve as a diffusion barrier (e.g., nickel). 
         [0023]    A layer of photosensitive material, such as photoresist, is deposited over the second metal layer ( FIG. 1   b,  block  116 ). In  FIG. 2   g,  a photosensitive film layer  24  has been deposited on the second metal layer  22 . The photosensitive film layer  24  is typically about 1 to 10 microns thick. This layer  24  is patterned and developed using methods well-known to those of skill in the art. 
         [0024]    A mask is placed over the photosensitive material, such as photoresist, and then exposed and developed. The metal in the developed areas is then etched away ( FIG. 1   b,  block  118 ). The remaining photosensitive material is also removed using methods well-known to those of skill in the art ( FIG. 1 , block  118 ). In  FIG. 2   h,  the exposed areas of the second metal layer which were not protected by the mask are etched away, leaving only the patterned second metal layer. These remaining areas of the second metal layer  22  form interconnect circuitry, bond pads, discrete passive component attach pads, etc. 
         [0025]    In one embodiment shown in  FIG. 2   i,  the metal circuitry on the second surface  82  of the wafer  14  may be protected by an optional coating  26  of insulation, such as polyimide, BCB, etc. The coating  26  may be deposited and then patterned (for instance, by forming, patterning, developing, and etching photoresist in a manner known to those of skill in the art) to form the desired coating  26 . 
         [0026]    The layer of protective material  10  initially formed over the passivation layer  12  on the first surface  80  of the wafer  14  is removed using methods well-known to those of skill in the art. With reference to  FIG. 2   j,  the passivation layer  12  is now the top-most layer on the first surface  80  of the wafer  14 . 
         [0027]    The “build-up” fabrication discussed above in  FIGS. 1   a - 1   b  and  2   a - 2   j  may be carried out at a substrate level. Where the substrate is a wafer, the wafer may be subsequently singulated at package assembly, forming IC dies. The IC dies created from the fabrication process described in  FIGS. 1   a - 1   b  and  2   a - 2   j  (including other embodiments where the substrate is not a wafer) serve as the semiconductor device that will be implemented in the IC device package. The IC dies are used to form flip chips or wafer level chip size packages (CSP), although other types of chips may be used. 
         [0028]    With reference to  FIG. 3 , an exemplary flip-chip  36  with fabricated structures on the bare silicon side of the chip  36  is shown attached to an electronic package&#39;s substrate, here a PCB, such as a package 4-layer laminate substrate  34 . (The chip  36  may have components on the front, or passivation, side of the chip in other embodiments; however, these are not pictured in this embodiment.) The chip  36  is attached to the 4-layer laminate substrate  34  with solder balls  32 . The area of fabrication  50  on the silicon side of the chip  36  includes a metal layer  16  which provides RF shielding and/or circuit grounding. Components  30 ,  28  may be mounted on attach pads  70 ,  68  formed over the metal layer  16 . Component  30  is wirebonded  54  to metal bond pad  52  while component  28  is also wirebonded  56 ,  60  to metal bond pads  52 ,  22 . Metal bond pad  52  also serves as an interconnect. Component  28  is also wirebonded  66  to a bond pad  58  on the package substrate  34 . Leads  62 ,  64  connect the metal layer  16  to substrate connection pad  58 , or ground, and thus provide ground-signal-ground shielding. 
         [0029]    Various components can be attached to the attach pads. The active and passive components which may be attached include, but are not limited to, crystals, transceiver ICs, power management ICs, EEPROM ICs, switches, baluns, capacitors, etc. The components may be attached in a variety of ways, including soldering and attaching with a conductive epoxy. These components may be attached and interconnected at wafer level prior to wafer dicing, or attached after saw singulation, or may be attached and interconnected at package assembly, after the chip has been attached to the product substrate. 
         [0030]      FIG. 4  shows an exemplary plan view of a multi-chip module using IC chips  36 , in this case, flip-chips, with fabricated structures on the bare silicon side of the chip. In this exemplary embodiment, a number of different components have been attached to the chips  36  mounted on the four-layer substrate  34 . These components include a crystal  48 , a power management IC  46 , a balun  44 , a switch  42 , a transceiver IC  38 , and an EEPROM IC  40 . In other embodiments, any number of different components and arrangements may be employed and may be mounted on chips other than flip-chips; a wide range of package substrates, with different numbers of layers which may be made of various materials may also be employed. A side elevation of this package is shown in  FIG. 5  (with some passives omitted for clarity). In this exemplary embodiment, the height of the package  72 , including the substrate and the attached components does not exceed 1.5 mm. 
         [0031]    Using the approaches described above, the size of electronic packages may be reduced. This is particularly important given the trend towards miniaturization, especially for portable products such as cellular phones. 
         [0032]    While the preceding description has described specific embodiments, it will be evident to a skilled artisan that various changes and modifications can be made to these embodiments. For example, metal or conductive layers other than those described and shown may be used (e.g., platinum, tantalum, etc.). A skilled artisan will recognize that such conductive layers may be deposited or formed by methods and techniques other than those described herein (e.g., copper may be formed by a dual damascene technique known to those of skill in the art). The specification and drawings, therefore, are to be regarded in an illustrative rather than a restrictive sense.