Abstract:
A dual bond pad structure for a wafer with laser die attachment and methods of manufacture are disclosed. The method includes forming a bonding layer on a surface of a substrate. The method further includes forming solder bumps on the bonding layer. The method further includes patterning the bonding layer to form bonding pads some of which comprise the solder bumps thereon. The method further includes attaching a laser diode to selected bonding pads using solder connections formed on the laser diode. The method further includes attaching an interposer substrate to the solder bumps formed on the bonding pads.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to semiconductor structures and, more particularly, to a dual bond pad structure for a wafer with laser die attach and methods of manufacture. 
       BACKGROUND 
       [0002]    Silicon photonics chips are developed for high speed interconnects between dies. Waveguides can be built on silicon on insulator (SOI) wafers and can be integrated with CMOS devices; however, this requires a connection be made between a laser and the waveguide, which is a difficult from both a structural standpoint and a fabrication processing standpoint. For example, the laser die is attached to the wafer using a solder bump, but solder bump height for the laser must be smaller than that of other solder bumps connecting to an interposer. Thus, different solder bump processes must be used for attachment of the laser to the wafer, increasing fabrication time and costs. 
       SUMMARY 
       [0003]    In an aspect of the invention, a method comprises forming a bonding layer on a surface of a substrate. The method further comprises forming solder bumps on the bonding layer. The method further comprises patterning the bonding layer to form bonding pads some of which comprise the solder bumps thereon. The method further comprises attaching a laser diode to selected bonding pads using solder connections formed on the laser diode. The method further comprises attaching an interposer substrate to the solder bumps formed on the bonding pads. 
         [0004]    In an aspect of the invention, a method comprises: forming a bonding layer on a substrate; patterning the bonding layer with two different masks to form bonding pads for connecting an interposer substrate and a laser diode; forming solder bumps on a set of the bonding pads, using one of the masks patterned to have openings corresponding to the set of the bonding pads; attaching the laser diode to another set of the bonding pads by a reflow process of solder connections attached to the laser diode; and reflowing the solder bumps to connect the interposer substrate to the set of the bonding pads after the attaching of the laser diode. 
         [0005]    In an aspect of the invention, a structure comprises: a first set of bond pads and a second set of bond pads; solder bumps electrically connected to the first set of bond pads, the solder bumps having a first height; an interposer substrate electrically connected to the solder bumps; and solder connections electrically connected to a laser diode and the second set of bond pads, the solder connections having a second height smaller than the first height and the laser diode being positioned below the interposer substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0006]    The present invention is described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention. 
           [0007]      FIGS. 1-6  show fabrication processes and respective structures in accordance with aspects of the present invention; 
           [0008]      FIGS. 7-10  show fabrication processes and respective structures in accordance with additional aspects of the present invention; and 
           [0009]      FIGS. 11-13  show fabrication processes and respective structures in accordance with additional aspects of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    The invention relates to semiconductor structures and, more particularly, to a dual bond pad structure for a wafer with laser die attach and methods of manufacture. More specifically, the present invention provides fabrication processes and resultant structures for bonding both a laser die and an interposer substrate with solder bump processes. Advantageously, the processes of the present invention can minimize the number of masks needed in order to form the bonds pads for both a laser die (diode) and an interposer substrate. 
         [0011]    The dual bond pad structure of the present invention can be manufactured in a number of ways using a number of different tools. In general, though, the methodologies and tools are used to form structures with dimensions in the micrometer and nanometer scale. The methodologies, i.e., technologies, employed to manufacture the bond pad structure of the present invention have been adopted from integrated circuit (IC) technology. For example, the structures of the present invention are built on wafers and are realized in films of material patterned by photolithographic processes on the top of a wafer. In particular, the fabrication of the dual bond pad structure of the present invention uses three basic building blocks: (i) deposition of thin films of material on a substrate, (ii) applying a patterned mask on top of the films by photolithographic imaging, and (iii) etching the films selectively to the mask. 
         [0012]      FIG. 1  shows a structure and respective fabrication processes in accordance with aspects of the present invention. In embodiments, the structure  10  includes a silicon on insulator wafer, comprising an oxide or other insulator layer  14  bonded or otherwise attached to a wafer  12  (e.g., silicon substrate). In embodiments, the insulator layer  14  can be a buried oxide layer. 
         [0013]    The structure  10  further includes front end of the line (FEOL) structures and back end of the line (BEOL) structures, generally represented at reference numeral  16 . In embodiments, the FEOL structures comprise any combination of active and passive devices such as, for example, field effect transistors (FETs) and waveguide structures (with diffusers); although other devices are also contemplated by the present invention. The BEOL structures can comprise any combination of wiring and interconnect structures, for example. The FEOL and BEOL structures can be formed using conventional CMOS technologies comprising lithography, etching and deposition of materials as should be understood by those of skill in the art. 
         [0014]    Still referring to  FIG. 1 , a bond pad layer  18  is deposited on a surface of an uppermost BEOL layer. For example, the bond pad layer  18  can be deposited on an oxide film (or other interlevel dielectric material), in electrical connection with wiring layers of the BEOL structures. The bond pad layer  18  can comprise plural layers deposited using sputtering techniques, as well as other deposition processes such as physical vapor deposition (PVD), etc. In embodiments, the bond pad layer  18  can comprise, as an example, TiW/Cu/Ni; although other bonding materials are also contemplated by the present invention. 
         [0015]    In  FIG. 2 , a resist  20  is formed over the bond pad layer  18 . The resist is then patterned by exposure to energy (light) to form openings  20   a . A metal plate (portion of subsequently formed bond pad)  22  is then formed within the openings  20   a . The metal plate  22  will act as a bond pad for a laser die (diode). In embodiments, the metal plate  22  can be a gold pad, formed by an electroplating process. In embodiments, the metal plate  22  can be other materials such as, for example, Nickel, Copper, Platinum, etc. The resist  20  can then be removed using conventional processes, e.g., oxygen ashing techniques. 
         [0016]    In  FIG. 3 , a resist  20 ′ is formed on the bond pad layer  18  and the metal plate  22 . The resist is then patterned by exposure to energy (light) to form openings  20   b . A solder bump  24  is formed within the openings  20   b , on the bond pad layer  18 . The solder bump  24  can be a controlled collapse chip connection (C4) for interconnecting an interposer substrate to the underlying wafer and its circuitry. In embodiments, the solder bump  24  can be a tin-based alloy or a copper pillar, deposited using electroplating processes. The resist  20 ′ can then be removed using conventional processes, e.g., oxygen ashing techniques. 
         [0017]    As shown in  FIG. 4 , the bond pad layer  18  can be patterned, to form discrete bond pads  18 ′ and  18 ″. The bond pads  18 ′ and  18 ″ can be electrically isolated from one another. The patterning can be performed using conventional wet etching processes, with selective chemistries to the materials of the bond pad layer  18 . 
         [0018]      FIG. 5  shows the connection of a laser die (diode)  26  to the bond pads  18 ″, formed in the processes described above. In embodiments, the laser diode  26  includes a solder bump  26 ′ formed on the laser diode devices, which is electrically connected (attached) to the bond pads  18 ″ during a reflow process as should be understood by those of skill on the art. The reflow process can also reflow the solder bump  24 ′. In embodiments, the laser diode  26  can be aligned with the bond pads  18 ″ using known pick and place processes. As in each of the embodiments, the solder bump  26 ′ will be of a different height than the solder bump  24 ′, preferably of a smaller height, and the bond pads will be discrete bond pads electrically isolated from one another on the surface of the substrate. 
         [0019]    In  FIG. 6 , thereafter, the interposer substrate  28  is connected to the solder bump  24 ′ through a reflow process as is known to those of skill in the art. In this way, it is now possible to connect both the interposer substrate  28  and the laser diode  26  to the wafer using a dual bond pad fabrication process, with different height solder bumps for the interposer substrate  28  and the laser diode  26 . As shown in this embodiment and which may be applicable for each of the subsequently described embodiments, the interposer substrate  28  is positioned above the laser diode  26 . 
         [0020]      FIGS. 7-10  show fabrication processes and respective structures in accordance with additional aspects of the present invention. More specifically,  FIG. 7  shows a structure  10 ′ similar to that of  FIG. 1 , which includes a silicon on insulator wafer, comprising an oxide or other insulator layer  14  bonded or otherwise attached to the wafer  12 . The structure  10  further includes front end of the line (FEOL) structures and back end of the line (BEOL) structures, generally represented at reference numeral  16 . A bond pad layer  18  is deposited on a surface of an uppermost BEOL layer, as described with respect to  FIG. 1  such that no further explanation is required. 
         [0021]    Still referring to  FIG. 7 , a masking layer  30  is patterned on the bond pad layer  18 . For example, a silicon nitride or SiO 2  can be deposited on the bond pad layer  18  using conventional deposition processes, e.g., CVD, PECVD, etc. A resist is formed over the masking layer  30 , which is then patterned by exposure to energy (light) to form openings. An etching process is then performed through the openings to remove exposed masking layer material, resulting in the pattern of the masking layer  30  shown in  FIG. 7 . The resist can then be removed using conventional processes, e.g., oxygen ashing techniques. 
         [0022]    In  FIG. 8 , a resist  20  is formed over the bond pad layer  18  and the masking layer  30 . The resist is then patterned by exposure to energy (light) to form openings  20   b . A solder bump  24  is then formed within the openings  20   b , on the bond pad layer  18 . The solder bump  24  can be a controlled collapse chip connection (C 4 ) for interconnecting an interposer substrate to the underlying wafer and its circuitry. In embodiments, the solder bump  24  can be a tin-based alloy or a copper pillar, deposited using electroplating processes. The resist  20  can then be removed using conventional processes, e.g., oxygen ashing techniques. 
         [0023]    As shown in  FIG. 9 , the bond pad layer  18  can be patterned to form discrete bond pads  18 ′,  18 ″. In this embodiment, the bond pads  18 ′ and  18 ″ comprise the bond pad layer  18 , only. The patterning can be performed using conventional reactive ion etching processes, with selective chemistries to the materials of the bond pad layer  18 . In embodiments, the masking layer  30  and the solder bump  24  will protect the bond pads  18 ′,  18 ″ during this selective etching process. The masking layer  30  can then be removed using conventional etching processes, known to those of skill in the art. 
         [0024]      FIG. 10  shows the connection of the laser diode  26  and interposer substrate  28 , similar to that already described with respect to  FIGS. 5 and 6 . Specifically, the laser diode  26  is attached to the bond pads  18 ″ during a reflow process of the solder bump  26 ′. The reflow process can also reflow the solder bump  24 ′. In embodiments, the laser diode  26  can be aligned with the bond pads  18 ″ using known pick and place processes. Thereafter, the interposer substrate  28  is connected to the solder bump  24 ′ through a reflow process as is known to those of skill in the art. In this way, it is now possible to connect both an interposer substrate  28  and a laser diode  26  to the wafer using a dual bond pad fabrication process, with different height solder bumps for both the interposer substrate  28  and the laser diode  26 . 
         [0025]      FIGS. 11-13  show fabrication processes and respective structures in accordance with additional aspects of the present invention. More specifically,  FIG. 11  shows a structure  10 ″ similar to that of  FIG. 1 , which includes a silicon on insulator wafer, comprising an oxide or other insulator layer  14  bonded or otherwise attached to the wafer  12 . The structure  10  further includes front end of the line (FEOL) structures and back end of the line (BEOL) structures, generally represented at reference numeral  16 . A bond pad layer  18  is deposited on a surface of an uppermost BEOL layer, as described with respect to  FIG. 1  such that no further explanation is required. 
         [0026]    Still referring to  FIG. 11 , a resist  20  is formed over the bond pad layer  18 . The resist is then patterned by exposure to energy (light) to form openings  20   a ′. A metal plate  32  is then formed in within the openings  20   a ′. The metal plate  32  will act as a bond pad for both the laser diode and the interposer substrate, as described herein. In embodiments, the metal plate  32  can be plural layers or a single layer of metal. For example, the metal plate can be a nickel and gold pad, formed by an electroplating process. In embodiments, the metal plate  32  can be other materials such as, for example, Nickel, Copper, Platinum, etc., or any combinations thereof. The resist  20  can then be removed using conventional processes, e.g., oxygen ashing techniques. 
         [0027]    In  FIG. 12 , a resist  20 ′ is formed on the bond pad layer  18  and the metal plate  32 . The resist is then patterned by exposure to energy (light) to form openings  20   b  exposing the metal plate on an interpose connection side of the structure. A solder bump  24  is then formed within the openings  20   b , on the metal plate  32 . The solder bump  24  can be a controlled collapse chip connection (C4) for interconnecting an interposer to the underlying wafer and its circuitry. In embodiments, the solder bump  24  can be a tin-based alloy or a copper pillar, deposited using electroplating processes. The resist  20 ′ can then be removed using conventional processes, e.g., oxygen ashing techniques. 
         [0028]    As shown in  FIG. 13 , the bond pad layer  18  can be patterned, to form discrete bond pads  18 ′ comprising the bond pad layer  18  and the metal plate  32 . The patterning can be performed using conventional reactive ion etching processes, with selective chemistries to the materials of the bond pad layer  18 . The laser diode  26  and interposer substrate  28  can be connected to the bond pads  18 ″′, similar to that already described with respect to  FIGS. 5 and 6 . Specifically, the laser diode  26  is attached to the bond pads  18 ″′ during a reflow process of the solder bump  26 ′. The reflow process can also reflow the solder bump  24 ′. In embodiments, the laser diode  26  can be aligned with the bond pads  18 ′ using known pick and place processes. Thereafter, the interposer substrate  28  is connected to the solder bump  24 ′ through a reflow process as is known to those of skill in the art. In this way, it is now possible to connect both an interposer substrate  28  and a laser diode  26  to the wafer using a dual bond pad fabrication process, with different height solder bumps for both the interposer substrate  28  and the laser diode  26 . 
         [0029]    The method(s) as described above is used in the fabrication of integrated circuit chips. The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor. 
         [0030]    The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.