Patent Publication Number: US-10312216-B2

Title: Systems and methods for bonding semiconductor elements

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/449,466, filed Mar. 3, 2017, now U.S. Pat. No. 9,905,530, which is a continuation of U.S. patent application Ser. No. 15/147,015, filed May 5, 2016, now U.S. Pat. No. 9,633,981, which is a divisional of U.S. patent application Ser. No. 14/822,164, filed Aug. 10, 2015, now U.S. Pat. No. 9,362,257, which is a continuation of U.S. patent application Ser. No. 14/505,609, filed Oct. 3, 2014, now U.S. Pat. No. 9,136,240, which claims the benefit of U.S. Provisional Application No. 61/888,203, filed Oct. 8, 2013, the content of each of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the formation of semiconductor packages, and more particularly, to improved systems and methods for bonding semiconductor elements together. 
     BACKGROUND OF THE INVENTION 
     Traditional semiconductor packaging typically involves die attach processes and wire bonding processes. Advanced semiconductor packaging technologies (e.g., flip chip bonding, thermo-compression bonding, etc.) technologies are gaining more traction in this industry. For example, in thermo-compression bonding, heat and pressure are used to form a plurality of interconnections between semiconductor elements. 
     While advanced packaging technologies are increasingly utilized there are many limitations in these technologies including, for example, limitations related to the relative infancy of some advanced packaging technologies. Thus, it would be desirable to provide improved systems for, and methods of, bonding semiconductor elements together. 
     SUMMARY OF THE INVENTION 
     According to an exemplary embodiment of the present invention, a method of ultrasonically bonding semiconductor elements is provided. The method includes the steps of: (a) aligning surfaces of a plurality of first conductive structures of a first semiconductor element to respective surfaces of a plurality of second conductive structures of a second semiconductor element, wherein the surfaces of each of the plurality of first conductive structures and the plurality of second conductive structures include aluminum; and (b) ultrasonically bonding ones of the first conductive structures to respective ones of the second conductive structures. 
     According to another exemplary embodiment of the present invention, a semiconductor device is provided. The semiconductor device includes: (a) a first semiconductor element including a plurality of first conductive structures, at least a contact portion of each of the plurality of first conductive structures including aluminum; and (b) a second semiconductor element including a plurality of second conductive structures, at least a contact portion of each of the plurality of second conductive structures including aluminum. The contact portions of ones of the plurality of first conductive structures are in contact with, and are ultrasonically bonded to, respective ones of the contact portions of the plurality of second conductive structures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is best understood from the following detailed description when read in connection with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures: 
         FIGS. 1A-1C  are block diagram views of portions of an ultrasonic bonding machine illustrating a structure and method of bonding an upper semiconductor element to a lower semiconductor element in accordance with an exemplary embodiment of the present invention; 
         FIG. 2A  is a block diagram view of portions of an ultrasonic bonding machine illustrating a structure and method of bonding an upper semiconductor element to a lower semiconductor element in accordance with another exemplary embodiment of the present invention; 
         FIG. 2B  is an enlarged view of portion “ FIG. 2B ” of  FIG. 2A ; 
         FIG. 2C  is a view of  FIG. 2B  after ultrasonic bonding; 
         FIG. 3  is a block diagram view of portions of an ultrasonic bonding machine illustrating a structure and method of bonding an upper semiconductor element to a lower semiconductor element in accordance with yet another exemplary embodiment of the present invention; 
         FIG. 4A  is a block diagram view of portions of an ultrasonic bonding machine illustrating a structure and method of bonding an upper semiconductor element to a lower semiconductor element in accordance with another exemplary embodiment of the present invention; 
         FIG. 4B  is an enlarged view of portion “ FIG. 4B ” of  FIG. 4A ; 
         FIG. 4C  is a view of  FIG. 4B  after ultrasonic bonding; 
         FIG. 5A  is a block diagram view of portions of an ultrasonic bonding machine illustrating a structure and method of bonding an upper semiconductor element to a lower semiconductor element in accordance with another exemplary embodiment of the present invention; 
         FIG. 5B  is an enlarged view of portion “ FIG. 5B ” of  FIG. 5A ; 
         FIG. 5C  is a view of  FIG. 5B  after ultrasonic bonding; 
         FIG. 6A  is a block diagram view of portions of an ultrasonic bonding machine illustrating a structure and method of bonding an upper semiconductor element to a lower semiconductor element in accordance with yet another exemplary embodiment of the present invention; 
         FIG. 6B  is an enlarged view of portion of “ FIG. 6B ” of  FIG. 6A ; 
         FIG. 6C  is a view of a portion of  FIG. 6A  after contact between conductive structures; and 
         FIG. 7  is a flow diagram illustrating a method of ultrasonically bonding semiconductor elements in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As used herein, the term “semiconductor element” is intended to refer to any structure including (or configured to include at a later step) a semiconductor chip or die. Exemplary semiconductor elements include a bare semiconductor die, a semiconductor die on a substrate (e.g., a leadframe, a PCB, a carrier, etc.), a packaged semiconductor device, a flip chip semiconductor device, a die embedded in a substrate, a stack of semiconductor die, amongst others. Further, the semiconductor element may include an element configured to be bonded or otherwise included in a semiconductor package (e.g., a spacer to be bonded in a stacked die configuration, a substrate, etc.). 
     In accordance with certain exemplary embodiments of the present invention, inventive techniques (and structures) are provided for assembling a semiconductor device such as a package on package (i.e., PoP) structure. For example, a plurality of semiconductor elements (which may be packages) may be arranged in a stacked configuration. Each of the elements desirably includes aluminum (or aluminum alloy, or partially aluminum) conductive structures that are ultrasonically bonded together. Such a technique has certain advantages including, for example: a reduced density compared to other interconnection techniques (e.g., solder based PoP techniques); no solder mass reflow utilized in contrast to other interconnection techniques; and room temperature ultrasonic bonding enabled in certain applications through the use of an aluminum to aluminum interconnect. 
       FIG. 1A  illustrates portions of ultrasonic bonding machine  100 , including bonding tool  124  and support structure  150 . As will be appreciated by those skilled in the art, a thermo-compression bonding machine (such as machine  100 , or any of the other machine embodiments described herein) may include many elements not shown in the drawings herein for simplicity. Exemplary elements includes, for example: input elements for providing input workpieces to be bonded with additional semiconductor elements; output elements for receiving processed workpieces that now include additional semiconductor elements; transport systems for moving workpieces; imaging systems for imaging and alignment of workpieces; a bond head assembly carrying the bonding tool; a motion system for moving the bond head assembly; a computer system including software for operating the machine; amongst other elements. 
     Referring again to  FIG. 1A , upper semiconductor element  108  is retained (e.g., by vacuum, such as through vacuum ports defined by the holding surface of holding portion  110 ) by holding portion  110  of bonding tool  124 . Upper semiconductor element  108  includes upper conductive structures  112   a ,  112   b  on a lower surface thereof. Lower semiconductor element  160  includes semiconductor die  102  bonded to (or otherwise supported by) substrate  104 . Lower conductive structures  106   a ,  106   b  are provided on an upper surface of lower semiconductor die  102 . Substrate  104  in turn is supported by support structure  150  (e.g., a heat block of machine  100 , an anvil of machine  100 , or any other desired support structure). In the configuration shown in  FIG. 1A  (preparing for bonding), each of upper conductive structures  112   a ,  112   b  are generally aligned with opposing respective lower conductive structures  106   a ,  106   b . Semiconductor element  108  is moved downward through the motion of bonding tool  124  (as shown by the arrows  126  in  FIG. 1A ). Following this motion,  FIG. 113  illustrates contact between the respective conductive structures  106   a ,  112   a  and  106   b ,  112   b . Ultrasonic energy  114  is applied to upper semiconductor element  108  and upper conductive structures  112   a ,  112   b  through bonding tool  124  using an ultrasonic transducer (not shown but indicated in the drawings as “USG”, that is, ultrasonic generator). For example, an ultrasonic transducer that carries bonding tool  124  may in turn be carried by a bond head assembly of machine  100 . 
     During the ultrasonic bonding, lower conductive structures  106   a ,  106   b  may be held relatively stationary through the support of lower semiconductor element  160  by support structure  150  (e.g., a support surface of support structure  150  may include one or more vacuum ports to secure substrate  104  to support structure  150  during bonding). Ultrasonic energy  114  (along with optional bond force and/or heat) may cause partial deformation of the conductive structures. For example, conductive structures  106   a ,  106   b  and  112   a ,  112   b  are illustrated as being partially deformed in  FIG. 1C . Ultrasonic bonds are formed between respective pairs of conductive structures in  FIG. 1C . For example, ultrasonic bond  128   a  is formed between deformed conductive structures  112   a ′/ 106   a ′, and ultrasonic bond  128   b  is formed between deformed conductive structures  112   b ′/ 106   b ′. Conductive structures  106   a ,  106   b ;  112   a ,  112   b  may be formed of aluminum, or aluminum alloys, or may contain aluminum at their bond surfaces, etc. 
     The respective pairs of conductive elements  106   a ,  112   a ;  106   b ,  112   b  may be bonded together at room temperature (without heat being added during the bonding process). Optionally, additional heat may be applied, for example, to: (1) upper semiconductor element  108  through bonding tool  124 , thus heating upper conductive elements  112   a ,  112   b  during the bonding process; and/or (2) lower semiconductor element  160  through support structure  150  (e.g., heat block  150 ), thus heating lower conductive structures  106   a ,  106   b  during the bonding process. Such optional heating (e.g., through the bond tool and/or the support structure, etc.) is applicable to any of the embodiments of the present invention illustrated and described herein. 
     Semiconductor elements  160  and  108  illustrated in  FIGS. 1A-1C  may be any of a number of semiconductor elements configured to be bonded together. In one very specific example (which may also be applied to the other embodiments illustrated and described herein) semiconductor element  160  is a processor (e.g., a mobile phone processor which may also be known as an APU (application processor unit)) and semiconductor element  108  is a memory device configured to be bonded to the processor as shown in  FIGS. 1A-1C . 
     The conductive structures (i.e.,  112   a ,  112   b ,  106   a ,  106   b ) shown in  FIGS. 1A-1C  are illustrated as generic structures. These structures may take many different forms such as conductive pillars, stud bumps (e.g., formed using a stud bumping machine), electroplated conductive structures, sputtered conductive structures, wire portions, bond pads, contact pads, among many others. Various of the other drawings provided herein illustrate specific examples of such structures. In accordance with certain embodiments of the present invention the conductive structures include aluminum at the contact region (i.e., the bonding surface) where they will be bonded to another conductive structure. In such embodiments, the conductive structures may be formed of aluminum, or an aluminum alloy (e.g., aluminum alloyed with copper, aluminum alloyed with silicon and copper, etc.). In other examples, the conductive structures may include a base conductive material other than aluminum (e.g., copper) with aluminum (or aluminum alloy) at the contact region. Throughout the present application, if a conductive structure is referred to as being “aluminum” it is understood that the structure may be aluminum, may be an aluminum alloy, or may include aluminum (or an aluminum alloy) at a contact region of such conductive structure. 
       FIG. 2A  illustrates portions of ultrasonic bonding machine  200 , including bonding tool  224  and support structure  250 . Upper semiconductor element  208  is retained (e.g., by vacuum) by holding portion  210  of bonding tool  224 , and includes upper conductive structures  222   a ,  222   b  (i.e., conductive aluminum pads  222   a ,  222   b ) provided at a lower surface thereof. Lower semiconductor element  260  includes semiconductor die  202  bonded to (or otherwise supported by) substrate  204 . Lower conductive structures  206   a ,  206   b  are provided on an upper surface of lower semiconductor die  202 . Substrate  204  in turn is supported by support structure  250 . In the configuration shown in  FIG. 2A , each of upper conductive structures  222   a ,  222   b  are generally aligned with (and configured to be ultrasonically bonded to) opposing respective lower conductive structures  206   a ,  206   b . Lower conductive structure  206   a  includes copper (Cu) pillar  230  provided on an upper surface of lower semiconductor die  202 , and an upper aluminum contact structure  216  on an upper surface of Cu pillar  230 . Upper aluminum contact structure  216  may be, for example, electroplated or sputtered onto the upper surface of lower copper pillar  230 .  FIG. 2B  is an enlarged view of portion “B” of  FIG. 2A  and illustrates the top of lower conductive structure  206   a  at contact with upper conductive element  222   a.    
     Ultrasonic energy is applied to upper semiconductor element  208  through bonding tool  224  using an ultrasonic transducer (not shown). Ultrasonic energy may cause partial deformation of the conductive structures as illustrated in  FIG. 2C . That is, ultrasonic bond  228  is formed between deformed upper conductive structure  222   a ′ and deformed contact structure  216 ′ (as illustrated in  FIG. 2C ). 
     As will be appreciated by those skilled in the art, Cu pillar  230  (including electroplated or sputtered aluminum contact structure/portion  216 ) is just one example of a conductive structure including aluminum.  FIG. 2A  also illustrates another exemplary conductive structure  206   b . Lower conductive structure  206   b  is an aluminum structure (or aluminum alloy structure) such as a portion of aluminum wire (that may be bonded using a wire bonding process), an aluminum pillar, etc. 
       FIG. 3  illustrates portions of ultrasonic bonding machine  300 , including bonding tool  324  and support structure  350 . Upper semiconductor element  308  is retained (e.g., by vacuum) by holding portion  310  of bonding tool  324 , and includes upper conductive structures  322   a ,  322   b  (i.e, conductive aluminum pads  322   a ,  322   b ).  FIG. 3  illustrates the bonding of a packaged semiconductor device  360  (i.e., lower semiconductor element  360 ) to upper semiconductor element  308 . Lower semiconductor element  360  includes semiconductor die  302  bonded to (or otherwise supported by) substrate  304 . Lower conductive structures  306   a ,  306   b  are provided on an upper surface of substrate  304 . Substrate  304  in turn is supported by support structure  350 . Wire loops  320   a ,  320   b  are bonded between semiconductor die  302  and substrate  304  (while not shown in  FIG. 3 , die  302  may be flip chip bonded to substrate  304  as opposed to, or in addition to, the wire loop interconnections). A coating/encapsulation  334  (such as a epoxy molding compound) has been applied over die  302  and wire loops  320   a ,  320   b . As illustrated, the upper portions of lower conductive structures  306   a ,  306   b  are exposed above coating/encapsulation  334  to permit electrical connection to upper semiconductor element  308 . 
     In the configuration shown in  FIG. 3 , each of upper conductive structures  322   a ,  322   b  are generally aligned with (and configured to be ultrasonically bonded to) opposing respective lower conductive structures  306   a ,  306   b . As illustrated in  FIG. 3 , each of lower conductive structures  306   a ,  306   b  includes a respective Cu pillar  330   a ,  330   b  on an upper surface of substrate  304 , and a respective upper aluminum contact structure  316   a ,  316   b  on an upper surface of Cu pillars  330   a ,  330   b . Upper aluminum contact structures  316   a ,  316   b  may be electroplated or sputtered onto the respective upper surfaces of Cu pillars  330   a ,  330   b . As shown, semiconductor element  308  has been moved downward through the motion of bonding tool  324  (as shown by the arrows in  FIG. 3 ) so that  FIG. 3  illustrates contact between conductive structures  306   a ,  322   a  and  306   b ,  322   b . Ultrasonic energy (with optional heat and/or bond force) is applied to upper semiconductor element  308  (e.g., through bonding tool  324 ) using an ultrasonic transducer to form ultrasonic bonds between aluminum conductive structures  322   a ,  322   b  and respective aluminum contact structures  316   a ,  316   b.    
       FIG. 4A  illustrates portions of ultrasonic bonding machine  400 , including bonding tool  424  and support structure  450 . Upper semiconductor element  408  is retained (e.g., by vacuum) by holding portion  410  of bonding tool  424 , and includes upper conductive structures  412   a ,  412   b  (i.e., e.g., sputtered aluminum bumps, aluminum stud bumps, etc.) on a lower surface thereof. Lower semiconductor element  460  includes semiconductor die  402  bonded to (or otherwise supported by) support structure  404  (e.g., an FR4 support structure). Lower conductive structures  406   a ,  406   b  (i.e., e.g., sputtered aluminum bumps, aluminum stud bumps, etc.) are provided on an upper surface of lower semiconductor die  402 . Substrate  404  in turn is supported by support structure  450 . In the configuration shown in  FIG. 4A , each of upper conductive structures  412   a ,  412   b  are generally aligned with (and configured to be ultrasonically bonded to) opposing respective lower conductive structures  406   a ,  406   b . A detail of structures  412   a ,  406   a  (before ultrasonic bonding) is shown in  FIG. 4B . Referring again to  FIG. 4A , semiconductor element  408  has been moved downward through the motion of bonding tool  424  (as shown by the arrows in  FIG. 4A ) so that contact is shown between conductive structures  406   a ,  412   a  and  406   b ,  412   b . Ultrasonic energy  414  (with optional heat and/or bond force) is applied to upper semiconductor element  408  (e.g., through bonding tool  424 ) using an ultrasonic transducer to form ultrasonic bonds  428   a ,  428   b  between deformed upper aluminum conductive structures and respective deformed lower aluminum contact structures (see, e.g., completed ultrasonic bond  428   a ′ formed between deformed structure  412   a ′ and deformed structure  406   a ′ as illustrated in  FIG. 4C ). 
       FIG. 5A  illustrates portions of ultrasonic bonding machine  500 , including bonding tool  524  and support structure  550 . Upper semiconductor element  508  retained (e.g., by vacuum) by holding portion  510  of bonding tool  524 , and includes upper conductive structures  522   a ,  522   b  (i.e, conductive aluminum pads  522   a ,  522   b ). Lower semiconductor element  560  includes semiconductor die  502  bonded to (or otherwise supported by) substrate  504  (e.g., an FR4 support structure). Lower conductive structures  506   a ,  506   b  (i.e., e.g., sputtered aluminum bumps, aluminum stud bumps, etc.) are provided on an upper surface of lower semiconductor die  502 . Substrate  504  in turn is supported by support structure  550 . In the configuration shown in  FIG. 5A , each of upper conductive structures  522   a ,  522   b  are generally aligned with (and configured to be ultrasonically bonded to) opposing respective lower conductive structures  506   a ,  506   b . A detail of structures  522   a ,  506   a  (before ultrasonic bonding) is shown in  FIG. 5B . As shown, semiconductor element  508  has been moved downward through the motion of bonding tool  524  (as shown by the arrows in  FIG. 5A ) so that  FIG. 5A  illustrates contact between conductive structures  506   a ,  522   a . Ultrasonic energy (with optional heat and/or bond force) is applied to upper semiconductor element  508  (e.g., through bonding tool  424 ) using an ultrasonic transducer to form ultrasonic bonds  528   a ,  528   b  between deformed upper aluminum conductive structures and respective deformed lower aluminum contact structures (see, e.g., completed ultrasonic bond  528   a ′ formed between deformed structure  522   a ′ and deformed structure  506   a ′ as illustrated in  FIG. 5C ). 
       FIG. 6A  illustrates the ultrasonic bonding machine  600 , including bonding tool  624  and support structure  650 . In  FIG. 6 , a plurality of semiconductor elements have been bonded together in a stacked configuration, in accordance with the teachings of the present invention. Specifically, semiconductor element  660   a  includes semiconductor die  602   a  bonded to (or otherwise supported by) substrate  604   a , where conductive structures  606   a ,  606   b  (i.e., e.g., sputtered aluminum bumps, aluminum stud bumps, etc.) are provided on an upper surface of semiconductor die  602   a . Semiconductor element  660   a  is supported by support structure  650 . 
     Another semiconductor element  660   b  (including a corresponding semiconductor die  602   b  bonded to, or otherwise supported by, substrate  604   b —and including conductive structures  612   a ,  612   b  on substrate  604   b ) has been previously been bonded to semiconductor element  660   a . More specifically, bonding tool  624  previously bonded (e.g., ultrasonically bonded) element  660   b  to element  660   a  such that ultrasonic bonds  628   a ,  628   b  were formed between respective pairs of aluminum conductive structures  612   a ,  606   a  and  612   b ,  606   b . Element  660   b  also includes conductive structures  606   a ′,  606   b ′ which have been bonded to conductive structures of element  660   c  in a step described below.  FIG. 6B  illustrates a detailed view of ultrasonic bond  628   a  including deformed conductive structures  612   a ,  606   a.    
     Likewise, another semiconductor element  660   c  (including a corresponding semiconductor die  602   c  bonded to, or otherwise supported by, substrate  604   c —and including conductive structures  612   a ′,  612   b ′ on substrate  604   c ) has been previously been bonded to semiconductor element  660   b . More specifically, bonding tool  624  previously bonded (e.g., ultrasonically bonded) element  660   c  to element  660   b  such that ultrasonic bonds  628   a ′,  628   b ′ were formed between respective pairs of aluminum conductive structures  612   a ′,  606   a ′ and  612   b ′,  606   b ′. Element  660   c  also includes conductive structures  606   a ″,  606   b ″ which will be bonded to conductive structures of element  660   d  in a step described below. 
     As shown in  FIG. 6A , upper semiconductor element  660   d  is retained (e.g., by vacuum) by holding portion  610  of bonding tool  624 , and includes semiconductor die  602   d  bonded to (or otherwise supported by) substrate  604   d . Conductive structures  612   a ″,  612   b ″ (i.e., e.g., sputtered aluminum bumps, aluminum stud bumps, etc.) are provided on a lower surface of substrate  604   d . Conductive structures  612   a ″,  612   b ″ are generally aligned with (and configured to be ultrasonically bonded to) opposing respective conductive structures  606   a ″,  606   b ″. Semiconductor element  660   d  is moved downward through the motion of bonding tool  624  (as shown by the arrows in  FIG. 6A ). Following this downward motion, contact will occur between respective pairs of conductive structures  612   a ″,  606   a ″ and  612   b ″,  606   b ″ (see, e.g., the  FIG. 6C  detailed view of contact between structures  612   a ″,  606   a ″ prior to deformation through ultrasonic bonding). Ultrasonic energy is applied to upper semiconductor element  604   d  through bonding tool  624  using an ultrasonic transducer (not shown) to form the ultrasonic bonds between respective pairs of conductive structures  612   a ″,  606   a ″ and  612   b ″,  606   b″.    
     While specific exemplary upper and lower aluminum conductive structures have been illustrated, one skilled in the art would understand that a variety of shapes and designs of upper and lower aluminum conductive structures are permissible within the teachings of the present invention. 
       FIG. 7  is a flow diagram illustrating a method of bonding semiconductor elements together in accordance with an exemplary embodiment of the invention. As is understood by those skilled in the art, certain steps included in the flow diagram may be omitted; certain additional steps may be added; and the order of the steps may be altered from the order illustrated. At Step  700 , a first semiconductor element (e.g., including a semiconductor die on a substrate) is supported on a support structure of a bonding machine. The first semiconductor element (e.g., an upper surface of the semiconductor structure) includes a plurality of first conductive structures that are at least partially comprised of aluminum (see, e.g., structures  106   a ,  106   b  of element  160  in  FIG. 1A ; structures  206   a ,  206   b  of element  260  in  FIG. 2A ; structures  306   a ,  306   b  of element  360  in  FIG. 3 ; structures  406   a ,  406   b  of element  460  in  FIG. 4A ; structures  506   a ,  506   b  of element  560  in  FIG. 5A ; and structures  606   a ″,  606   b ″ of element  660   c  in  FIG. 6A ). At Step  702 , a second semiconductor element is retained by a holding portion of a bonding tool of the bonding machine (see, e.g., elements  108 ,  208 ,  308 ,  408 ,  508 , and  660   d  in the corresponding figures). The second semiconductor element includes a plurality of second conductive structures (e.g., on a lower surface of the second semiconductor element) that are at least partially comprised of aluminum. At Step  704 , the first conductive structures and the second conductive structures are aligned with one another (see, e.g.,  FIGS. 1A and 6A ) and are then brought into contact with one another. At optional Step  706 , the plurality of aligned first conductive structures and second conductive structure are pressed together with a predetermined amount of bond force. The predetermined amount of bond force may be a single bond force value, or may be a bond force profile where the actual bond force is varied during the bonding operation. At optional Step  708 , heat is applied to the plurality of aligned first conductive structures and/or second conductive structures. For example, heat may be applied to the first conductive structures using the support structure that supports the first semiconductor element. Likewise, heat may be applied to the second conductive structures using the bonding tool that retains the second semiconductor element At Step  710 , the plurality of first conductive structures and second conductive structures are ultrasonically bonded together to form ultrasonic bonds therebetween. 
     As will be appreciated by those skilled in the art, the present invention has particular benefits when an ambient/lower temperature bonding operation is desired as the present invention bonds aluminum materials to aluminum materials which may be readily accomplished with ultrasonic energy and/or bond force, often without the need for heat. 
     Although the present invention has been illustrated and described primarily with respect to two pairs of conductive structures ultrasonically bonded together, it is of course not limited thereto. In practice, semiconductor packages (e.g., advanced packages) assembled in accordance with the present invention may have any number of conductive structures, and may have hundreds of pairs (or even thousands) of conductive structures ultrasonically bonded together. Further, the conductive structures need not be bonded in pairs. For example, one structure may be bonded to two or more opposing structures. Thus, any number of conductive structures from one semiconductor element may be ultrasonically bonded to any number of conductive structures of another semiconductor element. 
     Although the present invention primarily describes (and illustrates) the application of ultrasonic energy through a bonding tool (e.g., where the bonding tool is engaged with an ultrasonic transducer), it is not limited thereto. Rather, the ultrasonic energy may be transmitted through any desired structure, such as for example the support structure. 
     As will be appreciated by those skilled in the art, the details of the ultrasonic bonding may vary widely depending on the specific application. Nonetheless, some non-limiting exemplary details are now described. For example, the frequency of the ultrasonic transducer may be designed in connection with the design of the conductive structures (e.g., pillar structures, etc.), such that a transducer resonant frequency substantially coincides with a resonant frequency of the given semiconductor element—in this regard, the conductive structures may act dynamically as a cantilever beam. In another exemplary alternative, the transducer may be operated at an off-resonant condition relative to the semiconductor element in a simple “driven” type fashion. 
     Exemplary ranges for the energy applied to the ultrasonic transducer (e.g., applied to piezoelectric crystals/ceramics in the transducer driver) may be in the range of 0.1 kHz-160 kHz, 10 kHz-120 kHz, 20 kHz-60 kHz, etc. A single frequency may be applied, or a plurality of frequencies may be applied during bonding (e.g., sequentially, simultaneously, or both). The scrub of the semiconductor element (i.e., vibrational energy applied to the semiconductor element held by the bonding tool) may be applied in any of a number of desired directions, and may be applied: through a bonding tool holding a semiconductor element (as illustrated herein); through a support structure supporting a semiconductor element; amongst other configurations. Referring specifically to the embodiments illustrated herein (where the ultrasonic energy is applied through a bonding tool holding a semiconductor element), the scrub may be applied in a direction substantially parallel to, or substantially perpendicular to, a longitudinal axis of the bond tool (or in other directions). 
     The vibrational energy applied by the ultrasonic transducer may be applied, for example, in the peak-to-peak amplitude range of 0.1 um to 10 um (e.g., with feedback control of constant voltage, constant current, or alternate control schemes including but not limited to ramped current, ramped voltage, or proportional feedback control based on one or more inputs). 
     As described herein, bond force may also be applied during at least a portion of the ultrasonic bonding cycle. An exemplary range for the bond force is 0.1 kg to 100 kg. The bond force may be applied as a constant value, or may be a bond force profile that changes during the bonding cycle. In a controlled bond force implementation, the feedback control of the bond force may be constant, ramped or proportional based on one or more inputs (e.g., ultrasonic amplitude, time, velocity, deformation, temperature, etc). 
     As described herein, one or more of the semiconductor elements may be heated prior to and/or during the bond cycle. An exemplary range of the temperature of a semiconductor element is between 20° C.-250° C. The heat (e.g., applied through one or both of the bond tool and the support structure, or other elements) may be applied as a constant value, or may be a temperature profile that changes during the bonding cycle—and may be controlled using feedback control. 
     Although the present invention has been illustrated and described primarily with respect to forming ultrasonic bonds between aluminum conductive structures on respective semiconductor elements, it is of course not limited thereto. That is, the teachings of the present invention may have applicability in forming ultrasonic bonds between conductive structures having varying compositions. An exemplary list of materials for the conductive structures being joined includes: aluminum to copper (i.e., forming ultrasonic bonds between aluminum conductive structures on one semiconductor element to copper conductive structures on another semiconductor element); lead free solder (e.g., primarily composed of tin) to copper; lead free solder to aluminum; copper to copper; aluminum to silver; copper to silver; aluminum to gold; and copper to gold. Of course, other combinations of conductive structure compositions (e.g., indium) are contemplated. 
     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.