Patent Publication Number: US-2023133526-A1

Title: Bonding systems for bonding of semiconductor elements to substrates, and related methods

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 63/272,802, filed Oct. 28, 2021, the content of which is incorporated herein by reference. 
    
    
     FIELD 
     The invention relates to bonding systems and processes (such as flip chip, thermocompression, and thermosonic bonding systems and processes), and more particularly, to improved systems and methods for bonding a semiconductor element to a substrate. 
     BACKGROUND 
     Traditional semiconductor packaging typically involves die attach processes and wire bonding processes. Advanced semiconductor packaging technologies (e.g., flip chip bonding, thermocompression bonding, etc.) continue to gain traction in the industry. For example, in thermocompression bonding (i.e., TCB), heat and/or pressure (and sometimes ultrasonic energy) are used to form a plurality of interconnections between (i) electrically conductive structures on a semiconductor element and (ii) electrically conductive structures on a substrate. 
     In certain flip chip bonding or thermocompression bonding applications, the electrically conductive structures of the semiconductor element and/or the substrate may include copper structures (e.g., copper pillars) or other material(s) that are subject to oxidation and/or other contamination. In such applications, it is desirable to provide an environment suitable for bonding. Conventionally, such an environment may be provided by using a reducing gas at the bonding area to reduce potential oxidation and/or contamination of the electrically conductive structures of the semiconductor element or the substrate to which it will be bonded. 
     Exemplary technologies related to bonding using a reducing gas are disclosed in the following patent documents, each of which is incorporated by reference herein: U.S. Pat. No. 10,861,820 (entitled “METHODS OF BONDING SEMICONDUCTOR ELEMENTS TO A SUBSTRATE, INCLUDING USE OF A REDUCING GAS, AND RELATED BONDING MACHINES”); U.S. Pat. No. 11,205,633 (entitled “METHODS OF BONDING OF SEMICONDUCTOR ELEMENTS TO SUBSTRATES, AND RELATED BONDING SYSTEMS”); and U.S. Patent Application Publication No. 2021/0265303 (entitled “METHODS OF BONDING OF SEMICONDUCTOR ELEMENTS TO SUBSTRATES, AND RELATED BONDING SYSTEMS”). 
     It would be desirable to provide improved methods of bonding semiconductor elements to a substrate with the use of a reducing gas. 
     SUMMARY 
     According to an exemplary embodiment of the invention, a bonding system for bonding a semiconductor element to a substrate is provided. The bonding system includes a bond head assembly for bonding a semiconductor element to a substrate at a bonding area of the bonding system; a reducing gas delivery system for providing a reducing gas to the bonding area during bonding of the semiconductor element to the substrate; and a gas composition analyzer configured for continuously monitoring a composition of the reducing gas during operation of the bonding system. 
     According to another exemplary embodiment of the invention, a method of bonding a semiconductor element to a substrate is provided. The method includes the steps of: (a) providing a reducing gas to a bonding area of a bonding system during bonding of a semiconductor element to a substrate; and (b) continuously monitoring a composition of the reducing gas during operation of the bonding system using a gas composition analyzer. 
    
    
     
       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. 
         FIG.  1    is a block diagram illustration of a bonding system for bonding a semiconductor element to a substrate in accordance with an exemplary embodiment of the invention; 
         FIG.  2    is a block diagram illustration of another bonding system for bonding a semiconductor element to a substrate in accordance with an exemplary embodiment of the invention; 
         FIG.  3    is a block diagram illustration of yet another bonding system for bonding a semiconductor element to a substrate in accordance with an exemplary embodiment of the invention; 
         FIG.  4    is a block diagram illustration of yet another bonding system for bonding a semiconductor element to a substrate in accordance with an exemplary embodiment of the invention; 
         FIG.  5    is a block diagram illustration of yet another bonding system for bonding a semiconductor element, having conductive structures, to a substrate in accordance with an exemplary embodiment of the invention; 
         FIG.  6    is a block diagram illustration of yet another bonding system for bonding a semiconductor element, having conductive structures, to a substrate in accordance with an exemplary embodiment of the invention; and 
         FIG.  7    is a flow diagram illustrating a method of bonding a semiconductor element to a substrate in accordance with an exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     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, a semiconductor chip, a semiconductor wafer, a BGA substrate, a semiconductor element, 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.). 
     As used herein, the term “substrate” is intended to refer to any structure to which a semiconductor element may be bonded. Exemplary substrates include, for example, a leadframe, a PCB, a carrier, a module, a semiconductor chip, a semiconductor wafer, a BGA substrate, another semiconductor element, etc. 
     As used herein, the term “bonding system” is intended to refer to any type of system or machine configured for bonding a semiconductor element to a substrate. Exemplary bonding systems include thermocompression bonding systems (TCB), thermosonic bonding systems, flip chip bonding systems, die attach systems, laser assisted bonding systems, etc. 
     In accordance with certain exemplary embodiments of the invention, a fluxless bonding system is provided using a reducing gas. 
     Aspects of the invention relate to a novel fluxless chip-to-substrate or chip-to-wafer system that avoids oxidation of metal and solder pads during bonding (e.g., during thermocompression bonding). 
     Exemplary systems include a “substrate oxide reduction chamber” (also referred to as a substrate cleaning compartment), a “substrate oxide prevention chamber” (also referred to as a substrate protection compartment), and a “reducing gas delivery system” (e.g., a localized chip and substrate oxide reduction bond head shroud, or other reducing gas delivery system) to eliminate the use of a fluxing process. 
     Aspects of the invention relate to using a reducing gas measurement system (e.g., a gas sampling system) (e.g., in a pump loop) to continuously monitor the reducing gas composition/concentration in a system that has a non-constant flow (i.e., the reducing gas may not always be flowing in the system at the same flow rate, or at all). 
     Exemplary aspects of the invention use a sampling pump and a tubing loop to continuously flow a reducing gas (e.g., formic acid vapor) from a reducing gas source (e.g., piping from a source, a pressurized vessel, a bubbler system, such as a formic acid bubbler system, etc.) through a gas composition analyzer at a constant rate. 
     Aspects of the invention provide a number of potential benefits over conventional systems and methods. For example, aspects of the invention decouple system flow and measurement system flow requirements. As such, if the system flow changes suddenly (which is needed on bonding systems such as thermocompression bonding machines), errors due to changing flow are not experienced by the gas composition analyzer. Further, a reducing gas sampling loop (e.g., a bubbler sampling loop) can perform measurements without requiring system process flow. Further still, using the inventive systems and methods, a reducing gas composition may be maintained within a desired tolerance. 
     Each of  FIGS.  1 - 6    illustrates a gas distribution system  170  that includes an enclosure  160 . Gas distribution system  170  provides a reducing gas  126  and a shielding gas  128 , as described in more detail below. Enclosure  160  houses (i) a vapor generation system  122 , (ii) a gas supply  118  (providing a carrier gas  118   a ), and (iii) a gas composition analyzer  150 . Gas composition analyzer  150  (e.g., a binary gas analyzer, a Fourier-transform infrared spectroscope (FTIR) gas analyzer, a mass spectrometer gas analyzer, a mass spectrometer in combination with a gas chromatograph, etc.) is configured for continuously monitoring a composition of a reducing gas (e.g., formic acid vapor) during operation of the bonding system  100 ,  100 ″,  300 ,  400 ,  300 ′, and  400 ′ (see  FIGS.  1 - 6   ). Gas composition analyzer  150  represents an analyzer including elements not shown, but required in certain applications, such as valves, pumps, flowmeters (e.g., mass flowmeters), etc. In the illustrated examples, vapor generation system  122  is a bubbler type system including an acid fluid  124  (e.g., formic acid, acetic acid, etc.) in a vessel  122   a  of the bubbler type system. A carrier gas  118   a  (e.g., nitrogen) is provided via piping  120  into acid fluid  124  in vessel  122   a , where the carrier gas  118   a  acts as a carrier for the acid fluid  124 . Collectively, carrier gas  118   a  (e.g., nitrogen) and acid fluid  124  are transported as reducing gas  126 . Further, it is understood that certain optional elements of the vapor generation system  122  (e.g., a valve(s) used to add/remove acid fluid  124  to vessel  122   a  to maintain a certain fluid level) are omitted from the illustrations for simplicity. It is understood that carrier gas  118   a  and reducing gas  126  are flowing within piping  120 ; however,  FIGS.  1 - 6    illustrate carrier gas  118   a  and reducing gas  126  with an arrow outside of piping  120  to increase clarity in the figures. 
     Although certain embodiments of the invention have been illustrated and described herein with reference to a reducing gas source that includes a bubbler type vapor generation system, the invention is not limited thereto. It is contemplated that the reducing gas source may have a number of different configurations such as a pressurized vessel containing reducing gas, a source of reducing gas that is common to a plurality of bonding systems, a connection (e.g., a valve, piping, etc.) for providing a reducing gas, etc. 
     Gas composition analyzer  150  may be configured to continuously monitor/analyze the composition of the reducing gas  126  during operation of the bonding system (e.g., at any time before, during, and/or after a bonding operation). The composition that is monitored/analyzed may be a breakdown of the elements of the reducing gas, for example, by weight, by volume, etc. (e.g., the percentage of formic acid versus the percentage of carrier gas). As used herein, the expression “during operation of the bonding system” means that the bonding system is ready for bonding (e.g., it is powered on so that bonding of a semiconductor element could occur) but an actual bonding operation may (or may not) be occurring. At a minimum, in order to be ready for bonding, gas composition analyzer  150  must be turned on such that the continuous monitoring may be performed. As such, “during operation of the bonding system” may include any time before, during, and/or after a bonding operation. 
     Further, gas composition analyzer  150  may be configured to monitor whether the composition of reducing gas  126  meets at least one criteria (e.g., percent weight of formic acid, percent volume of formic acid, saturation level, a desired composition, etc.). For example, such criteria for the reducing gas in some applications is the percentage of formic acid versus carrier gas (e.g., nitrogen) by weight. Exemplary ranges for the formic acid vapor (e.g., that meet the at least one criteria) in connection with the invention include: 1-16% formic acid by weight (and 84-99% nitrogen by weight); 2-15% formic acid by weight (and 85-98% nitrogen by weight); and 5-10% formic acid by weight (and 90-95% nitrogen by weight). Of course, the percentage of formic acid (or other acid fluid, such as acetic acid) by weight is just one example of a “criteria” within the scope of the invention. Another example criteria would be to detect if the formic acid (or other acid compound used in the reducing gas) is saturated in the carrier gas (e.g., in the nitrogen). Additional and/or different criteria may be defined, for example, by an operator. 
     Bonding systems  100 ,  100 ″,  300 ,  400 ,  300 ′, and  400 ′ (see  FIGS.  1 - 6   ), in connection with gas composition analyzer  150 , may be configured to alert an operator (e.g., user) when a given criteria is (or is not) met. 
     Bonding systems  100 ,  100 ″,  300 ,  400 ,  300 ′, and  400 ′ (see  FIGS.  1 - 6   ), in connection with gas composition analyzer  150 , may be configured to adjust the composition of the reducing gas  126  if the composition of the reducing gas  126  does not meet at least one criteria. For example, bonding systems  100 ,  100 ″,  300 ,  400 ,  300 ′, and  400 ′ may automatically adjust operations or settings (e.g., adjust the temperature and/or pressure of the vapor generation system  122 , adjust the fill level of the formic acid in the bubbler, etc.) to achieve a desired composition of reducing gas  126 . 
     In certain embodiments of the invention, reducing gas  126  must meet the at least one criteria (e.g., an acceptable chemical composition) prior to the bonding system  100 ,  100 ″,  300 ,  400 ,  300 ′, and  400 ′ being ready for bonding (e.g., before the bonding system can engage in a bonding operation). 
     Referring now specifically to  FIG.  1   , a bonding system  100  is provided. Bonding system  100  includes a support structure  102  for supporting a substrate  104  during a bonding operation (where substrate  104  includes a plurality of electrically conductive structures  104   a ). Support structure  102  may include any appropriate structure for the specific application. In  FIG.  1   , support structure  102  includes top plate  102   a  (configured to directly support substrate  104 ), chuck  102   c , and heater  102   b  disposed therebetween. In applications where heat for heating substrate  104  is desirable in connection with the bonding operation, a heater such as heater  102   b  may be utilized. 
     Bonding system  100  also includes bond head assembly  106 , which may be configured to move along (and about) a plurality of axes of bonding system  100  such as, for example, the x-axis, y-axis, z-axis, theta (rotative) axis, etc. Bond head assembly  106  includes heater  108  and bonding tool  110 . That is, in certain bonding systems (e.g., thermocompression bonding machines) it may be desirable to heat the bonding tool. Thus, while  FIG.  1    illustrates a separate heater  108  for heating bonding tool  110  (for heating semiconductor element  112  including a plurality of electrically conductive structures  112   a ), it will be appreciated that heater  108  and bonding tool  110  may be integrated into a single element (e.g., a heated bonding tool). 
     In connection with a bonding operation, semiconductor element  112  is bonded to substrate  104  using bonding tool  110 . During the bonding operation, corresponding ones of electrically conductive structures  112   a  are bonded (e.g., using heat, force, ultrasonic energy, etc.) to respective ones of electrically conductive structures  104   a.    
     In certain bonding applications (e.g., flip chip and/or thermocompression bonding with copper conductive structures), it is desirable to provide an environment suitable for bonding. Conventionally, such an environment may be provided by using a reducing gas at the bonding area to reduce potential contamination of the electrically conductive structures of the semiconductor element or the substrate to which it will be bonded. 
     Bonding system  100  also includes a reducing gas delivery system  140  for providing a reducing gas  126  to a bonding area during bonding of semiconductor element  112  to substrate  104 . Reducing gas delivery system  140  is illustrated as being integrated with bond head assembly  106 . Reducing gas delivery system  140  includes a bond head manifold  114  (carried by bond head assembly  106 ) for receiving and distributing fluids (e.g., gases, vapors, etc.) as desired in the given application. In  FIG.  1   , while bond head manifold  114  is illustrated in a cross-sectional view, the actual bond head manifold  114  at least partially surrounds bonding tool  110  (e.g., bond head manifold  114  surrounds bonding tool  110  in a coaxial configuration). Of course, bond head manifold  114  may have different configurations from that shown in  FIG.  1   . Further, it is understood that certain details of bond head manifold  114  (e.g., interconnection with piping  120 , structural details for distributing a reducing gas within bond head manifold  114 , structural details for distributing a shielding gas within bond head manifold  114 , structural details for drawing a vacuum through a center channel of bond head manifold  114 , etc.) are omitted for simplicity. 
     Bond head manifold  114  includes three channels  114   a ,  114   b ,  114   c  having different functions. Outer channel  114   a  receives a shielding gas  128  (e.g., nitrogen gas) from gas supply  118  (of gas distribution system  170 ). That is, a shielding gas  128  is provided from gas supply  118  (e.g., a nitrogen supply), through piping  120  (where piping  120  may include hard piping, flexible tubing, a combination of both, or any other structure adapted to carry the fluids described herein), to outer channel  114   a  of bond head manifold  114 . From outer channel  114   a  of bond head manifold  114 , the shielding gas  128  is provided as a shield from the outside environment. Inner channel  114   c  receives a reducing gas  126  (e.g., where the reducing gas is a saturated vapor gas) from vapor generation system  122  (included as part of gas distribution system  170 ) via piping  120 , and provides reducing gas  126  in the area of semiconductor element  112  and substrate  104  in connection with a bonding operation. 
       FIG.  1    illustrates gas distribution system  170  (including enclosure  160 , a vapor generation system  122 , gas supply  118 , and gas composition analyzer  150 ) as part of bonding system  100 . Details related to gas composition analyzer  150 , and its function, are recited above. As described above, gas composition analyzer  150  may be configured to continuously monitor/analyze the composition of the reducing gas  126  during operation of the bonding system. Also as described above, gas composition analyzer  150  may be configured to monitor whether the composition of the gas meets at least one criteria, and actions may be taken in connection with whether or not the composition meets the at least one criteria. 
     After reducing gas  126  is distributed in the area of semiconductor element  112  and substrate  104 , reducing gas  126  contacts surfaces of each of electrically conductive structures  104   a  and electrically conductive structures  112   a . The surfaces of electrically conductive structures  104   a / 112   a  may then include a reaction product (e.g., where the reaction product is provided as a result of (i) a surface oxide on electrically conductive structures  104   a / 112   a , and (ii) reducing gas  126  (and possibly heat provided by heater  108  and transferred to electrically conductive structures  104   a  via contact with electrically conductive structures  112   a , if desired)). This reaction product is desirably removed from the bonding area (i.e., the area where electrically conductive structures  112   a  of semiconductor element  112  are bonded to corresponding electrically conductive structures  104   a  of substrate  104 ) using vacuum provided through center channel  114   b  of bond head manifold  114  via exit piping  116 . 
     Thus,  FIG.  1    illustrates: (i) various elements of bonding system  100 ; (ii) a path of gas from gas supply  118  (i.e., as shielding gas  128  to outer channel  114   a  of bond head manifold  114 , and as carrier gas  118   a ); (iii) a path of reducing gas  126  from vapor generation system  122  to inner channel  114   c  of bond head manifold  114 , where it is released to the bonding area as reducing gas  126 ; and (iv) a path of gas (which may carry away a reaction product from surfaces of electrically conductive structures  104   a / 112   a ) drawn by vacuum through center channel  114   b  of bond head manifold  114 . 
     Semiconductor element  112  (carried by bond head assembly  106 ) is illustrated positioned above substrate  104 . Vapor generation system  122  has been activated to produce reducing gas  126  at the bonding area. More specifically,  FIG.  1    illustrates reducing gas  126  being provided at the bonding area, as well as shielding gas  128  being provided, and vacuum being drawn through center channel  114   b  of bond head manifold  114  via exit piping  116 . Thus, the flow of reducing gas  126  reaches desired portions of semiconductor element  112  and substrate  104  (e.g., electrically conductive structures  104   a  and electrically conductive structures  112   a ) for: removing contaminants from the electrically conductive structures  104   a  and electrically conductive structures  112   a ; and/or shielding electrically conductive structures  104   a  and electrically conductive structures  112   a  from further potential contamination. 
     Also illustrated in  FIG.  1   , respective ones of electrically conductive structures  112   a  (of semiconductor element  112 ) are aligned with ones of electrically conductive structures  104   a  (of substrate  104 ). In subsequent steps (not illustrated), the process proceeds to a bonding step (e.g., a thermocompression bonding step), for example, through the lowering of bond head assembly  106 . That is, electrically conductive structures  112   a  are bonded to corresponding electrically conductive structures  104   a . This may be through a thermocompression bonding process (e.g., including heat and/or bond force, where the bond force may be a higher bond force such as 50-300 N), and may also include ultrasonic energy transfer (e.g., from an ultrasonic transducer included in bond head assembly  106 ). 
     Although  FIG.  1    illustrates an exemplary bond head manifold  114  integrated with the bond head assembly  106  for: delivering the reducing gas; delivering the shielding gas; and providing vacuum, the invention is not limited thereto. For example, instead of such functions being provided through integration of a manifold with the bond head assembly, such functions may be provided through integration with a support structure for supporting the substrate. Further, such functions may be split between the bond head assembly and the support structure (and possibly other structures of the bonding system).  FIG.  2    is a block diagram of a bonding system  100 ″ with certain similar elements and functions to those illustrated and described with respect to  FIG.  1   , except that the manifold and its functions (delivering the reducing gas; delivering the shielding gas; and providing vacuum) are integrated into a support structure  202 . 
       FIG.  2    illustrates bonding system  100 ″ (e.g., a bonding machine, a flip chip bonding machine, a thermocompression bonding machine, etc.). Bonding system  100 ″ includes a support structure  202  for supporting a substrate  104  during a bonding operation (where substrate  104  includes a plurality of electrically conductive structures  104   a ). Support structure  202  may include any appropriate structure for the specific application. In  FIG.  2   , support structure  202  includes top plate  202   a  (configured to directly support substrate  104 ), chuck  202   c , and heater  202   b  disposed therebetween. In applications where heat for heating substrate  104  is desirable in connection with the bonding operation, a heater such as heater  202   b  may be utilized. 
       FIG.  2    also illustrates bond head assembly  106  (including heater  108  and bonding tool  110 ), which may be configured to move along (and/or about) a plurality of axes of bonding system  100 ″ such as, for example, the x-axis, y-axis, z-axis, theta (rotative) axis, etc. In  FIG.  2   , bond head assembly  106  carries a plate  107  for partially containing at least one of shielding gas  128  and reducing gas  126  (see description below). 
     Bonding system  100 ″ includes a reducing gas delivery system  240  for providing a reducing gas  126  to a bonding area during bonding of semiconductor element  112  to substrate  104 . Reducing gas delivery system  240  is illustrated as being integrated with support structure  202 . As opposed to a bond head manifold  114  carried by bond head assembly  106  (as in  FIG.  1   ),  FIG.  2    illustrates a manifold  214  carried by, and/or integrated with, support structure  202 . Manifold  214  is configured for receiving and distributing fluids (e.g., gases, vapors, etc.) as desired in the given application. In  FIG.  2   , while manifold  214  is illustrated in a cross-sectional view, the actual manifold  214  at least partially surrounds substrate  104 . Of course, manifold  214  may have different configurations from that shown in  FIG.  2   , while carrying out the functions of receiving and distributing fluids. Further, it is understood that certain details of manifold  214  (e.g., interconnection with piping  120 , structural details for distributing reducing gas  126  within manifold  214 , structural details for distributing shielding gas  128  within manifold  214 , structural details for drawing a vacuum through a center channel of manifold  214 , etc.) are omitted for simplicity. 
     Manifold  214  includes three channels  214   a ,  214   b ,  214   c  having different functions. Outer channel  214   a  receives shielding gas  128  (e.g., nitrogen gas) from gas supply  118  (of gas distribution system  170 ). That is, shielding gas  128  is provided from gas supply  118  (e.g., a nitrogen supply), through piping  120  (where piping  120  may include hard piping, flexible tubing, a combination of both, or any other structure adapted to carry the fluids described herein), to outer channel  214   a  of manifold  214 . From outer channel  214   a  of manifold  214 , shielding gas  128  is provided as a shield from the outside environment. Center channel  114   b  provides a vacuum for removal of reaction product from the bonding area (i.e., the area where electrically conductive structures  112   a  of semiconductor element  112  are bonded to corresponding electrically conductive structures  104   a  of substrate  104 ) via exit piping  116 . Inner channel  214   c  receives reducing gas  126  (e.g., where the reducing gas is a saturated vapor gas) from vapor generation system  122  (included as part of gas distribution system  170 ) via piping  120 , and provides reducing gas  126  in the area of semiconductor element  112  and substrate  104  in connection with a bonding operation. 
       FIG.  2    illustrates gas distribution system  170  (including enclosure  160 , a vapor generation system  122 , gas supply  118 , and gas composition analyzer  150 ) as part of bonding system  100 ″. Details related to gas composition analyzer  150 , and its function, are recited above. As described above, gas composition analyzer  150  may be configured to continuously monitor/analyze the composition of the reducing gas  126  during operation of the bonding system. Also as described above, gas composition analyzer  150  may be configured to monitor whether the composition of the gas meets at least one criteria, and actions may be taken in connection with whether or not the composition meets the at least one criteria. 
     After reducing gas  126  is distributed in the area of semiconductor element  112  and substrate  104 , reducing gas  126  contacts surfaces of each of electrically conductive structures  104   a  and electrically conductive structures  112   a . The surfaces of electrically conductive structures  104   a / 112   a  may then include a reaction product (e.g., where the reaction product is provided as a result of: (i) a surface oxide on electrically conductive structures  104   a / 112   a , and (ii) reducing gas  126  (and possibly heat provided by heater  108 , if desired)). This reaction product is desirably removed from the bonding area (i.e., the area where electrically conductive structures  112   a  of semiconductor element  112  are bonded to corresponding electrically conductive structures  104   a  of substrate  104 ) using vacuum provided through center channel  214   b  of manifold  214  via exit piping  216 . 
     Thus,  FIG.  2    illustrates: (i) various elements of bonding system  100 ″; (ii) a path of gas from gas supply  118  (i.e., as shielding gas  128  to outer channel  214   a  of manifold  214 , and as carrier gas  118   a ); (iii) a path of reducing gas  126  from vapor generation system  122  to inner channel  214   c  of manifold  214 , where it is released to the bonding area as reducing gas  126 ; and (iv) a path of gas (which may carry away a reaction product from surfaces of electrically conductive structures  104   a / 112   a ) drawn by vacuum through center channel  214   b  of manifold  214 . The aforementioned paths are illustrated in  FIG.  2    through various arrows. 
     Referring to  FIG.  2   , semiconductor element  112  (carried by bond head assembly  106 ) is positioned above substrate  104 . As shown in  FIG.  2   , vapor generation system  122  has been activated to produce reducing gas  126  at the bonding area. More specifically,  FIG.  2    illustrates reducing gas  126  being provided at the bonding area, as well as shielding gas  128  being provided, and vacuum being drawn through center channel  214   b  of bond head manifold  214  via exit piping  216 . Thus, the flow of reducing gas  126  reaches desired portions of semiconductor element  112  and substrate  104  (e.g., electrically conductive structures  104   a  and electrically conductive structures  112   a ) for: removing contaminants from the electrically conductive structures  104   a  and electrically conductive structures  112   a ; and/or shielding electrically conductive structures  104   a  and electrically conductive structures  112   a  from further potential contamination. 
     Also illustrated in  FIG.  2   , respective ones of electrically conductive structures  112   a  (of semiconductor element  112 ) are aligned with ones of electrically conductive structures  104   a  (of substrate  104 ). In subsequent steps, the process proceeds to a bonding step (e.g., a thermocompression bonding step), for example, through the lowering of bond head assembly  106 . That is, electrically conductive structures  112   a  are bonded to corresponding electrically conductive structures  104   a . This may be through a thermocompression bonding process (e.g., including heat and/or bond force, where the bond force may be a higher bond force such as 50-300 N), and may also include ultrasonic energy transfer (e.g., from an ultrasonic transducer included in bond head assembly  106 ). 
     Referring now to  FIG.  3   , exemplary bonding system  300  is illustrated. Bonding system  300  includes: a substrate source  300   a  (e.g., a wafer handler or other source) for providing a substrate(s)  104  (such as a wafer, a printed circuit board, etc.) on a support structure  300   a   1 ; and a processing system  300   b . Substrate  104  is configured to be transferred to processing system  300   b  (e.g., including a tunnel  302 , but may be a different type of structure). Tunnel  302  (or other structure, as desired) includes a substrate oxide reduction chamber  302   a , a substrate oxide prevention chamber  302   b , and a bonding area  302   c  (which is part of substrate oxide prevention chamber  302   b ). A reducing gas delivery system  308  is also included in processing system  300   b.    
     In the example shown in  FIG.  3   , tunnel  302  is configured such that substrate oxide reduction chamber  302   a  and substrate oxide prevention chamber  302   b  have a common boundary. Substrate oxide reduction chamber  302   a  is closed using entry door  302   a   1  (which closes opening  302   a   1   a ) and exit door  302   a   2  (which closes opening  302   a   2   a ). Another reducing gas delivery system  302   d  (which is illustrated interconnected, via piping  120 , with reducing gas delivery system  308  to use a common source of reducing gas  126  from gas distribution system  170 ) is provided to provide a reducing gas  126  (e.g., formic acid vapor) in substrate oxide reduction chamber  302   a . Although bonding system  300  is illustrated and described herein with reference to a single reducing gas source, the invention is not limited thereto. A plurality of sources of reducing gas are contemplated (e.g., one reducing gas source for each reducing gas location). 
       FIG.  3    illustrates gas distribution system  170  (including enclosure  160 , a vapor generation system  122 , gas supply  118 , and gas composition analyzer  150 ) as part of bonding system  300 . Details related to gas composition analyzer  150 , and its function, are recited above. As described above, gas composition analyzer  150  may be configured to continuously monitor/analyze the composition of the reducing gas  126  during operation of bonding system  300 . Also as described above, gas composition analyzer  150  may be configured to monitor whether the composition of the gas meets at least one criteria, and actions may be taken in connection with whether or not the composition meets the at least one criteria. 
     After processing (e.g., removal of oxides from conductive structures of substrate  104 ) in substrate oxide reduction chamber  302   a , a substrate transfer system (which may be part of a material handling system including support structure  102 , and which further may include support structure  300   a   1 ) is used to transfer substrate  104  through opening  302   a   2   a  to substrate oxide prevention chamber  302   b . Substrate oxide prevention chamber  302   b  includes an inert environment  306  (e.g., through a nitrogen supply, not shown for simplicity). A material handling system (e.g., including support structure  102 ) is used to move substrate  104  within substrate oxide prevention chamber  302   b  to a bonding area  302   c . While at bonding area  302   c , reducing gas  126  is provided by reducing gas delivery system  308 . 
       FIG.  3    also illustrates bond head assembly  106 , including heater  108 , and bonding tool  110 .  FIG.  3    also illustrates a main exhaust  304  which pulls exhaust gases (e.g., gases such as reducing gas vapors) through piping  304   a  and  114   b   1  (where piping  114   b   1  is coupled, directly or indirectly, to center channel  114   b  described above). Bond head assembly  106  carries a bond head manifold  114  for receiving and distributing fluids (e.g., gases, vapors, etc.) as desired in the given application. 
     In connection with a bonding operation, semiconductor element  112  (which is carried by bond head assembly  106  into tunnel  302  through opening  302   e ) is bonded to substrate  104  using bonding tool  110 . During the bonding operation, corresponding ones of electrically conductive structures of semiconductor element  112  are bonded (e.g., using heat, force, ultrasonic energy, etc.) to respective ones of electrically conductive structures of substrate  104 . Bond head manifold  114  (included as part of reducing gas delivery system  308 ) provides reducing gas  126  (e.g., where the reducing gas is a saturated vapor gas) in the area of semiconductor element  112  and substrate  104  in connection with a bonding operation (in the illustrated example, reducing gas  126  is able to enter tunnel  302  through opening  302   e ). After reducing gas  126  is distributed in the area of semiconductor element  112  and substrate  104 , reducing gas  126  contacts surfaces of each of electrically conductive structures of semiconductor element  112  and substrate  104 . 
       FIG.  4    illustrates exemplary bonding system  400 , which is similar in many respects to bonding system  300  of  FIG.  3    (where like elements have the same reference numerals, or a numeral beginning with a “4” instead of a “3”). Bonding system  400  includes a substrate source  400   a  (e.g., a wafer handler or other source) for providing a substrate(s)  104  (such as a wafer, a printed circuit board, etc.) on a support structure  400   a   1 . Substrate  104  is configured to be transferred to processing system  400   b  (e.g., including a tunnel  402 , but may be a different type of structure). Tunnel  402  (or other structure, as desired) includes a substrate oxide reduction chamber  402   a , a substrate oxide prevention chamber  402   b , and a bonding area  402   c  (which is part of substrate oxide prevention chamber  402   b ). 
     In the example shown in  FIG.  4   , tunnel  402  is configured such that substrate oxide reduction chamber  402   a  and substrate oxide prevention chamber  402   b  have a common boundary. A reducing gas delivery system  408  is also included in processing system  400   b . Substrate oxide reduction chamber  402   a  is closed using entry door  402   a   1  (which closes opening  402   a   1   a ) and exit door  402   a   2  (which closes opening  402   a   2   a ). Another reducing gas delivery system  402   d  (which is interconnected, via piping  120 , with reducing gas delivery system  408  to use a common source of reducing gas  126  from gas distribution system  170 ) is provided to provide a reducing gas  126  (e.g., formic acid vapor) in substrate oxide reduction chamber  402   a.    
       FIG.  4    illustrates gas distribution system  170  (including enclosure  160 , a vapor generation system  122 , gas supply  118 , and gas composition analyzer  150 ) as part of bonding system  400 . Details related to gas composition analyzer  150 , and its function, are recited above. As described above, gas composition analyzer  150  may be configured to continuously monitor/analyze the composition of the reducing gas  126  during operation of the bonding system. Also as described above, gas composition analyzer  150  may be configured to monitor whether the composition of the gas meets at least one criteria, and actions may be taken in connection with whether or not the composition meets the at least one criteria. 
     After processing (e.g., removal of oxides from conductive structures of substrate  104 ) in substrate oxide reduction chamber  402   a , a substrate transfer system (which may be part of a material handling system including support structure  102 , and which further may include support structure  400   a   1 ) is used to transfer substrate  104  through opening  402   a   2   a  to substrate oxide prevention chamber  402   b . Substrate oxide prevention chamber  402   b  includes an inert environment  406  (e.g., through a nitrogen supply, not shown for simplicity). A material handling system (e.g., including support structure  102 ) is used to move substrate  104  within substrate oxide prevention chamber  402   b  to a bonding area  402   c . While at bonding area  402   c , a reducing gas  126  is provided by reducing gas delivery system  408 . 
       FIG.  4    also illustrates bond head assembly  106 , including heater  108 , and bonding tool  110 .  FIG.  4    also illustrates a main exhaust  404  which pulls exhaust gases (e.g., gases such as reducing gas vapors) through piping  404   a  and  404   b . A manifold  214  is provided for receiving and distributing fluids (e.g., gases, vapors, etc.) as desired in the given application. As illustrated in  FIG.  4   , manifold  214  is carried by and/or integrated with support structure  102 , as opposed to the embodiment shown in  FIG.  3    (where bond head manifold  114  is carried by the bond head assembly  106 ). 
     In connection with a bonding operation, semiconductor element  112  (which is carried by bond head assembly  106  into tunnel  402  through opening  402   e ) is bonded to substrate  104  using bonding tool  110 . During the bonding operation, corresponding ones of electrically conductive structures of semiconductor element  112  are bonded (e.g., using heat, force, ultrasonic energy, etc.) to respective ones of electrically conductive structures of substrate  104 . Manifold  214  provides a reducing gas  126  (e.g., where the reducing gas is a saturated vapor gas) in the area of semiconductor element  112  and substrate  104  in connection with a bonding operation. After reducing gas  126  is distributed in the area of semiconductor element  112  and substrate  104 , reducing gas  126  contacts surfaces of each of electrically conductive structures of semiconductor element  112  and substrate  104 . 
     While exemplary bonding systems  300 ,  400  of  FIG.  3    and  FIG.  4    include substrate oxide reduction chamber  302   a ,  402   a  and associated structures, it is contemplated that simplified systems without substrate oxide reduction chamber  302   a ,  402   a  and associated structures, are within the scope of the invention, such as the systems of  FIG.  5    and  FIG.  6   . 
       FIG.  5    illustrates exemplary bonding system  300 ′. Bonding system  300 ′ includes: a substrate source  300   a  (e.g., a wafer handler or other source) for providing a substrate(s)  104  (such as a wafer, a printed circuit board, etc.) on a support structure  300   a   1 ; and a processing system  300   b ′. Substrate  104  is configured to be transferred to processing system  300   b ′ (e.g., including an inner environment chamber  320 , including a tunnel  302 ′, but may be a different type of structure). Tunnel  302 ′ (or other structure, as desired) includes a substrate oxide prevention chamber  302   b ′ and a bonding area  302   c  (which is part of substrate oxide prevention chamber  302   b ′). A reducing gas delivery system  308  is also included in processing system  300   b ′. Within processing system  300   b ′ (sometimes referred herein as main machine compartment), inner environment chamber  320  may include at least a portion of the substrate oxide prevention chamber  302   b ′ and the reducing gas delivery system  308 . 
     In the example shown in  FIG.  5   , tunnel  302 ′ includes entry door  302   a   1 ′ (which closes opening  302   a   1   a ′). A substrate transfer system (which may be part of a material handling system including support structure  102 ) is used to transfer substrate  104  through entry door  302   a   1 ′ to substrate oxide prevention chamber  302   b ′. Substrate oxide prevention chamber  302   b ′ includes an inert environment  306  (e.g., through a nitrogen supply, not shown for simplicity). A material handling system (e.g., including support structure  102 ) is used to move substrate  104  within substrate oxide prevention chamber  302   b ′ to a bonding area  302   c . While at bonding area  302   c , a reducing gas  126  is provided by reducing gas delivery system  308 . Reducing gas delivery system  308  is connected to gas distribution system  170  (which is the same gas distribution system  170  from  FIG.  1   ,  FIG.  2   ,  FIG.  3   , and  FIG.  4   ) via piping  120 . 
       FIG.  5    illustrates gas distribution system  170  (including enclosure  160 , a vapor generation system  122 , gas supply  118 , and gas composition analyzer  150 ) as part of bonding system  300 ′. Details related to gas composition analyzer  150 , and its function, are recited above. As described above, gas composition analyzer  150  may be configured to continuously monitor/analyze the composition of the reducing gas  126  during operation of the bonding system. Also as described above, gas composition analyzer  150  may be configured to monitor whether the composition of the gas meets at least one criteria, and actions that may be taken in connection with whether or not the composition meets the at least one criteria. 
       FIG.  5    also illustrates bond head assembly  106 , including heater  108 , and bonding tool  110 .  FIG.  5    also illustrates a main exhaust  304 ′ which pulls exhaust gases (e.g., gases such as reducing gas vapors) from the processing system  300   b ′ (sometimes referred to as the main machine compartment) or the inner environment chamber  320  through piping  304   a ′ and  114   b   1  (where piping  114   b   1  is coupled, directly or indirectly, to center channel  114   b  described above in connection with  FIG.  1   ). Bond head assembly  106  carries a bond head manifold  114  (included as part of reducing gas delivery system  308 ) for receiving and distributing fluids (e.g., gases, vapors, etc.) as desired in the given application. Details of an exemplary bond head assembly  106 , carrying exemplary bond head manifold  114  (included as part of reducing gas delivery system  108 ), are described above in connection with  FIG.  1   . 
     In connection with a bonding operation, semiconductor element  112  (which is carried by bond head assembly  106  into tunnel  302 ′ through opening  302   e ′) is bonded to substrate  104  using bonding tool  110 . During the bonding operation, corresponding ones of electrically conductive structures of semiconductor element  112  are bonded (e.g., using heat, force, ultrasonic energy, etc.) to respective ones of electrically conductive structures of substrate  104 . Bond head manifold  114  provides a reducing gas  126  (e.g., where the reducing gas is a saturated vapor gas) in the area of semiconductor element  112  and substrate  104  in connection with a bonding operation (in the illustrated example, reducing gas  126  is able to enter tunnel  302 ′ through opening  302   e ′). After reducing gas  126  is distributed in the area of semiconductor element  112  and substrate  104 , reducing gas  126  contacts surfaces of each of electrically conductive structures of semiconductor element  112  and substrate  104 . 
       FIG.  6    illustrates exemplary bonding system  400 ′, which is similar in many respects to bonding system  300 ′ of  FIG.  5    (where like elements have the same reference numerals, or a numeral beginning with a “4” instead of a “3”). Bonding system  400 ′ includes a substrate source  400   a  (e.g., a wafer handler or other source) for providing a substrate(s)  104  (such as a wafer, a printed circuit board, etc.) on a support structure  400   a   1 . Substrate  104  is configured to be transferred to a processing system  400   b ′ (e.g., including an inner environment chamber  420 , including a tunnel  402 ′, but may be a different type of structure). Tunnel  402 ′ (or other structure, as desired) includes a substrate oxide prevention chamber  402   b ′ and a bonding area  402   c  (which is part of substrate oxide prevention chamber  402   b ′). Within processing system  400   b ′ (sometimes referred herein as main machine compartment), inner environment chamber  420  may include at least a portion of the substrate oxide prevention chamber  402   b ′ and the reducing gas delivery system  408 . 
     In the example shown in  FIG.  6   , tunnel  402 ′ includes a substrate oxide prevention chamber  402   b ′. A reducing gas delivery system  408  is included in processing system  400   b ′. Substrate oxide prevention chamber  402   b ′ is closed using entry door  402   a   1 ′ (which closes opening  402   a   1   a ′). A substrate transfer system (which may be part of a material handling system including support structure  102 ) is used to transfer substrate  104  through opening  402   a   1   a ′ to substrate oxide prevention chamber  402   b ′. Substrate oxide prevention chamber  402   b ′ includes an inert environment  406  (e.g., through a nitrogen supply, not shown for simplicity). A material handling system (e.g., including support structure  102 ) is used to move substrate  104  within substrate oxide prevention chamber  402   b ′ to a bonding area  402   c . While at bonding area  402   c , a reducing gas  126  is provided by reducing gas delivery system  408 . Reducing gas delivery system  408  is connected to gas distribution system  170  (which is the same gas distribution system  170  from  FIG.  1   ,  FIG.  2   ,  FIG.  3   ,  FIG.  4   , and  FIG.  5   ) via piping  120 . 
       FIG.  6    illustrates gas distribution system  170  (including enclosure  160 , a vapor generation system  122 , gas supply  118 , and gas composition analyzer  150 ) as part of bonding system  400 ′. Details related to gas composition analyzer  150 , and its function, are recited above. As described above, gas composition analyzer  150  may be configured to continuously monitor/analyze the composition of the reducing gas  126  during operation of the bonding system. Also as described above, gas composition analyzer  150  may be configured to monitor whether the composition of the gas meets at least one criteria, and actions that may be taken in connection with whether or not the composition meets the at least one criteria. 
       FIG.  6    also illustrates bond head assembly  106 , including heater  108 , and bonding tool  110 .  FIG.  6    also illustrates a main exhaust  404 ′ which pulls exhaust gases (e.g., gases such as reducing gas vapors) from the processing area  400   b ′ (sometimes referred to as the main machine compartment) or the inner environment chamber  420  through piping  404   a ′ and  404   b ′. A manifold  214  is provided for receiving and distributing fluids (e.g., gases, vapors, etc.) as desired in the given application. As illustrated in  FIG.  6   , manifold  214  is carried by and/or integrated with support structure  102 , as opposed to the embodiment shown in  FIG.  5    (where bond head manifold  114  is carried by the bond head assembly  106 ). 
     In connection with a bonding operation, semiconductor element  112  (which is carried by bond head assembly  106  into tunnel  402 ′ through opening  402   e ′) is bonded to substrate  104  using bonding tool  110 . During the bonding operation, corresponding ones of electrically conductive structures of semiconductor element  112  are bonded (e.g., using heat, force, ultrasonic energy, etc.) to respective ones of electrically conductive structures of substrate  104 . Manifold  214  provides a reducing gas  126  (e.g., where the reducing gas  126  is a saturated vapor gas) in the area of semiconductor element  112  and substrate  104  in connection with a bonding operation. After reducing gas  126  is distributed in the area of semiconductor element  112  and substrate  104 , reducing gas  126  contacts surfaces of each of electrically conductive structures of semiconductor element  112  and substrate  104 . 
       FIG.  7    is a flow diagram illustrating an exemplary method of bonding a semiconductor element to a substrate. As is understood by those skilled in the art, certain steps included in the flow diagrams may be omitted; certain additional steps may be added; and the order of the steps may be altered from the order illustrated—all within the scope of the invention. 
     At Step  700 , a reducing gas (e.g., formic acid vapor) is provided to a bonding area of a bonding system (e.g., see bonding systems  100 ,  100 ″,  300 ,  400 ,  300 ′ and  400 ′ described herein) during bonding of a semiconductor element to a substrate. At Step  702 , a composition of the reducing gas is continuously monitored during operation of the bonding system using a gas composition analyzer (e.g., a binary gas analyzer, an FTIR gas analyzer, a mass spectrometer gas analyzer, etc.). The gas composition analyzer may be configured to monitor whether the composition of the reducing gas meets at least one criteria (e.g., percent weight of formic acid, percent volume of formic acid, saturation level, a desired composition, etc.) and to alert an operator or adjust the composition of the reducing gas if the composition of the reducing gas does not meet the at least one criteria. At optional Step  704 , the semiconductor element is bonded to the substrate at the bonding area of the bonding system using a bond head assembly of the bonding system. 
     Although the invention has been illustrated primarily with respect to one of bond head manifold  114  and manifold  214  for directing (i) the flow of reducing gas  126 , (ii) the flow of shielding gas  128 , and (iii) the pull of the vacuum, it is understood that the structure used to direct the flow patterns may be different from that illustrated. That is, the configuration of the structure used to provide and direct fluids (e.g., reducing gas  126 , shielding gas  128 , etc.) (and to draw vacuum) may vary considerably from that shown. 
     Although the invention has been described and illustrated with respect to the exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without parting from the spirit and scope of the present invention. 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.