Abstract:
A new process and structure for microcomponent interconnection utilizing a post-assembly activated junction compound. In one embodiment, first and second microcomponents having respective first and second contact areas are provided. A junction compound is formed on one of the first and second contact areas, and the first and second contact areas are positioned adjacent each other on opposing sides of the junction compound. The junction compound is then activated to couple the first and second microcomponents.

Description:
This invention was made with the United States Government support under 70NANB1H3021 awarded by the National Institute of Standards and Technology (NIST). The United States Government has certain rights in the invention. 

   BACKGROUND 
   The present invention relates generally to mechanisms for coupling micro-components, and more specifically to microcomponent interconnection utilizing post-assembly activation. 
   Extraordinary advances are being made in micromechanical devices and microelectronic devices, including micro-electro-mechanical devices (MEMs), which comprise integrated micromechanical and microelectronic devices. The terms “microcomponent,” “microdevice” and “microassembly” are used herein generically to encompass microelectronic components, micromechanical components, MEMs components and assemblies thereof. Generally, microcomponent devices have feature dimensions that are less than about 1000 microns. 
   Many methods and structures exist for coupling MEMs and other microcomponents together to form a microassembly. One such method, often referred to as “pick-and-place” assembly, is serial microassembly, wherein microcomponents are assembled one at a time in a serial fashion. For example, if a device is formed by coupling two microcomponents together, a gripper or other placing mechanism is used to pick up one of the two microcomponents and place it on a desired location of the other microcomponent. These pick-and-place processes, although seemingly quite simple, can present obstacles affecting assembly time, throughput and reliability, especially when electrically interconnecting microcomponents during microassembly. 
   For example, it is commonly accepted that about 1 mN of force is required to achieve an electrical contact of sufficiently low resistance between two gold conductors. However, many existing microassembly procedures, including some pick-and-place procedures, operate with application forces much lower than 1 mN. Thus, many existing microassembly procedures do not provide adequate electrical interconnection of microcomponents, thereby reducing the fabrication yield and assembly reliability. 
   To overcome this disadvantage, microcomponents may be temporarily positioned for coupling, such that electrical contacts to be coupled are in contact with one another, and electrical current may be provided to the contacts. Consequently, localized heating may occur and the contacts may diffuse with one another. As a result, an electrical interconnection of sufficiently low resistance may be achieved between the coupled microcomponents without requiring the 1 mN of force typically required for microassembly. 
   However, many microcomponents are not designed to withstand the electrical current required to achieve the localized heating necessary to adequately interconnect the microcomponents. Moreover, such a method is labor extensive and consumes part of the useful life of the microcomponents and assembly. 
   Accordingly, what is needed in the art is a microcomponent assembly and interconnection method that addresses the above-discussed issues of the prior art. 
   SUMMARY 
   The present disclosure relates to a new process and structure for microcomponent interconnection utilizing a post-assembly activated junction compound. In one embodiment, first and second microcomponents having respective first and second contact areas are provided. A junction compound is formed on one of the first and/or second contact areas, and the first and second contact areas are positioned adjacent each other on opposing sides of the junction compound. The junction compound is then activated to couple the first and second microcomponents. 
   In another embodiment, a substrate having a substrate contact area and first and second microcomponents each having a microcomponent contact area are provided. A junction compound is formed on the substrate contact area and/or the first and second microcomponent contact areas, and the first and second contact areas are positioned adjacent the substrate contact area. The junction compound is then activated to couple the first and second microcomponents to the substrate. 
   The present disclosure also provides a microcomponent assembly of first and second microcomponents. The first microcomponent has a first contact area and a connecting member, and the second microcomponent has a second contact area and an opening configured to engage the connecting member. A junction compound is located between the first and second contact areas, thereby coupling the first and second microcomponents. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates an elevation view of one embodiment of a first microcomponent prior to assembly according to aspects of the present disclosure. 
       FIG. 2  illustrates a plan view of one embodiment of a second microcomponent prior to assembly according to aspects of the present disclosure. 
       FIG. 3  illustrates a plan view of one embodiment of a microcomponent assembly in an intermediate stage of assembly according to aspects of the present disclosure. 
       FIG. 4  illustrates a plan view of one embodiment of a substantially completed microcomponent assembly according to aspects of the present disclosure. 
       FIG. 5  illustrates an elevation view of another embodiment of microcomponents prior to assembly according to aspects of the present disclosure. 
       FIG. 6  illustrates a plan view of one embodiment of a microcomponent substrate element prior to assembly according to aspects of the present disclosure. 
       FIG. 7  illustrates an elevation view of another embodiment of a microcomponent assembly constructed according to aspects of the present disclosure. 
   

   DETAILED DESCRIPTION 
   Referring initially to  FIG. 1 , illustrated is an elevation view of one embodiment of a first microcomponent  110  to be assembled according to aspects of the present disclosure. In one embodiment, the microcomponent  110  may have feature dimensions that are less than about 50 microns. In a more specific embodiment, the feature dimensions may be less than about 25 microns. Moreover, the first microcomponent  110  may be a nanocomponent, such as those having feature dimensions less than about 1000 nm. The first microcomponent  110  includes a substrate  115  and at least one connecting member  120  for coupling the first microcomponent  110  to a mating substrate or one or more mating microcomponents. Exemplary mating microcomponents are further discussed in relation to subsequent figures. The connecting members  120  may be formed integral to the first microcomponent  110 , or may be discrete features that are mechanically and/or electrically coupled to the first microcomponent  110 . The connecting members  120  may include barbed ends  125  configured to engage mating surfaces of one or more mating components. 
   The first microcomponent  110  may also include first conductive members  130 , which may be conductive traces or interconnects comprising gold, aluminum, copper or other materials, as known in the art. The first microcomponent  110  may also include silicon layers  140  supporting one or more of the first conductive members  130  within or over the substrate  115 . However, the first microcomponent  110  may also or alternatively include other insulation features electrically isolating the conductive members  130  from the substrate  115 , such as but not limited to trench isolation features. In one embodiment, as shown in  FIG. 1 , the first conductive members  130  may overhang the substrate  115  and/or the silicon layers  140 , thereby forming first electrodes  135 . 
   The first microcomponent  110  also includes first contact areas  117  on which first junction compound layers  150  are formed. In one embodiment, one or more of the first junction compound layers  150  are electrically isolated from the first conductive members  130 , such as by forming the first junction compound layers  150  a sufficient distance away from the first conductive members  130 . However, the first junction compound layers  150  may also be formed directly on or adjacent to one or more of the conductive members  130 , such as on the connecting members  120  and/or the electrodes  135 . Generally, the first contact areas  117  on which the first junction compound layers  150  are formed may include any surface of the first microcomponent  110  that may be contacted with another microcomponent or substrate. For example, the first junction compound may also be formed on contact areas  117  located on surfaces of the connecting members  120 , such as those of the barbed ends  125 , as shown in  FIG. 1 . 
   The first junction compound layers  150  may include indium, solder (e.g., a tin-based solder), alloys thereof or other conductive materials. The first junction compound layers  150  may be formed on the contact areas  117  by blanket or selective deposition, chemical vapor-deposition (CVD), metal-organic CVD (MOCVD), physical vapor deposition (PVD), atomic layer deposition (ALD), spin-on coating, electroplating, sputtering, ionized metal plasma deposition (IMP) or other conventional or future-developed thin-film deposition processes. An aperture mask, reticle or other patterning device may be employed to form the first junction compound layers  150  on the contact areas  117 , such as to prevent overspray of the first junction compound layers  150  outside of the contact areas  117 . The first junction compound layers  150  may have a thickness ranging between about 100 nm and about 1000 nm. 
   Referring to  FIG. 2 , illustrated is a plan view of one embodiment of a second microcomponent  210  to be assembled according to aspects of the present disclosure. As with the first microcomponent  110 , the second microcomponent  210  may have feature dimensions that are less than about 50 microns or, in a more specific embodiment, less than about 25 microns. The second microcomponent  210  may also be a nanocomponent. The second microcomponent  210  includes a substrate  215  having apertures  220  configured to receive the connecting members  120  of the first microcomponent  110 , such as by engaging the barbed ends  125  of the connecting members  120 . 
   As shown in  FIG. 2 , the second microcomponent  210  may also include second conductive members  230 , which may be conductive traces or interconnects comprising gold, aluminum, copper or other materials, as known in the art. The second microcomponent  210  may also include silicon layers  240  supporting one or more of the second conductive members  230  within or over the substrate  215 . As with the first microcomponent  110 , the second microcomponent  210  may include other isolation features, in addition to or in the alternative, that isolate the conductive members  230  from the substrate  215 . 
   In one embodiment, as shown in  FIG. 2 , the second conductive members  230  may overhang the silicon layers  240  and/or the substrate  215 , thereby forming second electrodes  235 . The second conductive members  230  may be capable of receiving electrical signals when contacted with the first conductive members  130 , as described below. Moreover, silicon layers  240  and/or the second conductive members  230  may each be formed in a recess or opening in the substrate  215 , such that they may flex or bend relative to the substrate  215 . For example, in the embodiment illustrated in  FIG. 2 , the silicon layers  240  and the second conductive members  230  are formed in openings  219  in the substrate  215 . The openings  219  may extend through the substrate  215 , thereby allowing the silicon layers  240  and second conductive members  230  to flex beyond the profile of the substrate  215  upon the application of an assembly force, as described below. 
   The second microcomponent  210  also includes second contact areas  217  on which second junction compound layers  250  are formed. As with the first junction compound layers  150 , the second junction compound layers  250  may be electrically isolated from or electrically coupled to the second conductive members  230 . Generally, the second junction compound layers  250  may be located on any contact area  217  which may contact another microcomponent or substrate including, in one embodiment, the inside surfaces of the openings  220  and on the electrodes  235 . 
   The second junction compound layers  250  may include indium, solder (e.g., a tin-based solder), alloys thereof or other conductive materials. The second junction compound layers  250  may be formed on the second contact areas  217  by blanket or selective deposition, chemical vapor-deposition (CVD), metal-organic CVD (MOCVD), physical vapor deposition (PVD), atomic layer deposition (ALD), spin-on coating, electroplating, sputtering, ionized metal plasma deposition (IMP) or other conventional or future-developed thin-film deposition processes. A mask, reticle or other patterning device may be employed to form the second junction compound layers  250  on the second contact areas  217 , such as to prevent overspray of the second junction compound layers  250  outside of the second contact areas  217 . Moreover, the second junction compound layers  250  may be similar in composition and fabrication to the first junction compound layers  150  formed on the first microcomponent  110 . 
   Referring to  FIG. 3 , illustrated is an elevation view of the first and second microcomponents  110 ,  210  in an intermediate stage of assembly according to aspects of the present disclosure. In the illustrated embodiment, the first and second microcomponents  110 ,  210  are positioned relative to each other and mated to preliminarily form a microassembly  310 . That is, the first microcomponent  110  is coupled to the second microcomponent  210  by inserting the barbed ends  125  of the connecting members  120  into the apertures  220  in the second microcomponent  210 . As such, a surface  270  of the second microcomponent  210  may be a retaining surface configured to engage the connecting members  120 . Those skilled in the art will recognize that the retaining surface  270  may be located elsewhere on the second microcomponent  210 , including within the openings  220 , such as in a tongue-and-groove arrangement. It should be understood that the connecting members  120  may be configured to form a permanent coupling with the apertures  220  in the substrate  215  of the second microcomponent  210 , or the connecting members  120  may be configured to form a temporary or removable coupling with the second microcomponent  210  (although such embodiments may require deactivation of the junction compound layers  150 ,  250 , the activation of which being described below). 
   In the embodiment shown in  FIG. 3 , the mating of the connecting members  120  of the first microcomponent  110  with the apertures  220  in the substrate  215  of the second microcomponent  210  causes the first and second conductive members  130 ,  230  to align and contact one another to form an electrical coupling. Accordingly, electrical signals may be communicated between the first and second microcomponents  110 ,  210  via the joined first and second conductive members  130 ,  230 . 
   As discussed above, the second conductive members  230  (and possibly the corresponding silicon layers  240 ) may be flexible, such that they bend away from the first microcomponent  110  when the first and second microcomponents  110 ,  210  are coupled. More specifically, as the connecting members  120  engage the apertures  220  in the substrate  215  of the second microcomponent  210 , the first electrodes  135  engage the second electrodes  235 , thereby exerting a force on the second electrodes  235  and causing the second electrodes  235  to flex away from a neutral position. Such an implementation may aid in maintaining a continuous electrical coupling between the first and second electrodes  135 ,  235 . That is, once the second electrodes  235  are flexed away from the first microcomponent  110 , they maintain a force against the first electrodes  135  by attempting to return to their neutral position. Consequently, an uninterrupted electrical connection may be more effectively maintained. 
   As the first and second microcomponents  110 ,  210  are mated, the engagement of the connecting members  120  with the apertures  220  in the substrate  215  of the second microcomponent  210  also brings the first junction compound layers  150  formed on the first contact areas  117  of the first microcomponent  110  into contact with the second junction compound layers  250  formed on the second contact areas  217  of the second microcomponent  210 , as shown in  FIG. 3 . In order to provide a more robust coupling of the first and second microcomponents  110 ,  210 , the junction compound layers  150 ,  250  may be activated, thereby adhering the two junction compound layers  150 ,  250  into a single coupling element. The activation of the junction compound layers  150 ,  250  may cause them to diffuse into each other to form a mechanical and/or chemical bond. For example,  FIG. 4  illustrates an elevation view of the microassembly  310  shown in  FIG. 3  after the junction compound layers  150 ,  250  have been activated, thereby forming activated junction compound layers  410 . 
   The first and second junction compound layers  150 ,  250  may be activated by myriad processes. In one embodiment, the junction compound layers  150 ,  250  may be activated by a heating process. For example, the microassembly  310  may be placed proximate a heat lamp, hot-plate or other heater or in an oven or other temperature-controlled process chamber, such that the junction compound layers  150 ,  250  may be at least partially liquefied. Thereafter, the microassembly  310  may be allowed to cool or may be quenched, such that the junction compound layers  150 ,  250  may solidify to form the junction compound layers  410 . In another embodiment, the microassembly  310  may undergo a solder reflow process, possibly one that may be performed to electrically couple other components in the microassembly  310 . Those skilled in the art are familiar with solder reflow processes, and will understand that many conventional or future-developed reflow processes may be employed to mechanically, electrically and/or chemically couple the first and second junction compound layers  150 ,  250 . In another embodiment, localized heating such as that achievable with a laser device may be employed to activate the first and second junction compound layers  150 ,  250 . A heated gripping or placing mechanism, or a gripping mechanism that includes a heater element, may also be employed during activation of the first and/or second junction compound layers  150 ,  250 , whereby activation may be at least partially performed by thermal energy transferred from the gripping mechanism to the junction compound layer(s). The first and second junction compound layers  150 ,  250  may also be activated by exposure to UV radiation or a chemical composition/catalyst. 
   The activation of the first junction compound layers  150  may also form a more robust coupling with the first contact areas  117 . Similarly, the activation process may provide more structural integrity between the second compound layers  250  and the second contact areas  217 . In view of this advantage, those skilled in the art will understand that some embodiments of the microassembly  310  may not incorporate the first or second junction compound layers  150 ,  250 . For example, the first junction compound layers  150  may be formed on the first microcomponent  110 , but the second junction compound layers  250  may be omitted from the assembly process. In such an embodiment, the activation of the first junction compound layers  150  may strengthen the bond of the first junction compound layers  150  to the first microcomponent  110  and may also form a bond with the second contact areas  217  of the second microcomponent  210 . Thus, employing both the first and second junction compound layers  150 ,  250  may not be necessary in all embodiments. Such an arrangement may decrease the time, costs and complexity of assembling the microassembly  310 . 
   Moreover, those skilled in the art will recognize that the first and second microcomponents  110 ,  210  may be coupled by the first and/or second junction compound layers  150 ,  250  in the absence of the mechanical coupling of the connecting members  120  and the apertures  220  in the substrate  215  of the second microcomponent  210 . In such an embodiment, the connecting members  120  may be modified for use as alignment aids, or may be omitted altogether. Again, such an arrangement may decrease the time, costs and complexity of assembling the microassembly (e.g., less complex pick-and-place operations), as well as the manufacture of the microcomponents  110 ,  210  themselves. In any case, the implementation of the junction compound layers  410  according to aspects of the present disclosure may provide a stronger ohmic contact between the first and second microcomponents  110 ,  210 , thereby reducing the resistance of the electrical coupling therebetween without requiring the use of excessive force to pick-and-place the microcomponents  110 ,  210  during assembly. 
   Although the first and second microcomponents  110 ,  220  shown in  FIGS. 1–3  each include eight electrical conductors  130 ,  230 , respectively, it should be understood that any number of such electrical conductors may be included in or on the microcomponents  110 ,  220  in various implementations, and that such implementations are intended to be within the scope of the present disclosure. 
   Referring to  FIG. 5 , illustrated is an elevation view of another embodiment of first and second microcomponents  510  prior to assembly according to aspects of the present disclosure. The microcomponents  510  may be or include nanocomponents, and may be substantially similar to the first microcomponent  110  shown in  FIG. 1 . For example, the microcomponents  510  each include a substrate  520 , first contact areas  530  and first conductive members  540 , and may each include first junction compound layers  550  formed on the first contact areas  530 . The substrates  520 , first contact areas  530 , first conductive members  540  and first junction compound layers  550  may be similar to the substrate  115 , first contact areas  117 , first conductive members  130  and first junction compound layers  150  shown in  FIG. 1 . For example, in one embodiment, as shown in  FIG. 5 , one or more of the first junction compound layers  550  may contact one or more of the first conductive members  540 , or be located very close to one of the first conductive members  540  such that activation of the first junction compound layers  550  may result in electrical contact between one or more of the first junction compound layers  550  and one or more of the first conductive members  540 . 
   The microcomponents  510  may also include first heating elements  560  each located proximate one or more of the first junction compound layers  550 . The first heating elements  560  may include circuitry  562  for receiving power signals from a power device in or on the first microcomponents  510  or other components (not shown). The first heating elements  560  may also include a resistor  564  or other electrical device configured to dissipate heat in response to power received via the circuitry  562 . In one embodiment, the resistor  564  may include one or more spans of aluminum, copper, doped silicon or other materials known in the art to dissipate heat under electrical power. The resistor  564  may have a conductivity of about 0.01 Ω-cm. 
   Referring to  FIG. 6 , illustrated is a plan view of an embodiment of a substrate element  610  prior to assembly according to aspects of the present disclosure. The substrate element  610  includes a support frame  620  (which may itself be a substrate), second contact areas  630  and second conductive members  640 . The substrate element  610  may also include second junction compound layers  650  formed on the second contact areas  630 . The second contact areas  630 , second conductive members  640  and second junction compound layers  650  may be similar to the second contact areas  217 , second conductive members  230  and second junction compound layers  250  shown in  FIG. 2 . In one embodiment, such as that illustrated in  FIG. 6 , one or more of the second junction compound layers  650  may be in electrical contact with one or more of the second conductive members  640 , or be located very close to one of the second conductive members  640  such that activation of the second junction compound layers  650  results in electrical contact between one or more of the second junction compound layers  650  and one or more of the second conductive members  640 . The substrate element  610  may also include one or more second heating elements  660  proximate one or more of the second junction compound layers  650 . The second heating elements  660  may be similar in composition and manufacture to the first heating elements  560 . 
   Referring to  FIG. 7 , illustrated is an elevation of a microassembly  710  formed by positioning and mating the first and second microcomponents  510  to the substrate element  610  and activation of the first and second junction compound layers  550 ,  650  to form junction compound layers  720 . Activation of the first and second junction compound layers  550 ,  650 , which may be similar to the activation of the first and second compound layers  150 ,  250  discussed above, provides additional mechanical coupling between the microcomponents  510  and the substrate element  610 . Activation of the first and second junction compound layers  550 ,  650  may also electrically couple the first and second conductive members  540 ,  640 , thereby providing a strong ohmic contact having sufficiently low resistance. 
   In one embodiment, the activation of the first and second junction compound layers  550 ,  650  may be performed by operating one or more of the heating elements  560 ,  660 . In such an embodiment, the heat dissipated by the heating elements  560 ,  660  may at least partially liquefy the first and second junction compound layers  550 ,  650 . After operating the heating elements  560 ,  660 , the resulting junction compound layers  720  may be allowed to cool or be quenched, thereby coupling the microcomponents  510  to the substrate element  610 . Those skilled in the art will recognize that one or more of the first heating elements  560  may be configured to dissipate sufficient heat to activate an immediately proximate first junction compound layer  550  as well as a more distal second junction compound layer  650  (and vice versa). Similarly, one or more of the first heating elements  560  may be configured to dissipate sufficient heat to activate more than the immediately proximate first junction compound layer  550 , including more distal ones of the first junction compound layers  550 . 
   Those skilled in the art will also recognize that, as discussed above, it is not necessary that each embodiment include both the first and second junction compound layers  550 ,  650 . That is, in some embodiments, forming only the first or second junction compound layers  550 ,  650 , or a combination thereof, may be sufficient to adequately couple the microcomponents  510  to the substrate element  610 . 
   In one embodiment, the microcomponents  510  may be positioned on and mated to the substrate element  610  prior to the activation of the first and second junction compound layers  550 ,  650 . In another embodiment, each of the microcomponents  510  may be positioned on and mated to the substrate element  610  and the corresponding junction compound layers  550 ,  650  may be activated prior to the positioning and mating of other microcomponents  510 . 
   The present invention has been described relative to a preferred embodiment. Improvements or modifications that become apparent to persons of ordinary skill in the art only after reading this disclosure are deemed within the spirit and scope of the application. It is understood that several modifications, changes and substitutions are intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.