Abstract:
In various embodiments, an assembly having a microstructure is provided, the device includes a cylindrical capture receptacle associated with a substrate, the capture receptacle comprising of a material having an expansion coefficient and comprising alignment structures having alignment projections extending inward from a periphery of the cylindrical capture receptacle. In one embodiment, the projections include a large width alignment projection and plurality of small width alignment projections. A plurality of medium width alignment projections also may be provided. A cylindrical key is associated with the microstructure and has a smaller circumference than the cylindrical capture receptacle and is comprised of a material having an expansion coefficient greater than the expansion coefficient of the cylindrical capture receptacle. The cylindrical key includes alignment receptacles spaced about a periphery of the cylindrical base to receive corresponding alignment projections. The alignment receptacles may include a large width alignment projection receptacle and a plurality of small alignment projection receptacles. A plurality of medium width alignment projection receptacles also may be provided.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is related to copending U.S. Application entitled ACTUATOR ENHANCED ALIGNMENT OF SELF-ASSEMBLED MICROSTRUCTURES, by Brewer et al., filed on a date even herewith, herein incorporated by reference in its entirety. 
     BACKGROUND 
     In wafer scale integrated circuits, separate component chips may be individually integrated with a host wafer using any of several established methods for chip level integration. 
     The alignment accuracy is a critical parameter in determining the utility of this technology. The accuracy of alignment directly impacts the integration densities, interconnect line widths and pitches, and the ability to fabricate 3D stacks of chips. Furthermore, in cooperative radiating or detecting systems, alignment is critical to the functionality of the system. 
     To insure proper placement and registration of the microstructures, the microstructures are formed as geometric blocks and recesses are etched from the wafer to provide receptacle sites with geometric profiles that are complementary to the profiles of the blocks. One example is shown in U.S. Pat. No. 5,545,291, by Smith et al., entitled METHOD FOR FABRICATING SELF-ASSEMBLING MICROSTRUCTURES, herein incorporated by reference in its entirety. Fluidic self-assembly may be used to integrate the individual device microstructures into receptacle sites on host electronic circuits using a liquid medium for transport. Placement and registration of the device microstructures into receptacles on a substrate carrying electronic microcircuits is controlled by shape recognition or by selective chemical adhesion or both. 
     Other examples of microstructure placement techniques and structures include U.S. Pat. No. 7,223,635 by Brewer, entitled ORIENTED SELF-LOCATION OF MICROSTRUCTURES WITH ALIGNMENT STRUCTURES; and U.S. Pat. No. 7,018,575, by Brewer et al., entitled METHOD FOR ASSEMBLY OF COMPLEMENTARY—SHAPED RECEPTACLE SITE AND DEVICE MICROSTRUCTURES; both herein incorporated by reference in their entireties. Further examples may be found in U.S. Pat. Nos. 6,946,322 and 5,783,856, herein incorporated by reference. 
     SUMMARY 
     In various embodiments, a device having a microstructure is provided, the device includes a capture receptacle associated with a substrate, the capture receptacle comprising of a material having an expansion coefficient and comprising alignment structures having alignment projections extending inward from a periphery of the capture receptacle. In one embodiment, the projections include a large width alignment projection and a plurality of small width alignment projections. A plurality of medium width alignment projections also may be provided in some embodiments. A key is associated with the microstructure and has a smaller circumference than the capture receptacle and is comprised of a material having an expansion coefficient greater than the expansion coefficient of the capture receptacle. The cylindrical key includes alignment receptacles spaced about a periphery of the cylindrical base to receive corresponding alignment projections. The alignment receptacles may include a large width alignment projection receptacle and a plurality of small alignment projection receptacles. A plurality of medium width alignment projection receptacles also may be provided in some embodiments. 
     In various embodiments, a device having a microstructure is provided, which includes a capture receptacle associated with a substrate and having alignment structures comprising groups of tabs extending inward from a periphery of the capture receptacle. The groups of tabs include a large width tab, two adjacent medium width tabs, and three adjacent small width tabs. The a key is associated with the microstructure and has a smaller circumference than the capture receptacle. The key includes alignment receptacles spaced in groups about a periphery of the base. The groups of alignment receptacles include a large width tab receptacle, two adjacent medium width tab receptacles; and three adjacent small width tab receptacles. 
     In various embodiments, a microstructure alignment system is provided, which includes a capture receptacle having spaced tabs extending inward from a periphery of the capture receptacle, a key sized to fit within the capture receptacle and comprising tab receptacles spaced about a periphery of the key. The generally cylindrical key has a material having a thermal expansion coefficient greater than a coefficient of expansion of the capture receptacle and is constructed such that expansion of the key material causes the tab receptacles to contact the spaced tabs so as to align the key within the capture receptacle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present invention will be better understood with regard to the following description, appended claims, and accompanying drawings where: 
         FIG. 1  is a simplified illustration showing a top view of an improved capture and alignment receptacle. 
         FIG. 2  is a simplified illustration showing a cross sectional side view of the receptacle along the 2-2 line of  FIG. 1 . 
         FIG. 3  is a simplified illustration showing a cross sectional top view of a key constructed to mate with the receptacle of  FIG. 1 . 
         FIG. 4  is a simplified illustration showing a cross sectional top view of a microstructure alignment system with the key in the receptacle. 
         FIG. 5  is a simplified illustration showing the key aligned within the receptacle. 
         FIG. 6  shows a cross sectional view along the 6-6 line of  FIG. 5  illustrating one possible embodiment of a microstructure assembly. 
     
    
    
     DESCRIPTION 
     Self-assembly methods can potentially dramatically lower the costs of electronically steered antennas, mm-wave imaging systems, and MMIC technology. In areas such as phased array antennas, CMOS, low cost MMIC technology, and millimeter wave imaging, the alignment accuracy of components that are assembled using self-assembly or other techniques such as automated placement, can be critically important. The alignment accuracy is a critical parameter in determining the utility of this technology since it sets the design rules for the integration process. The accuracy of alignment directly impacts the integration densities, interconnect line widths and pitches, and the ability to fabricate 3D stacks of chips. 
     Precise registration and alignment of a self-assembly structure is difficult to obtain with current systems. Prior U.S. Pat. Nos. 6,946,322, 5,545,291, 5,783,856, and 5,904,545, herein incorporated by reference, describe methods for fabricating self-assembling microstructures. The self-assembling microstructures are material blocks, or device and IC components that are either geometrically shaped or have external alignment keys for assembly and positioning. 
     In the case of the shaped blocks, these fit into recessed regions of a substrate and become integral with the substrate. The fabrication of the geometrically shaped microstructure utilizes crystallogaphically selective wet-chemical etching to tailor the sidewall profile of the microstructures. It has been realized by the present inventor that this approach has a number of disadvantages including: limited selection of sidewall profiles (difficult to implement for extremely thin device microstructures), poor orientation capability—limited selection of geometric shapes (IC or device design are typically to squares or rectangles), poor use of device and circuit area due to shaping of microstructure, limited applicability to materials that are difficult to etch (Al 2 O 3 , SiC, GaN, etc.), and poor compatibility of etch chemistry to shape the microstructure with fabricated devices and circuits on the microstructure. 
     In the case of the components with external alignment keys, the alignment accuracy is limited by the mechanical tolerance between the key and the complimentary shaped receptacle. There is a tradeoff between the optimum assembly throughput and the precision of the alignment. Typically, to achieve the highest assembly throughput the mechanical fit must be loose. 
     Some implementations provide a means for improving the alignment accuracy of self-assembled keyed device or integrated circuit components or other high throughput assembly means (i.e. pick and place). In various implementations and embodiments, improved alignment is to be achieved without compromising the assembly throughput or initial orienting process. Various implementations and embodiments may be utilized to improve assembly and transfer of integrated devices or integrated circuit components on a host circuit, as well as the processes for keying the components and making the complementary receptacle arrays. 
     To facilitate manufacturing, it is desirable to achieve precise alignment without compromising the assembly throughput, and preferably without significantly changing the orientation process. One way to achieve this is to improve the alignment mechanism of the self-assembled device or IC microstructures with their complementary shaped host receptacles. The improved microstructures ultimately will be transferred and integrated into host circuits. 
     As described in further detail below, various implementations and embodiments employ components that have alignment key structures and receptacles that are complementary shaped. In one embodiment of the invention, the thermal expansion difference between the key structure and the receptacle is used to gain an advantage in the mechanical tolerance between the key and receptacle by heating. This solves a long-standing problem of how to quickly assemble loosely fitting parts and achieve very high levels of alignment accuracy. 
     FIGS.  1 - 6   
       FIG. 1  is a simplified illustration showing a top view of an improved capture and alignment receptacle  105 , typically formed in a substrate (not shown). As used herein, the term substrate refers to any material in which one or more capture receptacles  105  may be formed. Thus, it may be a base material, i.e. a wafer or the like, or, it may be one or more layers on a base material or carrier (not shown). 
     In the embodiment of  FIG. 1 , the receptacle  105  is a cylindrical cavity with large, medium, and small alignment projections  110 ,  120 , and  130 , respectively, extending inwardly. Projection  110  is a single tab-like projection  110  with a large width  110   w  relative to the other projections  120  and  130 . Two tab-like projections  120  have a medium width  120  was compared to the other projections  110  and  130 . Three tab-like projections  130  have a small width  130  was compared to the other projections  110  and  120 . 
     The projections  110 ,  120 , and  130  are spaced about the periphery of the receptacle  105  and are grouped by corresponding width, i.e. large, medium, and small. The two medium width  120   w  projections  120  are located adjacent to each other, and the three small width  130   w  projections  130  are located adjacent to each other. 
     Referring to  FIG. 1 , in various embodiments, the sum of widths  130   w  of two adjacent projections of the small width projections  130  and a separation distance between the two adjacent projections of the small width projections  130  is greater than a width  120   w  of one of the medium width projections  120 . Furthermore, in various embodiments, the sum of the widths  120   w  of the two medium width projections  120  and a separation distance between the two medium width projections  120  is greater than a width  110   w  of the large alignment projection  110 . In various embodiments, the sum of the widths  130   w  of the three small width projections  130  and a separation distance between the three small width projections  130  is greater than a width  110   w  of the large width projection  110 . Also, in various embodiments, the sum of widths  130   w  of two adjacent projections of the three small width projections  130  and a separation distance between the two adjacent projections of the three small width projections  130  is greater than a width  120   w  of one of the medium width projections  120 . 
       FIG. 2  is a simplified illustration showing a cross sectional side view of the receptacle  105  along the 2-2 line of  FIG. 1 . In this embodiment, the large width projection  110 , the medium width projections  120 , and the small width projections  130  all have the same height,  110   h ,  120   h , and  130   h , respectively. 
       FIG. 3  is a simplified illustration showing a cross sectional top view of a key  155  constructed to mate with the receptacle  105  of  FIG. 1 . The key  155  is generally cylindrical with large, medium, and small width alignment projection receptacles  190 ,  180 , and  170 , respectively. The large, medium, and small width alignment projection receptacles  190 ,  180 , and  170  are longitudinal channels or grooves in the key  155 , located about a periphery of the key  155 . Projection receptacle  190  has a large width  190   w  relative to the other projection receptacles  180  and  170 . The two projection receptacles  180  have a medium width  180   w  as compared to the other projections  190  and  170 . Three projection receptacles  170  have a small width  170  was compared to the other projection receptacles  190  and  180 . 
     The projection receptacles  190 ,  180 , and  170  are spaced about the periphery of the key  155  and are grouped by corresponding width, i.e. large, medium, and small, to correspond with the projections  110 ,  120 , and  130  of the receptacle  105  (of  FIG. 1 ). 
     Referring to  FIG. 3 , in some embodiments, the sum of the widths  180   w  of the two adjacent medium width tab receptacles  180  and a separation distance between the two medium width tab receptacles  180  is greater than a width  190   w  of the large width tab receptacle  190 . Similarly, in some embodiments, the sum of the widths  170   w  of the three adjacent small width tab receptacles  170  and a separation distance between the three adjacent small width tab receptacles  170  is greater than a width  190   w  of the large width tab receptacle  190 . Also, in some embodiments, the sum of widths  170   w  of two adjacent tab receptacles of the three small width tab receptacles  170  and a separation distance between the two adjacent tab receptacles of the three small width tab receptacles  170  is greater than a width  180   w  of one of the medium width tab receptacles  180 . 
     Photolithographic methods may be used to fabricate alignment key structures on circuit and device-sized components for shape matching self-assembly. These “keyed” components may be designed to match corresponding receptacle  105  sites on a patterned assembly template (not shown). The alignment key enables close positioning and orientation of arrays of microstructures without shaping the microstructures themselves. The key  155  structures may be designed for 100 micron sized devices (not shown). 
     In one method for fabricating the alignment key  155  structure on small device structures, a photoresist process is used. The key  155  fabrication uses a single-step process in which thick SU-8 (a negative photo-epoxy resist) is applied and exposed to pattern the shape of the key  155 . After exposure, the SU-8 film is developed, the resulting structure undergoes a final hard-bake process to form the key  155  on the device (not shown). 
       FIG. 4  is a simplified illustration showing a cross sectional top view of a microstructure alignment system  100  with the key  155  in the receptacle  105 . The circular cross section of the receptacle  105  allows easy capture of the key  155 . Orientation of the key  155  is accomplished by engaging the projections  110 ,  120  and  130 . The key  155  is captured by the receptacle  105  and oriented until it engages the alignment projections  110 ,  120 , and  130 . The mating of the projections  110 ,  120 , and  130 , with the corresponding projection receptacles  190 ,  180 , and  170  fix the orientation of the key, along with any associated device. The projection receptacles  190 ,  180 , and  170  (and projections  110 ,  120 , and  130 ) are sized and spaced so that the key  155  can not align using the wrong projections  110 ,  120 , or  130 . 
     To engage, the key  155  drops into the receptacle  105  and is oriented until the projections  110 ,  120 , and  130  engage the projection receptacles  190 ,  180 , and  170 . This may be done by causing the key to rotate, such as by vibrating of the system, or by fluid motion. 
       FIG. 5  is a simplified illustration showing the key  155  aligned within the receptacle  105 . When the key  155  swells within the receptacle  105 , it creates a tighter fit, which improves precision. In some implementations, a final alignment is achieved by heating the keyed component (not shown) that is oriented in the receptacle  105 . The large difference between the thermal expansion coefficients of the SU-8 (112×10 −6 ° C. −1 ) key  155  and the silicon (2.6×10 −6 ° C. −1 ) receptacle material forms the basis of the enhanced alignment of the positioned components in the receptacles. This difference in the thermal expansion of a factor of approximately 40 allows large dimensional changes to be induced during moderate heating (150° C.). For example, a 1 millimeter key will undergo approximately a 16.8 micron expansion in diameter during a 150 degree Celsius heating, whereas the silicon receptacle will decrease in cross section diameter by approximately 0.4 microns. These dimensional changes are enhancing the alignment of a keyed component (not shown), which is captured and oriented in a receptacle  105 , to the receptacle  105  itself. 
     In some embodiments, the heating process may be carried out solely for alignment, or as part of a solder process so that the component (not shown) is simultaneously aligned, secured, and electrically connected to a substrate (not shown). 
     There are a number of possible mechanisms that can induce changes between the shape of a key  105  and a receptacle  155 . These include but are not limited to the following: thermal expansion differences between the key and the receptacle materials, swelling of the key structure by solvent uptake, solvent state change, piezoelectric, piezomagnetic, shape memory alloy or polymer expansion, etc. Thus, the key  155  and/or receptacle  105  may comprise, or employ, various materials that expand, to take up the space between the key receptacles  170 ,  180 , and  190 , and the receptacle projections  130 ,  120 , and  110 . After alignment, the key  155 , or attached device  150 , may be bonded, or otherwise secured, in place. 
     Various embodiments are able to provide more accurate final alignment because the projection receptacles  190 ,  180 ,  170  are located at a periphery of the key  155 . Thus, the projections  110 ,  120 , and  130  contact the key  155  at a periphery of the key  155 , shown in  FIG. 5 . This type of alignment mechanism allows the expansion of the key  155  to expand uninterrupted across the central span  105   e   1  or  105   e   2  of the key  155 , rather than having intermediate contact points to subsections within the central region. The number of gaps between the key  155  and the receptacle  105  is two, one on either side of the span  105   e   1  or  105   e   2 , which increases the expansion length. Because the coefficient of expansion times the span length provides the expansion, locating the contact points  110   t ,  120   t , and  130   t  at a periphery maximizes this effect, improving precision. 
     As illustrated in  FIG. 6 , using the different width alignment projections, i.e. large, medium, and small, after capture by the receptacle  105 , inhibits skewing and/or wedging of the key  155  within the receptacle  105  so that it does not seat cockeyed within the receptacle  105 , and allows proper seating of the device  150 . In some embodiments, engagement of the projections  110 ,  120 , and  130  with the corresponding projection receptacles  190 ,  180 , and  170  provides alignment within 5 microns of final alignment. 
     The summation of the expansion of the key  155  across the central span  105   e   1  or  105   e   2 , facilitated by locating the contact points  110   t ,  120   t , and  130   t  at the periphery of the key  155 , further enhances and allows greater precision alignment than is otherwise achievable with conventional alignment means. Thus, in some embodiments, alignments of below 1 micron are achievable. 
     In some embodiments (not shown) it is possible to have key material expand around a protruding “receptacle” projection. 
       FIG. 6  shows a cross sectional view along the 6-6 line of  FIG. 5  illustrating one possible embodiment of a microstructure assembly. The key  155  is associated with a microstructure device  150 , which is seated on a substrate  101 . As used herein, the term substrate  101  refers to any material in which one or more capture receptacles  105  may be formed. Thus, a substrate as used herein, may be a base material, i.e. a wafer or the like, or, it may be one or more layers on a base material or carrier. In some embodiments, a microstructure assembly may include many devices  150 , which may be aligned within respect to each other within an array. 
     The example embodiments herein are not intended to be limiting, various configurations and combinations of features are possible. Having described this invention in connection with a number of embodiments, modification will now certainly suggest itself to those skilled in the art. As such, the invention is not limited to the disclosed embodiments, except as required by the appended claims.