Patent Publication Number: US-11652082-B2

Title: Particle capture using transfer stamp

Description:
PRIORITY APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/883,007, filed on Aug. 5, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to transfer printing and stamps used in transfer printing, for example micro-transfer printing. 
     BACKGROUND 
     The disclosed technology relates generally to methods and tools for transfer printing. Conventional methods such as pick-and-place for applying integrated circuits to a destination (target) substrate are limited to relatively large components, for example having a dimension of a millimeter or more, and it can be very difficult to pick up and place ultra-thin, fragile, or small components using such conventional technologies. More recently, micro-transfer printing methods have been developed that permit the selection and application of such ultra-thin, fragile, or small components to a target substrate without causing damage to the components themselves. 
     Micro-transfer printing enables deterministically removing arrays of micro-scale, high-performance components from a native source wafer, typically a semiconductor wafer on which the components are constructed, and assembling and integrating the components onto non-native target substrates. In some embodiments, micro-transfer printing processes use engineered elastomer stamps coupled with high-precision motion-controlled print-heads to selectively pick up and print large arrays of micro-scale components from a source native wafer onto non-native destination substrates. In some embodiments, tethers are used to maintain position and alignment of components on a source wafer prior to the pick-up phase of a print operation and are broken or separated during the pick-up phase. In some embodiments, adhesion between an elastomer transfer device and a printable component can be selectively tuned by varying the speed of a print-head. 
     Micro-structured stamps may be used to pick up micro components from a source substrate, transport the micro components to their destination (e.g., a destination substrate), and print the micro components onto a destination substrate. The transfer device (e.g., a micro-structured stamp) can be created using various materials. Individual posts on a transfer device can pick up corresponding individual components and then print the corresponding components to their destination. Posts can be structured in an array fashion and can have a range of heights depending on the size of the printable material. For effective, high-yield printing, when picking up components, it is desirable to use a stamp having stamp posts that are engineered to be in close contact with the components (e.g., micro integrated circuits) being printed. High-yield printing includes low percentages of missing or misplaced components. Some print operations do result in a certain, albeit low, percentage of misplaced or missing components. 
     There is a need, therefore, for stamps and methods of printing that further improve high-yields of printing components such as semiconductor circuits and devices. 
     SUMMARY 
     While micro-transfer printing using an elastomeric stamp typically has a high yield, there are also commonly a small number of misprinted components. Components can be misprinted because they are misplaced, misaligned, misconnected (e.g., electrically), or totally missing (e.g., dropped during transfer or never properly picked up). Misprinted components can occur in embodiments where tethers are used to maintain position and alignment of components on a source wafer and subsequently broken or separated during pick up by a transfer device. It is desirable to improve the high yields of micro-transfer printing, including when tethers are used, in order to reduce or eliminate the number of repair print operations that are needed to replace or otherwise fix misprinted components. 
     The present disclosure includes the recognition that, in some embodiments where tethers are used, particles formed from breaking or separating tethers can interfere with proper pick up and/or printing of components. Such particles can become airborne after formation and interfere with, for example, subsequent print operations using the same source wafer. For example, particles can become deposited on contact surfaces of adjacent (or nearby) components such that adherence of stamp posts during a subsequent print operation is impaired. As another example, particle(s) can become deposited on a component such that electrical connection between the component and a destination substrate or intermediate substrate is impaired after or during printing. In yet another example, particle(s) can become deposited on the picked-up component, interfering with printing the component. 
     A solution that can be used in some embodiments is to use a stamp with oversized posts (relative to components being printed) such that each post overhangs and extends beyond its corresponding component during pick up in a direction substantially parallel to a surface of the source wafer. Such posts can more readily capture particles formed during breaking or separating tethers during component pick up. Elastomer stamp posts are well suited to capturing such particles because the particles will generally readily adhere thereto and particle capture can occur while print operations proceed as normal. In some embodiments, posts that are oversized specifically over a pre-determined tether location can be used. Posts can be cleaned between print operations to remove adhered particles and thereby be prepared for subsequent prints. Embodiments of the present disclosure provide systems, methods, and devices for reducing or capturing transfer printing (e.g., micro-transfer printing) particulate contamination, thereby increasing the transfer printing yield. 
     In certain embodiments of the present disclosure, a micro-transfer printing system comprises a source substrate having a substrate surface, components disposed in an array on, over, or in the substrate surface, each component having a component extent in a plane parallel to the substrate surface, a stamp comprising a stamp body and stamp posts extending away from the stamp body and disposed in an array over the stamp body, each of the stamp posts having (i) a post location corresponding to a component location of one of the components when the stamp is disposed in alignment with the source substrate, and (ii) a post surface extent on a distal end of the stamp post, wherein the post surface extent is greater than the component extent. The post surface extent can be greater than or equal to 105% (e.g., greater than or equal to 110%, greater than or equal to 120%, greater than or equal to 150%, or greater than or equal to 200%) of the component extent. 
     In some embodiments, each of the components is spaced apart from each nearest-neighbor component by at least a component separation distance and each of the stamp posts is spaced apart from each nearest-neighbor stamp post by at most a post separation distance, and the post separation distance is less than the component separation distance. 
     Some embodiments of a micro-transfer printing system comprise sacrificial portions disposed in an array over the source substrate and (i) each of the components is disposed completely over a different corresponding sacrificial portion of the sacrificial portions and (ii) each different corresponding sacrificial portion has a sacrificial portion extent (e.g., an area) greater than the component extent. The post surface extent can be less than the sacrificial portion extent. 
     In some embodiments of the present disclosure, each of the stamp posts extends at least one quarter of a distance (e.g., at least half of the distance or at least three quarters of the distance) from each component edge of one of the components to a corresponding sacrificial portion edge of the different corresponding sacrificial portions. The post surface extent can be less than or equal to 90% (e.g., less than or equal to 80%, less than or equal to 70%, less than or equal to 60%, less than or equal to 50%, less than or equal to 40%, less than or equal to 30%, or less than or equal to 20%) of the sacrificial portion extent. The post surface extent can be greater than or equal to the sacrificial portion extent or the post surface extent can cover the sacrificial portion extent. 
     According to some embodiments of the present disclosure, any one or all of (i) the sacrificial portions are laterally separated by anchors, (ii) each component in the array of components is physically connected to one of the anchors with a tether, and (iii) each of the stamp posts extends over at least a portion of the tether physically connecting the one of the components to the one of the anchors. In some embodiments, the sacrificial portions are laterally separated by anchors and each of the stamp posts extends laterally at least partially over a corresponding anchor of the anchors when the stamp is disposed in alignment with the source substrate. 
     In some embodiments, each of the stamp posts comprises a lateral post protrusion. The lateral post protrusion can extend at least partially over the corresponding tether or can extend at least partially over the corresponding anchor when the stamp is disposed in alignment with the source substrate, or both. According to some embodiments of the present disclosure, each of the components is physically connected to a tether and the lateral post protrusion is sized and shaped to extend laterally over at least a portion of or all of the tether. The lateral post protrusion can have a length-to-width aspect ratio of at least 0.5 (e.g., at least 1.0, 1.5 or 2.0). 
     In some embodiments, each of the stamp posts comprises a step. The step can extend laterally beyond each edge of the distal end of the stamp post. In some embodiments, each of the stamp posts comprises a step and the step comprises a lateral post protrusion. 
     According to some embodiments of the present disclosure, a method of micro-transfer printing comprises: providing a source substrate comprising sacrificial portions disposed in an array over the source substrate, the sacrificial portions laterally separated by anchors; providing a component disposed directly on or over each of the sacrificial portions and physically connected to an anchor with a tether, each component having a component extent and spaced apart from a neighboring component by a component separation distance; providing a stamp comprising a stamp body and stamp posts extending away from the stamp body and disposed in an array over the stamp body, each of the stamp posts having a post surface extent on a distal end of the stamp post, wherein the post surface extent is greater than the component extent; positioning the stamp to locate each stamp post in alignment with a corresponding component and pressing each of the stamp posts against the corresponding component to adhere the corresponding component to the stamp post; and removing the stamp from the source substrate, thereby fracturing the tether physically connecting the corresponding component and making particles (e.g., discrete grains) that subsequently adhere to the stamp. According to some embodiments, the method comprises: providing a destination substrate; transferring the stamp and adhered components to the destination substrate; pressing the components to the destination substrate with the stamp, to adhere the components to the destination substrate; and removing the stamp. The stamp can be cleaned to remove the particles from the stamp after removing the stamp. In some methods, at least a portion of the particles adhere to the distal end of the stamp post (e.g., on a post surface that contacts the corresponding component at the distal end of the stamp post, for example on a portion of the distal end that overhangs or extends beyond the picked-up component). The stamp post can comprise a step and at least a portion of the particles adhere to the step. 
     According to some methods, the stamp post comprises a lateral protrusion and positioning the stamp comprises positioning the lateral protrusion over one of the at least one tether, wherein at least a portion of the particles adhere to the lateral protrusion. 
     According to some embodiments of the present disclosure, a method of transfer printing a component comprises providing a stamp comprising a stamp post, the stamp post having a post surface extent on a distal end of the stamp post; providing a component disposed on a source substrate, wherein the component is physically connected to the source substrate by at least one tether and the component has a component extent that is smaller than the post surface extent; and removing the component from the source substrate, wherein removing the component comprises contacting the component to the stamp post and breaking (e.g., fracturing) or separating the at least one tether thereby causing particles (e.g., discrete grains) to form, and wherein at least a portion of the particles adhere to the stamp post while the stamp post is in contact with the component. At least a portion of the particles can adhere to the distal end of the stamp post while the stamp post is in contact with the component (e.g., on a post surface that contacts the corresponding component at the distal end of the stamp post, for example on a portion of the distal end that overhangs or extends beyond the picked-up component). 
     According to some embodiments, the stamp post comprises a step and at least a portion of the particles adhere to the step while the stamp post is in contact with the component. The stamp post can comprise a lateral post protrusion and the method can comprise positioning the lateral post protrusion over one of the at least one tether, wherein at least a portion of the particles adhere to the lateral protrusion while the stamp post is in contact with the component. 
     According to some embodiments, a method comprises: transferring the component from the source substrate to a destination substrate; pressing the component to the destination substrate; and separating the stamp from the component, wherein at least a portion of the particles are made airborne as a result of the separation and subsequently adhere to the stamp post. The method can comprise cleaning the stamp to remove the at least a portion of the particles from the stamp after removing the stamp. 
     In some embodiments, a sacrificial portion is disposed between the component and the source substrate and the method comprises etching the sacrificial portion so that the component is suspended over the source substrate by the at least one tether, each of the at least one tether being connected to an anchor adjacent to the sacrificial portion. 
     According to some embodiments of the present disclosure, a stamp for micro-transfer printing comprises a stamp body and stamp posts extending away from the stamp body disposed in an array over the stamp body, wherein each of the stamp posts comprises a lateral post protrusion, a step, or both a lateral post protrusion and a step. The step can extend laterally beyond each edge of the distal end of the stamp post. The lateral post protrusion can have a length-to-width aspect ratio of at least 0.5 (e.g., at least 1.0, 1.5 or 2.0). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, aspects, features, and advantages of the present disclosure will become more apparent and better understood by referring to the following description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1 A  is a cross section of a micro-transfer printing system having stamp areas and sacrificial areas of the same size according to illustrative embodiments of the present disclosure; 
         FIG.  1 B  is a plan view corresponding to the micro-transfer printing system of  FIG.  1 A  and illustrating cross-section line A along which  FIG.  1 A  is illustrated; 
         FIG.  1 C  is a plan view of a system having stamp areas and sacrificial areas of different sizes according to illustrative embodiments of the present disclosure; 
         FIG.  2 A  is a cross section of a component structure according to illustrative embodiments of the present disclosure; 
         FIG.  2 B  is a plan view corresponding to the component structure of  FIG.  2 A  and illustrating cross-section line A along which  FIG.  2 A  is illustrated; 
         FIG.  3 A  is a plan view of a stamp according to illustrative embodiments of the present disclosure; 
         FIG.  3 B  is a perspective of a stamp corresponding to  FIG.  3 A  according to illustrative embodiments of the present disclosure; 
         FIGS.  3 C- 3 E  are plan views of stamps with a stamp post protrusion over a component structure according to illustrative embodiments of the present disclosure; 
         FIG.  4 A  is a cross section of a stamp with a step according to illustrative embodiments of the present disclosure; 
         FIG.  4 B  is a bottom view of the stamp with the step of  FIG.  4 A  according to illustrative embodiments of the present disclosure; 
         FIG.  5    is a perspective of a stamp with a stamp post step and a stamp post protrusion according to illustrative embodiments of the present disclosure; 
         FIG.  6    is a flow diagram illustrating methods in accordance with embodiments of the present disclosure; 
         FIG.  7    is a cross section of a stamp, component, and source substrate with fractured tethers and contaminating particles useful in understanding embodiments of the present disclosure; 
         FIG.  8    is a cross section of a stamp, component, and source substrate with fractured tethers and captured particles according to illustrative embodiments of the present disclosure; 
         FIG.  9 A- 9 C  are sequential cross sections of a stamp, component, and destination substrate with fractured tethers and captured particles according to illustrative embodiments of the present disclosure; and 
         FIGS.  10 A- 10 C  are sequential cross sections of a cleaning surface and stamp with captured particles according to illustrative embodiments of the present disclosure. 
     
    
    
     Features and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, or structurally similar elements. The figures are not necessarily drawn to scale since the variation in size of various elements in the Figures is too great to permit depiction to scale. 
     DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS 
     The present disclosure provides structures and methods that enable, inter alia, transfer printing of components from a source substrate to a target substrate with improved transfer yields (and reduced transfer failures) providing a more robust manufacturing process with improved product yield (e.g., reducing or eliminating the need for repair print operation). Transfer printing can be micro-transfer printing, components can be micro-components, for example having at least one of a length or width less than or equal to 200 microns, and a source substrate can be a native component source wafer, such as a semiconductor wafer, having an extensive surface, for example having a dimension (for example a diameter) greater than or equal to 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 40 cm, or even larger. Target substrates can be any destination substrate, such as a display substrate, and can comprise any useful substrate material, such as glass, ceramic, metal, or polymer. A target substrate can be an intermediate substrate, for example used as part of a compound micro assembly process. Components can be formed on a source substrate, contacted by a stamp to pick up and remove them from the source substrate and adhere them to the stamp, and pressed against a target substrate to adhere the components to a target substrate. The stamp is then moved away from the target substrate, leaving the components on the target substrate. The pickup-and-print process (print operation) can be repeated (e.g., many times) with the stamp to transfer different components on the source substrate to the target substrate. 
     Referring to  FIGS.  1 A and  7   , in some embodiments of transfer printing according to the present disclosure, components  20  are released from a source substrate  10  by undercutting components  20 , for example by etching a sacrificial portion  12  of source substrate  10  on or over which components  20  are formed or otherwise disposed to form a space (e.g., a gap  12 ), such that components  20  are attached by a tether  14  to an anchor  16  of source substrate  10 . (One or more tethers  14  can be used, for example in combination with one or more anchors  16 .) Sacrificial portions  12  disposed in an array over source substrate  10  can be disposed in, on, or over source substrate  10  and, moreover, such sacrificial portions  12  can be designated portions of the source substrate  10  itself (e.g., an anisotropically etchable source substrate  10 ). 
     When components  20  are removed from source substrate  10  by a stamp  30 , tethers  14  attaching each component  20  to an anchor  16  are broken (e.g., fractured) or separated from anchor  16 , forming fractured or separated tethers  14 A (shown in  FIG.  7   ). According to some embodiments, the process of breaking (e.g., fracturing) tethers  14  or separating tethers  14  from anchors  16  can create particles  18  that contaminate stamp  30 , components  20 , source substrate  10 , or a target substrate (not shown in  FIGS.  1 A and  7   ). The particle contamination can inhibit picking up components  20  from source substrate  10  or inhibit printing picked-up components  20  on stamp  30  to the target substrate. For example, particle contamination can cause misplacement, misalignment, or misconnection (e.g., electrical misconnection). Particle contamination can also inhibit the subsequent transfer of components  20  from source substrate  10  to a target substrate, thereby causing transfer failures and reducing transfer yields for transfer-printing operations. 
     According to some embodiments of the present disclosure and as illustrated in  FIG.  8   , transfer yields can be improved by capturing at least some particles  18  with an enlarged stamp  30  with a greater extent (e.g., area) over substrate surface  11  of source substrate  10 . Such a greater extent can cause contaminating particles  18  to adhere to enlarged portions of stamp  30  (thereby becoming captured particles  19 ). After one or more print operations with stamp  30 , stamp  30  can be cleaned to remove captured particles  19  from stamp  30 . Thus, in some embodiments, captured particles  19  may be allowed to be build up near a periphery of a contact surface of posts  34  to reduce time spent cleaning stamp  30  while still improving printing yields through particle capture  19 . 
     Therefore, according to some illustrative embodiments of the present disclosure and referring again to the cross section of  FIG.  1 A  and the corresponding plan views of  FIGS.  1 B and  1 C , a micro-transfer printing system  99  comprises a source substrate  10  having a substrate surface  11  and components  20  disposed in an array on, over, or in the substrate surface  11  of source substrate  10 . Each component  20  has a component extent (e.g., area) in a plane parallel to substrate surface  11 , for example a component length  20 L of component  20  times a component width  20 W of component  20  (shown in  FIGS.  1 B and  1 C ). The component extent (e.g., area) can include all of the elements or components of component  20  (e.g., semiconductor materials, metal layers, electrical conductors, optical conductors, vias, contact pads, and dielectric structures) but does not include tether  14  or anchor  16 . 
     An example of a stamp  30  comprises a stamp body  32  and stamp posts  34  extending away from stamp body  32  disposed in an array over stamp body  32 . Stamp body  32  can comprise the same material as stamp post  34  and can be made in a common molding step. During a print operation, each stamp post  34  has a post location corresponding to and aligned with a component location of a component  20  on source substrate  10  so that stamp posts  34  can each contact a component  20  when stamp  30  is moved towards source substrate  10 . A post surface of a distal post end  34 D of each stamp post  34  has a post surface extent (e.g., area). The post surface extent of stamp post  34  can be over and substantially parallel to substrate surface  11  of source substrate  10 . As shown in  FIGS.  1 B and  1 C , the post surface extent can be a post length  34 L of stamp post  34  times a post width  34 W of stamp post  34 , for example if the post surface is a flat rectangular surface. Distal post end  34 D of stamp post  34  is opposite and remote from a proximal post end  34 P of stamp post  34  and proximal post end  34 P is in contact with or adjacent to stamp body  32 . Note that, as used herein, post length  34 L is not the distance between the proximal post end  34 P and distal post end  34 D (e.g., a height of stamp post  34 ). 
     Components  20  are separated in a horizontal direction DH by horizontal component separation distance  20 H and separated in a vertical direction DV orthogonal to horizontal direction DH by vertical component separation distance  20 V. Similarly, stamp posts  34  are separated in horizontal direction DH by horizontal post separation distance  34 H and separated in vertical direction DV orthogonal to horizontal direction DH by vertical post separation distance  34 V. Either or both of horizontal and vertical component separation distance  20 H,  20 V are a component separation distance and can be the smallest separation distance between adjacent components  20 . Adjacent components  20  are nearest-neighbor (e.g., adjoining or adjacent) components  20  between which there are no other components  20  in a corresponding direction (e.g., a horizontal or vertical direction). Likewise, either or both of horizontal and vertical post separation distance  34 H,  34 V are a post separation distance and can be the smallest separation distance between adjacent stamp posts  34 . Adjacent stamp posts  34  are nearest-neighbor stamp posts  34  between which there are no other stamp posts  34  in a corresponding direction (e.g., a horizontal or vertical direction). A post surface extent of distal post end  34 D of stamp post  34  can be greater than a component extent and a post separation distance can be less than a component separation distance in either or both of horizontal and vertical directions DH, DV. (As will be understood by those knowledgeable in the art, ‘horizontal’ and ‘vertical’ are arbitrary designations and can be interchanged.) Thus, portions of a distal end of stamp posts  34  can be exposed (for example over gap  12 ) and are not in contact with components  20  or substrate surface  11 . Exposed portions of stamp post  34  can be contacted by particles  18  when tethers  14  break (e.g., fracture) or separate and particles  18  adhere or stick to the exposed stamp post  34  portion thereby becoming captured particles  19 , so that the captured particles  19  do not contaminate other portions of, for example, stamp  30 , components  20 , substrate surface  11 , or target substrates. 
     Referring also to the more detailed illustration of components  20  in the cross section of  FIG.  2 A  taken along cross section line A of the plan view of  FIG.  2 B , each component  20  can comprise a semiconductor structure  22  (for example comprising one or more of a circuit, electrical conductors, patterned metal layers, dielectric layers, vias, etc., such as are found in integrated circuits) and electrical contact pads  24  that can connect electrodes (not shown) to any circuit formed in semiconductor structure  22 . Patterned dielectric layers, structures, or encapsulants  26  can electrically insulate semiconductor structure  22  and contact pads  24 . Dielectric encapsulant  26  can form tethers  14  or anchor  16 , or a portion of tethers  14  and anchor  16 . In some embodiments, tether  14  or anchors  16  can instead or in addition comprise portions of semiconductor structure  22  or source substrate  10 , for example semiconductor materials. 
     As shown in  FIGS.  1 A- 1 C , each component  20  can be disposed completely over a different corresponding sacrificial portion  12  (comprising a gap  12  when sacrificial portions  12  are etched) of source substrate  10  so that no portion of a component  20  extends beyond the corresponding sacrificial portion  12  in a direction parallel to substrate surface  11 . Thus, component edges  20 E defining edges of component  20  demarcating the component extent are within (or congruent with) a sacrificial portion  12  area demarcated by sacrificial portion edges  12 E. The distance between component edges  20 E in the horizontal direction define component length  20 L and the distance between component edges  20 E in the vertical direction define component width  20 W (or vice versa). Referring to  FIGS.  1 A and  1 B , in some embodiments of the present disclosure, stamp post  34  is aligned with and has a post surface extent similar to or the same as an extent (e.g., area) of sacrificial portion  12 . Referring to  FIG.  1 C , in some embodiments of the present disclosure, stamp post  34  has a post surface extent less than an extent (e.g., area) of sacrificial portion  12  but greater than the component extent. 
     Thus, according to some embodiments of the present disclosure, a post surface extent is greater than or equal to 105% of a component extent (e.g., greater than or equal to 110%, greater than or equal to 120%, greater than or equal to 150%, or greater than or equal to 200% of the component extent). Similarly, according to some embodiments of the present disclosure, a post surface extent is equal to or less than 100% of a sacrificial portion extent (e.g., equal to or less than 90%, equal to or less than 80%, equal to or less than 70%, equal to or less than 60%, equal to or less than 50%, equal to or less than 40%, equal to or less than 30%, or equal to or less than 20% of the sacrificial portion extent). According to some embodiments of the present disclosure, stamp post  34  extends at least one quarter of the way from a component edge  20 E to a sacrificial portion edge  12 E above which component  20  is disposed (e.g., at least one half of the way from component edge  20 E to sacrificial portion edge  12 E, or at least three quarters of the way from component edge  20 E to sacrificial portion edge  12 E of sacrificial portion  12  above which component  20  is disposed). 
     In some embodiments, and as shown in  FIGS.  1 A- 1 C , a post surface extent is equal to (as shown in  FIGS.  1 A,  1 B ) or less than (as shown in  FIG.  1 C ) a sacrificial portion extent. In some embodiments of the present disclosure, the post surface extent is greater than the sacrificial portion extent. Although it is possible in some such cases that in transfer printing a component  20  from source substrate  10  stamp post  34  can contact anchors  16 , such embodiments can have the advantage of completely covering sacrificial portions  12  even in the event of at least a partial misalignment between stamp posts  34  and components  20 , so that particles  18  can be effectively trapped and captured by stamp  30  thereby becoming captured particles  19 . For example, edges of stamp post  34  can extend at least 500 nm (e.g., at least one micron, two microns, five microns, ten microns, twenty microns, fifty microns, or 100 microns) beyond sacrificial portion edges  12 E in any one or more direction(s) substantially parallel to substrate surface  11 . Stamp post surface of stamp posts  34  can have a similar shape to an extent of component  20  (e.g., both being rectangular) or a different shape (e.g., one being rectangular and the other being circular). 
     In some embodiments of the present disclosure, stamp posts  34  as shown in  FIGS.  1 A- 1 C  have a rectangular cross section parallel to substrate surface  11 . In some embodiments, stamp posts  34  have a non-rectangular cross section parallel to substrate surface  11 , for example a polygonal, circular, oval, elliptical shape, or a shape whose perimeter comprises straight or curved line segments at any angle and of any number. Referring to  FIGS.  3 A- 3 D , in some embodiments of the present disclosure, distal post ends  34 D of stamp posts  34  comprise a portion (e.g., a rectangular portion) that extends primarily over component  20  (or other substantial portion of any shape that extends primarily over component  20 ) and a lateral post protrusion  38  that protrudes (e.g., extends) from the rectangular portion in a direction parallel to substrate surface  11 , for example at least partially over tether  14 .  FIG.  3 A  is a bottom view and  FIG.  3 B  is a perspective of a stamp  30  with a two-by-three array of stamp posts  34 , each having a lateral post protrusion  38 . Lateral post protrusion  38  can, but does not necessarily, have a rectangular shape, and can have a width  38 W that is less than a post width  34 W of stamp post  34  or a length  38 L that is less than a post length  34 L of stamp post  34 , or both, as shown in  FIGS.  3 A and  3 B . Lateral post protrusion  38  can have a length-to-width aspect ratio of, for example, at least 0.5, 1.0, 1.5, or 2.0 and can have a size and shape selected for capturing particles  18  (e.g., based on particular tethers  14  with which stamp  30  is designed to be used). 
       FIG.  3 C  illustrates stamp post  34  in accordance with  FIGS.  3 A and  3 B  in alignment with component  20 . Lateral post protrusion  38  is aligned with tether  14  so that lateral post protrusion  38  is disposed over tether  14  when stamp post  34  contacts component  20  and fractures tether  14 . By disposing lateral post protrusion  38  over tether  14  when tether  14  is broken (e.g., fractured) or separated, particles  18  that are formed by the breaking or separating can adhere to lateral post protrusion  38  or to other portions of the distal end of stamp post  34 . Stamp post  34  can extend over the sides (e.g., component edges  20 E) of component  20  on any one or more of the sides, including over the sides of lateral post protrusion  38 , as shown in  FIGS.  3 C and  3 D .  FIG.  3 C  illustrates lateral post protrusion  38  extending over the entire tether  14  up to anchor  16 ; in some embodiments, such as that of  FIG.  3 D , lateral post protrusion  38  extends over only a portion of tether  14 . In  FIG.  3 E , lateral post protrusion  38  extends entirely over tether  14  and lateral post protrusion  38  has a width equal to that of component  20 . In some embodiments, and as shown in  FIG.  3 E , stamp post  34  has a width equal to that of component  20 , does not extend beyond component  20  on a non-tether end of component  20 , and extends entirely over tether  14 . Some embodiments according to  FIG.  3 E  can have the advantage of providing a particle  18  trapping surface of stamp post  34  near to tether  14  without affecting portions of component  20  or stamp post  34  remote from tether  14 . A cross section corresponding to cross section line A of  FIGS.  3 C- 3 E  is illustrated in the component  20  cross section of  FIG.  2 A  and (including stamp  30 ) in the cross section of  FIG.  1 A . 
     According to some embodiments of the present disclosure, adjacent structures are structures between which no other structure is disposed, or no other structure is closer to both the adjacent structures. As is the case for the terms ‘horizontal’ and ‘vertical’, the terms ‘length’ and ‘width’ are generally arbitrary and can be exchanged, although ‘length’ often refers to the longer of the two dimensions of a surface or structure in comparison to ‘width.’ In any case, the appellations ‘length’ and ‘width’ can be exchanged and do not limit the particular embodiments of the present disclosure that they describe. 
     In some embodiments of the present disclosure, stamp posts  34  extend over at least a portion of anchors  16  of source substrate  10  and can contact anchors  16  when picking up components  20  with stamp  30 . In some embodiments, stamp posts  34  extend over but do not contact anchors  16 . Note that anchors  16  can refer to portions of source substrate  10  that are not sacrificed (are not sacrificial portion  12 ) and can therefore surround sacrificial portion  12 , as shown in  FIGS.  1 B- 1 C . Referring to  FIGS.  4 A,  4 B, and  5   , stamp posts  34  comprise a step  36  that extends from stamp body  32  only part of the way to distal post end  34 D. Step  36  can be formed in a common molding step as post  34 , after post  34  is formed, or as part of a two-step process in which a mesa is formed and then a second portion of post  34  is formed thereon. As shown in  FIG.  4 B  and  FIG.  5   , step  36  can surround the distal post end  34 D of stamp post  34 . Because step  36  is shorter than stamp post  34  it does not necessarily contact anchor  16  when distal post end  34 D contacts components  20  but can capture particles  18 , thereby reducing particulate contamination in the system (e.g., more effectively than stamp body  32  can). In some embodiments, step  36  can comprise a step lateral post protrusion  38 S. Step  36  can have a height that is no more than ten microns (e.g., no more than one micron, two microns, or five microns) less than a height of stamp post  34 . Step  36  can have a height that is no less than 50% (e.g., no less than 90%, 80%, 70%, or 60%) of the height of stamp post  34 . Step  36  can extend greater than or equal to one micron (e.g., greater than or equal to two microns, five microns, ten microns, 20 microns, 50 microns, 100 microns, or 250 microns) beyond stamp post  34  in a direction parallel to substrate surface  11 . Step  36  can have an extent (e.g., area) at least 110% (e.g., at least 120%, 150% or 200%) of a post surface extent. 
     According to some embodiments of the present disclosure and as illustrated in  FIG.  6   , a method of micro-transfer printing comprises providing a source substrate  10  comprising sacrificial portions  12  disposed in an array over source substrate  10  in step  100 . Sacrificial portions  12  can be laterally separated by anchors  16 . A component  20  is disposed directly on or over each sacrificial portion  12  and is physically connected to an anchor  16  with a tether  14  in step  110 . Each component  20  has a component extent and is spaced apart from an adjacent component  20  by a component separation distance (e.g., a horizontal component separation distance  20 H or a vertical component separation distance  20 V). In step  120 , a stamp  30  comprising a stamp body  32  and stamp posts  34  extending away from the stamp body  32  disposed in an array over stamp body  32  is provided. Each stamp post  34  has a post location corresponding to a component location of a component  20  and a post surface of a distal post end  34 D having a post surface extent on a distal post end  34 D of stamp post  34 . The post surface extent is greater than the component extent. Each stamp post  34  is pressed against a corresponding component  20  in step  130  to adhere the corresponding component  20  to the stamp post  34 . In step  140 , stamp  30  is removed from source substrate  10 , thereby breaking (e.g., fracturing) or separating tethers  14  and making particles  18  that, in step  150 , adhere to stamp  30 , for example at stamp post  34 . 
     In some embodiments of the present disclosure and as also illustrated in  FIGS.  9 A- 9 C , a target (e.g., destination) substrate  40  is provided in step  160 . Stamp  30  with adhered components  20  are transferred to target substrate  40  (as shown in  FIG.  9 A ) and components  20  are pressed to target substrate  40  with stamp  30  in step  170  (as shown in  FIG.  9 B ) to adhere components  20  to target substrate  40  while captured particles  19  remain adhered to stamp  30  and stamp  30  is removed in step  180  (as shown in  FIG.  9 C ). Referring to  FIGS.  10 A- 10 C , stamp  30  is transported to a cleaning surface  52  of a cleaning substrate  50  (e.g., an adhesive tape), as shown in  FIG.  10 A . In step  190  and as shown in  FIG.  10 B , stamp  30  is cleaned to remove captured particle  19  from stamp  30 , for example by pressing stamp posts  34  against a cleaning surface  52  of a cleaning substrate  50 . (As other examples, stamp posts  34  could be cleaned with a fluid or plasma.) Cleaned stamp  30  is then removed, leaving captured particles  19  adhered to cleaning substrate  50 , as shown in  FIG.  10 C . In subsequent cleaning steps, different portions of cleaning surface  52  of cleaning substrate  50  can be used to clean stamp  30  to avoid contacting captured particles  19  on cleaning surface  52  to stamp posts  34 . Stamp posts  34  with steps  36  can be cleaned, for example, in an ultrasonic bath. 
     The method illustrated in  FIG.  6    can be repeated by iteratively pressing stamp  30  against different components  20  on source substrate  10  in step  130  and transferring them to target substrate  40  in step  170 . For example, stamp  30  can be shifted relative to unprinted components  20  on source substrate  10  by a component separation distance between printings. Stamp  30  can be cleaned in step  190  after every transfer, as shown in  FIG.  6   , or after more than one print step (not shown in  FIG.  6   ). 
     According to some embodiments of the present disclosure, a stamp  30  for transfer printing (e.g., micro-transfer printing) comprises a stamp body  32  and stamp posts  34  extending away from stamp body  32  disposed in an array over stamp body  32 . Each stamp post  34  has a non-rectangular distal end (for example as shown in  FIGS.  3 A- 3 D  and  FIG.  5   ) or a step  36  distal end (for example as shown in  FIGS.  4 A,  4 B and  5   ). In some embodiments, step  36  surrounds the distal end of each stamp post  34  so that the step extends laterally beyond each edge of the post surface  34 D, as shown in  FIGS.  4 B and  5   . In some embodiments, the distal end of each stamp post  34  has a post length  34 L and a post width  34 W and comprises a lateral post protrusion  38  in a direction of post length  34 L having a post protrusion width  38 W less than the post width  34 W. 
     Such printed structures enable low-cost, high-performance arrays of electrically connected components such as integrated circuits or micro-light-emitting diodes (micro-LEDs) useful, for example, in display systems. For example, components  20  can be micro-assembled arrays of micro-components, such as integrated circuits or micro-LEDs, that are too small (e.g., with at least one of a width, length, height, and diameter of 0.5 μm to 50 μm such as a width of 1-8 μm, a length of 5-10 μm or a height of 0.5-3 μm), numerous, or fragile to be assembled by conventional means. Rather, these arrays are assembled using transfer-printing technology (e.g., micro-transfer-printing technology). Components  20  may be prepared on a native source substrate  10  and printed to a target (destination) substrate  40  (e.g., plastic, metal, glass, ceramic, sapphire, transparent materials, opaque materials, rigid materials, or flexible materials), thereby obviating the manufacture of components  20  on target substrate  40 . Components  20  (e.g., micro-components or chiplets) can be small integrated circuits, can be unpackaged dies released from a source substrate  10 , and can be micro-transfer printed. Components  20  can have, for example, one or more of a width from 1-8 μm, a length from 5-10 μm, and a height from 0.5-3 μm. Transfer-printable components  20  can have at least one of a width, length, and height from 2 to 1000 μm (e.g., 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, 20 to 50 μm, 50 μm to 100 μm, 100 μm to 250 μm, 250 μm to 500 μm, or 500 μm to 1000 μm). Components  20  can have a doped or undoped semiconductor substrate, for example having a thickness of 2 to 50 μm (e.g., 2 to 5 μm, 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm). Components  20  can be integrated circuits with a length greater than width, for example having an aspect ratio greater than or equal to 2 (e.g., greater than or equal to 4, 8, 10, 20, or 50) and, optionally, component contact pads  24  that are adjacent to the ends of transfer-printable components  20  along the length of the transfer-printable components  20 . In some embodiments, components  20  are electrically connected to target substrate  40  using connection posts (not shown). Examples of connection posts are described in U.S. patent application Ser. No. 14/822,864 and U.S. Pat. No. 10,262,966, the disclosures of which are each hereby incorporated by reference in its entirety. 
     A micro-transfer printable component  20  can be an active electrical component, for example including one or more active elements such as electronic transistors or diodes. Transfer-printable components  20  can be electronic processors, controllers, drivers, light-emitters, sensors, light-control components, or light-management components. Transfer-printable components  20  can be integrated circuits, for example CMOS integrated circuits made on or in a silicon semiconductor source substrate  10  (a wafer), light-emitting diodes (LEDs) or lasers, for example made on or in a GaN semiconductor source substrate  10  (a wafer), or silicon photodiodes. Alternatively, transfer printable component  20  can be a passive component, for example including one or more passive elements such as resistors, capacitors, or conductors such as electrical jumpers. In some embodiments, transfer printable component  20  is a compound micro-transfer printable component  20  that includes both active and passive elements. Transfer-printable component  20  can be a semiconductor component  20  having one or more semiconductor layers, such as an integrated circuit or chiplet. Transfer-printable component  20  can be an unpackaged die. In some embodiments, transfer-printable component  20  is a compound element having a plurality of active or passive elements, such as multiple semiconductor components with separate substrates, each with one or more active elements or passive elements, or both. In certain embodiments, the plurality of elements is disposed and interconnected on a compound-element substrate separate from the substrates of any semiconductor components or a different substrate. The compound element can be transfer printed itself after the elements have been arranged and interconnected thereon. 
     Printable component structures can be made in a semiconductor source substrate  10  (e.g., a silicon or GaN wafer) having a process side and a back side used to handle and transport the wafer. Transfer-printable components  20  are formed using lithographic processes in an active layer on or in the process side of a source substrate  10 . An empty release layer space (sacrificial portion  12 ) is formed beneath transfer-printable components  20  with tethers  14  connecting transfer-printable components  20  to anchors  16  on source substrate  10  in such a way that pressure applied against transfer-printable components  20  breaks tethers  14  to release transfer-printable components  20  from source substrate  10  (e.g., with stamp  30 ). Methods of forming such structures are described, for example, in U.S. Pat. No. 8,889,485. Lithographic processes for forming transfer-printable components  20  in source substrate  10 , for example transistors, wires, and capacitors, are found in the integrated circuit art. 
     According to some embodiments of the present disclosure, a source substrate  10  can be a source wafer, for example a semiconductor wafer such as a crystalline silicon or compound semiconductor wafer, or a glass, sapphire, quartz, or polymer substrate or any substrate material capable of supporting transfer-printable components  20 . Source substrate  10  can have a diameter greater than or equal to 10 cm (e.g., greater than or equal to 15 cm, 20 cm, 25 cm, 30 cm, 40 cm) or even larger. Source substrate  10  can have opposing substantially parallel sides and components  20  can be disposed on one of the sides. Source substrate  10  can be thin for example having a thickness of less than one mm (e.g., less than or equal to 700 microns, 500 microns, or 100 microns), or can be relatively thicker, for example having a thickness of one mm or more (e.g., two mm or more, or five mm or more). 
     Micro-structured stamps  30  (e.g., elastomeric stamps, visco-elastic stamps, PDMS stamps, electrostatic stamps, or hybrid elastomeric/electrostatic stamps) can be used to pick up components  20 , transport components  20  to target (destination) substrate  40 , and print components  20  onto target substrate  40 . In some embodiments, surface adhesion forces are used to control the selection and printing of components  20  onto target substrate  40 . In some embodiments, other forces adhere components  20  to stamp  30  (e.g., in combination with adhesive forces), for example electro-static or magnetic forces. This process may be performed massively in parallel. Stamps  30  can be designed to transfer a single component  20  or hundreds to thousands of discrete components  20  in a single pick-up and print operation. For a discussion of embodiments of micro-transfer printing generally, see U.S. Pat. Nos. 7,622,367 and 8,506,867, each of which is hereby incorporated by reference in its entirety. Stamps  30  can be constructed by photolithographically defining a master mold against which liquid material (e.g., PDMS) is cast and solidified to form stamp  30 . Stamp  30  is then removed from the master mold. Stamp  30  can have a rigid back to which stamp body  32  is adhered, for example a transparent rigid back comprising glass, on an opposite side of stamp body  32  from which stamp posts  34  extend. 
     The target (e.g., destination substrate  40  can be glass (for example a portion of a flat-panel display substrate), soda-lime glass, borosilicate glass, pyrex, metal, ceramic, polymer, or a semiconductor (for example a wafer or portion of a wafer). Target substrate  40  can have a thickness ranging from 0.5 mm to 10 mm. These ranges are illustrative and not limiting and other materials and sizes can be included or used. 
     According to various embodiments of the present disclosure, a native source substrate  10  can be provided with the transfer-printable component  20 , sacrificial portions  12 , and tethers  14  already formed, or they can be constructed as part of the process of the present disclosure. 
     Source substrate  10  and transfer-printable components  20 , stamp  30 , and target (destination) substrate  40  can be made separately and at different times or in different temporal orders or locations and provided in various process states. 
     In comparison to thin-film manufacturing methods, using densely populated source substrates  10  and transferring micro-transfer printable components  20  to a target substrate  40  that requires only a sparse array of micro-transfer printable components located thereon with a stamp  30  does not waste or require active layer material on a target substrate  40 . The present disclosure can also be used in transferring transfer-printable components  20  made with crystalline semiconductor materials that have higher performance than thin-film active components. Furthermore, the flatness, smoothness, chemical stability, and heat stability requirements for a target substrate  40  used in some embodiments of the present disclosure may be reduced because the adhesion and transfer processes are not substantially limited by the material properties of target substrate  40 . Manufacturing and material costs may be reduced because of high utilization rates of more expensive materials (e.g., source substrate  10 ) and reduced material and processing requirements for target substrate  40 . 
     As is understood by those skilled in the art, the terms “over” and “under” are relative terms and can be interchanged in reference to different orientations of the layers, elements, and substrates included in the present disclosure. For example, a first layer on a second layer, in some implementations means a first layer directly on and in contact with a second layer. In other implementations a first layer on a second layer includes a first layer and a second layer with another layer therebetween. 
     Having described certain implementations, it will now become apparent to one of skill in the art that other implementations incorporating the concepts of the disclosure may be used. Therefore, the disclosure should not be limited to certain implementations, but rather should be limited only by the spirit and scope of the following claims. 
     Throughout the description, where apparatus and systems are described as having, including, or comprising specific components, or where processes and methods are described as having, including, or comprising specific steps, it is contemplated that, additionally, there are apparatus, and systems of the disclosed technology that consist essentially of, or consist of, the recited components, and that there are processes and methods according to the disclosed technology that consist essentially of, or consist of, the recited processing steps. 
     It should be understood that the order of steps or order for performing certain action is immaterial so long as the disclosed technology remains operable. Moreover, two or more steps or actions in some circumstances can be conducted simultaneously. 
     PARTS LIST 
     
         
         A cross section line 
         DH horizontal direction 
         DV vertical direction 
           10  source substrate/source wafer 
           11  substrate surface 
           12  sacrificial portion/gap 
           12 E sacrificial portion edge 
           14  tether 
           14 A fractured tether 
           16  anchor 
           18  particle 
           19  captured particle 
           20  component 
           20 E component edge 
           20 H horizontal component separation distance 
           20 L component length 
           20 V vertical component separation distance 
           20 W component width 
           22  semiconductor structure 
           24  contact pad 
           26  dielectric encapsulant 
           30  stamp 
           32  stamp body 
           34  stamp post 
           34 D distal post end/post surface 
           34 H horizontal post separation distance 
           34 L post length 
           34 P proximal post end 
           34 V vertical post separation distance 
           34 W post width 
           36  step 
           38  lateral post protrusion 
           38 S step lateral post protrusion 
           38 L protrusion length 
           38 W protrusion width 
           40  destination substrate/target substrate 
           50  cleaning substrate 
           52  cleaning surface 
           99  micro-transfer printing system 
           100  provide source substrate step 
           110  provide component step 
           120  provide stamp step 
           130  press stamp against component step 
           140  remove stamp and component step 
           150  capture particles step 
           160  provide destination substrate step 
           170  press component against destination substrate step 
           180  remove stamp step 
           190  clean stamp step