Particle capture using transfer stamp

A micro-transfer printing system comprises a source substrate having a substrate surface and components disposed in an array on, over, or in the substrate surface Each component has a component extent in a plane parallel to the substrate surface. A stamp comprises a stamp body and stamp posts extending away from the stamp body disposed in an array over the stamp body. Each of the stamp posts has (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. The post surface extent is greater than the component extent.

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).

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 toFIGS.1A and7, in some embodiments of transfer printing according to the present disclosure, components20are released from a source substrate10by undercutting components20, for example by etching a sacrificial portion12of source substrate10on or over which components20are formed or otherwise disposed to form a space (e.g., a gap12), such that components20are attached by a tether14to an anchor16of source substrate10. (One or more tethers14can be used, for example in combination with one or more anchors16.) Sacrificial portions12disposed in an array over source substrate10can be disposed in, on, or over source substrate10and, moreover, such sacrificial portions12can be designated portions of the source substrate10itself (e.g., an anisotropically etchable source substrate10).

When components20are removed from source substrate10by a stamp30, tethers14attaching each component20to an anchor16are broken (e.g., fractured) or separated from anchor16, forming fractured or separated tethers14A (shown inFIG.7). According to some embodiments, the process of breaking (e.g., fracturing) tethers14or separating tethers14from anchors16can create particles18that contaminate stamp30, components20, source substrate10, or a target substrate (not shown inFIGS.1A and7). The particle contamination can inhibit picking up components20from source substrate10or inhibit printing picked-up components20on stamp30to 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 components20from source substrate10to 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 inFIG.8, transfer yields can be improved by capturing at least some particles18with an enlarged stamp30with a greater extent (e.g., area) over substrate surface11of source substrate10. Such a greater extent can cause contaminating particles18to adhere to enlarged portions of stamp30(thereby becoming captured particles19). After one or more print operations with stamp30, stamp30can be cleaned to remove captured particles19from stamp30. Thus, in some embodiments, captured particles19may be allowed to be build up near a periphery of a contact surface of posts34to reduce time spent cleaning stamp30while still improving printing yields through particle capture19.

Therefore, according to some illustrative embodiments of the present disclosure and referring again to the cross section ofFIG.1Aand the corresponding plan views ofFIGS.1B and1C, a micro-transfer printing system99comprises a source substrate10having a substrate surface11and components20disposed in an array on, over, or in the substrate surface11of source substrate10. Each component20has a component extent (e.g., area) in a plane parallel to substrate surface11, for example a component length20L of component20times a component width20W of component20(shown inFIGS.1B and1C). The component extent (e.g., area) can include all of the elements or components of component20(e.g., semiconductor materials, metal layers, electrical conductors, optical conductors, vias, contact pads, and dielectric structures) but does not include tether14or anchor16.

An example of a stamp30comprises a stamp body32and stamp posts34extending away from stamp body32disposed in an array over stamp body32. Stamp body32can comprise the same material as stamp post34and can be made in a common molding step. During a print operation, each stamp post34has a post location corresponding to and aligned with a component location of a component20on source substrate10so that stamp posts34can each contact a component20when stamp30is moved towards source substrate10. A post surface of a distal post end34D of each stamp post34has a post surface extent (e.g., area). The post surface extent of stamp post34can be over and substantially parallel to substrate surface11of source substrate10. As shown inFIGS.1B and1C, the post surface extent can be a post length34L of stamp post34times a post width34W of stamp post34, for example if the post surface is a flat rectangular surface. Distal post end34D of stamp post34is opposite and remote from a proximal post end34P of stamp post34and proximal post end34P is in contact with or adjacent to stamp body32. Note that, as used herein, post length34L is not the distance between the proximal post end34P and distal post end34D (e.g., a height of stamp post34).

Components20are separated in a horizontal direction DH by horizontal component separation distance20H and separated in a vertical direction DV orthogonal to horizontal direction DH by vertical component separation distance20V. Similarly, stamp posts34are separated in horizontal direction DH by horizontal post separation distance34H and separated in vertical direction DV orthogonal to horizontal direction DH by vertical post separation distance34V. Either or both of horizontal and vertical component separation distance20H,20V are a component separation distance and can be the smallest separation distance between adjacent components20. Adjacent components20are nearest-neighbor (e.g., adjoining or adjacent) components20between which there are no other components20in a corresponding direction (e.g., a horizontal or vertical direction). Likewise, either or both of horizontal and vertical post separation distance34H,34V are a post separation distance and can be the smallest separation distance between adjacent stamp posts34. Adjacent stamp posts34are nearest-neighbor stamp posts34between which there are no other stamp posts34in a corresponding direction (e.g., a horizontal or vertical direction). A post surface extent of distal post end34D of stamp post34can 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 posts34can be exposed (for example over gap12) and are not in contact with components20or substrate surface11. Exposed portions of stamp post34can be contacted by particles18when tethers14break (e.g., fracture) or separate and particles18adhere or stick to the exposed stamp post34portion thereby becoming captured particles19, so that the captured particles19do not contaminate other portions of, for example, stamp30, components20, substrate surface11, or target substrates.

Referring also to the more detailed illustration of components20in the cross section ofFIG.2Ataken along cross section line A of the plan view ofFIG.2B, each component20can comprise a semiconductor structure22(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 pads24that can connect electrodes (not shown) to any circuit formed in semiconductor structure22. Patterned dielectric layers, structures, or encapsulants26can electrically insulate semiconductor structure22and contact pads24. Dielectric encapsulant26can form tethers14or anchor16, or a portion of tethers14and anchor16. In some embodiments, tether14or anchors16can instead or in addition comprise portions of semiconductor structure22or source substrate10, for example semiconductor materials.

As shown inFIGS.1A-1C, each component20can be disposed completely over a different corresponding sacrificial portion12(comprising a gap12when sacrificial portions12are etched) of source substrate10so that no portion of a component20extends beyond the corresponding sacrificial portion12in a direction parallel to substrate surface11. Thus, component edges20E defining edges of component20demarcating the component extent are within (or congruent with) a sacrificial portion12area demarcated by sacrificial portion edges12E. The distance between component edges20E in the horizontal direction define component length20L and the distance between component edges20E in the vertical direction define component width20W (or vice versa). Referring toFIGS.1A and1B, in some embodiments of the present disclosure, stamp post34is aligned with and has a post surface extent similar to or the same as an extent (e.g., area) of sacrificial portion12. Referring toFIG.1C, in some embodiments of the present disclosure, stamp post34has a post surface extent less than an extent (e.g., area) of sacrificial portion12but 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 post34extends at least one quarter of the way from a component edge20E to a sacrificial portion edge12E above which component20is disposed (e.g., at least one half of the way from component edge20E to sacrificial portion edge12E, or at least three quarters of the way from component edge20E to sacrificial portion edge12E of sacrificial portion12above which component20is disposed).

In some embodiments, and as shown inFIGS.1A-1C, a post surface extent is equal to (as shown inFIGS.1A,1B) or less than (as shown inFIG.1C) 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 component20from source substrate10stamp post34can contact anchors16, such embodiments can have the advantage of completely covering sacrificial portions12even in the event of at least a partial misalignment between stamp posts34and components20, so that particles18can be effectively trapped and captured by stamp30thereby becoming captured particles19. For example, edges of stamp post34can 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 edges12E in any one or more direction(s) substantially parallel to substrate surface11. Stamp post surface of stamp posts34can have a similar shape to an extent of component20(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 posts34as shown inFIGS.1A-1Chave a rectangular cross section parallel to substrate surface11. In some embodiments, stamp posts34have a non-rectangular cross section parallel to substrate surface11, 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 toFIGS.3A-3D, in some embodiments of the present disclosure, distal post ends34D of stamp posts34comprise a portion (e.g., a rectangular portion) that extends primarily over component20(or other substantial portion of any shape that extends primarily over component20) and a lateral post protrusion38that protrudes (e.g., extends) from the rectangular portion in a direction parallel to substrate surface11, for example at least partially over tether14.FIG.3Ais a bottom view andFIG.3Bis a perspective of a stamp30with a two-by-three array of stamp posts34, each having a lateral post protrusion38. Lateral post protrusion38can, but does not necessarily, have a rectangular shape, and can have a width38W that is less than a post width34W of stamp post34or a length38L that is less than a post length34L of stamp post34, or both, as shown inFIGS.3A and3B. Lateral post protrusion38can 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 particles18(e.g., based on particular tethers14with which stamp30is designed to be used).

FIG.3Cillustrates stamp post34in accordance withFIGS.3A and3Bin alignment with component20. Lateral post protrusion38is aligned with tether14so that lateral post protrusion38is disposed over tether14when stamp post34contacts component20and fractures tether14. By disposing lateral post protrusion38over tether14when tether14is broken (e.g., fractured) or separated, particles18that are formed by the breaking or separating can adhere to lateral post protrusion38or to other portions of the distal end of stamp post34. Stamp post34can extend over the sides (e.g., component edges20E) of component20on any one or more of the sides, including over the sides of lateral post protrusion38, as shown inFIGS.3C and3D.FIG.3Cillustrates lateral post protrusion38extending over the entire tether14up to anchor16; in some embodiments, such as that ofFIG.3D, lateral post protrusion38extends over only a portion of tether14. InFIG.3E, lateral post protrusion38extends entirely over tether14and lateral post protrusion38has a width equal to that of component20. In some embodiments, and as shown inFIG.3E, stamp post34has a width equal to that of component20, does not extend beyond component20on a non-tether end of component20, and extends entirely over tether14. Some embodiments according toFIG.3Ecan have the advantage of providing a particle18trapping surface of stamp post34near to tether14without affecting portions of component20or stamp post34remote from tether14. A cross section corresponding to cross section line A ofFIGS.3C-3Eis illustrated in the component20cross section ofFIG.2Aand (including stamp30) in the cross section ofFIG.1A.

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 posts34extend over at least a portion of anchors16of source substrate10and can contact anchors16when picking up components20with stamp30. In some embodiments, stamp posts34extend over but do not contact anchors16. Note that anchors16can refer to portions of source substrate10that are not sacrificed (are not sacrificial portion12) and can therefore surround sacrificial portion12, as shown inFIGS.1B-1C. Referring toFIGS.4A,4B, and5, stamp posts34comprise a step36that extends from stamp body32only part of the way to distal post end34D. Step36can be formed in a common molding step as post34, after post34is formed, or as part of a two-step process in which a mesa is formed and then a second portion of post34is formed thereon. As shown inFIG.4BandFIG.5, step36can surround the distal post end34D of stamp post34. Because step36is shorter than stamp post34it does not necessarily contact anchor16when distal post end34D contacts components20but can capture particles18, thereby reducing particulate contamination in the system (e.g., more effectively than stamp body32can). In some embodiments, step36can comprise a step lateral post protrusion38S. Step36can 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 post34. Step36can have a height that is no less than 50% (e.g., no less than 90%, 80%, 70%, or 60%) of the height of stamp post34. Step36can 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 post34in a direction parallel to substrate surface11. Step36can 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 inFIG.6, a method of micro-transfer printing comprises providing a source substrate10comprising sacrificial portions12disposed in an array over source substrate10in step100. Sacrificial portions12can be laterally separated by anchors16. A component20is disposed directly on or over each sacrificial portion12and is physically connected to an anchor16with a tether14in step110. Each component20has a component extent and is spaced apart from an adjacent component20by a component separation distance (e.g., a horizontal component separation distance20H or a vertical component separation distance20V). In step120, a stamp30comprising a stamp body32and stamp posts34extending away from the stamp body32disposed in an array over stamp body32is provided. Each stamp post34has a post location corresponding to a component location of a component20and a post surface of a distal post end34D having a post surface extent on a distal post end34D of stamp post34. The post surface extent is greater than the component extent. Each stamp post34is pressed against a corresponding component20in step130to adhere the corresponding component20to the stamp post34. In step140, stamp30is removed from source substrate10, thereby breaking (e.g., fracturing) or separating tethers14and making particles18that, in step150, adhere to stamp30, for example at stamp post34.

In some embodiments of the present disclosure and as also illustrated inFIGS.9A-9C, a target (e.g., destination) substrate40is provided in step160. Stamp30with adhered components20are transferred to target substrate40(as shown inFIG.9A) and components20are pressed to target substrate40with stamp30in step170(as shown inFIG.9B) to adhere components20to target substrate40while captured particles19remain adhered to stamp30and stamp30is removed in step180(as shown inFIG.9C). Referring toFIGS.10A-10C, stamp30is transported to a cleaning surface52of a cleaning substrate50(e.g., an adhesive tape), as shown inFIG.10A. In step190and as shown inFIG.10B, stamp30is cleaned to remove captured particle19from stamp30, for example by pressing stamp posts34against a cleaning surface52of a cleaning substrate50. (As other examples, stamp posts34could be cleaned with a fluid or plasma.) Cleaned stamp30is then removed, leaving captured particles19adhered to cleaning substrate50, as shown inFIG.10C. In subsequent cleaning steps, different portions of cleaning surface52of cleaning substrate50can be used to clean stamp30to avoid contacting captured particles19on cleaning surface52to stamp posts34. Stamp posts34with steps36can be cleaned, for example, in an ultrasonic bath.

The method illustrated inFIG.6can be repeated by iteratively pressing stamp30against different components20on source substrate10in step130and transferring them to target substrate40in step170. For example, stamp30can be shifted relative to unprinted components20on source substrate10by a component separation distance between printings. Stamp30can be cleaned in step190after every transfer, as shown inFIG.6, or after more than one print step (not shown inFIG.6).

According to some embodiments of the present disclosure, a stamp30for transfer printing (e.g., micro-transfer printing) comprises a stamp body32and stamp posts34extending away from stamp body32disposed in an array over stamp body32. Each stamp post34has a non-rectangular distal end (for example as shown inFIGS.3A-3DandFIG.5) or a step36distal end (for example as shown inFIGS.4A,4B and5). In some embodiments, step36surrounds the distal end of each stamp post34so that the step extends laterally beyond each edge of the post surface34D, as shown inFIGS.4B and5. In some embodiments, the distal end of each stamp post34has a post length34L and a post width34W and comprises a lateral post protrusion38in a direction of post length34L having a post protrusion width38W less than the post width34W.

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, components20can 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). Components20may be prepared on a native source substrate10and printed to a target (destination) substrate40(e.g., plastic, metal, glass, ceramic, sapphire, transparent materials, opaque materials, rigid materials, or flexible materials), thereby obviating the manufacture of components20on target substrate40. Components20(e.g., micro-components or chiplets) can be small integrated circuits, can be unpackaged dies released from a source substrate10, and can be micro-transfer printed. Components20can 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 components20can 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). Components20can 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). Components20can 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 pads24that are adjacent to the ends of transfer-printable components20along the length of the transfer-printable components20. In some embodiments, components20are electrically connected to target substrate40using 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 component20can be an active electrical component, for example including one or more active elements such as electronic transistors or diodes. Transfer-printable components20can be electronic processors, controllers, drivers, light-emitters, sensors, light-control components, or light-management components. Transfer-printable components20can be integrated circuits, for example CMOS integrated circuits made on or in a silicon semiconductor source substrate10(a wafer), light-emitting diodes (LEDs) or lasers, for example made on or in a GaN semiconductor source substrate10(a wafer), or silicon photodiodes. Alternatively, transfer printable component20can 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 component20is a compound micro-transfer printable component20that includes both active and passive elements. Transfer-printable component20can be a semiconductor component20having one or more semiconductor layers, such as an integrated circuit or chiplet. Transfer-printable component20can be an unpackaged die. In some embodiments, transfer-printable component20is 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 substrate10(e.g., a silicon or GaN wafer) having a process side and a back side used to handle and transport the wafer. Transfer-printable components20are formed using lithographic processes in an active layer on or in the process side of a source substrate10. An empty release layer space (sacrificial portion12) is formed beneath transfer-printable components20with tethers14connecting transfer-printable components20to anchors16on source substrate10in such a way that pressure applied against transfer-printable components20breaks tethers14to release transfer-printable components20from source substrate10(e.g., with stamp30). Methods of forming such structures are described, for example, in U.S. Pat. No. 8,889,485. Lithographic processes for forming transfer-printable components20in source substrate10, for example transistors, wires, and capacitors, are found in the integrated circuit art.

According to some embodiments of the present disclosure, a source substrate10can 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 components20. Source substrate10can 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 substrate10can have opposing substantially parallel sides and components20can be disposed on one of the sides. Source substrate10can 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 stamps30(e.g., elastomeric stamps, visco-elastic stamps, PDMS stamps, electrostatic stamps, or hybrid elastomeric/electrostatic stamps) can be used to pick up components20, transport components20to target (destination) substrate40, and print components20onto target substrate40. In some embodiments, surface adhesion forces are used to control the selection and printing of components20onto target substrate40. In some embodiments, other forces adhere components20to stamp30(e.g., in combination with adhesive forces), for example electro-static or magnetic forces. This process may be performed massively in parallel. Stamps30can be designed to transfer a single component20or hundreds to thousands of discrete components20in 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. Stamps30can be constructed by photolithographically defining a master mold against which liquid material (e.g., PDMS) is cast and solidified to form stamp30. Stamp30is then removed from the master mold. Stamp30can have a rigid back to which stamp body32is adhered, for example a transparent rigid back comprising glass, on an opposite side of stamp body32from which stamp posts34extend.

The target (e.g., destination substrate40can 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 substrate40can 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 substrate10can be provided with the transfer-printable component20, sacrificial portions12, and tethers14already formed, or they can be constructed as part of the process of the present disclosure.

Source substrate10and transfer-printable components20, stamp30, and target (destination) substrate40can 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 substrates10and transferring micro-transfer printable components20to a target substrate40that requires only a sparse array of micro-transfer printable components located thereon with a stamp30does not waste or require active layer material on a target substrate40. The present disclosure can also be used in transferring transfer-printable components20made 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 substrate40used 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 substrate40. Manufacturing and material costs may be reduced because of high utilization rates of more expensive materials (e.g., source substrate10) and reduced material and processing requirements for target substrate40.

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