Multilayer release stacks for light-induced transfer of components

Abstract

A method and system for light-induced transfer of a component (15) from a donor substrate (10) to an acceptor substrate (20). The donor substrate (10) includes a transparent carrier (11) configured to carry the component (15) facing the acceptor substrate (20) and a release stack (S). The release stack (S) includes a light absorbing layer (12), a decomposition layer (16), a melt layer (13), and an adhesive layer (14). The light absorbing layer (12) has a high absorption coefficient to absorb a light beam (L) that causes heat conduction to the melt layer (13). The light absorbing layer 12 remains solid while the melt layer (13) is melted. The adhesive layer (14) adheres the component (15) to the melt layer (13) while the melt layer (13) is solid and releases adhesion when the melt layer (13) is melted (M). The decomposition layer (16) has an evaporation temperature that exceeds the melting temperature of the molten layer, forming bubbles (17) that facilitate release and movement when the molten layer (13) is liquid.

Description

[Technical field]

[0001] The present disclosure relates to methods and systems for light-induced transfer of components, such as chips, from a donor substrate to an acceptor substrate. The present disclosure also relates to donor substrates for use in such methods or systems. [Background technology]

[0002] Controlled movement of small components has various applications, for example in the placement of μLEDs. Light-induced movement can be used to selectively move components from a donor substrate to an acceptor substrate. To facilitate the movement, a release stack can be provided between the donor substrate and the components. In one technique, the components are glued onto a carrier substrate and released from the carrier by rapid blister formation. In another technique, a flat glass plate with a light-absorbing layer is covered with an adhesive. The components can be released by decomposition or melting of the adhesive when the light-absorbing layer is rapidly heated by a light pulse.

[0003] For each of the known methods, a tradeoff is made between efficiency (i.e., speed), yield, and level of control. None of these methods provide the desired level of control over the transfer process. Faster techniques provide lower yields. There remains a need for further improvements in the controlled transfer and placement of components. Summary of the Invention [Means for solving the problem]

[0004] Some aspects of the present disclosure relate to methods and systems for light-induced transfer of components from a donor substrate to an acceptor substrate. Other or further aspects relate to a donor substrate for use in such methods or systems. In general, a transparent carrier is configured to carry the components facing the acceptor substrate, and a release stack is disposed between the transparent carrier and the components to release one or more of the components from the donor substrate onto the acceptor substrate following irradiation of the release stack by a light beam through the transparent carrier.

[0005] As described herein, the release stack of the donor substrate includes a light absorbing layer, a decomposition layer, a melting layer, and an adhesive layer. The light absorbing layer is disposed between the transparent carrier and the decomposition layer. By providing the light absorbing layer with a relatively high absorption coefficient, the light beam can be efficiently absorbed, thereby heating the light absorbing layer. By thermally contacting the heated light absorbing layer with the melting layer through the decomposition layer, the absorbed heat can be conducted to the melting layer through the decomposition layer, and therefore the temperature of the decomposition layer and the melting layer can increase. By providing a relatively low melting temperature to the material of the melting layer, the material can be easily melted. By providing a relatively high melting temperature to the light absorbing layer (at least higher than the melting temperature of the melting layer), the light absorbing layer can remain solid while the melting layer is melted by the heat conducted from the light absorbing layer. By providing an adhesive layer between the component and the melting layer, the component can be easily adhered to the melting layer while the melting layer is solid. Furthermore, this adhesive force can be released when the melting layer is melted. By providing the decomposition layer with an evaporation temperature between the melting temperature of the melting layer and the melting temperature of the light absorbing layer, the material of the decomposition layer starts to evaporate after the melting layer melts. Within the decomposition layer, bubble formation increases the pressure within the layer, which results in the growth of a convex shape at the bottom of the melting layer where the decomposition layer melts. This encourages the release of the components by increasing the contact angle with the adhesive layer at the appropriate time. Thereby, the release of the components is accelerated more than in the situation where the decomposition layer was not present. As a result, the total heat transfer to the components is limited by the accelerated release, which weakens the potential loss of the components due to thermal damage. Furthermore, by splitting at least the adhesive layer between the components, the components can be moved more easily. For example, if a part of the adhesive layer can be released with the components without being connected to the surrounding parts of the adhesive layer, for example without holding the adjacent (not moved) components or other parts of the adhesive layer, the shear forces during the movement can be reduced. By splitting the decomposition layer, the bubble formation and the resulting change in curvature to a convex surface are limited only to the area of ​​the bottom of the components (or even to a smaller sub-area below it, if necessary).Similarly, the melt layer and / or the light absorbing layer may be split to provide additional benefits, such as additional separation and / or isolation of heat to the respective stacks. Although splitting has certain advantages, the components may in principle be released without the need for splitting. For example, parts of the (continuous) adhesive layer holding the components may be relatively weak and may simply detach from the surrounding adhesive layer when the melt layer between the components and the light absorbing layer melts locally to weaken the adhesion. For example, the components may be pulled, pushed, or possibly released from the carrier by various forces, such as gravity and / or accumulation of molten material with de-wetting or optional gas generation.

[0006] Typically, an area of ​​the light absorbing layer (e.g., forming part of a release stack that holds the respective components) is irradiated with a light beam through a transparent carrier. This can result in heating of the respective portions of the light absorbing layer. The heat can then be conducted to adjacent melt layers of the release stack, thereby at least partially melting the adjacent melt layers, preferably while the respective portions of the light absorbing layer remain substantially solid. As a result, the at least partial melting of the adjacent melt layers can cause a loss of adhesion between the adjacent melt layers and the respective portions of the adhesive layers of the release stack (which adhere the respective components to the adjacent melt layers). The loss of adhesion can therefore cause the release and movement of the respective components. For example, one or more light sources and / or masks are configured and controlled to generate one or more light beams to move the respective components as described herein.

[0007] In some embodiments, apart from the decomposition layer, which provides its function of creating pressure build-up in the layers via bubble formation, the low outgassing melting and adhesion layers in the laser release stack are used to rapidly move the components from the carrier towards the acceptor substrate. The low pressure build-up allows the components to be moved at low speeds (with little or no shock waves) and with little air (gas) turbulence around, the components can be substantially prevented from rotating while being moved. It is noted herein that bubbles formed in the decomposition layer are confined to the layers in the stack with little or no outgassing. In one embodiment, the stack comprises or essentially consists of a thermally stable light absorbing layer, a melting layer, and an adhesion layer. Preferably, the melting layer is a metal layer with a relatively low melting temperature. More preferably, the light absorbing layer is also a metal layer, but with a relatively high melting temperature. More preferably, the decomposition layer is a metal layer with its evaporation temperature between the melting temperature of the melting layer and the melting temperature of the light absorbing layer as well. The present invention is not limited to a metallic decomposition layer, and other materials or alloys with suitable properties may be applied. Most preferably, the adhesive layer consists essentially of a polymer adhesive having a decomposition temperature higher than and / or closely matching the melting temperature of the metallic melt layer. As a further advantageous (but not essential) option, the decomposition layer likewise has a melting temperature higher than the melting temperature of the melt layer, so that melting begins initially in the melt layer.

[0008] In some embodiments, the laser beam or other light source heats the light absorbing layer sufficiently quickly that the underlying metal layer begins to melt. While in the molten state, the polymer adhesive that bonds the component to the molten layer of metal may release, for example, by a dewetting effect. The surface tension of the liquid metal is generally much higher than the surface energy of the solid polymer, so that the adhesive forces between the two layers may be released. In contrast, the surface energy of the solid metal layer is generally very high, so that the molten layer of metal can stick to the decomposition layer of metal if its melting temperature is higher than the melting temperature of the molten layer (as described above). As a result, the molten metal of the molten layer adheres to the (generally still solid) metal of the decomposition layer, and the adhesive layer releases by dewetting. This process is accelerated when the temperature of the decomposition layer rises above its vaporization temperature and bubbles form at the bottom of the molten layer due to gas generation in the decomposition layer. This results in an increased curvature of the surface of the decomposition layer (becoming convex) and a molten layer of liquid on the decomposition layer, thereby promoting an earlier release of the adhesive forces. For example, only the polymer part is moved with the component. After transfer, the polymer layer may be removed from the component, for example via dry etching or pyrolysis.

[0009] In some embodiments, the polymer adhesive can be tailored to decompose slightly at the melting point of the molten layer to increase the component movement speed. During melting, the contact area between the adhesive and the molten layer can be reduced, for example, due to the high surface tension of the molten metal. Therefore, the material tends to round up. Even if the evaporation (decomposition) temperature of a polymer material such as SU-8 is about 350° C. at low heating rates, at very high heating rates, the decomposition of the polymer tends to occur at much higher temperatures. Selecting a polymer / metal combination (e.g., Sn+SU-8, Zn+polyimide) in which the polymer has a decomposition temperature higher than the melting temperature of the metal allows the components to be released without generating gas. Advantageously, the evaporation temperature of the decomposition layer is selected such that bubble formation and the formation of convex surfaces occurs, while the contact area between the molten layer and the adhesive layer is reduced in this process to trigger the release at that moment. Furthermore, for example, gravity or electrostatic forces can be used to release the components from the carrier and move them towards the acceptor substrate. In general, it is preferable to stay below the boiling point (evaporation temperature) of the molten material of the metal. In some cases, the evaporated metal can create additional pressure and deposit on cooler surrounding surfaces.

[0010] In addition to controlling the amount of gas generation, it is also preferable to heat the light absorbing layer as uniformly as possible to ensure that the molten layers of metal melt simultaneously. In some embodiments, a flat-top beam profile is used that specifically heats the stack on one component and does not interfere with adjacent components. Since it is also preferable to have very narrow (e.g., ≦5 μm) dicing streets between components to reduce the amount of substrate to be wasted, selectively heating a single component can become increasingly difficult. In particular, as the movement speed increases, it can become more difficult to control the timing of the jitter on the laser. Therefore, it is preferable to use a mask precisely aligned with the components to tune the laser pulse to the correct dimension.

[0011] Typically, since only a portion of the component needs to be moved (e.g., for a μLED display), the laser pulse can be (much) larger than the component. For example, a relatively large flat-top beam combined with a mask can result in a robust process that does not require a precise and expensive laser positioning control system. For example, the maximum laser spot size can be calculated as twice the component pitch minus the component size minus the laser precision. For example, 2 x 200 μm (component pitch) - 40 μm (component size) - 10 μm (laser precision) = 350 μm. At these large spot sizes, it can be relatively easy to obtain a uniform heat flux in the center, especially with beam shaping optics such as the πShaper.

[0012] To reduce the heat affected zone and further limit the amount of gas generation, in some embodiments, the size of the molten layer of metal underneath the component is reduced. For example, to automatically center the molten layer of metal underneath the component, the layer can be underetched in an etching bath. The more centered the component is when released, the better the transfer process will be.

[0013] Other or further improvements can be obtained by strategic movement of the components to ensure that the components are propelled straight down towards the acceptor substrate. For example, if there is gas generation below the components, this gas will generally escape most easily where there is the lowest flow resistance. Even with a nearly perfectly uniform heat flux, uneven pressure around the components can result in undesirable component trajectories, such as components rotating during movement. To alleviate this problem, for example, a checkerboard approach can be used in which components are moved alternately. By making sure that the moved component is or is not surrounded on both sides by adjacent components, the pressure build-up around the moved component can be more uniform. When the component trajectory can be better controlled straight down, a larger movement gap can be realized, which can be advantageous for industrialization since the height positioning does not need to be very precise.

[0014] For example, the heat flux and fluence can be controlled to improve performance. Preferably, the light absorbing layer is heated without going to its melting or vaporization temperature. Furthermore, it is preferred that the high intensity light does not reach the component to prevent damage. With regard to the layer thickness of the molten layer of metal, the thicker the layer, the higher the fluence is required to melt the entire layer. Furthermore, metals of different layers can diffuse and form an alloy. If there is relatively too much molten metal, the light absorbing layer can diffuse completely into the molten pool. If the light absorbing layer melts, non-uniformity effects can occur. To control the melting time, the pulse time and fluence can be controlled. The pulse time is preferably on the order of nanoseconds or picoseconds. A shorter pulse on the order of femtoseconds can result in a "cold" ablation of the light absorbing layer, while a longer pulse on the order of microseconds can increase the area affected by the heat. Generally, a longer pulse can have little effect, since most of the heat can be lost by the carrier and the heat sink of the component. The thickness of the adhesion layer can be increased to reduce the heat flow towards the component. By accelerating the release of the components with the aid of the decomposition layer, the duration of heat transfer to the components is reduced to prevent heat damage to the components, while the adhesive layer is allowed to be thinner. Although relatively high temperatures are achieved in the light absorbing layer and the melting layer, the components can remain relatively cool in this manner.

[0015] These and other features, aspects, and advantages of the presently disclosed apparatus, systems, and methods will become better understood from the following description, appended claims, and accompanying drawings. [Brief description of the drawings]

[0016] [Figure 1A] FIG. 13 illustrates the transfer of components from a donor substrate to an acceptor substrate by irradiating a release stack. [Figure 1B]FIG. 1 illustrates the relative temperatures and sequence for releasing components by light-induced heating of selective layers in a release stack. [Figure 2A] 13A-13C show further embodiments involving cutting and / or etching parts of the release stack. [Figure 2B] 13A-13C show further embodiments involving cutting and / or etching parts of the release stack. [Figure 3A] FIG. 1 illustrates the masking of light pulses to form a relatively narrow light beam and the relative thicknesses of various layers. [Figure 3B] FIG. 1 illustrates sequential release of components. [Figure 4A] FIG. 13 shows a photograph of components transferred to an acceptor substrate. [Figure 4B] FIG. 13 shows a photograph of components transferred to an acceptor substrate. [Figure 4C] FIG. 2 shows a portion of the stack remaining on the donor substrate. [Figure 5A] FIG. 13 illustrates further layers in the release stack. [Figure 5B] FIG. 13 illustrates further layers in the release stack. [Figure 6] FIG. 13 illustrates a sequence for releasing components with multiple light pulses. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The terminology used to describe certain embodiments is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural unless the context clearly indicates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and / or "comprising" specify the presence of a stated feature but do not exclude the presence or addition of one or more other features. Furthermore, it will be understood that the terms "consisting essentially of" and "essentially consists of" as used herein with respect to materials (e.g., metals, semiconductors, polymers) mean that additional components may be present as long as they do not materially affect the essential properties of the compound or composition. Alternatively or additionally, these terms may be used to indicate a major component having a mass percentage of, for example, >90%, >95%, >99%, >99.9% or 100% (or simply "consisting of" the major component). Furthermore, when a particular step of a method is referred to as succeeding another step, unless otherwise specified, it will be understood that the step may immediately follow said other step or that one or more intermediate steps may be performed prior to performing the particular step. Similarly, when a connection between structures or components is described, it will be understood that the connection may be established directly or through an intermediate structure or component, unless otherwise specified.

[0018] The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. In the drawings, absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. The embodiments may be described with reference to schematic and / or cross-sectional illustrations of idealized embodiments and intermediate structures of the invention in some cases. In the description and drawings, like numbers refer to like elements throughout. Relative terms and their derivatives should be construed to refer to the orientation previously described or shown in the drawings under consideration. These relative terms are for convenience of description and do not require that the system be construed or operated in a particular orientation unless otherwise stated.

[0019] This specification relates to the deployment of a low gas generation laser release stack for rapid transfer of components from a carrier towards an acceptor substrate. In the present invention, a self-limiting bubble formation mechanism is applied in a stack configuration that results in a convex curvature that allows for fast and efficient dewetting of the melt layer melted from the die during the transfer process. Thus, firstly, the components move slowly (without shock waves) due to low pressure build-up, and in the absence of turbulent ambient air or gas, the components tend not to rotate during transfer. This increases the yield of the final product due to improved control over the accuracy of the transfer. Secondly, the curvature formed by the self-limiting bubble in the decomposition layer facilitates more efficient dewetting of the melt layer melted from the microcomponents during the transfer process. This accelerates the release, thus reducing the release time, thereby reducing the contact time between the hot melted melt layer and the polymer adhesive layer. Thereby, a high level of control over the transfer process is achieved while providing a high yield of macrocomponents through an efficient transfer process with high throughput. It also allows for laser die transfer of larger components, as well as reducing debris from the die during the laser die release process. The stack consists of a thermally stable light absorbing layer, a thin decomposition layer that forms a bubble, a metal melting layer, and an adhesive layer. The melting and evaporation temperatures of the various layers are carefully selected to provide a specific functional effect at a specific time during the process.

[0020] The laser release stack consists of four functional layers: a light absorbing metal layer with a high melting temperature; a very thin decomposition layer responsible for bubble formation due to its evaporation temperature higher than the temperature of the metal molten layer (e.g., a metal with the desired evaporation temperature is preferred, but in some cases thin oxides such as Al2O3 or SiO2 or polymers with high decomposition temperatures can also be applied), a metal layer with a low melting temperature, and a polymer adhesive layer with a decomposition temperature that closely matches the melting temperature of the metal molten layer.

[0021] The working principle is that the laser beam (e.g., with a relatively long pulse on the order of tens of microseconds) heats the light absorbing layer sufficiently rapidly so that the underlying metal layer starts to melt. It is noted that the decomposition layer deposited between the metal layers is very thin (on the order of only tens of nanometers) to prevent it from impeding the flow of heat from the absorbing layer towards the molten layer. While the molten layer reaches its melting temperature, where it transforms from a solid state to a liquid during the relatively long pulse, the polymer adhesive that bonds the components to the molten layer of metal starts to release due to the dewetting effect. This occurs even without the decomposition layer, because the surface tension of the liquid metal is much higher than the surface energy of the solid polymer, and therefore the adhesion is easily lost between the two layers, whereas, in contrast, the surface energy of the solid metal layer is generally very high, and the molten layer of metal sticks to the metal layer, such as the light absorbing layer. Thus, the molten metal tends to dewet from the polymer part and choose to release the components together with the polymer part. However, due to the unfavorable aspect ratio of the molten layer, this process requires a significant amount of time. The thickness of the molten layer can be in the sub-micron range because thick metal layers require a large energy input to reach and sustain a molten state, resulting in thermal damage to the component. The lateral foot step of the molten layer can be on the order of tens of micrometers, comparable to the dimensions of a typical component. As a result of this aspect ratio, the thin molten liquid bridge formed by the molten molten layer requires significant time to naturally dewet from large polymer surfaces in order to substantially release the die. This increases the likelihood of undesirable thermal damage to the component.

[0022] To accelerate this dewetting process, while the laser pulse is still putting energy into the release stack while the melt layer melts, the decomposition layer of the present invention intervenes. With its evaporation temperature higher than that of the melt layer and lower than that of the light absorbing layer, the thin decomposition layer reaches its evaporation temperature in the above process, whereby bubbles are formed in the layer, causing the bubbles to make their surface convex. As the curvature increases, the contact angle between the melt layer and the adhesive layer increases, thereby facilitating the release. Importantly, the bubbles are laterally constrained throughout the etching or singulation process, preventing them from propagating laterally, thereby preventing them from affecting nearby adjacent dies on the wafer.

[0023] The present invention allows for selective transfer of components with small dicing streets between them. This is due to the fact that bubble formation is not the primary driver of the transfer process and therefore may be allowed to occur within a limited area underneath the components being transferred. Small dicing streets increase the amount of components that can fit on a single wafer. These small dicing streets cannot be obtained in a blister-assisted laser transfer process where blistering is the primary driver. This is due to the fact that in the conventional method, blistering is the primary driver, so the required blisters need to be large and larger than the components. Larger dicing streets are needed to prevent neighboring components from being prematurely released. Subsequently, conventional blister-assisted approaches require a focused laser beam and therefore precise laser alignment to ensure that the components are transferred straight down.

[0024] An important advantage of the present invention is the use of a four-layer stack that allows the components to be moved with limited or no gas generation (the gas generated by the decomposition layer is very limited and is only needed to form the microbubbles, not to actually push the die). This allows the component movement speed to be limited to ensure that the components follow the desired trajectory. The choice of materials is important: the surface energy, melting temperature and evaporation temperature need to be adapted to achieve the desired movement effect. The self-confinement of the formed bubbles allows to limit the impact on the neighboring dies during the laser die release, while the planar deformation of the molten melt layer caused by the microbubble formation allows a more efficient dewetting of the liquid bridge from the polymer adhesive. Although the polymer adhesive layer is moved together with the components, it can be easily removed afterwards, for example by oxygen plasma.

[0025] 1A illustrates transferring components 15 from a donor substrate 10 to an acceptor substrate 20 by irradiating a release stack "S". In some embodiments, the donor substrate 10 includes a transparent carrier 11 configured to carry the components 15 facing the acceptor substrate 20. Preferably, the release stack "S" is disposed between the transparent carrier 11 and the components 15 to release one or more of the components 15 from the donor substrate 10 onto the acceptor substrate 20. Generally, the release follows immediately after irradiating the release stack "S" with a light beam "L" through the transparent carrier 11.

[0026] In some embodiments, the release stack "S" includes a melt layer 13, for example, having a relatively low melt temperature "Tm13". In other or further embodiments, the release stack "S" includes a light absorbing layer 12 disposed between the transparent carrier 11 and the melt layer 13. In one embodiment, the light absorbing layer 12 has a relatively high absorption coefficient. This may allow for efficient absorption of the light beam "L", thereby causing the light absorbing layer 12 to heat up. In another or further embodiment, the heated light absorbing layer 12 is in thermal contact with the melt layer 13. This may allow for heat to be conducted to the melt layer 13. In this manner, the temperature of the melt layer 13 may be raised above its melt temperature "Tm13". Preferably, the light absorbing layer 12 has a relatively high melt temperature "Tm12", higher than the melt temperature "Tm13" of the melt layer 13. In this manner, the light absorbing layer 12 may remain essentially solid while the melt layer 13 is essentially melted by the heat conducted from the light absorbing layer 12. In some embodiments, the release stack "S" further comprises a decomposition layer 16 between the light absorbing layer 12 and the melt layer 13. In some embodiments, the decomposition layer may comprise a material having an evaporation temperature "Te16" that is higher than the melting temperature "Tm13" of the melt layer 13 and lower than the melting temperature "Tm12" of the light absorbing layer 12. In this manner, the decomposition layer 16 may form a bubble 17 while being heated above its evaporation temperature "Te16". The bubble 17 may facilitate or accelerate the release of the component 15 that may be attached to the melt layer 13 via the adhesive layer 14. The formation of the bubble 17 only accelerates the release and is not the primary driver for the release. The release is driven primarily by the change in adhesion between the various layers of the release stack "S" caused by the melting of the melt layer 13 and by a phase change from solid to liquid that changes the wettability (described further below). The bubble 17 promotes release by initiating movement of the interface between the melt layer 13 and the decomposition layer 16 and by changing the curvature of the melt layer 13, which in turn promotes a reduction in the contact area between the melt layer 13 and the layer below it (e.g., typically the adhesive layer 14). In other or further embodiments, the release stack "S" includes such an adhesive layer 14 disposed between the component 15 and the melt layer 13.This allows component 15 to easily adhere to melt layer 13 while melt layer 13 is solid, and release the adhesive force when melt layer 13 is melted (indicated by "M" in the figure).

[0027] Some embodiments include selectively irradiating areas of the light absorbing layer that form part of the release stack "S" that holds the respective components 15 with a light beam "L" through the transparent carrier 11. In this way, respective portions of the light absorbing layer 12 can be selectively (locally) heated. Preferably, the heat is conducted to the adjacent melt layer 13 of the release stack "S" through the decomposition layer 16 that is between the light absorbing layer 12 and the melt layer 13. In this way, the adjacent melt layer 13 can be at least partially melted. Preferably, the respective portions of the light absorbing layer 12 remain substantially solid while the melt layer is melting. Advantageously, melting of the adjacent melt layer 13 can cause a loss of adhesion between the respective portions of the adjacent melt layer 13 and the adhesive layer 14 of the release stack "S", which causes the respective components 15 to adhere to the adjacent melt layer 13. The loss of adhesion can result in the release and movement of the respective components 15. For example, the release can allow the components to be dropped and / or pushed from the donor substrate 10 to the acceptor substrate 20. In the present invention, the release of the component 15 is prompted by the formation of a bubble 17 in the decomposition layer 16 between the melt layer 13 and the light absorbing layer 12. The decomposition layer 16 has an evaporation temperature "Te16" that is higher than the melting temperature "Tm13" of the melt layer 13. After the melt layer 13 melts, the temperature is further increased while energy continues to be applied via the light beam "L" for the duration of the light pulse. This causes the decomposition layer to melt and then evaporate upon reaching the temperature "Te16", forming the bubble 17. The bubble formation advances the release of the component 15. Although the component 15 would be released even without the decomposition layer 16 in the stack "S", the formation of the bubble 17 hastens the moment of release, thereby allowing the component 15 to receive less heat during the transfer process. As a result, the component 15 suffers less heat damage during the transfer process.

[0028] Preferably, the donor substrate 10 is disposed above the acceptor substrate 20, so that gravity may assist the movement. Alternatively or additionally, the movement may be induced by a force following irradiation. For example, the release may be induced by melting and / or by at least some concomitant gas formation. Aspects of the present disclosure may also be embodied as a system including the donor substrate 10 described herein. For example, the system includes a light source configured to generate a light beam "L" as described herein, and / or a controller.

[0029] In some embodiments, the melt layer 13 comprises or consists essentially of a metal. The inventors have discovered that a melt layer of a metal can provide certain advantages to the present method and system, such as a steady connection to various types of adhesive materials and a well-controlled release of adhesion at a predictable melting point. Alternatively or additionally, other melt materials, such as semiconductor materials, alloys, etc., can be used as well. Advantageously, for example, for the melt layers described herein, a eutectic alloy can combine the adhesive properties of the constituent metals with the flow properties of a pure metal. Moreover, such an alloy can be directly transformed from a solid state to a liquid state or vice versa at a particular composition and temperature without passing two-phase equilibrium. Moreover, the eutectic temperature can be much lower than the melting temperature of two or more pure elements. As will be appreciated, a lower melting temperature "Tm13" is beneficial in selecting an appropriate material for the decomposition layer 16. This is because the evaporation temperature “Te16” of the decomposition layer 16 must be higher than the melting temperature “Tm13” of the melting layer 13 and lower than the melting temperature “Tm12” of the light absorbing layer 12.

[0030] According to other or further embodiments, the decomposition layer 16 may also be made of metal (although alternatives to metal are available). The evaporation temperature "Te16" of the decomposition layer 16 is related to the melting temperature "Tm13" of the melting layer 13, so the choice of material also depends on the choice of material for the melting layer 13. Similarly, the choice of material for the light absorbing layer 12 may also affect the choice of suitable candidate material for the decomposition layer 16, because the evaporation temperature "Te16" of the decomposition layer 16 must be lower than the melting temperature "Tm12" of the light absorbing layer 12. For example, if aluminum (Al) is used for the melting layer 13 and molybdenum (Mb) is applied as the light absorbing layer 12, the decomposition layer 16 may be made of, for example, silver (Ag), gold (Au), or copper (Cu). For example, the table below in this example shows the corresponding melting and evaporation temperatures (at ambient atmospheric pressure).

[0031] [Table 1]

[0032] The above materials are by no means the only candidates, and other metals or alloys or even non-metals with the desired properties that can be used for the decomposition layer 16 can be identified. For example, some oxides (Al2O3 and SiO2) have been mentioned before, which have been tested with acceptable results. Thus, the list of candidate materials is by no means limited to the mentioned materials, and it is considered possible for a person skilled in the art, aware of the requirements of the selection (described above), to identify various candidate materials depending on the material selection made for the fusing layer 13 and the light absorbing layer 12. For example, if the fusing layer 13 is made of, for example, zinc (Tm≈420°C), tin (Tm≈232°C), and / or indium (Tm≈156°C), other or additional candidates can be found.

[0033] In other or further embodiments, the light absorbing layer 12 includes or consists essentially of a metal. The inventors have discovered that a metallic light absorbing layer 12 can provide certain advantages to the present method and system, such as providing relatively good thermal conduction. Moreover, the inventors have discovered that when both the light absorbing layer 12 and the melting layer 13 are metal layers, the melted melting layer 13 may tend to adhere more to the light absorbing layer 12 than to the adhesive layer 14, especially when the adhesive layer 14 is not a metal layer. The same is true for the decomposition layer 16, where the melted melting layer 13 may tend to adhere more to the decomposition layer 16 than to the adhesive layer 14 while this layer is still solid. Similarly, when melted and about to vaporize (such as to form a bubble 17), the decomposition layer 16 made of a metal (e.g., silver (Ag)) also adheres well to the light absorbing layer 12 if the light absorbing layer 12 is made of a metal (e.g., Mb). Similar advantages may also be achieved using light absorbing layers made from semiconductors including, for example, silicon and silicon carbide.

[0034] In some embodiments, the adhesive layer 14 comprises or essentially consists of a polymer-based adhesive, preferably a cross-linked polymer such as an epoxy. Advantageously, polymer adhesives generally have a relatively low thermal conductivity compared to metals, and therefore the thermal conduction to the component 15 can remain relatively low. Moreover, the surface tension of liquid metals is generally much higher than the surface energy of solid polymers. Therefore, the adhesive force between the adhesive layer 14 and the melt layer 13 can be released. In contrast, the surface energy of a solid metal layer is generally relatively high, so that the melt layer 13 of metal can mainly stick to the decomposition layer 16 of metal and the light absorbing layer 12. This means that in some embodiments, only the polymer part is transferred together with the component. Also, other materials can be envisaged for the adhesive layer, which preferably comprises or is essentially formed by an organic layer and / or a non-metallic layer.

[0035] Regardless of the particular material, light absorbing layer 12 has a surface energy per unit area (e.g., mJ / m) that is, for example, at least 2, 3, 5, 10, 20, 50, or more times higher than adhesive layer 14. 2 ), the greater the difference in surface energies, the more likely the molten material will adhere to the light absorbing layer 12 rather than the adhesive layer 14. Generally, the surface energy of the melt layer 13 is lower than the light absorbing layer 12, and the melt layer 13 will melt at a lower temperature, most preferably at a higher temperature than the adhesive layer 14. In one embodiment, when the melt layer 13 in the release stack "S" of the selected component 15 melts, the melt layer 13 adheres primarily to the decomposition layer 16 (while still solid) and then to the light absorbing layer 12 of the release stack "S", while the adhesive layer 14 of the selected component 15 adheres primarily to the selected component 15. For example, the adhesive layer 14 is transferred to the acceptor substrate 20 along with the selected component 15, while the melt layer 13 remains primarily with the portion of the release stack "S" on the donor substrate 10. Preferably, the transferred adhesive layer 14 is removed from the selected component 15 after transfer. For example, the polymeric adhesive layer 14 may be removed from the component via wet or dry etching. For example, 50 percent or more, preferably 70 percent or more, or even 90 percent or more of the melted material adheres to light-absorbing layer 12. Most preferably, substantially all of the melted material remains with the stack on donor substrate 10.

[0036] FIG. 1B illustrates various temperatures "T" and a sequence for releasing components 15 by light-induced heating "H" of a selective layer in a release stack "S". Without being bound by theory, the graph illustrates the duration of the light pulse "Lp", the resulting heat transfer "H13" to the melt layer 13, the heat transfer "H14" to the adhesive layer 14, and the resulting melt layer temperature "T13" (arbitrary scale). Below the graph, the various stages of component release are illustrated. As illustrated in the graph, the melt layer temperature "T13" generally increases initially due to heat conduction "H13" caused by the light pulse "Lp" irradiating the light absorbing layer. When the melt layer temperature "T13" reaches the melting temperature "Tm13", the increase in temperature plateaus while the energy of heat conduction "H13" is used to melt the material, indicated by "M". The temperature increases further after the melt layer 13 melts, reaching a temperature "Te16". This is the temperature at which one or more bubbles 17 form in the decomposition layer 16, facilitating the release and movement of the component 15. As a further consequence to the melting of the molten layer 13, the contact between the molten layer 13 and the adhesive layer 14 is reduced and eventually lost, and thus the heat conduction "H14" to the adhesive layer 14 may be stopped even while the heat conduction "H13" to the molten layer 13 may continue. Advantageously, the stopped heat conduction "H14" to the adhesive layer 14 may mitigate the decomposition of the adhesive layer 14 and / or mitigate damage to the component 15 due to overheating. Thus, in effect, the molten layer 13 may also act as a buffer to protect the component 15 from being damaged.

[0037] In some embodiments, the relatively low melting temperature "Tm13" of the melt layer 13 is less than 1000 Kelvin (<~700°C), preferably less than 600 Kelvin (<~300°C). The lower melting temperature of the melt layer 13 requires less energy to melt, allowing, for example, a weaker light beam "L" and / or lower likelihood of component damage. For example, suitable materials for the melt layer may include aluminum (Tm≈660°C), zinc (Tm≈420°C), tin (Tm≈232°C), and / or indium (Tm≈156°C).

[0038] In other or further embodiments, the melting temperature "Tm12" or, in the case of a non-molten material of the light absorbing layer 12, the decomposition / evaporation temperature is higher than the melting temperature "Tm13" of the melting layer 13. Moreover, the melting temperature "Tm12" or, in the case of a non-molten material of the light absorbing layer 12, the decomposition / evaporation temperature is also higher than the evaporation temperature "Te16" of the decomposition layer 16, for example, by at least 10 Kelvin, preferably by at least 50 Kelvin, more preferably by at least 100 Kelvin, most preferably by at least 200 Kelvin, or even by 500 Kelvin or more. The greater the difference between the melting temperature Tm13 and the evaporation temperature Te16 on the one hand and the melting temperature Tm12 on the other hand, the easier it can be ensured that the light absorbing layer 12 remains substantially solid, while the melting layer 13 is at least partially melted and bubbles are formed in the decomposition layer by heat conducted from the light absorbing layer 12. Preferably, the melting temperature "Tm12" or decomposition / evaporation temperature in case of non-melting materials is at least 1000 Kelvin, ≧~700°C, more preferably at least 2000 Kelvin. Particularly suitable metals for use in the light absorbing layer 12 include molybdenum, which has a relatively high melting temperature of 2896K (2623°C). Also, other metals with relatively high melting temperatures such as chromium (2180K, 1907°C) may be used. As an alternative to metals, also other materials may be used for the light absorbing layer 12, for example semiconductor materials, or other materials that are capable of conducting heat to the melting layer 13 while remaining solid, and preferably have a relatively high absorptivity for the light beam "L". In some embodiments, a wetting control layer 12w may be provided between the (main) light absorbing layer 12 and the melting layer 13. For example, suitable materials for the wetting control layer 12w may include oxides such as aluminum oxide or silicon oxide. These materials also provide viable alternatives for the decomposition layer 16, with embodiments including a thin layer of aluminum oxide or silicon oxide providing a decomposition layer 16 with dual functionality, which may be advantageous in some applications.

[0039] In some embodiments, the light beam "L" irradiating the release stack "S" is configured to raise the temperature "T13" of the molten layer 13 above its melting temperature "Tm13" but remain below its evaporation temperature Te13. For example, the intensity and / or duration of the light beam "L" is adapted in relation to the absorbance of the light absorbing layer 12 to deposit a certain amount of the energy of the light beam "L" in the light absorbing layer 12 resulting in a certain increase in the temperature of the light absorbing layer 12, and to overwhelm a certain amount of heat conduction to the molten layer 13 sufficient to melt the molten layer 13 but not sufficient to cause substantial boiling and / or evaporation of the molten layer 13. The more the evaporation of the molten layer 13 can be suppressed, the more the release of the components 15 can be controlled. For example, explosive release of the components can be attenuated. Advantageously, the evaporation or boiling temperature of the molten layer can be much higher than its melting temperature, especially for a molten layer of metal. For example, the evaporation temperature Te13 of the molten layer 13 is higher than its melting temperature "Tm13" by at least 500 Kelvin, preferably by at least 1000 Kelvin, or even by 1500 Kelvin or more. The greater the difference between the melting and evaporation temperatures, the more easily evaporation of the molten layer can be prevented.

[0040] In some embodiments, the adhesive layer 14 has a decomposition temperature Td14 that is greater than the melting temperature "Tm13" of the melting layer 13 [Td14>Tm13], or greater than 500 Kelvins lower than the melting temperature "Tm13" of the melting layer 13 [Td14>(Tm13-500K)], preferably greater than 400 Kelvins lower than "Tm13", or greater than 300 Kelvins lower than "Tm13". The higher the evaporation or decomposition temperature Td14 of the adhesive layer 14, the better the prevention of inadvertent decomposition and the more controlled release of the components 15 can be obtained. It should be noted that the decomposition temperature Td14 of the adhesive layer 14 is generally applicable to prolonged exposure to that temperature. Therefore, it may be acceptable for the adhesive layer 14 to be exposed for a short period of time to the temperature of the adjacent melting layer 13 that exceeds the decomposition temperature Td14. Also, the molten material may tend to stick to light absorbing layer 12 and / or dewet from adhesive layer 14. For example, suitable materials for the adhesive layer may include photoresist materials such as SU-8. Also, other materials, such as polyimide, may be used.

[0041] As a non-limiting example, consider the following table with approximate parameters:

[0042] [Table 2]

[0043] In some embodiments, the light beam "L" illuminating the release stack "S" is provided as a relatively short light pulse, for example having a FWHM duration of less than 1 millisecond, preferably less than 100 nanoseconds, more preferably less than 10 nanoseconds, or even less than 1 nanosecond. For example, the light can be provided as a nanosecond or picosecond pulse. The shorter the light pulse, the higher the intensity per unit time relative to the duration of the pulse. This can cause a relatively short and strong heating of the stack, and preferably melting the components before the heat decomposes the adhesive layer 14 and / or before the heat damages the components 15.

[0044] In some embodiments, light absorbing layer 12 is configured to absorb at least 10 percent, preferably at least 20 percent, more preferably at least 50 or 60 percent, and most preferably at least 90 percent of the light beam "L" irradiating release stack "S". For example, light beam "L" has a wavelength between 100 nm and 2000 nm (e.g., monochromatic or broadband light), preferably a NIR laser (e.g., 1064 nm). Similarly, other wavelengths, e.g., UV, visible, or infrared, may be used, so long as the material of light absorbing layer 12 can sufficiently absorb that wavelength.

[0045] In some embodiments, the light beam "L" is configured to illuminate only a sub-area of ​​the light absorbing layer 12 that forms part of the selected release stack "S" that holds the selected component 15, without illuminating the immediate area of ​​the light absorbing layer 12, thereby releasing only the selected component 15 while the adjacent components remain attached to the donor substrate 10. For example, the light beam "L" has a beam width "WL" that is approximately equal to or less than the width "W15" of the selected component, and / or the light beam "L" is centered on the selected component. In one embodiment, a light beam "L" is generated having a relatively narrow beam width that illuminates one or more sub-areas of the release stack "S" corresponding to one or more components. In another or further embodiment, the light beam "L" is focused to a relatively narrow beam width, for example, using one or more lenses / mirrors that project a relatively small spot onto one or more sub-areas of the release stack "S". In another or further embodiment, a relatively wide light beam "L" is shaped or patterned, for example using a mask pattern, to generate one or more relatively narrow light beams that strike one or more sub-areas of the release stack "S". In one embodiment, the light beam "L" is generated, for example, by a laser that illuminates a particular component or portion of the mask pattern. Similarly, other light sources may be used, for example a flash lamp that illuminates a portion of the mask pattern or the entire mask.

[0046] 2A and 2B show further aspects including cutting and / or etching parts of the release stack "S". In some embodiments, the release stack "S" is at least partially split or diced (in a projection view) between and / or around the components 15, e.g., along lanes or cut lines "C". For example, one or more layers of the stack may be split before or after connecting the components, preferably at least before the transfer. Preferably, at least the adhesive layer 14 is split such that the portions of the adhesive layer 14 holding the different components 15 are separated from each other. In this way, the transfer of the individual components 15 may be better controlled with little interference of intermediate pieces of the adhesive layer 14. More preferably, the melt layer 13 is also split such that the portions of the melt layer 13 corresponding to the different components 15 are separated from each other. In this way, the melted material of the released components may remain separated from the melt layer 13 of adjacent components, e.g., preventing interference with the later released components. More preferably, the decomposition layer 16 is also divided such that the portions of the decomposition layer 16 corresponding to the different components 15 are separated from each other. In this way, the bubble 17 that forms in the decomposition layer 16 when the evaporation temperature Te16 of the decomposition layer 16 is reached fits itself into the patch under the component 15 to be separated. This prevents the adjacent components 15 from being inadvertently lost during the transfer. Most preferably, the light absorbing layer 12 is also divided such that the portions of the light absorbing layer 12 corresponding to the different components 15 are separated from each other. In this way, the heating of the light absorbing layer 12 remains better localized and / or the heat conduction to the adjacent areas of the light absorbing layer 12 corresponding to the adjacent components can be prevented. It can also be advantageous to align the laser to the components from the back side.

[0047] In some embodiments, as shown, for example, in FIG. 2B, at least a portion of melt layer 13 is removed to provide respective undercuts between components 15 and donor substrate 10. In one embodiment, the area of ​​melt layer 13 holding each component 15 is smaller than the area of ​​each component, for example, at least 2, 3, 4, 5, or more times. By providing a relatively small area of ​​melt layer 13, the material can be more easily melted to release the components without melting adjacent portions of melt layer 13. Preferably, the smaller area is still centered on each component, for example, to mitigate component rotation during movement. In connection with and according to some of these embodiments, thin decomposition layer 16 can also be of a similar size to melt layer 13, as shown in the figure. Self-contained bubble 17 formed by decomposition layer 16 reaching vaporization temperature Te 16 remains adhered to the surface of light absorbing layer 12 due to the surface tension of the layer. In another or further embodiment (not shown), the adhesive layer 14 can also have a smaller area, e.g., so that less material needs to be removed later. In another or further embodiment not shown, the light absorbing layer 12 can also have a smaller area to further improve thermal isolation with adjacent components. For example, portions of the melt layer 13 and / or other layers can be removed below the components by etching, indicated by "E". In another or further embodiment, the width "WL" of the light beam "L" is smaller than the width "W15" of the respective component 15 to be released. For example, the area or width "WL" of the light beam "L" can be adjusted to the area of ​​the melt layer 13.

[0048] FIG. 3A illustrates the masking of light pulses “Lp” to form a relatively narrow light beam L and the relative thicknesses of the various layers. In some embodiments, the mask 30 is aligned with the donor substrate 10. In one embodiment, the mask 30 includes a set of mask windows (open areas) aligned with a subset of the components 15 on the donor substrate 10. In another or further embodiment, a set of light spots (e.g., light pulses Lp) is used to sequentially or simultaneously illuminate the set of mask windows. In another or further embodiment, each light spot (e.g., laser spot) is larger than the respective mask window (where the light spot is illuminated, preferably located at the window center), e.g., has a full width at half maximum (FWHM) spot size (diameter) at least two, three, or more times larger than the width of the mask window, but is sufficiently small, e.g., four or five times smaller, such that the tail of the spot does not substantially illuminate another mask window. Typically, the laser spot has a Gaussian intensity profile. By masking the spot such that only the center of the spot passes through the mask window, the intensity profile can be relatively flat, which can benefit controlled release.

[0049] Preferably, the transparent carrier 11 of the donor substrate 10 is formed by a relatively thin foil, having a thickness "Ds" of, for example, less than 2 millimeters or even less than 1 millimeter. The thinner the transparent carrier, the easier it is possible to irradiate the stack through it (for example, by means of a mask). For example, the donor substrate 10 can be a flexible or rigid substrate. Typically, the components are very small, having a thickness "Dc", height, or other cross-sectional dimension of, for example, less than 100 micrometers, less than 50 micrometers, or even less than 30 micrometers. Typically, the release stack "S" has a much smaller thickness "Dr", for example less than 10 micrometers, or even less than 1 micrometer. Preferably, the components 15 are transferred contactlessly from the donor substrate 10 to the acceptor substrate 20 over a transfer distance "Dt" of, for example, between 1 micrometer and 100 micrometers, preferably between 20 micrometers and 60 micrometers. These ranges allow sufficient distance to prevent unwanted contact on the one hand, and sufficient closeness to allow controlled transfer on the other hand. Alternatively, other distances may be used as well. In some embodiments, it is preferred that the travel distance is greater than the thickness of the component, so that the technique may also be used for repair processes.

[0050] In one embodiment, the light absorbing layer 12 has a layer thickness of less than 500 nm, preferably less than 250 nm, for example between 50 nm and 150 nm. Providing a relatively thin light absorbing layer 12 may allow this layer to be heated relatively quickly. On the other hand, the layer may require some thickness to absorb light. In another or further embodiment, the melting layer 13 has a layer thickness of less than 500 nm, preferably less than 250 nm, for example between 50 nm and 150 nm. Providing a relatively thin melting layer 13 may allow this layer to be heated and melted relatively quickly. On the other hand, the layer may require some thickness to provide its function. In another or further embodiment, the melting layer 13 has a layer thickness of less than 1 micrometer, for example between 50 nm and 500 nm. According to another or further embodiment, the decomposition layer 16 should preferably be thin compared to the melting layer 13. The reason for this is that the decomposition layer 16 should preferably heat up relatively quickly after the melt layer 13 has reached the liquid phase, and furthermore, the heat conduction from the light absorbing layer 12 to the melt layer 13 should remain efficient. The decomposition layer 16 can therefore preferably be 5 to 20 times thinner than the melt layer 13. However, there is also a lower limit to the thickness, since the layer needs to be thick enough to be able to melt and form the bubble 17. The decomposition layer 16 therefore typically has a thickness of the order of a few tens of nanometers, and to give a numerical range, the thickness of the decomposition layer 16 can be between 5 and 100 nanometers, preferably between 5 and 50 nanometers. Furthermore, in principle, the thinner the adhesion layer 14, the less material needs to be washed off afterwards (if this is even necessary). On the other hand, the layer may need some thickness depending on its function, for example 250 nm or more. Also, other layer thicknesses can be used.

[0051] As a non-limiting example, a donor substrate was prepared as follows: Starting with a clean quartz / glass transparent carrier, a 130 nm light absorbing layer of molybdenum is sputtered onto the carrier. A 120 nm fused layer of aluminum is sputtered onto the previous layer. A 500 nm adhesion layer of SU-8 is spin coated onto the previous layer. The carrier and stack are soft baked at 95° C. for 2 minutes. The components are vacuum laminated onto the carrier / stack at 120° C. for 15 minutes. The temporary polymer tape is removed from the components. An oxygen plasma is applied at 500 W for 1 hour to remove the SU-8 between the components. The aluminum and molybdenum are etched in PES etchant 77-23-04 for 2 minutes. The SU-8 resist is hard baked at 250° C. for 3 hours. Of course, other materials, layer thicknesses, temperatures, etc. may be used.

[0052] In some embodiments, the mask 30 is formed by a pattern of light absorbing material disposed on a transparent carrier that forms respective mask windows that can be aligned with the portions of the release stack "S" that hold the respective components 15. By way of non-limiting example, the mask substrate was prepared as follows: Starting with a clean quartz / glass transparent carrier, a 130 nm light absorbing layer of molybdenum is sputtered onto the carrier. 2 μm of HPR504 resist is spin coated onto the light absorbing layer. The stack is soft baked at 95° C. for 2 minutes. The resist is selectively irradiated according to the mask pattern. The HPR504 resist is grown. The HPR504 is hard baked at 120° C. for 2 minutes. The molybdenum is etched in PS etchant for 30 seconds. The HPR504 resist is removed by microstripping. The mask substrate is cleaned. Advantageously, the same or similar light absorbing material can be used for the mask 30 for the light absorbing layers 12 in the release stack "S". Also, other materials, such as standard chrome on quartz masks, could be used because chrome melts at 1907°C and no damage would occur at the fluence and laser power to melt the aluminum layer.

[0053] FIG. 3B shows the sequential release of the components 15. In some embodiments, the components are released from the donor substrate 10 according to a particular sequence, where at least some of the components, preferably most of the components, and most preferably each component 15 in the sequence selected for release, either have four directly adjacent neighboring components on all sides (shown on the left side of FIG. 3B) or no directly adjacent neighboring components on any side (shown on the right side of FIG. 3B). In an embodiment, a combination (not shown) of, for example, having two directly adjacent neighboring components on a first set of two opposing sides and no directly adjacent components on a second set of opposing sides may also be used. For example, the absence of neighboring components may have been absent from the beginning or may have been released previously when they were surrounded by still-present components. By balancing the presence or absence of directly adjacent neighboring components on opposing sides, the release of the components may be more balanced, for example allowing the gas generation of the adhesive layer to push the components out in a directionally controlled manner. For example, the components may be released according to the checkerboard pattern shown. Other patterns may also be envisioned. Furthermore, while the release sequence provides particular advantages in combination with the particular release stacks described herein, it will be appreciated that the sequence may in principle benefit light-induced movement of components using any type of release stack, particularly where the components are released accompanied by gas generation within the stack.

[0054] 4A shows a photograph of components 15 transferred to an acceptor substrate 20 using the methods described herein. In this case, the transferred components are 40×40 μm pixels with a pixel pitch of 200 μm. 24B is a photograph of the surface of the bubble 17 remaining on the surface of the light absorbing layer 12 after the component 15 has been transferred. The convex curvature of the surface is clearly visible. FIG. 4C shows the portion of the stack S' left on the donor substrate 10. In this case, the molten aluminum on the molybdenum is visible after the component has been transferred. As can be seen, the width "Ws" of the remaining stack is about 15 μm, e.g., smaller than the transferred component.

[0055] FIG. 5A illustrates an embodiment in which donor substrate 10, e.g., stack "S", includes a thermal insulation layer 11i between transparent carrier 11 and light absorbing layer 12. As a result, both thermal insulation layer 11i and light absorbing layer 12 may be disposed between transparent carrier 11 and melt layer 13. In some embodiments, thermal insulation layer 11i has a relatively low thermal conductivity, e.g., lower than the thermal conductivity of the material forming transparent carrier 11. In other or further embodiments, thermal insulation layer 11i has a relatively high transparency (to light beam "L"), e.g., higher than the material forming light absorbing layer 12. Advantageously, the relatively transparent insulation may prevent or at least reduce heat conduction from light absorbing layer 12 back to transparent carrier 11 while allowing light beam "L" to pass through transparent carrier 11 to irradiate and heat light absorbing layer 12. In this way, heat may be more efficiently transferred to melt layer 13. In one embodiment, thermal insulation layer 11i is divided between components 15, e.g., as shown. This may further reduce the thermal conduction back to the transparent carrier 11 and / or reduce the thermal conduction between adjacent components. Although the thermal insulation layer 11i is illustrated herein with a specific embodiment, it will be understood that the layer may also be applied (whether divided or not) in combination with any of the other embodiments described herein.

[0056] FIG. 5B illustrates an embodiment in which the donor substrate 10, e.g., stack “S”, includes a dewetting layer 12d between the decomposition layer 16 and the melt layer 13. In general, dewetting describes the process of forcing a fluid to retract from a covered surface, in this case the melted material “M” of the melt layer 13 from the dewetting layer 12d. One factor describing spontaneous spreading and dewetting for a drop of liquid (e.g., with an ambient gas) on a surface solid is the so-called spreading coefficient “S”. Spontaneous spreading occurs when S>0, and partial wetting or dewetting may be observed when S<0. Alternatively or additionally, wetting and dewetting may be described by the equilibrium contact angle θc of a drop of liquid on the surface. The more the surface is wetted, the smaller the contact angle, and the more the surface is dewetted, the smaller the contact angle. In some embodiments, the dewetting layer 12d is applied to facilitate dewetting of the melted material “M” of the melt layer 13 compared to the light absorbing layer 12. For example, the expansion coefficient for molten material "M" on dewetting layer 12d is lower and / or the equilibrium contact angle is higher than the expansion coefficient for molten material "M" on light absorbing layer 12. Controlled dewetting has various advantages, such as retracting molten material "M", which can improve adhesive release of selected component 15. Retraction can also help push selected components by localized accumulation of material. Preferably, dewetting layer 12d has a melting temperature higher than that of melting layer 13, and potentially higher than or comparable to that of decomposition layer 16. Preferably, dewetting layer 12d has a relatively good thermal conductivity and / or is relatively thin, such that heat conduction from light absorbing layer 12 to melting layer 13 is little or not affected. For example, dewetting layer 12d can have the same or similar or higher thermal conductivity compared to light absorbing layer 12. In some embodiments, the dewetting layer 12d is formed by a (thin) coating, e.g. a monolayer, on the decomposition layer 16. As a result, the heated light-absorbing layer 12 can be in thermal contact with the melt layer 13 via the decomposition layer 16 and the dewetting layer 12d. The decomposition layer 16 and the dewetting layer 12d can be combined into a single functional layer if their materials fulfill the requirements of both these layers.For example, the possibility of using aluminum oxide or silicon oxide was suggested above as candidates for a layer providing the functions of both layers 16 and 12d above.

[0057] FIG. 6 illustrates releasing components 15 from donor substrate 10 by irradiating release stack “S” with multiple light pulses as described in the embodiments above. Some embodiments include irradiating respective areas of light absorbing layer forming part of respective release stacks holding respective components with a first light pulse L1 to heat respective portions of light absorbing layer to initiate and / or complete melting of adjacent portions of melt layer. Other or further embodiments include irradiating respective areas of light absorbing layer with a second light pulse L2 to further promote release of components 15 from partially or fully melted material “M” of melt layer 13. In one embodiment, first light pulse L1 is relatively long, e.g., long enough to completely melt melt layer 13 as shown. In another or further embodiment, melt layer 13 may be at least partially melted by first light pulse L1. In another or further embodiment, second light pulse L2 is relatively short and / or has relatively high power compared to first light pulse L1. In some embodiments, the first light pulse L1 causes a relatively slow melting of the melt layer 13, for example, with a longer pulse length of >1 ns, >10 ns, >100 ns, or even >1 μs. In other or further embodiments, the second light pulse L2 causes a relatively high heat flux, for example, with a pulse length of <1 μs, <100 ns, <10 ns, <1 ns, <100 ps, ​​or less. For example, the sudden high heat flux may further promote the release of the components 15 from the partially or fully melted material "M". For example, the second light pulse L2 may cause the formation of a bubble 17 by rapidly heating the decomposition layer 16 above its evaporation temperature Te16. The second light pulse L2 may also cause a shock wave in the melted material and / or at least partial decomposition of the adhesive layer 14. In some embodiments, the first light pulse L1 causes a reduction in the contact area of ​​the melted material, for example by dewetting on the light absorbing layer or optionally the dewetting layer.In some embodiments, the second light pulse L2 causes a final compression to release the components, e.g., by gas generation via decomposition or otherwise. Although this figure shows two separate light pulses, other or further embodiments may use a single modulated light pulse, e.g., with enhanced power at the end of the pulse, to achieve a similar effect. The use of three or more pulses may also be envisioned. In some embodiments, e.g., as shown, the decomposition temperature Td14 of the adhesive layer 14 is higher than the melting temperature Tm13 of the melting layer 13. In other embodiments, this may also be reversed [e.g., within certain limits, e.g., Td14>(Tm13-300K)], e.g., as shown in and described with reference to FIG. 1B.

[0058] It is to be understood that in interpreting the appended claims, the word "comprising" does not exclude the presence of other elements or acts than those recited in a given claim, the words "a" or "an" preceding an element does not exclude the presence of a plurality of such elements, and any reference signs in the claims do not limit their scope, and that any of the disclosed devices or parts thereof may be combined together or separated into further parts unless otherwise stated. [Explanation of symbols]

[0059] 10 Donor Substrate 11 Transparent carrier 11i Insulation layer 12 Light absorbing layer 12d Dewetting layer 12d' Dewetting layer 12w Wetness Control Layer 13 Dissolved layer 13' Dissolved layer 14 Adhesive layer 14' adhesive layer 15. Components 16 split layers 17. Bubble 20 Acceptor Substrate 21 Pad 30 Mask

Claims

1. A method for light-induced transfer of a component (15) from a donor substrate (10) to an acceptor substrate (20), comprising: a transparent carrier (11) configured to carry the component (15) facing the acceptor substrate (20); a release stack (S) disposed between the transparent carrier (11) and the components (15) for releasing one or more of the components (15) from the donor substrate (10) onto the acceptor substrate (20) following irradiation of the release stack (S) by a light beam (L) passing through the transparent carrier (11), the release stack (S) comprising: A melting layer (13) having a melting temperature (Tm13); a light absorbing layer (12) disposed between the transparent carrier (11) and the melting layer (13), the light absorbing layer (12) having an absorption coefficient for absorbing the light beam (L), thereby heating the light absorbing layer (12), the heated light absorbing layer (12) being in thermal contact with the melting layer (13) for conducting its heat to the melting layer (13), thereby raising the temperature of the melting layer (13) above its melting temperature (Tm13), the light absorbing layer (12) having a melting temperature (Tm12) higher than the melting temperature (Tm13) of the melting layer (13) such that the light absorbing layer (12) can remain solid while the melting layer (13) is melted by the heat conducted from the light absorbing layer (12); a decomposition layer (16) disposed between the melting layer (13) and the light absorbing layer (12), the decomposition layer (16) having an evaporation temperature (Te16) higher than the melting temperature (Tm13) of the melting layer and lower than the melting temperature (Tm12) of the light absorbing layer (12), and a layer thickness of the decomposition layer (16) smaller than a layer thickness of the melting layer (13); an adhesive layer (14) that adheres the component (15) to the melt layer (13) while the melt layer (13) is solid and releases adhesive force when the melt layer (13) is melted (M); The method comprises the step of irradiating areas of the light absorbing layer (12) forming part of the release stack (S) carrying respective components (15) with a light beam (L) passing through the transparent carrier (11) in order to heat respective portions of the light absorbing layer (12), the heat being conducted through the decomposition layer (16) to the melt layer (13) of the release stack (S), thereby melting the melt layer (13) and heating the decomposition layer (16) while the respective portions of the light absorbing layer (12) remain solid, and forming a melt layer (13) of the release stack (S). said melting of said decomposition layer (16) causes a loss of adhesion between said melt layer (13) and each portion of said adhesive layer (14) of said release stack (S) that adheres said respective components (15) to said melt layer (13), said loss of adhesion causing release and movement of said respective components (15), and said heating of said decomposition layer (16) causes localized gas generation resulting in bubble formation within said decomposition layer (16), thereby accelerating said loss of adhesion between said melt layer (13) and each portion of said adhesive layer (14).

2. The method of claim 1, wherein the decomposition layer (16) has a melting temperature (Tm16) higher than the melting temperature (Tm13) of the melting layer (13).

3. 3. The method according to claim 1 or 2, wherein the layer thickness of the decomposition layer (16) is less than 20% of the thickness of the molten layer, preferably less than 15% of the thickness of the molten layer, more preferably less than 10% of the thickness of the molten layer.

4. 4. The method according to any one of claims 1 to 3, wherein the layer thickness of the decomposition layer (16) is between 5 and 100 nanometers, preferably between 5 and 50 nanometers.

5. The fusing layer (13) comprises a first metal layer; the light absorbing layer (12) comprises a second metal layer; and / or The method of any one of claims 1 to 4, wherein the decomposition layer (16) comprises one or more of: a third metal.

6. The decomposition layer has an evaporation temperature (Te16) lower than the evaporation temperature (Te13) of the melting layer; or The method according to any one of claims 1 to 5, wherein the decomposition layer has an evaporation temperature (Te16) that is at most 15% higher than the evaporation temperature (Te13) of the molten layer.

7. The light beam (L) irradiating the release stack (S) raising the temperature (T13) of said melt layer (13) above its melting temperature (Tm13) but remaining below its evaporation temperature (Te13); 7. The method according to claim 1, further comprising: increasing the temperature (T13) of the melting layer (13) above the melting temperature (Tm13) and then increasing the temperature (T16) of the decomposition layer (16) above its evaporation temperature (Te16).

8. 8. The method according to claim 1, wherein the adhesive layer (14) has a decomposition temperature (Td14) that is greater than the melting temperature (Tm13) of the melt layer (13) or that is greater than 300 Kelvin lower than the melting temperature (Tm13) of the melt layer (13).

9. 9. The method of claim 1, wherein at least one of the adhesive layer (14), the melt layer (13), the decomposition layer (16), and the light absorbing layer (12) is divided between the components (15).

10. 10. The method according to any one of claims 1 to 9, wherein the area of ​​the molten layer (13) holding each component (15) is at least two times smaller than the area of ​​each component.

11. 11. The method of claim 1, wherein a mask (30) is aligned with the donor substrate (10), the mask (30) includes a set of mask windows aligned with a subset of the components (15) on the donor substrate (10), and a set of light spots is used to sequentially or simultaneously irradiate the set of mask windows for release of each component (15), each light spot being larger than each mask window being illuminated, and a diameter of the light spot FWHM is at least twice as large as a width of the mask window.

12. 12. The method of claim 1, wherein the light absorbing layer (12) is configured to absorb at least 50 percent of the light beam (L) irradiating the release stack (S), and the light beam (L) is configured to irradiate only a sub-area of ​​the light absorbing layer (12) that forms part of a selected release stack (S) holding a selected component (15) without irradiating an area immediately adjacent to the light absorbing layer (12), thereby releasing only the selected component (15) while adjacent components remain attached to the donor substrate (10).

13. 13. The method according to claim 1, wherein the melting temperature (Tm13) of the melt layer (13) is less than 600 Kelvin and the melting temperature (Tm12) of the light absorbing layer (12) is at least 100 Kelvin higher than the melting temperature (Tm13) of the melt layer (13).

14. a transparent carrier (11) carrying components (15) for light-induced transfer with the release stack (S) disposed between the transparent carrier (11) and the components (15) to release one or more of the components (15) from a donor substrate (10) following illumination of the release stack (S) by a light beam (L) passing through the transparent carrier (11), the release stack (S) comprising: A melting layer (13) having a relatively low melting temperature (Tm13); a light absorbing layer (12) disposed between the transparent carrier (11) and the melt layer (13), the light absorbing layer (12) having a relatively high absorption coefficient for absorbing at least 50 percent of a light beam (L) in a wavelength range between 100 nm and 2000 nm and having a pulse length of less than 10 nanoseconds, thereby heating the light absorbing layer (12), the light absorbing layer (12) being in thermal contact with the melt layer (13) for conducting the heat to the melt layer (13), thereby raising the temperature of the melt layer (13) above its melting temperature (Tm13), the light absorbing layer (12) having a relatively high melting temperature (Tm12) higher than the melting temperature (Tm13) of the melt layer (13) so that the light absorbing layer (12) can remain solid while the melt layer (13) is melted by the heat conducted from the light absorbing layer (12); a decomposition layer (16) disposed between the melting layer (13) and the light absorbing layer (12), the decomposition layer (16) having an evaporation temperature (Te16) higher than the melting temperature (Tm13) of the melting layer and lower than the melting temperature (Tm12) of the light absorbing layer (12), and a layer thickness of the decomposition layer (16) smaller than a layer thickness of the melting layer (13); A donor substrate (10) including an adhesive layer (14) that adheres the component (15) to the melt layer (13) while the melt layer (13) is solid and releases adhesion when the melt layer (13) is melted (M).

15. A system for light-induced transfer of a component (15), comprising:

15. A donor substrate (10) according to any one of claims 1 to 14, comprising a transparent carrier (11), a light absorbing layer (12), a melting layer (13), and a release stack (S) having an adhesive layer (14) for holding components (15), said adhesive layer (14) being divided between said components (15); an acceptor substrate (20); a controller and a light source configured to generate a light beam (L) that irradiates through the transparent carrier (11) an area of ​​the light absorbing layer (12) that forms part of the release stack (S) holding the respective components (15) in order to heat the respective portions of the light absorbing layer (12), the heat being conducted through a decomposition layer (16) to a melt layer (13) of the release stack (S), thereby melting the melt layer (13) and heating the decomposition layer (16) while the respective portions of the light absorbing layer (12) remain solid, and The melting of the melt layer (13) causes a loss of adhesion between the melt layer (13) and each portion of the adhesive layer (14) of the release stack (S) that adheres the respective components (15) to the melt layer (13), the loss of adhesion causing the release and movement of the respective components (15), and the heating of the decomposition layer (16) causes localized gas generation resulting in bubble formation within the decomposition layer (16), thereby accelerating the loss of adhesion between the melt layer (13) and each portion of the adhesive layer (14).

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