The present invention is related to the assembly of small components such as micro-electronic components or micro-electronic chips on a substrate. The present invention is more in particular related to the assembly and accurate positioning of small components on a substrate using a laser assisted transfer technique.
For positioning electronic chips on a carrier substrate, various techniques are known, such as the pick-and-place approach or the flip-chip approach. For very small components, such as chips having planar dimensions below 100 μm, the required absolute placement accuracy increases to such a degree that the above methods are no longer cost-effective for high-throughput processing, because the speed of these methods decreases with placement accuracy.
A technique which has been developed specifically for small components is known as Laser Induced Forward Transfer (LIFT). According to this technique the components are attached to a donor substrate. On the front surface of the donor substrate is a so-called dynamic release layer (DRL) to which the components are attached by an adhesive, unless the DRL has itself adhesive properties, in which case the components are attached directly to the DRL. The donor substrate is transparent to laser light of at least one or more specific frequencies. The donor substrate is aligned and positioned parallel to a receiver substrate with the components facing towards the receiver substrate, and a pulsed laser beam at one of said specific frequencies is directed to the back side of the donor substrate, at the location of a component. The laser pulse traverses the transparent donor substrate but not the DRL, the latter being non-transparent to the laser light. The DRL material is chosen such that the laser energy is absorbed by the material, transforming it into a gas at high pressure and temperature, that effectively releases the component from the donor substrate and projects it toward the receiver substrate. Depending on a number of parameters such as the laser power, the thickness of the DRL and the material of the DRL, the DRL may be completely vaporized at the location of the component, in which case the pressure of the expanding gas propels the component towards the receiver. Due to the high pressures occurring and due to several uncontrollable boundary conditions, the control over the component's position is however very difficult in this case. This basic LIFT technique is described for example in patent publication US 2006 0081572. A particular difficulty is that the gas formation exerts not only a thrust force on the component in the direction of the receiver substrate, but also transversal drag forces which tend to divert the component from its desired trajectory. Generally, the effective direction of the force which is exerted on the component depends on many parameters and is very sensitive to variations in the process. It is considered to be uncontrollable in the above-described basic LIFT technique.
A better control is obtainable by the LIFT method described for example in patent publication WO 2012 142177. In this approach the DRL is not fully vaporized, and the gas forms a blister of the remaining DRL material. The blister expands, thereby stretching the adhesive. The blister is thereby inflated, and the mass of the component creates momentum, and the component is peeled off from the adhesive as the blister becomes larger. Once the expansion of the blister comes to an equilibrium, the momentum tears the component away from the adhesive, thereby releasing the component and propelling it towards the receiver substrate. However, as the mass of ultra-small and thin components decreases due to their smaller lateral dimensions, the momentum of such components is insufficient for the required release. Higher laser power could be used, but this is likely to cause the blister to burst in an uncontrolled way, which will again lead to the uncontrolled propulsion of the component and the loss of placement accuracy as described above. Increasing the thickness of the DRL in order to enable higher laser power without bursting could be considered, but this would increase the size of the blister in the plane of the donor substrate.
Another problem related to the difficulty of controlling the transfer using existing LIFT techniques, is that a reliable transfer can only be obtained for small air gaps between the component to be transferred and the receiver substrate. Therefore, the air gap is limited to about 50 μm in many cases. When components need to be transferred to a substrate having a given topography, for example caused by previously transferred chips, or when components of various thicknesses need to be transferred, it may become necessary to increase the air gap, which is often impossible without excessive loss of the directionality of the transferred components.
It is clear that there is a need for a method that allows a more accurate positioning of small and/or thin components, with good controllability and good reliability, at high throughput. This aim is achieved by the method in accordance with the appended claims.
According to the method of the present invention, a nozzle location is predefined in a contact area between a blister forming layer produced on a transparent donor substrate and a component attached to the donor substrate. The component may be attached to the donor substrate by adhering it to the blister forming layer through an adhesive layer or it may be attached directly to the blister forming layer if the blister forming layer itself has adhesive properties. The component, for example an electronic chip, is to be positioned on a receiver substrate facing the donor substrate. The blister forming layer comprises at least a dynamic release layer (DRL). This is a layer consisting of dynamic release material, i.e. material that is vaporized when a pulsed laser beam of a given wavelength and flux density is directed to the donor substrate at the location of the component, from the back side of the donor substrate. The dynamic release layer may be a continuous (non-patterned) layer, or it may be a patterned layer. The application of the pulsed laser beam or multiple pulsed laser beams having the properties required to vaporize the dynamic release material thus creates a blister that contains vaporized dynamic release material. The blister expands until the nozzle is created at the predefined location, the nozzle allowing the vaporized dynamic release material to exit the blister and cause the release of the component and its propulsion towards the receiver substrate.
The nozzle is an opening that is narrow compared to the dimensions of the contact area between the blister forming layer and the component. The nozzle therefore releases a narrow jet of vaporized dynamic release material. The jet fully releases the component, which may already be partially released through the expansion of the blister, and propels the component towards the receiver substrate with a high degree of directionality in a well-controlled way, due to the narrowness of the jet combined with the well-defined position of the nozzle. The invention thereby solves the problem of the loss of directionality in presently known LIFT-techniques, whilst ensuring the effective release of the component, even when the latter is very small or thin. Due to the improved directionality a more accurate positioning of the component is obtained, even for very small or thin components. Due to the improved directionality, the invention also allows the application of a larger air gap between the donor substrate and the receiver substrate, compared to existing LIFT-based techniques.
The blister forming layer may be a stack of a DRL and a non-vaporizing layer, the latter being a layer that is able to form a blister when the dynamic release material underneath it is vaporized, but that does not itself vaporize under the influence of the laser pulse of the pulsed laser beam.
The nozzle location may be defined by the laser itself, for example by tuning the diameter of the laser beam relative to the surface of the area of contact, so that vaporization of the DRL takes place in an area that is small relative to the contact area. According to other embodiments, possibly combined with the previous embodiment, the nozzle location is defined by features integrated in the assembly of the donor substrate and the component, for example by patterning the DRL and/or by producing one or more local indentations and/or reinforcements in the contact area between the component and the blister forming layer.
The invention is in particular related to a method for positioning a component, more in particular a micro-component, on a receiver substrate, comprising the steps of: providing a donor substrate; producing a blister forming layer on the donor substrate, wherein said blister forming layer may be a single layer or a stack of sublayers, said blister forming layer comprising at least a dynamic release layer; attaching the component to the donor substrate by adhering the component to the blister forming layer either directly or through an adhesive layer, so that the component is in direct contact with the blister forming layer or via the adhesive layer across a contact area, said contact area covering the whole or a portion of the dynamic release layer; positioning the donor substrate substantially parallel to the receiver substrate, with the component facing the receiver substrate, the receiver substrate comprising on its surface facing the donor substrate an adhesive receiving layer; directing a pulsed laser beam to the back side of the donor substrate, i.e. to the side of the donor substrate facing away from the receiver substrate, with a footprint of the pulsed laser beam at the location of the component. i.e. at a location within the contact area between the component and the blister forming layer, the pulsed laser beam causing vaporization of at least part of the dynamic release layer, thereby creating a blister containing vaporized material of the dynamic release layer (vaporized dynamic release material), characterized in that the blister expands until at least one nozzle is created at a predefined location within the contact area, the at least one nozzle allowing the vaporized dynamic release material to exit the blister, thereby producing a jet of vaporized material, and causing the release of the component and its propulsion towards the receiver substrate. As a result, the component is positioned on the receiver substrate and attached to the receiver substrate by adhesion to the adhesive receiving layer.
According to an embodiment, the predefined location of the at least one nozzle is defined by applying a pulsed laser beam having a cross section that is considerably smaller than the contact area, and directing the pulsed laser beam at a spot within the contact area, so that the at least one nozzle is created at the position of the spot.
According to an embodiment, multiple pulsed laser beams are directed at multiple spots within the contact area, to thereby create multiple nozzles.
According to an embodiment, the predefined location of the at least one nozzle is defined by the location of at least one indentation in the blister forming layer, in the surface of said blister forming layer opposite the surface of the blister forming layer facing the donor substrate, i.e. in the surface of the blister forming layer opposite the surface by which the blister forming layer is attached to the donor substrate, the at least one indentation being positioned within the contact area.
According to an embodiment, at least one indentation is a point-type indentation, resulting in at least one nozzle producing a line-shaped jet of vaporized material, or at least one indentation is a line-type indentation, resulting in at least one nozzle producing a sheet-shaped jet of vaporized material.
According to an embodiment, the predefined location of at least one nozzle is defined by the location of at least one reinforcing element present on the surface of the blister-forming layer opposite the surface of the blister forming layer facing the donor substrate, i.e. on the surface of the blister forming layer opposite the surface by which the blister forming layer is attached to the donor substrate, and the at least one reinforcing element comprises an open area and reinforcing material around said open area, so that the predefined location of the at least one nozzle corresponds to the location of the open area.
According to an embodiment, at least one reinforcing element is a plate-shaped element formed of a reinforcing material, obtainable by depositing a layer of said reinforcing material on the blister forming layer and patterning said layer of reinforcing material, before attaching the component to the donor substrate. The reinforcing material may be a metal.
According to an embodiment, the blister forming layer is a dynamic release layer, i.e. a layer consisting of dynamic release material.
According to an embodiment, the blister forming layer comprises a stack of a dynamic release layer deposited on the donor substrate, and a non-vaporizing layer deposited on the dynamic release layer.
According to an embodiment, the blister forming layer comprises a patterned dynamic release layer, the patterned dynamic release layer comprising a patch of a dynamic release material, located on the donor substrate at a location within or overlapping the contact area, and a non-vaporizing layer on the patch, and said at least one indentation is present in the non-vaporizing layer and/or said at least one reinforcing element is present on the non-vaporizing layer.
According to an embodiment, the shape of the pulsed laser beam is adapted to one or more of the following: the shape of the component, the shape of the contact area, the number and/or position (location) of the indentations and/or of the reinforcing elements.
The invention is further related to a substrate for use in the method according to the invention, the substrate comprising a donor substrate and a blister forming layer on the donor substrate, wherein the blister forming layer is provided with at least one indentation in the surface of said blister forming layer opposite to the surface by which the blister forming layer is attached to the donor substrate, i.e. in the surface opposite to the surface facing he donor substrate, the at least one indentation being configured for predefining the location of at least one nozzle within the contact area between a component and the blister forming layer, wherein the component is to be attached to the donor substrate by adhering the component to the blister forming layer with the contact area between the component and the blister forming layer overlaying the at least one indentation.
According to an embodiment, the substrate further comprises at least one reinforcing element on the surface of the blister forming layer opposite the surface by which said blister-forming layer is attached to the donor substrate, i.e. to the surface of the blister forming layer opposite the surface facing the donor substrate, and the at least one reinforcing element comprises an open area and reinforcing material around said open area, the at least one reinforcing element being configured for predefining the location of at least one nozzle within the contact area between a component and the blister forming layer, wherein the component is to be attached to the donor substrate by adhering the component to the blister forming layer with the contact area overlaying the at least one reinforcing element, such that predefined location of the at least one nozzle corresponds to the location of the open area.
The invention is further related to a substrate for use in the method according to the invention, comprising a donor substrate and a blister forming layer on the donor substrate, wherein at least one reinforcing element is present on the surface of the blister forming layer opposite the surface by which said blister forming layer is attached to the donor substrate, i.e. opposite the surface facing the donor substrate, and wherein the at least one reinforcing element comprises an open area and reinforcing material around said open area, the at least one reinforcing element being configured for predefining a location of at least one nozzle within the contact area between a component and the blister forming layer, wherein the component is to be attached to the donor substrate by adhering the component to the blister forming layer with the contact area overlaying the at least one reinforcing element, such that the predefined location of the at least one nozzle corresponds to the location of the open area.
According to an embodiment, the blister forming layer comprises a patterned dynamic release layer, the patterned dynamic release layer comprising a patch of a dynamic release material, located on the donor substrate, and a non-vaporizing layer on the patch, and wherein said at least one indentation is present in the non-vaporizing layer in an area overlying the patch and/or said at least one reinforcing element is present in the non-vaporizing layer in an area overlaying the patch.
Before going into detail about the various embodiments for creating a nozzle at a predefined location, the context and general outline of the method of the invention is explained with reference to
Attached to the adhesive layer 3 is an array of components 4, which may for example be micro-sized chips 4 having a square shaped cross-section with a lateral dimension of about 100 μm. Although the invention is particularly advantageous for transferring components of this size and lower, the invention is not limited thereto. The components 4 may have various shapes and dimensions. For example, square or rectangular chips may be used with lateral dimensions ranging between a few tens of micrometres to hundreds of micrometres or more. The thickness may be up to 50 μm or even 100 μm or more.
The aim of the method is to transfer the components (e.g. chips) to a receiver substrate 5 provided, e.g. mounted, such that it faces the donor substrate. The receiver substrate 5 comprises an adhesive layer 6 to which the chips 4 will adhere when they are transferred. Any adhesive layer 6 that is applicable in existing LIFT techniques can be used here. The adhesive layer 6 may be a patterned layer, for example comprising adhesive material only at the locations where the chips 4 are to be received. The receiver substrate 5 may be a substrate to which the chips 4 are to be permanently attached, or a carrier substrate to which the chips are to be temporarily attached. The donor substrate 1 and the receiver substrate 5 are preferably aligned with respect to each other and possibly maintained at a given distance by one or more spacers (not shown) or by using motorized stages to which the donor substrate and the receiver substrate are respectively attached, so as to create an air gap between the two substrates, as generally known from existing LIFT-based techniques.
A laser beam 7 is directed at one of the chips 4 from the back side of the donor substrate 1, i.e. from the side of the donor substrate opposite to the side where the chips 4 are located, i.e. from the side of the donor substrate 1 opposite to the side facing the receiver substrate 5. In other words, the laser beam 7 is directed such that it has a footprint on the donor substrate at the location of the chip, i.e. at a location within the contact area between the component and the blister forming layer. In the context of the present invention, the footprint of the laser beam is defined as the projection of the laser beam on the donor substrate. The laser beam is preferably a pulsed laser beam. According to an embodiment, a single laser pulse (single pulsed laser beam) is applied for releasing the chip. However, it is also possible to apply several laser pulses (several pulsed laser beams) per chip. In the example shown, the laser beam is directed at a spot 8 at the centre of the initial contact area between the chip 4 that is to be irradiated and the blister forming layer 2 (hereafter ‘the contact area’). The spot thus corresponds to the footprint of the laser beam. Geometrical centrality is however not required and the position of the spot 8 may vary according to different embodiments, as will be further described.
At the initial moment of impact of the laser beam, as illustrated in
As illustrated in
According to the invention, the nozzle 11 is formed at a predefined location within the contact area. Different ways are possible for defining the location of the nozzle, in accordance with different respective embodiments of the invention, described hereafter. In each of the embodiments described in
An example of an embodiment of the invention is illustrated in
The chips 4 are attached to the DRL 15 through the adhesive layer 3 which may for example be a BCB (benzocyclobutene) layer. According to the embodiment illustrated in
As illustrated in
In any embodiment according to the invention, the laser beam 7 may be a Gaussian beam, i.e. a monochromatic beam whose amplitude envelope in the transverse plane is determined by a Gaussian function. The diameter of a Gaussian beam is defined within the present context as the width corresponding to the full width at half maximum of the amplitude (FWHM). The laser beam may also be a windowed ‘flat-top’ beam, whose amplitude profile is flat. The diameter of the beam is then defined essentially equal to the width of the amplitude profile. For example, for rectangular chips 4 with lateral dimensions of 90 μm×130 μm and thickness 80 μm, a Gaussian beam having a diameter of about 30 μm, wavelength 355 nm, and a pulse energy of about 9 μJ is appropriate in accordance with this embodiment of the invention, in combination with a DRL 15 in the form of a polyimide film having a thickness between 1 and 3 for example 1.4 and a very thin adhesive layer 3. In combination with a polyimide DRL 15 of 1 to 3 μm thickness, a BCB adhesive 3 with a thickness of less than 500 nm is suitable for placing chips 4 of the size indicated above, for example applying an air gap between the donor substrate and the receiver substrate of about 200 μm (i.e. about 120 μm between the chip 4 and the receiver substrate).
According to other exemplary embodiments, the location of the nozzle 11 is defined by a structural feature of the blister forming layer 2, integrated in this layer prior to the application of the laser beam 7. A first example of such an embodiment is illustrated in
In the embodiment illustrated in
The indentation 20 shown in
According to an embodiment, when the contact area between the component 4 and the donor substrate 1 has an irregular shape, for example an asymmetrical shape, a line-type nozzle may be created that replicates, fully or partially and on a smaller scale, the irregular shape of the contact area, for example in a central portion of said contact area. For this purpose, a line-type indentation 20 having said irregular shape is produced in the blister-forming layer prior to attaching the component to the donor substrate. In this way, the sheet-type jet may be adapted to the shape of the contact area.
For realizing the embodiment of
Alternatively, as illustrated in
Possible methods for preparing the donor substrate 1 to thereby produce a substrate for use in a method as illustrated in
According to a further embodiment, the location of the nozzle is defined by the presence of (the location of) a local reinforcing element on the blister forming layer 2. An example of such an embodiment is illustrated in
The shape and dimensions of the reinforcing element 25 are not limited to the ring-shape shown in the drawings. The reinforcing element 25 at least has an open area that determines the location of the nozzle, but the surrounding material (patterned layer of reinforcing material) of the reinforcing element may have any suitable shape and/or any suitable dimensions. The patterned layer of reinforcing material preferably has a closed circular or polygonal shape, but a non-closed shape such as a non-closed ring formed of separate strips may also have the desired effect. Preferred characteristics in terms of the shape or size of the reinforcing element may depend on the thickness and composition of the blister forming layer, the laser wavelength and/or laser power, or other parameters of the method. The reinforcing element 25 may be have an open area located in the centre of the contact area, or it may have an open area located out-of-centre relative to the contact area, for example as a function of the location of the centre of gravity of the component to be transferred.
The reinforcing element 25 may also be combined with a local indentation 20 in the DRL 15 or in the non-vaporizing layer 17. In this case, the local indentation 20 and the reinforcing element 25 are provided coaxially with respect to each other. When the indentation 20 is line-shaped as for example illustrated in
According to a further embodiment illustrated in
According to other embodiments, more than one nozzle is formed in the contact area between the blister forming layer and a component to be placed and the donor substrate. Such an embodiment is illustrated in
According to a further embodiment illustrated in
In any of the above-described embodiments, a number of parameters may need to be optimized, such as the dimensions of the indentations 20 and/or the reinforcing elements 25, the thickness of the DRL 15 and (if present) the non-vaporizing layer 17, the material of these layers, the type and thickness of the adhesive layer 3 (if present). These parameters may differ as a function of the size and shape of the components 4 that are to be transferred, the applied laser power, the laser diameter etc. The optimization of these parameters is therefore dependent on the specific case in terms especially of the component type and dimensions. This optimization is a process that can be performed by the skilled person on the basis of a reasonable number of trials. One example of suitable parameters in the context of the embodiment of
The method of the invention allows to achieve placement of a large number of components at high throughput rates, as the laser can be displaced quickly from one component to a next one when a plurality of small components attached to the donor substrate is to be transferred to a receiver substrate. Throughput rates of several hundred to tens of thousands of components per second are achievable.
The method is applicable for example for:
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.
Number | Date | Country | Kind |
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20182867.0 | Jun 2020 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2021/067266 | 6/23/2021 | WO |