Patent Publication Number: US-2023156926-A1

Title: Controlled deposition method of a donor material onto a target surface and plate therefor

Description:
BACKGROUND 
     The present application pertains to a method for controlled deposition of a donor material onto a target surface. 
     The present application further pertains to a plate comprising a donor material to be deposited onto a target surface. 
     The present application still further pertains to a deposition device comprising such a plate. 
     A method for controlled deposition of a donor material onto a target surface is known from US2017268107. According to the method disclosed therein, an optically transparent plate having a first surface with one or more wells and a second surface opposite the first surface is provided. After coating the first surface with a thin layer of light-absorbing material, the wells are filled with a donor material. The plate is then irradiated from the second surface with a pulsed light to induce heat in the well and in order to generate gas to transfer the donor material from the well onto a receiving substrate located adjacent to the plate. In this process, the heat flux around the well will determine how the donor material is be ejected. 
     The known method is very suitable for depositing a donor material on flat surfaces. There is a need however for a method that is also suitable for use with uneven surfaces. Such a situation may arise for example if the target comprises a plurality of layers and the donor material is deposited to provide for an electric connection between one product layer and a portion of another product layer extending below that one product layer. In another example, an electric connection is to be formed between a component carrier and electric terminals of a component arranged on the component carrier. 
     Reference is made further to the following prior art. 
     Hongyu Luo ET AL: “Laser-driven programmable non-contact transfer printing of objects onto arbitrary receivers via an active elastomeric microstructured stamp”, National science review, 6 Aug. 2019 (2019-08-06), pages 296-304, XP055728788, DOI: 10.1093/nsr/nwz109 Retrieved from the Internet: URL:https://academic.oup.com/nsr/article-pdf/7/2/296/32921935/ nwz109.pdf [retrieved on 2020-09-08]. Hongyu Luo ET AL disclose a laser-driven programmable non-contact transfer printing technique using an active elastomeric microstructured stamp that features cavities filled with air and embedded under the contacting surface, a micro-patterned surface membrane that encapsulates the air cavities and a metal layer on the inner-cavity surfaces serving as the laser-absorbing layer. The micro-patterned surface membrane can be inflated dynamically to control the interfacial adhesion, which can be switched from strong state to weak state by more than three orders of magnitude by local laser heating of the air in the cavity with a temperature increase below 100°C. 
     WO 2010/081137 A2 provides an imaging array fabrication process method, comprising fabricating an array of semiconductor imaging elements, interconnecting the elements with stretchable interconnections, and transfer printing the array with a pre-strained elastomeric stamp to a secondary nonplanar surface. 
     US 2017/306495 A1 specifies an apparatus for material deposition on an acceptor surface that includes a transparent donor substrate having opposing first and second surfaces, such that at least a part of the second surface is not parallel to the acceptor surface. The transparent donor substrate has a donor film on the second surface. An optical assembly is configured to direct a beam of radiation to pass through the first surface of the donor substrate and impinge on the donor film at a location on the part of the second surface that is not parallel to the acceptor surface, so as to induce ejection of droplets of molten material from the donor film onto the acceptor surface. 
     SUMMARY 
     It is an object of the present application to provide an improved deposition method suitable for deposition of a donor material onto an uneven target surface. In accordance therewith a method is provided as claimed in claim 1. 
     It is a further object of the present application to provide an improved plate for use in the improved method. In accordance therewith a plate is provided as claimed in claim 9. 
     It is a still further object of the present application to provide an improved deposition device that is suitable for deposition of a donor material onto an uneven target surface. In accordance therewith an improved device is claimed in claim 13. 
     The improved method as claimed in claim 1 comprises the following steps. 
     A first main side of a substrate is covered with a stretchable layer. The stretchable layer, e.g from a stretchable polymer like PDMS (Polydimethylsiloxane) or PU (Polyurethane), is attached thereto with a sealing around an enclosed area at the first main side. Therewith an enclosure is defined. 
     The stretchable layer has an outer surface facing away from the substrate that is patterned with one or more recessed areas, such as grooves, trenches, and wells. 
     The one or more recessed areas are filled with the donor material that is to be deposited on the target surface. 
     Subsequently, a relatively high pressure is provided in an interior of the enclosure as compared to a pressure in an exterior of the enclosure. For example pressurized gas or air is supplied inside the interior and/or an environment wherein the plate is arranged is evacuated. Also it may be contemplated to evaporate a substance in the interior to induce an increased vapor pressure therein. As a result of providing the relatively high pressure, a volume of the interior is increased so that the patterned surface of the stretchable layer is pressed against the target surface. 
     With the patterned surface of the stretchable layer being pressed against the target surface the substrate is irradiated with photon radiation at a second main side opposite its first main side. The photon radiation has an intensity and a duration that causes a transfer of donor material from the one or more recessed areas to the target surface. The photon radiation is transmitted through the substrate and the stretchable layer to within the one or more recessed areas, where it induces a vapor pressure at an interface of the donor material facing the flexible layer that results in an ejection of the donor material out of the one or more recessed areas towards the target surface. Due to the relatively high pressure in the enclosure, the stretchable layer is forced to conform to the uneven shape of the target surface. As a result, the patterned surface with the one or more recessed areas comprising the donor material are in close contact with the target surface, therewith providing for a good transfer accuracy. 
     In some embodiments the vapor pressure is induced by evaporation of the donor material. In other embodiments an auxiliary material is provided at the interface that is more easily evaporated than the donor material. Additionally or alternatively, an auxiliary material may be provided at the interface that has a relatively high absorption for the photon radiation that is used. 
     In embodiments the donor material is a viscous substance, so that it can easily deform in accordance with the deformation induced in the stretchable layer. In some of these embodiments the intensity and duration of the photon radiation is selected to at least partially cure the donor material. As in these embodiments, at least the donor material at the interface with the stretchable layer surface is at least partially cured, it is avoided that portions of donor material remain at the stretchable layer surface. In preferred embodiments the donor material is even fully cured while it is ejected towards the target surface. 
     Once the donor material is deposited onto the target surface, the stretchable layer can be released from the target surface. To that end, the plate may be pulled away from the target surface. In some embodiments, the enclosure is deflated by providing for a relatively low pressure in its interior as compared to a pressure in its exterior. E.g. the interior is evacuated and/or the exterior is pressurized. Once the plate with the stretchable layer is removed from the target surface, it can be made ready for reuse by refilling the recessed areas in the stretchable layer. In some cases, refilling is preceded by the step of cleaning the surface of the stretchable layer. 
     The improved plate as claimed in claim 9 comprises a substrate with a first and a second mutually opposite main sides. The first main side of the substrate is covered with a patterned layer that has a patterned surface to be directed towards the target surface. The patterned surface is patterned with one or more recessed areas that are filled with the donor material for deposition on the target surface. 
     The second main side of the substrate is to receive photon radiation that is to be transmitted through the substrate towards the recessed areas with the donor material. In use the photon radiation has an intensity and a duration that causes a transfer of donor material from the one or more recessed areas to the target surface. 
     The improved plate is characterized in that the patterned layer is of a stretchable material which is attached to said the first main side of the substrate with a sealing around an enclosed area at the first main side. Therewith an enclosure is defined with an interior and an exterior. The interior has a volume dependent on a difference in pressure in the interior relative to that in the exterior. 
     In some embodiments the plate has an opening that extends towards the interior of the enclosure, so that the pressure in the interior of the enclosure can be easily controlled. In some examples thereof the opening extends through the substrate. In other examples, the opening extends through the sealing or through the stretchable layer. 
     In some embodiments of the improved plate, the stretchable layer is reinforced with relatively rigid elements. Therewith the deformation can be controlled to therewith improve an alignment accuracy, while still allowing the stretchable layer to conform to the target surface. The relatively rigid elements may for example restrict deformation of the stretchable layer in the neighborhood of the recessed areas. As another example, the relatively rigid elements may be relatively rigid only in one direction and be more flexible in a direction transverse thereto. 
     In an example of these embodiments, the one or more relatively rigid elements locally prevent stretching, but preserve flexibility, and the one or more relatively rigid elements are provided at a side facing away from the substrate with a dielectric coating that provides for an at least substantially uniform heatflux within the recessed portions, in that the dielectric coating has a higher reflectivity for monochromatic photon radiation with a predetermined wavelength incident on a bottom wall of a recessed portion than a reflectivity for said monochromatic radiation incident on a side wall of said recessed portion. The application of the relatively rigid elements in this example, mitigates a damage of the dielectric coating when a pressure is exerted in the interior relative to the exterior of the enclosure. A more detailed description of exemplary dielectric coatings for this purpose is provided in European patent application 20167549.3 filed by the same applicant. 
     In some embodiments of the plate the stretchable layer is attached to the first main side of the substrate at further positions within the enclosed area as an alternative or additional measure to control deformation. 
     In some embodiments, the stretchable layer is attached to the first main side of the substrate at further positions within the enclosed area to locally restrict deformations. 
     In some embodiments of the improved plate a plurality of enclosures is formed on the substrate. The plurality of enclosures either have a respective stretchable layer or have a respective portion of a stretchable layer that is attached to the substrate with a respective enclosing sealing. In these embodiments, the inflation of the enclosures formed therewith can be independently controlled. In case a single stretchable layer is used, its deformation is controlled more strictly than in case it would be attached to the substrate by a single sealing. In variants of these embodiments a stretchable layer or a stretchable layer portion of an enclosure is attached to the first main side of the substrate at further positions within its enclosed area. 
     The deposition device provided herein, comprises in addition to an embodiment of the improved plate in addition a holder, a photon radiation source, a pressure regulation facility and a controller. 
     The photon radiation source is provided to render the photon radiation to be directed towards the second side of the plate. 
     The pressure regulation facility is provided to controllably induce a pressure difference between the interior of the enclosure relative to its exterior. To that end, in some embodiments, the pressure regulation facility is configured to control a pressure in the interior of the enclosure by evacuation of the interior of the enclosure and/or by supplying a gas or mixture of gasses, e.g. air in the interior of the enclosure. In some other embodiments, the pressure regulation facility is configured to control a pressure in the exterior of the enclosure by evacuation of the exterior of the enclosure and/or by supply a gas or a mixture of gasses, e.g. air into the exterior. In again some other embodiments the pressure regulation facility is configured to regulate a pressure in the interior and in the exterior. 
     The holder is provided to hold a target with a target surface facing the first surface of the plate. In some embodiments the holder is configured to hold the target at a fixed position relative to the plate. In other embodiments the holder is configured to move the target. The deposition device may be configured to position a fresh plate or a fresh portion of the plate in front of the radiation source and to position a subsequent portion of the target surface in front of the first surface of the fresh plate or fresh portion of the plate subsequent to a deposition step. 
     The controller is provided to control the pressure regulation facility and the photon radiation source. The controller has a first operational mode wherein it controls the pressure regulation facility to maintain a pressure inside said interior that is lower than said external pressure and wherein in maintains the photon radiation source in a deactivated state. The controller has a second operational mode wherein it controls the pressure regulation facility to maintain a pressure inside said interior that is higher than said external pressure. Therewith it presses the patterned layer towards the target surface, and with the patterned layer pressed against the target surface it causes the radiation source to render the photon radiation with an intensity and a duration that causes a transfer of donor material from the one or more recessed areas to the target surface. The duration of the heat irradiation is typically short, e.g. in terms of microseconds, but usually even shorter, i.e. in terms of nano-seconds. In practice good results with modest technical requirements may be obtained with a pulse duration in the order of a few to a few tens of ns. Nevertheless, in some cases an even shorter pulse duration may be applied, e.g. in the range of 10-500 ps. In a test phase the intensity can be varied from a relatively low value (e.g. corresponding to an exposure (fluence) of about 0.1 J/cm2 ) to a relatively high value (e.g. corresponding to an exposure (fluence) of about 1 J/cm2) to determine for which value or value range the transfer of the donor material is optimal in terms of deposition accuracy. As noted above, in some embodiments, the intensity and duration of the photon radiation is selected to at least partially cure the donor material at the interface with the walls of the recessed area from which it is ejected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A,  1 B  schematically show an embodiment of the plate as claimed herein. Therein  FIG.  1 A  is a plane view of the plate and  FIG.  1 B  is a cross-section according to IB-IB in  FIG.  1 A ; 
         FIGS.  2 A- 2 D  illustrate steps of an embodiment of the method as claimed,  FIG.  2 E  illustrates an alternative application of the method; 
         FIG.  3    shows an alternative embodiment of the plate as claimed; 
         FIG.  4    shows another alternative embodiment of the plate as claimed; 
         FIG.  5    shows an embodiment of a deposition device as claimed. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIGS.  1 A,  1 B  schematically shows a plate  1  that comprises a donor material  2  to be deposited onto a target surface  51  (See  FIG.  2 B ) of a target  5  ( FIG.  2 B ). Therein  FIG.  1 B  shows a cross-section according to IB-IB in  FIG.  1 A . The plate comprises a substrate  10  with a first main side  11  and a second main sides opposite thereto. The first main side  11  of the substrate  10  is covered with a patterned layer  4  that has a patterned surface  41  that is to be directed towards the target surface. The patterned surface  41  is patterned with one or more recessed areas. In the example of  FIGS.  1 A,  1 B  these comprise a first and a second trench  42   a ,  42   e  that are each filled with a proper portion  2   a ,  2   b  of the donor material  2 . In this example, the one or more recessed areas also comprise wells  42   c ,  42   d , and  42   e  that are also filled with a proper portion  2   c ,  2   d ,  2   e  of the donor material  2 . 
     In use, the second main side  12  of the plate  1  is to receive photon radiation to be transmitted through the substrate  10  towards the donor material. The photon radiation applied in said use has an intensity and a duration that causes a transfer of the donor material  2   a ,..., 2   e  from the one or more recessed areas  42   a ,..., 42   e  to the target surface  51  of the target (also denoted as acceptor)  5 . The patterned layer  4  is of a stretchable material and it is attached to the first main side  11  with a sealing  43  around an enclosed area  13  at the first main side  11 . Therewith the substrate  10 , the sealing  43  and the layer of a stretchable material  4  define an enclosure  6  with an interior  61  and an exterior  62  (See  FIG.  5   ). The interior has a volume V 61  dependent on a difference between a pressure P int  in the interior  61  and the pressure P ext  in the exterior  62 . 
     An embodiment of a method using the plate  1  is described with reference to  FIGS.  2 A- 2 E . 
     In a manufacturing step, not shown here, a first main side  11  of a substrate  10  is covered with a stretchable layer  4 . The stretchable layer  4  is attached to the first main side  11  with a sealing  43  that is provided around an enclosed area  13  at the first main side  11 . In some embodiments, the sealing is provided as an epoxy-based adhesive. In other embodiments, the material of the stretchable layer  4  forms itself a sealing. This is possible if the surface at the first main side  11  of the substrate  10  is locally roughened where the sealing is to be formed and the stretchable layer is mechanically adhered to the locally roughened surface. The substrate  10 , the stretchable layer  4  and the sealing  43 , either formed by the material of the stretchable layer itself or formed by a separate material, forms an enclosure  6  with an interior  61  and an exterior  62 . The stretchable layer  4  has an outer surface  41 , facing away from the substrate  10 , that is patterned with one or more recessed areas. In  FIG.  2 A , by way of example the recessed areas  42   a ,  42   b  area shown. 
     In a subsequent step the one or more recessed areas are filled with the donor material  2  to be deposited. In the example shown the recessed area  42   a  is already filled with a portion  2   a  of the donor material, and the recessed area  42   b  is being filled with another portion  2   b  of the donor material, here using a doctor blade 20. Exemplary donor materials for deposition are copper, aluminum, tungsten, chromium, polysilicon provided as particles in a suspension medium, which may further comprise a solvent and a binder. Other materials than metals are also suitable for use as a donor material. The donor material may for example be provided as an ink wherein conductive particles are suspended. Rheological properties of the donor material may be modified by additives or solvent, for example to obtain a shear-thickening, a shear-thinning, a thixotropic, a rheopectic or a Bingham plastic behavior. By way of example, the donor material is a viscous silver nanoparticle ink with a high metal load. In some embodiments the viscosity of the donor material is in a range of 100 - 1000 Pa.s. 
     When filling the recessed areas with the donor material, the interior  61  of the enclosure is typically held at a relatively low pressure P int , i.e. lower than the pressure P ext  prevailing in the exterior. This can be achieved by evacuating the interior  61 , and/or by pressurizing the exterior. 
       FIG.  2 B  shows the plate  1  having the recessed areas filled with the donor material  2   a ,  2   b  and with the interior  61  of the enclosure still held at a relatively low pressure.  FIG.  2 B  further shows the target (acceptor)  5 . As shown in  FIG.  2 B . the target  5  has an uneven surface  51 . 
       FIG.  2 C  shows a next step, wherein a pressure P int  is provided in the interior  61  of the enclosure  6  that is higher than a pressure P ext  in the exterior of the enclosure. Therewith a volume V 61  of the interior  61  is increased and the patterned surface  41  of the stretchable layer  4  is pressed against the target surface  51 , so that its shape becomes compliant with that of the target surface. 
       FIG.  2 C  also shows that in this state the second main side  12  of the substrate  10  is irradiated with photon radiation having an intensity and a duration that causes a transfer of donor material  2   a ,  2   b  from the recessed areas  42   a ,  42   b  to the target surface  51 . The transferred donor material  2   a ,  2   b  therewith forms elements  2   aa ,  2   bb  on the target surface. Due to the fact that the stretchable layer  4  in this state conforms to the target surface  51 ., the donor material can be very accurately deposited thereon. 
       FIG.  2 D  shows how the stretchable layer  4  is released from the target surface  51  by providing for a pressure P int  in the interior  61  of the enclosure  6  that is lower than a pressure P ext  in the exterior. Therewith the elements  2   aa ,  2   bb  formed by the deposited donor material remain at the target surface  51 . In the example shown the target surface is uneven, for example in that the target  5  comprises a plurality of layers  55 ,  56 . The elements  2   aa ,  2   bb  are for example electrical connections between these layers  55 ,  56 . 
       FIG.  2 E  shows another example, wherein a component  52  is mounted on a component carrier  5 , and wherein the method was used to apply electrical connections  2   aa ,  2   bb  between the component carrier  5  and contacts at a component surface  53  elevated above the carrier  5 . 
       FIG.  3    shows an alternative embodiment of the improved plate  1 , as seen at the first side  11  of the substrate  10 . Parts therein corresponding to those in the preceding figures have the same reference in the drawing. In the embodiment shown in  FIG.  3   , the stretchable layer  4  is reinforced with relatively rigid elements  45   a ,  45   b ,  45   c ,  45   d . The recessed areas  42   a ,...,  43   d  are provided in the reinforced portions of the stretchable layer. Therewith a deformation of the stretchable layer  4  to comply with a target surface is still possible, but local deformations in the neighborhood of the recessed areas are mitigated. In exemplary embodiments the reinforcement locally prevents stretching, but preserves flexibility. This is for example the case in an embodiment wherein the reinforced portions with the recessed areas are provided of a relative thin glass layer, e.g. a SiO2 layer, for example having a thickness in the range of 5-10 micron. These locally flexible, but non-stretchable portions may be provided at a side facing away from the substrate with a dielectric coating that provides for a uniform heatflux within the recessed portions as specified in more detail in European patent application 20167549.3 filed by the same applicant. Alternatively, or additionally, the stretchable layer  4  may be reinforced in regions outside the recessed areas. Alternatively, or additionally the stretchable layer  4  may be attached to the first main side  11  of the substrate  10  at further positions within the enclosed area to control the way in which it can be deformed by pressure differences. 
     As shown in  FIG.  4   , a plurality of enclosures is formed on the substrate  10 . Each enclosure has a proper stretchable layer portion  4 _ 1 ,  4 _ 2 ,..., 4 _ 9  of a stretchable layer  4  that is attached to the substrate with a proper enclosing sealing  43 _ 1 ,  43 _ 2 ,..., 43 _ 9 . The internal pressure in these enclosures can be independently controlled via respective channels  14 _ 1 ,  14 _ 2 ,..., 14 _ 9 . In the example shown, the stretchable layer portions are locally reinforced in the same way as shown in  FIG.  3   . In other embodiments, a reinforcement may be absent. Whereas in the example of  FIG.  4    a single stretchable layer  4  is used, alternative embodiments exist wherein one or more enclosures have a proper stretchable layer. It may be contemplated to use different stretchable materials for different enclosures dependent on their position on the plate  1 . 
       FIG.  5    schematically shows a deposition device  100  comprising an improved plate  1 , for example as shown in and described with reference to one of the preceding figures. 
     The deposition device  100  further comprises a holder 9 to hold a target  5  with a target surface  51  facing the first surface  11  of the plate  1 . The deposition device  100  further comprises a photon radiation source  3  to render the photon radiation that is to be directed towards the second side  12  of the plate  1 , as shown in  FIG.  2 C . 
     The deposition device  100  also comprises a pressure regulation facility  7  to controllably induce a pressure difference between said interior  61  relative to the exterior  62 . In the embodiment shown, the pressure regulation facility  7  is coupled via a first conduct  71  and an opening  14  in the plate  1  to the interior  61  of the enclosure  6 . The components of the deposition device  100  are arranged in a closed housing  110 , that confines the exterior  62  of the enclosure  6 . The pressure regulation facility  7  has a second conduct  72  with an opening in the exterior  62 . Therewith, the pressure regulation facility  7  can both control a pressure inside the interior as well as a pressure inside the exterior  62 . In other embodiments the pressure regulation facility  7  controls one of the pressures. For example an embodiment of the device  100  not having a closed housing, the pressure regulation facility  7  is used to control the pressure in the interior  61  of the enclosure  6  only. 
     The deposition device  100  comprises a controller  8  to control the pressure regulation facility  7  and the photon radiation source  3 , in  FIG.  5    with a control signal C 3  and a control signal C 7  respectively. 
     The controller  8  has a first operational mode wherein it controls the pressure regulation facility  7  to maintain a pressure inside the interior  61  that is lower than the pressure in the exterior  62 , and wherein in maintains the photon radiation source  3  in a deactivated state. The controller has a second operational mode wherein it controls the pressure regulation facility  7  to maintain a pressure inside the interior  61  that is higher than the pressure in the exterior  62 . Therewith the stretchable patterned layer  4  is pressed towards the target surface  51 . With the stretchable patterned layer  4  pressed against the target surface  51  as shown in  FIG.  2 C , it causes the radiation source  3  to render photon radiation R 3  with the proper intensity and duration that causes a transfer of donor material  2   a ,  2   b  from the one or more recessed areas  42   a ,..., 42   e  to the target surface  51 . Various options are available. In one option a large area of the second side  12  of the plate is irradiated with the proper intensity and duration that causes a simultaneous transfer of donor material in the recessed areas of the plate. By way of example, in that case an excimer laser is used as the photon radiation source  3 . Alternatively, a scanning laser is used that generates a laser beam that is scanned over the area with the donor material to be transferred as is schematically shown in  FIG.  2 C . Also in this case the laser can be a pulsed laser, but that is not necessary. In this case the duration with which the area is locally exposed to the radiation can alternatively (or additionally) be controlled with the speed with which the laser beam is scanned. Therewith the exposure duration is inversely proportional to the scanning speed. 
     Typically the controller  8  has a transient operational mode in which the photon radiation source  3  is kept in a deactivated state as long as the state wherein the stretchable patterned layer  4  is compliant with the target surface  51  is not yet achieved. Typically the controller  8  also has a release operational mode in which the stretchable patterned layer  4  is released from the target surface  51 , by reducing the relative pressure (relative to the external pressure) prevailing in the interior  61  as shown in  FIGS.  2 D and  2 E . 
     Further embodiments of the deposition device are provided with transport facilities to automatically replace the plate  1  by a fresh plate and to replace the target  5  by a new target once it has received the donor material. The controller  8  can therewith control such transport facilities.