EP3247529A1

EP3247529A1 - Angled lift jetting

Info

Publication number: EP3247529A1
Application number: EP16739876.7A
Authority: EP
Inventors: Zvi Kotler; Michael Zenou
Original assignee: Orbotech Ltd
Current assignee: Orbotech Ltd
Priority date: 2015-01-21
Filing date: 2016-01-05
Publication date: 2017-11-29
Also published as: WO2016116921A1; CN107206548A; US20170306495A1; TW201639654A; IL253169A0; CN107206548B; EP3247529A4; KR20170102984A

Abstract

An apparatus for material deposition on an acceptor surface 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, and including a donor film on the second surface. The apparatus additionally includes an optical assembly, which 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.

Description

ANGLED LIFT JETTING

FIELD OF THE INVENTION

The present invention relates generally to laser direct writing, and particularly to methods and systems for Laser Induced Forward Transfer jetting.

BACKGROUND OF THE INVENTION

Laser-Induced Forward Transfer (LIFT) is a technology for direct printing of various materials such as metals and polymers. LIFT provides high printing quality however advanced electronic devices comprise three-dimensional (3D) patterns that are hard to coat uniformly. Examples of prior art techniques are provided below .

U.S. Patent 6,792,326, to Duignan, whose disclosure is incorporated herein by reference, describes a material delivery system for miniature structure fabrication which has a substrate, a material carrier having a deposition layer, and a laser beam directed towards the material carrier element. The system operates in either an additive mode of operation, or a subtractive mode of operation so that a workpiece does not have to be removed from a tool when change of modes of operation takes place .

U.S. Patent 6, 805, 918, to Auyeung, et al . , whose disclosure is incorporated herein by reference, describes a method for laser transfer and deposition of a rheological fluid wherein laser energy strikes a target substrate comprising a rheological fluid, causing a portion of the rheological fluid to evaporate and propel non-evaporated rheological fluid onto a receiving substrate . U.S. Patent 7,277,770, to Huang, whose disclosure is incorporated herein by reference, describes a direct write process and apparatus for fabricating a desired circuit component onto a substrate surface of a microelectronic device according to a computer-aided design (CAD) .

U.S. Patent application publication 2005/0095367, to Babiarz, et al . , whose disclosure is incorporated herein by reference, describes a method of noncontact dispensing a viscous material onto a surface of a substrate, which uses a jetting valve having a nozzle directing the viscous material flow in a jetting direction nonperpendicular to the surface of the substrate. The nonperpendicular jetting direction results in the droplet producing a reduced wetted area on the substrate.

Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that, to the extent that any terms are defined in these incorporated documents in a manner that conflicts with definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered .

SUMMARY OF THE INVENTION

An embodiment of the present invention that is described herein provides an apparatus for material deposition on an acceptor surface including 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, and including a donor film on the second surface. The apparatus additionally includes an optical assembly, which 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.

In some embodiments, the second surface includes a periodic structure. In other embodiments, the second surface includes a multi-faceted structure. In yet other embodiments, the second surface includes first and second facets oriented at opposing angles and coated with different respective donor films. In alternative embodiments, the second surface includes first and second facets wherein only the first facet is coated with the donor film. In an embodiment, the second surface includes a curved structure.

There is additionally provided, in accordance with an embodiment of the present invention, an apparatus for material deposition including a transparent donor substrate having opposing first and second surfaces, such that at least a part of the second surface is non-planar, and including a donor film on the non-planar part of the second surface. The apparatus additionally includes an optical assembly, which 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 non-planar part of the second surface, so as to induce ejection of droplets of molten material from the donor film onto an acceptor surface.

There is additionally provided, in accordance with an embodiment of the present invention, a method for material deposition including providing a transparent donor substrate having opposing first and second surfaces and having first and second facets oriented at opposing angles on the second surface, and including a donor film on the first and second facets. The donor substrate is positioned in proximity to an acceptor substrate, with the second surface facing toward the acceptor substrate. A beam of radiation is directed to pass through the first surface of the donor substrate and impinge on the donor film at a location selected responsively to the first and second facets of the second surface, so as to induce ejection of droplets of molten material from the donor film on the first and second facets onto the acceptor substrate .

There is further provided, in accordance with an embodiment of the present invention, a method for material deposition including providing a transparent donor substrate, which has opposing first and second surfaces and has a donor film on the second surface. The donor substrate is positioned in proximity to an acceptor surface of an acceptor substrate, with the second surface facing toward the acceptor substrate and oriented at an oblique angle, i.e., at a non-normal angle, relative to the acceptor surface. A beam of radiation is directed to pass through the first surface of the donor substrate and impinge on the donor film while the second surface is oriented at the oblique angle so as to induce ejection of droplets of molten material from the donor film onto the acceptor surface.

The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which : BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic, pictorial illustration of a system for direct writing on a substrate, in accordance with an embodiment of the present invention;

Fig. 2 is a schematic side view showing details of the system of Fig. 1, in accordance with an embodiment of the present invention;

Figs. 3 - 6 are schematic, sectional views showing details of non-planar Laser-Induced Forward Transfer (LIFT) donors, in accordance with embodiments of the present invention; and

Fig. 7 is a schematic sectional view showing details of a non-planar LIFT donor, which is not parallel to an acceptor substrate, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

OVERVIEW

Embodiments of the present invention that are described hereinbelow provide methods and apparatus that enhance the capabilities and usability of Laser-Induced Forward Transfer (LIFT) techniques. The enhancements offered by these embodiments are useful for printing on electronic circuits comprising various types of substrates, and particularly for printing on three- dimensional (3D) structures. The disclosed techniques are by no means limited to these specific application contexts, however, and aspects of the embodiments described herein may also be applied, mutatis mutandis, to LIFT-based printing on substrates other than electronic circuit substrates. The enhancements include printing of both metallic and non-metallic materials.

In a typical LIFT-based system, a small distance between a donor surface and an acceptor substrate yields high printing quality on the substrate. However, printing on 3D structures on the substrate poses two challenges: a possible large distance between the donor surface and the lower surfaces of the acceptor, (yielding low printing quality on the acceptor) and a possible poor coating ("step coverage") of vertical sidewalls of the 3D structures of the substrate.

Embodiments of the present invention that are described hereinbelow overcome some of these limitations by providing different, novel types of donor structures and orientations, and corresponding methods of operation of LIFT systems. In some embodiments, a transparent donor substrate has opposing first and second surfaces, such that at least a part of the second surface is not parallel to an acceptor surface and comprises a donor film thereon. An optical assembly is configured to direct a beam of radiation to pass through the first surface of the donor substrate so as to impinge on the donor film at a location on the part of the second surface that is not parallel to the acceptor surface. The impingement induces ejection of droplets of molten material, such as metals and polymers, from the donor film onto the acceptor surface .

In other embodiments, the second surface comprises a multi-faceted, periodic structure, wherein at least some of the facets are coated with donor films. The multi- faceted structure comprises first substantially similar facets and second substantially similar facets, and the first and second facets are oriented at opposing angles and are coated with different respective donor films. In yet other embodiments, the second surface of the donor comprises first substantially similar facets and second substantially similar facets, which are not parallel to a horizontal surface of the substrate, as well as third substantially similar facets, which are parallel to the horizontal surface of the substrate but which are not coated with donor films. The third facets may be used for in-situ inspection of the LIFT process through the donor.

In alternative embodiments, the second surface comprises a curved structure.

In another embodiment, a transparent donor substrate has opposing first and second surfaces, such that at least a part of the second surface is non-planar and has a donor film on the non-planar part of the second surface. An optical assembly directs 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 non- planar part of the second surface, so as to induce ejection of droplets of molten material from the donor film onto an acceptor surface.

SYSTEM DESCRIPTION

Fig. 1 is a schematic, pictorial illustration of a system for direct writing on a substrate 24, in accordance with an embodiment of the present invention. This system and its components are shown here solely to illustrate the sort of environment in which the techniques described herein may be implemented. Such techniques may similarly be carried out using suitable equipment of other types and in other configurations. The system of Fig. 1 is built around a print and direct write apparatus 10, which operates on substrate 24 of an electronic circuit 12, such as a Flat panel Display (FPD) or a printed circuit board (PCB) , which is held on a mounting surface 14. In generic LIFT processes substrate 24 is also termed a receiver or an acceptor. The terms "Flat panel Display", "FPD", "printed circuit board", and "PCB" are used herein to refer generally to any sort of a dielectric or a metal or a semiconductor substrate on which conductive materials such as metals, or non-conductive materials such as dielectrics and polymers are deposited, regardless of the type of substrate material and the process used for deposition. Apparatus 10 may be used to deposit new layers such as printing of metal circuitry on various substrates or in any other electronic devices.

Apparatus 10 comprises an optical assembly 16, containing a laser and optics for Laser-Induced Forward Transfer (LIFT) . Optical assembly 16 and its operations are described with reference to Fig. 2 below. In some embodiments, direct printing applications, such as are performed by apparatus 10, for example as patterning or layer deposition on a PCB or FPD or any other applicable device, may comprise other diagnostics capabilities that may be in-situ (i.e., monitoring and inspecting during the printing process), integrated (i.e., monitoring and inspecting selected devices immediately after completion of the LIFT process), or offline, by a stand-alone diagnostics system.

A positioning assembly, in the form of a bridge 18, positions optical assembly 16 over pertinent sites on substrate 24 in question, by linear motion along the axes of apparatus 1. In other embodiments, the positioning assembly may be in other forms, such as a moving stage along one (X) axis, two (X, Y) axes, or three (X, Y, Z) axes below circuit 12 and static assembly 16. A control unit 27 controls the operation of the optical and positioning assemblies, and carries out additional functions such as temperature control, so as to carry out the required inspection, printing, patterning and/or other manufacturing and repair operations, as described below.

Typically, control unit 27 communicates with an operator terminal 23, comprising a general-purpose computer including a processor 34 and a display 36, along with a user interface and software.

Fig. 2 is a schematic side view showing details of apparatus 10, and particularly of optical assembly 16, in accordance with an embodiment of the present invention. A laser 13 emits pulsed radiation, which is focused by optics 15. The laser may comprise, for example, a pulsed Nd:YAG laser with frequency-doubled output, and the pulse amplitude of the laser may be controlled conveniently by control unit 27. (Control unit 27 may also be configured, albeit possibly by non-trivial means, to control the pulse duration.) Optics 15 are similarly controllable in order to adjust the location and size of the focal spot formed by the laser beam.

In some embodiments an additional laser (not shown) or any other illumination source (e.g., LED or lamp), with different beam characteristics, may be used. The additional laser may operate in another wavelength and with another optics setup, and may be used, for example, for surface inspection. Optical assembly 16 is shown in Fig. 2 in the LIFT configuration. Optics 15 focus the beam from laser 13 onto a donor 19, which comprises a donor substrate 17 with one or more donor films 18 deposited on substrate 17. Typically, substrate 17 comprises a transparent optical material, such as glass or a plastic sheet, or other types of transparent substrates, such as silicon wafers or flexible plastic foils. The beam from laser 13 is aligned (by motion assembly 18) with a selected site on substrate 24 of circuit 12, and donor 19 is positioned above the site at a desired gap width D from the substrate. Typically, this gap width is at least 0.1 mm, and the inventors have found that gap widths of 0.2 mm or even 0.5 mm or greater can be used, subject to proper selection of the laser beam parameters.

Optics 15 focus the laser beam through the outer surface of substrate 17 onto film 18, thereby causing droplets of molten material to be ejected from the film, across the gap and onto the surface of device substrate.

Fig. 3 is a schematic, sectional view showing details of a non-planar LIFT donor 22A, in accordance with an embodiment of the present invention. Donor 22A is transparent to a laser beam 28 and comprises two surfaces, a planar first (upper) surface 23A, typically perpendicular to laser beam 28 and parallel to substrate 24, and a second (lower) surface 21A, which faces substrate 24. In an embodiment, the lower surface of donor 22A is non-planar and comprises two or more facets, which are not parallel to substrate 24. In the example of Fig. 3, the lower surface of donor 22A comprises substantially similar facets 32, and substantially similar facets 26. Facets 32 are typically parallel to laser 28, and facets 26 have a slope (gradient) and are coated with one or more films of materials 26M to form a single layer or a multilayered stack of respective materials. In the disclosure and in the claims, a facet is assumed to have a surface which is flat and plane.

During a LIFT process, laser beam 28 provides pulsed radiation on donor 22A. The radiation passes through surface 23A and impinges on the donor film of a selected facet 26. Since the selected facet is not parallel to an acceptor surface 33A of substrate 24, herein assumed to be parallel to a base surface 35A of the substrate, ejection of droplets 30 of molten material from the donor film occurs at an angle 29 to acceptor surface 33A of substrate 24. Acceptor surface 33A of substrate 24 is also referred to herein as top surface 33A of the substrate. Typically, the ejection of droplets 30 is orthogonal to facet 26, and is indicated by an arrow 31. Thus, while laser beam 28 is perpendicular to substrate 24, the slope of facet 26 causes the angled ejection illustrated, so as to deposit droplets 30 on a sidewall of a structure 25A on substrate 24. As is illustrated in the figure, structure 25A has surfaces, such as the sidewall, which are not parallel to acceptor surface 33A, i.e., to base surface 35A. In the description hereinbelow, other structures 25B, 25C, 25D, 25E are mounted on substrate 24. The other structures have the same property as structure 25A described here, i.e., they have surfaces which are not parallel to the base surface of substrate 24.

In the example of Fig. 3, the angle of droplet ejection from coated facets is set primarily by the design of donor 22A. In typical LIFT processes, a small distance between donor 22A and substrate 24 (as well as structure 25A) yields high printing quality on substrate 24 and structure 25A. In addition, the multi-faceted structure provides easy jetting in predefined desired directions perpendicular to each of the facets, and thus enables high coating uniformity of sidewalls of a 3D structure.

In some embodiments, the lower surface of donor 22A comprises a periodic structure (as shown in Fig. 3) . In other embodiments, the structure of the lower surface of donor 22A may have a non-periodic structure with different slopes of facets along the lower surface of donor 22A. I.e., the structure may be different from the center of donor 22A to the edge of the donor. For example the slope angle of facets at the edge of donor 22A may be steeper than the angle of the facets at the center.

In an alternative embodiment, the lower surface of donor 22A may comprise more than two facets as will be described with respect to Fig. 5.

Fig. 4 is a schematic, sectional view showing details of a non-planar LIFT donor 22B, in accordance with an embodiment of the present invention. Donor 22B is transparent to laser beam 28 (not shown in Fig 4) . An upper surface 23B of donor 22B is parallel to top surface 33A of substrate 24. A lower surface 21B of donor 22B is non-planar and comprises a multi-faceted structure, such as substantially similar facets 40 and substantially similar facets 42, which are not parallel to acceptor surface 33A of substrate 24. Each facet thus has a different slope with respect to the acceptor surface of substrate 24. In an embodiment, the facets are oriented at opposing, not necessarily equal, angles (e.g., +45° and -30°) with respect to beam 28. Both facets may be coated with different respective donor films such as material 26M, as described with respect to Fig. 3, and another material.

Such dual material structures may be manufactured by various techniques, such lithography, direct evaporation (in the case of metal coating) , or by placing bi-angled (e.g., pyramidal) structures with different materials coated on each facet. (In some embodiments some of the facets may be left uncoated.) During LIFT operation the two materials may be ejected substantially simultaneously, for example by using two or more beams in parallel. Alternatively or additionally, a high repetition rate laser may be scanned to effectively achieve simultaneous jetting. The simultaneous ejection may be used to form a mixed material (e.g., a compound) on substrate 24. Further alternatively or additionally, the two materials may be printed consecutively to form mixed material structures.

Since facets 40 and 42 are not parallel to the surface of substrate 24, the ejection of droplets 30 of molten material from the donor film occurs at an angle to the surface of substrate 24, (i.e., angle 29 in Fig. 3) . In an embodiment both facets 40 and 42 are coated with films formed by similar or by different materials. In an alternative embodiment, only one facet (e.g., facet 40) is coated with a film. The ejection of droplets 30 from facet 40 is indicated by an arrow 41, and droplets 30 eject, typically at an orthogonal angle to surface 40, so as to coat the left sidewall of a structure 25B. An arrow 43 illustrates ejection of droplets 30 from facet 42, typically at an orthogonal ejection angle to facet 42, so as to coat the right sidewalls of structure 25B. Both ejections also coat the top surfaces of substrate 24 and structures 25B, which are parallel to the upper surface of donor 22B.

In some embodiments, the ejections of droplets 30 are performed simultaneously, and in the case of different materials on each facet, the ejections of droplets 30 may form a mixed film (e.g., a compound or an alloy) of the respective materials on substrate 24. In other embodiments, the ejection of droplets 30 from facet 40 is performed before or after the ejection of droplets 30 from facet 42. In the case of different materials on facets 40 and 42, the sequential ejections of droplets 30 may form a multi-layered structure or a mixed material structure in the same layer on substrate 24.

The ejecting angles of the droplets are defined by the slopes of facets 40 and 42 respectively. In some embodiments, the coated materials on facets 40 and 42 are similar, so as to print the same material across structures 25B and substrate 24. In other embodiments, the coated materials may be different, so as to print mixed or multi-layered materials on structures 25B and substrate 24.

Fig. 5 is a schematic, sectional view showing details of a non-planar LIFT donor 22C, in accordance with an embodiment of the present invention. Donor 22C is transparent to laser beam 28 (not shown in Fig. 5) . In some embodiments, donor 22C may be configured to be transparent to another laser or another illumination source, such as an LED or a lamp, that may be used for LIFT process inspection, as is described hereinbelow. An upper surface 23C of donor 22C is parallel to top surface 33A of substrate 24. A lower surface 21C of donor 22C comprises substantially similar facets 50 and substantially similar facets 52, which are not parallel to surfaces 33A and 35A of substrate 24, and substantially similar facets 54, which are parallel to surface 33A.

Facets 50 and 52 may be coated with the same materials or with different materials on each facet, as described with reference to Fig. 4. In some embodiments, facets 54 are not coated and may be used for in-situ inspection during a LIFT process so as to monitor the quality of the LIFT printing process. Alternatively or additionally, the uncoated facets may be used for additional inspection applications such as registration and/or alignment. The inspection via the uncoated facets may use the same laser as is used for ejection or an additional laser (not shown in Fig. 5) or any other suitable illumination source (e.g., a LED or a lamp) as is described above.

In other embodiments, facets 54 may be coated with material to be ejected, typically perpendicularly to substrate 24 in an ejection illustrated by arrow 55. The ejections from facets 50 and 52 (illustrated by arrows 51 and 53, respectively), are typically perpendicular to facets 50 and 52 respectively. Arrows 51 illustrate that droplets 30 from facets 50 coat the left sidewalls and the top surfaces of structures 25C. Arrows 55 illustrate that droplets 30 coat the top surfaces of structures 25C. Arrows 53 illustrate that droplets 30 coat the right surfaces of structures 25C. The ejection angles of facets 50 and 52 are set primarily by the respective slopes of the facets.

Fig. 6 is a schematic, sectional view showing details of a non-planar LIFT donor 22D, in accordance with an embodiment of the present invention. Donor 22D is transparent to laser beam 28. An upper surface 23D of donor 22C is parallel to top surface 33A of substrate 24. A lower surface 21D of donor 22D comprises one or more curved structures 71 which are coated by a donor film on top of a flat lower surface 77 of donor 22D. Each curved structure 71 has a thickness h and a width L. Structures 71 are also referred to herein as elements 71. By way of example, four curved elements 71 are shown in Fig. 6, and are assumed to be sections of respective spheres with equal radii of curvature 73.

However, it will be understood that elements 71 may comprise substantially any curved surface, and so, for example, may comprise sections of a cylinder, or sections of another curved entity such as an ellipsoid. Furthermore, elements 71 may be arranged in a periodic manner on surface 21D, or may be arranged to be non- periodic .

Typically, the width L of each element 71 is substantially larger that the thickness h of the same element, so as to avoid distortion of the spot of beam 28 when it impinges on element 71. In an embodiment, thickness h is about 100 pm or less, for a gap 79 between donor 22D and surface 33A in a range of 200 pm to 300 pm or more. Such values of the thickness and the gap ensure that the printing conditions between donor 22D and substrate 24 are substantially uniform. The curvature of element 71 and the location of beam 28 where it impinges on the element define an ejection angle 6_e of droplet 30 from the element, the droplet typically being ejected orthogonally to the region of impingement. Thus, an operator may control the position of beam 28 on the curved donor so as to achieve a required ejection angle of a given droplet 30 for a desired position on the substrate. In general, by controlling the positions of beam 28, donor 22D, and/or substrate 24, the operator may select the ejection angle of droplets 30 to be any angle within a continuous range, and may thus change the landing angle and the landing position of each droplet 30 on surface 33A and on structures 25D. In an embodiment, the continuous range of ejection angles lies between +30° and -30° measured with respect to beam 28.

For example, when beam 28 impinges on the center of element 71 (herein assumed to be parallel to surface 33A) , droplet 30 is typically ejected orthogonally to surface 33A, as is illustrated by arrow 72. In this case the droplet coats surface 33A or the top surface of 25D. When beam 28 impinges on the right side of element 71, ejection of droplets 30 from the donor film occurs at an angle, as is illustrated by arrow 74. In this case, the droplets land at a non-normal angle (such as angle 29 described in Fig. 3) to acceptor surface 33A, or on a left sidewall of structure 25D. Similarly, when beam 28 impinges on the left side of element 71, ejection of a droplet 30 from the donor film occurs at an opposite angle to that when the beam impinges on the right side of the element, as is illustrated by arrow 76. In this case, the droplet lands at an opposite angle (compared to the example represented by arrow 74) to acceptor surface 33A, or on a right sidewall of structure 25D.

In close packing of elements 71, width L is dictated by a maximal allowed ejection angle and thickness h of element 71. If 6_m is the maximal ejection angle, then the width of element 71 (for the element a section of a sphere) is given by the following equation:

2Sin(6_m)

1 - Cos(0_m) Thus for example, setting the thickness h to 100 μπι and assuming a maximal ejection angle of 30°, the curved surface width L is about 750 μπι, which is substantially larger than a typical spot size. Similar considerations apply for other compact curved structure cases.

Fig. 7 is a schematic sectional view showing details of a non-planar LIFT donor 22E, which is not parallel to surfaces 33A and 35A of substrate 24, in accordance with embodiments of the present invention. Donor 22E is tilted at a tilt angle 66, measured between a plane upper surface 23E of donor 22E, and a horizontal line parallel to surfaces 33A and 35A of substrate 24. Surface 23E acts as a defining plane surface of donor 22E, and tilt angle 66 is between surface 23E and a line parallel to surfaces 33A, 35A of substrate 24.

Donor 22E is transparent to laser beam 28 and comprises a lower surface 21E which is coated by donor films and which faces substrate 24 at an oblique angle. Structures 25E are located on substrate 24 and typically have a three-dimensional (3D) structure as shown in Fig. 7. In an embodiment, a user 11 of apparatus 10 (Fig. 1) identifies a topographic feature on the 3D structure of structures 25E and positions donor 22E so that the lower surface of the donor is aimed towards a surface of the 3D structure at an angle that is oblique, i.e., non-normal, to the surface. Once donor 22E and substrate 24 are positioned, the user directs beam 28 to impinge on donor 22E so as to eject material from the donor films, typically orthogonal to the lower surface of donor 22E, onto the 3D structure. For example, if angle 66 equals 10° and droplets 30 are ejected orthogonally to the lower surface of donor 22E, the droplets will be ejected at 100° with respect to the horizontal line parallel to substrate 24, and will land on the top surface of structures 25E at an angle of 80° (90° - 10°) measured relative to surface 33A of substrate 24.

In some embodiments, surface 21E of donor 22E comprises multiple facets, such as facets 62 and 64, which are typically coated by donor films. In other embodiments, surface 21E is planar (i.e., does not comprise facets), and is coated with a donor film.

During a LIFT process, laser beam 28 emits pulsed radiation onto donor 22E. The radiation passes through surface 23E and impinges on the donor films on the lower surface of donor 22E, so as to induce ejections of droplets of molten material from the donor film, onto the acceptor surfaces, comprising portions of surface 33A of substrate 24 and upper surfaces of structure 25E in the example of Fig. 7.

In a first case of a planar (non-faceted) surface

21E of donor 22E, the ejection angle from the donor film is constant across the donor, and thus, beam 28 ejects droplets towards structure 25E at an angle 90° + angle 66. As a result, droplets 66 land on the top surfaces of substrate 24 and structures 25E at a non-orthogonal angle. As described in the above example, angle 66 equals 10° and thus the ejection angle from donor 22E is 100° and the landing angle on the top surface of structures 25E is 80°. In the case of the droplets landing on a sidewall of structure 25E, which is orthogonal to the surface of substrate 24, the landing angle will typically be 10° with respect to the surface of the sidewall.

In a second case (shown in Fig. 7) the lower surface of donor 22E comprises substantially similar facets 62 and substantially similar facets 64. In this embodiment during the LIFT process, beam 28 passes through surface 23E and impinges on the donor film of facet 62 resulting in ejection (represented by arrow 68) of droplets 30 towards the right sidewalls and the horizontal top surfaces of structures 25E. In this case, the ejecting and landing angles depend on angle 66 and the slope angle of facet 62 with respect to surface 21E.

For example, if angle 66 equals 10°, the angle of facet 62 is 60° with respect to the lower surface of donor 22E, and the ejection is orthogonal to the surface of facet 62, then the angle of ejection from facet 62 (arrow 68) equals 10° + 60° + 90°, which equals 160° with respect to the lower surface of donor 22E. The landing angle of droplets 30 on the top surface of structures 25E will be 20° (90° - 70°), and the landing angle on the left orthogonal sidewalls of structures 25E will be 70°.

Similarly, beam 28 passes through the upper surface of donor 22E and impinges on the donor film of facet 64 resulting in ejection of droplets 30 (represented by arrow 70) towards the right sidewalls and the horizontal surfaces of structures 25E.

In both embodiments a non-zero tilt angle 66 provides specific locations on donor 22E that are closer to substrate 24 compared to a parallel donor-to-acceptor configuration. Smaller distance between the donor and the acceptor typically results high printing quality in a LIFT process .

In Fig. 7, the left side of donor 22E is lower than the right side due to tilt angle 66, and together with facets 62 and 64, may provide short distances between the films on donor 22E and structures 25E (so as to provide higher printing quality of droplets 30 on structures 25E at these short distances) compared to prior art systems. The tilted embodiment provides high printing performance in cases of non-uniform height across structures 25E, as shown in Fig. 7, where the right side of structure 25E is higher than the left side of the structure.

As is illustrated in Fig. 7, the combination of a non-zero tilt angle 66 and a multi-faceted structure on the lower surface of donor 22E provides a flexibility to adapt the LIFT process with respect to specific topographies of structures 25E. For example, in Fig. 7 the highest 3D structure is in the right side of structures 25E and thus the donor 22E is tilted down to the left. In an opposite case where the 3D structures are higher on the left side of structures 25E, donor 22E may be tilted down to the right, which means that tilt angle 66 is opposite to the angle shown in Fig. 7. For example, instead of 10°, angle 66 will be -10° (or 170°) . A combination of adaptable tilt angle and multi-faceted structure of the donor provides flexibility that can be used to achieve small distances between surface 21E of donor 22E and structures 25E, and thus, to provide high printing quality for any type of 3D features of structures 25E.

It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Claims

1. Apparatus for material deposition on an acceptor surface, comprising:

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, and comprising a donor film on the second surface; and an optical assembly, which 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.

2. The apparatus according to claim 1, wherein the second surface comprises a periodic structure.

3. The apparatus according to claim 1, wherein the second surface comprises a multi-faceted structure.

4. The apparatus according to claim 3, wherein the second surface comprises first and second facets oriented at opposing angles and coated with different respective donor films .

5. The apparatus according to claim 3, wherein the second surface comprises first and second facets and wherein only the first facet is coated with the donor film.

6. Apparatus for material deposition, comprising:

a transparent donor substrate having opposing first and second surfaces, such that at least a part of the second surface is non-planar, and comprising a donor film on the non-planar part of the second surface; and

an optical assembly, which 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 non-planar part of the second surface, so as to induce ejection of droplets of molten material from the donor film onto an acceptor surface.

7. The apparatus according to claim 6, wherein the second surface comprises a periodic structure.

8. The apparatus according to claim 6, wherein the second surface comprises a curved structure.

9. The apparatus according to claim 6, wherein the second surface comprises a multi-faceted structure.

10. The apparatus according to claim 9, wherein the second surface comprises first and second facets oriented at opposing angles and coated with different respective donor films .

11. The apparatus according to claim 9, wherein the second surface comprises first and second facets and wherein only the first facet is coated with the donor film.

12. A method for material deposition, comprising:

providing a transparent donor substrate having opposing first and second surfaces and having first and second facets oriented at opposing angles on the second surface, and comprising a donor film on the first and second facets; positioning the donor substrate in proximity to an acceptor substrate, with the second surface facing toward the acceptor substrate; and

directing a beam of radiation to pass through the first surface of the donor substrate and impinge on the donor film at a location selected responsively to the first and second facets of the second surface, so as to induce ejection of droplets of molten material from the donor film on the first and second facets onto the acceptor substrate.

13. The method according to claim 12, wherein the ejection of droplets of molten material from the donor film on the first and second facets is performed simultaneously .

14. The method according to claim 12, wherein the ejection of droplets of molten material from the donor film on the first and second facets is performed sequentially .

15. A method for material deposition, comprising:

providing a transparent donor substrate, which has opposing first and second surfaces and has a donor film on the second surface;

positioning the donor substrate in proximity to an acceptor surface of an acceptor substrate, with the second surface facing toward the acceptor substrate and oriented at an oblique angle relative to the acceptor surface; and

directing a beam of radiation to pass through the first surface of the donor substrate and impinge on the donor film while the second surface is oriented at the oblique angle so as to induce ejection of droplets of molten material from the donor film onto the acceptor surface .

16. The method according to claim 15, wherein positioning the donor substrate comprises identifying a three-dimensional (3D) shape of a topographical feature on the acceptor surface, and orienting the donor substrate responsively to the 3D shape.

17. The method according to claim 15, wherein the second surface comprises a curved structure.

18. The method according to claim 15, wherein the second surface of the donor substrate comprises a multi-faceted structure .

19. The method according to claim 18, wherein the multi- faceted structure comprises first and second facets oriented at opposing angles and coated with the donor film.

20. The method according to claim 19, and comprising ejecting the droplets from the donor film of the first and second facets, onto the 3D shape, simultaneously.

21. The method according to claim 19, and comprising ejecting the droplets from the donor film of the first and second facets, onto the 3D shape, sequentially.

22. The method according to claim 15, wherein the second surface of the donor substrate comprises a periodic structure.