Pattern transfer printing systems and methods

Pattern transfer printing (PTP) systems and methods are provided to improve the quality, accuracy and throughput of pattern transfer printing. PTP systems comprise a tape handling unit for handling a tape with pattern transfer sheets sections and for controllably delivering the pattern transfer sheets one-by-one for paste filling and consecutively for pattern transfer, with the tape moving from an unwinder roll to a re-winding roll. PTP systems further comprise a paste filling unit which enables continuous paste filling using a supporting counter roll opposite to the paste filling head, a wafer handling unit controllably delivering wafers for the pattern transfer in a parallelized manner that increases throughput, a paste transfer unit with enhanced accuracy and efficiency due to exact monitoring and wafer alignment, as well as a print quality control unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Chinese Patent Applications Nos. 02111321391.3 and 202122732445.7, both filed on Nov. 9, 2021, and Israel Patent Application No. 290194, filed on Jan. 19, 2022, which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. TECHNICAL FIELD

The present invention relates to the field of pattern transfer printing, and more particularly, to producing photovoltaic cells.

2. DISCUSSION OF RELATED ART

U.S. Patent Application Publication No. 2017/013724, which is incorporated herein by reference in its entirety, teaches an apparatus for generating a transfer pattern to be used in a transfer printing process. The pattern is generated in a substrate that could be a web substrate and that bears one or more trenches. A filler, e.g., high viscosity metal paste, to be transferred is made to fill the trenches within the web substrate. Upon completion of the trench of the substrate filled with filler, the filling head, which may include a scraper and a squeegee, is translated from the working zone in a synchronized movement, such that in course of the translation movement the filling head remains in full contact with the substrate.

Lossen et al. (2015), Pattern Transfer Printing (PTP™) for c-Si solar cell metallization, 5thWorkshop on Metallization for Crystalline Silicon Solar Cells, Energy Procedia 67:156-162, which is incorporated herein by reference in its entirety, teaches pattern transfer printing (PTP™) as a non-contact printing technology for advanced front side metallization of c-Si PV solar cells, which is based on laser-induced deposition from a polymer substrate.

SUMMARY OF THE INVENTION

The following is a simplified summary providing an initial understanding of the invention. The summary does not necessarily identify key elements nor limit the scope of the invention, but merely serves as an introduction to the following description.

One aspect of the present invention provides a pattern transfer printing (PTP) system comprising: a tape handling unit configured to handle a tape comprising, as sections thereof, a plurality of pattern transfer sheets having respective patterns of trenches, and to controllably deliver the pattern transfer sheets for paste filling and consecutively for pattern transfer, a paste filling unit configured to fill the trenches on the delivered pattern transfer sheets with conductive printing paste, a wafer handling unit configured to controllably deliver a plurality of wafers for the pattern transfer at a close proximity to the pattern transfer sheet, a paste transfer unit configured to transfer the conductive printing paste from a respective one of the pattern transfer sheets onto a respective one of the delivered wafers, by releasing the printing paste from the trenches upon illumination by a laser beam, wherein the tape handling unit is configured to move the tape in a step-and-repeat manner from an unwinder roll to a re-winding roll and optionally to clean and dry the tape after printing during such movement.

Another aspect of the present invention provides a pattern transfer printing (PTP) system comprising a wafer handling system in which each of two x,z-stages working in parallel comprise two chucks for holding wafers, each chuck ensuring wafer movement in y, θ-axis thus enabling faster wafer handling and continuous wafers movement during pattern transfer. Multiple cameras imaging incoming wafers enable more accurate wafer alignment within the printing system thus more accurate alignment of printed conductive lines onto wafer pattern.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide efficient and economical methods and mechanisms for pattern transfer printing and thereby provide improvements to the technological field of producing electrical contacts, and specifically of producing photovoltaic cells. Pattern transfer printing (PTP) systems and methods are provided to improve the quality, accuracy and throughput of pattern transfer printing. PTP systems comprise a tape handling unit for handling a tape with pattern transfer sheets and for controllably delivering the pattern transfer sheets one-by-one for paste filling and consecutively for pattern transfer, with the tape moving from an unwinder roll to a re-winding roll. PTP systems further comprise a paste filling unit which enables continuous paste filling using a supporting counter roll opposite to the paste filling head, a wafer handling unit controllably delivering wafers for the pattern transfer in a parallelized manner that increases throughput, a paste transfer unit with enhanced accuracy and efficiency due to exact monitoring and wafer alignment, as well as a print quality control. The PTP system may be configured to be used in a dual lane configuration with two parallel wafer flows so that the tape and the paste replacement and maintenance in each system are accessible from their front sides.

FIG.1Ais a high-level schematic illustration of a pattern transfer printing (PTP) system100, according to some embodiments of the invention.FIGS.1B and1Care high-level schematic illustrations of maintenance options and arrangements of PTP systems100in a dual-lane production line101, according to some embodiments of the invention.FIG.1Ais a schematic perspective front view of PTP system100,FIG.1Bis a schematic perspective view of a front side102of PTP system100, made accessible for easy maintenance, andFIG.1Cis a schematic top view of PTP systems100arranged in a dual-lane production line101.FIGS.2A and2Bare high-level schematic side view and front view illustrations, respectively, of units and elements in PTP systems100, according to some embodiments of the invention. The highly schematic side view illustration ofFIG.2Aprovides a non-limiting example for the arrangement of elements in tape handling unit200with respect to paste filling unit120(carrying out a paste filling stage203) and paste transfer unit350(carrying out a pattern transfer stage353, see, e.g., inFIGS.2A and2B), while the highly schematic front view illustration ofFIG.2Bprovides a non-limiting example for the arrangement of elements in wafer handling unit400and with respect to tape handling unit200. Units and elements illustrated inFIGS.2A and2Bare described briefly below, with more details of non-limiting embodiments providing in the consecutive figures. One or more control units105(see, e.g., inFIGS.2A and2B), may be configured to monitor and/or control the units of PTP system100, possibly via various processors, and coordinate the operation of PTP system100.

PTP system100is configured to apply patterns of conductive material onto wafers by non-contact printing. PTP system100comprises a tape handling unit200configured to handle a tape205(see, e.g.,FIG.2A) comprising, as sections thereof, a plurality of pattern transfer sheets205A,205B (see, e.g.,FIG.2A) having respective patterns of trenches, and to controllably deliver pattern transfer sheets for paste filling205A and consecutively for pattern transfer205B, respectively. Tape handling unit200is configured to move tape205in a step-and-repeat manner (sheet by sheet) from an unwinder roll222to a re-winding roll242. PTP system100further comprises a paste filling unit120configured to fill the trenches on delivered pattern transfer sheets205A with conductive printing paste. Tape handling unit200may be further configured to deliver the pattern transfer sheets one-by-one for the paste filling (denoted sheets205A) and/or for the pattern transfer (denoted sheets205B) with continuous monitoring of the tension and the Machine Direction (MD, along the tape movement) and Cross Machine Direction (CMD, perpendicularly to MD) positions of tape205. PTP system100further comprises a wafer handling unit400configured to controllably deliver a plurality of wafers90(see, e.g.,FIG.2B) for the pattern transfer, at a close proximity (e.g., in a range of between 0.1 mm and 0.5 mm) to the pattern transfer sheet. The PTP system100further comprises a paste transfer unit350configured to transfer the conductive printing paste from respective pattern transfer sheet205B onto respective delivered wafer90B, by releasing the printing paste from the trenches upon illumination by a laser beam80(illustrated, e.g., inFIG.3A).

The units of PTP system100are mounted on a rigid frame in a compact manner, to minimize the system's footprint. As a general design feature, tape handling is carried out along a vertical direction (denoted “z”) and along one horizontal direction (denoted “y”, termed machine direction, MD), while wafer handling is carried out along a perpendicular direction thereto, e.g., in another horizontal direction (denoted “x”, termed cross machine direction, CMD).

Tape handling unit200may be configured to deliver pattern transfer sheets one-by-one for the paste filling (e.g., pattern transfer sheet205A)—at a paste filling process stage203, by help of a moving paste filling head122—and/or for the pattern transfer (e.g., pattern transfer sheet205B)—in a paste pattern transfer unit carrying out paste transfer process stage353, by help of a movable scanner355(e.g., moveable along the x and y axes and optionally tiltable at an angle θ, or possibly an optical head that scans along the y axis, is moveable along the x axis and optionally tiltable at an angle θ), see, e.g.,FIG.2A. Details concerning tape205and pattern transfer sheets thereupon are provided below. It is noted that inFIG.2Bpattern transfer sheet205A is illustrated schematically at the plane of the drawing as it is located in the paste filling unit120almost vertically. For example, paste filling unit120and pattern transfer sheet205B plane may be set at an angle deviating 0-30° from the vertical x-z plane.

In embodiments, one or more top dancer225and bottom dancer245(see, e.g.,FIG.2A) may be configured to buffer the step-and-repeat movement of tape205from unwinder roll222and to re-winding roll242, respectively, as pattern transfer sheet205A is being filled with paste and/or as paste from pattern transfer sheet205B is being transferred, so as to ensure that these are carried out with the respective pattern transfer sheet in static positions. Top dancer(s)225and/or bottom dancer(s)245may be configured to maintain the tension in tape205moving through at least a part of PTP system100.

It is noted that in PTP system100, paste filling unit120is positioned almost vertically (along the z axis) to ensure a short travelling distance of pattern transfer sheet205A from paste filling to pattern transfer sheet205B at paste transfer unit350thus enabling to minimize changes of the filled paste condition (e.g., due to drying before printing) . For example, the near-vertical position may be configured to enable a smaller movement distance for the pattern transfer sheets from state205A to state205B, and thereby optionally to locate the laser scanner just behind the vertical filling unit, closer to roll227A positioned between205A and205B, illustrated schematically inFIG.2A. The near-vertical position of paste filling unit120is advantageous with respect to prior art horizontal position of paste filling units, as it reduces the distance between the paste filling position (205A) and the paste transfer position (205B) of the pattern transfer sheet205.

As illustrated schematically inFIG.1B, front side102of PTP system100may be configured to have unwinder roll222and re-winding roll242easily accessible for replacement and maintenance requirements, as well as have paste filling unit120easily accessible for paste filling and maintenance requirements—from same front side102. Moreover, as illustrated schematically inFIG.1C, PTP systems100may be arranged back-to-back, in dual-lane production line101, with each of front sides102of PTP systems100A,100B easily accessible for maintenance. Dual-lane production line101may be configured to include two lanes101A,101B, each with one or more (serially arranged) PTP systems100A,100B, which operate on two (or more) paths of wafers90(e.g., independent paths for higher throughput), using a relatively small footprint.

PTP system100may further comprise a tape re-use unit250(see, e.g.,FIG.2A) configured to clean pattern transfer sheets after the pattern transfer to provide reusable pattern transfer sheets. For example, tape re-use unit250may comprise a tape cleaning unit252in which tape205may be cleaned mechanically, e.g., using scraper(s), ultrasound, and/or other means, and/or chemically using cleaning solutions; and a tape drying unit255, with idle rolls244,246positioned as needed to maintain safe tape movements. Tape205may be moved by one or more tape drive motor(s)230(illustrated schematically), and further supported by one or more rolls227along the way of tape205through PTP system100. A non-limiting example for tape handling unit200is illustrated with more details inFIGS.3A-3E. A non-limiting example for tape re-use unit250is illustrated with more details inFIG.4.

Paste filling unit120(see, e.g.,FIG.2A) may comprise moveable paste filling head122and a countering moveable roll125configured to support a back side of pattern transfer sheet205A during the paste filling. A non-limiting example for paste filling unit120is illustrated with more details inFIGS.5A-5E.

In certain embodiments, wafer handling unit400may comprise at least one stage410enabling movement in x and z axes (termed in the following—the x,z-stage), with each stage410comprising at least one holder (e.g., chuck)415, and with each holder supporting wafer90and enabling wafer movement in y and θ axes (θ axis relates to rotation of a wafer with respect to the x-y plane). In certain embodiments, two x,z-stages410of wafer handling unit400may be configured to operate in parallel with respect to each other. Each stage410may comprise two holders415for holding wafers90, each holder415ensuring wafer movement in y, θ-axis thus enabling faster wafer handling and continuous wafers movement during pattern transfer. Multiple cameras imaging incoming wafers enable more accurate wafer alignment within the printing system thus more accurate alignment of printed conductive lines onto wafer pattern.

Wafer handling unit400(see, e.g.,FIG.2B) may comprise two stages410A,410B, with each stage410supporting two wafers90, e.g., via wafer holders415A,415B (e.g., vacuum chucks). Each stage410may support at least one wafer holder (chuck)415, e.g., two or three holders (chucks)415. As a non-limiting example, two holders (chucks)415A,415B for each of two stages410A,410B are illustrated. Stages410may be configured to enable movement along the x and z axes, while each holder (chuck)415may be configured to support wafer90and enable additional wafer movement at least along the y and θ axes, as explained below.

Wafer handling unit400may be configured to alternate two stages410A,410B during operation to enable parallel operation on wafers90by different units of PTP system100. For example, the position of wafer90A may be measured by a wafer alignment unit420while wafer90B received transferred paste by paste transfer unit350and wafer90C is inspected by a print quality control unit450, as disclosed herein. During the alteration of stages410, two wafers90may be processed by respective units, increasing the overall throughput of PTP system100. For example, wafer handling unit400may be configured to provide simultaneous (i) wafer measurement of two wafers90A (first and second wafers, mounted on holders (chucks)415A and415B on stage410A, respectively), (ii) pattern transfer to a third wafer90B (mounted on holder (chuck)415A on stage410B) and (iii) print quality control of a fourth wafer90C (mounted on holder (chuck)415B on stage410B). Then, wafer handling unit400may be configured to move stages410A,410B according to arrows411A, so that the wafers are move to the consecutive operations (e.g., wafer90A is moved from wafer measurement to pattern transfer, wafer90B is moved from pattern transfer to print quality control and wafer90C is moved out of the system, while a new wafer is moved to wafer measurement). Following the linear stage movements along CMD, stages410A,410B may be switched (arrow411B), so that wafer90are further processed, and the movements repeat cyclically, as illustrated schematically inFIG.6C).

Wafer handling unit400may further comprise mechanical elements such as input wafer conveyor412for supplying wafers90and mounting them on wafer holders415of respective stage410and output wafer conveyor419for receiving printed wafers90from wafer holders415of respective stage410. A non-limiting example for wafer handling unit400and a schematic description of its operation is illustrated with more details inFIGS.6A-6C.

Wafer alignment unit(s)420(e.g.,420A and420B, seeFIG.2B) may be configured to detect and measure features on wafers and to adjust the wafer position to the pattern transfer accordingly—is illustrated with more details in a non-limiting example inFIGS.6D and6E.

In certain embodiments, wafer handling unit400may comprise more than two stages410, accompanied with multiplication of any of wafer alignment unit420, paste transfer unit350and/or print quality control unit450—to further increase the throughput of PTP system100.

PTP system100may further comprise a tape stretching unit270(see, e.g.,FIGS.2A and7A) configured to affix and flatten respective pattern transfer sheet205B during the paste pattern transfer from pattern transfer sheet205B to wafer90B. PTP system100may further comprise a trench alignment monitoring unit300configured to monitor a position (e.g., in x, y and theta (tilt) directions) and a distortion of the trenches prior to the pattern transfer. A non-limiting example for tape stretching unit270and trench alignment monitoring unit300is illustrated with more details inFIGS.7A-7C.

Paste transfer unit350(e.g., a laser scanner) may comprise a laser scanner (scanning head)355(e.g., movable along CMD, e.g., by a linear stage, a ball-screw stage, etc.) configured to control the illumination of pattern transfer sheets205B by the laser beam for depositing the paste from the patterned trenches of pattern transfer sheets205B.

PTP system100may further comprise a print quality control unit(s)450(e.g.,450A and450B, seeFIG.2B) configured to control a print quality of the pattern transfer, in particular to detect tiny defects such as openings or gaps within the printed fingers or other defects in the pattern that was transferred onto the wafer. For example, print quality control unit(s)450may be based on imaging cameras, which transfer the acquired images of inspected wafers to processor(s)452for image processing. A non-limiting example for a print quality control unit450is illustrated with more details inFIG.8.

FIG.3Ais a high-level schematic side view illustration of tape handling unit200, according to some embodiments of the invention. Tape handling unit200may be configured to move tape205, while delivering pattern transfer sheets205A one-by-one for the paste filling (at paste filling unit120, see, e.g.,FIG.2A) and/or for the pattern transfer (at pattern transfer unit350) by continuously controlling the tape tensions and accurate position of the sheets in both MD and CMD coordinates.FIGS.3B-3Eare high-level schematic illustrations of tape205with pattern transfer sheets205B (see, e.g.,FIG.2A) and of paste pattern transfer unit350, according to some embodiments of the invention.

The CMD positions of unwinder roll222and re-winding roll242may be continuously controlled and if needed corrected by help of one or more control unit(s)105, e.g., by controlling driving motor(s) thereof. Top dancer(s)225and bottom dancer(s)245may be configured to support fast stepwise movements of pattern transfer sheets205A,205B (as segments of tape205) to their respective positions for paste filling and pattern transfer. Idle rolls227(only some of which indicated) may be configured to direct tape movement through tape handling unit200.

Tape handling unit200may be configured to enable fast and accurate provision and changing of the tape segments (pattern transfer sheets) used to print the wafers. Tape handling unit200may be further configured to have a compact design with a minimal footprint, and be set within a stable and rigid frame or chassis for supporting its operation and also for enabling easy maintenance. Tape re-use unit250may be set within the frame and in the path of tape205and enable reusing tape205—making the overall process more efficient and economical.

FIGS.3B-3Eare high-level schematic illustrations of tape205with pattern transfer sheets205B and of pattern transfer unit350, according to some embodiments of the invention, which are disclosed in more details in Chinese Patent Applications Nos. 202111034191X and 2021221306455, incorporated herein by reference in their entirety.

Highly schematicFIG.3Billustrates transfer of patterned paste from the pattern transfer sheet205B to substrate (e.g., wafer)90B using laser illumination by laser scanner(s)355. Pattern transfer sheets205B comprises a plurality of trenches210arranged in a specified pattern and configured to receive printing paste and release the printing paste from trenches210upon illumination by laser beam80onto a receiving substrate such as wafer90B.FIGS.3B and3Eschematically illustrate the filling of trenches110on an empty pattern transfer sheet on tape205with paste to yield filled pattern transfer sheet205A, which is then moved further in PTP system100to have the paste released from trenches210of pattern transfer sheet205B onto wafer90B. It is noted that while the tape is denoted generally by the numeral205, sections of tape205that are designed as used as pattern transfer sheets are denoted by numeral205A when they are in paste filling stage203and are denoted by numeral205B when they are in paste pattern transfer stage353(illustrated schematically inFIG.3Bby an arrow).

Pattern transfer sheets may further comprise at least one trace mark220that is located outside the specified pattern of trenches210and is configured to receive the printing paste. Trace mark(s)220is aligned with respect to respective trench(es)210and is wider than a width of laser beam80. Upon illumination by laser beam80, only a part of the paste in trace mark(s)220is released (off pattern transfer sheet205B), because the width of trace mark(s)220is larger than the width of laser beam80—yielding a gap that may be used to detect the actual position of the laser beam relative to the position of the corresponding trench.

Pattern transfer sheet may further comprise a plurality of working window marks223that are located outside the specified pattern of trenches210and are configured to receive the printing paste. Working window marks223are set at specified offsets with respect to specified trenches210of the specified pattern, with different working window marks223being set at different offsets. Working window marks223may be used to monitor the power of laser beam80needed for releasing paste from all the trenches.

In certain embodiments, pattern transfer sheet may comprise both trace mark(s)220and working window marks223, which may be configured to enable unambiguous detection by image processing, e.g., by a trench alignment monitoring unit300.

Pattern transfer sheet may further comprise a plurality of alignment marks (not shown) that are located outside the specified pattern of trenches210, aligned with respective trenches210, configured to receive the printing paste and used to provide initial laser scanner alignment with respect to the specified pattern of trenches210.

A trench alignment monitoring unit300may be configured to monitor the pattern transfer process optically, e.g., monitoring the transfer of the printing paste by emptying of trenches210and of marks220,223onto the substrate, as explained herein. One or more processor(s)356or controller(s), in communication with control unit(s)105, may be in communication with laser scanner(s)355(in paste transfer unit350) and imaging unit(s)300and be configured to adjust optical parameters of laser illumination by modifying the settings of power and position of laser scanner(s)355according to image analysis of images taken by imaging unit(s)300. These adjustments and modifications improve the quality and accuracy of pattern transfer stage353. For example, processor(s)356or controller(s) may be configured to calculate an alignment of laser beam80according to traces on pattern transfer sheet (after the paste is released therefrom), e.g., detect misalignment of laser scanner355upon detection of asymmetric trace(s) as disclosed in Chinese patent application Nos. 202111034191X and 2021221306455, incorporated herein by reference in their entirety. Processor(s)356or controller(s) may be further configured to calculate an effective working window of laser illumination80using remaining working window marks223on pattern transfer sheet (after the paste is released therefrom), and adjust laser power of the laser scanner355accordingly. Additional non-limiting details for PTP systems100are provided, e.g., in U.S. Pat. No. 9,616,524.

Disclosed PTP systems100and tape205may be used to print fine lines92of thick metallic paste to produce electronic circuits, e.g., creating conductive lines or pads or other features on laminates for PCBs or other printed electronic boards, or on silicon wafers, e.g., for photovoltaic (PV) cells. Other applications may comprise creating conductive features in the manufacturing processes of mobile phones antennas, decorative and functional automotive glasses, semiconductor integrated circuits (IC), semiconductor IC packaging connections, printed circuit boards (PCB), PCB components assembly, optical biological, chemical and environment sensors and detectors, radio frequency identification (RFID) antennas, organic light-emitting diode (OLED) displays (passive or active matrix), OLED illuminations sheets, printed batteries and other applications. For example, in non-limiting solar applications, the metallic paste may comprise metal powder(s), optional glass frits and modifier(s), volatile solvent(s) and non-volatile polymer(s) and/or or resin(s). A non-limiting example for the paste includes SOL9651B™ from Heraeus™.

FIG.3Cis a high-level schematic cross section illustration of tape (pattern transfer sheet)205, according to some embodiments of the invention. In certain embodiments, tape205may be transparent to laser illumination and comprise at least a top polymer layer214comprising trenches210and marks220,223(illustrated schematically inFIG.3B) which formed by press molding , pneumatic molding or laser molding thereon. In the illustrated non-limiting example, trenches210are illustrated as being trapezoid in cross section.

It is noted that while schematicFIG.3Cshows periodical trenches210, marks220and/or223(illustrated schematically inFIG.3B) may comprise trenches, recesses and/or indentations that are embossed in a similar manner into top polymer layer214, and may have similar or different profiles. For example, trenches210, trace marks220and/or working window marks223, and alignment marks may have various profiles (cross section shapes), such as trapezoid, rounded, square, rectangular and triangular profiles. In various embodiments, the pattern of trenches210on tape205may comprise continuous trenches210and/or arrays of separated dents. It is noted that the term “trenches” is not to be construed as limiting the shape of trenches210to linear elements, but is understood in a broad sense to include any shape of trenches210.

Tape205may comprise a top polymer layer214and a bottom polymer layer212, the bottom polymer layer212having a melting temperature that is higher than an embossing temperature of the top polymer layer214. In some embodiments, top polymer layer214may be made of semi-crystalline polymer and have a melting temperature, e.g., below 150° C., below 130° C., below 110° C. or have intermediate values. In some embodiments, top polymer layer214may be made of amorphous polymer and have a glass temperature below 160° C., e.g., below 140° C., below 120° C., below 100° C. or have intermediate values. Bottom polymer layer212may have a higher melting temperature than the melting temperature or the glass temperature of top polymer layer214. For example, bottom polymer layer212may have a melting temperature above 150° C., above 160° C. (e.g., bi-axially-oriented polypropylene), above 170° C., and up to 400° C. (e.g., certain polyimides), or have intermediate values.

In certain embodiments, top and bottom polymer layers214,212(respectively) may be between 10 μm and 100 μm thick, e.g., between 15 μm and 80 μm thick, between 20 μm and 60 μm thick, between 25 μm and 45 μm thick, or have other intermediate values—with bottom polymer layer212being preferably at least as thick as top polymer layer214. The polymer layers may be attached by an adhesive layer213that is thinner than 10 μm (e.g., thinner than 8 μm, thinner than 6 μm, thinner than 4 μm, thinner than 2 μm or have intermediate values) and is likewise transparent to the laser illumination. For example, in certain embodiments, top polymer layer214may be thicker than the depth of trenches210by several μm, e.g., by 5 μm, by 3-7 μm, by 1-9 μm, or by up to 10 μm. For example, trenches210may be 20 μm deep, top polymer layer214may be 20-30 μm thick and bottom polymer layer212may range in thickness between 25 μm and 45 μm (it is noted that thicker bottom polymer layer provide better mechanical performances). It is noted that the term “trenches” is not to be construed as limiting the shape of trenches210to linear elements, but is understood in a broad sense to include any shape of trenches210.

The temperature and thickness of top and bottom polymer layers (214,212respectively) may be designed so that top polymer layer214has good molding, ductility and certain mechanical strength, while bottom polymer layer212has good mechanical strength. Both top and bottom polymer layers (214,212respectively) may be designed to have good bonding properties.

FIGS.3D and3Eare high-level schematic illustrations of dynamic PTP system100, according to some embodiments of the invention. Dynamic PTP system100comprises at least one laser scanner optical head(s)355configured to illuminate with laser beam(s)80pattern transfer sheet205B with trenches210arranged in a first pattern206and holding printing paste in filled trenches92, which is then released onto wafers90upon the illumination by laser beam80from laser scanner optical head(s)355configured to have a fast-scanning axis along machine direction87(y axis, MD) and may be moved along cross machine direction85(x axis, CMD). The releasing of the paste from the trenches implements pattern transfer stage353, which is indicated schematically inFIGS.3D and3Eby arrows.

Dynamic PTP system100may comprises moveable stages410with wafer holders415affixing wafers90(e.g., by help of vacuum clamping) to moveable stage410during the releasing of printing paste92from pattern transfer sheet205B. Moveable stage410may comprise any type of stage or wafer holder that can affix and move wafers90. Moveable stage410may be moved by any type of actuator, e.g., by linear or step motors.

Dynamic PTP system100may further comprises controller(s) and/or processor(s)357, possibly associated with control unit(s)105, and configured to control laser scanner optical head355to direct laser beam80along trenches210(along machine direction87-MD), and at a cross machine direction85(CMD, scanning direction) across trenches210. Processor(s)357may further be configured to move moveable stage410(the movements are denoted schematically by numeral417) to yield a second pattern96of deposited paste on wafer90, which is different from first pattern206of trenches210on pattern transfer sheet205B. Advantageously, in contrast to current practice which is limited to transferring the same pattern (e.g., of lines) from pattern transfer sheet205B to wafer90, various embodiments of dynamic PTP system100enable to deposit the transferred metal paste onto wafer90at patterns (second pattern96) which are different from first pattern206of trenches210on pattern transfer sheet205B.

As illustrated schematically inFIG.3E, wafer90B may comprise a pattern of substantially parallel linear locations arranged with a certain receiving pitch p2, for receiving the paste release from trenches210of pattern transfer sheet205B, in a close proximity (e.g., in a range of between 0.1 mm and 0.5 mm) to pattern transfer sheet205B in such a way that the first trench on pattern transfer sheet205B is located exactly opposite to the first linear location on wafer90B. Scanning the paste-filled trench pattern206on pattern transfer sheet205B by laser beam80sequentially from the first trench to the last trench results in the deposition of the paste onto the specified locations on wafer90B to yield deposited paste in a specified pattern96. As processor(s)357and/or control unit105move wafer90B during the scanning (movements indicated schematically by numeral417), the paste is deposited at a different pitch (p2≠p1), depending on the direction and speed of motion.

It is noted that scanning along x-axis may be carried out in forward and/or backward directions, and respective movements417of wafer90may be adjusted accordingly. In the present disclosure cross machine direction85is illustrated in one direction, as a non-limiting example.

For example, first pattern206of trenches210on pattern transfer sheet205B may have a first pitch (“p1”) and second pattern96of deposited paste on wafer90may have a second pitch (“p2”), that may be smaller or larger than first pitch (“p1”), e.g., p1>p2or p1<p2. It is noted that second pattern96may differ from first pattern206over the whole extent of wafer90or over a part of the extent of wafer90. In some examples, the difference of pattern may comprise p1>p2in some area(s) of wafer90while p1<p2in other area(s) of wafer90.

In certain embodiments, with first pitch pi being larger than second pitch p2(p1>p2), processor357may be configured to move moveable stage410along scanning direction85(CMD, denoted417A) at a forward speed set to convert first pitch pi to second pitch p2. For example, with forward speed denoted as vFand the time between deposition of consecutive lines denoted as t, p2=p1−vF·t. Alternatively or complementarily, denoting the scanner speed across trenches210as vS=p1/t, the approximate relation between the pitches is p2=p1·(vS−vF)/vS.

In certain embodiments, with first pitch pi being smaller than second pitch p2(p1<p2), processor357may be configured to move moveable stage410against (in a contrary direction to) scanning direction85(CMD, denoted417B) at a backward speed set to convert first pitch p1to second pitch p2. For example, with backward speed denoted as vBand the time between deposition of consecutive lines denoted as t, p2=p1+vB·t. Alternatively or complementarily, denoting the scanner speed across trenches210as vS=p1/t, the approximate relation between the pitches is p2=p1·(vS+vB)/vS.

FIG.4is a high-level schematic illustration of tape re-use unit250, according to some embodiments of the invention. Tape cleaning unit252of tape re-use unit250may comprise a pre-cleaning compartment252A and a cleaning compartment252B configured to remove paste remains having different characteristics (e.g., pre-cleaning may remove rougher clumps of paste while cleaning may remove finer paste remains), and possibly may be preceded by a scraper device for removing paste smears. Tape cleaning may be carried out physically, e.g., by turbulent liquid flow, agitation, application of ultrasound, etc., and/or chemically, e.g., applying corresponding solvents. Fluid introduction to and removal from pre-cleaning compartment252A and/or cleaning compartment252B may be managed by a recirculation unit254(shown schematically), comprising, e.g., pump(s) and filter(s) for reusing respective cleaning solution(s). Tape drying unit255may follow tape cleaning unit252and be configured to dry tape205and prepare it for future use, prior to rolling tape205onto re-winding roll242. Idle rolls244,246and optionally additional rolls may be set to direct tape movement through and after tape re-use unit250. During the tape segment advance movement, one or more idles rolls248shown in the bottom part of unit250may move upward enabling smooth tape movement and continuous tension control performing as dancers, similar to dancers225,245. After finishing the segment advance, rolls248may go downwards under their own weight. Alternatively or complementarily, tape re-use unit250may comprise one or more dancers configured to maintain the tension in tape205moving through tape re-use unit250.

FIGS.5A and5Bare high-level schematic illustrations of paste filling unit120, according to some embodiments of the invention.FIG.5Ais a perspective view andFIG.5Bis a side view.FIGS.5C-5Eare high-level schematic illustrations of filling head122, according to some embodiments of the invention.FIGS.5C and5Eare schematic side view in cross section andFIG.5Dis a perspective view from below filling head122.

As illustrated schematically inFIGS.5A and5B, paste filling unit120may comprise a frame on which paste filling head122and bottom roll125are mounted, and with respect to which they are moved simultaneously. Movements of the paste filling head assembly may be controlled by one or more control unit(s)105e.g., via controlling respective flexible rack126attached to paste filling head122, drive motors124and/or gantry motion system128.

Bottom roll125may be configured to counter paste filling head122and support pattern transfer sheet205A of tape205during the filling of pattern transfer sheet205A with the paste by paste filling head122. Bottom roll125may be configured to roll during operation, possibly controllably.

Paste filling unit120may be configured to enable fast, uniform and accurate filling of the high viscosity paste into the trenches having a high aspect ratio. Paste filling unit120may be further configured to clean the surface of tape205after filling, e.g., disclosed in WIPO Publication No. 2015128857, which is incorporated herein by reference in its entirety.

As illustrated schematically inFIGS.5C-5E, and disclosed in more details in Chinese Patent Applications Nos. 2021106730065 and 2021213505781, incorporated herein by reference in their entirety, filling head122of paste filling unit120may comprise at least two feeding openings161,169, an internal cavity165and at least one dispensing opening160that are in fluid communication (see, e.g.,FIGS.5D and5E) and a pressurized paste supply unit155configured to circulate paste190through printing head150. The pressure in the pressurized paste supply unit may be adjusted to maintain continuous circulation of the paste through feeding openings161,169and internal cavity165and to control dispensing of the paste through dispensing opening(s)160. For example, pressurized paste supply unit155may comprise a pressurized paste reservoir154and a paste pump152in fluid communication with internal cavity165of printing head150, which are configurated to circulate the paste therethrough. In non-limiting examples, paste pump152may comprise rotating pressure-tight displacement systems with self-sealing, rotor/stator designs for dispensing precise volumes such as eco-PEN450™ from Dymax™.

In various embodiments, paste filling unit120comprises at least one pressure sensor140configured to measure the pressure of the circulating paste, e.g., pressure sensor140illustrated schematically inFIGS.5C-5Eand associated with a paste mixer130or pressure sensors140A,140B illustrated schematically inFIG.5C, at either ends of printing head150, as non-limiting examples. Alternatively or complementarily, pressure measurement may be implemented within elements of pressurized paste supply unit155, such as paste pump152and/or paste reservoir154. Paste filling unit120may further comprise at least one processor167and/or controller (shown schematically inFIG.5E), in communication with control unit(s)105and configured to adjust the pressure in pressurized paste supply unit155(or its components) with respect to the measured pressure of the circulating paste. Paste filling unit120may further comprise one or more paste mixer(s)130configured to mix the circulating paste. For example, paste mixer(s)130may be a static mixer, mixing the paste by utilizing its pressurization. In non-limiting examples, paste mixer(s)130may comprise plastic disposable static mixers such as GXF-10-2-ME™ from Stamixco™ made of large diameter plastic housing that includes multiple mixing elements.

Pressurized paste supply unit155may be further configured to introduce the paste into internal cavity165via at least one entry opening161of the at least two feeding openings and to receive the circulated paste via at least one exit opening169of the feeding openings in printing head150. Typically, entry opening(s)161and exit opening(s)169are at the top of printing head150, opposite to dispensing opening(s)160which faces the pattern transfer sheet with trenches which are to be filled by the paste. Alternatively or complementarily, entry opening(s)161and/or exit opening(s)169may be positioned on sides and/or extension(s) of printing head150.

Pressurized paste supply unit155may comprise pressure-controlled paste reservoir154, paste pump152and mixer130that are in fluid communication. Pressure-controlled paste reservoir154may be configured to deliver paste to paste pump152, which may be configured to deliver the paste through mixer130to entry opening(s)161. Pressurized paste supply unit155may be further configured to mix paste from exit opening(s)169with the paste delivered from pressure-controlled paste reservoir154to paste pump152. For example, as illustrated schematically inFIGS.5C and5E, paste190in paste reservoir154may be delivered (191) to paste pump152, mixing (192) with paste197exiting from exit opening(s)169of printing head150, to be pumped by paste pump152into mixer130. Paste193from mixer130may be delivered (194) to entry opening(s)161of printing head150, wherein paste196moves along internal cavity165and some paste195may be dispensed through dispensing opening(s)160to form patterns on the transfer sheet205A such as lines to be then printed (after the tape movement, from transfer sheet205B) on the receiving substrate such as wafer90(e.g., silver lines of about 20 μm width on silicon wafers for PV cells, see, for non-limiting examples, Lossen et al.2015). Remaining paste197is then mixed with paste191from paste reservoir154(e.g., delivered through nozzle163at junction151) to compensate for the dispensed amount, and the paste is circulated through Paste filling unit120to maintain its mechanical characteristics and support continued mixing of the paste to maintain its uniform composition. In certain embodiments, paste filling unit120may be further configured to modify paste composition, e.g., by adding additives such as solvents to keep the paste homogenized, possibly in relation to the monitored pressures throughout paste filling unit120. For example, additives such as solvents may be added to the paste entering mixer130if needed.

In various embodiments, printing head150, internal cavity165and dispensing slit as opening160limited by slit edges162(e.g., metallic slit lips) may be elongated (see, e.g.,FIG.5D) and configured with respect to paste properties (e.g., viscosity values), specified throughput and specified features (e.g., length, width and optionally cross section) of the lines or other elements that are to be dispensed by printing head150. In certain embodiments, dispensing opening160may comprise one or more slits, one or more opening, a plurality of linearly-arranged openings, e.g., one or more lines of circular or elliptical openings, and so forth.

In various embodiments, paste material may comprise conductive silver based metallic paste, and may typically be of high viscosity (e.g., in the range of several tens to several hundreds of Pa·s). For example, in non-limiting solar applications, the metallic paste may comprise metal powder(s), optional glass frits and modifier(s), volatile solvent(s) and non-volatile polymer(s) and/or or resin(s). A non-limiting example for the paste includes SOL9651B™ from Heraeus™.

Paste filling unit120may comprise one or more pressure sensor (s)140,140A,140B configured to measure the pressure of the circulating paste at one or more respective locations along the paste circulation path. For example, pressure sensor(s)140,140A,140B may be set adjacent to entry opening(s)161, exit opening(s)169, in fluid communication with internal cavity165of printing head150and/or in association with any of mixer130, paste reservoir154and/or paste pump152. Pressure-related indications from pressurized paste reservoir154and/or paste pump152may also be used to monitor paste circulation through Paste filling unit120and/or to monitor and possibly modify the paste properties such as its viscosity, e.g., by adding solvent. Paste filling unit120may further comprise at least one controller (e.g., as part of or in communication with control unit105and/or as at least one computer processor173as illustrated inFIG.10), in communication with any of the components of paste filling unit120, e.g., via communication link(s)) configured to adjust the pressure in pressure-controlled paste reservoir154and/or paste pump152with respect to the measured pressure of the circulating paste, e.g., as received from one or more pressure sensor (s)140,140A,140B. In non-limiting examples, any of pressure sensor(s)140may comprise, e.g., small profile, media compatible, piezoresistive silicon pressure sensors packaged in a stainless-steel housing (e.g., MEAS 86A™ from T.E. connectivity™ or equivalent sensors).

In various embodiments, pressure-controlled paste reservoir154and paste pump152may open adjacently to exit opening(s)169of printing head150and paste filling unit120may comprise a conduit135connecting the exit of mixer130to entry opening(s)161of printing head150. In some embodiments, pressure-controlled paste reservoir154and paste pump152may open adjacently to exit opening(s)169of printing head150, mixer130may be adjacent to entry opening(s)161of printing head150, and conduit135may connect paste pump152to mixer130. Pressure sensor140may be associated with mixer130. The dimensions and orientations of paste reservoir154and paste pump152may vary, e.g., both paste reservoir154and paste pump152may be set perpendicularly to printing head150(see, e.g.,FIG.5C), or one or both of paste reservoir154and paste pump154may be set at an angle to printing head150. For example, paste pump152may be set obliquely to spread its weight more evenly over printing head150, as illustrated schematically inFIGS.5D and5E.

In various embodiments, conduit135may be adjusted to conform to any arrangement of paste reservoir154, paste pump152and mixer130, so as to make paste filling unit120more compact or adjust it to a given space and weight distribution requirements within the printing machine. Holder145(see, e.g.,FIG.5C) is illustrated schematically as an attachment element for attaching paste filling unit120to the printing machine (see, e.g., U.S. Pat. No. 9,616,524 for a non-limiting example). In non-limiting examples, conduit135may be connected between an opening131in mixer130and an opening138of connector137at entry opening161in printing head150(see, e.g.,FIG.5C) or between opening131in paste pump152and opening138in mixer130(see, e.g.,FIG.5E) .

FIGS.6A-6Care high-level schematic illustrations of wafer handling unit400and of its operation, according to some embodiments of the invention.FIG.6Ais a side view,FIG.6Bis a partial perspective view andFIG.6Cis a schematic illustration of the wafer handling.

Wafer handling unit400is configured to increase the throughput of PTP system100by enabling parallel processing of different wafers90. Wafer holders415A,415B (seeFIG.6B, e.g., vacuum chucks) may be configured to move in parallel (e.g., along the horizontal x axis and also along vertical z axis) and apply wafer position corrections during movements along the horizontal y axis and with respect the wafer's tilting angle (denoted For example, each stage410A,410B may be configured to adjust both wafer holders415A,415B (that may adjust the wafer positions) along the x-axis and the z axis. Correspondingly, wafer handling unit400may comprise one or more motors413, e.g., a linear motor413A (illustrated schematically) for moving stage410A, along the x axis and a motor418A (illustrated schematically) for adjusting the position of wafer stage410A (with holders415A and415B) along the z axis. The positions along the y and θ axes are adjusted by each holder415separately. Accordingly, a linear motor413B (not shown), which is mounted in parallel to motor413A, moves stage410B along x axis and motor418B adjusts wafer stage410B (holders415A and415B) along the z axis. Both stages410A and410B are operated in parallel along the x axis by motors413A and413B and are separated when moving in opposite directions by changing their z-position by motors418A and418B, accordingly.

In various embodiments, wafer handling unit400may be configured to have two stages working in parallel which are each movable along x and z directions. Each stage410may comprise two holders415for holding wafers90, with each holder415ensuring wafer movement along the y and θ axes (θ denoting tilting of the wafer) thus enabling faster wafer handling and continuous wafers movements during the pattern transfer process. Multiple cameras may be configured to capture images of the incoming wafers to enable more accurate wafer alignment within the printing system thus more accurate alignment of printed conductive lines onto wafer pattern(s).

As illustrated schematically inFIG.6C, wafer handling unit400may be configured to move wafers90from input conveyor412through pre-alignment measurement stage (receiving the wafer at position90A), pattern transfer printing stage (receiving the wafer at position90B) and print quality control stage (receiving the wafer at position90C) to output conveyor419, while parallelizing wafer treatment so that wafers supported by either stage410A,410B are processed in parallel. (e.g., during pattern transfer90B to Wafer 1 (held by holder415A) of Stage 1 (410A), Wafer 2 (held by holder415B) of Stage 2 (410B) may already be pre-aligned (wafer90A), while Wafers 1 and 2 (held by holders415A,415B, respectively) of Stage 1 (410A) are pre-aligned (90A) and printed (90B), respectively, Wafer 1 (held by holder415A) of Stage 2 (410B) undergoes quality control (wafer90C), etc. Wafer handling unit400may be mounted on a granite base405(see, e.g., inFIG.6B) to stabilize all the modules and reduce inaccuracies that may result from frequent and fast movements of wafer stages and other moving parts.

Wafers90may be a silicon wafer, as used, e.g., for manufacturing PV cells of different types as described in detail, e.g., in Luque and Hegedus (eds.) 2011, Handbook of photovoltaic science and engineering, pages 276-277, incorporated herein by reference in its entirety.

FIGS.6D and6Eare high-level schematic illustrations of wafer alignment unit420, according to some embodiments of the invention. Each wafer90A may be identified by specified features thereof and its placement may be adjusted relative to the paste transfer printing unit according to the exact locations of the specified features. For example, selective emitter (SE) solar cells comprise localized lines (SE lines) of heavy doping in Si substrate onto which the metal contacts are printed by paste transfer. Wafer alignment unit420may be configured to measure the locations of the SE lines on wafer90A and the position of the wafer may be adjusted so that the paste transfer for each printed finger is done by paste transfer unit350with respect to the positions of the SE lines, as determined by wafer alignment unit420in order to increase the overall printing accuracy.

Wafer alignment unit420may comprise camera array(s)430with associated illumination, configured to measure the locations of specific features on wafer90A, e.g., of the SE lines. For example, wafer alignment unit420may comprise multiple imaging cameras configured to capture at least a part of a perimeter of wafer90, possibly most or all of the wafer perimeter. The cameras of array(s)430may be configured to image the wafer corners (using e.g., four cameras for the areas near the wafer corners) as well as features at a middle of the wafer (using, e.g., two or more cameras to image areas including two opposite ends of the specific features, such as several trenches located in the middle of the wafer).

In case of two wafer holders415A,415B with respective wafer per stage410, camera arrays430may comprise two respective sub-arrays430A,430B, each comprising, e.g., two rows of cameras, configured to measure wafer90A at the respective position (e.g., as Wafer 1 or Wafer 2, illustrated schematically inFIG.6C). In non-limiting examples, each camera sub-array430A,430B may comprise six cameras435with respective illumination sources (e.g., four LEDs boards422per sub-array configured to provide uniform illumination of the camera's Field of View (FoV) with high contrast of the SE lines images)—which may be configured to provide accurate x and θ coordinates of the SE lines and the SE pitch even if the SE pitch is not unform in the x direction (CMD).

Camera array(s)430may be mounted to the system chassis to ensure their stability and accuracy of the measurements. Processors425may receive the images from camera arrays430, apply high resolution image processing algorithms to yield an accuracy of the SE line measurements of one to few microns, and provide the data to control unit(s)105to adjust the wafer position relative to paste transfer unit350. Cameras435may be, for example, of 5 Mpix CMOS type, with an imaging lens, for example, of 25 mm focal length. It should be noted that number of cameras435in each array430affects the accuracy of wafer alignment to the transfer sheet pattern thus of the position of printed finger lines92onto SE lines on wafer90B (see, e.g.,FIG.3E). As a non-limiting example, the number of cameras may be six thus enabling to determine accurate x, θ-positions of the first and the last SE lines by four corner cameras as well as to estimate the SE pitch along the CMD by help of two intermediate cameras. In a non-limiting example, four LED boards422may be used to enable uniform illumination of FOVs of all the cameras by near-normal illumination, which enables high contrast imaging of the SE lines.

FIGS.7A-7Care high-level schematic illustrations of tape stretching unit270and trench alignment monitoring unit300, according to some embodiments of the invention.FIG.7Ais a front view (without tape205) with an inset side view andFIGS.7B and7Care perspective views from below (facing the front of tape stretching unit270) and from above (facing the back of tape stretching unit270and alignment monitoring unit300). Tape stretching unit270and trench alignment monitoring unit300may be set with respect to plate271and secured by supports273to the frame of PTP system100.

Tape stretching unit270may be configured to stretch tape205at the pattern transfer stage (e.g., pattern transfer sheet205B) to keep pattern transfer sheet (tape segment)205B straight and flat, avoiding deformations to the shape of paste-filled trenches thereupon and to prevent direct contact between pattern transfer sheet205B and wafer90B onto which the paste is transferred (e.g., keeping a gap of, e.g., in the range of 100 μm to 500 μm between pattern transfer sheet205B and wafer90B). Moreover, tape stretching unit270may be configured to avoid interference to wafer movements by wafer handling unit400. For example,FIGS.7A and7Billustrate schematically the use of vacuum bars280configured to affix and flatten tape205using vacuum application and a stretching mechanism275and may comprise recesses272for applying vacuum to the transfer sheet by keeping its planarity.

Trench alignment monitoring unit300may be configured to monitor the trenches' x, θ-positions and distortions, e.g., using multiple imaging cameras configured and/or located to capture ends of the trenches and to capture at least middle-sections of the trenches. For example, trench alignment monitoring unit300may be configured to measure the ends of the trenches using cameras285(e.g., four pairs of alignment cameras, one camera of each pair at each end of the trenches) as well as tilted cameras290(see, e.g., one of tilted cameras290illustratedFIG.7Cand in a larger scale on the left part side view inFIG.7A)—set to measure trench distortions at central portions of the trenches. Tilted imaging cameras290may be tilted with respect to the vertical z direction so as to capture the middle-sections of the trenches without obstructing the illumination of the trenches (e.g., not positioned above the pattern transfer sheet).

Corresponding image processing algorithms may be applied to the images of cameras285,290in one or more processor(s)310associated with control unit(s)105—to measure trench positions (e.g., x and θ-position(s)) and distortions, and optimize the positioning accuracy of laser beam80with respect to some or every paste-filled trench of pattern transfer sheet205B during scanning. The measurements may be used to increase accuracy and/or to reduce the required beam width (wider beams80were previously used to compensate for inaccuracies). Trench alignment monitoring unit300may further comprise illumination unit(s), e.g., LED boards287(see, e.g.,FIGS.7B and7C) located below the camera assemblies, configured to provide the required illumination of the trenches for the fields of view of respective cameras285,290. In certain embodiments, imaging cameras285and290may be assembled of the same CMOS camera and imaging lens as are used in the wafer alignment module.

Paste transfer unit350may comprise a high-power laser and optical head355, which forms laser beam80that releases the paste from the trenches in pattern transfer sheet205B onto wafer90B.

Optical head355may be movable and configured to be moved along CMD (x axis), e.g., with a velocity of about 0.5 m/s or more, with optical head355configured to focus laser beam80to specified spot shape(s) (that are effective in releasing the paste from the trenches of pattern transfer sheet205B) and to move this spot in along MD (y axis) with very high velocity, e.g. 500 m/s. Optical head355may be movable along CMD (x axis), e.g., by a precise linear motor to adjust the exact location of laser beam80with respect to the actual locations of the trenches on the pattern transfer sheet205B. Optical head355may be controllably tiltable (e.g., by the same or by an additional motor) to adjust for tilts of pattern transfer sheet205B that may remain with disclosed tape stretching, and as measured by trench alignment monitoring unit300. The laser used in pattern transfer unit350may be any of one of the following groups: a) CW, QCW, pulse; b) IR, NIR, Visible; c) solid state, fiber, gaseous, laser diode. The scanner for MD axis may be any commercially available linear scanner enabling the scanning velocity of several hundreds of msec. The motor assembly for CMD axis movement of optical head355may be based on a linear motor or a ball screw motor.

Paste transfer unit350may be controllable by control unit(s)105with respect to the illumination and the various movement parameters, possibly adjusted and monitored by associated processor(s).

FIG.8is a high-level schematic illustration of print quality control (QC) unit450, according to some embodiments of the invention. Print quality control unit450may be configured to detect defects in the pattern transfer using one or more cameras455configured to capture high resolution images (e.g., having 20 megapixels or more) of printed wafers90C, with corresponding illumination457(e.g., four dark field LEDs boards along the x direction, CMD, configured to provide uniform illumination of whole wafer Print quality control unit450may be configured to provide high contrast and avoid or reduce optical noise.

Print QC unit450may comprise two respective cameras455A,455B (the latter indicated schematically by an arrow, cameras455B are opposite to camera455A but are not visible onFIG.8, except for the schematic illustration of its FoV). Cameras455are configured to measure wafer90C at the respective position (e.g., as Wafer 1 or Wafer 2, illustrated schematically inFIG.6C). Processors452may receive the images from cameras455, apply high resolution image processing algorithms to detect tiny printing defects like small cuts or local misprints, and provide the data to control unit(s)105to correct parameters of the process. Cameras455A and455B may be, in a non-limiting example, of 20 Mpix CMOS type equipped with an imaging lens enabling FoV of about 230 mm by 230 mm The LED boards may be installed on two sides and on two height levels in order to ensure uniform illumination of the whole wafer, as is shown schematically inFIG.8.

Elements fromFIGS.1-8may be combined in any operable combination, and the illustration of certain elements in certain figures and not in others merely serves an explanatory purpose and is non-limiting.

FIG.9Ais a high-level flowchart illustrating a pattern transfer printing (PTP) method500, according to some embodiments of the invention.FIG.9Bis a high-level flowchart illustrating in general the parallel processes in pattern transfer printing (PTP) method500, according to some embodiments of the invention. The method stages may be carried out with respect to PTP system100described above, which may optionally be configured to implement method500. Method500may be at least partially implemented by at least one computer processor or by at least one control unit105(e.g., one or more personal computers, PCs and/or one or more programmable logic controllers, PLCs) or by their combinations). Certain embodiments comprise computer program products comprising a computer readable storage medium having computer readable program embodied therewith and configured to carry out the relevant stages of PTP method500. PTP method500may comprise the following stages, irrespective of their order.

As illustrated inFIG.9A, PTP method500may comprise handling a tape through a PTP system, the tape comprising, as sections thereof, a plurality of pattern transfer sheets having respective patterns of trenches—to controllably deliver the pattern transfer sheets for paste filling (stage510), filling the trenches on the delivered pattern transfer sheets with conductive printing paste (stage520), controllably delivering a plurality of wafers (one-by-one) for the pattern transfer (stage530), and transferring the conductive printing paste from a plurality of filled trenches on the pattern transfer sheets onto a respective one of the delivered wafers, by releasing the printing paste from the trenches upon illumination by a laser beam, e.g., by help of two dimensional x, y-scanning (stage540).

PTP method500may further comprise cleaning the pattern transfer sheets after the pattern transfer to provide reusable pattern transfer sheets, and optionally re-using the cleaned pattern transfer sheets (stage560).

PTP method500may further comprise supporting a back side of the pattern transfer sheet by a countering moveable roll during the paste filling (stage522). PTP method500may further comprise carrying out the trench filling at a nearly vertical position (stage524), e.g., at a nearly vertical angle (in the range of 0-30° from the vertical x-z plane). For example, the paste filling unit and the pattern transfer sheet plane may be set at an angle deviating 0-30° from the vertical x-z plane.

PTP method500may further comprise delivering the wafers using two alternating stages, with each stage supporting two wafers (stage532), controllably delivering the wafers for the pattern transfer at a close proximity (e.g., in a range of between 0.1 mm and 0.5 mm) to the pattern transfer sheet (stage534) and carrying out the wafer measurement (before printing), pattern transfer onto a wafer (printing) and a print QC inspection (after printing) simultaneously for at least three of the wafers (stage536), wherein at least two of the wafers are supported by the same stage. The wafers are then advanced by consecutively moving the stage along CMD. The stages may be alternated following the printed wafers release to the output conveyor, parallelizing the printing process to increase throughput. In certain embodiments, only two wafers (e.g., positioned on the same stage) are processed simultaneously, alternating between (i) wafer alignment (before printing) and pattern transfer onto a wafer (printing), and (ii) pattern transfer onto a wafer (printing) and the print QC inspection (after printing) for the respective pair of wafers.

PTP method500may further comprise affixing and flattening the respective pattern transfer sheet during the pattern transfer (stage542) and/or monitoring x,θ-positions and/or distortions of the trenches prior to the pattern transfer (stage544).

PTP method500may further comprise detecting and measuring features on the wafer and adjusting the pattern transfer accordingly (stage546).

PTP method500may further comprise inspecting the printing quality of the transferred paste pattern (stage550), e.g., by measuring an accuracy of the pattern transfer and/or detecting defects in the transferred pattern on the wafer

As illustrated inFIG.9B, PTP method500may comprise method stages implemented by tape handling unit200, pattern transfer unit350and wafer handling unit400, as illustrated schematically and described in detail herein.

PTP method500may comprise moving pattern transfer sheets from the unwinder roll towards the paste filling unit (stage510A), the filling of the trenches with paste (stage520), moving the filled sheets to the pattern transfer unit (stage510B), e.g., stretching and affixing the filled sheets in the transfer unit (stage542A), as disclsoed herein. Following paste removal from the sheets, PTP method500may comprise moving the used sheets towards the re-use unit (stage514), cleaning and drying the sheets (stage560A) and moving the cleaned sheets toward the re-winding roll, possibly for future use (stage560B).

PTP method500may further comprise measuring the positions of the trenches by the trench alignment unit (stage544A), laser-scanning the trenches to transfer the paste to respective wafers90(stages540A,540B,540C,540D), as provided by the wafer handling unit, until the trenches from the same sheet are laser-scanned onto the last provided wafer (stage544B).

PTP method500may further comprise handling the wafers using two stages410A,410B, which carry out the following stages, respectively: putting wafers on the wafer holders from the input conveyor (stages530A,530B), moving the wafers to the wafer alignment units (stages532A,532B), determining the wafer positions of the wafer holders (stages534A,534B), moving the wafer sequentially to the transfer printing unit, optionally during the printing of previous wafers (stages535A,535B and stages535C,535D, respectively for the two stages), and then moving the wafers to the print quality units (stages550A,550B), followed by releasing the wafers to the output conveyor (stages552A,552B) and returning the stages to their initial positions (stages553A,553B) to repeat stages530-553.

Advantageously, disclosed PTP systems may be optimized to increase accuracy, efficiency and throughput by providing continuous handling of wafers during pattern transfer and using dual-chuck wafer stages, alignment of wafers by multiple cameras, more accurate alignment of transfer sheet by multiple cameras at the print position and locating the paste filling module at near vertical position thus reducing time between paste filling and pattern transfer.

FIG.10is a high-level block diagram of exemplary computing device170, which may be used with embodiments of the present invention. Computing device170may include a controller or processor173that may be or include, for example, one or more central processing unit processor(s) (CPU), one or more Graphics Processing Unit(s) (GPU or general-purpose GPU-GPGPU), a chip or any suitable computing or computational device, an operating system171, a memory172, a storage system175, input devices176and output devices177. PTP system100, control unit(s)105, any of processors310,425,452and/or parts thereof may be or include a computer system as shown for example inFIG.10. The processors may comprise multiple cores configured to enable parallel processing of different tasks, for example processing of images of all the cameras of the wafer alignment unit or/and of the trench monitoring units or/and of the print quality units.

Operating system171may be or may include any code segment designed and/or configured to perform tasks involving coordination, scheduling, arbitration, supervising, controlling, or otherwise managing operation of computing device170, for example, scheduling execution of programs. Memory172may be or may include, for example, a Random-Access Memory (RAM), a read only memory (ROM), a Dynamic RAM (DRAM), a Synchronous DRAM (SD-RAM), a double data rate (DDR) memory chip, a Flash memory, a volatile memory, a non-volatile memory, a cache memory, a buffer, a short-term memory unit, a long-term memory unit, or other suitable memory units or storage units. Memory172may be or may include a plurality of possibly different memory units. Memory172may store for example, instructions to carry out a method (e.g., code174), and/or data such as user responses, interruptions, etc.

Executable code174may be any executable code, e.g., an application, a program, a process, task or script. Executable code174may be executed by processor173possibly under control of operating system171. For example, executable code174may when executed cause the production or compilation of computer code, or application execution such as VR execution or inference, according to embodiments of the present invention. Executable code174may be code produced by methods described herein. For the various modules and functions described herein, one or more computing devices170or components of computing device170may be used. Devices that include components similar or different to those included in computing device170may be used and may be connected to a network and used as a system. One or more processor(s)173may be configured to carry out embodiments of the present invention by for example executing software or code.

Storage system175may be or may include, for example, a hard disk drive, a floppy disk drive, a Compact Disk (CD) drive, a CD-Recordable (CD-R) drive, a universal serial bus (USB) device or other suitable removable and/or fixed storage unit. Data such as instructions, code, VR model data, parameters, etc. may be stored in a storage system175and may be loaded from storage system175into a memory172where it may be processed by processor173. In some embodiments, some of the components shown inFIG.10may be omitted.

Input devices176may be or may include for example a mouse, a keyboard, a touch screen or pad or any suitable input device. It will be recognized that any suitable number of input devices may be operatively connected to computing device170as shown by block176. Output devices177may include one or more displays, speakers and/or any other suitable output devices. It will be recognized that any suitable number of output devices may be operatively connected to computing device170as shown by block177. Any applicable input/output (I/O) devices may be connected to computing device170, for example, a wired or wireless network interface card (NIC), a modem, printer or facsimile machine, a universal serial bus (USB) device or external hard drive may be included in input devices176and/or output devices177.

Embodiments of the invention may include one or more article(s) (e.g., memory172or storage system175) such as a computer or processor non-transitory readable medium, or a computer or processor non-transitory storage medium, such as for example a memory, a disk drive, or a USB flash memory, encoding, including or storing instructions, e.g., computer-executable instructions, which, when executed by a processor or controller, carry out methods disclosed herein.

Aspects of the present invention are described above with reference to flowchart illustrations and/or portion diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each portion of the flowchart illustrations and/or portion diagrams, and combinations of portions in the flowchart illustrations and/or portion diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general-purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or portion diagram or portions thereof.

The aforementioned flowchart and diagrams illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each portion in the flowchart or portion diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the portion may occur out of the order noted in the figures. For example, two portions shown in succession may, in fact, be executed substantially concurrently, or the portions may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each portion of the portion diagrams and/or flowchart illustration, and combinations of portions in the portion diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.