GB2576922A

GB2576922A - An optical engine for an imprinter

Info

Publication number: GB2576922A
Application number: GB1814555.7A
Authority: GB
Inventors: Yde Leif; Lindvold Lars; Fagerbo Stensborg Jan
Original assignee: STENSBORG AS
Current assignee: STENSBORG AS
Priority date: 2018-09-06
Filing date: 2018-09-06
Publication date: 2020-03-11
Anticipated expiration: 2038-09-06
Also published as: GB201814555D0; GB2576922B; WO2020049121A1

Abstract

An apparatus, such as a nanoimprint lithography imprinter, for imprinting of surface relief structures has imprinting members 18, 22 arranged to define a nip therebetween. The nip has an imprinting contact area where, in use, one or more moulds engage with one or more sample substrates to imprint the surface relief structure therein. The imprinter includes an illumination arrangement, including at least one solid-state light-emitting device 74 such an LED or laser diode, arranged in use to project a beam B, preferably of ultraviolet or infrared radiation, onto a portion of the at least one substrate, defining an illumination region which cures a material disposed on the substrate. One imprinting member may be a rotatable cylinder 22 and the other may be a stage 18, the cylinder 22 and platform 18 being movable with respect to one another. The light source 74 may be located within the cylinder 22.

Description

(54) Title of the Invention: An optical engine for an imprinter

Abstract Title: Imprinting apparatus comprising illumination arrangement (57) An apparatus, such as a nanoimprint lithography imprinter, for imprinting of surface relief structures has imprinting members 18, 22 arranged to define a nip therebetween. The nip has an imprinting contact area where, in use, one or more moulds engage with one or more sample substrates to imprint the surface relief structure therein. The imprinter includes an illumination arrangement, including at least one solid-state light-emitting device 74 such an LED or laser diode, arranged in use to project a beam B, preferably of ultraviolet or infrared radiation, onto a portion of the at least one substrate, defining an illumination region which cures a material disposed on the substrate. One imprinting member may be a rotatable cylinder 22 and the other may be a stage 18, the cylinder 22 and platform 18 being movable with respect to one another. The light source 74 may be located within the cylinder 22.

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An optical engine for an imprinter

The present invention relates to an optical engine for an imprinter.

Nanoimprint Lithography (NIL) is a widely used technology for replicating nano- and micro-structures for a range of scientific and industrial applications. Commonly, wafers of silicon or silica (quartz) are utilised as substrates due to their high surface quality and uniformity. Much of the equipment used for NIL is based on a transfer from a stamping mould holding the required nano- or micro-structure to the aforementioned substrate material. The substrate is typically coated with a heat- and/or light-sensitive resin, into which the surface relief structure is stamped.

The actual NIL process of transferring the surface relief structure to the substrate and resin typically is achieved by either heat curing or curing by electromagnetic radiation (typically UV light) in a combination with applied pressure over the entire surface. In other words, the surface relief structure is applied over the entire surface in a single stamp process. As the process takes place over the entire surface at the same time it is imperative that the substrate is kept even and the pressure is tightly controlled, otherwise imperfections and errors may occur.

It is also known to perform imprinting using a roll to roll process where a nip is formed between two rollers, and a mould and sample substrate comprising a curable material are brought together at the nip. The imprinted sample is then cured using electromagnetic radiation (most commonly UV light) or heat curing. An example of such a system is shown in WO 00/30854.

Mercury vapour discharge lamps are commonly used as UV light curing sources for use in curing of photocurable polymers/resins/lacquers. Such lamps are widely used for production of surface relief patterns in diverse industries such as production of Optical Verification Devices, holograms for brand security, packaging, varius technical applications as light guides, Lab-on-a-chip, OLED light guides, stretchable light guides and electronics, solar cells, printed electronics, microfluidics, meta materials, furniture lacquers, protective coatings on car, wall and floor varnishes, resin curing in the printing industry amongst other possible applications.

To achieve a sufficiently high cure speed, high-power discharge lamps are typically used. These lamps operate on the principle of a glow discharge which is ignited by a high voltage pulse. The discharge facilitates the formation of a so-called arc-discharge characterised by a voltage of between 100 and 500 V and a high current in the range 10-50 A. The discharge medium is usually vapours of pure mercury or mercury vapours doped with halogens or gallium or iron.

Commonly, a discharge tube is formed from quartz and has a diameter between 10 and 30 mm and a length from 30 cm to 2 meters. Therefore, the size can be a problem since the light irradiated from the discharge is 360 degrees there is a need for directing the light into the direction of the curing media, as e.g. a wafer, a plate, a sheet or a web of material. This is done by a combination of reflective and refractive optics.

Furthermore, the use of reflective and refractive optics serve to collect, focus and define the width of the irradiated light. Focussing the light, increases the power density (irradiance) of the light irradiated by the discharge tube. The challenge of focussing light from a discharge tube is that it is an incoherent light-source of relative substantial size. This means that the tightest focus achievable is a 1:1 imaging of the discharge inside the tube. To achieve this, high numerical aperture optics are required to obtain optimal efficiency.

In addition, a tighter focus cannot be achieved by simply making the width of the discharge smaller decreasing the size of the electrodes of the discharge tube, because this leads to an increase in the electrical power dissipated by the discharge tube. As this type of discharge lamps have a poor conversion efficiency (~10%) of electrical power to photons, there is a vast amount of excess thermal energy that needs to be removed from the discharge process.

To complicate matters further, there are two processes each contributing to the excess heat: i) the discharge itself generate heat as it can be regarded as a resistive heater; and ii) the light from the arc-discharge can be regarded as a Planck black-body radiator emitting not only UV- and visible light (as desired) but also a significant amount of IR radiation as defined by the Planck black-body radiation law.

The generation of excess IR radiation has been found to cause sagging of the quartz tube leading to poor focussing and in worst-case failure of the lamp.The vast generation of IR radiation furthermore requires the use of substantial IR absorbing filters in the lamp design to prevent the substrate and resin from being thermally damaged.

A further issue when using a discharge tube based optical engine is stray light. It is important to understand that the light from the discharge lamp is emitted isotropically. This means that more than 50% of the emitted light is not collected by the primary optical system intended to form a line of focussed light in a nip. The part of the emitted light from the discharge tube not focussed by the primary optical system will be reflected and scattered from the surfaces inside the light emitting assembly. These light rays will tend to create parasitic light outside the focused line of light constituting the nip. The stray light might then cause uncontrolled pre-curing of the photocurable resin. To compensate for that, mechanical shields known as baffles are placed inside the optical arrangement. Due to the vast amount of excess IR light produced by the discharge lamp, these baffles need to be water-cooled. This adds to the complexity and size of the optical arrangement.

Therefore, there is a technical problem in the art that known methods for producing curing radiation for micro- and nano-scale surface relief structures are complex, inefficient and bulky. The present invention seeks, in embodiments, to address these problems.

According to a first aspect of the present invention, there is provided an apparatus for imprinting of surface relief structures from one or more moulds on to one or more sample substrates comprising a curable material, the apparatus comprising first and second imprinting members arranged to define an imprinting nip therebetween, the imprinting nip having an imprinting contact area where, in use, one or more moulds engage with one or more sample substrates to imprint the surface relief structure therein as the one or more sample substrates pass through the imprinting nip, wherein the apparatus further comprises an illumination arrangement arranged, in use, to project an illumination beam onto at least a portion of the or each sample substrate to at least partially cure the curable material, the illumination beam defining an illumination region, and wherein the illumination arrangement comprises at least one solid-state lightemitting device.

In one embodiment, the illumination arrangement comprises a plurality of solid-state light-emitting devices.

In one embodiment, the solid-state light-emitting devices are arranged in a line.

In one embodiment, the or each solid-state light-emitting device comprises a surface mounted device (SMD).

In one embodiment, one or more solid-state light-emitting device comprises a light emitting diode or a laser diode.

In one embodiment, the or each solid-state light-emitting device has an emission wavelength in the UV or IR regions.

In one embodiment, the or each light emitting diode has an emission wavelength in the region of 360 - 405 nm or in the region of 900 nm.

In one embodiment, the illumination arrangement further comprises a lens arrangement.

In one embodiment, the lens arrangement comprises a plurality of stacked lenses.

In one embodiment, the lens arrangement comprises one or more aspherical Fresnel lenses.

In one embodiment, the illumination region comprises a line having a line width in the region from 0.5 mm to 10 mm.

In one embodiment, the illumination line has a line width in the region from 1 mm to 5 mm.

In one embodiment, the illumination region extends across all or part of the width of the first or second imprinting member.

In one embodiment, the illumination arrangement is configured to enable the location of the illumination region to be varied with respect to the location of the imprinting contact area.

In one embodiment, the illumination arrangement is configured such that the illumination region either: overlaps at least a part of the imprinting contact area; is arranged behind the imprinting contact area of the nip such that at least a portion of the sample substrate is illuminated prior to reaching the imprinting contact area of the nip; or is arranged ahead of the imprinting contact area such that at least a portion of the sample substrate is illuminated after passing through the imprinting contact area of the nip.

In one embodiment, the first imprinting member comprises a rotatable cylinder arranged to carry the at least one mould.

In one embodiment, second imprinting member comprises a support roller.

In one embodiment, the second imprinting member comprises a stage arranged to support at least one sample substrate and wherein, in use, the stage and rotatable cylinder are movable with respect to one another.

In one embodiment, the stage is linearly movable relative to the rotatable cylinder in a direction perpendicular to an axis of rotation of the rotatable cylinder and the rotatable cylinder is arranged to rotate during said linear movement.

In one embodiment, the illumination arrangement is located within the interior of the rotating cylinder.

In one embodiment, the illumination arrangement is rotatable about an axis to vary the location of the illumination region.

In one embodiment, one or more solid-state light-emitting devices comprises an organic photoluminescent or electroluminescent material.

In one embodiment, one or more of the solid-state light-emitting devices comprises an organic LED or an organic photoluminescent material optically excited by a solid state LED or laser diode.

In one embodiment, the organic photoluminescent or electroluminescent material is located on an interior or exterior surface of the rotatable cylinder.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 shows a perspective view of a NIL imprinter including an optical engine according to an embodiment of the present invention;

Figure 2 shows a different perspective view of the imprinter of Figure 1 with an outer cover removed;

Figure 3 shows a plan view of the imprinter of Figure 1 with the outer cover removed;

Figure 4 shows a side sectional view of the imprinter of Figure 1 showing the internal components of the imprinter;

Figure 5 shows a front view of the imprinter of Figure 1 with outer surfaces rendered transparent to show internal components;

Figure 6 is a perspective section view showing the internal components of the imprinter of Figure 1;

Figures 7 and 8 are different perspective section views showing an optical engine forming part of the imprinter of Figure 1;

Figure 9 is a front section view through the optical engine of the imprinter of Figure 1;

Figure 10 is a front section view similar to Figure 9 but showing the optical engine in a rotated configuration to change the beam line angle;

Figure 11 shows a close up view similar to Figure 9 but showing a soft layer located on the cylinder;

Figures 12a and 12b show general schematic diagrams of the formation of a nip;

Figure 13 is a flowchart illustrating a method according to an embodiment of the present invention; and

Figures 14a to 14d show section views of different stages in the imprinting process. Figure 14a shows the start of the imprint process, Figure 14b and 14c show the imprinting process taking place and Figure 14d shows the imprinting process after a first imprint and/or curing step has taken place.

The present invention relates to, in embodiments, an optical engine for a nanoimprint lithography (NIL) imprinter operable to imprint nano- and micro-scale surface relief structures for use in functional structures. A non-exhaustive list of such functional structures comprises: lab-on-a-chip structures; diffractive optical elements; and other imprinted structures such as holograms.

An embodiment of the present invention will now be described with reference to Figures 1 to 14.

Figure 1 shows a perspective view of a nanoimprint lithography imprinter 10. The imprinter 10 comprises a main body 12 and an outer cover 14. The outer cover 14 is formed in two portions joined by a hinge 16. The outer cover 14 may be formed from a translucent material (as shown in Figure 1) such as plastic and is pivotable about the hinge 16 to provide access to the internal components of the imprinter 10. The colour and/or light transmission properties of the outer cover 14 are selected such that a user can view the internal components of the imprinter 10 but that radiation of particular wavelengths (e.g. UV radiation, IR radiation) is blocked or attenuated to protect a user from harmful radiation.

The imprinter 10 further comprises a movable stage 18 and a cylinder assembly 20. The cylinder assembly comprises a rotatable cylinder 22. In use, a sample substrate to be patterned with a surface relief structure is placed on the movable stage 18 and a mould for imprinting is placed on the rotatable cylinder 22. The stage 18 is then translated whilst the cylinder 22 is rotated in register such that the mould and sample substrate are brought together at the nip - the point where spacing between the base of the cylinder 22 and the surface of the stage 18 is smallest. At this point, the sample substrate is imprinted with the mould pattern as will be described later.

The stage 18 is substantially rectangular and comprises a substantially flat upper surface 24. The stage is supported on a guide rail 26. The guide rail 26 engages with a cooperating recess 28 formed in a lower surface of the stage 18. The stage 18 is movable from a first side to a second side of the imprinter 10 along the guide rail 26 by means of a drive arrangement 30. The drive arrangement 30 comprises a drive belt 32 which is driven by an electric motor 34. The drive arrangement 30 is arranged to translate the stage 18 back and forth parallel to the axis X-X (Figure 3).

In other words, the drive arrangement 30 is operable to move the stage in a first direction or a second direction opposite to the first direction, i.e. from left to right and from right to left as required. As the stage 18 is driven from one side to the other, the stage passes under the rotatable cylinder 22.

The stage 18 is maintained in a fixed plane by means of support guides 36 and a central roller 38 (Figure 5) which enable the stage 18 to be translated smoothly and without vibration or wobble.

Cylinder assembly

The cylinder assembly 20 will now be described. The cylinder assembly 20 comprises a pair of support members 40a, 40b which are pivotably attached to the main body 14 at rotational couplings 42a, 42b such that the cylinder assembly 20 is operable to pivot relative to the main body 14 about an axis Y-Y. The pivoting of the cylinder assembly 20 enables the spacing between the base of the rotatable cylinder 22 and the upper surface 24 to be varied and precisely controlled. In addition, the force applied to a sample substrate by the cylinder 22 can also be precisely controlled as will be described below.

The rotatable cylinder 22 is rotatably supported by the support members 40a, 40b and arranged to rotate about a cylinder axis C-C. The rotatable cylinder 22 is at least partially formed from a transparent or translucent material such as quartz, glass or a plastic material such as poly (methyl methacrylate) (PMMA). In this context, the terms “transparent” and “translucent” are intended to mean at least partially transparent or translucent to wavelengths of electromagnetic radiation used for curing the sample substrate as will be described later. This may include, but is not limited to, UV-radiation, visible light radiation and IR radiation (for example, near infra red light at a wavelength at or around 900 nm).

In this embodiment, the cylinder 22 has a material thickness of 5 mm. However, it may take any suitable thickness and may have any suitable thickness, for example, up to 10 - 15 mm. In use, a soft layer 22a (described later with reference to Figures 11 to 12) is applied to the outer cylindrical surface of the cylinder 22. In embodiments, the soft layer 22a has a thickness of 2 mm. A mould M is then applied to the outside of the soft layer 22a as will be described later.

The cylinder assembly 20 further comprises an optical engine 44 located within the interior of the rotatable cylinder 22. The optical engine 44 is shown generally in Figure 6 in section view. The optical engine 44 is arranged to project a pattern of electromagnetic radiation onto a portion of the sample substrate. In embodiments, the electromagnetic radiation is operable to cure a curable material of the sample substrate as will be described later.

The optical engine 44 is connected to the support members 40a, 40b and is arranged to remain stationary within the cylinder 22. The cylinder 22 is arranged to rotate around the optical engine 44.

Cylinder height and force adjustment

The pivotal connection of the support members 40a, 40b to the main body 12 is to enable height and force adjustment of the cylinder arrangement 20 and cylinder 22. This is to provide adjustment for different sample thickness and materials.

Figure 5 shows a front view of the imprinter 10 with the main body 12 and control knobs omitted for clarity. The movement and position of the cylinder arrangement 20 with respect to the stage 18 is controlled in three separate ways.

Firstly, the height of the cylinder 22 above the stage can be controlled by a height lever 46. Rotation of the lever 46 rotates an eccentric cam 48. Movement of the cam 48 lifts a member 50 which causes the cylinder arrangement 20 to be pivoted upwardly by a predefined amount. In embodiments, the cylinder arrangement 20 can be lifted by approximately 1mm.

Secondly, a thickness control 52 (Figure 1) can be adjusted to raise the height of the cylinder arrangement 20 by a predefined amount. This is achieved as follows. The thickness control 52 comprises a shaft 54 which passes through an extension 56 of the support member 40a. An eccentric cam 58 is arranged on the shaft 54 and is operable to engage with member 50 to lift/lower the support members 40a and 4b and cylinder arrangement 20 as desired.

Finally, the force with which the cylinder 22 is engaged with the stage 18 and the sample substrate can be set with the force control 60. The force control 60 comprises a slidable lever movable along a horizontal axis against a compression spring 62. The lever engages with a slide runner 64 which contacts, via a wheel, a hammer 66. The hammer 66 urges the cam 58 downward with a force proportional to the location of the slide runner 64 along the length of the hammer 66. In other words, if the slide runner 64 is at the far end of the hammer 66 (as shown in Figure 4), then the hammer 66 is constrained more strongly and will provide a greater force on the cam 58 than if the slide runner 64 is closer to the pivot point of the hammer 66.

Whilst the above description and figures describe and illustrate a mechanism having controls and other mechanical elements on one side of the imprinter 10 only, this need not be the case. For example, if desired, one or more of the controls described above (e.g. non-exhaustively, the height lever 46, the thickness control 52 and the force control 60) or mechanical elements (e.g. cams, levers, springs etc.) could be duplicated on the opposite side of the main body 12 if required.

Optical engine configuration

The optical engine 44 is shown in more detail in Figures 6 to 10. The optical engine 44 comprises a substantially cylindrical outer housing 68 which is located concentrically within the cylinder 22. The outer housing 68 is connected to the support members 40a, 40b via an adjustable connection 70 (see Figure 5) as will be described later. An inner housing 72 is located within the outer housing 68.

The optical engine 44 comprises an illumination source 74 in the form of a plurality of light emitting diodes (LEDs) forming an illumination strip. In this embodiment, the LEDs comprise surface mount technology (SMT) LED emitters having a centre wavelength of 395 nm. In embodiments, LEDs such as the LUXEON UV U line devices manufactured by Lumileds may be used. However, other illumination sources could be used, for example, UV LEDs at 360 nm, 365 nm, 385nm and 405nm, or a lamp source such as a mercury arc lamp.

The illumination source 74 is located at the base of the inner housing 72 within the outer housing 68. A widthwise aperture 76 is formed in the base of the outer housing 68 and the illumination source 74 projects downwardly towards the stage 18 through the apeture 76 and through the transparent/translucent cylinder 22.

The strip illumination source 74 comprises a plurality of 395nm LEDs which extend across some or all of the width of the stage 18 (i.e. in the direction Y-Y). In a specific embodiment, the LEDs have a curing width of 138 mm. The LED structure of the illumination source 74 emits in a 120 degrees forward direction. This leads to a simplified optical design of the focussing optics of the optical engine 44. The light emitting area is generally 2 mm² or less, and preferably 1.5 mm² for each LED. The width of the light emitting area (in this embodiment, in the direction X-X) can be 2 mm or less, and preferably 1.5 mm for each LED.

The use of surface mount technology (SMT) based LEDs has a number of advantages. Due to the small footprint of surface mounted devices such as SMT LEDs, they can be mounted in a limited space, enabling the use of an illumination source 74 within the interior of the cylinder 22 on a relatively small desktop system.

Further, the use of LEDs has numerous advantages over known arrangements. In the case of a blue/UV-emitting LED the spectral emission is in a narrow band and is not a broad band Planck black-body radiator as for a discharge lamp. This has the advantage that there is no problem of excess IR radiation, and baffles are not required. Furthermore, the LED structure emits in a 120 degree forward direction, which leads to simplified optical design of the focussing optics of the optical engine 44.

The illumination source 74 is focussed by a lens arrangement 78 which, in this embodiment, comprises a pair of stacked lenses and a protective glass cover. The lens arrangement 78 is operable to focus the emission from the illumination source 74 into a narrow beam line in a region on or adjacent the outer surface of mould M on the cylinder 22. The light will stay in focus when the thickness control 52 is adjusted.

Further, the use of solid state devices enables a significant reduction in the footprint of the light emission source. For example, a typical LED light source has a footprint of approxmiately 2 mm² when compared 16-20 mm² for a gas discharge tube. This enables more optimal focusing in a nip.

The focussing optics of the lens arrangement 78 comprises a condenser system. However, to ensure optimal light collection (where f#<1) and minimal lens aberrations, the condenser is made from aspherical Fresnel lenses as opposed to conventional plano-convex lenses. The design of the lens arrangement 78 furthermore facilitates a depth of focus providing a substantially undistorted line of focus in the nip after light has passed through the cylinder 22. The improved focussing facilitates a higher power density leading to a faster curing time of the radiation curable resin used to hold the surface relief pattern.

In embodiments, the illumination beam line has a width W (Figure 9) in the range from 0.5 to 10 mm, preferably in the range from 1 to 5 mm. In this embodiment, the width W is the width projected onto the outer surface of the mould M when in place on the cylinder 22. However, other arrangements or measurement points may be used.

The use a narrow curing beam has numerous benefits. For example, a high light intensity can be created in the nip, facilitating quick and efficient curing. The power density of light in the nip region depends upon the power of the illumination source 74 but also on the width of the focused beam. Assuming a width of the light stripe of 3.2 mm, the power density of radiation is, in embodiments, 4 W/cm².

An alternative value of measurement is to define the power per unit length along the nip (i.e. in the direction Y-Y). This value is independent of the focusing of the light source. In embodiments, the power per unit length is approximately 2 W/cm. On the assumption that the stage 18 moves at a speed of 6 m/min this provides a curing energy of 0.2 J.

As shown, the beam line is projected along an axis B-B which, in Figure 9, is substantially vertical and perpendicular to the upper surface of the stage 18.

However, in embodiments, the location and configuration of the beam line can be adjusted as required. For example, the vertical positioning of the illumination source 74 and/or lens arrangement 78 with respect to the outer and/in inner housings 68, 72 can be altered as desired to adjust the focal point of the illumination source 74 with respect to the outer surface of the mould M when in place on the cylinder 22 or to change the width W of the beam line.

As will be described in detail below, the beam line is intended to act as curing source to cure the material on the sample substrate. However, it may be desired to alter the point at which the sample is cured as it passes through the nip in order to improve the imprint or other such properties of the sample. For example, it may be desirable to partially cure the sample, or to initiate the curing process, shortly prior to imprinting with the mould. Alternatively, it may be desirable to cure the sample only after the sample has passed through the nip and the mould has left the required imprint in the sample.

To enable fine tuning of this function, the location of the beam line relative to the nip between the base of the cylinder 22 and the upper surface of the stage 18 can be adjusted. In embodiments, this is achieved by rotating the optical engine 44 relative to the stage 18.

As shown in Figure 5, the adjustable connections 70a, 70b comprises a pair of substantially elongate outer portions which are connected at both ends to a respective support member 40a, 40b. Note that in Figure 5 only the adjustable connection 70a is shown. However, connection 70b is shown partially in other figures. It is intended that, in embodiments, the adjustable connections 70a, 70b are substantially similar. In addition, in embodiments the adjustable connections 70a, 70b are operable in unison, i.e. to ensure the optical engine 44 rotates about an axis parallel to the stage 18.

An adjustment control 80 is provided to enable adjustment of the angle of the optical engine 44. The adjustment control and connection 80, 70 are connected to the outer housing 66 of the optical engine 44 and movable through an angle defined by the connections 70a, 70b to the support members 40a, 40b. This is used to adjust the focus of the light to be at the outer surface of the mould M.

Figure 10 shows the adjustment of the beam and the effect this has on the curing location. The effect is exaggerated in Figure 10 for clarity. In embodiments, the beam can be adjusted through an angle a which may be up to 10 degrees either side of the vertical centreline (shown in Figure 10), preferably up to 5 degrees either side of the vertical centreline. In Figure 10, the beam line is shown projected at an angle behind the vertical centreline and the nip, and so in this configuration an amount of pre-curing of the sample substrate will be carried out in this configuration.

In the alternative, post-stamping curing could be carried out by angling the beam line forwardly of the vertical centreline and nip.

In an alternative arrangement of the optical engine, an alternative surface mounted device-based light source may be used. For example, an organic LED (OLED) emitter at visible wavelength may be used as a curing source. Alternatively or additionally, a flexible electroluminescent (EL) layer or film may be added to the cylinder 22 either inside or outside the cylinder 22 and caused to emit curing radiation.

As a further variation, a photoluminescent layer such as a fluorescent or phosphorescent dye or other organic photoluminescent material may be used on the cylinder 22 and optically excited using a solid-state light source such as an LED or laser diode.

Soft layer and nip configuration

As described above, in order to create the required nip between the outer cylindrical surface of the cylinder 22 and the upper surface of the stage 18, it is necessary to provide a layer of soft material to enable the formation of a suitable nip. Such an arrangement is shown in Figures 11, 12a and 12b. Figure 11 is a view similar to Figure 9. Figures 12a and 12b are simplified general diagrams showing the nip and soft layer 22 configuration.

In one embodiment, the surface of the cylinder 22 is partly covered with a soft layer 22a of even thickness. The soft layer 22 is formed from a deformable material. In embodiments, the soft layer 22 is formed from a resilient material. The hardness of the soft layer 22a is in the range from 25 to 80 shore A.

The soft layer 22 has a hardness which is less than that of the cylinder 22. In other words, the cylinder 22 is used as a rigid or semi-rigid and transparent/translucent support surface, whilst the soft layer 22 is arranged to deform to form the nip with the upper surface 24 of the stage 18 as described.

As shown, the mould M is mounted on top of the soft layer 22a. In embodiments, the soft layer 22a and the mould M can be mounted by means of a double sided adhesive tape, or with a strip of tape in each corner.

In embodiments, the soft layer 22a has a thickness between 1 and 5 mm, preferably between 2 and 3 mm, preferably 2 mm. A plastics, polymeric, elastomeric or rubber material may be suitable. In examples, sheets of soft poly-vinyl chloride (PVC) are used.

In operation, the soft layer 22a can be deformed under pressure and the mould M will follow the deformed surface of the soft layer 22a. This way a nip can be formed and it will be possible to imprint on hard substrates like glass and wafers.

Figures 12a and 12b show the formation of the nip to define an imprinting contact area.

The nip geometry with an illumination source 74 inside the transparent imprint cylinder 22 furthermore facilitates the use of opaque substrate materials such as, for example, silicon wafers, metal plates, metallised polymer foils and plates and dyed substrates.

It is desired that the beam width W of the illumination beam is narrower than the width N of the nip. This is shown in Figure 12b. By using this arrangement, the whole of the curing energy can be used whilst the resin R is under pressure in the nip, resulting in an improved replication of the structure of the mould M. In some cases it will be important to be able to start curing before the nip or continue after the nip as set out above.

Whilst the above description relates to the use of a soft layer on the cylindrical outer surface of the cylinder 22, this need not be the case. Instead, a soft layer may be implemented on stage 18 such that the sample S is located on top of the soft layer on the stage.

In other words, the soft layer is required to be located between the cylinder 22 and the stage 18 in the nip, but may be located either between the cylinder 22 and the mould M or between the stage 18 and the substrate S. The use of a soft layer on the stage 18 is, in general, more suited to imprinting on foils or flexible substrates, and the use of a soft layer on the cylinder 22 is more suited to hard and inflexible substrates.

A method of operation of the imprinter will now be described with reference to Figures 13 and 14. Figure 13 shows a flow chart of the method according to an embodiment of the present invention. Figure 14 shows the imprinting process at different stages of operation.

Step 100: Configure imprinter and imprinting materials

At step 100, the imprinter 10 is prepared for imprinting. In use, a user may lift the movable section of the outer cover 14 which is pivotable about the hinge 16, to gain access to the interior of the imprinter 10.

As described, the upper surface 24 of the stage 18 is configured to receive a sample substrate S. The sample substrate S may take many forms, depending upon the required end-use.

For example, the sample substrate may comprise any elements suitable for receiving a surface relief structure through imprinting. The sample substrate may comprise a wafer or foil, or may be a device such as a photovoltaic element or a light emitting device (LED), or may be a microfluidic or plasmonic device.

In general, the sample S will have a surface which is partially or fully covered by a radiation-curable resin R into which an imprint can be made to form a surface relief structure.

Through the imprinting process, the sample substrate may be formed into, for example: a diffractive optical element; a diffractive structure for optical verification of anticounterfeiting; a nano- or micro-structured photovoltaic device; a nano- or microstructured LED; an optical waveguide; a microfluidic device; or may comprise a functional surfaces, e.g. super hydrophilic or super hydrophobic surfaces, or a surface that promotes or prevents cell-growth, a surface for replication of plasmonic structures, micro-arrays for biochemical use, a surface for creating a NIL etching mask pattern or a test sample to determine and quantify the properties of photo-curable resins.

To initiate the imprinting process, the user places a sample substrate S on the upper surface 24 of the stage 18. This is shown in Figure 14a. In embodiments, the substrate S is placed in a designated imprint area which may be marked on the stage 18.

Optionally, bearer stripes (not shown) having the same thickness as the substrate may also be placed either side of the substrate S.

Next, the imprinting plate (or mould) M is placed on the outer surface of the rotatable cylinder 22. The mould M may take any suitable form. However, in general it will be formed from a flexible material which is operable to conform to the curvature of the cylinder 22. The mould may be formed from any suitable material, for example, a polymeric material such as Polydimethylsiloxane (PDMS), Cyclic Olefin Copolymer (COC), Polyethylene, Polymethylpentene (PTX), Polypropylene (PP) ora light curing resin/polymer. The mould M comprises a pre-defined surface relief structure, the surface relief structure being arranged to be imprinted in the sample substrate S.

The mould M is placed on the cylinder 22 in a position which will ensure that the mould M is in register with, and rotatably aligned with, the substrate S so that when the stage 18 moves the substrate S to the nip, the mould M will engage with the sample S in the correct orientation and spatial location to transfer the desired pattern to the substrate.

Whilst a single sample S and mould M is shown and described, the invention is adaptable for use with multiple samples and moulds in a single imprint process. These samples could be aligned widthwise (i.e. along the axis Y-Y) or could be arranged in series (i.e. along the axis X-X). Corresponding moulds M can be arranged as appropriate on the cylinder 22. The use of different moulds mounted on the cylinder 22 at same time enable replication of different structures in the same imprint run.

The ability to process multiple samples in one process is particularly useful in increasing throughput of the process, and is not possible with conventional arrangements.

The imprinter 10 is then configured for the imprinting process. Firstly, the thickness control 52 is adjusted to correspond to the sum of the thicknesses of the mould M and the substrate S. This is to ensure that the surface relief structure is imprinted into the surface of the substrate S without undue compression or flattening of the substrate and mould M. The control 52, therefore, defines a minimum spacing between the base of the cylinder 22 and the upper surface 24 of the stage 18.

Next, the force control 60 can be set to determine the force or imprinting pressure which will be applied by the cylinder 22 to the substrate. The force control 60 can be adjusted as appropriate for the sample S and the mould M being used, and the structure intended to be formed.

The height adjustment control 46 can also be used at this time if required. In the “down” position, the cylinder 22 will be pressed against the substrate (and the substrate stripes) by the spring mechanism forming part of the force control 60. In the “up” position, if the correct settings are used, the cylinder 22 will be lifted approximately 1mm away from the sample surface.

The illumination source 74 can also be set at this stage; for example, the illumination intensity or the period for which the illumination source 74 will be activated. Further, as will be described below in steps 110 and 112, the stage 18 may make more than one pass through the nip and the sample S may be illuminated with curing radiation for any number of passes.

For example, in some situations no curing radiation may be needed and imprinting may be achieved with pressure alone. However, in alternative modes of operation, the sample S may be cured by the illumination source 74 for the first pass through the nip or on both passes through the nip.

At this step, the angle of the optical engine 44 with respect to the vertical centreline can be adjusted as appropriate to advance or retard the photocuring of the resin R on the sample S. As described above, this function helps fine-tuning the release process between the mould M and cured resin R.

Once the settings have been completed, the outer cover 14 can be closed and the imprinter 10 is ready for use and the imprinting operation can be initiated.

Step 102: Move stage

At step 102, the motor 30 and drive arrangement 30 are operable to move the stage 18 comprising the sample S containing radiation curable resin R towards the cylinder 22. The cylinder 22 rotates with the linear motion of the stage 18 and the sample S is then brought into contact with mould M containing a surface relief pattern to be transferred to the resin on the sample S. This is shown in Figure 14b where the sample S and the mould M have just been brought into contact. The method proceeds to step 104.

Step 104: Imprint/imprint and cure surface relief pattern

At step 104, the surface relief pattern formed into the surface of the mould M is transferred to the curable resin formed on the sample substrate S in the contact area between the mould M and the sample S in the nip. This is shown in Figure 14c.

The surface relief pattern formed in the mould M is transferred to the resin in a rotational process of the cylinder 22 which is facilitated by the friction between the resin and the mould M and the cylinder 22 holding the mould M.

The use of a narrow nip between the cylinder 22 carrying the mould M and the sample substrate S reduces the need for strict pressure control of the mould M and substrate S when compared to conventional NIL processes in which the full surface of the substrate is imprinted at once. As described above, the use of a soft layer 22a enables a nip to be formed even when using inflexible and rigid sample substrates S.

At this point, the illumination source 74 is used to cure the resin of the sample S. As described above, the illumination source 74 may be configured to illuminate the contact region in the nip between the mould M and the sample S in order to cure the resin immediately during the contact process. Alternatively or additionally, the angle of the illumination source 74 may be altered change the exposure region of the sample S to cure or partially cure the resin prior to engagement with the mould M in the contact area in the nip.

Alternatively or additionally, the angle of the illumination source 74 may be altered to change the exposure region of the sample S to cure the resin only after to engagement with the mould M in the imprinting contact area in the nip.

Whilst the above discussion describes “curing” and “imprinting” of the sample S, this of course is in reference to a portion of the sample S at any one time in a moving process. Due to the narrow region of contact between the sample S and the mould M on the cylinder 22, and the narrow beam width of the illumination source 74, only a part or strip of the sample S will be imprinted and/or cured at any one time.

Naturally, the whole or selected part of the sample S will be imprinted/cured as the sample S passes under the cylinder 22 through the imprinting contact area and out of the other side.

In use, the geometry of the stage 18 and cylinder 22 has numerous benefits over conventional arrangements. The arrangement of the present invention, with the cylinder 22 being suspended by the support members 40a, 40b and pivotable relative to the main body 12 with user-determined height and force relationships therebetween reduces the formation of bubbles in the photocurable resin and make use of vacuum superfluous, as normally would have been the case in conventional NIL imprinting.

Further, during the imprinting process, the configuration of the cylinder 22 and stage 18 passively accommodates for any unevenness or inhomogeneity in the substrate S. In conventional NIL systems, active and intricate systems are required make these compensations, adding to cost and complexity of the instrument.

Additionally, the use of a narrow curing beam line from the illumination source 74 has numerous advantages over known arrangements. The use of a narrow beam line makes it possible to achieve a higher power density or intensity of the curing light and thereby a shorter processing time for the curing process.

In addition, the combination of the imprinting method using the cylinder 22 and movable stage 18 provides imprinting of the mould M pattern in a narrow region of the sample S in combination with a narrow curing beam which has numerous advantages over the prior art. For example, the replication of the mould surface relief structure takes place in a narrow line of width N (Figure 12b) which is of the order of 1- 5 mm. This provides easy control of the applied pressure because a lower force is required to achieve an even pressure in the narrow imprinting and/or curing strip.

Once the imprinting and/or curing has been completed, the method proceeds to step 106.

Step 106: Move stage to end stop

After passing under the cylinder 22 and through the contact area between the sample S and the mould M, the stage 18 continues to an end stop at the opposing side of the imprinter 10. This is shown in Figure 14d.

At this stage, the sample S is now at the opposite end of the imprinter 10 and the opposite side of the cylinder 22 from the start position. The method then proceeds to step 108.

Step 108: Reverse stage direction

At step 108, the direction of the stage 18 is reversed and the stage 18 then moves laterally back towards the start position. The sample S, therefore, moves back underneath the cylinder 22 to the start position.

Depending upon the settings made in step 102, either the sample S is returned to the start position with no further imprinting/curing, or alternatively additional curing and/or imprinting steps may be completed. Depending upon this, the method will proceed either to step 112, 114 or directly to step 116.

Step 110: Further imprinting step

At step 108, the direction of the stage 18 is reversed. If set at step 100, on the return path the cylinder 22 can be maintained at the same height as for the first pass of the stage 18 under the cylinder 22.

Therefore, as the stage 18 passes back under the cylinder 22, the cylinder 22 rotates with the movement of the stage 18 and the mould M and the sample S are again brought into contact in the contact area of the nip. At this stage, step 112 may also be carried out to provide further curing.

Step 112: Further curing step

As determined in step 100, it is possible to perform a second curing step on the sample S as it passes back under the cylinder 22. The second curing step may be carried out in combination with a further imprint step at step 112 or may be carried out independently.

Step 114: Return to start position and finish

At step 114, the stage 18 returns to the start position. The process may be repeated any number of times as required. Depending upon the settings in steps 100, steps 110 and/or 112 may have been carried out prior to step 114.

However, if in step 100, the cylinder 22 is set to a greater height prior to the return of the stage 18 to the start position than in the first movement of the stage, the sample S will pass under the cylinder 22 without contacting the cylinder 22 or the mould M.

In addition, if selected in step 100, the illumination source 74 will not be illuminated and so no second curing step will be carried out.

The process may be repeated as necessary. If all imprint runs have been completed, the process stops and the user may remove the sample by lifting the outer cover 14 to gain access to the interior of the imprinter 10.

The desktop NIL imprinter of the invention has numerous advantages over conventional processes. The process is faster, more convenient and less error prone than known arrangements for imprinting of surface relief structures. The following is a nonexhaustive list of the applications for which the apparatus and method of the present invention could be used:

Replication of diffractive structures for optical verification devices on anti-counterfeiting; replication of diffractive optical elements; replication of nano- and microstructures for enhancing the light yield of photovoltaic devices; replication of nano- and microstructures for enhancing the light yield of light-emitting diodes (LEDs); replication of optical waveguides; replication of microfluidic devices; replication of functional surfaces, e.g. super hydrophilic or super hydrophobic surfaces; replication of surfaces either promoting or preventing cell-growth; replication of plasmonic structures; replication of micro-arrays for biochemical use; and evaluation of photo-curable resins.

Variations will be apparent to the skilled person and the skilled person would be aware that the configuration of elements may be varied as appropriate. For example, the optical engine need not be located within the interior of the cylinder and may be located elsewhere - for example, at one side projecting in.

Whilst the optical engine above has been described with reference to an imprinter having a rotatable cylinder and a stage, this need not be the case. First and second imprinting members may be provided but in a different form, for example, a pair of cooperating rollers which define a nip therebetween, or a rotatable cylinder as a first imprinting member and a roller as a second imprinting member. This is known as roll to roll processing. In such an arrangement, the sample substrates may be flexible or may form a roll of substrate material onto which a resin or other curable material is placed.

As noted above, different illumination sources may be used such as lamps and other LED sources at different wavelengths. Indeed, curing may be carried out using a thermal source rather than a light source and thermally-cured resins may be used. In addition, whilst a narrow beam width is described, this need not be the case and a larger illumination area may be used.

In addition, multiple sources may be used and selected depending upon the type of resin or cure to be achieved. For example, different wavelength curing sources may be selected depending upon the absorption spectra of the selected resin, with certain sources selected at areas of weak absorption by the curing resin so as to partially cure the sample, with a different wavelength source used which is in a stronger absorption wavelength of the resin to fully cure the sample.

The different wavelengths may be selected to, for example, partially cure the sample prior to the imprinting step and the fully cure the sample thereafter. Alternatively or additionally, different layers of resin material or mixtures or resin material having different absorption properties may be used and selective source wavelengths chosen to preferentially cure one material with respect to the other. For example, it may be desirable to cure or partially cure a thin surface layer of resin prior to the imprinting process and then cure the bulk of (potentially different) resin material thereafter.

Alternatively, different sources may be used for different samples in the same imprint process. For example, a portion of the width of the stage may be illuminated by a first wavelength and another portion of the width of the stage may be illuminated by a second wavelength different from the first wavelength.

Whilst the stage has been described as making a return process, this need not be the case and the sample may be removed after a single pass under the cylinder. Different drive mechanisms may be used to drive the stage. In a further alternative, the stage may remain fixed and the cylinder may be moved relative to the stage.

The suspension of the cylinder with respect to the stage may also take any suitable form that allows for variation in sample thickness and applied force. For example, instead of a pivoting arrangement at one side, the cylinder may be pivoted at a different point, or supported on rails to slide vertically.

Embodiments of the present invention have been described with particular reference to the examples illustrated. While specific examples are shown in the drawings and are herein described in detail, it should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular form disclosed. It will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention.

Claims

1. Apparatus for imprinting of surface relief structures from one or more moulds on to one or more sample substrates comprising a curable material, the apparatus comprising first and second imprinting members arranged to define an imprinting nip therebetween, the imprinting nip having an imprinting contact area where, in use, one or more moulds engage with one or more sample substrates to imprint the surface relief structure therein as the one or more sample substrates pass through the imprinting nip, wherein the apparatus further comprises an illumination arrangement arranged, in use, to project an illumination beam onto at least a portion of the or each sample substrate to at least partially cure the curable material, the illumination beam defining an illumination region, and wherein the illumination arrangement comprises at least one solid-state light-emitting device.

2. Apparatus according to claim 1, wherein the illumination arrangement comprises a plurality of solid-state light-emitting devices.

3. Apparatus according to claim 2, wherein the solid-state light-emitting devices are arranged in a line.

4. Apparatus according to claim 1,2 or 3, wherein the or each solid-state light-emitting device comprises a surface mounted device (SMD).

5. Apparatus according to any one of the preceding claims, wherein one or more solidstate light-emitting device comprises a light emitting diode or a laser diode.

6. Apparatus according to any one of the preceding claims, wherein the or each solidstate light-emitting device has an emission wavelength in the UV or IR regions.

7. Apparatus according to claim 6, wherein the or each light emitting diode has an emission wavelength in the region of 360 - 405 nm or in the region of 900 nm.

8. Apparatus according to any one of the preceding claims, wherein the illumination arrangement further comprises a lens arrangement.

9. Apparatus according to claim 8, wherein the lens arrangement comprises a plurality of stacked lenses.

10. Apparatus according to claim 8 or 9, wherein the lens arrangement comprises one or more aspherical Fresnel lenses.

11. Apparatus according to any one of the preceding claims, wherein the illumination region comprises a line having a line width in the region from 0.5 mm to 10 mm.

12. Apparatus according to claim 11, wherein the illumination line has a line width in the region from 1 mm to 5 mm.

13. Apparatus according to any one of the preceding claims, wherein the illumination region extends across all or part of the width of the first or second imprinting member.

14. Apparatus according to any one of the preceding claims, wherein the illumination arrangement is configured to enable the location of the illumination region to be varied with respect to the location of the imprinting contact area.

15. Apparatus according to claim 14, wherein the illumination arrangement is configured such that the illumination region either:

i) overlaps at least a part of the imprinting contact area;

ii) is arranged behind the imprinting contact area of the nip such that at least a portion of the sample substrate is illuminated prior to reaching the imprinting contact area of the nip; or iii) is arranged ahead of the imprinting contact area such that at least a portion of the sample substrate is illuminated after passing through the imprinting contact area of the nip.

16. Apparatus according to any one of the preceding claims, wherein the first imprinting member comprises a rotatable cylinder arranged to carry the at least one mould.

17. Apparatus according to claim 16, wherein the second imprinting member comprises a support roller.

18. Apparatus according to claim 16, wherein the second imprinting member comprises a stage arranged to support at least one sample substrate and wherein, in use, the stage and rotatable cylinder are movable with respect to one another.

19. Apparatus according to claim 18, wherein the stage is linearly movable relative to the rotatable cylinder in a direction perpendicular to an axis of rotation of the rotatable cylinder and the rotatable cylinder is arranged to rotate during said linear movement.

20. Apparatus according to any one of claims 16 to 19, wherein the illumination arrangement is located within the interior of the rotating cylinder.

21. Apparatus according to claim 20 when dependent upon claim 14, wherein the illumination arrangement is rotatable about an axis to vary the location of the illumination region.

22. Apparatus according to any one of the preceding claims, wherein one or more solidstate light-emitting devices comprises an organic photoluminescent or electroluminescent material.

23. Apparatus according to claim 22, wherein one or more of the solid-state lightemitting devices comprises an organic LED or an organic photoluminescent material optically excited by a solid state LED or laser diode.

24. Apparatus according to claim 22 or 23 when dependent upon claim 16, wherein the organic photoluminescent or electroluminescent material is located on an interior or exterior surface of the rotatable cylinder.

Intellectual

Property

Office

Application No:

GB1814555.7

Examiner: Mr Patrick Lucas