Patent Application
20210162540
This invention relates to a device for the laser-assisted machining of bodies or surfaces and processes using this device. The device is suitable for e.g. for producing three-dimensional structures, for example of or in bodies, or of or in surfaces of a material to be solidified, or for processing surfaces or bodies, preferably of glass or glass ceramic or metal, or metallic films or structures on a non-metallic surface, preferably by site-selective irradiation using two- or multi-photon absorption processes (hereinafter abbreviated as TPA for two-photon absorption or MPA for multi-photon absorption) or using pulsed lasers such as ultrashort pulse lasers.
3D lithography systems (also referred to as high-precision 3D printers) for the additive and subtractive production of multidimensional structures on surfaces/volumes of any shape by means of multi-axis systems using multi-photon processes are basically known.
From the prior art it is known, among other things, to produce three-dimensional bodies or surface structures e.g. by light-induced processes, in particular by organic cross-linking, by first producing only one layer or plane as a two-dimensional component of the structure to be created and then building up the three-dimensional structure of the body or surface structure by successively processing successive two-dimensional layers or planes. Examples of such two-dimensional processes are stereolithography, selective laser sintering (SLS) or 3D printing (3DP).
Processes faster than stereolithography offer three-dimensional processes in which material-modifying radiation interacts directly in the volume of a raw, solid or liquid starting material. From WO 03/037606 A1, the use of two- or multiphoton polymerization for the consolidation of organopolysiloxane-containing materials is known (polymerization takes place by two-(TPA) or multiphoton absorption).
DE 101 11 422 A proposes for such a method to—arrange the bath container with the material to be solidified on a—table which can be moved in the XY plane—and to provide a construction platform therein which can be moved in the Z direction in a controlled manner in order to be able to variably position the focal point in a suitable manner.
WO 2011/141521 A1 describes two different devices for the generation of three-dimensional structures from a material to be solidified due to light-induced organic cross-linking. The devices each have a laser source, a movable focusing optics for forming one or more laser foci and a material container for the material to be solidified. In the first device, the material container consists at least partially of a material which is transparent to the laser radiation used and is arranged or arrangeable in the beam path in such a way that the laser radiation can be introduced through the material container into the material to be solidified, the material container acting as an optically defined boundary surface, and a carrier unit which can be positioned relative thereto is arranged in the material container.
With the devices of WO 2011/141521 A1, it is possible to produce three-dimensional bodies of any shape from materials to be solidified in situ by light-induced cross-linking processes over a wide wavelength range using a wide variety of laser and optical systems. In general, a large number of material classes can be processed in parallel and over a large area.
According to the invention, laser-assisted processes are for example solidifications of liquid or pasty materials (organic polymers, inorganic-organic hybrid polymers, or organic or inorganic-organic polymers filled with nanoparticles) using MPA/TPA, the structural modification of the solubility of parts of already solid materials (organic polymers, inorganic-organic hybrid polymers) using MPA/TPA (in particular by breaking of bonds), the structural modification of physical properties of glasses or glass ceramics, whereby in the case of suitably pre-treated glasses/glass ceramics, e.g. phase transitions and/or redox reactions are triggered in their interior, which can lead to an altered, e.g. increased solubility compared to a solvent such as HF, NH4F or mixtures thereof, and the processing of solid surfaces (inorganic, organic, inorganic-organic or metallic) using MPA/TPA. The invention also includes laser-assisted surface treatments of metals and other materials: It is possible, for example, to structure metals using pulsed lasers, such as ultra-short pulse lasers, whereby material on the surface is vaporized or ablated. This process can be used, for example, to produce extremely fine bores. The aforementioned set pf processing methods is not to be understood as exhaustive.
In the present invention, the expression ‘being formed’ is to be understood as the product of laser treatment, in particular TPA or MPA or treatment with pulsed lasers, such as ultra-short pulse lasers, in general. This can be a solidified material, for example, if the TPA/MPA triggers a polymerization reaction in an organic or organic-inorganic hybrid material, it can be a structure formed by the dissolution of a solid when the TPA/MPA triggers a bond break; it can also be a structure that has different physical properties than the material that is not exposed with TPA/MPA, e.g. a polymerization reaction in an organic or organic-inorganic hybrid material, or it can be a structure formed by the dissolution of a solid when the TPA/MPA triggers a breaking of a bond, it can be a structure having physical properties other than those of the material not irradiated with TPA/MPA, which is e.g. is more soluble or less soluble, or any other structure formed directly or indirectly by site-selective irradiation using TPA or MPA.
As mentioned, the expression TPA/MPA is used according to the invention for two- and/or multiphoton polymerisation with a non-linear behaviour. A reaction only takes place in an area where the laser intensity exceeds this threshold. The reaction can therefore take place in a very narrow region, thus enabling the generation of highly accurate structures and does not take place outside the focal volume or not with sufficient intensity or with reduced efficiency, so that suitable intensity profiles can be produced by shaping the focal volume, which lead to different material properties in a single material, if necessary, in a single process step.
A polymerization reaction may be triggered by TPA/MPA on organic or organically modified inorganic materials, such as organically modified polysiloxanes or mixtures thereof, which have organically polymerizable C═C bonds or other light-induced polymerizable groups. These can be unfilled or filled with nanoparticles or microparticles. Alternatively, the TPA/MPA can trigger binding fracture processes, which allow solubility changes to be achieved to an adjustable extent. In addition, redox processes, restructuring processes and/or phase transitions, e.g. crystal formation in glasses and glass ceramics, can be induced by the TPA/MPA and, using suitable devices, strongly localized and controlled in three dimensions.
Metallic surfaces, metallic bodies (e.g. with dimensions in the cm or dm range) or metallic films or structures on the aforementioned materials can be processed in a locally selective manner using pulsed lasers, in particular ultra-short pulse lasers: Laser ablation, also called laser evaporation, is the removal of material from a surface by bombardment with pulsed (or cw) laser radiation. The laser radiation with high power density used here leads to quick heating and the formation of a plasma on the surface. However, ultra-short pulse lasers can further be used to produce superficially site-selective melting or evaporation without plasma formation or to form alloys. It is therefore possible to use ultrashort pulse lasers to structure metals very finely or to change their surface composition very finely. Ultra-short pulse lasers, for example, can be used to produce extremely fine drill holes. These must be placed exactly in the material, i.e. it is necessary that the energy input by the light beam falls exactly vertically or at a precisely defined angle onto the metal surface. If it is an object with an irregular surface, this cannot be achieved or only with considerable effort for the movement of the components.
Metallic structures processed with pulsed lasers, especially ultrashort pulse lasers, should also be subsumed under the expression “structure being formed” according to the invention.
Glasses can be processed with the help of the invention, likewise.
Furthermore, using polymers, metal can be applied to surfaces and materials of any shape using TPA/MPA and a metallization process: A substrate or body is coated with a polymer precursor and exposed with an ultra-short pulse laser to trigger a two- or multi-photon process. The solubility of the material in the exposed areas is increased compared to that in the unexposed areas, so that the material can be washed away from the exposed areas using a solvent or solvent mixture. This is followed by a surface metallization by coating processes such as vapor deposition, sputtering, electrodeposition or (pulsed) electrodeposition and then a lift-off of the remaining coated polymer, whereby the metallization remains only at the points on the substrate or body where the polymer is washed away. Thus, metal structures of less than 1 μm, preferably less than 500 nm and especially of 100 nm can be produced.
Devices which are suitable for the aforementioned processes, i.e. for laser-assisted processing of a material adhering to a substrate or of a substrate associated or substrate free body or of its surface, in particular by TPA/MPA and/or by treatment with a pulsed laser, for example an ultrashort pulse laser, generally have the following components:
The expression “sample collection” of the positioning system shall mean an area of the system on or to which the substrate or body may be supported or attached. It may, but does not have to, be a flat surface. The surface may also have apertures, or the specimen holder may be formed of or include a rod construction or the like. The sample holder is preferably a component of one of the carriers or the only carrier of the positioning system, which can be designed for example as a hexapod and in these cases in particular in the form of its second base. Instead, the sample holder can be connected to another component of the positioning system in any way, for example by screwing.
If the substrate or body is located directly on the sample holder of the device, it is located directly on this sample holder. In the case of using a positioning system that has a platform or base, the sample collection may be that platform or base. Alternatively, there may be a holder for the substrate or the body on the sample holder. In this and similar cases, the substrate/body in the sense of the invention is “indirectly” arranged on the sample holder.
In all cases, the substrate/body should be attached to the sample holder to prevent it from falling or being knocked over. This applies in particular if the substrate or body cannot lie on the sample holder in such a way that it is held securely and reliably by gravity on the sample holder. Since the device is suitable for very different processes and also for substrates/bodies of very different sizes and shapes, it would be desirable to design this attachment in such a way that the most diverse substrates/bodies can be held in the most diverse positions and arrangements without having to provide or redesign special solutions for the holder in each individual case. It is therefore the task of the present invention to design the device in question in such a way that any substrate or body of any size and in any position can be held securely in it.
The solution to this problem is to fix the substrate or the body on the sample holder by means of an air extraction system. Such an air extraction is known in the field of wafer processing under the name “wafer chuck”. The expression ‘chuck’ is therefore intended to characterise this type of carrier below. The chuck according to the invention has the form of a hollow body, the upper side of which is designed as a perforated plate with or without grooves for supporting the substrate or body and which has a suction opening for controllable air suction. This suction opening can be of any design, e.g. in the form of the entire bottom surface or in the form of an opening with or without a valve and in varying sizes and shapes. This allows the substrate or the body to be fixed by suction forces (vacuum).
The attached figures explain the invention in more detail, wherein:
In a special version of the invention, the perforated plate of the chuck is designed to be removable and the rest of the hollow body is designed in such a way that its upper side can be closed off by perforated plates of different sizes and/or shapes, so that substrates or bodies of any shape can be accommodated, such as wafer-shaped substrates, microscopy glasses, assembled or unassembled printed circuit boards, electrical or electrical/optical (micro)components which have not yet been encapsulated or packaged electro-optical or optical components with or without glass fibres, or Fiber optic arrays, whereby this list is only exemplary and not restrictive.
In an alternative design, which can also be used cumulatively with the previous one, the chuck is divided into several areas whose air extraction can be controlled separately. The control can, for example, be carried out using valves. Substrates or bodies of different shape and size can be held on such a chuck. For example, the chuck may have an inner area in contact with the central holes of the hole plate to fix small bodies or substrates, and around that area one or more ring-like and/or striped areas which may be used in addition to the suction if the bodies or substrates are larger. The vacuum in the individual areas can be selected differently and the areas can also be activated and deactivated separately. So it can be advantageous to build up a stronger vacuum in rings further outside in order to be able to hold even large substrates or bodies with, for example, different centres of gravity, in a stable manner.
In the event that the device according to the invention uses a substrate which is not completely flat on its backside, as may occur, for example, with an assembled printed circuit board or an electrical or optical or electro-optical component, an additional carrier may be provided on the chuck. This carrier can be a flexible or non-flexible, fixed carrier, designed to still allow the substrate to be aspirated by the chuck. It should have such a tightness and any number of holes and grooves that an arbitrarily shaped and arbitrarily large hole pattern of the chuck can hold any sample in the vacuum. This can be a rigid or flexible overlay, such as a rubberised overlay (mat) or a silicone mat, into which preferably small holes and/or grooves are formed. Flexible mats are inexpensive for holding uneven bodies or substrates on the underside, such as electrical or (electro)optical components, which often have solder balls or the like on their underside. Such unevenness can be absorbed by a flexible mat into which they are pressed.
The chuck serves as a variably designed or configurable sample holder; if required, however, it can also be designed and used for equalization and compensation of a wedge error. The use of wedge error compensation is known to the expert from the prior art.
In a first specific configuration of the invention, a single or first carrier in the form of a device enabling at least three translational and three rotational degrees of freedom is used for the positioning system. It is preferred to have up to six legs mounted on a first base, the length and angle of which are variable and which are connected to a second base in a suitable arrangement (e.g. a hexapod).
Hexapods are known from the prior art. They are characterized by the presence of three linear axes and three rotational axes, often arranged on very small surfaces, and have high dynamics. The dead weight and the fraction of mass that has to be moved are very small, so that they have a low inertia and can achieve high accelerations and final speeds, which makes them suitable for very fast processes with movements of any kind. All axes usually show (nearly) identical dynamic behavior, very low crosstalk of the axes and high stiffness. The advantage of hexapods lies above all in the free definition of the pivot point. Due to the mobility of the hexapod or comparable devices, structuring is also possible on curved surfaces, such as concave mirrors or other free-form surfaces.
In addition to said first carrier, the positioning system may also comprise, in specific configurations, a second carrier capable of movement in the X-Y direction and/or the Z axis and/or having an axis of rotation. This carrier is also referred to as positioning stage. It can be connected or attached to the first carrier in any way, for example by means of clamps, or the second carrier can be embedded in the first carrier and/or hold it by means of a suction vacuum.
In accordance with the invention, a second carrier, if present, is used as the second carrier, which enables linear positioning in the planes of the room and/or positioning about at least one rotatable axis (e.g. mountable on the X-Y positioning stages, e.g. a positioning table or another positioning stage not necessarily designed as a table). This could be, for example, a carrier in which a rotation axis is mounted on a positioning unit that can be moved in the X-Y direction. The positioning unit can perform movements in the X and Y directions, and the rotation axis can perform a rotary movement, whereby the length of the rotation axis in the Z direction is preferably variable, e.g. by extending and retracting the rod, so that the height of the first carrier can be adjusted by the second carrier. The second carrier can also be made up of several partial beams (partial positioning stages). Irrespective of whether it represents a single positioning stage or is made up of several subunits, the second carrier can be mounted in any position, e.g. air cushioned, and be driven in any way, e.g. mechanically and/or piezoelectrically.
If there is a second carrier, it can serve as the base of the device, for example if it is a linearly movable table or an axis rotating in the Z direction. In these cases, the first carrier is arranged on the second carrier. However, it is not mandatory that the first carrier is attached to the second carrier. Depending on requirements, the second carrier can instead be arranged on the first carrier, or both carriers can be arranged side by side, with the sample holder usually located at one side end of the carrier structure
In a second specific configuration of the invention, the positioning system comprises the second carrier as described above, but not the first.
The expression ‘focusing optics’ is defined by invention as a focusing device, preferably a lens or lens system, which may be housed in a housing and have additional components.
Each focusing optics may be movable relative to other elements of the beam guide and/or the material container and/or the material to be solidified and/or the carrier unit, so that only the focusing optics need to be moved for positioning and remaining elements of the beam guide may be permanently installed. Particularly in the case of positioning via a movement of the optics, the laser beam can with particular advantage be guided via optical waveguides at least in partial areas of the beam guidance.
To avoid imaging errors during focusing, hybrid optics consisting of diffractive optical elements and conventional lenses can be used according to the invention. The diffractive optical elements are made of quartz glass, organopolysiloxane-containing materials, liquids or any combination of materials, for example in layer systems or structured layers. They can be optically initiated by electrical potentials, magnetic signals or surface tensions that can be variably adjusted, for example by molecular layers that change their orientation by applying a voltage in such a way that the polarity of the surface can be changed in a controlled manner. When using focusing optics, which are used without refractive index adjustment, variable penetration depths of the light into the material result in a positioning error due to refraction at the air-material interface (i.e. the movement of the focal volume does not correspond to the movement of the optics). This deviation in the Z-positioning of the focal volume can be compensated by a correction factor, e.g. a factor implemented in the machine software, or, if necessary, by a correction wheel on the focusing optics, which makes it possible to minimize the imaging errors / aberrations to the desired working position.
The device and the method of the present invention are advantageously not limited by diffraction limitations of the focusing optics, because on the one hand there is a different absorption behaviour than with linear single-photon absorption and on the other hand a threshold value process is exploited. The absorption profile (approximately Gaussian or Lorenz profile) for multiphoton absorption is still narrower, allowing better resolution because there is a non-linear relationship between photon density and absorption behavior.
In a large part of the embodiments of the invention, the focusing optics are located above the material or body to be processed and thus also above the sample holder. However, it can also be arranged below the material or body to be processed or laterally to it, as shown as an example in
The focusing optics can be an air lens. The latter can be dense compared to the material to be processed, so that it can dip into the latter in such a way that a direct boundary surface between objective and material is formed. Alternatively, an (oil-) immersion lens can be used, the cover glass of which can be used as a substrate, for example. Alternatively, the transparent carrier surface is used as ‘cover glass’ and focused into the material above the carrier surface.
In the case of a positioning system with a carrier that enables three translational and three rotational degrees of freedom, the laser focus or foci can always be positioned perpendicularly or at a desired angle to the substrate surface or to the virtual or actual surface to be processed using the device according to the invention. It can be arbitrarily shaped, for example flat, or have a regular or irregular curvature and/or contain different components, such as edge emitters, photonic integrated circuits and/or other passive and active elements, including microfluidic elements and/or also electronic components and/or any combinations thereof, which is not restrictive, but exemplary, as any arrangement of components and/or components with any function (such as optical, photonic, electrical, electronic, magnetic, piezoelectric, etc.) can be processed. The positioning is carried out by moving the device described above (first carrier together with second carrier or alone) with the sample holder, possibly supplemented by a movement of the focusing optics, which, however, is not mandatory. It can take the form of linear and/or rotary positioning in and/or around one, two, three or more axes. In particular, due to the characteristics of the positioning system and especially when using a first carrier as defined above, any inclination angle and/or surface geometry and/or surface morphology and/or surface topology and/or arrangement is possible.
In particular, the positioning system, which has three translational and three rotational degrees of freedom, can be synchronized with the pulsed laser source as an active process, so that the sample material can be processed in a controlled manner by variable laser pulse sequences, which can run along arbitrarily shaped 3D trajectories. Thus the sample is controlled and dynamically moved by the positioning system during the complete light exposure process. In addition, the positioning system can be controlled in such a way that, despite curved or uneven surfaces of the sample, the laser beam always falls perpendicularly onto the substrate through the focusing optics, as the sample can be aligned corresponding to the direction of the laser beam by means of the positioning system.
In an advantageous design, the control and regulation of the positioning system is based on a measurement of the position of the sample relative to the direction of the laser beam. In particular, it is proposed to integrate the principle of the light pointer method into the system in order to determine the position of the sample (with corresponding feedback loop for control). A light beam is reflected from the sample into a detector (such as a diode, preferably a four quadrant diode) or an array of detectors, from the substrate holder, a substrate (without components) and/or a substrate with components (can be a bare sample or an assembly) into the detector. The exact position of the substrate holder and the substrate is determined by alignment marks and the deflection of the light beam on the detector. A calibration to determine the reference position is carried out when the light falls vertically along the optical axis, an incorrect adjustment can already be taken into account. The individual detector surfaces are read mathematically and the deviations from the original position are determined in situ. A control with feedback loop moves the hexapod in all spatial directions in such a way that the fastest and shortest movement is always possible and the light always hits the sample to be processed in a perpendicular direction, regardless of its configuration (shape, waviness, etc.).
The combination of the innovative positioning system with translational and rotational degrees of freedom with a focusing optics designed for immersion in the material to be processed offers special advantages. This is because the focusing optics can be moved along a substrate that is completely immersed in the material to be processed and of any shape in such a way that the radiation is focused precisely and perpendicular to the surface at the desired anchor points. The orientation of the material surface then becomes irrelevant. For sufficiently small structures, patterning may also be performed in a droplet of the material which, under appropriate surface tension and adhesion conditions, may also adhere to substrate surfaces which are inclined to the horizontal or which are oriented downward so that the droplet hangs on the substrate surface. When structuring in a droplet, the bath container can be omitted.
For a better general understanding of the invention, a schematic representation of a specific design of the device conforming to the invention is given in
Any structure that can hold at least a very small amount of processable material, e.g. a drop thereof or a very thin layer thereof, or the body to be processed, can serve as a substrate. The substrate may, but only in some cases, such as the one described above, be translucent, e.g. made of glass. Instead, of course, other materials are suitable as substrates, e.g. metals. In order to demonstrate the diversity and variability of the substrates that can be used, some examples are given below, which should not be understood as restrictive under any circumstances.
In a first embodiment it is e.g. a flat substrate without side walls. This substrate can be covered with a layer of material to be processed, e.g. to be solidified, which is to be structurally solidified or otherwise processed and left on the substrate using the method according to the invention. The invention is therefore for example suitable for the modification of surfaces, for example. For example, the substrate may be a lens or a concave mirror, or a body or vessel with studs or other predetermined structures.
Alternatively, a small amount, e.g. a drop, or a liquid or pasty layer can be applied to the substrate, in which processing takes place from the substrate surface, e.g. solidification of a three-dimensional structure, which is subsequently freed from unsolidified surrounding material, i.e. “developed”. In such cases, the substrate may be covered with a sacrificial layer or a layer on which the solidified material adheres only weakly in order to detach it from the substrate. In such a drop or in such a layer, a three-dimensional structure can also be formed using suitable solidifiable materials, which becomes more soluble than the area not affected by the 2- or multi-photon polymerization by a subsequent treatment. In this configuration, the cover glass of an oil immersion lens can be used as a substrate.
If a small amount of material to be solidified is used, the meniscus properties and thus the external shape of the material adhering to each other by cohesion can be controlled by surface modification and functionalization of the surfaces to adjust the interfacial energies. For this purpose, the material properties can be adjusted, e.g. by introducing hydrophobic or hydrophilic groups into the polymerizable material.
In a second embodiment, the substrate is a manufacturing component, such as an optical or optoelectronic component or a photonic chip or a photonic integrated circuit (PIC), or a (partially) assembled or unassembled printed circuit board, or generally a component with active and/or passive components, such as actuators, sensors or mirrors, or other components, such as glass fibers or glass fiber ribbons. If the components are small enough or their distance from each other in the component is small enough, a single drop of material to be processed, especially to be solidified, is often sufficient, which can be applied to a surface or into a cavity (if available) of the component. However, any prior art coating process can be used, with or without external limitation of the area to be coated. Using the method according to the invention, one or more preferably optical components are then structured for this component, selected e.g. from waveguides, collimators, microlenses, gratings, diffractive optical elements, combinations of refractive and diffractive elements and phase elements, which are formed directly on the bottom of the component or on a structure already present in the component. The solidifiable material can be selected such that the component structured in accordance with the invention is either freed of residual material after structuring and/or that the entire solidifiable material is pre-crosslinked beforehand by light and/or heat treatment and/or that the entire solidifiable material is completely pre-crosslinked measured against its possible maximum conversion of the crosslinkable chemical groups and/or that the entire solidifiable material is subsequently post-consolidated by heat or floodlight. As is known from the prior art, in such cases the component structured by TPA/MPA has a different secondary or tertiary structure so that it differs physically (e.g. by its refractive index and/or its mechanical and/or chemical and/or dielectric and/or magnetic properties) from the environment hardened by heat or floodlight. The second embodiment is illustrated in
In a specific version of this embodiment, a waveguide is structured and then freed (“developed”) from the surrounding material, whereupon a material different from this material (solid, liquid or gaseous) is introduced, which serves as cladding and whose refractive index is preferably chosen so that the refractive index difference between the waveguide and the cladding is higher than that between the waveguide and the material from which it was structured. In this way, high NA can be produced while at the same time exploiting the 3D capability.
In a third embodiment, solidifiable material or material whose bonds can be broken by the TPA/MPA process is arranged between two substrates, of which the substrate arranged on the sample holder can be of any nature, e.g. as explained in the first two embodiments, while the second substrate must be translucent. The irradiation can be carried out from above or below or from both sides, whereby two transparent substrates or carriers are of course available for irradiation from below and above.
In a fourth embodiment, a relatively large body is created using 2PP structuring. For this purpose, the substrate can be designed as a material container for a bath of solidifiable material, as shown for example in the above-mentioned WO 2011/141521 A1, or the material can be held as a meniscus between an arbitrarily shaped substrate and a focusing lens, such as a microscope objective. The shape of the meniscus can be further improved by incorporating appropriate surface functionalities into the material used. This is achieved, for example, by modifying the hydrophobic/hydrophilic material properties described above. To ensure that there is always a sufficient amount of material to be exposed between the focusing optics and the substrate, as might be necessary, for example, for the production of large structures, the material can be supplied by a dispenser, e.g. with a (micro)pump and/or a microfluidic element. Two different versions of this embodiment are shown in
In a fifth embodiment, the substrate is attached to spacers which are located on the sample holder or the chuck or similar in such a way that a space is formed between the substrate and the holder, on which, for example, a drop of material to be solidified hangs, which is controlled by the light radiation through the substrate using the laser and the focusing optics. A three-dimensional structure can be formed in this drop, as described above for the first embodiment. Here, too, the shape of the drop can be influenced as described above. This embodiment can also be used for positive resists. The structures are written into a coating on the substrate by breaking the bond. Afterwards a metallization can be developed and applied and the unexposed material can be removed by a lift-off. The embodiment is shown in
In a sixth embodiment, the substrate comprises a translucent area which is provided on both sides with material to be processed, in particular to be solidified. If this area is sufficiently thin, a suitable choice of focusing optics (e.g. a low NA) can cause simultaneous solidification of the areas on both sides of the surfaces of the translucent area, since, as mentioned above, voxels with lengths of up to approx. 100 μm or even more can be solidified for very low NA and small magnifications if the centre of the voxels lies within the translucent area. In this way, suitable materials can be used, e.g. thin glasses or glass ceramics or other transparent materials, if necessary also in the form of tubes, which can be coated on both sides. For this purpose, a holder can be used which allows the substrate to be coated on both sides with the liquid or pasty material without contaminating the device. When using lenses with very high NA, structures in the lower micrometer range or nanostructures of below 100 nm on both sides of a thin, transparent substrate of any shape can be achieved, provided that the material is at intensities within the FWHM (Full Width Half Maximum) or slightly below when crosslinked.
In a seventh embodiment, the focusing optics dip into the material to be solidified on the substrate, as described for the second design of WO 2011/141521 A1, wherein the substrate can, however, have any shape other than that described in WO 2011/141521 A1, e.g. a shape as in one of the embodiments one, two and six.
The substrate can, of course, be arranged on the supporting surface in any orientation, e.g. diagonally, in all the above-mentioned embodiments; a preferred direction in e.g. X, Y or Z is not required.
In an eighth embodiment, the substrate can be rotated about an X-axis, e.g. above a material bath into which it can be immersed. It is supported by the X-axis, which is coupled to a sample holder of a device that can perform three translational and three rotational movements. This may be the first carrier of the invention. The rotation is initiated by the laterally mounted carrier. This embodiment is shown in
In a ninth embodiment,
Depending on the optics and material used, structural units (voxels) of less than 100 nm up to 100 μm can be produced in a material to be solidified, as mentioned above. By adjusting the laser intensity and the threshold process, infinitesimally small volume elements can be created in theory. By combining refractive and diffractive optics, the optical path of the laser pulses through the optics or the light path through the optics can be kept short and imaging errors can be reduced. Conversely, for certain structuring tasks, mapping errors can also be introduced during structuring. The generated voxels can more or less overlap (besides the classical voxel-to-voxel approach, the process can work by moving the focal volume in three spatial directions with the first carrier and by using the first carrier of possible arbitrary tilt/shape under a kind of “continuous pulse mode”). If the light-matter interaction is well understood, the cross-linking result or a comparable result can be very well influenced in other than cross-linking reactions and form in its entirety the one- to three-dimensional structure to be produced. Depending on the size of the voxels produced, it is possible to provide the structure with a porosity that can be scaled at will. This is particularly important for the generation of scaffold structures to stimulate cell growth (“scaffolds”). Such scaffold structures can advantageously have a pore structure in the range from 10 nm to 10 mm, preferably from 1 μm to 5 mm, wherein a porosity on nanometer scale (0.5 to 10 nm) can be adjusted by the light-matter interaction for differently crosslinking materials, such as mixtures of acrylates with (meth)acrylates, epoxides with (meth)acrylates, styrylene with (meth)acrylates and/or epoxides. Porosity can also be influenced by the addition of solvents or (functionalised) nanoparticles or microparticles. Likewise, all embodiments can be mixed with materials containing norbon groups in any proportions, using three types of mixtures: (1) those which are physically mixed; (2) those which are prepared at the molecular level by chemical synthesis with different groups which may be bound, for example, covalently and/or by hydrogen bonds and/or by van der Waals bonds; (3) those which are prepared by physical mixing of materials of (1) and (2). In the process, suitably modified nanoparticles or mixtures of nanoparticles and microparticles can also be introduced, as described in WO 2012/097836 A1.
Structuring exposure of an already (partially or even completely) solidified material with TPA/MPA or (partially or completely) solidification of a structured material exposed with TPA/MPA can in turn be used to create areas with different chemical and/or physical properties, e.g. different secondary or tertiary structure, in one and the same body from one and the same material, whereby these different physical properties, can be e.g. a varying refractive index or varying mechanical properties, can be. It is irrelevant whether the chemical functionalities are chemically bound, for example covalently, or whether the mixture is physically produced.
When laser radiation is introduced through a (possibly) second, translucent substrate, it is particularly advantageous that there is no contact between the optics and the material to be solidified. This enables rapid movement and positioning of the optics. No turbulence is generated in the material and there is less resistance compared with positioning a submerged optic. Furthermore, the optics need not be sealed against the material to be solidified.
If metals are to be structured or if the development of vapours or gases is to be feared in other processes which can be used in accordance with the invention, a structure is preferably used which protects the optics from harmful repositioning from the process by, for example, placing a glass in front of the objective, housing the entire optics and/or also introducing a gas stream of a carrier gas, such as dry nitrogen or dry argon or dry compressed air or mixtures of different gases, into the processing volume in order to remove substances arising from the process in the reaction area by, for example, suction. Since there is no contact between the optics and the material to be solidified, aggressive materials that would damage the optics can also be processed.
In the case of a focusing optics that can be immersed in the material, this itself forms a defined optical interface for the laser beam entering the material to be solidified. In contrast to the aforementioned version, the solidification can take place at any point in the material to be solidified, without the need for an additional positionable carrier unit, since the optics can be positioned within the material in the desired manner, can be immersed almost at any depth and the location of the solidification is not limited by the working distance of the optics.
It is clear from the above explanations that the device according to the invention can be used as described in its various forms and claimed below in all laser-assisted processes in which a material adhering to a substrate or a substrate associated or free body or its surface is to be processed, the laser-assisted process being, in particular, one which can carry out TPA/MPA and/or in which a pulsed laser treatment takes place. Some such procedures (“more specific procedures”) will be explained in more detail below with reference to the figures. The device according to the invention can be used in any of the mentioned designs, unless specific arrangements of the device are explicitly mentioned.
Among other things, these methods include those for modifying a surface of a substrate (13) comprising a liquid or solid material (12) to be processed or for processing a drop or a liquid or pasty layer (12) on or on a substrate (14), the substrate resting on or attached to the sample receptacle of a device according to the invention. In this embodiment of the process, the substrate may be an object which can be used in optics, preferably a lens or a concave mirror, or a body or vessel or hollow body provided with predetermined structures, or an optical, electrical or optoelectronic component or component. For example, a drop of material (12) to be processed can adhere to a substrate (15) and be exposed in a structured manner by means of the focusing optics, wherein when the drop is below the substrate, the exposure is either through the substrate, the substrate being transparent for the radiation of the laser source, or wherein the device has the configuration of claim 13, wherein the focusing optics can be in direct contact with the material to be processed.
Further methods are those for processing a negative resist, a positive resist, an e-beam resist (e.g. of PMMA) (12) and the like, which is arranged between two substrates, wherein one of these substrates rests on or is attached to the sample holder of a device according to the invention and the other, through which focusing is performed, is transparent or opaque.
Further methods are directed towards the production of a body within a bath container with liquid or pasty, solidifiable material, wherein the bath container is arranged (rests) on the sample holder of a device according to the invention, in which the focusing optics (6) are located above the sample holder in such a way that in the course of the operation of the device it is located above the substrate (7) or body (7) held by the sample holder, or wherein the body is solidified from a carrier located within the material, said carrier being attached to the sample holder of a device arranged rotatably about an axis arranged in a plane, said axis being laterally coupled to a component of the positioning system and preferably laterally displaceable in a direction forming a right angle with said axis, said carrier being preferably immersed into the solidifiable material during the process.
Further procedures are based on the processing of a body (a three-dimensional body, but also e.g. of a foil) or a liquid or pasty material, which is located in a bath container with side walls (18) or on or on or under a substrate (15) of any shape, wherein the body or the bath container or the substrate is located on or at the sample holder of a device according to the invention and the focusing optics (6) is located c below the substrate (7) or body (7) held by the sample holder during the process, wherein the sample holder consists of or comprises a mounting (19) enabling a position of the material or body to be processed spaced from the positioning system (9, 10, 11) and having free space to receive the focus optics.
Further methods are aimed at processing a material adhering to a substrate, wherein the material is located in a meniscus between the focusing optics of a device according to the invention located below the sample holder and the substrate, wherein the substrate rests on, is attached to or adheres to the sample holder.
Further methods are directed at the processing of an at least partially thin-walled, translucent body, wherein the body is so directed at or on the sample holder of an inventive device, in which the focusing optics (6) are preferably located above the sample holder, such that surfaces on both sides of the thin wall of the body can be processed simultaneously.
Further processes are aimed at processing a glass or metallic body or a body comprising metallic or glass components using a device according to the invention, wherein the body either rests directly on or is attached to the sample holder or wherein the body is on a substrate attached to or on the sample holder. Of course, this body can also be three-dimensional or foil-shaped.
As can be seen from the above explanations, the material to be processed can be a material to be solidified in a number of designs. A material to be solidified in the sense of the invention is an organic material or an inorganic-organic hybrid material, in particular an organopolysiloxane-containing material which can be solidified photochemically in each case. The material to be solidified can be, in particular, a material filled with nanoparticles or microparticles or an unfilled material. Filled materials may have certain unbound additive materials that can give the material certain desired properties, such as optical, electro-optical, electrical, mechanical and/or magnetic properties.
The material to be solidified is often processed solvent-free and preferably low-solvent (e.g. with only a few, usually 1-3 wt. % solvents, which are difficult or impossible to remove from an inorganic-organic material after its manufacture). If no solvent is used, materials can have a very high viscosity depending on their chemical structure. However, many materials that can be solidified with TPA/MPA are liquid or pasty even without solvents. Working with a solvent-free material has a number of advantages. Thus, the structures produced with it do not usually contain any small molecule, possibly toxic or otherwise questionable compounds.
If the fully solidified moulded body is to be separated from the substrate (negative-resist process), the latter may be functionalised in a known manner (by monomolecular or thicker layers) in such a way that detachment during the development process is possible using a solvent or by “lifting” the structure by means of tweezers or other specially arranged device (e.g. a knife). A sacrificial layer can also be applied to the substrate, on which the solidified moulded body adheres well, but dissolves in the development process (the removal of adhering bath material), so that the structure produced stands out from the substrate.
Alternatively, TPA/MPA can be used to dissolve chemical bonds in a material to be processed and then wash out the areas made more soluble as a result (positive-resist process). This material is preferably solid and then exists in the form of a body.
If glasses or glass-ceramics or other transparent bodies are to be processed with the device in accordance with the invention, redox processes or restructuring processes are triggered by the TPA/MPA in the focus area, for example, which cause a change in the solubility of the glass or the glass-ceramic or other transparent body. The more soluble components can then be washed out or etched, in the case of glass/glass ceramics for example with HF, NH4F or mixtures thereof.
For the processing of metals, metallic or metal-coated shaped bodies or metallic surfaces on a non-metallic substrate are used. In the focus range of the short pulse laser, metal is liquefied, vaporized or sublimated.
In one design form, a device according to the invention has an optical system for spatially dividing the laser beam and generating at least two or more spatially separated laser foci or intensity maxima, which is hereinafter referred to as parallelization. This allows the beam energy of the laser to be spatially directed simultaneously to two or more voxels, so that solidification occurs simultaneously at two or more locations. Relatively large structures and shaped bodies can thus be produced in a short time. If n voxels are produced simultaneously, the production time of the structures to be produced can be accelerated by a factor of n, depending on the element to be produced. This factor n corresponds at least to the number of intensity maxima or laser foci generated by beam splitting that cause multiphoton polymerization.
By means of parallelization, the invention enables not only a parallel generation of voxels of a single functional element, but also a parallel generation of two or more functional elements. (By “functional element” we mean any functional structure, i.e. an element that has any kind of (optical or other) function. A very simple example is a microlens.) A single structure can be created simultaneously using multiple focal points or multiple structures can be created simultaneously using one or more focal points. One or more optics can be used to create n foci. It is possible to produce several structures on the same substrate or to select a separate substrate for each structure.
Parallelisation can also be achieved by beam shaping or splitting a laser beam into several partial beams, which are then each focused and simultaneously solidify voxels at several points in the material. For this purpose, an amplitude mask can be used, which is brought into the beam path and generates a diffraction pattern in the far field of the beam. In addition, a microlens array, an Axikon lens, for example, for generating a ring-shaped focal plane or an electrically controllable spatial light modulator can be used as a dynamically variable phase mask, which effects a targeted distribution of the light intensity into several focal points and thus a partial parallelisation of the structuring process. In addition, the focal points can be moved in space by targeted dynamic modulation of the phase, which eliminates the need for mechanical displacement units.
In another version, the parallel production of the structures is generated by DLP (Digital Light Processing), a state-of-the-art projection technology. In this technique, images are generated by modulating a digital image onto a beam of light. Thus, it is also possible to simultaneously produce either the same structures in parallel or different structures by a variable control of the micro mirrors very quickly, precisely and above all simultaneously.
With the device according to the invention, the laser beam can be divided or spatially shaped in different ways. It can be achieved by using passive elements such as DOE's (Diffractive Optical Elements) in the form of phases or amplitude masks, or by using microlens arrays or active, preferably dynamically adaptable DOE's, spatial light modulators (SLM) or digital light processing (DLO, Digital Light Processing) via microelectromechanical (MEMS) or microoptical electromechanical (MOEMS) elements and combinations of these elements. Thus arbitrary intensity distributions can be generated, e.g. several focal points or arbitrarily shaped focal points or focal volumes, which allow the writing of a structure with several focal points or focal volumes. Especially advantageous are DOE's for phase modulation, because, compared to DOE's with amplitude masks, these have no or only low power losses. The use of active (transmissive or reflective) spatial light modulators is also possible. A one-dimensional grid with a grid distance of preferably less than 10 μm, preferably down to 1 μm or very perferred down to 100 nm, or a two-dimensional array with a pixel distance of less than 10 μm, preferably of 2 μm or less, can advantageously be used as a mask. The division of the laser beam into dynamically adjustable focal points or focal volumes allows the material properties to be adapted to the structure to be fabricated in a controlled manner. For example, refractive index profiles can be set for optical or photonic applications, variable mechanical properties, which is particularly advantageous in the manufacture of scaffold structures in tissue engineering or in special drug delivery structures, variable dielectric, piezoelectric or magnetic properties, whose property profiles permit novel designs and constructions in an advantageous way, as these can be individually adapted to the respective problem.
Multiple focusing optics can also be used. These can then be moved relative to the carrier material (substrate) so that several structures (with identical or different shapes) can be written simultaneously, each with a focal point or focal volume. The use of several focusing optics requires the laser power to be divided by conventional beam splitters into several beams, each of which is guided to one focusing optics. Finally, a combination of the above beam forming options is possible by first generating the desired intensity distribution of the radiation with a modulator and then focusing it through several optics. Likewise, one modulator or one mask per focusing optics can be used. This embodiment makes it possible to write several structures with several focal points or focal firing volumes at the same time. In an alternative, several focusing optics are used to process a single body or to create a single structure from a liquid or solid material. Such a embodiment with two laterally arranged focusing optics is shown in
The position of the focal point (or focal (focus) volume) relative to the material to be solidified can also be freely selected. This can be used to address different starting points for material modification. When using an active, dynamic spatial light modulator, however, the relative position of the focal points can also be dynamically varied. If a certain point in the material is to be processed in a focus area, its position can be corrected e.g. by software if the substrate surface (carrier surface) is known, while if the surface texture is unknown, the data of an optical detection system can be used, for example, in the form of a 3D scanner. The following is noted in this context:
Important in the (multi-photon) structuring (TPA/MPA) of liquid and/or pasty materials as well as of solid materials is the modification of these materials not only in the volume of the material, but especially also directly on the surface of the substrate. This usually requires an “anchor point” on the surface so that the following structure is in contact with an already solidified area or substrate. If this is not the case, areas in the liquid resin that have already been solidified can drift away from their target position, which impairs the structure quality. This can lead to a defective structure. If the anchor point was not found correctly on the substrate, it can happen, for example, in the case of additive structure generation, that the structure was generated correctly, but it cannot be found on the surface to be processed because it no longer adheres to the substrate when the structure is developed out and is placed in the developer solution. Finding the “anchor points” plays a role not only in the case of additive structure generation, but it is often important for all other applications possible according to the invention that the “anchor point” can be reliably detected as a receptor point for the structuring task for arbitrarily shaped surfaces. Preferred forms of implementation of the invention therefore concern the finding of such an anchor point (or, if applicable, several such anchor points).
In the device of this invention, either conventional dielectric mirrors or metal mirrors are used to guide the light beam from the laser into the focusing device.
The use of metal mirrors (e.g. glass coated with gold, silver, aluminium or chromium) makes it possible to structure very broadband, i.e. over a very large spectral range (wavelength range) of approx. 450 nm to 12 μm regardless of the angle of incidence, even with very short pulses (in the range of less than 100 femtoseconds). This is not possible with dielectric mirrors because the electric field of the pulses attacks the electronic bonds of the dielectric layers. To generate very short pulses, high-power short pulse lasers are used instead of the usual ultrashort pulse lasers, which can be used for structuring photochemically reactive materials (polymers, hybrid polymers, glasses) or moderately for metal surfaces: >4 W to some 10 W; pulse energies: from some nJ, e.g. 2 nJ to 120 J, pulse durations <120 fs). This is an important extension of the working conditions with regard to the light sources, as considerably larger process windows can be realized, whereby a large number of materials can be structured. In addition, the interaction time per irradiated pulse is considerably shorter, which can be of great relevance especially for sensitive materials. The structuring of metals, such as metallized surfaces or even shaped bodies or metallic layer systems, in particular magnetic materials, can thus be carried out precisely, efficiently and reliably. A further extension concerns the laser wavelengths that can be used for the process. In addition to the classical laser wavelengths used so far, pulsed lasers with wavelengths below those used so far, i.e. less than 520 nm, can also be used according to the invention. This is particularly advantageous as the efficiency of the process increases with shorter wavelengths and the process window can therefore be significantly increased. This in turn has an influence on the large number of materials that can then be structured using the process. In addition, the achievable structure size and the resolution of structures with smaller wavelengths should become significantly smaller.
In addition to high-power short pulse lasers, a large number of pulsed laser light sources can be used as beam sources, including solid-state lasers, diode-pumped solid-state lasers, semiconductor lasers, fiber lasers, etc. of any wavelength. With particular advantage, a Ytterbium laser system is used in one version of the invention. Its wavelength is in the range of green light when the frequency is doubled. The advantage of Ytterbium lasers over Ti sapphire laser systems, which have a wavelength of approx. 800 nm, is the wavelength of 1030 nm. This is 515 nm with frequency doubling in the green range, which can lead to an improved resolution.
The pulse durations required to efficiently trigger non-linear absorption are less than one picosecond. Ultra-short pulsed lasers in the femtosecond range allow multi-photon processes, which generally enable the triggering of light-induced processes. This includes the very localized initiation of cross-linking processes, ablation, redox reactions, phase transitions, restructuring by, for example, recrystallization, etc. In the following, the improvement of light-matter interactions and the more efficient stimulation of polymerization is described. Additional photoinitiators can be used for this purpose. The repetition rate is preferably adjustable between 1 kHz and 80 MHz, preferably between 10 kHZ and 80 MHz. The repetition rate is either determined by means of an acousto-optical modulator, or can be set externally by means of a voltage source, or is achieved in the laser itself (e.g. by Q-switches, by means of an intracavity Mach-Zehnder interferometer (MZI), etc.). In principle, an electro-optical modulator can also be implemented in the laser. In coordination with the given material system, wavelengths in the UV range, in the visible range and in the infrared range can be used. In particular, the lasers can have powers between 100 mW and 5 W, preferably between 150 mW and 2 W, and/or a pulse duration of less than 1 picosecond and/or a repetition rate between 1 and 80 MHz.
According to another proposal, the system can be equipped with a scanner, in particular a 2D scanner, combined with a movement in the third spatial direction in Z, which then describes a 3D scanner.
The synchronized movement of X, Y and Z directions with such a scanner system (e.g. a galvo scanner, i.e. two mirrors rotatable in one plane each to move the laser beam) with a small Field of View (FoV) is surprisingly suitable for producing structures on arbitrarily large surfaces without stitching, i.e. without joining structuring fields that necessarily result from the restricted FoV. For example, errors due to joining structures together on large surfaces in the continuous structure are avoided. The further away the light falls from the centre of the galvo mirror, the greater are the deviations or errors in the structural products. This problem is usually solved by using large galvo mirrors, which usually make the equipment very large and heavy (weighing more than 10 kg). This is avoided according to the invention. The scanner can thus also be very small to write areas of any size, so that the footprint of the system, i.e. the total size (area and height) of the system, remains small and the structure is essentially determined only by the size of the positioning device and the laser system with the optics required for the structuring process. At the same time, the arrangement is selected so that the three positioning axes can be moved in X, Y and Z (or only the scanner is used in combination with the Z positioning axis in a synchronised movement, then with the FoV, which is possible with the optics used, whereby larger surfaces can be stitched if needed, or synchronised movement of the scanner and the X, Y and Z positioning unit is carried out in all spatial directions). In the process this has the advantage that, in the course of the structuring process, acceleration and deceleration distances can be dispensed with, since the scanner system, in contrast to mechanical or piezoelectric motion components such as positioning tables and the like, has a negligible inertia or no creep. Thus, the structuring process is already faster per se. The speed is also increased by the scanner itself, because the laser beam can be moved considerably faster in X and Y direction than the sample, because the scanner mirrors have a negligible inertia. If such a scanner system is present, it is therefore possible in some cases (if the object lies within the FoV) to limit the movement of the sample to a minimum and to completely dispense with such a movement. By combining the scanner system with an X-Y stage or the first carrier comprising three rotatory and three translatory degrees of freedom, it is possible to work without stitching in the so-called Infinite FoV mode, where the scanner performs the fine movements and the stage or device performs the coarse movements. Thus, both advantages of the individual systems are combined: the speed and flexibility of the scanner with the large-area structuring option of the positioning stages. In particular, structures produced with the device without stitching can be used as master structures for further impression techniques. Both a single use and a multiple use of the same master are intended. Structuring can also be carried out in “Mixed Mode” synchronized with the XY movement; the entire field of view of the scanner, which is variable by the optics used, is used to write the structure, whereby the positioning stages then carry out the XY movement to the next structuring point.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16185823.8 | Aug 2016 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/070957 | 8/18/2017 | WO | 00 |
