EP4320448A1

EP4320448A1 - Method for processing a measuring probe for detecting surface properties or for modifying surface structures in the sub-micrometer range, and measuring probe

Info

Publication number: EP4320448A1
Application number: EP22744225.8A
Authority: EP
Inventors: Christopher Seiji KLEY; Martin Munz; Beatriz ROLDÁN CUENYA
Original assignee: Max Planck Gesellschaft zur Foerderung der Wissenschaften eV; Helmholtz Zentrum Berlin fuer Materialien und Energie GmbH
Current assignee: Max Planck Gesellschaft zur Foerderung der Wissenschaften eV; Helmholtz Zentrum Berlin fuer Materialien und Energie GmbH
Priority date: 2021-07-21
Filing date: 2022-07-20
Publication date: 2024-02-14
Also published as: CN117813518A; WO2023001920A1; EP4123314A1

Abstract

The invention relates to a method for processing a measuring probe which is provided to detect surface properties or modify surface structures in the sub-micrometer range. The method according to the invention comprises at least the following steps: Initially providing: a precursor which contains molecules that are polymerizable by light beams or electron beams; and a measuring probe at least comprising a holder with a tip with an upper end opposite the holder; and a light source or electron source for emitting light beams or electron beams at a wavelength and intensity satisfying a minimally required energy input for a polymerization of the precursor; and means for variably positioning the light source or electron source; and a control file and an electronic data processing device, with the control file describing at least a portion of the surface of the measuring probe and serving to control a change in position of the light source or electron source. In the subsequent step, the measuring probe is covered by the precursor and the measuring probe is arranged in the beam path of the light beams or electron beams, whereupon the precursor is exposed to the light beam or electron beam at a plurality of contacting positions, as specified in the control file, with the tip of the measuring probe being left out. Subsequently, the non-exposed regions of the precursor are removed by means of a water or solvent bath or a controlled air or gas flow, and optionally finally developing the regions polymerized by exposure. Furthermore, the invention comprises measuring probes that are manufactured by the method according to the invention.

Description

designation

Process for processing a measuring probe for detecting surface properties or for modifying surface structures in the sub-micrometer range and measuring probe.

technical field

The invention relates to a method for processing a measuring probe for detecting surface properties or modifying surface structures, in particular with a resolution in the sub-micrometer range, as is the case, for example, in scanning probe microscopy, and a measuring probe according to the method according to the invention, which is used, for example, for characterizing electrical , Chemical, photo-electrochemical, and catalytic properties of the surfaces of condensed matter or their local modification, especially on the surfaces of solids.

State of the art

Measuring probes of the generic type according to claim 1 are used to detect the properties of surfaces, in particular in the sub-micron range, for example in scanning probe microscopy (scanning probe microscopy, SPM), which includes atomic force microscopy (AFM), scanning tunneling microscopy (engl tunneling microscopy, STM) or also scanning electrochemical microscopy (SECM). They consist for the most part of a cantilever that can be hung on one side with a tip arranged on it, which sits near the free end (ie opposite a suspension) of the cantilever. The so-called tip is made of a predominantly conical or pyramidal body formed with a height above a base coinciding with a surface of the cantilever and having an upper end opposite mounting on the cantilever. The cantilever and tip can be manufactured monolithically, ie in one piece, or they can be made up of several components, usually two, namely precisely the cantilever and the tip. The entirety of cantilever and tip is also referred to as a cantilever, or more specifically, AFM cantilever (German: AFM cantilever). However, the measuring probes covered by the invention can also be those which have a tip which is not arranged on a cantilever but on another carrier or the tip is worked out of the carrier itself.

The properties of measuring probes as well as their modifications for special applications are crucial for the high-resolution, highly sensitive and quantitative detection of surface properties such as Essay 1 by IW Rangelow (Scanning proximity probes for nanoscience and nanofabrication, Microelectronic Engineering, Vol.83, 2006, 1449-1455 ) can be found. The vast majority of characterizations of the electrical properties of condensed matter (solids and liquids) by SPM are performed in air or in vacuum, as described in Paper 2 by RA Oliver (Advances in AFM for the electrical characterization of semiconductors, Rep. Prog. Phys ., Vol. 71, 2008, 076501 (37pp)) for the AFM method. Characterizations of the electrical, electrochemical and catalytic properties of solid surfaces in liquids as well as the photo-electric, photo-electrochemical and photo-catalytic properties using AFM and STM are of particular interest for applications in biology, medicine or chemistry. In Paper 3 by PLTM Frederix et al. (Assessment of insulated conductive cantilevers for biology and electrochemistry, Nanotechnology, Vol. 16 (2005) 997-1005) examples of this are presented. The latter areas of application are special Requirements for the design and manufacture of suitable measuring probes.

In addition to the characterization of solid-liquid interfaces, the measuring probes, in particular cantilevers, are also used for the manipulation of surfaces, e.g. for micro/nano-lithography. With the tips of the cantilever, for example, individual atoms on surfaces are moved or removed in order to create a designated surface structure.

This can be done purely mechanically by scratching or indenting, or by applying an electrical voltage if this leads to electrochemical interactions in the tip-sample contact. However, the cantilevers can also have special additional design elements, such as microfluidic channels, for carrying out lithography processes, as is described in article 4 by A. Meister et al. (FluidFM: Combining atomic force microscopy and nanofluidics in a universal liquid delivery system for single cell applications and beyond, Nano Leiters, Vol. 9, No. 6, 2009, 2501-2507).

The application of AFM and STM to characterize electrical, chemical, and/or (photo-)electrochemical as well as (photo-)catalytic properties of solid surfaces, and this also in liquids, is of particular interest in catalysis, battery and photovoltaic research and for the development of surfaces for electrochemical sensors. For this application, the measuring probes used must be electrically conductive at least at the tip and, in order to tap a voltage or a current to be detected with the tip, be equipped with appropriate means for voltage tapping / for current conduction. In the simplest case, the entire cantilever, ie including the tip and cantilever, is designed to be conductive through the use of appropriate materials. In order to minimize or even eliminate the occurrence of leakage currents and thus the spatial resolution of the To improve the conductive tips but also to increase the measurement sensitivity and accuracy, these are electrically insulated in the area of the tip up to the last, upper end. A number of methods have been proposed in the prior art for the production of such measuring probes with electrical insulation.

In Paper 5 by C. Kranz et al. (Integrating an ultramicroelectrode in an AFM cantilever: Combined technology for enhanced Information, Analytical Chemistry, Vol. 73, No. 11, 2001, 2491-2500) a method is presented in which a measuring probe in the form of a cantilever (cantilever and tip) made of silicon nitride is first coated with chromium by RF sputter deposition and then with gold. This conductive coating is then subsequently provided with an electrically insulating coating made of silicon nitride, which is applied using plasma-enhanced chemical vapor deposition (PECVD). All three coatings are also applied to the tip of the cantilever. In order to adjust the electrical conductivity at the tip of the cantilever, it is subsequently trimmed in several steps with a focused ion beam (FIB). A detailed description of this production method for cantilevers is also disclosed in EP 1 290431 B1.

In Article 6 by I.V. Pobelov et al. (Electrochemical current-sensing atomic force microscopy in conductive solutions, Nanotechnology, Vol. 24, 2013, 115501 1-10) discloses a similar approach in which a commercially available cantilever is first provided with a Ti/Au/Ti layer sequence (sputter deposition ) and then with a layer of silicon nitride, followed by a final layer of chromium (per PECVD). Here, too, the tip is also coated and then exposed with a focused ion beam and finally with wet etching.

US 2020/124636 A1 describes a cantilever for measurements in liquids that includes two special features. First is the cantilever carrying chip, which is connected to a ribbon cable for an electrical connection, is included in the solution. The ribbon cable is also to be designed as a handle for handling the cantilever. Second, an insulating coating of the cantilever including the tip with the polymer Parylene C using the Gorham process is described. In the Gorham process, a starting dimer is first passed through a pyrolysis chamber, where it breaks down into monomers, which then hit a cooled substrate where polymerization occurs on the surface. The process takes place in a vacuum and always affects the entire object to be coated. As probably not explained in patent specification US 2020/124636 A1, the upper end of the tip of the cantilever is also coated after the process and has to be subsequently removed from the coating with ablating methods (e.g. laser ablation or ion beam cutting) are freed. The Gorham process is described in detail in Review 7 by BJ Kim and E. Meng (Micromachining of Parylene C for bioMEMS, Polymer Advanced Technologies, Vol. 27, 2016, pp. 564-576).

An alternative are measuring probes which, as described in article 8 by K. Yum et al. (Individual Nanotube-Based Needle Nanoprobes for Electrochemical Studies in Picoliter Microenvironments, ACS Nano, Vol. 1(5), 2007, pp. 440-448). Here, a pointed metal wire is fitted with a nanotube at the tip. Both are then coated with gold (sputter deposition) and then coated with an electrically insulating layer of polymers by electropolymerization. Here, too, the tip is finally exposed with focused ion beam cutting.

The production methods known from the prior art for measuring probes for characterizing electrical and/or electrochemical properties of surfaces of solids or liquids or for manipulating surfaces, such as in lithography, have in common a process consisting of several steps Coating process with subsequent exposure of the tip of the measuring probe by invasive procedures. The process of exposing the tip is associated with a high risk of quality loss or even the risk of losing the tip apex of the cantilever.

task

The object of the present invention is to specify a method for processing a measuring probe for detecting surface properties or modifying surface structures in the sub-micron range, as an alternative to the methods known from the prior art, which is also gentler on the tip of the measuring probe and at the same time simplified and differentiated functionalization is made possible. Furthermore, it is the object of the invention to specify a measuring probe that can be manufactured in a simplified manner and functionalized in a differentiated manner.

The object is solved by the features of claims 1 and 11. Advantageous configurations are the subject matter of the dependent claims.

The method according to the invention for processing a measuring probe for detecting surface properties or modifying surface structures in the sub-micrometer range has at least the following steps.

In a first step, the means and precursors needed to carry out the method and also the measuring probe to be processed are provided. The order of provision is not essential for the implementation of the method, i.e. it is arbitrary.

Specifically, at least the following is provided. A measurement probe is provided which comprises at least a tip and a support, the tip having an upper end opposite the support. The measuring probe is suitable for detecting surface properties or modifying surface structures in the sub-micron range. The configuration required for this is sufficiently known to a person skilled in the art and can be found, for example, in Articles 1-10 and 12 mentioned in this document.

In one embodiment of the method according to the invention, the measuring probe provided is a so-called cantilever, i.e. it consists of a tip and a cantilever as a carrier, which can be manufactured monolithically or composed of several parts.

The cantilever can be any cantilever for use in scanning probe microscopy or for lithography systems. The length of the cantilevers is usually on the order of magnitude between 10 pm and 900 pm, in the longest extension along the cantilever. Cantilevers that are suitable for use in the method according to the invention can be purchased commercially or can be manufactured using suitable manufacturing methods of MEMS technology and microfabrication technology, such as photo or electron beam lithography and anisotropic chemical etching of silicon wafers.

According to another embodiment, the cantilever provided is designed to detect current or voltages on surfaces or in liquids and thus to record electrical, chemical, or (photo)electrochemical and (photo)catalytic properties on surfaces. In this embodiment, at least the tip is formed, and at least partially and at least at the upper end thereof, from a conductive material. The current present at the tip or a voltage present must also be able to be tapped with the cantilever, i.e. means for current conduction/voltage tapping must be provided, such as conductor tracks or cables. In the simplest case, the entire cantilever, tip and cantilever, is made of conductive material.

The material from which the electrically conductive component of the cantilever of the aforementioned embodiment is made has a maximum specific resistance of the order of 10 ² ohm-cm. Materials that meet this property and are used advantageously for the production of cantilevers are those from the group doped silicon, aluminum, gold, copper, platinum, silver or doped diamond, as corresponds to one embodiment. Alternatively, a cantilever made of non- or slightly conductive material can be provided with an electrically conductive coating, such as doped diamond, metals (such as aluminum, gold, iridium, platinum, silver, copper or tungsten), and their alloys or metal compounds such as Titanium nitride (TiN) or tungsten carbide (WC / W ₂ C).

In a further embodiment of the method according to the invention, the measuring probe provided is formed from a tip and a carrier, the tip being formed from a wire and the carrier from a micrometer-scale platform comprising the wire. The platform can be ring-shaped or disc-shaped, so that the longitudinal axis of the wire is perpendicular to the plane of the platform. The platform is made of an electrically insulating material and is (photo-) electrochemically inert. In the area between the platform and the end of the wire opposite the pointed end, the electrical insulation can be made by a classical method, such as partial immersion in a solution containing suitable polymer molecules. In order to provide a micrometer-scale platform, as an alternative to a disc placed on the wire, a kind of base could also be produced by controlled milling into the wire surface, for example by ion beam (focused ion beam (FIB) milling) or chemical etching. Furthermore, a precursor is provided which, as a precursor, contains at least molecules that can be polymerized by light or electron beams as the starting product.

This precursor is photo-polymerizable if it is polymerizable by light rays. Such a precursor undergoes a physicochemical transformation when exposed to electromagnetic radiation, which means an increase in the degree of crosslinking or the degree of polymerization. In addition to the polymerizable molecules, such a precursor mixture also contains photoinitiators and fillers. To activate the physicochemical processes, a photon energy or wavelength and intensity, which are determined by the polymerizing molecules or the photoinitiators, is a prerequisite, in that it is above a so-called exposure threshold value of the precursor mixture. The underlying physicochemical mechanisms and material requirements as well as the required photoinitiators, fillers, etc. are complex and diverse and e.g -548) explained and described in detail. In the following, when precursor mixtures are mentioned, it is not explicitly stated in each case which additives, in particular photoinitiators, are required for the polymerization and which these could be. In addition to the main matrix and the photoinitiators, the precursor formulation can also contain reactive diluents and crosslinking additives, such as in article 10 by X. Zhang et al. (Acrylate-based photosensitive resin for stereolithographic three-dimensional printing, J. Appl. Polym. Sei. 2019, 47487). Those skilled in the art are referred to a prior art consultation.

The precursor can also be given by molecules that polymerize through the energy input of an electron beam. The polymerisation is carried out here by the action of initiators, which are caused by the ionizing Radiation arise, triggered. The initiators are free radicals and radical ions generated by electron beams, and the formation of ion pairs is also important. Easily decomposing additives can also be added to aid the reaction, similar to the initiators in the case of electromagnetic radiation polymerization. However, this is usually unnecessary due to the ionizing effect of electron beams and the associated generation of free radicals.

The coating of the measuring probe with the precursor, in a next step of the method, is to be carried out by immersion in or covering with liquid formulations of the precursor or a precursor mixture or spraying, dusting, printing (ink printing) or other suitable methods. The coating may only need to be carried out after the measuring probe has been positioned (further step). The measuring probe provided is at least partially coated with the precursor mixture.

The selection of suitable precursors for a specific application depends on what may be special requirements for the measuring probes coated with them. If there is a requirement for measuring persons according to the method, it is advantageous to select precursor mixtures for the method which are electrically insulating after polymerisation. Electrical insulation is required to insulate the tip, except at the top end, to minimize or even eliminate electrical leakage currents and thus improve spatial resolution when characterizing surfaces, but also increase measurement sensitivity and accuracy. All materials which have a specific resistance of 10 ⁸ Ω cm or higher are to be regarded as electrically insulating within the meaning of the invention. Further fundamental criteria for the selection of suitable precursors or precursor mixtures are the shrinkage behavior in the course of the polymerization or crosslinking reaction and the structural stability of the resulting polymer as a function of the environmental conditions, such as temperature and the surrounding medium, and here in particular also over a wide pH range.

Also amenable to the invention is the additional use of precursors for photoinduced mass transport, such as described in Review 11b by Z. Sekkat and S. Kawata (see below).

The measuring probe is coated with the precursor with at least a layer thickness that ensures a layer thickness of a polymer formed by the polymerization of at least 10 nm.

For a next embodiment, the precursor mixture advantageously contains one selected from the group consisting of the following classes of compounds as the photopolymerizable flax:

Acrylates, epoxy resins, fluorocarbons, phenolic resins, amides, esters, imides, styrene, (poly)sulfides, urethanes, vinyls, silicones, xylylenes (including parylenes), UV-curable dimethylsiloxanes and carbamates/methacrylates based compounds. Among the acrylates, mention should be made in particular of multifunctional acrylate monomers, such as "Pentaerythritol tetraacrylate" and "Pentaerythritol triacrylate". A bis-phenol A novolak with a group functionality of 8 can be mentioned as an example of an epoxy resin.

Depending on the intended application of the measuring probes, instead of an electrically insulating polymer as a product of the polymerization for the coating of the measuring probes, a precursor mixture that includes one or more molecular components and possibly also nano- or micro-scale fillers such as nanoparticles, such as it also corresponds to an embodiment, be chosen in which such additives give the product one of the properties electrical conductivity, magnetic susceptibility, high mechanical stability or rigidity, high thermal stability or optical properties such as transparency and reflectivity or (electro)catalytic activity or suitability for electrochemical Sensing, including photo-electrochemical, conferred, as per an embodiment. With the addition of nanoparticles, e.g. made of gold or silver, the polymer can also be produced with metallic nanostructures which, under suitable conditions, enable the formation of surface plasmons, in particular localized surface plasmon polariton (LSPP) or propagating surface plasmon polaritons ( propagating surface plasmon polariton, PSPP). Such a functionalized polymer gives the measuring probe according to the method functionality for vibrational spectroscopy, in particular Raman spectroscopy, in particular surface enhanced Raman spectroscopy (SERS), and plasmon-enhanced catalysis. If the measuring probe is coated with such an excellent precursor mixture, also at selected locations, this enables the formation of conductor tracks and the like, for example, in the polymerisation step of the method. The coating of the measuring probe with a polymer functionalized as described is to be carried out, if necessary, on a conductive polymer that has already been deposited. The coating of the measuring probe with a functionalized polymer may not have to be deposited as a continuous layer on the previously deposited, lower layer made of an electrically conductive polymer. Functional areas that can be displayed in this way, with a size of a few square nanometers to micrometers, are advantageous for sensors, especially in liquids, since a two-dimensional pore structure with a high surface-to-volume ratio and the increased possibility of adsorption and interaction, for example of molecules from the liquid phase. Alternating coating with differently functionalized polymers, such as for insulation, electrical conductivity, pH stability or different polymers, to create a layer sequence is also possible. The polymerisation of the precursor is effected by light or electron beams emitted from a light or electron beam source to be provided.

Light within the meaning of the invention is electromagnetic radiation in a wavelength range from the UV range to the IR range, which corresponds to 100 nm to 10 pm. In particular, lasers are used for photopolymerization, such as titanium-sapphire femtosecond lasers with a wavelength of 800 nm. (Influence of baking conditions on 3D microstructures by direct laserwriting in negative photoresist SU-8 via two-photon polymerization, Journal of Laser Applications, Vol. 29, 2017, 042010) and 11b by Z. Sekkat and S. Kawata (Laser nanofabrication in photoresists and azopolymers, Laser & Photonics Review, Vol. 8(1), 2014, pp. 1-26) detailed and comprehensive information about possible light sources or lasers that can be used is given.

For the photopolymerization of a corresponding precursor, which comprises at least one photopolymerizable resin, a light source is provided which has a photon energy (wavelength) and light intensity (fluence) sufficient for photopolymerization of the photosensitive molecules of the selected precursor or in a precursor Mixture present photoinitiator. Means for directing (aligning to the measuring probe to be processed) and shaping (beam cross-section, intensity, etc.) of light beams from the light source such as lenses, lens systems, collimators, collimation masks, mirrors, choppers, filters, etc. are associated with the provision of the light source.

The light source can be a laser or a light-emitting diode, for example. The light source is advantageously a laser, as also explained above.

In order to polymerize a corresponding precursor by means of an electron beam, an electron source must be provided, such as that used in a Electron microscope is available that allows an acceleration voltage of 200 kV or higher.

In order to carry out the polymerisation of the precursor or a mixture of precursors at more than one location and thus to produce an extended and contiguous area of the polymerised product which is at least two-dimensional, the measuring probe and the light or electron beam have to be translated (moved) with respect to one another and if necessary also to swivel (rotate around a center of gravity in the measuring probe). In the vast majority of cases, this is effected by a movement of the light or electron beam, which takes place with means for variable positioning of the light or electron source, which are to be provided. The variable positioning takes place in the form of a translation and/or pivoting of the light or electron beams or the sources. Advantageously, the variable positioning means consist of motors or actuators capable of performing micro- and nanoscale steps. The smallest step size determines the possible resolution or fineness for details of manufactured two- or three-dimensional shapes. Although the displacement or pivoting of a sample table to be provided for this purpose, on which the measuring probe is to be arranged, is more complex, this is also possible with the same means as those for displacing/pivoting the light or electron beam, provided this does not cause the liquid precursor mixture to flow off caused to ensure processing in two or three dimensions (2D or 3D). It is essential that the position of the light or electron beam can be changed in relation to the measuring probe.

In a second step, the measuring probe to be processed is to be arranged in the beam path of a light or electron beam emitted by the light or electron source. When printing on the tip side of the measuring probe, its tip points in the direction of the incident beam. The arrangement may also be under a specific location in Make reference to a focus of the light or electron beam. The latter is particularly important when using a laser as the light source. The depth at which the polymerisation takes place in a layer of precursor molecules can be influenced by the position of the focus, which can be used for structuring the polymer as a product of the polymerisation.

In a third step, a control file and an electronic data processing system are provided, on which the control file for controlling the translation and pivoting of a beam incident on a measuring probe and, if necessary, a change in position of a focus is provided. For this purpose, at least part of the surface of the measuring probe is recorded in the control file, so that it is available as a digital model with absolute positions in the control file as an electronic file. The control file serves to shift and possibly also pivot the measuring probe in relation to the incident light or electron beam or vice versa, in that it serves as the basis for computer control of means for translation and pivoting. Control files are to be created with the help of optical or electron microscopic images of the real object, in this case the measuring probe. If necessary, a further optical imaging system or, for example, an external electron microscopic imaging system must be made available for this purpose in addition to a laser provided for photopolymerization. In a method that is standardized with regard to the shape of the measuring probe and its positioning, a control file obtained once beforehand is to be reused, so that the third step can also lie before the two previous ones and only the control file itself has to be provided.

In the following step, the precursor applied to the measuring probe, which can also be present in a precursor mixture, is exposed at several touching positions. The touching positions result from the size of the focal spot (focus) of the light or electron beam and the resulting polymerized area in which the Translation or pivoting only takes place by such an amount or the focal spots are positioned in such a way that the polymerized areas touch in an overlapping manner, resulting in a coherent polymerized 2D or 3D area. The precursor is exposed along a specific path by means of the control by the electronic data processing system, ie on the basis of the control file, in order to build up the polymer coating in layers (slicing). In general, each layer is in turn composed of lines (hatching). The trajectory is defined using control software on the electronic data processing system into which the control file was previously read.

The method according to the invention is to be addressed as a site-selective method in which only selected areas of a volume of the precursor that is provided are exposed, depending on the predetermined desired shape of the product.

Another parameter to be specified by the control file is the position of the focus of the light or electron beam in relation to the surface of the measuring probe. By shifting the focus away from the surface, the precursors can be polymerized in such a way that cavities and channels are formed between the polymerized product (polymer) and the surface of the measuring probe or in the polymer itself, as also corresponds to an embodiment which, for example, are to be used as microfluidic channels and reservoirs and which can be produced in particular by embedding at least one structured layer between a bottom layer and a top layer. The surface of the polymerized product (polymer) can also be structured in this way. By structuring with channel-like cavities according to the method according to the invention, in addition to the microfluidics for measuring probes that only provide one channel, several channels and possibly reservoirs can also be represented and these possibly also in correspondence with one another, so that, for example, solutions are mixed on the measuring probe in situ e.g. as part of a lab-on-a-chip implementation of measurements or reactions in a liquid environment. According to the invention, the measuring probe in the form of a cantilever is coated, as corresponds to one embodiment, on at least part of the carrier, which in the case of a cantilever is provided by the cantilever, in particular on its tip-side surface. The entire side of the carrier or cantilever does not have to be coated. However, the entire surface of the carrier or cantilever can be coated in an insulating manner, ie also the side surfaces and the opposite surface. Polymerization always takes place with the upper end of the tip spared. However, the coating also takes place on part of the side/surface area(s) of the tip. The recessed part of the tip is at least 5 nanometers and at most 50% in the vertical extent of the tip (fleas), i.e. at most 5 microns in the case of a tip height of 10 microns. Most advantageously, the recessed area around the top end of the tip is <7 pm ² , assuming that the apex of the tip can be approximately described by the surface of a fluffy sphere with a radius of at most 1 micron.

The exposure of the precursor or the precursor mixture is, in particular, carried out as a two-photon polymerization, as corresponds to one embodiment, in that this is based on the so-called two-photon absorption. Here, two photons are absorbed simultaneously by a molecule or an atom, which in the process changes into an energetically excited state. Higher resolutions can be achieved with two-photon polymerisation, also known as 2PP, especially in depth, i.e. along the direction of irradiation. In Paper 12 by S. Maruo and S. Kawata (Two-photon-absorbed photopolymerization for three-dimensional microfabrication, Proceedings IEEE The Tenth Annual International Workshop on Micro Electro Mechanical Systems. An Investigation of Micro Structures, Sensors,

Actuators, Machines and Robots, 1997, pp. 169-174) is the two-photon Polymerization explained in more detail. Two-photon polymerization is performed using a laser as the light source.

The exposed areas can also be finalized by further development steps, such as thermal treatment. This serves, for example, to increase the degree of crosslinking or to improve the mechanical or other physical properties.

After the exposure step, the non-exposed areas of the precursor or the precursor mixture are removed in a further step. The latter is done in a gentle manner by washing with or immersing in water or a suitable solvent. Depending on the precursor, removal by a stream of air or an inert gas can also be used for this purpose. Furthermore, if necessary, the exposed areas can also be developed, for example by immersing the measuring probe in a suitable developer solution.

In a first embodiment, the method according to the invention provides a measuring probe according to the invention for detecting surface properties or for modifying surface structures in the sub-micrometer range, which comprises at least one carrier and a tip arranged thereon. Carrier and tip can be monolithic or made up of components.

The electrically conductive measuring probe is characterized in that it is at least partially coated with a polymer which is formed as a product from a photopolymerizable precursor polymerizable by light or electron beams, with the exception of an upper part of the tip opposite the carrier. The layer thickness is at least 10 nm. The polymer is advantageously electrically insulating (ie with a specific resistance of 10 ⁸ W·ah or higher), so that the measuring probe can be used to record electrical/ electrochemical/catalytic/electro-catalytic properties of surfaces or liquids. The recessed part of the tip is at least 5 nanometers and at most 50% in the vertical extent of the tip (height), ie at most 5 microns in the case of a tip height of 10 microns. Most advantageously, the recessed area around the top end of the tip is <7 pm ² , assuming that the apex of the tip can be approximately described by the surface of a hemisphere with a radius of at most 1 micrometer.

The polymer is in particular the product of the photopolymerization of a resin from the group of photopolymerizable resins: acrylates, epoxy resins, fluorocarbons, phenolic resins, amides, esters, imides, styrene, (poly)sulfides, urethanes, vinyls, silicones, xylylenes (including parylenes) , UV-curable dimethylsiloxanes and carbamates/methacrylates as precursors, as also corresponds to one embodiment.

In a special embodiment, the measuring probe is in the form of a cantilever, which is provided with means for tapping off current or voltage with a conductor track whose width is smaller than the overall width of the cantilever.

In this case, the conductor track can either run completely on the tip side of the cantilever or partially along the opposite side (which can be referred to as the rear side) of the cantilever, which generally serves as a reflection surface for a laser beam of the optical component, e.g. of a detection system used in atomic force microscopy. or one of the edge faces connecting the tip side of the cantilever to its back.

In particular, it may be advantageous to uncoated the back, which serves as a reflective surface in the application of the cantilever to provide a to avoid reduction of the optical reflectivity. In general, the reflecting surface is arranged close to the free end of the cantilever in order to ensure high detection sensitivity for deflections of the tip from its resting position during use.

In a further special embodiment of the measuring probe according to the invention, only the tip-side surface of a cantilever is coated as a measuring probe, leaving out the upper end of the tip, while the edge surfaces of the cantilever remain uncoated and are thus available, for example, for the equipment with conductor tracks.

A possible embodiment also includes a special embodiment of a measuring probe according to the invention, in which a cantilever includes a chip carrying it, which is partially coated with the polymerized by light or electron beams, the electrically insulating coating not being present on the surface that is for makes electrical contact with a cable, terminal or trace, connects to an electrical circuit or voltage source.

In a next possible embodiment of the measuring probe according to the invention, it is provided with conductor tracks which are formed from an electrically conductive polymer and the conductive polymer is formed from a precursor polymerized by light or electron beams. The polymer is made electrically conductive by additives that result from a precursor mixture. A measuring probe designed in this way is in turn also to be provided in the method for processing according to the invention.

The method according to the invention can also be used to form a measuring probe whose tip-side surface is initially completely coated, including the tip, with an electrically conductive polymer, which is then in turn coated with a polymer according to the method according to the invention is coated with the exception of the tip. This coating is made in particular with polymers in which molecular or particle-like additives in the precursor give the product one of the properties electrical conductivity, magnetic susceptibility, high mechanical stability or rigidity, high thermal stability or optical properties such as transparency and reflectivity or electro-catalytic and catalytic Activity or suitability for electrochemical and photo-electrochemical sensing is conferred, as per an embodiment.

In the presence of nanoparticles, e.g. of gold or silver, in the functionalized polymer, which is designed as a non-contiguous layer on the previously deposited lower layer of an electrically conductive polymer, as also corresponds to one embodiment, the measuring probe is suitable for the Used in vibrational spectroscopy, particularly Raman spectroscopy.

In one embodiment, the measuring probe is equipped with channel-like cavities for microfluidics, which are provided with side walls by the polymer, which is formed by photopolymerization from a precursor that can be polymerized by light or electron beams.

The measuring probe according to the invention can be given by a measuring probe in which the tip is formed from a wire and the support from a disk surrounding the wire. The wire is advantageously cylindrical or conical and is provided at an upper end with a sharp tip, which is used to scan a sample surface. The coating with an electrically insulating polymer according to the method of the invention is present in the area between the platform and the top of the tip, excluding the latter. The platform can be designed in the form of a ring or disk, so that the longitudinal axis of the wire is perpendicular to the platform. The platform should be off be made of an electrically insulating material and be electrochemically inert. In the area between the platform and the end of the wire opposite the pointed end, the electrical insulation can be made by a classical method, such as partial immersion in a solution containing suitable polymer molecules. In order to provide a micrometer-scale platform, as an alternative to a disc placed on the wire, a kind of base could also be produced by controlled milling into the wire surface, for example by ion beam (focused ion beam (FIB) milling) or chemical etching.

With the method according to the invention, the number of steps is reduced compared to the prior art and, in particular, it is easier to process a measuring probe for detecting surface properties or for modifying surface structures in the sub-micrometer range and thus for a special use, e.g. the detection of electrical, chemical or (photo-) electrochemical and (photo-) catalytic properties of surfaces. The measuring probes according to the invention are characterized by economical production, flexibility and higher quality with regard to the design of the tip.

In addition to the reduction of work steps and the associated time savings, the method according to the invention leads to a higher quality of the tip apex (upper end of the tip), since compared to the methods in the prior art, the exposure required there, which is not residue-free or even leads to an unwanted modification of the apex of the tip and, if applicable, its conductive coating, is replaced by a non-invasive, gentle procedure in which the apex (top) area of the tip is spared from the coating.

In addition, the method according to the invention offers the possibility of using molecular or particle-like coatings produced by polymerization Functionalizing additives and additionally structuring them, for example by creating cavities, and thus providing a wide range of cost-effective measuring probes with high-quality tips.

An increase in throughput when manufacturing measuring probes can also be achieved with the method according to the invention, in which at least two or more measuring probes are processed simultaneously.

exemplary embodiments

The invention will be explained in more detail in 5 exemplary embodiments and with reference to five figures.

The figures show:

FIG. 1: Schematic representation of a measuring probe in the form of a cantilever processed according to the method according to the invention, in an oblique top view.

FIG. 2: Schematic representation of a measuring probe processed according to the method according to the invention in the form of a cantilever with a conductor track, in an oblique top view.

Figure 3: Schematic representation according to the invention

Process processed measuring probe in the form of a cantilever, with conductor track and additional conductive surfaces in a) oblique view of the side of the cantilever opposite the tip and b) oblique view of the tip side of the cantilever.

FIG. 4: Schematic representation, including two cross sections (CS#1, CS#2), of a measuring probe in the form of a cantilever processed according to the method according to the invention, with two microfluidic channels along the tip-side surface of the cantilever and two side surfaces of the tip jacket up to the upper end edge of the coating.

FIG. 5: Schematic representation of a measuring probe processed according to the method according to the invention, with a tip and a carrier.

Fig. 1 schematically shows a first exemplary embodiment of a measuring probe processed using the method according to the invention, here in the form of a cantilever 1. The cantilever consists of a cantilever 2 and a tip 3, which in the exemplary embodiment are made of doped silicon, which has a specific resistance in of the order of 10 ² Ohrrvcm. The cantilever 2 is coated with a polymer 5 with a layer thickness of 10 nm on the side on which the tip 3 is also arranged. The coating also covers the lower part of the tip 3, but not the upper end 4, so that the upper end of the tip 4 (the apex) is exposed. The polymer is electrically non-conductive and has a specific resistance of about 10 ⁸ W·ah or higher. In the exemplary embodiment, the polymer is to be polymerized by two-photon polymerization according to the method according to the invention, starting from a precursor mixture based on the negative photoresist SU-8 (Microchem Co., Westborough, MA, USA) with admixtures of a suitable solvent to adjust the viscosity and the photoinitiator triarylsulfonium salt dissolved in propylene carbonate.

A first exemplary embodiment of the method according to the invention is set out as follows.

In the first exemplary embodiment, the coating according to the method according to the invention is carried out on a cantilever which is electrically conductive due to a Pt coating. The length, width and thickness of the cantilever 2 are approximately 225, 27.5 and 3 micrometers. The height of the pyramidal tip is 15 microns and the Radius of curvature of tip apex (top of tip) is specified as 30 nanometers.

In the exemplary embodiment, the method according to the invention is implemented as a two-photon polymerization (2PP). The cantilever 1 is coated using a so-called 3D printer. The 3D printer provides a light source for emitting light beams in the form of a laser and the means for variable positioning of the light beam or laser beam. The measuring probe is placed in a focus of the laser beam in the 3D printer. In the exemplary embodiment, the cantilever to be coated is covered with a liquid precursor mixture that polymerizes when illuminated with a suitably pulsed infrared laser beam in the area of the laser focus and thus transitions locally from the liquid to the solid phase by polymerization. Typically, the front end of the laser optics, a lens, is immersed in the liquid precursor mixture such that a meniscus forms between the front lens surface of the laser optics and the liquid precursor mixture.

A 3D model of the structure to be printed as a control file is created using an electronic data processing system and then displayed layer by layer using software (slicing). Each layer is in turn built up line by line (hatching) in order to determine the trajectory of the laser focus, which systematically builds up the structure of the polymer to be formed from bottom to top by polymerization along this path. Accordingly, the so-called writing process starts on the tip-side surface of the cantilever and then moves layer by layer along the height axis of tip 3. Before the writing process, the cantilever is fixed on a flat substrate (sample holder table) and the surface position in coordinates with the help of an optical system in the control file read in. In particular in the area of the tip 3, this requires an accuracy in the sub-micron range. The slicing and hatching distances as well as the writing speed are selected in such a way that the required level of detail is achieved, especially in the finest area Components, ie here the tip 3. In the exemplary embodiment, the slicing and hatching distances are 100 nm and the writing speed is 1 mm/s. Optionally, larger components with correspondingly larger slicing and hatching distances and a higher speed can be written in order to limit the total writing time to a realistic level.

2 shows a further exemplary embodiment of a measuring probe according to the invention. The measuring probe consists of a cantilever with a conductor track 6 along its tip-side surface and the surface of the chip 2 carrying the cantilever. The electrically insulating cover layer 5 extends over the entire tip-side cantilever surface and the lateral surface of the AFM tip, with a relatively small area around the tip apex 4 being left free. The apex of the tip is electrically connected to the conductor track 6 .

3 shows a third exemplary embodiment of a measuring probe according to the invention. The measuring probe consists of a cantilever with a conductor path 9 along the reflector-side surface, the front edge surface 7, a tip-side surface in the vicinity of the tip 8, and the entire tip surface. The electrically insulating cover layer 5 extends over the entire cantilever surface and the lateral surface of the tip, leaving a relatively small area around the tip apex 4 free. The electrically insulating cover layer 10 extends over the entire surface of the cantilever on the reflector side. The tip apex is electrically connected via the conductive pads 7 and 8 and via the conductor track 9 which continues from the cantilever via the chip 2 carrying the cantilever.

A fourth exemplary embodiment is shown in FIG. 4. The measuring probe according to the invention consists of a cantilever with two microfluidic channels 21 along the tip-side surface and two side surfaces of the lace coats. The microfluidic channels 21 continue from the cantilever via the chip 2 carrying the cantilever, where they can optionally also further connect microfluidic components, such as reservoirs. The microfluidic channels 21 are embedded in the cover layer 5, which can in particular be electrically insulating and which extends over the entire cantilever surface and the jacket surface of the tip 3, with a relatively small area around the tip apex 4 being left open. Those surfaces in which microfluidic channels 21 are integrated are sealed with a cover layer 20 on the outside.

Another exemplary embodiment is shown in FIG. 5. The measuring probe according to the invention consists of a conical tip 11 at a front end, which is provided with an electrically insulating coating except for the area around the apex 14 of the tip. In the area between a ring-shaped or disk-shaped platform 16, the coating 13 is to be produced using the method according to the invention, in particular to avoid covering the apex. In the area below the disc-shaped platform, the coating 15 is to be produced on the wire surface 12 using a conventional method. The platform itself is also electrically insulating. However, this could also be partially coated with an electrically insulating polymer using the method according to the invention.

Claims

patent claims

1. Method of processing a measuring probe for the detection of

Surface properties or for modifying surface structures in the sub-micron range at least comprising the steps

• Provide

^■ a precursor which contains molecules that can be polymerized by light or electron beams;

^■ a measuring probe comprising at least one tipped support having an upper end opposite the support;

^■ a light or electron source for emitting light or electron beams with a wavelength and intensity that meet a minimum energy input required for polymerization of the precursor;

^■ means for variable positioning of the light or electron source;

^■ a control file and an electronic data processing system, the control file describing at least part of the surface of the measuring probe and serving to control a change in position of the light or electron source;

• Covering the measuring probe with the precursor and arranging the measuring probe in the beam path of the light or electron beams;

• Exposure of the precursor to the light or electron beam at several touching positions specified in the control file, leaving out the tip of the measuring probe and then

• Removal of the unexposed areas of the precursor using water or solvent bath or controlled air or gas flow.

2. The method according to claim 1, characterized in that the measuring probe is provided in the form of a cantilever, having at least one tip and one cantilever.

3. The method according to claim 1, characterized in that the tip of the measuring probe is formed from a wire and the support from a platform comprising the wire.

4. The method according to claim 1, characterized in that the tip of the provided measuring probe is conductive at least at the end that lies opposite the carrier and the measuring probe is equipped to pick up current or voltage present at the tip.

5. The method according to claim 1, characterized in that the precursor is mixed in a mixture with additives, the additives being suitable for a polymer having at least one of the properties of electrical conductivity, magnetic susceptibility, high mechanical stability or rigidity, high thermal stability or optical To impart properties such as transparency and reflectivity or (electro)catalytic activity or suitability for electrochemical sensors.

6. The method according to claim 5, characterized in that the additives of the precursor are in the form of nanoscale fillers.

7. The method according to claim 4, characterized in that the conductive portion of the tip is formed at least in part from a material selected from the group consisting of doped silicon, aluminum, gold, iridium, copper, platinum, silver, copper, tungsten, titanium nitride, tungsten carbide, and doped diamond.

8. The method according to claim 1, characterized in that the precursor as photopolymerizable resin at least one from the group of compound classes acrylates, epoxy resins, fluorocarbons, phenolic resins, amides, esters, imides, styrene, (poly) sulfides, urethanes, vinyls, silicones , xylylenes (incl. parylenes), UV-curable dimethylsiloxanes and carbamates/methacrylates.

9. The method as claimed in claim 1, characterized in that the precursor mixture is exposed to a light or electron beam at a plurality of touching positions specified in the control file and while omitting the tip of the measuring probe, the specified in the control file Positions are partially spaced from a surface of the measuring probe in contiguous areas, so that in particular channel-like cavities for microfluidics are formed.

10. The method according to claim 1, characterized in that the precursor is polymerized with a laser beam as a two-photon polymerization.

11. Measuring probe for detecting surface properties or for modifying surface structures in the sub-micron range, at least comprising a carrier and a tip, characterized in that the measuring probe is at least partially coated, with the exception of part of the tip, with a polymer formed by photopolymerization from a photopolymerizable or electron beam polymerizable precursor.

12. Measuring probe according to claim 10, characterized in that the polymer as a product of the photopolymerization of a resin from the group of photopolymerizable resins acrylates, epoxy resins, fluorocarbons, phenolic resins, amides, esters, imides, styrene, (poly) sulfides, urethanes, vinyls , silicones, xylylenes (including parylenes), UV-curable dimethylsiloxanes and carbamates/methacrylates as precursors.

13. Measuring probe according to claim 10 or 11, characterized in that channel-like cavities for microfluidics are formed on the measuring probe by the polymer, which is formed by photopolymerization from a precursor polymerizable by light or electron beam.

14. Measuring probe according to claim 10, characterized in that the measuring probe is given as a cantilever and the cantilever is provided as a means for tapping current or voltage with a conductor track whose width is smaller than the total width of the cantilever of the cantilever.

15. Measuring probe according to claim 11, characterized in that only the tip-side surface of the cantilever is coated, leaving out the upper end of the tip, with edge surfaces of the cantilever being uncoated.

16. Measuring probe according to claim 10, characterized in that the measuring probe is provided with at least one conductor track which is formed from an electrically conductive polymer and the electrically conductive polymer, which is formed by photopolymerization from a precursor which can be polymerized by light or electron beams and to which electrically conductive additives have been added .

17. Measuring probe according to claim 16, characterized in that the measuring probe is coated at least on the tip-side surface with an electrically conductive polymer, which is formed by photopolymerization from a precursor polymerizable by light or electron beam and to which electrically conductive additives are added, and this conductive layer is in turn coated at least partially and with the omission of part of the tip with a polymer which is formed by photopolymerization from a polymerizable by light or electron beam precursor to which at least one additive is added.

18. Measuring probe according to claim 17, characterized in that

Nanoparticles of gold or silver in the functionalized polymer, which is not designed as a cohesive layer on the previously deposited lower layer of an electrically conductive polymer, imprinted on the measuring probe a suitability for use in vibration spectroscopy, in particular Raman spectroscopy.

19. Measuring probe according to claim 10, characterized in that the tip is formed from a wire and the support from a platform encompassing the wire.