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

Abstract

The invention relates to a method for processing a measuring probe which is intended for detecting surface properties or for modifying surface structures in the sub-micrometer range. The method comprises at least the following steps. First, providing a precursor containing molecules polymerizable by light or electron beams and a measuring probe comprising at least one carrier with a tip having an upper end opposite the carrier and a light or electron source for emitting light or electron beams with a wavelength and intensity, which fulfil an energy input at least required for polymerization of the precursor and means for variable positioning of the light or electron source and a control file and an electronic data processing system, wherein the control file describes at least a part of the surface of the measuring probe and serves to control a change in position of the light or electron source. In the following step, the measuring probe is covered with the precursor and the measuring probe is arranged in the beam path of the light or electron beams, whereupon the precursor is exposed to the light or electron beam at several positions that touch each other and are specified in the control file, leaving out the tip of the measuring probe. The unexposed areas of the precursor are then removed by means of a water or solvent bath or controlled air or gas flow and, if necessary, the areas polymerized by exposure are finally developed. The invention also includes measuring probes which are manufactured using the inventive method.

Claims

1. Method for processing a measuring probe for detecting surface properties or for modifying surface structures in the sub-micrometer range, comprising at least the following steps providing of a precursor containing molecules that can be polymerized by light or electron beam; a measuring probe comprising at least one support with a tip 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 required energy input 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 a 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 positioning the measuring probe in the beam path of the light or electron beam; exposure of the precursor with the light or electron beam at several touching positions specified in the control file, leaving out the tip of the measuring probe and subsequently removal of unexposed areas of the precursor using a water or solvent bath or controlled air or gas flow.

2. Method according to claim 1, characterized in that the measuring probe is provided in the form of a cantilever, comprising at least a tip and a spring beam.

3. Method according to claim 1, characterized in that the tip of the measuring probe is formed from a wire and the carrier from a platform surrounding the wire.

4. Method according to claim 1, characterized in that the tip of the measuring probe provided is conductive at least at the end opposite the carrier and the measuring probe is equipped for tapping current or voltage applied to the tip.

5. Method according to claim 1, characterized in that the precursor is mixed in a mixture with additives, the additives being suitable for imparting to a polymer at least one of the properties of 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 sensor technology.

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

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

8. Method according to claim 1, characterized in that the precursor contains, as photopolymerizable resin, at least one from the group of the 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. Method according to claim 1, characterized in that the exposure of the precursor mixture with a light or electron beam is carried out at several contacting positions specified in the control file, and with the tip of the measuring probe cut out whereas the positions specified in the control file are partially spaced apart from a surface of the measuring probe in contiguous areas, so that in particular channel-like cavities for microfluidics are formed.

10. 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-micrometer range, comprising at least a carrier and a tip, characterized in that the measuring probe is at least partially coated, leaving out a part of the tip, with a polymer formed from a precursor polymerizable by light or electron beam by photopolymerization.

12. Measuring probe according to claim 10, characterized in that the polymer is formed 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 (incl. parylenes), UV-curable dimethylsiloxanes and carbamates/methacrylates as precursor.

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

14. Measuring probe according to claim 10, characterized in that the measuring probe is given as a cantilever and the cantilever is provided with a conductor path as a means for tapping current or voltage, the width of which is smaller than the total width of the spring beam 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 path which is formed from an electrically conductive polymer and wherein the electrically conductive polymer, which is formed from a precursor which can be polymerized by light or electron beam and to which electrically conductive additives are added, is formed by photopolymerization.

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 which can be polymerized 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 leaving out a part of the tip with a polymer which is formed by photopolymerization from a precursor which can be polymerized by light or electron beam and 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 continuous layer on the previously deposited lower layer of an electrically conductive polymer, the measuring probe is suitable for use in vibrational 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 surrounding the wire.

Description

EXAMPLES

[0063] The invention will be explained in more detail in 5 examples and with the aid of five figures.

The Figures Show:

[0064] FIG. 1: Schematic representation of a measuring probe in the form of a cantilever, processed according to the method of the invention, in oblique view.

[0065] FIG. 2: Schematic representation of a measuring probe processed according to the method of the invention in the form of a cantilever with conductor path, in oblique view.

[0066] FIG. 3: Schematic representation of a measuring probe processed according to the method of the invention in the form of a cantilever, with conductor path 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.

[0067] 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 of 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.

[0068] FIG. 5: Schematic representation of a measuring probe with a tip and a carrier processed according to the method of the invention.

[0069] FIG. 1 schematically shows a first example of a measuring probe processed using the inventive method, in this case in the form of a cantilever 1. The cantilever 1 consists of a spring beam 2 and a tip 3, which in the example are made of doped silicon that has a specific resistance in the order of 10.sup.?2 Ohm.Math.cm. The spring beam 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 resistivity of about 10.sup.8 ?.Math.cm or higher. In the embodiment example, the polymer is to be polymerized by two-photon polymerization according to the method of 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 for viscosity adjustment and the photoinitiator triarylsulfonium salt dissolved in propylene carbonate.

[0070] A first example of the inventive method is as follows.

[0071] In the first example, the coating according to the method of the invention is applied to a cantilever 1, which is electrically conductive due to a Pt coating. The length, width and thickness of the spring beam 2 are approximately 225, 27.5 and 3 micrometers. The height of the pyramidal tip is 15 micrometers and the radius of curvature of the tip apex (upper end of the tip) is 30 nanometers according to the specification.

[0072] In the embodiment example, the process according to the invention is implemented as 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 positioned in the 3D printer in a focus of the laser beam. In the embodiment example, the cantilever 1 to be coated is covered with a liquid precursor mixture, which polymerizes when illuminated with a suitably pulsed infrared laser beam in the area of the laser focus and thus changes locally from the liquid to the solid phase by polymerization. Typically, the front end of the optical system of the laser, a lens, is immersed in the liquid precursor mixture (immersion), so that a meniscus is formed between the foremost lens surface of the optical system of the laser and the liquid precursor mixture.

[0073] A 3D model of the structure to be printed is created as a control file 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 along this path from bottom to top through polymerization. Accordingly, the so-called writing process starts on the tip-side surface of the cantilever 1 and then moves layer by layer along the height axis of the tip 3. Before the writing process, the cantilever 1 is attached to a flat substrate (sample holder table) and the surface position is read into the control file in coordinates using an optical system. This requires an accuracy in the sub-micrometer range, especially in the area of the tip 3. 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, particularly in the area of the finest components, i.e. tip 3 in this case. The slicing and hatching distances are 100 nm and the writing speed 1 mm/s in this example. Optionally, larger components can be written with correspondingly larger slicing and hatching distances and a higher speed in order to limit the total write time to a realistic level.

[0074] FIG. 2 shows a further example of a measuring probe according to the invention. The measuring probe consists of a cantilever 1 with a conductor path 6 along its tip-side surface and the surface of the chip 2 that carries 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 out. The tip apex is electrically connected to the conductor path 6.

[0075] FIG. 3 shows a third example of a measuring probe according to the invention. The measuring probe consists of a cantilever 1 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 outer surface of the tip, with a relatively small area around the tip apex 4 being left out. The electrically insulating cover layer 10 extends over the entire reflector-side surface of the cantilever. The tip apex is electrically connected via the conductive surfaces 7 and 8 as well as via the conductor path 9, which continues from the cantilever via the chip 2, which carries the cantilever.

[0076] A fourth embodiment is shown in FIG. 4. The measuring probe according to the invention consists of a cantilever 1 with two microfluidic channels 21 along the tip-side surface and two side surfaces of the tip jacket. The microfluidic channels 21 extend from the cantilever further over the chip 2, which carries the cantilever, where they can optionally also connect further microfluidic components, such as reservoirs. The microfluidic channels 21 are embedded in the covering layer 5, which can be electrically insulating in particular and which extends over the entire surface of the cantilever and the lateral surface of the tip 3, whereby a relatively small area around the tip apex 4 is left out. Those surfaces in which microfluidic channels 21 are integrated are sealed on the outside with a cover layer 20.

[0077] A further embodiment example is shown in FIG. 5. The measuring probe according to the invention comprises a conical tip 11 at one 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 an annular or disk-shaped platform 16, the coating 13 is to be produced using the inventive method, in particular to avoid covering the apex. In the area below the disk-shaped platform, the coating 15 is to be produced on the wire surface 12 using a conventional process. The platform itself is also electrically insulating. However, this could also be partially coated with an electrically insulating polymer using the inventive method.