Photoresist for the production of nanostructures and methods using this photoresist for multi-photon 3D lithography to produce nanostructures with a high refractive index

Abstract

The invention relates to a photoresist for the production of nanostructures, a method using this photoresist for multi-photon 3D lithography for the production of nanostructures with a high refractive index, in particular for the production of a semiconductor structure on a substrate. The object of the invention, to provide an optimized photoresist for the production of nanostructures, and a method using this photoresist for the direct 3D laser structuring of nanostructures on a substrate, wherein the optimized photoresist exhibits good adhesion, increased lifetime, and increased laser light sensitivity, is achieved by providing the photoresist in the form of butyldithiocarbamic acid or carbon disulfide and n-butylamine, as well as at least one metal oxide or metal hydroxide and ethanol, with the addition of the components antimony(III) oxide, amorphous or crystalline antimony(III) trisulfide, n-nonane, isooctane, hexanol, polyethylene glycol 200, 300, or 400, polyethylene glycol, octanol,n-Propylamine, chloroform, and water are provided, and all components are heated with stirring at a speed of 50 to 1500 rpm and at temperatures in the range of 25-100°C for a time in the range of 60 to 720 min, and then cooled to room temperature, and that this photoresist is used as a negative resist in a multi-3D lithography process for the fabrication of nanostructures by etching metal chalcogenide nanostructures with high refractive index and high resolution.

Description

[0001] Photoresist for the production of nanostructures and methods using this photoresist for multi-photon 3D lithography to produce nanostructures with a high refractive index

[0002] The invention relates to a photoresist for the production of nanostructures and a method using this photoresist for multi-photon 3D lithography for the production of nanostructures with a high refractive index, in particular for the production of a semiconductor structure on a substrate.

[0003] Currently, various methods for the fabrication of small structures, especially structures in the micrometer and submicrometer range on substrates, are known.

[0004] One of the most widely used methods for producing small structures on substrates, especially structures in the micrometer and submicrometer range, is electron beam lithography based on photoresists.

[0005] In electron beam lithography (often abbreviated as E-beam lithography or EBL), individual shapes are drawn onto a surface covered with an electron-sensitive film, the photoresist, using a focused electron beam.

[0006] The electron beam alters the solubility of the photoresist, allowing the exposed or unexposed areas to be selectively removed by immersion in a solvent (development). As with photolithography, the purpose is to create very small structures in the photoresist that can subsequently be transferred to the substrate material, often by etching or deposition processes.

[0007] The main advantage of electron beam lithography is its ability to create user-defined patterns (by direct writing) with a resolution of less than 10 nm. This form of maskless lithography offers high resolution but low throughput, limiting its use to photomask fabrication, small-batch semiconductor manufacturing, and research and development. (https: / / en.wikipedia.org / wiki / Electron-beam_lithography)

[0008] Photoresists are used particularly in microelectronics and microsystems technology for the production of micrometer and sub-micrometer structures, e.g., for fabricating semiconductor structures on a substrate. A distinction is made between positive and negative photoresists.

[0009] Positive photoresists consist of a combination of film formers, such as cresol novolac resins, and photosensitive components, such as naphthoquinone diazides, dissolved in solvents, such as methoxypropyl acetate. The addition of the photosensitive component to the alkali-soluble photoresist reduces the layer's alkali solubility. The NCD groups block the OH groups of the cresol novolac resins, thus decreasing the alkali solubility (inhibiting effect). After exposure through an exposure mask in the UV range (308–450 nm), the photosensitive component reacts to form indenecarboxylic acid derivatives, removing the blocking effect and making the photoresist layer approximately 100 times more alkali-soluble in positive resists. After development, only the areas protected by the mask remain, while the exposed areas are removed. The refractive index of novolac-based photoresists ranges from 1.58 to 1.63.Photoresists offer excellent protection against liquid etching media from pH 0 to 12.

[0010] Negative photoresists consist of novolacs and bisazides, acid-forming agents, and amine components dissolved in safer solvents, such as methoxypropyl acetate (PGMEA). The chemical enhancement is based on acid formation during exposure and subsequent crosslinking of the amine with the novolacs. Since the acid (protons) is constantly regenerated during the crosslinking reaction, a single proton can cause a multitude of crosslinks, resulting in high sensitivity. The CAR composition, after exposure followed by annealing, leads to crosslinking of the exposed negative resist layer. This renders these areas insoluble, and they remain after development.

[0011] The unexposed areas, however, remain soluble and are removed by the developer. (https: / / www.allresist.de / faqphotoresists-0010funktionphotoresist / )

[0012] EP 3 767 668 A1 discloses a method for producing a semiconductor structure on a substrate, comprising the following steps: a) Deposition of a metal-organic precursor solution on a substrate and formation of a precursor surface, b) local heating of the precursor surface along a predetermined pattern, c) Rinsing the precursor surface with at least one organic solvent, d) Heating the rinsed precursor surface at an elevated temperature, and e) Obtaining a metal-chalcogenide semiconductor structure or a metalloid-chalcogenide semiconductor structure on the substrate, wherein - the semiconductor structure or the metalloid chalcogenide semiconductor structure obtained by step e) is at least one semiconductor selected from a group consisting of Sb2S3, ZnS, PbS, InS, CdS, SnS, CuS, and MnS, or - a selenium chalcogenide is added to the precursor solution before step a) and the metal-chalcogenide semiconductor structure or the metalloid-chalcogenide semiconductor structure obtained in step e) is given by a formula MeS 1-X See x , where Me is Zn, Pb, In, Cd, Sn, Cu or Mn, and Me2S 3-x See x , in which Me Sb is.

[0013] In step a), the precursor solution is deposited onto the substrate by spin coating, whereby the metal or metalloid semiconductor structure is obtained at least locally with a width of at most 50 nm, and the heating of the precursor surface in step b) is carried out by a method selected from a group consisting of electron beam irradiation and manipulation of the laser beam irradiation with an AFM tip.

[0014] The precursor solution of step a) is obtained by dissolving at least one metal compound or metalloid compound in an organic dithiocarbamate solution, wherein the organometallic precursor solution comprises an organometallic complex selected from a metal or metalloid compound consisting of a chalcogenide, an oxide or a hydroxide, or from a group consisting of Sb2O3, ZnO, PbO, In(OH)3, Cd(OH)2, Cu2O, SnO, and MnO.

[0015] The organic dithiocarbamate solution can contain an alcohol and at least one dithiocarbamate.

[0016] The heating process in step d) is carried out at a temperature of at least 250 °C and at most 600 °C.

[0017] The at least one organic solvent is preferably acetone and isopropanol.

[0018] It is advantageous if the rinsed substrate surface (silicon, silicon dioxide, F-doped tin oxide glass or a FET chip) is blown with a gas stream before step d).

[0019] If steps a) to e) of the method according to EP 3 767 668 A1 are repeated, a metal chalcogenide semiconductor structure or metalloid chalcogenide semiconductor structure can be obtained, with the heating of step d) being carried out at a temperature of at least 300 °C up to a maximum of 550 °C.

[0020] Although the method according to EP 3 767 668 A1 can also be used for multiphoton laser lithography, this method has the following disadvantages: i. The printed metal chalcogenide 3D structure adheres poorly to the substrate. Although defined Sb₂S₃ 3D structures are produced after the multiphoton laser lithography process, they all exhibit only weak adhesion to the substrate, as the printed Sb₂S₃ 3D structure detaches from the substrate as early as 5 minutes after printing in test trials. Due to this poor adhesion, the printed Sb₂S₃ 3D structures are washed off during the development process, rendering the method impractical. ii. The formulation of the Sb₂S₃ precursor solution (as a photoresist for multiphoton laser lithography) is not stable for long. Practical testing has shown that the formulation, as disclosed in EP 3 767 668 A1, only works when freshly prepared, meaning that the Sb₂S₃ precursor solution loses its functionality as a photoresist after a maximum of two weeks. This disadvantage severely limits the industrial / commercial applicability of the process using this formulation of the Sb₂S₃ precursor solution. iii. The Sb₂S₃ precursor solution (as a photoresist for multiphoton laser lithography) is not sensitive. Practical testing has shown that the sensitivity (i.e., the minimum energy required to generate well-defined features in the photoresist on the substrate), a crucial parameter of the process according to the disclosure of EP 3 767 668 A1, necessitates a laser power of 50 mW for 3D structuring, which is already the maximum power that current Nanoscribe laser lithography systems can deliver. This low sensitivity severely limits the applicability of the process using the Sb₂S₃ precursor solution of this formulation.

[0021] The publication by Wei Wang, Patrik Pfeiffer and Lukas Schmidt-Mende: “Direct Patterning of Metal Chalcoenide Semiconductor”, WILEY-YCH-Verlag GmbH &Co.KGaA, Weinheim 2020, https: / / doi.org / 10.1002 / adfm.202002685 Disclosed, starting from EP 3 767 668 A1, a laser lithographic process for the direct structuring of metal chalcogenide as well as antimony, trisulfide, zinc sulfide, lead sulfide and Copper sulfide nanostructures in which metal butyldithiocarbamate [made from butyldithiocarbamic acid (BDCA) and metal oxide or metal hydroxide] is used as the negative resist, this method also exhibiting the aforementioned disadvantages i), ii) and iii) of EP 3 767 668 A1. The invention is therefore based on the objective of providing an optimized photoresist (multiphoton laser lithography photoresist) and a method using this photoresist for multiphoton 3D lithography for the fabrication of nanostructures, in particular for the fabrication of a semiconductor structure on a substrate. which avoids the aforementioned disadvantages of the state of the art, in particular i. good adhesion of a printed metal chalcogenide 3D structure to various substrates, such as indium tin oxide (ITO), gold (Au), Ge15Sb20S65 and amorphous / crystalline Sb2S3, enables the fabrication of complex printed nanostructures, such as Fresnel zone plates (FZP) and circular lattices, on an Au substrate with high uniformity, ii. exhibits stability (significantly increased lifespan) for at least 2 months, enabling industrial / commercial application, and iii. exhibits a significantly increased sensitivity compared to the state of the art (i.e., only 40 mW laser power, which corresponds to 80% of the power requirement of the formulation according to EP 3767668 A1).

[0022] According to the invention, this problem is solved by the features of claims 1, 4, and 9. Further advantageous embodiments of the invention are specified in the dependent claims.

[0023] The provided photoresist comprises butyldithiocarbamic acid (BDCA) or carbon disulfide [(CS2) = carbon disulfide = carbon disulfide] and n-butylamine (C4H₄). 11 N) as well as the following additional components (individually or in combination): - Antimony(III) oxide (Sb2O3), - n-Nonan (C9H 20 ) or isooctane (C8H 18 ) or hexanol (C6H 14 O) and - Polyethylene glycol 200 or 300 or 400 (C 2n H 4n+2 O n+1 ).

[0024] The provided photoresist may also contain the following components (individually or in combination): - amorphous antimony(III) trisulfide (Sb2S3), - crystalline antimony(III) trisulfide (Sb2S3), - Water (H2O), - Chloroform (CHCl3), - Octanol (C8H 18 O) and - n-Propylamine (C3H9N).

[0025] The provided photoresist contains butyldithiocarbamic acid (BDCA) or carbon disulfide and n-butylamine, which corresponds to the prior art.

[0026] Surprisingly, it was found that for the optimized photoresist, the addition of further components (individually or in combination) in the form of antimony(III) oxide (Sb2O3), polyethylene glycol 200, 300, or 400, n-nonane, isooctane, and hexanol increases the adhesion of a printed metal chalcogenide 3D structure to various substrates, extends the stability period of the photoresist, and, in particular, exhibits a significantly increased sensitivity to laser light. These improvements compared to the prior art can be further optimized by mixing the optimized photoresist in a flask while stirring with a magnet at a speed of 50 to 1500 rpm and heating at a temperature of 25 to 100 °C for a period of 60 to 720 minutes, and then cooling it to room temperature.

[0027] In addition to the additives mentioned above, the optimized photoresist may also contain amorphous or crystalline antimony(III) trisulfide (Sb2S3), octanol, n-propylamine, water (H2O) and / or chloroform.

[0028] The optimized photoresist advantageously contains: 16.5 to 30 mmol butyldithiocarbamic acid (BDCA) or 1.5 to 3.0 ml carbon disulfide [(CS2) and 1.0 to 4.0 ml n-butylamine (C4H 11 N) as well as 0.25 to 2.0 mmol antimony(III) oxide (Sb2O3), 1.0 to 3.0 ml n-nonane (C9H 20 ) or isooctane (C8H 18 ) or hexanol (C6H 14 O) and 1.0 to 3.0 ml polyethylene glycol 200 or 300 or 400 (C 2n H 4n+2 O n+1 ).

[0029] Furthermore, the optimized photoresist may also contain the following components: 0.25 to 2.0 mmol amorphous or crystalline antimony (III) trisulfide (Sb2S3), 1.0 to 3.0 ml chloroform (CHCl3), 1.0 to 3.0 ml octanol (C8H) 18 O) and 1.0 to 3.0 ml n-propylamine (C3H9N) and 10 to 40 µl of water (H2O).

[0030] The optimization of the photoresist compared to the previously known photoresist is thus achieved by adding chalcogenides in the form of antimony(III) oxide or amorphous or crystalline antimony(III) trisulfide, replacing the proportion of ethanol with hexanol or n-nonane or isooctane and polyethylene glycols and / or octanol, reducing or replacing the proportion of n-butylamine with propylamine, and optionally adding water and / or chloroform. The optimized photoresist is then subjected to a defined heating process (heating in the range of 25-100°C) and a defined setting of the stirring speed (magnetic stirring in the range of 50-1500 rpm) for a period of 60 to 720 minutes.

[0031] The provided photoresist can be used as a negative resist in multi-photon 3D lithography for the fabrication of nanostructures, e.g. from metal chalcogenides such as antimony sulfide (Sb2S3), zinc sulfide (ZnS), lead sulfide (PbS) or copper sulfide (Cu2S), in which very small structures are created in the photoresist and subsequently transferred to the substrate material, e.g. by etching or other material deposition processes.

[0032] Based on the technical teaching of Wei Wang, Patrik Pfeiffer and Lukas Schmidt-Mende: “Direct Patterning of Metal Chalcoenide Semiconductor”, WILEY-YCH-Verlag GmbH &Co.KGaA, Weinheim 2020, https: / / doi.org / 10.1002 / adfm.202002685, an optimized photoresist is provided, the use of which leads to an improved method for the direct 3D laser structuring of metal chalcogenides, such as antimony sulfide (Sb2S3), zinc sulfide (ZnS), lead sulfide (PbS) or copper sulfide (Cu2S), and to an improved multi-photon 3D lithography method.

[0033] Examples of the specific composition of the optimized photoresist: A first optimized photoresist I consists of butyldithiocarbamate, antimony(III) oxide, amorphous antimony(III) trisulfide, n-nonane, isooctane, hexanol, carbon disulfide, n-butylamine, ethanol, polyethylene glycol 200, and water.

[0034] A second optimized photoresist II consists of butyldithiocarbamate, antimony(III) oxide, crystalline antimony(III) trisulfide, n-nonane, isooctane, hexanol, carbon disulfide, n-butylamine, octanol, ethanol.

[0035] A third optimized photoresist III consists of antimony(III) oxide, n-nonane, isooctane, hexanol, carbon disulfide, n-butylamine, polyethylene glycol 200 and propylamine.

[0036] A fourth optimized photoresist IV consists of butyldithiocarbamate, antimony(III) oxide, amorphous antimony(III) trisulfide, n-nonane, isooctane, hexanol, carbon disulfide, n-butylamines, ethanol, polyethylene 300, and chloroform.

[0037] A fifth photoresist V consists of carbon disulfide and n-butylamine, antimony(III) oxide, polyethylene glycol 300 and octanol and propylamine.

[0038] All optimized photoresists I to V are mixed in a flask under magnetic stirring at 50 to 1500 rpm and heating at 25 to 100 °C for 60 to 720 minutes. After the reaction, the optimized photoresists I to IV are allowed to cool to room temperature.

[0039] The process for fabricating a 3D metal chalcogenide structure on a substrate using the provided photoresist comprises the following steps: a) A photoresist solution is dropped onto a substrate containing indium tin oxide (ITO), gold (Au), Ge15Sb20S65 and amorphous / crystalline Sb2S3, so that a photoresist volume is formed on the substrate. b) The front end of an oil lens (e.g. Carl Zeiss Plan-Apochromat 63X / 1.4 Art. No.: 420782-9900-799) is immersed in the photoresist solution (or in the oil with the appropriate refractive index as a control). c) A pulsed laser with a wavelength of 780 nm is focused tightly onto the substrate surface by the oil immersion objective. The focused laser spot is scanned along a predetermined path, either via galvo mirrors or piezoelectric stages. A metal chalcogenide, e.g., Sb₂S₃, forms beneath the laser spot through multiphoton absorption. d) After laser scanning, the photoresist and the substrate are treated with at least one organic solvent (= development), whereby the unreacted photoresist is removed and the metal chalcogenide nanostructure with the desired morphology remains. e) The developed nanostructure and the substrate are annealed on a hot plate (heating / annealing step), whereby the metal chalcogenide nanostructure is stabilized in the "printed" state. Depending on the application, both amorphous and crystalline Sb₂S₃ can be obtained by controlling the heating temperature. At a heating temperature of 140–220 °C, amorphous Sb₂S₃ can be obtained for optical applications such as diffractive optical elements. At a heating temperature of 220–300 °C, crystalline Sb₂S₃ can be obtained for electrical applications due to the semiconductor properties of Sb₂S₃.

[0040] The photoresist volume is formed in step a), which in particular means that a photoresist volume is formed by dropping the photoresist solution onto the substrate.

[0041] The photoresist solution is not applied to the substrate in the form of a structured pattern. Instead, the photoresist solution preferably covers a volume on the substrate (e.g., a surface or film) in a structurally undefined manner, thus creating a precursor surface in the form of an at least partially closed photoresist layer.

[0042] The photoresist solution contains at least butyldithiocarbamate, antimony(III) oxide or amorphous antimony(III) trisulfide, carbon disulfide (or carbon dioxide), n-butylamine and an alcohol.

[0043] Direct irradiation with laser light is preferably achieved using multiphoton laser lithography. This technology employs a focused laser beam to perform a lithography process. The laser beam is preferably focused by a microscopy objective.

[0044] This multiphoton laser lithography is preferably performed with a laser power of at least 28 mW and at most 50 mW. The writing speed of the laser lithography is preferably set to at least 5 µm / s and at most 50 µm / s.

[0045] Laser lithography is capable of creating structures in the submicrometer range, especially in the range of a few hundred nm, particularly in the sub-1000 nm range.

[0046] In step a), the photoresist solution (as one embodiment) is dripped onto the substrate. This is a fast, simple, and cost-effective way to apply the photoresist solution to the substrate to form a precursor volume.

[0047] In this embodiment, the metal or metalloid nanostructure according to step e) has at least locally a width of less than 300 nm to a maximum of 4000 nm, so that semiconductor structures in the submicrometer range, in particular in the range below 800 nm, can be easily produced using this method.

[0048] The photoresist solution (dithiocarbamate solution) contains an alcohol, preferably only one of the following alcohols: ethanol, hexanol, octanol, polyethylene and glycol 200, or the combination of the following alcohols: ethanol, hexanol, octanol and polyethylene glycol 200.

[0049] Preferably, this is at least one dithiocarbamate solution belonging to the organic group, containing dithiocarbamate butyldithiocarbamate, particularly preferably n-butyldithiocarbamate, and the organic dithiocarbamate solution preferably contains an alcohol, preferably only one of the following alcohols: ethanol, hexanol, octanol, polyethylene glycol 200 or the combination of the following alcohols: ethanol, hexanol, octanol and polyethylene glycol 200.

[0050] The organic dithiocarbamate solution is preferably prepared by adding an amine, in particular a primary amine or a secondary amine, preferably butylamine or n-butylamine, or dibutylamine, preferably di-n-butylamine or propylamine, to a solution of carbon disulfide in an alcohol, preferably only one of the following alcohols: ethanol, hexanol, octanol, polyethylene glycol 200, or the combination of the following alcohols: ethanol, hexanol, octanol, and polyethylene glycol 200. Adding an amine to a solution of carbon disulfide in an alcohol, preferably one of the following alcohols: ethanol, hexanol, octanol, polyethylene, and PEG 200, or the combination of the following alcohols: ethanol, hexanol, octanol, and polyethylene glycol 200, forms a dithiocarbamate, in particular dithiocarbamic acid.

[0051] In another embodiment, a selenium chalcogenide is added to the photoresist solution before step a). In this respect, the selenium doping for the chalcogenide nanostructures can be carried out simply by adding the selenium chalcogenide to the photoresist solution before step a). Accordingly, in step e), a metal-chalcogenide nanostructure or a metalloid-chalcogenide nanostructure is preferably obtained, most preferably comprising a formula according to the formulas: MeS 1-x See x , where Me is preferably Zn, Pb, In, Cd, Sn, Cu or Mn, and Me2S 3-x See x , where Me is preferably Sb.

[0052] The addition of selenium, selenium chalcogenide or selenium oxide to the photoresist solution always takes place before step a).

[0053] In one embodiment of steps b) and c), the tightly focused laser spot within the photoresist volume is scanned along a predetermined pattern, with the treatment being carried out locally with the optimized photoresist having the following composition: A first optimized photoresist I used consists of butyldithiocarbamate, antimony(III) oxide, amorphous antimony(III) trisulfide, carbon sulfide, n-butylamine, ethanol, PEG 200, water. Alternatively, a second optimized photoresist II used consists of butyldithiocarbamate, antimony(III) oxide, crystalline antimony(III) trisulfide, carbon disulfide, n-butylamine, octanol, and ethanol. Alternatively, a third optimized photoresist III used consists of butyldithiocarbamate, antimony(III) oxide, carbon disulfide, propylamine, hexanol, isooctane, n-nonane.

[0054] Irradiation with a pulsed femtosecond laser at a wavelength of 780 nm decomposes the metal butyldithiocarbamate in step c) through the process of multiphoton absorption, yielding the desired metal chalcogenide. Multiphoton absorption is a nonlinear process that depends strongly (quadratically) on the light intensity. Since the light intensity reaches its maximum at the focal point of a laser, strong multiphoton absorption can be triggered at the focal point, which explains the operating mechanism and the resolution below the Abbe diffraction limit of multiphoton absorption lithography.

[0055] The at least one organic solvent of step d) is ethanol, isopropanol, chloroform and Novec 7100 engineered fluid, or the combination of the following alcohols: ethanol, isopropanol, chloroform and Novec 7100 engineered fluid.

[0056] In particular, the rinsing in step d) is preferably carried out by immersing the precursor surface in the first organic solvent for a predetermined rinsing time, preferably for one hour. Preferably, the surface of the precursor is immersed in isopropanol or acetone for one hour.

[0057] In a preferred embodiment, the rinsed precursor surface obtained in step d) is blown with a gas stream before step e). This has the advantage that residual moisture, in particular residual moisture from organic solvents, is removed before annealing in step d).

[0058] Preferably, nitrogen is used as the gas for the application of the gas stream, in particular to remove the residual moisture from the rinsed precursor surface before step e).

[0059] Preferably, the annealing / burning step e) is carried out at a temperature of 300 °C, in particular to achieve an Sb2S3 / Sb2S3- xSe x -To preserve the crystal structure.

[0060] In the annealing step e), the metal-organic complex is decomposed in particular and any remaining organic solvent is removed.

[0061] The annealing of step e) is preferably carried out for an annealing time of at least 20 min to at most 40 min, preferably at least 25 min to at most 35 min, preferably 30 min.

[0062] In a preferred embodiment, the substrate is selected from the group consisting of silicon, silicon dioxide, and a field-effect transistor (FET) chip. In particular, the substrate should be coated with one of the following materials: indium tin oxide (ITO), F-doped tin oxide glass (FTO), gold (Au), Ge15Sb20S65, amorphous Sb2S3, crystalline Sb2S3, or a combination of the following materials: indium tin oxide (ITO), F-doped tin oxide glass (FTO), gold (Au), Ge 15 Sb 20 S 65, amorphous Sb2S3, crystalline Sb2S3. The present method can preferably be used for the fabrication of free-form metal chalcogenide structures in the fields of micro-optics, diffractive optical elements, microrobotics, microfluidics, display units, integrated photonics, photonic crystals / materials, mechanical metamaterials, MEMS, sensors / actuators, nano- / microelectronic systems, optoelectronic components, biomedical engineering, biomimetics, cell scaffolds, photovoltaic devices and computer chips.

[0063] The purpose is also achieved by providing a device comprising a metal chalcogenide structure on a substrate, which is obtainable by the inventive method or a preferred embodiment of this method as explained above, and preferably obtained by this method.

[0064] The device is preferably a micro-optical or diffractive optical element, a microrobotic unit, a microfluidic unit, a display unit, an integrated photonic crystal / material, a mechanical metamaterial, MEMS, a sensor / actuator, a nano- / microelectronic system, an optoelectronic component, a biomedical engineering component, a biomimetic component, a cell scaffold, a photovoltaic device or a computer chip.

[0065] By providing this stable and high-performance photoresist in combination with setting a defined temperature in the tightly focused laser spot and adjusting different stirring speeds, the previously known method for the direct structuring of metal chalcogenide as well as antimony, trisulfide, zinc sulfide, lead sulfide and copper sulfide nanostructures, as described in the publication by Wei Wang, Patrik Pfeiffer and Lukas Schmidt-Mende: “Direct Patterning of Metal Chalcoenide Semiconductor”, WILEY-YCH-Verlag GmbH &Co.KGaA, Weinheim 2020, https: / / doi.org / 10.1002 / adfm.202002685, is significantly improved.

[0066] The invention also includes the use of the provided photoresist for direct 3D laser structuring in the sub-µm range.

[0067] In this direct laser structuring process, the surface of a substrate to be processed is first coated with a volume of the provided photoresist, and in a further step the coated photoresist volume is then scanned in a defined manner with a focused laser beam, whereby the material of the photoresist layer is locally treated by multiphoton absorption at the laser focal point with the highest light intensity.

[0068] The laser beam is advantageously focused.

[0069] The invention also involves manipulating the irradiation of the photoresist layer with laser beams using an AFM tip. This is achieved by externally or internally illuminating a field-enhancing, nanoscale tip (e.g., a plasmon scanning probe tip) to excite a region localized down to the nanometer scale, thus enabling targeted modification of the photoresist far below the optical diffraction limit, analogous to the described photolithography process.

[0070] The power of the laser radiation generated by the laser is in the range of 25 mW to 50 mW, advantageously 28 mW to 50 mW, with pulsed operation being particularly advantageous.

[0071] During scanning, the laser radiation creates regularly arranged geometries in the photoresist volume, whereby the technical properties of the photoresist volume (and possibly the base material) are specifically changed, so that a new functionality of the photoresist is created, e.g. metal chalcogenide (Sb2S3).

[0072] During scanning, the tightly focused laser generates a focal spot associated with multiphoton absorption. Only the central part of the focal spot can provide sufficient light intensity to initiate the multiphoton absorption process. This central part of the laser spot exhibits a tubular structure in the 3D dimension, and only this part is responsible for the microfabrication process (lithography). By moving the laser spot with galvo mirrors or by moving the photoresist with pizeoelectric stages along a predefined path, the 3D structuring within the Sb₂S₃ resist volume is achieved through multiphoton absorption-induced decomposition. The size of the tubular structure in the laser focus can be much smaller than the Abbe diffraction limit, enabling high-resolution 3D structuring (below the Abbe diffraction limit).

[0073] The invention is explained in more detail below with reference to the exemplary embodiments, without being limited to these. Example 1

[0074] The preparation of the photoresist (metal chalcogenide resist solution) is carried out by the following steps: a) 1 mmol antimony(III) oxide, 0.1 mmol amorphous antimony(III) oxide, 1.5 mL carbon disulfide, 2 mL n-butylamine, 1 mL ethanol and 0.5 mL polyethylene glycol 200 are mixed in a 50 mL three-necked vessel. This mixture is magnetically stirred for 16 hours at a temperature of 25 °C and 1500 rpm. b) After stirring for 16 hours at 25 °C, the mixture is heated to 90 °C for 40 minutes. Then, the mixture is magnetically stirred for 16 hours at 1500 rpm and a temperature of 25 °C. c) After stirring for 16 hours at 25°C, the mixture is heated to 90°C for 20 minutes. Then, the mixture is magnetically stirred for 16 hours at 1500 rpm and a temperature of 25°C. d) After stirring for 16 hours at 25 °C, the mixture is heated to 90 °C for 10 minutes. Then the mixture is magnetically stirred for 16 hours at 1500 rpm and a temperature of 25 °C. e) After stirring for 16 hours at 25 °C, the mixture is centrifuged for 30 minutes at 5000 rpm.

[0075] The metal chalcogenide resist thus synthesized (the photoresist produced) is used for the direct structuring of Sb2S3 nanostructures by means of multiphoton absorption lithography (e.g. with a commercial Nanoscribe Photonic Professional GT2 system).

[0076] The substrate consists of 170 µm thick 1.5 H cover glasses coated with a 3 nm thick chromium layer and a 50 nm thick gold layer, whereby the chromium was first applied to the cover glass by magnetron sputtering and then the gold was applied to the chromium layer by magnetron sputtering.

[0077] Multi-photon absorption is performed with a laser power of 40 mW.

[0078] After lithography, the substrate is treated either in only one of the following solvents: ethanol, isopropanol, chloroform and Novec 7100 Engineered Fluid, or in a combination of the following solvents: ethanol, isopropanol, chloroform and Novec 7100 Engineered Fluid.

[0079] The result is Sb2S3 nanostructures with the desired structure. Example 2

[0080] The preparation of the photoresist (metal chalcogenide resist solution) is carried out by the following steps: a) 1 mmol antimony(III) oxide, 0.1 mmol amorphous antimony(III) oxide, 1.5 mL carbon disulfide, 2 mL n-butylamine, 1 mL octanol and 1 mL ethanol are mixed in a 50 mL three-necked vessel. This mixture is magnetically stirred for 16 hours at a temperature of 25 °C and 1500 rpm. b) After stirring for 16 hours at 25 °C, the mixture is heated to 85 °C for 40 minutes. Then, the mixture is magnetically stirred for 16 hours at 1500 rpm and a temperature of 25 °C. c) After stirring for 16 hours at 25 °C, the mixture is heated to 85 °C for 20 minutes. Then, the mixture is magnetically stirred for 16 hours at 1500 rpm and a temperature of 25 °C. d) After stirring for 16 hours at 25°C, the mixture is heated to 85°C for 10 minutes. Then, the mixture is magnetically stirred for 16 hours at 1500 rpm and a temperature of 25°C. e) After stirring for 16 hours at 25 °C, the mixture is centrifuged for 30 minutes at 5000 rpm.

[0081] The synthesized metal chalcogenide resist (the prepared photoresist) is used for the direct structuring of Sb₂S₃ nanostructures by multiphoton absorption lithography using a commercial Nanoscribe Photonic Professional GT2 system. The substrate consists of 170 µm thick 1.5 H cover glasses coated with a 3 nm thick chromium layer and a 50 nm thick gold layer. First, the chromium was deposited onto the cover glass by magnetron sputtering, and then the gold was deposited onto the chromium layer by magnetron sputtering.

[0082] Multi-photon absorption is performed with a laser power of 40 mW.

[0083] After lithography, the substrate is treated either with only one of the following solvents: ethanol, isopropanol, chloroform and Novec 7100 Engineered Fluid, or with a combination of the following solvents: ethanol, isopropanol, chloroform and Novec 7100 Engineered Fluid.

[0084] The result is Sb2S3 nanostructures with the desired structure. Example 3

[0085] The preparation of the photoresist (metal chalcogenide resist solution) is carried out by the following steps: a) 1 mmol antimony(III) oxide, 0.1 mmol amorphous antimony(III) oxide, 1.5 mL carbon disulfide, 2 mL n-butylamine, 1 mL octanol and 1 mL ethanol are mixed in a 50 mL three-necked vessel. The mixture is magnetically stirred for 16 hours at a temperature of 25 °C and 1500 rpm. b) After stirring for 16 hours at 25 °C, the mixture is heated to 80 °C for 40 minutes. Then, the mixture is magnetically stirred for 16 hours at 1500 rpm and a temperature of 25 °C. c) After stirring for 16 hours at 25 °C, the mixture is heated to 80 °C for 20 minutes. Then, the mixture is magnetically stirred for 16 hours at 1500 rpm and a temperature of 25 °C. d) After stirring for 16 hours at 25 °C, the mixture is heated to 80 °C for 10 minutes. Then the mixture is magnetically stirred for 16 hours at 1500 rpm and a temperature of 25 °C. e) After stirring for 16 hours at 25 °C, the mixture is centrifuged for 30 minutes at 5000 rpm.

[0086] The synthesized metal chalcogenide resist (the prepared photoresist) is used for the direct structuring of Sb₂S₃ nanostructures by multiphoton absorption lithography using a commercial Nanoscribe Photonic Professional GT2 system. The substrate consists of 170 µm thick 1.5 H cover glasses coated with a 70 nm thick indium tin oxide (ITO) layer, the ITO being initially deposited onto the cover glass by magnetron sputtering.

[0087] The result is Sb2S3 nanostructures with the desired structure.

[0088] The provided optimized photoresists feature • consistent quality for at least 6 months, • a well-defined 3D structuring speed, • good adhesion to various substrates, and can form 3D structures with a refractive index of > 3.5.

[0089] Potential applications of the method using the provided photoresist include: • the production of components for lossless (down to ~60 nm) optical aperture near-field microscopy (FA nanoscopy) and • the production of optical metasurfaces (FA Nanooptics and FA Fiber Photonics)

[0090] The advantages of the provided technical solution, in particular compared to the technical solution according to EP 3 767 668 A1, are as follows: i. Due to the provided optimized photoresist, the printed metal chalcogenide 3D structure adheres to various substrates (good adhesion), including indium tin oxide (ITO), gold (Au), Ge 15 Sb 20 S 65and amorphous / crystalline Sb2S3, so that printed nanostructures remain on the substrate, e.g. in the form of complex structures such as Fresnel zone plates (FZP) and circular grids on an Au substrate, and the printed DOEs show a high uniformity, which proves the consistency of the optimized photoresist. ii. The optimized photoresist is stable for at least 6 months. This significantly increased lifetime of the Sb2S3 precursor solution (as a photoresist for multiphoton laser lithography) enables its industrial / commercial application. iii. The sensitivity of the optimized photoresist as a multiphoton laser lithography photoresist is significantly increased compared to prior art Sb₂S₃ precursor solutions. The optimized photoresist requires only 40 mW of laser power, which corresponds to 80% of the power requirement of the Sb₂S₃ precursor solution according to patent EP 3 767 668 A1.

[0091] All features described in the description, the exemplary embodiments and the following claims can be essential to the invention, either individually or in any combination. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 3 767 668 A1 [0012, 0019, 0020, 0021, 0090] Cited non-patent literature

[0000] (https: / / www.allresist.de / faqphotoresists-0010funktionphotoresist / )

[0011] Wei Wang, Patrik Pfeiffer and Lukas Schmidt-Mende:

[0021] Direct Patterning of Metal Chalcoenide Semiconductor", WILEY-YCH-Verlag GmbH &Co.KGaA, Weinheim 2020, https: / / doi.org / 10.1002 / adfm.202002685

[0021] Wei Wang, Patrik Pfeiffer and Lukas Schmidt-Mende: “Direct Patterning of Metal Chalcoenide Semiconductor”, WILEY-YCH-Verlag GmbH & Co. KGaA, Weinheim 2020, https: / / doi.org / 10.1002 / adfm.202002685 [0032, 0065] Carl Zeiss Plan-Apochromat 63X / 1.4 Item no.: 420782-9900-799

[0039]

Claims

[1] Photoresist in the form of a composition comprising butyldithiocarbamic acid or carbon disulfide and n-butylamine and other components which are present individually or in combination, characterized by that the components • Antimony(III) oxide, • n-nonane, isooctane, hexanol or ethanol and • Polyethylene glycol 200 or 300 or 400. [2] Photoresist according to claim 1, characterized by that the components • amorphous or crystalline antimony(III) trisulfide, • Octanol, n-propylamine, • Contain chloroform and / or water. [3] Photoresist according to claim 1, characterized by , that • 16.5 to 30 mmol butyldithiocarbamic acid or • 1.5 to 3.0 ml carbon disulfide and 1.0 to 4.0 ml n-butylamine as well as • 0.25 to 2.0 mmol antimony (III) oxide, • 1.0 to 3.0 ml n-nonane or isooctane or hexanol and • 1.0 to 3.0 ml of polyethylene glycol 200 or 300 or 400 are included in the composition. [4] Photoresist according to claim 3, characterized by , that • 0.25 to 2.0 mmol amorphous or crystalline antimony (III) trisulfide, • 1.0 to 3.0 ml chloroform, • 1.0 to 3.0 ml octanol, • 1.0 to 3.0 ml n-propylamine and • 10 to 40 µl of water are included in the composition. [5] Photoresist according to one or more of claims 1 to 4, characterized by that all components of the composition are heated with stirring in a range of 50 to 1500 rpm and at temperatures in a range of 25 to 100 C° for a time in a range of 60 to 720 min and then cooled to room temperature. [6] A method for multi-3D lithographic fabrication of a metal chalcogenide nanostructure with high refractive index and high resolution on a substrate comprising the steps: a) deposition of an organometallic precursor solution on a substrate and formation of a precursor surface, b) local heating of the precursor surface along a predetermined pattern by photon irradiation, c) rinsing the precursor surface with at least one organic solvent, d) heating the rinsed precursor surface at an elevated temperature, and e) obtaining a metal chalcogenide nanostructure or a metalloid chalcogenide nanostructure on the substrate, characterized by , that • the precursor solution in step a) is a photoresist according to one or more of claims 1 to 5, which is dripped onto the substrate as a solution and produces the precursor surface in the form of an at least partially closed photoresist layer, • the heating in step b) is carried out by scanning the photoresist layer with the aid of a photon beam from a laser, whereby the material of the photoresist layer is locally heated by multiphoton absorption at the location of the energy coupling, • the solvent in step c) is ethanol, acetone or isopropanol, • the temperature in step d) is in a range of 300 to 600°C and • the nanostructure is formed in step e) by final crystallization of a metal chalcogenide 3D semiconductor structure. [7] Method according to claim 6, characterized by that the laser beam is focused. [8] Method according to claim 7, characterized by that the intensity of the focused laser beam is from 28 to 50 mW. [9] Method according to claim 8, characterized by that the irradiation of the photoresist layer with laser beams is carried out using an AFM tip. [10] Method according to claim 6, characterized by that the metalloid chalcogenide 3D semiconductor structure formed by step e) is at least one semiconductor selected from a group consisting of Sb2S3, ZnS, PbS, InS, CdS, SnS, CuS, and MnS. [11] Use of a metal chalcogenide nanostructure produced by means of the photoresist as a negative resist in a method according to one or more of claims 6 to 10 for the production of free-form metal chalcogenide structures in micro-optics, microrobotics, microfluidics, integrated photonics, MEMS, biomedical engineering and biomimetics as well as in diffractive optical elements, display units, photonic materials, mechanical metamaterials, sensors, actuators, nanoelectronic systems, optoelectronic components, cell scaffolds, photovoltaic devices and computer chips.