WO2021096394A2

WO2021096394A2 - Use of chitosan compound in lithography

Info

Publication number: WO2021096394A2
Application number: PCT/RU2020/050325
Authority: WO
Inventors: Artem Konstantinovich GREBENKO; Anton Vladimirovich BUBIS; Albert Galiievich NASIBULIN
Original assignee: Autonomous Non-Profit Organization For Higher Education «Skolkovo Institute Of Science And Technology»
Priority date: 2019-11-15
Filing date: 2020-11-13
Publication date: 2021-05-20
Also published as: RU2738112C1; WO2021096394A4; WO2021096394A3

Abstract

The present invention provides the use of polysaccharides and their compounds as resists for electron beam lithography and photolithography for the manufacture of micro- and nano- electronic and optical components.

Description

USE OF CHITOSAN COMPOUND IN LITHOGRAPHY

Technical Field

The invention relates to the field of micro- and nanotechnology, in particular to the use of polysaccharide compounds in lithography for the manufacture of micro- and nano-electronic and optical components.

Background Art

At present, lithography is widely used to obtain micro- and nanostructures. Lithography in micro- and nanoelectronics is a method of forming a structure on a substrate, where the method comprises applying a resist material on a substrate, exposing the resist applied to electromagnetic radiation or an electron beam (exposure), followed by developing the exposed areas of the resist in a special solution.

Resists based on polymethyl methacrylate (PMMA) and its derivatives, epoxy and other resins, organic polymers and azides, rubber, polybutene etc. are often used as the resists for photolithography and electron beam lithography. These methods are characterized by high resolution and allow obtaining structures of small dimensions.

However, these methods of lithography using the traditional resists comprise the steps of heating and the use of materials and liquids (in particular, for the development of the resist and its removal), which relate to organic solvents, concentrated solutions of acids and alkalis, and, accordingly, do not allow obtaining components based on sensitive objects, in particular such as organic polymers, biological structures, for example, protein-based nanowires, DNA, artificial peptide systems, organic superconductors and semiconductors, which are not able to withstand all or some of the processing steps and retain their original structure.

Methods of lithography using materials of biological origin as resists, and water as a developer are described.

A method of electron beam lithography using a film of silk protein (fibroin) as a resist (Kim S. et al. "All-water-based electron-beam lithography using silk as a resist", Nature Nanotechnology, volume 9, pages 306-310 (2014)), and water as a developer is known. Aqueous solutions of fibroin are mechanically unstable, therefore it is rather difficult to work with them, and during the development process the resist is not completely removed from the exposed areas. In addition, for removing the unexposed resist, it is necessary to use plasma, ionic liquids, or concentrated acid solutions. Document WO2016162638 A1 describes the use of chitosan and/or alginates as resists for lithography. Chitosan was applied on a substrate from an aqueous solution of an acid, dried to remove water, exposed, the exposed areas were developed with an aqueous solution of an acid (acetic, citric, or tartaric), wherein the unexposed areas were removed using oxygen plasma or a solution of concentrated sulfuric acid with hydrogen peroxide.

Publication by M. Caillau et al. “Fifty nanometer lines patterned into silica using water developable chitosan bioresist and electron beam lithography”, Journal of Vacuum Science & Technology B, 35, 06GE01 (2017) describes the use of chitosan as a positive resist for electron beam lithography. A resist film was obtained from chitosan dissolved in an aqueous solution of acetic acid and was dried (at a temperature of 100 °C for 1 min). The exposed areas were developed with water, and the removal of the unexposed resist film was performed using oxygen plasma.

Publication by S. Voznesenskiy et al. "Study of Biopolymer Chitosan as Resist for Submicron Electronic Lithography", Solid State Phenomena, Vol. 213 (2014), pp. 180-185, also describes the use of chitosan in electron beam lithography. Chitosan was dissolved in 2.5% acetic acid solution and from the resulting solution, a film was formed, which was subsequently treated with 3% ammonia solution for 10 minutes to neutralize the film and was rinsed with water. The exposed areas of the chitosan film were developed using water, where incomplete clearing of the exposed areas from the resist material was observed. Removing the unexposed resist film from the substrate required either aggressive solvents such as concentrated acids or oxygen plasma.

Existing techniques based on water-soluble resists are poorly applicable for the manufacture of micro- and nanoelectronic and optical components based on sensitive organic objects, because they use incompatible solvents (for example, concentrated solutions of acids) or plasma. In addition, the incomplete removal of the resist after the development challenges (for example, wet etching) or does not allow (for example, lift-off lithography) further technological steps of obtaining structures.

Thus, there is a need to develop methods for producing micro- and nano- electronic and optical components suitable for obtaining micro- and nanoelectronic and optical components based on sensitive materials, in particular, on the surface of biological or organic objects.

Summary of Invention

One of the object of the present invention is to provide a method for obtaining micro- and/or nano- electronic and/or optical components, which would allow eliminating at least some of the disadvantages of the known methods for obtaining micro- and nano- electronic and optical components, or offer a useful alternative to the existing methods.

In particular, one of the objects of the present invention is to provide a method for obtaining micro- or nano- electronic or optical components, where the method would be suitable for using on substrates that are sensitive to aggressive effects, for example, for using on substrates representing biological objects.

One particular object of the present invention is to provide a method for developing exposed areas of a resist applied on a substrate, in particular during the production of micro- and nano- electronic and optical components.

Another particular object of the present invention is to provide a method for forming micro- or nano- electronic or optical components.

Embodiments of the present invention will be described below with indicating technical effects to be achieved. Further, upon reading the present description, a person skilled in the art will also appreciate other technical results achieved and problems solved.

The first aspect of the present invention relates to a method of developing exposed areas of a film of a polysaccharide compound, the film being applied on a substrate, where the method comprises contacting the film of the polysaccharide compound with a solution comprising at least one transition element.

One of the technical results achieved in the present invention consists in increasing the rate of removal of the resist material from the exposed areas versus the rate of removal of the resist from the unexposed areas, i.e. increasing the selectivity of removing the resist from the exposed areas versus the unexposed areas, compared to the known technical solutions, which are using water-developable and other resists with high compatibility with organic or biological objects. In particular, the proposed method allows providing complete removal of the resist from the exposed areas with minimal dissolution of the resist in the unexposed areas.

Increasing the selectivity of removing the resist from the exposed areas versus the unexposed areas enhances the contrast of the process, and, consequently, improves the degree of compliance of the resulting structure on the surface of the substrate with the exposed pattern.

The proposed method is fast, simple, compatible with sensitive substrates, which are adversely affected by such factors as heating, the action of concentrated solutions of acids and alkalis, organic solvents and plasma. Further, the proposed method reduces the negative impact on the environment. In particular, a resist suitable for use in the present invention can be obtained from waste of food production (e.g., shrimp farming). At the same time, the negative impact on the environment is reduced due to the fact that the processing products have a safe disposal route.

Furthermore, the proposed method allows conducting lift-off lithography, as well as direct manufacturing of microcontacts and good adhesion of metals in the developed areas.

In one particular embodiment, the exposed areas are the areas of the film irradiated with a stream of elementary particles, preferably an electron beam, and/or electromagnetic radiation, preferably deep UV radiation, extreme UV radiation, gamma radiation or X-ray radiation.

In another particular embodiment, the film of the polysaccharide compound applied on the substrate has a thickness of 20 to 190 nm, preferably 50 to 160 nm, more preferably 90 to 150 nm. The film thickness in the indicated ranges further enhances the contrast, which leads to increasing the degree of compliance of the resulting structures on the substrate to the exposed pattern.

In another particular embodiment, the polysaccharide compound is a polysaccharide or an amino derivative, nitro derivative, sulfo derivative, halogen derivative, phosphoric acid derivative, ether, ester or salt thereof.

In another particular embodiment, the polysaccharide compound is a copolymer, which, in addition to saccharide monomer units, also comprises non-saccharide monomer units.

In another more particular embodiment, the polysaccharide compound is a chitosan compound, a cellulose compound, in particular their salts or another derivative, in particular chitosan, cellulose, bee chitosan.

In another more particular embodiment, the salt is a salt of a monobasic, dibasic, tribasic, or tetrabasic acid.

In another more particular embodiment, the salt is a salt of an organic acid, in particular a salt of a carboxylic acid, in particular a salt of formic, acetic or propionic acid, or mixtures thereof.

In another more particular embodiment, the chitosan salt or another chitosan derivative is selected from the group consisting of chitosan acetate, formate, lactate, glycolate, succinate, chloride, citrate, phthaloyl chitosan, carboxymethyl chitosan, succinyl chitosan.

In another particular embodiment, the transition element is a d-block element or an f- block element.

In another particular embodiment, the transition element is a period 4 transition element, a period 5 transition element, a period 6 transition element, or a period 7 transition element.

In another particular embodiment, the transition element is selected from the group comprising zinc, nickel, copper, cobalt, iron. A solution comprising at least one transition element may comprise a mixture of two or more different transition elements.

In another particular embodiment, the solution comprising at least one transition element is a solution in a protic solvent, in particular in water, or in a mixture of solvents comprising one or more protic solvents. The solvent can be an inorganic solvent, an organic solvent, or a mixture thereof. A polar aprotic solvent can be used as well, optionally in a mixture with other solvents.

In another more particular embodiment, the solution comprising at least one transition element is a solution in a polar aprotic solvent or in a mixture of solvents comprising a polar aprotic solvent.

A solvent for preparing a solution comprising at least one transition element also shall dissolve a polysaccharide compound, in particular, the solvent shall dissolve it after exposing the film of the polysaccharide compound.

In another particular embodiment, the solution comprising at least one transition element is a solution of a salt of at least one transition element.

In another particular embodiment, the salt of at least one transition element is selected from the group comprising a salt of an inorganic acid and a salt of an organic acid. Non-limiting examples of a salt of an inorganic acid are chloride, nitrate, sulfate. Non-limiting examples of a salt of an organic acid are formate, acetate. Mixtures of two or more different salts, as well as mixed salts such as Mohr's salt (ammonium iron(II) sulfate) can also be used.

In another more particular embodiment, the salt of at least one transition element is selected from the group comprising chloride, nitrate, sulfate, formate, acetate, Mohr's salt (ammonium iron(II) sulfate).

In another particular embodiment, the concentration of at least one transition element in the solution is at least 1 mM, preferably at least 20 mM, more preferably at least 60 mM, even more preferably at least 200 mM. Increasing the concentration of the transition element further enhances the selectivity of removing the resist from the exposed areas versus the unexposed areas and the contrast of the process. At the same time, the maximum concentration of the transition element is not particularly limited and can be selected, e.g., on the basis of solubility or the ‘costs/effect achieved’ ratio. Non-limiting examples of the maximum concentration are 400 mM, 1M, 5M.

In another particular embodiment, the solution comprising at least one transition element has a pH of 4 to 7.5, preferably about 5.5. Increasing the pH further enhances the selectivity of removing the resist from the exposed areas versus the unexposed areas, but at the same time reduces the dissolution rate of the exposed resist, which, on the contrary, increases with decreasing a pH. Thus, it is possible to adjust a pH value depending on the desired selectivity and dissolution rate of the exposed resist. The pH range of 5 to 6.5 is a particular preferred embodiment, that allows achieving simultaneously high selectivity and dissolution rate values. It should be noted that the dissolution rate of the exposed resist at high pH values can be enhanced due to increasing the radiation dose during the exposure. Thus, an acceptable pH value can be higher than 6.5, for example, up to 7.5 or up to 9. Further, depending on the radiation dose, acceptable selectivity values can be obtained at a pH lower than 5, for example, from 4 or from 4.5.

In another particular embodiment, the solution comprising at least one transition element further comprises organic substances, in particular solvents, polymers, surfactants. In a more particular embodiment, the solvent is an alcohol.

In another particular embodiment, contacting the film with a solution comprising at least one transition element is carried out for a period of 10 seconds to 60 minutes, preferably 5 to 10 minutes, most preferably about 5 minutes. Increasing the contacting time allows enhancing the rate of removal of the resist from the exposed areas, while a longer contact time can lead to a decrease in film thickness in the unexposed areas. Thus, it is possible to select a value of the contact time depending on the required degree of removal of the resist from the exposed areas and the residual film thickness in the unexposed areas.

In another particular embodiment, the proposed method further comprises the step of contacting the film with a second solution comprising at least one second transition element other than the first transition element.

In another more particular embodiment, the method of the invention comprises contacting the film of the polysaccharide compound sequentially with a solution of nickel chloride and a solution of nickel sulfate, preferably with an aqueous solution of nickel chloride and an aqueous solution of nickel sulfate. Said particular combination of the steps allows further enhancing the selectivity and contrast of the process, which provides fast and complete removal of the resist material from the exposed areas and avoiding dissolution of the unexposed resist.

In another particular embodiment, the proposed method, after contacting the film with the solution comprising at least one transition element, further comprises the step of rinsing the film. Rinsing the film of the resist provides removing a residual solution comprising at least one transition element. Rinsing of the resist film is carried out with a suitable solvent, in particular suitable for removing the residual solution comprising at least one transition element. In a particular embodiment, the solvent is a protic solvent, preferably water, or a mixture of solvents comprising one or more protic solvents. The solvent can be an inorganic solvent, an organic solvent, or a mixture thereof. A polar aprotic solvent can be used as well, possibly in a mixture with other solvents.

In a particular embodiment, the rinsing step is carried out for a time period of 10 to 60 seconds. Said duration of the rinsing step increases the degree of clearing the developed area from the exposed resist and residues of the salt of a transition element, and at the same time, dissolution of the unexposed resist film is minimized. A longer contact of the resist film with water, in particular 10 min, provides complete clearing of the developed area, and at the same time, ions of a transition element begin to wash out from the area of the unexposed resist of the polysaccharide compound chelated with the ions of the transition element, which can result in the dissolution of the unexposed resist.

In another particular embodiment, the proposed method further comprises a step of drying.

In another particular embodiment, the substrate is or comprises carbon nanotubes, organic semiconductors, a protein, lipid structures, a DNA, biopolymer fibers, bacterial nanowires on its surface, or any combination thereof.

In one particular embodiment, the proposed method comprises the following sequential steps:

- contacting the film of a chitosan compound with about 400 mM aqueous solution of NiCh for about 5 minutes at a pH of about 5.5;

- contacting the film of a chitosan compound with about 400 mM aqueous solution of N1SO4 for about 5 minutes at a pH of about 5.5;

- rinsing with water for about 30 seconds;

- drying.

In a second aspect, the present invention relates to the use of a solution comprising at least one transition element as a developer for the exposed areas of a film of a polysaccharide compound.

The second aspect can be characterized by particular embodiments, similar to the particular embodiments of the other aspects of the present invention.

The third aspect of the present invention relates to a method of forming at least one component on a substrate, the method comprising the following steps: a. applying a film of a polysaccharide compound on the substrate; b. exposing pre-defmed areas of said film to a stream of elementary particles and/or electromagnetic radiation (exposure); c. developing the exposed areas of the film by carrying out the method of the first aspect of the present invention to obtain the substrate having a mask applied thereon; d. treating the substrate having a mask applied thereon by etching, depositing, doping, or any combination thereof; e. removing the mask from the surface of the substrate to obtain at least one component formed on the substrate, wherein the component is a micro- and/or nano- electronic and/or optical component.

According to the third aspect, the present invention allows enhancing the contrast of the process compared to the known processes using water-developable and other resists with high compatibility with organic or biological objects, and, therefore, provides enhancing the degree of compliance of the formed structure of micro- or nano- electronic or optical components to the exposed pattern.

The proposed method is also fast, simple, compatible with sensitive substrates that are adversely affected by such factors as heating, action of concentrated solutions of acids and alkalis, organic solvents and plasma. Further, the proposed method reduces the negative impact on the environment.

Furthermore, the proposed method allows carrying out lift-off lithography, and also provides direct manufacturing of microcontacts and good adhesion of metals in the exposed areas after development.

In one particular embodiment, the stream of elementary particles is an electron beam, and/or the electromagnetic radiation is deep UV radiation, extreme UV radiation, gamma radiation, or X-ray radiation.

In another particular embodiment, the film has a thickness of 20 to 190 nm, preferably 50 to 160 nm, more preferably 90 to 150 nm.

In another particular embodiment, applying a film on the substrate in step a. is carried out from a solution of a polysaccharide compound, which is preliminary filtered or subjected to centrifugation. A solution of a polysaccharide compound is a solution in water, another inorganic solvent, or an organic solvent. As the solvent, a solvent providing dissolving the polysaccharide compound is selected. Filtration and/or centrifugation of the solution of the polysaccharide compound prior to the application on the substrate allows obtaining a homogeneous solution of the polysaccharide compound for applying the film and, accordingly, a homogeneous film applied on the substrate, the film being without defects or with a minimum amount of defects.

In another particular embodiment, the proposed method further comprises after step a: temperature treatment of the substrate, and/or treatment of the substrate with a solution comprising at least one transition element, and/or treatment of the substrate coated with a film of the polysaccharide compound with at least one inorganic or organic substance. The temperature treatment of the substrate after step a. allows significant improving properties of the polysaccharide compound as a resist. The treatment of the substrate with a solution comprising at least one transition element allows obtaining in principle a developed film that can be easily removed from the substrate and then transferred to another surface. In a more particular embodiment, the solution for treating the substrate comprises a salt of at least one transition element. Thus, in a particular embodiment, the present invention also relates to a developed film of a polysaccharide compound. The treatment of the substrate coated with a film of a polysaccharide compound with at least one inorganic or organic substance may lead to a change of the properties of the film.

In another more particular embodiment, the organic substance for treating the substrate after step a. is glycerol.

In another more particular embodiment, an inorganic substance for treating the substrate after step a. is a salt, in particular a carbonate salt. In another more particular embodiment, an inorganic substance for treating the substrate after step a. is an alkali metal salt, preferably an alkali metal carbonate, more preferably sodium carbonate NaiCCb.

In another particular embodiment, etching is wet etching or dry etching. This allows modifying surfaces of the substrate to obtain a desired structure of the surface.

In another particular embodiment, removing the mask from the surface of the substrate is carried out by exposing to water or a solution, preferably a solution being free of transition elements, more preferably an aqueous solution which is free of transition elements. In another particular embodiment, removing the mask from the surface of the substrate is carried out by exposing to a solution comprising transition elements, preferably an aqueous solution comprising transition elements. Such removal methods provide complete removal of unexposed resist to obtain a structure on the surface of the substrate consistent with the pattern projected. Also, such removal methods allow carrying out lift-off lithography to obtain a structure on the surface of the substrate in accordance with a pre-defmed pattern. Such removal methods are simple, because, unlike traditional methods for removing unexposed film, in particular using plasma, there is no need for plasma generating equipment. Also, such methods are environmentally friendly, since there is no need to use toxic organic solvents, which are also traditionally used to remove unexposed film in the prior art methods. Because there is no need to use plasma, concentrated solutions of acids and alkalis and organic solvents to remove unexposed films, the proposed method is suitable for obtaining a structure on substrates that are sensitive to the action of plasma, concentrated solutions of acids and alkalis, and organic solvents, in particular, substrates based on organic materials and/or materials of biological origin.

In another more particular embodiment, the solution which is free of transition elements is a solution of an acid or a salt other than a salt of a transition element, preferably an aqueous solution of an acid or a salt other than a salt of a transition element. The presence of an acid or a salt can increase the rate of removing a mask from the substrate surface. A solution which is free of transition elements can be prepared in any suitable solvent. A solution of a polysaccharide compound is a solution in water, another inorganic solvent, or an organic solvent.

In another more particular embodiment, the solution of an acid has a concentration of 0.01 to 0.1 % wt.

The acid can have various basicity, for example, it can be monobasic, dibasic, tribasic, or tetrabasic. Accordingly, in another more particular embodiment, the acid is a monobasic, dibasic, tribasic, or tetrabasic acid.

In another more particular embodiment, the acid is an organic acid, in particular a carboxylic acid, in particular formic, acetic, propionic acid, or mixtures thereof.

In another more particular embodiment, the acid is a weak acid. The use of a weak acid allows reducing the impact on the environment while maintaining a high rate of removing a mask from the substrate surface.

In an even more particular embodiment, the acid is formic acid.

In another more particular embodiment, the solution that is free of transition elements is a solution of an alkali metal carbonate, preferably of a concentration in the range of 50 to 150 mM. The use of a low concentration of an alkali metal carbonate helps to reduce the environmental impact while maintaining a high rate of removing a mask from the substrate surface.

In another particular embodiment, the method of forming at least one component on a substrate is a lithography method, in particular a lift-off lithography method. In another particular embodiment, the steps of the method of forming at least one component on a substrate are carried out more than once to obtain a structure comprising more than one layer of components.

In another particular embodiment, the substrate having at least one component formed thereon is an integrated microcircuit.

The third aspect can be characterized by particular embodiments, similar to the particular embodiments of the other aspects of the present invention.

The fourth aspect of the present invention relates to a method of forming a mask of a polysaccharide compound, the method comprising the following steps: a. applying a film of a polysaccharide compound on the substrate; b. exposing pre-defmed areas of said film to a stream of elementary particles and/or electromagnetic radiation; c. developing the exposed areas of the film by carrying out the method of the first aspect of the present invention to obtain the substrate having a mask applied thereon.

In a particular embodiment, the method according to the fourth aspect of the present invention comprises after step a. treating the substrate with a solution comprising a salt of at least one transition element. The treatment of the substrate with a solution comprising the salt of at least one transition element allows obtaining in principle a developed film, which can be easily removed from the substrate and then transferred to another surface.

In a particular embodiment, the method according to the fourth aspect of the present invention further comprises the step of peeling off the developed film from the substrate and then transferring it to another surface.

The fourth aspect can be characterized by particular embodiments, similar to the particular embodiments of the other aspects of the present invention.

The fifth aspect of the present invention relates to a substrate having micro- and/or nano- electronic and/or optical components applied thereon, in particular, elements of an integrated microcircuit, wherein the substrate is or comprises carbon nanotubes, organic semiconductors, proteins, lipid structures, DNA, biopolymer fibers, bacterial nanowires, or any combination thereof.

The sixth aspect of the present invention relates to a substrate having elements of an integrated microcircuit (micro- and/or nanoelectronic and/or optical components) applied thereon, which are applied by a method according to the third aspect of the present invention.

The substrate according to the fifth and sixth aspects of the present invention can be intended for use as an electronic and/or optical component. The fifth and sixth aspects can be characterized by particular embodiments, similar to the particular embodiments of the other aspects of the present invention.

The essence of the invention is illustrated by the following drawings and examples of implementation.

Brief Description of Drawings

FIG. 1 (a) shows a scheme illustrating the proposed method of developing a positive resist based on polysaccharide compounds: a solution of a polysaccharide compound is prepared and applied on a surface of the substrate, in this example by centrifugation, to obtain a thin film. Then the film is irradiated with an electron beam or electromagnetic radiation, is developed in a solution of salts of transition elements, is rinsed and dried using an air flow. FIG. 1(b) shows an optical image of the Skoltech logo upon developing the film of chitosan formate with a molecular weight of 165 kDa, which has been exposed to radiation from a femtosecond krypton-fluorine laser with a wavelength of 248 nm (deep ultraviolet (D-UV)); scale 50 microns.

FIG. 2 illustrates the basic principles of the developing process, which are defined for the present invention. FIG. 2(a) shows the delay of a diffusion time for two competing processes versus the molecular weight of the polysaccharide compound in arbitrary units. In particular, the blue curve characterizes the time of dissolution of the polysaccharide compound versus the molecular weight, obtained from the scaling model (Beth A. Miller-Chou, Jack L. Koenig “A review of polymer dissolution.” Prog. Polym. Sci. 28 (2003) 1223-1270) of the processes of unraveling of the higher macromolecular structure of the polymer chain, and the orange curve characterizes the chelation time versus the molecular weight, obtained from the model of ion passage through membranes (Nikolaos A Peppast, David L. Meadows “Macromolecular Structure and Solute Diffusion Membranes: An Overview Of Recent Theories. ’’Journal of Membrane Science, 16 (1983) 361-377). The insert on the graph illustrates the qualitative correlation of the molecular weight of the polysaccharide with the exposure dose. FIG. 2(a) shows that the development process of the exposed resist is based on a balance between two conflicting processes: the dissolution of the polymer (a polysaccharide compound) and the formation of an insoluble complex of the polysaccharide compound with ions of the transition element. FIG. 2(b) shows the sensitivity of the resist in mC/cm² versus the pH of the developer solution. In this case, nickel was used as the transition metal, the concentration of the developer solution was 400 mM, and the development time was 10 minutes. This figure shows that the dissolution process, being much more sensitive to a pH than the complexation process, changes the dose required for complete removing the exposed resist. The data were obtained for a developer concentration of 400 mM, and in case of lowering the pH to a value of less than 5.0, strong dissolution of the unexposed areas is observed. In case pH exceeds 7.5, the dissolution of the polysaccharide becomes strongly suppressed, and all areas, whether exposed or not, are effectively chelated by ions of the transition element. FIG. 2(c) shows the spectrum obtained by X-ray photoelectron spectroscopy of the sample after etching (the decrease in the film thickness by 25%). This spectrum shows the presence of nickel in the depth of the film both in free and in bound state, which confirms the deep penetration of ions of transition elements into the film of the unexposed resist. FIG. 2(d) shows the slope of the contrast curve at 60% of the height g versus the concentration of ions of transition elements in the developer solution, mM. The development time is 5 minutes, the pH is fixed and is 5.5. It can be seen from the presented graph that, under the same other conditions, the behavior of the resist contrast curves becomes more linear and canonical with an increase in the concentration of the developer solution.

FIG. 3 shows the images of micro- and nanostructures obtained via lift-off lithography using chitosan acetate with a molecular weight of 700 kDa as a resist for electron beam lithography. The development (except for the case shown in image (b)) was carried out in two steps: first with a solution of nickel chloride with a concentration of 400 mM and pH 5.5 for 5 min, then with a solution of nickel sulfate with a concentration of 400 mM and pH 5.5 for 5 minutes. Then, the metal was sprayed: the lower Ti layer 1 nm thick and the upper Pd layer 11 nm thick. Next, the resist film was removed with a solution of formic acid with a volume concentration of 0.1% resulting in lift-off lithography. Image (a) is an optical photograph of an array of structures obtained by lift-off lithography in a dose test; scale 20 pm. The resulting structures consist of square elements with sides of 5 and 1 pm in combination with lines 250 nm thick and 1 pm long. This image illustrates that the structures formed are reproducible and are not a random result. Moreover, they show the dose vicinity versus the sensitivity, in which the formation of structures is possible. Image (b) obtained using scanning electron microscope illustrates structures on the substrate surface produced by lift-off lithography after developing with a high concentration (2500 mM) solution of a salt of a transition element; scale 10 pm. The width of the narrowest lines is about 100 nm. As can be seen, developing with a high concentration solution of a salt of a transition element can allow achieving fairly high resolution. Image (c) shows the critical dimensions obtained via lift-off lithography under the conditions described above; scale 1 pm. This image shows that the above described development conditions can allow obtaining 200 nm (width of the line) elements at a distance of about 500 nm from each other. Image (d) shows a single line from the array of the lines shown in image (c); scale 150 nm.

FIG. 4 shows the results of developing films of chitosan acetate of different thicknesses (90 and 200 nm) exposed under the same conditions. It can be seen that, at a film thickness of 200 nm, the edges of the structure are inhomogeneous and smoothed, the structure significantly differs from the pre-defmed template in the range of doses at which the resist is completely removed from the exposed area during the development. This difference increases with increasing the thickness, apparently due to the non-uniform diffusion of the chelating component.

FIG. 5 shows the results of developing films of chitosan acetate of different molecular weights (20, 65, 165, 200, and 700 kDa) during the dose test. LD corresponds to a test in which the exposure dose varies in a low dose range (25-750 pC/cm², current 50 pA), HD corresponds to a test in which the exposure dose varies in a high dose range (500-15000 pC/cm², current 10 nA). As can be seen, the molecular weight of the polysaccharide compound practically does not affect the properties of the polysaccharide compound as a resist, and for each molecular weight there is a dose range in which the development results in complete removal of the exposed resist and the avoidance of dissolution of the unexposed one.

FIG. 6 shows the results of the development according to the present invention of the films of various chitosan compounds: CA - chitosan acetate, CF - chitosan formate, CG - chitosan glycolate, CL - chitosan lactate, CS - chitosan succinate, CMC - carboxym ethyl chitosan. The presented data show that all the chitosan compounds tested allow complete removal of the exposed resist upon the development and the avoidance of dissolution of the unexposed one.

FIG. 7 shows the effect of removing impurities from a solution of chitosan acetate prior to applying it to a substrate on the morphology of the film obtained from the solution. Image (a) corresponds to a film of chitosan acetate obtained from the solution without additional purification. Image (b) corresponds to a film of chitosan acetate obtained from the solution subjected to centrifugation at 13,200 rpm (15,000 g) for 10 minutes. Image (c) corresponds to a film of chitosan acetate obtained from the solution subjected to centrifugation in a filter tube with a pore diameter of 100 nm. Image (d) corresponds to a film of chitosan acetate obtained from the solution filtered through a 200 nm syringe filter. As can be seen, the film of chitosan acetate obtained from the solution filtered through a syringe filter is characterized by the highest homogeneity and the minimum amount of defects. FIG. 8 shows the structures of the array of elements of the dose test, the structures being obtained upon developing the exposed film of chitosan acetate with solutions of various salts of transition elements, spraying a metal 20 nm thick and removing the unexposed film: nickel chloride, nitrate, acetate, sulfate and formate, copper sulfate, cobalt acetate separately or in a combination with a surfactant, Mohr's salt. This image shows that in principle it is possible to use various transition elements to prepare a developer. Each individual transition element, the corresponding salt cation, organic or inorganic additives to the developer composition influence the process and requires, in order to achieve the best effect, the adjustment of the development protocol: selection of concentrations, pH, time of treatment.

FIG. 9 shows the photographs obtained with an optical microscope, which illustrate the effect of the pH of the developer solution on the sensitivity and contrast of the resist. The data are presented for a film of chitosan acetate with a molecular weight of 65 kDa, a developer is based on nickel chloride a) pH 5.0, b) pH 5.5, c) pH 6.0, d) pH 6.5, e) pH 7.0, f) pH 7.5. All images show the same area of the dose test. From this test, the graph shown in FIG. 2(b) has been obtained.

FIG. 10 shows the photographs obtained with an optical microscope, which illustrate the effect of the rinsing step after developing the film with solutions of salts of transition elements. Each photograph shows a standard dose test with an increasing exposure dose. Image (a) corresponds to developing with a nickel-based developer without rinsing. Image (b) corresponds to developing along with water rinsing for 30 seconds. Image (c) corresponds to developing along with water rinsing for 10 minutes. As can be seen, in case of a longer rinsing after developing, a significant deviation of the developed structure from the exposed template is observed, because the ions of transition elements chelating the molecules of polysaccharide compounds are washed out of the film of unexposed resist, and, accordingly, the dissolution of unexposed areas occurs.

FIG. 11 shows the characteristic curves describing the relative residual thickness of the exposed film (h/ho) (the ratio of the residual thickness of the resist h to the initial thickness ho) of a resist based on chitosan acetate with a molecular weight of 65 kDa upon developing versus the exposure dose received by the resist (D) in logarithmic coordinates. The slope of the characteristic curve is called the resist contrast (g). Graph (a) shows the characteristic curve for the resist after developing with a 5 mM solution of a nickel salt. Graph (b) shows the characteristic curve for the resist after developing with a 2,500 mM solution of a nickel salt. Graphs (c) and (d) characterize the resist after developing only with a solution of nickel chloride with a concentration of 400 mM for 10 min (graph (c)) and with a solution of nickel chloride with a concentration of 400 mM for 5 min, followed by the treatment with a solution of nickel sulfate (two-step development) with a concentration of 400 mM for 5 min (graph (d)). The presented data show that graphs (a) and (c) include areas for which the slope of the curve (in particular, yr,n is the slope of the curve at a relative residual thickness of 60%) is less than 0.6. At the same time, it can be seen that the increase in the concentration of the transition element ion in the composition of the developer solution (from 5 mM in graph (a) to 2,500 mM in graph (b)) and the change of the anion in the developer solution (only chloride ion in graph (c) and the combination of chloride ion and sulfate ion in graph (d)) leads to an increase in the contrast of the resist.

Detailed Description of Invention

The following description provides the means and methods using which the present invention may be carried out, as well as provides examples of its implementation.

When characterizing some quantitative features, the term "about" is used. This term reflects the uncertainty that is inherent to the measurement of any quantitative feature, and denotes a range that is a quantitative characteristic ± measurement error. The measurement error may be 10%, more preferably 5%.

The term "a polysaccharide" used to describe the present invention refers to a high molecular weight compound comprising monosaccharide residues, at least some of which are linked by a glycosidic bond. In a particular case, the polysaccharide consists of monosaccharide residues linked by a glycosidic bond.

The term "a polysaccharide compound" refers to both a polysaccharide itself and its derivatives, in which a backbone of the polysaccharide is retained. Non-limiting examples of the polysaccharide derivatives are: amino derivatives, nitro derivatives, sulfo derivatives, halogen derivatives, phosphoric acid derivatives, ethers and esters, salts. The term "a polysaccharide compound" also includes copolymers which, along with saccharide monomer units, also comprise non-saccharide monomer units. The polysaccharide compound is characterized by decreasing its average molecular weight under the influence of radiation, as well as by the ability to form chelates with transition elements.

The specific non-limiting examples of the polysaccharide compounds are chitosan, bee chitosan (apisan), cellulose, starch, dextrin, pectin, galactomannan, alginic acid, their salts and other derivatives.

The term "chitosan" used to describe the present invention refers to a naturally occurring polysaccharide consisting of two types of monomer units, D-glucosamine and N-acetyl-D- glucosamine, linked by a P-(l 4)-glycosidic bond. The number of N-acetyl-D-glucosamine units corresponds to the degree of acetylation, which is a characteristic of chitosan. Chitosan is a non-toxic, biocompatible and biodegradable polymer.

The term "bee chitosan (apisan)" used to describe the present invention refers to chitosan isolated from the chitin cover of bees.

The term "a transition element" used to describe the present invention refers to chemical elements, the atoms of which, in the electron shell, have the valence electrons with the highest energy occupying the d- and f-orbitals. In the periodic table of chemical elements, the transition elements are located in groups 3-12 in periods 4-7.

The term "an inorganic solvent" used to describe the present invention refers to any known inorganic solvent. The specific non-limiting examples of inorganic solvents include water, ammonia, inorganic acids, aqueous solutions of inorganic salts.

The term "an organic solvent" used to describe the present invention refers to any known organic solvent. The specific non-limiting examples of organic solvents are alcohols (e.g., ethyl alcohol, glycerol), ethers (e.g., diethyl ether), esters (e.g., ethyl acetate, butyl acetate), ketones (e.g., acetone), hydrocarbons (e.g., hexane, heptane).

The term "lithography" used to describe the present invention refers to a set of physicochemical processes of forming on a substrate structures consisting of micro- or nano- electronic and/or optical components.

Resolution is an important parameter of the lithography process. It is determined by the number of lines of equal thickness that can be obtained without merging on 1 mm of the substrate surface.

Contrast (contrast ratio) is also an important parameter of the lithography process. This parameter characterizes the possibility to obtain a sharply differentiated border between the exposed and unexposed areas of the resist, i.e. characterizes the profile of the resist mask formed, and is directly related to the resolution of the resist: the higher the contrast, the higher the resolution. The contrast is determined from a curve that characterizes the correlation of the normalized residual thickness of the resist in the developed area (normalized to the initial thickness of the resist) with the logarithm of the dose. Contrast g is the slope of the given curve.

The term "resist" used to describe the present invention, in the field of micro- and nanoelectronics, refers to a coating used as protection during subsequent operations in the formation of a structure in the lithography process. The resist material shall be sensitive, for example, photosensitive, to the exposure to any radiation (e.g., optical, X-ray, an ion or electron beam), which, under the effect of this radiation, reveals in a change in its physicochemical properties, e.g., solubility.

Sensitivity is an important characteristic of a resist and is a minimum dose of radiation that shall be delivered to a resist region to ensure its complete development (complete removal of the exposed resist) within a reasonable time (usually 5-10 min).

The term "exposure" used to describe the present invention refers to the effect of radiation or a stream of elementary particles, in particular electrons, on the resist material.

The term "developing" used to describe the present invention refers to the treatment of a resist subjected to the exposure, with a solvent capable of dissolving and removing the resist material from the exposed areas.

The term "mask" used to describe the present invention refers to a relief structure that is formed on the surface of a substrate from a resist layer after it has been exposed and developed. Typically, the mask is a layer of the resist with holes of a certain shape. The shape and size of the holes determine the shape of the elements of micro- or nano- electronic or optical components that will be formed on the surface of the substrate in the lithography process.

The term "lift-off, also lift-off lithography, used to describe the present invention, refers to a method of forming micro- or nano- electronic or optical components on the surface of a substrate, wherein a mask having holes is formed on the surface of the substrate (by depositing a resist film, exposing particular areas of the film to radiation and then developing to form a mask), then a layer of a substance (usually a metal), from which micro- or nano- electronic or optical components shall be formed, is applied over the mask, followed by removing the mask, with leaving the applied substance in the form of a relief structure on the surface of the substrate in those places where the holes of the mask have been, while the substance that have been present in those places where the mask had no holes, i.e. on the surface of the unexposed resist, is removed along with the mask (the so-called "lift-off). Thus, the mask defines the shape of the resulting relief structure. In general, for accurate removal of the resist, the resist film shall be two or more times thicker than the layer of the applied substance, and, in addition, the walls of the resist shall have a negative slope, which will exclude the possibility of their coating with the material applied. This process is an alternative to etching, and, therefore, it is used for materials that are difficult to etch.

The term "etching" used to describe the present invention refers to the step of the lithographic process that consists in removing a portion of the material of the substrate from the areas not protected by the resist mask, i.e. in those areas where the mask has holes. Etching can be wet (liquid) and dry. Wet etching means the treatment with a liquid capable of dissolving the substrate material, while dry etching is the treatment of the substrate with plasma excited by a high-frequency electric field. Dry etching includes, but is not limited to, etching with oxygen-containing plasma, halogen-containing plasma (in particular, chlorine- and/or fluorine- containing plasma), and ion beam etching.

The term "doping" used to describe the present invention refers to the incorporation of small amounts of material into a substrate in order to change its properties in a controllable manner.

The methods of the present invention can be carried out using known equipment. Non limiting examples will be presented below.

In one embodiment of the present invention, polysaccharide compounds are used as the photosensitive resist. However, the present invention in principle is not limited to polysaccharide compounds only. Without wishing to be bound by a particular theory, the present inventors believe that any high molecular weight material having the following combination of properties can be used as a resist in the present invention: a decrease in the average molecular weight when exposed to electromagnetic radiation (including the stream of elementary particles), an increase in solubility with a decrease in the average molecular weight, and the ability to form chelate complexes with transition elements.

Applying a resist film of a polysaccharide compound onto a substrate can be accomplished by methods known in the art. For example, a solution of a polysaccharide compound of a suitable concentration in a suitable solvent is prepared, applied on a substrate, and then is dried. In an illustrative embodiment, a solution of the polysaccharide compound is prepared in water, another inorganic or organic solvent. The solvent for preparing the solution of the polysaccharide compound is selected such as to dissolve the polysaccharide compound. In a particular illustrative embodiment of the present invention, the concentration of the solution of the polysaccharide compound to be applied on the substrate is from 1% to 10%, depending on the molecular weight of the polysaccharide compound and the cation of the polysaccharide compound. Without wishing to be bound by a particular theory, the inventors believe that the lower the molecular weight of the polysaccharide compound, the higher the concentration of the solution to be applied on the substrate shall be in order to achieve sufficient viscosity. For each specific polysaccharide compound of a particular molecular weight, the concentration of the solution shall be adjusted in order to provide a proper thickness of the film under given rotation conditions when applying the film and specific substrate size. In one illustrative embodiment, applying the film of the polysaccharide compound on the substrate is carried out using a spin coating technique, which allows providing a uniform film of a particular thickness. In a particular illustrative embodiment, applying the film of a polysaccharide compound is performed using centrifugal force. In one particular embodiment, applying the film of a polysaccharide compound is performed by centrifugation. In a more particular embodiment, applying the film of a polysaccharide compound is carried out using a spin coater.

In one optional embodiment of the present invention, prior to applying, the solution of a polysaccharide compound is further purified using known techniques. In one illustrative embodiment, prior to applying, the solution of a polysaccharide compound is further centrifuged. In another illustrative embodiment, prior to applying, the solution of a polysaccharide compound is further filtered.

In one illustrative embodiment, upon applying to the substrate, the film of a polysaccharide compound is dried. In a particular embodiment, upon applying to the substrate, the film of a polysaccharide compound is dried in the air flow.

In one optional embodiment, upon applying the film, prior to the exposure, the substrate having the film applied thereon is subjected to a further treatment. In one illustrative embodiment, the substrate having the film applied thereon is subjected to a heat treatment. In one particular illustrative embodiment, the substrate having the film applied thereon is heated. In another particular illustrative embodiment, the substrate having the film applied thereon is cooled. In a particular embodiment, the substrate having the film applied thereon is heated to a temperature above the glass transition temperature of the polysaccharide compound. In another illustrative embodiment, the substrate having the film applied thereon is treated with a solution comprising at least one transition element, in particular a salt of the transition element. In a particular embodiment, treating the substrate having the film applied thereon with a solution comprising at least one transition element allows easy removing the developed film from the substrate and transferring it to another surface. In another illustrative embodiment, the substrate having the film applied thereon is treated with at least one organic or inorganic substance. In one particular embodiment, the organic substance is an organic solvent. In a more particular embodiment, the organic substance is an alcohol. In an even more particular embodiment, the alcohol is a polyhydric alcohol. In an even more particular embodiment, the organic substance is glycerol. In another particular embodiment, the inorganic substance is a salt, in particular a carbonate salt. In another particular embodiment, the inorganic substance is an alkali metal salt. In an even more particular embodiment, the inorganic substance is an alkali metal carbonate, in particular sodium carbonate.

In one embodiment, the film of a polysaccharide compound is exposed. In a particular embodiment, pre-defmed regions (areas) of the film of a polysaccharide compound are exposed. Exposing the polysaccharide compound results in decreasing the molecular weight of the polymer chains (depolymerization), which leads to the increase of the solubility of the polysaccharide compound. Exposing the film of the polysaccharide compound is carried out by known methods. In one illustrative embodiment, exposing the film of a polysaccharide compound is performed with a stream of elementary particles. In a particular illustrative embodiment, the stream of elementary particles is a stream of electrons (an electron beam). In one illustrative embodiment, the stream of electrons is provided using an electron microscope. In one illustrative embodiment, the stream of electrons is provided using an electron beam (electron) lithography system.

In another illustrative embodiment of the present invention, exposing the film of a polysaccharide compound is performed by electromagnetic radiation. In a particular illustrative embodiment, the electromagnetic radiation is radiation of ultraviolet range (UV radiation). In one particular illustrative embodiment, the UV radiation is "deep" UV radiation (deep ultraviolet (DUV)) with a wavelength of 248 nm. In an illustrative embodiment, "deep" UV radiation is provided by a laser. In a particular embodiment, the laser is a Kr/F (248 nm) excimer laser. In another particular illustrative embodiment, UV radiation is "extreme" UV radiation (extreme ultraviolet EUV) with a wavelength of 10-121 nm. In a more particular embodiment, exposing is performed by extreme UV radiation with a wavelength of about 13.5 nm. In another particular illustrative embodiment, the electromagnetic radiation is X-ray radiation with a wavelength of 10³-10 nm. In another particular illustrative embodiment, the electromagnetic radiation is gamma radiation with a wavelength of less than 10³ nm.

Without wishing to be bound by a particular theory, the present inventors believe that exposing involves the destruction of the polymer chains of the polysaccharide compound in the resist film with obtaining oligomers having a lower molecular weight and, accordingly, higher solubility compared to the parent polysaccharide compound.

In one embodiment, upon exposing, the film is contacted with a solution of a transition element to develop the exposed areas of the film. In a particular embodiment, developing the exposed areas of the film is carried out with a solution of a salt of a transition element with obtaining a resist mask on the surface of the substrate. The preparation of the solution of a salt of a transition element is carried out by known methods. In an illustrative embodiment, a solution of a salt of a transition element of a certain concentration is prepared, the pH of the solution is determined, and, if necessary, the pH is adjusted to a required value using appropriate methods. Without wishing to be bound by a particular theory, the inventors believe that ions of transition elements present in the developer solution are chemically reactive and interact with the film of a polysaccharide compound to form a chelate complex. Such a chelate complex is insoluble in water and organic solvents, because the protonated groups of the polysaccharide molecule are occupied by ions of the transition elements. The process of developing the exposed resist is based in general on a balance between two conflicting processes: the dissolution of the polymer (a polysaccharide compound) and the formation of an insoluble complex of the polysaccharide compound with ions of a transition element. Both processes depend on the average molecular weight of the polysaccharide compound, where the molecular weight can be locally altered by exposing to electromagnetic radiation (including exposing to an electron beam). Due to the fact that exposing the polysaccharide compound results in a decrease in the molecular weight of the polymer chains, the masses of the latter are in a range in which the dissolution dominates over chelation. The unexposed film, on the contrary, primarily interacts with the ions of the transition element, due to which it becomes insoluble. Thus, the solution of a transition element acts as an inhibitor of the dissolution.

In other words, when the resist based on the polysaccharide compound is exposed, the destruction of the polymer chains of the polysaccharide compound occurs in the exposed areas of the resist, which leads to a decrease in the average molecular weight of the polymer chains, and, as a result, treating the resist with a developer solution leads to the dissolution of the resist material in the exposed areas only, while the unexposed film of the polysaccharide compound does not dissolve. The inventors believe that the absence of the dissolution of the unexposed resist is due to the fact that the ions of the transition elements in the developer solution chelate the polymer chains of the polysaccharide compounds, which results in the stabilization of the unexposed film of the polysaccharide compounds and the decrease of the dissolution rate of the film when it is treated with a developer solution.

The implementation of the method requires decreasing an average molecular weight of the resist material when it is exposed, i.e. the process of destruction of polymer chains of the resist material shall dominate over the process of crosslinking of the polymer chains of the resist material with each other, and, in addition, the resist material shall be characterized by an increase in solubility with a decrease in molecular weight. Further, the resist material shall be capable of forming a chelate complex with ions of transition elements. Accordingly, for the purposes of the present invention, a high molecular weight material having the following combination of properties is suitable as a resist: decreasing a molecular weight upon exposing, increasing solubility with decreasing a molecular weight, and the ability to form a chelate complex with ions of transition elements. The polysaccharide compounds used in the present invention have said combination of properties. The inventors believe that the ability of polysaccharide compounds to form chelate complexes with ions of transition metals is due to the presence in the molecules of polysaccharide compounds of free functional groups, in particular amino groups, hydroxyl, carboxyl groups.

The profile of the developed exposed area can be characterized by the following parameters: the average residual thickness of the exposed area of the resist versus the average residual thickness of the unexposed area of the resist, the shape of the exposed area upon developing, in particular the slope of the wall relative to the substrate.

In one illustrative embodiment, the solution of a salt of a transition element is hot (heated), i.e. has a temperature higher than the ambient temperature, or cold (chilled), i.e. has a temperature below the ambient temperature. In one illustrative embodiment, the use of a cold solution of a salt of a transition element to develop the exposed resist provides improved resolution of the method of the present invention. In another illustrative embodiment, the use of a hot solution of a salt of a transition element to develop the exposed resist provides increasing the reaction rate.

In one embodiment, developing is followed by treating the substrate having a resist mask applied thereon. Treating the substrate having the resist mask applied thereon is carried out by known methods. In one exemplary embodiment, the substrate having the resist mask applied thereon is treated by etching to remove the surface layer of the substrate to a specific depth. In a particular embodiment, etching is wet etching. In a more particular embodiment, wet etching is treating the substrate with a liquid. In another particular embodiment, etching is dry etching. In a more particular embodiment, dry etching is ion (ion-plasma) etching. In a more particular embodiment, dry etching is treating the substrate with plasma.

In another illustrative embodiment, treating the substrate having a resist mask applied thereon is performed by depositing a material onto the substrate having a resist mask applied thereon. In a particular embodiment, the deposition is metal spraying. In a more particular embodiment, the deposition is vacuum spraying.

In another illustrative embodiment, treating the substrate having the resist mask applied thereon is performed by doping. In another illustrative embodiment, treating the substrate having the resist mask applied thereon is performed by any combination of said treatment methods.

In one embodiment, the mask is removed from the surface of the substrate with obtaining a relief pattern (image) on the substrate. Removing the mask from the surface of the substrate with obtaining a relief pattern on the substrate is carried out by known methods. In one illustrative embodiment, removing the mask from the surface of the substrate is carried out by water treatment. In another illustrative embodiment, removing the mask from the surface of the substrate is carried out by treating with a solution that is free of transition elements. In a particular embodiment, the solution that is free of transition elements is a solution of an acid. In a more particular embodiment, the solution of an acid is a solution of a weak acid. In an even more particular embodiment, the solution of an acid is a solution of formic acid. In an even more particular embodiment, the solution of an acid has a concentration of 0.01 to 0.1% wt or 0.01 to 0.1% vol. In another particular embodiment, the solution that is free of transition elements is a solution of a salt other than a salt of a transition element. In a more particular embodiment, the solution that is free of transition elements is a solution of sodium carbonate, preferably with a concentration of 100 mM. Removing the resist mask with a solution of an acid involves destroying the chelate complex of the polysaccharide compound with ions of transition elements, which is due to low pH values (acidic medium), leading to the dissolution of the resist film. When the resist mask is removed with water, the ions of the transition elements are diffused into water, resulting in destroying the chelate complex of the polysaccharide compound and dissolving the film of the polysaccharide compound. Said treatment of the substrate having the mask applied thereon allows fast and complete removal of the resist mask from the surface of the substrate with obtaining a high-resolution relief pattern on the substrate.

One of the non-limiting examples of a combination of the conditions which allow obtaining simultaneously high contrast, complete removal of exposed areas and minimal removal of unexposed areas, as well as providing the possibility of lift-off lithography, represents the following combination of the steps:

- contacting a film of a chitosan compound with about 400 mM aqueous solution of NiCh for about 5 minutes at a pH of about 5.5;

- contacting the film of the chitosan compound with about 400 mM aqueous solution of N1SO4 for about 5 minutes at a pH of about 5.5;

- rinsing with water for about 30 seconds.

In general, based on the principles described herein, a person skilled in the art will be able to select suitable conditions for carrying out the proposed methods, depending on the object to be solved.

The following are examples of implementation of the present invention. The present invention is not limited to the presented examples.

Examples General procedure

Preparation of the film.

A polysaccharide compound was dissolved in deionized water or MQ water to obtain a solution of a certain concentration (from 1 to 10%, depending on the molecular weight of the polysaccharide and the cation of the polysaccharide compound: the lower the molecular weight, the higher the concentration of the solution shall be to achieve a sufficient viscosity). Each specific polysaccharide compound of a particular molecular weight requires selecting a concentration of the solution in order to ensure a proper film thickness under given conditions of rotation and specific size of the substrate. Then the resulting solution was applied on a silicon dioxide substrate 5 mm thick using a spin coater at a rotation speed of 3500 rpm with an acceleration of 3500 rpm/(min*s) to obtain a film of a polysaccharide compound of a certain thickness. In some cases, prior to applying on the substrate, the solution for applying a film was further filtered to remove impurities: using centrifugation at 13,200 rpm (15,000 g) for 10 min, centrifugation in a test tube with a 100 nm filter, or filtration through a 200 nm syringe filter. It has been found that storing the solution for several months prior to applying a film does not affect the properties of the resist, but only changes the viscosity of the solution, which can result in an improper film thickness. Aging of a dry film, on the other hand, can significantly affect the processes of development and lift-off lithography.

Exposure.

Next, the substrate with the applied film was exposed to an electron beam or electromagnetic radiation. Electron beam exposure was performed using an electron lithography system. The accelerating voltage was kept constant at a value of 50 kV. The beam currents were in the range of 50 pA to 10 nA, which, in combination with a change in the irradiation time, allowed providing exposure doses in the range of 20 to 15,000 C/cm². The exposure to electromagnetic radiation of the ultraviolet range (deep ultraviolet) was performed using a femtosecond krypton-fluorine Kr/F (248 nm) laser working at 20 mJ/cm² energy density.

Development.

After the exposure, the film was developed in Petri dishes fixed on the orbital shaker working at a speed of 200 rpm. All tests were carried out at a temperature of 22 °C.

Metal deposition.

The deposition was carried out by vacuum spraying a titanium Ti layer 1 nm thick (bottom layer) and a palladium Pd layer 11 nm thick (upper layer) on a substrate having the resist mask applied. Removal of unexposed film and lift-off lithography.

Removing the film of the unexposed resist was carried out using a highly diluted solution (with a concentration of 0.1%) of formic acid, deionized water, or a solution of sodium carbonate NaiCCb with a concentration of 100 mM. It shall be noted that changing the ionic aqueous medium significantly affects the development process, and, therefore, the developer solution shall be prepared immediately before development.

Microscopy.

A Leica optical microscope was used to characterize the steps of the described method. To analyze the morphology, thickness, shape of the exposed areas, bottom cleanliness, and mechanical properties of the film after various types of the treatment, a Bruker Multimode V8 atomic force microscope was used in the Scan-Asist-Air and PeakForce-HR modes. Soft tips with spring constant k = 0.4 N/m were used.

Some of the tests carried out in accordance with the above procedure are described in more detail below.

Example 1.

A solution of 165 kDa chitosan formate in water was prepared, applied on a substrate in the form of a film, and the film was exposed to UV radiation according to a specific pattern. The development was carried out in two steps: first with an aqueous solution of NiCk (400 mM, pH 5.5, 5 min), then with an aqueous solution of M2SO4 (400 mM, pH 5.5, 5 min). After the development, rinsing with water was carried out for 30 seconds and a metal was sprayed. The unexposed film was removed with a 0.1% solution of formic acid. The optical microscope photograph of the pattern formed on the substrate is shown in FIG. 1(b).

Example 2.

This example is similar to Example 1, wherein, instead of 165 kDa chitosan formate, 65 kDa chitosan acetate was used and the exposure was performed with an electron beam. The optical microscope photograph of the pattern formed on the substrate is shown in FIG. 1(b).

Example 3.

This example is similar to Example 2, wherein the development was carried out with 400 mM solution of NiCh with different pH (5.0, 5.5, 6.0, 6.5, 7.0, 7.5) for 10 minutes. The dose tests for each pH are shown in FIG. 9, and the data obtained from the analysis of these tests are presented as a graph in FIG. 2(b). The graph shows that when the pH of the developer solution is less than 5, the dissolution of the exposed and unexposed resist is observed even at a very small exposure dose, which is due to the release of the ions of the transition element that chelate the polysaccharide compound from the unexposed film, leading to the dissolution of the unexposed resist. At a pH greater than 7.5 under the test conditions, dissolution of the exposed resist stops. As can be seen from the graph, at pH 6.5 and more, complete development of the exposed resist in an acceptable time requires higher doses of radiation during the exposure than at a lower pH.

Example 4.

This example is similar to Example 2, wherein the development was carried out for 5 min with an aqueous solution of NiCh with a pH of 5.5 with various concentrations: 5, 10, 25, 60, 90, 200, 500, 900, 5,000 and 9,000 mM. This example is illustrated by the graph in FIG. 2(d). The graph shows that increasing the concentration of the transition element in the developer solution enhances the contrast of the resist. Complete removal of the resist material from the exposed area and the absence of dissolution of the resist material in the unexposed area require the resist contrast being 0.6 or more. As can be seen from the graph, such contrast values are provided at a concentration of the developer solution of 60 mM or more.

Example 5.

This example is similar to Example 2, wherein 700 kDa chitosan acetate was used. The optical photographs of the structures on the substrate obtained as a result of lift-off lithography are shown in FIG. 3(a) and 3(c). FIG. 3(a) shows the structures obtained in the dose test involving increasing the exposure dose from the lower left corner to the upper right corner, where the dose changes slowly along the vertical, and changes quickly along the horizontal. It can be seen that changing the dose has provided almost the same results. FIG. 3(c) shows the minimum dimensions of the elements on the substrate that can be obtained under said conditions of carrying out the process.

Example 6.

This example is similar to Example 2, wherein 700 kDa chitosan acetate was used, the development was carried out with nickel chloride solution with a concentration of 2,500 mM. The structures obtained as a result of the lift-off lithography are shown in FIG. 3(b). It can be seen that developing with a high concentration solution of a transition element allows achieving a high resolution of the pattern formed on the substrate.

Example 7.

This example is similar to Example 2, wherein 700 kDa chitosan acetate was used and the films 90 and 200 nm thick were applied. The optical photographs of the structures obtained on the substrate as a result of the lift-off lithography in a dose test are shown in FIG. 4. It can be seen that at the film thickness of 200 nm, the edges of the pattern on the substrate are uneven and indistinct. Example 8.

This example is similar to Example 2, wherein chitosan acetate of various molecular weights was used for applying a film: 20, 65, 165, 200, and 700 kDa. For each molecular weight, a standard dose test was performed with a change in the exposure dose in the low (25- 750 pC/cm², current 50 pA) and high (500-15,000 pC/cm², current 10 nA) ranges. The data obtained are shown in FIG. 5. As can be seen, the molecular weight of the polysaccharide compound practically does not affect the properties of the polysaccharide compound as a resist.

Example 9.

This example is similar to Example 2, wherein films of various chitosan compounds of the same molecular weight of 165 kDa were applied: acetate, formate, glycolate, lactate, chitosan succinate and carboxymethyl chitosan. The data obtained are shown in FIG. 6. It can be seen that all the tested chitosan compounds allow providing a uniform film and complete removal of the exposed resist upon developing and the absence of dissolution of the unexposed one. The use of formate requires a longer time to prepare the solution. In case of chitosan succinate and carboxymethyl chitosan, a rather rapid dissolution of the film in water is observed even after chelation; therefore, it is necessary to adjust the time of rinsing with water after the development.

Example 9.

A solution of 65 kDa chitosan acetate in water was prepared and applied on a substrate in the form of films. The effect of the purity of the solution of a polysaccharide compound on the morphology of the resulting films was studied. In the first case, the solution was not subjected to an additional purification prior to applying; in the second case, the solution was centrifuged at 13,200 rpm (15,000 g) for 10 min prior to applying; in the third case, the solution was centrifuged in a test tube with a filter with a pore diameter of 100 nm, and in the fourth case, the solution was filtered through a 200 nm syringe filter. The photographs of the films obtained from said solutions are shown in FIG. 7. As can be seen, the film of chitosan acetate obtained from the solution filtered through a syringe filter with a pore diameter of 200 nm is characterized by the highest homogeneity and the minimum number of defects. Accordingly, the removal of impurities of up to 200 nm size from the solution of the chitosan compound prior to applying it on the substrate allows obtaining a more uniform film than the method lacking additional purification.

Example 10.

This example is similar to Example 2, wherein 700 kDa chitosan acetate was used, a metal was sprayed to a thickness of 20 nm, and the following solutions of salts of transition elements having the same concentration of 400 mM and pH 5.5 were used as developers: chloride, nitrate, acetate, sulfate and formate of nickel, copper sulfate, cobalt acetate alone or in a combination with a surfactant (Triton X-100), Mohr's salt. The development was carried out for 5 minutes. The results obtained are shown in FIG. 8. It can be seen that using only nickel formate does not allow achieving complete removal of the resist from the exposed area under the specified conditions, while the use of the solutions of the other salts of transition elements for the development allows providing selective removal of the exposed resist in the absence of the dissolution of the unexposed resist, followed by obtaining a high-resolution pattern on the substrate. However, in case of developing with a nickel formate solution, it is possible to select such conditions that, upon removing all the resist, can provide obtaining a distinct pattern on the substrate.

Example 11.

This example is similar to Example 2, wherein 700 kDa chitosan acetate was used and after the development (a) rinsing was not performed, (b) rinsing with water was performed for 30 seconds, (c) rinsing with water was performed for 10 minutes. The data obtained are shown in FIG. 10. As can be seen, the longer rinsing with water (10 min) after the development results in the significant deviation of the developed structure from the exposed template, because the ions of transition elements chelating the molecules of polysaccharide compounds are washed out from the film of the unexposed resist, and, accordingly, the unexposed areas dissolve.

Example 12.

This example is similar to Example 2, wherein the development was carried out (a) with 5 mM solution of nickel chloride with pH 5.5 for 5 min, (b) 2,500 mM and pH 5.5 for 5 min, (c) only with 400 mM solution of nickel chloride for 10 minutes or (d) successively with 400 mM solution of nickel chloride with pH 5.5 for 5 minutes and 400 mm solution of nickel sulfate for 5 minutes. The data obtained are shown in FIG. 11, which shows that the increase in the concentration of the ion of a transition element in the composition of the developer solution (from 5 mM in graph (a) to 2,500 mM in graph (b)) and the change in the anion in the developer solution (only chloride ion in graph (c) and the combination of chloride ion and sulfate ion in graph (d)) result in an increase in resist contrast.

Example 13.

This example is similar to Example 2, wherein 165 kDa chitosan succinate was used and the unexposed film was removed with water. The complete removal of the resist was observed within 1 min with obtaining a high resolution structure on the substrate.

Example 14. This example is similar to Example 2, wherein carboxymethyl chitosan was used and the unexposed film was removed with water. The complete removal of the resist was observed within 1 min with obtaining a high resolution structure on the substrate.

Claims

1. A method of developing exposed areas of a film of chitosan, a salt or derivative thereof, applied on a substrate, the method comprising: contacting the film of chitosan, a salt or derivative thereof, which has been applied on the substrate and exposed to, with a solution comprising at least one transition element.

2. The method of claim 1, wherein the exposed areas are areas of the film, which are irradiated by a stream of elementary particles, preferably by an electron beam, and/or by electromagnetic radiation, preferably by deep UV radiation, extreme UV radiation, gamma radiation or X-ray radiation.

3. The method of claim 1 or claim 2, wherein the film has a thickness of from 20 to 190 nm, preferably from 50 to 160 nm, more preferably from 90 to 150 nm.

4. The method of any one of claims 1-3, wherein the derivative of chitosan is an amino derivative, nitro derivative, sulfo derivative, halogen derivative, phosphoric acid derivative, ether, ester thereof.

5. The method of any one of the preceding claims, wherein chitosan is bee chitosan.

6. The method of claim 1, wherein the salt is a salt of a monobasic, dibasic, tribasic or tetrabasic acid.

7. The method of claim 1, wherein the salt is a salt of an organic acid, in particular a salt of a carboxylic acid, in particular a salt of formic, acetic or propionic acid or a mixture thereof.

8. The method of claim 1, wherein the salt of chitosan or another derivative of chitosan are selected from the group comprising chitosan acetate, formate, lactate, glycolate, succinate, chloride, citrate, phthaloyl chitosan and carboxymethyl chitosan.

9. The method of any one of the preceding claims, wherein the transition element is a d-block element or f-block element.

10. The method of any one of the preceding claims, wherein the transition element is a period 4 transition element, a period 5 transition element, a period 6 transition element or a period 7 transition element.

11. The method of any one of the preceding claims, wherein the transition element is selected from the group comprising zinc, nickel, copper, cobalt, iron.

12. The method of any one of the preceding claims, wherein the solution comprising at least one transition element is a solution of a salt of at least one transition element.

13. The method of claim 12, wherein the salt of at least one transition element is selected from the group comprising a salt of an inorganic acid and a salt of an organic acid.

14. The method of claim 12 or 13, wherein the salt of at least one transition element is selected from the group comprising a chloride, nitrate, sulfate, formate, acetate, Mohr’s salt (ammonium iron(II) sulfate).

15. The method of any one of the preceding claims, wherein a concentration of the at least one transition element in the solution is at least 1 mM, preferably at least 20 mM, more preferably at least 200 mM.

16. The method of any one of the preceding claims, wherein the solution comprising at least one transition element has a pH of from 4 to 7.5, preferably about 5.5.

17. The method of any one of the preceding claims, wherein the solution comprising at least one transition element further comprises organic substances, in particular solvents, polymers, surfactants.

18. The method of any one of the preceding claims, wherein contacting the film with the solution comprising at least one transition element is performed for a time period of from 10 s to 60 min, preferably from 5 to 10 min, most preferably about 5 min.

19. The method of any one of the preceding claims, further comprising a step of contacting the film with a second solution comprising at least one second transition element, which is other than the first transition element.

20. The method of claim 19, comprising contacting the film of chitosan sequentially with a solution of nickel chloride and a solution of nickel sulfate.

21. The method of any one of the preceding claims, further comprising a step of washing the film.

22. The method of claim 21, wherein the washing step is performed for a period of time of from 10 to 60 seconds.

23. The method of any one of the preceding claims, further comprising a step of drying.

24. The method of any one of the preceding claims, wherein the substrate is or comprises carbon nanotubes, organic semiconductors, a protein, lipid structures, a DNA, biopolymer fibers, bacterial nanowires or any combination thereof.

25. The method of any one of the preceding claims, comprising the following sequential steps:

- contacting the film of the chitosan compound with about 400 mM aqueous solution of NiCk for about 5 minutes at a pH of about 5.5;

- contacting the film of the chitosan compound with about 400 mM aqueous solution of N1SO4 for about 5 min at a pH of about 5.5; - rinsing with water for about 30 seconds;

- drying.

26. Use of a solution comprising at least one transition element as a developer for exposed areas of a film of chitosan, a salt or derivative thereof.

27. A method of forming at least one component on a substrate, the method comprising the following steps: a. applying a film of chitosan, a salt or derivative thereof on the substrate; b. exposing pre-defmed areas of said film to a stream of elementary particles and/or electromagnetic radiation (exposure); c. developing the exposed areas of the film by carrying out the method of any one of claims

1-25 to obtain the substrate having a mask applied thereon; d. treating the substrate having a mask applied thereon by performing etching, depositing, doping or any combination thereof; e. removing the mask from the surface of the substrate to obtain the at least one component formed on the substrate, wherein the component is a micro- and/or nano- electronic and/or optical component.

28. The method of claim 27, wherein the stream of elementary particles is an electron beam, and/or the electromagnetic radiation is deep UV radiation, extreme UV radiation, gamma radiation or X-ray radiation.

29. The method of claim 27 or claim 28, wherein the film has a thickness of from 20 to 190 nm, preferably from 50 to 160 nm, more preferably from 90 to 150 nm.

30. The method of any one of claims 27-29, wherein applying the film on the substrate at step a. is performed from a solution of chitosan, a salt and derivative thereof, wherein the solution is preliminarily filtered or subjected to centrifugation.

31. The method of any one of claims 27-30, further comprising after step a.: temperature treating the substrate, and/or treating the substrate with a solution comprising at least one transition element, and/or treating the substrate with at least one inorganic or organic substance.

32. The method of claim 31, wherein the organic substance is glycerol.

33. The method of any one of claims 27-32, wherein etching is wet etching or dry etching.

34. The method of any one of claims 27-33, wherein removing the mask from the surface of the substrate is performed by exposing to water or to a solution, preferably a solution, which is free of transition elements, preferably to an aqueous solution.

35. The method of claim 34, wherein the solution, which is free of transition elements, is a solution of an acid or a salt, which is other than a salt of a transition element.

36. The method of claim 35, wherein the solution of an acid has a concentration of from 0.01 to 0.1% wt.

37. The method of any one of claims 35-36, wherein the acid is a monobasic, dibasic, tribasic or tetrabasic acid.

38. The method of any one of claims 35-37, wherein the acid is an organic acid, preferably a carboxylic acid, in particular formic, acetic, propionic acid or a mixture thereof.

39. The method of any one of claims 35-38, wherein the acid is a weak acid.

40. The method of any one of claims 35-39, wherein the acid is formic acid.

41. The method of claim 34 or 35, wherein the solution, which is free from transition elements, is a solution of an alkali metal carbonate, preferably having a concentration in a range of from 50 to 150 mM.

42. The method of any one of claims 27-41, which is a lithography method, in particular a lift off lithography method.

43. The method of any one of claims 27-42, comprising performing the steps more than once to obtain a structure comprising more than one layer of the components.

44. The method of any one of claims 27-43, wherein the substrate h at least one component applied thereon is an integrated microcircuit.