WO2020114970A1

WO2020114970A1 - Fluoropolymer having alicyclic repeating units

Info

Publication number: WO2020114970A1
Application number: PCT/EP2019/083316
Authority: WO
Inventors: Mattia Bassi; Laura PONTA
Original assignee: Solvay Specialty Polymers Italy S.P.A.
Priority date: 2018-12-04
Filing date: 2019-12-02
Publication date: 2020-06-11

Abstract

The present invention pertains to a fluoropolymer having alicyclic structures in its main chain which possess peculiar molecular weight, intrinsic viscosity and carboxylic end groups concentration, which has been found useful for use in lithographic processes, to a method of patterning a layer of the same on a substrate so as to form a fluoropolymer patterned coating adhered to said substrate

Description

FLUOROPOLYMER HAVING ALICYCLIC REPEATING UNITS Cross-Reference to Related Application

[0001] This application claims priority to European Patent Application No.

18210095.8 filed on December 4, 2018, the whole content of this application being incorporated herein by reference for all purposes.

Technical Field

[0002] The present invention pertains to a fluoropolymer having alicyclic

structures in its main chain which has been found useful for use in lithographic processes, to a method of patterning a layer of the same on a substrate so as to form a fluoropolymer patterned coating adhered to said substrate.

Background Art

[0003] Fluoropolymers have been already used in the past in lithographic

processes, and more specifically as protective layers in certain

photolithographic methods, whereas the creation of a sacrificial

fluoropolymer layer is required for protecting/preserving chemical integrity of substrate during either radiation exposure of photoresist(s) and/or etching of photoresist(s) layers.

[0004] For instance, US9091913 discloses a method for producing a spatially patterned structure on a substrate, including the steps of:

(1) forming a layer of a material on at least a portion of a substructure of said spatially patterned structure;

(2) forming a barrier layer of a fluorinated material on said layer of material to provide an intermediate structure;

(3) forming a layer of a photoresist on said barrier layer;

(4) exposing said photoresist to spatially patterned radiation;

(5) developing said photoresist to substantially remove one of exposed or unexposed regions of said photoresist to provide a pattern of uncovered regions of barrier material between regions covered by photoresist; (6) removing portions of said barrier material that are uncovered by said photoresist to provide a pattern of uncovered regions of said layer of material;

(7) exposing said intermediate structure to at least one of a second material or radiation to cause at least one of a chemical change or a structural change to at least a portion of said intermediate structure; and

(8) removing remaining portions of said barrier layer using a fluorinated solvent. In the said method, the fluorinated material barrier layer substantially protects said layer of said material from chemical and structural changes during said forming said layer of said photoresist and said exposing said photoresist. The fluorinated material may be a fluorinated polymer, such as notably materials known under brand names CYTOP® or TEFLON®-AF which are known for including alicylic structure in main chain, or may be fluorinated compounds of formula C_nF₍2_n+2₎; while this document acknowledges that the presence of other chemical moieties beside CF2 may be tolerated, it specifically teaches that -COOFI groups would greatly alter the solubility property and therefore -COOH

compounds (carboxylic acids) may not be suitable. The method of this document can be used for creating diode junctions.

[0005] In this area, nonetheless, for a fluorinated polymer to be particularly

adapted to be used in a lithographic process, the said fluorinated polymer shall satisfy quite diverging requirements; from one side, this fluorinated polymer shall exhibit sufficient adhesion to the substrate on which it will be applied, so as to form a cohesive protective layer, which is not accidentally removed, inadvertently exposing substrate to be protected, or detaching in uncontrolled manner during handling of intermediate structures including said protective layer. At the same time, the said protective layer formed from the mentioned fluorinated polymer shall possess solubilization kinetics so as to enable easy and effective removal by action of appropriate solvents in time-effective manner.

[0006] While certain materials such as the aforementioned CYTOP® or

TEFLON®-AF have been tested in this field of use, there remains a need in this area for providing an improved fluorinated polymer possessing an optimized performances profile.

Summary of invention

[0007] .A first object of the present invention is hence a fluoropolymer comprising:

- repeating units having an alicyclic structure in main chain of said fluoropolymer and derived from at least one fluoromonomer A, and, optionally,

- repeating unit derived from at least one fluoromonomer B different from fluoromonomer A,

said fluoropolymer:

- possessing an intrinsic viscosity of at most 35 cc/g,

- possessing a weight averaged molecular weight (M_w) of at most 220 000; and

- comprising an amount of carboxylic end groups of at least 8.5 mmol/kg, said fluoropolymer being referred hereunder as polymer (F).

[0008] The Applicant has surprisingly found that by carefully selecting a polymer (F) possessing said alicyclic structure in the main chain, fulfilling the above recited requirements of intrinsic viscosity, weight averaged molecular weight and content of carboxylic end groups, such fluoropolymer possesses an outstanding balance of adhesion towards several

substrates, and yet possessing adequate solubilization and removal ability to render the same particularly useful for use in lithographic processes. Description of embodiments

[0009] The polymer (F)

[0010] As used herein, the expression“fluoromonomer” is to be understood to encompass monomers possessing at least one fluorine atom bound to a carbon atom. The said fluoromonomer may or may not comprise hydrogen atom(s) bound to its carbon atoms. When the fluoropolymer does not comprise any hydrogen atom(s) bound to its carbon atoms, said

fluoromonomer will be referred to as a“perfluoromonomer”.

[0011] As said, polymer (F) comprises repeating units having an alicyclic

structure in main chain of said fluoropolymer and derived from at least one fluoromonomer A. The fluoromonomer A of the polymer (F) of the present invention specifically includes two types of fluoromonomers, i.e.

fluoromonomers having an alicyclic structure in their monomeric form and fluoromonomers which do not have an alicylic structure in their monomeric form, but which upon cyclopolymerization provide for an alicyclic structure in the resulting repeating unit of polymer (F).

[0012] Fluoromonomer A is preferably a perfluoromonomer.

[0013] The repeating unit derived from said fluoromonomer A is preferably

represented by any one of the following formulae (1) to (3):

Rf8

Rf 5 R f6

(1) (2) (3) wherein:

in the formula (1 ) each of p, q and r which are independent of each other, is 0 or 1 , each of R^f1 and R^f2 which may be the same or different, is a fluorine atom, a C1 -C5 perfluoroalkyl group or a C1 -C5 perfluoroalkoxy group, and R^f3 is a C1 -C3 perfluoroalkylene group, which may have a Ci- C5 perfluoroalkyl group or a C1 -C5 perfluoroalkoxy group, as a substituent; in the formula (2), s is 0 or 1 , each of R^f4, R^f5, R^f6 and R^f7 which may be the same or different, is a fluorine atom or a C1 -C5 perfluoroalkyl group, and R^f8 is a fluorine atom, a C1 -C5 perfluoroalkyl group or a C1 -C5

perfluoroalkoxy group, provided that R^f4 and R^f5 may be connected to form a spiro ring when s=0; and

in the formula (3), each of R^f9, R^f1°, R^f11 and R^f12 which may be the same or different, is a fluorine atom or a C1-C5 perfluoroalkyl group or a Ci- C5 perfluoroalkoxy group.

[0014] The structure of the repeating unit of the above formula (1) may be

advantageously derived from fluoromonomers which do not have an alicylic structure in their monomeric form, but which upon

cyclopolymerization provide for an alicyclic structure in the repeating unit derived therefrom. As said, in formula (1) above, the perfluoroalkylene group represented by R^f3 may have a C1-C5 perfluoroalkyl group or a Ci- C5 perfluoroalkoxy group bonded as a substituent. Further, generally, in the formula (1), when q=o, then r=1 and/or alternatively when q=1 , then r=0. Specific examples of repeating units of formula (1) include notably those represented by the following formulae (4) to (19):

[0015] Among repeating units of the above formula (1), preferred are repeating units of formula (4), as above detailed.

[0016] Recurring units of formula (4) are obtained advantageously from radical cyclopolymerization of perfluoro(3-butenyl vinyl ether) of formula (4A): CF₂=CF-0-CF2-CF2-CF=CF₂. [0017] Further, the structure of the repeating unit of the above formula (2) may be advantageously derived from a fluoromonomer having an alicyclic structure in its monomeric structure. Further, in a case where in the structure of the repeating unit of the formula (2), when the spiro ring formed by R^f4 and R^f5 when s=0, is a 4- to 6-membered ring, such a ring may contain an ether oxygen atom as an element constituting the ring, and such a ring may have a perfluoroalkyl group bonded as a substituent.

[0018] Specific examples of repeating units of formula (2) include notably those represented by the following formulae (20) to (30):

[0019] Among repeating units of the above formula (2), preferred are repeating units of formula (20), (21) and (26), as above detailed. Recurring units of formula (20), (21) and (26) are obtained advantageously from radical polymerization of perfluoro(2,2-dimethyl-1 ,3-dioxole) of formula (20A), perfluoro(1 ,3-dioxole) of formula (21 A), and 2,2,4-trifluoro-5- trifluoromethoxy-1 ,3-dioxole of formula (26A), respectively:

[0020] Further, the structure of the repeating unit of the above formula (3) may be advantageously derived from a fluoromonomer having an alicyclic structure in its monomeric structure.

[0021] Specific examples of repeating units of formula (3) include notably those represented by the following formulae (31) to (33):

[0022] Among repeating units of the above formula (3), preferred are repeating units of formula (31), as above detailed. Repeating units of formula (31) are derived from perfluoro(2-methylene-4-methyl-1 ,3-dioxolane) of formula (31A):

[0023] As said, polymer (F) may comprise repeating unit derived from at least one fluoromonomer B different from fluoromonomer A.

[0024] Fluoromonomer B may be selected from the group consisting of:

(a) C2-C8 perfluoroolefins such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP);

(b) hydrogen-containing C2-C8fluoroolefins, such as vinylidene fluoride (VDF), vinyl fluoride, trifluoroethylene (TrFE), hexafluoroisobutylene (HFIB), perfluoroalkyl ethylenes of formula CH₂=CH-R_fi , wherein R_fi is a C1-C6 perfluoroalkyl group;

(c) C₂-C8 chloro- and/or bromo-containing fluoroolefins such as

chlorotrifluoroethylene (CTFE);

(d) perfluoroalkylvinylethers (PAVE) of formula CF₂=CFOR_fi , wherein R_fi is a C₁-C6 perfluoroalkyl group, such as CF3 (PMVE), C₂F₅ or C3F₇;

(e) perfluorooxyalkylvinylethers of formula CF₂=CFOXo, wherein Xo is a C₁-C₁₂ perfluorooxyalkyl group comprising one or more than one ethereal oxygen atom, including notably perfluoromethoxyalkylvinylethers of formula CF₂=CF0CF₂0R_f2, with R_f2 being a C₁-C3 perfluoro(oxy)alkyl group, such as -CF2CF3, -CF2CF2-O-CF3 and -CF3; and

(f) functional perfluoro(oxy)alkylvinylethers of formula CF₂=CFOYo_, wherein Yo is a C₁-C₁₂ perfluoro(oxy)alkylene group, optionally comprising one or more than one ethereal oxygen atom, which comprises at least one functional group selected from the group consisting of -SO₂X, -COX, - PO₂X, with X being a halogen or a -OX_a group, with X_a being H, an ammonium group or a metal cation.

[0025] Fluoromonomer B is preferably a perfluoromonomer, and is more

preferably selected from the group consisting of C₂-C8 perfluoroolefins, and most preferably fluoromonomer B is tetrafluoroethylene (TFE).

[0026] Polymer (F) may comprise repeating units derived from monomers

different from fluoromonomer A and fluoromonomer B; notably, polymer (F) may comprise recurring units derived from fluorine-free monomers, such as alpha-olefins (e.g. ethylene, propylene, butenes, hexenes), vinyl monomers (e.g. optionally substituted styrene-type monomers;

(meth)acrylic monomers). Nevertheless, it is generally preferred for polymer (F) to consist essentially of monomers which are perfluorinated, that is to say which do not comprise any C-H moiety. Minor amounts (e.g. less than 1 % moles, preferably less than 0.1 % moles, with respect to overall moles of repeating units) of repeating units derived from hydrogen- containing monomers may be tolerated, without this significantly affecting performances of polymer (F). According to these embodiments, polymer (F) preferably essentially consists of:

- repeating units having an alicyclic structure in main chain of said fluoropolymer and derived from at least one fluoromonomer A which is perfluorinated; and, optionally,

- repeating unit derived from at least one fluoromonomer B different from fluoromonomer A, which is perfluorinated.

[0027] Polymer (F) is advantageously an amorphous polymer. The expression

“amorphous” is hereby used in connection with polymer (F) for designating polymers which possess a heat of fusion of less than 5 J/g, preferably less than 3, more preferably less than 2 J/g, when determined according to ASTM D3418.

[0028] As said, according to a first variant of the present invention, polymer (F) may be a homopolymer essentially consisting of repeating units having an alicyclic structure in main chain of said fluoropolymer and derived from a fluoromonomer A which is perfluorinated. Homopolymers consisting of repeating units derived from a fluoromonomer A selected from the group consisting of perfluoro(2-methylene-4-methyl-1 ,3-dioxolane), perfluoro(2,2- dimethyl-1 ,3-dioxole), perfluoro(1 ,3-dioxole), 2,2,4-trifluoro-5- trifluoromethoxy-1 ,3-dioxole and perfluoro(3-butenyl vinyl ether) are exemplary preferred embodiments of polymer (F) according to this variant of the invention.

[0029] It is understood that because of their structure, repeating units having an alicyclic structure in main chain of said fluoropolymer and derived from a fluoromonomer A will generally lead to a homopolymer which is

substantially amorphous, as above detailed.

[0030] According to other variants of the present invention, polymer (F) may

comprise repeating units derived from at least one fluoromonomer B;

these repeating units may or may not contribute to form crystalline domains in polymer (F).

[0031] Nevertheless, in general, when polymer (F) comprises repeating units derived from at least one fluoromonomer B, as detailed above, the respective amount of repeating units derived respectively from

fluoromonomer A and fluoromonomer B are adjusted so that polymer (F) is substantially amorphous. According to these embodiments, polymer (F) comprises (and preferably consists essentially of):

- from 20 to 95 % moles, preferably from 30 to 80 % moles, more preferably from 35 to 50 % moles, with respect to the total moles of repeating units of polymer (F), of repeating units having an alicyclic structure in main chain of said fluoropolymer and derived from at least one fluoromonomer A, as above detailed; and

- from 5 to 80 % moles, preferably from 20 to 70 % moles, more preferably from 50 to 65 % moles, with respect to the total moles of repeating units of polymer (F), of repeating units derived from at least one fluoromonomer B different from fluoromonomer A, as above detailed.

[0032] The expression“consisting essentially of when used in connection with polymer (F) and its constituting repeating units is to be understood to mean that defects, end chains, impurities, chains inversions or branchings and the like may be additionally present in the polymer (F) in addition to the recited repeating units, without these components substantially modifying the behaviour and properties of the polymer (F).

[0033] According to certain preferred embodiments of this variant, polymer (F) is a copolymer comprising:

- repeating units having an alicyclic structure in main chain of said fluoropolymer and derived from at least one fluoromonomer A which is perfluorinated, as above detailed, and

- repeating unit derived from at least one fluoromonomer B different from fluoromonomer A, which is perfluorinated, as above detailed.

[0034] More preferably, polymer (F) is a copolymer comprising:

- repeating units derived from at least one fluoromonomer A selected from the group consisting of perfluoro(2-methylene-4-methyl-1 ,3-dioxolane), perfluoro(2,2-dimethyl-1 ,3-dioxole), perfluoro(1 ,3-dioxole), 2,2,4-trifluoro-5- trifluoromethoxy-1 ,3-dioxole and perfluoro(3-butenyl vinyl ether); and

- repeating unit derived from tetrafluoroethylene (TFE). [0035] Most preferably, polymer (F) is a copolymer comprising:

- repeating units derived from 2,2,4-trifluoro-5-trifluoromethoxy-1 ,3-dioxole; and

- repeating unit derived from tetrafluoroethylene (TFE).

[0036] The intrinsic viscosity of polymer (F) can be determined using the

Solomon-Ciuta equation on the basis of dropping time, at 30°C, of a solution obtained by dissolving the polymer (F) in Fluorinert® FC72

(known for being perfluorohexane) at a concentration of 1 g/dl using a Ubbelhode viscosimeter.

[0037] As said, polymer (F) possesses an intrinsic viscosity of at most 36 cc/g, preferably at most 35, more preferably at most 34 cc/g, when determined in Fluorinert® FC72 (known for being perfluorohexane) as solvent at a temperature of 30 °C.

[0038] While lower boundary for intrinsic viscosity is not particularly limited, it would be preferred for polymer (F) to possess an intrinsic viscosity of at least 10, preferably at least 12, more preferably at least 15 cc/g,

Fluorinert® FC72 (known for being perfluorohexane) as solvent at a temperature of 30 °C.

[0039] The weight average molecular weight (M_w) of polymer (F) can be

determined by gel-permeation chromatography (GPC) following general procedure described in ASTM D5296, typically using methoxy- nonafluorobutane (C4F9OCH3) (notably commercially available as

NOVEC^® 7100) as solvent, and calibration curve based on polystyrene standards.

[0040] The expression“weight average molecular weight (M_w)” is hereby used according to its usual meaning, that is to say for designating :

wherein M, is the molecular weight of the polymer chain i, and N, is the number of polymer chains i having the said molecular weight M,.

[0041] As said, polymer (F) possesses a weight averaged molecular weight (M_w) of at most 220 000, preferably of at most 210 000, more preferably of at most 200 000. [0042] This being said, although lower boundaries for M_w are not particularly critical, it has been found that a weight averaged molecular weight (M_w) of at least 10 000, preferably at least 20 000, more preferably at least 30 000 is beneficial for providing adequate film-ability properties.

[0043] The expression“amount of carboxylic end groups” is hereby used to

encompass the overall amount of carboxylic chain end in polymer (F) which may be present under their acidic form (-COOH), their acyl halide form (-COXx, with X_x being F, Cl or Br, generally X_x being F) and their carboxylate form (-COOX_b, with X_b being a (alkyl)ammonium, or a metal cation). Methods for determining amounts of carboxylic end groups in polymer (F) are known; said amount can be determined pursuant to the methodology described in PIANCA, M., et al. End groups in

fluoropolymers. Journal of Fluorine Chemistry. 1999, vol.95, p.71-84.

[0044] As said, polymer (F) comprises an amount of carboxylic end groups of at least 8.2 mmol/kg, preferably at least 8.5 mmol/kg, more preferably at least 8.8 mml/kg.

[0045] Upper amount of carboxylic end groups is not particularly critical; it is

nonetheless understood that this amount is generally at most 30 mmol/kg, preferably at most 27 mmol/kg, more preferably at most 25 mmol/kg.

[0046] Polymers (F) possessing a viscosity within the above mentioned

boundaries are particularly adapted for being used in coating processes, leading to liquid coating compositions possessing adequate viscosities for processing according to said techniques.

[0047] Tuning of viscosity, molecular weight and carboxylic end groups

concentration may be achieved either during polymerization for

manufacturing polymer (F), by acting on relative concentrations of inorganic peroxide initiators leading to the said polar end groups and acting on concentration of growing chains (so further impacting

M_w/viscosity), chain transfer agents controlling M_w/viscosity but also introducing alternative chain terminations, and other polymerization parameters including monomers’ concentration, pressure, temperature, etc... Further, post-treatment methods, such as fluorination,

depolymerisation, irradiation, and the like, may be used for further increasing or decreasing M_w/viscosity and/or modify the nature of end groups.

[0048] The invention also pertains to a coating composition [composition (CC)] comprising polymer (F) as above detailed, and a liquid medium.

[0049] Generally, the said liquid medium comprises an organic solvent. The said organic solvent is preferably selected from the group consisting of organic solvents containing at least one fluorine atoms, including notably perfluoroalkanes, perfluoroethers, hydrofluoroethers, fluoro-amines, perfluoro-amines, fluoro-cyclic organic compounds, or mixtures thereof.

[0050] The concentration of polymer (F) in the said coating composition

[composition (CC)] is not particularly limited, and will be adjusted by one of ordinary skills in the art for coping with liquid viscosity requirements of the coating technique which will be used for actually applying the said composition (CC).

[0051] It is nevertheless understood that the advantageous solubility behaviour of the polymer (F) is particularly advantageous for providing compositions (CC) having high polymer (F) content, and which hence can be easily used for applying coatings of appreciable thickness in effective manner.

[0052] The invention further pertains to a method for producing a patterned

structure on a substrate, including the steps of:

(1) applying the composition (CC), as above detailed, on at least a portion of the substrate, and remove the liquid phase, so as to obtain a shielding layer of polymer (F) onto said substrate;

(2) patterning the said shielding layer of polymer (F) so as to obtain a patterned shielding layer of polymer (F) comprising a pattern of covered and uncovered regions;

(3) at least partially removing uncovered regions of said patterned shielding layer of polymer (F), so as to obtain a patterned structure comprising a pattern of a shielding layer of polymer (F) on said substrate.

[0053] The step (1) of applying the composition (CC) may be effected by

spreading said composition (CC) onto said substrate according to known coating techniques, including notably as doctor-blade coating, metering rod (or Meyer rod) coating, slot die coating, knife over roll coating, gap coating, spin coating and the like, so as to obtain a wet layer; subsequent at least partial removal of the liquid medium, as above detailed, would advantageously lead to the said shielding layer onto said substrate.

[0054] Step (2) comprises patterning the said shielding layer of polymer (F) so as to obtain a patterned shielding layer of polymer (F) comprising a pattern of covered and uncovered regions. Methods of achieving said patterning are not particularly limited. According to preferred embodiments, step (2) comprises:

a sub-step (2A) of forming a layer of a photoresist on said shielding layer, so as to obtain a photoresist layer;

a sub-step (2B) of exposing said photoresist layer to patterned radiation, so as to obtain a patterned photoresist layer comprising radiation-modified and non-radiation modified regions; and

a sub-step (2C) of substantially removing either of the said radiation- modified and non-radiation modified regions, so as to obtain a patterned shielding layer of polymer (F) comprising a pattern of photoresist-covered and photoresist-uncovered regions.

[0055] The choice of photoresist is not particularly limited. Photoresists well

known in the art can be used, including positive and negative photoresists, that is to say photoresists whereas exposure to radiation makes the same more easily removable, e.g. more soluble (so-called“positive”

photoresists) and photoresists whereas exposure to radiation makes the same less removable, e.g. less soluble, for instance via

crosslinking/polymerisation (so-called“negative” photoresists).

[0056] The step (2B) of exposing the photoresist to patterned radiation may be obtained by irradiating the photoresist layer obtained from step (2A) interposing a mask opaque to radiation and possessing a patterned structure between the radiation source and the said photoresist layer.

[0057] When a positive photoresist is used, step (2B) may provide for radiation- modified region of the photoresist layer which are chemically modified, e.g. to effect de-polymerization/degradation and hence have advantageously acquired significant solvent-solubility and non-radiation modified regions of the said photoresist layer which have not been affected, and which hence advantageously maintain appreciable solvent-resistance.

[0058] When a negative photoresist is used, step (2B) may provide for radiation- modified region of the photoresist layer which are cured and hence have advantageously acquired significant solvent-resistance and non-radiation modified regions of the said photoresist layer which are not cured, and which hence advantageously maintain appreciable solvent solubility.

[0059] In sub-step (2C), generally either of said radiation modified regions or said non-radiation modified regions of the photoresist layer are advantageously removed. Removal of said regions may be achieved by standard means; it is nonetheless understood that treatment with an organic solvent will be among preferred means for the removal of either of said radiation modified regions or said non-radiation modified regions. The organic solvent used in this sub-step (2C) will be selected by one of ordinary skills in the art depending on the nature of the photoresist, among those which preferably are not able to attack neither the underlying shielding layer of polymer (F).

[0060] Result of sub-step (2C) is hence a patterned shielding layer of polymer (F) comprising a pattern of photoresist-covered and photoresist-uncovered regions, whereas advantageously the photoresist-covered regions are regions of shielding layer covered by regions of the photoresist layer which have not been removed in sub-step (2C).

[0061] In step (3), uncovered regions of said patterned shielding layer of polymer (F) are at least partially removed, so as to obtain a patterned structure comprising a pattern of a shielding layer of polymer (F) on said substrate.

[0062] Said removal is generally obtained by using an appropriate solvent able to solubilize polymer (F) but which is unable to solubilize the patterned regions of the photoresist layer. Conditions in step (3) are advantageously adapted so as to enable solely uncovered regions of said patterned shielding layer of polymer (F) to be at least partially removed by said appropriate solvent.

[0063] The choice of the said solvent is not particularly limited; it can be notably selected from the group consisting of organic solvents containing at least one atom of fluorine, such as perfluoroalkanes, perfluoroethers, hydrofluoroethers, fluoro-amines, perfluoro-amines, fluoro-cyclic organic compounds, or mixtures thereof.

[0064] The method of the invention may comprise additional steps, wherein the patterned structure obtained in Step (3) is used as an intermediate structure for deposing and/or patterning and/or removing additional layers.

[0065] Notably, the method may comprise a step (4) of applying an additional coating layer of a material (M) on the patterned structure comprising a pattern of a shielding layer of polymer (F) on said substrate, so as to obtain a patterned structure comprising a pattern of the shielding layer of polymer (F) coated with material (M); and may comprise an additional subsequent step (5) of removing the said pattern of the shielding layer of polymer (F) coated with material (M) so as to obtain a patterned structure comprising corresponding negative pattern of layer of material (M).

[0066] Material (M) may be an organic semiconductor material, an organimetallic material, a biological material, a metallic material and the like.

[0067] Similarly, the choice of the substrate is not particularly limited, and will depend upon the intended use of the patterned structure. For instance, substrate made of polyimides (PI), polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polyetherimide (PEI), polyamideimide (PAI), glass, silicon, silicon oxide, transparent mixed oxides such as indium tin oxides (ITO), indium zinc oxide, aluminium-doped zinc oxide (AZO), indium-doped cadmium oxide; aluminium, gallium or indium-doped zinc oxide (AZO, GZA or IZO), formulations containing carbon nanotubes, graphene, silver nanoparticles; inherently conductive polymers such as polyanilines, PEDOTPSS.

[0068] Substrates are generally flattened in shape, and may have the form of sheets or films, including flexible films. Substrates may comprise electrodes or other types of electrical connections, including notably metallic electrodes of Cu, Al, Mo, Ag, Mg or alloys combining more than one of said metallic elements.

[0069] Should the disclosure of any of the patents, patent applications, and

publications that are incorporated herein by reference conflict with the present description to the extent that it might render a term unclear, the present description shall take precedence.

[0070] The present invention will be now described in more detail with reference to the following examples, whose purpose is merely illustrative and not limitative of the scope of the invention.

[0071] EXAMPLES

[0072] Raw materials

[0073] Determination of intrinsic viscosity of polymer (F)

Intrinsic viscosity (h) [cc/g] was determined using the Solomon-Ciuta equation (reproduced below), measuring dropping time, at 30°C, of a solution obtained by dissolving the polymer (F) in FLUORINERT^® FC72 (perfluorohexane) at a concentration of 1 g/dl using a Ubbelhode viscosimeter:

(Solomon-Ciuta equation)

c

where c is polymer concentration [g/dl], h_G is the relative viscosity, i.e. the ratio between the dropping time of sample solution and the dropping time of solvent, r|_sp is the specific viscosity, i.e. h_G -1.

[0074] Determination of carboxylic end groups of polymer (F)

Amount of carboxylic end groups were determined according to the method described in PIANCA, M., et al. End groups in fluoropolymers. Journal of Fluorine Chemistry. 1999, vol.95, p.71-84. Concentration of relevant chain ends are expressed as mmoles of groups per kg of polymer (F) and encompasses carboxylic end groups in their acidic form (-COOH), acyl halide form (-COF) and salified form (-COOX_b, with X_b being

(alkyl)amonium or metal cation).

[0075] Determination of the thickness of polymer (F) on the substrate

[0076] The thickness of polymer (F) to the substrate was determined by using a Filmetrics F50 Automated Film Thickness Mapping. The complex refractive index values of polymer (F) used for calculating the thickness from the reflectance spectra were n489 nm= 1.331 ; k489 nm = 0 n589 nm= 1.329; k589 nm^— 0, P656 nm- 1.328, k656 nm^— 0.

[0077] Determination of the adhesion of polymer (F) to substrate [0078] The adhesion of polymer (F) to the polyimide (PI) substrate was

determined according to the ASTM D3359 - 17 standard method. Four square glass substrates having size of 2.54 cm x 2.54 cm (1”x1”) coated with PI were thoroughly cleaned by 10 min immersion in an ultrasonic bath in isopropylic alcohol (IPA) followed from 5 min baking at 100°C. A layer having thickness of 1.5 pm of polymer (F) was then obtained by spin coating on each substrate a composition (CC) of the polymer (F) in Fluorinert® FC40 (1 ,1 ,2,2,3,3,4,4,4-nonafluoro-N-(1 ,1 ,2,2,3,3,4,4,4- nonafluorobutyl)-N-(1 ,1 ,2,2-tetrafluoroethyl)butan-1-amine; otherwise known as perfluorodibutylethylamine) at 8.5% w/w concentration, followed by baking for 10 min at 100°C. After obtaining the cuts and applying and removing the adhesive tape as indicated in the method B of the ASTM standard, the adhesion was evaluated following the classification provided in said ASTM standard (0B = no adhesion; 5B = complete adhesion). The values summarized in the Table below were determined as the average of adhesion measured on the 4 samples.

[0079] Determination of the etching time of polymer (F)

[0080] The etching time of polymer (F) was determined by the following method.

Twelve square silicon substrates having size of 2.54 cm x 2.54 cm (1”x1”) were thoroughly cleaned by 10 min immersion in an ultrasonic bath in isopropanol (IPA) followed by 5 min baking at 100°C. A layer of 1.5 pm of polymer (F) was then obtained by spin coating on each substrate a composition (CC) of the polymer (F) in Fluorinert® FC40 at 8.5% w/w concentration, followed by 10 min baking at 100°C. An aliquot of 0.3 ml_ of a mixture containing Fluorinert® 7300 segregated hydrofluoroether (66%) and Fluorinert® FC3283 (mixture of perfluorocompounds, primarily with 9 carbon atoms) (34%) was dropped on layer of polymer (F) on the substrate on each of different specimens. So obtained specimens wetted with the solvent mixture above described were maintained at rest for variable residence times, said residence times being spread equally from 30 seconds to 180 seconds. After the prescribed time, each specimen was tilted so as to remove the solvent and rinsed twice with the same solvent mixture by dropping solvent and maintaining exposure for 2 seconds. At this point, thickness of residual undissolved layer of polymer (F) (if any) was determined for each specimen, according to the technique described before. Etching time mentioned in Table below was then defined as the shortest residence time required for completely detaching and removing the polymer (F), i.e. wherein thickness of residual layer of polymer (F) was substantially null, i.e. less than detection limit, of 10 nm.

[0081] Preparative Example 1

[0082] In a 90 liters horizontal reactor equipped with a mechanical stirrer

operating at 65 rpm, 55 I of demineralized water and 1.15 I of a

microemulsion, previously obtained by mixing 251 ml of a

perfluoropolyoxyalkylene having acidic end groups of formula

CF₂CI0(CF₂CF(CF₃)0)_n(CF₂0)_mCF₂C00FI, wherein n/m = 10, having an average molecular weight of 600, 162 ml of a 30% v/v NFUOH aqueous solution, 575 ml of demineralized water and 162 ml of GALDEN^® D02 perfluoropolyether of formula CF30(CF2CF(CF3)0)_n(CF20)_mCF3, wherein n/m = 20, having an average molecular weight of 450, were introduced. The reactor was heated and maintained at a set-point temperature of 85°C and 400 mbar of ethane charged. Then 3.3 kg of 2,2,4- trifluoro-5- trifluoromethoxy-1 ,3-dioxole (TTD), corresponding to the TTD initial load, were introduced and the pressure was brought to 15 absolute bar by introducing tetrafluoroethylene (TFE). Then, 24 g of ammonium persulfate (APS) as initiator were introduced. Pressure was maintained at set-point of 15 bar by continuous feeding of gaseous TFE up to a total of 7 kg and semi-continuous feeding of liquid TTD, which was added in 26 equal portions each 3.85% increase in TFE conversion, up to a total of 11.1 kg. Once 7 kg of TFE were fed to the reactor, the reaction was discontinued by cooling the reactor to room temperature and venting it. Then the latex was recovered and treated with nitric acid, separated from the aqueous phase, washed with demineralized water and dried in a convection oven at 90°C for 48 hours. Characterization data of the polymer so obtained are summarized in Table 1.

[0083] Preparative Example 2 of Comparison [0084] In a 90 liters horizontal reactor equipped with a mechanical stirrer operating at 65 rpm, 62 I of demineralized water and 600 ml of a microemulsion, previously obtained by mixing 131 ml of a

perfluoropolyoxyalkylene having acidic end groups of formula

CF₂CI0(CF₂-CF(CF₃)0)_n(CF₂0)_mCF₂C00H, wherein n/m = 10, having an average molecular weight of 600, 84.5 ml of a 30% v/v NFUOH aqueous solution, 300 ml of demineralized water and 84.5 ml of GALDEN^® D02 perfluoropolyether of formula CF30(CF2CF(CF3)0)_n(CF20)_mCF3, wherein n/m = 20, having an average molecular weight of 450, were introduced.

[0085] The reactor was heated and maintained at a set-point temperature of 75°C and 150 mbar of ethane charged. Then 1.8 kg of 2,2,4- trifluoro-5- trifluoromethoxy-1 ,3-dioxole (TTD), corresponding to the TTD initial load, were introduced and the set-point pressure of 15 absolute bar was achieved by feeding gazeous tetrafluoroethylene (TFE). Then 12 g of ammonium persulfate (APS) as initiator were introduced. Pressure was maintained at set-point of 15 bar by continuous feeding of a gaseous TFE up to a total of 3.5 kg and semi-continuous feeding of liquid TTD, which was added in 9 equal portions each 11.1 % increase in TFE conversion, up to a total of 5 kg. Once 3.5 kg of TFE were fed to the reactor, the reaction was discontinued by cooling the reactor to room temperature and venting it. Then the latex was recovered and treated with nitric acid, separated from the aqueous phase, washed with demineralized water and dried in a convection oven at 90°C for 48 hours. Characterization data of the polymer so obtained are summarized in Table 1.

[0086] Preparative Example 3 of Comparison

470 grams of the copolymer powder produced as in Preparative Example 2C, above detailed, were dissolved in 4.33 I of Galden^® D02TS at 80°C, keeping the temperature constant while stirring for 8 hours until a transparent solution was obtained. The solution was introduced in a 5 It photochemical glass reactor equipped with mechanical stirrer and two mercury vapour immersion UV lamps; said solution was first degassed by feeding nitrogen for 2 hours at 22°C, and then the degassed solution was subjected to fluorination for 90 hours at 50°C by feeding a mixture 1 :1 by volume of nitrogen and fluorine under UV radiation. The solution obtained after fluorination was filtered on polypropylene membranes having a maximum pore diameter of 0.2 pm under pressure at 0.15 MPa. The solvent was removed from the filtered solution by evaporation under vacuum with a temperature gradient starting from 50°C up to 250°C, until obtaining a dried polymer residue. Characterization data of the polymer so obtained are reported in Table 1.

Table 1

Data summarized above well demonstrate the criticality of the choice of the polymers of the present invention, fulfilling the recited requirements of molecular weight/intrinsic viscosity and polar end groups content, for addressing the conflicting needs in the intended field of use, combining a good adhesion after coating, and easy detachment/solubilization upon etching.

Claims

Claim 1. A fluoropolymer comprising:

- repeating units having an alicyclic structure in main chain of said

fluoropolymer and derived from at least one fluoromonomer A, and, optionally,

said fluoropolymer:

- possessing an intrinsic viscosity of at most 35 cc/g, when determined at 30°C in perfluorohexane;

- possessing a weight averaged molecular weight (M_w) of at most 220 000, when determined by GPC; and

Claim 2. The polymer (F) of Claim 1 , wherein fluoromonomer A is selected from the group consisting of fluoromonomers having an alicyclic structure in their monomeric form and fluoromonomers which do not have an alicylic structure in their monomeric form, but which upon cyclopolymerization provide for an alicyclic structure in the resulting repeating unit of polymer (F), and wherein fluoromonomer A is a perfluoromonomer.

Claim 3. The polymer (F) of Claim 2, wherein the repeating unit derived from said fluoromonomer A is preferably represented by any one of the following formulae (1 ) to (3):

(1) (2) (3) wherein:

in the formula (1) each of p, q and r which are independent of each other, is 0 or 1 , each of R^f1 and R^f2 which may be the same or different, is a fluorine atom, a C1-C5 perfluoroalkyl group or a C1-C5 perfluoroalkoxy group, and R^f3 is a C1 -C3 perfluoroalkylene group, which may have a Ci- C5 perfluoroalkyl group or a C1 -C5 perfluoroalkoxy group, as a substituent; in the formula (2), s is 0 or 1 , each of R^f4, R^f5, R^f6 and R^f7 which may be the same or different, is a fluorine atom or a C1 -C5 perfluoroalkyl group, and R^f8 is a fluorine atom, a C1 -C5 perfluoroalkyl group or a C1 -C5

Claim 4. The polymer (F) of Claim 2, wherein the repeating unit derived from said fluoromonomer A complies with formula (1), and is selected from the group consisting of those represented by the following formulae (4) to (19):

Claim 5. The polymer (F) of Claim 2, wherein the repeating unit derived from said fluoromonomer A complies with formula (2), and is selected from the group consisting of those represented by the following formulae (20) to (30):

Claim 6. The polymer (F) of Claim 2, wherein the repeating unit derived from said fluoromonomer A complies with formula (2), and is selected from the group consisting of those represented by the following formulae (31) to (33):

Claim 7. The polymer (F) according to anyone of the preceding claims, which comprises repeating unit derived from at least one fluoromonomer B different from fluoromonomer A, wherein fluoromonomer B is selected from the group consisting of:

(a) C2-C8 perfluoroolefins such as tetrafluoroethylene (TFE),

hexafluoropropylene (FIFP);

(b) hydrogen-containing C2-C8fluoroolefins, such as vinylidene fluoride (VDF), vinyl fluoride, trifluoroethylene (TrFE), hexafluoroisobutylene (HFI B), perfluoroalkyl ethylenes of formula CFh=CFI-R_fi, wherein R_fi is a C₁-C6 perfluoroalkyl group;

(c) C₂-C8 chloro- and/or bromo-containing fluoroolefins such as

chlorotrifluoroethylene (CTFE);

(e) perfluorooxyalkylvinylethers of formula CF₂=CFOXo, wherein Xo is a C₁-C₁₂ perfluorooxyalkyl group comprising one or more than one ethereal oxygen atom, including notably perfluoromethoxyalkylvinylethers of formula

CF₂=CF0CF₂0R_f2, with R_f2 being a C₁-C3 perfluoro(oxy)alkyl group, such as - CF2CF3, -CF2CF2-O-CF3 and -CF3; and

(f) functional perfluoro(oxy)alkylvinylethers of formula CF₂=CFOYo_, wherein Yo is a C₁-C₁₂ perfluoro(oxy)alkylene group, optionally comprising one or more than one ethereal oxygen atom, which comprises at least one functional group selected from the group consisting of -SO₂X, -COX, -PO₂X, with X being a halogen or a -OX_a group, with X_a being H, an ammonium group or a metal cation.

Claim 8. The polymer (F) according to claim 7, wherein said polymer (F) comprises (and preferably consists essentially of):

- from 20 to 95 % moles, preferably from 30 to 80 % moles, more preferably from 35 to 50 % moles, with respect to the total moles of repeating units of polymer (F), of repeating units having an alicyclic structure in main chain of said fluoropolymer and derived from at least one fluoromonomer A; and

- from 5 to 80 % moles, preferably from 20 to 70 % moles, more preferably from 50 to 65 % moles, with respect to the total moles of repeating units of polymer (F), of repeating units derived from at least one fluoromonomer B different from fluoromonomer A; and wherein preferably polymer (F) is a copolymer comprising:

- repeating units having an alicyclic structure in main chain of said

fluoropolymer and derived from at least one fluoromonomer A which is perfluorinated, and

Claim 9. The polymer (F) according to Claim 8, which is a copolymer

comprising (preferably consisting essentially of):

- repeating units derived from at least one fluoromonomer A selected from the group consisting of perfluoro(2-methylene-4-methyl-1 ,3-dioxolane),

perfluoro(2,2-dimethyl-1 ,3-dioxole), perfluoro(1 ,3-dioxole), 2,2,4-trifluoro-5- trifluoromethoxy-1 ,3-dioxole and perfluoro(3-butenyl vinyl ether); and

- repeating unit derived from tetrafluoroethylene (TFE),

and wherein polymer (F) is preferably a copolymer comprising (preferably consisting essentially of):

- repeating unit derived from tetrafluoroethylene (TFE).

Claim 10. The polymer (F) according to anyone of the preceding claims,

wherein said polymer:

- possesses a weight averaged molecular weight (M_w) of at most 210 000, preferably of at most 200 000, and/or of at least 10 000, preferably at least 20 000, more preferably at least 30 000; and/or

- comprises an amount of carboxylic end groups of at least 8.2 mmol/kg, preferably at least 8.5 mmol/kg, more preferably at least 8.8 mml/kg, and/or of at most 30 mmol/kg, preferably at most 27 mmol/kg, more preferably at most 25 mmol/kg; and/or

- possesses an intrinsic viscosity of at most 35, more preferably at most 34 cc/g, and/or of at least 10, preferably at least 12, more preferably at least 15 cc/g.

Claim 11. A coating composition [composition (CC)] comprising polymer (F) according to anyone of Claims 1 to 10, and a liquid medium, said liquid medium being preferably an organic solvent selected from the group consisting of organic solvents containing at least one fluorine atoms, including notably perfluoroalkanes, perfluoroethers, hydrofluoroethers, fluoro-amines, perfluoro- amines, fluoro-cyclic organic compounds, or mixtures thereof.

Claim 12. A method for producing a patterned structure on a substrate,

including the steps of:

(1) applying the composition (CC) according to Claim 11 , on at least a portion of the substrate, and remove the liquid phase, so as to obtain a shielding layer of polymer (F) onto said substrate;

Claim 13. The method of Claim 12, wherein Step (2) comprises:

a sub-step (2B) of exposing said photoresist layer to patterned radiation, so as to obtain a patterned photoresist layer comprising radiation-modified and non radiation modified regions; and

a sub-step (2C) of substantially removing either of the said radiation-modified and non-radiation modified regions, so as to obtain a patterned shielding layer of polymer (F) comprising a pattern of photoresist-covered and photoresist- uncovered regions.

Claim 14. The method of Claim 13 wherein the step (2B) of exposing the photoresist to patterned radiation is obtained by irradiating the photoresist layer obtained from step (2A) interposing a mask opaque to radiation and possessing a patterned structure between the radiation source and the said photoresist layer.

Claim 15. The method of Claim 14 wherein the photoresist is selected from the group of positive and negative photoresists, and wherein:

- when a positive photoresist is used, step (2B) provides for radiation-modified region of the photoresist layer which are chemically modified, e.g. to effect de polymerization/degradation and hence have advantageously acquired significant solvent-solubility and non-radiation modified regions of the said photoresist layer which have not been affected, and which hence

advantageously maintain appreciable solvent-resistance; and

- when a negative photoresist is used, step (2B) provides for radiation-modified region of the photoresist layer which are cured and hence have

advantageously acquired significant solvent-resistance and non-radiation modified regions of the said photoresist layer which are not cured, and which hence advantageously maintain appreciable solvent solubility;

and wherein in sub-step (2C), either of said radiation modified regions or said non-radiation modified regions of the photoresist layer are removed.

Claim 16. The method according to anyone of Claims 12 to 15, said method further comprising a step (4) of applying an additional coating layer of a material (M) on the patterned structure comprising a pattern of a shielding layer of polymer (F) on said substrate, so as to obtain a patterned structure comprising a pattern of the shielding layer of polymer (F) coated with material (M); and further comprising an additional subsequent step (5) of removing the said pattern of the shielding layer of polymer (F) coated with material (M) so as to obtain a patterned structure comprising corresponding negative pattern of layer of material (M).