WO2026013117A1

WO2026013117A1 - Method for producing monatomic fluorine for the fluorination of target materials and apparatus thereof

Info

Publication number: WO2026013117A1
Application number: PCT/EP2025/069560
Authority: WO
Inventors: José Guillermo GARCIA LORENZANA; Monica DE SETA; Luciana DI GASPARE; Ilya DEGTEV; Luca PERSICHETTI; Luca CAMILLI
Original assignee: Università Degli Studi Di Roma “Tor Vergata”; Consiglio Nazionale delle Richerche CNR; Universita degli Studi di Roma Tre; Universita degli Studi di Roma La Sapienza
Current assignee: Università Degli Studi Di Roma “Tor Vergata”; Consiglio Nazionale delle Richerche CNR; Universita degli Studi di Roma Tre; Universita degli Studi di Roma La Sapienza
Priority date: 2024-07-10
Filing date: 2025-07-09
Publication date: 2026-01-15
Anticipated expiration: 2027-01-10

Abstract

A method for producing monatomic fluorine for fluorination of a surface layer of a target material, comprising: purging (41) an interior space (25) of a processing chamber (11) comprising one or more walls (33) made of metal by evacuating the interior space (25) to a base pressure of 10^-10 to 10^-7 Torr; introducing (42) in the processing chamber (11) a fluorine-containing gas having a gas pressure of from 10^-8 to 10^-1 Torr for a fluorination time (t_F); stopping (43), at the end of the fluorination time, the inflow of fluorine-containing gas into the processing chamber; loading (45) into the processing chamber the target material to be treated; exposing (46) the target material within the processing chamber for an exposure time (t_E), and at the end of the exposure time, removing (47) the target material from the processing chamber. An apparatus for producing monatomic fluorine for fluorination of target materials is also disclosed.

Description

METHOD FOR PRODUCING MONATOMIC FLUORINE FOR THE FLUORINATION OF TARGET MATERIALS AND APPARATUS THEREOF

DESCRIPTION

The present invention relates to a method for producing monatomic fluorine for the fluorination of target materials and to a related apparatus.

Reacting surfaces with gases like fluorine or hydrogen may produce new compounds and change the properties of the surfaces in desirable ways. Fluorine is widely known as the element with the highest electronegativity. In its elemental form, fluorine is extremely reactive, and it forms solid or gaseous compounds. The synthesis of fluorine compounds is of interest in a number of technologies since they can form stable layers that are often used in coatings that exhibit chemical robustness, among other desired properties.

Italian patent application 102021000000704 A describes a surface coating process comprising a surface treatment of lithium metal with gaseous fluorine at a pressure of from 0.01 to 10 bar and at a temperature of -78°C to 180°C. The lithium metal is treated with an amount of gaseous fluorine of from 2.5xl0'⁹ to 0.51 of moles of fluorine per cm² of lithium metal. The surface treatment was aimed at making an anode for use in lithium metal batteries.

In "Topotactic fluorination of intermetallics as an efficient route towards quantum materials" by Jean-Baptiste Vaney et al., published in Nature Communications, vol. 13, 1462 (2022), the authors study fluorine insertion in intermetallics compounds to synthesize novel phases and promote functional materials such as permanent magnets or magnetocalorics. The method is based on the use of C-C4F8 perfluorocarbon reactant whose decomposition into CF2 radicals with high dissociation energy allows reducing sufficiently the reactivity of fluorine. Fluorine can then slowly diffuse through the material without decomposing it.

In "Structural Features, Oxygen and Fluorine Doping in Cu- based Superconductors" by E.V. Antipov et al., in Physica C, Vol. 282-287 p. 61 (1997), it is shown that fluorination of YBa2Cu30e+6 with XeF2 leads to a high-Tc superconductor.

S.R. Qiu et al. in "Self-Limiting Growth of Meta! Fluoride Thin Films by Oxidation Reactions Employing Molecular Precursors" , Physical Review Letters, vol. 85, No. 7, p. 115409 (2000), study the growth of FeF2 films by the reaction of XeF2 and SeFe with atomically clean polycrystalline Fe surfaces. The experiment was performed in an ultrahigh vacuum (UHV) including a turbomolecular-pumped dosing chamber.

US5888906 A describes a method of removing a layer of silicon oxide from at least a portion of a surface feature provided on an article comprising silicon. An article is placed in a reaction chamber and the method comprises introducing an interhalogen compound reactive with the silicon oxide layer into the reaction chamber so as to remove the silicon oxide layer from the portion of the surface feature, the interhalogen compound forming volatile by-product gases upon reaction with the silicon oxide layer. The temperature is increased during introduction of the interhalogen compound and unreacted interhalogen compound and volatile by-product gases from the reaction chamber are removed from the chamber.

US 2003/138986 A describes a method of making a release structure from a multi-layer structure comprising first and second etch-stop layers, a first sacrificial layer between the first and the second etch-stop layers, a cap layer and a second sacrificial layer between the second etch-stop layer and the cap layer with at least one access trench, wherein the second etch-stop layer includes a release feature. The method comprises creating an access opening in the cap layer; and etching portions of the first and the second sacrificial layers through the at least one access opening to form the release structure.

Herein, with fluorine-containing gas it is meant any group of gases containing fluorine. Commercial fluorine is typically provided as a diatomic gas (F2) diluted with a noble gas, such as Ar, Ne or He, or in stable fluorinated inorganic or organic gaseous compounds, for example XeF2 or C60F48. Fluorination may be achieved by exposing a target material to a fluorine congaing gas fluxed from a bottle, typically containing diatomic fluorine diluted in a noble gas.

It is generally known that monatomic gases are more reactive than diatomic gases, therefore, methods have been implemented to produce monoatomic gases. For example, in the case of hydrogen, the atomic gas may be produced by splitting the molecule, a process indicated also with "cracking". Thermal gas cracker sources for the production of highly reactive hydrogen atoms are commercially available, see for example TGC-H produced by the SPECS GROUP, available at https://www.specs- group.com/specs/products/detail/tgc- h/#: ~:text=The%20SPECS%20TGC%2DH%20is,heat%20load%20into %20the%20system.). The cracker allows the production of monatomic hydrogen in a controlled high vacuum atmosphere.

The Applicant has considered that in case of diatomic fluorine gas or, more generally, in case of fluorinated gaseous compounds, energy is needed for breaking the chemical bonds of the molecules to release the fluorine in a form that can be used for a direct fluorination process on a target material.

The Applicant has considered that a fluorination process using atomic fluorine generally requires a lower partial pressure and a lower quantity of fluorine to reach a thermodynamic equilibrium.

Known dissociation methods of fluorine molecules are reviewed in "Dissociation of molecules in plasma and gas: the energy" by A. V. Eletskii and B. M. Smirnov, Pure&App. Chem., Vol. 57, No. 9, p. 1235 (1985). Fluorine atom formation may include gas discharge, bombardment of the gas with an electron beam, ultraviolet radiation and the use of a heated surface.

The Applicant has considered a fluorination process carried out by exposing a target material within a processing chamber to a fluorine- containing gas that can be fluxed from a bottle or any other source that may typically contain diatomic fluorine diluted with a noble gas.

The Applicant has also observed that, generally, while fluorine-containing gas is introduced into the processing chamber, the amount of "contaminant" gases, different from the fluorine-containing gas, which are present within the chamber, is relatively high. However, if the inflow of the fluorine-containing gas from an external gas source into the processing chamber is halted, after a time, the amount of "contaminant" gases within the chamber decreases with time and eventually becomes several orders of magnitude lower compared to the continuous inflow gas into the chamber but monoatomic fluorine persists in the chamber.

The Applicant has in particular found that the introduction of fluorine- containing gas into a processing chamber under vacuum for a certain period of time may lead to the presence of monatomic fluorine within the chamber. The Applicant has also observed that, by maintaining the vacuum within the processing chamber after halting the introduction of the fluorine-containing gas, fluorine can be "stored" to be then present as monatomic fluorine gas within the interior space of the chamber.

Vacuum processing chambers have typically metallic wall(s) having respective inner surface(s) facing the interior space of the chamber.

Without wishing to be bound by any theory or explanation, it is believed that the fluorine-containing gas reacts with the inner surface(s) of the metallic wall(s) of the processing chamber by breaking the molecules of the gas and incorporating the fluorine in the wall surfaces, possibly as a metallic fluoride. By maintaining the vacuum within the chamber, the fluorine "stored" on the wall(s) can be later released as monatomic fluorine within the chamber.

In this way, monatomic fluorine with a low amount of contaminant gases can be produced in a high vacuum chamber, typically held at a base pressure of 1.3 x ICT⁸ to 1.3 x ICT⁵ Pa (IO^-10 to ICT⁷ Torr).

Within the processing chamber target materials can be exposed to the monatomic atmosphere for an exposure time. Since the chemical reaction on the walls' surfaces or across a surface layer of the target material occurs with monatomic fluorine rather than with molecular fluorine, breaking of the molecular bond of fluorine molecule is not necessary and thus the chemical reactivity of the fluorine may considerably increase.

The use of monatomic fluorine for fluorination may be advantageous with respect to the use of a gas containing F2, such as F2/He, since the monatomic fluorine has a higher chemical reactivity and thus less fluorine is needed to fluorinate a target material.

The present invention relates to a method for producing monatomic fluorine for the fluorination of one or more target materials, wherein the method comprises:

- purging an interior space of a processing chamber comprising one or more walls made of metal, wherein purging comprises evacuating the interior space to a base pressure of 1.3 x ICT⁸ to 1.3 x ICT⁵ Pa (10 ¹⁰ to IO’⁷ Torr);

- introducing in the processing chamber a fluorine-containing gas having a gas pressure of from 1.3 x 10'⁶ to 13 Pa (IO^-8 to 10 ¹ Torr) for a fluorination time;

- stopping, at the end of the fluorination time, the inflow of fluorine- containing gas into the processing chamber;

- loading into the processing chamber one or more target materials to be treated;

- exposing the one or more target materials within the processing chamber for an exposure time, and

- at the end of the exposure time, removing the one or more target materials from the processing chamber.

Preferably, exposing the one or more target materials is to monoatomic fluorine.

Preferably, each wall of the one or more walls has an inner surface facing the interior space and an outer surface opposite to the inner surface.

Preferably, the metal of the one or more walls of the processing chamber is selected in the group consisting of stainless steel, titanium, copper, nickel and aluminium.

In examples, the walls of the processing chamber are made of stainless steel.

In some embodiments, the inner surface of the one or more walls of the processing chamber is coated by a metallic coating layer selected in the group consisting of nickel, titanium, aluminum, copper, silver, and lithium fluoride. In some examples, the metallic coating layer has a thickness of from 1 to 1000 nm, preferably from 10 to 100 nm.

The provision of a metallic coating layer may increase the storage capacity on the walls' surfaces of the processing chamber and the chemical reactivity of the inner surface.

With gas pressure of the fluorine-containing gas it is meant the pressure of the gas entering the processing chamber.

Preferably, purging comprises evacuating the interior space of the processing chamber to a base pressure from 1.3 x IO^-8 to 1.3 x IO^-6 Pa (IO ¹⁰ to IO^-8 Torr).

In one embodiment, the fluorine-containing gas is F2 diluted in a noble gas (e.g. He, Ar or Ne) in a proportion 1 to 9 at a gas pressure of from 1.3 x IO^-4 to 1.3 x 10‘³ Pa (IO ⁶ to IO’⁵ Torr).

Preferably, after interrupting the inflow of fluorine-containing gas and before loading into the processing chamber the one or more target materials, the method comprises analyzing by means of a mass spectrometer the interior space of the processing chamber to detect if the partial pressure of any of the residual gases other than monatomic fluorine is below a first threshold partial pressure or equal to or above the first threshold partial pressure and to detect if the partial pressure of monatomic fluorine is below a second threshold partial pressure or equal to or above the second threshold partial pressure.

Preferably, if the partial pressure of any of the residual gasses other than monatomic fluorine is equal to or above the first threshold partial pressure or if the partial pressure of monatomic fluorine is below a second threshold partial pressure the method comprises introducing in the processing chamber a fluorine-containing gas for an additional fluorination time.

Preferably, at the end of the additional fluorination time, the interior space of the processing chamber is analyzed to detect whether residual gases other than monatomic fluorine have a partial pressure below or equal to or above the first threshold partial pressure and to detect whether monatomic fluorine have a partial pressure below or equal to or above the second threshold partial pressure. Preferably, if at the end of the additional fluorination time, the partial pressure of all residual gases other than fluorine is below the first threshold partial pressure and the partial pressure of the monatomic fluorine is equal to or above the second threshold partial pressure, the method may proceed with the step of loading the one or more target materials in the processing chamber.

In some embodiments and depending on the target material to be fluorinated, the presence of diatomic hydrogen above the first threshold partial pressure is not considered to be a relevant contaminant for the fluorination process of the target material(s). In embodiments, if the partial pressure of the one or more residual gases other than monatomic fluorine and diatomic hydrogen are below the first threshold partial pressure, the process may proceed with the loading of the one or more target materials into the processing chamber, provided that the partial pressure of monatomic fluorine is equal or above the second threshold partial pressure.

Preferably, purging the interior space of the processing chamber comprises heating the one or more walls of the processing chamber to a temperature of from 100°C to 180°C. Baking the walls of the processing chamber may speed up the purging of the chamber from residual gaseous species or impurities.

The Applicant has observed that, following the fluorination step, the processing chamber, which is kept under vacuum, may release monatomic fluorine for various days.

The Applicant has also observed that a temperature variation within the interior space of the processing chamber may affect the release rate of the previously introduced fluorine. In particular, the partial pressure of monatomic fluorine can be increased or decreased during samples' exposure by raising or lowering the temperature within the processing chamber, respectively.

In embodiments, exposing the one or more target materials within the processing chamber for an exposure time is carried out at ambient temperature (e.g. 20-30°C).

In an embodiment, during exposure of the one or more target materials to monatomic fluorine, the method comprises heating the one or more chamber walls of the processing chamber to a temperature of from 30°C to 100°C, preferably from 30°C to 90°C. Heating the interior space of the chamber may speed up release of monatomic fluorine from the inner surfaces of the chamber's walls.

In a further embodiment, during exposure of the one or more target materials, the method comprises cooling the one or more chamber walls of the processing chamber to a temperature of from 5°C to 15°C. Cooling the interior space of the processing chamber may slow down the release rate of the monatomic fluorine from the walls. A slower release of fluorine may allow a finer control of the fluorine dose applied to the target materials.

In addition or in the alternative, a decrease in the release rate may save monatomic fluorine to be used in a subsequent exposure of new target materials introduced in the processing chamber.

Preferably, after removing the one or more target materials from the processing chamber, the method comprises cooling the one or more walls of the processing chamber to a temperature of from 5°C to 15°C. Preferably, during cooling, the base pressure of the chamber is maintained at a value of from 1.3 x IO^-8 to 1.3 x IO^-5 Pa (1x10 ¹⁰ to IO^-7 Torr).

The Applicant has understood that the provision of an inner surface of the processing chamber having a roughness increases the total surface area and thus may increase the storage and the release of monatomic fluorine within the interior space of the chamber.

Preferably, the inner surface of the processing chamber is a corrugated surface having an average surface roughness (Ra) of from 1 to 1000 pm, more preferably from 10 to 500 pm.

In embodiments, the corrugated surface has an average surface roughness of 20 to 1000 pm, in particular from 50 to 500 pm.

Preferably, at least a portion of the inner surface of the processing chamber is covered by an AISI stainless steel wool.

Preferably, a portion of the inner surface of the processing chamber comprises metallic layers attached perpendicularly to the inner surface. The present invention concerns also an apparatus for carrying out the method for fluorinating one or more target materials. The apparatus comprises: a processing chamber comprising one or more walls made of metal, each wall having an inner surface facing an interior space and an outer surface; a vacuum system operatively connected to the interior space of the processing chamber and configured to evacuate the processing chamber to a pressure of from 1.3 x ICT⁸ to 1.3 x ICT⁵ Pa (IO^-10 to ICT⁷ Torr); a gas source of fluorine-containing gas connected to a gas inlet line receiving the gas from the gas source, the gas inlet line being configured to be in communication with the interior space of the processing chamber, and a transferring device configured to move a sample holder for transporting at least a target material in and out of the processing chamber.

Preferably, the apparatus comprises a heating element arranged in direct contact with the outer surface of processing chamber. The heating element is configured to heat the processing chamber walls at a temperature of from 30°C to 200°C.

Preferably, the apparatus comprises a cooling element in direct contact with the outer surface configured to cool the walls of the processing chamber. In an example, the cooling element is a water-cooling pipe, arranged on the outer surface of the processing chamber.

Preferably, the transferring device comprises a linear transferring arm having at one of its end a tray carrying a sample holder, the linear transferring arm being configured to move in and out of the processing chamber.

The present invention will now be described in more detail hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. In general, the same reference numeral will be used for possible variant embodiments of similar elements. Drawings illustrating the embodiments are not-to-scale schematic representations. FIG. 1 is a graph showing temperature and pressure dependent contributions to the gas Gibbs free energy per fluorine atom as a function of the pressure within a processing chamber for the molecular fluorine (solid line) and for the monatomic fluorine (dashed line).

FIG. 2 is a top view illustrating an apparatus suitable for carrying out a fluorination process of a target material, according to an embodiment of the invention.

FIG. 3 illustrates the apparatus of Fig. 2, where the sample holder configured to house the target samples is shown at a different position.

FIG. 4 is a perspective view of the processing chamber of the apparatus of Figs. 2-3, according to an embodiment of the invention.

FIG. 5 is a flow chart showing the main steps of a method of fluorinating a target material, in accordance with an embodiment of the invention.

FIG. 5A is a flow chart showing an embodiment of step 43 illustrated in Fig. 5.

FIG. 6 is an exemplary mass spectrometer spectrum of the interior space of the processing chamber 11 at ambient temperature following fluorination.

For the purpose of the present description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. In a typical fluorination process, the outer surfaces of a material A are exposed to some fluorine-containing gas to obtain the fluorinated compound AF_n, where n is the number of moles of fluorine per mole of the compound A that have reacted.

The Applicant has considered that when the fluorination process occurs at a pressure P and a temperature T in a processing chamber, if the gas employed is monatomic gas (F), the Gibbs free energies per formula unit of the product compound, g(AF_n), and of the reactant, g(A), at equilibrium, satisfy the following relationship g(A) + n Pmono (P,T)=g(AF_n) (1) which can be written as

Apmono(P,T) = ([g(AF_n)-g(A)]/n)-p₀ (2) where Ap mono (P,T) = Pmono (P,T)-|Jo, Pmono (P,T) is the chemical potential of atomic fluorine and po is the energy of a single F atom at zero temperature.

If the gas employed is diatomic gas (F2), at equilibrium, the Gibbs free energies satisfy the equation

(Pdia(P,T)-2p₀)/2 = ([g(AFn) - g(A)]/n)-p₀ (3) where pdia(P,T) is the chemical potential of molecular fluorine. Equation (3) can be written as

(Ap_dia(P,T) - E_d)/2 = ([g(AFn) - g(A)]/n)-po (4), where Apdia(P,T) = pdia(P,T)-E(F2), E(F2) is the energy of a fluorine molecule at zero temperature and Ed is the dissociation energy of the fluorine molecule, i.e. Ed = (2po - E(F2)) = 1.6 eV.

Equations (1) to (4) describe the balance of the Gibbs energy change in the reaction with the Gibbs free energy per fluorine atom in the monatomic gas (pmono(P,T)) or in the diatomic gas (pdia(P,T)/2). For convenience, the zero-temperature energy of the fluorine atom has been subtracted on both sides. All factors dependent on the initial and final product have been put on the right while factors dependent on the type of gas have been placed on the left.

Figure 1 is a graph showing the left-hand side of Eq. (2) (monatomic fluorine, dashed line) and the left-hand side of Eq. (4) (diatomic fluorine, solid line) as a function of the pressure within a processing chamber at ambient temperature. The data for Ap_mono(P,T) and Apdia(P,T) where obtained from the National Institute of Standards and Technology (NIST).

As an example, for a reaction characterized by a Gibbs free energy difference on the right hand side of Equations (2) and (4) of -1.13 eV (dotted line), the reaction with molecular fluorine is at equilibrium at a pressure of about 400 Pa (3 Torr), whereas the same reaction with monatomic fluorine is in equilibrium at a pressure of 1.3 x 10'⁷ Pa (IO^-9 Torr), thus many orders of magnitude smaller than in the case of diatomic fluorine, F2.

The Applicant noticed that using monatomic fluorine would allow to obtain a fluorinated material at a much lower pressure than that needed when using molecular fluorine, thereby greatly reducing the danger of using gaseous compounds comprising molecular fluorine.

Figures 2 and 3 illustrate a top view of an apparatus 10 suitable for carrying out fluorination of a target material, according to an embodiment of the present invention. Figure 3 differs from Fig. 2 only for the position of the sample holder in the apparatus. Some non-visible elements are shown with the dashed line.

The target material to be treated, can be any inorganic or organic material to be fluorinated either to produce a new fluorinated compound or for etching purposes. For example, a non-exhaustive list of elementary elements which form fluorides comprise lithium, beryllium, manganese, iron, cobalt, nickel, copper, silver, lithium, thallium. In some applications, it may be desirable to incorporate fluorine into quantum materials, such as in LaFeSiFx, NdFeAsOi-xFx, or YBa2Cu30eF_x, to change their physical properties. The target material can also be silicon or silicon dioxide or any other material to be etched.

The apparatus 10 comprises a vacuum processing chamber 11. The processing chamber 11 comprises an interior space 25, e.g. a cavity, configured to house one or more samples to be treated.

The vacuum processing chamber 11 comprises a chamber gas inlet 35 for the introduction of the gas into the chamber. During introduction of the fluorine-containing gas, the chamber gas inlet 35 is in fluid communication with the leak valve 17, which is set in an open position.

The processing chamber 11 has one or more walls 33, each wall having an inner surface, collectively indicated with 32a, the one or more inner surfaces defining the interior space 25 and an opposite outer surface collectively indicated with 32b.

In the non-limiting example of the figures, the processing chamber 11 is a cylindrical housing having a plurality of walls 33, namely a cylindrical side wall 33a and a top and bottom walls 33b, 33c (Fig. 4). A chamber having a spherical wall may also be used (not illustrated). In the following, the one or more walls will be collectively indicated with reference numeral 33.

The inner surface 32a of the one or more walls 33 of the processing chamber 11 is made of metal.

In particular, the one or more walls 33 are made of metal. A non- exhaustive list of suitable metals for the walls are stainless steel AISI 304, stainless steel AISI 304L, stainless steel AISI 316, stainless steel AISI 316L, titanium, copper, nickel, and aluminum.

In some embodiments, the inner surface 32a of the one or more walls 33 is covered by an inner coating layer of metallic material (not indicated in the figures).

The processing chamber 11 is a high-vacuum chamber configured to be evacuated by a vacuum system 15 operatively connected to the chamber. The vacuum system 15 is configured to evacuate the chamber 11 from atmosphere down to a base pressure from 1.3 x 10'⁸ to 1.3 Pa (IO^-10 to ICT² Torr), preferably from 1.3 x ICT⁸ to 1.3 x ICT⁶ Pa (lxlO^-10 to 10'⁸ Torr).

In an example, the vacuum system 15 comprises a primary dry pump coupled to a turbo molecular pump of known type and not indicated in the figure. Arrows 23 and 24 (Fig. 3) indicate the outflow direction of the gases from the processing chamber during evacuation of the same, as described in more detail in the following.

The pressure within the processing chamber 11 can be monitored by a pressure gauge 14.

Gases present within the processing chamber 11 may be analyzed by a residual gas analyzer or mass spectrometer 16.

The apparatus 10 comprises a source 21 of fluorine-containing gas connected to a gas inlet line 18 receiving the gas. The gas inlet line 18 is configured to be in communication with the interior space 25 of processing chamber 11.

In the embodiment of the figures, the source 21 of fluorine-containing gas comprises a bottle or cylinder 21a. A first sealed valve 21b is connected to the bottle 21a. The first sealed valve 21b is configured to have a closed position and an open position. When the first sealed valve 21b is in the closed position, the bottle 21 is hermetically sealed from the outside. When the first sealed valve 21b is in the open position, gas flows outside of the bottle 21a. The source 21 is equipped with a pressure gauge 21c arranged downstream of the first sealed valve 21b, with respect to the outflow direction of the gas from the gas source 21, for checking the quantity of gas in the bottle 21a. The bottle 21a with the attached first sealed valve 21b can be attached and detached to/from the rest of the equipment to allow the refilling of gas in the bottle. In particular, the source 21 can be attached and detached to/from the gas inlet line 18.

In examples, the fluorine-containing gas may be diatomic fluorine (F2) gas, preferably diluted with He or Ar. Other fluorine-containing gaseous compounds, such as CF4, C2F6 or SFe, may be used. In an example, the fluorine-containing gas is F2 with a dilution of 10% in He.

A second sealed valve 19 is arranged in the gas inlet line 18 downstream of the source 21 with reference to the inflow direction of the gas from the source. In particular, the second sealed valve 19 is arranged downstream of the first sealed valve 21b for interrupting the supply of the fluorine-containing gas to the gas inlet line 18. The second sealed valve 19 has an open position that allows the flow of the gas and a closed position.

A measurement of the pressure of the gas within the bottle 21a by means of the pressure gauge 21c can be made with the second sealed valve 19 closed and the first sealed valve 21b temporarily opened.

A leak valve 17, connected to the gas inlet line 18, is positioned downstream of the source 21 with reference to the inflow direction of the gas from the source 21. The leak valve 17 is configured to be in communication with the interior space 25 of the processing chamber 11. In the embodiment, the leak valve 17 is placed downstream of the second sealed valve 19 with reference with the inflow direction from the source 21.

Preferably, the leak valve 17 is a variable leak valve configured to adjust the flow rate of the gas leaked into the processing chamber 11. For example, the variable leak valve 17 has a variable flow orifice (not shown) for the adjustment of the flow rate. Typically, the flow rate of the variable leak valve 17 ranges from a null flow rate (i.e. leak valve closed) to a maximum flow rate (e.g. full open valve).

In particular, the amount of fluorine-containing gas introduced in the interior space 25 of the processing chamber 11 can be controlled by adjusting the flow orifice of variable leak valve 17. The leak rate adjustment may be controlled in known ways, manually or by electrical actuation.

In an embodiment, an electronic controller (not shown) may be provided, the electronic controller being operatively connected to the pressure gauge 14 and to the variable leak valve 17 for adjustment of the flow rate of the fluorine-containing gas in response to the pressure measured by the pressure gauge 14.

Preferably, the variable leak valve 17 is a UHV leak valve used for control of the flow of gas into a vacuum chamber from an external source (e.g. gas source 21), such as controlling gas flow during gas introduction, pressure regulation, and gas purging.

In some embodiments, the gas inlet line 18 is connected to an auxiliary pumping system 20 configured to exhaust, when needed, any residual gas from the gas inlet line 18. To this end, the pumping system 20 is connected to the gas inlet line 18 upstream the leak valve 17. In particular, the pumping system 20 is arranged in a supplementary gas line 26 connected to the gas inlet line 18. A third sealed valve 22 is arranged in the supplementary gas line 26 upstream the auxiliary pumping system 20. The third sealed valve 22 is configured to have an open position and a closed position. The auxiliary pumping system 20 may comprise a primary mechanical pump such as a dry pump. In some embodiments the primary pump may be coupled to a turbo molecular pump. During inflow of the fluorine-containing gas into the processing chamber 11, the third sealed valve 22 is in the closed position to shut-off the auxiliary pumping system 20, whereas the first and second sealed valves 21b and 19 are in the open position to allow the gas to enter the processing chamber 11.

For the outflow of the gas from the gas inlet line 18, the leak valve 17 and the first sealed valve 21b are in a closed position, whereas the second and third sealed valves 19 and 22 are in an open position. The pumping system 20 is operative to exhaust the gas inlet line 18 in an outflow direction indicated with arrow 24 (Fig 3).

The processing chamber 11 is configured to house a sample holder 12 for holding one or more target materials to be fluorinated (not shown in the figures).

The target materials are moved in and out the processing chamber 11 by a transfer device 13. The transfer device 13 comprises a tray 31 carrying a sample holder 12 configured to house one or more samples (i.e. the target materials) to be exposed to monatomic fluorine. In the embodiment of figures 2 and 3, the transferring device 13 comprises a high-vacuum sealed outer tube 13a, in the following indicated also with outer vacuum tube, and a transfer arm 13c that is configured to move telescopically in and out within the outer vacuum tube 13a.

The transfer arm 13c is operatively connected, at one end, to the tray 31. The transfer device 13 further comprises a magnetic handle 13b surrounding the outer vacuum tube for moving the samples to/from the processing chamber 11 by magnetic coupling. A through-aperture 34 in the wall 33 puts in communication the processing chamber 11 with the transfer device 13. In particular, the through-aperture 34 is a vacuum- sealed aperture. The transfer device 13 is configured to linearly move the tray 31.

In the embodiment of the figures, the apparatus 10 further comprises a load-lock chamber 27 configured to be put in communication with the processing chamber 11. In an embodiment, the load-lock chamber 27 has its own vacuum system (not shown) working at a base pressure of 1.3 x IO’⁸ to 1.3 x IO’⁵ Pa (IO’¹⁰ to IO’⁷ Torr).

A first gate valve 28 is interposed between the processing chamber 11 and the load-lock chamber 27. The first gate valve 28 is movable between a closed position for hermetically sealing the two chambers and an open position that allows communication between the two chambers. The load-lock chamber 27 can be used to move samples to/from the processing chamber 11. The transfer device 12 is configured to move to/from the load-lock chamber 27. The load-lock chamber 27 is in communication with the exterior by means of a second gate valve 29.

In an embodiment, after exposure to monatomic fluorine, the target samples are moved to the load-lock chamber 27. The apparatus 10 comprises a second transferring device 30, for example a wobble stick with tweezers at one end for grabbing the sample holder and to move it in and out the load-lock chamber 27.

In an embodiment (not shown in the figures), the load-lock chamber 27 is in communication with other chambers for pre- or post- processing of the target samples.

The gas release rate of monatomic fluorine within the interior space 25 of the processing chamber 11 may be varied by changing the temperature of the inner surface 32a of the walls 33. Increasing the temperature of the inner surfaces of the walls may cause an increase of the gas release rate of monatomic fluorine, whereas decreasing the temperature of the inner surfaces of the walls may cause a decrease of the gas release rate.

Figure 4 is a schematic perspective view of the processing chamber 11 shown in a plane XZ perpendicular to XY plane of Figures 2-3, according to an embodiment. In the embodiment, the processing chamber 11 may be heated or cooled to cause a variation of the temperature of the inner surface 32a of the walls 33. In the embodiment shown in the figure, heating and cooling elements are adjacent to and preferably in contact with the outer surface 32b of the processing chamber 11.

In particular, a heating element 49 is in contact with the outer surface 32b of the walls of the processing chamber 11 for heating the chamber walls 33. The heating element 49 is configured to be connected to a power source (not shown) at a first and second opposite ends 49a, 49b. In an example, the heating element 49 comprises a resistance wire conductor and an electrical insulating layer enveloping said wire conductor. The resistance wire conductor is coiled around the outer surface 32b of wall(s) 33. In examples, the temperature for heating may be of from 30°C to 100°C, more preferably from 30°C, to 90°C, the temperature being selected depending on the desired gas release rate of monatomic fluorine within the processing chamber 11.

The processing chamber 11 may be cooled to moderately low temperatures, such as from 5°C to 15°C, with respect to an ambient temperatures of typically 20-30°C. In the embodiment of Fig. 4, the chamber walls 33 are cooled by a cooling element 39, such as a watercooling pipe, arranged on the outer surface 32b of the processing chamber 11. In ways per se known, the water-cooling pipe 39 is connected to a source of cold water (not shown). Arrows DI and D2 indicate the inflow and outflow directions within the cooling element 39.

It is to be understood that other arrangements may be employed for heating and cooling the walls 32 of the processing chamber 11.

In Fig. 4, double-arrow Cl indicates the movement of the transfer arm 13c of the first transferring device 13 through the vacuum-sealed aperture 34. Arrow C2 indicates the direction for the connection with the gate valve 28 and arrow C3 indicates the direction for the connection with the leak valve 17.

A method for producing monatomic gas for the fluorination of a material is herein described with reference to Figs. 5 and 5A, which is a flow chart showing the main steps of a process 40, in accordance with an embodiment of the invention.

Before use, the processing chamber 11 is purged to eliminate any residual gas or impurity from its interior space 25 and/or from the inner surfaces 32a of the cavity and, if any, from all inner surfaces of devices opening into the interior space of the processing chamber until a base pressure is reached (step 41). The base pressure of the processing chamber is in the range of from 1.3 x 10'⁸ to 1.3 x 10'⁵ Pa (10 ¹⁰ to 10'⁷ Torr). To this end, the processing chamber 11 is evacuated by means of the high-vacuum system 15 with the gate valve 28 and the leak valve 17 in the closed position. The pumping system 15 remains active during all subsequent steps of the process.

Preferably, the purging step 41 further comprises the evacuation of the gas inlet line 18 by means of pumping system 20 connected to the gas inlet line 18. During this step, the first sealed valve 21b is in a closed position, while the second and third sealed valve 19, 22 are in an open position. The leak valve 17 is in a closed position.

Possible volatile gaseous species are evacuated from the processing chamber 11 and also from the gas inlet line 18 along respective outflow directions 23, 24 (Fig. 3).

Preferably, the purging step 41 comprises a baking step where the processing chamber 11 and the gas inlet line 18 are baked by using standard high-vacuum procedures to eliminate possible contamination. In particular, during baking, the one or more walls 33 and any element in communication with the interior space 25 and the gas inlet line are heated to a temperature from 100°C to 180°C.

During the purging step 41, the leak valve 17 is closed and/or the first sealed valve 21b is closed.

At the end of the purging step 41, the processing chamber 11 is at a base pressure below 1.3 x ICT⁶ Pa (IO^-8 Torr). In examples, the base pressure within the processing chamber is of from 1.3 x IO ⁸ to 1.3 x ICT⁵ Pa (lxlO^-10 to IO’⁷ Torr).

Following the purging step 41, the method comprises a fluorination step 42 for fluorination of the interior space 25 of the processing chamber 11. In one example, after the purging step 41, the leak valve 17 is closed, the first and second sealed valves 21b and 19 are open to allow the fluorine-containing gas, for example F2/He, to fill the gas inlet line 18 for a time, preferably from 1 sec to 10 sec.

In embodiments, after the gas inlet line 18 is filled, the first sealed valve 21b of bottle 21 is closed to maintain the purity of the gas in the bottle. Then, the gas stored in the gas inlet line 18 is allowed to enter the processing chamber 11 by opening the variable orifice of the leak valve 17 at a flow position.

In preferred embodiments, this process is repeated each time the gas in the gas inlet line 18 is exhausted.

In another embodiment, the first sealed valve 21b, as well as the second sealed valve 19, and the leak valve 17 are open to allow the fluorine- containing gas to enter the processing chamber 11 in a continuous flow. The inflow of fluorine-containing gas time is for a time tF indicated as fluorination time. The fluorination time tF may depend on more factors, such as the partial pressure of fluorine-containing molecules within the chamber 11 during fluorination and the condition of the inner surface 32a of the chamber 11 in terms of cleanliness and contamination. In addition, the fluorination time tF may depend on the presence, on the interior surface 32a of walls 33, of fluorine from previous fluorination cycles.

Preferably, in step 42, the variable leak valve 17 is set at a flow rate value for the incoming gas which is selected to maintain the pressure within the processing chamber 11 to a value from 1.3 x IO ⁶ to 13 Pa (10" ⁸ to IO’¹ Torr).

In a non-limiting example, the fluorine-containing gas is F2 diluted with helium, in a proportion of 9 to 1 of He/F2. The gas pressure of the fluorine-containing gas introduced in the chamber is of from 1.3 x IO ⁴ to 1.3 x 10‘³ Pa (IO"⁶ to 10‘⁵ Torr).

In some non-limiting examples, the fluorination time tF may range from 1 to 36 hours. As indicated above, the fluorination time may depend also on whether the processing chamber 11 is first exposed to fluorine- containing gas or if it has undergone previous fluorinations.

In case the processing chamber is first exposed to the fluorine- containing gas and according to an example, the fluorine-containing gas is He/F2 in a proportion of 9 to 1 and the internal pressure of the processing chamber 11 during fluorination is kept to a value of about 1.3 x ICT³ Pa (IO^-5 Torr) for several hours, e.g. tF = 16 h, at ambient temperature.

If the processing chamber 11 has been previously fluorinated, the fluorination time tF may be for example of 3 hours, always at ambient temperature.

In some embodiments, during fluorination, the processing chamber 11 is kept at a temperature higher than the ambient temperature, such as at a temperature of from 100°C to 180°C. The Applicant has observed that a relatively high temperature of the walls of the processing chamber may speed up the fluorination and the cleaning process.

In an example, at the beginning of the fluorination step, the temperature within the chamber 11 is kept at a temperature of from 100°C to 180°C for a fluorination time from 1 to 2 hours. Fluorine-containing gas enters into the processing chamber 11 and reacts with the heated inner surfaces 32a of the chamber walls 33 and possibly with some residual contaminants. During this process, volatile by-products leave the processing chamber 11 so as to effectively clean its inner wall(s) 32a. The flow rate of the fluorine-containing gas during the fluorination step 42 is for example in the range of from 1.3 xlO'² to 10 ¹ Pa litre/sec (IO^-4 to 10'³ Torr litre/sec).

Following the fluorination step 42, the variable leak valve 17 is closed so as to stop the inflow of the fluorine-containing gas into the processing chamber (step 43). In another embodiment, the first sealed valve 21b is closed to stop the inflow of the fluorine-containing gas into the processing chamber.

In some embodiments and with reference to Fig. 5A, after stopping the inflow of fluorine-containing gas (step 43), e.g. after closing the variable leak valve 17, the interior space 25 of the processing chamber 33 is analyzed to determine whether residual gases other than fluorine, which may act as contaminants for the samples to be treated, are present above a certain level.

In addition, the amount of monatomic fluorine within the chamber should allow the fluorination of the target materials. The interior space 25 of the processing chamber 11 is analyzed to detect the amount of monatomic fluorine.

In an embodiment, the amount of residual gases other than fluorine and the amount of monatomic fluorine can be measured by measuring the partial pressure of each gas species (step 44a in Fig. 5A). If the partial pressure of any of the residual gases other than fluorine is equal to or above the first threshold partial pressure or the partial pressure of monatomic fluorine is below a second threshold partial pressure, the method comprises (44b) repeating steps 42 and 43.

In an example, the first threshold partial pressure for any gas other than fluorine, is of 1.3 x ICT⁸ Pa (6xlO'¹⁰ Torr).

In an example, the second threshold partial pressure of monatomic fluorine is of 1.3 x ICT⁷ Pa (3xl0^-9 Torr).

The analysis of the interior space 25 of the processing chamber 11 can be carried out by a mass spectrometer 16. In an embodiment, the mass spectrometer 16 is a Residual Gas Analyzer (RGA) in communication with the interior space 25 of the processing chamber 11.

If residual gasses other than monatomic fluorine are detected to be below the first threshold partial pressure and if the monatomic fluorine is detected to be equal to or above the second threshold partial pressure, i.e. the prevalent gas within the processing chamber 11 is monatomic fluorine released from the inner surface(s) 32a of the one or more walls 34, the method proceeds with the subsequent steps described in the following.

Figure 6 is a graph illustrating a mass spectrometer spectrum of the interior space of the processing chamber 11 at ambient temperature after stopping the inflow of fluorinated gases (step 43). The partial pressure was measured for gas species having the mass-to-charge ratio (m/z) from 1 to 64, where m/z denote a dimensionless quantity formed by dividing the mass number of an ion by its charge number. In the spectrum, the monatomic fluorine (m/z=19) has a partial pressure 8.0xl0^-7 Pa (6xl0^-9 Torr) and diatomic hydrogen has a partial pressure 2.0xl0^-7 Pa (1.5xl0^-9 Torr). Other gas species exhibit a pressure lower than 6.7 xlO'⁸ Pa (5x10 ¹⁰ Torr), which are considered as random noise level, namely below the first threshold partial pressure. Typically, and depending on the target material to be treated, diatomic hydrogen is not considered to be a relevant contaminant during the fluorination process. The monatomic fluorine atmosphere at the end of steps 43 or 44 is indicated also by the expression "F atmosphere". Following step 43 or step 44, step 45 comprising loading the one or more target materials, indicated also with samples and not shown in the figures, into the processing chamber 11. During loading, the leak valve 17 is kept closed in order to expose the samples only to or essentially to monatomic fluorine.

Target materials to be processed may be first cleaned before their introduction into the processing chamber 11, in order to minimize impurities and contaminants on the samples' surfaces and to obtain the desired structural characteristics (for example atomic terraces).

In the embodiment of Figs. 2 and 3, the load-lock chamber 27 communicates with the exterior of the apparatus 10 by means of a second gate valve 29 through which the target materials may be loaded. The second gate valve 29 is then closed and the samples are handled by means of the second transferring device 30.

Preferably, the load-lock chamber 27 is kept at an ultra-high vacuum, at least of 1.3 xlO^-6 Pa (IO^-8 Torr), preferably at 1.3 xlO^-7 Pa (IO^-9 Torr) or at a lower pressure. Then, the first gate valve 28 is opened and the degassed samples move from the load-lock chamber 27 to the processing chamber 11.

The first transferring device 13 is configured to move the linear arm 13c and the attached tray 31 carrying the sample holder 12 from the loadlock chamber 27 to the processing chamber 11 (Fig. 2). Once the tray 31 is positioned within chamber 11 (Fig. 3) the first gate valve 28 is closed to avoid a continuous exposure of the load-lock chamber to the fluorine atmosphere.

In step 46, the samples are placed on the sample holder 12 to be exposed to the F atmosphere for an exposure time t . The time t of exposure may vary from a relatively short exposure, e.g. a few hours, to relatively long exposure, e.g. a few days. As indicated in the foregoing, the concentration of fluorine on the material may be controlled by controlling the exposure time t .

In examples, the exposure time t is from 1 hour to 48 hours.

The Applicant has observed that, following the fluorination step 42, the processing chamber 11 may release monatomic fluorine for various days into its interior space 25.

As described in the foregoing, increasing the temperature within the processing chamber 11 to moderately high temperatures, for example from 30°C to 90°C, may promote an enhanced release of monatomic fluorine into the processing chamber 11, thus reducing the exposure time for the target materials. Cooling the walls to moderately low temperatures, e.g. 15°C can reduce the release of fluorine and allow a finer control of the fluorine dose applied to the sample.

For example, cooling of the walls to about 10°C decreases the release of monatomic fluorine from the inner surface 32a of the processing chamber. When the processing chamber is not in use, maintaining at a relatively low temperature, e.g. 10°C, the walls of the processing chamber 11 may "save" monatomic fluorine for a later use.

At the end of the exposure time t , the first gate valve 28 is opened and sample is moved back to the load-lock chamber 27.

The load-lock chamber 27 may communicate with the exterior by means of a second gate valve 29. In other embodiments, the load-lock chamber 27 communicates with other chambers (not shown in the figure) for analysis and/or further pre or post processing of the fluorinated samples. When the gas partial pressure of monatomic fluorine within the processing chamber measured with the residual gas analyzer 16 becomes too low, e.g. the partial pressure of F is less than 4.0 xlO'⁷ Pa (3xlO'⁹Torr) as measured by the RGA, steps 42 and 43 are repeated.

In some embodiments, the inner surface 32a of the one or more walls 33 is a corrugated surface, namely a surface of uneven shape. In an embodiment, the inner surface 32a has an average surface roughness, Ra of from 1 to 1000 pm, preferably of 10 to 500 pm, where Ra is the arithmetic mean between the peaks and valleys of the inner surface.

In some examples, Ra is of from 20 to 1000 pm, preferably from 50 to 500 pm.

Without wishing to be bound by any theory or explanation, the Applicant believes that the surface roughness improves the yield of conversion of diatomic fluorine into atomic fluorine which can be incorporated to the chamber inner wall and the flux of fluorine available for fluorination of samples.

In some embodiments, the metallic inner surface 32a of the processing chamber 11, for example made by stainless steel, is coated by an inner coating layer (non indicated in the figures) that is selected in the group consisting of nickel, aluminum, titanium, copper, silver, and lithium fluoride. The coating layer may increase the storage capacity on the wall's surfaces and the chemical reactivity of the surface. In an example, where the walls 33 are made of stainless steel, the inner coating layer is a nickel plating layer.

In an embodiment, at least a portion of the inner surface of the processing chamber 11 is covered by an AISI stainless steel wool, which may be in the form of a curled tape positioned at the bottom of the chamber 11. This increases the surface that is exposed to the inner space 25 and has the purpose to improve the yield of conversion of diatomic fluorine into atomic fluorine which can be incorporated to the chamber and the flux of fluorine available for fluorination of samples.

In another embodiment, the inner surface area can be increased by incorporating other metallic elements such as metallic layers attached perpendicular to the inner surface 32a.

Example

The target material to undergo fluorination was a silver single crystal having a (001) outer surface. The process comprised the following steps: a) The processing chamber 11 was evacuated down to a pressure of about 1.3 xlO^-7 - 1.3 xlO^-6 Pa (10'⁹-10‘⁸ Torr)(step 41). b) Before loading the target material, the processing chamber was fluorinated with a mixture of He/F2 gas (nominal ratio of 9: 1) contained in bottle 21 (step 42). The sealed valves 21b and 19 were in the open position. The sealed valve 22 was in the closed position. During fluorination, the variable leak valve 17 was adjusted so as to have a pressure of 1.3 xlO^-3 Pa (10^-5 Torr) within the interior space 25 of the processing chamber 11. The fluorination time tF was about 3 hours. At the end of the fluorination time, the leak valve 17 of the processing chamber was closed and remained closed for the rest of the experiment. c) Following fluorination, an analysis of the mass spectrum of the interior space 25 of chamber 11 by means of mass spectrometer 16 revealed that a fluorine-rich atmosphere was obtained in processing chamber 11 with a monatomic fluorine partial pressure of 5.3 xlO'⁷ Pa (4xl0^-9 Torr). d) Before loading the target material into the processing chamber, the silver single crystal was cleaned in a preparation chamber (not indicated in the figures) using sputtering with Ar⁺ ions having an energy of 1-2 keV. e) The target material was then transferred into the load-lock chamber 27 through the gate valve 29. From the load-lock chamber the sample was transferred to processing chamber 11 through the gate valve 28. f) The gate valves 28, 29 were closed and the target material was exposed for an exposure time of 2 hours to the atomic fluorine present within the processing chamber 11.

At the end of the exposure time (t ), the target material was transferred in ultra-high vacuum to a chamber equipped with a scanning tunneling microscope (STM). The Applicant has noticed that step d) may turn out to be important for the production of flat terraces on the sample surface which are free of impurities. This may be an advantage for the analysis of the sample surface by scanning tunneling microscope (STM) measurements. However, step d) is optional and it is not required for the fluorination process per se.

The target material was analyzed with the STM. The (100) surface of the silver single crystal showed flat Ag terraces and well-defined steps of apparent height equal to (205 ± 10) pm. For an applied bias voltage of 0.5 V, the F atoms were identified on the (100) surface by an apparent topography having circular depressions of diameter of 1 nm and depth of 20 pm. Across a surface area of 30x30 nm², eighteen adsorbed F atoms could be observed.

Although the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations and modifications may be made, and are intended to be within the scope of the appended claims.

Claims

1. A method for producing monatomic fluorine for fluorination of a surface layer of one or more target materials, the method comprising:

- purging (41) an interior space (25) of a processing chamber (11) comprising one or more walls (33) made of metal, wherein purging comprises evacuating the interior space (25) to a base pressure of 1.3 xlO'⁸ to 1.3 xlO'⁵ Pa (lxlO^-10 to ICT⁷ Torr);

- introducing (42) in the processing chamber (11) a fluorine- containing gas at a gas pressure of from 1.3 xlO'⁶ to 13 Pa (10‘⁸ to 10'¹ Torr) for a fluorination time (tp);

- stopping (43), at the end of the fluorination time (tp), the inflow of fluorine-containing gas into the processing chamber (11);

- loading (45) into the processing chamber (11) one or more target materials to be treated;

- exposing (46) the one or more target materials within the processing chamber (11) for an exposure time (tp), and

- at the end of the exposure time (tp), removing (47) the one or more target materials from the processing chamber (11).

2. The method of claim 1, wherein each of the one or more walls (33) has an inner surface (32a) facing the interior space (25) and an opposite outer surface (32b).

3. The method of claim 1 or 2 further comprising, after interrupting (43) the inflow of fluorine-containing gas and before loading (45) into the processing chamber (11) the one or more target materials, analyzing by means of a mass spectrometer the interior space (25) of the processing chamber (44a) to detect if the partial pressure of any of the residual gases other than fluorine is below or equal to or above a first threshold partial pressure and to detect if the partial pressure of monatomic fluorine is below a second threshold partial pressure, if the partial pressure of any of the residual gasses other than fluorine is equal to or above the first threshold partial pressure or the partial pressure of monatomic fluorine is below a second threshold partial pressure, introducing in the processing chamber (11) a fluorine- containing gas for an additional fluorination time.

4. The method of any one of the preceding claims, wherein the fluorine-containing gas is diatomic fluorine diluted with a noble gas in a nominal ratio 1 to 9, the fluorine-containing gas being introduced into the processing chamber (11) at a gas pressure of from 1.3 xlO'⁴ to 1.3 xlO’³ Pa (10‘⁶ to IO’⁵ Torr).

5. The method of any one of the preceding claims, wherein the metal of the one or more walls (33) of the processing chamber (11) is selected in the group consisting of stainless steel, titanium, copper, nickel and aluminium.

6. The method of any one of the preceding claims, wherein the inner surface (32a) of the one or more walls (33) of the processing chamber (11) is coated by a metallic coating layer selected in the group consisting of nickel, titanium, aluminum, copper, silver, and lithium fluoride.

7. The method of any one of the preceding claims, wherein the fluorine-containing gas is selected in the group consisting of diatomic fluorine, diatomic fluorine diluted with a noble gas and gaseous fluorinated inorganic or organic compounds.

8. The method of any one of the preceding claims, wherein the exposure time (t ) is from to 0,5 to 36 hours.

9. The method of any one of preceding claims, further comprising, during exposure of the one or more target materials, heating the one or more chamber walls (33) of the processing chamber to a temperature of from 30°C to 100°C.

10. The method of any one of claims 1 to 8, further comprising, during exposure of the one or more target materials, cooling the one or more chamber walls (33) of the processing chamber to a temperature of from 5°C to 15°C.

11. The method of claim 2 or any one of claims 3 to 10 when dependent on claim 2, wherein the inner surface (32a) of the processing chamber (11) is a corrugated surface having an average surface roughness (Ra) of from 1 to 1000 pm, preferably from 10 to 500 pm.

12. The method of claim 2 or any one of claims 3 to 11, wherein the inner surface (32a) of the processing chamber (11) is a corrugated surface having an average surface roughness (Ra) of from 20 to 1000 pm, preferably from 50 to 500 pm.

13. The method of claim 2 or any one of claims 3 to 12 when dependent on claim 2, wherein a portion of the inner surface of the processing chamber (11) is covered by an AISI stainless steel wool.

14. The method of claim 2 or any one of claims 3 to 13 when dependent on claim 2, wherein a portion of the inner surface of the processing chamber (11) comprises metallic layers attached perpendicularly to the inner surface (32a).

15. An apparatus (10) for carrying out the method of any one of claims from 1 to 14 comprising:

- a processing chamber (11) comprising one or more walls (33) made of metal, each wall (33) having an inner surface (32a) facing an interior space (25);

- a vacuum system (15) operatively connected to the interior space of the processing chamber and configured to evacuate the processing chamber to a pressure from 1.3 xlO'⁸ to 1.3 xlO'⁵ Pa (10-¹⁰ to IO’⁷ Torr);

- a gas source (21) of fluorine-containing gas connected to a gas inlet line (18) receiving the gas from the gas source (21), the gas inlet line (18) being configured to be in communication with the interior space (25) of the processing chamber (11), and

- a transferring device (13) configured to move a sample holder (12) for transporting at least a target material in and out of the processing chamber (11).

16. The apparatus of claim 15, wherein the inner surface (32a) of the one or more walls (33) is a corrugated surface having an average surface roughness (Ra) of from 1 to 1000 pm, preferably from 10 to 500 pm.

17. The apparatus of claim 15 or 16, wherein the inner surface (32a) of the one or more walls (33) are coated by a metallic coating layer selected in the group consisting of nickel, titanium, aluminum, copper, silver and lithium fluoride.

18. The apparatus of any one of claims 15 to 17, further comprising a heating element (49) arranged in direct contact with the outer surface (32b) of processing chamber (11), the heating element (49) being configured to heat the one or more walls (33) of the processing chamber at a temperature of from 30°C to 200°C.

19. The apparatus of any one of claims of from 15 to 18, further comprising a cooling element (39) in direct contact with the outer surface (32b) of the one or more walls (33), the cooling element (39) being configured to cool the one or more walls (33) of the processing chamber (11).