METHOD FOR STRUCTURING A HYBRID SURFACE BY PLASMA EATTING

Description

TECHNICAL FIELD AND PRIOR ART

[0001] The invention relates to structuring techniques, making it possible to produce a hybrid structure, comprising for example patterns on a micrometric scale and etching of at least part of these patterns in order to give them a roughness on a nanometric scale.

[0002] This type of hybrid structure makes it possible in particular to create a surface which has antibacterial and antiviral properties), with a controlled rough texturing on at least part of the surface of the patterns.

[0003] Antibacterial surfaces are generally created either by plasma deposition with Si-rich precursors (by “HMDSO” plasma) (see the article by Zouaghi et al. 2018, Applied Surface Science, Volume 455, 15 October 2018, Pages 392-402: “Atmospheric pressure plasma spraying of silane-based coatings targeting whey protein fouling and bacterial adhesion management”), or by laser ablation of a metallic surface (S.Moradi et al.; ACS Appl. Mater. Interfaces 2016, 8, 27, 17631-17641, June 20, 2016, https: / / doi.org / 10.1021 / acsami.6b03644: “Effect of Extreme Wettability on Platelet Adhesion on Metallic Implants: From Superhydrophilicity to Superhydrophobicity”), or by electrolysis for to produce porous oxide (Thukkaram et al., ACS Appl. Mater. Interfaces, 2020: “Fabrication of microporous coatings on titanium implants with improved mechanical, antibacterial and cell-interactive properties”). We also know the article by Dionysia Kefallinou et al.“Optimization of Antibacterial Properties of “Hybrid” Metal-Sputtered Superhydrophobic Surfaces”, Coatings 2020, 10, 25, 30 Dec 2019.

[0004] None of these known techniques makes it possible to simply create on a substrate a surface that has both micrometric patterns and a finer structure, on the nanometric scale. A method for forming micrometric patterns on a substrate surface is known per se from WO2013 / 171420 A1. STATEMENT OF THE INVENTION

[0005] The invention firstly relates to a method for producing a hybrid structure, comprising the steps defined in claim 1

[0006] The polymerization of the resin may take place between the steps of forming a structure comprising a plurality of patterns and forming a roughness on at least a portion of the surface of the patterns, as defined in claim 1.

[0007] Each pattern has at least one dimension, measured parallel or perpendicular to the substrate, between 50 nm and 500 µm, for example 100 nm or 1 µm. Thus the patterns can be said to be "micrometric".

[0008] The patterns can be created in the mineral resin layer, for example using an optical or electronic lithography process or even a nano-printing technique.

[0009] The patterns, for example micrometric, can be either notched, cone-shaped, pyramid-shaped, or otherwise. These patterns provide a dewetting surface to which bacteria do not adhere, which can be further enhanced by grafting.

[0010] When applied to bacteria, their denaturation can result from roughness (nanostructure) but can also be obtained / reinforced by patterns having one or more salient shapes (cone or pyramids for example).

[0011] The roughness (corresponding to a nanometric structuring with a critical dimension for example less than 50 nm) can be obtained for example by an oxidizing process, of the type comprising at least one species or a gas making it possible to consume more or less the mineral phase of the resin, and thus to reveal areas having vacancies in atoms or molecules of Si and / or SiO 2 . These atoms or molecules of Si and / or SiO 2 are not consumed by this oxidizing process (the atoms of Si can nevertheless be oxidized into SiO 2 ). This oxidizing process is for example an etching by plasma, isotropic or anisotropic.

[0012] According to the invention, two stages or levels of structuring are therefore used: during step b), a lithography or nano-printing process applied to the mineral resin (preferably containing a controlled proportion of Si and / or SiO 2 , between 1 and 30% by molar mass) to have patterns, preferably on a micrometric scale, the shape, period and dimensions of which are defined by the parameters of this process; during step c), a random roughness is generated on the surface of said patterns, by removing carbonaceous parts, for example using an oxidizing process, for example again an oxidizing plasma, which can be isotropic or anisotropic.

[0013] The surface thus created is rich in Si and / or SiO 2 , which allows, in addition to the surface texture thus obtained, which is favorable to antibacterial and antiviral applications, to graft silanes onto it, for example to change the surface energy properties in order to increase the dewetting effect. The silanes therefore help with dewetting, and therefore advantageously complete the patterns or microstructures.

[0014] In a method according to the invention: the substrate may be for example made of silicon or a crosslinked negative resin or glass; and / or the roughness may be on the upper part and the lower part of the patterns and possibly on side walls which connect these upper and lower parts; and / or the roughness may have an average value of between 0.5 nm and 30 nm; and / or neighboring patterns may be separated by a distance of between 50 nm and 1 µm or even 500 µm; and / or the bottom (or lower part) of the patterns may constitute the resin in which the patterns are made, or perhaps the surface of said substrate; and / or at least one fluorinated agent or silane may be grafted onto at least part of the surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] THE Figures 1A and 1B represent examples of nano printing in a mineral resin with 4% Si and / or SiO 2 , The Figures 2A and 2Brepresent an example of post-printing mineral resin, with illustration of the presence of the elements Si and / or SiO 2; before ( Figure 2A ) and after ( Figure 2B ) implementation of the oxidizing process; The figures 3-5 represent SEM images (FOV = 3 µm) of surfaces obtained by an etching process without bias, with different plasmas, without ( figure 3 ) or with ( figures 4, 5 ) fluorinated species, the example of the figure 3 therefore not being in accordance with the invention; the figure 6 represents the evolution of the roughness Ra (in nm) of the surface of a resin treated according to the invention for a process duration of 200 seconds and SF 6 / O 2 ratios between 0 and 3:25; the figures 7-8 represent examples of treatment according to the invention, applied to surfaces having a proportion of Si and / or SiO 2 too high to obtain a hybrid structure; the figures 9-10represent examples of treatment according to the invention, applied to surfaces having an adequate proportion of Si and / or SiO 2 to obtain a hybrid structure; the figures 11-12 represent variants of methods according to the invention. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0016] In the context of the present invention, a mineral resin is chosen containing a proportion of Si and / or SiO 2 (denoted Si / SiO 2 in the following) of between 1% and 30% (in molar mass). As explained below, a resin comprising a higher proportion of Si / SiO 2 can be treated to reduce it by adding an organic compound, such as another resin or a precursor. Furthermore, if a resin comprises an insufficient proportion of Si / SiO 2 , Si implantation is possible to increase it.

[0017] The chosen resist, in particular its Si / SiO 2 proportion between 1% and 30%, is compatible with at least one optical or electronic lithography process or an alternative technique (such as nano-imprinting) to produce a first level of structures. For each resist, a qualification process can be carried out with respect to each technique as for example described in the article by Kretz et al. “Comparative study of calixarene and HSQ resist systems for the fabrication of sub-20 nm MOSFET device demonstrators”, published in Microelectronic Engineering, 78-79, 2005, 479-483. As explained further, optical or electronic lithography techniques do not allow the resist to be kept at the bottom of the patterns, which is however possible with the nano-imprinting technique (in this case, the depth h of the patterns is less than the thickness of the resist layer).Nanoprinting can also make it easy to create protruding shapes (cones or pyramids in particular) which will allow bacteria to be denatured.

[0018] Depending on the shape of the desired patterns and their dimensions, and depending on the properties of the resin and the technique chosen to form the patterns, the quantity of resin to be used is defined, as well as the parameters for spreading, exposure, development and the parameters of any intermediate annealing.

[0019] The example presented below uses nano-imprint resins, whether commercial or not. For example, we can take the EVG UVA resin (version 1 to 4). This resin mainly comprises two molecules, respectively 3.6 and 0.03% by mass in the material: Propyl Acrylate Si(OH) 3; Phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0020] The resin allows you to reproduce patterns: having a width and / or depth of between 50 nm and several hundred micrometers, for example between 50 nm and 500 µm; for a period (distance separating two neighboring patterns) which may be between 50 nm or 100 nm and several hundred micrometers, for example between 50 nm or 100 nm and 500 µm or even 1 mm.

[0021] The resin of this example contains 4% silicon, which is in the adequate range 1%-30% to carry out a process according to the invention.

[0022] The shaping by nano-imprinting of this resin is done here using a mold, for example a flexible mold made of PDMS, for example still based on acrylate (or another material compatible with this resin) transparent to the wavelength of 365 nm (photopolymerization wavelength, which takes place after nano-imprinting). This can be a reference mold EVG AS2, with which cavities 6 can be reproduced, 2 neighboring cavities being separated by a distance of 500 nm, each cavity having a height h (see Figure 2A) with a step width of 500 nm. These dimensions are given as an example: more generally, each pattern has at least one of its dimensions measured parallel (l) or perpendicular (h) to the substrate, between 50 nm and 1 mm. l can in particular be the width of the opening of the cavity, measured between the side walls 21 thereof; h can be the depth of this cavity, measured between the upper surface 22 of the pattern and its lower surface (or its bottom or its lower part) 23.

[0023] These cavities 6 are illustrated: in Figures 1A and 1B , which are scanning electron microscopy (SEM) images, with a field of view (FOV) of 3 µm ( Figure 1A ) And 6 µm ( Figure 1B ); more schematically in Figure 2A , which represents a cross-sectional pattern with a distribution of Si / SiO 2 species (symbolized by light dots) in the photopolymerized resin 11.

[0024] In the example illustrated by these figures, the parameters used for the resin shaping process are as follows (with “EVG Hercules cluster” type equipment): 500 mbar (pressure corresponding to the force relief applied to the flexible mold), lamp power of 600 mW / cm 2< (this power can be adjusted, for example between 50 and 600 mW / cm 2< ), for an exposure time of 8s, for an initial resin thickness of 800 nm.

[0025] Any other pattern shape can be made, for example cone-shaped or pyramid-shaped patterns or other. The process used is then adapted to the desired shape; for example, the shape of the mold is adapted to the desired pattern shape.

[0026] In order to generate roughness on the patterns produced, an oxidizing process is used, comprising at least one species or gas making it possible to slightly consume the mineral phase to reveal the areas having vacancies in Si / SiO 2 compounds. For example, and in a non-limiting manner, this gas can be composed of a fluorinated element (CF 4 , SF 6 ) and the Oxygen / Fluorine ratio can be modified in order to vary the roughness. Figure 2B represents the pattern of the Figure 2A , produced in the mineral resin 11, after implementation of the oxidizing process: the references 13a, 13b, 13c designate the roughnesses obtained (these are of course schematic representations), both on the upper parts 22 of the patterns, and on the sides 21 or on the bottom 23.

[0027] THE figures 3-5are comparative examples, for a commercial resin with a content of 4% in molar mass (version 4 of the UVA from EVG). These 3 figures are SEM images (FOV = 3 µm), and correspond to the implementation of various plasmas, without bias, at low temperature (for example between 50°C and 60°C) and for an etching time of 200 sec: there figure 3 corresponds to an O 2 plasma, without fluorinated species; we see in this figure that the gas has slightly consumed the resin at the foot of the patterns, but has not modified the roughness of the upper part or the lower part of the patterns (therefore not applying the teaching of the invention); the zones at the feet of the patterns are zones of constraints, in which the polymer chains may have undergone an elongation and where the silicon is distributed in a less homogeneous manner than elsewhere, which can explain the etching in these zones; The figure 4corresponds to the implementation of an SF 6 / O 2 plasma with a ratio of 1 / 25; we see in this figure that the gas has consumed resin in all parts and the average roughness Ra obtained on the surface is 15 nm; in this figure, as in the Figure 5 , Si is oxidized to SiO 2 , which is not consumed; The Figure 5 corresponds to the implementation of an SF 6 / O 2 plasma with a ratio of 3 / 25; we see in this figure that the gas has attacked the resin in all parts and the average roughness obtained on the surface is 25 nm; it is therefore greater than in the case of the figure 4 , for which the proportion of SF 6 was lower.

[0028] More generally, we have represented in figure 6 the evolution of the average roughness Ra obtained on the surface as a function of the SF 6 / O 2 ratio (the latter evolving between 0:25 and 3:25, with an intermediate point at 1:25) and this for the same resin as that used for the examples of figures 3-5. We can therefore see from this figure that it is possible to linearly adjust the average roughness obtained, in this example between 0.5 nm and 30 nm. A similar evolution is obtained for variable etching times but with a fixed SF 6 / O 2 ratio.

[0029] Using a resin with too high a Si / SiO 2 content does not allow the desired roughness to be obtained (for example SiArc with 40 - 50%, also known as JSR ISX412). However, it is possible to reduce this content to bring it back into the desired range, for example by adding an organic compound (resin or precursor).

[0030] In one example, an ISX412 resin and the IRGACURE 4265 precursor from BASF are used. At 0% added agent (or precursor), this material is non-printable; it becomes so with a proportion of 5 to 15% added agent, for printing times between 20 minutes (at 5% IRGACURE) and 5 minutes (at 15% IRGACURE), under a pressure of 30 bar and at 100°C.

[0031] In Figures 7-10 , examples are presented with 5% IRGACURE ( figures 7 and 8 ) and with 15% IRGACURE ( figures 9 and 10 , on which the patterns are made in the form of parallel strips), in which the resin is printed, then the whole can be covered with an organic resin 20 (which makes it possible to protect the underlying substrate for subsequent treatment only on the upper part of the patterns).

[0032] An etch-back step is applied to make the upper parts 22 of the printed patterns reappear, as illustrated in figure 7; but the roughness is not revealed (because the proportion of SiO 2 is too high, greater than 30%), and it is not revealed either by extending the etching (under O 2 / HBr plasma, with bias of 500 W) as presented on the figure 8 .

[0033] Using the 15% IRGACURE formulation, the roughness of the upper part of the patterns 24 is revealed from the etch-back stage ( figure 9 ) (because the proportion of Si / SiO2 is in the range 1-30%), and it is possible to completely remove the organic part 26 simply by extending the etching time ( figure 10 ; also under O 2 / HBr plasma with bias of 500 W).

[0034] Of the Figures 7-10 we can conclude that we can modulate the quantity of Si / SiO2 in order to bring it below the threshold of 30% (in molar mass) in order to allow the implementation of the process according to the invention.

[0035] In the examples described above, the resin layer 2 is deposited on a substrate 4 (see Figure 2A ) in silicon.

[0036] It is possible, as a variant, to deposit the resin on a layer 40 (see figure 11 ) of negative resin, after crosslinking or polymerization of the latter. We can then produce, as above, micrometric patterns by nano-imprinting in layer 2: this technique allows us to keep resin at the bottom of the patterns, as in Figure 2A . Alternatively, the micrometric patterns can be produced by optical or electronic lithography, using a mask 3, as shown in figure 11 . In this case, the background of the patterns is formed by the upper surface 4' of the underlying substrate but not by the resin in which the patterns are made.

[0037] So, the figure 12 represents micrometric patterns produced in a layer 2 of resin, by optical or electronic lithography, on a silicon support substrate 4, the upper surface 4' of which constitutes the background of the patterns.

[0038] Depending on the isotropic or anisotropic character of the plasma, the roughness can be formed only on the upper parts 22 of the patterns ( figure 12 ), or both on the upper parts 22 and the side parts 21. Similarly, within the framework of the Figure 2B above, the roughening can be carried out only on the upper part 22 and lower part 23 of the micrometric patterns, or also on the lateral parts 21, using an anisotropic plasma.

[0039] A structured surface obtained by a process according to the invention allows the grafting of fluorinated agents (which help with dewetting and therefore the evacuation of "dead" bacteria more easily in a solvent such as water) or silane. The grafting takes place on the nanometric patterns.

[0040] Whatever the method chosen, the patterns can have various shapes, for example circular, as illustrated in the Figures 1A-1B , 7, 8or in the form of parallel strips between them, as illustrated in figures 9, 10 .

[0041] A property of a structured surface obtained by a method according to the invention is that viruses cannot adhere to it due to the microstructures and the grafting carried out on the surface; the viruses are furthermore damaged by the roughness (nanometric structure) and where appropriate by the microstructure when it is of a protruding shape.

Claims

1. A method for producing a hybrid structure, including: - forming, on a substrate (4, 40), a layer (2) of mineral resin including a proportion of Si and / or SiO2 comprised between 1% and 30% by molar mass; - forming a structure including a plurality of patterns (6) in this layer, having at least one dimension (h, I), measured parallel or perpendicular to the substrate, comprised between 50 nm and 500 pm; - forming a roughness (Ra) on at least part of the surface of the patterns, by an oxidising method comprising at least one species or gas consuming part of the mineral phase.

2. The method according to claim 1, said oxidising method using a fluorinated element.

3. The method according to claim 2, said oxidising method using SF6 and / or CF4.

4. The method according to claim 3, said oxidising method using SF6, with a SF6 / O2 ratio comprised between 1:25 and 3:25.

5. The method according to one of claims 1 to 4, the roughness of the patterns being obtained by plasma, isotropic or anisotropic etching.

6. The method according to one of claims 1 to 5, the substrate (4, 40) being made of silicon or a crosslinked negative resin.

7. The method according to one of claims 1 to 6, said plurality of patterns in the resin layer (2) being obtained by nano-printing, or by optical or electronic lithography.

8. The method according to one of claims 1 to 7, the average roughness (Ra) obtained on at least part of the patterns being comprised between 0.5 nm and 30 nm.

9. The method according to one of claims 1 to 8, neighbouring patterns (6) being separated by a distance comprised between 50 nm and 1 mm.

10. The method according to one of claims 1 to 9, further including a step of grafting at least one fluorinated agent or silane.