WO2020021142A1

WO2020021142A1 - Method for transferring micro- and/or nano-structured patterns to arbitrary surfaces

Info

Publication number: WO2020021142A1
Application number: PCT/ES2019/070513
Authority: WO
Inventors: Gemma RIUS SUÑÉ; Olga MUNTADA LÓPEZ; Francesc Xavier PÉREZ-MURANO
Original assignee: Consejo Superior De Investigaciones Científicas
Priority date: 2018-07-24
Filing date: 2019-07-23
Publication date: 2020-01-30
Also published as: ES2775649B2; ES2775649A1

Abstract

The present invention refers to a method for transferring high-resolution micro- and/or nano-structured patterns to arbitrary surfaces, based on the use and manipulation of a sacrificial sheet. Furthermore, in the method of the present invention, the micro- and/or nano-structured patterns of the sacrificial sheet are transferred in such a way that they are in direct contact with the surface of interest, without using an adhesive material as an interface. Consequently, the present invention can be classified in the field of surface processing.

Description

Procedure for transferring micro-v / or nanostructured motifs to arbitrary surfaces

The present invention relates to a method of transferring micro- and / or nanostructured motifs of high resolution to arbitrary surfaces, from the use and manipulation of a sacrificial sheet. Furthermore, in the process of the present invention, the micro- and / or nanostructured motifs of the sacrificial sheet are transferred so that they are in direct contact with the surface of interest, without the use of an adhesive material as an interface.

Therefore, the present invention can be framed in the area of surface processing.

BACKGROUND OF THE INVENTION

The industrial interest in arranging micro and nano structures on surfaces is multiple. In the first place, the texture of micro / nano-metric dimensions allows surfaces to be provided with functional properties, such as hydrophilicity, hydrophobicity, greater adhesion, bacterio-fobicity, optical or chromatic effects, and, for Therefore, it is relevant in a wide variety of applications (antibacterial, antimicrobial, self-washable, decoration, etc.). These properties provide added value to a wide variety of products. On the other hand, micro and nano structures, such as micro and nano particles, micro and nano wires, aligned and / or properly positioned, can provide surfaces with advanced functionalities. For example, semiconductor nano-wire arrays can be used as light emitters, or interconnected semiconductor metal micro / nano wires can be used as sensors.

To achieve a good definition and positioning of micro and nano structures on surfaces, conventional lithographic techniques such as optical lithography or electron beam lithography are used, which are very efficient for defining micro and nanometric patterns on flat and low rough surfaces. However, most lithographic techniques cannot be used or have significant limitations to apply to surfaces with curvature or certain types of substrates. Having nanometric patterns on surfaces of arbitrary morphology responds to needs that appear in various fields such as decoration, construction or automotive, since many objects that are used daily have curved surfaces. Ultimately, a nanostructuring technology of high resolution, precision and flexibility surfaces would allow the creation of intelligent surfaces (in English 'smart surfaces') by including complex functionalities (for example, sensors that detect substances and emitters that emit signals).

Most of the methods reported to date that do not use lithography to define or transfer motifs on arbitrary surfaces are based on defining the motifs by structuring a mold that is subsequently transported to the surface of interest where a post-processing is performed (W02017201602A1, US2015202834A1 ). These methods have (i) limitations regarding the (production and) transfer of arbitrary shapes and sizes, understood as the ability to generate any design (in English, pattern), and ii) restrictions on the type of material which allows transfer, by only applying to certain materials or requiring mediating layers to improve adhesion.

Consequently, it is necessary to develop new procedures for obtaining micro- and / or nanostructured motifs on surfaces of any morphology and size.

DESCRIPTION OF THE INVENTION

The present invention relates to a high precision process for obtaining high resolution micro- and / or nanostructured motifs on an arbitrary surface of interest, that is, on a receiving substrate of interest. It is based on defining motifs directly on top of a sacrificial or transfer sheet, which, once these motifs are defined, is separated from the initial substrate and placed on the surface of interest of the receiving substrate. In the process of the present invention, the micro- and / or nanostructured motifs, initially defined on the slaughter or transfer sheet, are disposed, at the end of the process, in direct contact with the surface of interest of the receiving substrate.

The process of the present invention is simple and requires a small number of steps. Unlike the methods known in the state of the art and currently used, it does not require the prior manufacture of a mold, and does not consist of structure the slaughter or transfer sheet, but define solid motifs on its surface and transfer them to the surface of interest of the receiving substrate.

The process of the present invention allows the design of a wide variety of micro- and nanostructured motifs. It can be carried out with a wide variety of materials of different nature such as metals, ceramic materials, etc., and is compatible with most standard micro- and nano-manufacturing processes, including microelectronic processes and especially indicated to complement the Replication processes, such as roll-to-roll printing or plastics injection molding.

The process of the present invention has a special interest in the structuring of molds for injection of plastics and the structuring of printing rollers (in English roll-to-roll).

It is also interested in structuring surfaces of interest of receiving substrates to include in them functional properties such as color, hydrophobicity, hydrophilicity, self-washing or bacterio-fobicity.

The process of the present invention also has an interest in the manufacture of electronic, magnetic and / or optical devices where electronic, magnetic and / or optical functionality is of interest. Other functionalities related for example with plasmonic and / or phonic are derived from the nanometric dimensions of the micro- and / or nanostructured motifs and also have an interest in the manufacture of electronic, magnetic and / or optical devices.

In particular, the application of the transfer procedure of the present invention applied to complex, functional and / or active structures that allow adding intelligence to the surface (in English smart surfaces).

Finally, the process of the present invention has an interest in the transfer of motifs to surfaces of interest of receiving substrates so that said motifs serve as a mask for a selective attack of said substrate,

Therefore, in a first aspect, the present invention relates to a method of transferring micro- and / or nanostructured motifs onto a surface of interest (from here the "process of the invention") characterized in that it comprises the following steps:

a) depositing a polymeric slaughter sheet on a substrate to form a slaughter-substrate sheet system,

b) generate micro- and / or nanostructured motifs on the surface of the sacrificial sheet of the system obtained in step (a) by lithography or deposition methods with or without a mask,

c) separating the sacrificial sheet with the micro- and / or nanostructured motifs obtained in step (b) of the substrate by technically non-demanding mechanical means,

d) placing the sacrificial sheet on the surface of interest leaving the micro- and / or nanostructured motifs of the sacrificial sheet obtained in step (c) in direct contact with the surface of interest, while the sacrificial sheet assembly -surface of interest is immersed in water,

e) dry the set obtained in step (d), and

f) remove the slaughter sheet from the assembly obtained in step (e) by physical, chemical methods or a combination thereof.

In the process of the present invention, the term "micro- and / or nanostructured motifs" is understood as solid structures of lateral dimensions between 10 nm and 10 mhi, and thickness less than 1 mhi. The composition of said solid structures is metallic; The micro- and / or nanostructured motifs are composed of at least one metal or one metal alloy. The composition of the micro- and / or nanostructured motifs can be stratified

The term "surface of interest" is understood in the present invention as that surface of a receiving substrate where it is desired to generate micro- and nanostructured motifs. The surface of interest of the receiving substrate may be curved, machined or pre-structured. By "pre-structured surface" is understood, in the present invention as that surface that has been processed prior to the transfer of the micro- and / or nanostructured motifs to define therein, for example, a set of structures, a certain relief, a certain roughness or texture, or a certain composition. The surface of interest is not limited to a single surface within the receiving substrate; it can contemplate different surfaces within the same receiving substrate that are physically separated from each other.

Step (a) of the process of the invention relates to the deposition of a polymeric slaughter or transfer sheet on a substrate to form a slaughter-substrate sheet system.

By the term "polymeric slaughter or transfer sheet" refers to a sheet, usually composed mostly of a polymer, which is used to transfer the micro- and / or nanostructured motifs onto the surface of interest. The transfer or slaughter sheet is not part of the final piece with micro- and / or nanostructured motifs.

By the term "substrate" is understood in the present invention, as a stable and flexible substrate, to be able to be transferred without being damaged and to be able to adapt to any surface of interest, that is, to any surface of the receiving substrate.

The surface of the substrate can be curved, flat or structured. In a preferred embodiment of the present invention, the substrate of step (a) is a flat substrate.

The choice of the polymeric sacrificial sheet and the substrate is key in the process of the present invention, since it must fulfill the condition that the polymeric sacrifice sheet has sufficient adhesion with the substrate but at the same time is easily separable therefrom, that is, the polymeric sheet must be easily detached from the substrate.

The polymeric slaughter sheet must be mechanically stable to be transported to another substrate / surface of interest. It is also advantageous for the polymeric slaughter sheet to be flexible so as to be able to conform to curved end substrates.

Step (b) of the process of the invention relates to the generation of micro- and / or nanostructured motifs on the surface of the slaughter or transfer sheet of the slaughter-substrate sheet system obtained in step (a) by High resolution lithography or deposition methods with or without a mask. The micro- and / or nanostructured motifs are generated on the slaughter or transfer sheet by consolidated techniques based on lithography, or deposition methods with or without a mask. These methods allow a good adhesion of the micro- and / or nanostructured motifs to the slaughter or transfer sheet. The micro- and / or nanostructured motifs printed on the slaughter sheet will remain until the end of the procedure and will be printed on the surface of interest of the receiving substrate. The micro- and / or nanostructured motifs are composed of at least one metal or one metal alloy.

In a preferred embodiment of the process of the present invention, the composition of the micro- and / or nanostructured motifs is stratified, that is to say the composition varies along its thickness.

Examples of lithography types are optical lithography, electron beam lithography, nano-printing lithography, lithography based on atomic force microscopy, lithography based on block copolymers, deposition methods with or without a mask such as ion beam deposition focused, by focused electron beam or deposition with shading mask.

Step (c) of the process of the present invention relates to separating the micro- and / or nanostructured slaughter sheet obtained in step (b) from the substrate by mechanical means, for example, by detaching the polymeric layer manually by means of the help of tweezers.

Step d) of the process of the invention relates to the placement of the sacrificial sheet on the surface of interest so that the micro- and / or nanostructured motifs of the sacrificial sheet obtained in step (c) remain in direct contact with the surface of interest, the whole slaughter-surface sheet of interest being immersed in water.

As mentioned above, the surface of interest of the receiving substrate can have any morphology: for example, the surface can be curved or can be pre-structured or mechanized. Examples of area of interest are metal molds for plastic injection processes, printing rollers or curved parts for decoration.

In a specific implementation, the surface of interest may be previously immersed in a container with water and on it the sacrificial sheet is placed so that the micro- and / or nanostructured motifs of the sacrificial sheet are in direct contact with The surface of interest.

The slaughter-surface sheet assembly of interest must be immersed in water to promote adhesion. Simply placing the polymer motif layer on the chosen substrate would not provide sufficient mechanical adhesion and this would possibly be non-uniform, that is, there would only be local contact between the sheet and the substrate. Adhesion is the bonding force at the contact interface between two materials (in this case, between the micro- and nano-motifs and the polymer), and is described as van der Waals forces. Sufficient adhesion is necessary to i) enable the removal of the polymeric layer, while maintaining the motifs in the desired arbitrary substrate, and

ii) to favor the adhesion of the motifs to the substrate, that is, to enable their use, for example, in injection molding processes, to guarantee certain durability and robustness of the mold.

Adhesion at the microscopic level depends, on the one hand, on the roughness of both surfaces, but also on the degree of wetting of the intermolecular contact. In the transfer process of the present invention, adhesion is emphasized and facilitated by

i) metal / water surface tension / polymer motifs, and

ii) by the use of a flexible transfer sheet.

As mentioned above, the surface of interest where the motifs are transferred can have any morphology, for example the surface can be curved or can be pre-structured or mechanized.

Slow drying, that is the evaporation of water under appropriate conditions, is also key to achieving the desired adhesion. Step (e) of the process of the invention relates to the drying of the slaughter-surface sheet assembly of interest. For this stage (e) to be effective, it is sufficient to let the surface system rest of interest-slaughter sheet for a few hours in environmental conditions so that the remaining water is eliminated progressively and uniformly. Other alternatives such as high temperature drying and / or in a low humidity environment may be equally convenient.

The last step (f) of the process refers to the removal of the sacrificial sheet from the surface of interest by physical, chemical methods or a combination thereof. The method of disposal will depend on the material of the surface of interest, and should selectively remove the transfer or slaughter sheet without damaging the motives to be transferred or the surface of interest.

Examples of physical methods to eliminate the sacrificial sheet include attack by argon ions or by oxygen plasma.

In a preferred embodiment of the process of the present invention, chemical dissolution methods are used using solvents for organic materials such as acetone since the slaughter or transfer sheet is of polymeric type, and the reasons to be transferred to the surface of interest are composed of a metal or an alloy.

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and figures are provided by way of illustration, and are not intended to be limiting of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. General sequence of the process of the invention

FIG. 2. Concrete description of an implementation of the method of the invention

FIG. 3. Electron microscopy (SEM) images of motifs transferred to a flat and optically polished substrate (silicon substrate) using the method described in Figure 2 (A-11). FIG. 4. (A) Photograph of a polished and curved steel sheet where micrometric and nanometric motifs have been transferred using the procedure described in Figure 2. (BD) SEM images of the motifs transferred to steel sheet of Figure A using the method described in figure 2 (A-12). The SEM image of Figure D corresponds to a small area of the area shown in Figure C.

EXAMPLES

Next, the invention will be illustrated by tests carried out by the inventors, which demonstrates the effectiveness of the product of the invention.

In Figure 1 the following differentiated steps of the process of the present invention can be observed: (A) Deposition of a sheet (1) (transfer or sacrifice sheet) on a flat substrate (2).

The fact that the flat substrate is flat facilitates the use of lithography methods for the realization of the micro / nano structured motifs to be transferred. (B) The second step consists in generating the motifs (3) on the layer (1). The shape and positioning of the structures generated in this slaughter sheet will be maintained at the end of the process in the receiving substrate.

(C) The third step consists in the separation of the substrate from the sacrificial sheet (1) with the micro / nano structured motifs (3).

(D) (E) The fourth step consists in the transfer of the inverted sheet (1) with the structured micro / nano motifs (3) to the receiving / interest substrate (4). The transfer or sacrifice sheet is transferred turned upside down, so that the micro-nano structured motifs (3) are in direct contact with the receiving substrate (4).

(F) In the last step, the transfer sheet (1) is removed by physical, chemical methods, or a combination of both, obtaining the original motifs (3) on the surface of interest (4) In the following sequence of stages, see figure 2, the materials used experimentally are specified in parentheses.

(A) First, a polymer sheet (1) (polyimide) is deposited on a silicon substrate of very low roughness (optical polishing) so as not to limit the maximum resolution obtainable (2). The transfer sheet:

• allows the creation of a thin sheet on a flat substrate by spin coating (rotation deposition)

• It is compatible with lithography-based nano-manufacturing processes (and in particular electron beam lithography, metal deposition and lift-off), which allows the definition of structures on its surface

• It is easily detached from the initial flat substrate

• It is mechanically stable to be transported to another substrate

• It is flexible enough to be able to conform to curved, pre-structured or machined end surfaces

• It can be eliminated by selective attack without damaging the motives to be transferred or the surface of interest, for example by an oxygen plasma attack.

(B) The second step consists of an electron beam lithography process to define the motifs with high precision in the micro / nano scale. This process includes: the deposition of the layer of a sensitive resin (3) (PMMA), its irradiation with an electron beam and its development (MIBK: IPA), leaving areas of the covered polyimide and areas of the polyimide discovered

(C) It is convenient to deposit an additional layer of conductive material to avoid the accumulation of electrical charges in the polyimide and the PMMA during the electron beam exposure process. This additional layer can then be easily removed by immersion in water.

The next phase is the transfer of the motifs defined in resin to the silicon substrate or to the curved steel sheet, which consists of: (D) The deposition of a thin layer of metal (4) (Ti + Au) followed by (E) the removal of the electron-sensitive resin.

(F) The separation of the initial substrate from the flexible polymeric layer with the micro / nano metal motifs is very simple. It is done mechanically, and can consist simply of peeling off the layer manually, for example, with the help of tweezers.

(G) The separated layer is placed turned over pure water into a container.

(H1) The transfer to the surface of interest of the receiving substrate has been done manually. It is simply based on collecting the polymeric layer decorated with metal motifs and placing it in contact with the surface of interest of the receiving substrate. When turned upside down, the metal motifs are in direct contact with the surface of interest of the receiving substrate. Transfers have been made to a flat substrate (H1) (silicon substrate) and to a curved substrate (H2), steel sheet.

(I) Once dried, the polymeric layer used in the transfer is removed by a conventional method of etching, that is, a reactive ion attack.

As can be seen in figures 3 and 4, the method allows the reliable transfer of motifs, with sub-micrometric resolution (it has been demonstrated for motifs of lateral dimensions slightly below 300 nm) on both flat and curved surfaces. The maximum transfer area so far has been approximately 25 cm ² , although the method is expandable both in resolution (below 50 nm) and in maximum area (700 cm ² ).

Claims

1. A method of transferring micro- and / or nanostructured motifs onto a surface of interest characterized in that it comprises the following steps: a) depositing a sacrificial polymer sheet on a substrate to form a sacrificial-substrate sheet system,

b) generate micro- and / or nanostructured motifs on the surface of the sacrificial sheet of the system obtained in step (b) by lithography or deposition methods with or without a mask,

c) separating the micro- and / or nanostructured slaughter sheet obtained in step (b) of the substrate by mechanical means,

d) placing the sacrificial sheet on the surface of interest leaving the micro- and / or nanostructured motifs of the sacrificial sheet obtained in step (c) in direct contact with the surface of interest, where the sacrificial sheet assembly -surface of interest is immersed in water,

e) dry the set obtained in step (d), and

2. The method according to claim 1, wherein the substrate of step (a) is a flat substrate.

3. The method according to any of claims 1 or 2, wherein the micro- and / or nanostructured motifs are composed of at least one metal or an alloy.

4. The method according to claim 3, wherein the composition of the micro- and / or nanostructured motifs is stratified.

5. The method according to any of claims 1 to 4, wherein, in the step

(f), chemical dissolution methods are used.