WO2009071487A1

WO2009071487A1 - Method for making a micro-etching at the surface of a material

Info

Publication number: WO2009071487A1
Application number: PCT/EP2008/066410
Authority: WO
Inventors: Jean-Pierre Guin; Yi Fan Niu; Tanguy Rouxel
Original assignee: Universite De Rennes 1; Centre National De La Recherche Scientifique (Cnrs)
Priority date: 2007-12-03
Filing date: 2008-11-28
Publication date: 2009-06-11
Also published as: FR2924425B1; FR2924425A1

Abstract

The method of the invention first comprises selecting the material (1) from the group of glasses, glass-ceramics and ceramics containing at least one oxide, then forming a hollow micrometric imprint (2) in said surface (10) by applying a mechanical stress such as stamping, and finally immersing said surface (10) in an aqueous solution (6) having a pH higher than 7 for a duration sufficient for triggering a preferential dissolution of the material (21) located at the periphery of said imprint (2) in order to dig therein a cavity defining the micro-etching, said duration varying from a few hours to a few days.

Description

Method for micro etching the surface of a material

The present invention relates to a method for micro-etching the surface of a material, which consists of glass, ceramic or glass-ceramic.

By the terms "micro-engraving" or "micro-etching", the following description and the following claims will conventionally be understood to mean the making of one or more cavities of very small, punctiform and / or groove-like dimensions ( grooves) on the surface of said material, the dimensions of these cavities being at the micrometer scale, or even smaller.

These terms therefore also cover the fact of "nano-engraving" as well as "nano-engraving".

An object of the invention is to provide a method whose implementation is simple and inexpensive, not requiring the use of sophisticated devices, while achieving a very fine and very precise engraving, this in a controlled and reproducible manner. For this purpose, the process forming the subject of the invention first of all consists in selecting, from the family of glasses, glass-ceramics or ceramics, a material based on at least one oxide, and then forming, for example, applying a mechanical stress, a micrometric recess in said surface, and finally immersing this surface (with its imprint) in an aqueous solution whose pH is greater than 7 for a time ranging from a few hours to a few days, for example between 3 hours and 5 days -, which causes a preferential dissolution of the material located in the cavity and at the periphery of said cavity, so as to dig a cavity constituting the micro etching.

This process therefore comprises three successive phases, namely: a) the selection of a suitable material; b) a mechanical pressure action; c) a chemical action.

Moreover, according to a number of additional possible features of the invention: The impression is made by stamping or scratching by applying pressure.

The selected material contains at least one network formatter. This network former is one of the following elements: silicon, in its oxide form SiO ₂ ;

boron, in its oxide form B2O3;

phosphorus, in its oxide form P2O5;

germanium, in its GeO ₂ oxide form;

arsenic, in its oxide form As ₂ Os or AS2O3; zirconium, in its ZrO ₂ oxide form;

titanium, in its oxide form TiO ₂ ;

tin, in its oxide form SnO ₂ ;

aluminum, in its oxide form Al 2 O 3;

manganese, in its oxide form MgO; beryllium, in its BeO oxide form.

The pH of the aqueous solution is greater than or equal to 9. The aqueous solution is water, advantageously distilled. The aqueous solution is a sodium hydroxide solution (NaOH). The aqueous solution is hot water, whose temperature has a value of about 80 ^° C.

The treatment of the surface in the aqueous solution is carried out under pressure, and the temperature of the aqueous solution is higher than its normal temperature of boiling (at atmospheric pressure).

The immersion time of the impression in the solution is a few hours.

The imprint has a depth of between about 100 and 500 nm (nanometers) and a maximum width of between about 1 micron and 5 microns (micrometers).

It is possible to anneal the material after forming the impression and before immersion in the aqueous solution.

The impression is punctual, or almost punctual. The impression is linear, furrow-shaped, rectilinear and / or curvilinear.

The successive stages of formation, by application of a mechanical stress, of a hollow micrometer impression in the surface of the material, and of immersion in an aqueous solution whose pH is greater than 7, are repeated several times at the same place of said surface, which may allow to modify if necessary the geometry and the dimensions of the final engraving.

In order to obtain a given cavity size, particularly in terms of width and depth, the soaking time of the surface in the aqueous solution is determined by means of abacuses, as a function of the shape and dimensions of the tool used to make said imprint by stamping or scribing, and the pressure implemented for this operation.

Other features and advantages of the invention will appear on reading the description which follows, with reference to the appended drawings in which:

Figure 1 is a three-dimensional representation and imaged (by atomic force microscopy), a glass surface having a stamped imprint, before chemical treatment.

Figure 2 is a view similar to Figure 1 showing the cavity constituting the micro etching obtained after the chemical treatment.

Figure 3 is a sectional view of the cavity and the cavity, this view being intended to show the shapes and dimensions.

Figures 4 to 4E are diagrams showing the various steps of the method of the invention for producing a point cavity. Fig. 5 is a perspective view showing a stamping tool.

FIGS. 6, 6A and 6B are perspective views showing certain steps of the method of the invention for producing a pattern with linear cavities, by using the tool of FIG. 5. FIGS. 7A and 7B are detailed views showing the section of the cavity and cavity respectively obtained, corresponding to the sectional planes respectively referenced AA in Figure 6A, and BB in Figure 6B. Figure 8 is a side view of a pressure grooving tool.

FIG. 9 is a section on a larger scale of the active part of the tool, cut by the plane CC of FIG. 8.

Figure 10 illustrates how to proceed to draw a curvilinear groove in the surface of a material using this tool.

Figure 1 shows a portion of a plate 1 of oxide glass with flat surface 10, for example polished.

In the embodiment of the invention hereinafter described by way of example only, and in no way limiting, it is a soda-lime-silica glass of the kind commonly used, for example for the manufacture of windows. .

Within this glass, silicon (in its SiO ₂ form) is a network forming element while sodium (in its Na ₂ O form) is a network modifying element.

The molar content of Na ₂ O is greater than 10%, for example of the order of 13.5%.

The mechanical step of the method consists in forming in the surface 10 by stamping, that is to say by mechanical pressure, an indentation designated by reference 2 in FIG.

In the illustrated example, the impression was made by means of a pyramid-shaped diamond-shaped stamper tool with an approximately square base, with application of a load of 50 mN.

This kind of tool is used for indentation tests "Vickers".

The footprint 2 has a shape complementary to that of the tip of the tool. Its dimensions and its depth are functions of the intensity of the pressure developed during the indentation.

The mouth of the cavity 2 is surrounded by a bead 20 which protrudes from the plane of the surface 10 and which results from the creep of material related to the stamping operation.

In Figure 3 the scales in abscissa and ordinate are different. The graduation of the abscissa axis is in micrometers; that of the ordinate axis is in nanometers. On observing this figure, it can be seen that the width of the impression 2 (at the level of the surface 10) is about 2.5 micrometers, while its depth is about 350 nanometers, ie 0.35 micrometer.

The pressure developed by the "indenter" tool during stamping has the effect of locally modifying, at the right of the indentation and in its immediate vicinity, the atomic structure of the material. This is due to the introduction of structural defects and the diffusion of chemical species, eg sodium, in this area.

Stamping also creates a residual stress field around the indentation.

The subsequent step of the process consists in placing the previously stamped wafer in a tray containing an aqueous solution, such that at least the impression 2 is totally immersed therein.

This aqueous solution has a pH greater than 7, thus basic.

Preferably the pH is greater than 9.

In the embodiment described, the solution is distilled and hot water, at a temperature of 90 ^° C.

The mechanical stamping action on the surface 10 of the material 1 results in a localized densification of the material 1 as well as the creation of localized residual stresses at and near the cavity.

The ionic exchange between hydronium (H3O) cations present in water and sodium (Na ⁺ ) cations present in glass 1 raises the pH value, which leads to a hydrolysis of certain atomic bonds Si - O - If weakened by mechanical action, resulting in a progressive preferential dissolution of the skeleton of silica in the heart of the glass, in and around the footprint.

In practice, this phenomenon appears beyond a pH of 9. The dissolution of the material induces the formation of an increasingly larger cavity around the impression 2, as well as the disappearance of the bead 20. given immersion period, stabilization and stopping of the phenomenon of preferential chemical attack is observed. Advantageously, the wafer 1 is rinsed with distilled water and then dried.

The operation is then complete.

In practice, this immersion period is of the order of several hours, or even a few days, in the implementation mode described here.

Appropriate heating means are provided, of course, to maintain the temperature of the water tank at a value of 90 ⁰ C during this period, and to make a top-up of water, if necessary, to compensate evaporation. The treatment being completed, there is obtained a cavity 3, substantially larger than the imprint 2, of approximately parabola-shaped section, with a regular and solid wall, with a smooth surface.

With the observation of Figure 3, we see that the width of the cavity 3 (at the surface 10) is about 5 microns, while its depth is about 485 nanometers, 0.485 micrometer.

The stamping can be performed in a point manner by indentation tools having a non-pyramidal shape, for example conical, frustoconical or hemispherical.

The shape and dimensions of the tool, as well as the load applied to it, of course determine the shape and dimensions of the impression and the area around it, but also those of the resulting cavity.

Figures 4 to 4E illustrate very schematically the method of the invention for producing a micrometer cavity 3 in a material 1 based on at least one oxide, belonging to the family of glasses, glass-ceramics or ceramics.

The tool "indenter" (or stamper) 4 shown in Figures 4 and 4A has a tip end 40.

FIG. 4A shows the formation of a micrometric cavity 2 recessed in the surface 10 of the material, by axial pressure F of the tool 4. A protruding peripheral bead 20 surrounds the cavity 2.

FIG. 4B represents the latter, after removal of the tool 4. The zone of material 21 surrounding the cavity, shown hatched, is a densified zone, whose structure has been modified during the stamping action, under the action of residual stresses.

The Si-O chemical bonds are weakened under a hydrolysis reaction.

FIG. 4C shows the subsequent step of dipping the material 1 in an aqueous solution 6 whose pH is greater than 7, contained in a tank 5.

This is for example a hot sodium hydroxide solution (NaOH).

As an indication, its temperature is 80 ⁰ C and its pH is equal to 10.5. The liquid 6 causes a preferential and progressive dissolution of the material zone 21 surrounding the cavity, including the bead 20 (FIG. 4D).

It should be noted that there is also a certain uniform and homogeneous superficial dissolution of the material of the other parts of the part 1 which are in contact with the liquid 6, in particular of the surface 10. However, this dissolution is attenuated, significantly less important than for zone 21.

The dimensions of the cavity depend on the shape and size of the indenter, the force applied by it, and the soaking time.

The final dimensions of the cavity can be modulated by the time spent by the imprint of the surface in the solution. For example, for 50 mN, in a solution of 0.1 N NaOH brought to 80 ⁰ C, the maximum depth of the cavity is obtained after 35 hours of soaking. It is therefore possible to provide abacuses making it possible to anticipate the final dimensions of the cavity as a function of the soaking time for the given conditions.

After washing with distilled water and drying, the piece 1 illustrated in FIG. 4E is obtained, having a surface 10 hollowed out of a cavity 3 with a smooth and regular wall, devoid of any bead.

The removal of this bead is essential for certain applications, in particular for the subsequent application of a thin layer and / or if a perfect seal is required at the edge of the micro etching. It has been found that the use of a hot solution makes it possible to reduce the duration of immersion treatment, since the phenomenon of dissolution of the densified zone is all the more rapid and effective as the temperature of the bath is high.

Under these conditions, it may be advantageous to carry out this step at a high pressure, for example inside an autoclave, in which the temperature of the solution is high (higher than its normal boiling temperature), said However, the solution remains in the liquid phase. This speeds up the process.

Figures 5 to 7B relate to the realization of a micro engraved pattern formed of lines which, in this case, draw the letter "f" (lowercase). The stamping tool, shown in FIG. 5, is a plate 7, one face of which has a rib 70 with an inverted contour, symmetrical to that of the etching to be made. This rib has a V-section, with a sharp edge, and is made of a material hard enough to stamp correctly the glass material, glass ceramic or ceramic to be treated. FIG. 6 shows the pressing stamping operation P of the tool 7 against the surface 10 of this material 1. The edge of the rib 70 penetrates this surface, forming a linear impression 2 'therein.

Figures 6A and 7A show the shape of the latter, section "V", bordered by a bead. After immersion in the appropriate treatment solution, the micro-etching 3 'in "f" illustrated in FIGS. 6B and 7B is obtained.

Instead of embossing by stamping, it can be achieved by scratching with pressure application (not by removing material).

Figure 8 shows a tool 8 adapted to this procedure. This tool has a handle 81 for its gripping, and a working head 80, which connects to the handle 81 by a profiled portion 82 conferring a gooseneck configuration.

As can be seen in FIG. 9, the head 80 has a triangular section with a ridge 800 that is slightly blunted (rounded) so as to be able to penetrate forcefully into the surface 10 of the material 1, but without creating a crack. Of course, this head is made of a sufficiently hard material to stamp correctly the glass material, glass ceramic or ceramic 1 to be treated.

FIG. 10 shows how to draw a linear impression 2 "in the surface 10 by exerting on the head 80 a pressure Q, combined with a displacement R of the tool, by modifying the trajectory and orientation of the head during this displacement, it is possible to describe a line having the desired contour.

This procedure is similar to a kind of dynamic stamping.

The surface 10 is then chemically treated, by dipping in a suitable solution, according to the invention, in order to obtain the micro etching

It is thus possible to draw specific and varied patterns on the surface of the glass. After chemical treatment by immersion of this surface in the aqueous solution, slightly larger and deeper grooves are obtained than the constituent grooves of said patterns, with a smooth and regular wall, and of the same chemical composition as the solid material.

On the same surface, one can of course achieve engravings comprising both point and continuous cavities.

It is possible to repeat the same sequence of operations several times at the same place in order to obtain deeper and wider cavities in the end than with a single treatment.

According to a possible implementation of the method, when the material is glass or glass-ceramic, it is possible to anneal the material after making the surface impression and before immersion in the aqueous solution.

This treatment is carried out in an oven at a temperature slightly lower than the glass transition temperature Tg of said material. The treatment temperature T is, for example, equal to 0.9 Tg.

Thus, if Tg = 823 K (Kelvin), T = 741 K. The temperature rise in the oven is done gradually, in stages. The holding time of the material at the temperature T is for example of the order of 2 hours, after which it is allowed to cool naturally in the oven until the ambient temperature is restored. This additional heat treatment has the advantage of relaxing the residual stresses produced during the mechanical action of pressure and thus reducing the final size of the microgravure (depth and width).

The industrial applications of the invention are varied.

As examples only, the following can be mentioned:

- engraving of glass in the field of optics;

- production of very fine channels in the microfluidic domain;

surface texturing, especially in the biomedical field, for example on biocompatible prostheses; - production of reaction cuvettes in the field of microbiology;

- etching patterns on surfaces for molding plastic parts.

This statement is in no way limiting.

Claims

A method for producing a micro etching on the surface of a material, which first consists in selecting this material (1) in the family of glasses, glass-ceramics or ceramics, based on at least one oxide, then to form, by application of a mechanical stress, a micrometric cavity (2) recessed in said surface (10), and finally to immerse this surface (10) in an aqueous solution whose pH is greater than 7 for a time ranging from a few hours to a few days, which causes a preferential dissolution of the material located at the periphery of said cavity so as to dig a cavity (3) constituting the micro etching.

2. Method according to claim 1, characterized in that one forms said impression by stamping or scoring by applying a pressure.

3. Method according to claim 1 or claim 2, characterized in that the selected material contains at least one network former which consists of one of the following elements: silicon, in its oxide form SiO ₂ ;

boron, in its oxide form B2O3;

phosphorus, in its oxide form P2O5;

germanium, in its GeO ₂ oxide form;

titanium, in its oxide form TiO ₂ ;

tin, in its oxide form SnO ₂ ;

aluminum, in its oxide form Al 2 O 3;

manganese, in its oxide form MgO; beryllium, in its BeO oxide form.

4. Method according to any one of claims 1 to 3, characterized in that the pH of said solution is greater than or equal to 9.

5. Method according to any one of claims 1 to 3, characterized in that said aqueous solution is water, preferably distilled.

6. Method according to any one of claims 1 to 4, characterized in that said aqueous solution is a sodium hydroxide solution.

7. Method according to claim 5, characterized in that said aqueous solution is hot water, whose temperature has a value of the order of 80 ⁰ C.

8. Process according to any one of claims 1 to 7, characterized in that the surface treatment in the aqueous solution is carried out under pressure, and that the temperature of the aqueous solution is higher than its normal boiling temperature. .

9. Method according to any one of claims 1 to 8, characterized in that the immersion time of said imprint in the aqueous solution is a few hours.

10. Method according to any one of claims 1 to 9, characterized in that said footprint (2) has a depth of between 100 and 500 nm (nanometers) and a maximum width of between 1 and 5 microns (micrometers) about.

11. Process according to any one of Claims 1 to 10, characterized in that the material is annealed after forming the impression and before immersion in the aqueous solution.

12. Method according to any one of claims 1 to 11, characterized in that said footprint (2) is point, or almost punctual.

13. Method according to any one of claims 1 to 11, characterized in that said fingerprint is linear, groove-shaped, rectilinear and / or curvilinear.

14. Method according to any one of claims 1 to 13, characterized in that the successive steps of forming, by application of a mechanical stress, a micrometer cavity (2) recessed in the surface (10) of the material, and immersion in an aqueous solution whose pH is greater than 7, are repeated several times at the same location of said surface.

15. The method of claim 2, characterized in that in order to obtain a given cavity size, particularly in width and depth, the soaking time of the surface (10) in the aqueous solution is determined by means of abacuses, this according to the shape and dimensions of the tool used to make said impression by stamping or scoring, as well as the pressure implementation for this operation.