WO1997038301A1

WO1997038301A1 - Method for manufacturing an array of microelectrodes

Info

Publication number: WO1997038301A1
Application number: PCT/CA1997/000236
Authority: WO
Inventors: Gilles Y. Champagne; Michel Ladouceur; Jean Chevalet; My Ali El Khakani; Mohamed Chaker
Original assignee: Hydro-Quebec; Institut National De La Recherche Scientifique (Inrs); Centre National De La Recherche Scientifique (Cnrs)
Priority date: 1996-04-11
Filing date: 1997-04-08
Publication date: 1997-10-16
Also published as: CA2173932A1; JP2000517413A; AU2283797A

Abstract

The method for manufacturing an array of microelectrodes on an electrically insulated top surface of a substrate comprises the following sequence of steps. A thin layer of a metal or metal alloy is deposited by laser ablation onto the top surface of the substrate and through openings of a mask provided on this top surface. The array of microelectrodes is then revealed by removing the mask from the top surface. Advantageously, the method according to the present invention allows to manufacture microelectrodes made of any metal even inert metals and metal alloys and disposed in a precise design.

Description

METHOD FOR MANUFACTURING AN ARRAY OF MICROELECTRODES

FIELD OF THE INVENTION

The present invention relates generally to microelectrodes and to methods for manufacturing microelectrodes. More particularly, the present invention relates to a method for manufacturing an array of microelectrodes on an electrically insulated substrate.

BACKGROUND OF THE INVENTION

Microelectrodes may be defined as electrodes whose critical dimension is in the micrometer range. Recent studies have shown that by reducing the critical dimension of electrodes used in electroanalysis, the range of elements in a given solution that may be detected and quantified with an adapted sensor may be greatly extended. For example, detection, at the trace level, of the concentration of various heavy metals in water may be possible with a sensor provided with such microelectrodes. Advantageously, these sensors may be very useful for controlling the environment quality. Presently, one major challenge with the fabrication of those sensors is to obtain microelectrodes set in a precise given design with a simple and economically viable process. Another problem that arises with any physico-chemical process using electrodes or microelectrodes is the preservation of the nature and integrity of the electrode surface. A solution to this problem is to obtain electrodes made of a very stable material such as iridiu , rhodium etc. However, these inert materials, because of their very high hardness, their high point of fusion and extreme chemical inertia, are generally not very workable. They are difficult to transform or to deposit. Therefore, the method used for working with those inert materials is generally very complex and expensive. For the foregoing reasons, there is presently a need for a method of fabricating microelectrodes arranged in a precise design that is simple and low in cost and that allows to easily work with any metal, even inert material such as iridium.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for manufacturing an array of microelectrodes on a substrate that satisfies these needs. More particularly, an object of the present invention is to provide a method for manufacturing an array of microelectrodes on an electrically insulated top surface of a substrate. The method comprises the following sequence of steps: a) depositing by laser ablation a thin layer of an electrically conductive material onto the top surface and through openings of a mask provided on the top surface, the electrically conductive material being selected from the group consisting of metals and metal alloys; and b) revealing the array of microelectrodes by removing the mask from the top surface. Preferably, the method further comprises before step a), a step by which the mask is provided onto the electrically insulated top surface according to a photolithographic process.

The thin layer of electrically conductive material is preferably made of a metal selected from the group consisting of gold, silver, platinum, iridium, rhodium, ruthenium, rhenium and palladium and more particularly from the group consisting of iridium, rhodium, ruthenium and palladium or with a metal alloy comprising as main constituent at least one metal selected from the group consisting of iridium, rhodium, ruthenium and palladium.

Advantageously as mentioned hereinbefore, the method for manufacturing an array of microelectrodes according to the present invention allows to manufacture microelectrodes made of any metal, even inert metals and metal alloys, and disposed in a precise design. Also, this method which essentially makes use of laser ablation deposition on a masked substrate is simple and low in cost. Furthermore, the use of laser ablation according to the present invention allows the manufacturing of microelectrodes made of a metal alloy.

Advantageously and according to a preferred embodiment of the invention, it is possible to obtain a precise array or design of microelectrodes by using X-ray microphotolithography for masking the substrate, each icroelectrode having a critical dimension of less than 1 μm and preferably less than 0,5 m.

A non restrictive description of a preferred embodiment will now be given with reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic top view of a sensor provided with a first preferred embodiment of an array of microelectrodes made according to the teaching of the present invention; FIG. 2 is an enlarged fragmentary view of the array of microelectrodes shown in FIG. 1; FIG. 3 is a schematic top view of another sensor provided with a second preferred embodiment of an array of microelectrodes made according to the teaching of the present invention; FIG. 4 is an enlarged fragmentary view of the array of microelectrodes shown in FIG. 3; and

FIGS. 5a), 5b), 5c), 5d) and 5e) are schematic cross- sectional views illustrating the sequence of a method for manufacturing an array of microelectrodes on a substrate according to the present invention.

NUMERAL REFERENCE OF THE ELEMENTS

10 sensor

12 array of microelectrodes 14 microelectrodes (band-shaped or disk-shaped)

16 electric contact

18 counter electrode 20 sub icronic line

22 substrate

24 top surface of the substrate

26 thin film of silicon carbide (SiC) 28 photomask

29 openings of the photomask

30 resist

32 electromagnetic radiation

34 mask of resist 36 thin layer of metal

37 target

38 target holder 40 laser beam

42 plasma emission 44 upper portion of the mask of resist

46 openings of the mask of resist

48 lateral faces of the openings of the mask of resist

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to FIGS. 1 to 4, there are schematically illustrated two sensors (10) provided with preferred embodiments of arrays (12) of microelectrodes (14) made according to the teaching of the present invention. The array (12) of FIG. 1 is band-shaped and comprises a plurality of microelectrodes (14), each in the form of a band. As will be explained in more detail hereinafter, the width (w) of each band (14) may preferably vary from 1 μm to 20 μm, if a U.V. microphotolithography process is used for masking the substrate and from 0,1 μm to 1 μm, if an X-ray microphotolithography process is used. The distance (d) between each band (14) is preferably between 0,2 μm and 50 μm. The opposite ends of each band-shaped microelectrode (14) are connected to an electric contact (16). The array (12) is set between two electrodes (18) used as counter electrodes. The array (12) and counter electrodes (18) have substantially the same width which is preferably between 50 μm and 1000 μm. The length of the sensor (10) may vary from 1 to 10 mm.

As illustrated in FIGS. 3 and 4 and according to a second preferred embodiment of the invention, the array (12) of microelectrodes (14) may comprise a plurality of disk-shaped microelectrodes (14), each disk having a diameter varying from 0,5 μm to 20 μm. The distance between each disk (d) is preferably from 1 μm to 50 μm. The disks (14) are connected to the two electric contacts (16) by means of submicronic lines (20) connecting each disk (14) to an adjacent disk (14).

Referring now to FIGS. 5a) to 5e), there is schematically illustrated the sequence of a preferred embodiment of the method for manufacturing an array of microelectrodes (12) on a substrate (22) according to the present invention.

A) Insulation of the substrate

First, as illustrated in FIG. 5a), a top surface (24) of a substrate (22) is insulated. The substrate (22) used preferably consists of a onocristalline Si(100). Obviously, any other suitable substrate (22) such as quartz may be used. The top surface (24) of the substrate (22) may be electrically insulated according to any appropriate process known in the art, especially by depositing thereon a thin film of SiC (26) (e.g. thickness approximately 2 μm) . The purpose of this thin film (26) of coating may further allow to improve the chemical inertia of the top surface (24) of the substrate (22).

Advantageously, the substrate (22) is properly cleaned before the deposition of SiC by using standard cleaning process known in microelectronics. For example, the cleaning process may consist of successive immersion in a hot bath comprising trichloroethane, acetone, propanol and deionized water. The surface desoxydation process may consist of soaking the substrate (22) in a 18% diluted solution of hydrofluoric acid (HF) for about one minute. Preferably, this thin film of SiC (26) may be deposited by plasma enhanced chemical vapour deposition (PECVD) or laser ablation deposition. The PECVD system is preferably operated at 100 kHz with a power density of about 0,3 W/cm 2, a total gas pressure of 200 mTorr, a substrate temperature of 300°C and a gas flow rate of argon, methane and silane of respectively 640 seem (standard cubic centimeter), 77 seem and 33 seem. Generally, any film of SiC (26) deposited on a substrate

(22) with one of these techniques is highly compressive. Therefore, it may be preferable to thermal anneal the deposited film (26) in order to reach a proper low stress value.

B) Microphotolithoαraphv

As illustrated in FIG. 5c), the insulated top surface (24) of the substrate (22) is masked. Preferably, it may be masked according to a microphotolithography process. Photolithography processes are already known in other fields such as integrated circuit manufacturing. In general, light is shined through the non-opaque portions of a pattern, or photomask, onto a piece of specially coated substrate such as silicon or other semiconductor material. The portions of the coating exposed to light are removed, (e.g. by an immersion in a developer solution). The light used may consist of visible light, ultraviolet light, and X-ray light. Preferably, an X-ray light permits smaller feature sizes in the patterns.

The microphotolithography process which is advantageously usable according to the present invention may preferably comprise the following steps.

A layer of resist (30) is deposited on the insulated top surface (24) of the substrate (22). This resist (30) is sensitive to an electromagnetic radiation (32) having a wavelength at least in the range of the ultraviolet radiation. A photomask (28) is provided above the layer of resist (30) (see FIG. 5b). The photomask (28) has openings (29) defining a given pattern corresponding to a pattern of the array of microelectrodes (12) to be manufactured. Then, an electromagnetic radiation (32) having a wavelength at least in the range of the ultraviolet radiation is emitted through the openings (29) of the photomask (28) for exposing the resist (30). Finally, the exposed resist (30) is dissolved (e.g. in a developing chemical solution) for revealing a mask (34) on the insulated top surface (24) (see FIG. 5c).

If the critical dimension of each microelectrode (14) of the array (12) is less than 1 μm, the electromagnetic radiations used are preferably X-Rays. If this critical dimension is greater than 1 μ , the UV radiations are preferably used.

C) Laser ablation deposition Third, as schematically illustrated in FIG. 5d), a thin layer of metal (36) is deposited onto both the mask (34) and the insulated top surface (24) of the substrate (22) by laser ablation deposition. Pure metals such as gold, silver, platinum and preferably iridium, rhodium, ruthenium, rhenium and palladium may be deposited with this technique. The layer of metal (36) deposited may also comprise a metal alloy, preferably, an iridium, rhodium, ruthenium, rhenium or palladium alloy. The thickness of this layer (36) is preferably in the order of 0,4 μm. If a pure metal is to be deposited, the laser ablation deposition preferably comprises the following steps:

- positioning in a vacuum chamber, the substrate (22) with its masked top surface (24) and, above the masked top surface (24), setting on the target holder (38), a target (37) made of a metal to be deposited; and

- subjecting the target (37) to a laser beam (40) to thereby produce in the chamber a plasma emission (42) of the metal toward the masked top surface (24) of the substrate (22). The plasma emission (42) allows to deposit metal particles (neutrals and ions) onto the top surface of the mask (34) and the top surface (24) of the substrate (22). The growth of the thin layer (36) of the selected metal takes place on the top surface (24) .

The target (37) is preferably set at approximately 4 to 12 cm from the substrate (22). It should be noted that FIGS. 5a) to 5d) are only schematic illustrations of a method according to the present invention. Therefore, it should be understood that the distances in the figures do not necessarily correspond to reality. For example, the distance between the target (37) and the top surface of the substrate (22) illustrated in FIG. 5d) appears much more closer than reality. In most cases, the laser ablation deposition technique has the advantage of preserving the stoichiometry of the target (37) and of being easy to implement. Moreover, when this technique is used for depositing a layer of metal (36) on a masked top surface (24), it allows to deposit the material, either on the upper portion (44) of the mask (34) or on the insulated top surface (24) through the openings (46) of the mask (34). In other words, there is substantially no material deposited on the lateral faces (48) of the mask (34), thereby allowing to easily reveal the deposited array of microelectrodes (12), preferably by simple dissolution of the mask (34) (e.g. it is possible to dissolve the mask in a proper stripper, a stripper being a chemical solution that can remove the resist from a surface).

In general, the deposition of a layer (36) of material having a thickness of 0,4 μm requires approximately 100,000 laser shots. Therefore, with the laser ablation deposition technique, it is possible to produce a metal alloy by using more than one target (37), each made of a different material. Therefore, if a metal alloy is to be deposited, the laser ablation deposition preferably comprises the following steps:

- positioning in a vacuum chamber, the substrate (22) with its masked top surface (24) and, above the masked top surface (24), setting on the target holder (38) a plurality of targets, each target (37) being respectively made of one metal to be deposited and at least two of the targets being made of a different metal; and

- subjecting alternatively each of the targets to a laser beam to thereby produce in the chamber a plasma emission of a corresponding metal toward the masked top surface (24) of the substrate. This alternated ablation technique allows to deposit onto the top surface a thin layer of the desired alloy. For example, two targets, one made of iridium and the other made of rhodium, may be set above the substrate (22). With the same principle, it is also possible to proceed with a doping of the surface of a deposited material. Preferably, the surface of an iridium microelectrode may be doped with a metal such as rhodium, ruthenium or platinum.

Advantageously, because the laser ablation may occur at room temperature of approximately 25°C, the properties of the mask (34) which may be made of resist (30) (e.g. a resist HPR 504* manufactured by the company OCG or the resist SAL 605* manufactured by the company Shipley) are maintained stable. This is not the case when the mask (34) reaches temperatures in the order of 150°C.

D) Revealing the array of microelectrodes

Referring now to FIG. 5e), once the thin layer of metal (36) (or metal alloy) has been deposited, the array of microelectrodes (12) may be revealed. Preferably, it is revealed by a lift-off process which consists of dissolving the mask (34), thereby leaving only the metallic pattern or array of microelectrodes (12) on the insulated substrate (22). For example, following the deposition of the metal, the substrate may be soaked in a stripper such as the Microstrip 2001 manufactured by the company OCG which is a chemical solution allowing to dissolve the resist. The solution is preferably at a temperature around 70^°C, and the substrate is to be maintained in the solution for approximately 10 min.

E) Packaging process

Preferably, for using the array of microelectrodes (12) in electrochemical experimentations, the array (12) is connected to external connectors via the electric contacts

(16). It consists of bounding platinum wires to both the external connectors and electric contacts (16) of the array of

trade mark microelectrodes (12). The packaging process includes: (i) mounting the sensor (10) on a standard chip carrier, (ii) platinum wire bounding, and (iii) encapsulating the sensor. This is a standard and well known process used in microelectronics. Therefore, it is not necessary to define this step in detail.

EXAMPLES

For each of the following examples A, B, C and D, the substrate (22) used was a 2 to 4 inches diameter Si(100) substrate. The substrate was properly cleaned in successive hot baths of trichloroethane, acetone, propanol and deionized water. The temperature of the bath was approximately 40°C and the duration of each immersion in the bath was approximately 10 minutes. Then the substrate was submitted to a surface desoxydation process by soaking it for 1 minute in a 18% diluted hydrofluoridric acid solution.

A thin film of SiC (26) was deposited on the Si substrate by using a commercial PECVD system such as the Plasma II manufactured by the company Applied Materials. For obtaining a film of approximately 2 μ thick with a deposition rate in the order of 1 μm/h, the system was operated at 100 kHz with

₂ a power density of about 0,3 W/cm , a total gas pressure of

200 mTorr, a substrate (22) temperature of 300°C and an argon, methane and silane flow rate of approximately 640 seem, 77 seem and 33 seem respectively. The PECVD system allows to deposit a SiC film of 2 μm on a batch of twenty-two substrates in two hours.

Since the stress of such deposited film of SiC is very compressive, it was preferably thermal annealed in order to reach a proper low stress value. The thermal annealing was processed either with a slow thermal annealing process or with a rapid thermal annealing process.

trade mark The slow annealing process is performed in a classical furnace at approximately 600°C under a flow of nitrogen, for one hour.

The rapid annealing process is performed in a rapid thermal annealing (RTA) furnace at approximately 500°C, under a nitrogen atmosphere.

The stress in the film of SiC after the annealing process is less than 20 MPa.

Example A

This example concerns the fabrication of an array of microelectrodes (12) wherein each microelectrode (14) has a critical dimension equal or over 1 μm.

A positive resist (30) of approximately 1,4 μm of thickness was spin coated on the upper surface of the Sic film

(26). The resist (30) used was sensitive to U.V. rays, such as i_t the HPR 504 resist manufactured by the company OCG. The resist

(30) was then prebaked for 20 minutes, at approximately 100°C, then exposed to U.V. electromagnetic radiation (32) through a U.V. photomask (28). An aligner emitting U.V. radiations of approximately 365 nm was used. The resist (30) was developed in 1 minute in a developing chemical solution, such as the HPR D419*, and rinsed in deionized water. Once the pattern was revealed, the resist (30) was preferably submitted to a second thermal annealing called hard-bake for improving fixation and strength of the pattern in the resist (30). This hard-bake was performed at approximately 120°C for 30 minutes .

The laser ablation deposition was carried out in a vacuum chamber preferably maintained at 10 torr to 10 torr. The target (37) was made of iridium. Obviously, the target (37) could have been made of any other metal. Laser irradiation was provided by a pulse excimer laser, such as the HyperEX-400SM* manufactured by the company Lumonics, operated at 248 nm. A pulse energy of 100 mJ can be reached with this laser, with a pulse width of 12 ns and a repetition rate of 30 Hz.

trade mark The laser beam (40) was focused by a plano-convex lens with a i focal length placed outside the deposition chamber. The laser intensity on the target (37) reached was approximately 1,5 X 10 W/cm . With this laser intensity, the deposition rate of iridium was approximately 0,5 μm/h, if the substrate (22) was set at 6 cm of the target (37). Because the direction of the plasma emission (42) generated by the laser defines a straight line, the thin layer of iridium or any other metal was deposited either on the top surface of the resist (30) or on the top surface of the SiC. In other words, there was no deposition on the lateral faces (48) of the resist (30).

The target (37) used in this example was a disk having a diameter of 5 cm and a thickness of 1 mm and fixed onto the target holder (38). Preferably, during the deposition, the target holder (38) was rotated and laterally translated for allowing a uniform ablation. Preferably, the substrate (22) was set on a holder which was also rotated and laterally translated for allowing the deposition of a uniform layer of metal (36).

After the deposition, the resist (30) was dissolved by a lift-off process. The substrate (22) was soaked twice in a solution such as the stripper Microstrip 2001 manufactured by the company OCG for 10 minutes at 70°C. During these soaking, an ultrasonic agitation was maintained. The substrate (22) was then rinsed in deionized water. This lift-off process allows to remove the resist (30) and the layer of metal (36) deposited on the upper surface (44) of the resist (30).

The array of microelectrodes (12) obtained has been connected to external connectors for allowing its use in electrochemical processes. A process called packaging was used for this connection. This packaging process is well known and already used in microelectronics. It consists of bounding platinum wires having a diameter between 10 and 50 μm to the electric contacts (16) of the array (12) by acoustic bounding. Each of these platinum wires is then connected to the connectors of a standard microelectronic housing. This assembly

trade mark is then encapsulated by conventional techniques using epoxy and/or resist, in order to delimit the electrochemical interaction region of the sensor (10). This encapsulation can be also achieved by depositing a silicon carbide thin film.

Example B

This example concerns the manufacturing of an array of microelectrodes (12) wherein each microelectrode has a critical dimension of less than 1 μm, preferably between 0,1 μm and

1 μm. As mentioned hereinbefore, the substrate (22) was covered with a thin film (26) of SiC by using the same PEVCD process.

A resist (30) sensitive to X-rays such as the SAL 605 manufactured by the company Shipley was used. This resist (30) was spin coated on the upper surface of the Sic. The resist was then prebaked at 95°C for 30 minutes. An X-ray photomask (28) was used and set almost in contact with the Si wafer which was positioned at approximately 8 cm from the X-ray source. The

2 resist (30) was exposed to a X-ray dose of 10 J/cm and then post-baked for 8 minutes at approximately 115^°C. Then the mask (34) was revealed with MF312* stripper which is manufactured by the company Shipley. The following steps concerning the laser ablation deposition, lift-off and packaging process were the same as for the above-described example A and do not require more explanation.

Example C

This example concerns the manufacturing of an array of microelectrodes (12), each microelectrode (14) being made of a metal alloy. A masked and electrically insulated Si substrate prepared either as in example A or as in example B is used and positioned in the vacuum chamber. Two targets, one made of iridium, the other made of rhodium, are set above the masked wafer. These two targets are alternatively subjected to the laser beam (40). The deposited material on the masked substrate

trade mark is made of atoms of iridium and atoms of rhodium. The composition of the alloy corresponds to Ir ^Rnd-_y ^x being directly a function of the ratio n_Ir/n- + n_pn , where n_j is the number of laser shots on the iridium target and n_Rn is the number of laser shots on the rhodium target. The composition of the obtained alloy is also dependent on the deposition rate of each material at a given set of laser conditions (energy, intensity, ...). For example, if we assume an identical deposition rate for Ir and Rh and if the iridium target is subjected to approximately 75000 laser shots and the rhodium target to 25000 shots, the composition of the alloy deposited ^{is Ir}(0,75) ^Rh(0,25) ^*

Example D This example concerns the manufacturing of an array of doped microelectrodes (14). As for example C, a masked and insulated Si wafer is positioned in a vacuum chamber and two targets, one made of iridium and the other made of rhodium are set above the Si substrate. First, only the iridium target is subjected to the laser beam. A thin layer of iridium of approximately 0,4 μm thickness is first deposited. Then, for approximately the last fifty A, an alloy lr_χ Rh ₁__χ, as in example C is deposited for doping the layer of iridium with atoms of Rh. The portion of doped iridium is approximately 50 A thick; in this case x may vary, for example, from 0,9 to 1.

Although preferred embodiments of the invention have been described in detail herein and illustrated in the accompanying drawings, it is to be understood that the invention is not limited to these precise embodiments and that various changes and modifications may be effected therein without departing from the scope or spirit of the invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for manufacturing an array of microelectrodes (12) on an electrically insulated top surface (24) of a substrate (22), the method being characterized in that it comprises the following sequence of steps: a) depositing by laser ablation a thin layer of an electrically conductive material (36) onto said top surface (24) and through openings of a mask (34) provided on said top surface (24), said electrically conductive material (36) being selected from the group consisting of metals and metal alloys; and b) revealing the array of microelectrodes (12) by removing the mask (34) from said top surface (24).

2. A method according to claim 1, characterized in that it further comprises, before step a), a step by which the mask (34) is provided onto the electrically insulated top surface (24) according to a photolithographic process.

3. A method according to claim 1, characterized in that the thin layer of electrically conductive material (36) is made of a metal selected from the group consisting of gold, silver, platinum, iridium, rhodium, ruthenium, rhenium and palladium.

4. A method according to claim 1, characterized in that the thin layer of electrically conductive material (36) is a metal alloy comprising as main constituent at least one metal selected from the group consisting of iridium, rhodium, ruthenium and palladium.

5. A method according to claim 1, characterized in that, in step a), the laser ablation deposition comprises the following steps: - positioning in a vacuum chamber, the substrate (22) with its masked top surface (24) and, above said masked top surface (24), setting a target (37) made of a metal to be deposited; and

- subjecting the target (37) to a laser beam (40) to thereby produce in the chamber a plasma emission (42) of said metal toward the masked top surface (24) of the substrate (22), said plasma emission (42) allowing metal particles to deposit onto said top surface (24) of the substrate (22).

6. A method according to claim 5, characterized in that the metal of the target (37) is selected from the group consisting of iridium, rhodium, ruthenium and palladium.

7. A method according to claim 1, characterized in that, in step a) , the laser ablation deposition comprises the following steps:

- positioning in a vacuum chamber, the substrate (22) with its masked top surface (24) and, above said masked top surface (24), setting a plurality of targets (37), each target (37) being respectively made of one metal to be deposited and at least two of said targets (37) being made of a different metal; and

- subjecting each of said targets (37) to a laser beam (40) to thereby produce in the chamber a plasma emission (42) of a corresponding metal toward the masked top surface (24) of the substrate (22), said plasma emission (42) allowing metal particles to deposit onto said top surface (24) and make the thin layer of electrically conductive material (36) to grow as an alloy.

8. A method according to claim 7, characterized in that each of the targets (37) is made with a metal selected from the group consisting of iridium, rhodium, ruthenium and palladium.

9. A method according to claim 1, characterized in that it further comprises between steps a) and b), an additional step for doping by laser ablation deposition an upper surface of said deposited thin layer of metal (36).

10. A method according to claim 1, characterized in that the substrate (22) comprises a Si substrate having a top surface insulated with a thin film of SiC (26).

11. A method according to claim 2, characterized in that the microphotolithography process comprises the steps of:

- depositing a layer of resist (30) on the insulated and masked top surface (24) of the substrate (22), said resist (30) being sensitive to electromagnetic radiation having a wavelength at least in the range of the ultraviolet radiation;

- providing a photomask (28) above the layer of resist (30), said photomask (28) having openings (29) defining a given pattern corresponding to a pattern of the array of microelectrodes (12);

- emitting an electromagnetic radiation (32) having a wavelength at least in the range of the ultraviolet radiation through said openings (29) of the photomask (28) for exposing the resist (30); and

- dissolving the exposed resist for revealing the mask (34) on the insulated top surface (24).

12. A method according to claim 11, characterized in that the electromagnetic radiations are X-rays.

13. A method according to claim 12, characterized in that each microelectrode (14) of the array (12) has a critical dimension varying from 0,1 μm to 1 μm.

14. A method according to claim 1, characterized in that the array of microelectrodes (12) is band-shaped.

15. A method according to claim 1, characterized in that the array of microelectrodes (12) comprises a plurality of disk- shaped microelectrodes (14) interconnected by submicronic lines (20).

16. A method for manufacturing an array of microelectrodes (12) on an electrically insulated top surface (24) of a substrate (22), each microelectrode (14) of the array (12) having a critical dimension varying from 0,1 μm to 1 μm, said method comprising the following sequence of steps:

- providing a mask (34) on the electrically insulated top surface (24) according to a photolithographic process comprising the steps of:

- emitting electromagnetic radiation (32) having a wavelength at least in the range of the ultraviolet radiation through said openings (29) of the photomask (28) for exposing the resist (30); and

- dissolving the exposed resist for revealing the mask (34) on the insulated top surface (24); depositing by laser ablation a thin layer of an electrically conductive material (36) onto said top surface (24) and through openings of said mask (34) provided on said top surface (24), said electrically conductive material being selected from the group consisting of gold, silver, platinum, iridium, rhodium, ruthenium, rhenium, palladium and alloys thereof, the laser ablation deposition comprising the following steps:

- positioning in a vacuum chamber, the substrate (22) with its masked top surface (24) and, above said masked top surface (24), setting a target (37) made of a metal to be deposited; and - subjecting the target (37) to a laser beam (40) to thereby produce in the chamber a plasma emission (42) of said metal toward the masked top surface (24) of the substrate (22), said plasma emission (42) allowing metal particles to deposit onto said top surface (24) of the substrate (22); and

- revealing the array of microelectrodes (12) by removing the mask (34) from said top surface (24).

17. An array of microelectrodes (12), characterized in that it is obtained according to the method defined in claim 1.

18. An array of microelectrodes (12), characterized in that it is obtained according to the method defined in claim 6.

19. An array of microelectrodes (12), characterized in that it is obtained according to the method defined in claim 8.

20. An array of microelectrodes (12), characterized in that it is obtained according to the method defined in claim 9.

21. An array of microelectrodes (12), characterized in that it is obtained according to the method defined in claim 12.