HK1116260B - Fabrication process by liga type technology, of a monolayer or multilayer metallic structure, and structure obtained therewith - Google Patents

Description

The present invention relates to a new process for manufacturing by LIGA-type technology of a monolayer or multilayer metal structure, as well as a new monolayer or multilayer metal structure which can be obtained by this process.

DGC Mitteilungen No. 104, 2005, mentions the use of LIGA technology (Lithographie Galvanik Abformung: method designed by W. Ehrfeld of the Karlsruhe Nuclear Research Center, Germany) for the manufacture of high-precision metal watch parts, such as for example anchors or exhaust wheels.

A.B. Frazier et al., Journal of Microelectromechanical Systems, Vol. 2, No. 2, June 1993, describes the manufacture of metal structures by electrodeposition of metal in polyimide-based photoresist molds prepared using a process using a technology called LIGA-UV, similar to LIGA technology but with UV illumination instead of X-ray irradiation.

The process used for the manufacture of single-layer metal structures includes the following steps: create a sacrificial metal layer and a seeding layer for electroplating on a silicon support plate,spread a layer of photosensitive polyimide by spin-coating,carry out UV illumination through a mask corresponding to the desired imprint,develop by dissolving the non-irradiated parts so as to obtain a polyimide mould,galvanically deposit nickel or copper into the open part of the mould to the height of the mould,and remove the sacrificial layer and separate the metal structure obtained by electroplating from the support plate,and remove the polyimide mould.

This document describes the manufacture by this process of monolayer metal structures such as copper or nickel gears (see A and B pp. 89-91 and Figs. 3-7).

Frazier et al. also disclose a process for manufacturing two-layer metal structures involving the following steps: create on a silicon support plate a sacrificial metal layer and a seeding layer for electroplating,spread by spin-coating a layer of photosensitive polyimide,carry out through a mask matching the desired imprint an illumination with ultraviolet rays,develop by dissolving the unirradiated parts so as to obtain a polyimide mould,deposit nickel galvanically into the open part of the mould to the height of the mould so as to obtain a significantly higher surface,deposit by vacuum vaporization a thin layer of chromium under the mould,depose on a layer of polyimide by depositing the polyimide layer into the desired imprint (spin-coating),develop a new structure and by electroplating the mould,deposit the parts of the polyimide layer into the UV-coating and/or chlorinating layer,develop a new structure and by electroplating the mould,develop a new structure and/or remove the part of the chromium, by electroplating the mould,deposit a thin layer of chromium,depose on a layer of polyimide by deposition in the UV-coating and/hydro-acidating layer,deposition of the mould,develop a new structure and/develop a new structure,develop by electroplating the mould,deposing the mould,developing a new structure and/deposing the mould,depositing the mould,deform a new structure and/depositing the mould,depositing the mould, by electroplating the mould,de and/depositing the mould,depositing the parts of the mould,deform,depositing the mould,depositing the mould,deposing a new structure and/deposing the mould,deposing the mould,deposing the mould,deforming the mould,deforming the mould,deforming the mould,deforming the mould,deforming the mould, and the mould, and the mould, and the mould, and the mould, by dissolving the mould, by dissol

This paper describes the use of this process to make a metal plate topped with a bulge of general parallel-epipedal shape (see Fig.9 page 92) with the second layer completely superimposed on the first larger surface layer.

The processes described by Frazier et al. do not allow machining of the manufactured structures until they are detached from the silicon support plate, which is too fragile to withstand the mechanical stresses generated by machining.

EP0851295 describes another process for the manufacture of multilayer metal structures by LIGA-UV, such as a cog with a two-layer gear (Example 1) or a trilayer heat flux micro-sensor (Example 3). This process is similar to that described by Frazier et al. and also has the disadvantages described above.

A proposal has already been made in US 5,766,441 to manufacture a metal plate consisting of three layers formed by electromoulding and photolithography and having an inlet hole, an outlet hole, connected by a conduit. This metal plate is formed on a metal substrate (copper) of silicon, glass or ceramic. The plate thus formed is then detached from the substrate. The substrate is only used to perform the deposition and the formed plates are detached after the deposition of the layers has been performed.

It was further proposed in US 2005/0056074 and US 2003/0062652 to manufacture micro-mold inserts by forming micro-plots with a high length ratio on a substrate of nickel, stainless steel, titanium and silicon in particular by the LIGA process.

If the mechanical machining of parts made by LIGA on a silicon substrate is not possible due to its fragility, US 5.766.441 does not provide for the use of the copper substrate as a machining medium, as for US 2005/0056074 and US 2003/0062652, the elements formed on the metal substrate are not detached from the substrate which is not a working medium but an integral part of the formed structure.

The problem or purpose of the invention is to find a method of manufacturing a metal structure which does not present these disadvantages.

This problem is solved by the invention as defined by the claims.

The applicant has found that the use of a solid metal substrate instead of a silicon support plate covered with a sacrificial metal layer and a seeding layer makes it possible to machine the structure in situ after the electromoulding stage before the substrate is detached. Thus, when manufacturing a large number of structures (or parts) on the same substrate, the structures precisely positioned and fixed on it can be machined collectively. The additional step of positioning and immobilization of each structure after detaching the substrate for further machining is therefore no longer necessary.

In addition, in the case of the manufacture of multilayer metal structures, the use of a solid metal support allows machining upgrading (abrasion and polishing) at the end of each electrodeposition step to obtain a flat surface.

The invention thus concerns a process for manufacturing by LIGA technology of a monolayer or multilayer metal structure as defined in claim 1. The irradiation in such a LIGA process may be X-ray irradiation or UV irradiation, by illumination in normal mode through a mask, by illumination in laser mode to create a network of polymerized areas or by laser ablation.

The LIGA technology is preferably a LIGA-UV technology, i.e. a LIGA technology using UV irradiation.

According to a preferred embodiment, the invention relates to a manufacturing process by LIGA-UV technology of a single-layer machined metal structure, which includes the steps defined in claim 2.

A solid metal substrate is a solid metal plate of 1 to 5 mm thickness, of any shape, e.g. cylindrical or parallel-epipedal, whose surface area is chosen according to the number of structures manufactured on the same substrate, usually 10 to 3000, especially 50 to 1000.

The surface of the solid metal substrate, intended to be in contact with the electrolytic bath, may be polished or textured, for example by micro-billing, chemical etching, mechanical etching or laser etching.

The solid metal substrate is degreased and prepared for electromolding by appropriate treatment, for example degreasing in an alkaline medium, followed by neutralization in an acidic medium to passivate the surface, rinsing with distilled water and drying.

The photoresist is either a negative photoresist, based on a resin that can polymerize under the action of UV radiation in the presence of a photoinitiator, or a positive photoresist, based on a resin that can decompose under the action of UV radiation in the presence of a photoinitiator. The negative photoresist is for example based on an epoxy resin, an isocyanate resin or an acrylic resin. An advantageous epoxy resin is the octofunctional epoxy resin SU-8 (Shell Chemical). It is generally used in the presence of a photoinitiator selected from the triarylsulfonium salts, for example those described in US patents 4,058,401 and 4,882.245.

The photoresist can be spread by spin coating or by other techniques, such as dip coating, roller coating, extrusion coating, spray coating, or rolling (for dry films, for example acrylic resin).

The maximum thickness of the photoresist to induce the desired effect (photopolymerization or photodegradation) under the irradiation conditions of step (c) is about 1 mm. The maximum thickness of the photoresist layer that can be spread at once is about 150 μm depending on the technique of turret deposition.

The possible heating conditions of the photoresist to remove the solvent in step (b) are chosen according to the nature and thickness of the photoresist as specified by the manufacturer. For example, for a photoresist made of SU-8 epoxy resin and 140 μm thick, step (b) involves heating to 65 °C for 5 to 10 minutes and then to 95 °C for 30 to 60 minutes. For an acrylic film photoresist, this heating step to evaporate the solvent is not necessary.

If it is necessary to spread the photoresist several times and to heat the photoresist to evaporate the solvent, step (b) shall be performed after step (a) after the first spread of the photoresist and steps (a) and (b) shall be repeated as many times as necessary.

Step (c) consists of exposing the photoresist layer through a mask corresponding to the desired imprint to UV radiation of 100 to 2000 mJ/cm2 measured at a wavelength of 365 nm. This irradiation induces photopolymerization of the resin (negative photoresist) or photodegradation of the resin (positive photoresist).

Step (d) consists of annealing the resulting layer, if necessary to complete the photopolymerisation or photodegradation of step (c).

The step (e) consists of developing by dissolution of the unirradiated (negative photoresist) or irradiated (positive photoresist) parts using an appropriate aqueous solution or solvent, chosen according to the nature of the photoresist as indicated by its manufacturer. Examples of suitable aqueous solutions are low base alkaline solutions, e.g. sodium carbonate, and examples of suitable solvents are GBL (gammabutyrolactone), PGMEA (propylene methyl glycol ethyl acetate), and isopropanol.

Step (f) consists of galvanically depositing a metal or alloy into the open parts of the photoresist mould to a specified height less than or equal to the height of the photoresist mould using the solid metal substrate as the cathode, and machining up to a flat surface.

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The machining upgrading is generally done by abrasion and polishing, which results in a flat surface with surface irregularities not exceeding about 1 μm.

Step (g) consists of performing, if necessary to obtain the desired structure, further machining operations on the upper face of the electroformed metal structure, such as angling, engraving or decoration machining.

Step (h) consists of delaminating the machined metal structure from the solid metal substrate and separating the photoresist from the machined metal structure.

The lower face of the metal structure detached by delamination from the upper face of the solid metal substrate reproduces the surface condition of this upper face. It will thus be either textured (if the upper face of the metal substrate is textured, for example by etching or microbillage) or polished (if the upper face of the metal substrate has been polished). In the latter case, when observed with the naked eye, the surface appearance of the polished surface of the lower face of the structure is not different from the polished surface appearance obtained when polished on the upper face.

The separation or stripping of the polymerized photoresist from the machined mechanical structure is usually done by chemical attack or plasma treatment.

The invention of a method for manufacturing a monolayer metal structure on a solid metal substrate has many advantages over the known methods for manufacturing such structures on a silicon support plate.

It allows, first of all, any machining operation to be carried out on the upper surface of the structure obtained after electrostatic moulding before the substrate is detached and the polymerized photoresist mould separated, in particular its abrasion upgrading and possibly polishing to obtain a flat surface, and one or more other machining operations such as, for example, angling, engraving or decoration machining.

The method of the invention allows the manufacture of single-layer metal structures with an inserted object with a precise positioning of the object.

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Precise positioning and removable fixation of an object is not possible on top of a silicon support plate covered with a sacrificial metal layer and a seeding layer.

The invention therefore also concerns a new single-layer machined metal structure with an inserted object, which can be obtained by the process defined above.

The method of the invention also enables the manufacture of single-layer metal structures with a threaded hole in a precise position.

After the steps a) to e) have been completed, a screw 3 can be placed in a hole drilled on the solid metal substrate 1 which protrudes above the surface of the solid metal substrate (see Figure 5) and, when the metal structure is unwound by delamination, this screw can be unwound from the solid metal substrate. The screw is made of an inert material which does not adhere to the electroformed metal, e.g. Teflon® (PTFE).

It is not possible to drill into a silicon support plate because it is too fragile and breaks.

The invention therefore also concerns a new single-layer machined metal structure with a threaded hole, which can be obtained by the process described above.

The invention also relates to a process for manufacturing by LIGA-UV technology a multilayer machined metal structure with fully overlapping layers, which includes the steps defined in claim 3.

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Steps (a), (b), (c), (d), (e) and (f) are the same as those of the above described process of manufacturing a monolayer metal structure by LIGA-UV.

Step (g) consists of reproducing steps (a), (b), (c), (d) and (e) and activating the surface of the electroplated metal not coated with polymerized photoresist by electrochemical treatment.

Reproduce steps (a), (b), (c), (d) and (e) using in step (a) the flat surface obtained from step (f) as the substrate and in step (c) a new mask corresponding to the desired imprint for the new electroplated metal layer.

The surface of the electroplated metal not coated with polymerized photoresist is activated after the reproduction of step e) by applying a reverse current, by making the electroplated metal play the role of anode according to techniques well known in the art of surface treatment.

Step h) consists of reproducing step f): a metal or alloy is galvanically deposited in the open part of the new polymerized photoresist mould obtained from the reproduction of step e) and is leveled by machining, usually by abrasion and polishing, to obtain a flat surface (with surface irregularities generally not exceeding about 1 μm).

Step (i) consists of reproducing steps (g) and (h) if necessary to obtain the desired multilayer metal structure.

Step (j) consists of performing, if necessary to obtain the desired structure, further machining operations on the upper face of the electromoulded mechanical structure, such as angling, engraving or decoration machining.

Step k) consists of delaminating the machined metal structure from the solid metal substrate and separating the photoresist from the machined mechanical structure.

The lower face of the metal structure detached from the upper face of the solid metal substrate reproduces the surface state of the metal substrate. It will thus either be textured (if the upper face of the metal substrate is textured, for example by engraving or microbillage) or polished (if the upper face of the metal substrate has been polished). In the latter case, when observed with the naked eye, the surface appearance of the lower face of the structure is not different from the polished appearance obtained if polished on the upper face.

The separation or stripping of the polymerized photoresist from the machined mechanical structure is usually done by chemical attack or plasma treatment, thus freeing the machined metal structure.

The invention of a method for manufacturing a multilayer metal structure with fully overlapping layers on a solid metal substrate has many advantages over the known methods for manufacturing such structures on a silicon support plate.

It allows any machining operation to be carried out on the upper surface of the metal structure obtained after the final electromoulding step, before the substrate is detached, in particular an angling, engraving or decoration machining.

The process of the invention involves machining upgrading (abrasion and polishing) at the end of each electrodeposition step to obtain a flat surface, which improves the quality of the resulting multilayer metal structure, in particular some mechanical and/or appearance properties, as the subsequent electrolytic deposition is more regularly carried out on a polished surface than on a surface with irregularities.

This results in a new, multi-layered machined metal structure with completely overlapping layers and advantageous properties.

The invention therefore also concerns the multilayer machined metal structure with fully overlapping layers which can be obtained by the process defined above.

The method of the invention also allows, by the use of a solid metal substrate, the production of new multilayer metal structures with fully overlapping layers including an inserted object or thread in the first electromoulded layer, by a process analogous to that described above for monolayer metal structures.

The invention thus also concerns a multilayer machined metal structure with an inserted object or threaded hole in its first layer which can be obtained by the process defined above.

Other particularities and advantages of the invention will be apparent from the following detailed description, with reference to the attached drawings, which illustrate schematically and by way of example some forms of execution of the invention.

In these drawings: Figure 1 is a perspective view of a single-layered spring,Figures 2A to 2F are line AB cut-off views of Figure 1 representing the different stages of spring manufacture in Figure 1,Figure 3A is a bottom-up view, and Figure 3B is line AB cut-off view of a watch movement escape anchor in Figure 3A,Figures 4A to 4H are line cut-off views schematically representing the different stages of the manufacture of the spring in Figures 3A and 3B,Figure 5 is a partial cut-off view of an assembly of a screw in a solid metal substrate, and the one protruding above the surface of the screw.

The following examples describe the manufacture of this spring and anchor by the method of the invention, with reference to Figures 1 to 4H.

Example 1: Manufacture of a spring for lifting

Figure 1 shows a spring with a top side 2, a bottom side 1, a cylindrical hole 3 and an angled part 4. The dimensions of this spring are as follows: thickness 0,170 mm (± 7 μm), diameter 0,412 mm (± 2 μm), blade width 0,046 mm (± 2 μm) and volume of about 2 mm X 3,5 mm.

Figure 2A shows the structure obtained at step (b) of claim 2, which includes a layer of photoresist 6 covering the substrate 5.

Substrate 5 consisting of a stainless steel plate 1 mm thick and 150 mm in diameter was degreased and prepared for electroplating by degreasing with an alkaline solution, neutralization with an acid solution to passivate its surface, then rinsing with distilled water and drying. A first layer of negative photoresist based on SU-8 octofunctional epoxy resin 100 μm thick was then spread on substrate 5 by turret deposition, then heated to evaporate the soil for 5 minutes at 65 °C, then 20 minutes at 95 °C. The first layer of photoresist was then deposited on the second layer of photoresist at 100 μm for evaporation of the solvent for 45 minutes at 95 °C, then the same temperature.

Figure 2B corresponds to claim 2 (c) with UV illumination of about 500 mi/cm2 centred at 365 nm of the photoresist through a mask matching the desired imprint. The mask with a UV transparent support 7 and the opaque areas 7a formed by chromium deposits can be distinguished in this figure. The same support forming the mask can have a large number of areas corresponding to as many structures as can be manufactured in a single batch, all areas being obtained with very high contour resolution by photolithography, a technique well known in the microelectronics industry.

This UV 8 irradiation induces photopolymerization of the resin in exposed zones 6b, with unexposed zones 6a remaining unpolymerized.

The structure obtained at the end of step e) of claim 2 is shown in Figure 2C. The layer obtained at the end of step c) was annexed to complete the polymerization for 1 minute at 65 °C, then 15 minutes at 95 °C, then the unexposed photoresist was dissolved by passing through three successive baths of PGMEA (increasingly pure) for 15 minutes, rinsing in an isopropyl alcohol bath and drying.

Figure 2D shows the structure obtained at the end of step f) of claim 2 after galvanic deposition of nickel, then upgraded by abrasion and polishing to obtain a flat surface.

Figure 2E shows the structure obtained during step g) of claim 2 during an angling operation, with substrate 5, metal structure 9, polymerized resin mould 6b, angle hole 3a and milling machine 10 used for angling.

Figure 2F, which corresponds to the cut-out view in Figure 1, shows the spring obtained at the end of claim 2 step h) after detaching the metallic substrate by delamination and striping of the photoresist polymerized with N-methylpyrrolidone.

Example 2: Manufacture of an exhaust anchor for watch movement

Figures 3A and 3B show an anchor with a top side 1, a bottom side 2, a cylindrical hole 3, a fork 4 and a clearance 5. The dimensions of this anchor are as follows: first level thickness 0,105 mm (± 5 μm), second level thickness 0,07 mm (± 5 μm), total thickness 0,175 mm (± 10 μm), diameter 0,306 mm (± 1 μm), diameter AB 0,250 mm (± 4 μm), according to the enclosure of the order of 4 mm X 3 mm.

The structure obtained at step (b) of claim 3 process, which includes a layer of photoresist 7 covering substrate 6, is shown in Figure 4A. This structure was obtained according to the protocol described below.

Substrate 6 consisting of a 1 mm thick, 150 mm diameter stainless steel plate was degreased and prepared for electroplating by degreasing with an alkaline solution, neutralizing with an acid solution to passivate its surface, then rinsing with distilled water and drying. A first layer of negative photoresist based on epoxy resin SU-8 octofunctional of 70 μm thickness was then heated to evaporate the soil at 65 °C for 3 minutes, then 95 °C for 9 minutes. The first layer of photoresist was then deposited on the second layer of photoresist at 65 °C for 5 minutes, then heated to evaporate the soil at 95 °C for 35 minutes, then the same temperature was reached.

Figure 4B corresponds to step c) of claim 3 of UV illumination of about 450 mJ/cm2 centred at 365 nm, of the photoresist through a mask corresponding to the desired imprint.

The structure obtained at the end of step e) of claim 3 is shown in Figure 4C. The layer obtained at the end of step c) was annexed to complete the polymerization for 1 minute at 65 °C, then 15 minutes at 95 °C, and then the unexposed photoresist was dissolved by passing through three successive baths of PGMEA (increasingly pure) for 15 minutes, rinsing in an isopropyl alcohol bath and drying.

Figure 4D shows the structure obtained after performing step f) of claim 3 of galvanic deposition of nickel in the open parts of the polymerized photoresist mould, and upgrading by abrasion and polishing to a flat top surface, and reproduces steps a) and b) with two successive 50 μm layers of the same SU-8 epoxy resin photoresist, heated for 3 minutes at 65 °C, then 6 minutes at 95 °C for the first layer, and heated for 5 minutes at 65 °C, then 20 minutes at 95 °C for the second layer.

Figure 4E shows the reproduction of claim 3 (c) (during step g) with UV illumination of about 400 mJ/cm2 centred at 365 nm of the photoresist through a new mask matching the desired imprint. The mask with a UV-transparent support 12 and opaque zones 12a formed by chromium deposits are distinguished. This UV 9 irradiation induces photopolymerization of the resin in exposed zones 11b, with the non-exposed zones 11a remaining unpolymerized.

The structure obtained at the end of the reproduction of step e) of claim 3 (during step g) is shown in Figure 4F. The layer obtained at the end of the reproduction of step c) was annexed to complete the polymerization for 1 minute at 65 °C, then 15 minutes at 95 °C, and then the unexposed photoresist was dissolved by passing for 15 minutes in three successive baths of PGMEA (increasing purity), rinsing in an isopropyl alcohol bath and drying.

Figure 4G shows the structure obtained after the reproduction of step f) of claim 3 (during step h). A second galvanic deposit of the same metal, nickel, was made to a slightly higher height (10-30 μm) at the desired thickness and then upgraded by abrasion and polishing to obtain a flat surface.

Figure 4H, which corresponds to the cut-off view in Figure 3B, shows the anchor obtained at the end of step k) of claim 3, after detaching the metallic substrate by delamination and removal of the polymerized photoresist by plasma treatment.

Claims (17)

1. Process for fabricating a plurality of monolayer or multilayer metallic structures by a LIGA type technology, in which a layer of photoresist is spread over a solid metallic support consisting of stainless steel, a photoresist mould is created by irradiation or electron or ion bombardment, a metal or an alloy is electrolytically deposited in this mould, this metallic structure is mechanically machined, the said structure and the photoresist are separated from the solid metallic support and the photoresist is removed, characterised in that the surface of the said support is passivated in order to separate the metallic structure and the photoresist from the solid metallic support by delamination.
2. Process according to Claim 1 for fabricating a plurality of machined monolayer metallic structures by a UV-LIGA type technology, which comprises the following steps:

   a) spreading a layer of photoresist over a solid metallic support,

   b) heating the layer of photoresist, if necessary, in order to evaporate the solvent,

   c) exposing the layer of photoresist through a mask corresponding to the desired impression with 100 to 2000 mJ/cm² of UV radiation measured at a wavelength of 365 nm,

   d) if necessary, in order to complete the photopolymerisation or photodecomposition, annealing the layer obtained after step c),

   e) developing by dissolving the parts which have not been polymerised or photodecomposed,

   f) electrolytically depositing a metal or an alloy in the open parts of the photoresist mould, and levelling by machining so as to obtain a plane upper surface,

   g) if necessary, carrying out one or more other machining operations on the upper face of the electroformed metallic structures, and

   h) detaching the metallic structures and the polymerised photoresist from the solid metallic support by delamination, and separating the polymerised photoresist from the machined monolayer metallic structures.
3. Process according to Claim 1 for fabricating a plurality of machined multilayer metallic structures with fully superimposed layers by a UV-LIGA type technology, which comprises the following steps:

   a) spreading a layer of photoresist over a solid metallic support,

   b) heating the layer of photoresist, if necessary, in order to evaporate the solvent,

   c) exposing the layer of photoresist through a mask corresponding to the desired impression with 100 to 2000 mJ/cm² of UV radiation measured at a wavelength of 365 nm,

   d) if necessary, in order to complete the photopolymerisation or photodecomposition, annealing the layer obtained after step c),

   e) developing by dissolving the parts which have not been polymerised or photodecomposed,

   f) electrolytically depositing a metal or an alloy in the open parts of the photoresist mould, and levelling by machining so as to obtain a plane upper surface,

   g) repeating steps a), b), c), d), e) and activating by electrochemical treatment the surface of the electroformed metal not covered with polymerised photoresist,

   h) repeating step f),

   i) if necessary, repeating steps g) and h),

   j) if necessary, carrying out one or more other machining operations on the upper face of the electroformed metallic structures, and

   k) detaching the metallic structures and the polymerised photoresist from the solid metallic support by delamination, and separating the polymerised photoresist from the machined multilayer metallic structures with superimposed layers.
4. Process according to one of the preceding claims, according to which one or more etching, surface treatment, mechanical or laser marking operations are carried out on the metallic structures after having detached the metallic structures from the solid metallic support by delamination and before separating the photoresist.
5. Process according to one of the preceding claims, characterised in that the solid metallic support has an upper surface textured by microbeading or chemical, mechanical or laser etching.
6. Process according to one of the preceding claims, characterised in that the solid metallic support has a polished upper surface.
7. Process according to one of Claims 2 to 6, characterised in that removably fixed objects are placed on the solid metallic support after steps a) to e), and in that these objects are released from the solid metallic support when the metallic structures and the polymerised photoresist are being detached from the solid metallic support by delamination, so as to obtain monolayer metallic structures, or multilayer metallic structures with fully superimposed layers, comprising an inserted object.
8. Process according to one of Claims 2 to 6, characterised in that screws are placed in tapped holes of the solid metallic support after steps a) to e), these screws extending above the upper surface of the solid metallic support, and in that these screws are unscrewed when the metallic structures and the polymerised photoresist are being detached from the solid metallic support by delamination, so as to obtain monolayer metallic structures, or multilayer metallic structures with fully superimposed layers, comprising a threaded hole.
9. Machined monolayer metallic structure for clockwork movement obtained according to Claim 2 or one of Claims 4 to 8 dependent on Claim 2.
10. Machined monolayer metallic structure or machined multilayer metallic structure with fully superimposed layers, in which an insert is incorporated by the process according to Claim 7.
11. Machined monolayer metallic structure or machined multilayer metallic structure with fully superimposed layers, comprising a threaded hole formed by the process according to Claim 8.
12. Process for fabricating a monolayer metallic structure or multilayer metallic structure with fully superimposed layers by a LIGA type technology, which comprises the following steps:

    a) spreading a layer of photoresist over a solid metallic substrate,

    b) heating the layer of photoresist, if necessary, in order to evaporate the solvent,

    c) exposing the layer of photoresist through a mask corresponding to the desired impression with 100 to 2000 mJ/cm² of UV radiation measured at a wavelength of 365 nm,

    d) if necessary, in order to complete the photopolymerisation or photodecomposition, annealing the layer obtained after step c),

    e) developing by dissolving the parts which have not been polymerised or photodecomposed,

    f) electrolytically depositing a metal or an alloy in the open parts of the photoresist mould, and levelling by machining so as to obtain a plane upper surface, then

    g) in the case of a monolayer structure, if necessary, carrying out one or more other machining operations on the upper face of the electroformed mechanical structure, and

    h) detaching the metallic structure and the polymerised photoresist from the solid metallic substrate by delamination, and separating the polymerised photoresist from the machined monolayer metallic structure; or

    g) in the case of a multilayer structure with superimposed layers, repeating steps a), b), c), d), e) and activating by electrochemical treatment the surface of the electroformed metal not covered with polymerised photoresist,

    h) repeating step f),

    i) if necessary, repeating steps g) and h),

    j) if necessary, carrying out one or more other machining operations on the upper face of the electroformed mechanical structure, and

    k) detaching the metallic structure and the polymerised photoresist from the solid metallic substrate by delamination, and separating the polymerised photoresist from the machined multilayer metallic structure with superimposed layers,

    characterised in that a removably fixed object is placed above the solid metallic substrate after steps a) to e), and in that this object is released from the solid metallic substrate when the metallic structure and the polymerised photoresist are being detached from the solid metallic substrate by delamination, so as to obtain a monolayer metallic structure, or multilayer metallic structure with fully superimposed layers, comprising an inserted object.
13. Process for fabricating a monolayer metallic structure or multilayer metallic structure with fully superimposed layers by a LIGA type technology, which comprises the following steps:

    a) spreading a layer of photoresist over a solid metallic substrate,

    b) heating the layer of photoresist, if necessary, in order to evaporate the solvent,

    c) exposing the layer of photoresist through a mask corresponding to the desired impression with 100 to 2000 mJ/cm² of UV radiation measured at a wavelength of 365 nm,

    d) if necessary, in order to complete the photopolymerisation or photodecomposition, annealing the layer obtained after step c),

    e) developing by dissolving the parts which have not been polymerised or photodecomposed,

    f) electrolytically depositing a metal or an alloy in the open parts of the photoresist mould, and levelling by machining so as to obtain a plane upper surface, then

    g) in the case of a monolayer structure, if necessary, carrying out one or more other machining operations on the upper face of the electroformed mechanical structure, and

    h) detaching the metallic structure and the polymerised photoresist from the solid metallic substrate by delamination, and separating the polymerised photoresist from the machined monolayer metallic structure; or

    g) in the case of a multilayer structure with superimposed layers, repeating steps a), b), c), d), e) and activating by electrochemical treatment the surface of the electroformed metal not covered with polymerised photoresist,

    h) repeating step f),

    i) if necessary, repeating steps g) and h),

    j) if necessary, carrying out one or more other machining operations on the upper face of the electroformed mechanical structure, and

    k) detaching the metallic structure and the polymerised photoresist from the solid metallic substrate by delamination, and separating the polymerised photoresist from the machined multilayer metallic structure with superimposed layers,

    characterised in that a screw is placed in a tapped hole of the solid metallic substrate after steps a) to e), this screw extending above the upper surface of the solid metallic substrate, and in that the screw is unscrewed when the metallic structure and the polymerised photoresist are being detached from the solid metallic substrate by delamination, so as to obtain a monolayer metallic structure, or multilayer metallic structure with fully superimposed layers, comprising a threaded hole.
14. Machined monolayer metallic structure obtained according to Claim 12 or 13, characterised in that it is a piece of clockwork movement, in particular a spring.
15. Machined monolayer metallic structure, or machined multilayer metallic structure with fully superimposed layers, comprising an inserted object, characterised in that it can be obtained by a process according to Claim 12.
16. Machined monolayer metallic structure, or machined multilayer metallic structure with fully superimposed layers, comprising a threaded hole, characterised in that it can be obtained by a process according to Claim 13.
17. Machined multilayer metallic structure with fully superimposed layers which can be obtained by a process according to Claim 12 or 13, characterised in that it is an escapement anchor for clockwork movement.