CH704086A2 - Fabricating three-dimensional metal part e.g. cock using assembly of components obtained by photolithography and electroforming, comprises placing component in mold, and depositing photoresist layers on substrate through photomask - Google Patents

Abstract

The method comprises preparing a first mold comprising a cavity, placing a first component in the first mold, depositing photoresist layers on a substrate (1) through a photomask and irradiating the photoresist layer applied to the substrate through the photomask by masking all or part of an insert (4) with the exception of a sidewall of the insert, depositing an insulating layer on the insert, and polymerizing the photoresist layer and eliminating the non-polymerized photoresist layer. The method comprises preparing a first mold comprising a cavity, placing a first component in the first mold, depositing photoresist layers on a substrate (1) through a photomask and irradiating the photoresist layer applied to the substrate through the photomask by masking all or part of an insert (4) with the exception of a sidewall of the insert, depositing an insulating layer on the insert, polymerizing the photoresist layer and eliminating the non-polymerized photoresist layer so as to leave a portion of the photoresist layer constituting a cavity by a second photoresist mold intended to form a second level of the component, depositing a metal layer (8) in the cavity of the second photoresist mold by electroforming so that a growth of the metal layer encloses all or part of the insert by creating an intimate bond between the metal layer and a flank of the insert, machining a second metal layer to a predetermined thickness by a mechanical process, removing the polymerized photoresist layer from the mold of second level and the substrate, and obtaining a metal part comprising two superimposed levels overlapped one in the other formed by the insert and the electroformed metal layer. The first component is insert that forms a first level of the component. The metal layer forms a second component. The step of preparing the first mold for the insert comprises etching a part of the substrate not masked by the photoresist layer, where the etched part of the substrate constitutes the cavity of the first mold. A depth of the first mold is greater than or less than or equal to a thickness of the insert. The insert is composed of a single level or superimposed levels. A contour form of the flank of the insert along which the intimate connection between the levels of the part takes place is configured to maximize a contact surface between the insert and the metal layer. The insert is made of a first metal and a conductive material, and the electroforming metal of the second metal layer is made of a second metal that is different from the first metal. A thickness of the second photoresist layer (2b) is greater than the thickness of the insert, where the second photoresist layer covers a part of the insert by forming an additional space superimposed on an area including the flank of the insert. An independent claim is included for a metal part.

Description

Field of the invention

The present invention relates to the field of the manufacture of micro metal parts by electroforming in particular parts having at least two superimposed levels not necessarily included one in the other each having a predefined shape. Certain parts used in watchmaking, for example anchors with integrated dart, gears with staggered teeth, etc., are also objects of the invention as well as the method enabling them to be advantageously achieved.

Technical background

The process for manufacturing micro parts or components by irradiating a photosensitive layer with ultraviolet rays followed by an electroforming step is known and is described for example in patent EP0851295B1.

This process is derived from the LIGA technique (Lithography Galvanoformung Abformung) which consists in: depositing on a substrate a layer of 1 to 2000 μm of a photosensitive resin (photoresist); perform irradiation by means of a synchrotron or exposure to ultraviolet radiation through a mask; develop, that is to say, remove by chemical means the unpolymerized photoresist portions and thereby create a cavity or mold photoresist. electroforming a metal in this cavity to obtain a micro metal part.

The advantage of this technique is to make parts or mechanical components of great precision in X and Y and with a thickness of up to several millimeters. It is also possible to apply this method in several steps to obtain a component in several levels, each level being built on the previous one. Only parts whose upper level fully includes the lower level can be manufactured using this method.

This method is described further in the patent application EP1 225 477A1 and details the process of masking, irradiation and dissolution of the non-irradiated part. This technique is well known for the manufacture of timepieces such as, for example, gears, cams, rockers or bridges.

Several techniques for manufacturing multi-level parts based on the LIGA process are described in documents of the prior art, namely:

[0007] WO2007 / 104171A2 which describes a method for manufacturing a two-level part comprising a step of depositing a layer of attachment gold on the first level of the part preceding the deposition of the second level on the first. There is therefore no assembly between the levels, the layers adhere planar to one another by means of a layer of attachment.

[0008] WO2009 / 083 488A1 which describes a technique for manufacturing by the LIGA process of a part by forming a photoresist mold on a substrate in which a first uniform layer of a first metal is deposited galvanically and then a second layer of a second metal coating the first layer. This involves coating a 1-level piece with a metal to form a shell.

[0009] WO2010 / 020 515A1 which describes the manufacture of a multi-level part by producing a complete photoresist mold corresponding to the final part to be obtained before the step of galvanic deposition of the metal of the part in the mold. Only multilevel parts whose levels are included in one another are achievable by this method.

EP1 462 859A2 which describes a multi-level process for producing complex parts whose upper levels are a subset of the previous levels. Two different levels are formed in two photoresist deposits to form a mold. Before the electroforming phase of the part, a conductive layer is deposited on the walls of the mold so that the deposition of the metal particles is carried out homogeneously. As in the case of the method described in the previous document WO2010 / 020515A1, only multilevel parts whose levels are included one in the other are achievable according to this method.

EP1 916 567B1 describes a method for manufacturing a part composed of at least two elements, ie a metal part obtained by electroforming, and at least one added element obtained by another manufacturing method and comprising at least one flank in contact with the metal part. The connection between the reported element and the metal part is said intimate that is to say resulting from the growth by electroforming of the metal part along the side of the insert. The element or elements reported are thus entirely or partially enclosed in the electroformed deposited metal.

To obtain multi-level parts whose levels are not included in each other, the parts must be assembled together by embedding, crimping, screwing or other stamping.

These operations are delicate because of the small size of the parts involved and the low support spans. It happens that during this assembly, it deteriorates the parts involved.

At each operation, we add more inaccuracy resulting from the tolerances of the different parts to be assembled.

Brief description of the invention

Thus, one of the aims of the present invention is to facilitate subsequent assembly operations for obtaining parts obtained by the multi-level LIGA process whose levels are not necessarily included in the one. other.

Another object of the present invention is to manufacture three-dimensional metal micro-parts obtained by multilayer LIGA process self-assembled by interleaving performed in several electroforming phases. The different levels of these micro-parts may be composed of different materials.

These objects are achieved by a method described by claim 1.

The piece produced by the method comprises at least two levels interlocked in one another thanks to the growth of the second level of the piece around or in a part of the first level of the piece by growth of the metal layer. along a side of said first level. It is a self-assembly.

The positioning of a first level of the part is in a first mold obtained either by a deep etching of the substrate, or by the lithography process of a thick resin, or by a combination of the two methods. A second mold of a second level of the component is obtained by structuring by radiation, polymerization and development a photoresist layer.

Manufacturing according to the method of metal parts comprising at least two levels, requires at least the assembly of two elements each obtained by the LIGA process. The different levels are not necessarily included in one another and are positioned between them using photolithography. The method includes the following steps: forming a first mold etched in a silicon substrate or in polymerized resin placing an insert in the first mold, said first mold serving as a guide to the insert, irradiating through a photomask a layer of photoresist applied to the substrate defining a second level of the part, polymerizing this photoresist layer and removing the unpolymerized photoresist layer, the remaining photoresist portion constituting a second photoresist mold to form the second level of the part, deposition of a metal layer by electroforming on the substrate so that the growth of the metal layer is carried out at least on a portion of the flanks of the insert, obtaining the part by separating the substrate from the electroformed metal layer. The two levels of the part formed on the one hand by the insert element and on the other hand by the metal layer are thus integral. In a final step, the photoresist mold is removed.

The present invention also relates to a finished product in the form of a part according to claim 9 composed of at least two levels, both obtained by photolithography and electroforming, the first level being reported, and comprising at least one sidewall. in contact with the metal part of the second level, the connection between the metal elements is said to be intimate and results from the growth of the second level along the side of the insert.

The part is characterized in that the one or more inserts are guided and positioned by an engraved mold in a substrate or made of photoresist. The term "guided" means that the reported element or elements are held in the mold so as to prevent any displacement or movement of the element during the manufacturing process of the part and more particularly during the electroforming of the second level.

The growth of the metal layer on the substrate will enclose the insert and it will thus be part of the final part. The mold etched in the substrate or in photoresist is intended to position the insert before the metal deposition phase of the rest of the room. The indexing between the second electroformed metal part and the added metal element becomes very precise because the same mold which defines the second electroformed part also defines the reference position of the insert.

The element of the second level is nested and intimately connected to the first level of the insert element by at least one flank portion forming a contour comprising a series of convex and / or concave portions so that the second element of the second level encloses a portion of the contour of the insert.

According to a variant, the insert comprises at least one through orifice, of any shape, whose bottom is constituted by the bottom of the first mold. The periphery of the orifice is thus entirely formed by the metal of the piece. The second level electroformed metal fills the orifice from the substrate by bonding with the metal of the flanks of the orifice to spread over the base of the second mold to a predefined thickness. The base of the second mold consists of all or part of the upper surface of the insert and at least a surface portion of the substrate of the first mold.

According to another variant, the metal insert is placed in the first mold so as to form an adjacent space whose periphery is composed of a portion of the sidewall of the insert and a portion of the sidewall of the first and second molds. of photoresist. The shape of the space is thus defined by that of the flank portions of the insert and flank of the photoresist layers. The metal of the second layer forming the second level of the part fills the space by embedding the flank portion of the insert. This flank portion preferably comprises depressions and / or protuberances ensuring a solid coating excluding subsequent separation of the levels by shear forces.

It should be noted that the number of orifices and spaces adjacent portions of sidewalls of the insert is not limited to one for the same room. The insert may indeed have several orifices and / or more spaces between the sidewall of the layer and the walls of the mold cavity.

It is also noted that the number of reported elements is not limited to one for the same room.

As the insert is obtained by LIGA, it is in a conductive material. A step of depositing an insulating layer such as a lacquer for example on the insert can be carried out. This operation may be carried out either before removal of the insert in the mold, or subsequently, by selective deposition of the insulating layer by means of a mason mask. Another way to isolate the insert is the application of a thin photoresist undercoat on the substrate and its polymerization at least where the element will be located.

It should also be noted that the piece thus obtained may be formed of different materials such as NiP (nickel-phosphorus) for parts to be non-magnetic and / or slippery and Ni (nickel) for parts requiring good mechanical properties spring. The part can also be composed of gold and nickel if differences in density are needed in the same component. The different components of the part can be formed in different materials.

According to a third variant, the insert may be formed of several levels. The connection between the components is along the flanks of one of the levels of the patch.

The present invention also relates to a part composed of at least two levels each consisting of a metal layer obtained by photolithography and whose relative positioning is obtained by means of a photoresist mold or etched in the substrate, and by electroforming, characterized in that the metal layer of the second level is nested and intimately connected to an insert element by at least a surface and flank portion of the metal layer of said insert and in that the second level extends partially or entirely over the first level and an outer area in the vicinity of said first level so that the contour of an orthogonal projection of the second level includes all or part of the contour of the first level.

The levels of the room are intimately related to each other through the growth of the second metal layer in the first. This growth takes place on all or part of the surface of the insert, in an orifice and / or on a portion of the contour this metal layer. A separation of levels is not possible without destroying the room. The levels are thus self-assembled during the electroforming of the upper level and positioned with respect to each other precisely by photolithographic process.

Brief description of the figures

The invention will be better understood from the following detailed description with reference to the accompanying drawings in which: <tb> Fig. 1 <sep> illustrates the various steps of the method according to the invention to obtain a nested two-level part not necessarily included one in the other whose components of the two levels are defined by the LIGA method. The first component forming the two-level insert is inserted into a cavity of a photoresist mold. <tb> Fig. 2 <sep> illustrates a variant of the method in which the two-level insert is inserted into a mold obtained by etching in the substrate. <tb> Fig. 3 <sep> illustrates a variation of the method in which the single-level insert has a through hole which will be filled by the metal of the second layer forming the second level. <tb> Fig. 4 <sep> illustrates a variant of the method in which two elements are reported via an engraved mold in the substrate. <tb> Fig. <Sep> shows an example of a timepiece made by the method of the invention using a first mold etched in the substrate for the first level and two photoresist molds for the two upper levels.

Detailed description of the invention

According to FIGS. 1 to 4, the substrate 1 is generally a plate of glass, silicon or metal on which is deposited a conductive layer made for example by evaporation of chromium and gold. On this conductive layer is deposited and dried a photoresist layer sensitive to ultraviolet rays (or X-rays according to the chosen technology).

This photoresist layer 2a is then irradiated with an ultraviolet source through a glass plate on which has been structured a chrome pattern. This plate with its chrome cutout is called a photomask used in steps A and D illustrated in FIGS. 1 to 4.

The light arriving perfectly perpendicular to the photomask, only portions of photoresist unprotected by the chrome pattern will be irradiated. The flanks of the photoresist portions are thus perpendicular to the substrate.

In the particular case of a negative resin such as SU8, annealing of the photoresist layer causes polymerization in the areas having received UV radiation. This polymerized portion becomes insensitive to most solvents as opposed to non-irradiated areas that are dissolved by a suitable solvent.

In the case of a positive resin, generally used in the etching of a substrate, the resin is polymerized and rendered soluble by exposure to light. In some cases, the positive resin is used to etch an intermediate layer to mask the unetched areas.

The axes has top views in Figs. 1 to 4 define the corresponding sectional views of the first and second stage production steps of the part.

Step A illustrated in FIG. 1 and steps A, B illustrated in FIGS. 2 to 4are preliminary steps for preparing a mold that will serve as a guide for an insert element 4. This guidance may be done either by the outer part of the insert element 4 or by an orifice of said element as shown in FIG. fig. 3, or by a combination of both.

Step A consists in depositing and irradiating through a first photomask 3a, a first photoresist layer 2a previously applied to the substrate 1. This first photoresist layer 2a is polymerized according to the pattern of the photomask 3a and the parts of the uncured layer are removed chemically. The remaining photoresist portion forms a mold.

An element 4 also obtained by a LIGA process is reported in the mold and will define a first level of the multi-level component, (step B). This element 4 comprises in this example a first basic level 4 "and a protuberance format a second higher level 4. The contours of these levels 4 and 4 may be of any shape with vertical flanks because the element is derived from a LIGA photolithographic process. The shape of the cavity 5 of the mold is determined by the shape of the contour of the insert 4 which is in contact with the walls of the cavity 5 so as to prevent any displacement of the element 4 during the realization of the second level of the room. The example of FIG. 1 shows an insert element 4 with a six-sided base level 4 whose four sides are in contact with each of the four walls of the rectangular cavity of the mold.

In step C, a second photoresist layer 2b is deposited on the substrate 1 and irradiated using a second photomask 3b which masks all or part of the element 4 reported (step D). The thickness of this second photoresist layer 2b is equal to that of the added element 4, or greater than the thickness coming out of the mold of the insert element 4 as illustrated by FIG. 1. In the example of FIG. 1, the photoresist of the second layer 2b also penetrates into the spaces 6 and 6 left by the sides of the added element which are not in contact with the walls of the cavity 5 of the mold, cf. top view of the mold containing the insert 4 in steps B and D. '

This second layer of photoresist 2b constituting the base of the second level is polymerized in areas defined by the mask photo 3b. The remaining unpolymerized areas are removed so as to leave a portion of the photoresist layer 2b serving to form the base or bottom of a cavity 7 of a second mold to create the second level.

The following step E consists of depositing a metal layer 8 by electroforming matching the polymerized structures of the mold while enclosing the insert element 4 at the same time on the protuberance of its upper level 4 and all or part of the surface of its basic level 4 ". The metal layer 8 also covers a portion of the surface of the first photoresist layer 2a constituting the bottom of the cavity of the second mold together with a portion of the upper surface of the base level 4 of the element 4. In in this example, the cavity 7 of the second mold is defined so that the spaces 6 and 6 are not filled by the metal of the second layer.

This second metal layer 8 is then machined by a mechanical process to a predetermined thickness.

The last step F consists in releasing the piece formed by the insert element 4 and the metal layer 8 and in removing the polymerized photoresist mold.

Thus we obtain a multi-level piece (two levels) directly out of the mold and comprising a first level defined by the insert element 4 which is integral with a second level consisting of the metal layer formed by the electroforming. The levels of this piece are thus not necessarily included one in the other. There is more assembly tolerance between the metal parts of the two levels, because the positioning of the second level is provided by the mold in photoresist itself. During the operation of depositing subsequent levels, the metal of these levels matches the flanks or sides of the insert 4 and thus create an intimate connection therewith. By the term "sidewall", reference is made to the walls of the insert 4 without contact with the walls of the mold. The great advantage of this method is to be insensitive to the dimensions of the parts that will form the assembly, unlike the method applied until then, in which the insert is driven into an orifice of the base metal part and therefore had to be positioned with great precision.

FIG. 2 illustrates an example of a variant of the method in which the first mold for the insert is obtained by deep etching of the substrate and the second mold is obtained by the LIGA process.

In step A, a photoresist layer 2a is applied to a substrate 1 and a first photomask 3a is used to define the shape of the outline of the first mold. The deep etching operation B of the substrate is generally carried out by dry etching (plasma etching, for example DRIE, Deep Reactive Ion Etching) or wet etching (for example KOH etching, potassium hydroxide) involving a selective etching of the parts of the substrate. not protected by the resin structured by illumination through the photomask 3a. This deep etching results in a mold cavity 5 in which the insert 4 will be inserted.

In step C an insert element 4 obtained by the LIGA process is deposited in the mold etched in the substrate 1. In this example, the contour of the element 4 corresponds to that of the cavity 5 of the first mold.

In step D, a second photoresist layer 2b is applied to the substrate 1 with a second photomask 3b so as to extend both on the substrate 1 and / or on at least a part of the element. 4. This second layer of photoresist 2b is the mold of the second level.

After polymerization and removal of the unpolymerized photoresist, a metal layer 8 is deposited by electroforming in the mold in step E. This metal layer 8 grows from the surface of the insert element 4, in spaces 6 along flanks of the insert element 4, on the upper surface of the insert element 4 and on a surface portion of the substrate 1 in the vicinity of the insert element 4 in order to fully occupy the mold of the second level.

The upper surface of this metal layer 8 is also machined to a predefined thickness before the removal of the substrate 1 and the polymerized photoresist 2b of the mold. The metal part obtained in step F thus comprises two self-assembled levels that are not necessarily included in each other, similar to a part obtained by the variants of the method illustrated in FIG.

FIG. 3 illustrates an example of a variant of the method in which the insert element 4 comprises a single level and the assembly of the next level is by growth along the flanks of the single level of the insert element 4. The fig. 3 illustrates an example with insert element 4 having an orifice 6. Depending on the shape of the outer contour of the element and the spaces left between portions of flanks and the walls of the first mold, the assembly can also be carried out along the outer flanks of the element in addition to the assembly on the walls of the orifice 6, cf. the top view of the insert element 4 inside the cavity 5 in step C.

The bottom of the cavity 7 of the second mold in step E is constituted by a portion of the upper surface of the element 4, a surface portion of the substrate at the bottom of the orifice and the space 6 and a portion of the upper surface of the substrate 1 in the vicinity of the cavity 5 of the first mold. The second metal layer 8 thus grows along a portion of the outer side of the element 4 and along the flanks inside the orifice. This growth is limited as in the previous examples by the walls of the second mold formed by the second layer of photoresist 2b.

The depth of the first mold may be smaller than the thickness of the insert 4 so that it exceeds wholly or in part the first mold in which it is positioned as illustrated in FIG. 1. This depth may also equal or be greater than the thickness of the insert 4 as shown in FIG. 2respectively fig. 3.

FIG. 4 illustrates an example of a variant of the method in which two elements 4a and 4b are each reported in a respective cavity 5 and 5 of a mold etched in the same substrate 1. The depths of these cavities 5 and 5 may be different and the inserts 4a and 4b may comprise one or two levels, cf. Fig. 1and fig. 3. In this example, the cavities 5 and 5 have the same shape as the inserts 4a and 4b.

In step F, the electroformed metal layer 8 in the mold formed by the substrate 1 and the second photoresist layer 2b increases from the bottom of the recesses 5 and 5, the respective surfaces and flanks of each insert 4a and 4b and a portion of the upper surface of the substrate 1 in the vicinity of the cavities 5 and 5 ". This metal layer 8 thus completely fills the free volumes of photoresist cavities 5 and 5 of the first mold comprising the spaces 6a and 6b and the mold volume of the second level delimited by the photoresist layer 2b. The part obtained in step G comprises two attached elements 4a and 4b clamped in the metal of the electroformed layer 8.

The method of the invention and its variants also apply to parts with more than two levels. For example, FIG. 5 illustrates a timepiece, in this case a dart anchor 10 made by using a first mold etched in the substrate 1 in which is placed the insert element 4, here a dart obtained by a LIGA process which forms the first level n1 of the room. The second and third level n2, n3 forming the anchor are made using two molds formed by two layers of photoresist 2b, 2c superimposed. The second metal layer 8 forming the levels n2 and n3 is deposited so as to grow both on the substrate 1 and along the side of a port of the stinger 4 and in the two-level cavity of the second mold in photoresist.

The second level (n2) of the part 10 extends partially on the insert (4) and the third level (n3) extends partially or entirely on the second level (n2) and on an outer zone in the vicinity of said second level (n2) so that the contour of an orthogonal projection of the third level (n3) includes all or part of the contour of the insert (4) forming the first level n1.

The method of manufacturing this part comprises, after the polymerization of the second photoresist layer (2b), steps of forming a second mold which consist in: depositing and irradiating through a third photomask, a third photoresist layer 2c defined by masking at least one zone including a flank of the element 4, polymerizing the third photoresist layer 2c and removing the unpolymerized photoresist layer, the remaining photoresist portion constituting a cavity of the second mold, the orifice in the insert 4 being free of photoresist.

In the example of FIG. 5, the zone including a flank of the insert element 4 comprises the orifice of the stinger from which the second metal layer 8 will be electroformed.

The thickness of the second layer of photoresist 2b may be greater than the thickness of the insert (4), and it covers a portion of the insert (4) forming an additional space superimposed at the orifice of the insert (4). The second mold thus comprises a cavity formed of three superimposed levels formed by the orifice of the insert element 4 and spaces respectively defined by the second and third photoresist layer 2b, 2c. This cavity is then filled by the second electroformed metal layer 8 of the part which grows from the bottom of the orifice of the stinger to extend into the spaces formed by the two layers of photoresist 2b and 2c. After machining the surface of the third level, the substrate 1 and the photoresist mold are removed to release the anchor 10.

Numerous other multi-level timepieces such as the integrated dart anchor of FIG. 5, can also be made by the method, for example a wheel, a cam, a heart, a needle, a tray, etc. Their common feature is that they are all self assembled with another element (insert) to form a multi-level piece whose levels are not necessarily included in one another.

According to a variant, the method of the invention comprises an additional step of depositing an insulating layer, in the form of a lacquer, for example, on the insert element 4 before or after its placement in the first mold. . This insulating layer does not affect the strength of the final piece because the insert is firmly gripped in the second metal layer and this especially as the contour of the sidewall of the insert has a large number of convex portions and concave.

In the case of an insert without an insulating layer, the second metal layer grows on the metal of the insert in the same manner as on the surface of the substrate provided with a conductive layer. Clamping of the insert is made just as securely as in the variant with the insert covered with an insulating layer.

Claims (17)

1. Method of manufacturing a metal part comprising at least two levels, requiring at least the assembly of two elements obtained by photolithography and electroforming, this method comprising the following steps: - preparing a first mold comprising at least one cavity (5), placing a first element in the first mold, said first element being an insert (4) forming a first level of the part, depositing and irradiating through a photomask (3b), a photoresist layer (2b) applied to the substrate (1), by masking all or part of the insert (4) with the exception of at least a sidewall of the insert (4), - polymerizing the photoresist layer (2b) and removing the uncured photoresist layer, so as to leave a portion of the photoresist layer (2b) constituting a cavity (7) of a second photoresist mold for forming a second level of the room, - depositing a metal layer (8) by electroforming in the cavity (7) of the second photoresist mold so that the growth of the metal layer (8) encloses all or part of the insert (4) creating an intimate bond between the metal layer (8) and at least one side of the insert (4), said metal layer (8) forming a second element, machining the second metal layer (8) by a mechanical method to a predefined thickness, - removing the polymerized photoresist from the mold of the second level and the substrate (1), - Obtaining a metal part having two superimposed levels imbricated one in the other formed by the insert (4) and the electroformed metal layer (8). 2. Method according to claim 1 characterized in that the step of preparing the first mold for receiving the insert (4) comprises the following operations: depositing and irradiating through a first photomask (3a) a first photoresist layer (2a) applied to a substrate (1), polymerizing the first photoresist layer (2a), - Remove the uncured photoresist layer, the remaining photoresist portion constituting the first mold formed by the photoresist and having at least one cavity (5) configured to guide and position the insert (4). 3. Method according to claim 1 characterized in that the step of preparing the first mold for the insert (4) comprises the following operations: depositing and irradiating through a first photomask (3a) a first photoresist layer (2a) applied to a substrate (1), polymerizing the first photoresist layer (2a) and removing the uncured photoresist layer, - Burn the portion of the substrate (1) not masked by the photoresist, the etched portion of the substrate constituting a cavity (5) of the first mold. 4. Method according to one of claims 1 to 3 characterized in that the depth of the first mold is larger, smaller or equal to the thickness of the insert (4). 5. Method according to one of claims 1 to 4 characterized in that the insert (4) is composed of a single level or a plurality of superimposed levels. 6. Method according to one of claims 1 to 5 characterized in that the shape of the contour of the sidewall of the insert (4) along which is made the intimate connection between the levels of the room is configured so as to maximize the contact area between the insert (4) and the metal layer (8). 7. Method according to one of claims 1 to 6 characterized in that the insert (4) is made of a first metal and the electroforming of the second metal layer (8) is made of a second metal different from the first metal. 8. Method according to one of claims 1 to 7 characterized in that it comprises an additional step of depositing an insulating layer on the insert (4) before or after its placement in the first mold, said an insert (4) being composed of a conductive material. 9. Method according to claim 1 characterized in that it comprises, after the polymerization of the photoresist layer (2b), the following formation steps of the second mold in photoresist: depositing and irradiating through a third photomask, a third photoresist layer (2c) defined by masking at least one zone including a flank of the insert element (4), - polymerizing the third photoresist layer (2c) and removing the uncured photoresist layer, the remaining photoresist portion constituting a cavity of the second mold formed of three superimposed levels formed by the area including a sidewall of the insert (4) and spaces respectively defined by the second and third photoresist layers (2b, 2c). 10. The method of claim 9 characterized in that the thickness of the second photoresist layer (2b) is greater than the thickness of the insert (4), said second photoresist layer (2b) covering a portion of the insert (4) forming an additional space superimposed on the area including a sidewall of the insert (4). 11. Part consisting of at least two levels (n1, n2) each consisting of a metallic element obtained by photolithography and electroforming, by guiding and positioning at least a first insert element (4) in a first mold , said first insert (4) forming a first level (n1) of the part, characterized in that a second element forming a second level (n2) is interleaved and intimately connected to the first element (4) of the first level ( n1) by at least a portion of surface and sidewall of said first insert (4) and in that the second level (n2) extends partially or wholly on the first level (n1) and on an outer area in the vicinity of said first level (n1) so that the contour of an orthogonal projection of the second level (n2) includes all or part of the contour of the first level (n1). 12. Part according to claim 11 characterized in that the insert element (4) of the first level (n1) is constituted by a first metal and the second element of the second level (n2) is constituted by a second metal different from the first metal . 13. Part according to one of claims 11 or 12, characterized in that the second element of the second level (n2) is nested and intimately connected to the insert element (4) of the first level (n1) through at least one orifice (6) formed in the insert (4) of the first level (n1). 14. Part according to one of claims 11 to 13, characterized in that the element of the second level (n2) is nested and intimately connected to the insert element (4) of the first level (n1) by at least a portion contour forming blank comprising a series of convex and / or concave portions so that the second second level member (n2) encloses a portion of the contour of the insert (4). 15. Part according to one of claims 11 to 14, characterized in that the second element of the second level (n2) is nested and intimately related to the insert element (4) of the first level (n1) around at least a protuberance of the insert (4). 16. Part according to one of claims 11 to 15, characterized in that the second element of the second level (n2) is nested and intimately connected to a plurality of inserts (4) forming the first level (n1). 17. Part according to claim 11 characterized in that it comprises a second level (n2) extending partially on the insert (4) and a third level (n3) extending partially or entirely on the second level ( n2) and on an outer zone in the vicinity of said second level (n2) so that the contour of an orthogonal projection of the third level (n3) includes all or part of the contour of the insert (4) forming the first level ( n1).