CH705433B1 - Manufacturing micromechanics composite silicon-metal part useful in clock element, comprises manufacturing substrate with upper and lower layers, and selectively etching cavity in upper layer to define pattern in portion of silicon part - Google Patents

Abstract

The method comprises manufacturing a substrate (3) comprising an upper layer (5) and a lower layer (7) extending from an intermediate layer (9) made of silicon oxide, selectively etching a cavity in the upper layer to define a pattern in a portion of a first silicon part, continuing the etching of the cavity in the intermediate layer, and forming a first metal layer (63) from a portion of the cavity formed by a lower conductive layer to form a first metal part with a thickness of greater than 6 microns for insulating the first silicon part. The method comprises manufacturing a substrate (3) comprising an upper layer (5) and a lower layer (7) extending from an intermediate layer (9) made of silicon oxide, selectively etching a cavity in the upper layer to define a pattern in a portion of a first silicon part, continuing the etching of the cavity in the intermediate layer, forming a first metal layer (63) from a portion of the cavity formed by a lower conductive layer to form a first metal part with a thickness of greater than 6 microns for insulating the first silicon part, and releasing micromechanical component of metal-silicon composite substrate. The forming step comprises covering a photosensitive resin over the substrate, selectively performing photolithography on the photoresistive resin substrate depending on a predetermined portion of a metal pattern, and depositing the metal layer by plating from an upper surface of the lower conductive layer, which is vertical to the cavity grown from a bottom of the metal layer between the photoresistive resin and the intermediate layer or the upper layer for forming the first metal part in the pattern. The releasing step is carried out by eliminating the photoresistive resin. The lower conductive layer is made of conductive by doping an upper face of the lower layer and depositing a conductive layer. The photoresistive resin protrudes during photolithography of the upper layer of the substrate to continue the formation of the metal layer by plating between projections of the resin to form a second metal part of the micromechanical component above the silicon part. The method further comprises: machining the upper layer of the substrate to level the metal layer coated with the photoresistive resin after the formation step; and forming a second metal layer by electroplating in a portion of the cavity of the lower layer to form a second metal part along a thickness of the lower layer. The cavity in the lower layer of the substrate is etched to form a second silicon part of the micromechanical component according to a shape and a predetermined thickness before the releasing step. The second metal part forming step comprises covering the photoresistive resin beneath the substrate, selectively performing photolithography on the photosensitive resin in a predetermined part of an additional metal unit, and forming the second metal layer by electroplating a bottom of the cavity of the lower layer to form the metal part in the pattern. The photoresistive resin protrudes during photolithography from the lower layer of the substrate to continue the formation of the second metal layer by electroplating to form the second metal part below the second silicon portion. An independent claim is included for a micromechanics part.

Description

Field of the invention

The invention relates to a silicon-metal composite micromechanical component and its manufacturing process.

Background of the invention

Silicon is known tribologically for its low coefficient of friction. Its application in mechanical watchmaking is interesting especially for the exhaust systems and more precisely for the impeller gears of an escape wheel. However, silicon is also known mechanically for its weak plastic zone so that its adaptation in particular the usual techniques of driving on axis is made difficult by its brittle nature.

Summary of the invention

The object of the present invention is to overcome all or part of the drawbacks mentioned above by providing a manufacturing method advantageously for the production of a composite micromechanical part adapted to adapt to most horological applications.

For this purpose, the invention relates to a method for manufacturing a silicon-metal composite micromechanical component comprising the following steps: <tb> a) <sep> fabricating a substrate having an upper layer and a lower silicon layer between which an intermediate layer of silicon oxide extends; <tb> b) <sep> selectively etching at least one cavity in the top layer to define the pattern of a silicon part of said part; <tb> c) <sep> continue etching said at least one cavity in the intermediate layer, characterized in that it further comprises the following steps: <tb> d) <sep> growing a metal layer at least from a portion of said at least one cavity of the conductive upper face of the lower layer to form a metal portion of a thickness greater than 6 microns for isolating the silicon portion of destructive forces in the thickness of said part; <tb> e) <sep> release the silicon-metal composite micromechanical part of the substrate.

The method advantageously allows to obtain a monobloc piece that allows to enjoy tribological characteristics of silicon and mechanical properties of the metal.

According to other advantageous features of the invention: Step d) comprises the following steps: coating the top of the substrate with photoresist; selectively photolithography the photosensitive resin to photostructurate according to the predetermined pattern of the metal portion; depositing the metal layer by electrodeposition from the conductive upper face of the lower layer which is in line with the said at least one cavity by growing, from the bottom, the metal layer between the photostructured resin and the layer respectively; intermediate or upper to form the metal part according to said pattern; and in that step e) is performed by removing the photostructured resin. said conductive upper surface of the lower layer which is in line with said at least one cavity is made conductive by doping the lower layer and / or depositing a conductive layer; The photostructured resin during the photolithography step protrudes from the upper layer of the substrate in order to be able to continue the growth of said metal layer by electrodeposition at least between said projections of the photostructured resin in order to form a second metal part of the micromechanical part above the silicon part; The method comprises, after step d), a step of machining the upper face of the coated substrate in order to level the metal layer at the same height as the upper end of said photostructured resin; The metal layer comprises nickel; The method comprises, before the release step, steps for machining and etching at least one cavity in the lower layer of the substrate in order to form a second silicon part of the micromechanical part in a form and a determined thickness; The method comprises, between the machining and etching steps of the lower layer of the substrate and the release step, a step of growing a second metal layer by electrodeposition in at least a portion of said at least one cavity; the lower layer to form at least one additional metal part in the thickness of the lower layer; The growth stage comprises the following steps: coating the underside of the substrate with photoresist; selectively photolithography the photosensitive resin to photostructurate according to the predetermined pattern of the metal portion; depositing the second metal layer by electrodeposition from the bottom of said at least one cavity by growing, from the bottom, the second metal layer for forming the additional metal part according to said pattern; the photostructured resin during the photolithography step protrudes from the lower layer of the substrate in order to be able to continue the growth of the second metal layer by electrodeposition in order to form a second additional metal part of the micromechanical part below the second part of silicon; the method comprises, before the release step, a step of machining the underside of the coated substrate to level the metal portion at the same height as the lower end of said photostructured resin; the second electrodeposited metal layer comprises nickel; several micromechanical parts are manufactured on the same substrate.

The invention also relates to a silicon-metal composite micromechanical part comprising a portion formed in a silicon layer characterized in that said silicon portion comprises, at least over a portion of its thickness, a metal part of a thickness greater than 6 microns intended to isolate the silicon portion of destructive efforts.

The one-piece piece thus allows to take advantage of tribological characteristics of silicon and the mechanical characteristics of the metal.

According to other advantageous features of the invention: the metal part forms a jacket which covers the peripheral wall of said silicon part; the metal part forms a jacket in a cavity made in the silicon part in order to receive a pivot axis by driving; each jacket is connected to the wall of the silicon part by material bridges; the piece comprises a second metal part projecting from the silicon part; the second metal portion has teeth to form a wheel or pinion; each metal part comprises nickel; the silicon part comprises a toothing to form a wheel or a pinion; the part comprises a second silicon part formed from a second layer; the second silicon portion has at least a portion of its thickness an additional metal portion for isolating the second silicon portion of destructive efforts; the additional metal part forms a jacket in a cavity made in the second silicon part in order to receive a pivot axis by driving; said jacket is connected to the wall of said cavity by material bridges; the part comprises a second additional metal part projecting from the second silicon part; the second additional metal part has a toothing to form a wheel or a pinion; the second silicon part is mounted on the silicon part by means of an intermediate layer made of silicon oxide; the second silicon part comprises a toothing to form a wheel or a pinion.

Finally, the invention relates to a timepiece characterized in that it comprises at least one composite micromechanical component according to one of the preceding variants.

Brief description of the drawings

Other features and advantages will become apparent from the description which is given below, for information only and not limiting, with reference to the accompanying drawings, in which: <tb> figs. 1 to 7 <sep> are sections of a composite micromechanical component at different phases of the manufacturing method according to the invention; <tb> fig. 1b <sep> is a representation of FIG. 1in perspective. <tb> fig. 8 <sep> is a representation of a first example of a final step according to the method of the invention; <tb> fig. 9 <sep> is a representation of a second example of a final step according to the method of the invention; <tb> fig. <Sep> is a block diagram of the manufacturing method according to the invention; <tb> fig. 11 <sep> is a perspective representation of a gear train according to the invention; <tb> fig. 12 <sep> is a top view of a needle obtained according to the invention.

Detailed Description of the Preferred Embodiments

The invention relates to a manufacturing method 1 of a composite micromechanical component 51 silicon-metal. As shown in figs. 1 to 7, the method 1 comprises successive steps for forming at least one part 51, 51, 51 which can be complex and / or in several layers and / or with several materials. The object of the present method 1 is at least to provide a part having at least a silicon part and at least a metal part.

The first step 11 is to provide a substrate 3 of the type "silicon on insulator", well known by the acronym "SOI". The substrate 3 comprises an upper layer 5 and a lower layer 7 composed of mono or polycrystalline silicon. Between the upper 5 and lower 7 layers extends an intermediate layer 9 composed of amorphous silicon oxide (SiO2).

Preferably in this step 11, the substrate 3 is chosen so that, as shown in FIG. 1, the height of the upper and intermediate layers 9 corresponds to the final height of a portion 53 of the final micromechanical part 51.

In a second step 13, as visible in FIGS. 1 and 1b, cavities 37, 45 are selectively etched, for example by a method of the type DRIE (acronym well known from the English "deep reactive ion etching"), in the upper layer 5 of silicon. These two cavities 37 and 45 make it possible to form the pattern defining the inner and outer contours of the silicon part 53 of the micromechanical part 51.

In the example illustrated in FIG. 1, the cavity 37 is present on each side of the cavity 45 because, as shown in FIG. 1b, it is substantially annular and surrounds the cavity 45. Preferably, the proximal wall of the cavity 37 is selectively etched to form a toothing 55 on the peripheral edge of the portion 53. The cavity 45 is substantially cylindrical with a disc section and is coaxial with the annular cavity 37.

In a third step 15, etching by wet or dry chemical etching is performed to extend, in the intermediate layer 9, the cavities 37 and 45 so that the portion 53 is formed in the same pattern in the intermediate layer 9 until to partially discover the lower layer 7.

The method 1 according to the invention then comprises the implementation of a process 19 of the LIGA type (acronym well known from the German "Röntgenlithographie, Galvanoformung und Abformung") comprising a succession of steps (17, 21 and 23) for electrodepositing a particular shape to a metal on the upper face of the substrate 3 with a photostructured resin.

In a fourth step 17 is deposited on the upper face of the substrate 3, a layer of photoresist 57 as shown in FIG. 2. Step 17 can be performed for example using a mold casting method (also known as "mold casting"). Preferably, the photosensitive resin 57 is of the Su-8 type, for example the product "nano ™ Su-8" from the company Microchem Corp.

In a fifth step 21, a photolithography is carried out, that is to say that is exposed selectively to a radiation R, for example by means of a partially open mask M as visible in FIG. 2, to make an impression of said resin. Then, the resin 57 is developed, that is to say that all the portions of the resin 57 which have not been exposed to the radiation R are removed. The resin thus photostructured 71, 73 and 75 makes it possible to produce, according to the particular predetermined shape, the metal layer.

In the example of FIG. 3, the photostructured resin comprises a lower ring 71, an upper ring 73 and a cylinder 75. In the example of FIG. 3, the lower ring 71 is of a shape corresponding to the cavity 37. The upper ring 73 covers the lower ring 71 and, partially, the upper layer 5 of the substrate 3. Finally, the cylinder 75 has a height substantially equivalent to the thickness of the stack of rings 71 and 73 and is mounted centered in the cavity 45. In the example illustrated in FIGS. 1 to 12, the inner diameter of the upper ring 73 has a toothing 59.

Preferably in a sixth step 29 is deposited on the upper face of the substrate 3 a conductive layer 61 as shown in FIG. 4. This step can be carried out for example by a conventional sputter vacuum metallization method. Preferentially, the layer 61 comprises gold, that is to say pure gold or one of its alloys. The thickness of the layer 61 may be between 10 and 100 nm.

In a seventh step 23, the departure of a metal layer on the upper face of the substrate 3 is effected by electroplating, that is to say that a metal layer 63 is grown in order to form at least a metal part 41 of the micromechanical part 51. In the example illustrated in FIG. 5, the layer 63 begins substantially on the upper face of the lower layer 7 laid bare by the cavity 45.

The presence of the cylinder 75 of photostructured resin forces the growth of the metal layer 63 to be formed by successive annular layers between the cylinder 75 and the intermediate layer 9 and then between the cylinder 75 and the upper layer 5 of the substrate 3. This first electroplating phase makes it possible to form a first metal portion 41 in at least a portion of the cavity 45.

It is therefore understood in this first phase of step 23 that the micromechanical part 51 is now formed on a layer which comprises a portion 53 of silicon and silicon oxide including at least a portion of one of the cavities 45 has a metal part 41.

In the example illustrated in FIG. 5, the electrodeposition is continued which forms layers no longer in the cavity 45 but above and also on a part of the upper layer 5 of the substrate 3. The successive layers are then formed exclusively between the upper ring 73 and the cylinder 75 of photostructured resin. It is therefore understood that the layer 39 formed in the second phase is substantially annular in shape, the outer diameter of which has a toothing opposite to that 59 of the upper ring 73 of photostructured resin. At the end of step 23, it may happen that a layer 63 of metal is obtained on the entire upper face of the substrate 3 as can be seen in FIG. 5.

Preferably, the layer 63, that is to say in particular the metal parts 39 and 41 comprises nickel, that is to say pure nickel or one of its alloys. Preferably, the potential difference of the substrate 3 necessary for the electrocoating step 23 is made by contact on its lower and / or upper side.

In an eighth step 25, a machining of the upper face of the substrate 3 is performed, for example by honing, in order to level the height of the metal portion 39, obtained during said second phase of step 23, relative to to the thickness of the upper ring 73 and the cylinder 75 of the photostructured resin as shown in FIG. 6. This in particular makes it possible to correctly delimit the second metal part 39 comprising the reverse toothing (hereinafter referenced 59).

It is therefore understood in this step 25 that the micromechanical part 51 is now formed on two layers. The first layer comprises a portion 53 of silicon and silicon oxide at least a portion of one of the cavities 45 has a portion 41 metal. The second layer formed above the first is formed by a second metal portion 39.

In the ninth and tenth steps 27 and 31, as illustrated by the double lines in FIG. 10, a second portion 65 of silicon is formed in the lower layer 7 of the substrate 3. In step 27, a machining is performed on the underside of the substrate 3 in order to reduce the thickness to the value of the lower layer 7 final desired. In step 31, cavities 47, 49 are etched, for example by a method of the DRIE type, in the lower layer 7 made of silicon. These two cavities 47 and 49, in the same way as for the steps 13 and 15, make it possible to form the pattern defining the contour of the second silicon part 65 of the micromechanical part 51.

In the example illustrated in FIG. 7, the cavity 49 is present on each side of the cavity 47 because it is substantially annular and surrounds the cavity 47. Preferably, the proximal wall of the cavity 49 is selectively etched to form a toothing 67 on the peripheral edge of the second Part 65. The cavity 47 is substantially cylindrical with disc section and coaxial with the annular cavity 49.

Steps 27 and 31 do not have a preferred consecutivity, so that one can be initiated before the other and vice versa. Preferably, the machining step 27 may consist of a chemical-mechanical polishing such as a chemical abrasion break-in.

It is therefore understood that after these steps 27 and 31, the micromechanical part 51 is now formed on three layers. The first layer comprises a portion 53 of silicon and silicon oxide at least a portion of one of the cavities 45 has a portion 41 metal. The second layer above the first is formed by a second metal portion 39. The third layer below the first is formed by a second portion 65 of silicon.

The method 1 according to the invention then comprises, as illustrated by the triple lines in FIG. 10, the implementation of a new process 19 of the LIGA type comprising a succession of steps (17, 21 and 23) making it possible to electrodeposit in a particular form a metal on the underside of the substrate 3 to using a photostructured resin.

In an eleventh step 17 is deposited on the underside of the substrate 3 a layer of photoresist, for example using a mold casting type process. In a twelfth step 21, a photolithography is made to carry out the pattern of the growth of the future metal electrodeposition.

Preferably in a thirteenth step 29 is deposited on the underside of the substrate 3 a bonding layer. This step can be carried out, for example, by vacuum deposition, as mentioned above, of a layer of pure gold or one of its alloys.

In a fourteenth step 23, a metal layer is made by electroplating on the underside of the substrate 3 in order to form at least one additional metal portion 41 of the micromechanical part 51 in at least a portion of the cavity 47. .

It is therefore understood at this stage that the micromechanical part 51 is always formed on three layers. The first layer comprises a portion 53 of silicon and silicon oxide at least a portion of one of the cavities 45 has a portion 41 metal. The second layer above the first is formed by a second metal portion 39. The third layer below the first is formed by a second portion 65 of silicon, at least a portion of one of the cavities 47 has an additional portion 41 metal.

The electrodeposition step 23 may be continued to form layers no longer in the cavity 47 but below and possibly on a portion of the lower layer 7 of the substrate 3. The successive layers are then formed. exclusively between the resin, photostructured in step 21, into a second additional metal part 39.

Preferably, the electrodeposited metal layer, that is to say in particular the additional metal parts 39 and 41 comprises nickel, that is to say pure nickel or one of its alloys.

In a fifteenth step 25, a machining of the underside of the substrate 3 is performed, for example by lapping, in order to properly delimit the second additional metal portion 39. Similarly to the second part 39, the second additional metal part 39 may also comprise a toothing 59.

It is therefore understood at this stage that the micromechanical part 51 is now formed on four layers. The first layer comprises a portion 53 of silicon and silicon oxide at least a portion of one of the cavities 45 has a portion 41 metal. The second layer above the first is formed by a second metal portion 39. The third layer below the first is formed by a second portion 65 of silicon, at least a portion of one of the cavities 47 has an additional portion 41 metal. The fourth layer below the third is formed by a second additional metal portion 39.

Of course, the advantage of such a method is also to allow, advantageously, the production of several micromechanical parts 51 on the same substrate 3. In addition, with the aid of the above explanation and single, double and triple lines of fig. 10, it should be understood that the method 1 may not be completely realized, that is to say that according to the complexity of the micromechanical part 51 to be manufactured, its construction can be completed, for example, after step 25 , 31 or 25. Nevertheless, for each variant of construction, the method 1 comprises a last step 33 of freeing the micromechanical part 51 from the substrate 3. As examples, it is explained below several embodiments of the method 1 and / or the micromechanical part 51.

In a first embodiment, the release step 33 of the method 1 is performed after the step 25 of the construction of the metal portion 41 in the silicon portion 53 as visualized by the simple lines in FIG. 10. The release step 33 then consists in eliminating the lower layer 7 or the lower 7 and intermediate 9 layers. The micromechanical part 51 thus manufactured is free with respect to the rest of the substrate 3. It comprises, as visible in FIG. fig. 12, thus, on a single layer comprising a portion 53 of silicon or silicon and silicon oxide at least a portion of one of the cavities 45 has a portion 41 metal.

In a second embodiment illustrated in FIG. 8, it can be seen that, for example, the release step 33 of the method 1 is carried out after the step 31 of the construction of the second silicon part 65 as visualized by the double lines in FIG. 10. The release step 33 then consists in eliminating the parts 71, 73 and 75 of photostructured resin for example by means of a chemical and / or mechanical etching (which may be a method known by the English term "stripping") . The micromechanical part 51 thus manufactured is free with respect to the rest of the substrate 3. It thus comprises, on three stacked layers, a second metal part 39, a part 53 made of silicon and silicon oxide, of which at least a portion of a cavities 45 comprises a metal portion 41 and a second portion 65 made of silicon.

The micromechanical part 51 obtained according to said second embodiment of method 1 explained above and in relation with FIGS. 1 to 8 and 10 substantially comprises a consecutive stack of three parts of the wheel type respectively 39, 53 and 65 having a toothing 59, 55 and 67. This part 51 is preferably adapted to form an escape wheel for cooperating with a pallet anchor. coaxial exhaust. The teeth 55 and 67 in silicon are then advantageously intended to form the impulse teeth intended to cooperate with the pallets of said anchor. The toothing 59 metal then serves as an escape pinion intended to regulate the movement to which belongs the micromechanical part 51.

In a third embodiment illustrated in FIG. 9, it can be seen, for example, that the release step 33 of the method 1 is carried out after the step 25 of constructing the second additional metal part 39 as visualized by the triple lines in FIG. 10. The release step 33 then consists in removing not only the parts 71, 73 and 75 of photostructured resin on the upper part of the substrate 3 but also those present on the lower layer of said substrate. The micromechanical part 51 thus manufactured is free from the rest of the substrate 3.

The micromechanical part 51 thus comprises, as shown in FIG. 11, on four stacked layers, a second metal portion 39, a silicon and silicon oxide portion 53 of which at least a portion of one of the cavities 45 has a metal portion 41, a second portion 65 made of silicon, of which at least one portion of one of the cavities 47 has an additional portion 41 metal and a second additional portion 39 metal.

The micromechanical part 51 obtained according to said third embodiment of method 1 explained above and in relation with FIGS. 1 to 7 and 9 to 11comporte substantially a consecutive stack of four layers of the wheel type respectively 39, 53, 65 and 39 having a toothing 59, 55, 67 and 59.

In all these embodiments, the micromechanical parts 51, 51, 51 are advantageously driven not directly on a part 53 and 65 of silicon but on the metal parts 39, 39, 41 and 41 . Preferably so that, in particular, the metal portion 41 sufficiently insulates the silicon portion 53, the thickness is greater than 6 microns. Indeed, beyond this thickness and ideally from 10 micrometers, a metal such as nickel is able to elastically or plastically absorb the forces without restoring them to silicon.

It should be understood from reading the explanation above that the micromechanical parts 51, 51, 51 of the figures are only exemplary embodiments which shows that the method 1 allows for a stack up to four layers (two with metal and two with silicon and metal) without excessive complications. The configuration of the first embodiment could thus constitute the simplest of the micromechanical parts and, that of the third embodiment, a high complication.

In a variant shown in short broken lines in FIG. 10, step 29, carried out between steps 21 and 23, of depositing the attachment layer 61 can be moved between steps 15 and 17, that is to say between the etching of the intermediate layer 9 and the deposition of the photoresist layer 57. Preferentially, in this first variant, it will be chosen to boost the two silicon layers 5 and 7.

Of course, the present invention is not limited to the illustrated example but is susceptible of various variations and modifications that will occur to those skilled in the art. In particular, other metallic layers 63 may be envisaged, for example gold, aluminum, chromium or one of their alloys. Similarly, other bonding layers 61 may be envisaged if they are conductive and that they adhere perfectly to the metal chosen for the layer 63 of galvanic growth. However, it should be noted that the deposition step 29 of the layer 61 is not essential to the good progress of the galvanic growth if the two silicon layers 5 and 7 are doped.

Similarly other reasons that the teeth 55, 59, 59 and 67 can be etched as hooks or pawls. It should also be noted that the layer 63 can be made against said etched patterns such as the teeth 55, 59, 59 and 67 for example.

Similarly, the photolithography can, of course, form a negative or positive structure depending on the photoresist used or the intended application. The deposition of the resin layer 57 can also be envisaged to be carried out by a process known as "spray coating".

Finally, the metal layer 63 can be made both on an inner wall portion of a cavity 45 and on the peripheral wall of at least one of the silicon parts 53 and 65. The layer 63 can also be structured so that it is connected to said silicon wall by means of material bridges.

Claims (33)

A method of manufacturing (1) a silicon-metal composite micromechanical part (51, 51, 51) comprising the steps of: a) fabricating (11) a substrate (3) having an upper layer (5) and a lower layer (7) of silicon between which an intermediate layer (9) of silicon oxide extends; b) selectively (13) etching at least one cavity (37, 45, 45) in the top layer (5) to define the pattern of a silicon part (53, 53) of said part; c) continuing the etching (15) of said at least one cavity (37, 45, 45) in the intermediate layer (9); characterized in that it further comprises the following steps: d) growing (17, 21, 23) a metal layer (63) at least from a portion of said at least one cavity (37, 45, 45) formed by a conductive upper face of the lower layer (7) to form a metal portion (41, 41, 41) having a thickness greater than 6 microns for isolating the silicon portion (53, 53) of destructive forces in the thickness of said room; e) releasing (33) the silicon-metal composite micromechanical part (51, 51, 51) from the substrate (3). 2. Method (1) according to claim 1, characterized in that step d) comprises the following steps: - covering (17) photoresist (57) the top of the substrate (3); Selectively (21) photolithographing the photosensitive resin (57) in order to photostructurize it (71, 73, 75) according to the predetermined pattern of the metal part (39, 41); Depositing (23) the metal layer (63) by electrodeposition from the conductive upper face of the lower layer (7) which is in line with the said at least one cavity (37, 45, 45) by growing, from the bottom, the metal layer (63) between respectively the photostructured resin (75) and the intermediate layer (9) or upper (5) for forming the metal part (41, 41, 41) according to said pattern; and in that step e) is performed by removing (33) the photostructured resin (71, 73, 75). 3. Method (1) according to claim 2, characterized in that said conductive upper face of the lower layer (7) which is in line with said at least one cavity (37, 45, 45) is made conductive doping the lower layer (7) and / or depositing (29) a conductive layer (61). 4. Method (1) according to claim 2 or 3, characterized in that the photostructured resin (71, 73, 75) during the photolithography step (21) projects (73, 75) from the upper layer (5). ) of the substrate (3) in order to be able to continue the growth of said metal layer (63) by electroplating (23) at least between said projections of the photostructured resin (73, 75) in order to form a second metal part (39) the micromechanical part (51, 51) above the silicon part (53). 5. Method (1) according to one of the preceding claims, characterized in that it comprises, after step d), a step (25) of machining the upper face of the substrate (3) coated to level said metal layer (63) at the same height as the upper end of said photostructured resin (73, 75). 6. Method (1) according to one of the preceding claims, characterized in that the metal layer (63) comprises nickel. 7. Method (1) according to one of the preceding claims, characterized in that it comprises, before the release step (33), machining steps (27) and etching (31) of at least a cavity (47, 49) in the lower layer (7) of the substrate (3) to form a second silicon part (65) of the micromechanical part (51, 51) in a shape and a determined thickness. 8. Method (1) according to claim 7, characterized in that it comprises, between the steps (27, 31) of machining and etching of the lower layer (7) of the substrate (3) and the step of release (33), a step (17, 21, 23) of growing a second metal layer by electroplating in at least a portion of said at least one cavity (47) of the lower layer (7) in order to forming at least one additional metal part (41) in the thickness of the lower layer (7). 9. Process (1) according to claim 8, characterized in that the growth step comprises the following steps: - covering (17) of photoresist the underside of the substrate (3); Selectively (21) photolithography the photosensitive resin in order to photostructure it according to the predetermined pattern of the additional metal part (41); Depositing (23) the second metal layer by electrodeposition from the bottom of said at least one cavity of the lower layer (47) by growing therefrom, from the bottom, the second metal layer making it possible to form the metal part ( 41) according to said pattern. 10. Process (1) according to claim 9, characterized in that the photostructured resin during the photolithography step (21) projects from the lower layer (7) of the substrate (3) in order to be able to continue the growth of the second electrocoated metal layer (23) for the purpose of forming a second additional metal portion (39) of the micromechanical part (51) below the second silicon portion (65). 11. Method (1) according to one of claims 9 or 10, characterized in that it comprises, before the step (33) release, a step (25) for machining the underside of the substrate ( 3) coated to level the additional metal portion (39) at the same height as the lower end of said photostructured resin. 12. Method (1) according to one of claims 8 to 11, characterized in that the second electrodeposited metal layer (39, 41) comprises nickel. 13. Method (1) according to one of the preceding claims, characterized in that several micromechanical parts (51, 51, 51) are manufactured on the same substrate (3). 14. A silicon-metal composite micromechanical part (51, 51, 51) comprising a part (53, 53) formed in a silicon layer (5) characterized in that said silicon part comprises, at least on a portion of its thickness, a portion (39, 41, 41) metal of a thickness greater than 6 microns for isolating the portion (53, 53) silicon destructive efforts. 15. Micromechanical part according to claim 14, characterized in that the metal part forms a jacket which covers the peripheral wall of said silicon part. 16. Micromechanical part according to claim 15, characterized in that said jacket is connected to said peripheral wall by material bridges. 17. micromechanical part according to claim 15 or 16, characterized in that it comprises a second metal portion projecting from said silicon part. 18. Micromechanical part according to claim 14, characterized in that the metal part forms a jacket (41, 41) in a cavity (45, 45) made in the silicon part (53, 53). to receive by driving a pivot axis. 19. micromechanical part according to claim 18, characterized in that said jacket is connected to the wall of said cavity by material bridges. 20. micromechanical part according to claim 18 or 19, characterized in that it comprises a second portion (39) protruding from the metallic portion (53) of silicon. 21. micromechanical part according to claim 20, characterized in that the second portion (39) comprises metal toothing (59) to form a wheel or a pinion. 22. micromechanical part according to one of claims 14 to 21, characterized in that each portion (63, 39, 41, 41) metal comprises nickel. 23. Micromechanical part according to one of claims 14 to 22, characterized in that the portion (53) of silicon comprises a toothing (55) to form a wheel or a pinion. 24. micromechanical part according to one of claims 14 to 23, characterized in that it comprises a second portion (65) formed of silicon from a second layer (7). 25. micromechanical part according to claim 24, characterized in that the second portion (65) of silicon comprises at least a portion of its thickness an additional portion (41) for isolating the second part (65) silicon destructive efforts. 26. Micromechanical part according to claim 25, characterized in that the additional metal part forms a jacket (41) in a cavity (47) formed in the second portion (65) of silicon to receive by driving a pivot axis . 27. micromechanical part according to claim 26, characterized in that said jacket is connected to the wall of said cavity by material bridges. 28. micromechanical part according to one of claims 25 to 27, characterized in that it comprises a second additional portion (39) protruding from the metal part of the second (65) silicon. 29. micromechanical part according to claim 28, characterized in that the second additional portion (39) has a metal gear (59) to form a wheel or a pinion. 30. micromechanical part according to one of claims 25 to 29, characterized in that each metal portion (39, 41) comprises nickel. 31. micromechanical part according to one of claims 25 to 30, characterized in that the second portion (65) of silicon is mounted on the portion (53) of silicon with an intermediate layer (9) in silicon oxide. 32. micromechanical part according to one of claims 25 to 31, characterized in that the second portion (65) of silicon comprises a toothing (67) to form a wheel or a pinion. 33. Timepiece characterized in that it comprises at least one micromechanical part (51, 51, 51) according to one of claims 14 to 32.