CH701260A2 - Method for metal microstructure and microstructure obtained from the method. - Google Patents

Abstract

The process comprises supplying a conductive/insulative substrate (1) covered with a conductive priming layer, applying a photosensitive resin layer on conductive part of the substrate surface, leveling the surface of the resin layer to a desired thickness and/or surface condition using a cutting tool, irradiating the resin layer through a mask defining a desired design of the microstructure, dissolving the non-polymerized zones of the resin layer for making a place in the conductive surface of the substrate, and electro-galvanically depositing a metal layer from the conductive layer. The process comprises supplying a conductive/insulative substrate (1) covered with a conductive priming layer, applying a photosensitive resin layer on conductive part of the substrate surface, leveling the surface of the resin layer to a desired thickness and/or surface condition using a cutting tool, irradiating the resin layer through a mask defining a desired design of the microstructure, dissolving the non-polymerized zones of the resin layer for making a place in the conductive surface of the substrate, electro-galvanically depositing a metal layer from the conductive layer to form a block reaching the upper surface of the photosensitive resin layer, smoothing the resin and metal block to bring the resin blocks and metal blocks at the same level, separating the resin layer and electro-deposited block from the substrate, and eliminating the photosensitive resin layer of the structure for removing the microstructures. The cutting tool comprises a portion for cutting hard metal, ceramic, metal carbide, metal nitride or diamond. The metal is deposited beyond the height of the resin layer to expand on flattened surface of the resin so as to connect the pieces together by bridges. The step of connecting the metal parts comprises mounting a work plate on the substrate at a side opposite to the reference side of the joints, machining the exposed sides of the substrate, and removing the end pieces of the work plate. The step of separating the resin blocks and metal blocks comprises applying a transfer tape on the surface opposite to reference side of the pieces, fixing the work plate on the reference side opposite to the transfer tape, machining the exposed surfaces for obtaining desired thickness and/or surface condition, and removing the end piece of the work plate. An independent claim is included for a metal microstructure.

Description

The present invention relates to a method of manufacturing a metal microstructure by LIGA type technology. In particular, the invention relates to such a process for the manufacture of such a microstructure having more precise and better controlled dimensional characteristics than the processes of the prior art. The invention also relates to such a metal part obtained by this method.

[0002] The LIGA technology (Lithography Galvanik Abformung) developed by W. Ehrfeld of the Karlsruhe Nuclear Research Center, Germany) in the 1980s has proved to be of interest for the manufacture of high precision metal microstructures.

In principle, the LIGA technique involves depositing on a conductive substrate or coated with a conductive layer, a layer of a photosensitive resin, to be carried out through a mask corresponding to the contour of the desired microstructure irradiation X by means of a synchrotron; to develop, that is to say to remove by physical or chemical means the portions of the non-irradiated photoresist layer to define a mold having the contour of the microstructure, to electro-galvanically deposit a metal typically nickel in the photosensitive resin mold and then remove the mold to release the microstructure.

The quality of the microstructures obtained is not critical, but the need to implement expensive equipment (synchrotron) makes this technique little compatible with a mass production of microstructures to have a low unit cost.

This is why on the basis of this LIGA process have been developed analogous processes but using UV photosensitive resins. Such a method is for example described in A.B. Frazier et al., Entitled "Metallic Microstructures Fabricated Using Photosensitive Polyimide Electroplating Molds", Journal of Microelectromechanical Systems, Vol. 2, N deg. 2, June 1993 for the manufacture of metal structures by electrodeposition of metal in polyimide-based photosensitive resin molds. This process comprises the following steps: creating on the substrate a sacrificial metal layer and a priming layer for a subsequent electroplating step, - apply a layer of photosensitive polyimide resin, - UV irradiating the polyimide resin layer through a mask corresponding to the contour of the desired microstructure, developing by dissolving the non-irradiated portions of the polyimide layer so as to obtain a plurality of polyimide molds, electro-galvanically depositing nickel in the open parts of the molds up to the height of the latter, and separating the metallic structures obtained from the substrate and - Eliminate the polyimide molds to release the electroformed metal parts.

The electro-formed parts or microstructures are thus obtained in bulk. Once obtained, these parts are separated and must be glued to a plate to machine and / or rectify to bring them to the desired thickness and surface condition. These steps require high handling times and involve significant risks of arranging the parts upside down on said plate especially when the electroformed parts are small, typically pieces smaller than a millimeter. These processes induce a scrap rate and therefore cost costs that are not compatible with the requirements of an industrial process.

[0007] Furthermore, the processes of the prior art require a deposit of electro-shaped material that is sufficiently large to guarantee that all the pieces reach their minimum thickness independently of variations in the thickness of the resin on the surface of the substrate. This therefore leads to a consumption of unnecessary electro-deposited material.

In fact, the thickness variations of the resin deposited to form the molds are intrinsic to the current deposition techniques, typically the spin or spray coating. It should be noted in this connection that the nonuniformity of the resin layer in which the molds are formed requires the resin to be irradiated with an adjustment taking into account the maximum and the minimum of the thickness. This has the consequence of increasing the dispersion of the geometrical dimensions in the plane of the molds.

There is therefore a need for a method to overcome these drawbacks.

The present invention aims to overcome the aforementioned drawbacks as well as others by providing a method for manufacturing parts or microstructures having thicknesses and surface conditions better controlled and more precise than parts or microstructures obtained by the methods of the prior art.

The invention also aims at such a method for reducing the cost of electroforming both from the point of view of the manufacturing time as the amount of electro material deposited.

The invention also aims to improve the uniformity of the photolithographic exposure and thus the improvement of the geometric uniformity of the parts produced on the surface of the same substrate.

The present invention also aims to provide such a method that is simple and inexpensive to implement.

For this purpose the invention relates to a method of manufacturing a plurality of parts or metal microstructures characterized in that it comprises the steps of: a) providing a conductive substrate or an insulating substrate covered with a conductive conducting layer. b) applying on the conductive part of the substrate surface a layer of photoresist, c) flattening the surface of the photoresist layer to a desired thickness and / or surface condition; d) irradiating the resin layer through a mask defining the contour of the desired microstructure; e) dissolving the unpolymerized areas of the photosensitive resin layer to show in places the conductive surface of the substrate or the substrate if the latter is conductive. f) electro-galvanically depositing at least one layer of a metal from said conductive layer to form blocks substantially reaching the upper surface of the photoresist, g) flattening the resin and the electro-formed metal to bring the resin and the electro-formed blocks to the same level and thus forming electro-formed parts or microstructures, h) separating the resin layer and the electro-formed parts from the substrate, and i) removing the photosensitive resin layer from the parts or microstructures obtained at the end of step h) to release the parts or microstructures thus formed.

This method therefore makes it possible to produce a resin layer of a determined and constant thickness over the entire surface of the substrate. This makes it possible to expose a resin layer having a uniform thickness which allows the production of molds and finished parts having uniform dimensional accuracy in the plane for parts of the same substrate. Typically, the method of the invention makes it possible to guarantee an accuracy of +/- 2 μm over the thickness of the deposited resin, whereas the methods of the prior art are limited to a precision of the order of +/- 30 μm. (spinning deposit).

Furthermore, the planarization of the resin before the electroforming step of the parts makes it possible, on the one hand, to limit the amount of metal to be deposited in order to obtain earlier bridges between the pieces, as will be explained hereinafter. after (saving time) and, secondly, to obtain a wafer that is to say a set of electro formed parts connected together for bridges of much more regular material in thickness of the upper side to ensure a more consistent bonding on the work plate for subsequent machining operations.

In the case of a multilevel LIGA process, the planarization of the resin provides a tight tolerance on the thickness of the different levels over the entire extent of the substrate, so on all parts of the substrate.

According to a characteristic of the invention, the flattening step c) is carried out using a cutting tool and preferably using a tool comprising a cutting portion of hard metal, ceramic, metal carbide, metal nitride or diamond.

The use of such a tool to perform the planarization step avoids any contamination of the resin and / or the electroformed metal with residues resulting from grinding or polishing processes. In addition, machining using a cutting tool is not sensitive to differences in the thickness of the material to be machined (resin or resin and electroformed parts or parts glued to a work plate).

According to a first advantageous variant of the invention, during step f) the metal is deposited beyond the height of the mold to extend over the flattened surface of the resin and thus connect the pieces together by metal bridges to form a slab, step g) is eliminated and after step h), the metal parts interconnected by said bridges are subjected to the following steps of: j) fixing on a work plate by their reference face opposite the bridges, k) machining their exposed faces to the desired thickness and / or surface condition while eliminating the bridges, thereby releasing said pieces from each other l) releasing said finished parts of the work plate.

According to this first embodiment, the metal bridges between the parts allow: 1. the transfer of parts on the work plate for the thicknessing 2. to guarantee a regular pressing on the working plate at the time of the fixing of the parts on this one which makes it possible to reduce the dispersion of the dimension of finite thickness. 3. to guarantee the precise and regular arrangement of the parts for a subsequent additional machining operation (electro-erosion, machining by chip removal, diamond cutting, polishing, decorations, etc.)

In other words, it achieves a metal overgrowth during the LIGA deposition to create bridges between all parts and thus be able to manipulate the wafer which maintains the very regular and precise location of the parts obtained by the LIGA process. This slab can then be secured to a work plate. The mechanical recovery of the parts can be done on a CNC machine while benefiting from the precise positioning of the parts (marks can be electro formed directly on the slab).

The method of the invention advantageously to maintain the precise and regular arrangement of the parts after removal of electroformed material bridges to achieve multilevel parts by machining, to make decorations, to make coatings (selective or complete), to achieve chamfers or counterbores, batch assembly, etc. by means of numerically controlled machines, robots, for industrial production.

According to a second variant embodiment, step g) is eliminated and after the separation step h) the electro-formed parts are no longer interconnected, these parts are subjected to the following steps of, m) applying a transfer band on the face opposite to the reference face of said parts; n) fixation on a work plate by their reference face opposite to the band, o) machining of their exposed faces to bring them to the desired thickness and / or surface state p) releasing said finished pieces of the work plate.

According to a third embodiment, wherein after the separation step h) the electro-formed parts are not interconnected by metal bridges, but by the resin. These parts are subject to the following steps: q) attachment to a work plate by their reference face, r) machining their exposed faces to the desired thickness and / or surface state, s) releasing said finished parts of the work plate.

According to an advantageous characteristic of the invention, before step k) the parts still attached to the work plate are subjected to a machining step in the thickness of the parts.

The steps k) o) r) described above can of course be performed by cutting tools.

The method of the invention finds a particularly advantageous application for the manufacture of micromechanical parts of clockwork or tooling movements. In particular the parts may be selected from the group consisting of gears, escape wheels, anchors, pivoted parts, jumper springs, spiral springs and passive parts, cams, pushers, ferrules, molds, pins, cleats, electrodes for electro-erosion.

Other features and advantages of the present invention will emerge more clearly from the following detailed description of an exemplary embodiment of a method according to the invention, this example being given for purely illustrative and non-limiting purposes only, in conjunction with the accompanying drawing in which: - figs. 1a to 1h illustrate the process steps of a first embodiment of the invention for producing a plurality of gear wheels. - figs. 2a to 2k illustrate a first embodiment of the invention. - figs. 3a to 3k illustrate a second variant embodiment of the invention. - figs. 4a to 4j illustrate a third variant embodiment of the invention

Referring to FIGS. 1a to 1h will describe a first embodiment of the invention.

The substrate 1 used in step a) of the process according to the invention is for example formed by a silicon wafer, glass or ceramic on which was deposited by evaporation, a priming layer, c ' that is to say a layer able to start an electroforming reaction. Typically the priming layer is formed of a sub-layer of chromium 2 and a gold layer 3 (FIG 1a).

Alternatively, the substrate may be made of stainless steel or another metal capable of starting an electroforming reaction. In this case, the priming layer 2, 3 is no longer necessary. In the case of a stainless steel substrate, the latter will be degreased before use.

The photosensitive resin 4 used in step b) of the process according to the invention is preferably an octofunctional epoxy resin available from Shell Chemical under the reference SU-8 and a photoinitiator chosen from the salts. triarylsulfonium such as those described in US Patent 4,058,401. This resin is capable of being polymerized under the action of UV radiation. It will be appreciated that a solvent which has been found suitable for this resin is gammabutyrolactone (GBL) (Figure 1b).

Alternatively, a Novolac-type phenolformaldehyde-based resin in the presence of a DNQ photoinitiator (DiazoNaphtoQuinone) may also be used.

The resin 4 is deposited on the substrate 1 by any suitable means typically to the spin to the desired thickness. Typically the resin thickness is between 150 microns and 1 mm. Depending on the desired thickness and the deposition technique used, the resin 4 will be deposited in one or more times. Alternatively, the resin 4 can be deposited by the spray coating technique.

The resin 4 is then heated between 80 and 95 ° C for a period depending on the thickness deposited to remove the solvent. This heating dries and hardens the resin.

In step c), the substrate is mounted on the workpiece holder of a machine tool on which the surface of the cured photoresist layer is flattened to a thickness and / or a state of desired surface (Fig. 1c). This flattening operation is performed by means of a cutting tool 5 so as to avoid any contamination of the resin by residues that could cause a flattening by a conventional abrasion tool. Note that this planarization operation is preferably carried out dry, that is to say without any lubrication to prevent any chemical pollution of the resin. Typically, the cutting tool is a tool comprising a cutting portion of hard metal, ceramic, metal carbide, metal nitride or diamond. At the end of this step, a substrate coated with a resin layer 4 is obtained, the surface of which is perfectly flat and parallel to the substrate. The resin furthermore has a surface state having a value of Ra <25 nm and a desired thickness with a tolerance of ± 2 μm.

The surface condition obtained as well as the geometric precision of the thickness of the resin are particularly interesting in the case of a multilevel process because this surface state determines the surface state of the galvanic deposit grown from this surface and the controlled thickness makes it possible to guarantee the dimensions of each level of each piece.

The next step d) illustrated in FIG. 1d consists in irradiating the flattened resin layer by means of UV radiation through a mask 6 defining the contour of the desired microstructures and thus the insolated zones 4a and non-insolated zones 4b. Typically this UV irradiation is 200 to 000 mJ.cm -2, measured at a wavelength of 365 nm depending on the thickness of the layer. If necessary, a step of annealing the layer may be necessary to complete the photopolymerization induced by the UV irradiation. This annealing step is preferably carried out at 90 ° C to 95 ° C for 15 to 30 minutes. The exposed areas (light-cured) become insensitive to a large majority of solvents. On the other hand, non-insolated zones may subsequently be dissolved by a solvent.

The following step e) illustrated in FIG. 1econsisted to develop the non-insolated zones 4b of the photosensitive resin layer in order to reveal, in places, the conductive layer 3 of the substrate 1. This operation is carried out by dissolving the non-insolated zones 4b using a solvent chosen from GBL (gammabutyrolactone) ) and PGMEA (propylene glycol methyl ethyl acetate). A plurality of insolated photosensitive resin molds 4a having the contours of the metal structures are thus produced.

The following step f) illustrated in FIG. It is possible to deposit electro-galvanically in the molds a layer of a metal from said conductive layer 3 to form a plurality of blocks 71, 72, 73 reaching and exceeding the height of the molds. By metal in this context are of course included metal alloys. Typically the metal will be selected from the group consisting of nickel, copper, gold or silver, and as an alloy gold-copper, nickel-cobalt, nickel-iron, and nickel-phosphorus, nickel tungsten.

The electroforming conditions, in particular the composition of the baths, the geometry of the system, the voltages and current densities, are chosen for each metal or alloy to be electro-deposited according to the techniques well known in the art of the art. electroforming (see for example Di Bari GA "electroforming" Electroplating Engineering Handbook 4th Edition written by LJ Durney, published by Van Nostrand Reinhold Company Inc., NY USA 1984).

In a subsequent step g) illustrated in FIG. 1g the electro-formed block is leveled with the resin layer. This step can be done by abrasion and polishing or machining by a cutting tool in order to directly obtain microstructures having a flat upper surface having in particular a surface state compatible with the requirements of the watch industry for the production of high movement. of range.

The following step h) illustrated in FIG. 1heavailable to separate the resin layer 4a and the electro-deposited block 71, 72, 73 of the substrate 1. Once this delamination operation has been carried out, the photoresist layer 4a is removed from the delaminated structure in order to release the microstructures 71, 72 , 73 thus formed. To do this, the resin is removed in a final step by plasma etching.

The microstructure thus released can be used either directly or, where appropriate, after appropriate machining.

We will now describe a first variant of the invention in connection with FIGS. 2a to 2k. In this first variant, the steps illustrated in FIGS. 2a to 2e are identical to those described and illustrated in FIGS. 1a to 1e. In this first variant, during step f) the electro-galvanic deposition in the molds is performed until a plurality of blocks 71, 72, 73 reaching and exceeding the height of the molds so as to extend over the upper surface of the photosensitive resin 4a and form metal bridges 8 to connect the different blocks 71, 72, and 73 together (FIG 2f). Step g) is eliminated. Substrate 1 is then separated from the resin assembly 4a and blocks 71, 72, 73 electroformed during a delamination step (FIG. The resin 4a is then removed to release the blocks 71, 72, 73 interconnected by the bridges 8 forming a wafer 9. Typically the removal of the resin 4a is achieved by a plasma etching (FIG 2h). The wafer 9 is then typically bonded (glue 12) to a work plate 10 by its reference face Fref. opposite to the bridges, that is to say the face that was in contact with the substrate 1 (Figure 2i). The exposed faces are machined to set the blocks 71, 72, and 73 to the desired thickness and / or surface condition while eliminating the bridges 8 and forming finished or semi-finished parts. During this step, said blocks 71, 72, and 73 are released from each other while still being held in precise position and defined in the glue 12 (FIG 2i). at the end of this step, said parts obtained can either be released from the working plate 10 and then cleaned (FIG 2j), or taken again on a machine tool to perform batch machining (FIG 2k). At this stage, the parts can be subjected to various decorative and / or functional treatments, typically physical or chemical deposits.

We will now describe a second variant of the invention in connection with FIGS. 3a to 3k. In this second variant, the steps illustrated in FIGS. 3a to 3f are identical to those described and illustrated in FIGS. 1a to 1f. In this second variant, step g) is also eliminated and after step f), substrate 1 is separated from resin assembly 4a and electroformed blocks 71, 72, and 73 during a delamination step (FIG. 3g). The resin 4a is then removed to release the blocks 71, 72, and 73. Typically the removal of the resin is carried out by a plasma etching (FIG 3h). The electroformed blocks 71, 72, and 73 are no longer interconnected. A transfer band stretched over a frame 11 is then applied to the face opposite to the reference face Fref. said blocks, that is to say the face which was in contact with the substrate 1 (FIG 3i). The blocks 71, 72, and 73 glued on the transfer band are then typically fixed by gluing to a work plate 10 by their reference face, that is to say the face which was in contact with the substrate 1 (FIG. 3j). The frame is removed leaving the transfer band. The exposed faces of the blocks are then machined to form parts 71, 72, and 73 at the desired thickness and / or surface condition while eliminating the transfer band. During this step, said pieces are released from each other of the transfer band while being held in the glue 12 (FIG 3k). at the end of this step, said parts are released from the work plate 10 and then cleaned.

We will now describe a third variant of the invention in connection with FIGS. 4a to 4d. In this third variant, the steps illustrated in FIGS. 4a to 4f are identical to those described and illustrated in FIGS. 1a to 1f. In this third variant, step g) is also eliminated. This variant applies in the case where the adhesion of the electroformed resin-block assembly is not sufficient to allow direct machining of the blocks 71, 72, and 73 on the substrate 1. In this case, the substrate 1 of the resin assembly 4a and electro-formed blocks 71, 72, and 73 during a delamination step (Fig. 4g). The electroformed resin-block assembly is then bonded to a working plate 10 by their reference face, that is to say the face which was in contact with the substrate 1 (FIG 4h). The exposed faces of the blocks 71, 72, and 73 are then machined to form the parts to the desired thickness and / or surface state. The pieces are held by the resin 4a and by the glue 12 (FIG 4i). at the end of this step, said parts are released from the working plate 1 and the resin 4a is then removed to release the parts obtained. Typically the removal of the resin is achieved by plasma etching (Fig. 4j). According to the invention, it will also be noted that before the step illustrated respectively in FIGS. 1st, 2nd, 3rd, and 4th the steps illustrated and described respectively in connection with FIGS. 1b to 1d, 2b to 2d, 3b to 3d and 4b to 4d are repeated at least once to obtain multilevel parts.

The number of levels is not limited. For watch applications the typical number of levels is 1 to 5.

In the case of the production of multilevel resin molds, it is advantageous to deposit on the resin after step 1d, 2d, 3d, 4d a conductive layer for regular growth of the electro material deposited in the course of time. Subsequent step 1f, 2f, 3f, 4f.

Claims (10)

A method of manufacturing a plurality of metal microstructures characterized in that it comprises the steps of: a) providing a conductive substrate or an insulating substrate covered with a conductive conducting layer. b) applying on the conductive part of the substrate surface a layer of photoresist, c) flattening the surface of the photoresist layer to a desired thickness and / or surface condition d) irradiating the resin layer through a mask defining the contour of the desired microstructure; e) dissolving the unpolymerized areas of the photoresist layer to expose the conductive surface of the substrate; f) electro-galvanically depositing at least one layer of a metal from said conductive layer to form a block substantially reaching the top surface of the photoresist, g) flattening the resin and the electro-formed metal to bring the resin and the electro-formed blocks to the same level and thus forming electro-formed parts or microstructure, h) separating the resin layer and the electro-deposited block from the substrate, and i) removing the photosensitive resin layer from the structure obtained at the end of step g) to release the microstructures thus formed. 2. Method according to claim 1 characterized in that the flattening step c) is performed using a cutting tool. 3. Method according to claim 2 characterized in that the cutting tool is a tool comprising a cutting portion of hard metal, ceramic, metal carbide, metal nitride or diamond. 4. Method according to one of claims 1 to 3, characterized in that during step f) the metal is deposited beyond the height of the mold to extend over the flattened surface of the resin so as to connect the parts between them by metal bridges. 5. Method according to claim 4 characterized in that after step h), the metal parts interconnected by said bridges are subjected to the following steps of: j) fixing on a work plate by their reference face opposite the bridges, k) machining their exposed faces to the desired thickness and / or surface condition while eliminating the bridges, thereby releasing said pieces from each other I) releasing said finished parts of the work plate. 6. Method according to one of claims 1 to 3 characterized in that after the separation step g) the electro-formed parts are no longer interconnected and are subject to the following steps of: m) applying a transfer band on the face opposite to the reference face of said parts; n) fixation on a work plate by their reference face opposite to the transfer band, o) machining of their exposed faces to bring them to the desired thickness and / or surface state p) releasing said finished parts of the work plate. 7. Method according to one of claims 1 to 3 characterized in that after the separation step g) the metal parts interconnected by the resin are subjected to the following steps of: q) attachment to a work plate by their reference face, r) machining their exposed faces to the desired thickness and / or surface state, s) releasing said finished parts of the work plate and the resin. 8. Method according to one of claims 5 to 7, characterized in that before step k) the parts still attached to the work plate are subjected to a machining step in the thickness of the parts. 9. The method of claim 1, characterized in that before step e) steps b) c) and d) are repeated at least once to obtain multi-level parts. 10. Metal microstructure obtained according to one of the preceding claims, characterized in that it forms a micromechanical part of a clockwork or tooling movement and being selected in particular from the set consisting of toothed wheels, wheels and exhaust, anchors, pivoted parts, jumper springs, spiral springs and passive parts, cams, pushers, molds, pins, cleats, electrodes for EDM.