Abstract:
Micromechanical component and a method for its production having vertically arranged layers made of metallic materials, with the layers adhering firmly to one another at least in part. The layers of the micromechanical component are attached to each other via intermediate layers, with the intermediate layers being at least one sputtered layer which can be applied in the form of a metallic start plating to the underlying layer, which includes metallic and nonmetallic areas, and to which an upper metallic electroplated layer can be applied. Upon their completion, the layers yield the micromechanical component with layers that adhere to one another or layers which can be partially detached from one another.

Description:
BACKGROUND INFORMATION 
     1. Field of the Invention 
     The present invention relates to a micromechanical component, which is composed of multiple layers, for example electrically conductive and non-conductive layers or areas, or layers or areas made of metallic and non-metallic materials, and a method for its production. 
     2. Background Information 
     In a component used as a microvalve and described in German Patent Application No. 39 19 876, individual layers are processed by micromechanical production methods in the construction of the microvalve. For example, the surface of a silicon wafer is patterned by photolithography and predetermined areas partially removed in a subsequent etching step, thus forming the mechanical elements by processing these layers in a three-dimensional pattern. 
     Conventional production methods include UV gravure lithography for patterning the non-conductive areas and multilayer electroplating for producing metallic, conductive areas. In this case, a conductive start layer for later electrodeposition with the application of external current in the proper areas is also needed on non-conductive carrier layers. 
     Conductive metal layers applied as carrier layers to the entire surface of non-conductive substrates are known as metallic start platings. These start layers can be applied by resist-coating (spraying, dipping, spinning, etc.) or with the aid of various wet-chemical methods or PVD (physical vapor deposition) methods (vaporization, sputtering, etc.). They either have an intrinsic electrical conductivity that is sufficient for electroplating with the application of external current or are used as the nucleation layer for deposition of a metal layer without the application of external current, which, in turn, serves as the start layer for subsequent multilayer electroplating with the application of external current. 
     Wet-chemical methods (DMS-E methods) for patterning surfaces are also known from p.c. board technology discribed in European Patent Application No. 0 206 133), for example, in order to make the holes drilled into the p.c. board conductive. In this case, a start layer is patterned or applied selectively to the non-conductive areas of the p.c. board surface, thus making the entire surface electrically conductive. However, these processing methods are incompatible with the processes of UV gravure lithography and multilayer electroplating because they lack the necessary precision. 
     Methods which allow two metal layers on an intermediate layer to be separated are also known. To do this, the intermediate layer is selectively removed from the remaining materials in the form of a sacrificial layer by etching or stripping. This method leaves gaps measuring several μm thick between the layers to be separated, which is disadvantageous especially when tight-fitting surfaces need to be produced which will also be used as sealing surfaces. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a method for producing a micromechanical component according to the present invention has the advantage that, in carrying out the multilayer electroplating step, metallic start platings are applied which are compatible with the other processes and materials used in UV gravure lithography and multilayer electroplating. The metallic start plating according to the present invention makes it possible to deposit the new electroplated layer so that it adheres well to the layer beneath it, thus providing three-dimensionally patterned components in a layered structure. 
     The method according to the present invention for producing the micromechanical components has a particular advantage over previously known processes, especially with regard to the metallic start plating of a substrate that has electrically conductive and non-conductive areas, for the following reasons: 
     1: It is possible to use sputtering processes at substrate temperatures below 100° C., or wet-chemical processes in a pH range below pH 8.5 (very slightly alkaline or acidic values) which are compatible with the materials and production processes used in UW gravure lithography. The resists in the non-conductive areas thus continue to adhere to the substrate during the production steps and can be removed as needed at the end of the process chain using the Conventional. 
     2: The metallic surfaces of the conductive areas are chemically passivated by the individual process steps only to the extent that, prior to the application of each new plating, they can be reactivated as needed using standard methods, so that they can accept additional metal layers. This is the only way to ensure that the metallic electroplated layers deposited upon one another will adhere firmly to each other. 
     3. The sputtered layer is patterned by etching the lower electroplated layer. This ensures that the nucleation or start layer covers the non-conductive areas very precisely, leaving the metallic areas of the substrate unchanged. The adhesion between the electroplated layers can therefore be as strong as the adhesion between two unpatterned electroplated layers deposited upon one another. 
     According to another embodiment, the metallic start plating is designed so that one poorly adhering layer is provided in the form of a start layer in certain areas of the substrate. In these areas, the upper electroplated layer can be lifted away from the lower one, and moveable components can be created with as narrow a clearance as desired between their contact surfaces. Examples include sealing elements for fluid applications and normally closed switching elements. 
     The production method according to the present invention makes it possible to further develop the manufacturing methods using UV gravure lithography and multilayer electroplating in order to produce components with three-dimensional patterns and recesses. This is achieved with the use of the electrically conductive intermediate layers, which allow metals to be deposited electrolytically, i.e., with the application of external current, to surfaces that have metallic patterns and electrically insulating plastic. The metallic areas in the surface of the layers are generally composed of a lower electroplated layer, and the insulating areas are composed of a photopatterned resist (such as polyimide, AZ resist (photoresist) or solid resists). 
     Applications of the component according to the present invention are three-dimensional microcomponents made of metal with recesses, such as turbulent flow nozzles for fuel-air mixing in spark-ignition engines as well as microsensors or components which have additional movable structures such as microvalves, microrelays, microswitches, or micromotors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a top view of a substrate as a carrier layer, having a first layer with conductive and non-conductive areas. 
     FIG. 2 shows a cross-section of partial regions of the substrate illustrated in FIG.  1 . 
     FIG.  3   a  shows cross-sections of multiple layers on the substrate during a first step according to the first embodiment of the present invention. 
     FIG.  3   b  shows cross-sections of the multiple layers on the substrate during a second step according to the first embodiment. 
     FIG.  3   c  shows cross-sections of the multiple layers on the substrate during a third step according to the first embodiment. 
     FIG.  3   d  shows cross-sections of the multiple layers on the substrate during a fourth step according to the first embodiment. 
     FIG.  3   e  shows cross-sections of the multiple layers on the substrate during a fifth step according to the first embodiment. 
     FIG.  3   f  shows cross-sections of the multiple layers on the substrate during a sixth step according to the first embodiment. 
     FIG.  4   a  shows cross-sections of multiple layers on the substrate during a first step according to a second embodiment of the present invention. 
     FIG.  4   b  shows cross-sections of the multiple layers on the substrate during a second step according to the second embodiment. 
     FIG.  4   c  shows cross-sections of the multiple layers on the substrate during a third step according to the second embodiment. 
     FIG.  4   d  shows cross-sections of the multiple layers on the substrate during a fourth step according to the second embodiment. 
     FIG.  4   e  shows cross-sections of the multiple layers on the substrate during a fifth step according to the second embodiment. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows the basis for producing a micromechanical component, e.g., a substrate  1  as the carrier layer for additional layers to be applied. The substrate can be metal, silicon, ceramic, or glass; in the embodiment described below, it is made of glass. The usual thicknesses of this substrate range from 500 μm to 2 mm, and metallic start layers with good adhesion characteristics must be applied in order to use, in particular, electroplating processes with the application of external current. 
     In the beginning, substrate  1  is provided in a Conventional manner with conductive areas  2  and non-conductive areas  3 . For this purpose, the substrate is coated with a resist (such as a polyimide, AZ resist or solid resist) by spin-coating, spraying or lamination. The resist is exposed and developed with the desired pattern. Metal is then electrodeposited in the open regions in the resist. Conductive areas  2  in the lower electroplated layer are made of a metallic material (such as copper or nickel) and non-conductive areas  3  are made of the resist. FIG. 2 shows a cross-section of areas  2  and  3 . The subsequent production steps are explained on the basis of the sectional representations shown in FIGS.  3   a - 3   f  In a first production step FIG.  3   a  a layer  4  made of silver, palladium or platinum is sputtered onto the entire surface of substrate  1 , including areas  2  and  3 ; in the embodiment described below this layer is made of palladium. 
     The sputtering process is essentially known: the target is bombarded with high-energy ions from an ionized gas (such as argon). This ion bombardment causes atoms and/or molecules to be ejected from the target and accelerated onto substrate  1  at {fraction (1/100)} the kinetic energy of the ions. This produces a thin, highly uniform new surface layer on substrate  1 . Layer  4  is just a few nanometers thick if this sputtered layer  4  is to act as a nucleation layer for a subsequent metallic start layer to be applied without the application of external current (i.e., by deposition), and 5 nm to 100 nm thick if sputtered layer  4  itself is to serve as the start layer for subsequent electroplating processes with the application of external current. 
     In a second production step, as shown in FIG.  3   b , the lower metal layer is etched all the way through relatively porous sputtered layer  4  in conductive areas  2 . This step is advantageously carried out with a standard process (electrolytic activation) that is essentially known in multilayer electroplating, in which the previously produced arrangement is treated with a non-passivating electrolyte (such as an Ni strike bath containing Cl ions), with conductive areas  2  subsequently being eroded anodically several micrometers beneath sputtered layer  4 . 
     Sputtered layer  4  is not eroded in this production step, but loses its adhesion to the lower metal layer in areas  2  and can be stripped and removed from this metal layer in a flushing step. Non-conductive areas  3  are thus coated entirely without requiring photolithographic patterning with new lateral tolerances shown in FIG.  3   c.    
     To apply a further patterned layer, another photopatternable resist is applied, exposed, and developed, so that non-conductive areas  5  of the resist are retained shown in FIG.  3   d.    
     In the next production step, also shown in FIG.  3   d , the exposed areas of sputtered layer  4  and the exposed areas  3  of lower electroplated layer are chemically reinforced or plated with a metal (such as nickel) without the application of external current, i.e., in a redox reaction (visible only in the left-hand portion of FIG.  3   d ). But first, areas  2  of the lower electroplated layer is reactivated by anodic erosion and sputtered layer  4  also activated in a reducing bath (e.g., with sodium borohydride). Metal can now be deposited without the application of external current onto the surfaces that have been activated in this manner, thereby reinforcing sputtered layer  4 . The fact that chemical deposition is also carried out on the lower electroplated layer at the same time is not problematic in this case if a very similar material is used for both the electroplated layer and the chemically deposited layer. 
     With a method commonly used in multilayer electroplating, an upper metallic electroplated layer  7  can be applied with the application of external current to chemically deposited layer  6 , resulting in the arrangement shown in FIG.  3   e.    
     Metallic electroplated layers  2  and  7  now adhere to each other via chemically deposited layer  6  and, after lifting them away from substrate  1  and removing resist layers  3  and  5 , they can form a micromechanical component with complex patterns, including recesses, as shown in FIG.  3   f.    
     Alternatively, electrodeposited layer  7  can be deposited directly (shown at the right side of FIG.  3   d , and FIG.  3   e ) following the activation step in the case of the thicker variant of sputtered layer  4  (5 nm to 100 nm). 
     When using the production method described on the basis of the embodiment, note that the sub-processes described above are wet-on-wet procedures, for the metallic surfaces in areas  2  and sputtered layer  4  (or layer  6 ) should not come into contact with free oxygen between the individual production steps. This would reoxidize and thus passivate them, making them unsuitable for accepting additional metal layers. 
     The material of metal layer  6  deposited without the lS application of external current should have the closest possible chemical resemblance to the electrolytically deposited metal of layers  2  and  7  to ensure the desired chemical homogeneity and better adhesion between layers  2 ,  6 , and  7 . If a thick sputtered layer  4  is used, however, the metallic reinforcement applied without the application of external current (described above) is not necessary. 
     The photoresist in areas  5  for patterning upper electroplated layer  7  is preferably applied before activating the lower metal layer in areas  2  and sputtered layer  4 . The advantage of this is that the activation step has to be carried out only once. The disadvantage is that the resist patterns of the photoresist may not be sufficiently etched through in areas  5 . 
     On the basis of an embodiment illustrated in FIGS.  4   a - 4   e  production method using a metallic start plating is described for electroplating processes which allow individual areas of an upper metallic electroplated layer to be stripped from the lower metallic electroplated layer, while maintaining firm adhesion to the lower electroplated layer in all other areas. 
     As in the embodiment shown in FIG.  3   a , substrate  1  again has metallic, electrically, conductive areas  2  as well as electrically non-conductive areas  3 . Metallic areas  2  can be formed, for example, by the lower electroplated layer and the non-conductive areas by a resist that is patterned by UV gravure lithography in the known manner. 
     In a first production step, the entire surface of substrate  1  is sputtered, as described above, but in this case using titanium. This sputtered layer  10  is 200 nm to 400 nm thick. The production step must be carried out so that titanium sputtered layer  10  contains as little oxygen as possible, thus also forming as little stable oxide as possible, for this is the only way to pattern it in the next process step by etching shown in FIG.  4   b . It is therefore necessary in order to produce a good vacuum around substrate  1  prior to sputtering and to clean substrate  1  by etching (also using the sputtering technique). This should give lower electroplated layer  2  a smooth surface with little oxygen accumulating on the surface. 
     As shown in FIG.  4   b , titanium sputtered layer  10  is masked with a photopatternable resist and etched in a solution containing hydrogen fluoride (hydrofluoric acid). A resist  11  that can be processed in media which do not attack the plastic or resist  3  on substrate  1  is used for masking. After this etching mask is removed (resist areas  11 ), the arrangement shown in FIG.  3   c  appears, and the remaining multilayer electroplating steps can be carried out. 
     The subsequent deposition step with the application of external current and production of upper electroplated layer  12  shown in FIG.  4   d  are carried out after electrolytic activation of lower electroplated layer  2 . Sputtered layer  10  made of titanium is passivated and is not affected by these processes. The electrolyte and counterelectrode are thus not contaminated by titanium. 
     In further process steps, multiple electroplated layers can be formed between patterned resist areas. The resist is removed at the end of this process chain. Wherever two metallic electroplated layers  2 ,  12  are separated by a titanium sputtered layer  10 , the two layers  2  and  12  can be separated from each other by applying a mechanical force or a differential pressure. 
     In areas  2  of substrate  1 , which are not covered by titanium sputtered layer  10 , the properties of UV gravure lithography and multilayer electroplating are retained, as is the adhesion between electroplated layers  2  and  12 . 
     In order to detach the two electroplated layers  2  and  12  in the areas of sputtered layer  10 , it is not necessary to remove a sacrificial layer via long, lateral etching or stripping between electroplated layers  2  and  12  to be separated. Nor is any gap produced between the two mechanically separated electroplated layers  2  and  12 . The surface morphology of lower electroplated layer  2  is mapped onto upper electroplated layer  12 , making it possible to produce micromechanical components with moving parts shown in FIG.  4   e  which can be positioned close together, forming a seal.