Abstract:
A three-dimensional formed metallic structure with varying thickness including sloping flanks is formed on a substrate. A conductive layer is applied to the substrate initially, in the form of laterally spaced electrically isolated conductive islands. A cathodic potential is connected to at least one of the islands, leaving others unconnected, and deposition proceeds due to the cathodic potential. As metallic material is deposited and builds up, it eventually contacts adjacent islands, thereby coupling the cathodic potential to a wider area where deposition commences. Deposition is thickest at the at least one island initially coupled to the cathodic potential and thinner progressing away, forming flanks that are linearly sloped, curved or similarly formed by thickness variations the vary proceeding away from the initially coupled island or islands.

Description:
BACKGROUND OF THE INVENTION AND FIELD OF THE INVENTION 
     The technical field of the invention is the manufacturing of three-dimensionally shapable galvanic structures on substrates, having their possibilities and limitations according to prior art by structuring with a photosensitive resist and subsequent galvanic deposition. 
     PRIOR ART 
     Prior art describes the forming of galvanic structures, which are electrically conductive and find an extensive field of application in micromechanics, by coating with a photosensitive resist, by exposing and removing of certain parts of the applied resist and subsequent galvanic deposition from a galvanic fluid which is switched to a first potential, whereas the electrically conductive basis on the substrate as plating base is switched to an opposite potential. Galvanic structures obtained by said method generally have edge portions extending in vertical direction, as the incident light on the photosensitive resist always is perpendicular, so that only perpendicular resist structures can develop. Thus, only such galvanic structures may be provided, the flanks of which extend in the direction the inciding light had. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to give up resist structures predetermined by the inciding light as a pattern for galvanic structures and to provide the possibility of obtaining freely shapable galvanic structures the side surfaces (flanks) of which no longer being forced to extend in vertical or substantially vertical direction. The solutions proposed by the present invention are specified according to the invention disclosed. 
     Accordingly, structures which are shapable in vertical direction and galvanically deposited are provided as profiles on a substrate by structuring a conductive layer, which is applied before, in lateral direction. Said three-dimensionally shapable metallic structure provided by a galvanization method is also obtained if the substrate is provided with at least one conductive layer, one of said number of or the one conductive layer is structured in lateral direction by forming a number of island areas having no or no substantial conduction with respect to each other, and during galvanization, one of said island areas is provided as a core area and switched to a cathodic potential. The result obtained by said manufacturing method steps disclosed herein. 
     On the basis of the product obtained by said method, which product is a three-dimensionally shaped solid metallic structure with a more than distinct extension in vertical direction (“profile”), it may be recognized that no longer all vertical side surfaces of said structure are forced to extend in vertical or substantially vertical direction. However, this does not mean that all sides are compelled to have a beveled or curved extension, but only that at least one of the vertical flanks is a beveled or curved surface which could not be shaped by using a known manufacturing method. The “profile” according to the present invention is not a surface in the form of a laterally deposited layer. 
     Certainly, a photosensitive resist is still used, however, it is no longer the core and the basis for a galvanic deposition on the basis of exposed and etched guiding structures based on a photosensitive resist layer. According to the invention, said resist is used for shaping a three-dimensional structure in vertical direction by covering a major part of the core area and leaving only a small section free, thus permitting a cathodic potential to pass over into the galvanic bath. Starting from said potential in the galvanic fluid, a slowly growing layer is formed on said small section with cathodic potential. Said layer grows in vertical direction thereby also being forced to slightly enlarge in lateral direction. 
     As the invention provides further island areas, which are spaced in lateral direction, as second areas which are obtained from the plating base after their structuring, which plating base was at first deposited as a continuous conductive layer, an over-galvanization over isolated areas from the cathodic area to the subsequent structured area which is spaced apart therefrom and again electrically conductive but not switched to the cathodic potential. Said manner of controlling the over-galvanization in lateral direction permits to define the beveled surface dependent on the interspace and the width of said electrically not connected island areas, said beveled surface being obtained by a longer or shorter galvanization time. 
     Each respective front of said beveled surface growing in lateral direction—which is the growing profile—always grows discontinuously (stepwise) when reaching as an electrically conductive layer the subsequent conducting island. The subsequent expansion in lateral direction is much faster than when just reaching the end of said island area in lateral direction. Controlled by the stepwise lateral expansion and the substantial growth of the conducting structure thereby obtained, a solid structure of any shape may be provided on the substrate which structures so far could not be obtained by coating with resist, uncovering and usual galvanization methods. 
     In short words, the new method permits to control the lateral growth rate by determining the length and duration of the galvanization process on the one hand and—before starting the galvanization process—by applying defined geometric shapes as structures to the plating base subjected to the galvanic bath during galvanization. 
     The galvanic profile results from the ratio of the lateral growth rate with respect to the vertical growth rate. 
     The galvanic structures may be selected to comprise one of gold and nickel. The electrically conductive starting layer (plating base) may comprise the same materials. If a number of plating bases is used, they are isolated by intermediate layers, preferably SiN layers. If only one plating base is used, the substrate itself may have isolating function, not requiring an additional isolating layer to be provided on the substrate. 
     If the manufacturing method according to the invention does not use thick resist layers, no lateral frame is formed for those vertical surfaces which are not intended to be beveled. In this case, it is possible to let the beveled galvanic structure grow in all directions, e. g. in circular or ellipsoidal form. If concentric island areas are used for controlling the lateral growth speed, also concave or convex profiles may be obtained having a substantially unlimited height h. 
     If a thick resist structure is used, a free growth rate in lateral direction, defined by a stepped over-galvanization may only develop in those areas where the structured photosensitive resist does not define a limit. In the areas being provided with a thick resist layer, the growth rate is limited, the galvanic deposition being provided only in a direction where no limitation by resist is defined. 
     The coating with thick resist structures may advantageously be combined with a completely free plating base structure, so that in certain areas, the growth rate in lateral direction (x- and y-direction) is limited and localized, however, in another direction it is predetermined due to the structured plating base. 
     The inventive method is very inexpensive, particularly with respect to a known gray-tone lithographic method, this technology being based on reducing the size of the structures in the mask design in relation to the lithographic resolution. Thus, gray-tone lithography does no longer provide bright/dark areas but a mixture of gray tones which, however, may only be achieved by using a very complex mask design requiring an optical reduction device for exposure (compare “Microfabrication of complex surface topographies” in Sensors and Actuators, A 46-47, pages 89-94, 1995). In contrast to a gray-tone lithographic method which at first provides a three-dimensional resist profile, subsequently being coated with a thin metallic layer to permit a galvanic deposition, the method according to the present invention provides solid galvanic structures without resist layers positioned thereunder and without using exposure stepper devices, but only applying simple and wide-spread UV contact exposure devices. Said devices are considerably less expensive and thus the results obtained with them are also less expensive. 
     If, according to the present invention, x-ray lithographic methods (LIGA technique) are used for structuring the thick resist, three-dimensional structures of a height of several 100 μm may be obtained. If a UV photosensitive resist and contact exposure devices are used, the height of the thick (structured) resist layer is limited to about 100 μm due to the maximum exposure depth of said method. The limit thus provided only applies for manufacturing methods using thick photosensitive resists, those inventive manufacturing methods which work without resist limits as edge areas of the galvanic are not restricted in their height by said exposure depth, the height depending solely on the period of time during which galvanic deposition is effected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention(s) are described in detail on the basis of several embodiments. 
     FIG. 1 illustrates a substrate  10 . 
     FIG. 2 illustrates the step according to which a conductive starting layer (plating base)  11  has been applied to said substrate  10 . 
     FIG. 3 shows the lateral structuring of said plating base by providing a core area  11   k  and an island area  12   i  comprising a multitude of islands all of them being isolated in relation to each other. The corresponding isolating ring  13   a  being positioned at the inside of the window left by said core area, in which the individual isolated island areas  12   i  are disposed as line-shaped stripes  12   8 , 12   9 , 12   10  . . . spaced apart with respect to each other without having electric contact to said core area  11   k . 
     FIG. 4 is an embodiment of the inventive method and illustrates the application of a thick resist layer  14  on said core area  11   k , leaving free said island area  12   i  with the structured plating base. The right parallelepiped resist layer  14  with its window may be provided in a number of steps by coating with resist and lithography. 
     FIG. 5 shows the result of the galvanic deposition providing a beveled surface  20   a  formed inside the window according to FIG. 4, if said core area  11   k  is switched to a cathodic potential and said island areas  12   i  are electrically not connected (n.c.). 
     FIG. 6 shows the result obtained by the method after removing said resist layer  14 , the above-described plating base  11   k  still remaining (on the substrate) and said beveled surface  20   a  substantially protruding from said substrate  10  at a height h max . 
     FIG. 7 illustrates the result obtained by the method after removing said core area  11   k  of said plating base, whereby the structured part  12   i  of the plating base may also be removed. 
     FIG. 8 a  to FIG. 8 e  show an alternative embodiment of a galvanic method for manufacturing a beveled structure, according to that of FIG. 7, wherein two conductive layers applied one onto the other are separated by an isolating layer  13   b , a window  13   b ′ uncovering a part  23   k  of said first conductive layer  23  to obtain a growth rate controlled in lateral direction together with an island area  22   i  formed from the second conductive layer  21 . FIG. 8 e  schematically indicates an electrical connection (+) and (−) as well as n.c., said positive potential (+) being applied to the galvanic fluid GF and said negative potential (−) to said plating base  23  which is positioned at a lower level and said island areas  22   i  being electrically not connected (not connected). 
     FIG. 9 is a lateral sectional view illustrating the laterally controlled growth of the galvanic substance G, dependent on a core area  11   k  and island areas  12   1 , 12   2  . . .  12   i  which are spaced apart therefrom and electrically isolated with respect to said core area  11   k  by said substrate  10  or by an additional isolating layer  13   a.    
     FIG.  10  and FIG. 10 a  illustrate a setting of the developing beveled structure, whereby the inclination angle is marked on the Y-axis with respect to the ratio of the island length I and the intermediate distance s. The smaller the width of each island (line) in direction of the x-axis and the larger the interspace between two islands (space), the steeper the inclination angle of the structure formed by galvanization. 
     FIG. 11 a  and FIG. 11 b  show nickel and gold galvanic structures with beveled surfaces  20 ′, 20   a  on a structured substrate comprising stripes isolated with respect to each other which form the above indicated island area. One stripe  11   k  is prolonged with respect to the other stripes and serves as core area for a cathodic potential. 
     FIG. 12 shows a tilting mirror  40  as a field of application of the beveled galvanic structure, a pivot position α(alpha) of said mirror being changed by using beveled structures, whereby lower voltages are required to achieve a larger tilting angle with respect to the embodiment according to FIG. 13, showing a tilting mirror  30  with flat galvanic structures. 
     FIG. 13 shows a tilting mirror  30  with flat galvanic structures  91 , 90  having a small bevel angle β(beta) only—at equal control voltage. 
     FIG. 14 illustrates an beveled structure  20   a  growing in two plane directions x,y, the edge areas  20   b  of said structure not extending perpendicularly with respect to the substrate  10 , but forming a markedly curved side surface of the kind of a 1-e-function. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Subject to the field of application, a beveled structure on a substrate  10  is used in micromechanics (compare FIG.  12 ). There, a desired pivoting movement α(alpha) of a tilting mirror  40  which is positioned on a peg is considerably enlarged, whereby the electrostatic potentials (+) and (−) are smaller, if structures are used which approach the pivoting movement, such as wedge-shaped beveled structures  20   a  having a height h on the left and right side of the tilting mirror stator. In contrast thereto, FIG. 13 shows that a pivoting movement β(beta) of a tilting mirror  30  as illustrated there is only small when using equal potentials, if flat galvanic structures  90 , 91  being of considerably less height h 1  are used. If said galvanic structures  90 , 91  are thicker, the pivoting movement of the mirror is limited although smaller potentials may be used. If said galvanic structure  90 , 91  remains thin, a considerably higher voltage must be applied for a required pivot angle to generate comparable forces. 
     The beveled structure which was specified on the basis of its intended application is obtained by a method which is described according to FIGS. 1 to  7  or FIGS. 8 a  to  8   e  on the basis of each respective intermediate product obtained as a result of each step of the method. First, an electrically conductive starting layer  11  is applied on a substrate  10  which in this embodiment is non-conductive (FIG.  2 ). The metal ions of a galvanic solution GF providing a galvanic structure discharge at said starting layer. In contrast to prior art, the presence of a structured photosensitive resist on the plating base is not necessarily required, but the plating base  11  itself is structured in the x-y-plane to provide conductive island areas  12   i , which in this embodiment are formed as lines  12   8 , 12   9 , 12   10  in a window left free by a core area of said plating base  11 . An isolating stripe  13   a  extends circumferentially around the line structure of the structured island area  12   i  said stripe separating and isolating said core area  11   k  from said island area  12   i . In the present embodiment, the stripe  13   a  is the surface of the isolating substrate  10 . If the substrate  10  itself is not isolating,  13   a  would be a section of an intermediate isolating layer between the plating base  11  according to FIG. 2 and a conductive substrate  10 . 
     The term “isolating” is defined such that no substantial conduction of electric current is permitted, a slight leakage current which does not substantially lead to a strongly negative potential on the islands  12   i  not having detrimental effect. 
     A thick layer  14  of a photosensitive resist is applied on the core area  11   k  of FIG. 3, said thick resist layer  14  being partly (in the window) exposed to light and providing the product according to FIG.  4 . The conductive core  11   k  of said plating base  11  can still be seen on a small part stripe  11   k ′, the remaining core area being covered by said resist layer  14 . Consequently, the structured plating base area  12   i , having a multitude of stripe-shaped islands, remains uncovered. 
     If between FIGS. 4 and 5 a galvanic bath GF is provided above said window and above said resist layer  14  and said core area  11   k  is switched to a cathodic potential, whereas said galvanic fluid GF is switched to an anodic potential, a bevelled surface  20   a  develops in the window after a eriod of galvanic deposition, starting from the free stripe  11   k ′ of the cathode electrode, a controlled growth over the electrically isolated stripes taking place, limited by the remaining three vertical flanks of the thick resist  14 . 
     The galvanic shaping process starts at  11   k ′ and from there, the galvanic structure  20   a  grows in a growing direction −y, if the coordinate system y,x,h (y,x) according to FIG.  6  and FIG. 3 is used as basis. The growth in said growing direction −y is controlled by the interspace, width and geometry of the isolated metal stripes which are defined before the beginning of the galvanic bath. The galvanic material also grows in perpendicular direction with respect to the plane of said substrate  10  and is limited in three lateral directions by said resist. In the direction not limited by said resist  14 , a continuous growth in −y and h direction takes place by an over-galvanization from island to island. 
     Said island areas themselves being electrically not connected, the galvanic structure first grows in vertical direction, only slowly passing said isolated intermediate area, until it reaches the subsequent island area. This is illustrated in FIG. 9 which may be regarded in connection with FIG. 5 to explain the step-wise over-galvanization over said isolated areas between said islands  12   1 , 12   2 , 12   3 , etc. As soon as an island area is reached by said deposited galvanic substance G, the speed of lateral growth increases stepwise and the speed of vertical growth decreases for a moment. At the end of said island area, the speed of lateral growth decreases again and the speed of vertical growth increases. Thus, the galvanization of an area in lateral direction is effected hand in hand and alternating with a growth in vertical direction. As a result of this method, a bevelled structure  20   a  is obtained which by applying further method steps according to FIG. 6 and 7 may remain isolated on said substrate  10 , when removing said resist layer  14  (FIG. 6) and the remaining core area  11   k  of said plating base is also removed (FIG.  7 ). 
     FIGS. 11 a  and  11   b  show galvanic structures which were provided according to the described method by being limited on two sides with a resist structure. According to said Figures, a hill-shaped galvanic structure  20 ′ and  20   a , respectively, having two bevelled surfaces and a summit is formed, the zenith lying above said cathodic stripe  11   k  which corresponds to the stripe  11   k ′ of FIG.  9  and FIG.  4 . Metal stripes  12   1 ,  12   2 ,  12   3 , etc. are laterally spaced in relation to each other and isolated therefrom, as can also be seen from FIG.  9 . The right edge zones of FIG. 11 b  give a particularly distinct impression of the step-wise over-galvanization with subsequent vertical galvanization, the bevelled surface still showing distinct traces of the stripe structure of which it is formed. The groove structure is leveled only in further upward areas providing a bevelled surface which is substantially even. 
     The inclination angle according to FIG. 10 is controlled by defining an interspace s according to FIG. 10 a  and a width I of the stripes. If other structures are selected, not being stripes, but concentrical or ellipsoid shapes, the function of FIG. 10 may differ correspondingly. In general, the inclination angle of the bevelled surface formed is defined such that a larger interspace s and a smaller width I of the stripes result in a larger inclination angle. If the interspaces s are not equal in x-direction, other structures than bevelled structures may be obtained, the angle of the bevelled surface then depending on the interspace with respect to the cathode area  11   k ′. 
     FIGS. 8 a  to  8   e  describe an alternative production method. Starting from a substrate  10 , a first plating layer  23  is applied as conductive starting layer (FIG. 8 b ). An isolating layer  13   b  is applied on said conductive layer  23 , e. g. by vaporization or sputtering. At an appropriate place in said isolating layer, a core area  23   k  of said covered first conductive layer  23  is uncovered. The corresponding window is defined by reference numeral  13   b ′. An electric contact to the galvanic fluid may be provided here. Said covered conductive layer  23  serves as a lead-in or lead-out of electric current (FIG. 8 d , FIG. 8 e ). 
     On said isolating layer  13   b , island areas  22   i  are formed, structured either before providing said window according to FIG. 8 b  or thereafter from a second plating layer (by coating with a resist and exposure to light). Said island areas are electrically isolated from said first conductive layer  23  (FIG. 8 e ). 
     If the intermediate product shown in FIG. 8 e  is used as a basis for galvanization, firstly depositions are formed at said window  13   b ′ above said core area  23   k , said depositions galvanizing over by surging to said first stripes being directly adjacent to said window  13   b ′. Starting from there, a solid three-dimensional deposited structure develops—e.g. according to FIG.  9 —such that at the edges, no limitations by high or thick resist layers are provided. Thus, FIG. 8 e  is a basis for growth rates extending in all directions of the plane x/y and being controlled and influenced by the structure of said island areas  22   i  above and isolated from said conductive layer  23  positioned inside. 
     In FIG. 8 e , the electrical potentials (+) and (−) are indicated schematically which potentials are applied at the galvanic fluid GF and the conductive layer  23 . The island areas  22   i  are not connected (n.c.). 
     All embodiments of the methods as proposed by the present invention relate to structured surfaces. A structured surface develops from an expanded conductive layer having been applied by sputtering or vaporization, the kind of the metal used as a layer being subject to the selected (subsequent) galvanization. Subsequently, a coating with a thin, e. g. 1 μm structure resist layer is effected and the structure of the conductive layer may be obtained in a lithographic process by exposure and uncovering (etching or ion milling). Additionally, a galvanic pre-shaping step may be effected to provide a more stable structure. Also a metal of a small thickness of about 100 nm may additionally be sputtered.