Abstract:
A method for producing a micromechanical component, includes providing a first substrate, developing a micropattern on the first substrate, the micropattern having a movable functional element, providing a second substrate, and developing an electrode in the second substrate for the capacitive recording of a deflection of the functional element. The method further includes connecting the first and the second substrate, a closed cavity being formed which encloses the functional element, and the electrode bordering on the cavity in an area of the functional element.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a micromechanical component having a first substrate and a second substrate that is connected to the first substrate, the first substrate having a micropattern having a movable functional element, and the first and the second substrate being connected to each other in such a way that the functional element is enclosed by a cavity. Furthermore, the present invention relates to a method for manufacturing such a component. 
       BACKGROUND INFORMATION 
       [0002]    Micromechanical components, which are used, in the automotive field, as inertial and acceleration sensors, for example, normally have a micropattern having a movable functional element. The micropattern is also designated as a MEMS structure (microelectromechanical system). During the operation of the sensors, the deflection of a functional element is detected, for instance, by a change in the electrical capacity compared to a fixed reference electrode. 
         [0003]    A common method for producing a micromechanical component includes forming the micropattern on a functional substrate, and connecting the functional substrate to a cap substrate by a so-called wafer bonding method. A cavity is formed, in this manner, which encloses the functional element, whereby the functional element is sealed hermetically from the environment. Besides the micropattern, buried printed circuit traces are also formed in the functional substrate, which are situated below the functional pattern. These may be used as electrodes for the capacitive recording of the deflection of functional elements, as well as providing an electrical path to contact elements (bondpads) outside the frame-shaped cap. The cap of the functional substrate is usually carried out in a specified gas and pressure atmosphere, in order to set a corresponding pressure atmosphere in the cavity. As the adhesive for connecting the functional substrate and the cap substrate, seal glass (solder glass) is used, which is applied onto the substrate with the aid of a screen-printing technique, for instance. 
         [0004]    This construction of the component is connected to a series of disadvantages. The development of the buried printed circuit traces, which lead to contact elements next to the MEMS structure and outside the cap, results in a large surface requirement of the component. Furthermore, the method is complex, and requires a large number of process steps. For example, the method may bring along with it the use of more than ten lithographic patterning planes and lithographic patterning methods, whereby high production costs come about for the entire process. Critical process steps are also found in the method sequence which may lead, for instance, to the under-etching of a buried printed circuit trace. Moreover, the use of seal glass leads to a relatively wide bonding frame, which further increases the size of the component. In addition, the seal glass is laced with a solvent during its application, which has to be driven off during the bonding method. The problem is, however, that a residual portion of the solvent is able to remain behind in the seal glass, and be liberated into the cavity and change the specified pressure. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the exemplary embodiments and/or exemplary methods of the present invention to state an improved method for producing a micromechanical component and an improved micromechanical component, in which the abovementioned disadvantages are avoided. 
         [0006]    This object is attained by a method as described herein and by a micromechanical component as described herein. Further advantageous developments of the exemplary embodiments and/or exemplary methods of the present invention are further described herein. 
         [0007]    A method for manufacturing such a component is also provided, according to the present invention. The method includes providing a first substrate and developing a micropattern on the first substrate, the micropattern having a movable functional element. The method also includes providing a second substrate and developing an electrode in the second substrate for the capacitive detection of a deflection of the functional element. The first and the second substrate are connected, a closed cavity being formed which encloses the functional substrate, and the electrode bordering on the cavity in an area of the functional element. 
         [0008]    Since the second substrate has an electrode for the capacitive detection of a deflection of the functional element, one may do without the development of a buried printed circuit trace in the first substrate and a contact element connected to the printed circuit trace that is laterally offset with respect to the micropattern. As a result, the micromechanical component is able to be realized using a small component size. Then too, one is able to produce the component using a relatively small number of patterning planes, or rather, process steps, whereby the method becomes simple and cost-effective. Furthermore, there are no critical process steps having negative consequences, such as the under-etching of printed circuit traces mentioned above, so that also no costly measures are required for preventing such effects. 
         [0009]    According to one specific embodiment, the development of the electrode includes the developing of an insulation structure in the second substrate. A substrate area is framed in the second substrate via the insulation structure, which is used as an electrode. 
         [0010]    According to one additional specific embodiment, the micropattern is developed having a first metallic layer. A second metallic layer is developed on the second substrate. Connecting the first and second substrate takes place via the first and second metallic layer. This makes possible a hermetically sealed and space-saving connection between the two substrates. There is also no danger of the liberation of gas, whereby the cavity is able to be developed to have a very low and specified pressure. A connecting method that may be used is eutectic bonding or thermal compression bonding. 
         [0011]    According to a further specific embodiment, after the connection of the first and second substrate, substrate material is removed on a backside surface of the second substrate, in order to expose the electrode on the backside surface, so that it is able to be contacted from outside. Since the removing of substrate material is carried out only after connecting the substrates, the second substrate may have a relatively large thickness in the preceding method steps, whereby it is easier to carry out the method. After the removal of the substrate material, one may further develop a metallization on the backside surface of the second substrate, which contacts the exposed electrode. 
         [0012]    According to one additional specific embodiment, a terminal passing through the second substrate is developed in the second substrate. An electrical connection to the micropattern may be produced, passing through the second substrate, via the terminal. 
         [0013]    A micromechanical component is also proposed, according to the present invention. The component has a first substrate and a second substrate connected to the first substrate. The first substrate has a micropattern having a movable functional element. The first and the second substrate are connected to each other in such a way that the functional element is enclosed by a closed cavity. The micromechanical component is distinguished in that the second substrate has an electrode for the capacitive detection of a deflection of the functional element, the electrode bordering on the cavity in the area of the functional element. Because of the situation of the electrode in the second substrate, the component is able to be produced in a simple and cost-effective manner, and having a small size. 
         [0014]    In the following text, the exemplary embodiments and/or exemplary methods of the present invention will be explained in greater detail with reference to the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  shows a method for producing a micromechanical component, in a lateral sectional view. 
           [0016]      FIG. 2  shows a method for producing a micromechanical component, in another lateral sectional view. 
           [0017]      FIG. 3  shows a method for producing a micromechanical component, in another lateral sectional view. 
           [0018]      FIG. 4  shows a method for producing a micromechanical component, in another lateral sectional view. 
           [0019]      FIG. 5  shows a method for producing a micromechanical component, in another lateral sectional view. 
           [0020]      FIG. 6  shows a method for producing a micromechanical component, in another lateral sectional view. 
           [0021]      FIG. 7  shows a method for producing a micromechanical component, in another lateral sectional view. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The following  FIGS. 1 through 7  schematically show the production of a micromechanical component  300  which, for example, may be used as an inertial sensor in a motor vehicle. The usual processes and materials that are customary in semiconductor technology may be used in the production. 
         [0023]      FIGS. 1 and 2  show the production of a functional substrate  100  having a micromechanical or MEMS structure  150  for component  300 . At the beginning, a substrate  100  is provided, which has a semiconductor material such as silicon, for example. Substrate  100  may be a customary wafer having a diameter of 8 inches (20.0 mm). 
         [0024]    Subsequently, as shown in  FIG. 1 , a sacrificial layer  110  is applied onto substrate  100  and a functional layer  120  is applied onto sacrificial layer  110 . Sacrificial layer  110  may have silicon oxide. Functional layer  120  may be a so-called epi-polysilicon layer, that is, a polycrystalline silicon layer produced in an epitaxy method. Functional layer  120  may optionally be developed additionally to be doped, in order to increase the electrical conductivity and/or to provide layer  120  with a specified mechanical stress. The construction of substrate  100  with the layers  110 ,  120  may alternatively be implemented by a so-called SOI substrate (silicon on insulator), functional layer  120  being able to have monocrystalline silicon, in this case. 
         [0025]    As shown in  FIG. 1 , a thin metallic layer  130  is applied onto functional layer  120 , in addition. Metallic layer  130  may have a thickness in a range such as some 10 nm up to a few micrometers. Metals such as aluminum, copper and gold come into consideration as the material for layer  130 . The use of a metal alloy such as an aluminum-silicon-copper alloy is also possible. 
         [0026]    As shown in  FIG. 2 , metallic layer  130  is patterned. In this instance, a lithographic patterning method is carried out, in which first a patterned photoresist layer is produced on metallic layer  130 , and metallic layer  130  is submitted to an etching method of the pattern. Patterned metallic layer  130  is subsequently used as a mask for etching trenches  140  into functional layer  120 . The shape of a micropattern  150 , that is to be developed, is established via trenches  140 . The trench etching may be carried out, for example, with the aid of a DRIE method (deep reactive ion etching), in which an anisotropically acting etching plasma is used. 
         [0027]    In order to complete micropattern  150 , a part of sacrificial layer  110  is additionally removed, in order to expose electrode fingers or functional elements  151 ,  153 ,  154  as shown in  FIG. 2 . For this purpose, an etching medium or etching gas is brought in to sacrificial layer  110  via trenches  140 . In case sacrificial layer  110  has silicon oxide, as described above, hydrofluoric acid vapor may be used for this, for example. Functional elements  151  form a so-called z rocker, and are thus developed for deflection perpendicular to the substrate surface (z direction). Functional elements  153 ,  154  form an oscillator structure or comb structure, functional element  154  being immobile and functional elements  153  being deflectable parallel to the substrate surface (“x/y direction”) (cf.  FIG. 7 ). 
         [0028]    After the etching of sacrificial layer  110 , substrate  100  having micropattern  150  is essentially ready. Substrate  100  is therefore designated below as functional substrate  100 . Since only one lithographic patterning is carried out, the production of functional substrate  100  is connected with a relatively low cost. 
         [0029]      FIGS. 3 to 5  show the production of a cap substrate  200 , which is connected to functional substrate  100  to develop micromechanical component  300 . In this case, cap substrate  200  is used not only for hermetically sealing functional elements  151 ,  153 ,  154 , but is also used for capacitive coupling and electrical contacting. A substrate  200  is first supplied which may have a semiconductor material such as silicon. Substrate  200  may also be a wafer having a diameter of 8 inches, for instance. 
         [0030]    In substrate  200  supplied, trenches  210 , shown in  FIG. 3 , are developed which, as described below, are used for insulation and for the definition of substrate regions for capacitive and electrical coupling. To develop trenches  210 , an appropriate lithographic method and an etching method (such as a DRIE method) may be carried out. Trenches  210  have a depth of some 10 μm to a few 100 μm, for example. 
         [0031]    After that, an insulating layer  220  is applied over a large area onto substrate  200 , while filling up trenches  210 . Insulating layer  220  has an oxide, for instance, or alternatively another dielectric material, such as a nitride. Within the scope of an additional lithographic patterning method, insulating layer  220  is patterned, so that the shape shown in  FIG. 4  comes about, in which the semiconductor material of substrate  200  is exposed in partial sections. 
         [0032]    Substrate areas are framed or defined, via insulating layer  220  that is situated in trenches  210 , and they are used in micromechanical component  300  as electrodes  251  for the capacitive evaluation and as terminals  252  for the electrical contacting. Furthermore, a recess or cavity is defined in the area of an electrode  251  by patterned layer  220  on the surface of the substrate, which makes possible the motion of a functional element  151  in the direction of electrode  251 . A corresponding cavity or topography  240 , defined by layer  220 , is also provided at another section of substrate  200 , so that an unimpeded motion of functional elements  153  in the x/y direction is made possible, that is, perpendicular to the direction of motion of a functional element  151 . 
         [0033]    In order to increase the electrical conductivity of electrodes  251  and terminals  252 , doping of substrate  200  is able to take place optionally, before or after the production of trenches  210  and the development of patterned insulating layer  220 . For this purpose, for instance, a phosphorus glass (POC13) may be applied onto substrate  200  and subsequently a temperature step may be carried out so as to introduce phosphorus into substrate  200  as doping substance. 
         [0034]    A metallic layer  230  is subsequently applied onto substrate  200  or layer  220  and is patterned with the aid of a lithographic patterning method, so that cap substrate  200  is essentially ready ( FIG. 5 ). With respect to possible materials for metallic layer  230 , we refer to the above statements on metallic layer  130  of functional substrate  100 . A part of metallic layer  230  is situated on terminals  252 , and is used for their contacting. 
         [0035]    In addition, metallic layer  230  of cap substrate  200 , together with metallic layer  130  of functional substrate  100 , is used to connect to each other the two substrates  100 ,  200 , within the scope of a wafer bonding method, in a mechanically stable manner ( FIG. 6 ). By the connection of the two substrates  100 ,  200 , a cavity or a plurality of cavities enclosing functional elements  151 ,  153 ,  154  are formed, which are hermetically sealed from the environment via layers  130 ,  230  that function as a sealing frame. Substrates  100 ,  200  are furthermore connected in such a way that an electrode  251  borders on a cavity in an area above a functional element  151 . 
         [0036]    To connect substrates  100 ,  200 , a eutectic bonding process may be carried out, in which the two metallic layers  130 ,  230  form a eutectic alloy under the influence of temperature. Alternatively, it is possible to carry out thermal compression bonding, in which layers  130 ,  230  are connected to form a common layer by temperature influence and pressing together substrates  100 ,  200 . However, for reasons of clarity, layers  130 ,  230  in  FIGS. 6 and 7  are still shown as individual layers. With respect to the bonding method named, the materials of layers  130 ,  230  are appropriately matched to each other. 
         [0037]    The connection of the two substrates  100 ,  200  is also carried out in a specified atmosphere at a specified (such as a very low) pressure, in order to set a specified pressure in the cavity (cavities) between the two substrates  100 ,  200 . Because of the connection via the metallic layers  130 ,  230 , there is no danger of gas being given off, so that the pressure, once it is set, does not undergo any further change. The connection via layers  130 ,  230  is also electrically conductive and, compared to a seal glass connection, is able to be implemented in a more space-saving manner (smaller width of the sealing frame). 
         [0038]    After the connection of the two substrates  100 ,  200 , substrate material is also removed on a backside surface of cap substrate  200  up to at least insulating layer  220 . In this way, electrodes  251  defined by insulating layer  220  and terminals  252  are exposed on the backside surface as shown in  FIG. 6 , so that electrodes  251  and terminals  252  penetrate all the way through substrate  200  and its semiconductor material. The removal on the backside of the substrate may take place, for instance, by back grinding (for instance CMP chemical mechanical polishing). Functional substrate  100  may also be thinned backwards in an appropriate removal or grinding process. 
         [0039]    Moreover, as shown in  FIG. 7 , an additional insulating layer  260  is applied over a large area onto the backside surface of cap substrate  200 , and the latter is patterned within the scope of a lithographic patterning method, so that electrodes  251  and terminal  252  are, in turn, partially exposed. In this connection, saw marks may also be applied to layer  260  for cutting units apart. An additional metallic layer  270  is applied over a large surface onto the backside surface of substrate  200  and onto insulating layer  260  and is patterned lithographically, in order to provide electrodes  251  and terminals  252  with a metallization, via which electrodes  251  and terminals  252  may be contacted from the outside. After that, the cutting apart process may be carried out, whereby micromechanical component  300  is essentially finished. 
         [0040]    Component  300  has three wiring planes which are formed by functional layer  120  covered by metallic layer  130 , terminals penetrating through substrate  200  or through contacts  252 , and metallic layer  270 . Moreover, component  300  has a z rocker including functional element  151  and an oscillator structure including functional elements  153 ,  154 , whose oscillating directions are indicated in  FIG. 7  by arrows. 
         [0041]    In the operation of the z rocker of component  300 , the capacitance is measured between electrodes  251  and functional elements  151 , that act as reference electrodes, a deflection of functional elements  151  manifesting itself in a change in capacitance. In this connection, functional elements  151  may be contacted via a terminal  252 , that is assigned to the z-ROCKER, and via layers  230 ,  130 ,  120 . In order to make possible a differential evaluation, functional elements  151  may be connected to one another for an oppositely directed deflection, as indicated in  FIG. 7  with the aid of the different arrow directions. A comparable functioning comes about for the oscillating structure, in this case, the capacitance being measured between immobile functional element  154  and deflectable functional elements  153 . Functional elements  153 ,  154 , in this case, may be contacted via associated terminals  252  or via layers  230 ,  130 ,  120 . 
         [0042]    Because of the situation of electrodes  251  and terminals  252  in cap substrate  200  above micropattern  150 , a low installation height of component  300  is made possible. The method is also based on only six lithographic patterning planes or lithographic patterning processes, whereby the method takes on a simple and cost-effective form. It further proves favorable that the rear thinning of cap substrate  200  (and, if necessary, also functional substrate  100 ) is carried out only after the connection of substrates  100 ,  200 , so that the substrates are able to have a relatively large thickness in the preceding method steps. 
         [0043]    The method explained with reference to the figures and micromechanical component  300  represent specific embodiments of the present invention. Furthermore, additional specific embodiments may be realized, which include additional modifications of the present invention. In particular, instead of the specified materials, other materials may be used. 
         [0044]    A connection between a functional substrate and a cap substrate may, instead of via two metallic layers, also take place via one metallic layer applied onto the cap substrate, which is connected directly to a functional layer in a bonding method. One example that comes into consideration for this is a eutectic connection formation between the materials gold (metallic layer) and silicon (functional layer. 
         [0045]    Electrodes and terminals in a cap substrate may alternatively be developed with the aid of a “through-silicon via” method. In this case, trenches are developed in the substrate, the trenches are lined using an insulating layer, and subsequently, the trenches are filled up using a conductive layer. 
         [0046]    A micromechanical component may also be realized having a different number of functional elements. Furthermore, the production is possible of a component which has only one or more z rockers and no oscillating structure, the z rockers being able to be evaluated via electrodes and terminals of a cap substrate.