Abstract:
A micromechanical component having at least two caverns is provided, the caverns being delimited by the micromechanical component and a cap, and the caverns having different internal atmospheric pressures. The micromechanical component and cap are hermetically joined to one another at a first specifiable atmospheric pressure, then an access to at least one cavern is produced, and subsequently the access is hermetically closed off at a second specifiable atmospheric pressure.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a micromechanical component, and a method for manufacturing a micromechanical component. 
     BACKGROUND INFORMATION 
     It is known from the existing art that discrete sensors, e.g., rotation-rate sensors and acceleration sensors, can be manufactured micromechanically. It is likewise known that rotation-rate and acceleration sensors can be integrated in a common housing, together with one or more evaluation circuits, to constitute a sensor system. It is furthermore known to integrate micromechanical sensors and the associated evaluation circuit monolithically. Published German patent document DE 101 04 868 describes the packaging of a micromechanical sensor by way of a cap. The sensor and cap are anodically bonded, and delimit a cavern. It is furthermore described in published German patent document DE 102 43 014 to dispose two caverns in one micromechanical component. 
     SUMMARY 
     The micromechanical component according to the present invention has at least two caverns having different internal pressures. This advantageously makes possible the integration of multiple different micromechanical sensors, having different internal atmospheric pressures as determined by their design, into one common micromechanical component. In a micromechanical acceleration sensor the internal atmospheric pressure in the cavern is specified, for example, as 5 mbar to 1.5 bar. With this pressure, a suitable damping for the micromechanical deflection part of acceleration sensors can be established. For actively oscillating sensors, e.g., for rotation-rate sensors, the internal cavern pressure that is chosen should be very low in order to ensure high quality for the oscillator. Internal cavern pressures of &lt;10 −3  bar are advantageous here. 
     An advantageous example embodiment of the micromechanical component provides for at least two caverns to be delimited by one common cap. This makes possible a particularly compact construction for the micromechanical component. The number of steps for manufacturing such a component can moreover be reduced thereby. In particular, these two caverns have different internal atmospheric pressures. 
     It is also advantageous that at least one cavern has a closed-off access opening. A specifiable pressure in the cavern can easily be established by way of such an access opening. 
     A further advantageous example embodiment of the micromechanical component according to the present invention provides for the access opening to exist through a component substrate. Here the access opening can be particularly easily provided, and also closed off again, during sensor production. 
     It is also advantageous if the micromechanical component has a buried conductor structure. Buried conductor structures make it possible to configure the joining surface between the cap and the micromechanical component in particularly flat, and therefore sealed, fashion. 
     A particularly advantageous example embodiment of the micromechanical component according to the present invention provides for the component to have, at a contact region of a component substrate, at least one means for electrical contacting, in particular a metallization. This embodiment enables all the contacts and unburied conductor structures of the micromechanical component to be guided on the uncapped side of the micromechanical component, thus advantageously making possible complete capping of one side of the micromechanical component. 
     It is also advantageous that at least one cavern of the micromechanical component is sealed by way of a peripheral hermetic material join. The specified internal pressure in the cavern is thereby advantageously maintained over the service life of the micromechanical component. 
     It is also advantageous if several caverns are sealed by way of a common peripheral hermetic material join. Advantageously, regions of the micromechanical component can thus be provided with the same pressure in the relevant caverns. It is furthermore also possible to provide regions of differing pressure, in particular of stepwise better vacuum. 
     An advantageous example embodiment of the micromechanical component according to the present invention provides for the cap to be made of a silicon substrate that is joined to a glass layer. Such a cap can be particularly easily mounted with its glass layer onto a micromechanical component made of silicon, and secured by anodic bonding. 
     It is also advantageous if the cap, in particular the glass layer, has at least one recess to form a cavern. The recess in the cap advantageously enlarges the cavern. More space for micromechanical functional parts therefore exists in the cavern. 
     The method according to the present invention for manufacturing a micromechanical component provides that the micromechanical component and the cap are hermetically joined to one another at a first specifiable atmospheric pressure, an access to at least one cavern is then created, and then the access is hermetically closed off at a second specifiable atmospheric pressure. It is advantageous in this context that at least for one cavern, the internal atmospheric pressure can be already be specified during the process step of capping. 
     It is furthermore advantageous that different internal atmospheric pressures are specifiable in the individual caverns, with the result that, for example, different micromechanical sensors, having different pressures as determined by their design, can be manufactured. 
     It is moreover advantageous that the caverns made up of a cap and micromechanical component can be manufactured by way of joining processes at practically any desired process pressure, since the internal cavern pressure is still modifiable retrospectively by way of the access. 
     An advantageous example implementation of the method according to the present invention provides for the cap to be manufactured from a silicon substrate and a glass which are joined to one another by anodic bonding. It is advantageous in this context that in this easy fashion a cap can be manufactured and joined to a micromechanical component in a further process step of anodic bonding. 
     A further advantageous example implementation of the method provides for at least one recess to be produced in the glass, in particular by etching, in order to form a cavern. Advantageously, this example implementation enables the manufacture of a cap that makes possible, proceeding from a flat substrate and a flat glass, the formation of the largest possible cavern. 
     It is also advantageous that the micromechanical component and the cap are joined to one another by anodic bonding. Anodic bonding makes possible the production of hermetic joins. 
     It is furthermore advantageous that the access is produced in a component substrate of the micromechanical component. The access is produced, in simple and economical fashion, in the same manufacturing step in which trenches for the electrical insulation of parts of the component are introduced into the component substrate of the micromechanical component. 
     An advantageous example implementation of the method according to the present invention provides for the access to be closed off by way of a deposition process, e.g., a CVD method. A deposition process of this kind allows the access to be closed off at particularly low process pressures. This is advantageous for the production of caverns having a low internal atmospheric pressure. 
     It is additionally advantageous that the method steps of opening the accesses and subsequently closing them off at a specifiable atmospheric pressure can be performed several times successively. It is possible as a result to manufacture further caverns have different specifiable atmospheric pressures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the preparation of a substrate and of a glass. 
         FIG. 2  shows the joining of the substrate and glass by anodic bonding. 
         FIG. 3  shows the thinning of the glass layer. 
         FIG. 4  shows the etching of recesses into the glass. 
         FIG. 5  shows the application of a shield and parallelizing of the substrate. 
         FIG. 6  shows the alignment of a cap with respect to a micromechanical component. 
         FIG. 7  shows the joining of the component and cap. 
         FIG. 8  shows the production of an access opening to a cavern. 
         FIG. 9  shows the closing off of the access opening. 
         FIG. 10  shows the production of a back-side contact. 
         FIG. 11  shows an assemblage of multiple caverns in one micromechanical component. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows the preparation of a substrate and a glass for the manufacture of a cap. A cap substrate  100 , which in this example is made of silicon, is disposed and aligned with respect to a glass  150 . Glass  150  is made of Pyrex in this example. For joining, cap substrate  100  and glass  150  must exhibit a suitable roughness on the surfaces facing one another. 
       FIG. 2  shows the joining of substrate  100  to glass  150 . The joining is accomplished, for example, by way of the technique of anodic bonding. 
       FIG. 3  shows the thinning of the glass layer. Thinning action  300  of glass  150  is accomplished by grinding and chemical-mechanical polishing (CMP). The result is to produce, in this example, a glass layer  150  having a thickness of approx. 50 μm. 
       FIG. 4  shows the production of recesses in the glass. Recesses  400  in glass  150  can be produced, for example, by a buffered oxide etch (BOE) method. In the example shown, recesses  400  have a depth of approx. 5.5 μm. Provision can be made to leave supporting regions  450  when producing the recesses. 
       FIG. 5  shows the production of a shield and the parallelizing of the cap substrate. To produce a shield  550 , a metal layer is deposited onto regions of glass layer  150 , in particular in the region of recesses  400  and support region  450 . This metal layer can be made, for example, of aluminum, and here has a thickness of approx. 400 nm. The metal layer can be deposited, if necessary, in structured fashion, or can also be structured after deposition. Shield  550  can optionally have a contact tab  555 , such that a conductive connection can be contacted thereon. 
     In the next manufacturing step, cap substrate  100  is parallelized. Parallelizing action  560  is accomplished from the back side of cap substrate  100 . The purpose of parallelizing action  560  is to ensure that the substantially disk-shaped cap substrate  100  has approximately the same thickness (approx. 450 μm in this example) everywhere. Cap substrate  100 , glass layer  150 , and shield  550  together form a cap  500 . 
       FIG. 6  shows the alignment of the cap with respect to a micromechanical component. Micromechanical component  600  has a micromechanical functional layer  610  made of polycrystalline silicon, a dielectric layer  620  made of silicon oxide, and a component substrate  630  made of silicon. Micromechanical functional layer  610  has a connection region  640 , micromechanical structures  650 , and optionally support mounts  655 . On the surface facing toward micromechanical component  600 , glass layer  150  in cap  500  has bonding surfaces  660 . 
       FIG. 7  shows the joining of component and cap, in which cap  500  is anodically bonded to component  600  at bonding surfaces  660 . This material join of glass layer  150  to micromechanical functional layer  610  is hermetically sealed. As a result, cap  500  and micromechanical component  600  delimit at least one cavern  700 . 
       FIG. 8  shows the production of an access opening to a cavern. Firstly, a thinning action  800  of component substrate  630  to a thickness of approx. 125 μm occurs. Thinning action  800  is performed, for example, by grinding and polishing. Trenches  810  that isolate contact regions  830  from the remaining component substrate  630  are then introduced into component substrate  630 . In the same manufacturing step, an access opening  820  to cavern  700  is introduced into component substrate  630 . The internal atmospheric cavern pressure is equalized with the ambient pressure through access opening  820 . 
       FIG. 9  shows the closing off of the access opening. For this, component substrate  630  is coated with an oxide  900 ; this is done, for example, using a CVD method. Oxide  900  fills insulating trenches  810 , closes off access opening  820 , and furthermore coats component substrate  630 . The process pressure during coating, which can be less than 10 −3  bar, is thereby enclosed in cavern  700 . Contact region  830  is at least partially exempted from the coating with oxide  900 . 
       FIG. 10  shows the production of a back-side contact on micromechanical component  600 , a metallization  10  being applied onto contact region  830  and locally onto oxide  900 . Metallization  10  can be structured during application, or also in a later manufacturing step. Contacts to conductive regions in the interior of the micromechanical component, as well as contacts and conductive paths on the surface, can be produced by way of this process step. 
       FIG. 11  shows a micromechanical component according to the present invention having multiple caverns. The component is depicted schematically and in plan view. Caverns  700   a, b  are located in the interior of the micromechanical component, and in this example are formed by a single common cap on the component. The cap and component have joining surfaces  660  that, in this example, form a first bonding frame  113  and a second bonding frame  115  after anodic bonding. First bonding frame  113  encloses a cavern  700   a  that has a closed-off access opening  820 . A very low internal atmospheric pressure exists in this cavern  700   a ; an internal pressure of less than 10 −3  bar is conceivable. Cavern  700   a  accommodates a micromechanical functional element  111  that operates, as governed by its design, at very low pressures. This can be, for example, a micromechanical rotation-rate sensor or another high-quality micromechanical oscillator. The vacuum in cavern  700   a  is hermetically closed off from ambient pressure by bonding frame  113 . 
     In this example, the micromechanical component has three further caverns  700   b  that have no access opening  820  at all. These caverns  700   b  contain substantially the process pressure that existed during the process step of anodic bonding. These can be, for example, pressures between 5 mbar and 1.5 bar. Disposed in these caverns  700   b  are functional elements  110  that, as governed by their design, function at higher pressures or are more tolerant to higher working pressures. Micromechanical functional elements  110  can be, for example, acceleration sensor structures that operate in damped fashion at the indicated internal atmospheric pressure of caverns  700   b.    
     The three caverns  700   b  having the higher internal pressure are hermetically closed off by bonding frame  113  from the vacuum in fourth cavern  700   a . Furthermore, all the caverns  700   a, b  are hermetically closed off from the outside world by the common bonding frame  115 . In this example, the three caverns  700   b  having the higher internal pressure are not separated from one another by further bonding frames, since substantially the same internal cavern pressure exists in them in any case after the process step of anodic bonding. 
     Lastly,  FIG. 11  also depicts contact surfaces  10  produced by metallization. By way of these contact surfaces, the micromechanical component can, for example, be connected to an external evaluation circuit (not depicted here). It is also conceivable, however, to integrate the evaluation circuit into the micromechanical component. 
     Further embodiments of the micromechanical component are possible.