Abstract:
A method for producing a micromechanical component is proposed, a trench structure being substantially completely filled up by a first filler layer, and a first mask layer being applied on the first filler layer, on which in turn a second filler layer and a second mask layer are applied. A micromechanical component is also proposed, the first filler layer filling up the trench structure of the micromechanical component and at the same time forming a movable sensor structure.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for producing micromechanical components having trench structures commonly known from German Published Application DE 2004 036 035. 
     2. Description of Related Art 
     A disadvantage of the known micromechanical components, however, is that large trench structures in particular cannot as a rule be completely filled up, and moreover that in the case of a micromechanical component having movable sensor structures, cap wafers must be laboriously patterned so that the cap wafers are spaced away from the movable sensor structures. 
     SUMMARY OF THE INVENTION 
     The method according to the present invention in accordance with the main claim or with the features of the coordinated claims has, in contrast thereto, the advantage that even large trench structures can be substantially completely filled up in uncomplicated fashion by way of a first filler layer, and filler layers can simultaneously be used as a functional layer. By way of the functional layer, spacing elements can be formed to protect the movable sensor structures from contact with a cap wafer. For formation of the spacing elements, in the method for producing the micromechanical component a second filler layer is applied over the first filler layer having the first mask layer, and a second mask layer is applied over that. The first mask layer is thus “buried” under the second filler layer, with the result that, advantageously, in the context of an etching operation the first mask layer acts as a stop layer, so that the material (first filler layer and substrate material) located under the first mask layer is substantially not removed by the etching operation. 
     A third mask layer and a first insulating layer are preferably applied on the substrate material before application of the first filler layer. The functions of the third mask layer and of the first insulating layer are presented in  FIGS. 1A to 1L . 
     The first and/or the second filler layer are preferably made of a material having a low electrical resistance. For example, an epitaxial polysilicon (epi-polysilicon) layer, which is deposited preferably in doped fashion on the substrate material, can be used as a first and/or a second filler layer. 
     The first filler layer and/or the second filler layer are preferably applied or put on in such a way that the filler layers substantially completely cover the first side of the substrate material. It is thus possible to produce sensor structures and/or spacing elements proceeding from the entire first side of the substrate material, and not in a manner limited only to subregions of the first side of the substrate material. 
     The first filler layer is preferably planarized, proceeding from the first side of the substrate material, before the first mask layer is applied. Planarization advantageously forms a plane surface of the first filler layer, with the result that the first mask layer can be applied on the first filler layer substantially in one plane, preferably parallel to the main extension direction of the substrate material. 
     The second filler layer is preferably planarized, proceeding from the first side of the substrate material, prior to application of the second mask layer. Here as well, a plane surface of the second filler layer is advantageously formed, with the result that the second mask layer as well can advantageously be applied onto the second filler layer substantially in one plane parallel to the main extension direction of the substrate material. 
     In a (next) etching step, further trench structures and/or a spacing element and/or a sensor structure are preferably formed. The sensor structure is merely a precursor to a freely movable sensor structure. A movable sensor structure can accordingly be formed from the sensor structure. The spacing element preferably encompasses both the first and the second filler layer, and has a height that by preference is greater than the height of the (preliminary) sensor structure and of the movable sensor structure formed later. 
     At least some of the sensor structures preferably become movable sensor structures by way of a further etching step, a previously applied first insulating layer preferably being removed for this purpose (see  FIGS. 1A to 1I ). An oxide layer is preferably used as the first insulating layer; the oxide layer can be removed, for example, by way of a gas phase etching step. The movable sensor structures are preferably formed from the first filler layer. 
     In contrast to the sensor structure and the movable sensor structure, the spacing element preferably encompasses both the first and the second filler layer. If one or both of the filler layers is monocrystalline or polycrystalline, the spacing element then also exhibits a monocrystalline and/or polycrystalline structure. The sensor structure and the movable sensor structure preferably encompass only the first filler layer, and by preference are configured in either monocrystalline or polycrystalline fashion. As mentioned in the previous paragraph, the sensor structure becomes a movable sensor structure, for example, by way of a further etching step, so that the term “preliminary sensor structure” can also be used. 
     A cap wafer is preferably connected to the spacing element and/or to monocrystalline or polycrystalline regions of the filler layers, for example by anodic bonding or seal-glass bonding. It is also preferred, however, if the cap wafer is connected to at least one (preliminary, non-movable) sensor structure and/or to monocrystalline or polycrystalline regions of the filler layers. If the micromechanical component does not have a spacing element, the sensor structures are therefore advantageously not only thought of as precursors of the movable sensor structures, but additionally serve to reduce cap deflection in the region of the movable sensor structures. In the case of a micromechanical component without a spacing element, care must be taken in the context of the connection between an unpatterned cap wafer and the sensor structure that the movable sensor structures are not blocked by the unpatterned cap wafer. This can be ensured by using a connecting layer, for example seal glass. The necessary spacing from the movable sensor structures can be ensured by way of the thickness of the seal-glass layer. Let it be clarified once again in this context that the sensor structure for connecting to the cap wafer is not a movable sensor structure, but instead a (preliminary) sensor structure that has not become a movable sensor structure as a result of a further etching step. A “cap wafer” is to be understood as all components that can be used to seal off at least subregions of a micromechanical component. The spacing element or sensor structure having, for example, seal-glass-bonded cap wafers advantageously makes it possible also to use unpatterned cap wafers, so that laborious patterning of the cap wafer is eliminated. Especially in the context of the use of a spacing element, laborious patterning of, for example, Pyrex cap wafers prior to anodic bonding is no longer necessary. It is of course also possible, however, to use patterned cap wafers or even cap wafers patterned only in subregions, the patterning of the cap wafer enabling, for example, electrical contacting of the micromechanical component. 
     The cap wafer and/or a second side of the substrate material is preferably planarized. In the context of planarization of the second side of the substrate material, a planarization extending into a plane of the trench structure is advantageously performed. Planarization of the cap wafer and/or of the second side of the substrate material advantageously makes the micromechanical component thinner. In addition, planarization of the second side of the substrate material extending into a plane of the trench structure advantageously makes possible back-side contacting of the micromechanical component. 
     A further subject of the present invention is a micromechanical component produced according to the method described. In the micromechanical component, the trench structure that is required for through-contacting of the micromechanical component is filled up substantially completely by the first filler layer, the first filler layer also serving to implement the movable sensor structures. Advantageously, when a conductive first filler layer is used, the first filler layer can on the one hand create a precondition for back-side contacting and on the other hand can form the movable sensor structures. 
     The cap wafer is preferably connected via anodic bonding or seal-glass bonding to the spacing element and/or to the monocrystalline or polycrystalline regions of the filler layers. The spacing element is constituted in this context by the first and the second filler layer, and has a greater height than the movable sensor structure or the sensor structure. As a result of the greater height as compared with the movable sensor structure, the cap wafer can advantageously be connected to the spacing element directly by anodic bonding, with no need to perform patterning of the cap wafer and no interference with the movable sensor structures as a result of contact with the cap wafer. The spacing element thus advantageously makes possible anodic bonding between the cap wafer and the micromechanical component without patterning the cap wafer. 
     The cap wafer is preferably connected by seal-glass bonding to the sensor structures and/or to the monocrystalline regions, which optionally can also be embodied in polycrystalline fashion. Here as well, the cap wafer advantageously does not need to be patterned, since the seal glass ensures spacing between the cap wafer and the movable sensor structures. 
     The micromechanical component preferably has a first insulating layer and/or a third insulating layer. The first insulating layer is preferably deposited on the first side of the substrate material, and preferably covers at least the walls and the floor of the trench structure. The third insulating layer is preferably deposited on the second side of the substrate material, after the second side of the substrate material has been planarized as far as a plane of the trench structure. The first insulating layer is preferably created by way of a LOCOS method. The third insulating layer, on the other hand, is preferably produced using a CVD deposition method. 
     The micromechanical component is preferably planarized proceeding from a first side of the substrate material and/or from a second side of the substrate material. Planarization advantageously makes the micromechanical component thinner so that it can be better incorporated even into flat assemblies. 
     The micromechanical component is preferably planarized, proceeding from the second side of the substrate material, as far as a plane of the trench structure. This advantageously make possible back-side contacting of the micromechanical component if a conductive material is used as the first filler layer. 
     The cap wafer that is in contact with the micromechanical component is preferably a Pyrex wafer or a silicon wafer or a composite of a Pyrex and a silicon wafer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1T  schematically depict a method for producing a micromechanical component. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1A  schematically depicts a substrate material  2 , for example silicon, having a circuit region  21  and a conductive path  20 . A third mask layer  14 , made e.g. of silicon nitride, is applied on a first side  6  of substrate material  2 .  FIG. 1B  schematically depicts the manner in which a trench structure  3  was produced in substrate material  2 . By way of a subsequent (e.g. LOCOS) process, a first insulating layer  4  is deposited on substrate material  2 , the walls and floor of trench structure  3  being covered by first insulating layer  4  ( FIG. 1C ). The regions in which third mask layer  14  were applied remain free of third insulating layer  4 , however. After the removal of third mask layer  14 , for example by way of an etching step, gaps are created in first insulating layer  4  ( FIG. 1D ). Both these gaps and first trench structure  3  are filled up by a first filler layer  5  that is made, for example, of doped silicon ( FIG. 1E ); first filler layer  5  can grow in monocrystalline fashion into the gaps of insulating layer  4 . First filler layer  5  is then preferably planarized, as indicated by the dashed line in  FIG. 1E . After planarizing, a first mask layer  12 , made e.g. of silicon oxide, is preferably applied on the thereby substantially plane surface of first filler layer  5  ( FIG. 1F ).  FIG. 1G  schematically depicts the manner in which a second filler layer  13 , for example likewise made up of doped silicon, is applied over first mask layer  12  and first filler layer  5 . A second mask layer  12 ′, for example silicon oxide or photoresist, is then applied on second filler layer  13 . Second filler layer  13  is preferably planarized before the application of second mask layer  12 ′. First mask layer  12  is thus buried under second filler layer  13 . After an etching step, the result of the buried first mask layer  12  and second mask layer  12 ′ is preferably to create both a sensor structure  27 ′ and a spacing element  50  ( FIG. 1H ). Spacing element  50  is preferably formed from the first and the second filler layer  5 ,  13 , and has a height that is greater than the height of sensor structure  27 ′. Further trench structures  3 ′ are preferably also formed in the context of the etching step just mentioned. Subregions of first insulating layer  4  are then preferably removed by a further etching step, first insulating layer  4  being protected in the region of trench structure  3  by the first and the second filler layer  5 ,  13 , and not being removed. The removal of first insulating layer  4  creates movable sensor structures  27  from at least some sensor structures  27 ′, as depicted in  FIG. 1I . As a result of the application of first filler layer  5  and second filler layer  13  directly onto substrate material  2 , it is furthermore advantageously possible to form regions  8  of, for example, monocrystalline silicon if first filler layer  5  and second filler layer  13  are constructed by the deposition of epi-polysilicon. After the second planarizing step, regions  8  then preferably have the same height as a spacing element  50 . Regions  8  can, of course, also be made of polycrystalline silicon.  FIG. 1J  depicts a cap wafer  17  connected to spacing element  50  by anodic bonding. Movable sensor structures  27  do not come into contact with cap wafer  17  even if cap wafer  17  is unpatterned, since spacing element  50  and regions  8  have a height that is greater than the height of movable sensor structures  27 . In the exemplifying embodiment, cap wafer  17  rests both on spacing element  50  and on regions  8 . It is preferable to planarize cap wafer  17  proceeding from first side  6  of substrate material  2 , and to planarize substrate material  2  proceeding from a second side  9  of substrate material  2 . The planes to which planarization is to occur are indicated as B′, such that plane B′ of second side  9  of substrate material  2  extends into a plane of trench structure  3 . This advantageously makes possible back-side contacting of the completed micromechanical component  1 .  FIG. 1K  schematically depicts an embodiment of micromechanical component  1 .  FIG. 1L  schematically depicts another embodiment of micromechanical component  1 , in which cap wafer  17  has an add-on layer  25 , and a third insulating layer  15  was produced on second side  9  of substrate material  2 . Add-on layer  25  can be, for example, an insulator, but also an electrically conductive layer that optionally can be electrically contacted. An additional layer  10  is in contact with first filler layer  5  in trench structure  3 . Additional layer  10  is preferably an aluminum metallization. Also conceivable is a metallization that enables a flip-chip connection to other components.  FIG. 1M  schematically depicts an embodiment of a micromechanical component  1  to be produced without spacing element  50 . In this case, cap wafer  17  is connected via a connecting layer  23  to sensor structure  27 ′ and to regions  8 ; connecting layer  23  can be made, for example of seal glass. In this case as well, movable sensor structures  27  do not come into contact with the unpatterned cap wafer  17 .  FIG. 1N  depicts an embodiment of a micromechanical component  1  having a spacing element  50  and connecting layer  23 .  FIGS. 1O to 1T  depict an embodiment having contact pads  26 , contact pads  26  being applied on second filler layer  13  and being covered by a second insulating layer  15 . In combination with add-on layer  25 , a contact to cap wafer  17  is produced. In another alternative (not depicted), in principle no back-side contacting of the above-described micromechanical component  1  is necessary. It is likewise conceivable for cap wafer  17  to be patterned, for example, in the region of bonding pads in order to enable electrical contacting of micromechanical component  1  from first side  6 . In this case, however, cap wafer  17  need not be patterned in the region of movable sensor structures  27 , since connecting layer  23  (e.g. seal glass) ensures spacing between cap wafer  17  and movable sensor structures  27 . The partial patterning of cap wafer  17  just mentioned can be implemented both for cap wafers that are mounted on non-movable sensor structures  17  and for cap wafers that are mounted on spacing elements  50 .