Abstract:
A microstructured component includes at least: one chip having a microstructured area and a surface area, on which a nanostructured, self-organized coating is applied. The nanostructured, self-organized coating may be used as an antistick coating for repelling moisture or a surrounding molding material. Moreover, when using flip-chip and stack-chip technologies, an adhesive effect can be attained, so that additional joining areas can be dimensioned to be smaller.

Description:
BACKGROUND INFORMATION  
       [0001]     In this context, the microstructured component may, in particular, be a microelectronic or micromechanical component.  
         [0002]     Micromechanical sensors are distinguished by movable structures which are moved because of outer influences such as acceleration, rotational rates or pressure, these movements being converted into voltage signals or capacitance signals and subsequently evaluated.  
         [0003]     Accordingly, such components are also susceptible to mechanical disturbances which affect the component through the packaging. Particularly in automotive engineering with the wide temperature ranges and high climatic stresses occurring there, this sensitivity to mechanical stress often makes it difficult to use suitable modules with advantageous manufacturing methods, such as bonding techniques on the wafer level, etc., since in addition to the electronic properties of the component, the mechanical properties must also be kept stable over a wide temperature range and under the influence of moisture over long periods of time.  
         [0004]     In part, yaw-rate sensors are covered on their upper and lower sides with a gel in order to establish a defined boundary surface between chip and packaging and to intercept mechanical stress. For optical applications, particularly infrared applications for gas detection, penetration of gel into the optical structures can impair correct functioning considerably.  
       SUMMARY OF THE INVENTION  
       [0005]     The microstructured component according to the present invention and the method for producing it have the advantage, in particular, that the properties of the microstructured component may be adapted well to the specific requirements. In this context, coatings having water-repellent or dirt-repellent effect may be applied, in particular. The present invention is based on the surprising insight that self-organizing, nanostructured coatings can also be used in the field of microstructured components, i.e., particularly in the field of microelectronics and micromechanics for developing advantageous effects. Thus, advantageous properties can be achieved compared to the use of metal coatings or lacquers.  
         [0006]     According to the present invention, in particular, an antistick coating may be applied which, during the subsequent extrusion coating of the component into (in) a mold housing, forms a boundary layer, whereby it is possible to bring about a deliberate delamination of the chip or chips of the component from the molding material.  
         [0007]     Moreover, the placement of chips one upon the other can be facilitated by an improvement of the adhesion, e.g., by a mechanical toothing of the coated areas of the chips. In this manner, it is possible to improve bonding techniques of flip-chip technology, in which a direct joining and contacting of two chips with their patterned surfaces is formed, and chip-stack technologies, in which chip stacks are formed, so that additional interconnecting regions by adhesive polymers or sealing-glass interconnections may be smaller.  
         [0008]     The coatings may be applied, for example, by sol-gel processes or other processes. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  shows the process of coating a surface area of a component using a self-organizing nanostructure.  
         [0010]      FIG. 2  shows, in a) a sensor wafer in top view and side view, 
        b) the growth of the antistick coating on the sensor wafer, and     c) the sensor wafer with antistick coating.          
         [0013]      FIG. 3  shows side views of a sensor module with 
        a) antistick coating, and     b) antistick coating and molded housing.          
         [0016]      FIG. 4  shows a flip-chip process for producing a sensor module: 
        a) a sensor wafer and ASIC wafer in top view,     b) the sensor wafer and ASIC wafer after coating in side view,     c) the coated side of a sensor chip or ASIC chip, and     d) the chip arrangement prior to joining.         
     
    
     DETAILED DESCRIPTION  
       [0021]      FIGS. 1   a  through  1   d  describe a sol-gel process for producing self-organizing nanostructures. It is based on the networking of organic and/or inorganic molecules to form nanoscale powder or networked particles by the addition of energy.  
         [0022]     According to  FIG. 1   a , applied on a surface area  1  of a chip is a starting solution  2  having, for example, polymers, to which reaction accelerators  3  are fed. According to  FIG. 1   a , particles  4  thereby form in starting solution  2  which, according to  FIG. 1   b , increase in number and size and grow up to a critical size. According to  FIG. 1   c , the growth of particles  4  is stopped by a modification of the surface.  
         [0023]     The amount of the particle growth may be restricted, first of all, by a stability criterion that limits growth above a critical value. For instance, such a stability criterion may be the ratio of the energy stored in the particle to the surface tension. Moreover, the particle growth may be blocked by a growth inhibitor which alters the energy balance in the system. This may be achieved, for example, by a change in the surface tension, whereby the wetting of the surface with water or an aqueous solution is altered, as may be achieved, for instance, by the addition of rinsing agent or other agents lowering the surface tension.  
         [0024]     Particles  4  are subsequently networked by energy input, a networked surface structure  6  thereby being formed on surface area  1 .  
         [0025]      FIG. 2  describes the formation of self-organizing nanostructures as antistick coating, which may be used in particular on pressure sensors and mass flow sensors.  
         [0026]     Applied on a sensor-wafer surface  9  of a sensor wafer  10  is a mixture  12  of organic and inorganic components with a thickness of a few nanometers, e.g., less than or equal to 10 nm. By a self-organized growth of mixture  12 , an antistick coating  13 , shown in  FIG. 2   c , forms as a nanostructured surface area on sensor wafer surface  9 .  
         [0027]      FIG. 3  shows a practical application of the coating shown in  FIG. 2  in the case of a sensor module  15 . Sensor module  15  features a sensor chip  16  having a microstructured area  17  for measuring an acceleration, torques, rates of rotation or also, for example, infrared radiation for use in a gas detector. Secured on sensor chip  16  by a vacuum-tight joint  18 , e.g., sealing glass (low-melting, lead-containing glass), is a cap chip  19  in which a cavity  25 , surrounding the microstructured area, is formed or epitaxially deposited. Sensor chip  16  has bonding pads  20 , not covered by cap chip  19 , for the contacting of sensor module  15 .  
         [0028]     According to the present invention, nano-antistick coatings  23 ,  24  are applied according to the process described in  FIG. 2   a  through  2   c  on an outer surface  21  of cap chip  19  and a bottom side  22  of sensor chip  16 , as shown in  FIG. 3   a.    
         [0029]     According to  FIG. 3   b , after the contacting of bonding pads  20 , entire sensor module  15  is subsequently injected or molded into a mold housing  27  made of a plastic material or molding-compound material. In so doing, a defined boundary layer with delamination of the surfaces and the molding compound develops between antistick coatings  23 ,  24  and the molding material of mold housing  27 , which means any packaging stress, e.g., due to temperature changes, is no longer coupled into the active sensor structure in sensor module  15 .  
         [0030]     A use of self-organizing nanostructures for the preparation of boundary surfaces for subsequent assembly and joining techniques is described in  FIG. 4 . In this context, suitable topographies can be selectively represented that permit a robust joining in flip-chip or stacked-chip processes, in which two chips are placed one upon the other with their structured upper side, and a flip-chip module  37  having suitable contactings is thereby formed.  
         [0031]     According to  FIG. 4   a , a nanostructured surface  30  is formed according to the process of  FIGS. 1   a  through  1   d  on surface  9  of a sensor wafer  10  corresponding to  FIG. 2 . Moreover, a nanostructured coating  32  is formed on a surface of an ASIC wafer  31 . After bonding, sensor chips  34  and ASIC chips  35  are formed from wafers  10  and  31  by dicing. According to  FIG. 4   c , bonding pads  36  are formed on chips  34 ,  35  or at least on sensor chip  34 . In this context, bonding pads  36  may advantageously be left out from coatings  30 ,  32  by previous application of a lacquer.  
         [0032]     According to the present invention, a bonding technique or joining technique may already be carried out on the wafer level, i.e., sensor wafer  10  is placed on ASIC wafer  31  and secured, whereupon the individual sensor modules may subsequently be separated by sawing from the wafer stack thus formed. In this connection, adhesion is achieved between nanostructured coatings  30  and  32  of sensor chip  34  and ASIC chip  35 , e.g., by the toothing effect of the surface structures. This adhesion reduces the adhesion to be applied in the additional joining areas, so that the joining areas, formed, for example, as sealing-glass joints or also, for instance, as polymer joints, may be dimensioned to be smaller; for example, it is possible to provide only two or three joining points in addition to the adhesive effect of coatings  30 ,  32 .  
         [0033]     Bonding pads  36  themselves may also be coated, without impairing their electric conductivity, for example, by electrically conductive, nanostructured coatings  40  from SiC (silicon carbide) nano-crystallites for a sturdy joining.