Abstract:
A method for registering a plurality of substrates that are retained on a workpiece carrier onto an exposure mask for carrying out a photolithography process has the steps of registering and immobilizing the exposure mask onto an alignment panel having precisely fitting passthrough orifices for reception of one substrate for each passthrough orifice and inserting into the passthrough orifices of the alignment panel the substrates that are retained on the workpiece carrier.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method for registering a plurality of substrates that are retained on a workpiece carrier onto an exposure mask for carrying out a photolithography process. The present invention further relates to an exposure mask device for performing a photolithography process for a plurality of substrates that are retained on a workpiece carrier having an exposure mask.  
       BACKGROUND INFORMATION  
       [0002]     In contrast to semiconductor production of silicon wafers, which are processed individually, the manufacture of devices such as micromechanical sensors is accomplished using relatively small substrates. In this context, the base substrate is present in the form of a small cylindrical steel element. In order for the manufacturing process and for application of a circuit produced in thin-film technology onto such substrates to be cost-effective, the substrates are processed in multiple fashion. The individual base substrates are therefore retained in large numbers on a workpiece carrier, and processed together.  
         [0003]     High-pressure sensors that are utilized in many automotive engineering systems and in automation technology are fabricated on such substrates. Applications include, for example, direct fuel injection, common-rail technology for diesel vehicles, electrohydraulic brake systems, vehicle dynamics control systems, and many more.  
         [0004]     Pressure is sensed via the deflection of the sensor membrane, which is coated with a Wheatstone measurement bridge using thin-film technology. The circuit is patterned using a photolithographic manufacturing process. Contacting and passivation can also be performed using a production step of this kind. The quality of high-pressure sensors depends substantially on the accuracy with which the resistance features of the Wheatstone measurement bridge are positioned on the pressure membrane. The resistances must be centered as much as possible on the pressure membrane. This positional accuracy substantially influences the electrical properties of the measurement bridge, for example, the range of the signal furnished by the sensor.  
         [0005]     It is believed that the photolithographic process of patterning the functional layer to form the resistances is therefore essential in the production of a high-pressure sensor. A preconditioning of the surface of the functional layer, application of a photosensitive resist onto the functional layer, an oven step to condition the resist for exposure, exposure of the resist through an exposure mask, development of the exposed features, an oven step to condition the developed resist structure for etching, mapping of the resist image into the functional layer using an etching process, and subsequent stripping of the photoresist mask from the completed etched functional structure, are usually performed in this context.  
         [0006]     The location of the resistances may be determined in the exposure step. The substrates, previously diced and retained on a workpiece carrier, may then be exposed with sufficient positional accuracy relative to an exposure mask. In contrast to the exposure of silicon wafers in semiconductor production, in which the wafers can be registered as one piece with the exposure mask (e.g. a quartz mask) to be imaged, in the exposure of the previously diced plurality of substrates there may be a positional inaccuracy for each substrate with respect to the imaging exposure mask.  
         [0007]     It is believed that the substrates are often handled in immovably bolted-down workpiece carriers that must each be individually registered with respect to the exposure mask. This registration operation is performed manually.  
         [0008]     For example, in the projection exposure method of the Nagano Keiki Co. Ltd., a special workpiece carrier that is automatically positionable is provided in each case. This workpiece carrier is not identical for the subsequent processes.  
       SUMMARY OF THE INVENTION  
       [0009]     It is believed that the exemplary method of the present invention provides a method for registering a plurality of substrates that are retained on a workpiece carrier so as to make possible large-scale production of the structures with sufficient positional accuracy on the substrates, with no need to gang-switch over into an extra workpiece carrier.  
         [0010]     This is achieved by: 
        registering and immobilizing an exposure mask with respect to an alignment panel, the alignment panel having precisely fitting passthrough orifices for reception of one substrate for each passthrough orifice; and     inserting into the passthrough orifices of the alignment panel the substrates that are retained on the workpiece carrier.        
 
         [0013]     As a result of the use of an alignment panel having precisely fitting passthrough orifices into which the substrates are respectively inserted, only a single registration and immobilization of the exposure mask with respect to the alignment panel is performed. The workpiece carriers with the retained substrates can then, in the continuous production process, be moved in the direction of the alignment panel so that the substrates are inserted into the passthrough orifices and thereby automatically aligned.  
         [0014]     Manual operations to gang-switch the substrates from one workpiece carrier system into another are thus not needed. The workpiece carriers, populated with substrates, can now be processed entirely automatically and it is not necessary to register each populated workpiece carrier with respect to the exposure mask. Instead, the exposure mask is registered once with the alignment panel. In addition, only a single alignment panel is required for each exposure mask, and an alignment panel of this kind does not need to be placed onto each workpiece carrier that is to be exposed.  
         [0015]     Insertion of the substrates may be accomplished with helical motions, thus simplifying the threading-in of the substrates upon insertion into the passthrough orifices. Registration of the exposure mask onto the alignment panel may be accomplished using alignment marks that are provided on the exposure mask and in the alignment panel. The alignment marks may be positioned at mutually coordinated distances on the exposure mask and the alignment panel. They can be introduced upon manufacture of the exposure mask and alignment panel. It is also possible to introduce small inserted parts into the alignment panel as alignment marks. Registration may then be accomplished by automatic optical detection of the alignment marks.  
         [0016]     This may also be achieved, by way of an alignment panel having precisely fitting passthrough orifices for reception of one substrate for each passthrough orifice, and an arrangement for registering and immobilizing the exposure mask and alignment panel with respect to one another.  
         [0017]     It is believed to be particularly advantageous if the alignment panel has a vacuum conduit for pulling and immobilizing the alignment panel by suction onto the exposure mask device. The vacuum conduit may then extend in the rim region along the outer edge of the alignment panel. By the extraction of air, e.g., through a orifice in the exposure mask device, a vacuum is then generated in the vacuum conduit and the exposure mask device and alignment panel are joined to one another. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  shows a photolithographic process for producing thin-film structures according to an exemplary embodiment of the present invention.  
         [0019]      FIG. 2  is a cross-sectional view of an exposure mask device having an alignment panel and an oppositely located workpiece carrier having retained substrates.  
         [0020]      FIG. 3  shows the exposure mask device of  FIG. 2  shown with substrates that are inserted into the passthrough orifices of the alignment panel.  
         [0021]      FIG. 4  is a cross-sectional view of an alignment panel for the exposure mask device shown in  FIG. 2  and  FIG. 3  according to an embodiment of the present invention.  
         [0022]      FIG. 5  is a plan view of the alignment panel shown in  FIG. 4 .  
         [0023]      FIG. 6  is a cross-sectional view of a portion of the alignment panel shown in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION  
       [0024]      FIG. 1  shows an embodiment of a photolithographic process for manufacturing thin-film structures according to the present invention.  
         [0025]     In a first step a), a photoresist layer  1  is applied onto functional layer  2  of the substrate that is to be patterned. Functional layer  2  is located on an insulating layer  4 .  
         [0026]     In a second step b), an exposure mask  5  is registered onto substrate  3 , and photoresist layer  1  is irradiated with ultraviolet light. Exposed regions  6  of photoresist layer  1  form the desired pattern.  
         [0027]     In a third step c), the exposed photoresist layer  1  is developed so that photoresist layer  1  is removed in exposed regions  6 .  
         [0028]     In a fourth step d), the surface of substrate  3  is etched so that functional layer  2  is removed in exposed regions  6 .  
         [0029]     In a fifth step e), photoresist layer  1  is washed off so that a patterned functional layer  2  now remains.  
         [0030]      FIG. 2  shows, in cross section, an exposure mask device  7  for a photolithographic process of this kind. A plurality of substrates  3  are retained on a workpiece carrier  8 . Workpiece carrier  8  is mounted on a processing chuck  9  of exposure mask device  7  that is displaceable in the Z direction (arrow).  
         [0031]     Positioned opposite processing chuck  9  with workpiece carrier  8  is a holding frame  10  for holding exposure mask  5 , in particular a quartz mask. According to the present invention, an alignment panel  12  that is registered relative to exposure mask  11  may be secured on exposure mask  5 . Alignment panel  12  has a plurality of passthrough orifices  13 , each for reception of one substrate  3 . Passthrough orifices  13  fit precisely so that substrates  3  are optimally registered with exposure mask  5  when the latter is inserted into passthrough orifices  13  and alignment panel  12  is optimally registered with exposure mask  5 .  
         [0032]     A vacuum conduit  14  is provided in the rim region along the outer edge of alignment panel  12  in order to pull the alignment panel  12  into the exposure mask  5  by suction and to immobilize it. A corresponding peripheral vacuum conduit  15  is included in holding frame  10 . A orifice  16  in exposure mask  5  ensures the passage of vacuum from vacuum conduit  15  of holding frame  10  into vacuum conduit  14  of alignment panel  12 .  
         [0033]      FIG. 3  illustrates exposure mask  7  of  FIG. 2 , in which the processing chuck  9  is moved in the Z direction toward holding frame  10 . Substrates  3  are optimally aligned and fit precisely into passthrough orifices  13  of alignment panel  12 , and are thereby registered onto exposure mask  5 . In this position, exposure can now be performed, e.g., by UV radiation.  
         [0034]      FIG. 4  illustrates alignment panel  12  in cross section. As shown, passthrough orifices  3  have a bevel on the side of alignment panel  12 , facing toward workpiece carrier  8 , from which substrates  3  are introduced. The free play of substrates  3  in the Z axis upon introduction is thereby reduced. Registration of substrates  3  upon introduction into the precisely fitting passthrough orifices  13  may be accomplished with helical motions of workpiece carrier  8 , so that substrates  3  are guided into the optimum position.  
         [0035]     Additionally, alignment panel  12  has alignment marks  15  that can be implemented in the form of orifices, with which alignment panel  12  can be optically registered onto exposure mask  5 . Alignment marks (not depicted) are likewise provided in the corresponding positions on exposure mask  5 .  
         [0036]      FIG. 5  depicts alignment panel  12  in a plan view. As shown, a plurality of passthrough orifices  13  are introduced into alignment panel  12 . These are disposed in accordance with the associated exposure mask  5 .  
         [0037]     A peripheral vacuum conduit  14  extends in the rim region along the outer edge of alignment panel  12  in order to immobilize alignment panel  12  against an exposure mask  5  by suction. Provided in vacuum conduit  14  is an enlargement  17  that ends up located exactly beneath orifice  16  of exposure mask  5 , in order to ensure feedthrough of vacuum to holding frame  10 .  
         [0038]     Two alignment marks  18  are also provided on alignment panel  12  in order to register alignment panel  12  optically onto exposure mask  5 .  
         [0039]      FIG. 6  illustrates a portion of alignment panel  12  in cross section. Passthrough orifices  13  each have a bevel, so that substrates  3  can be threaded into the precisely fitting passthrough orifice  13  without mechanical damage. Alignment mark  15 , implemented as an orifice, is also shown.  
         [0040]     Alignment panel  12  furthermore has a shoulder  19  between the rim region and the region of passthrough orifices  13 . This shoulder  19  ensures that a defined spacing, useful for protecting the structures of exposure mask  5 , exists between the patterned region of exposure mask  5  and alignment panel  12  with substrates  3 .