Abstract:
In the manufacture of at least one passage in a silicon wafer, in a first method step, starting from a first side of the wafer, a first recess is produced in the wafer, and in a second method step, starting from a second side of the wafer, a second recess is produced in the wafer. The first recess and the second recess are produced such that together they form a passage between the first and second sides of the silicon wafer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to Application No. 10 2005 050 782.4, filed in the Federal Republic of Germany on Oct. 24, 2005, which is expressly incorporated herein in its entirety by reference thereto.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a micronozzle plate and a method for manufacturing a micronozzle plate.  
       BACKGROUND INFORMATION  
       [0003]     Different silicon-based or silicon glass-based micromechanically manufactured structures are believed to be conventional for atomizing liquids into droplets of an inhalable size (˜5 μm) in medical applications. The droplet mist may be obtained, for example, by creating a chamber which is delimited by a piezoelectrically driven diaphragm on one side and by a micronozzle plate on the other side. The chamber volume is reduced and thus a liquid in the chamber is expelled through nozzle openings in the micronozzle plate by operating the piezoelectrically driven diaphragm. The liquid is atomized in the process. Droplets of definite size may be produced via a suitable selection of nozzle geometry, chamber geometry, and piezoelectric excitation.  
         [0004]     For manufacturing a micronozzle plate from silicon, a method is described in German Published Patent Application No. 10 2004 050 051, in which defined nozzle openings are produced in a diaphragm manufactured by KOH etching, using the silicon DRIE (Deep Reactive Ion Etch) method with the aid of high-rate anisotropic etching.  
       SUMMARY  
       [0005]     The present invention relates to a micronozzle plate and a method for manufacturing a micronozzle plate.  
         [0006]     Oxidic nozzle structures may be produced using the method described herein. A partial oxidation of structures produced by trenching may be provided. For this purpose, areas not to be oxidized may be covered using nitride masking of the structure surfaces during the oxidation process. Subsequently structures may be hollowed via sacrificial layer etching of their cores made of semiconductor material such as Si 1-x Ge x  and micronozzles may thus be obtained.  
         [0007]     The second wafer side may be structured, e.g., by introducing a back cavity via KOH etching or another suitable etching method. The wafer may thus be eroded to the desired thickness in the area of the micronozzles.  
         [0008]     The oxidic structures may be used as either a positive mold or a negative mold for further structuring.  
         [0009]     Using the method described herein, it is possible to produce oxidic micronozzle structures having properties that were not manufacturable previously. Homogeneously thin-walled structures may be created over the entire height of the nozzles. The structures may have a high aspect ratio and a high degree of freedom in selecting the vertical and horizontal cross-sections over the nozzle channel depth is thus made possible.  
         [0010]     The micronozzle plate also has a number of advantages. The nozzle walls are oxidic. The nozzle walls may have a homogeneous wall thickness over the entire nozzle channel height. The arrangement of the nozzles may allow a high degree of freedom in selecting the vertical and horizontal cross-sections. This may result in a high degree of design freedom in optimizing the microfluidic properties. For example, it is possible to manufacture the micronozzle plate with nozzle structures having a high aspect ratio. The atomizing jet characteristic may be influenceable via the selected nozzle profile.  
         [0011]     Exemplary embodiments of the present invention are described in more detail below with reference to the appended Figures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  illustrates a masked semiconductor substrate.  
         [0013]      FIG. 2  illustrates the premolding of micronozzles by trenching.  
         [0014]      FIG. 3  illustrates the molding of micronozzles made of oxide.  FIG. 4  illustrates the exposure of the micronozzles made of oxide and schematically the micronozzle plate according to an example embodiment of the present invention.  
         [0015]      FIG. 5  illustrates a method according to an example embodiment of the present invention for manufacturing a micronozzle plate. 
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  illustrates a masked semiconductor substrate. To manufacture a micronozzle plate, a semiconductor substrate  100  is initially provided. Semiconductor substrate  100  may be made of silicon, germanium or a Si 1-x Ge x  compound (0≦x≦1).  
         [0017]     A first mask, e.g., a nitride layer  110 , is deposited on semiconductor substrate  100  as the later oxidation mask, e.g., in an LPCVD (Low-Pressure Chemical Vapor Deposition) process. Subsequently this nitride layer  110  is structured on a first side of semiconductor substrate  100  such that it is only preserved in the area of the later micronozzles, i.e., of a later first recess.  
         [0018]     Subsequently a second mask, e.g., a trench mask  120 , is applied to the first side of semiconductor substrate  100  and on nitride layer  110 . Trench mask  120  may be either a silicon oxide layer or also a pure varnish mask. The area of trench mask  120  above nitride layer  110  is structured, so that the outlines of the later micronozzles are established. For this purpose, the trench mask is removed in this area around the later micronozzles down to nitride layer  110 .  
         [0019]     The state of the wafer after structuring trench mask  120  is illustrated in  FIG. 1 .  FIG. 1  also illustrates a sectional view and the top view onto the area of a later micronozzle for this purpose.  
         [0020]      FIG. 2  illustrates the premolding of micronozzles by trenching. For this purpose, the contours of the later micronozzles are produced using a trench process  200 , e.g., a DRIE process or a Bosch process, directed to the first side of the masked semiconductor substrate. As an option, the remaining nitride layer  110  may be initially structured separately by removing the exposed areas of nitride layer  110  not protected by trench mask  120  arranged thereon. As a result of trench process  200 , trenches are produced on the first side of the wafer to a certain depth of semiconductor substrate  100 , and a first recess  210  is obtained in which columns  220  are arranged as premolds of micronozzles.  FIG. 2  again illustrates a sectional view of the wafer and a top view onto the area of a later micronozzle for this purpose. As illustrated, the columns include, in a layered structure, semiconductor substrate  100  on the bottom, nitride layer  110  thereon, and trench mask  120  thereon.  
         [0021]      FIG. 3  illustrates the molding of micronozzles made of oxide. For this purpose, the wafer from  FIG. 2  is subjected to a plurality of consecutive process steps. First, trench mask  120  is removed  300 . Trench mask  120  is removed  300 , for example, by gas phase etching or a BOE (Buffered Oxide Etch) process if trench mask  120  is an oxide mask, or by devarnishing, for example in oxygen plasma, if trench mask  120  is a varnish mask. Thereafter the wafer is thermally oxidized  350 , and a thermal oxide layer  352  is formed by surface oxidation of the accessible Si 1-x Ge x  areas of semiconductor substrate  100 . The remaining nitride layer  110 , which represents nitride covers on the raised structures or columns, has the role of an oxidation mask. Remaining nitride layer  110  determines inaccessible areas, e.g., on the top of the columns, and thus prevents thermal oxidation on their surfaces. As a result, the walls of the micronozzles are also manufactured from the accessible surfaces of the columns.  
         [0022]     Optionally, a second side of semiconductor substrate  100 , opposite the first side, may now be structured. For this purpose, the nitride on the back is masked and opened with the aid of an etching step. The exposed area of semiconductor substrate  100  is subsequently etched on the second side of the wafer using KOH wet etching or another suitable etching process. As a result of this etching  360 , a recess  390  is obtained in semiconductor substrate  100 . Recess  390  on the second side is arranged opposite the area of the later micronozzles on the first side. The mask is finally removed. The intermediary state achieved is illustrated in  FIG. 3 .  
         [0023]      FIG. 4  illustrates the exposure of the micronozzles made of oxide and schematically the micronozzle plate. For this purpose, remaining silicon nitride  110  is removed from the front of the wafer in a dry etch process, for example. The entire surface of the wafer is covered with thermal oxide on the first side except the surfaces of the raised structures previously covered by nitride, where semiconductor substrate  100  is exposed and forms a sacrificial layer for the subsequent process step. The remaining solid residual silicon core is etched out of the columns using selective etching  400  of the semiconductor substrate  100  against thermal oxide  352 . This may take place, for example, in a dry etching process using CIF 3 . While silicon is removed by etching  400 , thermal oxide  352  remains unaffected. As a result, a passage  410  and thus an access from the first side to the opposite second side of semiconductor substrate  100  is created. Hollow structures representing micronozzles  420  made of oxide remain on passage  410  made of a homogeneously thick oxide, e.g., thermal oxide  352 . The micronozzle plate illustrated schematically is thus created.  
         [0024]     Optionally, any further layers may be subsequently deposited. The oxide walls are thereby reinforced or used as a negative mold for further structuring.  
         [0025]      FIG. 5  schematically illustrates a method according to an example embodiment of the present invention for manufacturing a micronozzle plate including: (A) applying a first mask  110  on a first side of a semiconductor substrate  100 ; (B)applying a second mask  120  on first mask  110  and semiconductor substrate  100 ; (C) trench etching  200  of semiconductor substrate  100  through second mask  120  to a certain depth;, (D) removing  300  of second mask  120 ; (E) thermal oxidation  350  of semiconductor substrate  100  through first mask  110  and thus forming a thermal oxide  352  on the first side; (F) removing first mask  110  from semiconductor substrate  100 ; (G) etching  400  of semiconductor substrate  100  selectively with respect to thermal oxide  352  from the first side to an opposite second side and thus exposing micronozzles  420 .  
         [0026]     Semiconductor substrate  100  and first mask  110  may be trench etched  200  through second mask  120 .  
         [0027]     A recess  390  may be etched  360  on the second side to make semiconductor substrate  100  thinner in the area of micronozzles  420 . Etching step  360  of recess  390  may take place after manufacturing step (A) at any point in the overall manufacturing process.  
         [0028]     The exemplary embodiments described above may be combined in any desired manner.