Abstract:
An arrangement for applying metal nanoparticles onto a wafer or another substrate, is characterized by a metal or semiconductor part arranged in a liquid reservoir, laser or particle emitter for removing nanoparticles from the metal or semiconductor part in the liquid inside the liquid reservoir, and means for applying the removed metal particle containing liquid onto the substrate.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This patent application is filed herewith for the U.S. National Stage under 35 U.S.C. §371 and claims priority to PCT application PCT/EP2015/051701, with an international filing date of Jan. 28, 2015. The contents of this application are incorporated in their entirety herein. 
     
    
     STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       TECHNICAL FIELD 
       [0003]    The invention relates to an assembly for placing nanoparticles of metal or semiconductor material on a wafer or any other substrate. 
       BACKGROUND OF THE INVENTION 
       [0004]    In photolithography, metallic nanoparticles are placed on a substrate to form seeds. Metallic conductor paths can grow at such seeds if further metallic material is added. There are various methods for placing metallic nanoparticles. A common method is vapor deposition. 
         [0005]    Typically, metals having special properties are used. Such metals are, amongst others, gold, palladium, copper, aluminum, nickel, silver and tin. The metals are expensive and more or less poisonous. Upon vapor deposition of such metals there is a risk of loss of material. Also, there is a risk that the metals are breathed in or contacted to the skin of persons which get into contact with the metals. Consequently, there is a risk to human health. 
         [0006]    From DE 10 2010 018 073 A1, DE 10 2010 055 404 A1, and JP 2006 612 2845, laser ablation in liquids is known. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    It is an object of the invention to provide an assembly for placing nanoparticles of metal on a wafer or any other substrate of the above-mentioned kind, where practically no metallic material is lost and the health risk is reduced. 
         [0008]    According to the present invention, this object is achieved by:
       (a) a metal- or semiconductor piece present in a liquid reservoir;   (b) a laser for removing nanoparticles from the metal- or semiconductor piece inside the liquid in the liquid reservoir; and   (c) means for placing the liquid comprising the metal particles on the substrate.       
 
         [0012]    With such an assembly the nanoparticles of a metal- or semiconductor piece inside the liquid are removed by a laser or particle emitter. Consequently, they cannot freely fly around and be lost. There are no poisonous metal vapors. The material consumption is low. The nanoparticles remain in the liquid and are deposited together with the liquid on the substrate. 
         [0013]    According to a preferred modification of the invention the liquid is a curable polymer or any other curable plastic material. An example of a suitable polymer is an epoxide compound or benzocyclobutene. Such materials are photo-sensitive materials for the use in photolithography. They can easily be removed by etching. Positive illumination is possible as well as negative exposure. The polymer not only ensures that the metal particles will not bounce off the substrate surface upon placement but ensure a good adhesion for subsequently added components. 
         [0014]    Preferably, the metal is gold, silver, copper, palladium, aluminum, nickel, tin, an alloy of such metals, or a silicon based semiconductor. Such metals are good conductors and are, therefore, particularly suitable for the use in manufacturing semiconductor products, such as wafers or other substrates. It is understood, however, that other metals may also be used if this is required by the particular application. 
         [0015]    Preferably, the assembly is provided with flow generating means for generating a liquid flow in the range where the nanoparticles are removed from the metal- or semiconductor pieces. The flow generating means may be a pump. The flow generating means may, however, also comprise an ultrasound hammer pressing the liquid through a passage with a reduced diameter. The flow generating means ensures that the nanoparticle content in the liquid is evenly distributed with the same laser beam. 
         [0016]    In a further modification of the present invention, a jet is provided for placing the liquid comprising the nanoparticles on the substrate. The jet may be used to apply the liquid evenly thin and well-aimed on the substrate. 
         [0017]    In a particularly preferred embodiment of the invention, the metal- or semiconductor pieces are positioned in the range before the jet. The nanoparticles are, therefore, directly flowed through the jet after removing them from the metal- or semiconductor piece and deposited on the substrate. They cannot settle or accumulate inside the assembly. 
         [0018]    In a further modification of the invention the jet is an integrated part of a closed reservoir, wherein the reservoir is provided with a liquid inlet where pressurized liquid enters into the reservoir. The reservoir may be closed by a glass plate or another transparent cover on the side of the laser. The laser light enters the reservoir through the cover. Since the liquid is only very little compressible, each pressure exerted on the liquid will cause liquid to exit through the jet. 
         [0019]    Further modifications of the present invention are subject matter of the sub-claims. Embodiments are described below in greater detail with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0020]      FIG. 1  is a schematic view of a first embodiment; and 
           [0021]      FIG. 2  is a schematic view of a second embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIG. 1  is a schematic view of an assembly for the generation of metallic nanoparticles. The assembly is provided with a reservoir  2  with a liquid polymer, such as, for example an epoxide compound, designated with numeral  1 . A sensor provided at the reservoir  2  for detecting the polymer density is designated with numeral  20 . The polymer mass is moved by a pump  17  in the direction of the arrows through a pipeline  18 . The pipeline  18  extends to a chamber  14 . A metal- or semiconductor piece  8  is placed at the bottom of the chamber  14 . Depending on the application the metal- or semiconductor piece  8  consists of gold (Au), silver (Ag), copper (Cu), palladium (Pd), aluminum (Al), nickel (Ni), tin (Sn) or an alloy of such metals. Furthermore, it is possible to use a silicon-based semiconductor material. The surface of the metal- or semiconductor piece  8  is surrounded by the polymer. The upper side of the chamber  14  is closed by a glass plate. A laser with a scanning system  13  is arranged above the chamber  14 . The laser beam  12  is directed through the glass plate of the chamber  14  onto the metal- or semiconductor piece  8 . Metal particles (nanoparticles) are ablated from the surface of the metal- or semiconductor piece  8 . The nanoparticles ablated by such ablation process are accommodated by the polymer liquid. 
         [0023]    The chamber  14  has a reduced thickness in the range of the laser beam  12 . Thereby, it is achieved on one hand, that the laser beam  12  is absorbed by the polymer only by a little. On the other hand an increased flow velocity is achieved. Ablated metal particles may, therefore, not settle or accumulate. 
         [0024]    The polymer liquid accommodating the ablated particles is flowed through an outlet pipe  16  to a second reservoir  22  by the pump. The polymer with the nanoparticles  21  is collected in the second reservoir and is available there for further use. A sensor  19  in the reservoir  22  detects the density of the nanoparticles in the reservoir. 
         [0025]    The polymer liquid with the nanoparticles from the reservoir  22  may, for example, be used for re-wiring of wafer- and substrate surfaces. In this embodiment the polymer liquid with the nanoparticles may, for example, be applied to the substrate by spin coating. The material may be structured photolithographically with a mask afterwards. Cured polymer in the gaps in the structure may be removed in the usual way by edging or washing. In such a way very fine structures are achieved. 
         [0026]      FIG. 2  shows an assembly, where the polymer liquid is directly applied to a substrate. Polymer liquid  10  is present in a reservoir  200 . An outlet is provided at the lower end of the reservoir  200 . The outlet extends into an elongated chamber  40 . A hammer  50  sits in the chamber  40 . The hammer  50  is moved back and forth in the direction of arrow  52  by means of an ultrasound generator  30 . The chamber  40  is connected to a chamber  150  by a narrow channel  60 . The chamber  150  conically narrows towards the lower end. A capillary or a jet  100  is integrated thereto. A substrate  110  is positioned below the jet  100 . The substrate  110  or the jet  100  or both are adapted to be moved whereby material exiting the jet will be applied to the substrate at the desired spot. 
         [0027]    Metal- or semiconductor pieces  80  are arranged in the conical lower range of the chamber  150 . The chamber  150  is closed by a glass plate  140  at the upper end. Laser light may be moved with a quick scanner, based, for example, on an acousto-optic modulator  130  in the direction of the arrows  132  in an x- and y-direction. The laser light passes through the glass plate  140  and the polymer  150  towards the metal- or semiconductor pieces  80 . There, the nanoparticles  90  are ablated by means of laser ablation. The ablated nanoparticles  90  are accommodated by the polymer. If the hammer  50  moves towards the left in the drawing fresh polymer without any nanoparticles is pressed through the channel  60 . Thereby, a pressure is generated in the chamber  150 . Polymer liquid with nanoparticles  90  is ejected towards the outside through the jet  100  in the form of a drop  220  and applied to the substrate  110 . The polymer applied to the substrate  110  finally cures. This embodiment has the advantage that conductive paths may be produced without a mask and photolithographic methods. The nanoparticles with the polymer are directly on the substrate. 
         [0028]    The above-described assembly was described in great detail. It is understood, however, that this shall not be limiting the scope of the patent which is determined solely by the claims. Many alternatives and equivalent means are known to the person skilled in the art which may be used without deviating from the basic idea of the invention. In particular, the geometric set-up of the assembly, materials, diameters and amounts may vary without deviating from the basic idea of the invention.