Abstract:
A method for the production of a contact structure of a semiconductor component comprises the masking of at least one side of a semiconductor substrate with a coating and the partial removal thereof in at least one pre-determined region.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for the production of a contact structure of a semiconductor component. The invention further relates to an intermediate product in the production of a semiconductor component. 
     2. Background Art 
     Semiconductor components, in particular solar cells, comprise contact structures. These contact structures have a significant influence on the quality, in particular the efficiency, of the solar cells. A conventional method for applying the contact structures comprises the application of a mask by means of a spin-on or a spray-on method, the mask then being structured by means of a photolithographic process. These methods are very laborious and expensive, making it difficult for them to be implemented economically in the mass production of solar cells. 
     SUMMARY OF THE INVENTION 
     Therefore, it is the object of the invention to simplify a production method for contact structures of semiconductor components. Furthermore, it is the object of the invention to provide a semiconductor component comprising an economically producible contact structure. 
     This object is achieved by a method for the production of a contact structure of a semiconductor component, the method comprising the steps of providing a two-dimensional semiconductor component comprising a first side and a second side which is opposite to said first side, and masking at least one of the sides by coating at least one of the sides with a coating and partially removing the coating in at least one predetermined region. 
     This object is further achieved by an intermediate product in the production of a semiconductor component, the intermediate product comprising a two-dimensional semiconductor substrate comprising a first side and a second side which is opposite to said first side, and a mask which is applied to the semiconductor substrate and comprises openings which pass through the entire mask and are laterally bounded by steep flanks. 
     The gist of the invention is to provide a semiconductor substrate with a masking. The mask is advantageously produced by immersing the semi-conductor substrate into a resist solution which is then structured by means of laser ablation. A method of this type is simple and economical. Furthermore, a high accuracy is achieved. 
     Features and details of the invention will become apparent from the description of an embodiment by means of the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a semiconductor substrate after application of a dielectric layer and a resist layer; 
         FIG. 2  shows the semiconductor substrate according to  FIG. 1  after partially removing the resist layer; 
         FIG. 3  shows the semiconductor substrate according to  FIG. 2  after opening of the dielectric layer; and 
         FIG. 4  shows the semiconductor substrate according to  FIG. 3  after a metallization. 
     
    
    
     The Figures are only diagrammatic illustrations, in other words they are not to scale. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following is a description of a first embodiment of the invention with reference to  FIGS. 1 to 4 . A semiconductor component  1  initially comprises a flat, in other words two-dimensional, semiconductor substrate  2  with a front side  3  and a back side  4  which is arranged opposite thereto. The semiconductor component  1  is in particular a solar cell. The semiconductor component  2  consists of a semiconductor material, in particular of silicon. Other semiconductor materials are however conceivable as well. In a first step, a passivation layer  5  is applied to the front side  3  of the semiconductor substrate  2 , the passivation layer  5  also serving as an antireflection layer. The passivation layer  5  consists of a dielectric material, in other words it is electrically insulating. The passivation layer  5  advantageously consists of silicon nitride or silicon dioxide. It has a thickness of preferably less than 200 nm, in particular less than 100 nm. 
     The semiconductor substrate  2  is then provided with a coating  6 . The coating  6  is provided both on the front side  3  and on the back side  4 . It covers in particular the entire passivation layer  5 . It is of course conceivable as well for the coating  6  to be applied to only one of the sides  3 ,  4 . The coating is in particular a resist layer. It is applied by immersing the semiconductor substrate  2  into a resist solution. The process is thus referred to as dip coating. As a result, a thin resist layer is applied to both sides  3 ,  4  of the semiconductor substrate  2  when the semiconductor substrate  2  is immersed into the resist. The resist is resistant to subsequent etching and/or electrolyte baths. 
     The resist typically comprises an epoxy resin which is dissolved in organic solvents. After coating, the resist is allowed to dry at a temperature between 25° C. and 120° C., in particular at 100° C. At 150-160° C., an optional cross-linking step can be performed for curing the resist. The resist layer has a thickness in the range of 1-50 μm, in particular 5 to 15 μm. 
     A mask  7  is then produced by removing the coating  6  in predetermined regions. This is performed by means of a laser process, in particular a laser ablation. A method of this type allows openings  8  to be produced in the coating  6  with high accuracy. The openings  8  have a width B in the range of 1 μm to 100 μm, in particular in the range of up to 20 μm, in particular in the range of up to 10 μm. The openings  8  are in the shape of a channel. The accuracy of the arrangement and the dimensions of the openings  8  which is achievable by means of the laser process according to the invention is better than 5 μm, in particular better than 2 μm, in particular better than 1 μm. The openings  8  are laterally bounded by steep flanks  9 . The flanks  9  form an angle b of 70° -100°, in particular 80° -90° with the side  3  of the semiconductor substrate  2  disposed therebelow. 
     Advantageously, a liquid-jet guided laser is provided for laser ablation. The liquid jet may contain dopants such as phosphorous, boron, arsenic, antimony or compounds thereof. In a particular advantageous embodiment, the passivation layer  5  is opened as well when the coating  6  is partially removed by means of the laser process. This allows the semiconductor susbtrate  2  to be doped in the opened regions with the dopants contained in the liquid jet. Furthermore, the laser ablation process also allows a thin surface layer of the semiconductor substrate  2  to be removed. 
     Alternatively, the passivation layer  5  may also be opened in the region of the openings  8 , which are not covered by the mask  7 , by means of a wet chemical etching process instead of the laser process. 
     After opening the passivation layer  5 , the front side  3  of the semiconductor substrate  2  is exposed. At least one metal layer  10  is then deposited into the openings  8  so as to form a contact structure. The contact structure is advantageously comprised of several layers. Deposition of the metal layer  10  can be performed by means of a chemical and/or a galvanic process. The mask  7 , in particular the lateral flanks  9  thereof, prevents the contact structure from widening. The mask  7  has a thickness D in the range of 1 μm to 50 μm, in particular of 5 to 15 μm. 
     A detailed description of the contact structure and the deposition thereof in the openings  8  can be found in DE 10 2007 038 744. The contact structure advantageously comprises a barrier layer, a conductive layer arranged on said barrier layer and a cover layer arranged on said conductive layer. The barrier layer consists of a material, in particular a metal, which has a negligible diffusion coefficient and a negligible miscibility with respect to the material of the semiconductor substrate  2  and the conductive layer. The barrier layer in particular consists of electrolytically or chemically deposited nickel or cobalt. The barrier layer has high electrical conductivity. The barrier layer may in particular consist of copper. It may also comprise at least a proportion of silver. The cover layer advantageously consists of tin and/or silver and/or nickel. The cover layer is anti-corrosive. 
     In a final step, the mask  7  is stripped, in other words removed. 
     Applying the mask  7  and the metal layer  10  is of course not limited to the front side  3  of the semiconductor substrate  2 . It may also be applied to the back side  4  of the semiconductor substrate  2  or to both sides thereof.