Microfabricated structures and processes for manufacturing same

Abstract

Various techniques for the fabrication of highly accurate master molds with precisely defined microstructures for use in plastic replication using injection molding, hot embossing, or casting techniques are disclosed herein. Three different fabrication processes used for master mold fabrication are disclosed wherein one of the processes is a combination of the other two processes. In an embodiment of the first process, a two-step electroplating approach is used wherein one of the metals forms the microstructures and the second metal is used as a sacrificial support layer. Following electroplating, the exact height of the microstructures is defined using a chemical mechanical polishing process. In an embodiment of the second process, a modified electroforming process is used for master mold fabrication. The specific modifications include the use of Nickel-Iron (80:20) as a structural component of the master mold, and the use of a higher saccharin concentration in the electroplating bath to reduce tensile stress during plating and electroforming on the top as well as sides of the dummy substrate to prevent peel off of the electroform. The electroforming process is also well suited towards the fabrication of microstructures with non-rectangular cross sectional profiles. Also disclosed is an embodiment of a simple fabrication process using direct deposition of a curable liquid molding material combined with the electroforming process. Finally, an embodiment of a third fabrication process combines the meritorious features of the first two approaches and is used to fabricate a master mold using a combination of the two-step electroplating plus chemical mechanical polishing approach and the electroforming approach to fabricate highly accurate master molds with precisely defined microstructures. The microstructures are an integral part of the master mold and hence the master mold is more robust and well suited for high volume production of plastic MEMS devices through replication techniques such as injection molding.

1 . A method to generate a master mold used for micro-fabricating plastic substrates, said method comprising: 
 depositing a micro-structure pattern of photo-resist onto a substrate;    over-plating a first metal onto said pattern to generate a plurality of metal micro-structures;    removing said pattern of photo-resist from said substrate; and    over-plating a second metal onto said substrate and said plurality of metal micro-structures.    
     
     
         2 . The method of  claim 1  further comprising lapping said second metal and said plurality of metal micro-structures to create a planar surface.  
     
     
         3 . The method of  claim 2  further comprising removing said second metal from said substrate and said plurality of metal micro-structures, leaving said master mold comprising said substrate and said plurality of metal micro-structures.  
     
     
         4 . The method of  claim 1  wherein said substrate comprises nickel.  
     
     
         5 . The method of  claim 1  wherein said first metal comprises nickel.  
     
     
         6 . The method of  claim 1  wherein said first metal comprises an alloy of nickel and iron.  
     
     
         7 . The method of  claim 1  wherein said second metal comprises copper.  
     
     
         8 . The method of  claim 1  wherein said depositing said micro-structure pattern of said photo-resist comprises performing a photolithography process.  
     
     
         9 . The method of  claim 1  wherein said over-plating said first metal comprises performing an electroplating process such that said first metal is electroplated past a height of said photo-resist.  
     
     
         10 . The method of  claim 1  wherein said removing said pattern of said photo-resist comprises performing a stripping process using a remover solution.  
     
     
         11 . The method of  claim 1  wherein said over-plating said second metal comprises performing an electroplating process such that said second metal is electroplated past a height of said plurality of metal micro-structures.  
     
     
         12 . The method of  claim 2  wherein said lapping comprises performing a chemical-mechanical polishing process.  
     
     
         13 . The method of  claim 3  wherein said removing said second metal comprises performing an etching process.  
     
     
         14 . A method to generate a master mold used for micro-fabricating plastic substrates, said method comprising: 
 generating a micro-structure pattern on a substrate;    heating said micro-structure pattern to form a pattern of at least one quasi-semi-spherical feature on said substrate;    coating said substrate and said pattern of at least one quasi-semi-spherical feature with a seed layer; and    depositing a metal layer onto said seed layer.    
     
     
         15 . The method of  claim 14  further comprising polishing a back of said metal layer to form a planar surface.  
     
     
         16 . The method of  claim 15  further comprising removing said substrate from said metal layer, said seed layer, and said at least one quasi-semi-spherical feature.  
     
     
         17 . The method of  claim 16  further comprising removing said seed layer to leave only said polished metal layer as said master mold.  
     
     
         18 . The method of  claim 14  wherein generating said micro-structure pattern is accomplished using a photo-resist and photolithography techniques.  
     
     
         19 . The method of  claim 14  wherein said micro-structure pattern comprises photoresist.  
     
     
         20 . The method of  claim 14  wherein said substrate comprises one of silicon, glass, ceramic, plastic, and metal.  
     
     
         21 . The method of  claim 14  wherein said metal layer comprises an alloy of Nickel and Iron.  
     
     
         22 . The method of  claim 14  wherein said step of depositing a metal layer comprises an electroplating step.  
     
     
         23 . The method of  claim 16  wherein said substrate is removed using a chemical-mechanical polishing technique.  
     
     
         24 . The method of  claim 17  wherein said seed layer is removed using an etching technique.  
     
     
         25 . A method to generate a master mold used for micro-fabricating plastic substrates, said method comprising: 
 generating a micro-structure pattern of at least one quasi-semi-spherical feature on said substrate by dispensing droplets of a polymer material onto said substrate;    allowing said droplets of polymer material to cure;    coating said substrate and said pattern of at least one quasi-semi-spherical feature with a seed layer; and    depositing a metal layer onto said seed layer.    
     
     
         26 . The method of  claim 25  further comprising polishing a back of said metal layer to form a planar surface.  
     
     
         27 . The method of  claim 26  further comprising removing said substrate from said metal layer, said seed layer, and said at least one quasi-semi-spherical feature.  
     
     
         28 . The method of  claim 27  further comprising removing said seed layer to leave only said polished metal layer as said master mold.