Microprotrusion array and methods of making a microprotrusion

Abstract

A microprotrusion array is formed from a silicon wafer by a plurality of sequential plasma and wet isotropic and anisotropic etching steps. The resulting microprotrusions have sharpened tips or cutting edges formed by a wet isotropic etch.

What is claimed is:  
     
         1 . A method of forming a microprotrusion array comprising the steps of: 
 providing a substrate having a top surface and a bottom surface,    forming a patterned masking layer in a plurality of areas on said top surface, said areas of said patterned masking layer having a predetermined dimension corresponding to a microprotrusion and defining an exposed area of said top surface of said substrate around said areas of said masking layer,    etching said exposed area of said top surface of said substrate to a sufficient depth to form a plurality of microprotrusions, and    removing said masking layer from said substrate to expose said microprotrusions.    
     
     
         2 . The method of  claim 1 , further comprising the step of forming an oxide layer on said top surface of said substrate.  
     
     
         3 . The method of  claim 2 , wherein said patterned masking layer is a nitride layer.  
     
     
         4 . The method of  claim 1 , wherein said substrate is made of silicon.  
     
     
         5 . The method of  claim 1 , comprising the step of applying a patterned masking layer on said bottom surface of said base and etching a channel through said bottom surface to a top end of said microprotrusions.  
     
     
         6 . The method of  claim 3 , further comprising the steps of 
 providing an oxide layer on said bottom surface of said substrate,    etching an area of said oxide layer on said bottom surface of said substrate oriented below said microprotrusion, and    etching a channel extending between said bottom surface to said top surface.    
     
     
         7 . The method of  claim 6 , wherein prior to forming said nitride layer, said method comprises 
 etching a plurality of areas in said oxide layer on said bottom surface of said support, and    applying a second continuous nitride layer on said bottom surface to cover said oxide layer and etched area on said bottom surface.    
     
     
         8 . The method of  claim 6 , wherein subsequent to said etching of said oxide layer on said bottom surface, said method comprises 
 etching said nitride layer an said bottom surface to expose said etched area in said oxide layer on said bottom surface, and    etching a channel through said substrate extending between said bottom surface to said top surface of said base.    
     
     
         9 . The method of  claim 1 , further comprising the step of 
 forming an oxide layer on said top surface and said microprotrusions,    etching a portion of said oxide layer on said microprotrusions to expose a tip portion of said microprotrusions, and    etching said exposed tip portion of said microprotrusion to form a channel extending between said tip portion of said microprotrusion and said bottom surface of said base.    
     
     
         10 . The method of  claim 9 , further comprising the step of applying a photoresist layer to said microprotrusions.  
     
     
         11 . The method of  claim 10 , further comprising the step of etching said top surface around said photoresist layer on each of said microprotrusions to form an annular column.  
     
     
         12 . A method of forming a microprotrusion array comprising the steps of 
 providing a silicon substrate having a top surface with a masking layer,    removing a portion of said masking layer to form a plurality of substantially ring shaped portions of said masking layer on said top surface,    etching said top surface of said silicon substrate to form a channel extending through a center of each of said ring shaped portions, and to form an annular column around each of said ring shaped portions, and    removing said ring shaped portions of said masking layer to form a microprotrusion array.    
     
     
         13 . The method of  claim 12 , wherein said masking layer is an oxide layer on said substrate.  
     
     
         14 . The method of  claim 12 , wherein prior to removing said ring shaped portions of said masking layer, said method comprises 
 etching said silicon substrate around said ring shaped oxide portions to form a pointed tip.    
     
     
         15 . The method of  claim 13 , comprising 
 forming a plurality of ring shaped nitride portions on said oxide layer and etching said oxide layer around said ring shaped nitride portions to form said ring shaped portions from said oxide layer.    
     
     
         16 . The method of  claim 13 , after removing said ring shaped oxide portions, said method further comprises the steps of 
 forming a second oxide layer on said microprotrusion array to sharpen said microprotrusions, and    removing said second oxide layer to exposed said sharpened microprotrusions.    
     
     
         17 . The method of  claim 16 , comprising 
 applying a photoresist layer to said second oxide layer on said microprotrusions, and    etching said second oxide layer to form a ring shaped oxide layer prior to said step of etching said channels and annular portions.    
     
     
         18 . The method of  claim 13 , said method further comprising 
 applying an oxide layer to an inner and an outer surface of said annular columns, and thereafter etching said silicon around said ring shaped oxide portions to form pointed tips on said columns.    
     
     
         19 . The method of  claim 18 , further comprising applying a nitride layer onto said first oxide layer before etching said channels in said microprotrusions.  
     
     
         20 . The method of  claim 19 , further comprising applying a photoresist layer onto said nitride layer and top surface of said substrate prior to forming said channels.  
     
     
         21 . The method of  claim 20 , comprising the step of removing said photoresist layer prior to said step of forming said annular columns.  
     
     
         22 . The method of  claim 13 , further comprising 
 applying a nitride layer to said top surface of said substrate and ring shaped portions prior to forming said annular columns,    applying a photoresist layer to said nitride layer overlying said ring shaped oxide portions, and    forming said channels, and thereafter forming said columns.    
     
     
         23 . The method of  claim 22 , further comprising 
 forming an oxide layer on an outer surface of said column and an inner surface of said channel, and    removing said nitride layer from said columns, and further etching said silicon at an outer end of said columns to form a sharpened tip.    
     
     
         24 . The method of  claim 22 , wherein prior to etching said silicon substrate, said method further comprises 
 forming an oxide layer on an outer surface of said columns and on an inner surface of said channel where a portion of a top end of said column is free of said oxide layer, and    etching said portion of said top end to said column to form a beveled tip.    
     
     
         25 . The method of  claim 12 , further comprising cutting a beveled tip on said column.  
     
     
         26 . The method of  claim 25 , further comprising providing a dicing saw, and cutting said beveled tip with said dicing saw.  
     
     
         27 . The method of  claim 25 , wherein prior to cutting said bevel, said method further comprises encasing said column in a support medium.  
     
     
         28 . The method of  claim 27 , wherein said support medium is a wax.  
     
     
         29 . A method of forming a microprotrusion array comprising the steps of 
 providing a substrate having a top surface and a bottom surface;    forming a plurality of recesses in said top surface, said recesses defining inclined surfaces with respect to a plane of said top surface, said inclined surfaces forming an array of sharpened tips, and    removing a portion of said substrate around said sharpened tips to form an array of microprotrusions having an outer end formed by said sharpened tips.    
     
     
         30 . The method of  claim 29 , wherein said substrate is a material selected from the group consisting of silicon, silicon oxide, silicon nitride, epoxy resins, nickel and aluminum.  
     
     
         31 . The method of  claim 29 , wherein said substrate is polysilicon or amorphous silicon.  
     
     
         32 . The method of  claim 29 , wherein said inclined surfaces are formed by applying an anisotropic etchant to said top surface of said substrate and forming a beveled surface in a crystal plane of said substrate.  
     
     
         33 . The method of  claim 32 , wherein said anisotropic etchant is selected from the group consisting of potassium hydroxide, ethylene diamine pyrocatecol, ammonium hydroxide, sodium hydroxide, CsOH, and N 2 H 4 .  
     
     
         34 . The method of  claim 29 , wherein said inclined surfaces are formed by applying an isotropic etchant to said to surface of said substrate.  
     
     
         35 . The method of  claim 34 , wherein said isotropic etchant comprises a mixture of hydrofluoric acid, acetic acid and nitric acid.  
     
     
         36 . The method of  claim 29 , wherein said array of microprotrusions are formed by machining said top surface of said substrate around said sharpened tips.  
     
     
         37 . A method of forming a microprotrusion array, comprising the steps of 
 providing a substrate having a top surface and a bottom surface,    forming an array of microprotrusions on said top surface of said substrate, said microprotrusions having a top surface, and    forming at least one bevel on said top surface of each of said microprotrusions.    
     
     
         38 . The method of  claim 37 , wherein said microprotrusions have an outer surface, and said step of forming said bevel comprises 
 forming a non-oxidizing layer on said outer surface of said microprotrusions,    forming an oxide layer on said top surface of said microprotrusions,    etching said non-oxidizing layer to form an exposed area on said microprotrusions, and    etching said microprotrusions in said exposed area to form said bevel.    
     
     
         39 . The method of  claim 38 , further comprising applying a non-etching layer on said non-oxidizing layer.  
     
     
         40 . The method of  claim 38 , comprising removing said non-oxidizing layer.  
     
     
         41 . The method of  claim 37 , wherein said microprotrusions are formed by selectively etching said substrate.  
     
     
         42 . The method of  claim 37 , wherein said bevels are formed by selectively etching said substrate.  
     
     
         43 . The method of  claim 37 , wherein said bevels are formed by selectively etching said microprotrusions.