Method for forming free standing microstructures

Abstract

A method of forming free standing microstructures includes providing a substrate and forming a sacrificial layer on the substrate. A thin-film structural layer is then formed around and over the sacrificial layer. The sacrificial layer may be formed from an electrically conductive or non-electrically conductive material in certain embodiments of the invention. Nanometer-scale pores are then introduced through the thin-film structural layer by a non-lithographic method, such as anodic etching. Via the pores, at least a portion of the sacrificial layer is etched away or otherwise removed from underneath the thin-film structural layer. The free standing microstructures may be sealed by application of a sealing layer on top thereof. The microstructure may form an encapsulating cavity and provide integrated on-wafer packaging if separate microdevices are disposed inside the cavity. The entire process may be done at or near room temperature in some cases.

1 . A method of forming a free standing microstructure comprising: 
 providing a substrate;    forming a sacrificial layer on the substrate;    forming a thin-film structural layer around and over the sacrificial layer;    introducing nanometer scale pores in the thin-film structural layer; and    etching at least a portion of the sacrificial layer under the thin-film structural layer.    
   
   
       2 . The method of  claim 1 , further comprising the step of depositing a sealing layer over the porous thin-film structural layer.  
   
   
       3 . The method of  claim 1 , further comprising the step of forming a one or more microdevices on the substrate in a location disposed beneath the thin-film structural layer.  
   
   
       4 . The method of  claim 1 , wherein the sacrificial layer is a non-conductive sacrificial layer selected from the group consisting of polymers and ceramics.  
   
   
       5 . The method of  claim 1 , wherein the thin-film structural layer comprises an encapsulation microstructure that is substantially closed.  
   
   
       6 . The method of  claim 1 , wherein a seed layer is deposited prior to formation of the structural layer.  
   
   
       7 . The method of  claim 6 , wherein the seed layer is removed prior to etching at least a portion of the sacrificial layer under the thin-film structural layer.  
   
   
       8 . The method of  claim 1 , wherein the sacrificial layer and structural layer are formed at a temperature at or below 300° C.  
   
   
       9 . The method of  claim 2 , wherein the sacrificial layer, structural layer, and sealing layer are formed at a temperature at or below 300° C.  
   
   
       10 . The method of  claim 1 , wherein the structural layer is a polymer and pores are introduced therein.  
   
   
       11 . The method of  claim 10 , wherein the pores are introduced by ion irradiation followed by etching.  
   
   
       12 . The method of  claim 1 , wherein the structural layer is a metal and pores are introduced therein.  
   
   
       13 . The method of  claim 12 , wherein the metal is aluminum and an anodization etching process transforms the aluminum structural layer into porous alumina.  
   
   
       14 . The method of  claim 1 , wherein the structural layer comprises a ceramic and pores are introduced therein.  
   
   
       15 . The method of  claim 14 , wherein the ceramic comprises silicon and anodization etching transforms the silicon structural layer into porous silicon.  
   
   
       16 . The method of  claim 15 , wherein the sacrificial layer is electrically non-conductive and the structural silicon is doped to be conductive.  
   
   
       17 . A device produced by the method of  claim 1 .  
   
   
       18 . The method of  claim 2 , wherein the sealing layer is substantially impermeable to fluids.  
   
   
       19 . The method of  claim 1 , further comprising the step of cutting the substrate into a plurality of dies.  
   
   
       20 . The method of  claim 1 , wherein the substrate comprises a silicon wafer.