Dimensional silica-based porous silicon structures and methods of fabrication

Abstract

Methods of fabricating dimensional silica-based substrates or structures comprising a porous silicon layers are contemplated. According to one embodiment, oxygen is extracted from the atomic elemental composition of a silica glass substrate by reacting a metallic gas with the substrate in a heated inert atmosphere to form a metal-oxygen complex along a surface of the substrate. The metal-oxygen complex is removed from the surface of the silica glass substrate to yield a crystalline porous silicon surface portion and one or more additional layers are formed over the crystalline porous silicon surface portion of the silica glass substrate to yield a dimensional silica-based substrate or structure comprising the porous silicon layer. Embodiments are also contemplated where the substrate is glass-based, but is not necessarily a silica-based glass substrate. Additional embodiments are disclosed and claimed.

What is claimed is: 
     
         1 . A method of fabricating a dimensional silica glass substrate or structure having a porous silicon surface layer portion of the method comprising:
 providing a silica glass substrate;   extracting oxygen from the atomic elemental composition of a surface portion of the silica glass substrate by reacting a metallic gas with the surface of the silica glass substrate in a heated inert atmosphere to form a metal-oxygen complex in the surface portion of the silica glass substrate, wherein the inert atmosphere is heated to a reaction temperature sufficient to facilitate the oxygen extraction; and   removing the metal-oxygen complex from the surface portion of the silica glass substrate to yield a crystalline porous silicon surface portion in the surface of the silica glass substrate;   
     
     
         2 . A method as claimed in  claim 1  further the step of of:
 utilizing the porous silicon surface portion of the silica glass substrate as a seed layer and epitaxially growing or depositing a semiconductor or crystalline material overlayer on the porous silicon surface portion of the silica glass substrate. 
 
     
     
         3 . A method as claimed in  claim 2  wherein:
 the overlayer comprises a monocrystalline silicon layer, a microcrystalline silicon layer, a polycrystalline silicon layer, or an amorphous silicon layer; and 
 the method further comprises the step of recrystallizing the overlayer by annealing the overlayer at a temperature and duration sufficient to enhance crystallization and increase grain size in the overlayer. 
 
     
     
         4 . A method as claimed in  claim 1  further comprising utilizing the porous silicon layer as a seed layer for the epitaxial fabrication of a silicon-on-insulator structure. 
     
     
         5 . A method as claimed in  claim 4  further comprising the step of forming a separation layer configured to inhibit migration of impurities from the silica glass substrate to remaining portions of the structure. 
     
     
         6 . A method as claimed in  claim 1  wherein:
 the silica glass substrate comprises N-type or P-type dopants; and 
 the oxygen extraction and the metal-oxygen complex removal steps are tailored to leave significant amount of dopants in the crystalline porous silicon surface portion of the silica glass substrate. 
 
     
     
         7 . A method as claimed in  claim 1  further comprising the step of providing a topical film on the silica glass substrate for controlling the thickness, porosity or crystalline character of the resulting crystalline porous silicon surface portion of the silica glass substrate. 
     
     
         8 . A method as claimed in  claim 1  wherein the method comprises a patterning step where one or more inert blocking layers are provided over the silica glass substrate prior to reacting the metallic gas with the silica glass substrate. 
     
     
         9 . A method as claimed in  claim 1  wherein the method comprises a reducing agent doping step where the silica glass substrate is pre-treated with a gaseous reducing agent to infiltrate the surface of the silica glass substrate with the reducing agent and enhance the reaction of the metallic gas and the silica glass substrate. 
     
     
         10 . A method as claimed in  claim 1  wherein the silica glass substrate is characterized by a thermal strain point and the inert atmosphere is heated to a reaction temperature below the thermal strain point of the silica glass substrate. 
     
     
         11 . A method as claimed in  claim 1  wherein the metallic gas comprises Mg and a reaction with the silica glass substrate comprises:
   2Mg+SiO 2 →2MgO.
 
 
     
     
         12 . A method as claimed in  claim 1  wherein the metallic gas is provided in an amount that is sufficient for stoichiometric reaction conditions. 
     
     
         13 . A method as claimed in  claim 1  wherein a reaction of the metallic gas with the silica glass substrate generates reaction byproducts and the method comprises one or more byproduct removal steps. 
     
     
         14 . A method as claimed in  claim 1  wherein the substrate is subject to microwave or RF exposure while reacting the metallic gas with the silica glass substrate. 
     
     
         15 . A method as claimed in  claim 1  wherein the silica glass substrate is subject to electron beam irradiation prior to reacting the metallic gas with the silica glass substrate in the heated inert atmosphere. 
     
     
         16 . A method as claimed in  claim 1  wherein:
 the reaction of the metallic gas with the silica glass substrate additionally forms a metal-non-oxygen complex along a surface of the silica glass substrate; and 
 the method further comprises a post-reaction thermal treatment that is maintained in an inert atmosphere at a post-reaction temperature exceeding the reaction temperature for a period of time that is sufficient to evaporate the metal-non-oxygen complex. 
 
     
     
         17 . A method as claimed in  claim 1  wherein the method further comprises a post-reaction acid etching step for removing the metal-oxygen complex or amorphous silicon. 
     
     
         18 . (canceled) 
     
     
         19 . A method as claimed in  claim 1  further comprising the step of densifying the silica based structure by coating the crystalline porous silicon surface portion of the silica glass substrate with an additional glass or metal oxide layer and reacting a metallic gas with the crystalline porous surface portion of the glass substrate at the reaction temperature to yield a densified oxygen substrate. 
     
     
         20 . (canceled) 
     
     
         21 . A method as claimed in  claim 1  further comprising the step of forming one or more additional layers over the crystalline porous silicon surface portion of the silica glass substrate. 
     
     
         22 . A dimensional semiconductor on insulator substrate comprising a dimensional silica glass substrate, wherein an integral surface portion of the dimensional silica glass substrate comprises a porous silicon layer.