Methods of forming single crystal silicon structures

Abstract

A single crystal silicon etching method includes providing a single crystal silicon substrate having at least one trench therein. The single crystal silicon substrate is exposed to an anisotropic etchant that undercuts the single crystal silicon. By controlling the length of the etch, single crystal silicon islands or smooth vertical walls in the single crystal silicon may be created.

1 . A method of forming a plurality of single crystal silicon structures, comprising:
 forming trenches in a surface of a single crystal silicon substrate;   forming a liner over the surface of the single crystal silicon substrate and at least partially extending into each of the trenches; and   anisotropically wet etching exposed surfaces of the single crystal silicon substrate to form single crystal silicon structures, at least one of the single crystal silicon structures having a substantially different structure than at least one other of the single crystal silicon structures.   
     
     
         2 . The method of  claim 1 , wherein forming trenches in a surface of a single crystal silicon substrate comprises forming the trenches such that spacing between at least two adjacent trenches is different than spacing between at least two other adjacent trenches. 
     
     
         3 . The method of  claim 1 , wherein forming a liner overlying the surface of the single crystal silicon substrate and at least partially extending into each of the trenches comprises forming the liner to extend farther into at least one of the trenches than at least one other of the trenches. 
     
     
         4 . The method of  claim 1 , wherein anisotropically wet etching exposed surfaces of the single crystal silicon substrate comprises exposing at least one portion of the single crystal silicon substrate to a wet etchant for a shorter period of time than a least one other portion of the single crystal silicon substrate. 
     
     
         5 . The method of  claim 4 , further comprising exposing the at least one portion of the single crystal silicon substrate to a liner-stripping process to form at least one substantially vertical single crystal silicon structure. 
     
     
         6 . The method of  claim 4 , further comprising:
 filling the trenches located within the at least one other portion of the single crystal silicon substrate with a spin-on-dielectric;   oxidizing the spin-on-dielectric; and   performing steam densification to remove a portion of the single crystal silicon substrate enveloped by the spin-on-dielectric to form at least one single crystal silicon structure extending horizontally over the spin-on-dielectric.   
     
     
         7 . The method of  claim 1 , wherein forming a liner over the surface of the single crystal silicon substrate and at least partially extending into each of the trenches comprises forming a liner material over the surface of the single crystal silicon substrate and over upper portions of sidewalls of each of the trenches. 
     
     
         8 . The method of  claim 1 , wherein forming a liner over the surface of the single crystal silicon substrate and at least partially extending into each of the trenches comprises:
 forming a liner material over the surface of the single crystal silicon substrate and over surfaces exposed within the trenches; and   removing the liner material from bottoms of the trenches and from lower portions of sidewalls of the trenches.   
     
     
         9 . The method of  claim 8 , wherein removing the liner material from bottoms of the trenches and from lower portions of sidewalls of the trenches comprises performing at least one anisotropic dry etching process to selectively remove portions of the liner material from the bottoms of the trenches and from the lower portions of the sidewalls of the trenches. 
     
     
         10 . The method of  claim 1 , wherein anisotropically wet etching exposed surfaces of the single crystal silicon substrate comprises:
 forming the at least one of the single crystal silicon structures to comprise a fin structure exhibiting a substantially uniform width; and   forming the at least one other of the single crystal silicon structures to comprise a top structure and a pillar structure underlying the top structure, the top structure integral and continuous with the pillar structure and exhibiting a greater width than the pillar structure.   
     
     
         11 . The method of  claim 10 , wherein forming the at least one of the single crystal silicon structures comprises exposing a portion of the single crystal silicon substrate to a wet etchant for about 4 minutes at 26° C. 
     
     
         12 . The method of  claim 11 , wherein forming the at least one other of the single crystal silicon structures comprises exposing another portion of the single crystal silicon substrate to the wet etchant for from about 5 minutes to about 30 minutes at 26° C. 
     
     
         13 . The method of  claim 10 , further comprising removing the pillar structure of the at least one other of the single crystal silicon structures while maintaining the top structure of the at least one other of the single crystal silicon structures. 
     
     
         14 . The method of  claim 13 , wherein removing the pillar structure of the at least one other of the single crystal silicon structures while maintaining the top structure of the at least one other of the single crystal silicon structures comprises:
 surrounding the pillar structure of the at least one other of the single crystal silicon structures with a dielectric material; and   performing an oxidization and densification process to remove the pillar structure.   
     
     
         15 . A method of forming single crystal silicon structures, comprising:
 forming trenches in a single crystal silicon substrate;   forming a silicon nitride material over surfaces of the single crystal silicon substrate inside and outside of the trenches;   removing the silicon nitride material from bottoms and lower sidewall portions of the trenches while maintaining the silicon nitride material outside of the trenches and over upper sidewall portions of the trenches;   wet etching exposed surfaces of a first portion the single crystal silicon substrate for a first period of time to form first single crystal silicon structures; and   wet etching exposed surfaces of a second portion of the single crystal silicon substrate for a second, longer period of time to form second single crystal silicon structures exhibiting a different shape than the first single crystal silicon structures.   
     
     
         16 . The method of  claim 15 , wherein removing the silicon nitride material from bottoms and lower sidewall portions of the trenches while maintaining the silicon nitride material outside of the trenches and over upper sidewall portions of the trenches comprises anisotropically dry etching the silicon nitride material. 
     
     
         17 . The method of  claim 15 , wherein wet etching exposed surfaces of a first portion the single crystal silicon substrate comprises wet etching the exposed surfaces of the second portion of the single crystal silicon substrate for a sufficient amount of time to form silicon fins extending substantially vertically from the single crystal silicon substrate. 
     
     
         18 . The method of  claim 15 , wherein wet etching exposed surfaces of a second portion of the single crystal silicon substrate comprises wet etching the exposed surfaces of the second portion of the single crystal silicon substrate for a sufficient amount of time to form silicon pillars extending substantially vertically from the single crystal silicon substrate to integral silicon structures having outer perimeters extending laterally beyond outer perimeters of the silicon pillars. 
     
     
         19 . The method of  claim 15 , further comprising removing remaining portions of the silicon nitride material after wet etching the exposed surfaces of the first portion the single crystal silicon substrate and wet etching the exposed surfaces of the second portion of the single crystal silicon substrate. 
     
     
         20 . A method of forming single crystal silicon structures, comprising:
 forming trenches in a single crystal silicon substrate;   forming a liner material comprising one of a nitride material and an oxide material over surfaces of the single crystal silicon substrate inside and outside of the trenches;   performing at least one dry etching process to selectively remove portions of the liner material from lower portions of the trenches;   performing at least one wet etching process to selectively remove exposed portions of the single crystal silicon substrate and form structures exhibiting different shapes than one another;   forming a dielectric material over lower portions of at least a portion of the structures; and   performing an oxidization and steam densification process to remove the lower portions of the at least a portion of the structures.