Multiple-gate MOSFET device with lithography independnet silicon body thickness and methods for fabricating the same

Abstract

Multi-gate MOS transistors and fabrication methods are described, in which the transistor semiconductor body thickness or width is lithography independent, allowing scaled triple and quad-gate devices having semiconductor bodies smaller than a lateral gate length dimension. A form structure is provided over a semiconductor wafer starting structure, and spacers are formed along one or more sidewalls of an opening in the form structure. A semiconductor material is deposited in the opening by epitaxial growth or other deposition process, and the form structure and the spacer are removed. A gate structure is then formed along the top and sides of a central portion of the formed semiconductor body. The spacer may be L-shaped, providing an undercut or recess at the bottom of the semiconductor body sidewall, and the gate may be formed in the undercut area to allow fabrication of more than three gates.

1 - 19 . (canceled) 
   
   
       20 . A transistor, comprising:
 a semiconductor body comprising first, second, and third body portions individually comprising a generally planar first bottom surface overlying a starting structure, the first and third body portions individually comprising doped source/drains, the second body portion comprising a top, first and second sides extending laterally between the first and third body portions, and a lithography independent width between the first and second sides; and   a gate structure disposed along at least a portion of the top and sides of the second body portion, the gate structure comprising a conductive gate electrode and a gate dielectric disposed between the gate electrode and the second body portion;   wherein the second body portion comprises a second bottom surface spaced from the starting structure, and wherein the gate structure is disposed along at least a portion of the second bottom surface between the second body portion and the starting structure.   
   
   
       21 . The transistor of  claim 20 , wherein the gate structure comprises a lateral gate length, and wherein the lithography independent width of the second body portion is less than the lateral gate length of the gate structure. 
   
   
       22 - 23 . (canceled) 
   
   
       24 . A transistor, comprising:
 a semiconductor body comprising first, second, and third body portions individually comprising a generally planar first bottom surface overlying a semiconductor starting structure, the first and third body portions individually comprising doped source/drains, the second body portion comprising a second bottom surface spaced from the starting structure, first and second sides extending laterally between the first and third body portions, and a top; and   a gate structure disposed along at least a portion of the top and sides of the second body portion and along at least a portion of the second bottom surface between the second body portion and the starting structure, the gate structure comprising a conductive gate electrode and a gate dielectric disposed between the gate electrode and the second body portion.   
   
   
       25 . The transistor of  claim 24 , wherein the first, second, and third body portions are disposed along an axis generally parallel to a plane of the starting structure. 
   
   
       26 . The transistor of  claim 24 , wherein the semiconductor body comprises silicon, silicon germanium, germanium, or gallium arsenide. 
   
   
       27 . The transistor of  claim 24 , wherein the gate structure comprises a lateral gate length, and wherein the lithography independent width of the second body portion is less than the lateral gate length of the gate structure. 
   
   
       28 . The transistor of  claim 24 , wherein the gate structure comprises a lateral gate length, and wherein second body portion comprises a width between the first and second less than one half of the lateral gate length. 
   
   
       29 . The transistor of  claim 24 , wherein the width of the second body portion is about one third of the lateral gate length.