Method of forming finfet having fins of different height

Abstract

A device is fabricated on a silicon-on-insulator (SOI) wafer formed of a substrate, a bottom oxide layer on the substrate and an active silicon layer on the bottom oxide layer, where the active silicon layer has a surface opposite the bottom oxide layer. A first mask is formed over the surface at a first portion of the wafer, leaving a second portion of the wafer unmasked. The wafer is etched at the unmasked second portion of the wafer to form a depression in the active silicon layer. A thermal oxide layer is formed to substantially fill the depression, the first mask is removed, and fins are formed at the first and second portions of the wafer.

What is claimed is: 
     
         1 . A device comprising:
 an SOI wafer having a silicon layer having a top surface, the SOI wafer having a first portion and a second portion, the second portion including an etched depression having an oxidized bottom;   an oxide layer in the etched depression having an oxide layer top surface, the oxide layer top surface being substantially even with the silicon layer top surface; and   a plurality of mask portions on the silicon layer top surface and on the oxide layer top surface for defining a first plurality of fins at the first SOI wafer portion and a second plurality of fins at the second SOI wafer portion.   
     
     
         2 . The device of  claim 1 , including a first plurality of silicon fins beneath each of the plurality of mask portions and a second plurality of silicon fins beneath each of the plurality of second mask portions. 
     
     
         3 . The device of  claim 2 , wherein a height of the first plurality of fins is greater than a height of the second plurality of fins. 
     
     
         4 . The device of  claim 3  incorporated into at least one semiconductor die. 
     
     
         5 . The device of  claim 1 , wherein the device is selected from the group consisting of a set top box, a music player, a video player, an entertainment unit, a navigation device, a communications device, a personal digital assistant (PDA), a fixed location data unit, and a computer. 
     
     
         6 . A non-transient computer readable medium containing instructions that, when executed by a computer processor cause a device controlled by the computer processor to perform actions on an SOI wafer comprising a substrate, a bottom oxide layer on the substrate and an active silicon layer on the bottom oxide layer, the active silicon layer having a surface opposite the bottom oxide layer, the actions including:
 forming a first mask over the surface at a first portion of the wafer and leaving a second portion of the wafer unmasked;   etching the wafer at the unmasked second portion of the wafer to form a depression in the active silicon layer, the depression having a bottom;   forming a thermal oxide layer substantially filling the depression;   removing the first mask; and   forming fins at the first and second portions of the wafer.   
     
     
         7 . The non-transient computer readable medium of  claim 6 , the actions further including, before forming the first mask, forming a hardmask over the surface and wherein etching the wafer at the unmasked second portion comprises etching through the hardmask and into the active silicon layer. 
     
     
         8 . The non-transient computer readable medium of  claim 6 , wherein forming a thermal oxide layer substantially filling the depression comprises forming a thermal oxide layer filling the depression to a level substantially even with the surface. 
     
     
         9 . The non-transient computer readable medium of  claim 6 , wherein forming fins comprises forming a first plurality of second masks on the surface at the first portion of the wafer, forming a second plurality of second masks on the thermal oxide layer and patterning the wafer to remove portions of the silicon layer not protected by the first plurality of second masks or the second plurality of second masks. 
     
     
         10 . The non-transient computer readable medium of  claim 6 , wherein forming a thermal oxide layer comprises oxidizing the bottom of the depression. 
     
     
         11 . The non-transient computer readable medium of  claim 6 , the actions further including, before forming the first mask, forming a hardmask over the surface, and wherein etching the wafer at the unmasked second portion comprises etching through the hardmask and into the active silicon layer, wherein forming a thermal oxide layer comprises oxidizing the bottom of the depression until a thermal oxide layer on the bottom of the depression is substantially even with the surface and wherein forming fins comprises forming a first plurality of second masks on the surface at the first portion of the wafer, forming a second plurality of second masks on the thermal oxide layer and patterning the SOI wafer to remove portions of the silicon layer not protected by the first plurality of second masks or the second plurality of second masks. 
     
     
         7 . The non-transient computer readable medium of  claim 6 , wherein forming fins at the first and second portions of the wafer comprises forming fins having a first height at the first portion of the wafer and forming fins having a second height, less than the first height, at the second portion of the wafer. 
     
     
         8 . The non-transient computer readable medium of  claim 6 , wherein etching the surface comprises performing a wet etch or performing a dry etch or performing both a wet etch and a dry etch. 
     
     
         9 . The non-transient computer readable medium of  claim 6 , the actions further including forming a finFET device using the fins.