Semiconductor Device and Method

Abstract

In an embodiment, a method includes: forming a first fin extending from a substrate, the substrate including silicon, the first fin including silicon germanium; forming an isolation region around the first fin, an oxide layer being formed on the first fin during formation of the isolation region; removing the oxide layer from the first fin with a hydrogen-based etching process, silicon at a surface of the first fin being terminated with hydrogen after the hydrogen-based etching process; desorbing the hydrogen from the silicon at the surface of the first fin to depassivate the silicon; and exchanging the depassivated silicon at the surface of the first fin with germanium at a subsurface of the first fin.

What is claimed is: 
     
         1 . A device comprising:
 a first semiconductor region extending from a substrate, the first semiconductor region comprising silicon;   a second semiconductor region on the first semiconductor region, the second semiconductor region comprising silicon germanium, a surface of the second semiconductor region having a first germanium concentration, a subsurface of the second semiconductor region having a second germanium concentration, the first germanium concentration being greater than the second germanium concentration;   a protective cap on the second semiconductor region, the protective cap comprising silicon;   a metal gate stack extending through the protective cap to contact the surface of the second semiconductor region; and   a source/drain region in the second semiconductor region, the source/drain region being adjacent the metal gate stack.   
     
     
         2 . The device of  claim 1  further comprising:
 a lightly doped source/drain (LDD) region in the second semiconductor region, upper portions of the LDD region having a higher germanium concentration than lower portions of the LDD region. 
 
     
     
         3 . The device of  claim 1  further comprising:
 a lightly doped source/drain (LDD) region in the second semiconductor region, upper portions of the LDD region and lower portions of the LDD region having a uniform germanium concentration. 
 
     
     
         4 . The device of  claim 1  further comprising:
 gate spacers extending along the protective cap, the metal gate stack being disposed between the gate spacers. 
 
     
     
         5 . The device of  claim 1  further comprising:
 a gate spacer between the metal gate stack and the source/drain region, the gate spacer disposed on the protective cap. 
 
     
     
         6 . A device comprising:
 a fin extending from a substrate, the fin comprising a silicon portion and a silicon germanium portion on the silicon portion, the silicon germanium portion having a well region and a channel region, the channel region having a greater germanium concentration than the well region;   an isolation region around the silicon portion of the fin, the silicon germanium portion of the fin protruding above the isolation region;   a gate stack on the isolation region and the channel region; and   a source/drain region adjacent the channel region.   
     
     
         7 . The device of  claim 6 , wherein a top surface of the isolation region is level with a top surface of the silicon portion of the fin. 
     
     
         8 . The device of  claim 6 , wherein a top surface of the isolation region is disposed above a top surface of the silicon portion of the fin. 
     
     
         9 . The device of  claim 6 , wherein a top surface of the isolation region is disposed below a top surface of the silicon portion of the fin. 
     
     
         10 . The device of  claim 6  further comprising:
 a lightly doped source/drain (LDD) region in the silicon germanium portion of the fin, the LDD region having a lower region and an upper region, the upper region having a greater germanium concentration than the lower region. 
 
     
     
         11 . The device of  claim 6  further comprising:
 a lightly doped source/drain (LDD) region in the silicon germanium portion of the fin, the LDD region having a lower region and an upper region, the upper region and the lower region having a uniform germanium concentration. 
 
     
     
         12 . The device of  claim 6  further comprising:
 a semiconductor cap on the fin, the gate stack and the source/drain region extending through the semiconductor cap; and 
 a gate spacer on the semiconductor cap, the gate spacer disposed between the gate stack and the source/drain region. 
 
     
     
         13 . The device of  claim 6  further comprising:
 a gate spacer on the fin, the gate spacer disposed between the gate stack and the source/drain region. 
 
     
     
         14 . A device comprising:
 a fin extending from a substrate, the fin comprising a silicon portion and a silicon germanium portion on the silicon portion, the silicon germanium portion having a first lower region and a first upper region, the first upper region having a greater germanium concentration than the first lower region;   a lightly doped source/drain (LDD) region in the silicon germanium portion of the fin, the LDD region having a second lower region and a second upper region, the second upper region having a greater germanium concentration than the second lower region; and   a gate stack on the silicon germanium portion of the fin.   
     
     
         15 . The device of  claim 14 , wherein the first upper region has a same germanium concentration as the second upper region. 
     
     
         16 . The device of  claim 14  further comprising:
 a gate spacer on the LDD region, the gate spacer physically contacting the fin. 
 
     
     
         17 . The device of  claim 14  further comprising:
 a protective cap on the LDD region, the protective cap physically contacting the fin; and 
 a gate spacer on the protective cap. 
 
     
     
         18 . The device of  claim 17 , wherein the protective cap comprises a semiconductor material. 
     
     
         19 . The device of  claim 14  further comprising:
 an isolation region around the silicon portion of the fin, the silicon germanium portion of the fin protruding above the isolation region. 
 
     
     
         20 . The device of  claim 14 , wherein the first upper region extends along sidewalls and a top surface of the first lower region.