High mobility devices and methods of forming same

A method for forming a fin field effect transistor (finFET) comprising:

• forming a first fin extending upwards from a strain relaxed buffer (SRB) layer, wherein the first fin comprises a first semiconductor strip and a first nitride layer over the first semiconductor strip;
• forming a second fin extending upwards from the SRB layer wherein the second fin comprises a second semiconductor strip;
• forming an oxide layer over the first nitride layer and the second fin;
• patterning the oxide layer to expose the second fin while masking the first fin;
• replacing the second semiconductor strip with a third semiconductor strip;
• forming a sacrificial layer over the third semiconductor strip;
• and
• removing the sacrificial layer, remaining portions of the oxide layer, and remaining portions of the first nitride layer.

A method comprising:

• forming a first fin in a wafer, wherein the first fin comprises:
• a first strain relax buffer (SRB) layer portion;
• a first semiconductor strip on the first SRB layer portion;
• and
• a first pad nitride layer portion over the first semiconductor strip;
• forming a second fin in the wafer, wherein the second fin comprises:
• a second strain relax buffer (SRB) layer portion;
• a second semiconductor strip on the second SRB layer portion;
• and
• a second pad nitride layer portion over the second semiconductor strip;
• blanket depositing a barrier layer on a top surface of the wafer, wherein the barrier layer is disposed over the first pad nitride layer portion and the second pad nitride layer portion;
• removing the second pad nitride layer portion and the second semiconductor strip;
• epitaxially growing a third semiconductor strip over the second SRB layer portion;
• performing a selective chemical mechanical polish (CMP) on the third semiconductor strip using a slurry that selectively planarizes the third semiconductor strip at a higher rate than the barrier layer;
• and
• after performing the selective CMP, removing remaining portions of the barrier layer and the first pad nitride layer portion to expose the first semiconductor strip.