Structure and method for SRAM FinFET device having an oxide feature

A method, comprising:

• providing a substrate comprising a first silicon layer, a first germanium layer over the first silicon layer, and a second silicon layer disposed over the first germanium layer;
• forming a first fin structure over a first area of the substrate and a second fin structure over a second area of the substrate, the first fin structure comprising a first lower portion formed of the first silicon layer, a first middle portion formed of the first germanium layer, and a first top portion formed of the second silicon layer, the second fin structure comprising a second lower portion formed of the first silicon layer, a second middle portion formed of the first germanium layer, and a second top portion formed of the second silicon layer;
• forming a patterned oxidation mask layer to cover an entirety of the second fin structure and a source/drain region of the first fin structure while a channel region of the first fin structure is exposed;
• and
• after the forming of the patterned oxidation mask layer, oxidizing the channel region of the first fin structure to form a first oxide feature over sidewalls of the first lower portion, a second oxide feature over sidewalls of the first middle portion, and a third oxide feature over sidewalls of the first top portion.

A method, comprising:

• providing a substrate comprising a first semiconductor layer, a second semiconductor layer over the first semiconductor layer, and a third semiconductor layer disposed over the second semiconductor layer;
• forming a first fin structure over a first region of the substrate and a second fin structure over a second region of the substrate, the first fin structure comprising a first lower portion formed of the first semiconductor layer, a first middle portion formed of the second semiconductor layer, and a first top portion formed of the third semiconductor layer, the second fin structure comprising a second lower portion formed of the first semiconductor layer, a second middle portion formed of the second semiconductor layer, and a second top portion formed of the third semiconductor layer;
• forming a patterned mask layer to cover an entirety of the second fin structure and a first portion of the first fin structure while a second portion of the first fin structure is exposed;
• and
• after the forming of the patterned mask layer, oxidizing the second portion of the first fin structure to convert the first middle portion to a semiconductor oxide.