US Patent 10121870 Semiconductor device structure with strain-relaxed buffer

Semiconductor device structures are provided. The semiconductor device structure includes a fin structure over a semiconductor substrate. The semiconductor device structure also includes semiconductor wires stacked over the fin structure. The semiconductor device structure further includes a gate stack over the fin structure. The semiconductor wires are surrounded by the gate stack. In addition, the semiconductor device structure includes source or drain structures over the fin structure and on opposite sides of the semiconductor wires. The semiconductor device structure also includes strain-relaxed buffer structures between the source or drain structures and the fin structure. The strain-relaxed buffer structures and the semiconductor wires have different lattice constants.