US Patent 11855089 Method and structure for FinFET devices

A semiconductor device includes a silicon substrate; a semiconductor fin over the silicon substrate; and an isolation structure over the silicon substrate. The semiconductor fin includes a first portion and a second portion over the first portion. The first portion is surrounded by the isolation structure, and the second portion protrudes above the isolation structure. The second portion has a different crystalline lattice constant than the first portion. The first portion includes a first dopant, and the second portion is substantially free of the first dopant. The semiconductor device further includes a gate structure above the isolation structure and engaging multiple surfaces of the second portion.