A field effect transistor including a substrate which includes, a fin structure, the fin structure having a top surface. The field effect transistor further including an isolation in the substrate and a source/drain (S/D) recess cavity below the top surface of the substrate disposed between the fin structure and the isolation structure. The S/D recess cavity includes a lower portion, the lower portion further includes a first strained layer, a first dielectric film and a second dielectric film, wherein the first strained layer is disposed between the first dielectric film and the second dielectric film. The S/D recess cavity further includes an upper portion including a second strained layer overlying the first strained layer, wherein a ratio of a height of the upper portion to a height of the lower portion ranges from about 0.8 to about 1.2.