Abstract: A method of forming a semiconductor structure is disclosed. A fin structure is formed on a substrate and a trench is formed in the fin structure. The trench has a top corner, an upper portion having an upper sidewall and a lower portion having a lower sidewall. A first dielectric layer is then formed on the substrate and fills the lower portion of the trench. After that, a second dielectric layer is formed on the substrate and covers the top corner and the upper sidewall of the trench. The second dielectric layer also covers an upper surface of the first dielectric layer.

Abstract: A semiconductor device includes a substrate, a dielectric layer, a first tungsten layer, an interface layer and a second tungsten layer. The dielectric layer is disposed on the substrate and has a first opening and a second opening larger than the first opening. The first tungsten layer is filled in the first opening and is disposed in the second opening. The second tungsten layer is disposed on the first tungsten layer in the second opening, wherein the second tungsten layer has a grain size gradually increased from a bottom surface to a top surface. The interface layer is disposed between the first tungsten layer and the second tungsten layer, wherein the interface layer comprises a nitrogen containing layer. The present invention further includes a method of forming a semiconductor device.