Transistor and formation method thereof

Provided is a transistor and a formation method thereof. The formation method of the transistor include: providing a semiconductor substrate; successively forming, on the surface of the semiconductor substrate, a gate dielectric layer, a first barrier layer on the surface of the gate dielectric layer, and a sacrificial layer on the surface of the first barrier layer; forming an interlayer dielectric layer on the surface of the semiconductor substrate, wherein the surface of the interlayer dielectric layer is aligned to the top of the sacrificial layer; removing the sacrificial layer to form a slot; forming a second barrier layer, which covers the first barrier layer, in the slot, wherein the morphology of the second barrier layer and morphology of the first barrier layer on which the sacrificial layer has been removed are in complementation; forming a metal layer fully filling the slot on the surface of the second barrier layer, wherein the surface of the metal layer is aligned to the top of the interlayer dielectric layer. This invention reduces the leakage current of the gate of the transistor and improves the reliability and electrical properties of the transistor.