Method for protecting work function metal layer

The invention provides a method for protecting a work function metal layer, which comprises the following steps of: providing a substrate and a physical vapor deposition machine, and forming an active function metal layer on the substrate; setting a bias power supply of a physical vapor deposition machine table to be zero, and then depositing a first protection layer on the work function metal layer by utilizing the physical vapor deposition machine table; providing a bias voltage, wherein the bias voltage is used for increasing the energy of sputtering atoms formed by the physical vapor deposition machine; bias voltage is adopted by the bias power supply, and then a second protection layer is formed on the first protection layer through the physical vapor deposition machine. According to the invention, the first protection layer is formed on the work function metal layer without adopting a bias voltage, and then the second protection layer is formed on the work function metal layer by adopting the bias volta