A method includes depositing a first work-function layer and a second work-function layer in a first device region and a second device region, respectively, and depositing a first fluorine-blocking layer and a second fluorine-blocking layer in the first device region and the second device region, respectively. The first fluorine-blocking layer is over the first work-function layer, and the second fluorine-blocking layer is over the second work-function layer. The method further includes removing the second fluorine-blocking layer, and forming a first metal-filling layer over the first fluorine-blocking layer, and a second metal-filling layer over the second work-function layer.