A method includes bonding a first package component on a composite carrier, and performing a first polishing process on the composite carrier to remove a base carrier of the composite carrier. The first polishing process stops on a first layer of the composite carrier. A second polishing process is performed to remove the first layer of the composite carrier. The second polishing process stops on a second layer of the composite carrier. A third polishing process is performed to remove a plurality of layers in the composite carrier. The plurality of layers include the second layer, and the third polishing process stops on a dielectric layer in the first package component.