Provided is a method of planarizing a semiconductor device. The method includes providing a substrate. The method includes forming a first layer over the substrate. The method includes forming a second layer over the first layer. The first and second layers have different material compositions. The method includes forming a third layer over the second layer. The method includes performing a polishing process on the third layer until the third layer is substantially removed. The method includes performing an etch back process to remove the second layer and a portion of the first layer. Wherein an etching selectivity of the etch back process with respect to the first and second layers is approximately 1:1.