A method includes etching a semiconductor substrate to form a trench extending from a top surface of the semiconductor substrate into the semiconductor substrate. A first liner layer is formed on sidewalls and a bottom of the trench. The trench is filled with a dielectric material after depositing the first liner layer. The dielectric material and the first liner layer include substantially the same metal-contained ternary dielectric material. Excess portions of the dielectric material and the first liner layer over the top surface of the semiconductor substrate are removed.