Abstract: A two-step process for manufacturing a deep trench in a semiconductor device that prevents shorts and leakages between neighboring capacitors due to over etching is disclosed. The process comprises conducting a first etching step to remove a portion of a substrate to form a trench with a first determined depth therein; conducting a thermal oxidation to form an oxide film on the sidewall of the trench; and conducting a second etching step to remove a portion of the substrate under the trench to form a deep trench with a second determined depth.