A method for manufacturing a semiconductor device includes: providing a semiconductor substrate having a first side; forming a trench in the semiconductor substrate, the trench having a bottom and a sidewall extending from the bottom to the first side of the semiconductor substrate; forming an insulation structure including at least a first insulation layer and a second insulation layer on the sidewall and the bottom of the trench; forming a lower conductive structure in the lower portion of the trench; removing the second insulation layer in an upper portion of the trench while leaving the second insulation layer at least partially in a lower portion of the trench; and forming an upper conductive structure in the upper portion of the trench.