A method including forming a deep trench in a semiconductor-on-insulator substrate including an SOI layer directly on top of a buried oxide layer directly on top of a base substrate, masking only a top surface of the SOI layer and a sidewall of the SOI layer exposed within an upper portion of the deep trench with a dielectric material without masking any surface of the base substrate exposed within a lower portion of the deep trench, and forming a bottle shaped trench by etching the base substrate exposed in the lower portion of the deep trench selective to the dielectric material and the buried oxide layer.