a method for manufacturing insulating structures in a semiconductor substrate includes forming a first insulating layer on the semiconductor substrate , forming a stop layer on the first insulating layer , and forming a barrier layer on the stop layer . the barrier layer is selective with respect to the stop layer . a screen layer is formed on the barrier layer . a portion of the screen layer is selectively removed for forming an opening therethrough for exposing a portion of the barrier layer . the exposed barrier layer is removed for exposing a portion of the stop layer . the exposed stop layer is removed for exposing a portion of the semiconductor substrate . the method further includes removing the remaining barrier layer , and removing a portion of the exposed semiconductor substrate for forming a trench therein .