A method for forming a cavity in a semiconductor structure and an intermediate structure is provided. The method includes: (a) providing a semiconductor structure comprising: (i) a semiconductor substrate; (ii) a set of line structures on the semiconductor substrate, each line structure having a top surface and sidewalls, the line structures being separated by trenches therebetween, and (iii) an oxygen-containing dielectric material at least partially filling the trenches in-between the line structures, wherein the top surface of at least one of the line structures is at least partially exposed, and wherein the exposed part of the top surface is composed of an oxygen-free dielectric material; (b) forming a layer of TaSix selectively onto the oxygen-free dielectric material with respect to the oxygen-containing dielectric material (c) forming the cavity by selectively removing at least a portion of the oxygen-containing dielectric material with respect to the TaSix.