Methods for opening a hard mask and a silicon-on-insulator substrate in a single process chamber are disclosed. In one embodiment, the method includes patterning a photoresist over a stack including an anti-reflective coating (ARC) layer, a silicon dioxide (SiO2) based hard mask layer, a silicon nitride pad layer, a silicon dioxide (SiO2) pad layer and the SOI substrate, wherein the SOI substrate includes a silicon-on-insulator layer and a buried silicon dioxide (SiO2) layer; and in a single process chamber: opening the ARC layer; etching the silicon dioxide (SiO2) based hard mask layer; etching the silicon nitride pad layer; etching the silicon dioxide (SiO2) pad layer; and etching the SOI substrate. Etching all layers in a single chamber reduces the turn-around-time, lowers the process cost, facilitates process control and/or improve a trench profile.