A METHOD FOR PHOTOLITHOGRAPHY-FREE SELF-ALIGNED REVERSE ACTIVE ETCH

A layer of partially planarized organosilicate (DUO) is spin-coated onto a layer of high density plasma (HDP) oxide on a silicon wafer after the shallow trench isolation (STI) is filled with the HDP oxide. Then the DUO layer is etched using a specialized process specifically tuned to etch the DUO and high density plasma (HDP) oxide at a certain selectivity. The higher areas of the wafer topography (active Si areas) have thinner DUO and as the etch process proceeds it starts to etch through the HDP oxide in these areas (active Si areas). The etch process is stopped after a certain depth is reached and before touching down on the silicon nitride oxidation layer. The DUO is removed and a standard chemical-mechanical polish (CMP) is performed on the silicon wafer. After the CMP step the silicon nitride is removed, exposing the silicon substrate between the field oxides.