We investigated that Shallow Trench Isolation (STI) dry etching process using SiO2 hard-mask and KrF photo-resist in
90nm stand-alone flash device. As shrinkage of design rule, the thickness of photo-resist is reduced because of guarantee
for process margin in photolithographic process, but the etch process margin is smaller. For the reason, the hard-mask system for etch is needed. Generally, the STI dry etching process is composed of two or three steps, such as the ARC etch, the hard-mask etch, and the Si etch. In order to etch multi-stacked layer (ARC, Oxide hard-mask (SiO2), Si<sub>3</sub>N<sub>4</sub> as CMP stopping layer, and Si), we have controlled the parameters of etching (plasma power, gas, and pressure). In the SiO<sub>2</sub> hard-mask and Si<sub>3</sub>N<sub>4</sub> layer etching process, we use a mixture chemistry of CF<sub>4</sub>, CHF<sub>3</sub>, O<sub>2</sub>, and Ar and get an optimized condition for the multi-layer system. The SiO<sub>2</sub> layer is role of mask for Si layer because the selectivity between SiO<sub>2</sub> and Si is superior to others. Finally, we get a good horizontal and vertical profile of STI by using a mixture chemistry of Cl<sub>2</sub>, HBr, and O<sub>2</sub>.