Study of shallow trench isolation dry etching process using oxide hard mask and KrF photo-resist in 90 nm stand-alone flash device

Abstract

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), Si₃N₄ as CMP stopping layer, and Si), we have controlled the parameters of etching (plasma power, gas, and pressure). In the SiO₂ hard-mask and Si₃N₄ layer etching process, we use a mixture chemistry of CF₄, CHF₃, O₂, and Ar and get an optimized condition for the multi-layer system. The SiO₂ layer is role of mask for Si layer because the selectivity between SiO₂ and Si is superior to others. Finally, we get a good horizontal and vertical profile of STI by using a mixture chemistry of Cl₂, HBr, and O₂.