Etching of Thermally Grown SiO2 by NH4OH in Mixture of NH4OH and H2O2 Cleaning Solution

We have investigated the etching behavior of thermally grown SiO2 by ammonium hydroxide ( NH4OH) in NH4OH–H2O2–H2O cleaning solution (SC-1). The SiO2 etching rate increases with increasing impurity (boron or phosphorus) concentration in the SiO2 as well as concentration of NH4OH and temperature of SC-1 solution. Moreover, postoxidation SC-1 treatment with a low concentration of NH4OH (less than 3.15 wt% of NH4OH) does not degrade or improve oxide reliability. These indicate that if SC-1 treatment, which is performed after post-thin-oxide ( ∼20 nm) or high-impurity-doped Si oxide formation, is carried out in ULSI device fabrication processes, SC-1 with low temperature and low NH4OH concentration must be applied after those processes to minimize SiO2 thickness reduction and preserve oxide reliability.