Instability of SiO2 Film Caused by Fluorine and Chlorine Inclusion

We studied how the interaction between fluorine and chlorine in SiO2 influences oxide thickness change and metal oxide semiconductor (MOS) reliability. Anhydrous HF treatment on amorphous Si (a-Si) introduces a large quantity of fluorine into the gate oxide compared to HF solution treatment. When the oxide is formed in an HCl atmosphere, it contains a large quantity of chlorine. If the fluorine atoms diffuse into the chlorine-rich oxide, Si–Cl bonds are easily replaced by Si–F bonds and the equivalent thickness increases. This tendency is further enhanced as the oxide becomes thinner. Both fluorine and chlorine, introduced in excess during the fabrication process, degrade MOS reliability because Si–F and Si–Cl bonds are weaker than Si–O bonds.