Gate oxide integrity failure caused by molybdenum contamination introduced in the ion implantation

The gate oxide is the most fragile element of metal-oxide-semiconductor (MOS) transistor. Metal contamination is fatal to gate oxide integrity because metallic contamination in the gate oxide leads to high leak current and even gate oxide breakdown. In this paper, a case of gate oxide integrity failure was investigated. The fact that the emission spot locates in the bulk area instead of poly edge excludes the possibility of failure cause of poly/spacer etch, gate oxide thinning at the edge or gate oxide thinning at STI corner issue. Molybdenum (Mo) contamination was detected in the gate oxide of NMOS using magnetic sector secondary ion mass spectrometry because of its excellent sensitivity. The results showed that Mo contamination is introduced in the process of germanium pre-amorphization implantation mainly in the form of (⁹⁸Mo¹²C¹⁹F₂)⁺⁺, which has the same nominal mass to charge ratio as ⁷⁴Ge⁺. The different properties of poly-Si resulted in that NMOS but not PMOS was affected by the Mo contamination. Unlike iron (Fe) contamination, Mo contamination is rarely reported in the GOI failure. On the basis of that, suggestions have been proposed to greatly suppress the Mo contamination.