Case study: Root cause of fluorine detection during TiN ARC layer corrosion of AlSiCu metal lines

The present study examines the cause of fluorine detection during the corrosion of the TiN antireflection coat (ARC) layer of AlSiCu metal lines. When a crack is generated in the tetraethyl orthosilicate (TEOS) oxide or spin-on-glass (SOG) film of an LSI device, the corrosion of the TiN ARC layer (TiO_xN_y-oxidation) may occur due to residual moisture inside the device. In this case, concentrated fluorine is detected around the corroded TiN ARC layer by energy-dispersive X-ray spectroscopy (EDX) analysis. Fluorine concentration was correlated with the degree of corrosion on the TiN ARC layer, suggesting the contribution of fluorine to the corrosion of this layer. When a wider distribution of fluorine concentrations was evaluated, however, the concentration of fluorine and the degree of corrosion on the TiN ARC layer did not match; instead, a higher concentration of fluorine was observed near the crack of the TEOS oxide film. The corroded TiN ARC layer of the sample was then removed, and the Al line of the underlying layer was observed. Etching was observed on the Al line surface where a high concentration of fluorine was detected. More specifically, EDX analysis detected that fluorine reacted with the Al line in the underlying layer after diffusion through the TiO_xN_y film, causing decreased film density due to the corrosion of the TiN ARC layer.