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

• The corrosion of the TiN ARC layer may well occur from the residual moisture inside the device.
• For that case the concentrated fluorine was detected around the corroded TiN ARC layer.
• The identical trend of fluorine concentration with the corrosion degree on the TiN ARC layer.
• It was found that the detected fluorine reacted with the Al line in the under-layer.
• The fluorine had diffused through the TiOxNy film due to low density.

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 (TiOxNy-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 TiOxNy film, causing decreased film density due to the corrosion of the TiN ARC layer.