In-line through silicon vias etching depths inspection by spectroscopic reflectometry

• Inspection of high aspect ratio (up to 17:1) TSV depth and critical dimensions (CD).
• Monitoring realized by spectroscopic reflectometry using in-line wafer metrology tool.
• Application of rigorous coupled wave analysis (RCWA) for TSV CD and depth.

Through-silicon via (TSV) technology is a key feature for 3D circuit integration. The nondestructive metrology of deep-etched structures with aspect ratio of >10 and patterns with lateral dimensions in the range up to 5 μm remains an challenge and can be overcome by destructive control. In this paper the inspection of TSV depth and critical dimensions (CD) of their opening were performed nondestructively by an industrial thickness measurement tool (UV–VIS spectral reflectometer). The possibilities and limits of in-line optical tools for the characterization of the high density TSV array of high aspect-ratio square vias with tapered profile in Si were examined. TSV with CD from 3 up to 7 μm, pitch in the range of 7–11 μm, and etch depth of 50–70 μm were investigated. The TSV depth was determined using the interference effect between reflected waves from the top and bottom surfaces of the TSV structures. The rigorous coupled wave analysis (RCWA) is successfully applied to the analysis of the spectral reflectance for the determination of the TSV top and bottom CD and profile evaluation. It was shown that this method can be used for the monitoring of geometrical parameters of TSVs with dimensions from 3 μm and aspect ratios up to 17:1. The non-destructive measurement data provide excellent correlation with SEM results.

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