27 May 2011 Reflectometry for TSV etching depth inspection
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TSV (Through Silicon Via) is a vertical via that passes through a silicon wafer or chip. This technology is a major enabler for three-dimensional integrated circuits (3D ICs) of stacking different functional chips. Vertical stacking chips of 3D ICs allows gates to be placed closer and thereby provides more computing process in a compact space. As TSV technique with unique processing steps that are not used in standard 2D ICs, a number of new parameters need to be measured and controlled. TSV etching depth is a critical parameter for ensuring the performance of 3D ICs, thus metrology and inspection of the TSV etching depth are very profitability of the overall manufacturing process. Spectroscopic reflectometry (SR) is currently being used in industry to measure the internal reflectance of thin films, from which the thickness and other properties can be obtained. It is a non-contact and non-destructive in-line metrology tool. In this study, we demonstrate the use of SR by employing the fast Fourier transform (FFT) algorithm for measuring the etching via depth and the thickness of oxide layer in one shot measurement. First, the specifications of reflectometer system, such as spectral range and resolution of spectrometer for depth analysis are discussed. The depth resolution is better in the longer measuring spectral range, thus small difference of TSVs' depth can be well distinguished. The spectrometer with high resolution is used to collect the authentic spectrum from etching depth with high aspect ratio. We verified our system through a mutual measurement comparison with the national standard traceable step height system. Our system is capable of measuring step height up to 100 um and measurement precision is in the range of 0.6 um. In this report, TSV arrays with nominal CD 5~25 um, and aspect ratio up to 10 are measured. Metrology results from actual 3D interconnect processing wafers indicate our system provides excellent correlation to cross-section scanning electron microscope (SEM) measurement results. The maximum discrepancy between each other is smaller than 1 um.
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Wei-Te Hsu, Wei-Te Hsu, Yi-Sha Ku, Yi-Sha Ku, "Reflectometry for TSV etching depth inspection", Proc. SPIE 8082, Optical Measurement Systems for Industrial Inspection VII, 808226 (27 May 2011); doi: 10.1117/12.889238; https://doi.org/10.1117/12.889238

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