Development and Evaluation of Wafer-Level SiO₂ Film Thickness Reference Material

This paper developed a 12-inch wafer-level silicon dioxide (SiO₂) film thickness reference material intended for calibration applications in integrated circuit manufacturing lines, with a nominal film thickness of 50 nm. The standard was fabricated on a high-purity 12-inch silicon wafer using a thermal oxidation process to grow a dense SiO₂ film layer. In order to enhance usability and positional repeatability, photolithography was employed to pattern alignment and tracking marks on the wafer surface. Film thickness calibration was carried out using a laser-based spectroscopic ellipsometer, and an uncertainty evaluation model was established. The final thickness value was traceable to a national primary standard. Experimental results demonstrated that the standard exhibits good uniformity and stability across the full wafer area, with a certified thickness value of 53.86 nm and an associated expanded uncertainty of 0.60 nm (k=2). In addition, trace metal contamination on both the front and back sides of the wafer was analyzed using vapor phase decomposition coupled with inductively coupled plasma mass spectrometry (VPD-ICPMS) and total reflection X-ray fluorescence (TXRF). Concentrations of 19 common metal ions were found to be below 5 × 10¹⁰ atoms/cm², fully meeting the stringent contamination control requirements of semiconductor production environments.