Microscopic and Non-Site-Specific Measurement Method for Bond Strength of Direct Bonded Wafers and Dies

The demand for 3D integration and advanced packaging technologies is increasing. Direct bonding technologies are gaining popularity as methods to achieve further increases of the input/output densities. Although accurate evaluations of bond strength are essential for reliable wafer-level and die-level integration, the local bond strength is not measurable because of the limitations of conventional measurement methods. Here, we used a nanoindentation method for both wafer-to-wafer and die-to-wafer samples. These measurements provide insights into local bond strength and a wide range of uniformities. The obtained statistic value is equivalent to that obtained by the double-cantilever-beam method in an anhydrous atmosphere, implying that the value obtained by the nanoindentation method is not affected by the measurement environment or the true bond strength. The developed method also enabled the measurement of bond strength in die-to-wafer bonded samples, revealing bond-strength variations within individual dies and identifying potential improvements in the die-level bonding process.