Frequency‐comb‐referenced multiwavelength interferometry for high‐precision and high‐speed 3D measurement in heterogeneous semiconductor packaging

As Moore's law approaches its physical limits, the semiconductor industry has begun to focus on improving I/O density and power efficiency through 2.5D/3D packaging. Heterogeneous integration, which combines integrated circuit blocks from different linewidth processes into a single package, is central to these developments. To ensure stable connections with high yield in the back-end processes, high precision and high speed 3D surface measurement is the prerequisite. Existing methods such as white-light interferometry and confocal microscopy face challenges in balancing resolution, speed, and accuracy in 3D measurements. Here, we report a frequency-comb-referenced multiwavelength interferometry for the measurement of 3D sample profiles without 2π phase ambiguity for advanced packaging. Using four frequency-comb-referenced wavelengths with a fractional stability of 4.77 × 10^-12, the measurement range was extended from ∼400 nm (<i>λ</i>/2) to 1 mm, with the measurement repeatability of 0.258 nm for 32 measurements. The standard step-height samples with 500-µm and 4.5-µm steps, as well as real industrial microbumps in heterogeneous integration packaging, were all successfully measured. Therein, we devised a sequential phase detection method, which enables 5,000 times faster solution determination than the traditional recursive excess fraction method, while maintaining its reliability under noisy conditions. As 2.5D/3D packaging architectures become increasingly complex, our approach will readily meet the critical industrial demands for high-precision and high-speed measurement of multiscale features in advanced semiconductor packaging.