Conformal Photoresist Coating of a Silicon Blind Via Based on an Acoustic Resonance Atomizer

Driven by the ongoing trend in the electronics industry toward smaller form factors, three-dimensional interconnections have become effective approaches for high-density integration of chips and devices. Achieving a uniform photoresist coating over nonplanar wafer microstructures has emerged as a critical process in high-density integrated packaging. Conventional spin coating methods face limitations in achieving conformal photoresist coverage within a silicon blind via. To address this challenge, this study introduces a self-developed acoustic resonance atomization nozzle capable of generating micrometer-sized uniform droplets to enable conformal coating on nonplanar wafer surfaces. The influence of three key process parameters (substrate temperature, nozzle-to-substrate height, and coating speed) on the coating quality within a silicon blind via was systematically investigated, revealing the dynamic behavior of photoresist droplet deposition under thermal effects. A scanning electron microscope was employed to characterize the photoresist thickness profile on silicon blind via cross sections. The experimental results demonstrate that the optimized parameter set significantly improves the coverage uniformity within the silicon blind via, successfully achieving a conformal and defect-free photoresist layer in the silicon blind via with a diameter of 50 μm and a depth of 50 μm. This study validates the feasibility of the acoustic resonance atomization method for conformal silicon blind via coating and offers a simple, efficient, and highly uniform alternative for photoresist deposition on nonplanar structures in 3D integrated circuits.