Chiplet Encapsulation and Planarization with 100 μm Deep Gaps Using AlN Powder Spray + Sputter Hybrid Deposition

This study presents a hybrid chiplet encapsulation structure that integrates aerosol‐deposited (AD) and sputtered aluminum nitride (AlN) films to address thermal and mechanical challenges in advanced packaging. AD AlN rapidly fills high‐aspect‐ratio trenches (100 μm deep, 10 μm wide) at room temperature and provides an excellent coefficient of thermal expansion similar to silicon. After conformal filling, the overburden AD AlN is removed by mechanical polishing, enabling subsequent deposition of sputtered AlN for enhanced vertical heat dissipation. A 1.7 μm‐thick sputtered AlN film exhibited high thermal conductivity of 113 (+26.8/–21.5) W/(m * K), as measured by frequency‐domain thermoreflectance. A copper buffer layer was inserted between the silicon substrate and AD AlN to absorb impact stress during deposition, which effectively protected the substrate as confirmed by transmission electron microscopy‐energy dispersive X‐ray spectroscopy (TEM‐EDS) analysis. Scanning electron microscopy imaging revealed void‐free trench filling and smooth surface morphology. Warpage analysis identified overburden AD AlN as the main source of compressive stress, while the in‐trench and sputtered AlN layers had minimal impact. This dual‐deposition approach leverages the advantages of both methods—AD for rapid trench filling and sputtering for thermal performance—offering a scalable, thermally efficient, and mechanically robust solution for next‐generation electronic packaging.