Photosensitive Aqueous Alkaline Developable Magnetic Material for Inductor and Balun Transformers in 3D Wafer-Level Packages

In the high frequency of 5G-6G communication device applications, the planar inductor and balun transformer are the key passive device components in the low height wafer level packaging. The authors have been studied in the previous papers [1], [2], the patterning magnetic material at the surrounding balun transformers and inductors gave a high electric magnetic shielding effect [1] and high inductance with down sized coil having −45% [2], calculated by COMSOL® simulation. To obtain patterned magnetic material, the authors had investigated about i-line photosensitive type magnetic material which could be developed by a conventional aqueous alkaline developer for wafer process. The i-line sensitive negative tone magnetic materials were designed by using aqueous alkaline soluble polymer, crosslinker, photo-initiator, and magnetic particles with dispersion agent in the organic solvent. Lithographic performance was demonstrated by suing USHIO UV exposure with contact mask print exposure to form 200 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{m}$</tex> line and space and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$300 \mu \mathrm{m}$</tex> contact holes. However, it was found that there were many particle residues remained at the bottom of contact holes and on the substrates because of large specific gravity induced sinking of the magnetic particles at bottom during development process in water. The authors have investigated new rinse solution to overcome the patterning defect issue during the photo sensitive magnetic material lithography process, without suffering any lithographic performance.