Fabrication and characterization of epoxy/BaTiO3 composite embedded capacitor for high frequency behaviors

Embedded capacitor technology is an essential method for miniaturization and high performance of electronic package systems. High dielectric constant epoxy/ceramic composites have been of great interest as embedded capacitor materials for MCM-L applications, because they have good processability and compatibility with printed wiring boards (PWB), in addition to high dielectric constant. In previous work, epoxy/BaTiO₃ composite embedded capacitor films (ECFs) were successfully fabricated and the properties of the capacitors using newly developed ECFs were characterized. The ECFs were mainly composed of epoxy based polymer resin and barium titanate powder. The ECFs were so flexible and tacky before curing that the films could be formed on releasing film, easily detached from the releasing film, and transferred to the surface of interlayer within multi-layered organic substrate. But those ECFs were non-pattemed with the top and bottom electrodes for the dielectric properties measurement. In this study, using ECFs and devices specially designed for correcting stray effect around the capacitors, the dielectric constant and dielectric loss can be measured by the reflection coefficient measured with a network analyzer. For fabricating of test vehicles, ECFs patterning process, investigated in previous work, was applied. ECFs were coated on releasing film with 10_~15mum thickness. Then, ECFs were laminated and cured on Cu coated 4 inch Si wafer, and Cu was sputtered on ECFs. The sputtered Cu foil was patterned, which was used as a mask for ECFs patterning and top electrode. For forming via, Plasma etching which is one of the useful methods for removing the cured epoxy based polymer resin was performed. In the condition of O₂ and CF₄ mixed gases, the epoxy based polymer resin of epoxy/BaTiO₃ composite ECFs was removed by RIE (reactive ion etching) treatment. After RIE treatment, the agglomeration of BaTiO₃ powd- - ers with residue of epoxy based polymer resin was removed by ultrasonic cleaning treatment. The eliminated space by RIE & ultrasonic cleaning was electro-plated with Cu, then top and bottom Cu were connected. Finally, top Cu was patterned for top electrode. Then, using these test vehicles, the high-frequency characteristics are consistent with low frequency characteristics measured with an LCR bridge. The relative error between the high-frequency and the low frequency is estimated to be within 10%. The method is a practical way to obtain the characteristics of ECFs accurately and quickly in final form.