Dual Process Dielectric Formation for Decoupling Capacitors on Flexible Substrates

Large area, high density integrated capacitors within printed wiring boards can provide a substantial decoupling capacitance with very low parasitic inductance. Tantalum pentoxide (Ta₂O₅) is an excellent dielectric for this application due to the relatively high dielectric constant (~ 22-24), however the difficulty of fabricating large, defect-free capacitors has thus far prevented the realization of practical applications. This work demonstrates high performance capacitors with Ta₂O₅ dielectric developed with a two step oxidation scheme consisting of reactive sputtering followed by anodization. Thin films of Ta₂O₅ were deposited by reactive sputtering on silicon and also on Upilex^reg covered glass wafers using dc magnetron sputtering with a gas flow ratio of 10/90 O₂/Ar. In the two-step oxidation scheme, anodization is performed after reactively sputtering tantalum oxide films to obtain a densifled oxide structure. The electrical and physical properties of these two step sputtered/ anodized tantalum oxide films are shown to be superior to those of tantalum oxide films prepared by either anodization or sputtering alone. This work has shown that Ta₂O₅ is a potential dielectric for integrated capacitors that could be used in advanced packaging applications.