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A process for etching vias in extremely thick (85 to 152 μm) HD MicroSystems polyimide PI2611 was developed using commercial reactive ion etching tools. Sloped via profiles were obtained using a combination of hard masks made of aluminum and silicon dioxide thin films, combined with reactive ion etch steps in pure O2 and O2/CF4. The deep via profiles provided good step coverage. These vias, coated with a 3-μm-thick copper film, produced satisfactory electrical continuity between layers of package interconnects. The process is reproducible, reliable, and, hence, practically useful for fabricating a small number of parts in spite of extended etch periods.