A novel application of polyimide-W-Al/Cu for VLSI interconnect

Polyimide (PI)-W-Al/Cu interconnect metallurgy for wiring is proposed for device applications. The major advantages of this structure such as the ability to use an insulator with lower dielectric constant for performance, and contact etchability (good selectivity to the bottom substrate) without damage to underlying structures is reported. It is demonstrated that chemically vapor deposited (CVD) blanket W can be deposited into high aspect ratio polyimide contacts. Subsequently is can be planarized on polyimide surface by an etchback process involving chemical and mechanical polishing. In addition, the structure is successfully applied to bipolar devices with severe topography. The specific contact resistivities of 2-4×10^-8 Ω-cm ² are realized between PtSi Schottky diodes and the proposed structure with and without inorganic underlayers. Using Si₃N ₄ as an inorganic sodium barrier underlayer the same contact structure is applied to field effect transistors (FET) with shallow junctions (0.1 μm-0.13 μm) and 0.6 μm poly gate (150 nm) with thin silicide (20 nm) yielding ideal device behavior. The proposed structure can be repeated to provide multilevel metallization