Ta₂O₅ capacitors for 1 Gbit DRAM and beyond

摘要

A thermally robust Ta₂O₅ capacitorapplicable to the 1 Gbit DRAM and beyond was developed. From thedegradation-free Ta₂O₅ capacitor with aTiN/poly-Si top electrode, the sputtered-TiN was replaced by thePECVD-WN to improve the step coverage for the complicated capacitorstructure. The Ta₂O₅ capacitor with aPECVD-WN/poly-Si top electrode had a better thermal stability in thecomplicated capacitor structure than that with sputtered-TiN/poly-Si, asa result. Capacitance of more than 90 fF/cell and leakage current lowerthan 2×10-15 A/cell were obtained by applying theWN/poly-Si top electrode and a 3.5 nm Ta₂O₅capacitor dielectric to a cylindrical capacitor with rugged poly-Sisurface (projection area=0.4 μm2). TDDB measurementpredicted longer lifetime than 10 years at the device operating voltage.This new capacitor structure, therefore, surpasses the requirements forthe 1 Gbit DRAM