Integration of a split word line ferroelectric memory using a novel etching technology

A ferroelectric random access memory (FeRAM) was fabricated using a novel processing technology to investigate the characteristics of the FeRAM with a new cell structure. The new cell includes two split word lines (SWL's) which play roles not only as word lines but also as plate lines. This structure can enhance operation speed and prevent the decrease of remnant polarization of non-selected cell capacitors in write/read operation since SWL's can be driven independently. The cell capacitors were composed of Pt electrodes and the sol-gel derived Pb(Zr,Ti)O₃ films. An efficient procedure to realize the new cell structure is proposed by introducing a new etching method, which includes the one-step patterning of a metal-ferroelectric-metal (MFM) and a metal-ferroelectric (MF) using a metal mask (Ti or Ru) and an etch stopping layer (TiO₂ or RuO₂). The degradation of the ferroelectric capacitors due to etching process and interlayer dielectric (ILD) deposition process was almost recovered by annealing in oxygen. Memory operation was confirmed in the 2T/2C SWL FeRAM with the capacitor area down to 16 μm².