A highly reliable ferroelectric memory technology with SrBi sub(2)Ta sub(2)O sub(9 )-based material and metal covering cell structure

A multilevel metal process-based highly reliable ferroelectric memory (FeRAM) has been developed. Highly reliable characteristics have been attained by two techniques. One is a newly developed ferroelectric material with mixed superlattice crystal of SrBi sub(2)(Ta sub(x),Nb sub(1-x)) sub(2)O sub(9) and Bi sub(2 )(Ta sub(x),Nb sub(1-x))O sub(6), which provides an elevated remnant polarization while keeping a low coercive voltage. The other is a metal covering memory cell structure which makes the use of plasma silicon nitride (p-SiN) passivation possible without reduction of the ferroelectric thin film by a hydrogen plasma during p-SiN deposition, which results in no degradation of the characteristics of cell capacitors. The FeRAM cell capacitors with the above newly developed ferroelectric material and metal covering structure have been fabricated by using a 0.6- mu double level metal process. The fabricated cell capacitors show highly reliable characteristics such as the ensured retention of data written at a low voltage of 2.4 V and humidity resistance for 10 y under a high temperature of 70 degree C, which is promising for commercialization of FeRAM and its embedded LSIs.