A highly reliable ferroelectric memory technology with SrBi2Ta2O9-based material and metal covering cell structure

A multilevel metal process-based highly reliable ferroelectric memory (FeRA M) has been developed. Highly reliable characteristics have been attained b y two techniques. One is a newly developed ferroelectric material with mixe d superlattice crystal of SrBi2(Ta-x,Nb1-x)(2)O-9 and Bi-2(Ta-x,Nb1-x)O-6, which provides an elevated remnant polarization while keeping a low coerciv e voltage, The other is a metal;covering memory cell structure which makes the use of plasma silicon nitride (p-SiN) passivation possible without redu ction of the ferroelectric thin film by a hydrogen plasma during p-SiN depo sition, which results in no degradation of the characteristics of cell capa citors. The FeRAM cell capacitors with the above newly developed ferroelect ric material and metal covering structure have been fabricated by using a 0 .6-mu double level metal process, The fabricated cell capacitors show highl y reliable characteristics such as the ensured retention of data written at a law voltage of 2.4 V and humidity resistance for 10 y under a high tempe rature of 70 degreesC,which is promising for commercialization of FeRAM and its embedded LSIs.