When ferroelectric layer in FRAM is being deposited, the bottom electrode and poly-Si plug which maintains direct contact with the bottom electrode are exposed to the highly oxidizing gas atmosphere with high temperature. This may lead to the oxidation of poly-Si plug leading to poor contact property with adjacent electrode degrading contact resistance. If there are reactions between layers, these will cause the films peeling off by large volume expansion and high leakage current of ferroelectric film due to rough surface morphology of electrodes. Therefore, instead of adapting single electrode as the bottom electrode in stack capacitor, it is quite desirable to insert additional layer that can suppress the O and Si diffusion and we call this extra layer, "diffusion barrier". The known barrier materials exists in different form such as TiN, TaN, TiAlN, WSiN, TaSiN. In this research, TaSiN is used because of its excellent oxidation resistance, simple preparation method and moderate resistivity. TaSiN has amorphous phase which lack of grain boundary that may act as fast diffusion path of unwanted atoms and maintains this phase up to 800℃.In this study, we have analyzed the thermal stability and electrical compatibility of the diffusion barrier with LSCO(La-Co-Sr-oxide) and Ir, Ru, Pt metal electrodes. All specimens were annealed with RTA from 500∼800℃ in $O_2$ atmosphere and thermal stability and interfacial characteristics were observed with XRD, SEM, AFM and TEM. As a result, no visible compound formation except for the metal oxides were found through entire annealing temperature indicating that no reaction has occurred between the existing layers. Electrical compatibility were tested using HP4145B semiconductor analyzer and four-point probe. LSCO/Ir/TaSiN/Poly-Si structure has been proven to possess good electrical property by calculating the linear resistance of the structure from the acquired I-V curve and the resistance value is 2∼6μΩ up to 700℃ annealing temperature.
PZT film of 1000Å was deposited on LSCO/Ir/TaSiN/Poly-Si and P-E hysteresis curve and leakage current characteristics were observed using Precision Pro Material Analyzer and Keithly 617 Electrometer. As a result, the $2P_r$ value of $53.6μC/㎠$ and 1.5V coercive field were obtained. Also, the ferroelectric capacitor maintained the leakage current value of $10_{-8}A/㎠$ indicating that the LSCO/Ir/TaSiN/Poly-Si bottom electrode can be one of the possible bottom electrode structure in ferroelectric stack capacitor.
