(Ba,Sr)TiO3 dielectrics for future stacked-capacitor DRAM

Thin films of barium-strontium titanate (Ba,Sr)TiO3 (BSTO) have been invest igated for use as a capacitor dielectric for future generations of dynamic random-access memory (DRAM). This paper describes progress made in the prep aration of BSTO films by liquid-source metal-organic chemical vapor deposit ion (LS-MOCVD) and the issues related to integrating films of BSTO into a D RAM capacitor. Films of BSTO deposited on planar Pt electrodes meet the ele ctrical requirements needed for future DRAM. The specific capacitance and c harge loss are found to be strongly dependent on the details of the BSTO de position, the choice of the lower electrode structure, the microstructure o f the BSTO, the post-electrode thermal treatments, BSTO dopants, and thin-f ilm stress. Films of BSTO deposited on patterned Pt electrodes with a featu re size of 0.2 mu m are found to have degraded properties compared to films on large planar structures, but functional bits have been achieved on a DR AM test site at 0.20-mu m ground rules. Mechanisms influencing specific cap acitance and charge loss of BSTO films are described, as are the requiremen ts for the electrode and barrier materials used in stacked-capacitor struct ures, with emphasis given to the properties of the Pt/TaSi(N) electrode/bar rier system. Major problems requiring additional investigation are outlined .