Bum-Ki Moon

Lead Content Control in (Pb, La)(Zr, Ti)O3 Films Using Ar/O2 Sequential Rapid Thermal Process

A new method of controlling the lead (Pb) profile in (Pb, La)(Zr, Ti)O3 (PLZT) capacitor films with top and bottom SrRuO3 (SRO) electrodes has been developed using an Ar/O2 sequential crystallization process. This new technique makes it possible to realize good fatigue properties and a low leakage current density in the films. We found that the gas ambient of the rapid thermal process (RTP) affects Pb evaporation behavior during PLZT crystallization; an Ar ambient promotes Pb evaporation more than an O2 ambient. The Ar/O2 sequential RTP was introduced on the basis of the optimum design of the Pb profile in crystallized PLZT films. A good ferroelectric capacitor with a Pt/SRO/PLZT/SRO/Pt structure was achieved by controlling the Pb composition in the bulk of PLZT films as well as at the interfaces to the electrodes, resulting in high endurance and low leakage current density.

Comparison of Materials for the Ferroelectric Thin Film to be Integrated into High Density FeRAMs

Lead zirconate titanate (PZT) thin films with two different compositions have been used to fabricate integrated ferroelectric capacitors. The capacitors with the higher Ti content exhibited the more square hysteresis loops with peak 2Pr values of 67.3 μ C/ cm2 at room temperature. Static hysteresis loops are used to extract static coercive voltages for both compositions in the temperature range 25°C to 125°C. These static coercive voltages are used to extrapolate the imprint limited lifetime. The Ti rich composition exhibited the faster shift of the hysteresis loop during the imprint experiment resulting in a shorter extrapolated lifetime.

Characteristics of an Oxygen Barrier Based on Bi-layered Ir

For high-density ferroelectric random access memory devices (FeRAMs) with capacitor over plug (COP) structure, oxygen diffusion barriers based on bi-layered Ir have been investigated. This paper describes the detailed characteristics of the barriers. A bi-layered Ir barrier was fabricated by repeating the deposition and RTO treatment of an Ir metal film, which was very effective to obtain excellent barrier properties against oxygen diffusion. Surface roughening was shown after RTO, but can be suppressed by lowering the RTO temperature. The roughening is caused by the formation of a gaseous phase of IrOx during RTO, and not by the formation of Ir hillocks. The stress of the bi-layered Ir barrier is tensile after RTO, which makes further stacking of more layers on the barrier with good adhesion possible. Performance of this barrier was checked using the post annealing in 18O isotope ambient at 650°C for 2 hours. SIMS profile showed the barrier prevented the diffusion of 18O, effectively. The above results strongly suggest that the bi-layered Ir barrier can be applied to the COP structure for high-density FeRAMs.

Oxygen Diffusion Barriers for High-Density FeRAMs

For high-density ferroelectric random access memories (FeRAMs) with capacitor over plug (COP) structure, oxygen diffusion barriers have been investigated. This paper describes the excellent properties of two newly developed diffusion barriers, which are based on a) stoichiometric-IrO 2 films and b) surface treated Ir-films. The IrO 2 barrier was successfully optimized by forming stoichiometric IrO 2 , by deposition temperature control and by decreasing mechanical stress. Surface treatment of Ir-metal layer by using RTO (rapid thermal oxidation) was very effective for obtaining excellent barrier properties, which could be further improved by repeated deposition and RTO treatment leading to bi- or multilayer structures. When applied to fully stacked-PZT capacitors, both barrier types inhibited the oxidation of an underlying W-plug even after annealing at 650C for 2 hours in oxygen ambient. Q sw values of PZT capacitors were around 30 w C/cm 2.

Effective Orientation Control of Pb(Zr0.4Ti0.6)O3 Thin Films Using A New Ti/Pb(Zr0.4Ti0.6)O3 Seeding Layer

The effect of thin Ti/PbZr 0.4 Ti 0.6 O 3 seed layers on the properties of PbZr 0.4 Ti 0.6 O 3 (PZT) capacitors has been investigated. The seed layer is based on a bi-layer of thin Ti and thin PZT with a total thickness ranging from 10 to 25 nm, which was deposited on Ir/Pt or Ir/IrO 2 /Pt by sputtering. After crystallization of the seed layers the main 130-nm-thick PZT film was deposited and crystallized. As a result, a highly preferred (111)-orientation of the PZT was obtained on a 10-nm-thick seed layer, where the peak intensity ratios of (111)/{100} and (111)/{110} are about 100 and 20, respectively. The 10-nm-thick seed forms a pyrochlore phase with a very smooth surface, where the formation of the pyrochlore phase is attributed to Pb diffusion, resulting in a Pb deficient stoichiometry. The seed layer transformed to the perovskite phase during the main PZT crystallization. It is shown that an IrO 2 layer beneath the Pt can prevent Pt layer degradation related to the volume expansion due to the oxidation of Ir during the main PZT crystallization. Capacitors with the 10-nm-thick seed layer fabricated on the Ir/Pt and Ir/IrO 2 /Pt substrates showed typical 2 Pr values of 44.0 μC/cm 2 and 41.2 μC/cm 2 , respectively. The voltage found for 90%-polarization saturation is about 3.0 V, and the capacitors are fatigue-free at least up to 10 10 switching cycles.