Gerhard Beitel

Integration of H2 barriers for ferroelectric memories based on SrBi2Ta2O9 (SBT)

Abstract In this study, integration of an hydrogen barrier into a FeRAM process flow is investigated. It is reported in the literature that ferroelectric properties can be maintained after hydrogen annealing by using IrOx as a top electrode [16][17][18]. Advantage of materials like IrOx is less catalytic activity compared to Pt. However, we found that IrOx is not a promising candidate for top electrode barrier. (Pt)/IrOx/SBT/Pt capacitors are prone to shorting or exhibit high leakage. IrOx films are very easily reduced by reducing ambient which will result in peeling off. Also, IrOx films tend to oxidize Ti or TiN layers immediately. Therefore, other barrier materials or layer sequences like Ir/IrOx have to be considered. For protection of the entire capacitor an Encapsulation Barrier Layer (EBL) is required. In this study, LPCVD SiN is used. LPCVD SiN is a standard material in CMOS technology. Production tools are available and it is well known as hydrogen barrier. By modifying the deposition process and using a novel process sequence, no visual damage of the capacitors after SiN-deposition and FGA is seen. Also, no degradation of electrical properties after capacitor formation as well as after SiN-deposition and FGA is observed. However, after metal 1 and metal 2 processing, 2Pr values at 1.8V are reduced from 12μC/cm2to 2μC/cm2. Polarization at 5.0V is not affected.

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.