Marcus Kastner

FeRAM technology for high density applications

Abstract Ferroelectric random access memories (FeRAMs) are new types of memories especially suitable for mobile applications due to their unique properties like nonvolatility, small DRAM-like cell size, fast read and write as well as low voltage/low power behavior. Although standard CMOS processes can be used for frontend and backend/metallization processes, FeRAM technology development has to overcome major challenges due to new materials used for capacitor formation. In this paper, advantages and disadvantages of different ferroelectric materials and major development issues for high density applications are discussed. Results of a 0.5 μm ferroelectric process using SrBi 2 Ta 2 O 9 as ferroelectric layer, Pt as electrode material as well as two-layer tungsten/aluminum metallization are given as an example. Integration and reliability issues are reviewed.

Review of SrBi2Ta2O9 thin films capacitor processing

Abstract Ferroelectric memories (FeRAMs) are new types of memories especially suitable for mobile applications due to their unique properties like non-volatility, small DRAM-like cell size, fast read and write as well as low voltage/low power behavior. Although standard CMOS processes can be used for frontend and backend processes, FeRAM technology development has to overcome major challenges due to new materials used for capacitor formation. This work gives an overview of SrBi2Ta2O9 (SBT) thin films capacitor processing using Pt as electrode material. The study describes in detail SBT formation using metal organic deposition (MOD) as well as influence of electrode thickness and capacitor patterning on SBT electrical properties. Also, results for integration of the capacitor process into a 0.5μm CMOS process with 2-layer tungsten/aluminum metallization as well as stacked capacitor results are given.

Low temperature process and thin SBT films for ferroelectric memory devices

Abstract At crystallization temperatures of about 800°C bismuth layered oxide SrBi2Ta2O9 (SBT) deposited by MOD develops good ferroelectric properties for use in FeRAM devices. But scaling down the film thickness of SBT below 150 nm only shorts are measured at this crystallization temperture after top electrode deposition. Working Pt/SBT/Pt-capacitors are achieved by reducing the crystallization temperature. Also temperatures of 800°C are too high for integration of the SBT module in a stacked capacitor architecture for high density memory devices. Therefore, a process is needed to reduced the crystllization temperature of SBT, called ”Low Temperature Process“. In this work the electric properties of spin-on processed SBT crystallized in a temperature window from 650°C up to 800°C are investigated. As shown by XRD, transtion of the nonferroelectric Fluorite phase to the Aurivillius phase takes place at approximately 625°C. Increasing the cystallization temperature gives better crystaallized SBT films with bigger SBT graains. However, film prosity is also increasing with temperature. Electrical results of stoichiometric variations of SBT are presented. SEM pictures show that cluster formation is correlated with less film porosity at lower temperatures.

Influence of the measurement parameters on the reliability of ferroelectric thin films

Abstract The fatigue behavior of PZT thin films was investigated. The fatigue excitation signal was changed with respect to the shape, the amplitude, and the frequency of the signal. It is shown that the fatigue excitation signal has a strong influence on the fatigue behavior of the films. Additionally, electrical characterization of a single 1 μm2 SBT capacitor is reported.

Thickness dependent morphology and electrical characteristics of SrBi2Ta2O9 deposited by metal organic decomposition

Abstract The dependence of morphology of SrBi2Ta2O9 (SBT) deposited by Metal Organic Decomposition (MOD) on film thickness and annealing temperature during the crystallization anneal was investigated. From Atomic Force Microscope (AFM) images of these films it can be seen that nucleation and grain growth strongly depends on SBT thickness which also affects the electrical characteristics of the correspondent Pt/SBT/Pt-capacitors. In this work results of a morphological study of SBT films with thicknesses between 40 and 110nm and annealing temperatures between 650°C and 725°C will be presented.