Igor Kasko

Influence of deposition conditions on Ir/IrO2 oxygen barrier effectiveness

The influence of the deposition temperature during the reactive sputtering process on the microstructure of thin Ir and IrO2 films deposited on oxidized Si substrates was investigated and related to the oxygen barrier effectiveness. For this purpose differential thermal analysis combined with residual gas analysis by mass spectrometry was used for the investigation of the microstructural and chemical behavior of the as-sputtered IrO2 films upon heating. Moreover, in situ stress relaxation analyses up to 900 °C, in and ex situ x-ray diffraction measurements were done for various annealing conditions. The investigated polycrystalline IrO2 films exhibited a large compressive stress and a distorted lattice due to the sputter deposition process. It is demonstrated that a high deposition temperature involves a delayed relaxation of the IrO2 grains which is causing an extrinsic, enhanced defect controlled oxygen mobility for the annealing temperatures below the recrystallization. The well-known low intrinsic oxy...

Oxygen tracer diffusion in IrO2 barrier films

The 18O tracer diffusion method was used to investigate oxygen diffusion in reactively dc-sputtered IrO2 films. The profile measurements were done by secondary ion mass spectrometry. For the investigation of the oxygen diffusivity in the samples a temperature range from 600 to 765 °C was chosen. The oxygen tracer diffusion in IrO2 films was found to be described by an Arrhenius law with D0=(2.8±2.5)10−6 m2 s−1 and an activation energy of Ea=(2.73±0.07) eV. It was also shown that the extrinsic oxygen diffusion is strongly influenced by the film preparation conditions, which is especially important for the application of IrO2 films as an oxygen barrier in future memory device applications.

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.

An Overview of FeRAM Technology for High Density Applications

Ferroelectric random access memories (FeRAMs) are new types of memories especially suitable for mobile applications due to their unique properties such as 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 0.5μm ferroelectric process using SrBi 2 Ta 2 O 9 (SBT) as ferroelectric layer, Pt as electrode material, and 2-layer tungsten / aluminum metallization are discussed.

Investigation of oxygen diffusion barrier properties of reactively sputtered iro2 thin films

Abstract High quality IrO2 films are of great interest as electrodes and oxygen barrier layers for PZT and SBT based integrated non-volatile ferroelectric memories. The investigated IrO2 films were reactively DC-sputtered in an Ar/O2 atmosphere. Generic curves were used for the optimization of the film preparation. The microstructure of the sputtered films was characterized by XRD and it was found that the texture can be adjusted from (110) to (200) by slightly varying the oxygen partial pressure at higher substrate temperatures. This change in microstructure is accompanied by a compositional change from oxygen substoichiometric to oxygen overstoichiometric films. Moreover, the influence of the microstructure on thermal stability and oxygen barrier effectiveness was investigated by SIMS depth profiling using an 18O2 tracer diffusion method. Oxygen diffusion for process-relevant temperatures (550°-765°C) was systematically investigated and for the first time oxygen diffusion coefficients in IrO2 were determined by fitting a mathematical model to the measured profiles.