A. H. Mueller

In situ study of interface reactions of ion beam sputter deposited (Ba0.5Sr0.5)TiO3 films on Si, SiO2, and Ir

(Ba0.5,Sr0.5)TiO3 (BST) thin films were deposited on MgO, Si, SiO2 and Ir surfaces by ion beam sputter deposition in oxygen at 700 °C. In situ spectroscopic ellipsometry (SE) has been used to investigate the evolution of the BST films on different surfaces during both deposition and postannealing processes. First, the optical constants of the BST films in the photon energy range of 1.5–4.5 eV were determined by SE analysis on crystallized BST films deposited on MgO single crystal substrates. The interfaces in BST/Si and BST/SiO2/Si structure were examined by SE and Auger electron spectroscopy depth profiles. Subcutaneous oxidation in the BST/Ir structure was observed by in situ SE during both ion beam sputter deposition and postdeposition annealing in oxygen at 700 °C. A study of the thermal stability of the Ir/TiN/SiO2/Si structure in oxygen at 700 °C was carried out using in situ SE. The oxidation of Ir was confirmed by x-ray diffraction. The surface composition and morphology evolution after oxidation ...

Real-time observations of interface formation for barium strontium titanate films on silicon

Ba.5Sr.5TiO3 (BST) film growth by ion sputtering on bare and thermally oxidized silicon was observed in real time using in-situ spectroscopic ellipsometry and time of flight ion scattering and recoil spectrometry techniques. At the outset of BST film deposition on silicon, an approximately 30 A film with intermediate static dielectric constant (K∼12) and refractive index (n∼2.6 at photon energies of 1.5–3.25 eV) interface layer formed on bare silicon. The interface layer growth rate was greatly reduced on an oxidized silicon substrate. The results have profound implications on the static dielectric constant of BST.

Model for interface formation and the resulting electrical properties for barium-strontium-titanate films on silicon

The interface formation between sputtered barium strontium titanate (BST) films and both Si and SiO2 substrate surfaces has been followed using real-time spectroscopic ellipsometry and the mass spectrometry of recoiled ions. In both substrates an intermixed interface layer was observed and subcutaneous Si oxidation occurred. A model for the interface formation is proposed in which the interface includes an SiO2 film on Si, and an intermixed film on which is pure BST. During the deposition of BST the interfaces films were observed to change in time. Electrical characterization of the resulting metal–BST interface capacitors indicates that those samples with SiO2 on the Si surface had the best electrical characteristics.

Studies of ferroelectric film growth and capacitor interface processes via insitu analytical techniques and correlation with electrical properties

Abstract Precise control of composition and microstructure of multicomponent oxide thin films is critical for the production of ferroelectric and high dielectric constant thin film devices. In addition, the integration of film-based capacitors with semiconductor substrates, for device fabrication, requires good control of the composition and structureof the dielectric/substrate and top electrode / dielectric interfaces to control the capacitor properties. In order to understand the processes described above, we are using a variety of integrated complementary in situ analytical techniques including time-of-flight ion scattering and recoil spectroscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and ex situ methods such as transmission electron microscopy, scanning force microscopy, and scanning electron microscopy. Examples of studies recently performed by our group that are reviewed here include: (a) effects of microstructure on the oxidation of Ti-Al layers that can be used in a dual functionality as a diffusion barrier and bottom electrode for integration of ferroelectric capacitors with semiconductors; (b) studies of the surface and dielectric layer/bottom electrode interface during growth of BaxSr1−xTiO3 films on Ir/TiN/SiO2/Si for fabrication of BST capacitors for DRAMs; and (c) studies of the effect of interface contamination and structure on the electrical properties of BST capacitors for high frequency devices.

Combined Spectroscopic Ellipsometry and Ion Beam Surface Analysis for In-Situ Real-Time Characterization of Complex Oxide Film Growth

In-situ real time characterization of chemically and structurally complex thin films is becoming important as complex materials are finding more applications in electronic devices. To this end, a unique thin film growth and deposition system was constructed combining a multi-target sputter deposition system with spectroscopic ellipsometry and time-of-flight ion scattering and recoil spectroscopy. This system is demonstrated with studies on YBa 2 Cu 3 O 7−δ and BaSrTiO 3 films.

Development of Materials Integration Strategies for Electroceramic Film-Based Devices Via Complementary In Situ and Ex Situ Studies of Film Growth and Interface Processes

We review our studies of film growth and interface processes performed using complementary in situ and ex situ characterization techniques that provide valuable information critical to the development of materials integration strategies for the fabrication of electroceramic film-based devices. Specifically, we review our work performed using in situ time-of-flight ion scattering and recoil spectroscopy (TOF-ISARS) / X-ray photoemission spectroscopy (XPS) / spectroscopic ellipsometry (SE), in conjunction with ex situ TEM and other techniques to study film growth and interface processes critical to the fabrication of non-volatile ferroelectric memories (NVFRAMs), dynamic random access memories (DRAMs), and high frequency devices based on high-K thin films. TOF-ISARS involves three distinct but closely related experimental methods, namely: ion scattering spectroscopy, direct recoil spectroscopy and mass spectroscopy of recoiled ions, which provide monolayer-specific information on film growth and surface segregation processes. Spectroscopic Ellipsometry enables investigation of buried interfaces. XPS provides valuable information on the chemistry of surface and interfaces. Specifically, we discuss: a) studies of oxidation of Ti-Al layers and synthesis and properties of La 0.5 Sr 0.5 CoO 9 /Ti-Al heterostructured layers for integration of PZT capacitors with Si substrates, and b) studies of BaSr x Ti 1 m x O 3 layer integration with Si substrates relevant to DRAMs, high frequency devices and high-K gate oxides for integrated circuits. This review shows the power of combined in situ / ex situ analytical techniques to provide valuable information for material integration strategies for electroceramic thin film-based devices.

Real-time study of oxygen in c-axis oriented YBa2Cu3O7 - δ thin films using in situ spectroscopic ellipsometry

The oxygen transport process in c-axis oriented YBa2Cu3O7−δ thin films was investigated in real time during deposition and postdeposition oxidation using in situ spectroscopic ellipsometry (SE). Two transport regimes dominated by oxygen out- and in-diffusion have been observed during deposition by ion beam sputtering at 700 °C. The effect of oxygen partial pressure on the extent of oxidation of as-deposited films has also been studied during the postdeposition cooling process. The thermodynamic stability of the grown films was examined by real time SE during the postannealing process. The relaxation time for oxygen diffusion has been found to decrease with higher oxygen partial pressures. The imaginary part of the pseudodielectric function 〈e2〉 at an absorption peak was quantitatively correlated to the oxygen concentration. The pseudodielectric functions of oxygen deficient YBa2Cu3O6 films in the temperature range from 27 to 700 °C have been modeled using Lorentz oscillators.

In situ real-time studies of oxygen incorporation in complex oxide thin films using spectroscopic ellipsometry and ion scattering and recoil spectrometry

The surface termination of c-axis oriented YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) and the oxygen incorporation mechanism has been investigated using a unique combination of spectroscopic ellipsometry (SE) and time of flight ion scattering and recoil spectrometry (ToF-ISARS). The high surface sensitivity of the ToF-ISARS technique combined with the bulk oxygen sensitivity of SE are shown to yield complimentary information. The SE provided the film orientation and quality, while ToF-ISARS supplied surface compositional and structural information and enabled isotopic {sup 18}O tracer studies. It was determined that the O content of the film had little effect on the surface termination of the film, indicating a lack of labile Cu(1) sites at the c-axis oriented YBCO surface. Also, strong evidence for a Ba or BaO terminated structure is shown. The data related to the {sup 18}O tracer studies indicate that O from the reaction ambient incorporates only into the labile Cu(1) sites during both deposition and annealing, while stable O sites were populated with O from the sputtered target, indicating either the need for sputtered atomic O or sputtered YCuO complexes to occupy the stable Cu(2) sites.

In situ study of barrier layers using spectroscopic ellipsometry and mass spectroscopy of recoiled ions.

An in situ study of barrier layers using spectroscopic ellipsometry (SE) and Time-of-Flight (ToF) mass spectroscopy of recoiled ions (MSRI) is presented. First the formation of copper silicides has been observed by real-time SE and in situ MSRI in annealed Cu/Si samples. Second TaSiN films as barrier layers for copper interconnects were investigated. Failure of the TaSiN layers in Cu/TaSiN/Si samples was detected by real-time SE during annealing and confirmed by in situ MSRI. The effect of nitrogen concentration on TaSiN film performance as a barrier was also examined. The stability of both TiN and TaSiN films as barriers for electrodes for dynamic random access memory (DRAM) devices has been studied. It is shown that a combination of in situ SE and MSRI can be used to monitor the evolution of barrier layers and detect the failure of barriers in real-time.

Studies of ferroelectric heterostructure thin films and interfaces, via in situ analytical techniques

Abstract The science and technology of ferroelectric thin films has experienced an explosive development during the last ten years. Low-density non-volatile ferroelectric random access memories (NVFRAMs) are now incorporated in commercial products such as “smart cards”, while high permittivity capacitors are incorporated in cellular phones. However, substantial work is still needed to develop materials integration strategies for high-density memories. We have demonstrated that the implementation of complementary in situ characterization techniques is critical to understand film growth and interface processes, which play critical roles in film microstructures and properties. We are using uniquely integrated time of flight ion scattering and recoil spectroscopy (TOF-ISARS) and spectroscopic ellipsometry (SE) techniques to perform in situ, real-time studies of film growth processes in the high background gas pressure required to growth ferroelectric thin films. TOF-ISARS provides information on surface processes, while SE permits the investigation of buried interfaces as they are being formed. Recent studies on SrBi2Ta2O9 (SBT) and BaxSr1-xTiO3 (BST) film growth and interface processes are discussed.