Medium Energy Ion Spectroscopy Research Articles

Surface diagnostics by ion scattering spectroscopy in gaseous environment

Nowadays, it is important to perform in-situ analysis of composition and thickness of ultra-thin (∼5-50 Å) surface layers in the course of the surface exposure to plasma or its components. For this aim, a new experimental facility based on the MEPhI Mass Monochromator is being developed, where low and medium energy ion spectroscopy of samples is used just after or during plasma exposure/ion treatment. A differentially pumped energy analyzer is used for recoil ion spectroscopy under grazing incidence conditions in the automated ion mass monochromator. A built-in Penning plasma source is used for plasma/ion treatment of samples. In this paper, the influence of the working gas (during the plasma source operation) on the energy spectra of reflected and recoil ions is studied. It is shown that the peak shape of the energy spectrum of scattered H+ ions increases during gas injection, and, at the same time, the signal intensity of the ionized recoils from the sample decreases. Nevertheless, analysis of the surface composition and thickness of the outer layer could be done at pressures ranging up to 10-4 Torr.

Cation stoichiometry and electrical transport properties of the NdGaO3/(0 0 1)SrTiO3 interface

The interface formed between two wide band-gap insulators, NdGaO3 and SrTiO3 renders metallic behavior, similar to the LaAlO3/SrTiO3 interface. The interface conductivity depends strongly upon oxygen pressure during growth of the NdGaO3 film and subsequent annealing in oxygen. The conductivity of a (10 uc) NdGaO3/SrTiO3 film, pulsed laser deposited at low (pO2 = 10−4 mbar) oxygen pressure, vanishes after annealing at 600 °C in oxygen atmosphere. For a similar interface formed at high oxygen pressure (pO2 = 0.3 mbar), the metallic conductivity remains also after post annealing. Medium energy ion spectroscopy (MEIS) in random (non-channeling) direction showed that a substantial part of Ga is missing in films deposited at low pressure, while optimal stoichiometry is approached in films deposited at high pressure. Aligned (channeling) MEIS likewise show that the Ga/Nd ratio approaches the stoichiometric value as the pressure is increased from 10−4 to 0.3 mbar. This is interpreted as due to gallium desorption from a growing film at high temperature and low oxygen pressure while the re-evaporation of gallium is considerably suppressed at higher pressure. We discuss the possible role of stoichiometry on electrical transport properties.

Inhomogeneous Microstructure and Electrical Transport Properties at the LaAlO3/SrTiO3Interface

Medium-energy ion spectroscopy (MEIS), scanning transmission electron microscopy (STEM) and X-ray photoemission spectroscopy (XPS) were used to investigate the composition and microstructure of LaAlO3/SrTiO3 (LAO/STO) interfaces grown by pulsed laser deposition of LAO on TiO2-terminated STO substrates under different oxidizing conditions. MEIS and XPS indicated Sr/La and Al/Ti intermixing within several atomic layers at all studied interfaces. XPS and STEM revealed that La diffuses deeper than Al. Analysis of the MEIS data suggests inhomogeneous lateral distribution of the diffused elements. This is further supported by the observation of a large positive magneto-resistance at low temperatures. We discuss the role of lateral inhomogeneities on the formation of the electron gas at the LAO/STO interface.

Inhomogeneous Microstructure and Electrical Transport Properties at the LaAlO3/SrTiO3 Interface

Medium-energy ion spectroscopy (MEIS), scanning transmission electron microscopy (STEM) and X-ray photoemission spectroscopy (XPS) were used to investigate the composition and microstructure of LaAlO3/SrTiO3 (LAO/STO) interfaces grown by pulsed laser deposition of LAO on TiO2-terminated STO substrates under different oxidizing conditions. MEIS and XPS indicated Sr/La and Al/Ti intermixing within several atomic layers at all studied interfaces. XPS and STEM revealed that La diffuses deeper than Al. Analysis of the MEIS data suggests inhomogeneous lateral distribution of the diffused elements. This is further supported by the observation of a large positive magneto-resistance at low temperatures. We discuss the role of lateral inhomogeneities on the formation of the electron gas at the LAO/STO interface.

Strain state of GaN nanodisks in AlN nanowires studied by medium energy ion spectroscopy

Medium energy ion spectroscopy experiments have been performed on an ensemble of nanowires deposited by molecular beam epitaxy on Si(111), taking advantage of their reduced in-plane mosaicity. In particular, the strain in nanometric GaN insertions embedded in AlN sections deposited on top of GaN nanowires has been determined. The measured strain is consistent with atomistic valence force field calculations. This opens the way for the structural study of a new range of discontinuous nanowire-based nanostructures by medium energy ion spectroscopy and to the determination of the strain profile of nanodisks in nanowires at the monolayer scale.

Electrical and structural properties of ABO3/SrTiO3 interfaces

ABSTRACTElectrical transport and microstructure of interfaces between nm-thick films of various perovskite oxides grown by pulsed laser deposition (PLD) on TiO2- terminated SrTiO3 (STO) substrates are compared. LaAlO3/STO and KTaO3/STO interfaces become quasi-2DEG after a critical film thickness of 4 unit cell layers. The conductivity survives long anneals in oxygen atmosphere. LaMnO3/STO interfaces remain insulating for all film thicknesses and NdGaO3/STO interfaces are conducting but the conductivity is eliminated after oxygen annealing. Medium-energy ion spectroscopy and scanning transmission electron microscopy detect cationic intermixing within several atomic layers from the interface in all studied interfaces. Our results indicate that the electrical reconstruction in the polar oxide interfaces is a complex combination of different mechanisms, and oxygen vacancies play an important role.

Cationic Disorder and Phase Segregation inLaAlO3/SrTiO3Heterointerfaces Evidenced by Medium-Energy Ion Spectroscopy

Medium-energy ion spectroscopy (MEIS) has been used to study the depth profile and deduce the distribution of possible cationic substitutions in LaAlO3/SrTiO3 (LAO/STO) heterointerfaces. Analysis of La and Sr peaks in aligned and random MEIS spectra indicates that the surface layers of LAO on an STO substrate are not homogeneous and stoichiometric if the film thickness is less than 4 unit cell layers. This is possibly caused by a redistribution of La and Sr at the interface. Kelvin probe force microscopy reveals an inhomogeneous distribution of the surface potential in a 4 unit cell LAO film, indicating micrometer-sized regions of different compositions. Our findings provide a novel view on the microstructural origin of the electrically conductive interfaces.

Experimental observations of the thermal stability of high-k gate dielectric materials on silicon

High-k dielectric materials including zirconium oxide and hafnium oxide produced by atomic layer deposition have been evaluated for thermal stability. As-deposited samples have been compared with rapid thermal annealed samples over a range of source/drain dopant activation temperatures consistent with conventional complimentary metal oxide semiconductor polysilicon gate processes. Results of this initial investigation are presented utilizing analyses derived from X-ray diffraction (XRD), X-ray reflectometry (XRR), medium energy ion spectroscopy, high resolution transmission electron microscopy (HRTEM), tunneling atomic force microscopy, scanning electron microscopy, Auger electron spectroscopy and secondary ion mass spectroscopy. Changes in interface and surface roughness, percent crystallinity and phase identification for each material as a function of anneal temperature have been determined by XRD, XRR and HRTEM. Finally, high-k wet etch issues are presented relative to subsequent titanium silicide blanket film resistivity values.

In-depth concentration distribution of Ar in Si surface after low-energy Ar + ion sputtering

The in-depth concentration of Ar atoms in Si surface after Ar + ion sputtering was investigated using medium-energy ion spectroscopy (MEIS) and dynamic Monte Carlo simulation. The primary Ar + ion energy was 0.5, 1 and 3 keV, and the primary Ar + ion beam direction was varied from surface normal to glancing angle. In the case of the surface normal incidence, the MEIS result shows that the maximum atomic concentration of Ar atoms increases from 6% at the depth of 2 nm to 16% at the depth of 3 nm as the primary ion energy increases from 0.5 to 3 keV. However, in the case of the incident angle of 80°, that is 2.5% at the depth of 1.5 nm when the primary energy is 3 keV, in-depth Ar distribution cannot be observable when the primary ion energy is 0.5 keV. Dynamic Monte Carlo simulation reproduced the in-depth concentration distribution of Ar atoms quantitatively.

Nondestructive and quantitative depth profiling analysis of ion bombarded Ta2O5 surfaces by medium energy ion scattering spectroscopy

Ion beam sputtering has been widely used for sputter depth profiling with x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). However, the problem of surface compositional change due to ion bombardment remains to be understood and solved. So far sputtering processes have been usually studied by surface analysis tools such as XPS, AES, and secondary-ion mass spectrometry which use the sputtering process again. In this work, the altered surface layer of amorphous Ta2O5 thin films due to Ar+ ion bombardment was depth profiled nondestructively and quantitatively for the first time by medium energy ion spectroscopy (MEIS) as a function of the ion incidence angle and the ion dose with a depth resolution of better than 1.0 nm. The MEIS spectrum showed that the preferential sputtering of oxygen atoms developed with the ion dose and saturated in the ion dose of 3.1×1016 ions/cm2. The Ta mole fraction at the surface increased from 0.29 up to 0.42±0.03 at the saturation ion dose under normal incident 3 keV Ar+ ion bombardment, which corresponds to the stoichiometry of TaO1.4±0.2. The oxygen depletion depth was 2.6±0.8 nm at the saturation dose. The Ta concentration and the oxygen depleted depth decreased with the ion incidence angle. The MEIS experimental results were consistent with XPS results. These MEIS analysis results were compared with Monte Carlo simulation results and good agreement was obtained when both the sputtering and the ion beam induced diffusion were considered.

Helium Ion Beam Induced Arsenic Atom Displacement Studied by Medium-Energy Ion Spectroscopy

ABSTRACTAn arsenic atom displacement in As+ ion implanted Si induced by He+ ion beam irradiation has been studied by medium-energy (175keV) ion spectroscopy (MEIS). The He+ energy and dose dependences of the displaced arsenic atoms have been examined in the range of 30-175keV and ≤6×10-4C/cm2, respectively. The amount of the displaced arsenic atoms are found to be proportional to the dose and inversely proportional to the nuclear stopping power in the low-dose region, while it saturates at high-dose region. The dose-proportional region is composed of two different proportional coefficient segments.

The Performance Study of Ion Implanter Based Medium Energy Ion Spectroscopy with Solid State Detector

AbstractMedium-energy ion spectroscopy using a conventional ion implanter has been developed to study the properties of semiconductor subsurface regions. The system is equipped with solid state detector and operaties with He+ ion energy up to 200 keV. We have tested the system performance for various applications, such as, silicon diffusion through a thin Au layer, a low dose, low energy As implantion and damage of silicon surface caused by plasma treatment.