E. B. O. da Rosa

Stability of zirconium silicate films on Si under vacuum and O2 annealing

The effect of postdeposition annealing in vacuum and in dry O2 on the atomic transport and chemical stability of chemical vapor deposited ZrSixOy films on Si is investigated. Rutherford backscattering spectrometry, narrow nuclear resonance profiling, and low energy ion scattering spectroscopy were used to obtain depth distributions of Si, O, and Zr in the films. The chemical environment of these elements in near-surface and near-interface regions was identified by angle-resolved x-ray photoelectron spectroscopy. It is shown that although the interface region is rather stable, the surface region presents an accumulation of Si after thermal annealing.

Annealing of ZrAl x O y Ultrathin Films on Si in a Vacuum or in O 2

ZrAl x O y films deposited on Si were submitted to thermal annealings in a vacuum or an oxygen atmosphere. Elemental compositions as functions of depth were established using ion beam techniques such as Rutherford backscattering spectrometry and narrow nuclear resonance profiling. In addition, chemical composition profiles were obtained by angle-resolved X-ray photoelectron spectroscopy. The as-deposited film is amorphous, has an abrupt interface with the Si substrate, and its chemical composition is a double oxide with approximate stoichiometry Zr 4 AlO 9 . Atomic transport and chemical reaction induced by thermal annealing were investigated by the above mentioned techniques and by low energy ion scattering spectroscopy. We have observed that Al, O, and Si migrate during annealing, whereas Zr is essentially immobile. Oxygen from the gas phase was heavily incorporated into the oxide films during annealing in O 2 , mostly in exchange for previously existing oxygen.

Composition, atomic transport, and chemical stability of ZrAlxOy ultrathin films deposited on Si(001)

The stability of a ZrAlxOy film sputtered on Si upon thermal annealing in vacuum or in O2 was investigated. X-ray diffraction indicated that the as-deposited film was amorphous and remained so after annealing. Rutherford backscattering, narrow nuclear resonance profiling, and low-energy ion scattering provided the average composition of the film and the depth distributions of different elements. Chemical analysis of these elements was accessed by x-ray photoelectron spectroscopy. Annealing in vacuum produced thickness inhomogeneities and/or transport of very small amounts of Si from the substrate into the overlying film, with formation of Si precipitates. Annealing in O2 led to oxygen exchange throughout the film, as well as Si transport in slightly higher amounts than in vacuum. Differently from the observed upon annealing in vacuum, Si was either incorporated into the Zr,Al–O framework or oxidized in SiO2.

Interaction of SiC thermal oxidation by-products with SiO2

We investigated oxygen incorporation and exchange during thermal growth of silicon oxide films on silicon carbide. This investigation was carried out in parallel with the thermal growth of silicon oxide films on silicon for comparison. We provide experimental evidence that oxidation by-products of silicon carbide out-diffuse and interact with the silicon oxide overlayer, incorporating C and O. This and other results are in sharp contrast to those obtained for silicon samples, constituting a key issue in the stability of any dielectric material used on silicon carbide.

Analytical energy loss distribution for accurate high resolution depth profiling using medium energy ion scattering

An analytical approach to ion energy loss distributions capable of simplifying medium energy ion scattering (MEIS) spectral analysis is presented. This analytical approach preserves the accuracy of recent numerical models that evaluate energy loss effects overlooked by standard calculations based on the Gaussian approximation. Results are compared to first principle calculations and experimental MEIS spectra from 0.2-to1.5-nm-thick HfO2 films on Si, supporting the application of this analytical model for proton scattering in the kinetic energy range from 100to200keV.

Narrow nuclear resonance profiling of Al with subnanometric depth resolution

Abstract We report on the use of the narrow and isolated resonance at 404.9 keV in the cross-section curve of the 27 Al(p,γ)28Si nuclear reaction for profiling Al in ultrathin aluminum oxide films on Si. The samples were characterized as-deposited and after thermal annealing, so that Al transport could be studied. An estimated depth resolution of approximately 0.4 nm near the surface of the films could be obtained owing to: (i) the very small resonance width; (ii) the high stopping power of Al2O3 for 404.9 keV protons; (iii) the high energy stability of the proton beam provided by the 500 kV HVEE ion implanter at Porto Alegre; and (iv) an apparent thickness magnification by a factor between 2.0 and 2.4 with the use of glancing incidence. This technique is compared to other methods for Al profiling like medium energy ion scattering and some sputtering-based techniques.

Ion beam studies of high-k ultrathin films deposited on Si

Abstract The stability of ultrathin films on Si, which are materials candidates for replacing SiO 2 in Si-based microelectronic devices (so-called “high- k dielectrics”), was investigated using ion beam analysis techniques, namely high and low energy ion scattering (RBS and ISS) and narrow nuclear resonance profiling combined with isotopic substitution. The materials studied were Al 2 O 3 , ZrSi x O y , HfSi x O y , AlZr x O y and GdSi x O y . The mobility of different atomic species – especially Si and O – could be observed upon thermal annealing, involving the surface, bulk and interface regions of the films. These atomic transports may have serious consequences concerning application in the microelectronics industry. The potentialities and limitations of each of the IBA methods used are discussed.