J. E. E. Baglin

Formation of thin films of NiSi: Metastable structure, diffusion mechanisms in intermetallic compounds

The formation of NiSi films from the reaction of Ni2Si with (100) and (111) silicon substrates was found to be controlled by a lattice diffusion process with an activation energy of 1.70 eV. In order to correlate kinetic information obtained by Rutherford backscattering with x‐ray diffraction data, ‘‘standard’’ diffraction powder patterns for both Ni2Si and NiSi have been established. The existence of a metastable hexagonal form of NiSi has been confirmed. Observations on the formation of Ni2Si confirm previous investigations. The diffusion process at work during the formation of NiSi is discussed in terms of the crystalline anisotropy of this compound and compared to what is known about diffusion in other silicides.The formation of NiSi films from the reaction of Ni2Si with (100) and (111) silicon substrates was found to be controlled by a lattice diffusion process with an activation energy of 1.70 eV. In order to correlate kinetic information obtained by Rutherford backscattering with x‐ray diffraction data, ‘‘standard’’ diffraction powder patterns for both Ni2Si and NiSi have been established. The existence of a metastable hexagonal form of NiSi has been confirmed. Observations on the formation of Ni2Si confirm previous investigations. The diffusion process at work during the formation of NiSi is discussed in terms of the crystalline anisotropy of this compound and compared to what is known about diffusion in other silicides.

Ion-beam patterning of magnetic films using stencil masks

Previously, ion-beam irradiation has been shown to locally alter the magnetic properties of thin Co/Pt multilayer films. In this work, we have used ion-beam irradiation through a silicon stencil mask having 1-μm-diam holes to pattern a magnetic film. Regularly spaced micrometer-sized regions of magnetically altered material have been produced over areas of a square millimeter in Co/Pt multilayers. These magnetic structures have been observed by magnetic force microscopy. The patterning technique is demonstrated with mask–sample spacing as large as 0.5 mm. In addition, smaller regions of magnetic contrast, down to 100 nm, were created by using two masks with partially overlapping micrometer holes. Such patterned magnetic films are of interest for application in high-density magnetic recording.

Shallow junctions by high‐dose As implants in Si: experiments and modeling

Shallow (<0.2 μm) n+ layers in Si with high conductivity (<40 Ω/⧠) have been formed by high‐dose (2×1016 cm−2) As implants. Experimental observations of As distributions and carrier concentrations are successfully simulated by a computer program which accounts for both the concentration dependent diffusion and As clustering effects. Reduction of electrical carriers in high‐dose As implanted Si during moderate temperature (∼800 ° C) heat treatments is readily explained by the kinetics of As clustering. Physical limitations on the conductivity which can be achieved by thermally annealed As implants in Si are also discussed.

The formation of silicides from thin films of some rare‐earth metals

The formation of silicides from thin films of the rare‐earth (or related) elements Y, Tb, and Er, on both (100) and (111) Si substrates, has been investigated simultaneously with backscattering and x‐ray diffraction. The silicon‐rich compounds of the type R‐ESi2−n form almost directly with no, or only poorly distinct formation of other silicides at temperatures from about 300 to 500 °C. For all three metals, the reactions with (111) Si require temperatures some 100 °C higher than the reactions with (100) Si, a difference in behavior which is quite important considering the relatively low reaction temperatures. The reactions of Er and Tb with (100) Si are quite sudden, indicating that nucleation is probably the controlling mechanism.

Diffusion marker experiments with rare‐earth silicides and germanides: Relative mobilities of the two atom species

A marker study of the silicides (and germanides) of rare‐earth elements obtained from metallic thin films on Si (and Ge) substrates indicates that Si(and Ge) atoms constitute the dominant diffusing species during the formation of these two types of compounds. Rutherford backscattering is used to distinguish between pairs of elements having different atomic weights but very similar with respect to their chemical and metallurgical behavior. An experiment conducted with the diffusion bilayer sample Ge‐Tb on Si confirms the results obtained with bilayers of the type Y‐Tb on Si (or Ge). Examination of the structure of the silicides which are formed provides clues about the difference in mobility between the Si and the metal atoms.

Oxidation mechanisms in WSi2 thin films

The utilization of WSi2 thin films as gate electrodes in field‐effect transistors depends on the ability of this material to form a continuous electrically insulating SiO2 overlayer. In the steam oxidation of WSi2 films deposited on polysilicon, SiO2 forms on the surface by means of the rapid diffusion of Si through the WSi2 which appears in this case to be quite inert. During the initial stages of the steam oxidation of WSi2 films deposited on SiO2, removal of Si from the silicide (to form SiO2) apparently leads to the formation of free W, rather than the anticipated tungsten‐rich W3Si3.

Formation of iridium silicides from Ir thin films on Si substrates

The formation of iridium silicides from the interaction of iridium films with single‐crystal silicon substrates has been studied from 350 to 1000 °C. Three distinct phases, IrSi, IrSi1.75(?), and IrSi3, were identified. Different modes of formation were observed and investigated. IrSi and IrSi1.75 form in layers parallel to the substrate at temperatures from 350 to 900 °C. The growth of IrSi3 from nuclei that spread laterally occurs at about 1000 °C, where possible the kinetics were systematically studies.

Enhanced Cu‐Teflon adhesion by presputtering prior to the Cu deposition

Adhesion of Cu to Teflon has been studied by depositing Cu to Teflon with and without a presputtering prior to the Cu deposition. Without presputtering, a weak adhesion is observed, with a value of 1 g/mm, which fails the scotch tape test. With a presputtering using 500 eV Ar+ ions, the adhesion rapidly increases, becoming evident after a sputtering of 10 s, and reaches maximal increases of 50 times at longer sputtering times. All the Cu films deposited after presputtering show strong adhesion, and can only be removed by forceful scratching with sharp tools. The presputtering was shown to change both the surface morphology of Teflon, with the deposited Cu following the morphologies created, and the interface chemical bonding between Cu and Teflon as revealed by x‐ray photoelectron spectroscopy. Exposure of the presputtered Teflon to air prior to the Cu deposition shows no effect on the strong adhesion obtained. An interface bonding model is suggested for the enhanced adhesion observed.

Ion beam annealing of semiconductors

The first use of an intense pulsed ion beam to anneal ion‐implanted semiconductors is reported. Helium ion channeling shows that a single 80‐ns pulse 200‐keV H+ ions at ∼100 A/cm2 produced good crystallinity in silicon implanted with 1014 As/cm2 at 100 keV.

Strong metal-support interactions for Pt and Rh on Al2O3 and TiO2: application of nuclear backscattering spectrometry

Abstract The phenomenon of Strong Metal-Support Interactions (SMSI) has been explained previously in terms of a chemical bonding between dispersed metal atoms and cations of certain supports. In this study, planar specimens of Pt Al 2 O 3 , Rh Al 2 O 3 , Pt TiO 2 , and Rh TiO 2 were heated in hydrogen or oxygen and the resulting changes were observed by the technique of Nuclear Backscattering Spectrometry (together with electron microscopy). Significant and complex diffusion effects were found to occur, being dependent on the particular metal/support combination plus the environment and temperature to which it is exposed. This goes beyond the original mechanistic concept and the results suggest a much wider range of SMSI processes.