R. D. Thompson

Low Schottky barrier of rare‐earth silicide on n‐Si

Disilicide of rare‐earth metals (Dy, Er, Ho, and Gd) and Y have been formed by reacting the metallic film on both n‐ and p‐type silicons at around 350 °C for Schottky‐barrier height measurement using I‐V technique. A passivation coating of W, or Pt, or both was used to prevent the rare earth from oxidation. Schottky‐barrier heights of about 0.4 eV on n‐Si and 0.7 eV on p‐Si were determined.

Effect of a substrate on the phase transformations of amorphous TiSi2 thin films

The crystallization of an amorphous TiSi2 evaporated film has been studied on both poly‐Si and SiO2 substrates. A metastable form of TiSi2 (base‐centered orthorhombic; a=3.62 A, b=13.76 A, and c=3.605 A) [P. G. Cotter, J. H. Kohn, and R. A. Potter, J. Am. Ceram. Soc. 39, 11 (1956)] is formed first at a temperature of approximately 350 °C on both substrates. This phase consumes the entire amorphous layer before undergoing a polymorphic transformation to face‐centered orthorhombic TiSi2 (a=8.24 A, b=4.78 A, and c=8.54 A) [F. Laves and H. J. Wallbaum, Z. Kristallogr. 101, 78 (1979)] at 600 and 800 °C on poly‐Si and SiO2, respectively. These transformations were investigated using in situ resistivity, x‐ray diffraction, and transmission electron microscopy. The room‐temperature resistivities observed were 96 and 20 μΩ cm for the base‐centered and face‐centered TiSi2, respectively. The enhanced polymorphic transformation on poly‐Si over SiO2 is explained by a lowering of surface energy barrier to nucleation.

Ion induced adhesion via interfacial compounds

Strong, stable adhesion of Cu thin films deposited on Al 2 O 3 (sapphire) can be obtained by presputtering the substrate surface with 500 eV Ar + ions before deposition of copper. The existence of a well-defined optimum fluence of sputtering ions suggests that the interface atomic configuration can be optimized to favor the formation of Cu-Al-O chemical bonding. The existence of a ternary bonding environment is inferred independently from a new dominant peak in the XPS spectrum from interface copper, whose occurrence is correlated with the optimized adhesion conditions.

Interdiffusion in copper–aluminum thin film bilayers. I. Structure and kinetics of sequential compound formation

Interdiffusion in Cu–Al thin film bilayers at temperatures between 160 and 300 °C has been studied by a combination of glancing‐incidence x‐ray diffraction, Rutherford backscattering spectroscopy, and transmission electron diffraction and microscopy. A sequential intermetallic compound formation was observed in samples with an excess amount of Cu with θ‐CuAl2 forming first, followed by η2‐CuAl, and γ2‐Cu9Al4. In samples with excess Al, the θ‐CuAl2 is the first and the last phase formed. The thickening of these compounds was found to obey a parabolic relationship with time, and especially the thickening of θ‐CuAl2 can be described by a prefactor of 7.4 cm2/s and an activation energy of 1.31 eV.

Growth of CoSi2 on Si(001): Structure, defects, and resistivity

Epitaxial films of CoSi2 on Si(001) have been grown by molecular‐beam epitaxy, and their electrical and structural properties studied by resistivity and Schottky barrier height measurements, by Rutherford backscattering spectroscopy (RBS), and by transmission electron microscopy (TEM). Most growth conditions successful on Si (111) have been found to result in misoriented grains when applied to Si(001). However, single‐orientation (001) CoSi2 films, with low resistivities (16 μΩ cm) and low ion channeling minimum yields (χmin=5%) have been obtained by direct codeposition of Co and Si at ∼500 °C at Co‐rich stoichiometries. Single orientation (001) CoSi2 films have also been obtained by using a template method on epitaxially grown Si buffer layers, but the resistivities of these films have not been as good. A Schottky barrier height of 0.71 eV has been measured for single‐orientation CoSi2(001)/Si(001). This is significantly higher than the barrier height of 0.64 eV for CoSi2(111)/Si(111).

Phase transformations of alloys on a reactive substrate: Interaction of binary alloys of transition and rare‐earth metals with silicon

Transition and rare‐earth metals have been found to interact with single‐crystal Si in a way that allows a division into three distinct classes: near noble, refractory, and rare earth. Recently, attention has turned to the reaction of their binary alloys with Si. In this paper we will try to demonstrate that by regarding the alloy‐Si reaction as a phase transformation of alloys under the influence of a reactive substrate, we can undertake a systematic approach for the study of this kind of phase transformations involving ternary elements. In essence we show that the kinetic path taken by the alloy‐Si interaction can be understood and anticipated from the reaction characteristics of the proper metal/Si bilayers and the reaction in the alloy itself. Results will be shown for Er‐Pt, and Gd‐Ti alloys on Si which confirm this systematic approach, which is also supported by previously published data.

Schottky barrier of nonuniform contacts to n‐type and p‐type silicon

A current‐voltage measurement and thermionic emission theory have been applied to discrete parallel diodes (nonuniform diodes) with the unusual result that the sum of the apparent Schottky barriers to n Si and p Si is not equal to the band gap of Si.

Microstructural stability of epitaxial CoSi2/Si (001) interfaces

Epitaxial films of cobalt silicide grown on (001) Si by molecular beam epitaxy have been characterized by transmission electron microscopy. Apart from (001) oriented CoSi2 grains, regions of 〈221〉 type orientations were also found. The 〈221〉 oriented domains were found to be associated with pronounced facetted depressions on the (001) Si surface. Empirical observations suggest that the formation of 〈221〉 CoSi2 domains and the formation of other types of silicide stoichiometries may be related. It is demonstrated that these microstructural instabilities may be suppressed by the codeposition of cobalt and silicon rather than simply by depositing cobalt and reacting with the Si substrate to produce (001) CoSi2.

Structure and growth kinetics of RhSi on single crystal, polycrystalline, and amorphous silicon substrates

Growth kinetics of rhodium silicide in the temperature range of 375–450 °C have been studied on three different silicon substrates: single crystal, polycrystalline, and amorphous. The methods of analysis and specimen characterization utilized in this study are Rutherford backscattering spectroscopy (RBS), Seemann–Bohlin x‐ray diffraction, cross‐sectional transmission electron microscopy (TEM), sheet resistivity via four‐point probe, and Schottky barrier height measurements obtained from the current‐voltage relationship. Our results conclude that all three silicon substrates form an identical rhodium silicide compound, RhSi, indicating that the crystallinity of the substrate has no effect on the resulting rhodium silicide. The growth of RhSi was determined to be diffusion‐limited and the activation energy of growth was similar for single crystal (1.88±0.04 eV) and amorphous silicon (1.86±0.07 eV), yet it was slightly lower (1.71±0.08 eV) for polycrystalline silicon. The difference can be attributed to the ...

Thermal stability of the Al/PdxW100−x/Si contact systems

Interactions of thin films of Al and Pd‐W alloys (Pd80W20 and Pd20W80) deposited on Si and on SiO2 have been studied using Auger‐electron spectroscopy, Rutherford backscattering spectrometry, x‐ray diffraction, and forward current‐voltage measurements of Schottky‐barrier height. For the bilayer films deposited on the inert substrate of SiO2, Pd reacts with Al, forming Al‐rich Al‐Pd intermetallic compounds at 400 °C. Furthermore, in the Pd‐rich alloys (Pd80W20) Al permeates through the whole alloy film readily at 500 °C, while in the W‐rich Pd20W80 the integrity of the alloy film is preserved even following annealing at 600 °C. For the bilayer films deposited on single‐crystal Si, the results of annealing show extraction of Pd to both sides of the alloy, forming Pd2Si at the Si side and Al‐Pd intermetallic compounds at the Al side. In the case of the Pd‐rich alloy (Al/Pd80W20/Si) contact deterioration due to Al penetration to the substrate interface is observed at 500 °C and possibly at 400 °C. In the case...