Theoretical models of Schottky-barrier height formation are reviewed. A particular emphasis is placed on the examination of how these models agree with general physical principles. New concepts on the relationship between interface dipole and chemical bond formation are analyzed, and shown to offer a coherent explanation of a wide range of experimental data.

Recent advances in Schottky barrier concepts

The use of titanium-based contact barrier layers in silicon technology

Publisher Summary This chapter focuses on formation and characterization of transition-metal silicides. Many deposition techniques can be applied to form thin silicide layers on very large-scale integration (VLSI) structures. The common methods are vacuum evaporation with filament or e-gun, sputtering, and chemical vapor deposition. The silicon for the silicide may be drawn from the silicon substrate in a subsequent metal-silicon reaction, in which case a metal film only is deposited. Modern methods of analysis of thin films are mainly based on the detection of beams that are emitted from or scattered by the film as a result of irradiation by a primary incident beam. Several transition metal silicides have been identified as semiconductors. The relatively high resistivity of these silicides and the ability to vary the resistivity and the thermal coefficient of resistance makes these materials attractive for thin-film resistors.

Formation and Characterization of Transition-Metal Silicides

It is shown that the wide diversity of behavior observed from common Schottky barriers is difficult to reconcile with the traditional view of a homogeneous barrier height which is determined by Fermi level pinning, but is consistent with the presence of inhomogeneities in the barrier height. The demonstrated inhomogeneity in Schottky barriers, which is shown to have a dominant effect on electron transport, is suggestive of a dependence on the barrier height on the interface structure. Experimental and theoretical results obtained from high-quality epitaxial Schottky junctions are also discussed to show the correlation between the interface structure and the barrier height.

On the inhomogeneity of Schottky barriers

Material reactions as a result of thermal treatment were studied on thin‐film Al/silicide/Si systems with CoSi2, PtxNi1−xSi, and MoSi2 for the silicide. Auger electron spectroscopy and Rutherford backscattering analysis showed the transport of Si and the metal released from the silicide into the Al and transport of Al into the silicide. X‐ray diffraction showed the formation of Co2Al9 at 400 °C, PtAl2, NiAl3, and PtNiAl2 at 275 °C, of which the latter disappeared above 450 °C, and MoAl12 at 535 °C, as well as free Si. The Co2Al9 formation followed a linear time dependence with an activation energy of 2.3 eV. The MoAl12 formation followed a parabolic time dependence with an activation energy of 3.6 eV. A thin tungsten layer between Al and the silicide proved to be effective as a diffusion barrier below 500 °C, at which temperature WAl12 was formed. The microstructure was studied by scanning and transmission electron microscopy, electron microprobe analysis, and scanning Auger electron spectroscopy. The reaction resulted in the formation of Si islands with a size up to about 10 μm, containing Al‐rich inclusions, and the intermetallic compound with Si inclusions in between the islands.

Aluminum‐silicide reactions. I. Diffusion, compound formation, and microstructure

An electrical and structural characterization of the Al/Pd2Si thin‐film system on n‐type Si was performed with the use of Schottky barrier contacts and subsequent heat‐treatment cycles Contact barrier energy φBn, as extracted from current–voltage and capacitance–voltage measurements, decreased initially from about 071 eV, characteristic of the Pd2Si interface, to a value of 065 eV Auger electron spectroscopy analysis indicates the observed decrease in φBn corresponds to the decomposition of the Pd2Si layer A drastic alteration of the diode morphology accompanied the decrease in φBn Successive heat treatments at higher temperatures and longer times produced little subsequent change in the structural form of the surface, but yielded an increase in φBn to a value greater than 081 eV Additional data indicated that Al may enter the n‐type Si as a compensating impurity during prolonged heat treatments

H. Grinolds

Papers

Study of Al/Pd2Si contacts on Si