Thin Film Silicide Formation by Thermal Annealing: Study of Kinetics, Moving Species, Impurity Effect, and Electrical Properties

Citation

Lien, Chuen-Der (1985) Thin Film Silicide Formation by Thermal Annealing: Study of Kinetics, Moving Species, Impurity Effect, and Electrical Properties. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/t5r5-5267. https://resolver.caltech.edu/CaltechETD:etd-03272008-074200

Abstract

Growth kinetics, dominant moving species (DMS), impurity effect, and electrical properties of thermally formed silicides have been studied by using MeV⁴He⁺ Rutherford backscattering spectrometry, ¹⁸O(p,α)¹⁵N nuclear reaction analysis, four—point probe measurement, and I—V measurement.

The growth kinetics (including growth rate and activation energy of growth rate) measurements are done for silicides formed on different kinds of Si substrates, viz., single crystalline (100) Si (Si^c) and amorphous evaporated Si (Si^e). Results show that the substrate can have different effects on different silicides. Some silicides grow much faster on Si^e than on Si^c (e.g., NiSi₂,CoSi₂), some show the reverse phenomenon (e.g., Co₂Si, CoSi), and some have similar growth rates (e.g., NiSi, Ni₂Si, Pt₂Si, PtSi) (see Table 2). Some silicides are more uniform and form at lower temperature on Si^e than on Si^c (e.g., CrSi₂, NiSi₂, CoSi₂). These interesting phenomena are discussed and explained in terms of the different properties between the samples with either substrate (see Chapter 2).

When studying the formation of a silicide, one would like to know the DMS in silicide during the silicide formation. Not only is it an important property of the silicide but it is closely related to the silicide formation. The DMS is, in general, measured by inert marker experiments. In Chapter 3, we use such marker experiments to study the DMS in a silicide during silicide formation and two other silicide reactions (viz., solid-phase-epitaxy (SPE) of Si^e through silicide and silicide oxidation). The reason for measuring the DMS for the two additional types of silicide reactions is that all these reactions are related and additional information can be obtained from this comparison. The results, in fact, show that in all three reactions, the DMS in the silicide is the same when the silicide formation is diffusion—controlled. An explanation is given (with some assumptions) by considering the detailed atomic motion inthe silicide during these reactions (see Chapter 3).

Inert marker experiments can identify the DMS in a silicide. They cannot, however, distinguish whether the DMS diffuses by an interstitial (or grain boundary) or a vacancy mechanism. One possible way to determine the diffusion mechanism of the moving species is by using tracer experiments. The problem with the tracer studies is that the measured tracer profiles can be (and have been) misinterpreted. We review several models that were used to explain the tracer profiles, point out incorrect considerations and finally give a plausible model to explain what information can be obtained from the tracer experiments (see Chapter 4).

During marker experiments, one may find that the marker used to monitor the DMS can affect the growth rate of silicide, and sometimes even change the DMS. This points to a general problem, namely, how foreign atoms (impurities) introduced in a sample affect the properties of silicide. Since the effect of impurity is important in our thin film reactions, we have systematically studied the effect of oxygen on the growth rates of silicide, and its redistribution, by using a rare isotope of oxygen, ¹⁸O, as an impurity. The results are explained in terms of a modified model which was originally proposed by Scott (see Chapter 5).

Finally, we study the electrical properties of Co silicides. Co silicides formed from Si^e (silicides thus formed are more uniform than that formed from Si^c) are used for the measurements of Schottky barrier height, resistivity, Hall mobility, and carrier concentration. From the result of this study, we suggest that that CoSi₂ is a potential candidate for contacts to shallow junctions and as an interconnection material in VLSI (see Chapter 6).

Further works, arising out of the implications of these studies, are suggested and summarized in the last chapter of the thesis.

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