The kinetics of silicide growth are classified into three different categories: (a) diffusion controlled, (b) nucleation controlled, (c) others (reaction rate controlled). These are analyzed with the aim of understanding both the phenomenology of growth and the specific atomic mechanisms of phase formation. Diffusion-controlled growth is discussed with respect to the Nernst-Einstein equation. Stress relaxation is considered as a possible cause of reaction-rate control. The relative merits of two different types of marker experiments are compared. A few silicides are discussed in terms of what can be inferred about diffusion mechanisms. The competition between reaction-rate and diffusion control phenomena is shown to have specific effects on the sequence of phase formation; it is also related to the formation of some amorphous compounds. Reactions between silicon and alloyed metal films are used to illustrate the respective influences of mobility and driving force factors on the kinetics of silicide growth; they can also be used to underline the dominance of nucleation over diffusion in some silicide formation processes.

Kinetics of formation of silicides: A review

Silicides have been a topic of intensive research for more than a decade. The driving force for these investigations has certainly been the interesting materials aspects of the silicides and their applications in integrated circuits. The advantages of easy formability and low resistivity for both CoSi2 and TiSi2 have led to an intensive use of these silicides in self-aligned processes for simultaneous silicidation of source, drain and gate. The fundamental investigations of these silicides include thermodynamic and kinetic aspects of phase formation, interactions with doped Si and related defect generation, and the interaction with oxide and metals. Specific issues related to the technological implementation of silicides in a full process will be discussed in view of the trend to scale the silicided area both in the vertical and in the lateral dimensions.

Silicides for integrated circuits: TiSi2 CoSi2

Special aspects of diffusion in thin films

The low resistivity of the titanium disilicide makes this material attractive for gate and interconnect metallizations. TiSi2 has been formed by reacting Ti films with polycrystalline and monocrystalline silicon in the temperature range 400–1100 °C. The interaction is investigated by use of sheet resistance, x‐ray diffraction, and stress measurements. It has been found that Ti and Si react very rapidly to form both TiSi and TiSi2 at temperatures ? 700 °C and only TiSi2 at temperatures ≳ 700 °C. The TiSi2 films are associated with a very low resistivity (∼15 μΩ cm), high tensile stress [∼ (1–2) ×1010 dyn/cm2)], and a rough surface. Silicided structures are mechanically stable. It is proposed that the silicon, as the predominant diffusing species, first diffuses into titanium to completely convert titanium into TiSi and then into TiSi to form TiSi2.

Thin film interaction between titanium and polycrystalline silicon

Influence of the nature of the Si substrate on nickel silicide formed from thin Ni films

Backscattering of MeV He ions has been used to investigate the composition and growth kinetics of metal silicides formed from thin films of Pd, Ti, Cr, and Mo evaporated onto Si. In each system studied, one silicide phase predominated (Pd2Si, TiSi2, CrSi2, and MoSi2). The thickness of the phase increased with (time)0.5 for Pd2Si and TiSi2, and linearly in time for CrSi2 and MoSi2. It was found that these two time dependencies correlate directly with the reaction sensitivity to a thin oxide interface (<100 A) and to the extent of the silicide formation in the neighborhood of a typical device contact region.

J. W. Mayer

Papers

Growth Kinetics Observed in the Formation of Metal Silicides on Silicon