Studies of the properties and characteristics of transition metal silicides have been stimulated by their (potential) use in integrated circuit technology. This review describes some of the most recent studies in this field of research. Formation mechanisms of silicides are discussed in some detail. A division is made between near-noble and refractory metal silicidation which aids in the understanding of differences in formation mechanisms of the various silicides. The evolution of the components of thin film stress during metal silicidation is also elucidated. In the review of the practical uses of these materials, emphasis is placed on specific processes involving laterally confined (self-aligned) silicide film formation as more advanced applications require film formation only in certain localized regions on a Si wafer. Specific attention is paid to the silicidation processes of TiSiz and CoSiz. The electronic structure of silicides is discussed on the basis of band-structure calculations and photoemission experiments. The important electrical characteristics of films are then examined in terms of the microstructure of the films. A review of the crystallographic (epitaxial) orientation relationships between silicide films and monocrystalline Si is given. The epitaxial growth of CoSiz and FeSiz on and in Si is discussed thoroughly. The review of epitaxial silicide formation is used as the basis for a description of some futuristic applications of these materials. One such application utilizes the semiconducting properties of a FeSiz phase while another employs the Schottky-barrier characteristics of silicide/Si interfaces for the formation of advanced transistors. The latest electrical results obtained from the semiconducting material and from a so-called permeable base transistor are presented.

Scanning tunneling microscopy studies of nucleation and growth in a reactive, epitaxial system: Co/Si (111) CoSi, layers formed by the thermal reaction of vapor-deposited Co films on Si( 100) substrates have been studied by transmission electron microscopy, and x-ray diffraction. It is shown that first a layer of CoSi is formed between Co and Si. Only thereafter is the formation of CoSi, initiated at the Si/CoSi interface. In view of the similarity of the crystal structure and the small lattice mismatch between the Si and the CoS&, epitaxy of aligned (100) CoSiz is expected to occur. However, in addition to an aligned (100) orientation, CoSi? occurs in a number of orientations, including a (110) preferential orientation. Many individual grains are composed of subgrains, slightly rotated with respect to each other and connected by small-angle boundaries. It is shown that the observations can be largely attributed to the geometrical lattice match between CoSi, and Si. A comhuter program has been developed that searches systematically for a large number of possible geometrical matches. It allows us to calculate epitaxial relationships between CoSiz and the Si( 100) substrate. The probability of various fits is estimated on the basis of their strain energy and coincidence site density, showing good correspondence with the experimental observations.

We studied the diffusion of ion-implanted Ga in SiO2 by means of Rutherford backscattering spectrometry. We also investigated the doping of Si from a Ga-implanted SiO2 layer. It turned out that Ga occurs in three different chemical states in SiO2. In one chemical form it is virtually immobile, which we relate to Ga-on-Si sites in the network. A second type of Ga exhibits a very high diffusion coefficient. We have found that the formation of this type of Ga occurs by the same mechanism under almost all of the experimental circumstances. An interstitial GaOH molecule is proposed to be the diffusing species in this case. Finally, there is a third form in which Ga diffuses independently of the other diffusing species. The higher activation energy of this diffusion process suggests the diffusion of gallium in some substitutional form.