Thin films of tungsten silicide with resistivities of 30 – 35 μΩ-cm have been formed by sputter depositing 71 nm of W metal onto (100) oriented, 5 Ω-cm, p-type silicon wafers that were etched in BOE 500 solution. The samples were fast radiatively processed in an RTA system under high vacuum for time anneals ranging from 15 – 50 seconds at a temperature of ∼ 1100°C. The inevitable oxide barrier at the interface is shown to decrease with increasing RTA time.

A ternary compound results from the fast radiative processing of Ni/Ti bilayers on Si<100> substrates. In the Ti-Ni-Si system, Ni is the dominant moving specie at low temperatures while Si starts to diffuse at 575°C. For bilayers with Ti in excess, the final product,above 750°C, is a mixture of ternary compound and TiSi2 whereas excess Ni leads to a layer of NiSi between the substrate and the ternary layer, at tempera-tures below 700° C.

The growth of ZrSi2 and Zr2CuSi4 has been achieved by rapid thermal processing in vacuum. Fast heating rates and temperatures of at least 950 °C are required to form smooth Zr disilicide with a room-temperature resistivity of 34 μΩ cm. In agreement with the bulk phase diagram, the ternary compound can be prepared by reacting Cu with the disilicide. This phase is formed through the diffusion and the insertion of Cu atoms into the twin faults of the pseudolamellar C 49 Zr silicide structure; it belongs to the same Cmcm space group. Electrical measurements indicate that ZrSi2 is an electron conductor whereas a mixed conduction mechanism is found for the ternary samples.

The reactions in both metal-metal-Si (M-M-Si) and metal-boron-Si (M-Bi-Si) are discussed in terms of compound formation, solid solubility, and thermodynamical equilibrium. In M-M-Si systems, the formation of stable ternary compounds is accessible via two routes: the reaction of Si with an intermetallic compound or the reaction of a metal with a silicide. From a literature survey, it is apparent that only a minority of systems contain ternary phases with high heats of formation, a condition necessary to avoid phase separation into binary phases. For alloys or bilayers interactions with Si, intermetallic compound formation is rare, probably because of the identity of the moving species and the energetically more favorable M-Si bonding. Physical parameters affecting stability and solubility of silicides are the differences in metallic radii, electronegativity and number of valence electrons. For structures consisting of a thin silicide film on B-doped Si, we show that part of the stability predictions based on data obtained for M-B, B-Si, and M-Si couples could be misleading and are invalidated when compared to previously established phase diagrams.

The growth of copper silicide has been studied by rapid thermal processing (RTP) of 500 Å of Cu on Si substrates. Interaction between the diffusing metal and Si starts at 250–300 °C. Annealing at higher temperatures yields complete silicidation to Cu3Si. This leads to strong modifications of the Auger line shapes of both Si and Cu. A plasmon peak located 20 eV below the main peak is the fingerprint in the Cu spectrum. Strong features at 80, 85.6, 89.2, and 93.2 eV as well as a 1 eV shift of the 90.4 eV peak appear in the Si L2,3VV spectrum. Whether for Cu films annealed in nitrogen or in vacuum, exposure of the silicide to air results in the growth of silicon oxide at room temperature and continues until the silicide layer is totally converted. This repeatable and controllable oxidation of silicon is accompanied by changes in resistivity and color reflecting the extent of the process. For Cu/CoSi2/Si structures, the cobalt silicide acts as a transport medium for the growth of the copper silicide and also serves as a cap preventing the oxidation of the final CoSi2/Cu3Si/Si contacts

Confirming the results obtained for Ti-Co bilayers on Si and in accordance with the phase diagram, the high temperature formation and stability of three ternary silicides Ti0.75Co0.25Si2 (T phase), TiCoSi (E) and Ti4Co4Si7 (V) is reported. The Si rich T phase grows for Ti / CoSi2 and Co / TiSi2 structures. The tetragonal V compound is obtained by annealing Ti (400 Å) / Co (250 Å) / Si (900 Å) / SiO2 whereas orthorhombic TiCoSi is prepared using Ti / CoSi / Si3N4 samples.

Rapid thermal processing of Co/Ti/Si samples induces the growth of cubic intermetallic compounds as a first step of the reaction. For temperatures above 750°C, a ternary phase Ti0.75Co0.25Si2−x appears simultaneously with disilicides of the excess metal, in excess with respect to that stoichiometry. In the reverse Ti/Co/Si structures, Co is also the main diffusing species at low temperatures. Co atoms react at both interfaces, this time to form Co silicides and intermetallic compounds. As soon as Si atoms become mobile, the same ternary phase formation occurs. The existence of this stable silicide of a new type is confirmed by the analysis of bulk samples of the same composition prepared by arc melting.

Thin film interactions for ternary systems are presented and compared with those for bulk samples. The various outcomes of the reaction such as solid solution, phase separation or ternary compound formation are analyzed using specific examples in each case. As a possible first step of the reaction, the alloying behavior of the metals is described using Miedema's model.

Thin films of tungsten silicides have been formed on samples of W(50 nm)/Ti(5 or 10 nm)/Si〈100〉 by rapid-thermal annealing. The results of the experiments show that by interposing a thin layer of Ti at the W-Si〈100〉 interface, the temperature at which WSi2 is first detected is lowered to 570–600 °C, and the W-Si reaction rate is increased, as compared to the W/Si〈100〉 samples. The resulting WSi2 film has an electrical resistivity of about 115 μΩ cm with a smooth surface. Neither the W-rich silicide phase, W5Si3, nor the hexagonal WSi2 phase is found in the annealed samples. The growth kinetics are monitored using a four-point probe, x-ray diffraction, scanning electron microscopy, and scanning Auger analysis.

W-Ti bilayers on Si have been processed by fast thermal annealing in air, in N2/H2(5%), and vacuum (1 E-3 and 1 E-6 Torr). The results indicate that the W layer on top of Ti acts as an effective protection barrier against oxidation of Ti in all atmospheres except air. Titanium-rich silicides are formed after 500 °C, while TiSi2 is completed at about 600 °C. At 700 °C a bilayer of WSi2/TiSi2 is found. Silicon is found to be the diffusing specie during the formation of WSi2. Finally, a ternary silicide, Ti0.6W0.4Si2, starts to form after 780 °C. The final ternary silicide phase has’an Mlectrical resistivity of about 60 μΩ-cm.