C. S. Petersson

Formation of thin films of NiSi: Metastable structure, diffusion mechanisms in intermetallic compounds

The formation of NiSi films from the reaction of Ni2Si with (100) and (111) silicon substrates was found to be controlled by a lattice diffusion process with an activation energy of 1.70 eV. In order to correlate kinetic information obtained by Rutherford backscattering with x‐ray diffraction data, ‘‘standard’’ diffraction powder patterns for both Ni2Si and NiSi have been established. The existence of a metastable hexagonal form of NiSi has been confirmed. Observations on the formation of Ni2Si confirm previous investigations. The diffusion process at work during the formation of NiSi is discussed in terms of the crystalline anisotropy of this compound and compared to what is known about diffusion in other silicides.The formation of NiSi films from the reaction of Ni2Si with (100) and (111) silicon substrates was found to be controlled by a lattice diffusion process with an activation energy of 1.70 eV. In order to correlate kinetic information obtained by Rutherford backscattering with x‐ray diffraction data, ‘‘standard’’ diffraction powder patterns for both Ni2Si and NiSi have been established. The existence of a metastable hexagonal form of NiSi has been confirmed. Observations on the formation of Ni2Si confirm previous investigations. The diffusion process at work during the formation of NiSi is discussed in terms of the crystalline anisotropy of this compound and compared to what is known about diffusion in other silicides.

The formation of silicides from thin films of some rare‐earth metals

The formation of silicides from thin films of the rare‐earth (or related) elements Y, Tb, and Er, on both (100) and (111) Si substrates, has been investigated simultaneously with backscattering and x‐ray diffraction. The silicon‐rich compounds of the type R‐ESi2−n form almost directly with no, or only poorly distinct formation of other silicides at temperatures from about 300 to 500 °C. For all three metals, the reactions with (111) Si require temperatures some 100 °C higher than the reactions with (100) Si, a difference in behavior which is quite important considering the relatively low reaction temperatures. The reactions of Er and Tb with (100) Si are quite sudden, indicating that nucleation is probably the controlling mechanism.

Diffusion marker experiments with rare‐earth silicides and germanides: Relative mobilities of the two atom species

A marker study of the silicides (and germanides) of rare‐earth elements obtained from metallic thin films on Si (and Ge) substrates indicates that Si(and Ge) atoms constitute the dominant diffusing species during the formation of these two types of compounds. Rutherford backscattering is used to distinguish between pairs of elements having different atomic weights but very similar with respect to their chemical and metallurgical behavior. An experiment conducted with the diffusion bilayer sample Ge‐Tb on Si confirms the results obtained with bilayers of the type Y‐Tb on Si (or Ge). Examination of the structure of the silicides which are formed provides clues about the difference in mobility between the Si and the metal atoms.

Observations on the hexagonal form of MoSi2 and WSi2 films produced by ion implantation and on related snowplow effects

MoSi2 and WSi2 films produced by As‐ion implantation through the respective metallic films deposited on Si substrates were analyzed by backscattering and x‐ray diffraction. The backscattering results indicate that As atoms are snowplowed into Si during the formation of the silicides. Crystallographic observations on similar samples both before and after various heat treatments provide evidence for the existence at low temperatures of the hexagonal phase of WSi2, presumably unreported up to now, which is similar to the corresponding phase of MoSi2. In the case of the W disilicide, however, the temperature for the transition, hexagonal to tetragonal, is so low that the low‐temperature phase is unlikely to be obtained by the usual diffusion‐controlled mechanisms.

Properties of tungsten silicide film on polycrystalline silicon

Tungsten silicide on polycrystalline Si becomes increasingly important as interconnections and gate electrodes for metal‐oxide‐semiconductor field‐effect transistor(MOSFET) integrated circuits. Annealing behaviors of coevaporatd tungsten silicide on P‐doped poly‐Si are studied by x‐ray diffraction, He+‐backscattering, transmission electron microscopy (TEM), and secondary ion mass spectroscopy (SIMS). High‐temperature annealing of silicides results in crystallization and homogenization of tungsten silicide as well as phosphorus out‐diffusion from the poly‐Si. Their effect on device fabrication is also discussed.

Refractory metal silicide formation induced by As+ implantation

Refractory metal silicides WSi2, TaSi2, and MoSi2 have been successfully formed by implanting As+ through the respective metal films deposited on Si. These ion‐beam‐induced silicides can be formed on 〈100〉 single‐crystal Si substrates as well as on polycrystalline Si films. The formation and annealing of these silicides have been studied by He+ backscattering, x‐ray diffraction, and sheet resistivity measurements. Apparently both the ion beam bombardment and some elevation of temperature during implantation are essential for silicide formation. Annealing these ion‐beam‐induced silicides reduces their resistivity and changes their crystallographic structure. The redistribution of implanted As is also observed.

Silicides of ruthenium and osmium: Thin film reactions, diffusion, nucleation, and stability

The reactions of ruthenium and osmium thin films with their silicon substrates lead to the formation of the following phases: the isomorphous Ru2Si3 and Os2Si3, and OsSi2. Ru2Si3 forms by a diffusion controlled mechanism from approximately 450 to 525 °C; the activation energy is 1.8 eV. Os2Si3 grows by the same process and with the same activation energy as Ru2Si3, but at slightly higher temperatures (for equivalent rates). OsSi2 grows at about 750 °C by a nucleation controlled mechanism. With an alloy of ruthenium containing 33 at.% rhodium, one obtains RuSi, which forms by a diffusion controlled mechanism with an activation energy of 2.4 eV from 400 to 475 °C, and Ru2Si3. In the case of the ruthenium alloy, the formation of Ru2Si3 is not diffusion controlled; the controlling process is akin to a nucleation mechanism. Ru2Si3 and Os2Si3 form by silicon motion. This is also true of OsSi2, but the high formation temperature results in some metal motion also during the formation of that phase. The diffusion ...

Interface effects in the formation of silicon oxide on metal silicide layers over silicon substrates

Samples of several metal silicides grown over silicon substrates and samples of pure silicon were oxidized at the same time in an atmosphere of wet oxygen. The rates of silicon oxide growth were analyzed in terms of both linear and parabolic coefficients. The biggest difference is seen between the linear coefficients for metallic silicides on the one hand and pure silicon on the other, with a semiconducting silicide occupying an intermediate position. While the question of why metallic oxides are not always generated simultaneously with SiO2 remains a mystery, the results suggest a possible interpretation.

The behavior of boron (also arsenic) in bilayers of polycrystalline silicon and tungsten disilicide

Boron doping additions in polysilicon‐WSi2 bilayers tend to segregate preferentially in the silicide layer during heat treatments at temperatures between 600 and 1000 °C. This is in contrast to arsenic impurities which under the same conditions diffuse through the silicide and evaporate. The boron analyses were obtained by means of the 10B(n, α) 7Li reaction with thermal neutrons. The arsenic analyses were obtained by means of Rutherford backscattering. The results are compared with results previously obtained from similar samples doped with phosphorous.

Growth ‘‘kinetics’’ and growth mechanisms for disilicide layers obtained through implantation

Layers of NbSi2 and MoSi2 were grown by means of the implantation of germanium and arsenic ions through films of the respective metals, previously deposited on single crystal silicon substrates. The doses used varied from 1 to 15×1015 ions/cm2 with energies of 150, 200, and 250 keV. The thickness of the silicide layers increases in proportion to the square root of the implanted doses. This observation and other evidence indicate that the process is dominated by the atomic mechanisms encountered in radiation‐enhanced diffusion, whereas ballistic mixing effects remain unimportant. The growth of disilicide layers during implantation is discussed with respect to (1) what is known about the growth of these disilicide layers during simple annealing, and (2) what is anticipated for diffusion‐controlled solid state processes.