No abstract

Si sputtering yields and Si to SiO2 etch rate ratios have been determined by measuring the depth of the etched craters after Ar+ ion bombardment. The experiments have been performed with energies down to 50 eV both with and without Cl2. Surprisingly high Si sputtering yields are obtained in a Cl2 environment by low-energy Ar+ ions. Hence, the influence of Cl2 on the Si sputtering mechanism is much larger for low ion energies than for high ion energies. Whereas the Si sputtering yield is enhanced by the presence of Cl2, the SiO2 sputtering yield is hardly affected. Therefore, large differences in the etch rate (high selectivities) between Si and SiO2 are obtained at low ion energies.

Sputtering of Si in a Cl2 environment by Ar+ and Xe+ ions with energies down to 75 eV has been investigated. Mass spectra and time-of-flight distributions of the sputtered species have been measured. Under 75-eV Ar+-ion bombardment of the Si target, SiCl, SiCl2, SiCl3, and/or SiCl4 are sputtered. When increasing the ion energy the SiCl4 contribution decreases in comparison with SiCl. This is caused by the fact that the newly formed Si-Cl compounds are sputtered at a high rate compared to the rate of SiCl4 formation. Time-of-flight distributions indicate that under 100-eV Ar+-ion bombardment the species are not sputtered by a collision-cascade mechanism. The spectra can be fitted by Maxwell–Boltzmann distributions at a high (>2000 K) temperature. Increasing the Ar+-ion energy to approximately 250 eV the time-of-flight spectra of the sputtered species change from Maxwell–Boltzmann-like into spectra as expected for a collision-cascade mechanism. For low-energy Xe+ ion bombardment the sputtered species also show Maxwell–Boltzmann time-of-flight distributions. The change from Maxwell–Boltzmann to collision-cascade distributions occurs at higher ion energies than for Ar+-ion bombardment. The results obtained for low ion energies are discussed in terms of evaporation from an ion-induced hot spot.

Laser ablation deposition was used to grow polycrystalline Cu-Ni and Ag-Ni thin films on amorphous substrates at room temperature. X-ray diffraction was employed to determine the phases present and the residual macrostress and to analyze the structural imperfection in terms of crystallite size and microstrain. For confirmation and complementary microstructural data transmission electron microscopy was applied. Analysis of the gross composition was achieved by electron probe microanalysis and x-ray fluorescence. The films contained substantially less Cu and Ag than the targets, which was caused by preferential scattering of ablated Cu and Ag species upon incidence at the growing films. The Cu-Ni films were entirely composed of a CuxNi1−x solid solution. The Ag-Ni films were composed of a AgxNi1−x solid solution and of pure Ag and pure Ni. The nonequilibrium AgxNi1−x solid solution could contain up to 44 at. % Ag. The residual macrostress in the Cu-Ni films was compressive, whereas it was tensile in the Ag-Ni films. The occurrence of these stresses could be interpreted as due to the combined effects of atomic peening and cooling after deposition and, in the case of the Ag-Ni films, of stress relaxation by partial decomposition of the AgxNi1−x solid solution during film growth. The microstrains in the AgxNi1−x solid solutions were higher than in similarly prepared pure elemental Ag and Ni films. Compositional inhomogeneity of the AgxNi1−x solid solution crystallites contributed in particular to this effect. The strain-free lattice parameters of the solid solutions were found to be in fair agreement with those predicted by Vegard’s law.