Single crystal type A and type B CoxNi1-xSi2 layers have been grown on Si(111) by deposition of Co-Ni alloy in UHV and annealing. The dependence of CoxNi1-xSi2 layer orientation on the thickness of deposited metal is similar to that observed for pure nickel reaction. Silicon deposition along with the Co-Ni alloy allows the growth of type B oriented CoxNi1-xSi2. Auger, LEED, RBS and TEM analyses suggest that the composition of the ternary silicide layers is inhomogeneous. The advantages and disadvantages of this material in device application will be briefly discussed.

Epitaxial YSi2-x films have been fabricated. The smooth ∼430 Å thick silicide films on Si(111) substrates were characterized by a Rutherford backscattering minimum channeling yield, Xmin = 8%. The best previously reported result, Xmin = 26%, was achieved using a relatively exotic e-beam heating method. By contrast we formed YSi2-x using a straightforward furnace annealing technique. We used improved Si surface cleaning procedures, sputter-deposited Y films, and performed two-stage anneals in a vacuum of ∼ 10−8 torr. The results of our work establish YSi2-x as one of the best epitaxial silicides. We describe our preparation technique as well as the evidence for epitaxy. Electrical measurements (Schottky barrier, temperature dependent resistivity, Hall effect) are also presented. Low temperature resistivity of YSi2-x is found to obey simple T5 Bloch's law. Based on resistivity data, YSi2-x appears to have a Debye temperature of 310 K. According to Hall measurements, it is an electronic conductor with n = 2.7 × 1022 cm−3 and the mean free path of electrons is ∼ 87 Å at 4.2 K. We measure a Schottky barrier height of 0.36 eV between YSi2-x, and n-type Si.

Transmission and scanning electron microscopy, Rutherford backscattering-channeling and Read camera glancing angle x-ray diffraction techniques have been applied to study the epitaxial growth of nickel and cobalt germanides on germanium.

NiGe, Co5Ge7 and CoGe2 were found to grow epitaxially on both (001) and (111)Ge. More extensive epitaxy on (111)Ge is correlated with better lattice matches at the germanide/Ge interfaces than those on (001)Ge for these epitaxial germanides.

CoSi2 epitaxial layers with thickness ranging from 24 nm to 170 nm have been grown onto porous Si substrates by molecular beam epitaxy. The X-ray rocking curves and transmission electron microscopy (TEM) are used to examine the strain relaxation and interface quality. Backscattering with channeling is used to characterize the crystallinity of the epilayers. The results show that it is necessary to grow a thin buffer Si layer in order to improve the interfacial sharpness and crystallinity of the epilayers; near perfect crystallinity is then obtained as the thickness of the CoSi2 films exceed 50 nm. TEM results reveal that both CoSi2/Si and CoSi2/porous-Si interfaces are flat and layer thickness is uniform. It is found by TEM that the dislocation density of CoSi2 grown on porous Si is much lower than that on single-crystal Si. For thin CoSi2 grown on porous Si, the TEM and strain measurement results imply that part of the film is pseudomorphic where no dislocations are observed. Average strains of CoSi2 films grown on porous Si substrates with thicknesses greater than 30 nm show a lower strains comparing to that on crystalline Si. This suggests that by using porous Si as substrates the stress energy in the epilayer can be accommodated by the Si buffer layer that bridged over the trenches of porous Si.

The technique of Double Crystal X-Ray Diffractometry (DXD) and ion beam channeling are applied to investigate, as a function of thickness, the average perpendicular strain and crystal quality of CoSi2 layers grown by MBE on 〈111〉Si. The results show that thin layers (from 20 to 30 nm) are partially relaxed but with a strain greater than that expected for a free CoSi2 lattice. For layers thicker than 30nm the magnitude of the CoSi2 strain incrgases to 1.7%, somewhat less than the maximum magnitude strain expected for coherent growth (2.1%). For layers thicker than 50 nm, the perpendicular strain relaxes very slowly, with the strain at 225 nm only 5% less than that at 50nm. It was concluded that a coherent epitaxial layer does not form initially and the relaxation of the strained layers is not consistent with a planar growth mechanism of the CoSi2 epilayers. Therefore the concept of a critical thickness, below which the epilayers are strained and above which the epilayers are relaxed, cannot be applied to our CoSi2/Si system.

Epitaxial NiSi2 of single orientation was grown on laterally confined (111)Si. Striking oxide opening size effects on the growth of NiSi2 epitaxy were observed. The formation temperature of NiSi2 on (111)Si was found to be as low as 550°C inside oxide openings 1.8 μm or smaller in size. Epitaxial NiSi2 of single orientation which is identical to that of (111)Si substrate was formed inside oxide openings of or smaller than 1.8, 1, and 0.8 μm in size in samples annealed at 550-750, 800, and 850-900°C, respectively. Preliminary results on the epitaxial growth of CoSi2 are also reported.

Thermally grown NiSi layers on <111> Si substrates were irradiated by 35 nsec Nd glass laser pulses in the energy density range 0.3−2.0 J/cm2. Time resolved reflectivity measurements were performed during the irradiation to detect surface melting. The samples were analyzed by 2.0 MeV He+ Rutherford Backscattering Spectrometry in combination with channeling effect. The measured threshold for surface melting was 0.5 J/cm2. Irradiation at energy densities higher than 1.3 J/cm2 changed the silicides layer composition because of the mixing with the underlying silicon. In the intermediate energy density range (0.7−1.1 J/cm ) slight changes in composition were observed, a strong alignement of NiSi molecules along the <111> substrate direction was however observed. The measured Xmin was about 30%. It seems then that an epitaxial NiSi phase can be grown by pulsed laser irradiation with a suitable choice of the incident energy density. Work is in progress to identify this new NiSi phase by TEM. However this ordered phase is a metastable one since after anunealing at 250°C, 30min the channeling yield reduction disappeared without any appreciable change in composition.

In recent papers, we have described a depth profiling method using chemical beveling and Auger line scan measurement, quick and easy to perform, with a sufficient resolution to check the abruptness of chemical interfaces obtained in epitaxial growth of III-V compounds.

The variation law of chemical species concentrations at the interfaces is tighly related to the mecanisms of initial growth. We present here a theoretical analysis applied to chemically beveled interfaces with sharply graded concentrations.

We show on two examples of LP-MOCVD quantum wells (InP/GaInAs/InP and GaInP/GaAs/GaInP) the good agreement between experimental and theoretical curves, assuming exponentially varying concentrations. Finally, we discuss the correlations with the dynamics of the first steps of the LP-MOCVD growth.