Formation of ternary Co_1-xPd_xSi₂ on Si (100) by Pd ion implantation in CoSi₂/Si (100) heterostructures

Single crystalline metal/silicon heterostructures, such as CoSi₂ on Si (100), are promising materials for microelectronic and optoelectronic applications. The crystalline perfection of epitaxial CoSi₂/Si (100) heterostructures is limited by the lattice mismatch of -1.2% between CoSi₂ and Si, leading to the formation of misfit and threading dislocations as a result of elastic strain in the layer. In the present work, a first attempt was made to reduce the lattice mismatch by substituting a few percent of the Co atoms by Pd, which has a larger covalent radius than Co. Single crystalline CoSi₂/Si (100) heterostructures with a suicide thickness of about 130 nm were implanted at 450°C with 260 keV Pd⁺ ions. The doses were varied between 4.6 × 10¹⁵ and 2.8 × 10¹⁶/cm². Rapid thermal annealing was employed to homogenize the Pd distribution within the silicide layer. The samples were characterized using Rutherford backscattering spectrometry, transmission electron microscopy, electrical resistivity measurements and X-ray diffraction. The results show that up to 2% of the Co atoms can be replaced by substitutional Pd atoms. The ternary suicide layers exhibit channeling minimum yields of 3-5%. Larger Pd concentrations lead to the precipitation of PdSi as a second phase.