MBE Growth and Characterization of Cobalt Disilicide/silicon Thin Film Systems

The growth and structural characterization of heteroepitaxial CoSi_2 grown on Si(111) and Si(100) substrates have been studied by RBS/channeling, RHEED, and TEM techniques. The growth process of an epitaxial CoSi _2 thin film from a room-temperature codeposited Co:Si mixture of different Co/Si ratios on Si(111) substrates was studied by the RBS/channeling technique as a function of annealing temperature. The results demonstrate that in order to grow high quality (111) CoSi_2 thin films at a relatively low temperature, it is essential to start from a stoichiometric mixture. The Si interface analysis favors an eight-fold (with over-coordinated Si) interface model. The RBS/channeling technique has also been used to study the crystalline quality and strain of epitaxial CoSi_2 columns embedded in a Si epitaxial matrix, fabricated by the codeposition of Si and Co onto heated Si(111) substrates, at a Si/Co ratio significantly higher than 2. The results show that the shape of the CoSi_2 lattice depends on the aspect ratio of the CoSi_2 columns. These measurement results are explained by energy calculations. Epitaxial Si layers have been grown under a variety of growth conditions on CoSi_2(100) layers by MBE. The structural properties of the Si overgrowth were studied by RHEED, RBS/channeling, and TEM. A strong influence of the CoSi_2 surface reconstruction on the Si overgrowth has been observed. The growth of Si on CoSi_2(100) ( sqrt{2} x sqrt{2 })R45^circ surface at 460^circC or above results in the outdiffusion of Co atoms from the CoSi_2 layer. This process breaks up thin CoSi _2 layers (10 nm or less). Seeded growth from the Si substrate is credited for the good crystalline qualities for Si epitaxial layers (chi_ {rm min} < 6%) for such cases. The electron diffraction pattern shows that the CoSi _2 grains are single crystals. High quality nanometer-size CoSi_2(100) grains (chi_{rm min} = 4.7%), embedded in a nearly perfect Si matrix ( chi_{rm min} = 2.2%) on Si(100) substrates have been fabricated by depositing Si on CoSi_2 islands. Strain measurements show that the CoSi_2 lattice remains cubic. Energy calculations and channeling results indicate that the CoSi_2 lattice is homogeneously expanded by 1.2%, so that it matches the host Si lattice without the formation of any dislocations.