Synthesis and characterisation of silicide thin films for evaluation of specific contact resistivity of multi-layered silicon-based ohmic contacts

Electrical contacts to devices which pose low resistance continue to be of interest as the dimensions of devices decrease and nanotechnology demands better means of creating electrical access. Continued improvement in the performance of ohmic contacts requires techniques to better characterise and quantify the performance of such contacts. In order to study and estimate the resistance of such contacts or the resistance posed by the interface(s) in such contacts, accurate test structures and evaluation techniques need to be used. The resistance posed by an interface is quantified using its specific contact resistivity (SCR), which is denoted using ρc (units: Ωcm2). Cross Kelvin resistor (CKR) test structures have been used for the measurement of low values of SCR. A simplified approach to this problem of SCR evaluation (developed previously at RMIT University) using the CKR test structures with varying contact sizes was used and during this work was shown to be accurate for the estimation of low values (less than10-8 Ωcm2) of SCR. The silicides of interest in this study were titanium silicide (TiSi2) and nickel silicide (NiSi). These thin films are known for their low resistivity and low barrier heights to both n-type and p-type silicon. The research involved thin film formation and substantial materials characterisation of these thin films. The silicide thin films were formed by vacuum annealing metal thin films on silicon substrates. Silicide thin films formed from metal films deposited by DC magnetron sputtering and electron beam evaporation were compared. The composition, crystallographic orientation, and morphology of these thin films were studied using spectroscopy (AES, SIMS, RBS, in situ Raman spectroscopy), diffraction (Bragg-Brentano and glancing angle XRD, RHEED), and microscopy techniques (TEM, SEM, and AFM). TiSi2 and NiSi thin films were also found to be suitable for microsystems fabrication due to their ability to withstand wet etching of silicon using potassium hydroxide. The SCR of aluminium-titanium silicide ohmic contacts was evaluated to be as low as 6 x 10-10 Ωcm2, which is the lowest reported for any two- layer single-interface contact. Characterisation of ohmic contacts comprising of aluminium, nickel silicide, and doped silicon (with shallow implants) were also carried out using the same technique. SCR values as low as 5.0 x 10-9 Ωcm2 for contacts to antimony-doped silicon and 3.5 x 10-9 Ωcm2 to boron-doped silicon were evaluated