| Metal silicides have attracted considerable attention in recent years as low resistivity metal contact and interconnect materials in microelectronics. Historically, polycrystalline silicon has been used as the gate contact material. However, as device size decreases, the higher resistance of polycrystalline silicon can degrade device performance. Metal silicides provide low metal like resistivities and high temperature stability. Ideal silicides for practical applications need to have stable phases, low processing temperatures and mechanical compatibility with silicon, in order to reduce defects and roughness at the silicon-silicide interface. NiSi, one of the nickel silicide phases, fulfills all these criteria. It has a resistivity of 14muO-cm, and a large processing temperature window (350--750°C). NiSi actually surpasses other commonly used silicides such as COSi2 and TiSi2 1 in these properties, while avoiding problems generally faced with these silicides2.; Prior to the use of NiSi, its formation mechanism must be understood. The objective of this research is to develop analytical procedures to monitor phase transformations, in our case NiSi, in real-time, using non-destructive techniques. To this end, we studied the formation of NiSi films on Si using Rutherford Backscattering spectrometry, atomic force microscopy, X-ray photoelectron spectroscopy, and real-time single wavelength and spectroscopic ellipsometry.; Several nickel silicide phases (Ni2Si, NiSi, NiSi2), with different properties, form in various temperature ranges below 1000°C. Three phases, Ni2Si, NiSi, NiSi2, were identified in this temperature range, and their optical databases in the 2--4 eV range were established. We demonstrated that we can identify the phases and the extent of phase formation from optical data obtained via spectroscopic ellipsometry in real-time, and modeled the data using the optical databases established. We have also observed the onset of agglomeration of the silicide for long time anneals at temperatures of 500--700°C, which is much lower that 1000°C, where agglomeraton is expected to occur. This premature agglomeration is obviously not desirable for device performance.; In this research, we have demonstrated that ellipsometry, which is a non-destructive, non-invasive technique, can be used as a real-time monitoring tool. We have successfully monitored the formation of the nickel silicide phases, especially NiSi, in situ and in real-time.; 1A. Lauwers, Q. F. Wang, B. Deweerdt, and K. Maex, Appl. Surf. Sci. 91, 12 91995). 2Y. Hu, and S. P. Tay, J. Vac. Sci. Technol. A 16, 1820, (1998). |
