Formation of TiN/$TiSi_2$ bilayer from TiX and its utilization as a diffusion barrier for the W bit-line process in capacitor on bit-line (COB) structured dynamic random access memory (DRAM) device have been discussed in this paper. Since the thickness of $TiSi_2$ formed on Si substrate is very thin and uniform, the $TiN_{X}$ contacted $n^{-}$ and $n^{+}$ junction revealed good lectrical properties. The compact structure of the overlying TiN without any grain boundary voiding enabled the $TiN_X$ to be used as a diffusion barier for the W process.