Retarded C54 transformation and suppressed agglomeration by precipitates in TiSi2 films

We report the effects of excess Si phase on the C54 transformation and the thermal stability of TiSi2 thin films as a function of Si/Ti (x) ratio. The resistivity and x-ray diffraction data of TiSix(x = 2.1-2.4) films showed a retardation of C54-TiSi2 transformation with incremental molar ratio x; t he TiSix (x = 2.1-2.3) films were completely transformed to C54-TiSi2 with rapid thermal annealing (RTA) of 750 degrees C, while the TiSix (x = 2.4) f ilms were transmuted to C54-TiSi2 over the RTA of 800 degrees C. Transmissi on electron microscopy study revealed that the growth of Si precipitates in the Si-rich TiSix films competes with the grain growth during the transfor mation of C49 to C54 TiSi2 phase, resulting in the increase of C54 transfor mation temperature. An excellent sheet resistance (R-s) and its standard de viation in concert with a reliable gate oxide integrity were attained from the Si-rich TiSi2/polycrystalline-Si (poly-Si) structure up to the solid st ate annealing of 850 degrees C for 60 min. These attributes are due to the reduced solid state reaction at TiSi2/Si interface and the suppressed TiSi2 agglomeration by Si precipitates. The average R-s of the 0.12-mu m-wide Ti Si2(800 Angstrom)/poly-Si gate lines is lower than 4.5 Omega/square, demons trating a robust gate electrode structure for gigabit scale device applicat ion. (C) 2000 American Institute of Physics. [S0021-8979(00)01106-3].