Journal of Vacuum Science & Technology A, Vol.20, No.3, 754-761, 2002
Stress changes in chemical vapor deposition tungsten silicide (polycide) film measured by x-ray diffraction
Stresses in chemical vapor deposited polycide tungsten silicide (poly-Si/WSi2) were evaluated at each stage of the fabrication. The individual layers of the Si/SiO2/poly-Si/WSi2/poly-Si multilayered structure were deposited sequentially on separate wafers and subjected to x-ray diffraction analysis in the as deposited and annealed conditions to determine the changes in strain occurring in WSi2. Samples cut from wafers containing all the layers were either heat treated at 1193 K for 30 min or capped with a 25 nm thermal oxide and the strain in the WSi2 film was also analyzed by x-ray diffraction. The change in strain of the WSi2 layer, following each step of the fabrication process, was evaluated by the lattice parameter variation of the c axis. The stress is affected by the layers of the multilayered film. An as deposited poly-Si layer on top of WSi2 reduces its stress, since it introduces a compressive component. The stress in WSi2 is further reduced upon annealing. Poly-Si also maintains a Si supply at the poly-Si/SiO2 interface thus eliminating Si out-diffusion during heat treatment in an oxygen containing ambient. Capping the system by a thin oxide layer modifies the stress pattern of the WSi2 which becomes compressive.