Residual stresses in the failure of W–Pt–Ag metallizations on oxidized Si

Abstract

Compressive decohesion failure of W–Pt–Ag metallizations on oxidized Si was examined by separating the thermal residual and intrinsic stresses. Two kinds of experiments were performed. In the first kind, the thermal and intrinsic stresses were obtained independently. Intrinsic stresses in films of W, Pt, or Ag on SiO 2 /Si were found by measuring the Si substrate curvature. W films 200 nm and 400 nm thick were deposited by d.c. magnetron sputtering under a variety of Ar pressures and a variety of deposition power settings, while Pt and Ag thicknesses were fixed at 200 nm and 4100 nm, respectively. It was found that higher intrinsic stresses in the W result when the film thickness is small, the Ar pressure is low, and the deposition power is low. The W–Pt–Ag metallization intrinsic stress was obtained by superposing the individual film stresses. The measured intrinsic metallization stress was then added to a calculated thermal stress to determine the W–Pt–Ag metallization total stress state. In the second kind of experiment, a large number of metallizations experienced a thermal cycle, and the fraction of decohesion failures was observed. The total metallization stress state for various processing conditions was then correlated with the fraction of decohesion failures, which in turn led to a threshold value of stress, below which the probability of decohesion failure was essentially zero.