Sputter-deposited Ti1−xWx diffusion barriers in microelectronic devices have been reported by many groups to be Ti deficient with respect to the target composition. In the present experiments, polycrystalline TixW1−x alloys were grown on oxidized Si(001) substrates at temperatures Ts between 100 and 600 °C by ultrahigh-vacuum magnetron cosputter deposition from pure W and Ti targets in 5 mTorr (0.65 Pa) Ar and Xe discharges. Films deposited in Ar were found by Rutherford backscattering and Auger electron spectroscopies to be increasingly Ti deficient with increases in the Ti sputtering rate and/or Ts at a constant W sputtering rate. TRIM calculations and Monte Carlo gas-transport simulations were used, in combination with the experimental results, to show that the Ti loss was due primarily to differential resputtering of the growing film by energetic Ar particles backscattered from the heavier W target. This effect is exacerbated at elevated film growth temperatures by Ti surface segregation in the alloy. The use of Xe, rather than Ar, as the sputtering gas greatly reduces both the flux and the average energy of backscattered particles incident at the substrate such that measurable Ti loss is no longer observed.

It has been observed experimentally that when a free shear layer is perturbed by a disturbance consisting of two waves with frequencies ω 0 and ω 1 , components with the combination frequencies (mω 0 ± nω 1 ) (m and n being integers) develop to a significant level thereby causing flow randomization. This spectral broadening process is investigated theoretically for the case where the frequency difference (ω 0 − ω 1 ) is small, so that the perturbation can be treated as a modulated wavetrain. A nonlinear evolution system governing the spectral dynamics is derived by using the non-equilibrium nonlinear critical layer approach. The formulation provides an appropriate mathematical description of the physical concepts of sideband instability and amplitude-phase modulation, which were suggested by experimentalists. Numerical solutions of the nonlinear evolution system indicate that the present theory captures measurements and observations rather well.

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