Stress development in Mo/Si and Ru/Si multilayers

The stress evolution of Mo/Si and Ru/Si multilayers sputtered under the same processing conditions has been investigated. A series of Mo/Si multilayers was also prepared with varying sputtering pressures. The stress evolution of each multilayer displays a well-defined modulation concurrent with the deposition of Mo (Ru) and Si. Large stress develops during the early stages of deposition of each successive layer with Mo (Ru) exhibiting apparent tension and Si exhibiting apparent compression. In the Mo/Si multilayers, these initial transients cause curvature changes of similar to 2.5 to 4.5 N/m depending on the sputtering pressure. For Ru/Si the transients exceed 8 N/m and extend across a larger fraction of the total layer thickness. Intermixing and reaction at the interfaces of Mo/Si and Ru/Si multilayers lead to a volume contraction and consequently a contraction of the bilayer period. Moreover, volume contraction due to intermixing is a stress generating mechanism that may explain the initial transients in the stress evolution. The volume of the interdiffused regions of Mo/Si and Ru/Si multilayers was estimated by measuring the contraction of the bilayer period using x-ray diffraction. The results show a strong correlation with the size of the initial stress transients suggesting that intermixing may cause them.