Tensile crack patterns in Mo/Si multilayers on Si substrates under high-temperature bending

Abstract

Mo/Si multilayers with a single-layer thickness in the nanometre range (60 Mo/Si layers in total) were deposited on Si(100) substrates by dc magnetron sputtering. Upon uniaxial bending at elevated temperatures between 300 and 440 °C in vacuum, unconventional crack patterns formed in the multilayers. Tensile stress within the multilayer stack and Si substrate due to bending during thermal treatment was estimated to be on the order of 100 MPa. A combination of external bending, residual and thermal stresses is considered to be the reason for this phenomenon. Cracks had either a sinusoidal or a spiral shape. The surface frequency of the spirals observed was ∼10 cm^-2, with a track width of ∼30 μm and a spiral diameter of ∼300 μm. In general, cracking was accompanied by complete local de-bonding of the whole Mo/Si multilayer stack from the substrate. Fracture patterns were studied by optical microscopy. In addition, the morphological parameters of the remaining non-delaminated multilayers were determined by means of X-ray reflectometry supported by investigation of phase content by wide-angle X-ray scattering .