NER: Debonding and Fracture of Ultra-Thin Films

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AbstractDebonding and fracture of ultra-thin (2 to 20 nm) films deposited on substrates (such as silicon) is an important problem in the manufacture of micro-electronic components. Internal stresses are developed in the thin films during their deposition, because there is a molecular mismatch at the interface between the thin film and its substrate. These stresses can result in both debonding (separation of the thin film from the substrate) and fracture.Traditional studies of stress-deformation behavior involve large material samples. The resulting descriptions of behavior assume that the material extends to ``infinity'' (perhaps 50 nm) in all directions. But within the immediate neighborhood of a phase interface, the material is subjected to long-range intermolecular forces from the adjoining phase, and the observed material behavior is different.Proposed herein is a novel extension of continuum mechanics to the near molecular scale to treat nanoscale fracturing and debonding phenomena. This theory employs known bulk material behavior outside an interfacial region and corrects this bulk material description within the interfacial region through the introduction of a body force (mutual force) that accounts for the difference in intermolecular forces when a portion of the material is replaced by an adjoinging phase. It is conjectured that this theory can provide a means to incorporate nanoscale modeling at a crack tip into macroscale fracture problems in order to predict fracture initiation and propagation from first priciples without (or with minimal) empirical parameter fitting.