NER: Debonding and Fracture of Ultra-Thin Films

沉积在衬底（如硅）上的超薄（2 ~ 20 nm）薄膜的脱粘和断裂是微电子元件制造中的一个重要问题。 在薄膜沉积过程中，由于薄膜与其衬底之间的界面处存在分子失配，因此在薄膜中产生内应力。 这些应力会导致薄膜的脱粘（薄膜与基体的分离）和断裂。 由此产生的行为描述假设材料在所有方向上延伸到“无限大”（可能为50 nm）。但是在相界面附近，材料受到来自相邻相的长程分子间力的作用，所观察到的材料行为是不同的，本文提出了一种新的连续介质力学扩展到近分子尺度来处理纳米尺度的断裂和脱粘现象。该理论采用已知的界面区域外的体材料行为，并通过引入体积力（相互力）来校正界面区域内的该体材料描述，该体积力（相互力）解释了当材料的一部分被相邻相取代时分子间力的差异。据证实，这一理论可以提供一种手段，将纳米级建模在裂纹尖端到宏观断裂问题，以预测裂纹的萌生和扩展从第一原理没有（或与最小）的经验参数拟合。

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.