Abstract We report a form of chemical mechanical polishing (CMP) in which ceria abrasive particles polish a silicon wafer surface in a water environment. The Car-Parrinello molecular dynamics (CPMD) method, which enables chemical reaction dynamics in non-equilibrium systems to be treated non-empirically, was used. The first application of CPMD was to a model including a silica surface rubbed by a ceria cluster to ascertain the fundamental tribochemical phenomena in the CMP process. The model consisted of a hydrogen-terminated silica surface (a representative model of an oxidized wafer surface) and H4Ce6O12 cluster placed in the vicinity of an asperity in the silica surface. H2O molecules were explicitly considered in order to reflect the presence of slurry water. An external load and shear force were applied to the cluster. Under conditions of finite temperature and friction, a Ce-O-Si bridging bond formed at the interface between the silica surface and the ceria cluster. Subsequently, another Ce-O-Si bridging bond formed. These newly formed bridging bonds changed the silicon atom into a five-coordinated one. Because this state was probably unstable, a pyramid structure was rapidly restored by breaking the original Si-O bond in the asperity, meaning that the wafer surface became flattened. By referring to static density functional theory (DFT) calculations, we concluded that this bond dissociation event was due to multiple Ce-O-Si bonds forming. To discuss the effect of slurry water, a similar CPMD simulation, but without H2O molecules (i.e., dry friction), was performed. Here, the Si-O bond dissociation reaction did not take place even if multiple Ce-O-Si bonds formed. This means slurry water is needed for CMP to occur and it probably helps to weaken the Si-O bond. The second application of CPMD was to a model consisting of a thin water layer sandwiched between silica and ceria plates for studying the effect of the surface orientation of the ceria. Two low-index CeO2 surfaces, (1 0 0) and (1 1 1), were modeled. A chemical event wherein Ce-O-Si bridging bonds formed on the ceria/silica interface could be observed in both models. However, the bond dissociation reaction of the original Si-O bond on the silica surface proceeded only in the model with the (1 1 1) surface, and not on the (1 0 0) surface. This difference in reactivity could mainly be explained by the arrangement of atoms of each surface. The (1 1 1) surface provides hexagonal adsorption sites that inherently form a structure with five-coordinated silicon atoms, which are important intermediates in the CMP process. On the other hand, the (1 0 0) surface exhibits square adsorption sites which hardly form the required intermediate. We successfully examined the effect of the surface orientation of the ceria in addition to the fundamental CMP mechanism wherein multiple Ce-O-Si bonds initiate a chemical reaction including Si-O bond scission.

中文翻译：

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用于化学机械抛光工艺的功能材料设计的二氧化铈/二氧化硅滑动界面的第一性原理分子动力学研究

摘要 我们报告了一种化学机械抛光 (CMP)，其中氧化铈磨粒在水环境中抛光硅晶片表面。使用了 Car-Parrinello 分子动力学 (CPMD) 方法，该方法能够非经验地处理非平衡系统中的化学反应动力学。CPMD 的第一个应用是一个模型，该模型包括由氧化铈簇摩擦的二氧化硅表面，以确定 CMP 过程中的基本摩擦化学现象。该模型由以氢为末端的二氧化硅表面（氧化晶片表面的代表性模型）和放置在二氧化硅表面粗糙附近的 H4Ce6O12 簇组成。明确考虑 H2O 分子以反映浆水的存在。外部载荷和剪切力被施加到集群上。在有限温度和摩擦条件下，在二氧化硅表面和二氧化铈簇之间的界面处形成了Ce-O-Si桥键。随后，形成了另一个 Ce-O-Si 桥键。这些新形成的桥键将硅原子变成了五配位的原子。因为这种状态可能是不稳定的，通过破坏粗糙中的原始 Si-O 键，金字塔结构迅速恢复，这意味着晶片表面变得平坦。通过参考静态密度泛函理论 (DFT) 计算，我们得出结论，这种键离解事件是由于形成了多个 Ce-O-Si 键。为了讨论泥浆水的影响，进行了类似的 CPMD 模拟，但没有 H2O 分子（即干摩擦）。这里，即使形成多个 Ce-O-Si 键，Si-O 键解离反应也不会发生。这意味着 CMP 需要浆料水，它可能有助于削弱 Si-O 键。CPMD 的第二个应用是由夹在二氧化硅和二氧化铈板之间的薄水层组成的模型，用于研究二氧化铈表面取向的影响。对两个低指数 CeO2 表面 (1 0 0) 和 (1 1 1) 进行建模。在两种模型中都可以观察到在氧化铈/二氧化硅界面上形成 Ce-O-Si 桥键的化学事件。然而，二氧化硅表面原始 Si-O 键的键解离反应仅在具有 (1 1 1) 表面的模型中进行，而不在 (1 0 0) 表面上进行。这种反应性的差异主要可以通过每个表面原子的排列来解释。(1 1 1) 表面提供六边形吸附位点，其固有地形成具有五个配位硅原子的结构，这是 CMP 过程中的重要中间体。另一方面，(1 0 0) 表面表现出正方形的吸附位点，很难形成所需的中间体。除了基本的 CMP 机制外，我们还成功地检测了氧化铈表面取向的影响，其中多个 Ce-O-Si 键引发了包括 Si-O 键断裂在内的化学反应。