Molecular-level fundamentals for ultra-planarization and ultra-cleaning processes

点击翻译按钮获取中文摘要

Fine particles are frequently used as abrasives in ultra-planarization and ultra-cleaning processes for substrates, that is, chemical mechanical polishing (CMP). Understanding of the mechanism of CMP is indispensable for finer polishing. It is therefore necessary to understand surface forces and frictional forces between a particle and a substrate and between the particles. In this research project, we have elucidated at the molecular level the mechanism of frictional forces between a silica particle and a silicon wafer in aqueous electrolyte solutions. It is found that (1)as for monovalent electrolytes, the frictional force significantly decreases with increasing the electrolyte concentration and this order corresponds to the absolute value of hydration energy of the cations, indicating that the frictional force depends on the amount of free water around the cations ; (2)the frictional force is extremely sensitive to the molecular-scale roughness of the silica surfaces and significantly depends on the cleaning procedure of the surfaces ; (3)the frictional force complicatedly varies with the cationic valency, where it decreases with the hydration energy of divalent cations and then increases ; (4)as for trivalent cations, the mechanism of the frictional force is more complex due to the interaction of anions with the cations ; (5)the frictional force significantly decreases with increasing the solution pH, due to the presence of hairy layer with thickness of 1.0-1.5 nm formed at the silica surfaces at pH>10 ; (6)the relationship between the hairy layer and the electrolytes is rather complicated. Using computer simulations, we have investigated (1)how the frictional force between a particle and a smooth substrate depends on the force load and (2)how to remove the particulate contaminants on the smooth substrate.