Fundamental studies of chemical mechanical planarization (CMP) processes of tungsten and copper.

摘要

Atomic force microscopy (AFM) has been used to study the interfacial frictional properties of tungsten and copper surfaces in a variety of aqueous solutions. Bare or alumina (Al₂O₃) coated Si₃N ₄ tips have been used to emulate the microasperity contact with the tungsten or copper surfaces. This experimental approach has proven to be versatile in providing atomic level insight into the chemical mechanical planarization (CMP) of tungsten and copper.; It has been demonstrated through the course of this dissertation that the interfacial friction and adhesion of tungsten surface is influenced substantially by the solution + composition of the AFM tip (Si₃N₄ or Al₂O₃), and the concentration and composition of an oxidizing agent. The interfacial friction of tungsten was observed to reach a maximum value at a pH located between the isoelectric points (IEP's) of the tip and tungsten. Friction is influenced in this way due to the variation in the magnitude and sign of surface charges, which depend on the solution pH.; The extent of surface oxidation has been correlated with the interfacial friction of tungsten surfaces and material removal rates by systematically varying the concentration and composition of the oxidizing agents (KNO ₃, KClO₃, and KIO₃) in the solution. It has been proposed that the material removal primarily occurs through a tip-mediated dissolution process of WO₃ on the surface. It has been proposed that the dissolution process provides a pathway of energy dissipation and increases the interfacial friction of the tungsten surface composed of this oxide.; Finally, this microscopic approach has been used to investigate copper surfaces under CMP conditions. In this investigation, the formation of a thicker reaction overlayer, the presence of higher interfacial friction, and the tip-mediated/localized dissolution of copper interfaces were observed in acidified solutions of BTA, while little change in the interfacial properties of the copper film was observed in neutral solutions of BTA. It has been proposed that energy dissipation through the dissolution process of BTA-Cu overlayer enhances the interfacial friction.