Tribometrology of CMP Process

Abstract

NORM GITIS AND RAGHU MUDHIVARTHI INTRODUCTIONStudies of mechanical and chemical-mechanical surface finishing treatments have long been a part of tribology, a science of friction and wear (material removal). During chemical-mechanical polishing or planarization (CMP), surfaces of both the object being treated (e.g., the semiconductor wafer) and the finishing tool (e.g., the polishing pad), together with the polishing slurry between them, constitute a rather classical tribological system. This is sometimes referred to as a three-body interface [1-3], because it includes two solids in relative motion and the slurry containing abrasive particles at the interface. Modern CMP machines may have an abrasive pad conditioner rubbing the pad during wafer polishing, which keeps one of the surfaces in a state of constant change. A tribological system is typically characterized by classical parameters of the coefficient of friction between the surfaces and by their wear rate.The field of tribology has seen a number of theoretical models for various materials and interfaces [4]. Based on these models, the formulas for the calculation of both friction and wear have been derived. Unfortunately, these equations cannot be used directly by process and equipment design engineers unless the coefficient is known. Indeed, friction and wear properties of a tribological interface depend on macro-, micro-, and nanogeometry of the Microelectronic Applications of Chemical Mechanical Planarization, Edited by Yuzhuo Li

Investigations and Applications in Advanced Materials Processing

“…During the planarization process, the friction force generated by the abrasive particles removes the chemical reacted surface. Then, processing parameters such as the chemical content, the size of the particles, the speed of rotation, etc., contribute to the efficient material removal rate (MRR) in the planarization process [8,9]. Xie et al [10] developed a novel slurry by employing the potassium ions to facilitate the MRR of silicon wafers, with excellent stability and dispersity for colloidal silica.…”