Engineering the Interaction Forces to Optimize CMP Performance
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Engineering the Interaction Forces to Optimize CMP Performance G. B. Basim, I. Vakarelski, P. Singh, B. M. Moudgil Department of Materials Science and Engineering and Engineering Research Center for Particle Science and Technology, University of Florida, Gainesville, FL 32611. ABSTRACT The main objective of Chemical Mechanical Polishing (CMP) process is to planarize the metal or dielectric layers deposited on the wafer surfaces in microelectronics device manufacturing. In CMP, slurries containing submicrometer size particles and chemicals are used to achieve planarization. An effective polishing requires an optimal material removal rate with minimal surface deformation. Therefore, it is important to control the particle-substrate interactions that are responsible for the material removal and the particle-particle interactions, which control the slurry stability and consequently the defect density. This paper discusses the impact of interaction forces on polishing, and underlines the scientific guidelines to formulate consistently high performing CMP slurries.
INTRODUCTION Rapid advances in the microelectronics industry demand a decrease in the sizes of the microelectronic devices and use of new materials as connector or dielectric layers (1). As the minimum feature size approaches to 0.1µm, a very thin layer of material removal is required with atomic level planarity and clean surface finish during manufacturing (2). Furthermore, the new materials such as copper and low-k dielectrics introduce new challenges into CMP since they are more sensitive to defect formation (3). These trends necessitate the improved control of interaction forces in polishing both in terms of providing slurry stability at the extreme pH and ionic strength conditions and at the particle-surface interaction level to achieve the desired material removal rates. It is suggested that a perfectly planarized surface with minimal deformation can be achieved by using monosized particulates (4). In practical applications, however, there may be oversize particles in the slurries in the form of larger size particles (hard agglomerates), or the agglomerates of the primary slurry particles (soft agglomerates). The polishing tests conducted in the presence of hard agglomerates (at parts per million concentration) verified a significant degradation in the polishing performance (5). The Atomic Force Microscopy (AFM) analysis showed increasing surface roughness and deformation (scratches and pit formations) on the wafer surfaces with significant variation in the material removal rate response. CMP slurries are filtered before polishing to remove hard agglomerates. Nevertheless, even after filtration significant defect counts have been observed on the polished surfaces (6). These are attributed to the possibility of particulate agglomeration during the polishing operations due to the local variations in the particle concentration, ionic strength or pH. Systematic analysis conducted in the presence of soft agglomerates showed significant surface deforma
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