Effects of Particle Concentration in CMP
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EFFECTS OF PARTICLE CONCENTRATION IN CMP
Wonseop Choi, Seung-Mahn Lee and Rajiv K. Singh Department of Material Science and Engineering and Engineering Research Center for Particle Science and Technology, University of Florida, Gainesville, Florida 32611-6400, USA
ABSTRACT This paper reports on characterization of the surface coverage of particles by in-situ lateral friction force measurement during chemical mechanical polishing. The lateral friction force apparatus was made to operate close to real CMP conditions. For these experiments a sapphire wafer of constant surface roughness was used. For both 2psi and 4psi down force we observed increase in lateral friction forces with increasing solid loading. The lateral friction forces have been found to be significantly dependent on the contact area at the wafer-pad-slurry interface, thus showing that in-situ dynamic friction force changes in the surface coverage of particles. From these results, we conclude that the enhancement of frictional force is due to increased contact area at the wafer-pad-slurry interfaces. The lateral friction force measurement can provide an understanding of wafer-pad-slurry interactions.
INTRODUCTION Chemical mechanical polishing (CMP) has been widely accepted for local and global planarization of dielectric and metal films in ultralarge scale integration metallization processes [1],[2]. However, CMP is still a largely empirical process, and there is intense speculation as to the phenomena occuring at the wafer-pad-slurry interface, the understanding of which is vital for process optimization and development of in situ monitor. There is no in-situ measurement techniques to verify the phenomena occuring at the wafer-pad-slurry interface, which is the key in determining the abrasion mechanism. From the abrasion mechanism model developed by Brown and Cook [3], the mechanics of the interaction volume between polishing particle and the glass surface has been described by the penetration depth model of spherical particle, removing a glass volume of dimensions proportional to the penetration. Bielmann et al. [4] reported the different removal rate mechanism in tungsten CMP, which is related to the contact surface area between particles and polished surface controlling the reaction rate. Recently, Mahajan et al. [5],[6] showed the transition from the indentation mode to the surface area mode as particle size decreased and concentration of particle increased. Friction forces are a measure of how much contact the pad makes with the surface, which is important in determining the abrasion mode [1]. In non-chemical or solely mechanical polishing the chemical effect is negligible and removal is related to volume of surface materials gouged by the particle. The particle size and number of particles are critical to controlling the removal rate of the undesirable material during CMP [7]. In our previous work, Mahajan et. al reported the in-situ lateral force technique for dynamic measurement of surface roughness in oxide. In this study, we have reported t
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