The Adhesion of Pad Particles on Wafer Surfaces during Cu CMP
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The Adhesion of Pad Particles on Wafer Surfaces during Cu CMP
Jae-Hoon Song, Ja-Hyung Han, Yi-Koan Hong, Young-Jae Kang, Jin-Goo Park Ju-Ho Maeng*, Young-Man Won* Div of Materials and Chemical Engineering, Hanyang University, Ansan, 426-791, Korea +82-31400-5226, +82-31-417-3701, [email protected] *Saesol Diamond, Ansan, 425-833, Korea
ABSTRACT The adhesion force of pad and alumina were experimentally and theoretically investigated in slurry solutions of different pHs. The isoelectric point (IEP) of pad particles was measured to be around pH 3. The wafer surfaces showed negative zeta potentials in the investigated pH ranges with exception of FSG and Ta. Cu and Ta showed higher interaction forces than dielectric materials. The lowest adhesion force was measured between pad particle and wafer surfaces in a slurry solution of pH 11. The magnitude of adhesion force of pad particles was lower than alumina particles. INTRODUCTION Cu CMP has been implemented to fabricate multilevel Cu interconnections due to lower
electrical resistance (1.7 µΩ⋅cm), superior resistance to electro-migration and reduced RC time delay compared with aluminum (2.66 µΩ⋅cm) [1]. During Cu CMP, polished surfaces are more vulnerable to defects such as particles, scratches, dishing, erosion, and corrosion due to its nature and the complexity of slurry chemistry. As the circuit line width continues to decrease, the removal of those defects on polished dielectric and metal films has become a challenge in post Cu CMP cleaning process [2]. In particular, abraded pad particles can be generated during pad conditioning in CMP process. If they exist on pad surface, they can be strongly adhered on wafers due to the stress and higher temperature during polishing. The purpose of this study is to investigate the effects of slurry pH on the adhesion force of pad particles on Cu, Ta, TEOS, SiLKTM, Aurora and FSG surfaces. Since the smallest possible
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adhesion force between pad particles and wafer surfaces is highly desirable for reducing pad particle contamination, the adhesion force of pad particle on wafer surfaces was theoretically and experimentally studied. EXPERIMENTS In order to investigate the behavior of surfaces as a function of pH, the zeta potentials were measured using a laser electrophoresis zeta potential analyzer (LEZA 600, Otsuka Electronics, Co.). The zeta potentials of pad particles and wafers were measured. In order to obtain the large amounts of pad particles, IC 1000 pad (Rohm and Haas) was severely polished on purpose by a diamond disk in dry air. Cu and Ta particles (Aldrich, 1 µm) were used instead of Cu and Ta wafers due to the high conductivity of these surfaces. The zeta potentials of substrates of the TEOS, SiLKTM, Aurora and FSG were also measured. The adhesion force of particles on surface was measured using an Atomic Force Microscope (AFM, Park Scientific Instruments, CP Research) by directly measuring the force required to remove them from a surface [3]. The pad particle was attached on a Si3N4 tipless cantil
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