Interaction between abrasive particles and film surfaces in low down force Cu CMP
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Interaction between abrasive particles and film surfaces in low down force Cu CMP Yuchun Wang, Isaac Zomora, Joe Hawkins, Renjie Zhou, Fred Sun, Roy Martinez, Jian Zhang, Bin Lu, Shumin Wang Cabot Microelectronics, 870 N. Commons Drive, Aurora, Illinois 60504 A robust copper slurry should have high removal rate, efficient planarization, optimal over polishing window and fast clearing without corrosion. These requirements were addressed in the choice of abrasive particles, film formation for copper passivation, selectivity of copper to barrier, and interactions between particles and film surfaces. The performance results of low dishing erosion and surface finish are discussed with the proposed mechanism.
Introduction In copper-low k CMP for 90 nm and 65 nm, a robust copper CMP slurry at low down force should have high copper removal rate, efficient planarization, decent overpolishing window and fast clearing time without corrosion. The choice of abrasive particles in conjunction with film forming species is critical to achieve good planarity and residue free Cu CMP. In this paper we present how the Cu slurry was developed based on the understanding and proposed mechanism of interactions between different particles (alumina, silica, specially treated alumina particles) and film surfaces of Cu and Ta. Experimental Wafers from Sematech were polished on Applied Materials’ Mirra (200mm wafers) and Reflexion (300mm wafers). In each run a new pad (A110 from Cabot Microelectronics) was started with 3M disk DI water conditioning for 20 min, followed by 6 dummy Cu wafers before monitor wafers. Dishing and erosion were measured on HRP200 and VX310 Atomic Force Profiler. For electrochemistry study, slurries were introduced to a mini-polishing cell with 3 electrodes (Cu, Pt, and HgSO4) connected to EG&G potentiostat. Focused ion beam (FIB) analysis was done at external lab. Results and discussions Abrasive particles To compare the Cu removal rate, silica and alumina particles were mixed with standard copper chemistry to prepare copper slurries. Figure 1 shows that under the same conditions especially at lower down force, alumina gave much higher Cu removal rate. In addition, alumina had lower removal rate on tantalum and TEOS, giving better selectivity of Cu to Ta and TEOS. The high selectivity with alumina particles gave lower erosion during copper over polishing. In order to maintain colloidal stability, engineered alumina particles with special surface treatment were chosen in the copper slurries. Cu film passivation Passivation is essential in copper slurries to achieve planarization and over polishing window. Figure 2 compares adequate Cu passivation (smooth surface) and insufficient
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passivation causing high dishing and pattern dependent corrosion (1). On the other hand, over passivation would cause low Cu rate and metal residue especially at metal 2 and above. For low k Cu CMP, a dense but soft passivation layer is desired to achieve low dishing at high removal rate. Selection of abrasive particles in com
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