A novel experimental technique utilizing UV-enhanced fluorescence was developed and used to measure fluid film thicknesses and general flow patterns during conditioning on a polishing pad. The method was successfully applied to several case studies for analyses of how conditioners with different working face designs (i.e. complex vane, full-face and partial-face), in conjunction with different platen angular velocities, affected fluid transport. In general, for all discs types, fluid across the pad followed similar trends where films were thickest near the wafer track center and thinnest near the pad edge (measurements showed a thickness range of appx. 0.5 to 1.1 mm). For all discs, the time for the film thicknesses to reach steady-state increased in proportion to the distance away from the pad center (times ranged between 12 and 62 s). The full-face conditioner consistently produced the thinnest films and reached steady-state the fastest. In contrast, the complex vane conditioner created the thickest films and took longest to reach steady-state. The work demonstrated the significance of understanding and visualizing the mechanisms that can contribute to fluid transport during CMP and how our novel technique could contribute, in the near future, to a greater understanding of fluid transport during in-situ conditioning.
We investigated the tribological, thermal and kinetic aspects of SiO2 and Si3N4 polishing on blanket and patterned wafers for STI CMP. Results showed the absence of anomalous tribological vibrational behaviors thanks to synergies between the colloidal CeO2-based slurry and application-specific conditioner. Removal rates for the two processes showed non-Prestonian behavior as both mechanical and chemical factors were at work. However, Si3N4 was much more non-Prestonian than SiO2. As expected, Si3N4 polishing resulted in COFvalues that were approximately one-half of their SiO2 counterparts resulting in high SiO2-Si3N4 removal rate selectivity. A modified Langmuir-Hinshelwood model was used to simulate removal rates allowing us to conclude that the process was mechanically-limited for SiO2 and highly chemically-limited for Si3N4. Patterned wafer polishing time traces showed that COFcould be utilized as a real-time indicator for end-point detection and that, after 6 min of polishing, we observed the total removal of SiO2 with a hard stop on Si3N4. End-points reached were also consistent with our blanket wafer polishing data. Regardless of pattern density and pitch, SiO2 removed was not proportional to polish time. This was a result of the low colloidal ceria nano-particle content in the slurry which was explained via a phenomenological model.
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