Tribological, Thermal and Kinetic Characterization of SiO <sub>2</sub> and Si <sub>3</sub> N <sub>4</sub> Polishing for STI CMP on Blanket and Patterned Wafers
Juan Cristobal Mariscal, Jeffrey McAllister, Yasa Sampurno, Jon Sierra Suarez, Mark L. O’Neill, Hongjun Zhou, Malcolm Grief, Dave Slutz, Ara Philipossian
Abstract
We investigated the tribological, thermal and kinetic aspects of SiO 2 and Si 3 N 4 polishing on blanket and patterned wafers for STI CMP. Results showed the absence of anomalous tribological vibrational behaviors thanks to synergies between the colloidal CeO 2 -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, Si 3 N 4 was much more non-Prestonian than SiO 2 . As expected, Si 3 N 4 polishing resulted in COF values that were approximately one-half of their SiO 2 counterparts resulting in high SiO 2 -Si 3 N 4 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 SiO 2 and highly chemically-limited for Si 3 N 4. Patterned wafer polishing time traces showed that COF could be utilized as a real-time indicator for end-point detection and that, after 6 min of polishing, we observed the total removal of SiO 2 with a hard stop on Si 3 N 4 . End-points reached were also consistent with our blanket wafer polishing data. Regardless of pattern density and pitch, SiO 2 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.