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.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials