• Current researchers: Jeff Shearer
• Related Fisher group references:
  • Effects of Plasma Processing Parameters on the Surface Reactivity of OH(X2) in Tetraethoxysilane/O2 Plasmas During Deposition of SiO2, K. H. A. Bogart, J. P. Cushing, and E. R. Fisher, J. Phys. Chem. B 101, 10016-10024 (1997).
  • Mechanisms of SiO2 Deposition from Tetramethylcyclotetrasiloxane, Dimethyldimethoxysilane and Tetramethylsilane Plasmas, J. Zhang, D. S. Wavhal, and E. R. Fisher, J. Vac. Sci. Technol. A. 22, 201-218 (2004).
  • Surface Reactivity of OH Molecules During Deposition of SiO2 from Siloxane-Based Plasmas, J. Zhang and E. R. Fisher, J. Phys. Chem. B 108, 9821-9828 (2004).
  • Investigation of Gas Phase Species and Deposition of SiO2 Films from HMDSO/O2 Plasmas, D. S. Wavhal, J. Zhang, M. L. Steen, and E. R. Fisher, Plasma Process. Polym., 3, 276-287 (2006).

SiO2 is used extensively as a dielectric for integrated circuits and finds additional applications in optics, food packaging, and corrosion protection layers. SiO2 can be deposited by plasma enhanced chemical vapor deposition (PECVD) from a variety of alkoxysilane precursors including tetraethoxysilane (TEOS) and hexamethyldisiloxane (HMDSO) among others. Past studies in our group have focused on the deposition mechanisms for thin SiO2 films. Results from these studies indicate that the components in the starting material are retained in the film, and various functional groups are not completely decomposed by the plasma.

SiO2 films deposited from 100% alkoxysilane precursors contain hydrocarbon and hydroxyl contamination, which degrade the dielectric properties of the film by disrupting the tetrahedral SiO2 network. Addition of an oxidant such as O2 can eliminate these contaminants, and we have shown that although O2 addition causes the deposition rate to drop by more than 50%, it improves the dielectric capacity for films deposited from a variety of different precursors. One of the species that may play an important role in these processes is the OH radical, and our IRIS studies on the surface reactivity of OH radicals in alkoxysilane/O2 systems suggest that it has a moderately high surface reactivity. Oxygen can influence the film properties in other ways as well, and our experiments have shown that post-deposition oxidation using O2 plasma treatment resulted in a denser silicon dioxide material.

Our work in this area is currently being extended to the study of SiO2 coatings on TiO2 nanoparticles. Titania nanoparticles are already used in a variety of commercial products including paint and cosmetics. However, their utility is limited in many applications by the nanoparticles’ tendency to aggregate. One potential approach to minimize aggregation is to deposit a film on the TiO2 nanoparticles. PECVD is well-suited to this task as it offers better surface coverage than other methods and may allow the deposition of a more uniform coating over the nanoparticles’ surfaces. Parameter studies are currently being performed in HMDSO/O2 plasmas to understand how O2 addition in the feedgas influences the film deposition rate.