Molecular structure effects on dry etching behavior of Si-containing resists in oxygen plasma

Abstract

The authors have studied the influence of Si-O bonding in the polymer structure of Si-containing resists on O2 plasma etch behavior. Three polymers were synthesized with the same Si wt % (12.1%) and varying number of Si-O bonds (0, 1, or 2). The etch resistance during the plasma process was measured by monitoring the film thickness removed using real-time in situ ellipsometry. After plasma exposure, surface chemical changes and roughness were characterized by x-ray photoelectron spectroscopy and atomic force microscopy, respectively. For O2 plasma exposure without substrate bias, all polymers showed the formation of a ∼1 nm SiO2 layer at the surface that acted as a barrier to further oxygen etching. Adding Si-O bonds to the polymer structure at constant wt % Si greatly reduced the etch rate and Si loss during oxygen plasma etching relative to the case of no such bonds. Polymers with one Si-O bond in the polymer structure showed identical etch behavior to polymers with the same wt % Si and two Si-O bonds. However, increasing the number of Si-O bonds in the structure decreased the glass transition temperature of the polymer, leading to the formation of micron-sized wrinkles after plasma exposure. When a substrate bias was applied, the etch rate and the rate of Si loss increased due to sputtering of the SiO2 layer by energetic ions. For 90% N2/O2 discharges with substrate bias, a typical oxygen-based pattern transfer plasma condition, the etch rates of the polymers with the Si-O bond were lower and the SiO2 layer thickness formed was larger than that formed in pure O2 discharges with substrate bias. For all gas discharge conditions, polymers with pre-existing Si-O bonds showed less Si loss. © 2010 American Vacuum Society.