Effects of plasmas on porous low dielectric constant CVD SiOCH films

Plasma etch and ash processes can alter surface and bulk properties in porous low-k films leading to poor device performance and reliability. Plasma-induced changes in film surface chemistries and topographies can result in increased water absorption, surface roughness, and metal intrusion. In this work, the effects of oxidizing and reducing plasmas on film surface roughness, porosities and chemistries are examined in a CVD porous low-k dielectric. Film surface chemical compositions were studied using X-ray photoelectron spectroscopy (XPS). Water and diiodomethane contact angle measurements were used to determine the polar and dispersive components of film surface energies. Atomic force microscopy (AFM) was employed to measure changes in surface roughness after ashing. Surface roughnesses were described by both vertical amplitudes and horizontal wavelengths, thus, creating “real” topographic film description. Changes in film densities were measured using spectroscopic ellipsometry. To study moisture adsorption, these films were exposed to liquid and vapor D2O. The extent of D2O adsorption was monitored by FTIR. Both oxidizing and reducing ashes appear to densify the top layer of the low-k film, but oxidizing ashes do not adsorb measurable quantities of D2O while reducing ashed samples show significant deuterium oxide uptake.