Paper PS-MoM7
Impact of Reducing and Oxidizing Post Etching Plasma Treatments on Porous SiOCH Integration

Monday, October 20, 2008, 10:20 am, Room 304

For 45 nm interconnect technology node and beyond, porous SiOCH (p-SiOCH) materials with porosity higher than 25% and a dielectric constant lower than to 2.5 are being introduced. However the porosity brings serious integration issues such as a high sensitivity of porous materials to etching and ashing plasma exposures and the risk of metallic precursor diffusion into the dielectric during conformal barrier deposition. This work focuses on the development of post etching plasma treatments using reducing and oxidizing chemistries. Such plasma treatments can be used as i) ashing processes and/or ii) post cleaning processes (wafer and/or reactor walls) and/or iii) “pore sealing-like” processes to prevent metal barrier diffusion. p-SiOCH wafers (porosity of 26% and k=2.35) prepared by plasma enhanced chemical vapour deposition have been etched and post etched in a dual frequency capacitive reactor. Plasma induced modifications of p-SiOCH have been investigated both on blanket and patterned wafers using volume and surface analyses techniques such as infrared spectroscopy (in transmission and in multiple internal reflexion), ellipsometry (spectroscopic and porosimetric), x-ray photoelectron spectroscopy and water contact angle. For each chemistry (NH₃, H₂, CH₄ and O₂), we have optimized the plasma conditions minimizing the p-SiOCH modifications such as carbon depletion, new bonds formation (Si-H, Si-OH,..) and moisture uptake. After methane based plasma treatments (CH₄/N₂) a carbon rich layer (a few nanometers thick) presenting hydrophobic properties is deposited on the p-SiOCH surfaces. After NH₃ and O₂ based plasmas, the surface becomes hydrophilic and carbon free. Infrared analyses show no moisture uptake after CH₄ based plasmas while a significant amount of water uptake is detected after NH₃ and O₂ plasmas. Furthermore, dielectric constant (k) measurements after the different plasma treatments demonstrate that the k increase is strongly related to the formation of silanol groups and moisture uptake. The capabilities of the plasma treatments presented in this study to remove post etch-residues from the p-SiOCH surface and to prevent the barrier diffusion into p-SiOCH will be also addressed.