Paper PS-MoM8
Effects of Plasma Etch and Ash Processes on Porous Low-k Film Surfaces in a Dual-Damascene Flow

Monday, October 20, 2008, 10:40 am, Room 304

Porous ultra low k dielectrics (k < 2.4) are being integrated into current and future technology nodes. As film dielectric values are driven lower, new interactions are observed between the films and the plasma etch environments to which they are exposed. Some of these interactions are extensions of the chemical sensitivities previously observed for k=2.4 materials (i.e., plasma ash damage), while others are a result of the change in the microstructure of the films as additional porosity is incorporated to decrease dielectric constant (i.e., pore size, pore connectivity, etc.). Post-etch and ash film surface roughness has often been observed with porous dielectrics and the etching and ashing process window to achieve a smooth dielectric surface decreases as the porosity increases. In this work, post-etch and/or ash film surface roughness effects will be examined for several different structures. The focus of the work is on a k=2.2 porous carbon doped oxide film utilizing a via first trench last integration scheme. Surface roughness phenomena are observed both on planar and vertical surfaces. In some cases, plasma modification to the film from one step is only observed several steps beyond the damage point. The sensitivity of the film requires careful control of every step of every plasma exposure to minimize cumulative and/or combinatory effects. Results will be presented highlighting some of the process spaces explored. This work was performed by the Research Alliance Teams at various IBM Research and Development Facilities.