Effect of low-k surface roughness on subsequent metal layers

Porous interlayer dielectric materials suffer detrimental changes in surface chemistry and topography upon exposure to plasma ash/etch processes. These changes typically result in increased water absorption, roughness, permittivity, and metal intrusion. Moreover, the nature of the low-k surface will affect roughness, wetting, adhesion, and, consequently, the resistance of subsequently deposited barrier layers. In this study, we employ silylation agents dissolved in supercritical CO2 to repair H-2-ash damaged low-k methylsilsesquioxane (MSQ) and to functionalize TEOS (dense-SiO2) films. Fourier transform infrared spectroscopy (FTIR) was performed using normal incidence transmission and grazing angle attenuated total reflection (GATR) techniques to verify surface chemistry modification prior to metal deposition. Contact angle measurements reveal a relationship between the polar and dispersive components of surface tension and surface roughness. Atomic force microscopy (AFM) was utilized to determine changes in surface topography after ashing and subsequent repair as well as determining the degree of roughness transfer to sputter-deposited metal films. These data provide insight into the chemical and topographical changes resulting from ashing and silylation of porous MSQ, and suggest implications for the roughness of subsequent barrier layers.