Lateral solvent diffusion characterization of low k dielectric plasma damage and ALD barrier film closure

The lateral diffusion of toluene solvent molecules was employed to probe the porous structures of plasma damaged low k dielectrics and ultra-thin ALD copper diffusion barriers. A change in the pore structure of a microporous CVD low k was determined from the absence of diffusion after the plasma treatment of a thin film (<270 nm). This indicated a densification or reduction of the pore structure below the 6.8 Å probe molecule size. Atomic layer deposited layers of WNC and TaN were probed for defect channels when deposited on porous low k substrates. Toluene was able to penetrate through microchannels in the films and diffuse laterally inside the underlying porous low k. This allowed a non-line-of-site assessment of ALD film surface closure. In both cases the refractive index changes resulting from toluene filling of the low k pores was observed optically by ellipsometry or optical microscopy.