Fourier Transform Infrared Spectroscopy of Moisturized Low- $\kappa$ Dielectric Materials

A dense plasma enhanced chemical vapor deposition (PECVD) SiCOH film and a porous ultralow-κ (pULK) film have been investigated by means of the Fourier transform infrared spectroscopy. Structural differences between both materials have been found in particular in the amount of silanol groups and in the location and shape of the Si-O-Si stretching vibration band. Furthermore, moisturized samples of these materials have been investigated in situ during outgassing in rough vacuum. It has been observed that the pULK film contains only about 25% of the water amount found in the dense SiCOH film in saturation at 80% relative humidity and room temperature. A comparison of the water-related species in the investigated dielectric films with a liquid water spectrum identified hydrogen-bonded water-silanol groups in both materials and hydrogen-bonded water-water groups in the pULK film. During the outgassing process, no indication of shrinking or other structural changes were found, except for a shift in the silanol-associated vibration band to slightly higher wavenumbers. The achieved results are in good agreement to previous electrical characterization of both dielectric films.