The degradation of porous ultra-low-k material, like SiCOH, under plasma processing continues to be a problem in the next generation of integrated-circuit fabrication. Due to exposure with many species during plasma treatment, such as photons, ions, radicals, etc., it is difficult to identify the mechanisms responsible for plasma-induced damage. Some studies have attempted to decouple plasma-generated species in order to study the effect of individual components and possible synergistic effects [1,2]. Using a vacuum beam apparatus with a calibrated VUV lamp and Ar ion gun, we show that 147 nm VUV photons and the presence of molecular O2 cause a loss of methylated species in SiCOH, creating a silica-like structure on the upper layer of the exposed material. The extent of the VUV/O2 induced damage as well as the effect of Ar ion bombardment is dependent on the interconnectivity, and thus diffusivity, of the material. In highly interconnected material, Ar+ bombardment may seal pores, restricting O2 diffusion into the film and reducing damage compared to VUV/O2 alone. The effects of vacuum beam exposures are shown to be comparable to plasma exposures under 'plasma cure' (no energetic ion bombardment) and some rf-biased conditions. Using Fourier-transform infrared (FTIR) spectroscopy and mercury probe measurements, we show that VUV/O2 exposure causes loss of carbon, resulting in a hydrophilic, damaged layer that is susceptible to H2O absorption, which leads to an increased dielectric constant. These results suggest that both VUV photons and high-energy ions can play important roles in the generation of plasma-induced damage.

[1] Jinnai B, Nozawa T, Samukawa S 2008 J.Vac. Sci. Technol. B 26 1926.

[2] Uchida S et al. 2008 J. Appl. Phys. 103 073303