VUV radiation inherent in plasma discharges have been shown to be a concern during plasma processing of low-k materials [1, 2]. VUV photons are known to break Si-C bonds, thereby transforming the material into a SiOx-like material post-exposure. Damage to samples exposed to a Xe VUV lamp (λ = 147 nm) in a vacuum chamber compared to corresponding effects in an Ar/O­2 plasmas (λ = 104, 106, and 130 nm) suggests that chemical modification is limited by the penetration depth of the VUV photons, which is in turn dependent on wavelength. The formation of a SiOx-like layer near the surface of the material, which deepens as more carbon is lost, introduces a dynamic change of integrated VUV absorption throughout the material over time. As a result, the rate of carbon loss is continuously changing during the exposure. We present a model that captures this dynamic behavior and compare the model to experimental data by fitting a parameter that represents the effective carbon photolysis using a procedure described previously [3]. For sample exposures to argon plasmas, the model shows good agreement with the experimentally obtained carbon loss profile, inferred from post-processing, ex-situ Fourier transform infrared spectroscopy (FTIR). For O2 plasma, there is evidence that an additional effect, perhaps oxygen radicals, plays a major role in chemical modification at short times near the surface of the material. By contrast, we conclude that VUV photons contribute more to damage in the bulk. By exposing samples to VUV radiation in He plasmas (λ = 58 nm), it may be possible to treat and modify the surface of low-k films with high energy, low penetrating VUV photons to limit damage to the near-surface.

[1] B. Jinnai, T. Nozawa, and S. Samukawa, J. Vac. Sci. Tech. B 26, 1926 (2008).

[2] J. Lee and D. B. Graves, J. Phys. D: Appl. Phys. 43, 425201 (2010).

[3] M. J. Titus, D. G. Nest, and D. B. Graves, J. Phys. D: Appl. Phys. 42, 152001 (2009).