Impact of wavelength of UV light and UV cure time on chemical and mechanical properties of PECVD deposited porous ultra low-k films

We report a method to improve the chemical stability and the mechanical properties of a plasma enhanced chemical vapour deposited ultra low-dielectric constant material. This enhancement in the properties was achieved through extended UV cure times using a broad band lamp, emitting light at wavelengths higher than 200 nm. These longer cures also increased significantly the Young’s modulus, but the dielectric constant did increase less than the experimental error. It is also demonstrated that this improved property depends on the chemical bonds present in the film, such as Si–CH3, as well as on the density of the film. Films with a dielectric constant of 2.06, Young’s modulus of 4.9 GPa and perfect resistance against 0.5% HF for up to 300 s, were obtained. Another type of UV cure, using a narrow band lamp with wavelength of 172 nm, induced completely different chemical resistance characteristics of the resulting films.

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► Ultra low-k films have been fabricated with a dielectric constant of approximately 2.0, E of approximately 5 GPa.
► These films had an excellent chemical stability against 0.5% HF wet etching.
► The wet etch stability was improved when applying a UV cure with longer than 200 nm wavelength light.
► The wet etch stability worsened when UV cured with light with wavelength of 172 nm.
► The chemical composition of the film was the most important factor that determined the wet chemical etch resistance.