| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF-ThP |
| Session: | Thin Films Poster Session |
| Presenter: | Ha Nguyen, University of Wisconsin - Madison |
| Authors: | H.M. Nguyen, University of Wisconsin - Madison F.A. Choudhury, University of Wisconsin - Madison J.L. Shohet, University of Wisconsin - Madison |
| Correspondent: | Click to Email |
Methyl depletion of organosilicate (SiOCH) films due solely to the absorption of plasma vacuum-ultraviolet (VUV) photons has been a crucial concern in plasma processing of interconnects. Research on determining VUV photon penetration into SiOCH films is still of great interest. Several systematic studies [1,2] have been published on how parameters such as absorption coefficient, penetration depth, and quantum yield of methyl depletion chemical processes depend on film porosity, VUV dose, and particularly VUV wavelength. These studies contributed significantly to the advance of this research field. However, these studies did not address an important question of how VUV photoabsorption changes during the course of VUV irradiation. This results in the concentration of Si-CH3 bonds being reduced with time. This in turn affects how the VUV-penetration depth varies with time. In this work, we aim at addressing this question by using time-dependent density functional theory (TDDFT) to model the absorption spectrum in a continuous photon energy range of 0 to 20 eV for an octamethylsilsesquioxane, (CH3)8Si8O12, molecule, which is chosen from among siloxane-based molecular precursors of low-k films as a benchmark case as the first step to understand VUV photoabsorption of SiOCH films. Our calculated results show that for the whole range of VUV photoabsorption energies, the absorption cross-section decreases substantially as the number of Si-CH3 broken bonds increases. This decrease of the absorption cross-section, however, occurs at different rates, which depend strongly on VUV photon energy (e.g., the highest and lowest rates are in the ranges of 10-15 eV and 7-10 eV, respectively). These interesting results suggest that the modification of VUV photoabsorption during plasma processing is a paramount factor to determine the penetration of VUV photons into low-k dielectric films.
This work was supported by the Semiconductor Research Corporation under Contract 2012-KJ-2359.
References:
[1] T. V. Rakhimova et al, Appl. Phys. Lett. 102 (2013) 111902.
[2] T. V. Rakhimova et al, J. Phys. D: Appl. Phys. 47 (2014) 025102