UV cure of oxycarbosilane low-k films

Abstract

Advanced spin-on k≈2.3 films with ~40% porosity were enabled by liquid phase self-assembly (LPSA) mechanism on Si substrates. The as-deposited films were exposed to UV light with λ=172nm, 222nm, 254nm or 185/254nm at 400°C for times spanning from 1 to 20min. The optical, mechanical, chemical and electrical properties of the resulting films are discussed with focus on the impact of and on the backbone carbon (Si–R–Si). On the one hand, photons with wavelengths of about 172nm are detrimental to the electrical and chemical properties of the low-k films, but on the other hand, they notably improve the mechanical properties. The induced damage is reduced by shortening the UV treatment but at the expense of the template removal efficiency. Furthermore, an exposure to 222nm light as short as 3min is more efficient in terms of template removal when compared to 2h thermal cure. When the films are cured for 20min, the best combination of k and Young's modulus is obtained. UV-cure using 254nm or dual band 254/185nm photons seems to have a negligible contribution to the template removal efficiency within the investigated doses. Higher intensity sources are necessary in order to better understand the effective contribution of these photon energies. In all cases, the backbone carbon content is not affected by the UV and VUV photons. Finally, the HF etching mechanism is discussed and the role of the interfacial layer between the low-k film and the SiO2 substrate is highlighted.