The ITRS scaling of ultra-large-scale integrated circuits requires mechanically robust materials with low k-value. Low-k materials recently used in the Cu/low-k integration scheme have k-values between 2.5 and 3.0. One of the limiting factors in further reduction of k-value is mechanical robustness, since major way to decrease k-value is increasing the material porosity. The PECVD low-k deposition of ultra low-k films uses a porogen-based approach. The matrix material is deposited by oxidation of alkylsilanes in a plasma-enhanced chemical vapor deposition (PECVD) process. The porogen molecules, usually cyclic hydrocarbons, are introduced into a SiOCH film by co-deposition with the matrix material. To create porosity, the porogen is removed from the films using UV-assisted-thermal curing.The porogen molecules are photo-dissociated by UV-light with the formation of volatile hydrocarbons and non-volatile carbon-rich residues (porogen residue) [1]. We have shown recently that SiOCH glasses with improved mechanical properties and ultra-low-k value could be obtained by controlled decomposition of the porogen molecules prior to the UV-hardening step [2]. The controlled removal of porogen can be performed by H2-based afterglow plasma treatment of PECVD film [1,2].

In this work we study the effect of narrow band 172 nm and broadband >200 nm UV-sources in the new curing scheme of the PECVD dielectrics. The data are compared with the PECVD films fabricated in the conventional UV-curing scheme. The effect of both 172 nm and >200 nm UV-sources is comparable for porogen-containing conventional PECVD films. However, the porogen-free films cured with 172 nm UV-source shows approximately twice as higher Young’s modulus (YM) of 6.64 GPa (k100kHz ~ 2.2, 44% open porosity) than those cured with >200 nm UV with YM of 3.38 GPa (k100kHz ~ 2.0, 48% open porosity). The mechanical properties, optical properties 150 nm - 800 nm, dielectric constants at 100 kHZ and 4 GHz, porosities and pore size distributions, bonding structure are presented. The impact of porogen on optical characteristic and therefore on photochemical UV-hardening mechanism is discussed. The achieved mechanical properties are explained on a basis of the percolation of rigidity theory and random network concepts.

[ 1 ] A. M. Urbanowicz, K. Vanstreels, D. Shamiryan, S. De Gendt and M. Baklanov, Electrochem. Solid State Lett., 12, H292 (2009).

[ 2 ] A. M. Urbanowicz, K. Vanstreels, P. Verdonck, D. Shamiryan, S. De Gendt and M. R. Baklanov, accepted at J. Appl. Phys.107,xxx, (2010).