Interaction of O and H Atoms with low- k SiOCH films pretreated in He plasma
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1 1156-D01-06
Interaction of О and Н Atoms with low-k SiOCH films pretreated in He plasma O. V. Braginsky, A. S. Kovalev, D. V. Lopaev, Y. A. Mankelevich, E. M. Malykhin, O. V. Proshina, T. V. Rakhimova, A. T. Rakhimov, A. N. Vasilieva, D. G. Voloshin, S. M. Zyryanov, M. R. Baklanov1 Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia 1 IMEC, Leuven, Belgium
ABSTRACT The effect of He plasma pretreatment on the interaction of O and H atoms with SiCOH low-k materials is studied using a special experimental system designed for this purpose. The experimental system allowed separate studies of the effects of He plasma, VUV light and He 21S0 metastable atoms. It is shown that carbon depletion by oxygen atoms can be significantly reduced by He plasma pretreatment. Considerable increase of CH and CH2-CH2 groups in the surface area of low-k films is observed when the films were exposed to VUV light and metastable atoms generated by He plasma. FTIR and ellipsometry showed the formation of a densified surface layer. This carbon rich densified surface layer decreases damage of the low-k film when it is exposed to O2 plasma. The impact of H atoms on low-k surfaces noticeably differs from O atoms effect. The H atoms saturate all unbonded remaining carbon bonds thereby promoting improvement of SiOCH structure. INTRODUCTION It is known that pretreatment of SiCOH low-k materials in He plasma afterglow significantly reduces the plasma damage during the following exposure in NH3 and O2 plasma. It was speculated that VUV photons formed in He plasma are able to modify the surface of the low-k material, create active surface centers that stimulate recombination (deactivation) of active radicals formed in the strip plasma [1]. The recombination decreases the number of active radicals penetrating into the pores of low-k materials. The experimental technique used for the loss probability study and the results of analysis are described in our previous publication [2]. It was shown that the loss probabilities of O and H radicals are described in the frames of Langmuir–Hinshelwood theory of heterogeneous recombination of physically adsorbed atoms (PO sites with bond enthalpy D(P-O)~0.2 eV) and chemisorbed atoms (SO sites with bond enthalpy D(S-O)~1.6 eV). It was concluded that the surface recombination is the main mechanism of the O and H atoms loss. The reaction of these atoms with the carbon containing groups has a secondary order contribution. Therefore, the surface recombination defines the profile of the radicals concentration in low-k films and, therefore, the depth of plasma damage. The atoms penetrate into the pores due to random walk mechanism. The measured recombination coefficients allowed us to estimate the typical penetration depth (Lpen~24 nm) of O atom into the studied low-k materials with pore diameter close to 2 nm. This depth is in reasonable agreement with the experimentally determined depth of the CH3 groups depletion. Using an approach based on comparison of SiCH3 reactions with so
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