Extendibility of the PECVD Porogen Approach for ULK Materials
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Extendibility of the PECVD Porogen Approach for ULK Materials Olivier Gourhant1, Vincent Jousseaume2, Laurent Favennec1, Aziz Zenasni2, Patrick Maury1, Lucile Mage2, Patrice Gonon3, and Gilbert Vincent3 1 STMicroelectronics, 850, rue Jean Monnet, Crolles Cedex, 38926, France 2 CEA Grenoble, LETI, 17, rue des martyrs, Grenoble cedex 9, 38054, France 3 CNRS-LTM, 17, rue des martyrs, Grenoble Cedex, 38054, France ABSTRACT The increase of integrated circuits performances requires ultra-low dielectric constant (ULK) materials to minimize the drawbacks of miniaturization. Amorphous SiOCH are promising candidates for ULK materials as porosity can be introduced via a two steps elaboration. In a first step, organo-silicon species and organic species are co-deposited by PECVD. Then, a thermal annealing, alone or assisted by UV radiation, removes the organic labile phase and creates pore inclusions into the final material. In this work, the extendibility of this porogen approach is investigated in order to lower the dielectric constant. An increase of the porogen loading in hybrid film is studied by tuning the precursors ratio injected in the plasma gas feed. The increase of organic species amount is operated in order to create more pores sites. However, the post-treatment does not lead automatically to higher porosity. Actually, an increase of the porosity is observed only until a porogen loading limit and decreases above this limit. The shrinkage of the film during the post-treatment can explain this limitation. For high ratios of porogen, the film shrinkage increases drastically and leads to a decrease of the porosity finally created. At last, the link between porosity and dielectric constant is enlightened and a minimum in term of K value is reached with both post-treatments: dielectric constant of 2.1 and 2.3 are obtained using respectively thermal treatment and UV curing. INTRODUCTION As device dimensions are continuously scaled down, the introduction of ultra-low dielectric constant (ULK) materials is needed to reduce propagation delay, cross-talk noise and power dissipation in interconnections. These insulators are composed of an amorphous SiOCH structure in which porosity is introduced via a two steps porogen approach described as followed. In a first step, organo-silicon species, as matrix precursor, and organic species, as sacrificial phase precursor, are co-deposited by plasma enhanced chemical vapor deposition (PECVD). Then, a post-treatment is performed to remove the labile phase. This post-treatment involves thermal degradation of the organic phase into gaseous species which are then extracted from the film, leading to the creation of porosity. The introduction of pores decreases the thin film density and thus the dielectric constant is lowered. Recently, an increasing interest appeared on UV radiation to sustain the thermal treatment [1,2]. This UV curing accelerates the porogen removal and enhances the mechanical properties of the porous material [3,4]. In this paper, the extendibility of the poro
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