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B1.4.1

Mechanical properties of porous MSQ films: Impact of the porogen loading and matrix crosslinking. F. Ciaramella1, V. Jousseaume1, S. Maitrejean1, B. Rémiat1, M. Verdier2, and G. Passemard3 (1) CEA-DRT-LETI - CEA/GRE, 17 rue des Martyrs, 38054 Grenoble cedex 9, France (2) LTPCM, Domaine Universitaire, 1130 rue de la Piscine, 38402 Saint Martin d'Hères, France (3) STMicroelectronics, 850 rue Jean Monnet, 38926 Crolles, France ABSTRACT Semiconductor industry needs a continuously improvement of integrated circuits performance and an increase of integrated density on silicon. The 2004 ITRS Roadmap underlines the need of dielectric material for ILD with dielectric constant (k) lower than 3 for the 90 nm node and than 2.4 for the 45 nm node. In this work, porous films with k value lower than 2.2 were processed using a porogen approach. Firstly, a material composed of a methylsilsesquioxane (MSQ) matrix and of organic nanoparticles (called porogen) is deposited and baked. Then, this composite is thermally cured to allow the porogens degradation and matrix crosslinking. Different k values were obtained by varying the porogen loading in the composite. Mechanical properties of composite and porous films (before and after porogen removal respectively) were investigated using nanoindentation and FTIR analysis for different porogen loadings (between 0 and 40 %). The composite modulus is higher than the porous film modulus for high porogen loading. This result is interpreted in term of matrix crosslinking. Mechanical properties were also modelized using foam mechanical models. For high porosity level, the best Young modulus fitting is obtained with tetrakaidecaedric cells, which seems in good agreement with porosity morphology. INTRODUCTION In order to reduce the RC time delay of ULSI circuits, metals with low resistance and interlayer dielectric films with an Ultra Low dielectric constant (ULK) should be integrated. One promising ULK material is a porous methylsilsesquioxane (MSQ) deposited using a porogen approach to create the porosity in the film and reduce the dielectric constant (k). Porous low k dielectric integration difficulty is due to numerous issues including plasma damage, metal barrier deposition, chemical mechanical polishing and packaging [1]. For example, nanopores introduction in a dielectric matrix drastically deteriorates film mechanical properties, which limits the yield of Chemical Mechanical Polishing (CMP) in Cu-ULK process integration. To address these issues, the use of a new integration scheme has been reported. This scheme used a post integration porogen removal approach, wherein the porous dielectric material is integrated through Chemical Mechanical Polishing (CMP) in a dense state [2]. In this work, the mechanical properties of composite (dense) films (MSQ+porogens) and porous MSQ films are studied for different porogen loadings using nanoindentation measurements. The material crosslinking is evaluated using Fourier Transform Infra Red spectroscopy. Mechanical properties are compared with pre