Ultra Low k Mesoporous Silica Films: Synthesis, Film Properties and One-Level Copper Damascene Evaluation
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Ultra Low k Mesoporous Silica Films: Synthesis, Film Properties and One-Level Copper Damascene Evaluation Changming Jin,# J. Liu, X. Li, C. Coyle, J. Birnbaum, G. E. Fryxell, R. E. Williford and S. Baskaran*, Pacific Northwest National Laboratory, 902 Battelle Boulevard Mail Stop K2-44, PO Box 999, Richland, WA 99352 # International SEMATECH, 2706 Montopolis Dr., Austin , TX 78741 *author for correspondence: [email protected] ABSTRACT Spin-on mesoporous silica films were prepared on eight-inch wafers at SEMATECH by condensation of a silicate network around surfactant micellar structures. Copper singledamascene one-level test structures were built using mesoporous silica as the intermetal dielectric. No major structural failures were observed after chemical mechanical planarization on both blanket films and patterned wafers, indicating relatively good mechanical integrity for a highly porous structure. A simple silane spin-coating step used at SEMATECH on the films appears to be insufficient for complete dehydroxylation and silylation. The electrical test results on the metal comb structures showed good capacitance and leakage current distributions. However, capacitance and leakage current changes were observed after each post-CMP process step, and these changes could be correlated to moisture desorption/outgassing, which was also noted during k measurement. With controlled film synthesis and dehydroxylation conditions, mesoporous silica films with k ≤ 2.0 and elastic modulus of 4.0 GPa have been synthesized at PNNL. The results of the Cu one-level metal screening tests at SEMATECH combined with properties obtained at PNNL indicate that mesoporous molecularly-templated silicate films hold promise as ultra low k intermetal dielectrics. INTRODUCTION The semiconductor industry is currently targeting new intermetal dielectric films with k < 2.5 for interconnects in the sub-150 nm technology node. As the metal line width continues to decrease, and the packing density of metal lines on the semiconductors continues to increase, dielectric films with k < 2.0 will be soon required. Porous silica films with nanometer-scale porosity are potentially useful as ultra low dielectric constant films in advanced semiconductor interconnects. Mesoporous silica films with pore sizes in the range of 1 to 10 nm have been synthesized from solution precursors by a surfactant-templating process (1-3) in which the pores are formed in a spin coated (4-7) or dip coated film (8-9) upon removal of the surfactant. Although the term “mesoporous” refers generally to materials with pore sizes > 1 nm, it is now most commonly used to describe materials prepared by the surfactant-templating approach. Mesoporous silica films with low dielectric constants ( ≈1.8 to ≈2.5 ) have been demonstrated using cationic and non-ionic surfactants (10-12). This molecularly templated synthesis approach allows rational control of the porosity, pore size, pore shape, film texture and thickness, and can result in good mechanical properties in the film (12). In this pa
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