Impact of curing condition on chemical stability of ultralow-k PMO material.
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Impact of curing condition on chemical stability of ultralow-k PMO material. M. B. Krishtab1,2, L. Zhang1, Q. T. Le1, K. Vanstreels1, L. Souriau1, M. Phillips3 and M. R. Baklanov1 1
IMEC, Leuven, Belgium St. Petersburg Electrotechnical University 3 SBA Materials, Inc., Albuquerque 2
ABSTRACT In this work a new generation of periodic mesoporous organosilica (PMO) low-k dielectrics with targeted k-values 2.0 and 1.8 is evaluated. In addition, impact of two different curing processes on properties of the mesoporous material is analyzed. It is shown that removal of templating organics with thermal annealing leads to formation of mechanically robust and chemically very stable material, while application of UV-assisted curing with broadband lamp (λ > 200 nm) causes pronounced decrease of film ability to sustain in diluted HF solution. The explanation of that phenomenon is given in terms of silica-ring structures formed within organosilica skeleton.
INTRODUCTION Introduction of Cu/low-k technology was assigned to mitigate delays in signal propagation and to reduce power consumption and cross-talk noise in actual ULSI devices [1]. However continuous scaling following Moore’s law requires further decrease of the k-value of inter-layer dielectrics thus keeping industry in searching for new low-k materials satisfying numerous strict requirements posed by integration processing. Being the main driving force of material’s dielectric constant diminishing, porosity leads at the same time to dramatic degradation of mechanical strength, chemical stability and increased extent of low-k materials damage in course of their implementation in damascene structure. This negative effects are amplified in the case of ULK materials with k-value approaching 2.0. Large free volume and consequently fully interconnected pore structure of these materials makes them more vulnerable both to treatment with plasma and cleaning chemicals. Therefore more attention should be paid to adjustment of structure and composition of low-k film skeleton. In this work we have analyzed Spin-on low-k materials having intrinsically better control of matrix structure and composition in comparison with PECVD low-k dielectrics. Additionally we have investigated evolution of OSG skeleton structure under exposure to broadband UV-light and traced its correlation with chemical stability of the material.
EXPERIMENT Preparation of the low-k materials used in this work starts from mixture of organosilica source, representing certain ratio between tetraethylorthosilicate (TEOS), terminally alkylated silicate ester and alkyl-bridged silicate, and surfactant, type and concentration of which are largely responsible for the pore structure of the resulting material. Then that mixture undergoes soft baking at 150˚C for 2 minutes. That step is crucial since in the course of that short annealing the solvent is evaporating inducing self-assembly of surfactant and formation of templated organosilica skeleton. One common way to remove the organic template is to apply another high-tem
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