Pore sealing of SiOCH ultra low-k dielectrics with polyimide Langmuir-Blodgett film
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Pore sealing of SiOCH ultra low-k dielectrics with polyimide Langmuir-Blodgett film S.I. Goloudina1, A. S. Ivanov1, M. B. Krishtab1,3, V.V. Luchinin1, V.M. Pasyuta1, I. V. Gofman2, V. P. Sklizkova2, V. V. Kudryavtsev2 and M. R. Baklanov3 1
Saint Petersburg Electrotechnical University (ETU), 197376 St. Petersburg, Russia 2 Institute of Macromolecular compounds RAS, 199004 Saint-Petersburg, Russia 3 IMEC, Leuven, Belgium
ABSTRACT Continuous decrease of the feature size of transistors in modern integrated circuits (ICs) constrains thickness of auxiliary dielectric layers in interconnects because of their relatively high dielectric constant, which reduces the efficiency of low-k material integration. Dielectric materials used today as barrier or etch-stop layers are usually SiN (k ~ 7.0) and SiCN (k ~ 4.8), which k-value significantly exceeds that of recent ultra low-k materials (k < 2.2). In our work we have investigated thin films of rigid-chain polyimide (PI) with a k-value of about 3.2-3.3. This film was deposited using a Langmuir-Blodgett (LB) technique and can be as thin as several monolayers. The intermolecular interaction of densely packed precursor macromolecules within a monolayer formed at the water-air interface makes it possible to avoid penetration of precursor material inside the pores. The latter peculiarity of the deposition process results in a pore sealing effect using a 4 nm PI film. INTRODUCTION Introduction of first low-k materials as new intermetal dielectrics, at the end of last century, was rather challenging from the viewpoint of technology. However, it allowed benefiting from higher operational frequency of final devices due to reduction of RC delays. Starting from dense F-doped silica glasses (FSG), new materials have been evolving into complex porous organosilica composites aimed at further decrease the dielectric constant. Apart from a lower k-value, porosity imparts the material lots of detrimental properties, such as decreased mechanical strength, thermal conductivity, as well as susceptibility to chemical and plasma treatments. Moreover, the fully interconnected structure of modern ultra low-k (ULK) materials (k < 2.2) significantly hampers scalability of traditional techniques for deposition of thin barrier layer, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD). To address this issue, new techniques of pore sealing should be developed. One potential candidate is Langmuir-Blodgett deposition, which operates with 2D-layers suspended at the liquid-air interface. Sequential transfer of these layers to the substrate by dipping it in the trough allows a fine control of the thickness and composition of deposited layer. Applicability of this technique to pore sealing originates from the possibility of domain formation within a 2D-layer submitted to a certain compression. Therefore, control of domain size by external conditions (precursor, temperature, surface pressure) may result in a sealing effect on almost any porous substrate using an extremely thin layer of se
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