Ultra Low-k Materials Based on Self-Assembled Organic Polymers
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Ultra Low-k Materials Based on Self-Assembled Organic Polymers M. Pantouvaki1, L. Zhao2, C. Huffman1, K. Vanstreels1, I. Ciofi1, G. Vereecke1, T. Conard1, Y. Ono3, M. Nakajima3, K. Nakatani3, G. P. Beyer1 and M. R. Baklanov1 1 Imec, Kapeldreef 75, B-3001 Leuven, Belgium. 2 Intel Assignee at Imec, Kapeldreef 75, B-3001 Leuven, Belgium. 3 Sumitomo Bakelite Co, Ltd, Yokohama, Kanagawa, 245-0052, Japan. ABSTRACT The material properties of two ultra low-k organic polymers are characterized for copper interconnect integration. The k-values are 2.2-2.3 for both. Compared to OSG materials of similar k-values, these polymers have lower porosity and smaller pore size, achieved using selfassembled chemistry. Both materials demonstrate excellent resistance to plasma damage: no water uptake was detected after exposure to selected etching plasmas. This characteristic, combined with the small pore size and low porosity, results in the successful integration of the organic low-ks in 80 nm spacing with no significant increase in the integrated k-values. It is found that higher open porosity in polymer A is accompanied by higher leakage current, which is not however linked to lower dielectric breakdown lifetimes. INTRODUCTION Interconnect scaling requires the development of low-k materials with dielectric constants lower than 2.5 for the 22 nm technology node and beyond. Such low dielectric constants (kvalues) are possible by reducing the electronic polarisability of a material or by incorporating porosity, or by a combination of both. The two main categories of low-k materials that are being researched by the industry are carbon-doped organo-silicate glasses (OSG) and organic polymers. In order to achieve ultra low-k values (k < 2.5) porosity is commonly incorporated in either case. For OSG materials, this is done by including a sacrificial porogen during material deposition, which is subsequently removed by thermal decomposition leaving behind pores. Increasing the ratio of porogen to SiOCH matrix results in increased porosity and lower k-values. However, due to the hybrid nature of these materials, this is accompanied by large pore size (> 1 nm), susceptibility to hydrophilization upon exposure to certain plasmas, or carbon residues due to incomplete porogen decomposition [1-3]. Such effects impose challenges for the material integration in narrow-pitch interconnects. Large pore size results in material damage during barrier deposition, hydrophilization allows for water uptake and k-value increase, while porogen residues are responsible for increased leakage current [4-6]. Self-assembled organic polymers on the other hand are mono-component structures with virtually no polar bonds. As such, they can exhibit very low k-values for relatively lower porosity compared to OSG materials, as shown in Figure 1. By using self-assembled chemistry, the porosity of polymers can be engineered to achieve small pore size, improving their resistance to process-induced damage and improving also their mechanical properties. In addition, such materia
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