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By Zsolt Tőkei, Mikhail Baklanov, Ivan Ciofi, Yunlong Li & Adam Urbanowicz, IMEC, Leuven, Belgium

ABSTRACT

Porous low-k materials are required as interlayer dielectrics in future technology nodes in order to compensate for the RC-delay and power consumption increase associated with continuing device shrinkage. Porous low-k films are typically composed of silica and silsesquioxanes containing organic hydrophobic groups. The exposure of such films to a plasma ambient leads to an unwanted increase of the leakage current and of the dielectric constant of the film. The fundamentals of plasma damage, including low-k material modification and moisture adsorption, are explained and potential ways of reducing plasma damage are discussed.
Moisture adsorption also degrades the dielectric reliability margin. This phenomenon is becoming a major challenge but so far has not been adequately addressed nor systematically investigated. Desorbing moisture by thermal anneal improves the electrical properties including reliability performance, but the resulting low-k reliability is still far below that of an optimized integration scheme. Several electrical characterization methods (time-dependent dielectric breakdown (TDDB), triangular voltage sweep (TVS) and thermal desorption spectroscopy (TDS)) were combined to measure the reliability margin, to identify the physical mechanism(s) and to find ways of restoring the margin degradation.