High aspect ratio quarter-micron electroless copper integrated technology (invited lecture)

Copper metallization is under intensive investigation for Ultra-Large-Scale-Integration (ULSI) applications and the electroless technology has been demonstrated as a promising technology for sub-0.25 mu m features on large silicon wafers. In this work we demonstrate the integration of several electroless deposition recipes of different thin-film materials for the processing of high aspect ratio via contacts and trenches. The integrated process includes the deposition of both copper and barrier-material by electroless deposition from an aqueous solution due to an electrochemical oxidation-reduction reaction that takes place on the liquid-solid interface. The reaction starts on a seed layer and continues on the deposited layer as a self catalytic process. The deposition is very conformal due to the fact that the reaction is surface reaction limited. The ions diffusivity in the solution is high enough so there is a large enough supply of complexed ions inside the trench until its opening becomes very small. A simplified model is derived that shows that the conformality is improved as the ions concentration increased and the deposition rate is reduced. In this work we present also the material properties of the electroless barrier, the integration concepts, and experimental results of the fully integrated structure. Also presented is the integrated barrier/Cu/barrier process where the copper is positively patterned, planarized by a chemical mechanical process, and capped by a top barrier that is deposited by a self aligned process.