The chemistry of additives in damascene copper plating

Abstract

Copper plating baths used for forming integrated circuit interconnects typically contain three or four component additive mixtures which facilitate the superfilling of via holes and trench lines during damascene plating. Extensive study over the last two decades has provided researchers with an understanding of the underlying mechanisms. The role of cuprous intermediates in the copper deposition reaction has long been acknowledged, but it is not yet fully understood. In this paper we describe the results of an electrochemical study of the interaction of the organic additives used with copper and copper ions in solution. It is shown that cuprous intermediates near the copper surface affect the overpotential and the kinetics of plating. The additives regulate the presence of cuprous species on the surface; levelers and suppressors inhibit Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> formation, whereas accelerating additives enhance Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> formation. Acceleration by the bis(sodiumsulfopropyl) disulfide (SPS) additive results from accumulation of cuprous complexes near the surface. Adsorbed cuprous thiolate [Cu(I)(S(CH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> SO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> H) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ad</inf> ] is formed through interaction of Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ions and SPS rather than Cu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> and mercaptopropane sulfonic acid (MPS).