Copper electroplating for future ultralarge scale integration interconnection

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Abstract
Copper has received considerable attention during the past few years because of its low electrical resistivity, high melting temperature, and high electromigration resistance. Since electrochemical plating has several advantages compared to physical vapor deposition and chemical vapor deposition due to its low cost and low processing temperature, it becomes the most attractive technique for the implementation of Cu metallization. In this article, we report an electroplating scheme for Cu deposition and study aspects of copper electroplating related to chemical additives effected on Cu deposition. A low resistivity Cu film (∼2 μΩ cm) could be obtained when metallic ion concentration is decreased or current density is increased. The detailed correlation between film resistivity, electrolyte concentration, current density, and film morphology is given in this study. In addition, chemical additives in electrolyte solutions also play important roles in copper electroplating. In this report, thiourea and polyethylene glycol, which are usually added in printing circuit board electroplating to influence nucleation, have been used as gap filling promoters to help Cu filling. The results show that addition of thiourea and polyethylene glycol could help in forming smooth Cu film but does not promote Cu filling ability. Hydroxyl amine sulfate, which has both amino and sulfate groups, is proposed for use as a gap filling promoter in helping Cu electroplating. In this work, we demonstrate that Cu could be electroplated into fine trenches (at 0.3 μm dimension with aspect ratio of 3) when hydroxyl amine sulfate is present and no voids are formed.

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