Pulse Electroplating of Nanotwinned Copper Using MPS-PEG Two-Additive System for Damascene via Filling Process

Abstract

High density nanotwinned copper films were pulse electroplated using an optimized electrolyte. In order to find out the influencing factors on the formation of nanotwins, series contents of MPS were added to the electrolyte during the pulse electroplating process. It was found that the copper films electroplated without MPS had large grains but a few nanotwins. And the grain size was about 0.9 μm on average, and the texture components of (110) and (111) crystal orientations were calculated as 49% and 27.8%, respectively. Differently, when 10 ppm MPS was added, the microstructure was changed to columnar grain with high density of horizontal nanotwins and the crystal orientation was also changed to highly (111) orientated one. However, when the MPS content was continuously increased from 10 ppm to 40 ppm, the microstructure and crystal orientation were almost unchanged as detected by the secondary ion microscopy of focus ion beam and X ray diffraction. Specifically, when 40 ppm MPS was used, the average grain size was 0.6 μm, and the texture components of (110) and (111) crystal orientations were 3.45% and 95.1%, respectively. It demonstrated that the nanotwinned copper can be electroplated at a large concentration range of MPS, which also meant that the filling ability of nanotwinned copper electrolyte could be adjusted by MPS content without influencing the microstructure. Finally, these electrolytes with different contents of MPS were used in the Damascene via filling. The results showed that when the content of MPS was 40 ppm, the Damascus via was completely filled without voids. The achievement of via filling with nanotwinned copper makes the application of nanotwinned copper possible in Integrated Circuit (IC) fabrication, which also greatly promotes the development of interconnected material for next generation.

Keywords

pulse electroplating / nanotwinned copper / via filling / Damascene process

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