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24 October 2000 Investigation of near-room-temperature self-annealing of electrochemical-deposited (ECD) blanket copper films
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Proceedings Volume 4227, Advanced Microelectronic Processing Techniques; (2000)
Event: International Symposium on Microelectronics and Assembly, 2000, Singapore, Singapore
Self-annealing of ECD blanket copper films on an IMP Cu (200nm)/IMP TaN PECVD SIO2 (500nm)/Si multi-layer structure with varying ECD CU thickness from 0.5micrometers to 3 micrometers is described and investigated. Sheet resistance, stress and surface topography evolution as a function of time have been monitored to provide a better understanding to the grain growth and surface agglomeration aspects of the self-annealing process. Resistivity changes, which exhibit a sigmoidal curve, are closely related with the grain size growth, which occurs during the recrystallization. However, this microstructural evolution should not be correlated to the stress relaxation effect because the films of the difference in time dependence. The self-annealing process of ECD Cu films lasts from a few hours to days and weeks depending on the plated thickness of the Cu film. The initiation of self-annealing is accompanied by an abrupt rise in the standard deviation of the sheet resistance, reflecting the possibility of abnormal grain growth during the process. Changes in the time dependence of this decrease with film thickness can be understood in view of the physical constraint of a 2D grain growth at the film boundary for thinner films. The coalescence mechanism of small grains until a full recrystallization of the layer into large twinned grains, which is used to explain the sheet resistance drop is supported by an increase in surface roughness of the ECD Cu film characterized by AFM. Diffusion or desorption of contaminant/additives in the relatively dirty process of ECD into the copper films could be a mechanism for the unusual stress release. It is found that the increase in the rate of stress relaxation scales with the thickness of the ECD Cu film. A change of the dominant factor for stress release from curvature dependent to film thickness dependent is speculated for this behavior.
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Weng Hong Teh, Leong Tee Koh, Shou Mian Chen, Joseph Xie, Chao Yong Li, and Pang Dow Foo "Investigation of near-room-temperature self-annealing of electrochemical-deposited (ECD) blanket copper films", Proc. SPIE 4227, Advanced Microelectronic Processing Techniques, (24 October 2000);

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