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Characterization of Room Temperature Recrystallization Kinetics in Electroplated Copper Thin Films

Treger, Mikhail A.

The lack of an energetic model for the seemingly spontaneous room temperature recrystallization of electroplated copper thin films has proven to be a technological bottleneck in the optimization of copper interconnect microstructure for the microelectronics industry. The inability to either achieve large grained interconnect microstructures by simple annealing or explain them by a posteriori analyses necessitates a new approach. Synchrotron x-ray diffraction was utilized to obtain real-time grain size, crystallographic texture, and strain data about the recrystallization in the geometrically simpler case of blanket electroplated Cu films. The observation of a bimodal size distribution between as- deposited and recrystallizing grains during led to the development of a theoretical framework for combining x-ray data and the canonical Johnson-Mehl-Avrami-Kolmogorov (JMAK) kinetics model. Under this framework, analysis of variations in plated Cu film and vapor deposited underlayer structures established that film recrystallization speed is a function of initial 111 film texture, and that this dependency is modulated by underlayer deposition conditions and plated film thickness. Verification of the new x-ray analysis was performed by combined use of complementary destructive and non-destructive characterization techniques which are more commonly accessible in the industrial setting. These included cross-sectional focused ion beam milling and scanning electron microscopy (x-FIB/SEM), electron back scatter diffraction (EBSD), and four-point probe electrical resistivity measurements. Comparative real-time in situ x-ray and resistivity studies revealed the formation of electron percolation paths which prematurely short-circuited the latter analysis. An effective resistivity model is proposedto extend the current canonical one-dimensional analysis to be compatible with multi-dimensional recrystallization. X-ray analysis of plated films whose initial stress state had been modified by delamination or the photoresist masking of substrate stresses revealed a significant change to the recrystallization kinetics. Complementary real-time EBSD analysis localized the initiation of recrystallization to the free surface of the film. The combination of this with quantitative activation energy measurements was then the basis for a comprehensive theoretical energetics model.

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More Information

Academic Units
Materials Science and Engineering
Thesis Advisors
Noyan, Ismail C.
Degree
Ph.D., Columbia University
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