Title: Characterization of Room Temperature Recrystallization Kinetics in Electroplated Copper Thin Films
Description: 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.