Texture Evolution in Cu Films and Lines
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0990-B08-23
Texture Evolution in Cu Films and Lines Chia-Jeng Chung1, David Field2, No-Jin Park3, and Christy Woo4 1
Materials Science and Engineering, Washington State University, Pullman, WA, 99163
2
MSE, WSU, Spokane Street, Pullman, WA, 99163
3
Kumoh Institute of Technology, Gumi City, Korea, Democratic People's Republic of
4
Advanced Micro Devices, Sunnyvale, 94086, United Kingdom
1. INTRODUCTION Significant challenges exist in the manufacture and reliability of Cu interconnect lines used in modern integrated circuit devices. The microstructural character of damascene lines evolves within a confined trench and varies with line width and dielectric material. Evolution of crystallographic texture within such lines depends upon the geometrical parameters of the trench in that the stress state during annealing changes with height to width ratio (h/w). Additionally, surface or interface energy minimization controls structure evolution at certain h/w ratios. Thermodynamic principles (a tendency to achieve low energy configurations) drive texture evolution in copper films and damascene lines during annealing. Some researchers have shown that strong {111} out of plane texture is generated when surface energy minimization dominates texture evolution [1, 2] and others suggest that this brings a reliability improvement in Cu line performance (similar to that observed in Al lines) [cf. 3]. In contrast, {100} textures are formed when strain energy dominates structure evolution in FCC films [1]. Annealing twin grains that form in low to moderate stacking fault energy metals, such as copper, invariably reduce texture strength. Previous analysis of texture evolution in such films has failed to include twin boundary development and the concomitant textures that form during annealing. In the present study damascene lines were fabricated from electroplated Cu films using standard industrial practice. The analysis focuses on the sources of various and competing energies for structure evolution. Surface and interface energies, strain energy and grain boundary energy are all important factors in determining the structure that evolves during annealing. Furthermore, trench geometry determines local stress state and affects the overall energetics of structure formation. It was hypothesized that wider twin grains generally develop in narrow lines as compared with wider lines of the same depth. 2. EXPERIMENTAL DETAILS Copper damascene lines were fabricated using standard procedures described below. Blanket films of oxide were deposited onto the silicon wafer substrates. A multi-chamber,
ultra-high vacuum deposition system was employed to deposit Ta followed by Cu using physical vapor deposition (PVD).The Ta layers were sputtered to improve the Cu adhesion and to form the barrier to preventing the diffusion between Cu and Si. The damascene lines were fabricated from electroplated Cu films with an overburden thickness of 750 nm and subsequently annealed at 250ºC for one hour. The final step in this process was chemical mechanica
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