Observation of Grain Growth in Cu Films by In-Situ EBSD Analysis
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Observation of Grain Growth in Cu Films by In-Situ EBSD Analysis D.P. Field1, M.M. Nowell2, and O.V. Kononenko3 1 Mech. and Matls. Eng, Washington State Univ, Pullman, WA 99164-2920 USA 2 TexSEM Laboratories, Draper, UT 84020 USA 3 Institute of Microelectronics, Russian Academy of Science, Chernogolovka, RUSSIA
ABSTRACT Recrystallization, grain growth and crystallographic texture evolution in Cu films is an area of importance for IC interconnect fabrication as the film characteristics influence the resulting line microstructure. This study examines Cu films deposited by partially ionized beam deposition onto a sublayer of tantalum nitride and additionally onto alphaC:H. The films were annealed in-situ in the SEM chamber and intermittent orientation imaging was used to characterize the grain growth and crystallographic texture evolution in the films. Both initial and final textures are weak in each of the films analyzed, but are a function of sublayer material and thickness. Grain size in the Cu films is significantly smaller for the tantalum nitride sublayer than for the α-C:H sublayer. INTRODUCTION Optimization of interconnect microstructure for improved manufacturability and reliability has long been a subject of ongoing research, initially for Al structures and now for Cu metallization. This research remains critical as minimum feature sizes continue to shrink in increasingly complex integrated circuits. Failures in Cu interconnects, either stress induced or from electromigration processes, are likely a function of the Cu microstructure that evolves during processing. Optimization of this structure requires an understanding of both structure/property relationships as well as microstructural evolution during processing. As typical interconnects go through many processing steps that involve temperatures up to 400ºC or more, it is important to understand the effects of elevated temperature on the evolution of Cu microstructures. This structural evolution is a function of sublayer materials and thicknesses, bath chemistry for electroplated films, and initial deposition conditions. Partially ionized beam (PIB) deposition is a technique that employs a potential near the substrate surface that accelerates ionized particles toward the film during deposition [1]. The highly charged particles increase the energy of the film as the accelerating potential is increased. This results in more uniform microstructures than films that have lower energies where inhomogeneous structures are sometimes present [2]. The self-annealing phenomenon in electrodeposited Cu films, where recrystallization occurs at room temperature, is well-documented. The same process can occur in sputtered structures, particularly those obtained during PIB deposition. The following discussion describes structure evolution during high temperature annealing in Cu films of two different
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