Helium Ion Beam Microscopy for Copper Grain Identification in BEOL Structures

Abstract

Abstract. Grain size determination in advanced metallization structures requires a technique with resolution ~2nm, with a high signal-to-noise ratio and high orientation-dependant contrast for unambiguous identification of grain boundaries. Ideally, such a technique would also be capable of high-throughput and rapid time-to-knowledge. The Helium Ion Microscope (HIM) offers one possibility for achieving these aims in a single platform. This article compares the performance of the HIM with Focused Ion Beam, Scanning Electron and Transmission Electron Microscopes, in terms of achievable image resolution and contrast, using plan-view and cross-sectional imaging of electroplated samples. Although the HIM is capable of sub-nanometer beam diameter, the low signal-to-noise ratio in the images necessitates signal averaging, which degrades the measured image resolution to 6-8nm. Strategies for improving S/N are discussed in light of the trade-off between beam current and probe size, accelerating voltage, and dwell time.

Sidewall Texture and Microstructure of iPVD Copper Seed in Narrow Damascene Trenches

“…The discrepancy has increased in recent years as features became narrower: the grain growth behavior of copper in patterned features now departs significantly from that observed in blanket samples. 9,10 Although increased incorporation of plating bath additives in the features has long been postulated to account for the observed differences, 4 recent results suggest that grain growth is in fact decoupled from impurity diffusion. 11 An alternate hypothesis focuses on texture effects on grain growth.…”

“…12 After plating the microstructure of ECD copper transforms spontaneously. [1][2][3][4][5][6][7][8][9][10][11] X-ray synchrotron and resistivity studies of this transformation have been carried out on blanket ECD Cu films deposited on both textured and untextured substrates. The effect of texture is clear in these studies.…”