Channeling effects during focused-ion-beam micromachining of copper

Abstract

The rapid introduction of copper metallization for semiconductor devices has prompted increased research into focused-ion-beam micromachining of copper. Studies with the aim of increasing the material removal rate of Cu by focused-ion-beam micromachining have been complicated by variable micromachining behavior apparently resulting from differing Cu film morphologies produced by the various Cu deposition procedures. This work examined the micromachining behavior of thin copper films produced by physical-vapor deposition (PVD) and electroplating, as well as single-crystal copper samples. PVD copper films were found to be preferentially textured along 〈111〉, with a columnar grain structure. Channeling effects within this type of grain structure provide a geometric enhancement of the material removal rate of 30% when the sample normal is tilted 12° from the incident ion beam, regardless of sample rotation. Single-crystal (111) copper was found to exhibit similar material removal rate enhancement (averaged over 360° rotation) when tilted 12°, verifying that the etching enhancement observed in the PVD films is directly related to their 〈111〉 texture. Compared to the PVD film, electroplated (EP) copper thin films contained a significantly more random grain orientation. Consequently, the EP films did not exhibit any appreciable variation in material removal rate beyond the expected cosine dependence when tilted with respect to the incident Ga+ beam normal. Micromachining of the electroplated films, which have larger randomly oriented grains, results in grain decoration due to preferential etching producing severe micromachining-induced topography.

Fabrication of nanodot plasmonic waveguide structures using FIB milling and electron beam‐induced deposition

“…Focused ion beam (FIB) milling (Phillips et al 2000;Gonzalez et al 2001;Tseng 2005) has been employed for fabricating nanostructures used in a wide variety of products including nano-cavity lasers, photonic crystals, as well as chemical and biological sensors based on sub-wavelength aperture arrays. In this work, we employed FIB milling for gold nanopillar formation on planar substrates.…”

Theoretical Simulation and Focused Ion Beam Fabrication of Gold Nanostructures for Surface-Enhanced Raman Scattering (SERS)

“…Focused ion beam (FIB) milling [21][22][23] is an extremely important tool for fabrication of various types of nanostructures used in a wide variety of products including photonic crystal waveguides, nanocavity lasers, as well as chemical and biosensors based on subwavelength aperture arrays. In this work, we employed FIB milling for gold nanopillar formation on optical fiber tips and planar substrates.…”

FIB etching of Cu with minimal impact on neighboring circuitry, including dielectric

“…The difficulty in FIB milling of Cu has been discussed several times [1,2] and milling nonuniformities only gets worse when a low-k dielectric is in the process [3]. The purpose of this paper is to report on success in FIB editing devices with interconnects of copper, SiO 2 and low-k dielectrics.…”

“…Later it was revealed that the situation was even worse when low-k dielectrics were included in the interconnect stack [3] because those chemistries which offered help with copper over SiO 2 actually make the situation worse for copper over low-k. The lack of uniform etching was proven by P Russell's group at NCSU to be due to channeling [2]. Because of the great variation in sputter yield (up to 10x) with copper grain orientation [2], circuit edit requires a chemistry with copper selectivity relative to neighboring dielectrics.…”

“…The lack of uniform etching was proven by P Russell's group at NCSU to be due to channeling [2]. Because of the great variation in sputter yield (up to 10x) with copper grain orientation [2], circuit edit requires a chemistry with copper selectivity relative to neighboring dielectrics. This selectivity can not be achieved by increasing the etch rate of copper but rather decreasing the etch rate of the dielectric.…”