Cross Section Investigations of Compositions and Sub‐Structures of Tips Obtained by Focused Electron Beam Induced Deposition

Abstract

The spatial evolution of compositions and sub‐structures inside focused‐electron‐beam‐deposited tips from dicobalt‐octacarbonyl Co2(CO)8 precursor at 25 keV and varying beam current (20 pA – 3 μA) is extensively studied for the first time by means of energy dispersive X‐ray spectroscopy, transmission electron microscopy, back‐scattered electron imaging, and ion‐induced secondary electron imaging. Transverse and longitudinal tip cross sections and lamellae were prepared by focused ion beam milling. Two sub‐structure types can be distinguished: a nano‐composite sub‐structure is grown during the initial deposition stage (small‐aspect‐ratio tips). It consists of cobalt nano‐crystals embedded in a carbonaceous matrix. A second distinct cobalt‐grain‐rich sub‐structure develops in high‐aspect ratio tips. Both sub‐structures vary in appearance and composition with increasing beam current: the initial nano‐composite sub‐structure increases in cobalt content and nano‐crystal size, and the cobalt‐grain sub‐structure develops polycrystal‐, texture‐, whisker‐, or platelet‐like habits. The directed precursor flux from a micro‐tube prevents a radial symmetry of the sub‐structures with respect to the impinging focused electron beam, at medium to high beam current. Homogeneous nano‐composite high‐resolution tips with small diameter and length were obtained at low beam current. Observations suggest an additional contribution to pure electron induced precursor molecule decomposition. The influence of electron beam heating and related chemical reactions is discussed.

Influence of hydrogen silsesquioxane resist exposure temperature on ultrahigh resolution electron beam lithography

“…Heating of the resist under electron beam exposure was considered negligible ͑i.e., Ͻ1°C͒ taking into account the small e-beam probe size, relatively low beam current and accelerating voltage, thin resist thickness, and good heat conductivity of the Si substrate. This assumption is consistent with data from reports on direct measurement 9 as well as with modeling 10 and analytical evaluation 11,12 of e-beam induced temperature rise. A cascade of Peltier elements was mounted on the stage equipped with an Al heat absorber allowing us to control the temperature of the substrate in range from −20 up to 90°C.…”

A critical literature review of focused electron beam induced deposition

“…87 At low beam currents ͑20 and 112 pA͒, the surface of the tips is smooth and the material consists of nanocomposite material ͑1-2 nm Co crystals embedded in an a-C-and O-rich matrix͒. The surface of the longer tips ͑dwell times of 300-600 s͒ is still smooth, but on the inside a crust and a core form at the bottom of the tips.…”

Absolute cross sections for dissociative electron attachment and dissociative ionization of cobalt tricarbonyl nitrosyl in the energy range from 0 eV to 140 eV

“…Most precursor molecules employed for FEBID have originally been designed for use in CVD, 7 where high deposit purity with respect to the metal content is reached at elevated temperatures through thermally induced metalligand bond rupture. In FEBID, however, although in some cases local beam induced heating may play a role, 17,18 the dissociation mechanism of the precursor molecules should be very different, i.e., be electron induced. In principle, the molecules should only be dissociated at the impact site of the electron beam, leaving behind a chemically and structurally well-defined deposit while the volatile ligand fragments are pumped away.…”