Two-stage gas amplifier for ultrahigh resolution low vacuum scanning electron microscopy

Abstract

We describe a magnetic field assisted, two-stage secondary electron gas amplification process for low vacuum scanning electron microscopy. The field of an ultrahigh resolution magnetic immersion objective lens and the electric field of an annular electrode configuration partition the amplification volume into two regions in which the electric and magnetic fields are parallel and crossed, respectively. The fields confine secondary electrons to axial and radial oscillations within the detector volume, until all of the kinetic energy imparted by an anode is dissipated through inelastic collisions with gas molecules. The electron confinement yields high gas amplification efficiency at short working distances and low gas pressures, facilitating high resolution imaging at low electron beam energies. Charging of insulating specimens is stabilized by positive ions produced in the gas ionization cascade. Furthermore, the signal to background level and bandwidth of this detector are superior to those of earlier generations of environmental secondary electron detectors. The combination of low vacuum, short working distance, and low beam energy is attractive to the semiconductor metrology industry, in particular, for critical dimension measurements on photolithographic masks.

Electron flux controlled switching between electron beam induced etching and deposition

“…Images shown in Fig. 2 were acquired using a gaseous secondary electron ͑SE͒ detector for magnetic immersion electron lenses, 25 and those in Figs. 3, 5, and 6 were acquired using the off-axis gaseous SE detector 26 shown in Fig.…”

Structure of Low-Density Nanoporous Dielectrics Revealed by Low-Vacuum Electron Microscopy and Small-Angle X-ray Scattering

“…High magnification secondary electron (SE) imaging of untreated, bulk AG monoliths was achieved using a recently developed magnetic-field-assisted gas cascade detector. 16,27 This detector uses the field of a magnetic immersion electron lens to induce axial and cycloidal SE oscillations inside the detector volume. The resulting magnetic confinement leads to an intense gas ionization cascade which amplifies the SE signal and generates gaseous ions.…”

“…These ions are used to stabilize charging under the conditions imposed by ultra-high resolution magnetic immersion electron lenses. 16,27 Wide field width SE imaging of AG skin layers was done using a pinhole electron lens and a standard, off-axis gaseous detector. 17 Bright-field TEM imaging was performed using a Philips CM300FEG electron microscope operated at 300 kV.…”

Fabrication of a single sub-micron pore spanning a single crystal (100) diamond membrane and impact on particle translocation

“…Pores were fabricated using electron beam induced etching (EBIE) and the entrance side imaged using an FEI Nova NanoSEM variable pressure [51] field emission -scanning electron microscope (FE-SEM) equipped with a magnetic field-assisted gaseous secondary electron detector (GSED). [52] The FE-SEM chamber was filled with water (Milli-Q) vapour to a pressure of 13 Pa to mediate EBIE and suppress charging of the electrically insulating diamond surface. Prior to EBIE, the diamond substrate was coated ex situ with a ~ 30 nm graphitic carbon coating to further suppress surface charging during electron irradiation.…”