The technology of high‐resolution focused ion beams has advanced dramatically in the past 15 years as focusing systems have evolved from laboratory instruments producing minuscule current densities to high current density tools which have sparked an important new process: direct micromachining at the micrometer level. This development has been due primarily to the exploitation of field emission ion sources and in particular the liquid‐metal ion source. Originally developed in the early 1960’s as a byproduct of the development of electrostatic rocket engines, the liquid‐metal ion source was adapted for focused beam work in the late 1970’s, when it was demonstrated that submicrometer focused ion beams could be produced with current densities greater than 1 A cm−2. Ions can be produced with liquid‐metal ion sources from elements including Al, As, Au, B, Be, Bi, Cs, Cu, Ga, Ge, Fe, In, Li, P, Pb, Pd, Si, Sn, and Zn. In the past decade, focused ion beam systems with liquid‐metal ion sources have had a signific...

High‐resolution focused ion beams

The present paper reviews the results of experimental investigations of the photodoping of amorphous chalcogenides by metals, and in particular by silver. The kinetics of the photodissolution of the metal are described as also is the influence on the photodissolution rate of such factors as the wavelength and intensity of light, the composition and temperature of the semiconductor, and an external electric field. A separate section describes lateral diffusion. The properties of photodoped semiconductors (electrical, optical, photoelectric, etc.) are presented. The results in the literature are analysed, giving answers to such fundamental questions as the following. Where is the actinic light which is efficient for the photodissolution absorbed? Which is the diffusion-limiting step? What is the state of the diffusing species (neutral atoms or ions)? The dissolution of silver induced by electron or ion beams and the photodissolution of group II metals are mentioned. The experimental results are fol...

Photodoping of amorphous chalcogenides by metals

The incorporation of impurities into solids by bombardment with energetic ions is a non-equilibrium process which can result in intriguing near-surface property changes. This review initially examines the basic ion-solid interaction processes and outlines how such processes can lead to the modification of the composition, structure and surface topography of materials. Ion implantation has been exploited in widely diverse fields both as a powerful research tool for investigating solid state material processes and properties, and as a means of controllably modifying the electrical, physical, chemical, mechanical and optical properties of solid surfaces. These aspects receive major attention in this review which attempts to provide a balanced overview of the impact of ion implantation on solid state science and technology. In particular, special emphasis is given to implantation processes and applications in semiconductors which have received an enormous amount of attention in recent years, stimulated no doubt by the strong technological driving forces within the microelectronics industry. Ion bombardment processes and interesting property changes in metals are also discussed, and a selection of important technological applications is given. Finally, an overview of more recent investigations and applications is presented, including ion implantation into insulators and polymers, insight into crystal growth processes, adhesion of thin films to substrates, and research into ion bombardment of ices which has astrophysical significance.

https://iopscience.iop.org/article/10.1088/0034-4885/49/5/001/pdf

Materials modification with ion beams

Silver sensitized germanium selenide/polymer bilevel resist system has been used to pattern structures in SiO2 on silicon. Using reactive sputter etching in an SF6 plasma for developing germanium selenide gives superior results compared to CF4 or CHF3 in terms of sensitivity; 500:1, contrast; 7, and sensitivity; 50 mJ/cm2 at 436 nm. By this method 1‐μ lines and spaces and 1‐μ contact holes have been defined in germanium selenide. These have been transferred into polymer and SiO2 using standard reactive sputter etching with O2 and CHF3, respectively.

Development of silver sensitized germanium selenide photoresist by reactive sputter etching in SF6

Generation of submicron monodisperse aerosols in electrosprays

Liquid indium ions sources were operated in a transmission electron microscope. The formation of a Taylor cone was directly observed during source operation. In addition, dynamic instabilities were observed on the needle shank behind the Taylor cone with the formation of liquid droplets which grew in size and left the shank. Droplets on the shank were also found in SEM observations of rapidly frozen liquid gold ion sources. The surface of silicon targets on which the ion current from a gallium ion source was allowed to impinge was studied by Rutherford backscattering spectrometry. The amount of material emitted from the ion source was measured as a function of the angle of emission and the ion current. A comparison of these emitted mass distributions with the corresponding current distributions indicated that the average mass to charge ratio of the beam decreased with angle of emission. In addition, the ratio of the amount of material to the total charge leaving the source was found to increase monotonica...

Droplet emission in liquid metal ion sources

A negative resist consisting of a layer of germanium selenide ∠1800 A thick with a surface layer of silver selenide ∠100 A thick was irradiated with 10 to 38 keV He, N, Ar, and Xe ions. While polymer resists require an incident ion to pass through the entire thickness of the resist film for exposure, germanium selenide films can be exposed with ions which penetrate only the ∠100 A thick silver selenide surface layer. Thus, germanium selenide is an attractive resist system for low energy focused ion beam lithography. Resist sensitivities of ∠1013 to 1015 ions/cm2 were measured. Both nuclear and electronic stopping contribute to exposing the resist. Submicron lines have been produced in germanium selenide with a 20 keV finely focused ion beam.

Germanium selenide: A resist for low‐energy ion beam lithography

Resist materials and processes are described for use with low energy ion beam lithographic tools Ion implanted regions on polymer and (SiO2) resists serve as in situ etch masks during reactive ion etch development of unexposed regions Presumably, nonvolatile inorganic compounds formed from the implanted ions act as the in situ masks Two classes of resist have been employed (1) an inorganic SiO2 layer exposed by In+ ions and developed in a fluorocarbon plasma and (2) a thick organic polymer exposed by In+ and developed in an oxygen plasma For the latter, Rutherford backscattering spectroscopy was used to analyze the amount and depth distribution of the implanted ions before and after the reactive ion etching process (RIE) Between 5% and 15% of the implanted species are lost during the RIE development Ionic organic resists exhibited deeper In+ distributions after a 3 keV implant and subsequent reactive ion etching than insulating organic materials Conducting resists are required for finely focussed i

Plasma‐developed ion‐implanted resists with submicron resolution

The optical emission close to the Taylor cone tips of liquid gallium and gold ion sources has been studied as a function of wavelength and ion current. The optical emission may be interpreted as due to excitations caused by binary collisions, among which Ga‐Ga+ collisions play a dominant role. The release rate of neutrals from the source inferred from the optical‐emission curves is consistent with the idea of contributions to the total ion current from field evaporation and field ionization, with the latter becoming increasingly important at higher currents. It is difficult to account for the origin of the neutrals by thermal evaporation at the tip.

Optical emission: A probe of neutral atoms in liquid‐metal ion sources

The optical spectrum of gallium atoms produced and excited near a self‐formed high‐field emission tip of a liquid metal gallium ion source has been observed in detail. The spectrum reveals several interesting features. The dispersed neutral gallium lines exhibit asymmetric tails extending over tens of angstroms. The broadening is identified as due to quadratic stark effect. The maximum broadening is limited by field ionization of the atom from its excited state. The agreement with classical results is reasonable. A background continuum has also been observed, which may be due to transition radiation arising from collision of electrons, produced during field ionization, with the liquid‐metal tip.

D. Barr

Papers

Droplet emission in liquid metal ion sources

Germanium selenide: A resist for low‐energy ion beam lithography

Plasma‐developed ion‐implanted resists with submicron resolution

Optical emission: A probe of neutral atoms in liquid‐metal ion sources

Giant stark broadening of atomic gallium emission lines near a high field tip