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

The modification to the structure and microstructure of chalcogenide films in contact with metals has been determined by electron microscopy and diffraction and the distribution of metal through these films has been determined by Auger electron spectroscopy. Chemical changes that occur when metal films are in contact with chalcogenides have been examined by X-ray photo-electron spectroscopy. Diffusion of metals into chalcogenides upon ultraviolet and electron irradiation has been examined using electron optical techniques. Extensive diffusion occurs when copper or silver is in contact with chalcogenides. Silver and copper chalcogenides are formed. The resulting concentration profile of these metals through chalcogenide films can be qualitatively explained by the existence of two diffusion mechanisms, a fast interstitial mechanism and a slow substitutional mechanism. A study of the sensitivity of amorphous chalcogenide films and amorphous chalcogenide/silver films to electron beams of varying intensity has shown that the structural and composition changes that occur in the irradiated area depend on the particular chalcogenide, whether the film is supported by a substrate and the thermal conductivity of the substrate. These studies have demonstrated the high resolution attained in patterns written by electron beams and possible electron lithographic applications. The sensitivity of chalcogenide/silver films to ultraviolet radiation has also been demonstrated. This phenomenon is associated with breaking of the silver-chalcogen bond in the silver chalcogenide surface film.

https://iopscience.iop.org/article/10.1088/0022-3719/20/26/010/pdf

The dissolution of metals in amorphous chalcogenides and the effects of electron and ultraviolet radiation

Pulsed neutron diffraction has been used to study the short- and intermediate-range order of vitreous g-Ag 4 Ge 3 Se 9 . By utilizing the techniques of isotopic substitution and temperature variation, it has been possible to estimate four of the six partial pair-distribution functions for the first coordination shells. Measurements at T = 10 K extending out to wavevectors Q ≈ 34 A −1 provide accurate results for the bond lengths and coordination numbers. Comparison is also made with results derived from a variant of the maximum entropy method. Ge is fourfold-coordinated by Se at an average interatomic distance of 2.37 ± 0.005 A which is consistent with the GeSe 4/2 tetrahedron also being a structural unit in the Ag-doped Ge Se glass. Ag is predominantly bonded to Se at an average distance of 2.68±0.01 A and is threefold-coordinated. This low coordination might be a key factor in understanding the fast ion motion in this system. The temperature dependence of the structure factor, S ( Q ), and the radial distribution functions were investigated. The Ge Se and Se Se correlations solely reflect increased thermal vibrations of the atoms, whereas the Ag correlations behave quite differently with increasing temperature up to 170°C. The Ag correlations change rapidly and become liquid-like at elevated temperatures reflecting the diffusive motion of Ag. The first sharp diffraction peak at 1.04 A −1 in S ( Q ) exhibits the anomalous temperature dependence typical of chalcogenide glasses in that the peak becomes narrower and increases in amplitude with increasing temperature (∼ 2% from room temperature to 170°C).

Structure of vitreous AgGeSe

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.

V. E. Lamberti

Papers

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