Richard E. Honig

Sputtering of Surfaces by Positive Ion Beams of Low Energy

Silver, germanium, and germanium‐silicon alloy surfaces have been bombarded with the inert gas ions Ne+, A+, Kr+, and Xe+, at energies between 30 and 400 ev. Primary beam intensities between one and ten μa/cm2 were obtained in an oscillating electron source of the Heil type. The secondary particles sputtered off, neutrals as well as positive and negative ions, were identified and recorded in a 180° mass spectrometer of 5.5‐inch radius. They are partly background gases adsorbed on the surface, partly atoms and molecules characteristic of the sample. Among the latter particles, neutrals were about 100 times more abundant than those emitted as positive ions. Rather low yields (about one sample atom per 100 incident ions with 400‐ev energy) and relatively high threshold energies (40–50 ev for an angle of 30° between beam and surface) are believed to be due to surface contamination. Retarding potential measurements showed that over 80% of the particles sputtered have initial energies of less than 5 ev. After b...

Mass Spectrometric Study of the Molecular Sublimation of Graphite

The emission of neutral and charged carbon molecules from spectroscopically pure graphite has been studied by rate of vaporization experiments in a 180° mass spectrometer. Small filaments (diameter: 0.015 in.), heated by ac up to 2600°K, yielded neutral particles which were converted into positive ions by bombardment with low‐energy electrons. C3+, C2+, and C1+ ions were found. Although the effects of fragmentation and of differences in ionization cross sections may not be negligible, it is believed that carbon vapor consists largely of C3 molecules. Graphite was found to emit negative ions containing from one to eight carbon atoms. C2—, C4—, and C3— were the most abundant species, in that order. A search was made for carbon particles emitted as positive ions, but none were found.Heats of activation were obtained for the neutrals and the more abundant negative ions from the slopes of logp vs 1/T plots. Identical heats measured for C1 and C3 (178±10 kcal/mole at 2400°K) suggest that these two species may s...

LASER-INDUCED EMISSION OF ELECTRONS, IONS, AND NEUTRAL ATOMS FROM SOLID SURFACES

Studies of various solids--- conductors, semiconductors, and insulators-- -irradiated in a vacuum with a focused beam from a pulsed ruby laser are described. Work was undertaken to detect and identify the ions, electrons, and neutral atoms emitted. The targets studied include Cu, Mo, Ta, W, stainless steel, and graphite, semiconductors of Ge and SiC, and one insulator Al/sub 2/O/ sub 3/. The ion spectra obtained include considerable concentrations of singly and multiply charged species typical of the target and also species representing background gases. (C.E.S.)

Secondary ion quadrupole mass spectrometer for depth profiling--design and performance evaluation.

A quadrupole-based secondary ion mass spectrometer designed for depth profiling is described which combines ultrahigh vacuum construction with high sputtering rate, detection sensitivity, depth resolution, mass spectral purity, and abundance sensitivity. Impurities such as B and Al implanted in Si can be profiled to levels below one part per million atomic (ppma), at a depth resolution equal to that obtained by commercial ion microprobes. The primary beam consists of 5-keV, mass-analyzed (40)Ar(+) ions, focused to about 70 microm in diameter. Its high current density (>25mA/cm(2)) permits adequate beam rastering and electronic signal-gating to optimize depth resolution. A secondary ion extraction lens and spherical energy filter are responsible for achieving abundance sensitivities of five to six orders of magnitude on the low mass side of a matrix peak. The ultrahigh vacuum environment of the sample dramatically reduces molecular peaks containing H, C, and O, allowing even hydrogen to be profiled to concentrations below 10 ppma. Because large amounts of data are generated by multi-element depth profiling, means for automated instrument control and data acquisition have been developed.

Surface and thin film analysis of semiconductor materials

Abstract In the field of semiconductor materials characterization, interest has shifted in recent years from bulk problems to surfaces and thin films, and from average composition to three-dimensional concentration profiles. This paper reviews nine major methods available today for the determination of surface and thin film composition, placing particular emphasis on basic principles and up-to-date instrumentation. Major considerations that determine the choice of a given method include: area and depth to be sampled; sensitivity, resolution and reproducibility; number of elements to be detected; and equipment price. To illustrate the capabilities and limitations of these methods, a number of practical examples are presented. Finally, the nine major methods are compared in terms of the most important practical parameters.

Low‐energy ion‐scattering spectrometry (ISS) of the SiO2/Si interface

The interface between Si and thermally grown SiO2 has been examined in detail by low‐energy 4He+ ion scattering. The oxide composition is shown to be stoichiometric to within 15–20 A of the interface. ISS depth profiles clearly establish a region of excess Si that extends from the interface into the oxide for 15–20 A, corresponding to four or five molecular layers. The amount of excess Si is calculated from the experimental data as 1.4×1014 atoms/cm2 per monomolecular layer (about 20% excess).

The development of secondary ion mass spectrometry (SIMS): A retrospective

Abstract Contrary to common opinion, secondary ion mass spectrometry (SIMS) has been with us for more than half a century under various guises, the most recent reincarnation being FAB (fast atom bombardment). This retrospective traces the SIMS lifetime from its roots in the 1930s, through basic studies in the 1950s and 1960s, to the present explosive development of inorganic and organic applications. Special attention is given to the various desorption modes of organic ions from solid and liquid surfaces.

Energy Distribution of Ions Formed in the rf Spark Source

Utilizing the ion source and electrostatic analyzer of a double‐focusing mass spectrograph, the energy distribution of the ions formed by the pulsed rf vacuum spark has been determined for various materials and sparking conditions. Upon emerging from the electrostatic analyzer, the ion beam has a width, in the y direction, which is principally due to its angular divergence α and its energy spread β. By suitably reducing the widths of the defining slits, α can be made negligibly small. The beam width is then a nearly linear function of β alone, and a photoplate, placed just beyond the exit of the electrostatic analyzer, is used to determine the energy distribution of the ions produced in the source. A convenient energy scale is put on the same photoplate by exposing it to thermal ions (energy spread about 0.5 eV) which are accelerated to selected voltages while the deflecting voltage in the electrostatic analyzer is kept constant. In the present study, a 1×2 in. photoplate could be shifted by external mean...

RESPONSE OF ION-SENSITIVE PLATES AS A FUNCTION OF ION ENERGY.

To attempt a better understanding of the mechanism of ion detection with ion‐sensitive plates, a study was made of sensitivity as a function of ion energy, and of blackening as a function of exposure. Various commercially available and experimental plates used in mass spectrography were investigated. A dc beam of Cs+ ions was used to expose evenly areas 0.1 by 0.25 cm on the plates, which were placed between the ion beam monitor collector and the magnetic sector entrance boundary of an AEI type MS7 double‐focusing mass spectrograph. Thus, after leaving the ion source, the ions traversed only the electrostatic sector portion of the instrument. For the sensitivity study, exposures were made with ion energies ranging from 0.1 to 20 keV on Ilford Q2, Kodak SWR, Kodak‐Pathe SC5, and RCA thin‐film plates made by the direct evaporation of AgBr onto glass (described in a companion paper by Honig, Woolston, and Kramer). In addition, blackening as a function of exposure was determined at various energies for each i...

EVIDENCE OF LASER‐INDUCED STIMULATED BRILLOUIN SCATTERING IN CdS

Experimental results are presented which indicate two forms of damage in CdS irradiated by either a normalmode or Q‐switched ruby laser at power densities near 108 W/cm2. The primary damage occurs as a deep crater coaxial with the incident laser beam. This crater contains many periodic transverse fractures whose spacing suggests a phonon frequency of ∼ 100 MHz, and which is attributed to stimulated Brillouin scattering. The second site is in the region where the refracted light beam exits from the crystal.