On the energy distribution of doubly charged atomic ions emitted from liquid metal ion sources

Classified abstracts 6923-6931 MeV helium-ion or proton beams with a demagnification system consisting of piezo-driven objective slits and a magnetic quadrupole doublet. M i n i m u m beam spot sizes of 1.3 x 2.2/~m 2 for helium ions and 2.2 x 4.0 am 2 for protons have been achieved. The factors which m a y limit the m i n i m u m spot size are discussed using a Monte Carlo simulation procedure. Rutherford backscattering image mapping of 3-dimensional structures is demonstrated. K Inoue et al, Nucl lnstrum Meth Phys Res, B30, 1988, 580-591. 30 6923. The microbeam facility at the University of Montreal The 4.5 M V Dynamitron injector for our 6 MV T a n d e m is now used to provide a proton beam for a dedicated PIXE, RBS, P I G E microbeam facility. An electrostatic quadrupole triplet lens produces a beam spot of 20 # m diameter. The target chamber, which is a modified 4 in. Dependex cross, houses an electron flood gun, and SB detectors. The targets are m o u n t e d on a stepper motor controlled H P T 040 micromanipulator. A 30 m m 2 Si(Li) detector ( F W H M = 154 eV at 5.9 keV) is used for PIXE measurements. Data on the impurities found in "water trees", which are associated with breakdown in electrical cables, will be presented. P F Hinrichsen et ai, Nucl lnstrum Meth Phys Res, B30, 1988, 276-279. 30 6924. Activities for the construction of a new Heidelberg proton microprobe A new microprobe system is described which will provide easier operation, especially for outsider, users, a micro- and macro-PIXE facility, improved accuracy for quantitative analysis and an improved scanning system. The probe will have crossed slits as object, a magnetic quadrupole doublet lens and electrostatic deflector plates. Ion optical calculations were done up to third order, using the T R A N S P O R T and O X R A Y computer programs. The image spot size is investigated as function of the geometrical arrangement. A collimation line has so far been built. The scattering at slit edges of the geometrical shape used in the old microprobe is compared with the scattering at the edges of the simpler cylindrical shape. The latter proved to be slightly superior. J Scherer et al, Nucl lnstrum Meth Phys Res, B30, 1988, 265 270. 30 6925. A high ionization efficiency source for partially ionized beam deposition The design and testing of a high ionization efficiency source for a partially ionized beam deposition (PIBD) system are described. The vaporized m~terial from a crucible is partially ionized at the crucible exit, where the vapor has its highest density. The system can provide ionization efficiencies of up to 5% (ion/atom ratio) at ion energies ranging from 0.2 to 6 keV. Measurements of the ion current versus substrate bias potential along with the deposition rate are reported using A1 as source material. A uniform ion beam intensity has been obtained over a 6-cm-diam substrate at a distance of 30 cm above the source. If the ionization source is placed a few centimeters away from the crucible, as it is in the conventional PIBD design, the ionization efficiency would reduce to < 0 . 2 % (ion/atom ratio). The reduction can be easily explained by geometry consideration. S-N Mei and T - M Lu, J Vac Sci Technol, A6, 1988, 9 12. 30 6926. A time resolved study of velocity distributions in pulsed molecular beams We have studied with 12-#s resolution the time evolution of the characteristic flow velocity and parallel temperature of a supersonic gas jet produced by a commercial pulsed valve. The gases studied were H2, He, Ne, Oz, Ar and a seed mixture of 5% O2 in He. The gases were supplied to the pulsed valve at 100- and 1000-Tort inlet pressure. Our results indicate that the time required to reach an equilibrium flow condition is essentially independent of the gas species used, but is a function of the inlet pressure. Furthermore, the static Mach number obtained in the expansion is found to deviate from that predicted for a cw expansion with the same nozzle K n u d s e n n u m b e r Kn0 with increasing inlet pressure. This leads to the conclusion that the effective diameter Deerthrough which the gas expands is a function of inlet pressure, and that the observed equilibration time is in fact the time required for the valve opening to reach this effective value. The results obtained should be applicable to any pulsed valve with similar mechanical bandwidth and gas passage geometry. Benjamin N Eldridge and Ming L Yu, J Vac Sci Technol, A6, 1988, 11451149.

30 6927. A Monte Carlo investigation of the runaway of H + ions in helium Theoretical and experimental works have shown that at high values of e/N (the ratio o f electric field strength to gas n u m b e r density) the reduced mobility of H + ions drifting in helium exhibits a rapidly increasing value, termed the 'runaway mobility'. In the present work, a M o n t e Carlo simulation technique has been used to investigate the ion motion in the runaway. Comparisons of the dependence of apparent mobility on the n u m b e r density of helium show agreement with the results obtained by the experiments. S Ushiroda et al, J Phys D : Appl Phys, 21, 1988, 756-762. 30 6928. On the energy distribution of doubly charged atomic ions emitted from liquid metal ion sources The energy distribution of G a 2+, A u 2+ and Pr 2+ ions emitted from Ga, A u and Pr liquid metal ion sources has been studied as a function of source current, I, and angle of emission, ~, and the results are compared with those obtained for the singly charged atomic ions emitted from these sources. It was found that for all three doubly charged species the FWHM of their energy distribution is angle independent, whereas the FWHM of the energy distribution of the singly charged species is not. For Au 2+ and Pr 2+ ions the ~ I ~ M was found to vary as/oz9 and/035 respectively. It is concluded that in order to explain these experimental results interactions other than ion ion ones have to be taken into account, both for the singly and doubly charged atomic ions. It is also suggested that the processes responsible for the energy spread of the singly and doubly charged ions are of the same nature but differ in magnitude. S Papadopoulos, J Phys D : Appl Phys, 21, 1988, 194-199. 30 6929. The electron-beam column for a high-dose and high-voltage electronbeam exposure system Ex-7 The electron optical column is designed for the electron-beam (EB) exposure system EX-7 employing a vector scanned variably shaped beam (VSB) on a continuously moving stage. The column, which utilizes a high current density of 200 A/crn 2 and a high voltage of 50 kV, has been designed for a 0.25 p m patterning. Generation of triangular shapes in added to rectangular shapes reduces shot numbers to enhance throughput. An octapole deflector with small deflection distortion, has breen developed for beam shaping. The ray tracing method using an analytical expression for the electric and magnetic field was used to design the objective focusing and deflection system, which is composed of a magnetic lens and dual channel electrostatic octapole deflectors. Beam edge resolution including the electron-beam interaction effect is about 0.12 # m and distortion is <0.01 /an at the final beam convergence semi-angle of 8 m r a d and field size of 600/~m square. As a result, a 0.25 # m resist pattern has been obtained over 600 # m field. Main deflection field stitching error was < +0.04 # m (3or) without deflection distortion correction. S Tamamushi et ai, J Vac Sci Technol, B6, 1988, 209 212. 30 6930. Design and performance of an U H V beamline to produce low and hyperthermal energy ion beams We have constructed and tested a U H V beamline to produce beams of alkali metal and noble gas ions over the energy range < 2 0 eV to 10 keV with energy resolution AE/E of 1% or better. At the sample position, we have attained tens of n a n o a m p s of current for keV energy beams in a 12-ram beam spot with about + 1° angular divergence, and n a n o a m p s of current at 25 eV in a 4-mm beam spot with _+2 ° angular divergence. By applying Liouville's theorem to the beam's emittance and using waist-towaist transport through the beam optics, the current on the sample is maximized while limiting the spot size and angular divergence. To achieve useful current at the lowest energies, special attention was paid to minimizing space-charge effects. Beam emittances measured at the sample position are consistent with Liouville's theorem. Equations for waist-to-waist transport are derived in the Appendix. D L Adler and B H Cooper, Rev Sci Instrum, 59, 1988, 137-145. 30 6931. Scanning positron microbeam The construction and operation of a scanning positron microbeam is reported. The positrons are obtained from a double remoderated positron beam with a normalized brightness-per-volt of 1.8 × 105e+ s - ~c m - 2 r a d - 2 V 1 C i - ~. The beam of 8000e + s ~ is brought to a 10 x 50-/~m2 focus by a sectored lens and is scanned across a test grid. Possible applications

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