6152. A stabilised flow control system for ion source gas from volatile liquids

Classified abstracts 6147-6155 (110) oriented tungsten field emitters. These sites are capable of producing at least 10 to 15 nA beams of Hz+ in half angle apertures of 16 mrad. Because the basic physical process involved in the field ionization of H, is known to yield energy spreads of 1 eV (FWHM), good ion-optical properties are inherently available. This technique is practical in that one may readily and reproducibly localize the emission, but it remains to address the question of whether or not the localized emission structures provide stable beam currents for extended periods of time. Field ion micrographs of these sites indicate that they are protruberances 200 A in diameter with field enhancement factors of 1.5. The current from these relatively large structures is not affected by surface rearrangement on the atomic scale caused by field induced chemical reactions or molecular contamination. The ability of these sites to provide a stable ion current then depends solely on the structural integrity of the protruberance. As ion bombardment is a factor in microboss growth, the first few surface layers of the field emitter and the microboss itself are radiation damaged tungsten and hence subject to electromechanical detachment. Heating the embossed field emitter to 80&l 100 K allows greater ion currents to be drawn from the microboss before detachment occurs. However, these investigations indicate that to provide long term ion current stability a complete anneal (1100 K) of the embossed field emitter, most likely in the presence of an electric field such that the emitter is the anode, thereby holding the microboss in place and simultaneously halting the ion bombardment, is required. The fundamental field ionization mechanism generates ion currents stable to within 0.1% indicating the stability achievable after recrystallization of the surface. P R Schwoebel and G R Hanson, J Vat Sci Technol, B3, 1985, 214219. 30 6147. A high speed EBL column designed to minimize beam interactions The writing strategy and electron optical aspects of the Perkin-Elmer AEBLE 150 EBL system are discussed. For a specific submicron EBL writing task, an ‘optimum’ area for a variable shaped beam is derived. For specific column properties, an optimum gun brightness is chosen to image the shape at maximum beam interactions limited current. The writing system takes advantage of a continuously moving stage to allow a moderate scan field, exploiting in-lens deflection to use a very large aperture angle with a 2 mm field. Experimental data indicates a current density of 100 A cm-* in rectangular or triangular shapes up to 2 pm in size. Edge resolution is less than 0.15 pm for shapes containing less than 1.5 PA of current. A series of beam profiles taken with a 300 ns exposure cycle shows that the deflection systems will support high speed lithography on insensitive resists. L H Veneklasen, J Vat Sci Technol, B3, 1985, 185-189. 30 6148. A combined electron and ion beam lithography system In scanning beam microfabrication processes, including resist exposure, direct maskless ion implantation, and micromachining, ions and electrons have complementary roles. It is advantageous to have, within a single beam machine, finely focused and precisely coregistered beams of both ions and electrons. The requirement for the ion beam and the electron beam to have a common axis and to be. focused at the target by a high resolution lens with short working distance can be met both by solely electrostatic and by combined magnetic and electrostatic lenses. Such lenses, and complete probe-forming systems incorporating them, are considered. J R A Cleaver and H Ahmed, J Vat Sci Technol, B3, 1985, 16147. 30 6149. An experimental variable shaped electron beam lithography system An experimental variable shaped electron beam lithography system has been built to verify the theoretical design considerations and fundamental control method. The electron beam column consists of four magnetic lenses, two square apertures, two ahgners, an angular aperture, a set of blanking plates, and a position deflection yoke. The size of the beam spot is varied by a set ofelectrostatic deflection plates. In order to maintain the current density in the spot constant, as the size of the beam spot varies, the centre of the shaped deflection plates is placed to coincide with the image of the gun crossover, and the-shaped deflection plates position can be electrically adiusted. The acceleration voltage is 20 kV. The field size is 2.5 mm square. The maximum spot size is lO_pmr. The maximum current density is 1 A cm-*. The system is controlled by an EG 3003 computer. The beam blanking switching time is 50 nS. Fu-min He et al, J Vat Sci Tech&, B3, 1985, 121-123. 30 6150. Yaw corrected precision X-Y stage for high-throughput electronbeam lithography systems Overhead time associated with a work stage is an important factor

determining the throughput of step-and-repeat-type electron-beam lithography systems. In addition to increasing stage speed, utilization of large field electron optics contributes to reduction of such overhead time. However, when using large field optics, the stage is required to have minimal yaw to prevent field stitching error. Accordingly, a high-speed, high-precision work stage with a piezodrive yaw correction function has been developed for construction of high-throughput e-beam systems. To avoid leakage, magnetic field variation, and vacuum contamination, only the work table is located in the vacuum chamber. The table is driven by X-Y-drive mechanisms located outside the chamber. To achieve high speed positioning, a unique, light-weight X-Y table structure using a PTFE slide bearing has been incorporated. To correct yaw error at the stage, the work table can be rotated k8 arcsec with a piezoactuator. Positioning and yaw correction for the table are carried out with a closedloop control system that utilizes three-axis (X, Y, and yaw) laser interferometers. A maximum velocity of 100 mm s- i, + 2 pm positioning accuracy, 130 ms movement time including vibration settling for a 6.5 mm step, and a yaw of less than kO.3 arcsec has been achieved. Shigeo Moriyama et al, J Vat Sci Technol, B3, 1985, 102-105. 30 6151. Application of a focused ion beam system to defect repair of VLSI masks A scanning ion beam lithography system has been used for the rework of chromium-on-glass mask plates to repair defects in the VLSI circuit pattern. By using submicrometer diameter beams of gallium and of gold ions to sputter selected areas of the mask, both clear and opaque areas have been generated on the substrate. P J Heard et al, J Vat Sci Technol, B3, 1985, 87-90. 30 6152. A stabilised flow control system for ion source gas from volatile liquids A simple system is described for the control of gas flow from a volatile liquid into an ion source. The system uses a Peltier cell to control the temperature of the liquid and hence its vapour pressure. The vapour is metered from above the liquid into the ion source through a long capillary tube. Since there are no moving parts in contact with the vapour, it is very well suited for use with corrosive substances. The system described is extremely stable, has a wide dynamic range and is suitable for many other applications such as gas chromatography and mass spectrometry. A M Smith and R L Dalglish, J Phys E: Sci hit-urn, 18, 1985, 387-389. 30 6153. Charge and energy transfer in collisions of Cs+ ions with a cesiated W(110) surface A beam of Cs+ ions with an energy of 500, 1000, or 2000 eV is scattered from a cesiated W(110) target. The angle of incidence is 45 or 75” with respect to the surface normal. The charge state and energy of the scattered particles are measured. The influence of hydrogen coadsorption on the final charge state is investigated. All scattered cesium particles are neutrals when the surface work function is smaller than 2.6 eV. The scattered particles have suffered a pronounced energy loss. From the measurements an extrapolation is made to conditions relevant for surface conversion negative ion sources. P W van Amersfoort et al, J appl Phys, 58, 1985, 2312-2316. 30 6154. Metastable He+ (2s) production by a rf ion source 3He+(2S) production by a rf ion source has been measured by detecting the 30.4 nm radiation emitted when the 2S state is quenched in a high electric field. The production was maximum when extraction voltages and were low. The highest fraction gas pressures in the source He+(2S)/He+(lS) observed was 0.08%. This fraction is estimated to be accurate to within a factor of two. C Moreau et al, J Whys D: Appl Phys, 18, 1985, 169-176. 30 6155. Broad-beam electron source A new type of broad-beam electron source has been developed. The use of a plasma as the source of electrons permits balanced operation of multipleaperture electron optics. As a result, far higher total beam currents are obtainable with this source than are possible using single-aperture electron extraction. At the same time, the required working gas flow is low enough to permit operation in a high-vacuum environment. The electron beam energy is controllable over a range from below 100 eV to at least 1000 eV. This unique combination of performance characteristics for a broad-beam electron source should result in its use in a wide variety of applications. H R Kaufman and R S Robinson, J Vat Sci Technol, A3,1985,1774-1778. 731