Beam system

The practical implementation of cone-beam systems requires a choice of scanning geometry and of a reconstruction method. The good answers to both these questions simultaneously can hardly be obtained. 

Scanning electron beam systems are available commercially, and are commonly used for mask generation. Electron projection systems are also used to obtain resolution over a large field. Current cathode sources have a short lifetime, limiting use in production processes. 

To achieve smaller dimensions there are systems that use x-rays instead of optical photons (150). These systems require a collimated x-ray source which is often expensive. Additionally, systems have been developed that use ion beams to expose the resist. Either an x-ray or ion beam system requires specialized resists and exposure systems. 

Double-beam AA spectrophotometers are still marketed by instrument manufacturers. A double-beam system compensates for changes in lamp intensity and may require less frequent re-zeroing than a single-beam instrument. These considerations had more merit some years ago when hollow cathode lamps suffered from some instability. It should be noted, however, that the optical... 

For large telescope apertures, Na LGS offer improve sampling of the atmospheric turbulence due to their much higher altitude. Single beam systems are now being developed for and deployed on 8-10 m class telescopes. Since resonant backscattering from the mesospheric Na layer is the method chosen for most LGS projects, we will concentrate mostly on this technique. 

Fig. 2. Schematic illustration of a Kaufman source ion beam system (Sharp et al., 1979).

The addition of In and Ga and selenization at high temperature were crucial in obtaining the 13.4%-efficient device. Photovoltaic device fabrication was completed by a CBD of about 500 A of CdS, followed by RF sputtering of 500 A of intrinsic ZnO and 3500 A of Al203-doped conducting ZnO. Bilayer Ni/Al top contacts were deposited in an e-beam system. The final step in the fabrication sequence is the deposition of lOOnm of MgF2 as an antirellection coating. 

IR spectrometers have the same components as UY/visible, except the materials need to be specially selected for their transmission properties in the IR (e.g., NaCl prisms for the monochromators). The radiation source is simply an inert substance heated to about 1500 °C (e.g., the Nernst glower, which uses a cylinder composed of rare earth oxides). Detection is usually by a thermal detector, such as a simple thermocouple, or some similar device. Two-beam system instruments often work on the null principle, in which the power of the reference beam is mechanically attenuated by the gradual insertion of a wedge-shaped absorber inserted into the beam, until it matches the power in the sample beam. In a simple ( flatbed ) system with a chart recorder, the movement of the mechanical attenuator is directly linked to the chart recorder. The output spectrum is essentially a record of the degree of... 

The particle beam system is a simple transport device, very similar to a two-stage jet separator. The solvent vapour is pumped away, while the analyte particles are concentrated in a beam and allowed to enter the mass spectrometric source. Here they are vapourized and ionized by electron impact. 

Foundations are always constructed of reinforced concrete. Blast resistant buildings can be supported on pited or soil supported mats. Spread footings arc used with a grade beam system to minimize relative displacements between individual footings,... 

Electron beam systems can be conveniently considered in two broad categories those using scanned, focused electron beams which expose the wafer in serial fashion, and those projecting an entire pattern simultaneously, onto a wafer. Electron beam projection systems have been investigated extensively since they offer the potential of higher exposure rates as a... 

Figure 36. " Family tree of electron beam systems.

Figure 40. Operating modes for electron beam systems left — raster scan coupled with continuous table motion right — vector scan, step and repeat.

Figure 42. Diagram of a compound shape electron beam system...

As in all processing steps, cleanliness of the exposure hardware is of paramount importance. Any particle that lands on the resist prior to exposure, will shield the film underneath the particle from the exposing radiation and give rise to opaque spots in the case of positive resist, or pinholes in the case of negative resists. Particulate contamination is especially troublesome with electron beam and ion beam systems where the probability of a particle landing on a substrate is increased relative to other techniques because of the much longer exposure times involved. 

Multi-row detector systems are referred to as cone-beam systems. With a moving conveyor they become helical cone-beam systems. The cone-beam designation is in contrast to the fan-beam geometry used in Figures 3 and 4, where the source and detectors are aU in a single plane. 

Figure 6 A multi-row detector array is used in a cone-beam system. In this case, the detector rows fall along circular arcs centered on the X-ray source s x, y coordinate values. Detectors of equal size therefore subtend equal angles with respect to the source. This characteristic and other system and data-analysis considerations often make curved detector rows more attractive than straight ones like those of Figures 3 and 4.

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