Scanning electron beam systems

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. 

The most obvious way to improve throughput in scanning electron beam systems is to combine a variable shaped beam column, with a continuously moving table. The shaped beam ensures maximum beam current, and the continuously moving table potentially eliminates many overhead times. Registration can be accomplished without stopping the table, either by means of a laser interferometer, or through direct beam to sample reference. 

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

Radiation cross-linking of polyethylene requires considerably less overall energy and less space, and is faster, more efficient, and environmentally more acceptable. Chemically cross-linked PE contains chemicals, which are by-products of the curing system. These often have adverse effects on the dielectric properties and, in some cases, are simply not acceptable. The disadvantage of electron beam cross-linking is a more or less nonuniform dose distribution. This can happen particularly in thicker objects due to intrinsic dose-depth profiles of electron beams. Another problem can be a nonuniformity of rotation of cylindrical objects as they traverse a scanned electron beam. However, the mechanical properties often depend on the mean cross-link density. ... 

Modifications to Electron Beam System. The retarding potential field was introduced into our vector scan system by attaching a O-to-20 KV, 2 mAmp external power supply to the wafer holder. This is shown diagrammatically in Figure 2. Whereas the wafer is at ground potential in the standard system, in our modified system the net potential at the wafer can vary from 0 to 20 KV. Thus, the electrons are accelerated down the column at a standard operating potential, exit the final lens and are retarded by the variable electrostatic field near the wafer plane. 

In electron-beam direct-write lithography, the scanning electron beam of the exposure systems is focused to a small spot that is controlled [i.e., deflected and turned on and off (blanked)] by a computer as it is scanned across the surface of the resist film. Masks are not used in this exposure process. Two beam-forming approaches are employed. The first uses a Gausssian round beam. The second... 

Imaging system Light optical Light optical Scanning electron beam Electron optical Scanning solid probe... 

Another basic approach of CL analysis methods is that of the CL spectroscopy system (having no electron-beam scanning capability), which essentially consists of a high-vacuum chamber with optical ports and a port for an electron gun. Such a system is a relatively simple but powerful tool for the analysis of ion implantation-induced damage, depth distribution of defects, and interfaces in semiconductors. ... 

An electron gun produces and accelerates the electron beam, which is reduced in diameter (demagnified) by one or more electromagnetic electron lenses. Electromagnetic scanning coils move this small electron probe (i.e., the beam) across the specimen in a raster. Electron detectors beyond the specimen collect a signal that is used to modulate the intensity on a cathode-ray tube that is scanned in synchronism with the beam on the specimen. A schematic of the essential components in a dedicated STEM system is shown in Figure 2. 

A variation on depth profiling that can be performed by modern scanning Auger instruments (see Sect. 2.2.6) is to program the incident electron beam to jump from one pre-selected position on a surface to each of many others in turn, with multiplexing at each position. This is called multiple point analysis. Sets of elemental maps acquired after each sputtering step or each period of continuous sputtering can be related to each other in a computer frame-store system to derive a three-dimensional analysis of a selected micro volume. 

As the beam travels down the column, a number of electromagnetic lenses are used to guide the beam to the sample [44], The condenser lenses are part of the illumination system and are used to deliver electrons from the electron gun crossover to the sample. The condenser lenses determine the beam current reaching the sample. The objective, or final, lens determines the final spot size of the beam. A set of scanning coils are also present in the instrument column to scan the beam in a raster pattern over an area of the sample. At each point, data is collected and the points are combined to form the image. More detail on the data collection is given in the image formation section. 

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