This article traces the important milestones in the development of high-resolution, field-emission, scanning electron microscopes (SEM). Such instruments are now capable of producing images of the surfaces of biological specimens that rival, in terms of resolution and contrast, those produced by conventional transmission electron microscopy (TEM). Even though one of the first instruments to produce a useful transmission electron microscope image was, in fact, an early scanning microscope, TEM reached its full potential for biological imaging almost 30 years sooner than did SEM. The main reason for this slow rate of development is the dependence of any scanning technique on source brightness. The only suitable electron source was the field-emission source, originally developed in the 1930's. Making this into a stable and reliable electron source for microscopy required many technical barriers to be overcome. An additional delay may have been caused by the great success that attended the introduction of early SEM instruments. These instruments which employed heated, tungsten hairpin cathodes, were inexpensive and reliable, but they that were also far from optimal in terms of optical performance. Their market success may have engendered the sense of inertia and complacency that further delayed the introduction of low aberrations objective lenses and field-emission sources for almost 20 years after they were first introduced to electron microscopy. In addition, the fact that these early SEMs accustomed users to operating with a much higher beam voltage than was either necessary or wise, lead many to assume that the SEM was incapable of producing high-resolution images of biological surfaces. This left them open to fascination with newer ahd slower techniques that, on balance, were less suitable than optimized SEM for most of their imaging needs. In parallel to these developments in instrumentation, major improvements were also made in the way that the specimen surface was prepared before placing it into the vacuum and radiation environment of the microscope.

The development of field-emission scanning electron microscopy for imaging biological surfaces

Organic materials exposed to an electron beam for patterning a substrate (1) to make an optoelectronic organic device which includes a source, a drain, gate dielectric layer (4), and a substrate for emitting light

Structured organic materials and devices using low-energy particle beams

An electron beam lithography system includes a laser for generating a laser beam, and a beam splitter for splitting the laser beam into a plurality of light beams. The intensity of the light beams is individually modulated. The light beams are of sufficient energy such that, when they impinge on a photocathode, electrons are emitted. Modulation of the light beams controls modulation of the resulting electron beams. The electron beams are provided to an electron column for focusing and scanning control. Finally, the electron beams are used to write a scanning surface, for example, using an interlaced writing strategy.

Multiple electron beam lithography system with multiple beam modulated laser illumination

A mask for use with a sample preparation apparatus that prepares an ion-milled sample adapted to be observed by an electron microscope is offered. It is possible to prepare the sample having a desired cross section by the use of the mask. The mask, which defines the boundary between irradiated and unirradiated regions on the sample surface, has an edge portion having an increased thickness compared with the other portions. When the edge portion of the mask is etched, the original shape is almost maintained. Thus, the side surface of the mask is kept on the center axis of the ion beam.

Mask and apparatus using it to prepare sample by ion milling

A calibration mask having a plurality of marks previously formed thereon is loaded, and a deflector is used to control deflection of electron beams so that the electron beams are incident on a mark of the calibration mask. The electron beams, having passed through the mark, impinge on a first Faraday cup having a first mark and on a second Faraday cup having a second mark. Then, positional coordinates on an XY stage are detected when electrical quantities detected by the Faraday cups are largest. The positional coordinates on the above mentioned XY stage are detected for each of the marks of the calibration mask. Then, according to the positional coordinates on the XY stage detected in this manner and a difference in height between the marks, the inclination of the electron beams is calculated for the position input to each mark of the calibration mask. Thus, the inclination of electron beams can be accurately measured.

Method of measuring and calibrating inclination of electron beam in electron beam proximity exposure apparatus, and electron beam proximity exposure apparatus

The system for drawing a pattern on a resist layer covering a semiconductor wafer, comprising an electron gun housing unit provided with a plurality of small-sized electron guns (wherein the housing unit has a hollow column section for releasing an electron beam, and a micro deflection unit is disposed inside for adjusting the inclination of the electron beam), a movable stage capable of moving in the X-Y directions, a wafer stage disposed on the movable stage to support a semiconductor wafer, a mask wafer having struts on its rear side for supporting membranes on which a pattern to be transferred is formed, a mask stage for holding the mask wafer, a matching detection unit for detecting a misalignment between the mask wafer and the semiconductor wafer, and an inclination means connected to the micro deflection unit and the matching detection unit for inclining the electron beam.

Takao Utsumi

Papers

Low energy electron beam lithography