A scanning electron microscope comprises an electron source, a condenser lens to condense electron beams emitted therefrom as fine probes onto a specimen, a beam deflection system to scan the condensed electron beams on the specimen in two dimensions, and a secondary electron detector to detect secondary electrons emitted from the specimen by exposure to the electron beam. A scanning electron microscope has an electron gun for producing an electron beam that is sharply focused onto a specimen to be observed. The beam is scanned across the specimen. As a result, secondary electrons and other electrons are produced from the specimen. A specimen image is displayed on the viewing screen of a display device according to the secondary electrons or other electrons. A scanning electron microscope accelerates electrons emitted by an electron source of a heating electron emission type or a field electron emission type, collimates the accelerated electrons in a fine electron beam using an electrostatic lens or a magnetic field lens, scans a specimen two-dimensionally with the primary electron beam, detects secondary electrons generated by the specimen irradiated with the primary electron beam or secondary signal electrons and forms a two-dimensional electron image by applying intensities of detection signals as brightness modulating inputs to a cathode-ray tube that is scanned in synchronism with a scanning operation using the primary electron beam. The scanning electron microscope accelerates electrons emitted from the electron source to which negative voltage is applied, toward an anode whose voltage is the ground voltage, and scans an observed sample with the primary electron beam. The scanning electron microscope is, in general, an apparatus for observing an enlarged image of the surface of samples by emitting an electron beam from an electron beam gun, collimating the beam with electronic lenses, and scanning the sample surface with the collimated electron beam by means of a deflector, in order to form image signals by detecting secondary electrons such as secondary or reflected electrons generated from the sample by the electron beam irradiation.

In a scanning electron microscope, as an electron beam hits a specimen, secondary electrons, backscattered electrons, X-rays, and cathodoluminescence are produced, and these are detected. In a scanning electron microscope, the shape of the objective lens is an important factor that determines the instrumental resolution. When a sample is placed on the stage, and irradiated by the electron beam, secondary electrons according to a rugged state of a sample surface are discharged from the sample surface targeted for measurement. A number of types of scanning electron microscope are provided, such as the ESEM (environmental scanning electron microscope), the VPSEM (variable pressure scanning electron microscope) and the LPSEM (low pressure scanning electron microscope) which operate using an imaging gas to amplify secondary electrons produced by the target sample. Such systems operate by irradiating the target sample with an electron beam which in turn causes the emission of electrons from the sample, which can include the emission of secondary electrons. The secondary electrons are then accelerated towards an anode, which can be used as a detector. In an ESEM, the electron beam is emitted by an electron gun and passes through an electron optical column of an objective lens assembly having a final pressure limiting aperture at its lower end thereof. The environmental scanning electron microscope allows the specimen to be maintained in its "natural" state, without subjecting it to the distortions caused by drying, freezing, or vacuum coating normally required for high-vacuum electron beam observation. The relatively high gas pressure easily tolerated in the ESEM specimen chamber acts effectively to dissipate the surface charge that would normally build up on a nonconductive specimen, blocking high quality image acquisition. The environmental scanning electron microscope also permits direct, real-time observation of liquid transport, chemical reaction, solution, hydration, crystallization, and other processes occurring at relatively high vapor pressures, far above those that can be permitted in the normal scanning electron microscope specimen chamber.

Today, the scanning electron microscope is widely used, mainly for the study of surfaces as well as transparent specimens. Two major applications for the scanning electron microscope are analytical inspection and lithography. Lithography has a broad range of industrial applications, including the manufacture of semiconductors, flat-panel displays, micromachines, and disk heads. Microlithography processes for making miniaturized electronic components, such as in the fabrication of computer chips and integrated circuits, involve using photoresists. Generally, a coating or film of a photoresist is applied to a substrate material, such as a silicon wafer used for making integrated circuits. The substrate may contain any number of layers or devices thereon. The lithographic process allows for a mask or reticle pattern to be transferred via spatially modulated light to a photoresist film on a substrate. Those segments of the absorbed aerial image, whose energy exceeds a threshold energy of chemical bonds in the photoactive component (PAC) of the photoresist material, create a latent image in the photoresist. In some photoresist systems the latent image is formed directly by the PAC. Scanning electron microscopes have long been used to inspect or observe semiconductor devices. Among such scanning electron microscopes, there are electron beam testers in which electrons obtained from the sample are energy-discriminated, an electric potential contrast image is created based on discriminated electrons, and inspections are performed for defects in the wiring of semiconductor devices. Many semiconductor integrated circuits, typically comprised of thousands of active devices such as transistors, are fabricated simultaneously on the wafer's surface. The small size of these semiconductor devices in such integrated circuits as microprocessors requires an instrument with very high powers of magnification to view and inspect them adequately. Additionally, the various devices and other components that together form such a microprocessor are made from numerous different layers of materials. As a scanning electron microscope offers both sufficient magnification and sufficient depth of field to inspect ICs both during and after processing, the scanning electron microscope is the inspection tool of choice for the semiconductor industry.

The scanning electron microscope has become a most valuable tool for examining and measuring patterns of these dimensions which are in the micron to sub-micron range. Since the microprocessing has been greatly improved in the semiconductor industry, scanning electron microscopes have been widely used for examining the processing of semiconductor elements or processed semiconductor elements in place of an optical microscope. Optical inspection of semiconductor wafers for defects detection is considered an effective and low cost method and is, therefore, the most widely used approach. A scanning electron microscope with a measurement function has been used for control of semiconductor sample dimensions or other similar purposes. There are two dimensional measurement modes: a manual measurement mode and an auto measurement mode. In the manual measurement mode, an operator visually makes a measurement using a measurement cursor. In the auto mode, line profile creation, edge detection, and measurement calculation are carried out according to predetermined auto measurement parameters. A scanning electron microscope or measuring the size of a specific pattern used on the semiconductor manufacture line is promoted in automation so as to prevent raising of dust by a person in the same way as with other devices or to improve the processing capacity. Typically, in critical dimension analysis of an integrated circuit component the electron microscope measures the apparent width of a structure when determining its dimensions. The apparent width of the structure is compared to critical dimension specifications in order to determine the compliance of the integrated circuit component.