Microscopes are used in the semiconductor industry as a means for a high magnification of inspection of a sample. The sample is positioned perpendicular to the axis of objective lens. The microscope light shines on the sample, reflecting the light back to the lens and allowing the image to be seen depending on how well it is illuminated and positioned. The characteristics of the sample are also important.
The most common type of microscope used in the semiconductor industry is the optical, or light, microscope. Other microscopes include electron microscopes and scanning probe microscopes, which are made to view samples smaller than 200 nanometers. Due to the sizes of the components involved with microfabrication, optical microscopes are preferred.
Optical microscopes have 6 basic parts: the lamp, the nose piece, the aperture diaphragm, the field diaphragm, the stage, and the eye piece. The lamp is used to illuminate the sample. The nose piece holds multiple objectives in order to change the viewing magnification. The aperture diaphragm is used to adjust the contrast and resolution, while the field diaphragm adjusts the field of view. The stage holds the sample. The eye piece, of course, is used for magnifying the image.
Optical microscopes can be classified as high power or low power. A high-power microscope will be able to magnify a sample from 100x to 1000x, and theoretically even more. Low-power microscopes however are only able to magnify a sample from 5x to 60x. Some can magnify up to 100x. For the semiconductor industry, a high-power microscope is a necessity.
Optical microscopy can be conducted in either brightfield illumination, darkfield illumination, or interference contrast. Brightfield illumination is the normal mode that an optical microscope views samples with. It provides uniform illumination of the sample and a full cone of light to focus the sample. Darkfield illumination is somewhat the opposite of brightfield illumination in the sense that the inner circle of the light cone is blocked. The reflected light comes from feature edges and irregularities, allowing an excellent method for spotting defects. Interference contrast uses polarized light divided by a Wollaston prism. When the displaced light hits the sample, it returns to the prism through different paths, providing the contrast which gives this mode its name.