Optical projection system

Projection optical lithography has been the mainstream technology in the semiconductor industry for the last two decades [2]. Figure 9.2 shows a schematic depiction of an optical projection system consisting of a laser light source, a mask, a projection lens, and a resist-coated wafer. The projection of the pattern of the mask onto the resist layer provides a demagnification ratio of up to 4x. 

Figure 3.18 Schematic illustration of an optical projection system employed in photolithography.

Figure 5.15 shows a ray diagram for a light-optical projection microscope. The light source is placed behind a condenser system which collects the light which is diverging from the source and illuminates the specimen. The presence of the variable aperture near to the condenser lens permits control of the area of the specimen which is... 

Even though projection optics embodies the inherent limitation of pattern transfer just mentioned, this technique has become a dominant approach in high-resolution work. A key reason for this success is the ability of projection printing to use reduction refraction optics with high numerical apertures. The resolving power of projection systems can be approximated by ... 

Microfabricated devices capable of switching optical light beams, also termed MOEMS, have gained attention about a decade ago for applications like optical fiber switches, microscanners, or digital micromirror arrays. Particularly, the latter devices have found widespread application in video projection systems for office presentations, home cinema, and very recently, the replacement of classical projectors in movie theaters. Other applications, for example, for head-up displays on auto windscreens are in development. In all cases, arrays of small micromirrors are used for the modulation of light. 

Kerth et al. (214) reported excimer laser (308 nm) projection lithography obtained with a modified full-field scanning projection system (Perkin-Elmer M500). The modifications included an anamorphic optical system for transforming the nearly collimated rectangular excimer laser beam into the arc shape. They obtained images of l- xm lines with nearly vertical (85 ) wall profiles. 

Microelectromechanical systems (MEMS) combine the electronics of microchips with micromechanical features and microfluidics to create unique devices. The multitude of MEMS applications continues to grow including many types of accelerometers, radio frequency (RF) devices, variable capacitors, strain and pressure sensors, deformable micromirrors for image projection systems, vibrating micro-membranes for acoustic devices, ultrasound probes, micro-optical electromechanical systems (MOEMS) and MEMS gyroscopes, to name a few. 

Since we are dealing with a vacuum tube, the upper limit of the screen which can be reached by present-day technology is about 73 cm. Piaures with a 2 m diameter can be obtained in projection television (PTV). For each of the three colors a small (monochrome) cathode-ray tube is used. Their images are optically projected and superimposed on a projection screen using a lens system. In such a way a composite picture in full color is shown on the screen (Fig. 7.3). In order to obtain high illumination levels on the large screen, much higher current densities have to be used in PTV than in direct-view cathode-ray tubes. 

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