Abstract: A process to correct distortions due to optical proximity effects is described. A two reticle per pattern approach is used. The first, or primary, reticle contains the image that is to be transferred to the photoresist. It is used to expose the resist in the usual way to the correct dosage of light needed to optimally activate it. For a primary reticle bearing a line pattern, the second, or correction, reticle bears a pattern of rectangles which are located and dimensioned so that, when aligned relative to the primary reticle, they overlap all line ends in the pattern. The amount by which the rectangles overlap the lines is similar to the amount by which serifs (if they had been used) would overlap. The amount by which the rectangles extend outside the line ends is not critical (provided it is at least as large as the inside overlap amount). This property allows a single rectangle to be shared by many line ends.

Abstract: Conventional optical lithography has a lower limit of about 180 nm because the projection system is opaque to radiation of wavelength shorter than this. This limitation has been overcome by using, in a standard photoreduction system, light in the form of a train of short duration high intensity pulses. Because of two-photon interactions, light having half the wavelength of the illuminating radiation is then generated in the focal plane. There are thus two aerial images present while the photoresist is being exposed. One is the conventional long wavelength image and its associated CD while the other is the short wavelength image with its smaller CD. Since the resist is sensitive to only the shorter wavelength, only the lower CD image remains after development.

Abstract: A process and apparatus are described for a projection system having improved depth of focus. This has been achieved by introducing into a standard projection system, of the type suitable for photolithography, both a quadrupole mask in the pupil plane of the illuminator lens and a phase-type filter in the pupil plane of the projection lens. Detailed data for the design of both these filters is provided. If these guidelines are followed the result is a projection system whose depth of focus has been increased to a sufficient degree to allow the formation, in a single exposure, of a photoresist wafer suitable for simultaneously etching both isolated and densely packed contact holes.

Abstract: An improvement in the structure for mounting blades of a ceiling fan, characterized in that a motor comprising a bottom formed with a plurality of threaded holes, an annular ring-like mounting secured to the bottom of the electric motor by screws and provided with a plurality of brackets each having a groove which gradually decreases in size from an upper portion toward an lower portion thereof, each of the blades provided with a rod having a tongue which gradually decreases in size from an upper end to an lower end thereof, the tongue being configured so that the upper end of the tongue has same size of the upper portion of the groove while the lower end of the tongue has same size of the lower portion of the groove thereby enabling the tongue to fit into the groove but not slide out thereof.