Moiré pattern

About: Moiré pattern is a research topic. Over the lifetime, 1917 publications have been published within this topic receiving 27176 citations. The topic is also known as: moiré fringes & moire pattern.

Overlay measurement technique using moire patterns

Abstract: Misalignment between two masking steps used in the manufacture of semiconductive devices in a wafer is determined by having a special alignment pattern on each of two masks used in the process and forming images of the masks on the semiconductor devices with the images of the alignment patterns being superimposed over one another to form a Moire pattern. The Moire pattern is compared with other Moire patterns known to correspond to particular amounts of misalignment of the masks to see if it corresponds to an acceptable alignment.

Measurement of slopes of structural deflections by speckle-shearing interferometry

Abstract: A specimen illuminated by coherent light is imaged by a camera through a shearing mechanism so that the speckle from one point on the surface can be made to interfere with the speckle from a neighboring point. The resultant speckle pattern is recorded. By mechanically interfering the recorded speckle pattern corresponding to deformed and undeformed states of the specimen, respectively, using double-exposure technique, a speckle-moire-fringe pattern is generated. These fringes which depict derivatives of deflections of the specimen are made visible by spatial-filtering technique. Speckle-moire fringes can also be obtained in real time. This method is a new interferometry and will be referred to as “speckle-shearing interferometry”. Speckle-shearing interferometry has the same function as Ligtenberg's technique. However, it does not have the sometimes inconvenient requirement of Ligtenberg's technique that the surface of the specimen must be of mirror quality. The new technique will be particularly useful in studies of flexural deformation such as flexed beams and plates. Although speckle-shearing interferometry is an interferometric method, it overcomes several of the limitations associated with holographic and speckle interferometries, namely: (1) the setup is simple and does not need laborious alignments of optical components, (2) it does not require stringent mechanical and ambient stabilities, (3) coherent requirement of light is greatly relaxed, and (4) the sensitivity is reduced that somehow fills the gap in sensitivity between moire techniques and holographic or speckle interferometry.

Shadow moire topography by means of the phase-shift method

Abstract: We propose using the phase-shift technique to improve such shortcomings inherent to conventional shadow moire topography as low sensitivity and difficulties in computational processing. Because in shadow moire the reference grating and the deformed grating are mutually dependent, it is not possible to produce phase shifts of the fringe by moving the grating. However, fringe shifting that is actually constant regardless of fringe orders is achieved by changing both the gap between a specimen and the grating and the angle of illumination. This proposal is justified by a simulation test and some experimental results are shown for the verification of this trial.

Moire inspection system

Abstract: A moire interferometry system for detecting defects in a surface of a panel. The moire interferometry system is adapted to be used as a defect detection tool and not specifically as a surface measurement tool. The system includes a moire projection system having a light source and master grating projecting grating lines onto a surface panel to be inspected. A viewing system with a detection means records an image of the surface with the master grating lines on it as viewed through a submaster grating. The intersection of the projected lines on the panel and the lines in the submaster grating produce moire fringes. Phase shift interferometry techniques are used to produce a phase map of the surface for a plurality of phase shifted moire fringes. A derivative operation is performed on the image, and that image thresholded to identify areas of pixels having the greatest change in contour. The resulting image can then be used to locate and quantify deviations in the contour of the panel which exceed predetermined tolerances to identify defects. The system provides an unambiguous quantitative means for characterizing defects which does not require skilled operators or the application of highlighting fluid to the surface.