Abstract: A reticle that is within specifications is inspected to generate baseline candidate defects and their location and size. After using the reticle in photolithography, the reticle is inspected to generate current candidate defects and their location and size. An inspection report of filtered candidate defects and their images is generated so that these candidate defects include a first subset of the current candidate defects and their images and exclude a second subset of the current candidate defects and their images. Each of the first subset of candidate defects has a location and size that fails to match any baseline candidate defect's location and size, and each of the excluded second subset of candidate defects has a location and size that matches a baseline candidate defect's location and size.

Abstract: A reticle that is within specifications is inspected to generate baseline candidate defects and their location and size. After using the reticle in photolithography, the reticle is inspected to generate current candidate defects and their location and size. An inspection report of filtered candidate defects and their images is generated so that these candidate defects include a first subset of the current candidate defects and their images and exclude a second subset of the current candidate defects and their images. Each of the first subset of candidate defects has a location and size that fails to match any baseline candidate defect's location and size, and each of the excluded second subset of candidate defects has a location and size that matches a baseline candidate defect's location and size.

Abstract: A reticle that is within specifications is inspected so as to generate a baseline event indicating a location and a size value for each unusual reticle feature. After using the reticle in photolithography, the reticle is inspected so as to generate a current event indicating a location and a size value for each unusual reticle feature. An inspection report of candidate defects and their images is generated so that these candidate defects include a first subset of the current events and their corresponding candidate defect images and exclude a second subset of the current events and their corresponding excluded images. Each of the first included events has a location and size value that fails to match any baseline event's location and size value, and each of the excluded second events has a location and size value that matches a baseline event's location and size value.

Abstract: A reticle that is within specifications is inspected so as to generate a baseline event indicating a location and a size value for each unusual reticle feature. After using the reticle in photolithography, the reticle is inspected so as to generate a current event indicating a location and a size value for each unusual reticle feature. An inspection report of candidate defects and their images is generated so that these candidate defects include a first subset of the current events and their corresponding candidate defect images and exclude a second subset of the current events and their corresponding excluded images. Each of the first included events has a location and size value that fails to match any baseline event's location and size value, and each of the excluded second events has a location and size value that matches a baseline event's location and size value.

Abstract: A method for identifying lithographically significant defects. A photomask is illuminated to produce images that experience different parameters of the reticle as imaged by an inspection tool. Example parameters include a transmission intensity image and a reflection intensity image. The images are processed together to recover a band limited mask pattern associated with the photomask. A model of an exposure lithography system for chip fabrication is adapted to accommodate the band limited mask pattern as an input which is input into the model to obtain an aerial image of the mask pattern that is processed with a photoresist model yielding a resist-modeled image. The resist-modeled image is used to determine if the photomask has lithographically significant defects.

Abstract: A method for identifying lithographically significant defects. A photomask is illuminated to produce images that experience different parameters of the reticle as imaged by an inspection tool. Example parameters include a transmission intensity image and a reflection intensity image. The images are processed together to recover a band limited mask pattern associated with the photomask. A model of an exposure lithography system for chip fabrication is adapted to accommodate the band limited mask pattern as an input which is input into the model to obtain an aerial image of the mask pattern that is processed with a photoresist model yielding a resist-modeled image. The resist-modeled image is used to determine if the photomask has lithographically significant defects.

Abstract: Techniques that use the design databases used in each of the expose/etch steps during construction of phase shift masks are described. A model or reference image is rendered, accounting for systematic variations, from the design databases to represent what a layer of the PSM should look like after processing. The reference image is compared to an optically acquired image of a specimen phase shift mask to find defects. The technique of the present invention can be used to inspect EAPSM, APSM and tritone masks. The technique inspects all layers in one pass and is therefore more efficient.

Abstract: A method and apparatus for inspecting patterned transmissive substrates, such as photomasks, for unwanted particles and features occurring on the transmissive, opaque portions and at the transition regions of the opaque and transmissive portions of the substrate. A transmissive substrate is illuminated by a laser through an optical system comprised of a laser scanning system, individual transmitted and reflected light collection optics and detectors collect and generate signals representative of the light transmitted and reflected by the substrate as the substrate is scanned repeatedly in one axis in a serpentine pattern by a laser beam which is focused on the patterned substrate surface. The defect identification of the substrate is performed using only those transmitted and reflected light signals, and other signals derived from them, such as the second derivative of each of them.

Abstract: An automated photomask inspection apparatus including an XY state (12) for transporting a substrate (14) under test in a serpentine path in an XY plane, an optical system (16) comprising a laser (30), a transmission light detector (34), a reflected light detector (36), optical elements defining reference beam paths and illuminating beam paths between the laser, the substrate and the detectors and an acousto-optical beam scanner (40, 42) for reciprocatingly scanning the illuminating and reference beams relative to the substrate surface, and an electronic control, analysis and display system for controlling the operation of the stage and optical system and for interpreting and storing the signals output by the detectors. The apparatus can operate in a die-to-die comparison mode or a die-to-database mode.

Abstract: A method and apparatus for inspecting patterned transmissive substrates, such as photomasks, for unwanted particles and features occurring on the transmissive, opaque portions and at the transition regions of the opaque and transmissive portions of the substrate. A transmissive substrate is illuminated by a laser through an optical system comprised of a laser scanning system, individual transmitted and reflected light collection optics and detectors collect and generate signals representative of the light transmitted and reflected by the substrate as the substrate is scanned repeatedly in one axis in a serpentine pattern by a laser beam which is focused on the patterned substrate surface. The defect identification of the substrate is performed using only those transmitted and reflected light signals, and other signals derived from them, such as the second derivative of each of them.

Abstract: In each configuration, at least one TDI sensor is used to image the portions of interest of the substrate that are substantially uniformly or critically illuminated. In one configuration, the substrate is compared to the expected characteristic features prestored in memory. In a second configuration, a first and second pattern in a region of at least one substrate are inspected by comparing one pattern against the other and noting whether they agree with each other. This is accomplished by illuminating the two patterns, imaging the first pattern and storing its characteristics in a temporary memory, then imaging the second pattern and comparing it to the stored characteristics from the temporary memory. Then the comparisons continue sequentially with the second pattern becoming the first pattern in the next imaging/comparison sequence against a new second pattern. With each comparison whether there has been agreement between the two patterns is noted.

Abstract: An automatic inspection system including an illuminator for illuminating a reticle or photomask to be inspected, while optically projecting a magnified image of the reticle or photomask onto a plurality of detector elements. A carriage assembly moves the object at a constant velocity to allow the detector elements to sequentially view the entire surface to be inspected. The detector elements are responsive to the intensity of light incident thereupon and are periodically scanned to obtain a two-dimensional measured representation of the object. A database adaptor formulates a two-dimensional representation from the design database description corresponding to the scanned object simultaneously and in synchronism with the scanning of the photomask or reticle. The measured and database adapted representation of the scanned object are input to a signal processor for alignment and defect detection.

Abstract: Optical inspection apparatus for detecting defects in a visually perceptible pattern including image acquistion means for inspecting the pattern on a pixel-by-pixel basis, developing digital data signals corresponding to each pixel and feeding the signals so developed to an imaging enhancement means. The imaging enhancement means compensates for equipment related degradations in the images and converts the digital data signal value corresponding to each pixel into a corrected signal value by operating on the digital data signal with a two dimensional finite impulse response filter. The corrected signal values of the image enhancement means are received by a defect detection means which evaluates the signal values for defects in the pattern. Any defects so determined are recorded and/or displayed on data recording means.

Abstract: Apparatus 20 for inspecting photomasks 26 and the like by comparison of duplicate die patterns, including improved defect detection. Two-dimensional pixel representations of two die patterns are formed, with pixels having values or black or white or shades or grey, depending upon the features of the die patterns. Defects in the die patterns are found by a defect detector circuit 60 at points of non-agreement between the pixel representations. Two window matrices 130 and 134 of adjacent pixels are defined for corresponding areas of the two die patterns. The center matrix of each window matrix is defined as a comparison matrix 132 and 136. An error value is computed for subsets of the window matrix by summing the squares of the differences between each of the pixel values of each subset and the corresponding pixel values of the opposite comparison matrix. If there is no defect and any misalignment between the two representations minimal, at least one error value will be less than a threshold error value.

Abstract: An automatic inspection system for inspecting holes in a mask including carriage means 30, illumination means 44, optical means 48, photosensitive detector means 46, and signal processing means 56. The mask 34 to be inspected is positioned by the carriage means in a horizontal plane. The optical means projects a focused image of a portion of the mask onto the photosensitive detector means. Photodiodes in the detector means are responsive to light from the illumination means that is transmitted through the holes in the mask. The signal processing means scans the outputs of the photodiodes and stores in memory a digital representation of the mask. The signal processing means performs inspection measurements and comparison tests. A smoothness checker circuit 240 measures the local radius of curvature of each hole at several places and compares the measurements to predetermined curvature limits to detect nicks and sharp protrusion defects.

Abstract: Defect detection apparatus including a mechanical and optical system for scanning duplicate areas of a photomask to be inspected, electronic means for converting the optically scanned information to digitized form, memory for storing such information, and means for comparing information obtained from one inspected area to the other inspected area to determine differences therebetween, such differences being classified as defects. The detection is accomplished using a vector gradient within a matrix technique to develop candidate and cancellor information which is then logically manipulated to qualify the data obtained from each pixel matrix and then, after qualification, is used to determine whether or not a defect has been detected. The subject invention has particular application to the detection of defects occurring at pattern corners within the inspected photomask and is specifically directed to overcoming difficulties previously encountered in detecting such defects.