Insystems, Inc.

Optical Specialties, Inc.

Lawrence H Lin

Victor A Scheff

Robert B Howe

Daniel L Cavan

Richard L Fusek

A patterned specimen inspection system achieves the inherent advantages of the die to statistical image (DSI) inspection mode for repetitive and random patterns and simultaneously achieves the inspection speed of the optical pattern filtering (OPF) mode. A preferred embodiment entails producing a patterned specimen wafer image with coherent optical spatial frequency filtering, as in the OPF mode, and carrying out defect detection by pixel comparison, as in the DSI mode. For repetitive and random pattern areas, implementation of the invention increases the inspection speed of the DSI mode to approach that of the OPF mode because image spatial filtering enables the use of a large sized unit pixel. For the repetitive pattern, the ability to use a large unit pixel size results from the complete removal of light energy from the repetitive patterns in the image. For the random pattern, spatial filtering can remove a large portion of the light energy from pattern features, but light energy from some pattern features remains. The optical dynamic range (ODR) for defect detection sets the minimum required electrical dynamic range (EDR) of the electronic imaging system for converting the total optical energy present in a pixel into an electrical signal for defect data processing. With spatial filtering, the ODR for a unit pixel size matching that used in the OPF mode is reducible to a manageable level to enable increased inspection speed. Thus, the invention overcomes certain major limitations and retains unique advantages of the OPF and DSI inspection modes.

Method of high speed, high detection sensitivity inspection of

An inspection system (2) employs a beam of monochromatic light (12) that travels through a Fourier transform lens (16) before striking a specimen wafer (4) at an angle (.THETA.) with respect to the normal (26) of the specimen wafer (4) to produce diffracted light (28b ) and 28c) that has a broad spatial frequency spectrum which can be selectively filtered to produce a dark field image pattern of the various sized defects in an inspection area (22) of the wafer. The nearly collimated beam of monochromatic light strikes the wafer at an angle (.THETA.) with respect to the normal of the wafer of between zero degrees and a predetermined maximum angle. For the inspection system disclosed, the predetermined maximum angle is the angle formed when the beam of monochromatic light is as far away from the optic axis as possible yet still within the numerical aperture of the Fourier transform lens (16). Moreover, if a specific range of defect sizes is anticipated, the system can be optimized by setting the angle (.THETA.) at which the collimated beam of monochromatic light strikes the wafer to the angle (.THETA.) which allows the system to collect those spatial frequencies which are best representative of the anticipated range of defects sizes.

Inspection system with in-lens, off-axis illuminator

In an imaging system (10) for detecting defects in a specimen (14) having a repetitive pattern (16), a spatial filter (50) receives a spatial frequency spectrum produced by a Fourier transform lens (34) and blocks preselected spatial frequency components thereof. The spatial filter includes an array of substantially parallel opaque stripes (70a-70c) that are positioned on a substantially transparent substrate (72). In one embodiment, the stripes are spaced apart by equal distances (78) and are of increasing widths (76a-76c) that correspond to the orders of diffraction of the Fourier transform pattern (45) produced by the Fourier transform lens. The spatial filter can be used to filter light spots forming a Fourier transform pattern for specimens having repetitive pattern sizes included within a specified range of sizes.

Spatial filter for optically based defect inspection system

An inspection system (10, 100) employs a Fourier transform lens (34, 120) and an inverse Fourier transform lens (54, 142) positioned along an optic axis (48, 144) to produce from an illuminated area of a patterned specimen wafer (12) a spatial frequency spectrum whose frequency components can be selectively filtered to produce an image pattern of defects in the illuminated area of the wafer. Depending on the optical component configuration of the inspection system, the filtering can be accomplished by a spatial filter of either the transmissive (50) or reflective (102) type. The lenses collect light diffracted by a wafer die (14) aligned with the optic axis and light diffracted by other wafer dies proximately located to such die. The inspection system is useful for inspecting only dies having many redundant circuit patterns. The filtered image strikes the surface of a two-dimensional photodetector array (58) which detects the presence of light corresponding to defects in only the illuminated on-axis wafer die. Inspection of all possible defects in the portions of the wafer surface having many redundant circuit patterns is accomplished by mounting the wafer onto a two-dimensional translation stage and moving the stage (40) so that the illuminated area continuously scans across the wafer surface from die to die until the desired portions of the wafer surface have been illuminated. The use of a time delay integration technique permits continuous stage movement and inspection of the wafer surface in a raster scan fashion.

Inspection system for array of microcircuit dies having redundant

An apparatus and a method employ on a subject at least one holographic optical element that develops two beams of focused light whose focal configurations appear in predetermined locations which correspond to the position of the subject in the system. In a first preferred embodiment, two holographic optical elements are recorded on a subject that is to be aligned and supported by a holder assembly. During exposure of the holographic optical elements, the light rays passing through the plate converge of two focal points that have position coordinates which define their locations in the coordinate space of the optical system. Each focused point of light strikes a position sensitive detector which develops output signals that represent the position coordinates of the focused point of light in the system. After it has been removed from and returned to the holder assembly, the plate is aligned in proper position the two focused points of light strike the areas on the detectors which provide output signals that correspond to the position coordinates produced during exposure. In a second preferred embodiment, a single holographic optical element is recorded on the surface of a glass plate and develops the first and second beams of light that converge to different focal points in the optical system.

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Alamo, CA, United States of America

Lawrence H Lin