News Column

Patent Issued for Reticle Defect Inspection with Systematic Defect Filter

May 21, 2014

By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent by the inventors Li, Bing (Milpitas, CA); Ma, Weimin (Fremont, CA); Blecher, Joseph M. (San Jose, CA), filed on June 1, 2012, was published online on May 6, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8718353 is assigned to KLA-Tencor Corporation (Milpitas, CA).

The following quote was obtained by the news editors from the background information supplied by the inventors: "Generally, the industry of semiconductor manufacturing involves highly complex techniques for fabricating integrating circuits using semiconductor materials which are layered and patterned onto a substrate, such as silicon. Due to the large scale of circuit integration and the decreasing size of semiconductor devices, the fabricated devices have become increasingly sensitive to defects. That is, defects which cause faults in the device are becoming increasingly smaller. The device is fault free prior to shipment to the end users or customers.

"An integrated circuit is typically fabricated from a plurality of reticles. Generation of reticles and subsequent optical inspection of such reticles have become standard steps in the production of semiconductors. Initially, circuit designers provide circuit pattern data, which describes a particular integrated circuit (IC) design, to a reticle production system, or reticle writer. The circuit pattern data is typically in the form of a representational layout of the physical layers of the fabricated IC device. The representational layout includes a representational layer for each physical layer of the IC device (e.g., gate oxide, polysilicon, metallization, etc.), wherein each representational layer is composed of a plurality of polygons that define a layer's patterning of the particular IC device.

"The reticle writer uses the circuit pattern data to write (e.g., typically, an electron beam writer or laser scanner is used to expose a reticle pattern) a plurality of reticles that will later be used to fabricate the particular IC design. A reticle inspection system may then inspect the reticle for defects that may have occurred during the production of the reticles.

"A reticle or photomask is an optical element containing at least transparent and opaque regions, and sometimes semi-transparent and phase shifting regions, which together define the pattern of coplanar features in an electronic device such as an integrated circuit. Reticles are used during photolithography to define specified regions of a semiconductor wafer for etching, ion implantation, or other fabrication process.

"After fabrication of each reticle or group of reticles, each reticle is typically inspected by illuminating it with light emanating from a controlled illuminator. A test image of a portion of the reticle is constructed based on the portion of the light reflected, transmitted, or otherwise directed to a light sensor. Such inspection techniques and apparatus are well known in the art and are embodied in various commercial products such as many of those available from KLA-Tencor Corporation of Milpitas, Calif.

"During a conventional inspection process, the test image of the reticle is typically compared to a baseline image. Typically, the baseline image is either generated from the circuit pattern data or from an adjacent die on the reticle itself. Either way, the test image features are analyzed and compared with features of the baseline image. Each difference value is then compared with a predetermined threshold value. If the test image varies from the baseline image by more than the predetermined threshold, a defect is defined and reported.

"Each difference detected between two images has the potential of resulting in a printable defect. Conversely, some of the detected defects will have no effect on the resulting integrated circuit. Depending on whether this threshold is set too high or two low, this technique can fail to capture small defects and can also capture a high number of 'false' defects.

"There is a continuing need for improved inspection techniques to accurately and reliably detect defects on reticles or the like, while reducing the number of detected 'false' defects."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "The following presents a simplified summary of the disclosure in order to provide a basic understanding of certain embodiments of the invention. This summary is not an extensive overview of the disclosure and it does not identify key/critical elements of the invention or delineate the scope of the invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

"In one embodiment, a method of inspecting a photolithographic reticle is disclosed. A stream of defect data is received from a reticle inspection system, wherein the defect data identifies a plurality of defects that were detected for a plurality of different portions of the reticle. Before reviewing the defect data to determine whether the reticle passes inspection and as the stream of defect data continues to be received, some of the defects are automatically grouped with other most recently one or more received defects so as form groups of substantially matching defects. Before reviewing the defect data to determine whether the reticle passes inspection and after all of the defect data for the reticle is received, one or more of the groups of defects that have a number above a predetermined threshold are automatically filtered from the defect data so as to form filtered defect data. The filtered defect data may then be provided to a review station for determining whether the reticle passes.

"In a specific implementation, reviewing the defect data to determine whether the reticle passes inspection is performed manually. In another embodiment, the defect data is received one defect image at a time and automatically grouping is accomplished by determining whether each defect image, as it is received, matches an existing seed group if present and adding such defect image to such matching existing seed group. Otherwise, a new seed group comprising such defect image is formed. In a further aspect, determining whether each defect image matches an existing seed group if present and adding such defect image to such matching existing seed group is accomplished by comparing such defect image to a plurality of seed groups one at a time until a match is found if present. In another aspect, comparing such defect image to a plurality of seed groups one at a time until a match is found if present is accomplished by first determining whether such defect image has a substantially matching shape as a one of the seed groups and only if there is a substantially matching shape, comparing pixel-by-pixel such defect image to the seed group with the substantially matching shape. In yet a further aspect, it is determined that such defect image is grouped with a particular one of the seed groups when the pixel-by-pixel comparison results in less than a 2 by 2 pixel difference.

"In another implementation, automatically grouping is accomplished in a temporal order of last to first received defect data. In another aspect, automatically grouping and filtering is performed without human intervention. In another example, the predetermined threshold has an adjusted value that depends on a level of uniformity of an area that surrounds the defect of such particular group. In a further aspect, the predetermined threshold has an adjusted value that is set so that a particular group is not filtered if such particular group's defect is surrounded by a substantially blank background. In yet a further aspect, the predetermined threshold has an adjusted value that is higher for a first group that has a 1 dimensional defect than a second group that has a two dimensional defect. In a specific implementation, the predetermined threshold for a particular group's defect type is proportional to 1/log(A), wherein A is an area of unique background pattern.

"In certain embodiments, the invention pertains to a system for inspecting a photolithographic reticle. The system includes at least one memory and at least one processor that are configured to perform at least some of the above described operations. In other embodiments, the invention pertains to computer readable media having instructions stored thereon for performing at least some of the above described operations.

"These and other aspects of the invention arc described further below with reference to the figures."

URL and more information on this patent, see: Li, Bing; Ma, Weimin; Blecher, Joseph M.. Reticle Defect Inspection with Systematic Defect Filter. U.S. Patent Number 8718353, filed June 1, 2012, and published online on May 6, 2014. Patent URL:

Keywords for this news article include: Electronics, Semiconductor, KLA-Tencor Corporation.

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Source: Electronics Newsweekly

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