AnalysisF E A T U R E S

Image Management: A New Approach forYield Analysis by Bert Plambeck, Program Manager

As volumes of defect data are generated in the semiconductor manufacturing process, manufacturers look to sophisticatedsystems that can help extract meaningful information needed for rapid analysis and resolution of yield problems. Beingable to quickly determine the root cause of a yield excursion or a process problem is the essence of yield engineering. WhileSPC or pareto charts help yield analysis, review of images generated by the inspection, metrology or failure analysis toolsduring the fabrication process can help expedite the process of determining of the root cause of a yield excursion. With theaddition of the VARS image management system to its suite of yield enhancement solutions, KLA-Tencor enhances the capability of its inspection and metrology systems and increases the overall value of its solutions to customers.

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Image management is becoming anincreasingly important part of thediagnostic process, providing criticalinformation about the nature andsource of yield-limiting process problems. Defect images are valuablein process analysis. For instance, aCD SEM edge profile image illumi-nates information derived fromBosung curves, and overlay imagestaken across the wafer can visuallyquantify CMP process uniformity.Collecting images one at a time onpolaroids and storing them in bindersin the lab were helpful to yield engi-neers in the past. However, as time-to-information becomes ever morecritical to resolve yield problemsquickly, going through binders ofpolaroids and unorganized data filesto identify images associated with the defect under review has become a laborious and time-consuming exer-cise. Manual image storage methodsdo not facilitate easy informationaccess, information sharing or transferwithin or between fabs necessary for

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rapid resolution of yield problems. For images to bemeaningful, it is important that they are captured fromthe inspection and metrology tools, saved along withthe associated defect data and made available instanta-neously to engineers or the yield management system.

The VARS systemThe VARS image management system stores andretrieves images generated from a wide variety of on-line and off-line equipment including defect review stations, scanning electron microscopes (SEM),metrology equipment and focused ion beam (FIB) systems. With a large online capacity expandable tohold millions of images, it links all the image gatheringtools in the fab to a single database allowing economicalstorage and fast access and retrieval of images alongwith the relevant inspection data. User stations at eachimage-generating tool are utilized for image acquisitionand transfer to VARS’ central host for storage and distribution. Once stored, images can be reviewed one-at-a-time with a one-second retrieval time or as agallery of images created using user-defined search criteria. Images can be easily imported into reports andprinted in full color or black-and-white with printeroptions that allow the user to include image related dataon the image printout.

F E A T U R E S

Figure 1. VARS connectivity in a fab.

Figure 2. VARS user inter face.

Control Panel allows users to record or playback inone second, perform multiple parameter searches,display selected images in gallery format, imagetag list, view another station’s live video, enableautomatic data interface from other vendor’s inspec-tion tools.

Data Window shows user-definabledata structure which allows users to savedata associated with the defect imageunder review.

Image Window displays images select-ed by user for record or playback.

Whether within a single fab orbetween fabs located half a worldapart, VARS enables and enhancescommunication. Web access can beadded to the VARS host that allowsusers to access/download data andimages stored on the host using anInternet browser. Within seconds of addition of images to the VARSdatabase, they become available to any authorized person in thecompany via the Intranet or theInternet. Users can format theimage browser screen to displayimages and the associated defectdata. Access is controlled throughpassword protection. A key advan-tage which an image managementsystem provides is the transfer ofyield and process examples from anestablished fab to a remote fab. Ayield engineer can search a remotedatabase for defects that are similarto those appearing in the local line.When a match is found, the causeand corrective action can be deter-mined from engineering analysisdone previously, saving time andeffort.

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Imaging the futureImages will play an important rolein fabs in the future. Multiple toolsacross the fab are generating greaterand greater volumes of images —images, that when stored and managed efficiently, can providesolutions to current problems andopportunities for optimizing yield inthe future. As inspection, metrologyand yield enhancement systemsbecome fully integrated, images will add a new dimension to yieldmanagement — when available in real time, images will support, clarify and expedite the analysis of yield limiting problems. VARS is the springboard for creating a complete image management system for the fab of the future — a systemthat will enable better process visualization, whether the process is in a fab across the hall or an operation half the world away.

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