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Image Management: A New Approach for Yield Analysis by Bert Plambeck, Program Manager
As volumes of defect data are generated in the semiconductor manufacturing process, manufacturers look to sophisticated systems that can help extract meaningful information needed for rapid analysis and resolution of yield problems. Being able to quickly determine the root cause of a yield excursion or a process problem is the essence of yield engineering. While SPC or pareto charts help yield analysis, review of images generated by the inspection, metrology or failure analysis tools during the fabrication process can help expedite the process of determining of the root cause of a yield excursion. With the addition 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. Image management is becoming an increasingly important part of the diagnostic process, providing critical information about the nature and source of yield-limiting process problems. Defect images are valuable in process analysis. For instance, a CD SEM edge profile image illuminates information derived from Bosung curves, and overlay images taken across the wafer can visually quantify CMP process uniformity. Collecting images one at a time on polaroids and storing them in binders in the lab were helpful to yield engineers in the past. However, as timeto-information becomes ever more critical to resolve yield problems quickly, going through binders of polaroids and unorganized data files to identify images associated with the defect under review has become a laborious and time-consuming exercise. Manual image storage methods do not facilitate easy information access, information sharing or transfer within or between fabs necessary for 20
Autumn 1998
Yield Management Solutions
rapid resolution of yield problems. For images to be meaningful, it is important that they are captured from the inspection and metrology tools, saved along with the associated defect data and made available instantaneously to engineers or the yield management system. The VARS system
The VARS image management system stores and retrieves 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 to hold millions of images, it links all the image gathering tools in the fab to a single database allowing economical storage and fast access and retrieval of images along with the relevant inspection data. User stations at each image-generating tool are utilized for image acquisition and 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 a gallery of images created using user-defined search criteria. Images can be easily imported into reports and printed in full color or black-and-white with printer options that allow the user to include image related data on the image printout.
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Imaging the future
Images will play an important role in fabs in the future. Multiple tools across the fab are generating greater and greater volumes of images — images, that when stored and managed efficiently, can provide solutions to current problems and opportunities for optimizing yield in the future. As inspection, metrology and yield enhancement systems become fully integrated, images will add a new dimension to yield management — 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 system that will enable better process visualization, whether the process is in a fab across the hall or an operation half the world away.
Figure 1. VARS connectivity in a fab.
Whether within a single fab or between fabs located half a world apart, VARS enables and enhances communication. Web access can be added to the VARS host that allows users to access/download data and images stored on the host using an Internet browser. Within seconds of addition of images to the VARS database, they become available to any authorized person in the company via the Intranet or the Internet. Users can format the image browser screen to display images and the associated defect data. Access is controlled through password protection. A key advantage which an image management system provides is the transfer of yield and process examples from an established fab to a remote fab. A yield engineer can search a remote database for defects that are similar to those appearing in the local line. When a match is found, the cause and corrective action can be determined from engineering analysis done previously, saving time and effort.
Image Window displays images selected by user for record or playback. Control Panel allows users to record or playback in one second, perform multiple parameter searches, display selected images in gallery format, image tag list, view another station’s live video, enable automatic data interface from other vendor’s inspection tools.
Data Window shows user-definable data structure which allows users to save data associated with the defect image under review.
Figure 2. VARS user interface.
Autumn 1998
Yield Management Solutions
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