Analysis F
E
A
T
U
R
E
S
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.