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Rapid acoustic inspection for 300MM wafer generation (Part 2)

Posted: 09 Jan 2012 ?? ?Print Version ?Bookmark and Share

Keywords:wafer inspection? transducer? acoustic imaging?

But software needs to relate the data it receives with specific die on the wafer pair, and to do this it "draws a box" around the image of the die and analyzes the features inside the box. If the features match those that the user has identified as belonging to good die,�the die within the box is accepted; if not, it is rejected.

After scanning has been completed, the robot transfers the wafer to a drying stage where remaining water is removed. The robot then lifts the wafer from the drying stage, re-aligns it, and replaces it in the original FOUP or transfers it to an adjacent FOUP.

Technically, the AW300's transducer is performing C-Mode Time Domain Pulse-Echo scanning, meaning that it is using echoes from internal material interfaces, including gap interfaces, to acquire data over the x-y dimensions at a defined depth (typically the bondline) within the wafer pair. The transducer and associated software are capable of using other acoustic imaging modes such as Frequency Domain Imaging and B-Scan Imaging, which are more analytical and not normally needed in high-throughput inspection. It can also perform a non-imaging function by measuring the distance from the transducer to the top surface of the wafer at each x-y position, thereby mapping the surface flatness of the wafer. This too is an analytical function, but requires little or no time and can provide useful information when flatness-related anomalies appear.

Exactly how the new system is used varies from user to user. In some applications it may be suitable to use the acoustic data to define the whole wafer pair as accept or reject. In many situations, identifying and removing defective die is the norm. For extremely small die, when a defect of 5? or larger is identified, the user may choose to remove not only that single die but also the 8 die that border it. This approach makes sense because a typical defect among such small die has a good chance of extending into nearby die.

About the author
Tom Adams is a consultant for Sonoscan Inc.

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