Overlay Excursion Monitoring & Control

Due to throughput constraints, metrology tools only measure the overlay of a subset of wafers. The measurements are used to determine if the overlay of a wafer or lot is in spec and to determine feedback parameters for the APC. Because only few wafers are measured, this overlay control is not very reliable.

In contrast, the alignment measurement is performed on all wafers. The measured alignment data consist of a lot of information about the overlay performance of the exposure.

The second OVALiS module, ONYX, improves overlay control by comparing this alignment data of different wafers and lots. ONYX identifies overlay problems in an early stage using very advanced ONYX metrics.

By ensuring that the ONYX metrics give an accurate correlation between alignment data and the resulting overlay, ONYX is able to:

• Select wafers that should be measured by overlay metrology
• Improve the reliability of overlay control
• Reduce overlay measurement effort

Of course, the correlation of the ONYX metrics is automatically tracked over time, to accommodate process changes. Instead of a random or fixed choice of wafers to be measured, ONYX thus offers an intelligent sampling of overlay wafers to achieve the best possible overlay excursion monitoring and control.

Next OVALiS module: OSMIUM