Inline Wafer Edge Inspection System for Yield Enhancement of Thin Wafers

Wafer edge defects can occur anywhere throughout
production, and only continuous monitoring allows waferdamaging
equipment or processes to be identified quickly in
order to apply corrective measures, to avoid in-process wafer
breakage by removing affected wafers from further processing,
and to maximise yield. A thorough wafer edge inspection that
covers the entire circumference in as densely spaced intervals as
reasonably possible, becomes crucial. This particularly holds true
for microscopic defects, which eventually grow and ultimately
lead to breakage. For such a monitoring to be most effective, it
should cover many processing steps, work for any wafer material,
and do so reliably and fully automated, without the need of
an operator processing images and changing recipe settings in
production tools for being able to handle various wafers with
different optical surface properties.
This research presents a novel optical non-reflective measurement
technology, that could satisfy exactly these requirements by
combining wafer edge inspection with widely used pre-alignment
in one single step. The so-called Ranging Edge Detection (RED)
technology is independent of optical wafer surface properties such
as transparency, reflectivity or absorption, and able to operate
inline without the need of frequent recalibration or adaptation
of settings for different materials. Based on this technology
the proprietary Wafer Edge Screener has been developed to
profile and quantify the wafer edge thickness alongside the wafer
cirumference. Combined with absolute edge positioning data to
gain additional information about defect size, shape and location,
a Wafer Edge Screener can also derive parameters such as e.g.
wafer alignment or bow.
Measurements of wafers made of different materials and with
various defects were performed and are presented. Each defect
was quantified in shape and extension, showing that Wafer
Edge Screeners are promising and reliable automatic inline
wafer edge inspection tools which are gathering only useful
information in order to determine the integrity of wafer edges.