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Photomask degradation via haze defect formation is an increasing troublesome yield problem in the semiconductor fab.
Wafer inspection is often utilized to detect haze defects due to the fact that it can be a bi-product of process control
wafer inspection; furthermore, the detection of the haze on the wafer is effectively enhanced due to the multitude of
distinct fields being scanned. In this paper, we demonstrate a novel application for enhancing the wafer inspection tool's
sensitivity to haze defects even further. In particular, we present results of bright field wafer inspection using the on
several photo layers suffering from haze defects.
One way in which the enhanced sensitivity can be achieved in inspection tools is by using a double scan of the wafer:
one regular scan with the normal recipe and another high sensitivity scan from which only the repeater defects are
extracted (the non-repeater defects consist largely of noise which is difficult to filter). Our solution essentially combines
the double scan into a single high sensitivity scan whose processing is carried out along two parallel routes (see Fig. 1).
Along one route, potential defects follow the standard recipe thresholds to produce a defect map at the nominal
sensitivity. Along the alternate route, potential defects are used to extract only field repeater defects which are identified
using an optimal repeater algorithm that eliminates "false repeaters". At the end of the scan, the two defect maps are
merged into one with optical scan images available for all the merged defects. It is important to note, that there is no
throughput hit; in addition, the repeater sensitivity is increased relative to a double scan, due to a novel runtime
algorithm implementation whose memory requirements are minimized, thus enabling to search a much larger number of
potential defects for repeaters.
We evaluated the new application on photo wafers which consisted of both random and haze defects. The evaluation
procedure involved scanning with three different recipe types:
Standard Inspection: Nominal recipe with a low false alarm rate was used to scan the wafer and repeaters were
extracted from the final defect map.
Haze Monitoring Application: Recipe sensitivity was enhanced and run on a single field column from which on
repeating defects were extracted.
Enhanced Repeater Extractor: Defect processing included the two parallel routes: a nominal recipe for the random
defects and the new high sensitive repeater extractor algorithm.
The results showed that the new application (recipe #3) had the highest capture rate on haze defects and detected new
repeater defects not found in the first two recipes. In addition, the recipe was much simpler to setup since repeaters are
filtered separately from random defects.
We expect that in the future, with the advent of mask-less lithography and EUV lithography, the monitoring of field and
die repeating defects on the wafer will become a necessity for process control in the semiconductor fab.
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