ARP deploys sub-surface nanoscanner for wafer reject minimization
3D image of a segment of a wafer with dies. |
See full article here: http://arphotonics.net/ASMC2014_5.8.pdf
Fig.
1. Intricate patterns on a wafer undergoing fab process.
In the
inspection stage, a wafer is rejected when the accumulated number of defects on
a wafer exceeds the prescribed limit. When
the number of rejected wafers is over the specified number, the lot is rejected
and the inspection stage informs the detection of process excursions. Then the probable cause of excursions is investigated
in the defect sourcing stage. Therefore,
the resolution and accuracy of the inspection system is of crucial importance. However, the current state-of-the-art (SOTA),
high cost and highest sensitivity inspection machine available at the market
place fails to detect defects that are hidden below layers. Consequently, even a wafer passes through the
inspection, the final devices may fail because the inspection system was not able
to detect the smaller and hidden defects.
For example a SOTA inspection system that cost on the order of a million
Dollar, have the highest resolution of 0.15
µm (150 nm); thus will miss defects smaller than this size. As the modern fab process is defining feature
sizes down to 60 nm or less, the fab inspection technicians are facing with the
challenge of detecting and identifying defects that are only a few nanometers
in dia. The TeraScan from ARP addresses
this deficiency by introducing a resolution of 1 nm.
Fig.
2. Position of terahertz is in between the microwave and infra-red (IR).
Another
issue is detecting very small defects that are embedded in the sub-surface
layers. Modern fab processes involve
layer-by-layer construction and defining devices on a wafer (the so called
bottom-up process) where tens of layers are stacked one on top of the previous. Common optical inspection system can see only
on the surface and the resolution is limited. Thus, defects buried under the top surface
must be detected early in the process before it progresses towards completion. This is not possible by instruments built
around visible light or IR which is offered by the current SOTA.
Terahertz
portion of the electromagnetic spectrum (Fig. 1) provides some unique features
that are not available from other sources.
Terahertz can penetrate most materials except metals; thus, it provides
the opportunity to inspect not only the surface but also the sub-surface
interior layers of a multi-layered substrate.
Unlike X-ray, terahertz is non-ionizing; therefore, it does not perturb
or damage delicate features which in some cases are only a few nanometers. Yet, because of its very high sensitivity,
terahertz can detect defects of nanometer size. These
combination of terahertz properties and a smart positioning system incorporated
in ARP’s terahertz inspection, provides unique opportunity to successfully inspect
wafers at early stage of defect formation as well as after-process device
failure analysis. Once the fab technicians are able to identify
the cause of defect formation, appropriate measure may be taken to prevent its
reoccurrences. ARP’s terahertz scanner
is designed to help exactly this situation.
Sample data are shown below. Fig.
3 shows that the scanning resolution is 1 nm and difference between adjacent
layers are detectable. Fig. 4 shows the
reconstructed surface texture generated from a series of surface scan. Any defects such as, inclusions, cracks,
non-uniformity, or very small particulate material can be clearly detected and
identified by this technique.
Fig. 3. Scan resolution ~1 nm showing two separate layers. |
Fig.
4. Reconstructed surface texture generated from a series of surface scan.
About
Applied Research & Photonics
Located
in Harrisburg, PA, Applied Research & Photonics, Inc. (ARP) is a
nanotechnology company with the core products in the terahertz area. ARP has demonstrated a number of
products based on its proprietary dendrimer nanotechnology. ARP’s terahertz spectrometer,
TeraSpectra, uses a high-power terahertz source enabling high resolution
spectrometry. It has a wider
terahertz range (up to ~30 THz) for probing molecular phenomena on time scales
from a few femto-seconds to a few tens of pico-seconds. Designed and manufactured in
Harrisburg, TeraSpectra offers the capability of solving a
Anis Rahman, PhD
Applied Research and Photonics, Inc.
470 Friendship Road, Suite 10
Harrisburg, PA 17111, USA
Phone: +1 (717) 623-8201
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