Tech Briefs Magazine - November 2024 - 13

tals and pinpoint the stage of the process
where issues may have arisen.
Possible causes could include material
defects, temperature fluctuations, or
problems within the hot zone. Advanced
metrology equipment like SAM
can help crystal growers detect minute
flaws, defects, and map these [into
their process variation] to correct any
problems going forward, " said Hari
Polu, President of OKOS, a Virginia-based
manufacturer of SAM and industrial
ultrasonic non-destructive
(NDT) systems.
SAM Enables Rapid SiC Defect
Detection
SiC stands as a highly promising material
for electronic devices with high
temperature, high frequency, and
high-power requirements. Nevertheless,
the commercialization of numerous
SiC-based electronic
counters
challenges due to
extended defects.
An essential consideration for the
practical use of SiC devices pertains to
challenges associated with the quality of
SiC wafer crystals. During the growth of
SiC crystals, localized disruptions in
structural uniformity occur, leading to
crystal defects like stacking faults and
dislocations. It is widely acknowledged
that certain defects have a detrimental
impact on device functionality.
To increase the yield and reliability of
SiC devices, it is therefore, important to
identify potential defects through advanced
metrology systems like SAM. Recent
advances in SAM also facilitate the
detection of much smaller defects than
previously possible.
" Advanced SAM systems make it possible
to move to a higher level of failure
analysis because of the level of detection
and precision involved. In the past,
detecting a 500-micron defect was the
goal; now it is a 50-micron defect. With
this type of testing, we can inspect materials
and discover flaws that were previously
undetected, " said Polu.
In fact, SAM seems to address at least
one of the elements identified by the
National Institute of Standards and
Technology (NIST) as necessary for
the U.S. to lead the global semiconductor
manufacturing industry once again.
NIST's recent report titled Strategic
Opportunities for U.S. Semiconductor Manufacturing
identifies seven grand challenges
that need critical attention from a metrology
perspective to achieve the vision
Tech Briefs, November 2024
Scanning Acoustic Microscopy (SAM) technology is enabling rapid 100 percent inspection and providing
a critical advantage in quality control and production of SiC crystal growth. (Image: OKOS)
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13
devices envarious
of
a U.S.-led global semiconductor industry.
In addition, the report identifies
32 Path Forward Elements that describe
potential strategies for addressing the
challenges.
For one of the grand challenges, Advanced
Metrology for Future Micro-electronics
Manufacturing, SAM essentially
answers one of the Path
Forward Elements, namely " rapid,
high-resolution, non-destructive techniques
for characterizing defects and
impurities and correlating them with
performance and reliability. "
Scanning Modes and Models
SAM functions by directing focused
sound from a transducer at a small
point on a target object. The sound hitting
the object is either scattered, absorbed,
reflected, or transmitted. By
detecting
the
direction
of scattered
pulses as well as the " time of flight, " the
presence of a boundary or object can be
determined as well as its distance.
To produce an image, samples are
scanned point by point and line by line.
Scanning modes range from single layer
views to tray scans and cross-sections.
Multi-layer scans can include up to 50
independent layers.
Depth-specific information can be extracted
and applied to create two-and
three-dimensional images that can be
analyzed to detect and characterize
flaws such as cracks, inclusions, and
voids.
Smaller manufacturers and independent
testing labs are likely to have a tabletop
SAM model that provides a scan
envelope of over 300 mm with a maximum
scan velocity of 500 mm/s and
accuracy and repeatability of +/- 5.0
micron. Software allows using saved
data to virtually re-scan, view, and analyze
data for simultaneous real-time
analysis or post collection review. Often,
such tabletop units are used to analyze
data for failure analysis, product
inspection, quality control, R&D, process
validation, as well as to determine
product reliability, in process quality
control, and vendor qualification.
As requirements rise to accommodate
testing for higher levels of production,
SiC crystal growers, silicon
carbide wafer manufacturers, and
semiconductor fabs will often utilize a
larger system with the capability of
high-speed inspection. The challenge,
however, is to perform this inspection
at extremely high throughput with 100
percent inspection to identify and remove
SiC crystals or sliced wafers that
do not meet quality requirements. This
necessitates more advanced equipment
that can simultaneously inspect several
layers, often on multiple channels,

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Tech Briefs Magazine - November 2024

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