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Wafer
inspection, a critical process in
semiconductor manufacturing, ensures the
quality of base materials through
physical and optical means. It performs
non-destructive or minimally invasive
examination of the wafer's surface
topography, electrical properties, and
internal structure to guarantee chip
functionality and reliability, directly
impacting the yield of semiconductor
chips.
1.Wafer Fabrication and Inspection
Process
Wafer inspection serves as the
cornerstone of quality control in the
front-end of semiconductor manufacturing
and is a critical step to ensure process
integrity and chip performance. It
encompasses the following aspects:
(1)
Patterned
Wafer Inspection
For wafers with patterned
circuitry, image comparison techniques
are employed to identify pattern defects
such as opens and shorts.
The process focuses not
only on physical defects on the wafer
surface but also on pattern
abnormalities including discontinuities
and electrical shorts in the circuit
patterns.The inspection system typically
compares images of test chips on the
wafer with those of adjacent chips (or a
known defect-free “golden” chip).Image
processing software accurately locates
and classifies defects through a
subtraction process.It is conducted
during production to verify that the
circuit patterns on each wafer conform
to design specifications.Moreover,
patterned wafer inspection is required
at various stages of wafer processing to
detect and correct potential defects
early.
Patterned Wafer
Inspection Principles
(2)Non-patterned
Wafer Inspection
The surface quality and
cleanliness of wafers are critical to
chip performance. During wafer
production processes such as
single-crystal pulling, slicing,
grinding, and polishing, various defects
may occur on the wafer surface,
including residues, crystal defects, and
mechanical damage. Unpatterned wafer
defect inspection is used both in
outgoing silicon wafer quality control
and in front-end semiconductor
manufacturing processes. It detects and
locates defects such as particles,
contamination, scratches, cracks, pits,
and voids on silicon and epitaxial
wafers, thereby helping to improve
semiconductor yield and reliability.
The inspection process
employs laser scanning technology, where
a laser beam performs a radial scan
across the rotating wafer surface. When
the laser encounters particles or other
defects on the wafer, the imperfections
scatter a portion of the laser light.
Depending on the light intensity
distribution, the scattered light can be
detected directly (dark-field
illumination) or measured as a loss in
the intensity of the reflected beam
(bright-field illumination). This method
is used to verify whether a wafer meets
quality standards before production
begins.
Schematic Diagram of
Unpatterned Wafer Inspection Principles
2.Lasers
for Wafer Inspection
In semiconductor wafer
inspection applications, laser
parameters must meet extremely stringent
requirements. Different wafer materials
require specific laser wavelengths,
along with high power stability, high
beam pointing stability, high
reliability, and low amplitude noise.
(1)CW UV Laser
CNI offers a series of
wavelengths including 261 nm, 266 nm,
313 nm, 320 nm, 325 nm, 349 nm, 355 nm,
360 nm, and 375 nm. With continuous
output power ranging from 1 to 6000 mW,
these lasers support 24/7 continuous
operation. They are primarily used for
photoluminescence-based defect detection
in Si or SiC wafers.
266/320/355nm
UV Lasers
(2) PS UV laser
CNI offers lasers with
wavelengths such as 193 nm, 213 nm,
266 nm, and 355 nm. Among these, the
266 nm and 355 nm models deliver output
power ranging from 1 to 8000 mW, with
repetition rates up to 80 MHz or higher
than 120 MHz, and an M² factor of less
than 1.2. These high-power picosecond
ultraviolet lasers are primarily used
for process control and inspection
during silicon manufacturing.
266/355nm
PS UV laser
(3)Visible Lasers
CNI offers a range of
laser wavelengths including 405 nm,
450 nm, 457 nm, 520 nm, 532 nm, 633 nm,
and 671 nm. Standard visible lasers with
output power from 1 to 50 W are
available in homogenized surface output,
linear fan-beam output, or single-mode
fiber-coupled output configurations.
These lasers are designed for dark-field
wafer defect detection, support 24/7
continuous operation, and have a
lifespan exceeding 20,000 hours.
Ultra-High Stability Visible Laser
(4)Infrared
Lasers
CNI provides infrared
lasers with wavelengths including
808 nm, 915 nm, 940 nm, 980 nm, 1064 nm,
1270 nm, 1550 nm, 2100 nm, and 3800 nm.
With power levels up to hundreds of
watts, these lasers are suitable for
applications such as wafer inspection,
wafer heating, and wafer debonding.
Fiber-Coupled
High-Power Infrared Laser
As semiconductor
processes advance to sub-3 nm nodes, the
requirements for wafer surface defect
detection accuracy have reached the
sub-nanometer level. Leveraging its non-contact
measurement, nanometer-scale
precision, and high-efficiency
automation capabilities, laser
technology has become a core enabler
across the entire wafer inspection
workflow—from macroscopic defect
screening to microscopic topography
analysis.
Today, laser technology
is redefining the boundaries of
detection accuracy and efficiency
through multidimensional
sensing capabilities and intelligent
algorithm optimization. To
further overcome challenges in
precision, cost, and reliability,
laser-based systems must also embrace interdisciplinary
collaboration and industry
chain integration, ensuring
they meet the semiconductor industry’s
escalating demands for high yield and
efficient inspection. |
