CERN
Photolithography
and
Chemical etching
Rui de Oliveira
CERN
TS DEM
TS-DEM
Rui de Oliveira
Geneva - 21 November 2008
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Contents
CERN
History of photolithography
Usage of photolithography
Principles of photolithography
Detailed process of the production steps
Photolithography at CERN
Conclusions
Rui de Oliveira
TS-DEM
CERN
Definition of Photolithography
g p y
A process in
involving
ol ing the
photographic transfer
of a
pattern
to a
surface
for
etching
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History of photolithography
CERN
•
Lithography
Invented by Aloys Senefelder, 1796 (Germany)
lithography (greek lithos: stone and graphein: write)
technique based on a special use of limestone to multireplicate an image on paper
•
Photography
Albert Magnus (Germany) (1193–1280) discovered silver
nitrate (light sensitive compound)
The first permanent photograph was an image produced in
1826 by the French inventor Nicéphore Niépce
•
Photolithography
Alphonse Louis Poitevin (France) invented
photolithography in 1855
1935- Louis Minsk of Eastman Kodak developed the first
negative photoresist
p
1940- Otto Suess of Kalle Div. of Hoechst AG,, developed
the first positive photoresist
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Contents
CERN
History of photolithography
Usage of photolithography
–
–
–
–
daily
y life
semiconductor industry, PCB industry
chemical milling, electroforming
MEMS
Principles of photolithography
Detailed process of the production steps
Photolithography at CERN
Conclusions
Rui de Oliveira
TS-DEM
CERN
Daily life
• All electronics boards and components
• Offset lithography or offset printing
• Lots of pictures are made by the help of photolithography:
posters, screen printed images
• Special products like:
– LCD displays
– Heads for inkjet printers
– Accelerator sensors for air bag ignition
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CERN
S
Semiconductor
industry
•
•
•
•
Creation of metal lines for interconnection
Mask areas for selective dopings
Patterning of protective layers
Micromachining of silicon
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CERN
PCB
C industry
•
•
•
•
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Creating all the conductive tracks
Protective layers (soldermask)
Legend ink layer
Micro via generation
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CERN
•
•
•
•
•
•
•
•
•
•
•
Chemical milling and electroforming
Wave guides
Heat sinks
Decorative items
Ink jet nozzles
Optical parts
Fuel cell parts
Mi
Micro
sprockets
k t
Lead frames
Encoder discs
Name plates
Flow sensors
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Thin metal plates +
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MEMS
micro electro mechanical systems
Main applications
•
•
•
•
•
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Ink jet printer heads
Pressure sensors
Accelerometers (automotive, gaming)
Mi
Micro
motors
Magnetic sensors and actuators by
electroforming
g magnetic
g
materials
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Contents
CERN
History of photolithography
Usage of photolithography
Principles of photolithography
- principle
- etching/ electroforming
- positive/
iti / negative
ti iimages and
d resists
i t
Detailed process of the production steps
Photolithography at CERN
Conclusions
Rui de Oliveira
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CERN
Photolithography principle
Base material
Photoresist deposition
UV
Resist exposure
Resist development
Etching
support
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metal
resist
mask
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CERN
Et hi / l t f
Etching/electroforming
i
etching
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Electroforming
Adding metal by galvanoplasty processes
Creating molds for micro 3d objects
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P iti /
Positive/negative
ti image
i
Same image
Negative resist
U light
UV
g t sta
starts
ts tthe
e po
polymerisation
y e sat o
in the polymer
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Positive resist
U light
UV
g t deg
degrades
ades links
s in tthe
e po
polymer
y e
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Contents
CERN
History of photolithography
Usage
g of photolithography
p
g p y
Principles of photolithography
Detailed p
process of the production
p
steps
p
–
–
–
–
–
Artwork
Resist deposition
Exposure
p
3 problems
p
Resist development
Etching
Photolithography at CERN
Conclusions
Rui de Oliveira
TS-DEM
CERN
Artwork generation
• Glass masks (sub micron precision) 20 cm x 20 cm
– photographic emulsion on soda lime glass (cheapest)
– Fe2O3 on soda lime glass
– Cr on soda lime glass
g
– Cr on quartz glass (most expensive, needed for deep UV litho)
• Polyester films (10 um precision)
i i ) 80 cm x 60 cm
– Laser exposure of a photosensitive layer on a polyester film
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Resist deposition
• Spinning
S i i - semiconductor
i
d t production
d ti
– Highest resolution
• Dip coating - fine lines for PCBs or 3D objects
– Fine lines, large sizes
• Curtain coating - solder mask deposition
– Fast, not accurate, cheap
• Spray - liquid resist, solder mask deposition
– 3d best coverage, best quality for solder mask
• Screen printing - solder mask deposition
– Medium quality solder mask, fast when the image is directly
printed without photolithography
• Dry
y film lamination- PCB p
production
– Fast, good resolution
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Spinning resist
CERN
Very precise deposition
Uniform thickness
Ultra thin :down to 1 μm
Large window in the process
Good repeatability
Clean rooms needed class 100 to 1
Solvent based resists
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Hot roll lamination
CERN
PCB
Hot roll
Solid photoresist
Hot roll
Large volume/area capability
Fast deposition
Dry process
Medium class clean room
Large size
More “environment friendly”
Resolution 30μm line/space
not compatible to 3D shapes
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Solid photoresist roll
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EXPOSURE
collimated/diffuse light problem
Collimated UV
Application:
pp
fine line PCBs, standard
semiconductors
Diffuse light
Error up to 5 μm
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C lli t d UV lamps
Collimated
Precise large size lens
up to 12 inches
The lens quality is the
base of this system
Source alone for multipurpose application
or
Combined with a high precision mechanical
system for alignment: “Mask aligner”
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EXPOSURE
light absorbtion problem
Application:
fine line PCBs with solid resist
Thick resists for electroforming
After development
th precision
the
i i is
i lost
l t
Thin resist ok
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Problem with thick
negative resist
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Laser UV direct exposure
UV direct exposure
No mask!
resist
25 μm lines
100 μm thick resist
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Increasing local energy can beat
light absorbtion in the resist
Precision: 0.5 μm to 2 μm
(depending on laser type)
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X ray exposure ‘LIGA’
LIGA technology uses X-ray lithography to
obtain polymer structures with extremely
high
g aspect
p
ratios (lateral
(
precision
p
bellow
1μm in a 0.1 to 2mm thick polymer).
LIGA, a German acronym for ″Lithographie,
G l
Galvanoformung,
f
Abformung,"in
Abf
"i English
E li h
(X-ray) Lithography, Electroplating, and
Molding.
Because of the high collimation of X-rays
needed, the source must be synchrotron
light
This technology is the base of many MEMS,
It beats the limitation of light absorbtion in
the photoresist
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CERN
EXPOSURE
light diffraction problem
Ultra thin patterns
Semiconductor prototypes
Diffraction in glass
Less with quartz
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El t
Electron
beam
b
exposure
Current dedicated systems have
produced line widths of 10 nm or smaller
The primary
Th
i
advantage
d
t
off electron
l t
beam
b
lithography is that it is one way to beat
the diffraction limit of light and make
features in the nanometer regime
High accuracy but sensitive to electric
and magnetic fields
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Electron scattering in resist
Positive resist
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Chemical development
CERN
Exposed Resist
Metal
Base plate
Horizontal spray chemical
Development :acqueus or solvent
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Etching
CERN
•
•
•
•
Most metals can be etched (isotropic etching)
Most Polymers also (isotropic etching)
Silicon etching can be anisotropic
Polyimide etching can be anisotropic
anisotropic
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isotropic
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CERN
S
Spray
Chemical
Ch i l
etching
But also dry etching
Laser direct ablation
Not described
Human hand
or
Industrial equipment
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Highest accurate equipment
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Contents
CERN
History of photolithography
U
Usage
off photolithography
h t lith
h
Principles of photolithography
Detailed process of the production steps
Photolithography at CERN
–
–
–
–
fine line PCBs
large size PCBs
chemical micro-via circuits
gas detectors
Conclusions
Rui de Oliveira
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CERN
Fine line and large size at CERN
15 µm line and space
LHCb VELO hybrid
Pitch adaptor
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4 meter long flex
LHC injection kicker prototype
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Micro via PCB structure
standard hole
SBU
4 layers
Std PCB core
4 layers
Buried hole
SBU
4 layers
Micro-via
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μvias – Process
Cu
μ Chemical Via
Dielectric
Glue
Metallization
Cu n-1
Cooper Etching
Glue Etching
Dielectric Etching
Anisotropic
p
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Mi i l Via
Minimal
Vi di
diameter
t ≈ 40 μm
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ALICE Pixel Detector
CERN
Aluminum bus
Size: 160 mm x 16 mm
5 layers
layers, chemical micro via
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GEM manufacturing
g
GEM foils are produced at
CERN using proprietary
process
Process based on anisotropic
etching of polyimide
50 μm Kapton
5μ
μm Cu both sides
Photoresist coating,
masking and
exposure to UV light
Metal
M
t l chemical
h i l
etching
Kapton
K
t chemical
h i l
etching
Second masking
Metal etching
and cleaning
GEM operation
p
principle
p
p
A potential difference of ~500V is applied to each GEM foil.
Primary electrons released by the radiation drift towards holes where
the
h high
hi h electric
l
i field
fi ld triggers
i
an electron
l
multiplication
l i li i (avalanche)
(
l
h ) process
Ions
5 µm
50 µm
55 µm
70 µm
Electrons
GEM detector
A GEM Detector consists of:
• a drift electrode
• 3 GEM foils
• a readout electrode
Semi-cylindrical GEM detector
3 GEM foils before being mounted into detector
Examples
p
of GEMs
33 cm
10 cm
30 cm
25-200 µm holes, 50-300 µm pitch
30 cm
10 cm
Wide range of shapes and sizes
1500-2000 foils manufactured at CERN
1 cm2 to 1000 cm2
CERN
Conclusions
• Old technology but still the best to face
future challenges
– PCB fabrication
– Semiconductor industry
– MEMs
• Easy
y to set up
p but extremely
y complicated
p
for sub-micrometer range patterns
• Future competition (cost still too high)
– Direct laser imaging, electron beam lithography
– Direct laser ablation
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