Lithography Explored
Leslie Chapman
June 27, 2007
TEKS Objectives
• (A) plan and implement investigative
procedures including asking questions,
formulating testable hypotheses, and
selecting equipment and technology.
• (B) identify uses of electromagnetic waves in
various technological applications, such as
fiber optics, optical scanners, microwaves,
and microfabrication.
• (C) communicate valid conclusions.
Language (SIOP) Objectives
Students will:
• Discuss their plan in groups.
• Write their plan and have it reviewed by
instructor prior to starting experiment.
• State and justify their conclusions.
THE ASSIGNMENT
•
Design a CD label for your favorite
music artist using the UV
Lithography technique.
Lithography Process
Post
Exposure
Bake
Prepare
Substrate
Apply
Photoresist
Develop
Expose
Softbake
Background Information
• Process
through which
very small 3-D
UV Light
features can be
Mask
produced.
(transparency
with design)
• Involves a
Positive
series of steps
Photoresist
that creates
(S-1813)
Substrate (CD)
successive
layers of
Substrate – process
materials.
The
photoresist
is exposed to radiation
starts here.
Silicon
is
using
Photoresist
– a the mask which contains a pattern
the
preferred
Lithography Process
• Create a mask.
• Start with a
substrate
• Cover surface
with
photoresist.
• Soft bake
• Expose the
wafer to energy
• Develop the
wafer
Types
of Lithography
X-ray
UV
Photo
Changing light source = type of lithography
Photo
X-ray
UV Light
Industrial Uses of Lithography
• Electronics and
Telecommunications
– Television, radio and
printers
– Calculators and watches
– Video cameras and
computers
(microprocessor)
– Cell phones and
waveguides
• Aviation and
Aerospace
– Airplanes, meterology
equipment and
Spaceships
• Automobile
– Cars (microchips
trigger inflation of air
bag)
– Traffic light (signals)
• Pharmaceutical
– Lab on a chip
– Portable blood
analyzers (microchipbased sensing
devices)
Applications of Lithography
• Complex MEMS Ratchet • A truly amazing MEMS
device. It is a sophisticated
Mechanism
MEMS Thermal Actuator
Incredible MEMS Clutch mechanism. This is actually a complex device
that required a working clutch mechanism. Gears are 50 microns across.
An early micromotor built in the SUMMiT technology.
For size comparison a microscopic dust mite is
shown on top.
Applications of X-ray Lithography
Micro gears
Micro motor core
Switching mechanism
Examples [9]
[9] http://www.ca/sandia.gov/liga/tech.html
THE ASSIGNMENT
•
•
•
•
Work in pairs to Design a CD label for your
favorite music artist using the UV
Lithography technique.
Each pair will design two CD labels
–
–
One CD will be the control.
The other CD will be varied (photoresist or exposure
time).
State and justify the impact your variation had
on the final product.
Constraints
–
–
Design must be drawn in black ink only.
Design must be able to fit on a CD.
• Create a design
• Transfer the design to transparency
paper (inkjet or copy machine)
• Keep the transparency clean
1. Prepare Substrate
•
•
Clean with
isopropanol
Bake at 115°C
for 60 seconds
Post
Exposure
Bake
Prepare
Substrate
Apply
Photoresist
Develop
Expose
Softbake
2. Apply Positive Photoresist
• Photoresist is spin
coated on to CD
• Students will dip CD
in S-1813 to get even
spread.
• Effective for λ 340 –
450 nm
Post
Exposure
Bake
Prepare
Substrate
Apply
Photoresist
Develop
Expose
Softbake
3. Softbake
• 115°C for 60
seconds
• Complete when
photoresist is
hard to the touch.
• Temp. range:
5 – 550°C (41 1022°F)
Post
Exposure
Bake
Develop
Expose
Prepare
Substrate
Apply
Photoresist
Softbake
4. Expose
• Long wave UV mini
lamp (Intensity = 230
μW/cm2)
• Exposure time: 25
seconds
Post
Exposure
Bake
Prepare
Substrate
Apply
Photoresist
Develop
Expose
Softbake
5. Develop
•
•
•
Post
Exposure
Bake
•
Prepare
Substrate
Immerse wafer in solution
for 40 – 60 seconds.
Agitation is
recommended.
Quickly remove the wafer
from the developer bath
and rinse with deionized
water bath for 30 seconds
(using the wafer holder).
Place the wafer on a
clean room wipe.
Dry the wafer holder.
Apply
Photoresist
Develop
Expose
Softbake
6. Post Exposure Bake
• Bake at 115°C
for 60 seconds
•
•
•
Set a hotplate to
the required
temperature.
Place the wafer on
the hotplate, start
timing.
When the time is
up, remove the
wafer.
Reminders
• Aprons, gloves and safety goggles
required at all times.
• UV goggles required during exposure.
• The more photoresist present, the
longer the bake time.
Teacher Expectations
•
•
•
•
Thorough Planning
Mask Design
Implementation
Conclusions explained
Points (for Instructor) to Consider
• Give time limit on mask design. Students may
design on computer or by hand. Intricacy of
design may impact exposure quality.
• Thickness of photoresist impacts bake time
• Exposure time could impact image seen on
substrate
• Substrate surface must be very clean
• Students must wear UV goggles when
operating UV lamp
Time Frame
Three class periods (50 minutes each)
1. Day One – Background Info, Mask
Design, Substrate Preparation,
2. Day Two – Wafer Preparation, Apply
photoresist, Softbake
3. Day Three – Expose, Develop, State
Conclusions
THANK YOU
•
•
•
•
•
•
Dr. Kim
Mr. Creary
Dr. Conkey
Dr. Srinivasa
Mr. Derry
Colleagues in the program