Transcript Micromirror Lithography

Micromirror Lithography
David Chen
EECS 277
Overview
What is Lithography?
What are Micromirrors?
Successful Research
Future
What is Lithography?
It is the backbone of nearly all
semiconductor device fabrication processes.
It allows for high precision and tiny devices.
It allows for mass production.
For the most part, it removes human error
from the manufacturing process, giving high
yield production.
What is Lithography?
The procedure for lithography is as follows:
 Start with a wafer
 Deposit or grow layer of desired material
 Spin coat photoresist
 Pattern photoresist by exposure
 Etch layer underneath or deposit/grow new
layer
 Remove photoresist
 Repeat
What is Photoresist?
Light sensitive material
Changes molecular bond after
exposure to certain wavelengths
of light
Used to make planar patterns
determined by photomasks
Protects layers underneath during
etching
Can be easily removed after each
process
Example of Lithography
A familiar device: CMOS inverter
Link
7 different photoresist patterns
7 different photomasks
Very simple device
Masks Cost How Much?!?
Costs per mask-set
65nm ~ $1million
45nm ~ $2.2million
32nm ~ $4million
28nm ~ $8million
Bearable for high volume manufacturers
Outrageous for small companies or prototyping
Masks also deteriorate after use!
Why are masks so expensive?
Very high resolution structures require
expensive processes such as electron beam
etching or laser etching (also lithography)
Unique pattern means masks are custom made
per client order
Need an alternative
What other things produce high resolution
images…
AKA high definition images…
AKA HD…
We Already Have the Technology!
Made famous by Texas Instrument’s DLP
(digital light processing) televisions
DMD- digital micromirror device
Project high resolution images
What Are Micromirrors?
MEMS (Micro-electro-mechanical systems)
Array of millions of mirrors on a tiny chip
Each mirror can be independently controlled
On/Off states
TV vs. Maskless Lithography
Even though they’re HD, TV pixels are still
way too big for lithography
We are trying to pattern photoresist on the
sub-micron scale!
Need a HUGE lens to focus the array to a
smaller scale
Making a huge lens is hard.
One Solution from MIT: ZPAL
Using an equal number of
array of diffracting lenses
fabricated by lithography,
each beam of light can be
focused individually.
Feature sizes can be
much smaller than the
beam width!
Results from test
Well defined structures
Low roughness
Features on spot size scale
Done using UV light
Future Improvements
Smaller wavelength light


EUV (extreme UV) 120nm-10nm
X-Ray 10nm-1pm
Higher refractive mediums

Liquid immersed fabrication
= Smaller spot size
Benefits of Micromirror Lithography
Programmable “mask”

Vs. permanent photomask
No cost for prototype masks

Vs. $millions per set
Instant mask production

Vs. weeks to months per set
All of the above = Cheaper!
Resources
http://www.eetimes.com/showArticle.jhtml;jsessionid=ONC4WJBQY
CVL0QSNDLRSKHSCJUNN2JVN?articleID=211100224
http://jas.eng.buffalo.edu/education/fab/invFab/index.html
http://www.eetimes.com/showArticle.jhtml;jsessionid=ONC4WJBQY
CVL0QSNDLRSKHSCJUNN2JVN?articleID=211100224
http://nanoweb.mit.edu/zpal/Presentations/SPIE_2005_web.pdf
http://nanoweb.mit.edu/zpal/Presentations/EIPBN-2004-Alpha.pdf
http://nanoweb.mit.edu/zpal/Presentations.html
http://nanoweb.mit.edu/zpal/Presentations/EIPBN-2004-SSP.pdf