Polymers Used in
Microelectronics
and MEMs
An Introduction to
Lithography
Page 1
NSF STC
Integrated Circuits
Polymer Synthesis
CHEM 421
Micro-electro-mechanical Devices
(MEMS)
Polymer Synthesis
CHEM 421
Moore’s Law
Polymer Synthesis
CHEM 421
Year
Processor
Name
Transistor
Count
Minimum
Feature size
1971
1972
1974
1976
1978
1982
1985
1989
1993
1997
1999 (Feb.)
1999 (Oct.)
2000
Source: Intel
4004
8008
8080
8085
8086
80286
80386
Intel486
Pentium
Pentium II
Pentium III
Pentium III
Pentium IV
2300
3500
6000
6500
29000
134,000
275,000
1.2 million
3.1 million
7.5 million
9.5 million
28 million
42 million
10 micron
10 micron
6 micron
3 micron
3 micron
1.5 micron
1.5 micron
1 micron
800 nanometer
350 nanometer
250 nanometer
180 nanometer
130 nanometer
Industry Road Map
Polymer Synthesis
CHEM 421
The Drivers in Microelectronics
Polymer Synthesis
CHEM 421
• Cost: more for less!
–$1000 bought:
16MB in 1993
1000MB in 2000
–A single transistor costs about the same as a
single printed word in a local newspaper
AMD Athlon chip
Local Newspaper
22 million transistors
80 pages x 1600 words per page
$200
$0.50
J. Phys. Org. Chem. 2000, 13, 767.
The Drivers in Microelectronics
Polymer Synthesis
CHEM 421
• Size
– Wafer processing time independent of
feature dimension
»Printing smaller features or larger wafers
allows a greater number of devices to be
made in the same amount of time,
improving manufacturing yields
• Speed
–Smaller feature sizes also improve computing
speeds by decreasing the travel distance of
electrical signals
The Chip-making Process
Polymer Synthesis
CHEM 421
Example – A State-of-the-Art $5 Billion Fab Line
Up to
20X
1 Time
Semiconductor Manufacturing
Polymer Synthesis
CHEM 421
Photolithographic Process
Polymer Synthesis
CHEM 421
• Spin Coat
• Expose
• Bake
• Develop
Silicon Substrate
• Etch
• Strip
Process can be repeated up to
30 times: Solvent Intensive!
Imaging Process
Polymer Synthesis
CHEM 421
Handbook of Microlithography, Micromachining and Microfabrication v. 1,
P. Rai-Choudhury, ed. SPIE Optical Engineering Press, 1997.
Photolithographic Process
Photoresist
Substrate
Polymer Synthesis
CHEM 421
Coat
h
Negative
Mask
Positive
Exposure
Develop
Etch
Strip
J. Phys. Org. Chem. 2000, 13, 767.
Important Properties of a
Photoresist
• Resist Thickness (etch resistance)
• Solubility for deposition/development
• Wettability
• Lithographic performance
–Sensitivity, contrast
• Transparency
(more important for 193 nm and beyond)
Polymer Synthesis
CHEM 421
Optics of Imaging
Polymer Synthesis
CHEM 421
R = resolution = smallest feature size
R   / NA
•  is the wavelength of light
• NA is the numerical aperture (a function of the optics)
Wavelength
Notation
Source
Feature Size
365 nm
i-line
mercury
lamp
365+ nm
248 nm
193 nm
157 nm
DUV
193 nm
157 nm
KrF
excimer
laser
ArF
excimer
laser
F2 excimer
laser
500 - 100 nm 130 - 70 nm*
90 - 45 nm*
Magic!!!!! (aka phase shifting masks…)
Synthesis
“Transitions” in Optical LithographyPolymer
CHEM 421
365 nm
G- and I-line Resists
Polymer Synthesis
CHEM 421
OH
• Novolac resin
– Base-soluble positive resist (TMAH)
– Variety of structures and MW’s
OH
CH2
CH3
CH3
• Diazonapthaquinone (DNQ)
– Photoactive compound (Wolfe Rearrangement)
– Inhibits base-dissolution of novolac
O
O
O
C
CO2H
N2
h
H2O
-N2
R
R
R
R
G- and I-line Resists
Dissolution Rate
(nm/sec)
1,000 —
novolac
resin &
photocatalysis
products
100 —
novolac
resin
10 —
1—
novolac
resin &
DNQ
0.1 —
Polymer Synthesis
CHEM 421
G- and I-line Resists
Polymer Synthesis
CHEM 421
• An “engineer’s approach”
• Fast N2 outgassing can damage the resist film
–Controlled by using a less-intense light
source or a less sensitive resist
• Wavelength limited resolution (350 nm)
• Low contrast (competitive rates of dissolution)
Synthesis
“Transitions” in Optical LithographyPolymer
CHEM 421
365 nm
248 nm
Evolution from I- and G-Line to
248 nm (DUV)
Polymer Synthesis
CHEM 421
• Demand increases for smaller features:
R   / NA
• Diazoquinone novolac photoresists lacked
sensitivity at 248 nm
• Introduced at 0.365 micron (365 nm)
Motivation for Chemical
Amplification
Polymer Synthesis
CHEM 421
• Challenges Encountered:
– First exposure tools for 248 nm had low
output intensity
– Need increased sensitivity to avoid use of
extremely bright sources, which are
expensive
• Chemical amplification invented
(Frechet, Willison and Ito)
Exposure to photons initiates a chain reaction or
promotes a cascade of reactions (500-1000) that
changes resist solubility in exposed regions
Chemical Amplification
Polymer Synthesis
CHEM 421
CH CH2
• DUV exposure generates
catalytic amount of acid
from a photoacid generator
(PAG)
CH CH2
H+
O
O
O
• 1-2 min PEB to trigger
deprotection
O
+
H
O
O
CH
CH2
H+
O
O
• Catalytic chain length is
extremely long
– About 500 - 1000
carbonate cleavages
per proton
OH
CH
H
CH2
O
C
O
OH
J. Phys. Org. Chem. 2000, 13, 767.
Acc. Chem Res. 1994, 27, 150.
Photoacid Generators (PAG)
2,6-Dinitrobenzyl tosylate
Polymer Synthesis
CHEM 421
New fluorinated PAGs
Ionic PAG Mechanism
Photolysis of diaryliodonium salts
Polymer Synthesis
CHEM 421
Synthesis
2-Nitrobenzyl Ester PAG MechanismPolymer
CHEM 421
o-Nitrobenzyl Rearrangement
DUV Resists
Polymer Synthesis
CHEM 421
Extremely high contrast
Initial resistance in
manufacturing setting
Applicable at i-line with
sensitizers
Levinson, Harry J. Principles of
Lithography. SPIE Press, 2001.