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Page 1 NSF STC
Polymers Used in Microelectronics
and MEMs
An Introduction to An Introduction to
LithographyLithography
Polymer SynthesisCHEM 421
Integrated Circuits
Polymer SynthesisCHEM 421
Micro-electro-mechanical Devices (MEMS)
Polymer SynthesisCHEM 421
Moore’s Law
Year Processor Transistor MinimumName Count Feature size
1971 4004 2300 10 micron1972 8008 3500 10 micron1974 8080 6000 6 micron1976 8085 6500 3 micron1978 8086 29000 3 micron1982 80286 134,000 1.5 micron1985 80386 275,000 1.5 micron1989 Intel486 1.2 million 1 micron1993 Pentium 3.1 million 800 nanometer1997 Pentium II 7.5 million 350 nanometer1999 (Feb.) Pentium III 9.5 million 250 nanometer1999 (Oct.) Pentium III 28 million 180 nanometer2000 Pentium IV 42 million 130 nanometerSource: Intel
Polymer SynthesisCHEM 421
Industry Road Map
Polymer SynthesisCHEM 421
The Drivers in Microelectronics
• Cost: more for less!
–$1000 bought:$1000 bought: 16MB in 199316MB in 1993
1000MB in 20001000MB in 2000
–A single transistor costs about the same as a A single transistor costs about the same as a single printed word in a local newspapersingle 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.
Polymer SynthesisCHEM 421
The Drivers in Microelectronics
• Size– Wafer processing time independent of Wafer processing time independent of
feature dimensionfeature 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
Polymer SynthesisCHEM 421
Example – A State-of-the-Art $5 Billion Fab Line
The Chip-making Process
Up to 20X
1 Time
Polymer SynthesisCHEM 421Semiconductor Manufacturing
Polymer SynthesisCHEM 421
Silicon Substrate
• Expose
• Strip
• Etch
• Develop
• Bake
• Spin Coat
Process can be repeated up to 30 times: Solvent Intensive!
Photolithographic Process
Polymer SynthesisCHEM 421
Imaging Process
Handbook of Microlithography, Micromachining and Microfabrication v. 1, P. Rai-Choudhury, ed. SPIE Optical Engineering Press, 1997.
Polymer SynthesisCHEM 421
Photolithographic Process
J. Phys. Org. Chem. 2000, 13, 767.
Coat
Exposure
Develop
Strip
Etch
Photoresist
Substrate
Maskh
PositiveNegative
Polymer SynthesisCHEM 421
Important Properties of a Photoresist
• Resist Thickness (etch resistance)Resist Thickness (etch resistance)
• Solubility for deposition/developmentSolubility for deposition/development
• WettabilityWettability
• Lithographic performanceLithographic performance
–Sensitivity, contrastSensitivity, contrast
• TransparencyTransparency(more important for 193 nm and beyond)(more important for 193 nm and beyond)
Polymer SynthesisCHEM 421
Optics of Imaging
R = resolution = smallest feature sizeR / NA
• is the wavelength of light• NA is the numerical aperture (a function of the optics)
Magic!!!!! (aka phase shifting masks…)Magic!!!!! (aka phase shifting masks…)
Wavelength Wavelength 365 nm 248 nm 193 nm 157 nm
NotationNotation i-line DUV 193 nm 157 nm
mercury KrF ArF F2 excimer Source Source lamp excimer excimer laser laser laser
Feature Size Feature Size 365+ nm 500 - 100 nm 130 - 70 nm* 90 - 45 nm*
Polymer SynthesisCHEM 421“Transitions” in Optical Lithography
365 nm365 nm
Polymer SynthesisCHEM 421
G- and I-line Resists
• Novolac resinNovolac resin– Base-soluble positive resist (TMAH)Base-soluble positive resist (TMAH)– Variety of structures and MW’sVariety of structures and MW’s
• Diazonapthaquinone (DNQ)Diazonapthaquinone (DNQ)– Photoactive compound (Wolfe Rearrangement)Photoactive compound (Wolfe Rearrangement)– Inhibits base-dissolution of novolacInhibits base-dissolution of novolac
OH
CH3
OH
CH3
CH2
O
N2
R
O
R R
C
O
H2O
R
CO2H
h
-N2
Polymer SynthesisCHEM 421
G- and I-line ResistsD
isso
luti
on
Ra
te(n
m/s
ec)
1,000 —
100 —
10 —
1 —
0.1 —
novolacresin
novolacresin &
photocatalysis products
novolacresin &
DNQ
Polymer SynthesisCHEM 421
• An “engineer’s approach”An “engineer’s approach”
• Fast NFast N22 outgassing can damage the resist film 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)
G- and I-line Resists
Polymer SynthesisCHEM 421“Transitions” in Optical Lithography
365 nm365 nm
248 nm248 nm
Polymer SynthesisCHEM 421
Evolution from I- and G-Line to 248 nm (DUV)
• Demand increases for smaller features:Demand increases for smaller features:
R / NA
• Diazoquinone novolac photoresists lacked Diazoquinone novolac photoresists lacked sensitivity at 248 nmsensitivity at 248 nm
• Introduced at 0.365 micron (365 nm)Introduced at 0.365 micron (365 nm)
Polymer SynthesisCHEM 421
Motivation for Chemical Amplification
• Challenges Encountered:Challenges Encountered:
– First exposure tools for 248 nm had low First exposure tools for 248 nm had low output intensityoutput intensity
– Need increased sensitivity to avoid use of Need increased sensitivity to avoid use of extremely bright sources, which are extremely bright sources, which are expensiveexpensive
• Chemical amplification invented Chemical amplification invented (Frechet, Willison and Ito)(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
Polymer SynthesisCHEM 421
Chemical Amplification
• DUV exposure generates DUV exposure generates catalytic amount of acid catalytic amount of acid from a photoacid generator from a photoacid generator (PAG)(PAG)
• 1-2 min PEB to trigger 1-2 min PEB to trigger deprotectiondeprotection
• Catalytic chain length is Catalytic chain length is extremely longextremely long
– About 500 - 1000 About 500 - 1000 carbonate cleavages carbonate cleavages per protonper proton
J. Phys. Org. Chem. 2000, 13, 767.Acc. Chem Res. 1994, 27, 150.
CH CH2
O
O
O
H+
CH CH2
O
O
O
CH CH2
O
OH
O
H+
CH CH2
OH
C
O
OH
H+
Polymer SynthesisCHEM 421
Photoacid Generators (PAG)
2,6-Dinitrobenzyl tosylate New fluorinated PAGs
NO2
NO2
CH2O S
O
O
CH3
I B
F3C
F3C
F3C CF3
CF3
CF3
CF3F3C
Polymer SynthesisCHEM 421
Ionic PAG Mechanism
Photolysis of diaryliodonium salts
Crivello, J. V.; Lam, J. H. W.; M acromolecules. 1977, 10, 1307-1315.
I2
CF3
CF3
B4
Diphenyliodonium tert-(3,5-bis(trif luoromethyl) phenyl boronium
hvI
2
CF3
CF3
B4
*
I + +CF3
CF3
B4
I + S HI SH +I H+S= solvent, polymer, or other compounds
Polymer SynthesisCHEM 421
2-Nitrobenzyl Ester PAG Mechanism
o-Nitrobenzyl Rearrangement
N+ O–
O
O Ts
H
OTs
N
OTs
OH
ON
HO
ON
HO S
O
O
h
Reichmanis, E.; Smith, B. C.; Gooden, R.J . Polym. Sci.: Polym. Chem. Ed. 1985, 23, 1
N O
HO
OTs
O
O
CH3+
Sulfonic acid
R R R
RR
R= NO2 or CF3
Polymer SynthesisCHEM 421
DUV Resists
Levinson, Harry J. Principles of Lithography. SPIE Press, 2001.
Extremely high contrast
Initial resistance inmanufacturing setting
Applicable at i-line with sensitizers
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