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Semiconductor Manufacturing
Polymer Synthesis
CHEM 421
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*
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
Synthesis
“Transitions” in Optical LithographyPolymer
CHEM 421
365 nm
248 nm
Chemical Amplification
CH
CH
CH2
• DUV exposure generates catalytic
amount of acid from a photoacid
generator (PAG)
CH2
H+
O
Polymer Synthesis
CHEM 421
• 1-2 min PEB to trigger
deprotection
O
O
H+
O
O
• Catalytic chain length is extremely
long
O
CH
CH2
– About 500 - 1000
carbonate cleavages per
proton
H+
O
O
OH
CH
H
CH2
O
C
J. Phys. Org. Chem. 2000, 13, 767.
Acc. Chem Res. 1994, 27, 150.
O
OH
Challenges with Chemical
Amplification
Polymer Synthesis
CHEM 421
• What if trace amounts of base (NMP solvent)
was found in the air in a FAB?
• Catalyst
susceptible to
poisoning by
atmospheric
bases
Levinson, Harry J. Principles of Lithography. SPIE Press, 2001.
Model for Constructing a ChemicallyPolymer Synthesis
CHEM 421
Amplified Resist
Backbone
CH
CH2
CH
CH2
Etch
Barrier
Acidic
Group
OH
O
O
O
Protecting
Group
Levinson, Harry J. Principles of Lithography. SPIE Press, 2001.
Low- and High-Activation Energy
Chemically Amplified Resists
Polymer Synthesis
CHEM 421
• Copolymer of hydroxy styrene and
t-BOC protected hydroxy styrene
• Good hydrophilic/hydrophobic balance
• IBM’s Apex Resist
• Low activation energy, very reactive
• PAB below Tg
•
•
•
•
IBM’s ESCAP Resist
High activation energy, lower reactivity
Allows for high T bake
PAB above Tg
• removes stress
• removes residual solvent
• higher density films
• Low diffusion of PAG
Synthesis
“Transitions” in Optical LithographyPolymer
CHEM 421
365 nm
248 nm
193 nm
Absorption of Resins
Polymer Synthesis
CHEM 421
1.8
Poly(p-hydroxy styrene)
1.5
1.1
Absorption
Coefficient
(micron-1) 0.8
0.5
Optimal range
0.3
Polyacrylate
0.1
190
200 210 220 230
240 250 260 270 280 290 300
Wavelength (nm)
310 320
330 340 350
Design Criteria for 193 nm Resists
• Optical transparency
• Hydrophilicity
• High Tg (130-170 °C)
• Good etch resistance
• Easily blocked hydroxyl group
Polymer Synthesis
CHEM 421
Synthesis
Photoresists for 193 nm LithographyPolymer
CHEM 421
CH3
CH3
CH2 C
CH3
CH2 C
O
OCH3
CH2 C
O
OH
O
• Extremely transparent at 193 nm
• Tunable composition
• Property diversity
O
C(CH3)3
• Good hydrophilicity
• High activation energy
PAG
cleavable group
• Easily synthesized
CH3
CH3
CH2 C
CH3
CH2 C
O
OCH3
O
OH
• But poor etch resistance…
CH2 C
O
OH
Synthesis
Photoresists for 193 nm LithographyPolymer
CHEM 421
Hydrophilicity
Cleavable
group
Dry etch resistance &
transparency
Synthesis
Photoresists for 193 nm LithographyPolymer
CHEM 421
AT&T / Lucent / Agere
O
O
+
O
O
O
AIBN
THF
O
O
O
O
O
“Transitions” in Optical Lithography
Polymer Synthesis
CHEM 421
365 nm
248 nm
193 nm
Absorption
at 157 nm??!!
157 nm
Polymeric Materials Outlook for
157 nm Resist Design
Polymer
Absorbtion
Coefficient
(157 nm)
Polymer Synthesis
CHEM 421
Thickness (nm)
(OD = 0.4)
Poly(hydrosilsesquioxane)
0.06
6667
Poly(tetrafluoroethylene)
0.70
571
Poly(tetrafluoroethylene-coethylene) (30% TFE)
1.34
298
Poly(dimethylsiloxane)
1.61
248
Poly(vinyl alcohol)
4.16
96
Poly(methyl methacrylate)
5.69
70
Poly(norbornene)
6.10
66
Polystyrene
6.20
64
Poly(p-hydroxystyrene)
6.25
64
Poly(p-chlorostyrene)
10.15
39
R. R. Kunz et.al. J. Vac. Sci. Technol. B 17(6), Nov/Dec 1999
Emerging 157 nm Resist Platforms
Polymer Synthesis
CHEM 421
SO2
CF3
OH
A. E. Feiring and J. Feldman,
DuPont WO 00/67072.
CF3
O.D. @ 157 nm
1.4 micron-1
O.D. @ 157 nm
3.1 micron-1
H. Ito, G. Walraff, et. al. IBM
CF3
CH2
CH2 CH
C
H
CH
2
O
C
C
m
O
O
F3C
n
x
O
O
CF3
O
O
CF3
F3C
OCH3
G. Willson, UT
O.D. @ 157 nm
2.7 micron-1
y
O
OH
G. Willson, UT
F3C
CF3
R. Dammel, Clariant
O.D. @ 157 nm
2.5 micron-1
C. Ober, Cornell
OH
O.D. @ 157 nm
2.8 micron-1
Poly(TFE-co-NB-co-EVE)
Polymer Synthesis
CHEM 421
•Lowers Absorbance
•Increases CO2 Solubility
•Provides Contrast
•Increases Etch
Resistance
•Increases Tg
•Lowers Absorbance
•Increases CO2
Solubility
EVE is Ester Vinyl Ether
Poly(TFE-co-NB-co-EVE)
TFE
(mol %)
NB
(mol %)
FG
(mol %)
Tg
(°C)
50
50
0
125
38
59
3
126
40
41
55
52
5
7
Mn /
MWD
Polymer Synthesis
CHEM 421
Liq. CO2
Sol.
Abs.
@ 157 nm
Insol.
1.4
Insol.
1.38
115
3600 /
1.32
Insol.
1.29
92
3500 /
1.42
Insol.
To be
determined
??
3300 /
1.47
157/193 nm Photoresists
Teflon® AF as Backbone Material
Polymer Synthesis
CHEM 421
• Due to its amorphous structure and rigid backbone, Teflon® AF has unique
properties that are desirable in a photoresist backbone
Tetrafluoroethylene
(TFE)
2,2-Bis(trifluoromethyl)-4,5difluoro-1,3-dioxole
(PDD)
Advantages
Teflon® AF
Challenges
• very low absorbance
• cost of PDD monomer
• rigid structure (good etch
resistance)
• need functional monomer without
significantly increasing absorbance
• forms smooth films
• broad range of Tgs available
157/193 nm Photoresists
Absorbance at 157 nm and 193 nm
Absorbance [a10(mm-1)]
193
(nm)
Teflon® AF
0.154
0.004
CO2 Synthesized
Copolymer
0.153
0.019
• Values for Teflon® AF and
the CO2 synthesized
copolymer are very close
and well below 1 mm-1 at
157 nm
• Values at 193 nm are
slightly different but both
extremely low
2.5
2
-1
157.6
(nm)
Optical Density
a 10 (m m )
Sample
Polymer Synthesis
CHEM 421
1.5
T
1
0.5
0
145
155
165
175
185
wavelength (nm)
Teflon AF
CO2 Synthesized Copolymer
195
157/193 nm Photoresists
Teflon® AF as Backbone Material
• In order for a Teflon® AF
derivative to serve as a
photoresist, a functionalized
monomer that can be
cleaved by an acid must be
incorporated into the
backbone
CF2 CF2
CF
O
F 3C
Polymer Synthesis
CHEM 421
CF
O
Protected
Functional
Monomer
CF3
PAG
• After cleaving with a photo
acid generator (PAG) the
functional monomer will
exhibit different solubility
properties from unexposed
regions
CF2 CF2
CF
O
F 3C
CF
O
CF3
Acidic
Group
157/193 nm Photoresists
EVE/PDD/TFE Plackett-Burman Experiment Scheme
•
Chose to explore Ester Vinyl Ether (EVE)
as a prototype for potential EVE derived
functional monomers
•
Conducted a Plackett-Burman
experimental scheme varying five
parameters (composition, initiator
concentration, temperature, pressure and
reaction time) to study the reaction of EVE
with PDD and TFE
Exp. #
1
2
3
4
5
6
7
8
EVE/PDD/TFE
(mol %)
7/73/20
25/55/20
25/55/20
25/55/20
7/73/20
7/73/20
25/55/20
7/73/20
Initiator
(mol %)
1
0.2
0.2
1
1
0.2
1
0.2
Polymer Synthesis
CHEM 421
poly(TFE-co-PDD-co-EVE)
Temp (oC)
15
35
15
15
35
35
35
15
Pressure
(psi)
3500
3500
3500
1500
3500
1500
1500
1500
Rxn Time
(hr)
4
4
0.5
4
0.5
4
0.5
0.5
157/193 nm Photoresists EVE/TFE/PDDPolymer
Synthesis
Absorbance
CHEM 421
VASE® Absorbance [a10(mm-1)] Measurements
Sample
REH-004
REH-013
REH-005
Composition
(mol %)
7/73/20 EVE/PDD/TFE
(Charged)
12/59/29
EVE/PDD/TFE
18/54/28
EVE/PDD/TFE
157.6
(nm)
193
(nm)
0.128
0.013
0.252
0.011
0.574
0.017
• Absorbance values at 157 nm increase with increasing EVE
content but still remain well below 1 (mm-1)
• Values at 193 nm are very low and vary only slightly
Bilayer Resist Processes
Levinson, Harry J. Principles of
Lithography. SPIE Press, 2001.
Polymer Synthesis
CHEM 421
Top-Surface Imaging
Polymer Synthesis
CHEM 421
Levinson, Harry J. Principles of
Lithography. SPIE Press, 2001.
Comparisons
Single Layer
Resist
Spin coating
Bi-Layer
Resist
1st Spin coating
Polymer Synthesis
CHEM 421
Top-Surface
Imaged Resist
Spin coating
2nd Spin coating
Negative
Exposure
Expose
Expose
Develop
Silylate
O2RIE
O2RIE
Develop
“Transitions” in Optical Lithography
Polymer Synthesis
CHEM 421
365 nm
248 nm
193 nm
?
E-beam
EUV
157 nm
X-ray
More Reading Materials
Polymer Synthesis
CHEM 421
“Advances in Patterning Materials for 193 nm
Immersion Lithography”
Chem. Rev. 2010, 110, 321–360
“Organic imaging materials: a view of the future”
J. Phys. Org. Chem. 2000, 13, 767