Plasmonic Imaging for Optical Lithography X-ray Wavelengths at Optical Frequencies
Optical Lithography Simulation and Photoresist ...
Transcript of Optical Lithography Simulation and Photoresist ...
Optical Lithography Simulation and PhotoresistOptimization for Photomask Fabrication
Benjamen M. Rathsack1, Cyrus E. Tabery1, Steven A. Scheer1, MikePochkowski2, Cece Philbin3, Franklin Kalk3, Clifford L. Henderson4, Peter D.
Buck5 and C. Grant Willson1
March 15, 1999
1Department of Chemical Engineering, The University of Texas at Austin
2 ETEC Systems Inc., 9100 S. W. Gemini Dr., Beaverton, OR 970083 DPI Reticle Technology Center LLC, 2011 Greenhill Dr., Round Rock, TX 78664
4 Georgia Institute of Technology, 7778 Atlantic Dr., Atlanta, GA 30332 5 Dupont Photomask Inc., 1955 Division St. Gresham, OR 97030
Photomask Fabrication OptimizationGoal: Improve resolution and process latitude for photomask fabrication using laser pattern generators
Method: Line edge optimizationof exposure image and resistdevelopment response
Results: Sub 0.30 µm resist features on photomasksubstrates
UV Light
Reduction Lens
Exposed ResistPattern
Silicon Substrate
Photomask
Photomask Fabrication Process
• Laser pattern generatorexposes a pattern in theresist
• Developer dissolves awaythe exposed regions of resist
• Etch transfers the reliefimage into the chromium
Chromium
Quartz
Photoresist
Laser exposure
Development
Etch
Exposed resist
Novolac/DNQ Resist Chemistry
Photoactive Compound Photoreaction
Photoresist polymer matrix synthesis
N2
Diazonaphthoquinone Carbene Ketene Intermediate
O
N2
S
R
O
hν
O
S
R
OO
O
C
S OO
R
O
OH
O
S R
O
O
Indenecarboxylic Acid
H2O
H+
Novolac Resin
OH
CH3
+ H2C=O
CH2
OH
CH3
( )n
Photomask Resist Characterization
0204060
80100120
0 200 400 600 800 1000 1200 1400Time (s)
Tem
pera
ture
(ºC)
Commercial
Univ. Texas
Chromium 70 nm
Resist 570 nmChromium Oxide 35 nm
Quartz 6.35 mm
Coated Photomask Substrate
Photomask Post Application Bake
• I-line photoresists are coated onantireflective (AR3) substrates
• A hotplate was built to mimicthe post application bake (PAB)of production photomasks
• Photokinetics measured through exposure parameters (Dill’s A, B and C)
• Generate development ratefunction (R(m)) for resists
•Methodology–Bleach resist with light at 365 nm
–Photoactive compound undergoes chemical change–Photoproducts do not absorb light– Measure transmittance of resist film as a function of exposure dose
TransimpedanceAmplifiers
500 W HgArc Lamp Source Electronic
Shutter
Water Filter
Bandpass Filter
Beam Splitter
Resist Sample
UV-Enhanced Silicon Photodetectors
Neutral DensityFilter
Automated DataAcquisition System
Photokinetics Experiment
SpatialFilter
Photoresist Reaction Kinetics
• Dill parameters A, B and CA = bleachable component in resist
B = non-bleachable
component in resist
C = rate of photochemical
reaction in resist
• Rigorous A,B and C ExtractionSimultaneous solution to the thin filmoptics and the Beer-Lambert equations
A = 0.808 1/µmB = 0.086 1/µmC = 0.010 cm2/mJ
0.50
0.60
0.70
0.80
0.90
0 200 400 600
Exposure Dose (mJ/cm2)
Tra
nsm
ittan
ce (
%)
Experimental
Calculated
Mult-Wavelength DissolutionRate Monitor
Broadband Light Source
PC Card Spectrometers
PC DataAcquisitionSystem
Ref
lect
ance
WavelengthT
hick
ness
Time
Data Analysis I(λ,t)
Puddle Developer Cell withDeveloping Resist Film
Lithography Simulation
m’(x,z)
I(x)
z
x
E(x,z)
m(x,z)
Rig
orou
s P
hysi
cal
Rel
atio
nshi
psE
mpi
rica
lR
elat
ions
hips
ResistProfile
Input Parameters
PEB Time & Temp
Photokinetics Parameters
Development Rate Model
OutputSimulation
Optical Equations
Optical Equations
Photochemistry
Diffusion Equations
Dissolution Theory
Exposure Tool
Resist Optical Properties
m(x,z) à relative photoactive compound concentration
∇m à relative photoactive compound concentration gradient
E(x,z) à exposure energy distribution
Basis of Line Edge Optimization(0.5 µm Space in Resist)
-1000 -500 0 500 1000Horizontal Direction (nm)
Rel
ativ
e In
tens
ity
Develop Time Contours
Aerial Image
Output: Resist ProfileSidewall angle θ and feature size w
w
θ
PROLITH 2 v6.04
Relative PAC (m)Exposure Dose + Kinetics (A, B and C)
∇m
Lithographic Imaging Equation
dx
dm
dx
dR
xTH
*
γ=
dm
dRTH = γ
R = Dissolution ratex = Horizontal positionm = Relative PAC Concentrationγ TH = Theoretical resist contrast x* = Nominal edge of resist feature
–Maximize the change indevelopment rate at theedge of the resist feature
–Maximize ∇m = (dm/dx)through exposure dose andgiven aerial image
–Adjust location ofdissolution rate notch (γ ΤΗ)to the edge of the nominalresist edge (target m) withdeveloper concentration
Simulated Optimum Exposure Dose forPhotomask Lithography
2.0
2.4
2.8
3.2
100 150 200 250 300
Exposure Dose (mJ/cm2)
PA
C g
radi
ent (
m-1
)
IP3600PFI88A5
Determined exposure dose thatresulted in the maximum ∇∇m
Best DosesIP3600 ≅ 210 mJ/cm2
PFI88A5 ≅ 260 mJ/cm2
Determined m at the edge of theresist feature at the dose givingmaximum ∇m
Target mIP3600 = 0.3
PFI88A5 = 0.3
m(x,z) of IP3600 with a 210 mJ/ cm2 dose
Optimal Development Rate Function (R(m))
Note:Resists A, B, PFI88A, E and Fhave large dissolution ratenotches, however, the notchesoccur at high m. These resisthave been optimized for highthroughput on Si (high m ~low dose).
Optimal resist for masklithography has…
Large dissolution Notch
near Target m
R(m) response of six I-line resistsdeveloped with 0.26N TMAH
0
10
20
30
40
50
60
0.4 0.5 0.6 0.7 0.8
Relative PAC (m)Di
ssol
utio
n Ra
te (n
m/s
)
ABIP3600PFI88A5EF
Target m Notch
Optimal Dissolution Notch Location
IP3600 Notch Locationm ≅ 0.35
(developed w/ 0.20 N TMAH)
0
20
40
60
80
0 0.2 0.4 0.6 0.8Relative PAC (m)
Dis
s. R
ate
(nm
/s)
0.26NModel(0.26N)0.23NModel(0.23N)
0.20NModel(0.20N)
Target m
Lower developer concentration shifts notch toward the target m
PFI88A5 Notch Locationm ≅ 0.45
(developed w/ 0.23 N TMAH)
0
20
40
60
80
0 0.2 0.4 0.6
Relative PAC (m)
Dis
s. R
ate(
nm/s
)
0.26N
Model (0.26N)
0.23N
Model (0.23N)
Low Developer Conc.
Target m
Low Developer Conc.
Standing Waves in Photomask Resists
• Lower developer concentration amplifies influence of standing waves
• Hotplate built that mimics thebake profile of photomask surface
• Developed post-exposure baketo minimize standing waveson photomasks
0
2040
6080
100120
140
0 100 200 300Time (s)
Tem
pera
ture
(ºC
)
MIN
MAX
Photomask Post-Exposure Bake
0
5
10
15
20
25
0 200 400 600Thickness (nm)
Dis
solu
tion
Rat
e (n
m/s
)
IP3600 developed with0.20 N TMAH (NMD-W)
Photomask post-exposure bake improvesprocess latitude
IP3600/ 0.23N TMAH (NMD-W)/90 s dev. time/ 110 mJ/cm2/ 0.5 µm space
No PEB PEBFocus
+0.4 µm
Best Focus
-0.4 µmScum
StandingWaves
Scum
Simulated Process LatitudeImprovements for IP3600
IP3600 (TOK)/ 0.26N TMAHNMD-W/ No PEB
IP3600 (TOK)/ 0.20N TMAHNMD-W/ PEB
PROLITH 2/ 6.04/ 0.5 µm isolated space/ 82º+ sidewall angle/ ± 5% linewidth latitude
Current Photomask Process Improved Photomask Process
Simulated Process Latitude Improvementsfor High Resolution Resists
PFI88A5 (Sumitomo)/ 0.26NTMAH NMD-W/ PEB
PFI88A5 (Sumitomo)/ 0.23NTMAH NMD-W/ PEB
PROLITH 2/ 6.04/ 0.5 µm isolated space/ 82º+ sidewall angle/ ± 5% linewidth latitude
High-Resolution Photomask Process
Improved High-ResolutionPhotomask Process
Focus-Exposure Process LatitudeImprovements (0.5 µm space)
0.35
0.4
0.45
0.5
0.55
0.6
0.65
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
Cri
tical
Dim
ensi
on ( µ
m)
90100111123
0.35
0.4
0.45
0.5
0.55
0.6
0.65
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8Focus (µm)
Cri
tical
Dim
ensi
on ( µ
m) 122
132
144
Current Photomask Process
Improved Photomask Process
High Resolution Photomask Process
IP3600/ 0.26N TMAH (NMD-W)/60 s dev./ No PEB
IP3600/ 0.20N TMAH (NMD-W)/180 s dev./ PEB
PFI88A5/ 0.26N TMAH (NMD-W)/180 s dev./ PEB
Manufacturing trials at the DPI Reticle Technology Center
Focus (µm)
0.35
0.4
0.45
0.5
0.55
0.6
0.65
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8Focus (µm)
Cri
tical
Dim
ensi
on ( µ
m)
144160177.78197.53219.48243.87
Focus-Exposure Process LatitudeImprovements (0.3 µm spaces)
Improved Photomask Process
Current Photomask Process
High Resolution Photomask Process
IP3600/ 0.26N TMAH (NMD-W)/60 s dev./ No PEB
IP3600/ 0.20N TMAH (NMD-W)/180 s dev./ PEB
PFI88A5/ 0.26N TMAH (NMD-W)/180 s dev./ PEB
Manufacturing trials at the DPI Reticle Technology Center
0.25
0.29
0.33
0.37
0.41
0.45
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
Cri
tical
Dim
ensi
on (
177197219243
0.25
0.29
0.33
0.37
0.41
0.45
-0.8-0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
Focus(µm)
Cri
tical
Dim
ensi
on (
µm) 132
144156
0.25
0.29
0.33
0.37
0.41
0.45
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
Cri
tical
Dim
ensi
on(
132
137
SCUMMEDFEATURES
Focus(µm) Focus(µm)
µm)µm
)
High Resolution Optical PhotomaskLithography
PFI88A5/ 0.26N TMAH NMD-W/ 180 s dev. time/ PEB/ 220mJ/cm2
0.5 µm isolated resist space 0.3 µm isolated resist space
Optimal Photomask Process forSub 0.30 µm Resist Features
Process Conditions• High Resolution I-line resists
• Higher exposure energy
• Lower developer concentration
• Longer development time
• Post-exposure bake
Process Parameter Optimization• Sub-0.30 µm resist features
• Improved focus-exposure process latitude
• Reduce Scumming/ defects
• Reduced CD sensitivity to dose
• Reduce pattern density effects
0.25 µm isolated resist space
PFI88A5/ 0.26N TMAH NMD-W/ 180 s dev. time/ PEB/ 220mJ/cm2
Acknowledgements
• ETEC Systems Inc.• SRC/ National Semiconductor Fellowship• Sumitomo, Shipley, Clariant, Olin and TOK• FINLE Technologies• J. A. Woollam (Ron Synowicki)