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9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
1
DUV Processing and Chemistry1. Photoresist : DUV CAR processing
•Why DUV ?? Less diffraction with shorter wavelengths and less impact on depth of focus compared to increasing NA!
•R = k1λ/NA•R measured as minimum usage feature size in microns
•k1 process factor; λ = exposure wavelength; NA numerical aperture
•Depth of Focus (DOF) at image plane (wafer):
•DOF = k2λ/NA (k2 process factor)
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry1. Photoresist : DUV CAR processing
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry1. Photoresist : DUV CAR processing
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry1. Photoresist : DUV CAR processing
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR
•Novolak resins : too Absorbing at 248 nm = Sloped sidewalls
•So we need a new less absorbing resin when switching to shorter wavelengths!!
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR
http://willson.cm.utexas.edu/Research/Sub_Files/Photomask_Lithography/Files/DUV%20BACUS%20Paper.PDF
* DUV Photoresists: cannot use Novolakresins : too Absorbing: Need new resin: PHS:polyhydroxyl Styrene.
* Need new photo -dissolution reaction : PAC would not work: PAG and Thermal energy
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DNQ dissolution
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR
DUV Photoresist: Dissolution Inhibition mechanism:DNQ/Novolak Vs DNQ/PHS Not enough “contrast” selectivity!So We need a new dissolution mechanism for PHS resin systems!
diss
olut
ion
rate
[µm
/min
]
novolak resin+ diazonaphthoquinone sensitizer
novolakresin
novolak resin+ photolysis productsR
R0di
ssol
utio
n ra
te [µ
m/m
in]
PHS + sensitizer
PHS resinR
R0
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV Solubility switch
CAR Basic Idea: Photo Acid generator creating acid (H+) upon exposure to DUV radiation, thermal energy added to activate H+ to diffuse and react with blocking group causing polymer to be soluble in basic solution.
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: CAR
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: Positive CAR
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR
DUV Photoresist: PAG: Photo Acid Generator:
Designed to create H+ ion ( proton or acid) upon exposure to 248 nm wavelength radiation.
Thermally activating this acid with a post exposure bake causes the H+ to act as a catalyst and “deblock” the blocking group from the PHS. This make the PHS soluble in the exposed areas.
KEY delay time is between the exposure dose and the PEB activating bake!! Called PED delay.
This delay for DUV photoresists and tools (exposure and tracks) is specified as: CD change per time unit as: < 5 nm /hour!!
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR
* Deep UV Photoresists
Mixture: Resin, PAG, Solvent, and additives : Bases: OH to prevent environmental effects by adding more PAG without increasing photo speed can add base. AZ has a photobase: OH liberated with exposure to 248 nm radiation.
Resin: PHS Polyhydroxystyrene: All DUVphotoresists use this resin as Novolak for i-line photo absorbs too much 248 nm
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR
from http://www.fabtech.org/features/lithography/articles/body6.215.php3
Chemically Amplified Resist: Basic composition
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: Positive CAR PAGs
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: 248nm DUV CAR Types
Blocking or protection Groups make PHS resin insoluble
OH OH
OH
O O
H3 CCH3
CH3
O O
O
O
CH3
CH3CH3
O
O
CH3
CH3CH3
OH
O O
H3 CCH3
CH3
O OH
O
H3 C
O OH
O
O
CH3
CH3CH3
O OH
O
O
CH3
CH3CH3
O
O
CH3
AcetalAcetal
ESCAPESCAP
t-BOCt-BOC
O OH O
O
CH3
CH3
H3C
H3C
L&S
C/H
IL
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR Types
DUV CAR Photo resist : Activation energy Ea for H+ to “De-block or de-protect “defines types
Blocking Groups Bonded to resin to make it insoluble in TMAH developerI: t-Boc: Low Ea ( IBM and Shipley)* low post exposure bake temperature for amplification: 90C 60 secPED: very bad: 6nm/minII. Acetal: Low to Medium Ea ( room temperature)* low post exposure bake temperature for amplification: 110C 60 secPED: <5nm/hourIII. ESCAP: Environmentally Stable Chemically Amplified Photoresist(IBM and Shipley) High Ea* high post exposure bake temperature for amplification: 135C 90secPED: Very good <3nm/hour, Uses the “annealing” idea to improve PED
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR Types
DUV CAR Photo resist :KEY INVENTIONS:Blocking Groups Bonded to resin to make it insoluble in TMAH developerI: t-Boc* t - Boc Protected Polyhydroxystyrene PHS I : Shrinks & cracks* t - Boc Protected Polyhydroxystyrene PHS II : Shipley APEX-EPRO: > Excellent isolated linewith preformance.> Excellent profiles ( tops are very square)CON:> Poor delay stability> Very sensitive to airborne amine & ammonia contamination> Large PEB hotplate sensitivity: low activation energy material: low post exposure bake temperature for amplification: 90C 60 sec
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition
from http://www.fabtech.org/features/lithography/articles/body6.215.php3
CAR: De-protection reaction: hv > H+ > Ea
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR Types
from http://www.fabtech.org/features/lithography/articles/body6.215.php3
I: t-Boc Medium Ea: CAR: De-protection reaction: hv > H+ > dT
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR Types
II. Acetal:
* Acetal Protected Polyhydroxystyrene PHS : Sumitomo AZ 3200* t-Boc /Acetal Protected Polyhydroxystyrene PHS : TOK, AZ3300PRO: > Excellent contact hole preformance.> Good delay and airborne contamination sensitivity> OK for poly etchCON:> Less shelve life stability> Poor isolated linewidth control> PEB hotplate sensitivity: low activation energy material: low post exposure bake temperature for amplification> Outgas on optics: SVGL Scanners ( Aldehyde + hv = polymer. Also ethanol)
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR Types
II. Acetal: Low Ea: Deprotection Mechanism
lower TONworks with any mineral aciddoes not require non-nucleophilic anionsrequires no or lower bake temp.
O OHH
O OHH3C
OR
HH
��������
O R
H3C
HO R
���
H +
+
����
���� ���� +products
PAG
����
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR Types
III. ESCAP: Environmentally Stable Chemically Amplified Photoresist
* ESCAP Protected Polyhydroxystyrene PHS : Shipley UV, AZ DX3100* Copolymer and Terpolymers
PRO: > Good isolated linewidth performance.> Excellent profiles> Excellent delay and airborne high low activation energy material: high post exposure bake temperature for amplification: 135C 90secCON:> Dense linewidth fair> Line edge roughness: Acid diffusion and or internally scattered light> PEB hotplate sensitivity: bake temperature uniformity issue
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR Types
III. ESCAP (t-Alkyl): High Ea
high TONrequires superstrong acidsrequires non-nucleophilic anionsrequires higher bake temp.
O O
OO H
����
��������
������
O OHH
CO2++
H
����H +
������
PAG ���� +products
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR Types
# Parameter T-boc ESCAP Acetal AcetalShinEtsu
0 Optimized Features dense L/S Isolated C/H allC/H dense L/S
iso-dense bias small medium largeSidewall tops Very square rounded rounded
1 Shipley APEX-E UV6TOK DP-5XX-7XX DP2XX -4XXAZ DX3100/3300 DX3200
JSR K2G MXXY R11JEShinEtsu SEPR-4000 SEPR-4000
Sumitumo
30 ppb2 PED unfiltered 6nm/minute <3 nm/hr <5 nm/hr <5 nm/hr
nm/hr
3 PED @5ppb NH3 30min scummed +10 % CD/2hr +15 % CD/2hr -5 % CD/2hrtime 20 nm /2 hr 30 nm /2 hr 10nm/2hr
3a PCD poor poor 72 hours 0.0 nm7 nm/C UV6
4 PEB 4 nm/C 6 nm/C 0 nm/C 1 nm/Cnm/C <3 nm/C
5 Shelve life months 10 12 4 6
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR Types
# Parameter T-boc ESCAP Acetal AcetalShinEtsu
6 Resolution nm 200nm 100 nm 100 nm 100 nm
7 Line slimming nm 0 -4 2 No( 1st to 170th exposure) nm
8 Activation Energy medium High low low
9 Softbake temp C 90 130 90 100
10 PEB temp C 90 130 110 110
11 Thermal Stablity Hardbake: C <120C 150C <130C <140Cmono-dispersed
12 Substrate Poisoning :FootingSiN bad bad good good
SiON poor good goodTIW good poor NA
13 Etch Rate normalizedMetal (Cl2) 0.74 0.54 0.64 0.64Oxide (F2) 0.24 0.27 0.27
Poly (Br, Cl2) 0.44 0.7 0.7BARC (O2) 1 1.45 1.45
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR Types
# Parameter T-boc ESCAP Acetal AcetalShinEtsu
14 Dark loss 53 113 200A/min devno exposure A
15 Exposed shrinkage % 0.4 3.5 400/7000A 5 minno PEB 5.70%
16 Exposed shrinkage % 8.5 7.2 7.2with PEB
16 Outgas coat lens none none yes yesaldehyde aldehyde
17 Speed E size mj/cm2Eth
Shipley 15 15TOK 25 25AZ 38 40 40
JSR 40 35 25 25ShinEtsu 30 / 10
Sumitumo
18 Acid generated PAG Weak Strong Weak mediumphenolic acid carboxylic acid
19 Contrast moderate high highRmin A/sec 4 5 0.82 0.3Rmax A/sec 1340 990 3500 3000
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: Contamination Issues
Since at acid (proton or H+) is generated after exposure, it can be naturalized by materials that act as bases OH-.
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: Contamination Issues
Contamination measured as PED ( post - expose-delay) = CD change pre unit time after exposure before PEBThese “Alkali” acting contaminates can come from various sources: It just takes ppb concentrations.
•Air borne: amines, ammonia, NMP, paints, glues, plasticoutgassing: Causes T=topping
• CORRECTION: filtered air ( acid treated C) Restrict materials ESCAP photoresists
•Substrates that act as H+ getters: SiN TiN SiON BPSG causes footing
• CORRECTION: non –H+ getter interface film: BARC
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: Contamination Issues
•All DUV photoresist require BARCs to correct “swing” curve effect
• CORRECTION for footing: non –H+ getter interface film: BARC
•BUT BARC’s are have acid H+ groups that allow them to be thermally cured So if they are not 100% cured and contain H+ they can diffuse into DUV photoresist and cause lifting or pinching at interface!
60
70
80
90
100
110
120
0.8 0.85 0.9 0.95 1 1.05 1.1 1.15
Ener
gy [m
J/cm
2 ]
1.2 1.25
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR 193 nm
* Here we go again with 193nm. Search for that non-absorbing resin!!
Meta-cresol novolak
Poly-(4-hydroxystyrene)
Polyacrylates(aliphatic)
200
225
250
275
300
325
375
350
400
175
0.4
0.8
1.2
1.6
2.0
2.4
2.8
0.0
Wavelength [nm]
Abso
rptio
n co
effic
ient
[1/µ
m]
ArF193 nm
KrF248 nm
i-line365 nm
Source: R.D. Allen et al., IBM J. Res. Develop. 41 (1/2), 95-104 (1997)
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry2. Photoresist Composition: DUV CAR
Absorption from AZ
* Beyond i-line, resist chemistry for optical lithographies is dominated by the demands of the base polymer absorption:
248 nm resists:Novolak is opaque use of PHSPHS is not inhibited use of CA deprotection
193 nm resists:PHS is opaque use of aliphatic compoundsAliphatics etch too fast use of alicyclic compounds
157 nm resists:“Everything” is opaque fluorocarbons, silanols, or, finally,
the end of SLR resists?
9/7/03 ECE580/DUV/DUV.ppt Steve Brainerd
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DUV Processing and Chemistry3. DUV Other processes: Silylation