1. 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

•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)


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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!!


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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


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DUV Processing and Chemistry2. Photoresist Composition: DNQ dissolution


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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


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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.


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DUV Processing and Chemistry2. Photoresist Composition: CAR


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DUV Processing and Chemistry2. Photoresist Composition: Positive CAR


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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!!


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* 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


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from http://www.fabtech.org/features/lithography/articles/body6.215.php3

Chemically Amplified Resist: Basic composition


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DUV Processing and Chemistry2. Photoresist Composition: Positive CAR PAGs


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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


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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


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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


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DUV Processing and Chemistry2. Photoresist Composition


CAR: De-protection reaction: hv > H+ > Ea


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I: t-Boc Medium Ea: CAR: De-protection reaction: hv > H+ > dT


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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)


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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

��


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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


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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


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# 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


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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


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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


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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-.


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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


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•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


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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)


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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?


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DUV Processing and Chemistry3. DUV Other processes: Silylation

1. Photoresist : DUV CAR processing

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