NPRLNanoscale Physics Research Laboratory
Chemically Amplified Molecular Resists
IeMRC Conference Sept 2007
J. Manyam, F.P.Gibbons, R.E. Palmer, A.P.G. RobinsonNanoscale Physics Research Laboratory, The University of Birmingham
M. Manickam, J.A. PreeceSchool of Chemistry, The University of Birmingham
http://nprl.bham.ac.uk
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Outline
• Project Overview & Objectives• Review of Relevant Prior Work• IeMRC Project Results • Conclusions and Acknowledgments
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Lithography Components
Energy - causes (photo)chemical reactions that modify resist dissolution rateMask - blocks energy transmission to some areas of the resistAligner- aligns mask to previously exposed layers of the overall designResist - records the masked pattern of energy
Energy
Mask + Aligner
PhotoresistWafer
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Positive Tone Resist
Positive tone resists are generally polymers which are prone to breaking on irradiation
hν
After scission of the polymer chain, the fragments have increased solubility in suitable solvents.
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Negative Tone Resist
Negative tone resists are generally polymers which are prone to crosslinking on irradiation
hν
After crosslinking of the polymer chain, the fragments have decreased solubility in suitable solvents
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Resist Requirements for NGL
After ITRS Roadmap, 2006 Update
Year
Feat
ure
Size
(nm
)
120
100
80
60
40
20
02005 2010 2015 2020
DenseSparse
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Why Polymeric Resists?
Historically resists have almost always been polymeric, [1] as they readily form smooth amorphous films by spin coating
PMMA fragment
[1] “Photoresist Materials”, C. Grant Willsonet al, SPIE, 3049, p 28
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The etch resistance of polymers is often low, and that together with pinhole density considerations requires the use of thick films.
Thick films can lead to:
• Pattern collapse on development • Inadequate optical transparency• Beam spreading (with charged particles).
Polymer Disadvantages
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[2] L. Merhari et al, Microelec.Eng., 63, 391 (2002)
Pattern collapse in KRS-XE on development. [2]
Pattern Collapse
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Line Edge Roughness
Image from www.tpd.tno.nl/smartsite910.html
Line edge roughness is affected by various factors including, lithographic noise, processing conditions, and polymer or polymer aggregate size
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Line Edge Roughness
Negative Tone
Crosslinking Chain Scission
Positive Tone
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Line Edge Roughness
[4] After ITRS, 2005, [5] R.L. Brainard et al,Microelec. Eng., 61-62, 707 (2002)
0
2
4
6
8
10
12
2002 2004 2006 2008 2010 2012 2014 2016 2018
Lin
e W
idth
Ro
ug
hn
ess
(nm
)
Year
0
2
4
6
8
10
120 2 104 4 104 6 104 8 104 1 105
Rad
ius
of
Gyr
atio
n (
nm
)
Molecular Weight (g/mol)
Line Width Roughness [4]Radius of Gyration [5]
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Molecular Resists
Molecular resists have been proposed to address the problems of polymeric resists.
Currently, molecular resists are capable of high resolution and high etch durability, but have poor sensitivity. We intend to address the latter without unduly affecting the former.
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Review of Prior Work Low Molecular Weight Resists
•
Amorphous Molecular Materials•
Calixarenes
•
Catechols•
Fullerene and its Derivatives
•
Molecular Resists/Molecular Glasses
•
Oriented materials (Liquid Crystals)•
Triphenylene Derivatives
•
Very Small Polymers•
Polystyrene
•
Poly(α-methylstyrene)
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Fullerene Resists
The first demonstration of C60 as a resist was by Rao [4] et al, who showed that exposure to 514.5 or 488.0 nm light to a dose of 5 W/cm2 caused a photopolymerisation of the molecules.
[4] A.M. Rao, et al, Science, 259, 955 (1993)
hν
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Fullerene Resists
Advantages of this Resist• Very high etch resistance (Etch Rate = 1/7.5 of silicon)• High resolution (<20 nm)
Disadvantages of this Resist:• Very low sensitivity10 mC/cm2
• Requires vacuum sublimation for coating
Tada and Kanayama found that the fullerene C60 demonstrates negative tone behaviour on irradiation with electrons. [5]
[5] T. Tada, et al, Jpn. J. Appl.
Phys., 35, L63 (1996)
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Fullerene Resists
To improve the solubility and therefore allow spin coating fullerene derivatives were synthesised by the addition of one or more addends to a fullerene cage
Methano Diels Alder
RR
R
R
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Fullerene Derivatives
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Fullerene Response to Irradiation
As well as allowing film formation by spin coating the addition of addends improved the sensitivity of the materials.
The best 20 keV sensitivity seen for fullerene derivatives is around 350 µC/cm2.
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Triphenylene Resists
Several polysubstituted triphenylenes, such as 2,3,6,7,10,11- hexapentyloxytriphenylene (C5/C5), shown here,
are liquid
crystalline materials. [6]
[6] N. Boden, et al, Liquid Crystals 15, 851 (1993)
C5H11O OC5H11
OC5H11
OC5H11C5H11O
C5H11O
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Polysubstituted TriphenylenesR1 R2
R1
R2R1
R2
R1 R2
R1
R2R1
R2
C5H11O O
OC5H11
OC5H11C5H11O
C5H11O
X CH2
N C5H11O O
OC5H11
OC5H11O
C5H11O
X CH2
N
XCH2
N
T98.0R1 = C5H11OR2 = C5H11O
T98.6R1 = C5H11OR2 = C7H15O T98.7
R1 = C5H11OR2 = C9H19O
T98.1R1 = C5H11OR2 = C2H5O
T98.4R1 = C5H11OR2 = C4H9O
T98.2R1 = C5H11OR2 = C3H7O
T98.5R1 = C5H11OR2 = C6H13O
T98.8R1 = C6H13OR2 = C6H13O
T98.12R1 = C5H11OR2 = C1H3O T98.15
R1 = C5H11OR2 = OHT98.13
R1 = C7H15OR2 = C3H7O T98.14
R1 = C8H17OR2 = C2H5O
T98.10R1 = C8H17OR2 = C2H15O T98.11
R1 = C5H11OR2 = C5H10COOHT98.9
R1 = C7H15OR2 = C3H7O
SYMMETRIC
ASYMMETRIC
n n
n
LC02-01 - X=CH2, n = 5
LC02-04 - X=CO, n = 5
LC02-03 - X=CO, n = 3
LC02-02 - X=CH2, n = 7
LC02-05 - X=CH2, n = 5
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Triphenylene Response to Irradiation
All of the tripheny- lene derivatives we have tested have a sensitivity in excess of 850 µC/cm2.
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Etch Durability
Etchant: SF6Temperature: 25°Cµ’wave power: 250 Wrf power: 20 WSF6 flow rate: 5 sccmPressure ~ 0.001 torrDC Self Bias 110 V
1/1
1/2
1/3
1/4
1/5
1/6
1/7
1/8
500 700 900 1100 1300
TriphenylenesFullerene Derivatives
Etc
h R
atio
(R
esis
t/S
ilico
n)
Molecular Weight (AMU)
PMMA
SAL601
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Fullerene and Triphenylene Patterning
Both the fullerene derivatives (a) and the triphenylenes (b & c) are capable of sub 20 nm patterning.
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The Sensitivity Problem
However, like most LMW resists, whilst very small feature sizes are possible and etch ratios are high, the sensitivity is poor.
The best fullerene derivative studied requires a dose of 370 µC/cm2, whilst for the triphenylene 880 µC/cm2 is need to expose the material.
Solution ChemicalAmplification
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Chemical Amplification
Chemical amplification is frequently used to improve sensitivity
O O OH
O
H++ R N
O
O
CH2CH
OH
CH2CH
O
CH2CH
O
R N+H+
-CH3OH
Positive Tone Negative Tone
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Fullerene CA Resist
We initially used the crosslinker hexa methoxymethylmel- amine (HMMM) together with various photo-acid generators such as triphenyl-sulfonium triflate
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Fullerene CA ResistMF03-04MF03-04[CA]
650 µC/cm2
7.5 µC/cm2
MF03-04:PAG:HMMM1 mg :0.23 mg:1.5 mg
20 keV ExposurePEB = 100 °C / 60 s
10 s MCB Development
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Fullerene CA Resist
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Fullerene CA Resist
R R
R
R
RR
RR
O
O O O
O OO
O
Tetra, Penta, Hexa Mix
OH
OH
S+ S S+SbF6
- SbF6-
OO
OO
OO
1.8
Methanofullerene: MF03-04
Crosslinker: DEN438
Photoinitiator:Triarylsulfonium hexaflutoantimonate salts
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Fullerene CA Resist
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Triphenylene CA Resist
0
20
40
60
80
100
120
10-7 10-6 10-5 0.0001 0.001 0.01 0.1
C5/C0Triphenylene epoxideTriphenylene epoxide + PITriphenylene epoxide + C5/C0 + PI
No
rmal
ised
Film
Th
ickn
ess
(%)
Dose (C/cm2)
610 µC/cm2
7.5 µC/cm2
17.5 µC/cm2
5530µC/cm2
Sensitivity
- Triphenylene Epoxide Derivative
- Additional Derivative
- Photoinitiator
C5H11O
HO
C5H11O OH
C5H11O
OH
C5H11O
O
C5H11O O
C5H11O
O
O
O
O
S+ S S+SbF6
- SbF6-
Resolution40 nm lines patterned in C5/epoxide:C5/C0:PI using a line dose of 800 pC/cm, PEB 100°C/120 s, developed in MCB for 10s
40 nmEtch RatioThe etch ratio was approximately 2.5 times that of SAL 601
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IeMRC Project Results
• Triphenylene Chemically Amplified Systems• Fullerene Chemically Amplified Systems
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Through careful optimisation:-Sensitivity is sub 10 µC/cm2
C5epoxide:C5C0:Pag07-01 (1:0.66:1)No PAB
Dose=900pC/cmPEB 100ºC, 2 mins
Develop: Acetone (1:1) IPA 15 secRinse: IPA 5 sec
25nm lines, 200nm pitch
C5epoxide:C5C0:Pag07-01 (1:0.66:1)No PAB
Dose=600pC/cmPEB 100ºC, 2 mins
Develop: Anisole (1:1) IPA 15 secRinse: IPA 5 sec
25nm lines, 70nm pitch
Triphenylene CA Resist
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Triphenylene Derivatives- C5/C0 and C5epoxide
- Sensitivity is sub 10 µC/cm2
- PEB at 100°C
C5/C0 PAG07-01C5epoxide
C5H11O
O
C5H11O O
C5H11O
O
O
O
O
22nm Sparse Lines
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Triphenylene Derivatives- C5/C0 and C5epoxide
- Sensitivity is sub 10 µC/cm2
- Lower PEB at 80°C
C5/C0 PAG07-01C5epoxide
C5H11O
O
C5H11O O
C5H11O
O
O
O
O
26nm Sparse Lines
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Triphenylene Derivatives- C5/C0 and C5epoxide
- Sensitivity is sub 10 µC/cm2
- PAB at 60°C for 10mins
C5/C0 PAG07-01C5epoxide
C5H11O
O
C5H11O O
C5H11O
O
O
O
O
15nm Sparse Lines
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Triphenylene Derivatives- C5/C0 and Cl06-10
- Sensitivity is sub 10 µC/cm2
C5/C0 PAG07-01CL06-10
20nm Sparse Lines 50nm Sparse LinesCL06-10:PAG07-01
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Triphenylene Derivatives- C5/C0 and Powderlink Crosslinker
C5/C0 PAG04-01CL06-01 (Powderlink 1174)
30nm resolution but the sensitivity was approximately 200 µC/cm2
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Fullerene CA Resist
O
O
O
O OMe
OMe
OMe
OMe
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Fullerene CA Resist
Tri, Tetra Penta Mix
R R
R
R
RR
RR
O
O O O
O OO
O
Tetra, Penta, Hexa Mix
OH
OH
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Fullerene CA Resist
- Fullerene Derivative
- Crosslinker
- Photoinitiator0
20
40
60
80
100
10-7 10-6 10-5 0.0001 0.001 0.01
MF03-04MF03-04:CL:PI (1:2:1)
No
mal
ised
Film
Th
ickn
ess
(%)
Dose (C/cm2)
550 µC/cm28 µC/cm2
SensitivityTri, Tetra Penta Mix
OO
OO
OO
1.8
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Fullerene CA Resist
20 nm SparsePatterns
Pattern Collapse at 1:4lines and spaces
Dose = 480 pC/cm Dose = 500 pC/cm
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Fullerene CA Resist
- Fullerene Derivative
- Crosslinker
- Photoinitiator
Tri, Tetra Penta Mix
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15 nm SparsePatterns
25 nm hp DensePatterns
Dose = 240 pC/cm Dose = 140 pC/cm
Fullerene CA Resist
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Fullerene CA Resist
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12 nm SparsePatterns
20 nm hp DensePatterns
Dose = 300 pC/cm Dose = 200 pC/cm
Fullerene CA Resist
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12 nmDose = 300 pC/cm Dose = 60,000 pC/cm
Comparison with Best Non CA Resist
14 nm
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Conclusions and Future Directions•
Prior to the IeMRC project we had shown chemical amplification but
could not retain resolution.
•
Resolution is now at least as good as the non-CA resists, and sensitivity is improved by more than 2 orders.
•
Etch durability is still equivalent to that of SAL601, but should be increase if possible (see poster).
• Resist Aging study under way (see poster).
• Is higher resolution achievable with a better tool?
• Is it possible to extend the resist to exposure by EUV as well?
• Fullerene with integrated crosslinker?
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AcknowledgmentsDr H.M. Zaid, Dr J.C. Barnard, Dr A.J. Parker, Dr M.R.C. Hunt Nanoscale Physics Research Laboratory, University of Birmingham
Dr U. Jonas, Prof. F. DiederichLaboratorium für Organische Chemie, ETH Zentrum, Switzerland
Dr S. Diegoli, Dr E. J. Shelley, Dr D. Philp, Dr M.T. Allen, Prof. K.D.M. HarrisSchool of Chemical Sciences, The University of Birmingham, UK
Dr T. Tada, Dr T. KanyamaJoint Research Center for Atom Technology, NAIR, Japan
Dr C. FigguresSowerby Research Centre, BAe Systems, UK
J. Mackevich, R. Brainard, T. Zampini, K. O’ConnellRohm and Haas (Electronic Materials), Marlborough USA