NPRL Nanoscale Physics Research Laboratory Chemically Amplified Molecular Resists IeMRC Conference Sept 2007 J. Manyam, F.P.Gibbons, R.E. Palmer, A.P.G. Robinson Nanoscale Physics Research Laboratory, The University of Birmingham M. Manickam, J.A. Preece School of Chemistry, The University of Birmingham http://nprl.bham.ac.uk
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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
NPRLNanoscale Physics Research Laboratory
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.