Chemically Amplified Molecular Resists

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


Outline

• Project Overview & Objectives• Review of Relevant Prior Work• IeMRC Project Results • Conclusions and Acknowledgments


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


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.


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


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


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


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


[2] L. Merhari et al, Microelec.Eng., 63, 391 (2002)

Pattern collapse in KRS-XE on development. [2]

Pattern Collapse


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


Line Edge Roughness

Negative Tone

Crosslinking Chain Scission

Positive Tone


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]


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.


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)


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


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)


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


Fullerene Derivatives


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.


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


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


Triphenylene Response to Irradiation

All of the triphenylene derivatives we have tested have a sensitivity in excess of 850 µC/cm2.


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


Fullerene and Triphenylene Patterning

Both the fullerene derivatives (a) and the triphenylenes (b & c) are capable of sub 20 nm patterning.


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


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


Fullerene CA Resist

We initially used the crosslinker hexa methoxymethylmel- amine (HMMM) together with various photo-acid generators such as triphenyl-sulfonium triflate


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


Fullerene CA Resist


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


Fullerene CA Resist


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


IeMRC Project Results

• Triphenylene Chemically Amplified Systems• Fullerene Chemically Amplified Systems


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


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




- Lower PEB at 80°C


C5H11O

O

C5H11O O

C5H11O

O

O

O

O

26nm Sparse Lines




- PAB at 60°C for 10mins


C5H11O

O

C5H11O O

C5H11O

O

O

O

O

15nm Sparse Lines


Triphenylene Derivatives- C5/C0 and Cl06-10


C5/C0 PAG07-01CL06-10

20nm Sparse Lines 50nm Sparse LinesCL06-10:PAG07-01


Triphenylene Derivatives- C5/C0 and Powderlink Crosslinker

C5/C0 PAG04-01CL06-01 (Powderlink 1174)

30nm resolution but the sensitivity was approximately 200 µC/cm2


Fullerene CA Resist

O

O

O

O OMe

OMe

OMe

OMe


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


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


Fullerene CA Resist

20 nm SparsePatterns

Pattern Collapse at 1:4lines and spaces

Dose = 480 pC/cm Dose = 500 pC/cm


Fullerene CA Resist

- Fullerene Derivative

- Crosslinker

- Photoinitiator

Tri, Tetra Penta Mix



25 nm hp DensePatterns


Fullerene CA Resist


Fullerene CA Resist



20 nm hp DensePatterns


Fullerene CA Resist


12 nmDose = 300 pC/cm Dose = 60,000 pC/cm

Comparison with Best Non CA Resist

14 nm


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?


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

Chemically Amplified Molecular Resists

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