Minimizing Linewidth Roughness in Step and Flash Imprint Lithography

Niyaz Khusnatdinov, Gerard M. Schmid, Cynthia B. Brooks, Dwayne LaBrake, Douglas J. ResnickMolecular Imprints, Inc., 1807C West Braker Lane, Austin TX 78758

Mark W. Hart, Kailash Gopalakrishnan, Rohit Shenoy, Ron JihIBM Almaden Research Center, 650 Harry Road San Jose, CA 95120-6099

Ying Zhang, Edmund Sikorski, Mary Beth RothwellIBM Thomas J. Watson Research Center, 1101 Kitchawan Road, Route 134Yorktown Heights, NY

10598-0218

Jordan Owens, Arnie FordSematech ATDF, 2706 Montopolis Drive, Austin, Texas 78741-6499

dresnick@militho.com

Line Width Roughness

4Line Width Roughness (LWR) (nm, 3σ)– Variation of CD– Leads to variation of MOS gate width– Affects device speed of individual transistors– Leads to IC timing issues

0.81.21.72.43.4LWR

1622324565DRAM½ Pitch

20192016201320102007

ITRS Roadmap

Future nodes have no known solutions

Where is the industry with respect to the roadmap?

Where is the industry with respect to the roadmap?

An Example: EUVL

4 For S-FIL®, the imprint process adds no additional LWR4 The problem of LWR is transferred to the fabrication of the template

? Insensitive resists? Non-chemically amplified resists

LWR ~ 8 nm*

ZEP520A

4Throughput requirements of EUVL require 4 the use of fast chemically amplified resists

– Low exposure dose:– Too few photons (~2/nm2)– Shot noise– Material issues:– Acid Diffusion, PAG Concentration, Quenching, etc.

*SPIE 2007

Template Fabrication

4LWR from a template fabricated with a CA resist (imprint results)4LWR generated from ZEP520-based templates

– 30nm semi-dense features: imprints and etched features– 42nm dense features: imprints and etched features– 32nm dense features: template images, imprints and etched features– Extendibility to 26nm half pitch

4Summary

Resist appliedto ~10 nm of Cr

Expose/develop e-beam resist, descum

Etch chrome,strip resist

Etch quartz,Strip chrome

6025 Quartz

ResistCr

E-beam Exposure Cl2/O2 Fluorine based chemistry

LWR from a template fabricated using a CA resist

1.893scale, nm / pixel

3.785profile sampling step, nm

8176.637total line length, nm

-90.800line orientation, degree

4line number

-12.867sigma inf <3s >

2.509185.884pitch

0.7418.369right LER <3s >

1.1675.965left LER <3s >

1.37111.272LWR <3s >

2.01894.933line width

standard deviation, nmmean, nmparameter

90nm HP

Imprinted 90nm lines

CA resist sensitivity: ~ 11 µC/cm2

0.60 electrons/nm2

LWR = 11.3nm, 3σ

CA resist sensitivity: ~ 11 µC/cm2

0.60 electrons/nm2

LWR = 11.3nm, 3σ

30nm Semi-dense Template patterns: DetailsDevice structures:

*20nm features not writtenSEM structures:1:1 L/S, 1:3 L/S†1:1 L/S start at 50nm

1:1 L/S

1:3 L/S

Device structures: 1fin, 2fin

1:3 L/S

20nm*

30nm

40nm

50nm†

60nm

70nm

80nm

30 to 70nm

30 to 70nm

30nm Semi-Dense Features for IBM Storage-Class Memory Test Structures

BOx

Si

Ox

Template Imprint

X-Section of Processed FinsEtched SOI Fins

ZEP520A

30nm Device: Imprint LWR Analysis

30 nm Vertical Device

parameter mean st.dev.

Line Width, nm 40.807 1.273

LWR <3s>, nm 2.43 0.153

Line Space, nm 82.706 1.738

Pitch Left, nm 123.497 2.935

Pitch Right, nm 124.158 1.316

LER Left <3s>, nm 2.68 0.244

LER Right <3s>, nm 2.416 0.375

100nm

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200 250 300 350 400

X, nm

Nor

mal

ized

Hei

ght

SEM LWR Analysis: After Etch

40nm field #11

LWR 2.05 1.79 2.4LER 1.01

30nm field #6

LWR 1.91 2.15 2.56LER 1.76

30nm Device: LWR After Etch

Data for Wafer #1 and Wafer #25

30

35

40

45

50

0

0.5

1

1.5

2

2.5

3

3.5

4

0 2 4 6 8 10 12 14 16

CD-1 (nm)

CD-25 (nm)

LWR-1 (nm)

LWR-25 (nm)

Crit

ical

Dim

ensi

on (

nm)

LWR

(nm)

Line Number

LWR = 2.61nm

• LWRimprint = 2.43nm, 3σ

• LWRetch = 2.61nm, 3σ

• Both CD and LWR track fromone wafer to the next:

CD correlation: 0.928LWR correlation: 0.528

40nm Device: LWR After Etch

45

50

55

60

65

0

0.5

1

1.5

2

2.5

3

3.5

4

0 2 4 6 8 10 12 14 16

CD40-1

CD40-25

LWR40-1

LWR40-25

Crit

ical

Dim

ensi

on (n

m)

LWR

(nm)

Line Number

Data for Wafer #1 and Wafer #25

• LWRimprint = 2.43nm, 3σ

• LWRetch = 2.62nm, 3σ

• Both CD and LWR track fromone wafer to the next

CD correlation: 0.907LWR correlation: 0.954

LWR = 2.62nm

Radial Etch Dependence Wafer #25: 30nm and 40nm

Radial Dependence of 30 nm and 40 nm Devices on Wafer #25

y = 0.0462x + 45.996

y = 0.0403x + 30.816

0

10

20

30

40

50

60

0 20 40 60 80 100

Distance from wafer center (radius), mm

CD

, nm

42nm Half Pitch: Imprint thru Etch

CD 41.3.nm 39.3nm 40.7nm 38.4nmLWR 2.8nm 2.5nm 2.7nm 2.9nm

Imprint Descum Oxide Etch Clean

2.172.542.042.082.402.462.412.04LER Right <3s > nm

2.992.002.812.292.502.302.332.47LER Left <3s > nm

3.112.643.132.782.722.343.212.36LWR <3s > nm

41.4341.7940.3441.4341.1341.0441.6741.16Width med, nm

44.5744.5443.3844.0243.7943.7945.0043.17Width max, nm

39.0439.3437.6238.1938.6939.0338.8038.79Width min, nm

87654321Results / Line

Imprint Statistics1 2 3 4 5 6 7 8

32nm HP: Template Images

32nm 36nm

40nm 44nm

Template: CD and LWR Analysis

parameter mean standard deviation

Line Width, nm 31.886 0.518

LWR <3s>, nm 3.121 0.409

sigma inf <3s>, nm 3.510 -

Line Space, nm 32.149 1.121

Pitch Left, nm 64.136 1.003

Pitch Right, nm 63.878 1.240

Slope Angle Left, degree 96.029 0.673

Slope Angle Right, degree 96.117 0.645

LER Left <3s>, nm 4.326 0.447

LER Right <3s>, nm 4.074 0.368

32nm

30

32

34

36

38

40

42

44

46

0

1

2

3

4

5

6

7

8

30 32 34 36 38 40 42 44 46

Measured CD (nm)

LWR (nm)

Coded CD (nm)

4 CD is linear from 32 to 44nm (to within about 5%)4 LWR is small, and independent of critical dimension

32nm Imprint Evaluation

4 Imprints #1 and #2 are taken from the same location

4 Imprint #3 is located 2mm from Imprint #1

32nm

Template: LWR = 3.1nm

#1

#2

#3

32nm Imprint Evaluation

4 CDmean = 34.72nm, 1.62nm 3σ4 LWRImprint = 2.73nm, 3σ (LWRTemplate = 3.12nm)

2.60LWR <3s > nm

0.4935.24Line Width, nm

σmeanparameter

3.054LWR <3s > nm

0.3634.246Line Width, nm

σmeanparameter

2.549LWR <3s > nm

0.3534.554Line Width, nm

σmeanparameter

28nm Half Pitch Imprints

-5.446sigma inf <3s >, nm

3.598LWR <3s >, nm

1.35729.453Line Width, nm

standard deviationmeanparameter

26nm Half Pitch Imprints

1.45252.605Pitch Left, nm

1.19432.037Line Space, nm

-3.740sigma inf <3s >, nm

3.150LWR <3s >, nm

0.66520.524Line Width, nm

std deviationmeanparameter

3.363.183.623.113.053.062.64LWR, 3s nm

20.2720.7521.5820.9320.2120.0019.95Width med nm

22.6522.8724.8523.7922.1122.4621.76Width max nm

17.2817.9119.3019.3417.4917.6617.66Width min nm

7654321Results / Line

LWR Summary

4To a first approximation, LWR is independent of CD, pattern density, and process step

4 Total # lines measured: 1304 LWRmean = 2.87nm4 LWRmin = 1.70nm4 LWRmax = 4.39nm4 3σ = 1.71nm

0

1

2

3

4

5

15 20 25 30 35 40 45 50

TemplateImprintEtchFit

LWR

(nm

)

Measured CD (nm)

Conclusions

4 Low values of LWR can be obtained. The key is to use high resolution and slow electron beam resists, such as ZEP520A when writing thetemplates

4 LWRs less than 3nm, 3σ are routinely obtained. Feasibility for obtaining LWRs < 2nm has been demonstrated

4 Low LWR is maintained through etch, and for features as small as 20nm

NEXT STEPS

4 Better characterization of LWR after exposure and development of the e-beam resist

4 Extending the study to VSB pattern generators

Acknowledgments

The Authors gratefully acknowledge the templates and imprints provided by:

DNPHoya

ToshibaThe authors would also like to thank S.V. Sreenivasan

and Mark Melliar-Smith for supporting this work

This work was funded in part by NIST-ATP