Dave guest lecture - People @ EECS at UC Berkeley · λ >= 193 nm λ = 13.5 nm Multilayer coatings...

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1 1 © Patrick Naulleau, 2008 EUV Lithography Patrick Naulleau Center for X-ray Optics, Lawrence Berkeley National Laboratory 2 © Patrick Naulleau, 2008 Outline • Introduction • Review of key optics concepts for lithography • EUV Capabilities/Challenges • EUV patterning and resists • Mask defects and printing

Transcript of Dave guest lecture - People @ EECS at UC Berkeley · λ >= 193 nm λ = 13.5 nm Multilayer coatings...

Page 1: Dave guest lecture - People @ EECS at UC Berkeley · λ >= 193 nm λ = 13.5 nm Multilayer coatings used to render surfaces reflective at EUV ... 2008 33 Modeling Resist Using Simple

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1© Patrick Naulleau, 2008

EUV Lithography

Patrick Naulleau

Center for X-ray Optics, Lawrence Berkeley National Laboratory

2© Patrick Naulleau, 2008

Outline

• Introduction

• Review of key optics concepts for lithography

• EUV Capabilities/Challenges

• EUV patterning and resists

• Mask defects and printing

Page 2: Dave guest lecture - People @ EECS at UC Berkeley · λ >= 193 nm λ = 13.5 nm Multilayer coatings used to render surfaces reflective at EUV ... 2008 33 Modeling Resist Using Simple

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3© Patrick Naulleau, 2008

EUV: extension of optical lithography

Wafer

Mask

λ

Mask

λ

Wafer

PhotoresistPhotoresist

λ >= 193 nmλ = 13.5 nm

Multilayer

coatings used

to render

surfaces

reflective at

EUV

4© Patrick Naulleau, 2008

The mask serves as the circuit master in lithography systems

wafer

mask

Projection optics

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5© Patrick Naulleau, 2008

Review of key optics concepts

for lithography

• Diffraction

• Resolution

• Depth of focus

• Partial coherence

• Etendue

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Diffraction

W WW

λ = 13.5 nm

W = 300 nm

z =

0.2 µm

z =

1 µm

z =

5 µm

z =

25 µm

Angular spread, θ = asin(λ/W)

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7© Patrick Naulleau, 2008

Image formation: inverse diffraction

• Function of lens is to invert diffraction process

• θ = asin(λ/W) => Wmin = λ/sin(θmax)

θmax

Resolution ∝ Wmin = λ/sin(θmax) = λ/NA

Res = k1 λ/NA

NA = sin(θmax)

8© Patrick Naulleau, 2008

Depth of focus

• Let DOF be proportional to distance where

single-sided blur = resolution

θmax

dmax NA = λ/NA

DOF ∝ dmax = λ/NA2

DOF = k2 λ/NA2

Blur = d NA

d

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9© Patrick Naulleau, 2008

Concept of partial coherence factor (σσσσ)

• Most fundamentally, σ is the ratio of mask-side

resolution limit to coherence width (Wc)

Wc

• Large Wc = small σ

• Determines area over which object components

add coherently

10© Patrick Naulleau, 2008

Critical illumination: σσσσ = ratio of NAs

NApo

Projection

optic pupilCondenser

optic pupil

Projection

optic object

plane

NAci

Wc ∝ 1/NAci Reso ∝ 1/NApo

σ = Reso/Wc = NAci/NApo

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11© Patrick Naulleau, 2008

Pupil fill: alternative view of σσσσ

σ = NAci/NApo = rs/rL

NApo

Projection

optic pupilCondenser

optic pupil

Projection

optic object

plane

NAci

rsrL

Example view of pupil fill for σ = 0.35

Projection lens pupil

12© Patrick Naulleau, 2008

Etendue: space-bandwidth product

NA=0.25

NA=0.0625Field size = 6x96 mm2

• The optic etandue (maximum accepted space-

bandwidth product) is

• Field of view area X acceptance solid angle

• 6*96*0.01 mm2 sr ~ 7 mm2 sr

Projection optic

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13© Patrick Naulleau, 2008

NA=0.7Source size = 1 mm2

• A 1 mm source with 45-degree collection would

have an etendue of ~2 mm^2 sr (min σ = 0.53)

• A 0.1 mm source with 70-degree collection would

have an etendue of ~0.04 mm^2 sr (min σ = 0.08)

Projection optics etendue limits usable

source etendue and thus power

Collector optic

14© Patrick Naulleau, 2008

6 mirrors8 mirrors

NA = 0.1

4 mirrors

Increasing NA demands more mirrors

• More mirrors means

lower throughput

• But, larger NA means

larger etendue

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15© Patrick Naulleau, 2008

EUV Patterning Capabilities: modeling

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Extendibility of EUVBinary amplitude mask, σ = 0.7, no OPC, no bias correction

Page 9: Dave guest lecture - People @ EECS at UC Berkeley · λ >= 193 nm λ = 13.5 nm Multilayer coatings used to render surfaces reflective at EUV ... 2008 33 Modeling Resist Using Simple

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17© Patrick Naulleau, 2008

Optical transfer function vs NA

Binary amplitude mask, σ = 0.5, no aberrations

18© Patrick Naulleau, 2008

Optical transfer function through sigma

Binary amplitude mask, NA = 0.32, no aberrations

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19© Patrick Naulleau, 2008

Optical transfer function through illumination type

Binary amplitude mask, NA = 0.32, no aberrations

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8-nm possible at 0.5 NA with

conventional mask

8-nm elbow pattern

Binary amplitude mask, dipole illumination, no OPC, no bias correction

Pole radius = 0.2Pole offset = 0.8

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21© Patrick Naulleau, 2008

EUV-specific challenges

Long-range “proximity” correction required

Short wavelength -> high scatter -> large position dependent flare

Position dependent mask bias correction

required

Tilted mask plane: shadowing by 3D mask structure

Strict reticle flatness requirementsTilted mask plane: system not telecentric at reticle

Use electrostatic clamping, mag. Lev.

stages

Vacuum clamping cannot be used. Air-bearing motion

mechanisms are complex

Reflective mask leads to potential “buried” phase

defects (< 3-nm tall)

EUV sources are inefficient producers of radiation

Source chamber cannot be physically separated from

imaging optics chamber

Hydrocarbons & water vapour are cracked by EUV,

contaminating mirror surfaces – C deposition &

oxidation of coatings

All solid materials strongly absorb EUV radiation

EUV radiation is not transmitted through the atmosphere

Challenge

Extremely high sensitivity mask blank

inspection required

Efficient thermal management of waste

heat from high input powers required

Contain any debris produced by source –

particles & ions

Minimize hydrocarbons and water vapour

content in the tool. Needs cleanliness of

ultra high vacuum (UHV)

Refractive optics not possible. Use only

reflective mirrors & reticles

Tool must operate in vacuum environment

Consequence

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Top 3 Critical Issues

1. Reliable high-power source and collector module

• Largely industrial effort

2. Availability of defect-free masks and mask infrastructure

3. Resist resolution, sensitivity & Line Edge Roughness (LER) met simultaneously

Ref: 2008 International EUVL Steering Committee

EUVL critical issue list

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23© Patrick Naulleau, 2008

• Numerical aperture = 0.3

• Spatial resolution = 12 nm*

• Supports approximately 200 user shifts per year with nearly 100% uptime

• Unique programmable coherence illuminator enables world’s finest projection EUV resolution

• Supports:

• Resist development

• Mask development

• Mask defect studies

ALS Undulator BL12.0.1.3

Coherence control module

Mask stage

2-mirror projection optics

Wafer stage and height sensor

Coherence monitor

Berkeley EUV Nano-patterning tool designed to support advanced EUV research

24© Patrick Naulleau, 2008

Worldwide user base including industry, academia, and research institutes

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25© Patrick Naulleau, 2008

Simultaneously meeting resolution, sensitivity, and LER crucial issue for EUV resists

10 mJ/cm2

10 mJ/cm210 mJ/cm2

1.2 nm0.8 nm0.6 nm

32-nm half pitch (21-nm iso) - 2013*22-nm half pitch (15-nm iso) -201616-nm half pitch (11-nm iso) -2019

* 2007 ITRS RoadmapLER: Line Edge Roughness

26© Patrick Naulleau, 2008

Although most EUV resists are based on 193 or 248 nm systems, EUV interaction with resist these materials is fundamentally different

• EUV energy (92 eV) many times higher than Photo Acid Generator (PAG) activation energy

• EUV interacts with all atoms, cannot be made to preferentially interact with PAG

• Photons do not directly activate PAG but rather generate secondary electrons upon interaction with first encountered atom

–Secondary electrons eventually activate PAG

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27© Patrick Naulleau, 2008

Although most EUV resists are based on 193 or 248 nm systems, EUV interaction with resist these materials is fundamentally different

H

O

C

Photo Acid Generator (PAG)

Visible photons, only enough energy to interact with PAG

hνVis

hνEUVe-

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Chemically amplified resists now approaching 20 nm

22 nm HP 20 nm HP

Resist C

12.7 mJ/cm2

50-nm resist thickness

24 nm HP

Resist D

15.2 mJ/cm2

Page 15: Dave guest lecture - People @ EECS at UC Berkeley · λ >= 193 nm λ = 13.5 nm Multilayer coatings used to render surfaces reflective at EUV ... 2008 33 Modeling Resist Using Simple

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29© Patrick Naulleau, 2008

High pattern fidelity at small feature sizes

22 nm HP 20 nm HP24 nm HP

30 nm 1:1 contacts

Resist D, film thickness = 50 nm

30© Patrick Naulleau, 2008

Rinse agents for LER reduction without resolution or sensitivity trade-offs

Data courtesy of Tom Wallow, AMD

Baseline Process Rinse Agent Process

CD = 41.7 +/- 0.8 nm

LER = 4.3 +/- 0.4 nmCD = 40.6 +/- 0.6 nm

LER = 3.2 +/- 0.4 nm

• Rinse agent applied instead of water after development

• ~1-nm reduction in LER observed

• No effect on resolution or sensitivity

XP5494-C resist,

Y-Monopole

Berkeley METBerkeley MET

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31© Patrick Naulleau, 2008

Repeated printing of 35 nm contacts shows

variation NOT dominated by photon noise

RHEM ResistBerkeley METAnnularE0 = 10mJ/cm2

focus

+50 nm

Esize +15%

• 35-nm 1:2 contacts

• RMS size variation = 3.2 nm

• Reproducible size variation through dose and focus

• Contact variation must be dominated by mask

32© Patrick Naulleau, 2008

Optical mask error enhancement factor (MEEF) does not explain observed contact variation

Mask Ideal Resist

MEEF = 12.8 nm error on 35 nm contacts

(wafer coordinates)Aerial-image

modeling includes full EUV wavefront

Actual Mask

• 35 nm 1:1 contacts on 5x EUV mask

• RMS 1x diameter variation = 1.1 nm

• Resist var. = 1.1 nm

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33© Patrick Naulleau, 2008

Modeling Resist Using Simple

Point-Spread-Function (PSF) Method

“Deprotection blur” function PSF

* C. Ahn, H. Kim, K. Baik, “A novel approximate model for resist process,” Proc. SPIE 3334, (1998).

** Gregg Gallatin, “Resist Blur and Line Edge Roughness,” Proc. SPIE 5754, (2005)

• PSF resist modeling* is fast and convenient

• Model easily generated

• Provides intuitive link to resist resolution limit

• Few parameters makes model less susceptible to extrapolation errors

• Resist process well approximated by deprotection function**

34© Patrick Naulleau, 2008

Resist blur dominates MEEF

Mask 20-nm Blur Resist

MEEF = 3.62.8 nm error on 35 nm contacts

(wafer coordinates)Aerial-image

modeling includes full EUV wavefront

Actual Mask

• 35 nm 1:1 contacts on 5x EUV mask

• RMS 1x diameter variation = 1.1 nm

• Resist var. = 4.0 nm

Page 18: Dave guest lecture - People @ EECS at UC Berkeley · λ >= 193 nm λ = 13.5 nm Multilayer coatings used to render surfaces reflective at EUV ... 2008 33 Modeling Resist Using Simple

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35© Patrick Naulleau, 2008

Resist blur dominates MEEF

0 50 100 150 200 250 300 350 400 4500

0.2

0.4

0.6

0.8

1

Image Position (nm)

No

rma

lize

d D

ep

rote

ctio

nAerial image aloneResist-blurred deprotection image

36© Patrick Naulleau, 2008

The mask serves as the circuit master in lithography systems

wafer

mask

Projection optics

Page 19: Dave guest lecture - People @ EECS at UC Berkeley · λ >= 193 nm λ = 13.5 nm Multilayer coatings used to render surfaces reflective at EUV ... 2008 33 Modeling Resist Using Simple

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37© Patrick Naulleau, 2008

Pattern defects on become replicated problems on

the wafer, although attenuated by optic and resist

Data courtesy of Ted Liang, Intel

Details published at Photomask Japan, 2006

Mask: 60-nm defect Resist: 9% CD Change

38© Patrick Naulleau, 2008

Buried (phase) defects become intensity after band-limited imaging and further enhanced by defocus

Modeled aerial image of

programmed 100-nm isolated

defects through focus (100-nm

steps)

100-nm defects not expected

to be printable at Esize)

Modeled aerial image of

programmed 100-nm isolated

defects through focus (100-nm

steps)

100-nm defects not expected

to be printable at Esize)

Modeled defect

at surface:

parameters

based on latest

LLNL process

Modeled defect

at surface:

parameters

based on latest

LLNL process

Focus-100 nm +100 nm-200 nm-300 nm-400 nm

-600 nm-700 nm -500 nm-800 nm-900 nm-1000 nm

+600 nm+500 nm +700 nm+400 nm+300nm+200 nm

+800 nm

Page 20: Dave guest lecture - People @ EECS at UC Berkeley · λ >= 193 nm λ = 13.5 nm Multilayer coatings used to render surfaces reflective at EUV ... 2008 33 Modeling Resist Using Simple

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39© Patrick Naulleau, 2008

Programmed “buried” defects developed

to study critical mask issues

buried defectsTop view of

programmed defect cell

absorber

pattern

substrate

resulting phase defect

reflective multilayer

absorber pattern

60-nm defects

70-nm defects

buried defect

40© Patrick Naulleau, 2008

off-axis ZP (µµµµscope objective)

CC

D

mask

Illumination window

The world’s highest-performance EUV microscope dedicated to photomask research

• International EUV program’s primary tool for at wavelength mask defect inspection and cross correlation with complimentary techniques

• Spatial resolution approaching 90 nm at the mask (23 at wafer)

• Working with partners regarding future upgrades. Special attention to supporting the development of commercial tools.

NA = real-time selectable

0.25–0.35 (4x)

Res. ≥ 93 nm (23 @ 4x)

Mag = 800–1000x

See poster

Ken Goldberg / [email protected]

ALS BL 11.3.2

Page 21: Dave guest lecture - People @ EECS at UC Berkeley · λ >= 193 nm λ = 13.5 nm Multilayer coatings used to render surfaces reflective at EUV ... 2008 33 Modeling Resist Using Simple

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41© Patrick Naulleau, 2008

The CXRO mask inspection microscope provides an unparalleled view into defect printability

AerialImages

5 µm

0.00 µm

0.78

1.64

2.43

3.26

4.14

4.96

z1 µm

amplitude-defect repair sites

G. Yoon, et al.

SAMSUNG

Aerialimages

through focus

1 µm1 µm

Defects:

phase

absorber

through-focus

W. C

ho

200

7S

EM

AT

EC

H

Materials Sciences Division 41MSD Retreat August 12, 2008

Ken Goldberg / [email protected]

42© Patrick Naulleau, 2008

NA=0.7Source size = 1 mm2

• A 1 mm source with 45-degree collection would

have an etendue of ~2 mm^2 sr (min σ = 0.53)

• A 0.1 mm source with 70-degree collection would

have an etendue of ~0.04 mm^2 sr (min σ = 0.08)

Implications of etendue limits for

mask inspection microscopy

Collector optic