www.thalesgroup.com

Ion Beam Figuring precision optics for synchrotron radiation sources

L. PEVERINI, J. J. FERME & C. du JEU

Thales SESO S.A.S., Aix en Provence, 13593, France

email: luca.peverini@fr.thalesgroup.com

2 / 2 / Ion beam profiling (IBP) approaches for SR optics

IBP schemes for “1D” grazing incidence X-ray mirror optics (Silicon, SiO2 and Zerodur)

L. Peverini et al., Ion beam profiling of aspherical X-ray mirrors, NIM A 616 (2010) 115–118 (technology)

V.I.T.A. de Rooij-Lohmann et al., Roughness evolution of Si surfaces upon Ar ion erosion , Applied Surface Science 256 (2010) 5011–5014 (in-situ)

Off-set scan

• Sample/spot moving

• Slow process

• High resolution

Single Blade Scan

• Sample/slit moving

• Slow process

• Interesting for coating

Gap Scan

• Sample Stationary

• very fast

• Requires Broad Beams

v=v2(x)

x

v=v1(x)

x

d(x)

v=v2(x)

x

v=v1(x)

x

d(x)

x

v=v(x)

d(x)

x

v=v(x)

d(x)

v= )

d(x)

x

v=v(x)

d(x)

x

v=v(x)

d(x)

v= )

d(x)v=v(x)

x

d(x)

x

d(x)

v=v(x)

x

d(x)

x

d(x)Removal of material by

sputtering

ion beam

Tight slope error specification along the longitudinal direction (< 500 nrad)

Non-contact polishing method possibility to use in-situ metrology

3 / 3 / Fabrication and testing

miroir Direction scan X

Source IBF

Ion beam

TOP view

X

Z

Y

L = +/- 1700 mm

UHV 10-6 mbar 10-7 mbar

L = 1500 mmTypical processing scheme Substrate scanning - offset scan Mirror prepared by traditional polishing

Reference system

flat/spherical Reference

ZYGO

R

R=∞

TESTING Layout (HFM)

Phase shifting interferometry 1 shot measurements

Grazing geometry (angle q~4-20 deg) simulate final SR use

Gravity does not play a role (difficult with LTP instruments – laser deflectometry very popular in the SR community)

Double-pass reduces reference errors

Useful technique in phase of integration adjustement of deformable mirrors

Clean room environnent Phase Shifting Interferometry (PSI)

objective

4 / 4 / IBP convergence

0.4- 0.2- 0 0.2 0.450-

0

50

100

150

200

Removal Function (theory)

Removal Function (experimental)

Profiling error

Mirror coordinates [mm]

Surf

ace

Heig

ht

[nm

]

Convergence rely on: 1) Flux stability during scanning and several days (especially when using an iterative approach) 2) Removal rate determination accuracy 3) Reference system used for both metrology/IBP 4) Accurate metrology data manipulation to extract pure surface data (image and signal processing) 5) Possibility to account for systematic errors (fabrication+metrology) 6) Well defined operational sequences and well trained staff

P0-P1

5 / 5 / µ-Roughness and IBP

-3-3.5-4-4.5-5-5.5-6

7

6

5

4

3

2

1

0

-1

k[log({1/nm})]

PS

D[l

og

(nm

4)]

-3-3.5-4-4.5-5-5.5-6

8

7

6

5

4

3

2

1

0

-1

k[log({1/nm})]

PS

D[l

og

(nm

4)]

100µm 100µm

2.69

0.00

3.62

0.00

100µm 100µm

s = 0.11 nm s = 0.08 nm s = 0.27 nm s = 0.24 nm

µ-roughness preservation prooved for Removed thickness ranging 20 3000 nm Regardeless of initial morphology and roughness amplitude (periods 10-1000 µm)

After IBP After IBP Before IBP Before IBP

Smoothing observed for initially flat surfaces

Roughness preservation for initially rougher substrates

Physics of ions intercation is more critical @ AFM spatial scales (p<10 µm) …ion energy, angles etc.

AFM studies E. Ziegler et al., Evolution of the surface finish of an X-ray mirror exposed to a low-energy ion beam, NIM A (2010)

F. Frost, B. Ziberi, A. Schindler, B. Rauschenbach, Appl. Phys. A 91 (2008) 551 (nanopatterning)

6 / 6 / PSI data traitement for deterministic polishing

the 1st requirement is the data repeatability: Turbulence, thermal gradients, CCD noise & laser coherence surface data are mixed to all these artifacts with different spatial/temporal dependencies

Air bubbles and thermal gradients Data are rejected if this condition is not achieved

7 / 7 / TSESO metrology capabilities

accuracy (difference between 2 statistically independent acquisitions) typically 60 - 150 nrad

High Frequency Noise 50 – 100 nrad

repeatability (difference between 2 consecutive measurements) typical 25- 70 nrad

Processing and values data confirmed by LTP customer measurements (next slides) Some mirrors have complex parabolic shape and multistripe design heavy image/signal processing requiring customized scripts adapted to each specific situation Automation and standardisation is necessary for smooth industry productivity but require a big effort and highly specialized staff 1 m

8 / 8 / Metrology validation for slope errors ~0.5-0.6 µrad

LTP

slope(LTP)-slope(PSI)<50 nrad (stdev)

9 / 9 / Metrology validation PSI vs LTP for slope error < 0.3 µrad

High Frequency introduces a factor ~2 in the slope error estimation. 1)Correlated signal in LTP data (partial laser cohérence) 2)Shape obtained from LTP is smoothened naturally by the integral operator 3)PSI need to be filtered for slope error evaluation therefore part of the surface signal might be suppressed

PSI/LTP data treatement @ high frequency…

Excellent shape agreement LTP LTP

LTP

stdev(LTP-PSI)~0.5 nm !!!

Before final correction

10 / 10 / HF noise (speckles)

a) Speckles are independent on the mirror size and the surface microtopography (in a morphological sense) b) The pattern observed is characterized by a « round » shapes regardeless of the surface morphology and PSI

geometry c) The speckle pattern is static d) The recording method can enhance this effect (especially using large statistical sampling necessary to average

environmental artifacts) e) 1D LTP data from 2 different customers presents very similar features

« Cleaned » speckle pattern obtained using a lateral shift dx>x (speckles corr. length) and low

frequency FFT filtering

Refs R. Cerbino, L. Peverini, M. A. C. Potenza, A. Robert, P. Bo¨secke, and M. Giglio, Nature Phys. 4, 238 (2008) S.Berujon, E. Ziegler, R. Cerbino, and L. Peverini1,*PRL 108, 158102 (2012)

11 / 11 / 1st APPLICATION – short mirrors for nanofocusing

Variable range of curvature

t = 5 mm

R = 20-800 m

Specification Shape errors < 0.75 nm-rms Slope errors r.m.s < 500 nrad

TORPEDO (parabolic) width profiles for elliptical shaping (variable inertia)

12 / 12 / Mirror length L=130 mm

50- 40- 30- 20- 10- 0 10 20 30 40 5050-

40-

30-

20-

10-

0

10

before IBP (stripe 1)

after IBP (stripe 1)

IBF corrections - shape errors

mirror coordinate [mm]

surf

ace

heig

ht

[nm

]

PTVafter2 46.891 nm

PTVbefore2 2.54 nm

50- 40- 30- 20- 10- 0 10 20 30 40 506-

4-

2-

0

2

4

6

Slope

Sl 1 106

Sl 2 106

x1 1000 x2 1000 x3 1000 x4 1000

Before correction

stdev S l2( ) 106

1.791 µrad

After correction

stdev S l1( ) 106

0.298 µrad

PTV before = 46.891 nm PTV after = 2.54 nm Shape r.m.s = 0.5 nm (specification 0.75 nm)

slope error r.m.s (before IBP)= 1800 nrad slope error (after IBP)= 298 nrad

High accuracy data (near-normal incidence PSI) Spatial resolution 0.24 mm (LTP FWHM~ 2.5 mm spot)

13 / 13 / 2nd application: flat mirror 1.09 m long

1.09 m

Pt

Rh

105 mm

30 mm

Determination of optimal number of images to be averaged Environmental stabilisation The choice of the metrology method in order to extract the real surface : 1)Three flat approach ( surface profile over 1 line only)

2) Replacement of reference optics with different statistical errors require a large number of optics to improve the statistics)

3) Mapping of the optical cavity - full surface available but time consuming and heavy when several iterations are needed critical environment stabilisation

Specification: Slope errors < 300 nrad (L=1 m) Radius > 40 km

Theta=4 deg

14 / 14 / Statistical methods

500- 400- 300- 200- 100- 0 100 200 300 400 50040-

20-

0

20

40

Bande - T OP - C0 - P1-P2-P3

Ias 109

Ibs 109

Ics 109

Ias Ibs Ics

310

9

IM 109

x1 1000

500- 400- 300- 200- 100- 0 100 200 300 400 50040-

20-

0

20

40

Bande - T OP - C+ - P1-P2-P3

Ids 109

Ie s 109

Ifs 109

Ids Ie s Ifs

310

9

x1 1000

500- 400- 300- 200- 100- 0 100 200 300 400 5001-

0

1

2

Slope

Sl 1 106

Sl 2 106

Sl 3 106

x1 1000

500- 400- 300- 200- 100- 0 100 200 300 400 5001-

0.5-

0

0.5

1

1.5

Slope

Sl 4 106

Sl 5 106

Sl 6 106

x1 1000

stdev S l1( ) 106

0.372 stdev S l2( ) 106

0.283 stdev S l3( ) 106

0.288stdev S l4( ) 10

6 0.321 stdev S l5( ) 10

6 0.301 stdev S l6( ) 10

6 0.307

500- 400- 300- 200- 100- 0 100 200 300 400 50040-

20-

0

20

40

Bande - T OP C- ; P1-P2-P3

Igs 109

Ih s 109

Ii s 109

Igs Ih s Ii s

310

9

x1 1000

500- 400- 300- 200- 100- 0 100 200 300 400 5001-

0

1

2

Slope

Sl 7 106

Sl 8 106

Sl 9 106

x1 1000

stdev S l4( ) 106

0.321 stdev S l5( ) 106

0.301 stdev S l6( ) 106

0.307

Tilt and local radius fluctuation due to environment Slope errors seems to be more stable because are insensitive to tilt fluctuation of the wavefront

Strong height fluctuation observed on the edges of the substrate The effect is averaged out using statistics

The surface is probed using 3x3 statistically independent configurations

15 / 15 / Analysis on the usefull lenght 1m

500- 400- 300- 200- 100- 0 100 200 300 400 50050-

0

50

100

150

before IBP (stripe 1)

after IBP (stripe 1)

before (s tripe 2)

after (stripe 2)

IBF corrections - shape errors

mirror coordinate [mm]

surf

ace

heig

ht

[nm

]

PTVbefore 93.033 nm

PTVafter 21.135 nm

PTVbefore2 75.92 nm

PTVafter2 24.597 nm

500- 400- 300- 200- 100- 0 100 200 300 400 5002-

0

2

4

Slope

Sl 1 106

Sl 2 106

Sl 3 106

2

Sl 4 106

2

x1 1000 x2 1000 x3 1000 x4 1000

Before correction

stdev S l1( ) 106

0.5 µrad

stdev S l3( ) 106

0.544 µrad

After correction

stdev S l2( ) 106

0.192 µrad

stdev S l4( ) 106

0.295 µrad

SLOPES

Profiles

Stripe 1

Stripe 2

Stripe 1

Stripe 2

16 / 16 / Sliding Windows – mirror length 0.1 m1 m

0.45- 0.44- 0.43- 0.42-2- 10

7-

1- 107-

0

1 107-

2 107-

Dg10

x1g10

0 166.667 333.333 500 666.667 833.333 1 103

0

1

2

3

4

5

6

7

8

9

10

sigma rms (sliding windows W=20 mm)

sigma PV (sliding windows W=20 mm)

1 nm

4 nm

Sliding windows -Mirror length=1 m

window position [mm]

hei

ght

stati

stiq

ue

rm

s [n

m]

0 166.667 333.333 500 666.667 833.333 1 103

0

0.16

0.32

0.48

0.64

0.8

0.96

1.12

1.28

1.44

1.6

slope rms (sliding windows W=20 mm)

slope PV (s liding windows W=20 mm)

Sliding windows

window position [mm]

slo

pe

stat

isti

qu

e [µ

rad

]

0.05- 0.04- 0.03- 0.02-1- 10

6-

5- 107-

0

5 107-

1 106-

Dg10

x1g10

0 13.333 26.667 40 53.333 66.667 800

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

sigma rms (sliding windows W=20 mm)

sigma PV (sliding windows W=20 mm)

4 nm

0.35 nm

Sliding windows -Mirror length=100 mm

window position [mm]

hei

gh

t st

ati

stiq

ue

rm

s [n

m]

0 13.333 26.667 40 53.333 66.667 800

0.18

0.36

0.54

0.72

0.9

1.08

1.26

1.44

1.62

1.8

slope rms (sliding windows W=20 mm)

slope PV (s liding windows W=20 mm)

Sliding windows

window position [mm]

slo

pe

stat

isti

qu

e [µ

rad

]

Mirror length = 1 m Mirror length = 0.1 m

PTV ~ 4 nm

Stdev ~ 1 nm

Sliding windows of 20 mm moved @ each pixel

PTV ~ 1.5 nm

Stdev ~ 0.35 nm

Scanning length

17 / 17 / Sliding Windows & shape error scaling

Shape error scaling; L=1 m Shape error scaling; L=0.1 m

0 20 40 60 80 1000

1

2

3

windows size [mm]

surf

ace

stat

isti

qu

e [n

m]

PTV

sigma

W

0 20 40 60 80 1003

3.5

4

4.5

5

5.5

windows size [mm]

surf

ace

stat

isti

qu

e [n

m]

PTV

sigma

W

0 200 400 600 800 1 103

0

5

10

15

20

windows size [mm]

surf

ace

stat

isti

qu

e [n

m]

PTV

sigma

W

0 200 400 600 800 1 103

3

4

5

6

windows size [mm]

surf

ace

stat

isti

qu

e [n

m]

PTV

sigma

W

<all windows>

<PTV/stdev>

<all windows>

<PTV/stdev>

The ratio PTV/stdev scale linearly regardeless of the mirror size

deviation connected with sampling

18 / 18 / Conclusion

a) The use of ion beam is prooved to preserve roughness and improve the surface

errors in a deterministic fashion (slope errors <300 nrad, L=1 m)

b) ion beam technology is today routinely used in our SR mirror production lines

c) High frequency errors (speckles) need to estabilish the possibility to suppress

this signal from PSI and LTP data to overcome the limit of PSI metrology

d) Ultimate figuring performances are today metrology limited

e) IBP requires tight operational procedures and well trained staff

f) Traditional and deterministic ion polishing remain complementary techniques

that needs to be matched

g) Increase of difficulty between short and long mirrors is mainly linked to surface metrology

19 / 19 / Acknowledgements

Agence Nationale de la Recherche (ANR) and the AXOC team for support and the R&D on nanofocusing optics

The metrology labs in BESSY, SOLEIL & ESRF for useful discussion and sharing

of LTP data

R. Cerbino (University of Milan) for usefull discussion on speckles metrology and image processing

The X-ray team and staff Thales SESO

Eric Ziegler (ESRF) and Igor Kozhevnikov (Institute of Crystallography, Russia)