Recent advances in etched multilayer X-ray optics

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Recent advances in etched multilayer X-ray optics

J. André, A. Sammar, S. Bac, M. Ouahabi, M. Idir, G. Soullié, R. Barchewitz

To cite this version:

J. André, A. Sammar, S. Bac, M. Ouahabi, M. Idir, et al.. Recent advances in etched multilayer X-ray optics. Journal de Physique III, EDP Sciences, 1994, 4 (9), pp.1659-1668. �10.1051/jp3:1994231�.

�jpa-00249215�

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J Phys. III Fiance 4 (1994) 1659-1668 SEPTEMBER 1994, PAGE 1659

Classification Physic-s Abstracts

61.10

Recent advances in etched multilayer X-ray optics

J. M. Andrd ('), A. Sammar ('), S. Bac ('. 2), M. Ouahabi ('), M. [dir ('. 2), G. Soullid

('. ₂₎ and R. Barchewitz ('. ₂₎

(') Laboratoire de Chimie Physique (LCP), Universitd Paris 6, U-A- CNRS 176, 11 _rue Pierre et Marie Curie, 75231 Paris Cedex 05, France

(2) Laboratoire pour l'Utilisation du Rayonnement Electromagn6tique (LURE), Universitd Paris11, 91405 Orsay Cedex, France

(Recei>.ed J9 Noi,ember 1993, ret,ised 31 Januaiy J994, accepted 3 March 1994)

Rksumk. Nous pr6sentons ^les rdcents progrbs r6alis6s _au Laboratoire de Chimie Physique de l'Universitd Paris 6 dans le domaine de l'optique X utihsant des multicouches gravdes. Nous donnons des rdsultats _concernant les rdseaux d'amplitude multicouches, les monochromateurs

multicouches h haute rdsolution, les polychromateurs ^X et les lentilles lindaires multicouches dites de Bragg-Fresnel.

Abstract. We present ^the recent advances achieved in the Laboratoire de Chimie Physique of

Universitd Paris 6, in the field of the soft X-ray etched multilayer optics. Modellings and characterizations _are given for the laminar multilayer amplitude gratings, the highly resolutive X- ray multilayer monochromators, the X-ray polychromators and the Bragg-Fresnel multilayer linear

lenses.

Introduction.

By combining the thin film deposition techniques with the technology of microstructure

manufacturing, it is _now possible to make new X-ray optical devices based _on etched

multilayer structures. Since the beginning of the eighties, the LCP deals with the modelling

and the characterizations of the performances of these devices in the soft X-ray _range. We present ^the principle of several devices based _on laminar multilayer gratings and Bragg-Fresnel optics, and _recent results conceming their characterizations.

1. Laminar multilayer amplitude grating (LMAG).

The LMAG is _a grating ^obtained by etching _a multilayer interferential mirror (MIM) down to the substrate, according to a periodic rectangular profile [I (See Fig. I.) The system is doubly periodic (in-depth with period d and laterally with period D). Thus _a LMAG diffracts in _an

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1660 JOURNAL DE PHYSIQUE III N° 9

~x ~

Z detector

k

D 6° ~

rD

mulfilayer structure

period d

substrate

Fig, I. Scheme of _a laminar muhilayer amplitude grating (LMAG).

optimal manner a wavelength A _at _a multilayer diffraction order _m and at a grating diffraction order _p, _on condition that the glancing angle 60 ^satisfies the following relationship [2]

mA

=

d sin

oll

+ 2 ~°~

~° _P~ _P~

)~ ^jij

sin o~ ^D sin~ o~ ^D

~

It results that the optimal angle _Ho to diffract _at the order _p, depends _on _p. Different dynamical theories _have been developed to calculate the diffraction patterns and the efficiencies of the

LMAGS differential theory [3, 4] and partial summation method [5]. Figure 2 shows in

comparison the observed and computed diffraction patterns at

=

1.33 _nm for _p

= I (?a),

p =

0(2b), _p

= + 1(2c) with _a LMAG with the following features MIM _: 80 Mo/C bilayers

,

d

=

4.4 _nm

, y = d ~Jd

=

4/7

grating _: D

= i ~m, r

=

o.5

2. Highly resolutive X-ray multilayer monochromator (HRXMM).

The purpose of this device is _to achieve _a Bragg monochromator with both _a _narrow bandwidth

given by Sammar et al. [6]. The fundamental idea is to diminish both the _average absorption reflectivity (similar to the reflectivity of MIMS). The principle of such _a device _was recently given by Sammar et al. [6]. The fondamental idea is to diminish sboth the average absorption

coefficient of the diffractive medium and the reflection factor at each interface in order to decrease the bandwidth. To keep a high peak reflectivity while getting a narrow bandwidth, it is necessary that a sufficiently large number of multilayer periods N contributes _to the

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N° 9 RECENT ADVANCES IN ETCHED MULTILAYER X-RAY OPTICS 1661

Theory Experiment

0.06

-1

(-1) ~)

0.04

0.

0.02 0

~' ~7 _7.5 ₈ _8.5 ₉ _9.5 _lo

9. 5

0.07

~

~ b)

I (0) _~'~~

'l I o

~ 0 0.02

(

0.

~ 9 5 10

j~

~ ~~

7 7.5 ~ ~ ~

8.5

0.04

0.

~~

~

(+li

C) ^0.03

o~~

o o.oi

~ ~o

~ 9 9 5 1°

0

7 7.5 8

9. 5

Glancing angle 80 (deg) Glancing angle 80 (deg)

Fig. 2. -Experimental and theoretical efficiencies _at A

=

1.33 _nm of _a LMAG whose features _are given in the text.

constructive interferences involved in the Bragg diffraction. In practice, one has to make _a

LMAG with _narrow multilayer bars (I.e. small f~ and _a large ^number ^of periods

N. The value of r and N needed to reach _a specified theoretical performance, can be deduced from dynamical calculations [3].

Figure 3 shows the Al Ka and W Ma, p spectra ^obtained by means of _a HRXMM and of the

corresponding MIM. The characteristics of the structures are MIM _: 150W/Si bilayers,

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M'M HRXMM

12000 l6tU

, ^Al Ka jq~ ^N ^Ka

( 10O00 #

t 120O

I ₈₀₀₀ p _~~

Gj ^#

~~y~

s 6°°l (

T ~ ^S© w M~~

G 4D0 ~

'

W Ma,j $ ^~

° 2°°° 5 _20O

o

~~ _{~_5} ₉ _9.5 _lo _lo-s _ii _11.5 12 8 8.5 9 9.5 I° '°.~ _~~ ~~.~ ~~

Glanclng angle fo (dog) ~~"~~~~ ~~~' '~~°~~

Fig. 3. Al Ku and W Ma. p _spectra obtained with _a HRXMM and the corresponding MIM. The

features of the device~ _are given in the text.

d= 2.4nm; HRXMM _: D

= ~m; r =0.16. The improvement in resolution is very

spectacular, thus the spectral bandwidths of Al Ka _are about 15 and 50 eV when analyzed with the HRXMM and the MIM respectively. Note the difference between the positions of the lines diffracted by the MIM and the HRXMM arises from _a modification of the average refractive index induced by ^the etching. Indeed the efficiency of the zeroth order of _a LMAG _can be

calculated in first approximation [5] _as the reflectivity of _a homogeneous medium whose refractive index is averaged by the proportion of multilayer medium with respect to vacuum. A

modification in the value of this avarage refractive index affects both the peak efficiency and the angular position.

Neither the nominal _nor the effective characteristics of the HRXMM _are optimal, _so that at the view of these first results, the HRXMMS appear as promising tools for highly resolutive X- ray spectroscopy.

3. X-ray polychromator.

The purpose of this device is _to spatially split _a polychromatic beam into several quasimonoc-

hromatic beams. The principle of the device _was given in _a paper by Andrd et al. [8]. It is based

on the unique property of the LMAG mentioned in section I. According to equation (I), for _a

given glancing angle o~ at each diffraction order p of the LMAG corresponds _a wavelength A~ satisfying this equation. The radiation of wavelength _A~ is emitted _at _an angle

o with respect to the surface given by the grating law

p A~ = D [cos o _cos Hoi (2)

The spectral ^bandwith ^of ^each quasimonochromatic ^beam is governed by the _same conditions

as those mentioned for the HRXMM and the angular splitting is conditioned by the grating period D. Using the synchrotron radiation provided by the Super-ACO _storage ring facility, _we

have experimentally evidenced the features of this

« polychromator _» in the 800-1300 eV energy range [7]. The experiment ^is ^conducted as follows (see Fig. 4).

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detector

GRATING RULE SCAN MODE ~

~~~f

~ijoj

/

^~ij+ij

/

MONOCHROMATOR

-~

fi ki

6

o

'

detector DETECTORSCANMODE

k(~ _,,

kjoj

l'

kin

/

POLYCIIROMATICBEAM

60

Fig. 4. Experimental layouts ^for the study of the performances of the

« polychromator _».

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ii By help of _a double-crystal monochromator equipped with beryl crystals, one illuminates the _« polychromator _» _at _a given glancing _{angle o~} and _one _scans the detector to follow

a given

order _p. This operation gives the energy calibration, the energy efficiency and the selectivity of the system.

ii) One illuminates the _« polychromator _» for the _same glancing angle _Ho with _a polychroma-

tic radiation and _one records the diffraction pattem.

A typical diffraction pattern ^recorded through _a _« 5 _~m Al ₊ 16 _~m Be _» filter, is shown in

figure ^5. The characteristics of the device _are MIM _: loo W/C bilayers d

= 4.12 _nm

,

y =

d ~/d

=

0.4

LMAG _: D

= I ~m, r

=

0.09

19547

P EneW (eV)

S 862

4 882

~ 904

-2 926

~ / ~

l 1000

2 to28

3 t058

13

4 to89

5 1t22

6 11 57

7 11 95

« 8 1235

9 1277

LJ t0 1323

ii 1372

#~ 12 1425

* 13 1471

I

~

o

-3

'~ -5

9 lo II 12 13 14 16 17 18 19 20 21

obervatlon angle (deg)

Fig. 5. Diffraction pattern ^of a « polychromator _» illuminated by the synchrotron white radiation. The features of the device _are given in the _text.

4. Bragg.Fresnel linear _zone plates (BFLZP).

The purpose of the device is _to focuse _an X-ray beam in _a line whose widths is of the micron order. The principle of this kind of optics was given by ^Aristov et al. [9] basically it consists in combining the Fresnel and the Bragg diffractions. This lens is obtained by etching a

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multilayer _structure according to the pattern ^of a linear Fresnel _zone plate. One distinguishes

the positive and the negative BFLZPS whose definitions _are given by the figure 6. We have measured [10] in the conical configuration (I.e. the lines _are parallel to the direction of the X- ray beam), the performances of _a positive and _a negative BFLZP with the following features _:

MIM : 25 W/Si bilayers, d

= 5.3 _nm, _y

= dJd

=

0.4.

BFLZP; _a

=

II _~Lm

,

outermost _zone width

= 0.4 _~Lm

dimension

=

210 _~Lm

2a

fia

Fig. 6. Topview of _a Bragg-Fresnel ^linear zone plate (BFLZP). For the positive BFLZP, the black bars correspond to the multilayer structure while the white bars correspond to vacuum. The opposite

situation _occurs for the negative BFLZP.

The incident radiation is the white beam provided by the Super-ACO _storage ring. ^The data

are recorded by using a gas detector collimated by a 13 _~Lm pinhole and high resolution

holographic plates (2 000 1/mm). In first approximation, the theory gives the focusing ^distance r~ ^as

~

i~ =

~ (3)

pA

where _p is the order of focusing. Note that _a refined geometrical theory of the BFLZP

diffraction [I Ii gives _a _more accurate relationship between the distance r~ ^and ^the ^geometry.

In _our conditions (Bragg angle

=

4° _; A

=

0.71 nm) one has rj =

162 _mm. Figures 7 show the angular distribution of the diffracted radiation in _a direction perpendicular to the specular direction, for different distances of the detector with respect to the BFLZP. The focus line width measured in the first order focal plane using the holographic plates is less 15 _~Lm which

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NEGATIVE ^LINEAR BRAGG-FRESNEL MULTILAYER LENS

12~uo CONICAL

~~~~~;~

E =1750 eV ^~~'

»FOCALDISTANCE(

I

fl

t

Theory

obervatlon angle (deg) a)

Fig. 7. -Experimental and theoretical diffraction patterns ^of positive ^and negative BFLZS whose features _are given _in the text.

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POSITIVE LINEAR BRAGG-FRESNEL MULTILAYER LENS

iqom CONICALDIFFRACfION

=1?50eY

Experiment

q~ _

( Iz

) (

tP m

~ ji

g ^~

j ^'

]

/

q~~

d~

q~ ^~ w'

$~~~'§ ~~~%C~

~ W

obervation angle (deg) b)

Fig. 7 (t.onfiniietl).

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corresponds to the _source size with the demagnification of _our experiment (0.01). The

experimental _curves _may be compared to the theoretical spatial distribution calculated in the framework of _a dynamical theory [12]. The agreement ^between experiment and theory is fairly

well especially conceming the lack of background beyond the first focus for the

negative BFLZP.

Acknowledgments.

The authors _are indebted _to R. Rivoira, B. Vidal (Universitd d'Aix-Marseille III, France) and Socidtd Matra for the multilayer manufacturing, C. Khan Malek, P. Gudrin, F. R. Ladan and

H. Launois (L2M/CNRS, Bagneux, France) and S. Sainsen (CNET, Bagneux, France) for the

etching of the multilayers, P. Troussel, D. Schirmann (CEA, Limeil, France) and A. Mirone (Center for Advanced research in Space Optics, Trieste, Italy) for their assistance during the

experiments, and B. Pardo (IOTA, Orsay, France) for his collaboration to the theory.

References

II Hawryluk A. M., Ceglio N. M., Stearns D. G., Danzmann K., Kuhne M., Muller P., Proceedings of SPIE 688 (1986) 81-90 _;

Berrouane H., Andrd J.-M., Barchewitz R., Khan Malek C., Rivoira R., Opt. Commun. 76 (1990) it I- Ii 5.

[2] Berrouane H., Khan Malek C., Andrd J.-M., Ladan F. R., Rivoira R., Barchewitz R., Opt. Eng. 31 (1992) 213-218.

[3] Pardo B., Andrd J.-M., Sammar A., J. Opt. (Paris) 22 (1991) 141-148 Sammar A., Andrd J.-M., Pardo B., Opt. ^Commun. 86 (1991) 245-254.

[4] Ndvikre M., J. Opt. Sac. Am. A 8 (1991) 1468-1473.

[5] Sammar A., Ouahabi M., ^Barchewitz R., Andrd J.-M., Opt. Commun. 99 (1993) 309-315.

[6] Sammar A., Andrd J.-M., Ouahabi M., Pardo B., Barchewitz R., C. R. Acad. Sci. Paris, Sdrie II 316 (1993) 1055-1060.

[7] Bac S., Soull16 G., Mirone A., Idir M., Gudrin P., Ladan F.-R., Troussel P., Barchewitz R., (submitted to J. Opt.).

[8] Andrd J.-M., Sammar A., Khan Malek C., Troussel P., Bac S., Barchewitz R., Pardo B., Berrouane H., Moreno T., Ladan F. R., Rivoira R., Schirmann D., Rev. Sci. Instrum 63 (1992) 1399-1403.

[9] Aristov V. V., Erko A. I., Martinov V. V., Ret,. Phys. Appl. 23 (1988) 1623-1630 Erko A. I., J. X-ray Sci. Technol 2 (1990) 297-316.

[10] Idir M., Mirone A., Soullid G., Gudrin P., Ladan F.-R., Launois H., Sammar A., Andrd J. M., Barchewitz R., Proceedings of _« X-Ray Microscopy IV _» (Moscow, Russia, September 1993).

[I ii Dhez P., Erko A. I., Khzmalian E., Vidal B., Appl. Opt. 31 (1992) 6662-6667.

[12] Sammar A., Andrd J.-M., J. Opt. Sac. Am. A 10 (1993) 2324-2337.