Design of multilayer X-ray mirrors and systems T. Holz*, R. Dietsch*, S. Braun**, A. Leson** * AXO DRESDEN GmbH, Germany ** Fraunhofer IWS Dresden, Germany Introduction CHARACTERISTICS 1D periodicity of layer stack nm layer thickness with pm accuracy on cm 2 areas laterally graded thickness / normally constant layer thickness period thickness ranging from 1nm to 10nm (30nm) Number of layer pairs (N=50, N>1000) high reflectivity und tailored resolution SOURCE OPTICS SAMPLE HRTEM of a Ni/C multilayer (/5 layer pairs, d=4.40nm) and reciprocal space image of electron diffraction 1
Multilayers for X-ray optics λ = 2d sin Θ Multilayer optics Crystal optics λ 0.01nm 0.1nm 1nm 10nm L-lines (Br..Ca ) K-lines (Si..Be) WKα MoKα CrKα CoK α CuK α NaKα MgKα AlKα SiK α OKα CKα BKα NKα SiLα Be Kα E 100 kev 10 kev 1 kev 100 ev Design of multilayers for XRD application SOURCE OPTICS SAMPLE X-ray wavelength λ material system σ rms throughput, reflection efficiency period number, number of bilayers N divergence period thickness d reflection width thickness ratio Γ spectral resolution depth graded thickness source usage efficiency lateral graded / constant thickness capture angle deposition method stability, reproducibility σ d thin film growth regime σ rms geometric conditions (distances, mirror length, d-range, source size) 2
Overview of of reflecting hard hard x-ray optics 10 0 Integrated reflectivity 10-1 10-2 10-3 10-4 10-5 Be 110 forbidden area theoretical limit for 100% peak reflectivity Si 111 Crystals Ge 111 10-6 10-6 10-5 10-4 10-3 10-2 10-1 10 0 Ε/Ε high-resolution ML's High-Z Low-Z ML's depth-graded ML's (Mirrors) Ch. Morawe et al. ESRF - Grenoble - France Selected material combinations for multilayer optics in the hard X-ray range 1,0 0,9 reflectivity refractive index contrast n, δ N eff reflectivity 0,8 0,7 0,6 W/C (bulk) Ni/C (bulk) Mo/B 4 C (bulk) C/C (bulk) 0,5 5 10 15 20 25 30 Cr Kα Cu Kα Co Kα Mo Kα E γ / kev step function of absorption Simulation: first order Bragg peak reflectivity of Ni/C, W/C, Mo/B 4 C multilayers (d= 4 nm / N= 100) and C/C multilayers (d=3nm / N= 1000) Ideal periodic layer stack arrows at Cr, Co, Cu, Mo Kα 3
Shape of graded multilayer optics boundary values for the d - range parallel beam geometry parabolic focusing geometries elliptic, flat parallel beam arrangements Guinier-, Debye-Scherrer-, Bragg-Brentano-geometry Thickness gradient and capture angle BRAGG condition increase of period thickness [%] 200 180 160 140 120 100 elliptic mirror parabolic mirror flat mirror 5 30 55 80 Miroor length [mm] capture angle [degree] 0.6 0.5 0.4 0.3 0.2 0.1 0 5 30 55 80 Mirror length [mm] elliptic mirror parabolic mirror flat mirror simulation e.g. Cu Kα same period thicknes d 0 at the top of the mirror at 120mm focal distance 4
High precision deposition methods Sputtering and PLD view into the magnetron sputtering chamber Homogeneity: 99.9% (6 diameter) Cu Ka reflectivity of Mo/Si-system: d=2.0nm R>60% run-to-run stability: 99.9% Dual beam Puls Laser Deposition interaction of plasma plumes during ablation Homogeneity: 99.8 % (length of 80 mm) 99.5 % (width of 40 mm) Cu Kα-reflectivity of a Ni/C-Multilayer d=3.0nm: R = 68 % run-to-run stability: 99.5 % Sputtering - reproducibility of deposition Mo/Si multilayer d = 6.93 nm N = 60 used in EUV-Lithography R = 70.1% at 13.4 nm (α = 3 ) reflectometry Cu Kα 5
Large area dual beam PLD - reproducibility of deposition Ni/C-system d = 3.04 nm N = 75 Θ = 0.019 ( 0.33 mrad) Used in imaging X-ray optical arrangements 8 kev X-ray optical elements parabolic mirrors Typical performance: mirror length: 20mm 80mm type: convex, concave mean reflectivity: 75% (Cu, Co), 70% (Mo) Kβ reduction over Kα : > 200 : 1 Divergence: <0.03 e.g. Cu 0.04x12mm 2, 1.6kW, I o > 3.5 10 9 cps Used as Primary beam optics Diffracted beam optics Systems: Kirkpatrick-Baez-arrangement, Beam compressor, X-Pointer, Twin Mirror arrangement 6
DXC 2003 Workshop W2 - Optics X-ray optical elements elliptic mirrors Typical performance: mirror length: 60mm 80mm throughput: 75% (Cu, Co), 70% (Mo) Kβ reduction over Kα: >150 : 1 e.g. Cu 0.04x12mm 2, 1.6kW, I o > 3 10 9 cps >80% of gross intensity within 200µm slit for type 150/500 Fig. from: Schuster et. al, SPIE 1999 Used as Primary optics in SAXS Guinier geometry Debye-Scherrer-arrangement X-ray optical systems for imaging the X-ray focus 1D 2D Twin arrangement (a) Kirkpatrick-Baez-arrangement (d) X-ray Pointer (b) side-by-side optical systems, Montel-optics (e) Beam compressor (c ) b 1 (a ) Θ b parabola 1 conca ve parabola 1 (c) p p b (d) parabola 2 convex F= F parabola 2 (e) (b) b 2 (7) Fig.(d), (e) from: Schuster et. al, SPIE 1999 7
Kβ suppression, resolution Θ intensity [cps] 10 7 10 6 10 5 10 4 10 3 *Holz et al., Parallel beam X-ray optics for Cu and Mo radiation Denver X-ray Conference 1999 Kβ Cu Si 400 W Lα Kα 1,2 intensity [cps] Twin Mirror arrangement 600 400 200 Quartz triplet Cu Kα 1 Cu Kα 2 10 2 62 64 66 68 70 72 2Θ [degree] 0 67.00 67.50 68.00 68.50 69.00 2Θ [degree] Kα suppression, spectral resolution without crystal optics Θ Si 111 Twin Mirror arrangement 10 6 10 5 Co 200 Quartz triplet intensity [cps] 10 4 10 3 10 2 10 1 Co Kβ Co Kα 1 Co Kα 2 intensity [cps] 150 100 50 29 30 31 32 33 34 35 2Θ [degree] 0 71.00 71.50 72.00 72.50 73.00 73.50 2Θ [degree] 8
Summary Multilayers are characterized by a high reflectivity of more than 80% for all commonly used X-ray wavelengths Angular resolution is between single crystal optics (0.005 ) and total reflection /HOPG optics (0.5 ) Reproducibility and stabilty of the deposition technologies meet requirements of XRD-application Multilayers can be combined to X-ray optical systems for imaging the X-ray focus onto the sample with tailored beam characteristics 9