B 1s
BN below
1st La layer
suboxide
Controlling interface chemistry in 6.x nm La/B
multilayer optics
[D.S.Kuznetsov et al., Optics Letters, Vol. 40, No. 16 (2015)]
Goal: high performance (reflectivity) of optics
High optical contrast for high performance of x-ray multilayers requires:
1) Controlling interface chemistry
- Passivation of material(s)
2) Minimization of ballistic intermixing of atoms
3) Minimization of morphological roughness
-
Single-layer roughness
-
Roughness development (build-up) in multilayer
Dmitry Kuznetsov, Marko Sturm, Robbert van de Kruijs, Andrey Yakshin, Eric Louis and Fred Bijkerk
Industrial Focus Group XUV Optics, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands
d.kuznetsov@utwente.nl
Conclusions and results
Fully-passivated LaN layers synthesized
Adverse effect of BN formation minimized
New 6.x nm reflectivity record:
64%, AOI=1
.
5°
[PTB]
Program on further performance improvement identified
Literature
1. Igor A. Makhotkin, “Short period La/B and LaN/B multilayer mirrors for ~6.8 nm wavelength”, Optics
Express, Vol. 21, No. 24 (2013)
2. N. Ooi et al., “Structural properties of hexagonal boron nitride”, Modelling Simul. Mater. Sci. Eng. 14,
515–535 (2006)
3. A. I. Efimov “Properties of inorganic compounds”, Handbook, Khimiya, Leningrad, 1983
4. N. I. Chkalo et al., “High performance La/B4C multilayer mirrors with barrier layers for the next
generation lithography”, Applied Physics Letters 102, 011602 (2013)
Acknowledgements
We acknowledge the support of the Industrial Focus Group XUV Optics at the MESA+ Institute at the
University of Twente, the industrial partners ASML, Carl Zeiss SMT GmbH, as well as the Province of
Overijssel. Physikalisch-Technische Bundesanstalt (PTB) is acknowledged for reflectivity measurements.
6.x nm multilayers: complexity on atomic scale
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
2
3
4
5
R
efl
ec
tivity
lo
ss
, %
Interfacial roughness/diffuseness, Å
6.X nm La/B
13.5 nm Mo/Si
[IMD 5.02]
B
La
Wafer
B
interface
zones
3.4 nm
Each layer
~
7-10 monolayers!
Performance is highly dependent on
interfacial roughness / diffuseness
Unprecedented level of interface control is required
6.x nm multilayers: application-driven motivation
EUV photolithography (EUVL):
Fabrication of new-generation chip patterns
XRF material-analysis:
Ultrasensitive detection by X-ray fluorescence
EUV telescopes:
Space research
B
La
LaB
6 (LaB
x)
Wafer
B
LaB
6 (LaB
x)
Passivation of lanthanum: nitridation
Magnetron sputtering deposition in nitrogen gas atmosphere
[1]
Enthalpy, kJ/mol: ∆H(BN) = -255
[2]
>> ∆H(LaB
6
) = -130
[3]
XPS analysis: BN formation during nitridation
B
LaN
BN
,
LaB
6 (LaB
x)
Wafer
B
Protected
interface
B
LaN
Wafer
Protected
interface
Fully-passivated
LaN
B
BN formation
negligible
Optimized system
New 6.x nm reflectivity record
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
6.60
6.65
6.70
6.75
Wavelength, nm
64%
Previous record
[4]
:
R=58.6%, AOI*=20
.
9°
14
16
18
20
22
6.69
6.79
6.89
6.99
50-period La/B MLS
[PTB]
R,%
Wavelength, nm
1
.
5°
17°
Protection of top interface,
but risk of BN formation at the bottom interface
*(AOI: off-normal incidence)
o LaN/B
o 220 periods
o AOI*=1.5°
o [PTB]
Influence of AOI
15°
13°
R, %
