Light scattering of optical components at 193 nm and 13,5 nm [Elektronische Ressource] / von Sven Schröder

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• Physik

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• Publié par: friedrich-schiller-universitat_jena
• Publié le: 01 janvier 2008
• Nombre de lectures: 6
• Langue: English
• Poids de l'ouvrage: 9 Mo

Extrait

Friedrich-Schiller-Universitat¨ Jena
¨Physikalisch-Astronomische Fakultat
Light scattering of optical components
at 193 nm and 13.5 nm
Dissertation
zur Erlangung des akademischen Grades
doctor rerum naturalium (Dr. rer. nat.)
vorgelegt dem Rat der Physikalisch-Astronomischen Fakultat¨
der Friedrich-Schiller-Universita¨t Jena
von Dipl.-Phys. Sven Schr¨oder
geboren am 30. Juli 1975 in ErfurtGutachter
1. Prof. Dr. rer. nat. Andreas Tunnerm¨ ann
2. Prof. Dr. rer. nat. H. Angus Macleod
3. Prof. Dr. rer. nat. Theo Tschudi
Tag der letzten Rigorosumsprufung: 8. Juli 2008¨
Tag der offentlichen Verteidigung: 17. Juli 2008¨Contents
1 Introduction 1
2 Definitions 4
2.1 Specular reflectance and transmittance . . . . . . . . . . . . . . . . . . 5
2.2 Light scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1 Total scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.2 Angle resolved scattering . . . . . . . . . . . . . . . . . . . . . . 5
2.2.3 Bulk scattering coefficient . . . . . . . . . . . . . . . . . . . . . 6
2.3 Roughness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3.1 Rms roughness . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3.2 Power Spectral Density function . . . . . . . . . . . . . . . . . . 6
3 Theoretical models of scattering and roughness 9
3.1 Specular reflectance and transmittance of imperfect interfaces . . . . . 9
3.2 Scattering of single surfaces . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3 Scattering of thin film coatings . . . . . . . . . . . . . . . . . . . . . . 12
3.3.1 Theories for the visible spectral range . . . . . . . . . . . . . . . 13
3.3.2 X-ray scattering theories . . . . . . . . . . . . . . . . . . . . . . 15
3.3.3 Harmonization of the solutions . . . . . . . . . . . . . . . . . . 15
3.4 Roughness and roughness evolution models . . . . . . . . . . . . . . . . 16
3.5 Volume scattering of bulk materials . . . . . . . . . . . . . . . . . . . . 20
4 Independent roughness measurement techniques 22
4.1 Optical profilometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.2 Electron microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.3 X-ray methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.4 Atomic force microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.5 R´esum´e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5 Experimental set-ups for scatter measurements at 193nm and 13.5nm 28
5.1 Instrumentation for 193 nm . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1.1 Vacuum system . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.1.2 Light source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315.1.3 Beam preparation system . . . . . . . . . . . . . . . . . . . . . 31
5.1.4 TS set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.1.5 ARS set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.1.6 Detection system . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.1.7 Operation and performance . . . . . . . . . . . . . . . . . . . . 34
5.2 Instrumentation for 13.5nm . . . . . . . . . . . . . . . . . . . . . . . . 36
5.2.1 Vacuum system . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.2.2 Light source . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.2.3 Beam preparation system . . . . . . . . . . . . . . . . . . . . . 37
5.2.4 Spectral purity filter system . . . . . . . . . . . . . . . . . . . . 38
5.2.5 ARS set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.2.6 Detection system . . . . . . . . . . . . . . . . . . . . . . . . . . 40
5.2.7 Operation and performance . . . . . . . . . . . . . . . . . . . . 40
5.3 Uncertainty budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6 Scattering of optical components at 193 nm and 13.5 nm 44
6.1 Coatings and bulk materials for applications at 193nm . . . . . . . . . 44
6.1.1 ARS modeling methodology . . . . . . . . . . . . . . . . . . . . 45
6.1.2 Fluoride HR coatings on CaF : influence of substrate polish . . 532
6.1.3 Bulk scattering of synthetic fused silica . . . . . . . . . . . . . . 62
6.2 Coatings for applications at 13.5nm . . . . . . . . . . . . . . . . . . . . 68
6.2.1 Roughness measurements of EUV mirrors using 193nm scattering 69
6.2.2 Mo/Si mirrors on fused silica: influence of substrate polish . . . 74
6.2.3 Characterization of degradation effects of EUV mirrors . . . . . 83
7 Conclusions 87
Bibliography 90Nomenclature
ACF autocorrelation function
AFM atomic force microscopy
ARS angle resolved scattering
CS Coblentz sphere
DUV deep ultraviolet
DWBA distorted-wave Born approximation
EUV extreme ultraviolet
GHS generalized Harvey-Shack theory
HSFR high-spatial frequency roughness
LGT linear growth theory
MSFR mid-spatial frequency roughness
PMT photomultiplier tube
PSD power spectral density function
PSI phase-shift interferometry
RR Rayleigh-Rice theory
SEM scanning electron microscopy
TEM transmission electron microscopy
TS total scattering
VPT vector perturbation theory
XRR X-ray reflectivity
XRS X-ray diffuse scatteringα bulk scattering coefficient
β dynamic scaling exponent
β isothermal compressibilityT
δ optical layer thickness deviation
ΔΩ detector solid angles
λ wavelength
σ (bandwidth limited) rms roughness
σ rms roughness∞
τ (lateral) correlation lengthc
TS total backscatteringb
TS total forward scatteringf
d thickness
F focal length
f spatial frequency
H thickness of one multilayer period
k Boltzmann constantB
L length of illuminated volume
M number of layers
N multilayer period
n index of refraction
p photoelastic coefficient
P incident poweri
R specular reflectance
R specular reflectance of ideally smooth interface0
T specular transmittance
T fictive temperaturef1 Introduction
The progress of optical technology towards ever shorter wavelengths is accompanied
by drastically increasing demands on optical components. For optics at 193nm in
1 2the DUV and 13.5nm in the EUV spectral ranges, in particular light scattering
from interface and bulk imperfections becomes crucially important [2] and must be
quantified. On the other hand, scattered light carries information about its origins,
which can be exploited to improve DUV and EUV optics. Unfortunately, there is
a serious lack of appropriate measurement and analysis tools. This thesis is therefore
dedicatedtothedevelopmentofinstrumentationaswellasofmeasurementandanalysis
techniques for the thorough investigation of light scattering at 193nm and 13.5nm.
Semiconductor projection lithography is the major driving force for technological de-
velopments at these wavelengths. However, DUV radiation is also utilized for micro-
machining, micro surgery, and ophthalmology [3]; and EUV (or soft X-ray) radiation
enables new methods in spectroscopy, interferometry, and astronomy [4].
The resolution of a lithographic reduction projection system can be expressed as [5]:
W ∼ λ/NA, where W is the minimum half pitch of the structures, λ is the exposure
wavelength, and NA is the numerical aperture. Consequently, the urgent demand for
ever decreasing structure dimensions imposed by Moore’s law [6, 7] can be met by
increasing NA or by reducing λ. The latter was the most convenient approach in the
past.
Meanwhile, DUV lithography at the ArF excimer wavelength of 193nm has become
the state-of-the-art technology. Further reductions in wavelength, however, require
enormous effort. EUV lithography at 13.5nm is the most promising candidate for
next-generation lithography. Nevertheless, several critical problems have to be solved,
not the least regarding optical components with high throughput and stability [8, 9].
Full implementation of EUV lithography is planned between 2013 and 2016 [10].
To bridge the gap until EUV lithography is ready for application, 193nm lithography
is being pushed to its ultimate limit using sophisticated imaging techniques in order
to keep pace with Moore’s law [7]. Recently, a catadioptric immersion objective with
NA=1.35 was presented which enables W =45nm utilizing 193nm radiation [11].
1Deep ultraviolet spectral range, reaching from approximately 300nm down to 190nm.
2Extreme ultraviolet spectral range, between 5nm and 40nm [1].
1These radical developments at DUV and EUV wavelengths lead to extraordinary de-
mands on optical components regarding low losses and high image quality. Optical
scattering, on the one hand, withdraws power from the specular direction and reduces
the throughput. On the other hand, scattered radiation may propagate through the
optical system. In particular scattering within the field of view of an imaging element
(near-angle scattering or flare) crucially influences contrast and resolution [12, 13, 14].
Since scattering constitutes a diffraction problem, it exhibits a strong wavelength de-
−2 −4pendence (∼ λ , ∼ λ ). Scattering becomes thus even more critical as the wave-
lengths of application shift from the visible to the deep or extreme UV spectral ranges.
Surfaces, coatings, and materials suitable for DUV or EUV optics are generally much
more difficult to process