Particle emission from extreme ultraviolet light sources [Elektronische Ressource] / von Thomas Brauner

Sujets

• Physik

Informations

• Publié par: friedrich-schiller-universitat_jena
• Publié le: 01 janvier 2008
• Nombre de lectures: 70
• Langue: Deutsch
• Poids de l'ouvrage: 11 Mo

Extrait

Particle Emission from
Extreme Ultraviolet Light Sources
Dissertation
zur Erlangung des akademischen Grades
doctor rerum naturalium
vorgelegt dem Rat der Physikalisch-Astronomischen Fakulta¨t der
Friedrich-Schiller-Universitat Jena¨
von Diplom-PhysikerThomas Brauner
geboren am 23.03.1976 in WittlichGutachter:
1. Prof. Dr. R. Sauerbrey, Forschungszentrum Dresden-Rossendorf (Deutschland)
2. Prof. Dr. H. Fiedorowicz, Military University of Technology Warszawa (Polen)
3. Prof. Dr. D. Ruzic, University of Illinois at Urbana-Champaign (USA)
Tag der letzten Rigorosumsprufung: 26.04.2007¨
Tag der ¨offentlichen Verteidigung: 29.05.2007Contents
1 Introduction 1
1.1 Extreme Ultraviolet Radiation . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.1 Optical Properties of EUV Radiation . . . . . . . . . . . . . . . 2
1.1.2 Sources of EUV Radiation . . . . . . . . . . . . . . . . . . . . . 4
1.1.3 EUV Metrology . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Properties of Hot Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2.1 Basic Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2.2 Thermodynamic Plasma Models . . . . . . . . . . . . . . . . . . 8
1.2.3 EUV Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.3 Laser Produced Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.4 Gas Discharge Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.5 Particle Emission from Hot Plasmas and Optics Lifetime . . . . . . . . 16
1.6 Scope of this Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2 Experimental Setup of the Laser Produced Plasma 21
2.1 Laser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2 Target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3 Angular Dependence of EUV Emission from an LPP source 26
3.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4 Debris Emission Measurements of an LPP Source 33
4.1 Debris and Optics Lifetime Diagnostics . . . . . . . . . . . . . . . . . . 33
4.1.1 Quartz Crystal Monitor . . . . . . . . . . . . . . . . . . . . . . 33
iCONTENTS ii
4.1.2 Post-Exposure Diagnostics . . . . . . . . . . . . . . . . . . . . . 34
4.1.3 In-situ Reflectivity Measurement . . . . . . . . . . . . . . . . . 36
4.2 Angular and Distance Characteristics of Debris Emission . . . . . . . . 37
4.3 Debris Mitigation Systems for LPP . . . . . . . . . . . . . . . . . . . . 40
4.3.1 Electric Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.3.2 Magnetic Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.3.3 Mechanical Shutters . . . . . . . . . . . . . . . . . . . . . . . . 43
4.3.4 Buffer Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.4 Debris Mitigation with a Buffer Gas . . . . . . . . . . . . . . . . . . . . 45
4.4.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.4.2 Debris Mitigation at Different Buffer Gas Pressures . . . . . . . 47
4.4.3 Debris Mitigation at Different Repetition Rates . . . . . . . . . 50
4.4.4 Further Enhancement of Collector Lifetime . . . . . . . . . . . . 52
5 Experimental Setup of the Gas Discharge Produced Plasma 54
5.1 Circuit and Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.2 Vacuum Setup and Debris Mitigation . . . . . . . . . . . . . . . . . . . 56
6 Debris Emission Measurements of a GDP Source 58
6.1 Ion Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
6.1.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . 58
6.1.2 Ion Spectrum of a GDP Source . . . . . . . . . . . . . . . . . . 63
6.1.3 Ion Spectrum with Buffer Gas Flow . . . . . . . . . . . . . . . . 66
6.1.4 Hydrogen Addition to Xenon Fuel . . . . . . . . . . . . . . . . . 69
6.1.5 Effect of Different Repetition Rates . . . . . . . . . . . . . . . . 72
6.2 Evaluation of a Gas Curtain for Debris Mitigation . . . . . . . . . . . . 74
6.2.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6.2.2 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.2.3 Pressure Distribution . . . . . . . . . . . . . . . . . . . . . . . . 76
6.2.4 Ion Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
6.2.5 Temperature Development . . . . . . . . . . . . . . . . . . . . . 79
6.2.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79CONTENTS iii
7 Transmission Test Stand for Debris Mitigation Tools 81
7.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
7.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
Appendix 85
A Charged Particles in a Planar Capacitor 85
B Charged Particles in a Magnetic Field 87
Summary and Conclusion 89
Bibliography 92
Acknowledgements 100
Zusammenfassung (deutsch) 101
Lebenslauf (deutsch) 105
Ehrenwortliche Erklarung (deutsch) 106¨ ¨Chapter 1
Introduction
In the past years, the density of transistors on a microchip has doubled approximately
every eighteen months. This fact is often referred to as Moore’s law, named after one
of the founders of the well-known technology company Intel [1]. The semiconductor
industry is very interested in continuing the pace of this progress. However, the cur-
rent manufacturing technology is at its limits and will require some major changes in
order to further increase the integration. The general direction of research and de-
velopment in that field are coordinated by the International Technology Roadmap for
Semiconductors [2].
Today’s microchips are fabricated by optical lithography technology. In optical
lithography, the semiconductor wafer is coated with a photosensitive material called
photo resist. The desired pattern is projected with a mask onto the photo resist,
where it causes a photochemical reaction. Depending on the nature of the photo
resist, the exposed or the unexposed areas can be chemically dissolved, so that the
photo resist takes on the projected pattern. This then enables selective etching in the
areas without photo resist. In this way the pattern can be etched into the surface of
the wafer. Similarly, it is possible to grow additional layers of semiconductor crystal
selectively on areas that are coated or uncoated with photo resist. By combining these
techniques, and performing them many times with different masks, very small and
complex structures can be given to the wafers.
The minimum possible structure size that can be achieved by this technique is
determined by the optical resolution RES of the imaging. This is given by
k λ1
RES = , (1.1)
NACHAPTER 1: INTRODUCTION 2
where λ is the wavelength of the light being used, NA the numerical aperture of
the imaging system and k an application dependent coefficient. Another important1
parameter is the depth of focus (DOF), given by
k λ2
DOF = , (1.2)
2NA
where k is - as k in 1.1 - an application dependent coefficient. For diffraction-limited2 1
imaging,k andk equal 0.61. It can easily be seen that there are two ways to decrease1 2
the structure sizes: The wavelength used λ can be decreased or the numerical aperture
NA can be increased.
In the past twenty years, the lithography process was improved by continuously
decreasing the wavelength of the light used. Lasers are used as a light source, provid-
ing monochromatic light at high intensities. Throughout this development, no major
changes had to be implemented to the rest of the lithography system. At the moment,
microchipproductionisdoneusingexcimerlasersinthevacuumUV(VUV)usingopti-
cal components made of calcium fluoride or magnesium fluoride. However, the shortest
commercially available laser wavelength is 157 nm.
For the lithography of smaller structures both parameters λ and NA are under
consideration. The continued reduction of the wavelength leads to extreme ultraviolet
(EUV) lithography. For scaling up the numerical aperture, the refractive index of the
light path needs to be increased. This approach leads to immersion lithography. The
work in this thesis is concerned with extreme ultraviolet lithography.
1.1 Extreme Ultraviolet Radiation
1.1.1 Optical Properties of EUV Radiation
Electromagnetic radiation in the wavelength range of about 5-20 nm is usually called
extreme ultraviolet radiation. The most important feature of EUV radiation is that
it is strongly absorbed in any known medium - even in gases at low pressures. Two
immediate conclusions can be drawn from this fact: First, only reflective optics can
be used for imaging as there are no transmissive optical elements for EUV radiation.
Second, the whole imaging system, from the light source to the wafer, has to be in high
vacuum.CHAPTER 1: INTRODUCTION 3
Figure 1.1: Reflectivity of ruthe-
nium and palladium for EUV ra-
diation. For this figure a 50 nm
thicklayerofthemetalonanickel
substrate was assumed. The sub-
strate and the coating were both
assumed to have no roughness at
all. Therefore this graph repre-
sents an ideal grazing incidence<