Demagnifying X-ray lithography [Elektronische Ressource] / vorgelegt von Christiane Zimprich

Sujets

• Physik
• Astronomie

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2003
• Nombre de lectures: 22
• Langue: Deutsch
• Poids de l'ouvrage: 4 Mo

Extrait

Demagnifying X-Ray Lithography
Von der Fakult¨at fu¨r Mathematik, Informatik und
Naturwissenschaften der Rheinisch-Westf¨alischen Technischen
Hochschule Aachen zur Erlangung des akademischen Grades einer
Doktorin der Naturwissenschaften genehmigte Dissertation
vorgelegt von
Diplom-Physikerin Christiane Zimprich
aus Schwalmstadt.
Berichter: Universit¨atsprofessor Dr. B. Lengeler
Universit¨atsprofessor Dr. H. Lu¨th
Tag der mu¨ndlichen Pru¨fung: 25. April 2003
Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfu¨gbar.Contents
1 Introduction 1
2 Synchrotron Radiation 5
2.1 Generation of X-Rays . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Interaction with Matter . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.1 Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.2 Refractive Index . . . . . . . . . . . . . . . . . . . . . . . 13
3 Imaging with PRXL 15
3.1 Imaging Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2 Effective Aperture . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3 Numerical Aperture . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.4 Diffraction Limited Spot Size . . . . . . . . . . . . . . . . . . . . 19
3.4.1 Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.4.2 Depth of Field. . . . . . . . . . . . . . . . . . . . . . . . . 20
3.5 Chromatic Aberration . . . . . . . . . . . . . . . . . . . . . . . . 21
4 Lithography 23
4.1 Typical Process Outline . . . . . . . . . . . . . . . . . . . . . . . 23
4.2 Lithographic Resists . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.2.1 Sensitivity and Contrast . . . . . . . . . . . . . . . . . . . 25
4.2.2 Polymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
iii CONTENTS
4.2.3 Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2.4 Proximity Effect . . . . . . . . . . . . . . . . . . . . . . . 29
4.3 Lithographic Methods . . . . . . . . . . . . . . . . . . . . . . . . 30
4.3.1 Optical Lithography . . . . . . . . . . . . . . . . . . . . . 30
4.3.2 Electron-Beam Lithography . . . . . . . . . . . . . . . . . 31
4.3.3 X-Ray Lithography . . . . . . . . . . . . . . . . . . . . . . 31
5 X-Ray Masks 33
5.1 Gold Masks on Silicon . . . . . . . . . . . . . . . . . . . . . . . . 33
5.1.1 Substrate . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5.1.2 Tri-Level Resist . . . . . . . . . . . . . . . . . . . . . . . . 34
5.1.3 Reactive Ion Etching . . . . . . . . . . . . . . . . . . . . . 36
5.1.4 Electroplated gold . . . . . . . . . . . . . . . . . . . . . . 39
5.2 Masks by the IMT . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6 Experimental Results 43
6.1 Setup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
6.2 Enhancement of the Field of View . . . . . . . . . . . . . . . . . . 45
6.2.1 Condenser Lens . . . . . . . . . . . . . . . . . . . . . . . . 46
6.2.2 Diffuser . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
6.3 Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
6.3.1 FReLoN-Camera . . . . . . . . . . . . . . . . . . . . . . . 48
6.3.2 AR-N 7700.18 . . . . . . . . . . . . . . . . . . . . . . . . . 48
6.4 Demagnifying Lithography . . . . . . . . . . . . . . . . . . . . . . 49
6.4.1 Monochromatic versus Pink Beam . . . . . . . . . . . . . . 50
6.4.2 Different Doses . . . . . . . . . . . . . . . . . . . . . . . . 51
6.4.3 Different Developments . . . . . . . . . . . . . . . . . . . . 52
6.5 Structure Edges . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53CONTENTS iii
7 Monte Carlo simulations 57
7.1 Simulation model . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
7.1.1 Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . 58
7.1.2 Simulated sample . . . . . . . . . . . . . . . . . . . . . . . 59
7.1.3 Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . 61
7.1.4 Photoelectrons . . . . . . . . . . . . . . . . . . . . . . . . 62
7.1.5 Fluorescence . . . . . . . . . . . . . . . . . . . . . . . . . . 65
7.1.6 Auger electrons . . . . . . . . . . . . . . . . . . . . . . . . 65
7.2 Simulation results . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
7.2.1 Electron trajectories . . . . . . . . . . . . . . . . . . . . . 66
7.2.2 Dose distribution in the resist . . . . . . . . . . . . . . . . 67
7.2.3 Influence of photoelectrons . . . . . . . . . . . . . . . . . . 69
7.2.4 Influence of Auger electrons . . . . . . . . . . . . . . . . . 73
7.2.5 Influence of fluorescence . . . . . . . . . . . . . . . . . . . 76
8 Outlook 77
8.1 Different lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
8.2 Adjusting the resists . . . . . . . . . . . . . . . . . . . . . . . . . 78
9 Summary 87
List of Figures 91
Bibliography 93iv CONTENTSChapter 1
Introduction
In the past decades, a rapidly proceeding miniaturization and integration of elec-
tronic circuits has accompanied the spreading of computers and electronic con-
trol systems in our world. In the course of this development, the interest in the
fabrication of mechanical and optical devices in the micrometer-range, so-called
MOEMS (microoptoelectromechanical systems), has also been growing in recent
years. Thesensorsforairbagsandantilockbrakingsystemsareonlytwoofmany
examples that illustrate the importance of these systems in the modern world.
The ongoing miniaturization demands a decrease in the minimum feature sizes
that can be fabricated. Figure 1.1 shows a roadmap for the development of the
transistorgatelengthsinmicroelectronics. Withthisdecreaseofthefeaturesize,
thedemandgrowsforfurtherdevelopmentsinlithography. Inopticallithography,
this development is leading to a decrease in the wavelength from around 400 nm
over 193 nm nowadays to the extreme ultraviolet with 13.4 nm in the future to
provide a resolution that is high enough to image the decreasing features. The
wavelengths can also be reduced even further to soft x-rays with about 1 nm and
below. Theuseofharderx-raysisofinterestespeciallyformicromachiningappli-
cations, since the long absorption lengths at these energies allows the structuring
of very thick resist layers with thicknesses up to 1 mm.
A critical point in lithography is the fabrication of masks, since the features on
the mask have to shrink in accordance with the features on the final sample. The
useofdemagnifyinglenssystemshasbeenastandardtoolforopticallithography
for several years. This is an advantage for the mask productions, since the mask
features are allowed to be larger than the resulting features on the specimen.
With decreasing wavelength of the light, however, the standard optical systems
for the visible and ultraviolet regime cease to function. Equivalent optics for
x-rays, however, havenotbeenavailableforalongtime, andithasbeencommon
knowledge since the times of W. C. R¨ontgen that refractive lenses do not work
12 CHAPTER 1. INTRODUCTION
Figure 1.1: Development of the printed gate lengths for transistors from the 2001
international roadmap for semiconductors [1].
for x-rays [2]. Indeed, the refraction of x-rays in matter is a very weak effect.
Nevertheless, A. Snigirev et al. [3] could demonstrate in 1996 the working of the
firstrefractivelensesforhardx-rays. Thelensesconsistingofalignedandcrossed
drill holes are able to focus x-rays, but due to their cylindrical shape they have a
strong spherical aberration, which limits their use for imaging applications. This
problem can be overcome with parabolic refractive x-ray lenses (PRXL), which
were first used in 1998 [4]. These lenses have since been used as optics for a
wide variety of tasks in microscopy and microtomography [4–10] for hard x-rays
between 8 and 100 keV.
TheaimofthisthesisistoshowthatthePRXLcanbeusedasademagnification
tool in lithography with hard x-rays. In chapter 2, the generation of synchrotron
radiation will be discussed briefly together with the basic concepts of its inter-
action with matter. A description of PRXL and their imaging characteristics
follows in chapter 3. Chapter 4 gives a short introduction into lithography. This
chapter will not only deal with x-ray but also with optical and electron-beam
lithography. Another focus will be the resist technology, which is similar for all
lithographic processes. The fabrication of the masks that are used in the x-ray
lithography experiments will be described in chapter 5. In chapter 6, the experi-
mental setup and the results of the demagnifying x-ray lithography experiments3
are presented. The difficulties that arise in these experiments due to secondary
electronsarefurtherinvestigatedbymeansofMonteCarlosimulationsinchapter
7. Some improvements for the demagnifying x-ray lithography will be discussed
in chapter 8.4 CHAPTER 1. INTRODUCTIONChapter 2
Synchrotron Radiation:
Generation and Interaction with
Matter
The basic concept of a synchrotron was developed to accelerate charged particles
such as electrons. A magnetic field keeps the particles on a circular orbit during
the acceleration process. This field is changed synchronously with the increas-
ing particle energy so that the radius of the orbit is kept constant. A drawback
of these accelerators is, however, that electrons with high energies