KEYWORDS: Ions, Helium, Electrons, Electron beam lithography, Line edge roughness, Monte Carlo methods, Ion beam lithography, Extreme ultraviolet lithography, Silicon, Scanning helium ion microscopy
Helium ion beam lithography (HIBL) is a novel alternative lithographic technique with the capacity of fabricating highresolution and high-density features. Only limited research has been performed exploring HIBL to date. HafSOx (Hf(OH)4–2x−2y(O2)x(SO4)y·qH2O) is a negative-tone inorganic resist that is one of several candidate resist materials for extreme ultraviolet lithography (EUVL) and e-beam lithography (EBL), and has been demonstrated to show high resolution, moderate sensitivity and low line-edge roughness (LER) in both EUVL and EBL. To date, no ion beam lithography work on HafSOx has been reported. In this study, we tested HafSOx as an HIBL resist and achieved a high sensitivity compared with EBL with a turn-on dose D100 ~ 2-4 μC/cm2. We obtained sub-10 nm line widths with low LER. A simple Monte Carlo simulation suggests that ionizing excitation accounts for most of the incident He ions’ energy loss.
We report studies of the thermal and non-thermal interaction of benzene and toluene vapors with the Ru(0001) surface, a
model cap layer for multilayer mirrors (MLM), using temperature programmed desorption (TPD), X-ray photoelectron
spectroscopy (XPS), low energy ion scattering (LEIS), electron stimulated desorption (ESD), low electron energy
diffraction (LEED), and scanning tunneling microscopy (STM). A low energy electron source (100 eV) is used to
simulate radiation damage on the surface produced by EUV photons. Heating of adsorbed hydrocarbons leads to a
stepwise dehydrogenation and buildup a self-limited carbon monolayer. Graphene monolayer and bilayer formation on
Ru by hydrocarbon pyrolysis or by carbon segregation from the sample bulk is examined as a possible way to reduce the
surface contamination rate. The binding energy of the hydrocarbon molecule is found to be smaller on a graphene layer
than on disordered carbon. Electron bombardment of both bare and graphene covered Ru surface in the presence of
benzene and toluene leads to C-buildup. However, the presence of a graphene monolayer on Ru surface reduces the
electron-induced carbon growth rate at low electron flux conditions.
The aim of this work is to explore the thermal and non-thermal interaction of toluene, benzene and isobutene vapor with
a crystalline Ru(10-10) surface, a model surface for Ru capping layers used in EUV lithography. Our main objective is to
provide insights into the basic processes that affect the reflectivity of Ru-coated Mo/Si multilayer mirrors that are
exposed to EUV radiation. A low energy electron beam is employed to mimic excitations initiated by EUV radiation.
Temperature programmed desorption (TPD), x-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS),
and electron-stimulated desorption (ESD) are used to analyze the surface reactions. Pyrolysis of a chemisorbed
hydrocarbon layer on the Ru surface leads to the dehydrogenation and buildup a self-limited carbon monolayer. Carbon
film growth on the Ru(10-10) crystalline surface under 100 eV electron bombardment in hydrocarbon vapor is measured
over a range of pressures and temperatures near 300 K. The carbon growth rate is ~10 times higher in the presence of
toluene vapor than in the presence of benzene or isobutene vapor. The estimations of the adsorption energy, the steadystate
coverage of the molecules on the surface and the cross-sections for electron-stimulated dissociation are presented.
A graphene-like carbon layer is probed as possible way to reduce the surface contamination rate.
The primary, publicly reported cause of optic degradation in pre-production extreme-ultraviolet (EUV) lithography systems is carbon deposition. This results when volatile organics adsorb onto optic surfaces and then are cracked by EUV-induced reactions. Hence the deposition rate depends on the adsorption-desorption kinetics of the molecule-surface system as well as the basic photon-stimulated reaction rates, both of which may vary significantly for different organic species. The goal of our ongoing optics-contamination program is to estimate the contamination rate of species expected in the tool environment by exposing samples to in-band 13.5 nm light from our synchrotron in the presence of fixed partial pressures of admitted gases. Here we report preliminary results of contamination rates on TiO2-capped samples for species observed in resist-outgassing measurements (benzene, isobutene, toluene and tert-butylbenzene) in the pressure range (10-6 to 10-4) Pa which all display an unexpected logarithmic dependence on pressure. This scaling is in agreement with previous EUV exposures of other species at NIST as well as independent measurements of coverage performed at Rutgers University. These results are consistent with a molecular desorption energy that decreases with coverage due to molecular interactions (Temkin model). Use of the proper scaling law is critical when estimating optic lifetimes by extrapolating over the 3-to-6 orders of magnitude between accelerated-testing and tool-environment partial pressures.
Our aim is to characterize the surface processes that affect the reflectivity of TiO2 - capped multilayer mirrors used in EUV lithography. Low energy electron beam is employed to mimic excitations initiated by EUV radiation. Temperature programmed desorption (TPD), x-ray photoelectron spectroscopy (XPS), and low energy ion scattering (LEIS) are used to analyze the surface reactions. Carbon film growth on the TiO2 (011) crystalline surface is measured during 10 to 100 eV electron bombardment in benzene or methyl methacrylate (MMA) vapor over a wide range of pressures and temperatures near 300 K. Low energy secondary electrons excited by EUV photons contribute substantially to carbon accumulation on clean TiO2 cap layers. For benzene on clean TiO2 secondary electron effects dominate in the initial stages of carbon accumulation, whereas for C-covered TiO2, direct photoexcitations appear to dominate. The adsorption energy, the steady-state coverage of the molecules on the surface and the cross-sections for electron-stimulated dissociation are key parameters for understanding and modeling the processes on the EUVL mirrors.
This paper describes our initial investigation into building a greater understanding of the complex mechanism occurring during extreme ultraviolet (EUV) exposure of resist materials. In particular, we are focusing on the number and energy of photoelectrons generated and available for reaction with photoacid generators (PAGs). We propose that this approach will best enable the industry to develop resists capable of meeting resolution, line width roughness (LWR), and sensitivity requirements.
Our goal is to provide insights into surface processes that affect the reflectivity and lifetimes of TiO2 and Ru-capped
multilayer mirrors used in extreme ultraviolet (EUV) lithography. Several surface-sensitive ultrahigh-vacuum
techniques are used to characterize thermally-induced and electron-induced surface reactions of methyl methacrylate
(MMA), a model for hydrocarbons found in EUV lithography vacuum chambers; low-energy electron beams are used to
mimic excitations initiated by EUV radiation. Carbon film growth is measured on TiO2 surfaces during electron
bombardment (at 20 eV and 100 eV) in MMA vapor; C growth rates are compared on Ru surfaces. The initial rates on
the clean surfaces are very different: a C film grows more rapidly on TiO2 than on Ru. However, the limiting growth
rates are the same for C thicknesses greater than ~1 to 1.5 nm, when MMA interacts with a C film. Irradiation of the C
films in O2 gas, or in MMA + O2, has a mitigating effect on TiO2 surfaces.
We characterize the interaction of ethyl alcohol (C2H5OH) vapor with a crystalline Ru(1010) surface, a model
surface for Ru capping layers used for extreme ultraviolet lithography (EUVL) optics. Our main objective is to provide
fundamental insights into the basic physical processes that affect the reflectivity of Ru-coated Mo/Si multilayer EUV
mirrors that are exposed to EUV radiation. While ethanol has been used previously as a gaseous hydrocarbon in EUV
mirror lifetime tests, there appear to be no published reports describing the basic surface chemistry of ethanol on Ru.
We use ultrahigh vacuum surface science methods, and find that fractional monolayers (ML) of ethanol dissociate
almost completely on clean Ru(1010); H2 and CO desorb upon heating to ~500 K, and leave a fractional ML of carbon
on the surface. At coverages greater than a few tenths of a ML, ethanol desorbs in molecular form at temperatures below
300 K. Weakly chemisorbed ethanol in the first ML desorbs at ~210 K with a binding energy of 0.55 eV. Multilayer
ethanol desorbs at ~155 K. Repeated dosing of ethanol followed by heating to ~600 K causes accumulation of a carbon
monolayer which becomes unreactive to ethanol. Also, we find that an oxygen monolayer is unreactive, with little or no
dissociation of ethanol observed. Electron bombardment of Ru at 300 K in 5×10-8 Torr ethanol can lead to accumulation
of a carbon film >1nm thick.
The ability to predict the rate of reflectivity loss of capped multilayer mirrors (MLMs) under various conditions of
ambient vacuum composition, intensity, and previous dose is crucial to solving the mirror lifetime problem in an EUV
stepper. Previous measurements at NIST have shown that reflectivity loss of MLMs exposed under accelerated
conditions of dose and pressure can be a very complicated function of these variables. The present work continues this
effort and demonstrates that reflectivity loss does not scale linearly for accelerated exposure doses over the range of
0-350 J/mm2 either for partial pressures of MMA in the range 10-8-10-7 Torr or acetone in the range 10-7-10-6 Torr. We
suggest that this nonlinear scaling may be the result of a varying damage rate as the surface of the growing
contamination layer moves through the EUV standing wave created by exposure of any MLM to resonant radiation. To
further investigate the potential influence of these resonance effects, we report new measurements showing large
variations of the secondary electron yield as a function of thickness of carbon deposited on top of a MLM.
Metallic ruthenium capping layers ~2 nm thick protect and extend the lifetimes of Mo/Si multilayer mirrors
used in extreme ultraviolet lithography (EUVL) applications. However, Ru-capped mirrors experience a loss of
reflectivity after prolonged exposure to EUV radiation. In the present work, we use ultrahigh vacuum surface science
methods to address several aspects of Ru surface chemistry that may impact on Ru capping layer stability and mitigation
processes. (1) We characterize the composition and stability of Ru surfaces that simulate surfaces of Ru-capped
multilayer mirrors, under exposure to different background gases (water, methyl methacrylate (MMA)) and to electron
irradiation. Evidence for some mitigation of carbon accumulation during electron bombardment in MMA + water vapor
is found. (2) We report the photon-energy dependence of secondary electron yield (SEY) measurements for clean Ru,
O-dosed and C-dosed Ru, and Ru-capped multilayer mirrors using synchrotron radiation near 13.5 nm at Brookhaven
National Synchrotron Light Source (NSLS). Much of the radiation-induced chemistry on the surfaces of capping layers
is induced by low-energy secondary electrons rather than direct photoexcitation, so the SEY is an important parameter
affecting mirror lifetimes in EUVL.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.