Optics contamination remains one of the challenges in extreme ultraviolet (EUV) lithography. Dependence of
contamination rates on key EUV parameters was investigated. EUV tools have optics at different illumination angles. It
was observed that at shallower angles, the carbon contamination rate and surface roughness was higher on the optics
surface. This is a concern in EUV optics as higher roughness would increase the scattering of the EUV radiation.
Secondary ion time of flight mass spectrometer (TOF-SIMS) data indicated that the carbon contamination film might be
a polymer. Three chemical species were used to investigate the dependence of polymerization and reactivity on the
contamination rate. Acrylic acid was found to have a measurable contamination rate above background compared to
propionic acid and methyl methacrylate. Secondary electron dissociation is one of the mechanisms considered to be a
cause for the growth of the carbon contamination film. Multiple experiments with two substrates having different
secondary electron yields were performed. The substrate with the higher secondary electron yield was found to give a
higher contamination rate.
Optics contamination remains one of the challenges in extreme ultraviolet (EUV) lithography. In addition to the
desired wavelength near 13.5 nm (EUV), plasma sources used in EUV exposure tools emit a wide range of
out-of-band (OOB) wavelengths extending as far as the visible region. We present experimental results of
contamination rates of EUV and OOB light using a Xe plasma source and filters. Employing heated carbon
tape as a source of hydrocarbons, we have measured the wavelength dependence of carbon contamination
on a Ru-capped mirror. These results are compared to contamination rates on TiO<sub>2</sub> and ZrO<sub>2</sub> capping layers.
We describe a null-field ellipsometric imaging system (NEIS) that provides for the real-time imaging of carbon
deposition profiles on extreme-ultraviolet (EUV) optics in a vacuum system. NEIS has been demonstrated at NIST on a
small chamber that is used for EUV optics lifetime testing. The system provides images of carbon deposition spots with
sub-nanometer resolution thickness measurements that maintain good agreement with those from ex-situ spectral ellipsometry (SE) and x-ray photoelectron spectroscopy (XPS). The system will be implemented on several synchrotron beamlines for real-time monitoring of carbon film growth on optics during EUV irradiation.
The impact of carbon contamination on extreme ultraviolet (EUV) masks is significant due to throughput loss and
potential effects on imaging performance. Current carbon contamination research primarily focuses on the lifetime of the
multilayer surfaces, determined by reflectivity loss and reduced throughput in EUV exposure tools. However,
contamination on patterned EUV masks can cause additional effects on absorbing features and the printed images, as
well as impacting the efficiency of cleaning process. In this work, several different techniques were used to determine
possible contamination topography. Lithographic simulations were also performed and the results compared with the
Carbon contamination of extreme ultraviolet (EUV) masks and its effect on imaging is a significant issue due to lowered
throughput and potential effects on imaging performance. In this work, a series of carbon contamination experiments
were performed on a patterned EUV mask. Contaminated features were then inspected with a reticle scanning electron
microscope (SEM) and printed with the SEMATECH Berkeley Microfield-Exposure tool (MET) . In addition, the
mask was analyzed using the SEMATECH Berkeley Actinic-Inspection tool (AIT)  to determine the effect of carbon
contamination on the absorbing features and printing performance.
To understand the contamination topography, simulations were performed based on calculated aerial images and resist
parameters. With the knowledge of the topography, simulations were then used to predict the effect of other thicknesses
of the contamination layer, as well as the imaging performance on printed features.
Typical extreme ultraviolet (EUV) photoresist is known to outgas carbon-containing molecules, which is of particular
concern to the industry as these molecules tend to contaminate optics and diminish reflectivity. This prompted extensive
work to measure these species and the quantities that they outgas in a vacuum environment. Experiments were
performed to test whether the outgassing rate of these carbon-containing molecules is directly proportional to the rate at
which the EUV photons arrive and whether a very high power exposure will cause the same amount of outgassing as a
much lower power exposure with the dose unchanged.
One of the remaining challenges for the commercialization of EUV lithography is the lifetime of
the Mo/Si multilayer optics and masks. The lifetime is dominated by carbon contamination on the surfaces
of the optics, which is caused by residual hydrocarbons in the vacuum chamber when optics are exposed to
EUV radiation. One of the possible sources of the hydrocarbons in the chamber is resist outgassing. To be
able to understand which type of hydrocarbons are harmful to EUV mirror reflectivity, three hydrocarbon
species - benzene, tert-butanol and diphenyl sulfide - which are thought to be representative of commonly
outgassed species from EUV photoresist were selected. The goal of this work was to measure the
contamination rate from these three species and to be able to draw conclusions about other species. The
results of the experiments showed that after 8 hours of exposure there was not enough contamination to be
significantly measurable. In addition to these hydrocarbon species, we also used vacuum grease and carbon
tape as an outgassing source for hydrocarbons. Comparatively, high contamination rates were achieved
with vacuum grease and carbon tape.
Extreme ultraviolet (EUV) photoresists are known to outgas during exposure to EUV radiation in the vacuum
environment. This is of particular concern since some of the outgassed species may contaminate the nearby EUV optics
and cause a loss of reflectivity and therefore throughput of the EUV exposure tools. Due to this issue, work has been
performed to measure the species and quantities that outgas from EUV resists. Additionally, since the goal of these
measurements is to determine the relative safety of various resists near EUV optics, work has been performed to measure
the deposition rate of the outgassed molecules on Mo/Si-coated witness plate samples. The results for various species
and tests show little measurable effect from resist components on optics contamination with modest EUV exposure
With the commercialization of extreme ultraviolet (EUV) lithography underway, there is
considerable effort underway to improve EUV photoresists, so that they can meet the <i>ITRS 2006 update</i>
requirements for resolution, line edge roughness and sensitivity. Nevertheless, the present limited
availability of EUV exposure tools, and the high cost of such tools, has hampered the resist development
effort. We have developed a simple, low-cost, technique to characterize different photoresist formulations
for printing sub-100-nm features using EUV radiation. In the method presented here, a transmission mask
is placed in close proximity to the resist sample and the resist is exposed through the mask. The mask used
for this technique is a silicon nitride membrane with 50 nm gold layer which is patterned using a focused
ion beam tool. The source for EUV light is a xenon based discharge plasma source from Energetiq. After
developing, the resist images are measured in a scanning electron microscope to determine the feature size.
Here we present results demonstrating sub-100 nm feature size using this method.
The Mo/Si multilayer mirrors used for extreme ultraviolet (EUV) lithography can become contaminated during exposure
in the presence of some hydrocarbons [1-3]. Because this leads to a loss in the reflectivity of the optics and throughput
of the exposure tools, it needs to be avoided. Since photoresists are known to outgas during exposure to EUV radiation
in a vacuum environment, the careful choice of materials is important to preserving the EUV optics. Work therefore has
been performed to measure the species and quantities of molecules that outgas from EUV resists when exposed to EUV
Extreme ultraviolet (EUV) lithography is one of the promising techniques for the fabrication of semiconductor features at or below 32 nm. One of the key parameters that can affect photoresist performance is their absorption characteristics at EUV wavelengths. The measurement of the absorption length or absorbance is important because it causes the dose to vary through the thickness of resist which can result in underexposure deeper in the resist. One method for measuring absorption length of a resist is by direct measurement of the transmission of EUV radiation through the resist when it is on a transparent membrane. The results of these measurements show the absorbance for different photoresists currently used for extreme ultraviolet lithography.
Extreme ultraviolet lithography (EUVL) is the most likely next generation lithography technique which uses radiation near 13.4 nm wavelength. At this short wavelength, most materials readily absorb the radiation, making refractive lens optical systems unusable. We demonstrate a novel method for fabrication of highly efficient optics for extreme ultraviolet (EUV) radiation using focused ion beam (FIB). These optics are based on Fresnel zone plates, similar to those used for x-ray microscopy, but with a geometry to improve the efficiency for EUV radiation. A typical zone plate has concentric rings with a radially decreasing feature size such that the path of light through every second zone to the focus differs by one optical wavelength following the Bragg's Law. An optic with a net efficiency of 21% can be achieved for 13.4 nm radiation using the standard zone plate design with 86 nm thick zones made from Mo and mounted on a 50 nm silicon nitride membrane. Further improvement in the efficiency can be achieved by fabricating blazed zone plates, which can have a net efficiency of 40% when fabricated on a 50 nm silicon nitride membrane. These lenses are cheap to manufacture and easy to align for imaging since it is a single optic. The preliminary data will be presented on the fabrication of both standard and blazed zone plates optimized for EUV radiation.