Out-of-band radiation in extreme ultraviolet (EUV) exposure tools remains one of the critical issues that must be addressed before the implementation of this lithography technique for high-volume manufacturing. The out-of-band spectrum at the intermediate focus of EUV sources that use a CO2 laser-produced plasma is dominated by scattered radiation from the drive laser, which operates near 10.6-μm wavelength. To reduce the unwanted heating of optical components in the exposure tool caused by the infrared wavelength, a 10.6-μm wavelength-absorbing gas can be used to reduce the number of photons at this wavelength reaching the intermediate focus. Gaseous sulfur hexafluoride (SF6), whose υ3 infrared active mode is vibrationally excited by radiation around 10.6-μm wavelength, can be used to function as a molecular absorber and thus, mitigate part of the infrared radiation. In this work, the optical absorption of gaseous SF6 is experimentally investigated at the CO2 laser wavelengths close to 10.6 μm as well as the EUV wavelength. Various considerations affecting the use of a gas-based spectral filter are also discussed in this paper.
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.
The development of resists that meet the requirements for resolution, line edge roughness and sensitivity remains one of
the challenges for extreme ultraviolet (EUV) lithography. Two important processes that contribute to the lithographic
performance of EUV resists involve the efficient decomposition of a photoacid generator (PAG) to yield a catalytic acid
and the subsequent deprotection of the polymer in the resist film. We investigate these processes by monitoring the
trends produced by specific masses outgassing from resists following EUV exposure and present our initial results. The
resists tested are based on ESCAP polymer and either bis(4-tert-butylphenyl)iodonium perfluoro-1-butanesulfonate or
bis(4-tert-butylphenyl)iodonium triflate. The components originating from the PAG were monitored at various EUV
exposure doses while the deprotection of the polymer was monitored by baking the resist in vacuum and detecting the
cleaved by-product from the polymer with an Extrel quadruple mass spectrometer.
Next generation high volume manufacturing lithography tools will likely use CO2 laser produced plasma sources to
generate extreme ultraviolet (EUV) radiation needed for resist exposures. Existing mitigation techniques for out-of-band
radiation from these sources result in reduced EUV (13.5 nm) transmission to the resist plane which decreases desired
throughput. New methods to suppress the 10.6 μm radiation, which dominates the out-of-band spectrum at the
intermediate focus (IF), need to be examined. A spectral filter design that uses an infrared absorbing gas to target the
mitigation of 10.6 μm in these EUV tools may provide another alternative to suppress the unwanted radiation. This work
explores infrared absorption of gases at 10.6 μm while focusing on gaseous sulfur hexafluoride (SF6) whose υ3 infrared
active mode is vibrationally excited by 10.6 μm photons. A compact tunable CO2 laser is used to measure the room
temperature, low fluence absorption of SF6 in the range of 10.53-10.65 μm. In addition, the EUV transmission of SF6 as
a function of pressure is estimated based on the absorption cross section measured for wavelengths between 11-17 nm.
Design considerations such as the EUV transmission vs. infrared absorption tradeoff are discussed.
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 TiO2 and ZrO2 capping layers.
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
experimental data.
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.
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) [1]. In addition, the
mask was analyzed using the SEMATECH Berkeley Actinic-Inspection tool (AIT) [2] 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.
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
doses.
A method to evaluate the sensitivity of photoresists used for extreme ultraviolet (EUV) lithography has been developed.
EUV sources produce out-of-band radiation and the reflective optics used in EUV tools reflect some of this out-of-band
light on the wafer plane. The effect of exposing these photoresists to this unwanted light can reduce the image contrast
on the wafer, and thereby reduce the image quality of the printed images. To examine the wavelengths of light that may
have an adverse effect on these resists, a deuterium light source mounted with a monochromator has been designed to
determine how sensitive these photoresists are to light at selected wavelengths in the range 190-650 nm.
The photon-stimulated emission of organic molecules from the photoresist during exposure is a serious problem for
extreme-ultraviolet lithography (EUVL) because the adsorption of the outgassing products on the EUV optics can lead
to carbonization and subsequent reflectivity loss. In order to accurately quantify the total amount of outgassing for a
given resist during an exposure, we have constructed a compact, portable chamber that is instrumented with a spinning
rotor gauge and a capacitance diaphragm gauge that, unlike the more commonly used ionization gauge or quadrupole
mass spectrometer, provides a direct and accurate measurement of the total pressure that is largely independent of the
composition of the outgas products. We have also developed a method to perform compositional analysis on the outgas
products and, more generally, on any contaminants that might be present in the stepper vacuum. The method involves
collecting the vacuum contaminants in a trap cooled to liquid-nitrogen temperature. Once collected, the products from
the trap are transferred to a system for analysis with gas chromatography with mass spectrometry. We will describe the
workings of the instruments in detail as well as results of initial tests.
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
radiation [4-7].
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