Actinic mask defect inspection and metrology requires high-brightness extreme-ultraviolet (EUV) sources. The self-absorption of radiation limits the in-band EUV radiance of the source plasma and makes it difficult to attain the necessary brightness and power from a conventional single unit EUV source. One possible solution is through multiplexing of multiple low etendue sources. NANO-UV is delivering a new generation of EUV light source, the CYCLOPS, in which a micro-plasma-pulsed discharge source is integrated to a photon collector based on an in situ active plasma structure. The source module is characterized by high brightness, low etendue, and high irradiance at moderate output power without the use of external physical optics. Such a source could form the basic building block of EUV source through spatial-temporal multiplexing of several units to deliver the brightness and power required for actinic mask metrology. We report on the EUV source development including the extensive numerical modeling, which provided the basic parameters required for high irradiance operating regimes. A new Sn-alloy cathode material enhances the output. Based upon the multiplexing concept, a family of specially configured multiplexed source structures, the HYDRA design, is being introduced to address the mask metrology needs.
The roll out of EUV lithography for HVM, including the associated tools for actinic mask and mask blank defect
inspection, require reliable and powerful EUV radiation sources. NANO-UV has developed a unique EUV/soft X-ray
source, the CYCLOPSTM, based on a fast, micro-plasma pulsed discharge, incorporating the i-SoCoMoTM technology; an
intrinsic plasma structure to provide photon collection and delivery. We report on the EUV light source development,
including the extensive numerical modelling which provided the basic parameters required for high power or high
irradiance operating regimes. Without using external physical optics, a peak irradiance exceeding 1018 ph/cm2/s, in a 3
nm bandwidth around 13.5nm, has been recorded at a distance 74 cm downstream from the source, which was operating
at 1 kHz in a He:N2:Xe gas admixture at up to 0.5J per pulse operation. A new Sn-alloy cathode material has enhanced
the output by a factor of 1.5 with the power now delivered in a sub-cm size spot being greater than 20W in 3nm band,
with a typical étendue below 10-2 mm2•sr. NANO-UV can meet the HVM source requirements with its HYDRATM spatial/temporal multiplexed source development. A multiplex of 12 units form HYDRATM -12P having the potential of
reaching 240W (within 3 nm EUV band) at IF demonstrates multiplexing principle.
EUV sources for actinic mask metrology, particularly for defect inspection, require extremely high brightness. The selfabsorption
of radiation limits the in-band EUV radiance of the source plasma and makes it difficult to attain the
necessary brightness and power from a conventional single unit EUV source. One possible solution is through
multiplexing of multiple low etendue sources. NANO-UV is delivering a new generation of EUV light source with an
intrinsic photon collector, the i-SoCoMo™ concept, where a micro plasma pulsed discharge source is integrated to a
photon collector based on an in situ active plasma structure. The source is characterized by high brightness, low etendue
and very high irradiance, at moderate output power, without the use of external physical optics. Such a source could form
the basic building block, through multiplexing of several units, to satisfy the very high brightness and moderate power
requirement of the EUV sources required for actinic mask metrology. Based upon this multiplexing concept, a family of
specially configured multiplexed source structures, the HYDRA™ design, is being introduced to address the mask
metrology needs.
EUVL solution for HVM at the 22 nm node requires a high power long-term EUV source operation with hundreds of watts at the intermediate focus output. EUV mask blank and mask defects inspections require at-wavelength tools with high brightness. Theoretical analysis with a 2-D radiation MHD code Z* has been performed to address key issues in EUV plasma sources with radiation transfer. The study shows that self-absorption defines the limiting brightness of a single EUV source, which cannot meet the requirements of the HVM tool with high efficiency and is not sufficient for critical metrology applications, given the limiting etendue of the optics. It is shown that the required irradiance can be achieved by spatial multiplexing, using multiple small sources. We present here details of the study, as well as experimental results from a novel EUV light source with an intrinsic photon collector demonstrating high brightness, the i-SoCoMo concept, where an impulse micro discharge plasma source is integrated to a photon collector based on an active plasma structure. The small physical size and low etendue properties of the i-SoCoMo unit allows a large number of such sources to be put together in one physical package and be operated in a multiplexed fashion to meet necessary power requirements.
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