High-brightness extreme-ultraviolet light sources are required for mask inspections and metrology, including mask blank inspection, actinic pattern inspection, and aerial image measurement system to improve yield and lower cost of ownership. Laser-produced plasma (LPP) light sources have the highest potential to achieve the brightness requirements for all the range of mask inspection tools currently foreseen. High brightness of LPP sources (100 to 1000 W/mm2 sr) is the result of a smaller source size ( ∼ 0.1 mm) than that of competing technologies. Since brightness is inversely proportional to the area of the source, smaller source size corresponds with greater brightness and hence greater inspection throughput.
At the Laboratory for Energy Conversion of ETH Zurich, a fully operational continuous-running multi-kHz LPP light source has been developed over the last five years and is now undergoing system optimization. Adlyte, a spin-off of ETH Zurich, is working with industry leaders to commercialize this LPP source. Individual subsystem configuration and the physical boundary conditions and limitations that affect power, brightness, stability, and lifetime management are discussed. This integrated system produces a measured brightness of 259 W/mm2 sr. Outlook for the future growth and integration of the source in high-volume manufacturing tools is then discussed.
The next generation of semi-conductor devices will be manufactured using extreme ultraviolet lithography with a laser-produced
plasma as a candidate 13.5nm light source. A primary challenge, particularly for metrology tools, is the
stability and the brightness of the generated EUV at the intermediate focus. In the experimental facility at ETH a novel
collecting system is studied to optimize brightness and stability, and to avoid contamination after the intermediate focus.
Different experimental studies are shown to confirm the design's success for both the EUV beam quality and lack of
contamination after the intermediate focus.
EUV actinic mask inspection requires a light source with high brightness, high uptime and a small footprint. Adlyte
Corporation has developed reliable, compact and cost-effective EUV sources for mask metrology and inspection
applications with potential to be extended for scanner high volume manufacturing. The EUV source will generate high
brightness of up to 1 kW/mm2·sr. An industry-proven high power Nd:YAG laser irradiates high-frequency tin droplets
with 1.6 kW of power in short pulses. For extended operational lifetime and with high reliability, the collector
integrates two methods to mitigate ionic and neutral debris, and actively manages the thermal load. Latest operational
data will be presented.
Within the vast range of laser materials processing applications, every type of successful commercial laser has been
driven by a major industrial process. For high average power, high peak power, nanosecond pulse duration Nd:YAG
DPSS lasers, the enabling process is high speed surface engineering. This includes applications such as thin film
patterning and selective coating removal in markets such as the flat panel displays (FPD), solar and automotive
industries. Applications such as these tend to require working spots that have uniform intensity distribution using
specific shapes and dimensions, so a range of innovative beam delivery systems have been developed that convert the
gaussian beam shape produced by the laser into a range of rectangular and/or shaped spots, as required by demands of
each project. In this paper the authors will discuss the key parameters of this type of laser and examine why they are
important for high speed surface engineering projects, and how they affect the underlying laser-material interaction and
the removal mechanism. Several case studies will be considered in the FPD and solar markets, exploring the close link
between the application, the key laser characteristics and the beam delivery system that link these together.
Powerlase has made significant steps forward in developing reliable and cost-effective, kilowatt-class laser modules with short pulse duration and small footprint, for use as EUV drivers. These characteristics in parallel to EUV target requirements are essential for the generation of 115W of in-band EUV power at the intermediate focus. These laser modules can be coupled to the EUV target by using our flexible spatial and temporal multiplexing approach in order to scale up the laser average power on target. The multiplexing method developed by Powerlase is modular and optimised for maximum EUV collection angle. To further this goal we are currently evaluating target materials such as xenon in various phases and forms and also have a programme in place to investigate suitable tin targets.
Powerlase has made significant advances towards making the LPP EUV source the most likely choice for a full production EUV lithography machine. Our main achievement was enhancing the performance of the LPP driver and particularly increasing the average power per laser module. This was achieved by increasing the electrical to optical conversion efficiency of our gain modules. In order to increase the conversion efficiency of the in-band EUV, we are currently using cryogenic solid xenon, as well as other target materials. The combination of an efficient and cost effective laser driver with appropriate choice of target material significantly lowers the Cost of Ownership (CoO) of the LPP EUV source, including day to day running, making it comparable to the cost of Discharge Produced Plasma (DPP) sources.
We have recently made significant advances in the performance of our laser driver module employed in our laser produced plasma (LPP) EUV source. We increased the average power output from the laser whilst minimising the overall Cost of Ownership (CoO) and footprint of the system. In addition to minimising the CoO of the laser solution, it is necessary to choose an appropriate target that can attain the overall requirements of EUVL. We are currently investigating xenon in its various phases, as well as other target materials, in order to increase the conversion efficiency of the source and therefore further drive down its CoO. We have prepared a source roadmap in response to industry demands, and it shows that the combination of our demonstrated laser technology with available targets will meet the objectives for a production level source.
Electrical to EUV conversion efficiency is a key parameter for systems scaled to EUV emission in the 100W regime. Improvement in efficiency of conversion from laser radiation at the EUV source, reduces the required laser power and as such can lend itself to reduced heat load and debris emission. Also, improvement in the electrical to laser conversion efficiency results in a direct reduction in cost of ownership. Laser solutions optimised for efficient conversion to high M2 CW laser radiation are not optimised in design for efficient short-pulsed operation; the mode of operation required for EUV generation. Aspects of both EUV source and laser design are discussed, with a view to optimising conversion efficiency for scalable EUV solutions.