Excimer lasers are the commonly used light sources for photo-lithography industries; one challenge is to minimize the production interruption by providing a reliable source of DUV (193 nm) photons. This requires CaF<sub>2</sub> optics with high transmission and optical uniformity at 193 nm over a long lifetime. However, CaF<sub>2</sub> crystal can possess defects due to mis-orientation and dislocations in the sub-grain boundaries, which can act as an absorption or scattering center leading to transmission loss and thermal stress induced birefringence in the CaF<sub>2</sub> crystal. In addition, the CaF<sub>2</sub> surface can suffer from different mechanical stress due to cleaning and finishing processes leading to formation of surface imperfections/fractures known as sub-surface damage. This sub-surface damage layer is prone to damage under high fluence 193 nm exposure and can lead to fluorine escape from the CaF<sub>2</sub> lattice. Protective coatings for CaF<sub>2</sub> optics have been developed to prevent surface fluorine depletion from 193 nm exposure. However, these protective coatings can also develop defects due to imperfections in the coating fabrication process and/or photochemical reaction initiated by 193 nm photons in presence of traces of oxygen, water vapor or carbon dioxide. Therefore, to provide uninterrupted 193 nm photons a robust protective coating is required to extend the lifetime of CaF<sub>2</sub> optics. Generally, field learnings for high fluence protective coating can require from 6 months to a year of normal operation and thus validation of protective coatings based on field data alone can hinder the adoption of improved technology. To expedite this selection process, an accelerated 193 nm exposure setup was built to test high fluence protective coatings from different suppliers at various elevated fluences for a short period of time (~2-3 weeks). This setup was successful in screening the best high fluence protective coating under highly accelerated 193 nm exposure. Additionally, based on the relative performance of the protective coatings under accelerated conditions and use case in-laser fluence conditions, the lifetime for the high fluence protective coatings were estimated for the use case scenario.
Key sustainability opportunities have been executed in support of corporate initiatives to reduce the environmental footprint and decrease the running cost of DUV light sources. Previously, substantial neon savings were demonstrated over several years through optimized gas management technologies. Beyond this work, Cymer is developing the XLGR 100, a self-contained neon recycling system, to enable minimal gas consumption. The high efficiency results of the XLGR 100 in a production factory are validated in this paper. <p> </p>Cymer has also developed new light source modules with 33% longer life in an effort to reduce raw and associated resource consumption. In addition, a progress report is included regarding the improvements developed to reduce light source energy consumption.
Cymer continues to address several areas of sustainability within the semiconductor industry by reducing or eliminating consumption of power and specific types of gas (i.e. neon, helium) required by DUV light sources in order to function. Additionally, Cymer introduced a new recycling technology to reduce the dependence on production of raw gases. In this paper, those initiatives that reduce the operational cost, environmental footprint, and business continuity risk will be discussed.
Cymer has increased the efficiency of its light sources through improvements that have resulted in energy output increase while maintaining the same or requiring less power consumption. For both KrF and ArF systems, there have been component , system, and architecture improvements  that allowed customers to increase energy efficiency and productivity. An example of module improvements is the latest MO chamber that helped reduce power consumption by ~15%. Future improvements aim to continue reducing the power consumption and cost of operation of the install base and new systems.
The neon supply crisis in 2015 triggered an intensive effort by the lithography light source suppliers to find ways to minimize the use of neon, a main consumable of the light source used in DUV photolithography. Cymer delivered a multi-part support program to reduce natural resource usage, decrease overall cost of operation, and ensure that chipmaker’s business continuity risk is minimized. The methods used to minimize the use of neon for 248 nm and 193 nm photolithography that offered significant relief from supply constraints and reduction of business continuity risk for chipmakers were described in previous work . In this paper, results from the program will be presented.
In addition, techniques to capture the neon effluent and re-purify it within the semiconductor fabs have been pursued. For example, Cymer has developed and validated a neon recycling system for ArF light sources that resides within the chipmaker’s fab. Cymer has partnered with a global gas supplier to develop a system capable of capturing, recycling and delivering <90% of the total neon gas required by multiple ArF light sources through automated operation, including online analysis. In this paper, the neon recycle system performance as demonstrated by a quantitative analysis of facility-supplied gas versus the recycled neon in ArF light source performance will be discussed.
Similarly, DUV light sources have historically used helium as a purge gas in the critical line narrowing module (LNM) to achieve stable wavelength and bandwidth control. Helium has a low coefficient of index of refraction change vs. temperature relative to nitrogen and provides efficient cooling and purging of critical optics in the LNM. Previous work demonstrated how helium consumption can be reduced and still achieve stable performance under all operating conditions . In this paper, results of eliminating the use of helium will be described.
Chipmakers continued pressure to drive down costs while increasing utilization requires development in all areas. Cymer’s commitment to meeting customer’s needs includes developing solutions that enable higher productivity as well as lowering cost of lightsource operation. Improvements in system power efficiency and predictability were deployed to chipmakers’ in 2014 with release of our latest Master Oscillating gas chamber. In addition, Cymer has committed to reduced gas usage, completing development in methods to reduce Helium gas usage while maintaining superior bandwidth and wavelength stability. The latest developments in lowering cost of operations are paired with our advanced ETC controller in Cymer’s XLR 700ix product.
Semiconductor market demand for improved performance at lower cost continues to drive enhancements in excimer
light source technologies. Increased output power, reduced variability in key light source parameters, and improved
beam stability are required of the light source to support immersion lithography, multi-patterning, and 450mm wafer
applications in high volume semiconductor manufacturing. To support future scanner needs, Cymer conducted a
technology demonstration program to evaluate the design elements for a 120W ArFi light source. The program was
based on the 90W XLR 600ix platform, and included rapid power switching between 90W and 120W modes to
potentially support lot-to-lot changes in desired power. The 120W requirements also included improved beam
stability in an exposure window conditionally reduced by 20%. The 120W output power is achieved by efficiency
gains in system design, keeping system input power at the same level as the 90W XLR 600ix. To assess system to
system variability, detailed system testing was conducted from 90W – 120W with reproducible results.