Thomas P. Duffey

Next-generation 193-nm laser for sub-100-nm lithography

The next generation 193 nm (ArF) laser has been designed and developed for high-volume production lithography. The NanoLithTM 7000, offering 20 Watts average output power at 4 kHz repetition rates is designed to support the highest exposure tool scan speeds for maximum productivity and wafer throughput. Fundamental design changes made to the laser core technologies are described. These advancements in core technology support the delivery of highly line-narrowed light with <EQ 0.35 pm FWHM and <EQ 0.95 pm at 95% included energy integral, enabling high contrast imaging from exposure tools with lens NA exceeding 0.75. The system has been designed to support production lithography, meeting specifications for bandwidth, dose stability (+/- 0.3% in 20 ms window) and wavelength stability (+/- 0.05 pm average line center error in 20 ms window) across 2 - 4 kHz repetition rates. Improvements in optical materials and coatings have led to increased lifetime of optics modules. Optimization of the discharge electrode design has increased chamber lifetime. Early life-testing indicates that the NanoLithTM core technologies have the potential for 400% reduction of cost of consumables as compared to its predecessor, the ELX-5000A and has been discussed elsewhere.

ArF lasers for production of semiconductor devices with CD < 0.15 μm

The present day notion of the extensibility of KrF laser technology to ArF is revisited. We show that a robust solution to ArF requirements can be met by significantly altering the lasers core technology-discharge chamber, pulsed power and optics. With these changes, a practical ArF tool can be developed. Some of the laser specifications are: Bandwidth: 0.6 pm (FWHM) 1.75 pm (95% Included Energy); Average Power: 5 W; Repetition Rate: 1000 Hz; Energy Stability (3(sigma) ): 20% (burst mode) 8% (continuous); Pulse Width: 25 ns.

Production-ready 4-kHz ArF laser for 193-nm lithography

Semiconductor chip manufacturing is on the verge of a new production process node driving critical feature sizes below 100 nm. The next generation of 193 nm Argon Fluoride laser, the NanoLithTM 7000, has been developed in response to this recent technology development in the lithography industry. The NanoLithTM 7000, offering 20 Watts average output power at 4 kHz repetition rate, is designed to support the highest exposure tool scan speeds for maximum productivity and wafer throughput. Technology improvements to support the move from pilot production to full production will be described. With core technology defined and performance to specification established, attention turns to cost of operation, which is closely tied to module lifetime and reliability. Here we present results of the NanoLithTM 7000 system lifetest tracking all optical performance data over a 4.4 Billion shot. The system is operated in firing modes ranging from 1-4 kHz, and up to 75% duty cycle. Overall system performance measured to date both in the lab and in the field suggests that this laser meets all the production requirements for 193 nm lithography.

Feasibility of highly line-narrowed F2 laser for 157-nm microlithography

Highly line-narrowed F2 laser operation in the VUV has been achieved for the first time by means of a master oscillator/power amplifier laser design. Different concepts have ben investigated experimentally for the master oscillator (MO) in order to obtain narrowband spectra. The diffraction grating based design showed to be limited to a FWHM of approximately 0.4 pm. The spectral FWHM of the MO could be further reduced to below 0.3 pm with a double etalon-based resonator. Single pass amplification was employed to increase the beam energy density of the beam up to 50 mJ/cm2. The spectral FWHM of the amplified light is slightly larger than the FWHM of the correspondent MO radiation, indicating saturation and/or inhomogeneous broadening of the F2 amplifier medium. Experimental data obtained from broadband operation and ASE measurements suggests that the free running bandwidth of F2 lasers result form spectral gain-narrowing of the laser medium.

Comparison of ArF and KrF laser performance at 2 kHz for microlithography

Exposure tools for 193nm lithography are expected to use Argon-Fluoride lasers at repetition rates of at least 2kHz. We are showing that, by revisiting several key technologies, the performance and reliability of ArF lasers at 2 kHz are trending towards a level comparable to KrF lasers.

Dependence of compaction in fused silica on laser pulsewidth at 248 nm (Abstract Only)

Designers of DUV lithographic lenses are faced with serious materials problems relating to compaction and color-center formation in fused silica, especially at 193 nm. However, these problems, while less sever, are not negligible at 248 nm. Compaction appears to be the more serious, since it degrades imaging performance and effectively sets the lifetime limit for the lens. Previous damage studies have clearly shown that fused silica compacts as a function of the parameter grouping (NI2/(tau) ), where (tau) is the pulsewidth. This fact has strongly influenced the design of the excimer laser light source by stressing repetition rate over pulse energy as a way of achieving high average power, and by driving the optical pulsewidth to be as long as possible. These studies, however, have emphasized the dependence of damage rates on the energy density I(mJ/cm2), whereas the optical pulsewidth (tau) has been given only cursory attention and has not been well controlled during the damage experiments. In this paper we report the results of an experiment to more clearly establish the functional dependency of compaction on laser pulsewidth.

Advances in DUV light source sustainability

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 [1], system, and architecture improvements [2] 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 [3]. 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 [1]. In this paper, results of eliminating the use of helium will be described.