Kazuaki Hotta

Development of Sn-fueled high-power DPP EUV source for enabling HVM

Discharge-produced plasma (DPP)-based EUV source is being developed at Gotenba Branch of EUVA Hiratsuka R&D Center. A high-repetition-rate high voltage power supply (HVPS) was developed and put into operation on the magnetic pulse compression (MPC)-driven DPP source, enabling 8-kHz operation with 15 J/pulse of maximum charging energy and 0.11 % of stability. SnH4 gas was used as a fuel gas in order to obtain high conversion efficiency. SnH4-fueled Z-pinch source demonstrated EUV power of 700 W/2&pgr;sr within 2 % bandwidth around 13.5 nm. Using a nested grazing-incidence collector, EUV power at the intermediate focus which is defined as an interface to the exposure tool reached 62 W with 3.3 mm2sr of etendue. Tin deposition rate on the collector surface, which is the concern in any tin-fueled EUV sources, was decreased by four orders of magnitude as a result of debris-shield development. Cleaning processes were also developed to enhance total lifetime of the collector. A sequence of intentional deposition and cleaning process for the ruthenium grazing-incidence mirror sample was repeated 13 times. By measuring reflectivity of the mirror, it was confirmed that halogen cleaning process worked very effectively and did not get the mirror damaged after such a long-term cleaning experiment.

Dependence of laser parameter on conversion efficiency in high-repetition-rate laser-ablation-discharge EUV source

Two projects are being conducted in EUVA under the support of NEDO and member companies; private project and national project. The private project is responsible for power improvement of a source module targeting realization of 115-W prototype. The national project covers wide area of remaining issues on a collector module to achieve sufficient reliability. In the private project, a laser-ablation-discharge-produced plasma (LADPP) is being researched as a candidate of high-power EUV source. LADPP has fascinating properties such as long lifetime, high collection efficiency, and high thermal input. More than 15 % of collection efficiency could be obtained with LADPP because of its small plasma size. Pulse repetition frequency has reached 20 kHz and 580 W/2πsr were achieved so far. In order to increase conversion efficiency (CE), detailed diagnostics of LADPP were carried out. Especially, dependence of CE on laser pulse duration is derived from the experiment. As a result, dynamics of LADPP was understood and solution to increase CE and improve frequency scalability was understood. A fundamental experiment predicted that CE can be increased 60 %.

Ultra-line-narrowed high power F2 laser system for microlithography

An ultra-line-narrowed, ultra-high-repetition-rate, high-power injection locked F2 laser system for 157 nm exposure tools has been developed. The laser system consists of a low-power oscillator laser having an ultra-narrow spectral bandwidth and a high-gain amplifier with a resonator. The injection locked system achieved a spectral bandwidth 25 W and an energy stability (3-sigma) <10% at a 5 kHz repetition rate, parameters that satisfy requirements of high NA refractive type exposure tools. The jitter reduction between the oscillator laser and the amplifier laser is essential for stable synchronization of two-stage (injection locked and master oscillator power amplifier) laser systems. We solved this problem by a specially developed jitter suppression technique and with long-duration oscillator laser pulses.

Development of debris-mitigation tool for HVM DPP source

Debris-mitigation tools (DMTs) have been used in DPP sources and the performance has been well proven in alpha sources. In beta and HVM sources, requirement to the DMT is increasing to fulfill the power and lifetime requirements simultaneously. In order to bring DPP technology into HVM level, a high-performance DMT has been developed. It has high mitigation performance for both neutral and ionic debris, large collection angle of the collector having high optical transmission, and withstand large thermal input from the discharge source head. Experiments were carried out using mirror samples and proved sufficient performance with which no sputtering and deposition were observed.

Br lamp for F2 laser wavelength calibration

Recently, we have developed a novel Br lamp for the F2 laser wavelength calibration. In order to examine the validity of this lamp, we measured emission lines of this lamp in 157 nm region and analyzed them. From our result, it has been confirmed that the spectral profile of the 157.6387 nm (2P3/2 - 4P5/2) emission line of Br atom is unchangeable to the parameters of lamp designs and lamp operating conditions. One of the reasons will be shown here. Hence our novel Br lamp is to be the promising candidate for the 157 nm F2 laser wavelength calibration.

Sn film and ignition control for performance enhancement of laser-triggered DPP source

A laser-triggered DPP source is being developed and showing considerable progress toward HVM. Performance, in terms of power and lifetime, of DPP sources has been proven by long-term usage in lithography development fields. Since high-performance debris-mitigation tools are used in DPP sources, collector lifetime is not an issue. However, it is worth developing the technology to enhance overall lifetime of the collector module. In order to suppress both neutral and ionic debris, two technologies, which can be simultaneously used in a DPP source, have been developed. First, a discharge ignition by using two lasers was developed. It was able to reduce the amount and energy of fast ions which could sputter a collector by a factor of 5. In addition to fast ion reduction, CE enhancement of 60 % was obtained. Second, an active control of liquid tin layer, which acts as a fuel material, electrode protection and cooling medium, could reduce particle debris and lower the load of a debris-mitigation tool. Implementing these technologies is considered to provide enhancement of the lifetime of the collector module and support HVM readiness.

Tin-Fueled High-Repetition-Rate Z-pinch EUV Source for Semiconductor Lithography

Summary form only given. Extreme ultraviolet (EUV) is the potential candidate for the light source used in next generation semiconductor lithography. In EUV lithography (EUVL), IC pattern as small as 32-nm pitch or below will be realized by using 13.5-nm radiation. There are two major schemes to obtain high-power EUV; laser-produced plasma (LPP) and discharge-produced plasma (DPP). DPP seems to provide more cost-effective source and easier way to obtain necessary EUV power than LPP. EUV is not a coherent radiation so that emitted radiation is collected by optics and transferred to an exposure tool. In volume production, significant amount of IC chip should be yielded. From these points of view, EUV radiation must be emitted from very small volume but have sufficient average power. In our development, Z-pinch plasma is employed to achieve such a high temperature and density micro plasma. It is very important to increase conversion efficiency (CE) of electrical energy input to 13.5-nm radiation. Xe used to be used as fuel material because of its easiness of handling and cleanliness. However, Sn is the best choice from the view point of CE. Despite its handling difficulties, Sn is now being commonly used in many EUV researches. In case of gas-discharge-produced plasma, it is necessary to feed the gas into the discharge region between the electrodes. For this purpose, we utilize SnH4 gas, which is in gaseous state at room temperature and able to be controlled like Xe. EUV source for semiconductor lithography is also required to work at pulse repetition frequency more than 7 kHz. By using high rep-rate (8 kHz) and high-average-power (120 kW) pulsed power driver, and low-inductance Z-pinch load, radiation characteristics of SnH4-fueled Z-pinch were investigated. Radiation energy, radiation stability, plasma image, temporal radiation behavior of Z-pinch were investigated. As a result, EUV power within 2 % bandwidth at 13.5 nm reached 700 W/2 pisr.

Line Narrowing and Injection Locking of F2 Lasers

To realize an ultranarrow-linewidth and high-output-power F2 laser for next-generation lithography, line narrowing in a F2 laser injection locking system (ILS) that consists of a line-narrowed oscillator and an amplifier with a resonator was investigated. We found out that the time-resolved instantaneous spectrum of the oscillator laser pulse narrows from a start time of discharge and scarcely depends on laser pulse shape. Furthermore, the spectral shape of the ILS is locked to the instantaneous spectral shape of the line-narrowed injection laser when the amplifier discharge starts. We first realized a F2 laser with a linewidth (FWHM) below 0.2 pm and a pulse energy of more than 5 mJ (25 W at 5 kHz repetition rate).