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This paper describes the development of a LPP EUV source using a CO"2 laser with tin droplet targets. Burst power of 100W and average power of 25W has been achieved. Collector mirrors have been fabricated with >50% reflectivity and show stable EUV images. Multiple debris mitigation techniques preserve mirror reflectivity. Manufacturing of the first production systems is in progress.

The application of a dense plasma focus pinch discharge as a light source for extreme ultraviolet (EUV) lithography is discussed. For operation with xenon gas, the radiation emitted at around 13.5 nm is analysed with temporal, spectral or spatial resolution. We describe and compare the operating characteristics and plasma dynamics of the device when energized at positive and negative polarity of the charging voltage. The thermal load distribution, heat deposition and wear of the electrodes are measured and compared for both configurations. High-repetition rate burst mode data show characteristic transients. Source size data are also obtained when tin powder is used as the target element. More favourable performance characteristics were generally obtained for operation of the pinch discharge at negative polarity. (Some figures in this article are in colour only in the electronic version)

With the emergence of EUVL as the chosen technology for next-generation lithography (NGL) systems, significant effort has been spent in developing light sources consistent with the challenging requirements of the scanner manufacturers as well as meeting the aggressive demands of the end users for high-volume manufacturing (HVM). A light source with extremely high power and brightness is required for integration into a scanner tool based on reflective optics with multilayer (ML) coatings, since it needs to be designed for highest throughput at a wavelength of 13.5 nm. Over the past six years at Cymer Inc., we have pursued the research and development of DPPs to meet the demands for commercial HVM tools. A dense plasma focus (DPF) configuration was chosen because it provides an open geometry with large possible collection angle and can be operated over a wide parameter range. The main thrust of our research and development is devoted to achieving the challenging industry demands on light-source performance, requiring extremely high output power (

Laser produced plasma (LPP) systems have been developed as a viable approach for the EUV scanner light source for optical imaging of circuit features at sub-32nm and beyond nodes on the ITRS roadmap. This paper provides a review of development progress and productization status for LPP extreme-ultra-violet (EUV) sources with performance goals targeted to meet specific requirements from leading scanner manufacturers. We present the latest results on power generation, stable and efficient collection, and clean transmission of EUV light through the intermediate focus. We report on measurements taken using a 5sr collector optic on a production system. Power transmitted to intermediate focus (IF) is shown. The lifetime of the collector mirror is a critical parameter in the development of extreme ultraviolet LPP lithography sources. Deposition of target material as well as sputtering of the multilayer coating or implantation of incident particles can reduce the reflectivity of the mirror coating during exposure. Debris mitigation techniques are used to inhibit damage from occuring, the results of these techniques are shown. We also report on the fabrication of 5sr collectors and MLM coating reflectivity, and on Sn droplet generators with droplet size down to 30μm diameter.

This paper describes the development of laser produced plasma (LPP) technology as an EUV source for advanced scanner lithography applications in high volume manufacturing. EUV lithography is expected to succeed 193 nm immersion technology for critical layer patterning below 32 nm beginning with beta generation scanners in 2009. This paper describes the development status of subsystems most critical to the performance to meet joint scanner manufacturer requirements and semiconductor industry standards for reliability and economic targets for cost of ownership. The intensity and power of the drive laser are critical parameters in the development of extreme ultraviolet LPP lithography sources. The conversion efficiency (CE) of laser light into EUV light is strongly dependent on the intensity of the laser energy on the target material at the point of interaction. The total EUV light generated then scales directly with the total incident laser power. The progress on the development of a short pulse, high power CO2 laser for EUV applications is reported. The lifetime of the collector mirror is a critical parameter in the development of extreme ultra-violet LPP lithography sources. The deposition of target materials and contaminants, as well as sputtering of the collector multilayer coating and implantation of incident particles can reduce the reflectivity of the mirror substantially over the exposure time even though debris mitigation schemes are being employed. The results of measurements of high energy ions generated by a short-pulse CO2 laser on a laser-produced plasma EUV light source with Sn target are presented. Droplet generation is a key element of the LPP source being developed at Cymer for EUV lithography applications. The main purpose of this device is to deliver small quantities of liquid target material as droplets to the laser focus. The EUV light in such configuration is obtained as a result of creating a highly ionized plasma from the material of the droplets. Liquid tin is the material of choice to be used as a target due to the relatively high CE of the laser energy into in-band EUV radiation. Results obtained with the droplet generator and technical challenges related to successful implementation of the device are discussed.

This paper provides a detailed review of development progress for a laser-produced-plasma (LPP) extreme-ultra-violet (EUV) source with performance goals targeted to meet joint requirements from all leading scanner manufacturers. We present the latest results on drive laser power and efficiency, source fuel, conversion efficiency, debris mitigation techniques, multi-layer-mirror coatings, collector efficiency, intermediate-focus (IF) metrology, mass-limited droplet generation, laser-to-droplet targeting control, and system use and experience. Results from several full-scale prototype systems are discussed. In addition, a multitude of smaller lab-scale experimental systems have also been constructed and tested. This paper reviews the latest experimental results obtained on these systems with a focus on the topics most critical for an HVM source. Laser produced plasma systems have been researched as probable light source candidates for an EUV scanner for optical imaging of circuit features at 32nm and beyond nodes on the ITRS roadmap. LPP systems have inherent advantages over alternative source types, such as Discharge Produced Plasma (DPP), with respect to power scalability, etendue, collector efficiency, and component lifetime. The capability to scale LPP power with repetition rate and modular design is shown. A path to meet requirements for production scanners planned well into the next decade is presented. This paper includes current testing results using a 320mm diameter near-normal-incidence elliptical collector, the first to be tested in a full-scale LPP system. With the collector in-situ, intermediate focus (IF) metrology capability is enabled, and data is presented that describes the quality of light at IF.

We report on the approach for a high-power high-beam-quality drive laser system that is used for a laser-produced plasma (LPP) EUV source. Cymer has conducted research on a number of solutions for a multi-kW drive laser system that satisfy high volume production requirements. Types of lasers to be presented include XeF at 351 nm and CO2 at 10.6 micron. We report on a high efficiency XeF amplifier with a 3rd harmonic Nd:YLF master oscillator operated in the 6 to 8 kHz range and a CO2 laser system with Q-switched cavity dumped master oscillator and RF pumped fast axial flow amplifiers operated in the 10 to 100 kHz range. CO2 laser short pulse gain and optical isolation techniques are reported. Optical performance data and design features of the drive laser system are discussed, as well as a path to achieve output power scaling to meet high volume manufacturing (HVM) requirements and beyond. Additionally, the electrical efficiency as a component of cost of operation is presented. Development of a drive laser with sufficient output power, high beam quality, and economical cost of operation is critical to the successful implementation of a laser-produced-plasma (LPP) EUV source for HVM applications. Cymer has conducted research on a number of solutions to this critical need. We report our progress on development of a high power system with two gas-discharge power amplifiers to produce high output power with high beam quality. We provide optical performance data and design features of the drive laser as well as a path to output power scaling to meet HVM requirements. Development of a drive laser for LPP EUV source is a challenging task. It requires multi-kW laser output power with short pulse duration and diffraction limited beam quality. In addition, this system needs to be very reliable and cost-efficient to satisfy industry requirements for high volume integrated circuit manufacturing. Feasibility studies of high power laser solutions that utilize proven laser technologies in high power optical gain modules and deliver required beam properties have been performed and are reported.

Metrology concepts and related results are discussed for characterization of extreme ultraviolet (EUV) light sources based on laser-produced plasmas using metal foil and droplet targets. Specific designs of narrow-band EUV detectors employing multilayer mirrors and broadband detectors for droplet steering are described. Spatially resolved plasma imaging using in-band EUV pinhole cameras is discussed. A grazing-incidence flat-field EUV spectrometer is described that has been employed for spectroscopy in the 6 nm - 22 nm range. In addition, spectroscopic data of out-of-band radiation in the ultraviolet and visible spectral regions are presented. Results obtained for different wavelengths of the incident laser radiation and for both tin- and lithium foil- and droplet- targets are discussed.

In a laser produced plasma (LPP) EUV source the multilayer mirror (MLM) collector optic will be exposed to a flux of energetic ions and neutral atoms ejected from the plasma as well as condensable vapor from excess target material. We are investigating various techniques for reducing the contamination flux and for in-situ removal of the contamination. The protection strategies under investigation must be compatible with gaseous and condensable target materials such as Xe, Sn, In, Li, and other elements. The goal is to develop MLM structures that can withstand elevated temperatures and develop protective barrier coatings that reduce erosion of the mirror surface. Results of MLM exposure to energetic ion beams and thermal atomic sources are presented. Changes in EUV reflectivity of MLM structures after exposure to ions and deposition of target material have been performed on samples cleaned by these developmental processes. In this paper, we will summarize our initial results in these areas and present techniques for mitigation of MLM damage from the source.

Efficient conversion of laser light into EUV radiation is one of the most important problems of the laser-produced plasma (LPP) EUV source. Too low a conversion efficiency (CE) increases the amount of power the drive laser will have to deliver, which, besides the obvious laser cost increase, also increases the thermal load on all the components and can lead to increased debris generation. In order to meet the requirements for a high-volume manufacturing (HVM) tool and at the same time keep the laser power requirements within acceptable limits, a CE exceeding 2.5% is likely to be required. We present our results on optimizing conversion efficiency of LPP EUV generation. The optimization parameters include laser wavelength, target material, and laser pulse shape, energy and intensity. The final choice between parameter sets that leads to the required minimum CE is dependent on the debris mitigation solutions and the laser source available for a particular parameter set.

A commercially viable light source for EUV lithography has to meet the large set of requirements of a High Volume Manufacturing (HVM) lithography tool. High optical output power, high-repetition rate, long component lifetime, good source stability, and low debris generation are among the most important parameters. The EUV source, being developed at Cymer, Inc. is a discharge produced plasma source in a dense plasma focus (DPF) configuration. Promising results with Xe as a working gas were demonstrated earlier. To scale the DPF parameters to levels required for HVM our efforts are concentrated on the following areas: (1) thermal engineering of the electrodes utilizing direct water cooling techniques; (2) development of improved pulsed power systems for > 4 kHz operation; (3) study of erosion mechanisms for plasma facing components; (4) development of efficient debris mitigation techniques and debris shields; (5) studies of plasma generation and evolution with emphasis on improving conversion efficiency and source stability; (6) development of EUV metrology techniques and instrumentation for measurements of source size; and (7) development of an optimized collector optic matched to our source parameters. In this paper, we will present results from each of these key areas. The total in-band EUV output energy now approaches 60 mJ/pulse into 2πsr and the conversion efficiency has been increased to near 0.5 %. Routine operation at 4 kHz in burst-mode, and continuous operation at 1 kHz has been demonstrated. Improved at-wavelength source metrology now allows a determination of EUV source size utilizing imaging, and monitoring of key features of the spectrum on a pulse-to-pulse basis. With effective suppression of debris generated from the anode by several orders of magnitude, UV/EUV-catalyzed carbon growth now presents the limit in producing a clean source.

Improved performance and specific results are reported for several test and prototype extreme ultraviolet EUV light sources devel- oped for next-generation lithography. High repetition rate and high-power CO2 laser-produced plasma sources operating on tin droplet targets are described. Details of laser architecture, source chambers and system operation are given. Stable output power, efficient light collection, and clean EUV transmission could be achieved for hours of operation. We review progress during integration of light sources with collector mirrors reaching EUV power levels at intermediate focus of 60 W and 45 W, respectively, with duty cycles of 25% and 40%. Far-field EUV images of the collected light were recorded to monitor the source output perfor- mance during extended tests of collector longevity and debris protection with system operation time exceeding 50 h. Development results on EUV spectra, out-of-band OOB radiation, and ion debris obtained with dedicated metrology setups are also described. Angle-resolved mea- surements with ion energy analyzer and Faraday cups reveal the contri- butions of individual ion charge states in related spectra. Our laser- produced EUV light source technology has now reached a level of maturity in full integration where prototype sources can be delivered and pilot line introduction can be prepared. © 2009 Society of Photo-Optical Instru