Max C. Schürmann

Sn DPP source-collector modules: status of alpha resources, beta developments, and the scalability to HVM

For industrial EUV (extreme ultra-violet) lithography applications high power extreme ultraviolet (EUV) light sources are needed at a central wavelength of 13.5 nm, targeting 32 nm node and below. Philips Extreme UV GmbH and XTREME technologies GmbH have developed DPP (Discharge Produced Plasma) Alpha tools which run in operation at several locations in the world. In this paper the status of the Alpha Sn-DPP tools as developed by Philips Extreme UV GmbH will be given. The Alpha DPP tools provide a good basis for the development and engineering of the Beta tools and in the future of the HVM tools. The first Beta source has been designed and first light has been produced. Engineering steps will folow to optimize this first generation Beta Sn-DPP source. HVM tools target EUV power levels from 200W to 500W in IF. In this paper we show that the power requried for HVM can be generated with Sn-DPP sources. Based on Alpha Sn-DPP sources we show that repetition frequency and generated EUV pulse energy is scalable up to power levels that match the HVM requirements.

Tin DPP source collector module (SoCoMo) ready for integration into Beta scanner

As the traditional techniques used in optical photolithography at 193 nm are running out of steam and are becoming prohibitively expensive, a new cost-effective, high power EUV (extreme ultra-violet) light source is needed to enable high volume manufacturing (HVM) of ever shrinking semiconductor devices. XTREME technologies GmbH and EUVA have jointly developed tin based LDP (Laser assisted Discharge Plasma) source systems during the last two years for the integration of such sources into scanners of the latest and future generations. The goals of the consortium are 1) to solve the wavelength gap - the growing gap between the printed critical dimensions (CD) driven by Moores Law and the printing capability of lithographic exposure tools constrained by the wavelength of the light source - and 2) to enable the timely availability of EUV light sources for high volume manufacturing. A first Beta EUV Source Collector Module (SoCoMo) containing a tin based laser assisted discharge plasma source is in operation at XTREME technologies since September 2009. Alongside the power increase, the main focus of work emphasizes on the improvement of uptime and reliability of the system leveraging years of experience with the Alpha sources. Over the past period, a cumulated EUV dose of several hundreds of Mega Joules of EUV light has been generated at the intermediate focus, capable to expose more than a hundred thousand wafers with the right dose stability to create well-yielding transistors. During the last months, the entire system achieved an uptime - calculated according to the SEMI standards - of up to 80 %. This new SoCoMo has been successfully integrated and tested with a pre-production scanner and is now ready for first wafer exposures at a customers site. In this paper we will emphasize what our innovative concept is against old type of Xe DPP and we will present the recent status of this system like power level, uptime and lifetime of components as well. In the second part of the paper the EUV source developments for the HVM phase are described. The basic engineering challenges are thermal scaling of the source and debris mitigation. Feasibility of the performance can be demonstrated by experimental results after the implementation into the beta system. The feasibility of further efficiency improvement, required for the HVM phase, will also be shown. The objectives of the HVM roadmap will be achieved through evolutionary steps from the current Beta products.

Xenon DPP Source Technologies for EUVL Exposure Tools

The learning gained in previous developments for EUV Micro Exposure and Alpha Tools builds the basis for the EUVL source development at XTREME technologies and Philips EUV. Field data available from operation of these tools are in use for continuous improvements in core technology areas such as plasma generation and forming, component reliability, debris mitigation and optical performance. Results from integration and operation of alpha tool sources are presented in the areas power performance, component lifetime and debris mitigation efficiency. The analysis results and simulation work of the realized EUV source concept are discussed and innovative concepts for component and module improvements are introduced. The technological limit for the Xenon based sources seems to be reached on alpha performance level. Therefore the next EUV source generations are based on Tin to increase the efficiency and full performance of those sources. For the Betatool and HVM source generations a joint development work between XTREME technologies and Philips EUV is introduced. The related work is content of another presentation of this conference.

Progress on Xe-DPP source development for alpha phase

EUVL source development at XTREME technologies benefits from the learning gained in previous developments for EUV Micro Exposure and Alpha Tools. Field data available from operation of these tools represent the basis for continuous improvement in core technology areas such as plasma generation and forming, component reliability, debris mitigation and optical performance. Results from integration and first operation of alpha tool sources are presented in the areas power performance, component lifetime and debris mitigation efficiency. The analysis results and simulation work of the realized EUV source concept are discussed and innovative concepts for component and module improvements are introduced. In term of intermediate focus power, 4W has been achieved. Moreover the factor of 1.6 higher IF power to previous results has been implied to demonstrate capability for the achievement of more than 5W. For the Beta-tool and HVM source generations a joint development work between XTREME technologies and Philips EUV is introduced. The related work is content of another presentation of this conference.

Thermal management design and verification of collector optics into high-power EUV source systems

A dual-mirror grazing incidence collector produced by Media Lario Technologies was integrated into a high-power, Xefueled gas discharge produced plasma (GDPP) source test stand at XTREME technologies, and tested at power levels responding to the productivity demands of the extreme ultra-violet (EUV) lithography beta exposure systems. The test campaign conducted at different source repetition rates in steady state and transient operating modes provided data for the verification and improvement of the thermo-optical model of the source-DMT-collector system used for the thermooptical design of the collector. The final thermo-optical model of the steady state regime was cross-validated by the numerical solution of the transient tests, which is solely based on the experimental temperature readings. Among the salient results, the cooling system integrated on the collector removed the 1 kW heat load absorbed by the dual-mirror optics, maintaining the temperature of the optics within 20-25 °C temperature range, with an input cooling water temperature of 18.6 °C. Additional validation came from tests performed on a single-mirror collector in a vacuum based, thermo-optical visible test bench installed at Media Lario Technologies, which provided a closed loop validation of the thermal budget, finite element model, and Monte Carlo ray tracing optical prediction.

EUV source development for high-volume chip manufacturing tools

Xenon-fueled gas discharge produced plasma (DPP) sources were integrated into Micro Exposure Tools already in 2004. Operation of these tools in a research environment gave early learning for the development of EUV sources for Alpha and Beta-Tools. Further experiments with these sources were performed for basic understanding on EUV source technology and limits, especially the achievable power and reliability. The intermediate focus power of Alpha-Tool sources under development is measured to values above 10 W. Debris mitigation schemes were successfully integrated into the sources leading to reasonable collector mirror lifetimes with target of 10 billion pulses due to the effective debris flux reduction. Source collector mirrors, which withstand the radiation and temperature load of Xenon-fueled sources, have been developed in cooperation with MediaLario Technologies to support intermediate focus power well above 10 W. To fulfill the requirements for High Volume chip Manufacturing (HVM) applications, a new concept for HVM EUV sources with higher efficiency has been developed at XTREME technologies. The discharge produced plasma (DPP) source concept combines the use of rotating disk electrodes (RDE) with laser exited droplet targets. The source concept is called laser assisted droplet RDE source. The fuel of these sources has been selected to be Tin. The conversion efficiency achieved with the laser assisted droplet RDE source is 2-3x higher compared to Xenon. Very high pulse energies well above 200 mJ / 2&pgr; sr have been measured with first prototypes of the laser assisted droplet RDE source. If it is possible to maintain these high pulse energies at higher repetition rates a 10 kHz EUV source could deliver 2000 W / 2&pgr; sr. According to the first experimental data the new concept is expected to be scalable to an intermediate focus power on the 300 W level.

Design and fabrication considerations of EUVL collectors for HVM

The power roadmap for EUVL high volume manufacturing (HVM) exceeds the 200W EUV in-band power at intermediate focus, thus posing more demanding requirements on HVM sources, debris suppression systems and collectors. Starting from the lessons learned in the design and fabrication of the grazing incidence collectors for the Alpha EUVL scanners, Media Lario Technologies is developing HVM optical solutions that enable designed-in lifetime improvements, such as larger source-collector distances, optimized collection efficiency through larger collected solid angles, and customized EUV reflective layers. The optical design of an HVM collector is described together with the selection of the sacrificial ruthenium reflective layer. The water cooling layout of the collector is evolved from the integrated cooling technology developed at Alpha level into an innovative cooling layout that minimizes the thermal gradients across the mirrors and allows controlling the optical performance at the far-field plane. Finally, the evolution of the collectors manufacturing technologies for HVM is discussed. XTREME technologies and Philips Extreme UV support this work by integrating the collector in the complete source collector module (SoCoMo). At system level, each component of the SoCoMo is part of a development and improvement plan leading to a comprehensive system that will fulfill the 200+ W EUV in-band power at intermediate focus.

Protected and enhanced silver for mirrors: damage mechanisms and how to prevent them

In order to manufacture mirrors metal based coatings (Al, Au and Ag) are applied, as they enable a high reflectivity and at the same time a broad spectral bandwidth. Of all metals, Ag provides the highest reflectivity from VIS to IR. Silver is a noble metal. However, corrosion activators (e.g. S and Cl) can lead to corrosion. Thus, a protective layer is required to prevent the corrosion and sustain the high reflectivity of the mirror. However, damage of the Ag-coating can occur, even in the case of protected-Ag. Inhomogeneous film growth of the protective layer can lead to a permeation of corrosion activators and thus to a damage of the Ag. But also the deposition of impervious protective layers is not sufficient for long-term environmental stability. Hygroscopic air borne particles can weaken the protection and therefore subsequently lead to a permeation of corrosion activators and thus to a damage of the Ag. These damage mechanisms lead to criteria for a durable and efficient protection. AlOxNy and nanolaminates have been tested with respect to these criteria. In particular the protection based on nanolaminates shows a great potential for the protection of Ag. In addition, also the optical performance can be improved by UV-enhancement based on different nanolaminates.

Study on the lifetime of Mo/Si multilayer optics with pulsed EUV-source at the ETS

As EUV lithography is on its way into production stage, studies of optics contamination and cleaning under realistic conditions become more and more important. Due to this fact an Exposure Test Stand (ETS) has been constructed at XTREME technologies GmbH in collaboration with Fraunhofer IOF and with financial support of Intel Corporation. This test stand is equipped with a pulsed DPP source and allows for the simultaneous exposure of several samples. In the standard set-up four samples with an exposed area larger than 35 mm2 per sample can be exposed at a homogeneous intensity of 0.25 mW/mm2. A recent update of the ETS allows for simultaneous exposures of two samples with intensities up to 1.0 mW/mm2. The first application of this alternative set-up was a comparative study of carbon contamination rates induced by EUV radiation from the pulsed source with contamination rates induced by quasicontinuous synchrotron radiation. A modified gas-inlet system allows for the introduction of a second gas to the exposure chamber. This possibility was applied to investigate the efficiency of EUV-induced cleaning with different gas mixtures. In particular the enhancement of EUV-induced cleaning by addition of a second gas to the cleaning gas was studied.

Multi-technique study of carbon contamination and cleaning of Mo/Si mirrors exposed to pulsed EUV radiation

Comparative lifetime studies of Mo/Si multilayer mirrors have been conducted at the Exposure Test Stand (ETS) using a pulsed Xe-discharge EUV source at XTREME Technologies GmbH (Göttingen, Germany). Due to the large, homogeneous exposed sample area a multi-technique study of EUV induced carbon contamination and cleaning can be conducted using standard surface science techniques. EUV-reflectometry, X-ray photoelectron spectroscopy (XPS), small-angle X-ray reflectometry (SAXR), and Out-of-band (OOB) reflectometry (200 - 1000 nm) were applied to investigate exposed samples and study EUV-induced changes of the surface composition. With this approach the influence of EUV-dose, cleaning-gas pressure and composition, and capping-layer material of the Mo/Si multilayer samples on the degradation and cleaning mechanism can be studied.