There are many applications for non-contact measurement of the displacement and velocity of moving objects, especially
when achieved at low cost. An optical displacement sensor has been developed that can be compared to expensive laser-interferometry
sensors, however at a cost compatible with requirements for consumer products. This miniature Laser-Doppler Interferometer works on all light scattering surfaces. The first large-scale application is in PC-mice.
The measurement principle employs so-called "Laser Self Mixing", which occurs when laser light scattered on a surface,
within the coherence length, is coupled back into the laser cavity. When the object is moving, the back-scattered light is
continuously shifting in phase relative to the laser light at the laser mirror. This results in a periodic perturbation of the
feedback into the laser cavity, which causes modulations of the light intensity in the cavity. The frequency of these
modulations is proportional the speed of the object. A VCSEL, optimized for this application, is used as light source, a
photo-diode in the sensor measures the intensity fluctuations and, finally, an integrated circuit transfers the photo-diode
signal into velocity or displacement information. To determine the direction of the movement, a triangle modulation of
the laser-current is used, which modulates the laser-temperature and hence the laser frequency.
Next to the applications in PC-mice a much wider range of applications as input device in consumer products can be
envisaged. For instance menu navigation by finger movement over a sensor in remote controls, mobile phones and lap
tops. Furthermore a wide field of applications is envisaged in the manufacturing of industrial equipment, which requires
non-contact measurement of the movement of materials. The small form factor of less than 0.2 cubic centimeters allows
applications previously considered impossible.
Extreme ultraviolet lithography (EUVL) is the leading technology for patterning at the 32 nm technology node and be-yond. EUVL light at 13.5 nm is used to print circuits. This light is produced by heating fuel (Xe, Sn) in EUV sources to a very high temperature by using either magnetic compression or laser irradiation. Today EUV source power remains the number one concern for implementation of EUVL in high volume manufacturing. Over the last few years, much pro-gress has been made in EUV source performance and availability. Today, alpha level high power (~10 W) EUV sources have been integrated in alpha level EUVL scanners. Medium and low power EUV sources are used for in-house metrol-ogy and performance studies on EUV mask blanks, EUV masks, photoresists, and optical elements. These compact dis-charge sources with medium power in the range of 10-100 mW/sr/2% bandwidth and low power EUV tubes are being used by various R&D labs for development of mask, optics, and resists. Previously, development of EUVL was mostly located at beamlines; today, these low power EUV sources are instrumental in allowing in-house R&D projects. In this paper, the latest status of high power EUV sources, low and medium power metrology sources, and some of their appli-cations are described.
In this paper, we report on the recent progress of the Philips Extreme UV source. The Philips source concept is based on a discharge plasma ignited in a Sn vapor plume that is ablated by a laser pulse. Using rotating electrodes covered with a regenerating tin surface, the problems of electrode erosion and power scaling are fundamentally solved.
Most of the work of the past year has been dedicated to develop a lamp system which is operating very reliably and stable under full scanner remote control. Topics addressed were the development of the scanner interface, a dose control system, thermo-mechanical design, positional stability of the source, tin handling, and many more.
The resulting EUV source-the Philips NovaTin(R) source-can operate at more than 10kW electrical input power and delivers 200W in-band EUV into 2π continuously. The source is very small, so nearly 100% of the EUV radiation can be collected within etendue limits. The lamp system is fully automated and can operate unattended under full scanner remote control. 500 Million shots of continuous operation without interruption have been realized, electrode lifetime is at least 2 Billion shots. Three sources are currently being prepared, two of them will be integrated into the first EUV Alpha Demonstration tools of ASML.
The debris problem was reduced to a level which is well acceptable for scanner operation. First, a considerable reduction of the Sn emission of the source has been realized. The debris mitigation system is based on a two-step concept using a foil trap based stage and a chemical cleaning stage. Both steps were improved considerably. A collector lifetime of 1 Billion shots is achieved, after this operating time a cleaning would be applied. The cleaning step has been verified to work with tolerable Sn residues. From the experimental results, a total collector lifetime of more than 10 Billion shots can be expected.
In EUV lithography, extreme ultraviolet radiation of 13.5 nm wavelength is used to print feature with resolutions consis-tent with the requirements of the 45 nm technology node or below. EUV is produced by heating xenon, tin, or other ele-ments to a plasma state, using either magnetic compression or laser irradiation. The key concerns-identified at the third EUV-Symposium-are the ability to supply defect-free masks and to increase source component lifetimes to meet the wafer throughput requirements for high volume manufacturing. Source availability and performance, however, made steady progress within the last years on two lines of actions: High power sources for high volume production and medium and low power sources for allowing in-house metrology and performance studies on EUV-mask-blanks, EUV-Masks, photoresists and optical elements.
For "volume production sources" 50 W of collected EUV powers are already available by various suppliers. Compact discharge sources of medium power in the range of 10-100 mW / sr / 2% bandwidth and low power EUV-tubes of low-est cost of ownership and superior stability are ideal for peripheral metrology on components for EUV-Lithography. These low power sources supplement beamlines at storage rings by transferring EUV-applications to individual R&D labs. Proceeding integration of those EUV sources into tools for technology development like open frame and micro-exposers, and in tools for actinic metrology is the best proof of the progress. As of today, the first EUV sources and measurement equipment are available to be used for EUV system, mask, optics and component as well as lithography process development. With the commercial availability of EUV-plasma sources other applications using short wave-length, XUV-radiation will be feasible in a laboratory environment. Some examples of XUV applications are discussed.
The paper describes recent progress in the development of the Philips's EUV source. Progress has been realized at many frontiers: Integration studies of the source into a scanner have primarily been studied on the Xe source because it has a high degree of maturity. We report on integration with a collector, associated collector lifetime and optical characteristics. Collector lifetime in excess of 1 bln shots could be demonstrated. Next, an active dose control system was developed and tested on the Xe lamp. Resulting dose stability data are less than 0.2% for an exposure window of 100 pulses. The second part of the paper reports on progress in the development of the Philips' Sn source. First, the details of the concept are described. It is based on a Laser triggered vacuum arc, which is an extension with respect to previous designs. The source is furbished with rotating electrodes that are covered with a Sn film that is constantly regenerated. Hence by the very design of the source, it is scalable to very high power levels, and moreover has fundamentally solved the notorious problem of electrode erosion. Power values of 260 W in 2p sr are reported, along with a stable, long life operation of the lamp. The paper also addresses the problem of debris generation and mitigation of the Sn-source. The problem is attacked by a combined strategy of protection of the collector by traditional means (e.g. fields, foiltraps... ), and by designing the gas atmosphere according to the principles of the well known halogen cycles in incandescent lamps. These principles have been studied in the Lighting industry for decades and rely on the excessively high vapor pressures of metal halides. Transferred to the Sn source, it allows pumping away tin residues that would otherwise irreversibly deposit on the collector.
The paper describes progress of the Philips’ hollow cathode triggered (HCT) gas discharge EUV source. The program
has been focussed on three major areas: (1) Studying the basic physics of ignition, pinch formation and EUV
generation. The paper reports on progress in this area and particularly describes the underlying atomic physics both for
Xe and Sn. (2) Discharge based on Sn. Results on overall efficiency more than 5 times the Xe efficiency are reported as
well as high frequency operation up to 6.5 kHz. This system shows all the necessary ingredients for scaling to
production power levels. (3) Integration of the Xe source in an alpha tool. Results on integration issues like electrode
life time, collector life time and dose control will be presented.
The paper describes recent progress on the development of an EUV source based on a hollow cathode triggered gas discharge (HCT). The principle of operation has been described in previous publications. When operated with Xe, a repetition frequency up to 4 kHz, conversion efficiency of 0.55% inband radiation in 2π and a pinch size below 3mm in length was demonstrated. Today's requirements on a commercial EUV source for volume production of wafers still exceed the current performance by large factors both in terms of output power and life time. This paper will discuss the roadmap to high power and will also show elements of the way to extended life time. Particular focus will be put onto the physical limits of Xe as radiator and the advantages of using Sn instead. It will be demonstrated that the spectral efficiency of Sn is a factor of 3 higher than Xe.
The paper describes the physical properties and recent technical advances of the hollow cathode triggered pinch device (HCT) for the generation of EUV radiation. In previous publications we have demonstrated continuous operation of the untriggered device at 1 kHz in pure Xe. The newer generations operate with a triggering facility which allows a wider parameter space under which stable operation is possible. Repetition frequencies of up to 4 kHz could be demonstrated. Many of the experiments are performed in repetitive bursts of variable lengths and spacing. This allows also to demonstrate that there is only little transient behavior upon switching on and off the source. Conversion efficiencies into the 2 percent frequency band around 13.5 nm are about 0.4 percent in 2p, comparable to the values reported from other groups. Another important parameter is the size of the light emitting region. Here we have studied the influence of electrode geometry and flow properties on the size, to find a best match to the requirements of the collection optics. A major problem for the design of a complete wafer illumination system is the out-of-band portion of the radiation. Especially the DUV fraction of the source spectrum is a concern because it is also reflected to some extend by the Mo-Si multilayer mirrors. We show that the source has a low overall non-EUV part of the emission. In particular, it is demonstrated that there is very little DUV coming out of the usable source volume, well below the specified level.