SPICE is an imaging spectrometer operating at vacuum ultraviolet (VUV) wavelengths, 70.4 – 79.0 nm and 97.3 - 104.9 nm. It is a facility instrument on the Solar Orbiter mission, which carries 10 science instruments in all, to make observations of the Sun’s atmosphere and heliosphere, at close proximity to the Sun, i.e to 0.28 A.U. at perihelion. SPICE’s role is to make VUV measurements of plasma in the solar atmosphere. SPICE is designed to achieve spectral imaging at spectral resolution >1500, spatial resolution of several arcsec, and two-dimensional FOV of 11 x16arcmins. The many strong constraints on the instrument design imposed by the mission requirements prevent the imaging performance from exceeding those of previous instruments, but by being closer to the sun there is a gain in spatial resolution. The price which is paid is the harsher environment, particularly thermal. This leads to some novel features in the design, which needed to be proven by ground test programs. These include a dichroic solar-transmitting primary mirror to dump the solar heat, a high in-flight temperature (60deg.C) and gradients in the optics box, and a bespoke variable-line-spacing grating to minimise the number of reflective components used. The tests culminate in the systemlevel test of VUV imaging performance and pointing stability. We will describe how our dedicated facility with heritage from previous solar instruments, is used to make these tests, and show the results, firstly on the Engineering Model of the optics unit, and more recently on the Flight Model. For the keywords, select up to 8 key terms for a search on your manuscript's subject.
Physikalisch-Technische Bundesanstalt (PTB) has more than 20 years of experience in the calibration of space-based instruments using synchrotron radiation to cover the ultraviolet (UV), vacuum UV (VUV), and x-ray spectral range. Over the past decades, PTB has performed calibrations for numerous space missions within scientific collaborations and has become an important partner for activities in this field. New instrumentation at the electron storage ring, metrology light source, creates additional calibration possibilities within this framework. A new facility for the calibration of radiation transfer source standards with a considerably extended spectral range has been put into operation. The commissioning of a large vacuum vessel that can accommodate entire space instruments opens up new prospects. Finally, an existing VUV transfer calibration source was upgraded to increase the spectral range coverage to a band from 15 to 350 nm.
SPICE is a high resolution imaging spectrometer operating at extreme ultraviolet wavelengths, 70.4 – 79.0 nm and 97.3 -
104.9 nm. It is a facility instrument on the Solar Orbiter mission. SPICE will address the key science goals of Solar
Orbiter by providing the quantitative knowledge of the physical state and composition of the plasmas in the solar
atmosphere, in particular investigating the source regions of outflows and ejection processes which link the solar surface
and corona to the heliosphere. By observing the intensities of selected spectral lines and line profiles, SPICE will derive
temperature, density, flow and composition information for the plasmas in the temperature range from 10,000 K to
10MK. The instrument optics consists of a single-mirror telescope (off-axis paraboloid operating at near-normal
incidence), feeding an imaging spectrometer. The spectrometer is also using just one optical element, a Toroidal Variable
Line Space grating, which images the entrance slit from the telescope focal plane onto a pair of detector arrays, with a
magnification of approximately x5. Each detector consists of a photocathode coated microchannel plate image
intensifier, coupled to active-pixel-sensor (APS). Particular features of the instrument needed due to proximity to the Sun
include: use of dichroic coating on the mirror to transmit and reject the majority of the solar spectrum, particle-deflector
to protect the optics from the solar wind, and use of data compression due to telemetry limitations.
The development of suitable radiation sources for extreme ultraviolet lithography (EUVL) is a major challenge. For the optimization of these sources and for the determination of the parameters needed for the system design and the system integration these sources have to be characterized in terms of the absolute in-band power, the spectral distribution in the EUV spectral region and the out-of-band spectral regions, the spatial distribution of the emitting volume and the angular distribution of the emission. For improving the lifetime of such sources, generally accepted as one key risk with EUVL, another task, the debris emitted from sources under development has to be investigated. Therefore, JENOPTIK Mikrotechnik GmbH is co-operating with the Laser Laboratorium Goettingen, the Physikalisch-Technische Bundesanstalt (PTB) and the AIXUV GmbH in developing ready-for-use metrology tools for EUVL source characterization and optimization. The set of the tools employed for EUV-source characterization is presented in detail as well as concepts for calibration and measurement procedures.
Photodiodes are used as easy-to-operate detectors in the extreme ultraviolet spectral range. The Physikalisch-Technische Bundesanstalt calibrates photodiodes with an 0.3% or better relative uncertainty for the spectral responsivity. These calibrations are based on the comparison of the photodiodes to a primary detector standard using monochromatized synchrotron radiation with a rather low radiant power of about 1 μW. At the customer’s, these diodes may be used for strongly pulsed radiation and very different radiant powers. The linearity of the photodiode signal with incident radiant power was studied with EUV radiation. We used quasi-monochromatic direct undulator radiation to achieve high radiant power. The linearity of the photodiodes was tested with quasi-DC illumination for different photon beam spot sizes. A systematic and significant variation of the maximum external photocurrent with the photon beam spot size is shown. The maximum current in linear operation (less than 1% relative saturation) decreased from about 3 mA for 6 mm photon beam diameter to 0.2 mA for 0.25 mm diameter. The corresponding irradiance increased from 30 mW/cm<sup>2</sup> for the 6 mm aperture to about 2 W/cm<sup>2</sup> for the 0.25 mm aperture. This behaviour is attributed to a change in the effective serial resistance with the photon beam size. The values derived from the saturation measurement vary between 65 Ohm for a 6 mm and 540 Ohm for a 0.25 mm beam. The effect can be explained by the finite conductivity of the thin front contact layer which carries the current to the electrode.
The development of suitable radiation sources is a major challenge for extreme ultraviolet lithography (EUVL). For the optimization of these sources and for the determination of the parameters needed for the system design and the system integration these sources have to be characterized in terms of the absolute in-band power, the spectral distribution in the EUV spectral region and the out-band spectral regions, the spatial distribution of the emitting volume and the angular distribution of the emission. Also the source debris has to be investigated. Therefore, JENOPTIK Mikrotechnik GmbH is co-operating with the Laser Laboratorium Goettingen, the Physikalisch-Technische Bundesanstalt (PTB) and the AIXUV GmbH in developing ready-for-use metrology tools for EUVL source characterization and optimization. The set of the tools employed for EUV-source characterization is presented in detail as well as concepts of for calibration and measurement procedures.
This paper presents first results to assess the feasibility of a cleaning strategy for EUV production tools. The EUV experiments were performed in a dedicated UHV contamination chamber connected to the DLW20 dipole beam line at the PTB laboratories at BESSY II in Berlin. An in-situ reflectometry system has been implemented inside the contamination chamber to allow for real-time detection of mirror reflection changes. The reproducibility of the in-situ reflectometry system has proven to be about 0.03%, allowing the measurement of reflection changes below 0.1%. Cleaning cycles were performed at producation tool power density levels, i,e,, 10-30 mW/mm<sup>2</sup> broadband radiation, on capped Mo/Si mirror samples. Carbon was deposited intentionally at ypical hydrocarbon pressures in the 10<sup>-8</sup> mbar regime. Cleaning was done at background levels of hydrocarbons and 10<sup>-4</sup> mbar molecular oxygen. First results show that cleaning of a mirror at high power densities and typical tool conditions can restore the reflection close to its initial value.
Extensive investigations on the lifetime of EUVL optics using synchrotron radiation [1, 2, 3] have been performed at the radiometry laboratory  of the Physikalisch-Technische Bundesanstalt (PTB) at the BESSY II electron storage ring in the past. Nevertheless, synchrotron radiation shows a very different time structure as compared to the radiation of EUVL sources to be used in lithography tools.
To assess the question, whether the different time structure of the radiation has an impact on the contamination behavior of EUVL optics, an irradiation experiment was performed using synchrotron radiation of different time structure available at the BESSY II electron storage ring: Keeping all other parameters constant, radiation from the normal operation mode of BESSY II, which resembles quasi-cw- illumination, and the special single bunch operation mode, which gives pulsed synchrotron radiation with 1.25 MHz repetition rate were used to irradiate samples in a defined residual gas environment. The reflectance of the samples were measured before and after the illumination to determine the loss in reflectance due to irradiation.
Although the time structure of the single bunch mode still differs considerably from those of potential EUVL sources, trends in the contamination behavior could possibly be observed.
Extreme ultraviolet lithography requires vacuum conditions in the optical train. In order to maintain sufficient energy throughput, reflection reduction of multilayer mirrors due to contamination has to be minimized. We report on oxidation and carbonization experiments on MoSi mirrors under exposure with EUV radiation from a synchrotron. To mimic the effects of EUV radiation we also exposed samples using an electron gun. The oxidation rate was found to be ~0.015 nm/h per mW/mm<SUP>2</SUP> of EUV radiation under vacuum conditions that are typical for a high throughput EUVL system, I.e. 10<SUP>-6</SUP> mbar H<SUB>2</SUB>O. This oxidation can to a large extend be suppressed by using smart gas blend strategies during exposure, e.g. using ethanol. A deposition rate of 0.25 nm/h was found when the hydrocarbon pressure of Fomblin was reduced to 10(superscript -9 mbar. We demonstrate that carbonization can be suppressed by admitting oxygen during electron gun exposure.
Degradation of EUV optics during irradiation is a crucial topic as regards lifetime and performance in EUV lithography. To simulate irradiation conditions for future lithography tools, PTB (the German national metrology institute) operates two dedicated beamlines at the electron storage ring BESSY II. Both, undispersed undulator radiation from an EUV optimized undulator as well as focused and filtered bending magnet radiation can be used. Both beamlines provide EUV radiation with power densities of several mW / mm<SUP>2</SUP>. A dedicated irradiation chamber with sample load lock and differential pumping allows components such as substrates, multilayer mirrors or filters to be exposed to EUV radiation under different vacuum conditions. At the same laboratory, high-accuracy EUV reflectometry can be performed for proximate assessment of the resulting performance.
The development of EUV lithography, has made high-accuracy at-wavelength metrology necessary. Radiometry using synchrotron radiation has been performed by the German national metrology institute, the Physikalisch-Technische Bundesanstalt (PTB), for almost 20 years. Recently, PTB has set up four new beamlines for EUV metrology at the electron storage ring BESSY II. At a bending magnet, a monochromator for soft X-ray radiometry is routinely used for reflectometry and detector characterisation. A reflectometer designed for mirrors up to 550 mm in diameter and 50 kg in mass will be operational in January 2002. Detector characterisation is based on a primary detector standard, a cryogenic electrical substitution radiometer. Measuring tools for EUV source characterisation are calibrated on this basis. Detector testing at irradiation levels comparable to the anticipated conditions in EUV tools is feasible at a plane grating monochromator, installed at an undulator optimised for EUV radiation. A test beamline for EUV optics alignment and system metrology has been installed, using undispersed undulator radiation. Bending magnet radiation is available at a station for irradiation testing. A focusing mirror collects a radiant power of about 10 mW within the multilayer bandwidth and a 1 mm² focal spot.
Mo/S multilayer mirrors have been exposed to intense monochromatic EUV radiation in order to investigate a possible deterioration of the mirror reflectance under different vacuum conditions. Power densities up to 3 mW/mm<SUP>2</SUP> were applied at the PB undulator beamline at BESSY II, applying a hydrocarbon enriched vacuum. The mirror reflectance has been monitored in situ during several hours of exposure. Vacuum pressures of 3 X 10<SUP>-8</SUP> mbar (without hydrocarbons) and 10<SUP>-7</SUP> mbar (with hydrocarbons) at EUV intensities of 3 mW/mm<SUP>2</SUP>, respectively 0.2 mW/mm<SUP>2</SUP> have been applied. The reflectance of the mirrors decreased when exposed to EUV radiation in hydrocarbon enriched vacuum, while no loss in reflectance was observed when no hydrocarbons were added to the vacuum. Ozone-cleaning experiments, using UV produced ozone from air at atmospheric pressure, were performed and show that Mo/S mirrors do not suffer from prolonged exposure to ozone.
High-accuracy characterization of optical components has been one of the main services of the PTB radiometry laboratory at BESSY I. Now, after the shut down of BESSY I with the end of 1999, PTB is operating two new beamlines suitable for EUV reflectometry at their new laboratory at BESSY II. As at BESSY I, synchrotron radiation from a bending magnet is used for reflectometry but additionally a beamline at an undulator covering the same spectral range from 50 eV to 1800 eV can be used for special applications where, e.g., high radiant power or very high spectral purity is needed. In this paper, the characteristics of the beamlines are presented. We present the results of the beamline characterization on photon flux, spectral resolution, spectral purity and beam stability with special respect to the EUV photon energy range. During the phase of simultaneous operation of BESSY I and II in 1999, a direct comparison was done for reflectance measurements at high equality Mo/Si EUV mirrors. The results showed perfect agreement: (68.98 +/- 0.17)% at BESSY I and (69.10 +/- 0.24)% at BESSY II. The wavelength scale was calibrated using the absorption resonances of Ar, Kr, and Xe whose energies are known with a relative uncertainty of about 10<SUP>-4</SUP>. The measured peak positions agreed within this uncertainty.
The Physikalisch-Technische Bundesanstalt (PTB), Germany's national metrology institute, has been operating a radiometry laboratory at the BESSY I 800 MeV electron storage ring since 1982. The BESSY I electron storage ring is optimized for radiometry and is used as a primary source standard with calculable spectral photon flux with relative uncertainties below 0.4 percent. A cryogenic electrical- substitution radiometer is used as a primary detector standard with a relative uncertainty in the determination of the radiant power of about 0.2 percent. Various experimental stations allow for the use of undispersed, calculable synchrotron radiation from bending magnets up to a photon energy of 15 keV and of monochromatorized synchrotron radiation in the 3 eV to 1500 eV spectral range, respectively. Major activities comprise the calibration of radiation detectors rand radiation sources as well as the characterization of optical components in the VUV and soft x-ray spectral range with low uncertainty. Among radiometric calibrations for different applications, extended work has been performed for solar and astronomical missions like SOHO, AXAF and XMM.