At Laser-Laboratorium Goettingen different types of laser-plasma EUV sources
based on gas and cluster targets were tested to optimize the spatially resolved EUV
radiation with respect to maximum EUV intensities, small source diameters, and
pointing stability. The EUV radiation is generated by focusing a Q-switched Nd:YAG
laser at 1064nm into a pulsed gas puff target. By the use of different target gases,
broad-band as well as narrow-band EUV radiation is obtained, respectively. The
influence of the laser and target gas parameters on the plasma shape and EUV intensity
was investigated by the help of specially designed EUV pinhole cameras, utilizing
evaluation algorithms developed for standardized laser beam characterization. The
properties of the gas jet determine crucial parameters of the source. A directed gas
jet in vacuum with a high number density is needed for an optimal performance of
the source. Therefore, conical nozzles with different cone angles were drilled with an
excimer laser to produce a supersonic gas jet. The influence of the nozzle geometry
on the gas jet was analyzed with a Hartmann-Shack wavefront senor, the first time to
our knowledge. The deformation of a planar wavefront after passing the gas jet was
analyzed with this sensor, out of which the gas density distribution was reconstructed.
Thus, the gas jet was optimized resulting in an increase of EUV emission by a factor
of two and decreasing the plasma size at the same time.
At Laser-Laboratorium Goettingen different types of laser-plasma EUV sources based on gas and cluster targets were tested to optimize the spatially resolved EUV radiation with respect to maximum EUV intensities, small source diameters, and pointing stability. The EUV radiation is generated by focusing a Q-switched Nd:YAG laser at 1064nm into a pulsed gas puff target. By the use of different target gases, broad-band as well as narrow-band EUV radiation is obtained, respectively. The influence of the laser and target gas parameters on the plasma shape and EUV intensity was investigated by the help of specially designed EUV pinhole cameras, utilizing evaluation algorithms developed for standardized laser beam characterization. In addition, a rotatable pinhole camera was developed which allows spatially and angular resolved monitoring of the soft X-ray emission characteristics. With the help of this camera a strong angular dependence of the EUV intensity was found. The results were compared with fluorescence and Rayleigh measurements for visualization of the target gas jet. To explain these results a theoretical model was developed, including the reabsorption of the EUV radiation in the surrounding target gas. In addition, an EUV-sensitive Hartmann sensor was utilized to characterize the wavefront of 13nm radiation before and after reflection from Mo/Si multilayer mirrors.
utilizing a laser-based source for the generation of 13nm radiation. The EUV plasma is produced by focusing a Nd:YAG laser into a pulsed xenon or oxygen gas jet. The alternate use of these two target gases accomplishes either an intense broad-band (Xe) or a less intense narrow-band line emission (O2) at 13nm.
Different types of nozzles were tested in order to optimize the emitted radiation with respect to maximum EUV intensities, small source dimensions and pulse-to-pulse stabilities. The investigation of these crucial source parameters was performed with specially designed EUV pinhole cameras, utilizing evaluation algorithms developed for standardized laser beam characterization. In addition, a rotatable pinhole camera was developed which allows spatially and angular resolved monitoring of the soft X-ray emission characteristics. With the help of this camera a strong angular dependence of the EUV intensity was found, indicating reabsorption of the EUV radiation in the surrounding gas. The results were compared with Rayleigh scattering measurements for visualization of the target gas density.
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.
In order to improve the efficiency of optical components for microlithography, metrology for comprehensive characterization of DUV and VUV radiation and the related optics has been developed at Laser-Laboratorium Gottingen. The performance of optical components is assessed by measuring absorptance, scatter losses and damage thresholds during ArF and F2 laser irradiation. Absolute linear and non-linear absorption coefficients are determined by high-resolution laser calorimetry, which provides greatly enhanced accuracy as compared to transmissive measurements. This technique accomplishes also fast monitoring of laser induced degradation phenomena. The absorptance data are compared with the results of accompanying high-resolution laser-induced fluorescence measurements.
For an assessment of the optical quality of DUV/VUV optics, a specially designed wavefront analyzer based on the Hartmann-Shack principle is employed. This device, which also allows accurate beam characterization of ArF and F2 laser in the near- and far-field, can be used as an alternative to interferometric measurements for "at wavelength" testing of optics, e.g. for on-line monitoring of compaction or lens heating in fused silica.
At Laser-Laboratorium Gottingen different laser-plasma sources were tested, which are going to be used for characterization of optical components and sensoric devices in the wavelength region from 11 to 13nm. In all cases EUV radiation is generated by focussing a Q-switched Nd:YAG laser into a gas puff target. By the use of xenon or oxygen as target gas, broadband as well as narrowband EUV radiation is obtained, respectively. Different types of valves and nozzles were tested in order to optimize the emitted radiation with respect to maximum EUV intensities, small source diameters and pointing stability. The investigation of these crucial source parameters was performed with specially designed EUV pinhole cameras, utilizing evaluation algorithms developed for standardized laser beam characterization. In addition, a rotatable pinhole camera was developed which allows spatially and angular resolved monitoring of the soft X-ray emission characteristics. With the help of this camera a strong angular dependence of the EUV intensity was found. The results were compared with fluorescence measurements for visualization of the target gas jet. To explain these results a theoretical model was developed, including the absorptance of the EUV radiation in the surrounding target gas.
The successful implementation of EUV lithography systems strongly relies both on the efficiency of the employed optical components and the precise control of the relevant source parameters. Utilizing a laser-based plasma source for the generation of 13nm radiation, metrology for comprehensive characterization of EUV radiation and the related optics is developed at Laser-Laboratorium Goettingen. A soft X-ray plasma is produced with the help of a Nd:YAG laser which is focused into a pulsed xenon or oxygen gas jet. The alternate use of these two target gases accomplishes either a very intense broadband emission (Xe), or a less intense narrow-band line emission (O2) at the wavelength of 13nm. Additional filtering with the help of Mo/Si mirrors yields quasi-monochromatic 13nm radiation, as needed for testing of optical components, especially reflectometry. The performance of the EUV source is monitored with respect to source diameter, emission characteristics, and 13nm conversion efficiency by the help of different diagnostic tools, including EUV sensitive pin-hole cameras, photo-diodes and an EUV spectrometer. Moreover, first wavefront measurements of EUV radiation are performed with the help of a Hartmann wavefront analyzer, which was sensibilized for 13nm radiation.
A laser-based EUV plasma source is described, which is going to be utilized for characterization of EUV optical components and sensoric devices in the wavelength region from 11 to 13nm. EUV radiation is generated by focusing a Nd:YAG laser into a double stream gas puff target. By the use of different target gases, broadband as well as narrow-band EUV radiation can be obtained. The emission characteristics of the radiation is monitored by the help of different diagnostic tools including a pinhole camera, an EUV spectrometer, and various EUV photodiodes, either directly or after reflection from multilayer mirrors. Moreover, first wavefront measurements of EUV radiation are performed with the help of a specially designed wavefront analyzer based on the Hartmann-Shack principle, which was sensibilized for 13nm radiation. This device can be used as an alternative to interferometric measurements for an assessment of the optical quality of EUV optics, e.g. for at wavelength monitoring of aberrations (including Zernike analysis), as well as for on-line monitoring of heating effects.
A laser-based EUV plasma source for diagnostics purposes was developed, which is going to be utilized primarily for characterization of EUV optical components and sensoric devices. The emission characteristics of the generated 13nm radiation is monitored by the help of different diagnostic tools, including a pinhole camera, an EUV spectrometer and various EUV photodiodes. Moreover, first wavefront measurements of EUV radiation were performed with the help of a specially designed wavefront analyzer based on the Hartmann-Shack principle, which was sensibilized for 13nm radiation.
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