Recovery of Multilayer-Coated Zerodur and ULE Optics for Extreme-Ultraviolet Lithography by Recoating, Reactive-Ion Etching, and Wet-Chemical Processes.

Extreme-ultraviolet lithography requires expensive multilayer-coated Zerodur or ULE optics with extremely tight figure and finish specifications. Therefore it is desirable to develop methods to recover these optics if they are coated with a nonoptimum multilayer films or in the event that the coating deteriorates over time owing to long-term exposure to radiation, corrosion, or surface contamination. We evaluate recoating, reactive-ion etching, and wet-chemical techniques for the recovery of Mo/Si and Mo/Be multilayer films upon Zerodur and ULE test optics. The recoating technique was successfully employed in the recovery of Mo/Si-coated optics but has the drawback of limited applicability. A chlorine-based reactive-ion etch process was successfully used to recover Mo/Si-coated optics, and a particularly large process window was observed when ULE optics were employed; this is an advantageous for large, curved optics. Dilute HCl wet-chemical techniques were developed and successfully demonstrated for the recovery of Mo/Be-coated optics as well as for Mo/Si-coated optics when Mo/Be release layers were employed; however, there are questions about the extendability of the HCl process to large optics and multiple coat and strip cycles. The technique of using carbon barrier layers to protect the optic during removal of Mo/Si in HF:HNO(3) also showed promise.

High-efficiency MoRu-Be multilayer-coated gratings operating near normal incidence in the 11.1-12.0-nm wavelength range.

MoRu-Be multilayer coatings were applied to two diffraction gratings for the purpose of enhancing their normal-incidence efficiency in the 11.1-12.0-nm wavelength range. The grating substrates were replicas of a holographic master grating that had a blazed groove profile with 2400 grooves/mm and a 2-m radius of curvature. The relatively low average microroughness (0.8 nm) of the grating surfaces contributed to the relatively high groove efficiency of the grating substrates and the reflectance of the MoRu-Be multilayer coatings. The peak efficiency, measured with synchrotron radiation, was 10.4% in the second diffraction order at a wavelength of 11.37 nm.

MoRu-Be multilayer-coated grating with 10.4% normal-incidence efficiency near the 11.4-nm wavelength.

A MoRu-Be multilayer coating was applied to a diffraction grating to enhance the grating's normal-incidence efficiency near 11.4 nm wavelength. The holographic grating substrate had a blazed groove profile with 2400 grooves/mm and a microroughness of 0.8 nm. The efficiency in the second diffraction order, measured with synchrotron radiation, was 10.4% at a wavelength of 11.37 nm.

Molybdenum-strontium multilayer mirrors for the 8-12-nm extreme-ultraviolet wavelength region.

Mo-Sr multilayer mirrors were successfully deposited by dc-magnetron sputtering and characterized in situ with synchrotron radiation. Normal-incidence (3.6 degrees ) reflectance of 23.0% at 8.8 nm, 40.8% at 9.4 nm, and 48.3% at 10.5 nm were measured before the samples were exposed to air. After exposure, as a result of the reactivity of Sr with oxygen and water vapor, the reflectance of these multilayers decreased rapidly. Attempts to use thin layers of C to passivate the surface of these Mo-Sr multilayers were unsuccessful.

Survey of Ti-, B-, and Y-based soft x-ray-extreme ultraviolet multilayer mirrors for the 2- to 12-nm wavelength region.

We have performed an experimental investigation of Ti-, B(4)C-, B-, and Y-based multilayer mirrors for the soft x-ray¿extreme ultraviolet (XUV) wavelength region between 2.0 and 12.0 nm. Eleven different material pairs were studied: Ti/Ni, Ti/Co, Ti/Cu, Ti/W, B(4)C/Pd, B/Mo, Y/Pd, Y/Ag, Y/Mo, Y/Nb, and Y/C. The multilayers were sputter deposited and were characterized with a number of techniques, including low-angle x-ray diffraction and normal incidence XUV reflectometry. Among the Ti-based multilayers the best results were obtained with Ti/W, with peak reflectances up to 5.2% at 2.79 nm at 61° from normal incidence. The B(4)C/Pd and B/Mo multilayer mirrors had near-normal incidence (5°) peak reflectances of 11.5% at 8.46 nm and 9.4% at 6.67 nm, respectively, whereas a Y/Mo multilayer mirror had a maximum peak reflectance of 25.6% at 11.30 nm at the same angle. The factors limiting the peak reflectance of these different multilayer mirrors are discussed.

In situ reflectance measurements of soft-x-ray/extreme-ultraviolet Mo/Y multilayer mirrors.

With a new ultrahigh-vacuum deposition/ref lectometer system, Mo/Y multilayer mirrors were deposited by dc-magnetron sputtering and characterized in situ with synchrotron radiation. The Mo/Y multilayer mirrors, measured before exposure to air, had near-normal-incidence reflectances as high as 46% at wavelengths near 11.4 nm. After several days of exposure these samples typically had a relative reflectance loss of ~10% as a result of oxidation of the top Mo layer. The best Mo/Y multilayers were fabricated with base pressures below the low 10(-9) Torr range and after a bakeout to reduce water vapor in the chamber.

Mo/Y multilayer mirrors for the 8-12-nm wavelength region.

Mo/Y multilayer mirrors were deposited by dc magnetron sputtering under different deposition conditions. They were characterized by reflectance measurements at normal and grazing angles of incidence, by transmission electron microscopy, and by Auger depth profiling. Normal-incidence peak reflectances of 34% and 22% were measured at wavelengths of 11.5 and 8.1 nm, respectively. Interface roughness and contamination of the layers during deposition limit the peak reflectance of these Mo/Y mirrors.

Mo/Y multilayer mirrors for the 8-12-nm wavelength region.

Mo/Y multilayer mirrors were deposited by dc magnetron sputtering under different deposition conditions. They were characterized by reflectance measurements at normal and grazing angles of incidence, by transmission electron microscopy, and by Auger depth profiling. Normal-incidence peak reflectances of 34% and 22% were measured at wavelengths of 11.5 and 8.1 nm, respectively. Interface roughness and contamination of the layers during deposition limit the peak reflectance of these Mo/Y mirrors.

Extreme-ultraviolet Mo/Si multilayer mirrors deposited by radio-frequency-magnetron sputtering.

Mo/Si multilayer mirrors with a high reflectance at normal incidence in the 130-135-Å spectral region have been deposited by rf magnetron sputtering. A new and quick technique was used to calibrate the deposition rates. Characterization by transmission electron microscopy (TEM) and grazing-incidence x-ray diffraction (XRD) indicated good thickness control of the deposition process and low interface roughness. However, the TEM and, indirectly, the XRD reflectance measurements, indicated that the interfaces are asymmetric. A brief review discussing the origin of the modulation of the Bragg peak intensities in the XRD reflectance is given. An analytical formula was derived for periodic multilayers that describes the effect of asymmetric interfaces on the amplitude of the Bragg peak modulation. Theoretically, in XRD reflectance measurements, any asymmetry in the interdiffusion of the Mo-Si interfaces results in a decrease of the usual amplitude modulation of the Bragg peaks. Extreme-ultraviolet (XUV) reflectance measurements were also made with synchrotron radiation on a new high-resolution reflectometer. The near-normal-incidence peak reflectances measured at λ = 134 Å were ~ 59% for the best multilayer mirrors. Good fits to both XRD and XUV reflectance measurements have been obtained with a model that allows for interface asymmetry.

Extreme-ultraviolet optical constant determination near an absorption edge.

The determination of optical constants from the reflectance versus angle of incidence data in the extreme ultraviolet region near an absorption edge may be affected by instrument spectral resolution.