A silicon-based, sequential coat-and-etch process to fabricate nearly perfect substrate surfaces

For many thin-film applications substrate imperfections such as particles, pits, scratches, and general roughness, can nucleate film defects which can severely detract from the coating's performance. Previously we developed a coat-and-etch process, termed the ion beam thin film planarization process, to planarize substrate particles up to approximately 70 nm in diameter. The process relied on normal incidence etching; however, such a process induces defects nucleated by substrate pits to grow much larger. We have since developed a coat-and-etch process to planarize approximately 70 nm deep by 70 nm wide substrate pits; it relies on etching at an off-normal incidence angle, i.e., an angle of approximately 470 degrees from the substrate normal. However, a disadvantage of this pit smoothing process is that it induces defects nucleated by substrate particles to grow larger. Combining elements from both processes we have been able to develop a silicon-based, coat-and-etch process to successfully planarize approximately 70 nm substrate particles and pits simultaneously to at or below 1 nm in height; this value is important for applications such as extreme ultraviolet lithography (EUVL) masks. The coat-and-etch process has an added ability to significantly reduce high-spatial frequency roughness, rendering a nearly perfect substrate surface.

Multilayer mirror technology for soft-x-ray projection lithography

<p>Recent advances in multilayer mirror technology meet many of the stringent demands of soft-x-ray projection lithography (SXPL). The maximum normal-incidence reflectivity achieved to date is 66% for Mo/Si multilayers at a soft-x-ray wavelength of 13.4 am, which is sufficient to satisfy the x-ray throughput requirements of SXPL. These high-performance coatings can be deposited on figured optics with layer thickness control of ˜ 0.5%. Uniform multilayer coatings are required for SXPL imaging optics, for which maintaining the surface figure is critical to achieving diffraction-limited performance.</p> <p>In contrast the coatings on the condenser optics will be graded to accommodate a large range of angles of incidence. Graded multilayer coatings can also be used to modify the figure of optical substrates without increasing the surface roughness. This offers a potential method for precise fabrication of aspheric imaging optics.</p>

Ion-assisted sputter deposition of molybdenum-silicon multilayers

X-ray multilayer (ML) structures that are fabricated by the use of magnetron-sputter deposition exhibit a degradation in structural quality as the deposition pressure is increased. The observed change in morphology is attributed to a reduced mobility of surface adsorbed atoms, which inhibits the formation of smooth, continuous layers. The application of a negative substrate bias produces ion bombardment of the growing film surface by sputtering gas ions extracted from the plasma and permits direct control of the energy density supplied to the film surface during thin-film growth. The technique supplements the energy lost to thermalization in high-pressure deposition and permits the fabrication of high-quality ML structures at elevated processing pressures. A threefold improvement in the soft-x-ray normal-incidence reflectance at 130 A results for substrate bias voltages of the order of ˜ - 150 V for Mo-Si ML's deposited at 10-mTorr Ar.

Chirped multilayer coatings for increased x-ray throughput

Chirped Mo-Si multilayer coatings, where the multilayer period is systematically varied throughout the deposition process, exhibit an increased x-ray bandwidth at normal incidence with a corresponding increase in the integrated reflectance of as much as 20% at lambda ~ 13 nm. The increased bandwidth is accompanied by a slight reduction in peak reflectance. The relation between the integrated and peak reflectance is used to determine the chirp required to optimize the x-ray throughput of a multiple-element optical system.

Normal-incidence x-ray mirror for 7 nm

Multilayer (ML) structures composed of alternating, ultrathin layers of Ru and B(4)C have been grown by dc magnetron sputtering. The ML microstructure has been characterized using x-ray diffraction and highresolution transmission electron microscopy, and the normal-incidence reflectivity has been measured using synchrotron radiation. It is found that, under optimum deposition conditions, the ML structures exhibit smooth and compositionally abrupt interfaces, with a normal-incidence reflectivity as high as 20% at 7.2 nm. The reflectivity decreases when the ML structures are annealed at 500 degrees C owing to interdiffusion and com-pound formation at the interfaces.

Time-resolved measurement of double-pass amplification of soft x rays

We report the first time-resolved measurements of emission from a double-pass soft x-ray laser cavity. In these experiments the output signal from a selenium x-ray laser had two temporal components clearly identifiable as the single- and double-pass emission, with the double-pass amplified signal more intense than the single pass. In addition to an unequivocal demonstration of double-pass amplification of soft x rays, the data provide information about of the time-dependent gain in these x-ray laser media, suggesting an effective gain-length profile which rises more slowly and falls-off more rapidly than predicted by state of the art hydrodynamics and kinetics codes.

Demonstration of guided-wave phenomena at extreme-ultraviolet and soft-x-ray wavelengths

We report an explicit demonstration of classical guided-wave propagation at XUV and soft-x-ray wavelengths. Experiments were performed using narrow-band synchrotron radiation at 5, 20.8, 21, and 30 nm. Free-standing gold transmission gratings served as waveguide structures. These structures had a 300-nm grating period with waveguide channel widths as small as 100 nm and were as thick as 700 nm in the direction of guided-wave transmission. Guided-wave phenomena were manifest in strongly asymmetric diffraction patterns resulting from the angular tilt of the transmission-grating normal from the incident-beam direction.