David P. Gaines

Nonspecular x-ray scattering in a multilayer-coated imaging system

We present a rigorous theoretical treatment of nonspecular x-ray scattering in a distributed imaging system consisting of multilayer-coated reflective optics. The scattering from each optical surface is obtained using a vector scattering theory that incorporates a thin film growth model to provide a realistic description of the interfacial roughness of the multilayer coatings. The theory is validated by comparing calculations based on measured roughness to experimental measurements of nonspecular scattering from a Mo–Si multilayer coating. The propagation of the scattered radiation through the optical system is described in the context of transfer function theory. We find that the effect of nonspecular scattering is to convolve the image with a point spread function that is independent of the coherence of the object illumination. For a typical soft x-ray imaging system, the scattering within the image field from the multilayer coatings is expected to be slightly greater than for single surfaces (as normal...

Multipass amplification of soft x rays in a laser cavity

We report the first demonstration to our knowledge of multipass amplification of soft x rays. A gain medium of neonlike selenium ions was placed within a resonant cavity composed of a multilayer mirror and a beam splitter designed for normal-incidence use at the 20.63- and 20.96-nm laser lines of the neonlike selenium. The laser-cavity output was time resolved and exhibited three distinct temporal components identifiable as the single-, double-, and triple-pass amplified emission. In these experiments, multipass amplification was limited by the finite duration of the gain medium.

Soft x‐ray projection lithography

Recent advances in x‐ray optics have made possible the practical consideration of soft x‐ray projection imaging for the fabrication of high density integrated circuits.

Double pass amplification of laser radiation at 131 Å

Abstract We report an explicit demonstration of double pass amplification of soft X-ray laser radiation at 131 A, the shortest wavelength demonstration to date. Using efficient ( R =60%), narrowband ( λ Δλ =13 ), normal incidence, multilayer mirrors, double pass amplification was achieved on the 131 A and 132.7 A laser lines of neon-like molybdenum. The laser output was time resolved, exhibiting two distinct temporal components clearly identifiable as the single pass and double pass amplified emission.

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.

Radiation hardness of molybdenum silicon multilayers designed for use in a soft-x-ray projection lithography system

A molybdenum silicon multilayer is irradiated with 13.4-nm radiation to investigate changes in multilayer performance under simulated soft-x-ray projection lithography (SXPL) conditions. The wiggler-undulator at the Berlin electron storage ring BESSY is used as a quasi-monochromatic source of calculable spectral radiant intensity and is configured to simulate an incident SXPL x-ray spectrum. The test multilayer receives a radiant exposure of 240 J/mm(2) in an exposure lasting 8.9 h. The corresponding average incident power density is 7.5 mW/mm(2). The absorbed dose of 7.8 × 10(10) J/kg (7.8 × 10(12) rad) is equivalent to 1.2 times the dose that would be absorbed by a multilayer coating on the first imaging optic in a hypothetical SXPL system during 1 year of operation. Surface temperature increases do not exceed 2 °C during the exposure. Normal-incidence reflectance measurements at λ(0) = 13.4 nm performed before radiation exposure are in agreement with measurements performed after the exposure, indicating that no sign icant damage had occurred.

Reflection mask technology for x-ray projection lithography

We report the first demonstration of the fabrication and characterization of soft x‐ray reflecting masks suitable for x‐ray projection lithography. We have patterned efficient (R>50%) normal‐incidence x‐ray mirrors to produce reflecting masks with measured x‐ray contrasts>500:1 over a sufficiently wide spectral range. Calculations indicate that masks on silicon substrates are thermally stable for a production‐type lithographic facility.

X-Ray Laser Cavity Experiments

We report progress toward the development of multipass, soft x-ray laser cavities operating in a spectral range around 200 Å. Experimental results on the characterization of normal incidence multilayer mirrors, the survival of multilayer mirrors in the hostile x-ray laser environment, and the performance of double pass cavities at 206 Å to 209 Å are presented.

Nonspecular scattering from multilayer mirrors at normal incidence

The first measurements are reported of non-specular scattering of EUV radiation normally incident on a multilayer mirror. The scattering from a Mo/Si multilayer mirror has been measured as a function of angle and wavelength. A peak in the angular distribution of scattered light is observed which is due to the correlation of the roughness of different interfaces. The scattering from correlated roughness can be described by a simple kinematic theory of scattering. In the region of the Bragg reflectivity peak dynamical effects lead to a reduction in the scattering from the simple kinematic theory. The total integrated scatter (TIS) has been measured and is found to peak on the short wavelength side of the Bragg peak. The TIS is less than 1% of the incident intensity.

Multilayer coatings on figured optics

Soft x-ray projection lithography (SXPL) requires uniform, high reflectivity multilayer (ML) coatings on figured optical surfaces with lens speeds (f) between 3 and 6 and diameters of 10 to 15 cm. High reflectivity Mo-Si ML coatings for operation near 13 nm were deposited on f 3.4 and f 6 optics 5 and 7.5 cm in diameter using planar dc magnetron sputtering. Measurements of the normal incidence reflectivity (NIR) of 63% at 13 nm uniform over the central 5 cm of the figured surface were obtained. Comparison of the measured values to model calculations of the wavelength dependent reflectivity indicate that the ML period is uniform to better than 0.04 nm over this region.