Andrew M. Hawryluk

Soft x‐ray projection lithography using an x‐ray reduction camera

Soft x‐ray projection lithography can now be realized with recent developments in x‐ray optics. Using new x‐ray optical components and spherical imaging optics, we have designed an x‐ray reduction camera which is capable of projecting with soft x‐ray radiation, a 5× demagnified image of a mask onto a resist coated wafer. The resolution of this design is ∼100 nm with a depth of focus of ±5.6 μm and a 0.5‐cm‐diam image field. We use x‐ray reflecting masks (patterned x‐ray multilayer mirrors) which are fabricated on thick substrates and can be made relatively distortion free. Our design uses a laser produced plasma for the x‐ray source. Better resolution and/or larger areas are possible with improvements in optic figures and source characteristics.

Use of interference lithography to pattern arrays of submicron resist structures for field emission flat panel displays

We report on the fabrication of square arrays of submicron resist dots and holes using interference lithography—a relatively simple and inexpensive way of generating periodic structures over large areas. The arrays are formed by exposing a layer of resist to a two-beam interference pattern followed by a second exposure after rotating the sample by 90°. Arrays with periods of 0.67–3.2 μm were fabricated. The size of the structures is accurately controlled by varying the exposure dose. The exposure latitude for patterning arrays of dots is ±16% for a ±10% change in structure width when an optimum size-to-period ratio is chosen. Compared to dots, holes are patterned with a smaller process window. We show that arrays of dots with diameters as small as 0.20 μm, sidewall slopes of 88°, and aspect ratios as high as 3:1 can be produced. These structures are well suited for the production of field emission flat panel displays.

Time-resolved x-ray transmission grating spectrometer for studying laser-produced plasmas.

The development of a new time-resolved x-ray spectrometer is reported in which a free-standing x-ray transmission grating is coupled to a soft x-ray streak camera. The instrument measures continuous x-ray spectra with 20-psec temporal resolution and moderate spectral resolution (deltalambda >/= 1 A) over a broad spectral range (0.1-5 keV) with high sensitivity and large information recording capacity. Its capabilities are well suited to investigation of laser-generated plasmas, and they nicely complement the characteristics of other time-resolved spectroscopic techniques presently in use. The transmission grating spectrometer has been used on a variety of laser-plasma experiments. We report the first measurements of the temporal variation of continuous low-energy x-ray spectra from laser-irradiated disk targets.

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.

Fabrication of sub‐0.5 μm diameter cobalt dots on silicon substrates and photoresist pedestals on 50 cm×50 cm glass substrates using laser interference lithograph

We have fabricated arrays of 120‐nm‐diam cobalt dot masks on 300 nm centers using laser interference lithography. The density of the cobalt dot arrays is ≳109 dots/cm2. The standard deviation of the average cobalt dot diameter is 7.4% over a 5‐cm‐diam silicon substrate. Single crystal silicon pedestals were formed using a chrome dot mask array to demonstrate that these subquarter micrometer features can be used to fabricate high density self‐aligned gated field emitter arrays. We have exposed uniform photoresist pedestals on 50 cm×50 cm glass substrates using laser interference lithography to demonstrate that this technique can be scaled to expose large areas. The base diameter of the photoresist pedestals is 330 nm and the height is 250 nm. The center‐to‐center spacing is 670 nm. The standard deviation of the base diameter of the photoresist pedestals is 3% over an 8 μm×8 μm region.

Front-end design issues in soft-x-ray projection lithography

We present a protocol for the design of an illumination system (front end) for a soft-x-ray projection lithography tool. The protocol is illustrated by specific front-end designs. The most complete design analysis is for a laser-driven system. Other drivers; undulator, synchrotron orbital radiation, and plasma discharge, are also discussed.

Wavelength considerations in soft-x-ray projection lithography

The choice of the operational wavelength for a soft-x-ray projection lithography system affects a wide variety of system parameters such as optical design, sources, resists, and multilayer mirrors. Several system constraints limit the choice for the operational wavelength. In particular, optical imaging requirements place an upper limit and throughput issues place a lower limit on the wavelength selection. We have determined that there are several discrete wavelength regions between 10 and 25 nm that satisfy the system-imposed constraints of high resolution, large depth of focus, and high throughput.

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.

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.