ABSTRACT
Soft x-ray projection lithography (SXPL) is an attractive technique for the fabrication of high-speed, high-density integrated circuits. In an SXPL stepper, the x-ray imaging mirrors consist of multilayer coatings deposited onto high precision substrates. The stepper is intended to fabricate ultra-high spatial-resolution structures with a minimum feature size of <0.1 µm. To achieve this resolution, the imaging mirrors must maintain a very precise surface figure while being exposed to x radiation. Failure to achieve and maintain the mirror surface figure will distort the wavefront propagating through the imaging system and will degrade system resolution. The required surface figure accuracy for each imaging mirror depends upon the required resolution, the wavelength, and the optical design. For conventional SXPL stepper designs, the total (peak-to-valley) surface figure error budget per mirror is approximately ±1 nm. Due to material properties at soft x-ray wavelengths and practical fabrication considerations, x-ray multilayer mirrors have limited reflectivities. A fraction of the incident x radiation is absorbed in the multilayer coating. This absorbed radiation constitutes a thermal load on the mirror, thereby distorting its shape and compromising the accuracy of its surface figure. In this paper, we analyze the thermally induced distortion on the imaging optics and conclude that the maximum allowable thermal distortion limits the maximum allowable x-ray power transported to the wafer and limits the minimum acceptable multilayer mirror reflectivity. The penalty for either insensitive x-ray resists or inefficient mirror reflectivity is a decrease in system throughput which cannot be compensated with increased source power either collected by condenser optics or generated by the source.
ABSTRACT
This special issue contains a collection of papers describing results that were presented at the Second Topical Meeting on Soft-X-Ray Projection Lithography sponsored by the Optical Society of America and held 6-8 April 1992 in Monterey, California, along with several additional papers submitted after that meeting. These papers are being published in this collection to make them readily available to a larger audience than would normally occur with a proceedings and also to take advantage of the critical review process.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
We present a baseline analysis of issues affecting the economic viability of Soft X-Ray Projection Lithography (SXPL). This analysis is intended to serve as a starting point, and to provide an initial assessment of the relative importance of cost factors in a SXPL system. We presume a "conventional" SXPL system design and focus on wafer exposure costs. A baseline model for system component costs and performance specifications is presented, and the dependence of wafer exposure cost on elements of the model is analyzed. Within the guidelines of our model, we find that direct cost items (e.g., cost of the laser driver) are not nearly as critical as technical performance parameters (e.g., mirror reflectivity) in determining wafer exposure costs.
ABSTRACT
In the past half decade or so there has been a technological revolution in our ability to generate, control, manipulate, focus, and detect x rays. The emergence of x-ray lasers and synchrotron insertion devices has increased the brightness of laboratory x-ray sources 8 to 12 orders of magnitude over what was available in the late 1960s. In addition, the past few years have been witness to significant advances in the development of normal incidence x-ray mirrors and beam splitters, diffraction limited x-ray lenses, x-ray microscopy, x-ray holography, x-ray waveguides, and CCD x-ray detector arrays. Utilizing these new capabilities, workers in the field are taking the first steps toward the development of sophisticated soft x-ray optical systems, including soft x-ray interferometers, high-intensity x-ray lasers, and projection optics for x-ray lithography. Details of these developments are discussed, as is the question, Why is this happening now?
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
A gold transmission grating has been coupled to a high-resolution Wolter-design grazing-incidence reflection x-ray microscope to produce an imaging x-ray spectrometer of unprecedented spatial resolution, spectral range, and collection solid angle. In a series of test experiments conducted at 1.75-2 keV, the instrument demonstrated a spectral resolving power, lambda/Deltalambda, of 200 and a 1-D spatial resolution of 1 microm. The spectrometer's large collection solid angle, approximately 2 x 10(-5) sr, and broad spectral range, from the near UV to 3.2 keV, make it a very versatile instrument for laser-fusion applications.
ABSTRACT
Design considerations and fabrication procedures for Fresnel zone plates appropriate for high-resolution coded imaging of x-ray and particle emission from laser produced plasmas are presented. Fabrication results for free standing zone plate structures of high Z material (gold), large zone number (100
