Keith Powell

X-ray holography for VLSI using synthetic bilevel holograms

The gains are pointed out of the potential replacement of the usual patterned transmission x-ray mask, in consideration of high-resolution proximity lithography for VLSI, by a diffraction element, or bilevel in-line hologram, to be projected under near-field conditions using synchrotron radiation. The hologram can be configured to correct for diffraction blurring due to projection, and be designed for pre-determined gaps between mask and wafer. The adjustment of experimental parameters can account for the waveguide effects that arise from mask elements with small features which are several hundred x-ray wavelengths thick.It is shown that the hologram, for projection printing at the 50nm feature size, at mask to wafer gaps of 10micrometers or greater, can be fabricated in a similar fashion to a high-resolution mask. The calculation of the hologram is computationally intensive, but a database of calculated features is envisaged.

A generalisation of the error diffusion method for binary computer generated hologram design

Abstract A generalisation of the error diffusion algorithm is obtained by considering a filter for binarisation errors in the reconstruction plane as an error diffusion mask in the hologram plane. The method of projection onto convex sets is used to determine an optimum filter function. Simulated and experimental results are presented. The new method gives superior results over the original error diffusion algorithm.

Restoration and frequency analysis of smeared CCD images

Image smear caused by frame transfer in CCD detectors is considered in terms of an image restoration problem, and an efficient method of achieving smear removal is described and demonstrated. A frequency analysis of the image smearing process identifies optimal regimes for the operation of the CCD.

Picosecond optical correlation using dynamic holography in polyacetylene.

An image-processing system based on four-wave mixing in a film of polyacetylene less than 100 nm thick is demonstrated with a 1-ps processing cycle time. Image phase conjugation and cross correlation are performed with a resolution space-bandwidth product of 0.68 x 10(5) (equivalent to 261 x 261 pixels) in the phase-conjugate image. The light source was amplified optical pulses from a colliding-pulse mode-locked dye laser at a wavelength of 625 nm.

Estimating the effects of structural vibration on adaptive optics system performance.

This paper presents analytical tools developed for estimating the effects of structural vibration on closed-loop adaptive optics system image quality. The general equation for the normalized intensity distribution of an image subject to structural vibration is derived. The resulting two-dimensional theoretical point spread function is computed numerically and compared with empirical data obtained on sky at the Multiple Mirror Telescope Observatory. A simplified analytical expression for the normalized intensity distribution is derived for long exposures and used to quantify the effects on Strehl and spot full width at half-maximum as a function of vibration amplitude, telescope diameter, and observation wavelength.

Zone plate achromatic doublets

Zone plates as used in high resolution x-ray microscopy have focal lengths which are proportional to the x-ray energy. This means that in techniques such as elemental and chemical state mapping, which require images to be made at more than one energy, refocusing is required which can lead to loss of image registration. Using two zone plates, in a similar fashion to achromatic refractive lens doublets for visible light, it is possible to focus two x-ray energies to the same spot.

Simulated annealing in the design of broadband multilayers containing more than two materials

A new method of design for multilayer structures with broadband spectral responses is presented. A stochastic design approach is utilized, based upon a simulated (SA) annealing algorithm, which optimizes the multilayer structure for a particular set of criteria. In particular, we consider a mirror for which the requirement is for high reflectivity, over a broad wavelength range, in the soft x-ray region, as might be compatible with the output from a laser plasma source. The design algorithm is used to maximize a merit function for the structure by manipulating the ordering, the thickness and the material types of each of the constituent layers. The merit function may also be configured to include a number of other desirable properties for the high reflectivity mirror including broad angular response, polarization response and uniformity of reflectivity over a prescribed wavelength range.

Nanotubes and microtubules as quantum information carriers

In the foreseeable future silicon based electronics will reach limits in miniaturization and switching speeds, imposed by fundamental physical constraints. The quest for smaller gates and higher processing speeds with the attendant increase of chip functional density will reach the point where quantum effects dominate. Alternative strategies will then be required to overcome the limitations of silicon; among the most promising are those exploiting the properties of biological molecules, notably microtubules. These have the advantages associated with carbon chemistry, including the scope for constructing large highly complex macromolecular assemblies, and share the exciting electronic properties of semi- and superconductors. Biological systems have the potential to bypass the limiting effects of single particle quantum systems through the interactions of complex molecules, necessarily based on hydrocarbon polymers.

Mixed-proximity holographic mask technology for 50-nm VLSI by x-ray lithography

The development of mixed proximity and binary phase holographic x-ray masks for feature sizes of 50nm is continued for mask to wafer gaps of 50micrometers for printing into photoresist with 1nm x-rays. The maximum gap for binary holographic correction for image blurring on reconstruction is shown to be limited by the symmetry impressed by the binary phase encoding. The computation of the holograms is described. A hologram is calculated in patches limited in size by computational restrictions and procedures are described for superposition at the wafer of structures reconstructed from adjacent patches. The fabrication of binary masks is well suited to electron beam writing.