Donald Lawrence White

Elastic Wave Propagation in Piezoelectric Semiconductors

A plane elastic wave propagating in a piezoelectric crystal may be accompanied by longitudinal electric fields which provide an additional elastic stiffness. When the crystal is also semiconducting, these fields produce currents and space charge resulting in acoustic dispersion and loss. A linear theory of this effect is developed, taking into account drift, diffusion, and trapping of carriers for both extrinsic and intrinsic semiconductors. Conductivity modulation sets an upper limit on strain amplitude for a linear theory. The directional characteristics and the magnitude of the effects are illustrated for CdS and GaAs. The Appendix treats the interaction of an arbitrary acoustic plane wave with the electromagnetic fields in a piezoelectric crystal (based on a treatment by Kyame [J. J. Kyame, J. Acoust. Soc. Am. 21, 159 (1949); 26, 990 (1954).]) and further shows explicitly that only the effects of longitudinal electric fields need be considered.

New absorptive mode reflective liquid‐crystal display device

A new liquid‐crystal alphanumeric display device is described. The device is of the guest‐host type and involves the orientational change of a pleochroic dye (guest) in a cholesteric liquid‐crystal mixure (host) by the application of an external electric field. The cholesteric nature of the host permits the operation of the device in the reflective mode with excellent brightness since no external polarizers are required. Good contrast ratios have been obtained for new pleochroic dyes (guests) which have higher optical order parameters than those previously employed. The theory of light absorption in a cholesteric liquid crystal having both homogeneous and homeotropic boundary conditions is developed and aspects of contrast ratio and its relation to human perception are described.

Acousto‐optic light deflectors using optical activity in paratellurite

Light deflector designs which use the anomalously low shear wave acoustic velocity and high acousto‐optic figure of merit in single‐crystal paratellurite, first proposed by Uchida and Ohmachi, have been made practical by exploiting this materials birefringence to circularly polarized light. Dixons equations for Bragg interaction in birefringent materials are found to be equally applicable to optically active materials when linearly polarized propagation modes are replaced by circularly polarized modes. For specific ratios of sound‐to‐light wavelengths, there is a substantially expanded angular range over which Bragg interaction can take place. One effect of this increased range is to permit longer interaction lengths between light and sound, which greatly reduces the acoustic power required. In paratellurite, for visible light, this expanded range occurs for sound frequencies below 100 MHz, in the region of acceptable acoustic loss. Examples of possible designs include a deflector only 3×5×7 mm having a...

Coded multiple exposure holograms.

Experiments have been performed in which 1000 holograms have been superimposed one upon the other in the same area of photographic emulsion. Each hologram was formed with a uniquely coded reference beam allowing reconstruction of only one of the superimposed holograms while the unaddressed holograms contribute incoherent noise. Signal-to-noise ratios are calculated and measured as a function of the number of superimposed exposures. For the 1000-exposure hologram, the observed signal-to-noise ratio for any one of the individual holograms was 10 dB.

Diffraction-limited soft-x-ray projection imaging using a laser plasma source

Projection imaging of 0.1-microm lines and spaces is demonstrated with a Mo/Si multilayer coated Schwarzschild objective and 14-nm illumination from a laser plasma source. This structure has been etched into a silicon wafer by using a trilevel resist and reactive ion etching. Low-contrast modulation at 0.05-microm lines and spaces is observed in polymethylmethacrylate.

Synchrotron radiation sources and condensers for projection x-ray lithography

The design requirements for a compact electron storage ring that could be used as a soft-x-ray source for projection lithography are discussed. The design concepts of the x-ray optics that are required for collecting and conditioning the radiation in divergence, uniformity, and direction to illuminate the mask correctly and the particular x-ray projection camera used are discussed. Preliminary designs for an entire soft-x-ray projection lithography system that uses an electron storage ring as a soft-x-ray source are presented. It is shown that, by combining the existing technology of storage rings with large collection angle condensers, a powerful and reliable source of 130-A photons for production line projection x-ray lithography is possible.

Use of trilevel resists for high-resolution soft-x-ray projection lithography

A projection optical system with 20:1 reduction has been used with radiation at ∼36 nm to evaluate resists for use in soft‐x‐ray projection lithography. The high absorption of soft x rays by carbon‐based polymers requires that an imaging resist layer be very thin. The sensitivities and contrasts of several such resists are reported. By incorporating a thin imaging layer into a trilayer resist scheme, we have exposed, developed, and transferred features as small as 0.2 μm into silicon.

Diffraction‐limited soft x‐ray projection lithography with a laser plasma source

A laser plasma source of extreme ultraviolet and soft x‐ray radiation has been used to print diffraction‐limited features using soft x‐ray projection lithography. A spherical condenser optic, a Si/Ge transmissive mask and a Mo/Si multilayer‐coated Schwarzschild objective having 20:1 reduction ratio were employed to pattern selected single‐layer and trilevel resists. At a numerical aperture of 0.12, a 0.1‐μm line and space pattern is clearly delineated and weak modulation is observed for the analogous 0.05‐μm pattern.

Soft-x-ray projection lithography : printing of 0.2-μm features using a 20 : 1 reduction

We demonstrate nearly diffraction-limited printing of 0.2-microm features, using soft x rays of approximately 36-nm wavelength. An open-stencil transmission mask with minimum features of 4 microm was imaged by a twentyfold-reduction Schwarzschild-type objective onto silicon wafers coated with various e-beam resists. Implications for soft-x-ray projection lithography are discussed.

Reflective mask technologies and imaging results in soft x‐ray projection lithography

In this work we investigate and compare a variety of technologies for patterning high resolution Mo/Si multilayer reflective x‐ray masks for use at wavelengths near 13 nm. The patterning methods investigated include: absorbing layers deposited on top of multilayer reflectors, reflective coating removal by reactive ion etching and ion damage of multilayer regions to form a planar mask structure. Large area samples were prepared by each of the above methods and reflectivity measurements made to determine the expected mask contrast. The reflectivity data are compared with simulation for the absorber overlayer and etched multilayer measurements. Our results indicate that reflectivity changes between 5 and 300 were effected. Fine patterning tests show that mask features as fine as 0.1 μm can be achieved in each technology. The advantages, process complexity, and limits of each method are discussed. We also report the first use of an x‐ray reflectance mask to print 0.1 μm features in resist. The developed resis...