R-3 Repository :: Browsing by Author "Wilson, William L."

Browsing by Author "Wilson, William L."

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Amorphous Gd-C0 rf sputtered films with perpendicular magnetic anisotropy: effects of electrical dc bias on composition
(1975) Goldfarb, Ronald Barry; Wilson, William L.
Amorphous gadolinium-cobalt films with uniaxial magnetic anisotropy perpendicular to the film plane have been made by rf bias sputtering. Film composition has been controlled by selection of source target composition and by adjusting a negative dc bias voltage applied to the films during deposition. For bias voltages in the range studied, cobalt content increased by .25 percent per volt. Perpendicular anisotropy was observed for atomic fraction of cobalt in the range .75 to .85, and for bias voltage in the range -5 to -1 volts dc. Uniformity in composition, thickness, and magnetic properties were observed across the surface of the films.
An electron-beam controlled discharge laser o the C-->A transition of xenon fluorite
(1985) Stiegler, Harvey J.; Wilson, William L.; Tittel, Frank K.; Sauerbrey, R. A.
A XeF(C->A) laser utilizing an electron-beam controlled electric discharge for excitation was investigated. Studies were made of He, Ne, and Ar as buffer gases with various combinations of NF, F2, and Xe. The partial pressure of the various gas components was varied to find a mixture which would achieve optimum performance. Energy deposition by the discharge was confirmed by observing the intensity of fluorescence. Positive optical gain was achieved for a duration of 3 ns to 4 ns and a peak gain of > 1% cm was measured. Spectral narrowing and gain sufficient to overcome cavity losses were evidence of laser action. Output observed from the laser was on the order of 1 uJ/liter of active volume. Performance was limited by inability to rapidly deposit sufficient energy into the discharge. The possibility of a longterm absorption phenomenon related to the electric discharge may also have limited performance.
Automated Evaluation of Critical Features in VLSI Layouts Based on Photolithographic Simulations
(IEEE, 1997-11-01) Sengupta, Chaitali; Cavallaro, Joseph R.; Wilson, William L.; Tittel, Frank K.; Center for Multimedia Communication
In this paper, we address the problem of identifying and evaluating “critical features” in an integrated circuit (IC) layout. The “critical features” (e.g., nested elbows and open ends) are areas in the layout that are more prone to defects during photolithography. As feature sizes become smaller (sub-micron range) and as the chip area becomes larger, new process techniques (such as, using phase shifted masks for photolithography), are being used. Under these conditions, the only means to design compact circuits with good yield capabilities is to bring the design and process phases of IC manufacturing closer. This can be accomplished by integrating photolithography simulators with layout editors. However, evaluation of a large layout using a photolithography simulator is time consuming and often unnecessary. A much faster and efficient method would be to have a means of automatically identifying “critical features” in a layout and then evaluate the “critical features” using a photolithography simulator. Our technique has potential for use either to evaluate the limits of any new and nonconventional process technique in an early process definition phase or in a mask house, as a postprocessor to improve the printing capability of a given mask. This paper presents a CAD tool (an Integrated CAD Framework) which is built upon the layout editor, Magic, and the process simulator, Depict 3.0, that automatically identifies and evaluates “critical features”
Computer controlled intracavity second harmonic generation in a CW Dye Ring Laser
(1980) Marshall, Charles McAlister; Tittel, Frank K.; Wilson, William L.; Kim, Dae M.
The purpose of this research has been to develop a source of high power narrowline ultraviolet radiation suitable for spectroscopic applications. This was accomplished by using intracavity second harmonic generation in a computer controlled continuous wave dye ring laser. A DEC POP 11/3 minicomputer was used to control laser tuning elements and nonlinear crystal temperature to provide constant UV output powers of over 1 mW with a short term linewidth of + 5 MHz at the peak of the Rh6G gain curve. The computer system with a CAMAC interface provided control of laser calibration and scanning as well as data acquisition and storage over the wavelength range from 285 to 35 nm. The spectrometer development included the design-of an astigmatically compensated ring laser to provide optimal conversion of intracavity fundamental power to second harmonic UV output. Both Brewster cut and normal incidence crystals were analyzed to determine the most efficient insertion technique. The Brewster cut crystal was found to provide the highest output powers with the fewest complications. The system development also included techniques for long range temperature tuning of the nonlinear crystal to provide constant UV output over continuous frequency intervals of 32 GHz. The performance of the spectrometer was evaluated through studying the absorption spectra of SO around 3 nm. A simultaneous visible output at 6 nm was used to provide a reference spectra of the well documented fluorescence of I2.
Design, construction, and operation of a submillimeter waveguide laser system and Stark modulator
(1977) Jenkins, James Alan; Wilson, William L.
A submillimeter laser system, consisting of a methanol waveguide laser and its CO^ laser pump, was built. The CQ laser used ZnSe optics and was diffraction grating tuned, making available over 8 lines in the 9.6um and 1.6um bands. The typical output power level was 12W. This CO laser provided the pump radiation for a waveguide laser which used a precision-bored Cu tube to (l) confine the discharge plasma and the pump radiation and (2) serve as a waveguide for the submillimeter radiation field. Cu mirrors placed at the ends of the tube defined the laser cavity. A coupling hole in each mirror allowed 1.6um CO radiation to enter the cavity at one end and 118.8um radiation, generated by a rotational transition in methanol, to leave at the other end. The 3mW of submillimeter light generated was used to study the effects of Stark modulating methanol in a cell through which the light was passed. A 2% modulation index was observed for a Stark cell pressure of 3umHg and a Stark electric field of amplitude 1V/cm and frequency 2Hz. It was found that the Stark effect was linear and that an increase in electric field led to a decrease in submillimeter wave absorption in the cell.
Electrical characterization of thin-film lithium niobate
(1985) Fabiny, Larry; Rabson, Thomas A.; Wilson, William L.; Rau, Carl
The electrooptic properties of a thin film of lithium niobate were studied. The film was deposited on an n-type silicon substrate by RF sputtering. The short circuit photocurrent was measured as a function of time, and the voltage dependence of current and capacitance under light and dark conditions was measured. Photocurrents up to 16.1 pA were obtained with a light intensity of .5 mW/cm . With one exception, all photocurrent flowed from the A1 contact to the Si substrate. The current was linear for | Vapp | < .5 volts. At higher voltages, a thermal current was generated. It was found that the current required several minutes to reach its steady state value when the applied voltage was changed. The film was shown to possess some of the ferroelectric properties present in bulk crystals. Although no crystallographic studies have been done, the electrical measurements indicate that the LN film is polycrystalline.
Enhanced Microlithography Using Combined Phase Shifting and Off-axis Illumination
(Japanese Journal of Applied Physics, 1995-12-01) Erdelyi, Miklos; Bor, Zsolt; Cavallaro, Joseph R.; Szabo, Gabor; Wilson, William L.; Sengupta, Chaitali; Smayling, Michael C.; Tittel, Frank K.; Center for Multimedia Communication
Off-axis illumination is a promising optical microlithography technique which can be used to improve the image quality of line-space patterns. With this method the image is produced by the zero and first order diffracted beams. Due to the intensity difference between these two order diffracted beams the contrast of the image cannot be unity. This paper demonstrates the optical enhancement that can be achieved by a combination of interferometric phase shifting and off-axis illumination. In such an arrangement the mask is illuminated symmetrically from both the front and back sides, and not two but in fact four–(two zero and two first)–order beams produce the image. We show experimentally that the contrast of the image can be improved if the phase difference between the reflected and transmitted beams is π, and the intensity of the transmitted beam is about 13% of the reflected beam. This improved quality image with feature sizes of 0.4 µm was recorded in a photoresist using an Ar+ ion laser operating at 457.9 nm.
Enhanced VLSI Manufacturability Using an Integrated CAD Framework
(SME Press, 1994-01-01) Fossati, Humberto M.; Tittel, Frank K.; Wilson, William L.; Cavallaro, Joseph R.; Center for Multimedia Communication
Continued improvements in VLSI performance, circuit density and production costs are possible, in part, do to significant advances in lithography. As feature sizes get smaller, design houses are faced with either improving the resolution of their optical lithography lines, or step-up to the cost of newer x-ray based machines. The work at Rice University proposes to integrate design and process-specific CAD tools to provide further use of optical lithography equipment, while reducing feature sizes to improve manufacturability. By integrating photolithography simulators to layout editors, and by providing expert information on the simulated optical and physical resolution of the feature to the designer, compact and smaller circuits can be designated, which are governed by local design rules. This work is complemented by the development of a novel phase shifting technique at Rice based on interferometry which allows for the manufacture of features with high contrast and reduced feature size.
Growth of Large-Sized 2D Ultrathin SnSe Crystals with In-Plane Ferroelectricity
(Wiley, 2023) Chiu, Ming-Hui; Ji, Xiang; Zhang, Tianyi; Mao, Nannan; Luo, Yue; Shi, Chuqiao; Zheng, Xudong; Liu, Hongwei; Han, Yimo; Wilson, William L.; Luo, Zhengtang; Tung, Vincent; Kong, Jing
Tin (II) selenide (SnSe) is an emerging 2D material with many intriguing properties, such as record-high thermoelectric figure of merit (ZT), purely in-plane ferroelectricity, and excellent nonlinear optical properties. To explore these functional properties and related applications, a crucial step is to develop controllable routes to synthesize large-area, ultrathin, and high-quality SnSe crystals. Physical vapor deposition (PVD) constitutes a reliable method to synthesize 2D SnSe, however, effects of various growth parameters have not yet been systematically investigated, and current PVD-synthesized flakes are often thick (>10 nm) with small lateral sizes (<10 µm). In this work, high-quality 2D SnSe crystals are synthesized via low-pressure PVD, which display in-plane ferroelectric domains observed by piezoresponse force microscopy and polarization-dependent reflection spectroscopy. Detailed studies regarding the roles of various parameters are further carried out, including substrate pre-annealing, growth duration, temperature, and pressure, which enable to rationally optimize the growth and obtain 2D SnSe crystals with lateral sizes up to ≈23.0 µm and thicknesses down to ≈2.0 nm (3–4 layers). This work paves the way for the controlled growth of large-area 2D SnSe, facilitating the future exploration of many interesting multiferroic properties and applications with atomic thickness.
An Integrated CAD Framework Linking VLSI Layout Editors and Process Simulators
(SPIE, 1996-03-01) Sengupta, Chaitali; Erdelyi, Miklos; Bor, Zsolt; Cavallaro, Joseph R.; Smayling, Michael C.; Szabo, Gabor; Tittel, Frank K.; Wilson, William L.; Center for Multimedia Communication
As feature sizes in VLSI circuits extend into the far sub-micron range, new process techniques, such as using phase shifting masks for photolithography, will be needed. Under these conditions, the only means for the circuit designer to design compact and efficient circuits with good yield capabilities is to be able to see t he effect of different design approaches on manufactured silicon, instead of solely relying on conservative general design rules. The Integrated CAD Framework accomplishes this by providing a link between a layout editor (Magic), advanced photolithographic techniques such as phase shifted masks, and a process simulator (Depict). This paper discusses some applications of this tool. A non-conventional process technique involving interferometric phase shifting and off-axis illumination has been evaluated using the tool. Also, a feature of the CAD Framework which allows representation of a phase shifted mask, together with its layout analysis capability has been used to compact a piece of layout by inserting phase shifted elements into it.
Interferometric Phase Shift Technique for High Resolution Deep UV Microlithography
(SPIE, 1994-09-01) Tittel, Frank K.; Cavallaro, Joseph R.; Kido, Motoi; Smayling, Michael C.; Szabo, Gabor; Wilson, William L.; Center for Multimedia Communication
A new phase shifting technique based on interferometry has been developed which is especially suited for deep-UV microlithography. Using only a single layer chromium mask, with no additional phase shift elements, significant resolution and contrast enhancement over conventional transmission lithography can be achieved. Both computer simulations, as well as experiments using a CCD camera and UV photoresist confirm the capabilities of this new approach. Using a relatively simple experimental setup and an illumination wavelength of 355 nm, lines with feature sizes as find as 0.3 um were achieved.
Investigation of GaAs modulators at 10.6 and 337 microns
(1977) Epton, Paul Joel; Wilson, William L.
An attempt was made to electrooptically modulate the 1.6 |i,m light from a COj laser. The modulator was a 13 m thick epitaxial layer of GaAs grown on a degenerately doped GaAs substrate. The modulator was situated in a microwave cavity and DC biased into Limited Space-Charge Accumulation (LSA) mode oscillation. The electric field for the electrooptic effect was provided by the DC bias pulse and the microwave oscillation. Bias pulse heating of the GaAs substantially changed its infrared transmission and prevented observation of any electrooptic modulation that occurred. A study was also carried out of wide bandwidth amplitude modulation of the 337 p,m light from an HCN laser. The modulator was a 1 thick epitaxial layer of GaAs grown on an insulating GaAs substrate. The doping density of the epilayer was ND = 4.61x1 cm and NA 2.45x1^3 cm. The modulator was immersed in liquid helium, freezing out the free carriers on the donor impurities. Pulsed microwave radiation was used to impact ionize the impurities for modulation, and the transmission of the GaAs increased as the neutral donors were ionized. A peak in the modulation index of 29% was obtained at 2 mW of absorbed microwave power for the GaAs situated in a terminated waveguide. A 1% modulation index with better coupling of the 337 pm light and poorer microwave coupling was obtained for a microwave cavity configuration. From a measurement limited by the detector bandwidth, the modulator risetime was found to be less than 15 ns.
Kinetics and laser studies of electron beam excited Xe¿Br*
(1982) Williams, Richard Allen (b. 1936); Wilson, William L.; Tittel, Frank K.; Glass, Graham P.
The goal of this work was to determine the kinetic processes involved in the formation and removal of the triatomic excimer XeBr , and to study the potential of this molecule to be used in a high power, narrow pulse width laser system. Initial investigation involved the study of the fluorésence emission characteristics of XeBr, centered at 44 nm for various electron beam pumped mixtures of argon, xenon and several different bromine donors. From these experiments, formation and quenching processes were determined. Three-body collisional quenching of XeBr was identified as the primary formation mechanism for the triatomic species. Quenching rates for Xe.Br and XeBr were measured; the XeBr radiative lifetime was determined to be 245 + 3 ns. Laser experiments were performed after the kinetics of the molecule were determined. Many different parameters were varied, including gas composition and cavity characteristics. Although no definite evidence of laser action was seen, some alignment sensitive effects were noted.
Laser ionization studies of supersonic semiconductor clusters
(1985) Liu, Yuan; Tittel, Frank K.; Curl, Robert F.; Wilson, William L.
Cold silicon and germanium clusters have been produced in a supersonic molecular beam by laser vaporization of a silicon or germanium rod. The cluster beam is characterized by laser ionization studies and time of flight mass analysis. Both large Si and Ge clusters are found to have similar fragmentation patterns. They fisson into stable subunits rather than lose atoms sequentially. Two-color stepwise ionization experiments reveal that large Si and Ge clusters have an intermediate state with a lifetime of approximately 1 ns, thereby establishing the feasibility of resonant two photon ionization (R2PI) spectroscopy on these clusters.
Measurement and control of deposition temperature of Gd-Co rf sputtered films
(1977) Chen, Che-Tsung; Wilson, William L.
A vacuum evaporated Chromel-Constantan Thin Film Thermocouple (TPTC) is developed and used to measure the deposition temperature of rf sputtered amorphous gadolinium-cobalt films. Deposition temperature can be varied with the type and the amount of thermal backing which affixes the substrates to the substrate holder. By controlling the temperature of cooling water running through the substrate holder control of the deposition temperature can be achieved to some degree. Results indicate that under normal deposition conditions the temperature on the substrate surface is around 1 °C. Results also indicate that gallium has better heat conduction and less temperature scatter than silicone grease when the same deposition parameters are maintained. Magnetic properties such as saturation magnetization, stripe period, anisotropy constant, exchange stiffness, and wall energy are investigated near the thermocouple junction where the deposition temperature is definitely known. A few Gd-Co-Mo films are also prepared during this research work and their magnetic properties are illustrated.
Mixed P and N type conduction in RF sputtered Hg1-xCdXTe thin films
(1983) Liou, Tain-I; Wilson, William L.; Estle, Thomas L.; Brotzen, Franz R.
RF sputtered HgjCdTe thin films were deposited on <111> silicon substrates. Different values of negative bias were applied to the film during growth. X-ray diffraction was used to investigate the crystal structure of the films. Van Der Pauw and Hall measurements were used respectively to obtain resistivities and carrier concentrations of films at room temperature (3°K). Carrier concentration variation with temperature was also measured. A series of films were deposited with different substrate temperatures in order to investigate the effect on crystal structure and electrical properties. When substrate bias was increased, it was found that the film thickness decreased» the crystallographic order of the films became worse, and the room temperature resistivity increased. Measurement of carrier concentration versus temperature between 77°K and 3°K showed the films to be p type when the temperature was around 77°E and n type at high temperatures. It was also found that when the substrate temperature was increased during deposition, the crystal structure improved somewhat. Room temperature resistivity decreased, and the carrier type gradually changed from n type to p type as the deposition temperature was increased. A theoretical model using both a non-degenerate approximation as well as taking into account degenerate considerations was developed to compare with the experimental data.
A New Interferometric Phase-Shifting Technique for Sub-half-micron Laser Microlithography
(SPIE, 1995-02-01) Erdelyi, Miklos; Sengupta, Chaitali; Bor, Zsolt; Cavallaro, Joseph R.; Kido, Motoi; Smayling, Michael C.; Tittel, Frank K.; Wilson, William L.; Szabo, Gabor; Center for Multimedia Communication
This paper reports recent progress in achieving sub-half-micron feature sizes with UV laser illumination based on a novel interferometric phase shifting (IPS) technique. In the IPS arrangement, the intensity and amount of phase shift of the shifted beam can be controlled continuously and independently using the same mask. Consequently the method can be considered as a convenient general testbed for practical phase shifting concepts such as strong, weak and attenuated phase shifting. Recent measurements of the lithographic performance of a new concept are reported where phase shifting is combined with off-axis illumination. Experimental as well as simulation data are used to demonstrate this new method. A lithography simulator, Depict from Technology Modeling Associates, Inc. and a related Integrated CAD Framework which is being developed at Rice University was used to simulate and evaluate the performance of the IPS scheme.
A New Phase Shifting Method for High Resolution Microlithography
(SME Press, 1994-01-01) Kido, Motoi; Cavallaro, Joseph R.; Szabo, Gabor; Wilson, William L.; Tittel, Frank K.; Center for Multimedia Communication
One of the most promising lithographic technique for the future designs of DRAMs is the phase-shifting mask technique. Conventional phase shifting-masks, however, are difficult to fabricate as they require regions of different optical thickness. We present a new phase shifting technique that does not use any phase shifting materials. A special interferometer and a mask that has both transmitting areas and reflective areas accomplish the required phase-shift at the image plane. Using this technique we have demonstrated phase shifting effects using a CCD camera. We also present the results of a computer simulation for the critical resolution of this new method in comparison with the conventional phase shifting approach.
Optimization of ZeF(C-->A) excimer laser performance
(1985) Zhu, Yunping; Tittel, Frank K.; Wilson, William L.; Dunning, F. Barry
The goal of this work has been the optimization of the XeF(C-A) laser performance and the study of the kinetic processes involved in the formation and removal of the diatomic excimer XeF(C). Significantly improved XeF(C-»A) laser performance has been achieved using e-beam excitation of a multi-component gas mixture that has permitted synthesis of near optimum medium properties for which XeF(C) is produced efficiently while transient absorptions are minimized. This approach has yielded a laser pulse energy density and intrinsic efficiency of 3J/litre and 2%, respectively, values that are comparable to those of B-»X rare gas-halide excimer lasers. Furthermore, simultaneous laser action of XeF(B-»X) at 351 nm and XeF(C~>A) at 475±1nm was realized.
Phase holographic studies of the conductivity of Fe-doped LiNbO¿
(1979) Bienvenu, Michael Patrick; Rabson, Thomas A.; Kim, Dae M.; Tittel, Frank K.; Wilson, William L.
The writing process involved in volume phase holographic storage in LiNbO3 has been extensively studied, but no quantitative work exists concerning the decay of holograms. Since direct electrical conductivity measurements are difficult, if not impossible, decay rate measurements can provide an accurate figure for the material's conductivity. A coupled-wave theory developed by Kogelnik is presented describing diffraction by a phase grating with unslated fringes in a lossy medium. Next, a dynamic theory of hologram grating developed by Kim is presented. Using classical E-M theory, the hologram decay is predicted to be a sum of exponentials. Experimental data on writing and decay processes is presented which agree well with Kim's theoretical predictions, but which differ markedly from the expected decay behaviour. An excellent fit to the experimental decay curves was obtained by assuming a time dependent conductivity of the form a(t) = CJQ + e. The data show that T, the time constant involved, varies with the iron doping level in the crystal. A model is proposed to explain the phenomenon, involving metastable trapping centers releasing electrons into the conduction band.

Browsing by Author "Wilson, William L."

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