Karl W. Beeson

Chemical vapor deposition of cobalt silicide

We have deposited polycrystalline cobalt silicide films by chemical vapor deposition using Co2(CO)8 or HCo(CO)4 as the Co source and SiH4 or Si2H6 as the Si source. The Co:Si ratio of the films is controlled by changing the deposition temperature, and CoSi2 stoichiometry is obtained at 300 °C using SiH4 or at 225 °C when Si2H6 is the Si precursor. Carbon or oxygen contamination of the films is <0.5 at. % at deposition temperatures above 200 °C. Resistivities of films deposited near CoSi2 stoichiometry are typically 200 μΩ cm and drop to 40 μΩ cm upon annealing at 900 °C.

Photochemical laser writing of polymeric optical waveguides

We report a rapid one‐step laser writing process for forming optical channel waveguides by photochemically lowering the index of refraction in selected areas of thin, highly photosensitive polymeric flims. We have demonstrated the concept by forming single‐ and multimode waveguides in films composed of poly(methylmethacrylate) containing (4‐N‐N‐dimethylaminophenyl)‐N‐phenyl nitrone. The effects of ultraviolet fluence on the refractive index of the films and on channel lightwave confinement were examined. Low loss (1.5 dB/cm) channels were produced with ultraviolet fluences as low as 20 mJ/cm2.

61.5: LED-Based Light-Recycling Light Sources for Projection Displays

LED-based light sources utilizing novel light-recycling cavities have been developed that have small output etendue. A portion of the light emitted by the LED source is recycled back to the LEDs to enhance both the average brightness of the source and the brightness of the cavity output. Experimentally, we have achieved brightness enhancement factors of approximately 1.3x–2.0x.

CO2 laser‐induced chemical vapor deposition of titanium silicide films

We have developed a CO2 laser‐induced chemical vapor deposition (CVD) process to deposit films of titanium silicide from a gaseous mixture of SiH4 and TiCl4. Such films are suitable for gate electrodes, interconnects, and contacts on present and future generations of very large scale integrated circuits. Films deposited at a 400 °C substrate temperature are amorphous and have a resistivity of 300 μΩ cm. Annealing at 800 °C converts the films to polycrystalline TiSi2 with a resistivity of 20 μΩ cm. The initial film composition can be varied by changing the SiH4/TiCl4 gas ratio. The CO2 laser induces thermal chemical reactions in the CVD reactor. Observed gas phase reaction products are those predicted by thermodynamics.

Excimer laser‐induced chemical vapor deposition of titanium silicide

A pulsed ArF excimer laser has been used to deposit thin conductive films of titanium silicide on silicon and silicon oxide substrates. The films are deposited from a gas mixture of titanium tetrachloride and silane by initiating photochemical reactions near the heated substrate. The resistivity, composition, crystal structure, and morphology of the films vary as a function of gas composition and substrate temperature. Films deposited at 400 °C, with SiH4/TiCl4 mole ratios of ∼2, have resistivities of 300 μΩ cm, which drop to 20–30 μΩ cm on annealing at 650–700 °C. At higher deposition temperatures (450–550 °C) the films have resistivities of ∼110 μΩ cm and show similar annealing behavior. The as‐deposited films are a mixture of amorphous and a metastable Ti‐Si crystalline phase. On annealing they convert to polycrystalline TiSi2. Films deposited at 400–450 °C are smooth and show conformal step coverage. The film roughness increases at higher deposition temperatures.

Interstitial Photodynamic Therapy-A Focused Review.

Multiple clinical studies have shown that interstitial photodynamic therapy (I-PDT) is a promising modality in the treatment of locally-advanced cancerous tumors. However, the utilization of I-PDT has been limited to several centers. The objective of this focused review is to highlight the different approaches employed to administer I-PDT with photosensitizers that are either approved or in clinical studies for the treatment of prostate cancer, pancreatic cancer, head and neck cancer, and brain cancer. Our review suggests that I-PDT is a promising treatment in patients with large-volume or thick tumors. Image-based treatment planning and real-time dosimetry are required to optimize and further advance the utilization of I-PDT. In addition, pre- and post-imaging using computed tomography (CT) with contrast may be utilized to assess the response.

Chemical Vapor Deposition of Molybdenum Silicide

A cold-wall reactor has been used to deposit molybdenum silicide films from a mixture of MoF/sub 6/ and SiH/sub 4/. The composition of the resulting films can be controlled by the deposition temperature, and MoSi/sub 2/ stoichiometry is obtained with a substrate temperature of 200/sup 0/C. The film composition is independent of SiH/sub 4//MoF/sub 6/ reactant gas ratios in the range of 1-10. The as-deposited films are generally amorphous as determined by x-ray analysis. Annealing at 950/sup 0/C in argon converts the films to tetragonal polycrystalline MoSi/sub 2/.

Laser etching of LiNbO3 in a Cl2 atmosphere

Single‐crystal LiNbO3 is etched in an atmosphere of 500‐Torr Cl2 by focusing a 257‐nm, frequency‐doubled CW argon‐ion laser beam onto the surface. The observed laser intensity threshold for etching is consistent with a process involving surface melting of the crystal. A single laser scan forms a shallow depression with marked ripples transverse to the direction of laser polarization, while repeated scans give a groove with a nearly triangular cross section. During laser etching, reacted material is redeposited on the crystal surface. This material is subsequently analyzed for chemical composition. The LiNbO3 surface is partially depleted of Li and O both at the etched grooves and at significant distances away from the grooves. Studies at low light intensities suggest that photochemical generation of gas‐phase Cl radicals is responsible for the O depletion and part of the Li depletion. In addition, a dark reaction between Cl2 and LiNbO3 depletes only Li.

Fast photolytic laser writing of gold lines on a prenucleated substrate

Laser written gold lines with resistivities as low as 4.5 μΩ cm and writing speeds up to 2.5 mm/s have been achieved by photolytic decomposition of gold metallopolymer thin films on alumina substrates prenucleated with a very thin (∼20 A) nonconducting layer of sputtered gold. Laser writing is done at 257 nm with a frequency‐doubled Ar+ laser and is followed by a subsequent annealing step at 250 °C for 30–200 min to produce conducting lines.

Viewing-angle-enhancement system for LCDs

An enhanced liquid crystal display (LCD) design with minimal contrast ratio or color shift with increased viewing angle and with improved performance in high brightness environments has been developed. Contrast ratios of greater than 50 :1 have been demonstrated at ±60° (vertical and horizontal) on an active matrix LCD. The operating principles of the key components of this new design will be described.