W. D. Brown

Femtosecond laser-induced periodic structure writing on diamond crystals and microclusters

Three-dimensional (3D), periodic nanowriting on diamond clusters is reported in this letter. Concentric circular rings were observed on diamond microclusters, nucleated near the periphery of a laser-irradiated region, when chemical-vapor deposited diamond was processed in air, with laser pulses of 380 fs duration and at a wavelength of 248 nm. Periodic ripples also have been observed on single-crystal and polycrystalline diamond surfaces. Further, it is experimentally shown that the periodicity of these corrugated two-dimensional and 3D structures is shorter than that of the laser wavelength used (248 nm for the excimer fs laser and 825 nm for the Ti–sapphire fs laser).

Interaction of aluminum with hydrogenated amorphous silicon at low temperatures

Annealing effects on aluminum/hydrogenated amorphous silicon (a‐Si:H) contacts in the temperature range from 100 to 300 °C were studied. Al was evaporated on device‐quality, phosphorus‐doped (n+) a‐Si:H films deposited in a UHV plasma‐enhanced chemical‐ vapor‐deposition system. Both electrical measurements and surface morphological analyses were performed to characterize the interaction. The transmission line model technique was used to measure sheet resistance and contact resistivity. For samples where Al covered the entire a‐Si:H surface during annealing, sheet resistance and contact resistivity were found to decrease monotonically with annealing temperature; whereas, samples annealed after patterning of the Al pads exhibited a minimum in sheet resistance and contact resistivity at temperatures between 150 and 200 °C. Optical and scanning electron microscopy, surface profilometry, and Raman spectroscopy were used to study the surface morphology. Interaction of Al with a‐Si:H was observed to initiate at ...

A review of techniques for polishing and planarizing chemically vapor-deposited (CVD) diamond films and substrates

Abstract State-of-the-art polycrystalline chemically vapor-deposited (CVD) diamond films and substrates have rough surfaces and non-uniform thicknesses which can adversely affect their application. Polishing and planarization can be used to remedy these drawbacks. In recent years, many polishing and planarization techniques have been reported, each having technological advantages and disadvantages. A specific polishing technique should be chosen based on these advantages and disadvantages, depending on the particular CVD diamond film application. Polishing and planarization techniques are reviewed in this paper. Parameters considered include polishing rate, surface finish requirements, and economic impact. To aid in the understanding and evaluation of diamond polishing techniques for applications, polishing mechanisms are also reviewed. Finally, CVD diamond applications and their surface roughness requirements are presented.

Aluminum‐induced crystallization and counter‐doping of phosphorous‐doped hydrogenated amorphous silicon at low temperatures

Aluminum metal‐induced crystallization and doping of hydrogenated amorphous silicon (a‐Si:H) have been investigated. Aluminum was evaporated onto device quality a‐Si:H films deposited in an ultrahigh vacuum plasma‐enhanced chemical vapor deposition system. These Al/a‐Si:H structures were annealed in the 100–300 °C range. Electrical, surface morphological, and chemical characterizations of the material were performed. The transmission line model technique was used for electrical characterization. Raman spectroscopy showed that crystallization of the interacted a‐Si:H film underneath Al pads initiates at temperatures as low as 180 °C. X‐ray diffraction analysis showed very good polycrystallinity of the interacted film. Electrical measurement, Hall measurement and x‐ray photoelectron spectroscopy analysis results revealed that a‐Si:H film in contact with Al becomes heavily doped by Al during crystallization as a result of annealing at relatively low temperatures.

A comparison of mechanical lapping versus chemical-assisted mechanical polishing and planarization of chemical vapor deposited (CVD) diamond

Abstract Polishing and planarization of CVD diamond substrates are essential steps in the processing of synthetic diamond for applications in the semiconductor industry. Using the methods of mechanical lapping and chemical-assisted mechanical polishing (CAMP), CVD diamond samples were polished against a cast-iron scaife and an alumina plate, respectively, using the same pressure on the samples. A diamond slurry was used in the mechanical lapping process, and a heated liquid chemical was used in a patented chemical-assisted mechanical polishing and planarization (CAMPP) process. The diamond samples were analyzed at several time intervals during the lapping and polishing processes, and during a combination of the two processes in which mechanical lapping preceded CAMPP. The polishing rate and surface characteristics of the diamond samples were the primary analytical measurements made, and the data were used to compare the relative lapping/polishing efficiencies of the two processes in an effort to develop an optimized process for producing highly polished CVD diamond substrates.

Correlation of stress behavior with hydrogen-related impurities in plasma-enhanced chemical vapor deposited silicon dioxide films

The presence of undesirable hydrogen-related impurities and the resulting stress instability in chemical vapor deposited silicon dioxide films are important issues. In this work, the bonding nature and stress behavior of relatively low-temperature deposited silicon dioxide films deposited at high rates were investigated. Films were deposited at 1000 A/min and at a substrate temperature in the 250–350 °C range. A considerable change in stress was observed in these films upon annealing in the 250–400 °C temperature range. Both as-deposited and annealed films were then stored in a cleanroom environment for long periods of time, and their stress was monitored intermittently. In parallel, Fourier transform infrared studies were performed on an identical set of as-deposited and annealed films to investigate changes in the bonding nature of the films during aging. Thus, film stress and their bonding nature were studied concurrently over an extended period of time. Si–H and silanol (Si–OH) were identified as impu...

THERMAL DIFFUSIVITY MEASUREMENT OF SOLID MATERIALS BY THE PULSED PHOTOTHERMAL DISPLACEMENT TECHNIQUE

A simple, noncontact technique for the measurement of thermal diffusivity of solids is experimentally demonstrated. The technique is based on the photothermal displacement effect. Excellent agreement between the quasistatic theory of photothermal displacement and the experiment has been obtained. The technique has been demonstrated by measuring the thermal diffusivities of GaAs and InGaAs/AlGaAs multiple quantum wells.

Comparison of infrared, Raman, photoluminescence, and x-ray photoelectron spectroscopy for characterizing arc-jet-deposited diamond films

Impurities and growth-related defect structures are mainly responsible for low thermal conductivity of chemical vapor deposited diamond films. Different quality arc-jet-deposited, free-standing diamond samples were obtained from industry. Fourier transform infrared (FTIR), Raman, and x-ray photoelectron spectroscopy (XPS) were used to determine the quality of these samples. The nondiamond carbon was estimated from the 1560 cm−1 broad peak intensity, the CHx integrated peak absorbance, and the C1s plasmon loss features for Raman, FTIR, and XPS studies, respectively. The diamond quality was also determined from the Raman diamond peak full width at half maximum (FWHM) and XPS valence band spectra. It was observed that the higher the hydrogen content (determined by FTIR), the darker the color of the film, the larger the nondiamond 1560 cm−1 peak intensity, and the larger the FWHM of the Raman diamond peak at 1332 cm−1. Negligible difference in the C1s diamond bulk plasmon loss peak was observed for films of w...

Post-deposition processing of low temperature PECVD silicon dioxide films for enhanced stress stability

Abstract High rate plasma-enhanced chemical vapor deposited (PECVD) silicon dioxide films are attractive for multichip module (MCM) applications, but the incorporation of various hydrogen-related impurities in these films and the resulting stress instabilities make their properties less than desirable. Annealing of such films was performed in different ambients at temperatures significantly below the oxide densification temperature. The changes in the bonding nature and stress of these films, as a result of annealing, and during aging were studied. A considerable shift in the Si–O characteristic peaks and a decrease in the full width at half maxima (FWHM) of the Si–O stretching peak were observed for films annealed in nitrogen or a steam-nitrogen ambient at atmospheric pressure. During subsequent aging, these films showed negligible change in these parameters indicating their stability. Whereas, the films which were annealed in the chamber following deposition without breaking vacuum did not exhibit any appreciable change in Si–O peak position and FWHM during annealing but a very large change in these parameters during subsequent aging indicating their worst stability. Similar results were obtained from a stress stability study on these films. The results of this study suggest that moisture, which diffuses into the film during aging and/or annealing reacts with strained Si–O bonds and forms silanol (Si–OH). During annealing, the silanol reacts to reconstruct Si–O bonds and releases water as a by-product, thus the reason for the improvement in film quality is that the strain of the newly-formed Si–O bonds is much less than the strain of the original Si–O bonds.

RESIDUAL STRESS BEHAVIOR OF THIN PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITED SILICON DIOXIDE FILMS AS A FUNCTION OF STORAGE TIME

Residual stress in thin silicon dioxide films has been studied as a function of storage time. Films of varying microstructure and impurity content were deposited by plasma-enhanced chemical vapor deposition. Initially, all the films exhibited compressive stress, the magnitude of which was found to increase rapidly with time for the first few hours after deposition. For all the deposited thin films, this increasing compressive stress eventually saturates and then begins to decrease with time. The time at which the transition occurs depends on film thickness and quality, whereas, for relatively thicker films deposited under identical conditions, a saturation in compressive stress after long aging time was observed. No existing model of thin oxide films successfully explains the observed time variation of stress. In this paper, the variation of film stress as a function of storage time and film properties, such as porosity and impurity content, is discussed. Three driving forces, namely, surface reactivity, ...