R. A. Moore

Method of construction of composite one-dimensional photonic crystal with extended photonic band gaps

A method of photonic band gap extension using mixing of periodic structures with two or more consecutively placed photonic crystals with different lattice constants is proposed. For the design of the structures with maximal photonic band gap extension the gap map imposition method is utilised. Optimal structures have been established and the gap map of photonic band gaps has been calculated at normal incidence of light for both small and large optical contrast and at oblique incidence of light for small optical contrast.

Low-temperature crystallisation of amorphous-silicon films for the fabrication of thin-film transistors

Abstract This paper reports on the crystallisation of low-pressure chemical-vapour deposited (LPCVD) amorphous silicon films for obtaining large grain polycrystalline layers. TEM and SEM studies are presented for samples 0.05–0.2 μm thick deposited in the temperature range from 495°C to 635°C, the pressure range 0.15 to 1.0 Torr and annealed in the temperature range 510°C to 610°C. The average grain size of the crystallised films is a function of the film thickness, the deposition rate and temperature, and the annealing temperature. An average grain size of 600 nm has been obtained in 200 nm thick films deposited at 540°C and annealed for 72 h at 550°C. Plasma-enhanced CVD of silicon dioxide produced by the reaction of silane and nitrous oxide is examined for the production of device quality silicon dioxide. Self-aligned silicon gate TFTs were fabricated on crystallised silicon deposited at 540°C and annealed at 550°C.

Investigation of strain induced effects in silicon wafers due to proximity rapid thermal processing using micro-Raman spectroscopy and synchrotron x-ray topography

Thermal stress induced by rapid thermal oxidation (RTO) and rapid thermal doping (RTD) of 001 silicon wafers was analysed using micro-Raman spectroscopy and synchrotron x-ray topography. The RTO wafers exhibited elevated stress levels as the process time was increased. The maximum magnitude and topographical distribution of the strain was found to agree with theoretical predictions. A maximum compressive strain of 320 MPa was observed after 166 s of RTO. The introduction of boron into the silicon lattice via the RTD process enhanced the rate at which the stress in the wafer exceeded the yield stress. Stress relief was subsequently accomplished through the formation of slip and misfit dislocations. The thermally induced stress and dislocation density increased with the time spent at the process peak temperature.

Micro-Raman investigations of the degree of relaxation in thin SiGe buffer layers with high Ge content

Virtual substrates with high Ge content x of 0.25<x<0.5 for metal oxide semiconductor field effect transistor (nMOSFET) structures are grown by molecular beam epitaxy (MBE). Thin strain-relaxed SiGe buffers are of special importance for this application, therefore, sub-100 nm layer growth procedures have been developed. Micro-Raman spectroscopy has been extensively employed for measurements of Ge content and the degree of relaxation (r) in our virtual substrates. Two growth stages – a very low temperature (VLT) stage and overgrowth at 550 °C (OT stage) were used to provide the high relaxation in thin SiGe layers. Implementation of this process under careful temperature control within 50 °C during the VLT growth stage allows us to regulate precisely the degree of relaxation. The role of low temperatures and of Sb surfactants during the VLT growth stage for process-window widening is studied. The Sb pre-buildup is found to increase the degree of relaxation in a higher temperature range during the VLT stage. Optimum processing conditions are determined and high uniformity of composition and residual-strain distribution on virtual substrate wafers are demonstrated.

Boron diffusion from a spin-on source during rapid thermal processing

Proximity rapid (3 min) thermal diffusion has been investigated as a technique for fabricating shallow p-type junctions in submicron metal oxide semiconductor field effect transistors. A layer of spin-on dopant, deposited on a silicon wafer, was used as a dopant source for boron. Sheet resistance measurements, secondary ion mass spectrometry and Fourier transform infrared spectroscopy were used to evaluate the spin-on dopant and rapid thermal diffusion efficiency. Spin-on dopant post-spin baking process was optimised to avoid organic contamination during rapid thermal diffusion. Oxygen content in the rapid thermal diffusion ambient was essential to ensure successful deglazing of the doped oxide and spin-on dopant layers. The oxygen content also affected the doping efficiency of the product and source wafers. For process times less than 2 min, the doping level in the source wafer is less than in the product wafer. For process times greater than or equal to 3 min however, the doping efficiency for both wafers is the same.

Spectroscopic characteristics of SiO and SiO2 solid films: Assignment and local field effect influence

A number of thin SiOx (x=1, 2) films formed on silicon and reflection-absorption substrates were investigated using infrared transmission and aluminized glass techniques. The application of these techniques to SiO and SiO2 films at normal and oblique incidence of light allows the observation of both the longitudinal and transverse optical phonons. The longitudinal-transverse optical phonon splitting is analyzed in terms of a dispersive local field effect.

Spectroscopic Investigations of Borosilicate Glass and Its Application as a Dopant Source for Shallow Junctions

Borosilicate glass was investigated as a dopant source for proximity rapid thermal diffusion. A borosilicate gel was spun onto a silicon wafer and the layer was rapid thermally processed to convert it to a borosilicate glass. Fourier transform infrared spectroscopy, spectroscopic ellipsometry, and sheet resistance measurements were used to understand and subsequently optimise the conversion of the gel to a borosilicate glass. The optimum conversion step, which avoided any boron loss from the borosilicate glass layer, was a curing step of 900°C for 45 s. Secondary ion mass spectrometry was used to measure the boron dopant profile of a silicon wafer that was doped with the borosilicate glass layer. The wafer had a surface dopant concentration of 4.7 × 10 19 cm -3 and a junction depth of 65.5 nm. Junction diodes, which were fabricated using the glass layer as a dopant source, displayed excellent characteristics, with very low leakage currents and a near ideal forward slope.

Optical properties of diamond films grown by MPCVD method with alternating nanodiamond injection

Transparent polycrystalline diamond films with grain size ranging from a few tens to hundreds of nanometres were prepared on fused silica substrate by Microwave Chemical Plasma Vapour Deposition method (MPCVD). The new technique, called alternating nanodiamonds injection, was applied for substrate pretreatment. It was demonstrated that nanodiamonds injected on fused silica substrate serve as nucleation centres and make possible an increase in nucleation density to 1010 cm-2. The influence of MPCVD parameters such as methane concentration, total pressure and substrate temperature on the crystalline structure and optical properties of diamond films were investigated by using micro-Raman spectroscopy and scanning electron microscopy, transmittance and reflectance measurements in the wavelength range of 400-1000 nm. Under appropriate MPCVD parameters, diamond films with optical transmission ~70% from 650 to 1000 nm and high content of diamond phase were fabricated.

Micro-Raman study of stress distribution generated in silicon during proximity rapid thermal diffusion

Micro-Raman spectroscopy has been used for analysing the thermally induced stress distributions in silicon wafers after proximity rapid thermal diffusion (RTD). A compressive stress was found on the whole silicon wafer after 15 s RTD. After 165 s RTD, the distribution of the stress across the wafer was found to be different: compressive at the edge and tensile at the middle. Thermal stress was relieved in the RTD wafers via slip dislocations. These slip dislocations were observed in the product wafers using optical microscopy. Slip lines propagated from the wafer edge to the wafer centre in eight preferred positions of maximum induced stress. The thermally induced stress and the slip dislocation density increased with time spent at the RTD peak temperature.

Confined optical modes and amplified spontaneous emission from a microtube cavity formed by vacuum assisted filtration

The authors demonstrate a new route to the fabrication of individual aluminosilicate microtubes that can act as micron-scale optical cylindrical resonators. The microtubes were prepared using a simple vacuum assisted wetting and filtration through a microchannel glass matrix. Microphotoluminescence spectra of the microtube cavity show sharp resonant modes with quality factors up to 3200. A strong reduction of the emission decay time at high excitation power confirms the occurrence of amplified spontaneous emission from a single microtube.