Characterization of thin-film amorphous semiconductors using spectroscopic ellipsometry

Optical microscopes are essential equipment for observing and analysing cultured cells. In observations using a normal optical microscope, as the contrast of cells is rather low, phase contrast and differential interference microscopes are commonly used. In some cases, specific proteins in cells are fluorescently labelled and observed using a fluorescence microscope. In such observations, cells are generally cultured on a glass surface and observed through the glass. Therefore, spherical aberration occurs due to the refraction of light on the glass surface. This spherical aberration becomes larger when using an objective lens with higher magnification and higher numerical aperture, resulting in a decrease of spatial resolution and contrast. Here, we found that by observing cells cultured on an extremely thin silicon nitride (SiN) film (50 nm thick) under a conventional optical microscope, we could directly observe the cells at high resolution without spherical aberration. This improvement of spatial resolution was confirmed with both inverted and upright optical microscopes. Using a normal 100 × objective lens without oil immersion, we were able to directly observe melanosomes in melanoma cells and analyse their dynamic movement. We believe that using our original sample holder with thin SiN film will make it easy to observe live cells at high resolution and that this method will contribute to a wide range of biological research.

Silicon nitride and silicon nitride-based ceramics have several favorable material properties, such as high hardness and good wear resistance, which makes them important materials for the coating industry. This thesis focuses the synthesis of silicon nitride, silicon oxynitride, and silicon carbonitride thin films by reactive magnetron sputtering. The films were characterized based on their chemical composition, chemical bonding structure, and mechanical properties to link the growth conditions to the film properties. Silicon nitride films were synthesized by reactive high power impulse magnetron sputtering (HiPIMS) from a Si target in Ar/N 2 atmospheres, whereas silicon oxynitride films were grown by using nitrous oxide as the reactive gas. Silicon carbonitride was synthesized by two different methods. The first method was using acetylene (C 2 H 2 ) in addition to N 2 in a Si HiPIMS process and the other was co-sputtering of Si and C, using HiPIMS for Si and direct current magnetron sputtering (DCMS) for graphite targets in an Ar/N 2 atmosphere. Langmuir probe measurements were carried out for the silicon nitride and silicon oxynitride processes and positive ion mass spectrometry for the silicon nitride processes to gain further understanding on the plasma conditions during film growth. The target current and voltage waveforms of the reactive HiPIMS processes were evaluated.

Optical characterization of ns-SiN:H in the infrared by spectroscopic ellipsometry

We present a method that employs the metal-assisted chemical etching technique and a subsequent NH3 plasma treatment for obtaining silica nanoparticles (SNPs) uniformly distributed on an amorphous silicon-rich silicon nitride (SRN) film. These particles ranging from 50 to 300 nm are formed directly from the SRN films, and their density is related to the flow rate of the precursor gas (SiCl4). We determined that the SNPs are a SiOx compound (x > 1) with amorphous structure. Furthermore, the chemical composition of the bulk of the remaining SRN film after the etching in a HF/H2O2-based solution and plasma treatment maintain the properties of a pristine one if the initial thickness of the film is large enough (≥ 1 µm). This method enables the formation of silica nanoparticles directly on a silicon-rich silicon nitride film that could have potential optoelectronic applications, implicit in the optical measurements.

Amorphous silicon nitride thin films have been deposited by chemical vapor deposition (CVD) techniques using SiCl4, NH3, H2 gaseous mixtures onto silicon single crystals. The effects of deposition temperature and the flow rates of reactants on the deposition rate have been studied. The characteristics of nitride interface charge have been studied by fabricating metal–nitride–oxide–silicon (MNOS) structure. The experimental results show that the rate of deposition reaction is controlled by surface reactions. The apparent activation energy of silicon nitride deposition reaction is about 29.4 kcal/mol. The nitride charge density was obtained by measuring the flatband voltage of C–V plots. The positive initial nitride charge density in MNOS structure decreases with increasing the deposition temperature or the flow rate of ammonia. The negative electric field was applied to the gate of MNOS structure, and it was found that the trapped positive charge density in silicon nitride film decreases with increasing NH3/SiCl4 ratio of flow rate, and is hardly influenced by the deposition temperature.

Microemitter resistor arrays are one popular approach to obtaining an infrared scene projector capable of wide dynamic range. Typically, the array operates in a two-level architecture wherein the array resides suspended on support legs. In the microbridge pixel structure, the support legs films must have low thermal conductivity, high mechanical strength, minimal stress and good thermal stability. Usually, silicon nitride (SiNx) films can meet the requirement and have been used as support films in dynamic infrared scene generation. While compared with the silicon nitride films, the silicon oxide (SiOx) films have a lower thermal conductivity. If the SiOx films can also be used as support films in the device instead of SiNx films, it can reduce the thermal loss further. Namely, the SiOx films can make the pixel to achieve higher temperature and higher radiance with lower power than silicon nitride films do. In this work, SiOx and SiNx films were deposited in a PECVD reactor .The stress, Young modulus, Hardness, thermal stability, and infrared optical absorption properties of the two types of films were investigated and compared.

Physical, chemical and electrical properties of Si rich silicon nitride (SiN) film deposited by using the SiH4–NH3 system have been studied. By changing the volume ratio of NH3 to SiH4 from 100 to 1/30, samples with varying excess Si content within SiN films can be obtained. The current conduction mechanism of the SiN film can be represented by the superposition of Poole-Frenkel current, field ionization current and hopping current as reported by Sze in the Si3N4 films without Si excess. Energy levels of trapping centers responsible for Poole-Frenkel current become shallow while their densities remain nearly constant as a function of the Si content. From the dependence of the shift characteristics of C–V curves, it has been deduced that the maximum charge storage within the SiN film is controlled by current conduction through the film.

Influences of the nitrogen content on the morphological, chemical and optical properties of pulsed laser deposited silicon nitride thin films

In the present work, silicon nitride, and oxide films, as well as two-layered SiNx/SiO2 and three-layered SiO2/SiNx/SiO2 structures, were fabricated on p-type Si-substrates. The structure and element composition was studied by scanning electron microscopy and Rutherford backscattering spectroscopy, respectively. It was shown, spectral positions of photoluminescence maxima, as well as edge absorption, were determined by stoichiometry of SiNx layers. No electroluminescence signal was registered from single-layered silicon nitride films. The intense band at 1.9 eV dominated the electroluminescence spectra of single-layered silica film as well as two- and three-layered structures. It was attributed to silane groups in SiO2 layers. The contribution of emission from silicon nitride layers into electroluminescence of the two- and three-layered structures is discussed.

Silicon nitride (SiN) films formed by liquid-source chemical vapor deposition (LSCVD) were analyzed for photonic applications. While this deposition technique for SiN has strengths in its low reaction temperature (>80 °C) and fast deposition rate (>50 nm/min), the material properties, such as its composition, chemical bond, and optical absorption bands in waveguides, have not been studied quantitatively. Hence, we probed SiN films to understand the material characteristics by ultraviolet-to-midinfrared ellipsometry, on-chip waveguide absorption spectrometry, Rutherford backscattering/hydrogen forward-scattering spectrometry, and Fourier-transform infrared spectrometry. As interpreted by a combination of the series of analyses, the N–H bond concentration of higher than 1021 cm−3 leaves an absorption notch (>6.5 dB/cm) at a wavelength of 1550 nm, which cannot be avoided even by systematically varying the deposition conditions. However, except for that absorption range, a low-loss SiN waveguide (0.5–1.0 dB/cm) with a practically applicable high refractive index (∼1.85) can be formed at the deposition temperature of 100 °C. This basic materials research, which combines multiple spectrometric analyses, will help to improve our understanding of a LSCVD SiN film for photonics circuit integration.

This paper addresses the low-temperature deposition processes and electronic properties of silicon based thin film semiconductors and dielectrics to enable the fabrication of mechanically flexible electronic devices on plastic substrates. Device quality amorphous hydrogenated silicon (a-Si:H), nanocrystalline silicon (nc-Si), and amorphous silicon nitride (a-SiN/sub x/) films and thin film transistors (TFTs) were made using existing industrial plasma deposition equipment at the process temperatures as low as 75/spl deg/C and 120/spl deg/C. The a-Si:H TFTs fabricated at 120/spl deg/C demonstrate performance similar to their high-temperature counterparts, including the field effect mobility (/spl mu//sub FE/) of 0.8 cm/sup 2/V/sup -1/s/sup -1/, the threshold voltage (V/sub T/) of 4.5 V, and the subthreshold slope of 0.5 V/dec, and can be used in active matrix (AM) displays including organic light emitting diode (OLED) displays. The a-Si:H TFTs fabricated at 75/spl deg/C exhibit /spl mu//sub FE/ of 0.6 cm/sup 2/V/sup -1/s/sup -1/, and V/sub T/ of 4 V. It is shown that further improvement in TFT performance can be achieved by using n/sup +/ nc-Si contact layers and plasma treatments of the interface between the gate dielectric and the channel layer. The results demonstrate that with appropriate process optimization, the large area thin film Si technology suits well the fabrication of electronic devices on low-cost plastic substrates.

A fractal aggregation behavior in amorphous silicon nitride (SixNy) films deposited by microwave electron cyclotron resonance plasma chemical vapor deposition is reported. The fractal structure and dimension of 1.45 obtained by experiment and computer simulation are all in excellent agreement with the result predicted by the cluster-cluster-aggregation model. The forming of fractal structure is related to the change of discharge mode between ring plasma and bulk plasma.

IR transmittance studies of hydrogen-free and hydrogenated silicon nitride and silicon oxynitride films deposited by reactive sputtering

Improvement in the passivation quality of catalytic-chemical-vapor-deposited silicon nitride films on crystalline Si at room temperature

A novel method is applied to determine the fixed positive charge density Q/sub f/ in plasma-enhanced chemical vapor deposited silicon nitride (SiN/sub x/) films on crystalline silicon surfaces. In this method, both surfaces of the SiN/sub x/-passivated silicon wafers are charged using a corona chamber and the deposited charge density is measured by means of a Kelvin probe. Subsequently, the carrier lifetime is measured and Q/sub f/ is determined from the dependence of the measured carrier lifetime on the corona charge density. This measurement technique allows us for the first time to determine the crucial parameter Q/sub f/ under illumination. In contrast to previous studies, a very high Q/sub f/ of about 2.3 /spl times/ 10/sup 12/ cm/sup -2/ is found, which is in good correspondence with CV measurements carried out in the dark. Finally, we show that the injection level dependence of the surface recombination velocity is mainly due to recombination in the space charge region at the Si/SiN/sub x/ interface.