Silicon nitride

About: Silicon nitride is a research topic. Over the lifetime, 32678 publications have been published within this topic receiving 413599 citations. The topic is also known as: N₄Si₃.

Etching mechanism of silicon nitride in HF-based solutions

Abstract: A reaction mechanism for the etching of silicon nitride layers in aqueous hydrofluoric acid solutions is proposed. The surface of consists of groups that are etched from the solid matrix via three possible routes. Depending on the pH, these groups are protonated to At the rate-limiting step consists of an elimination of and a subsequent addition of or HF to the vacant surface site to form Si-F. At the elimination of is assisted by followed by a transfer of one of the fluorides of to the vacant site. All subsequent reaction steps to remove the SiF unit are nucleophilic substitution reactions with low activation energies. The etch rates and mechanism of different types of silicon nitride films are compared with that of etching. Therefore, etch selectivity between these two materials can be explained. The theory is also applicable for silicon hydrogen passivation. © 2001 The Electrochemical Society. All rights reserved.

Optimal wavelength scale diffraction gratings for light trapping in solar cells

Abstract: Dielectric gratings are a promising method of achieving light trapping for thin crystalline silicon solar cells. In this paper, we systematically examine the potential performance of thin silicon solar cells with either silicon (Si) or titanium dioxide (TiO2) gratings using numerical simulations. The square pyramid structure with silicon nitride coating provides the best light trapping among all the symmetric structures investigated, with 89% of the expected short circuit current density of the Lambertian case. For structures where the grating is at the rear of the cell, we show that the light trapping provided by the square pyramid and the checkerboard structure is almost identical. Introducing asymmetry into the grating structures can further improve their light trapping properties. An optimized Si skewed pyramid grating on the front surface of the solar cell results in a maximum short circuit current density, Jsc, of 33.4 mA cm−2, which is 91% of the Jsc expected from an ideal Lambertian scatterer. An optimized Si skewed pyramid grating on the rear performs as well as a rear Lambertian scatterer and an optimized TiO2 grating on the rear results in 84% of the Jsc expected from an optimized Si grating. The results show that submicron symmetric and skewed pyramids of Si or TiO2 are a highly effective way of achieving light trapping in thin film solar cells. TiO2 structures would have the additional advantage of not increasing recombination within the cell.

Micromachined capillary electrophoresis device

Abstract: A micromachined structure for handling fluids with an applied high voltage, i.e. for electrophoresis, includes a glass or other highly insulative substrate on which are formed very small diameter capillary channels of e.g. silicon nitride. Due to the absence of a silicon substrate, this structure is highly electrically insulative. The silicon nitride channels are formed by a micro-machining and etch process, so that they are initially defined in an etched sacrificial silicon wafer by conformal coating of etched features in the silicon wafer with a silicon nitride layer, which is then patterned to define the desired channels. The silicon wafer is bonded to the glass substrate and the bulk of the silicon wafer is sacrificially etched away, leaving the desired silicon nitride channels with supporting silicon mesas. The remaining silicon nitride "shell" is bonded to the glass substrate and substantially duplicates the etched features in the original silicon wafer. The capillary channels are of a material such as low stress silicon nitride and there is no electrical shorting path to the highly insulative glass substrate.

Preventing nanoscale wear of atomic force microscopy tips through the use of monolithic ultrananocrystalline diamond probes.

Abstract: Nanoscale wear is a key limitation of conventional atomic force microscopy (AFM) probes that results in decreased resolution, accuracy, and reproducibility in probe-based imaging, writing, measurement, and nanomanufacturing applications. Diamond is potentially an ideal probe material due to its unrivaled hardness and stiffness, its low friction and wear, and its chemical inertness. However, the manufacture of monolithic diamond probes with consistently shaped small-radius tips has not been previously achieved. The first wafer-level fabrication of monolithic ultrananocrystalline diamond (UNCD) probes with <5-nm grain sizes and smooth tips with radii of 30-40 nm is reported, which are obtained through a combination of microfabrication and hot-filament chemical vapor deposition. Their nanoscale wear resistance under contact-mode scanning conditions is compared with that of conventional silicon nitride (SiN{sub x}) probes of similar geometry at two different relative humidity levels ({approx}15 and {approx}70%). While SiN{sub x} probes exhibit significant wear that further increases with humidity, UNCD probes show little measurable wear. The only significant degradation of the UNCD probes observed in one case is associated with removal of the initial seed layer of the UNCD film. The results show the potential of a new material for AFM probes and demonstrate a systematic approach to studying wearmore » at the nanoscale.« less