Mixture Of BCl3 Research Articles

Polarity Effect on the Heteroepitaxial Growth of B<sub>x</sub>C on 4H-SiC by CVD

The chemical vapor deposition (CVD) growth of boron carbide (BxC) layers on 4H-SiC, 4°off substrates was studied. Depending on the polarity of the substrate, different results were obtained. On Si face, the direct CVD growth at 1600°C under a mixture of BCl3+C3H8 systematically led to polycrystalline BxC films, whatever the C/B ratio in the gas phase. On the C face, heteroepitaxial growth was obtained for C/B ratios = 12 or higher with a step bunched morphology. If a boridation step (10 min at 1200°C under BCl3 flow) was used before the CVD growth, then heteroepitaxy was successful on both substrate polarities. To explain these results, a mechanism is proposed which involves the nature of the chemical bonds at the early stage of nucleation. It is suggested that a full B coverage of the SiC surface should favor the nucleation of the B-rich (0001) plane of BxC, promoting thus the heteroepitaxial growth along this direction.

Laser Induced Dielectric Breakdown for Chemical Vapor Deposition by Hydrogen Reduction of Volatile Boron Halides BCl3 and BF3

A possibility of deposition from laser-induced plasma is investigated in search for an economic and simple method for obtaining isotopic compounds from enriched gaseous precursors although no isotopic compounds are used in this the proof-of-principle work. A breakdown in mixtures of BCl3 and BCl3 with hydrogen, argon, and methane are studied both theoretically and experimentally. Equilibrium chemistry calculations show the deposition of boron, boron carbide, and carbon is thermodynamically favorable in BCl3 systems and only carbon in BF3 systems. Dynamic calculation of expanding plasma is performed using fluid dynamics coupled with equilibrium chemistry. Condensed phases of boron, boron carbide, and graphite are predicted with maximum concentrations in peripheral zones of the plasma. In experiment, plasma is induced in mixtures BCl3, H2 + BCl3, H2 + Ar + BCl3, H2 + BCl3 + CH4, BF3, H2 + BF3, H2 + Ar + BF3, and H2 + Ar + BF3. The gases are analyzed before, during, and after laser irradiation by optical and mass spectrometry methods. The results show the composition of reaction products close to that predicted theoretically. The conversion of precursor gases BCl3 and BF3 into gaseous and condensed products is 100% for BCl3 and 80% for BF3. Solid deposits of up to 30 mg are obtained from all reaction mixtures. Due to technical reasons only FTIR characterization of the BCl3 + H2 + CH4 deposit is done. It points to presence of condensed boron and boron carbide predicted by the model. Overall, the calculations and preliminary experimental results imply the chemical vapor deposition with laser induced plasma is promising for conversion of gaseous enriched precursors into elemental isotopes and their isotopic compounds.

Modification of the n-Surface Profile of AlGaInN LEDs by Changing the Gas-Mixture Composition During Reactive Ion Etching

The kind of profile produced during the reactive ion etching of AlGaInN light-emitting-diode (LED) heterostructures on the surface that became free after removal of the growth substrate is studied in relation to the composition of the gas mixture used in the etching process. It is shown that using a mixture composed of Cl2 and Ar, taken in a 3:2 ratio in terms of flow rates, leads to the thinnest profile, whereas a 2 : 1 gas mixture of BCl3 and Ar provides the largest structural elements. To study the effect of the kind of profile on the quantum efficiency (QE), flip-chip LEDs are fabricated on a silicon substrate. The LEDs are etched in different modes after the growth substrate is removed. Etching in the Cl2:BCl3:Ar mixture with a flow ratio of 6:10:11, which leads to intermediate sizes of the etching profile elements, is optimal for obtaining maximum light extraction from a LED chip at a wavelength of 460 nm. The variation of the kind of profile with the gas-mixture composition suggests that the profile parameters can be tuned to the wavelength used. An analysis of how the QE of LED chips depends on the etching duration in the three-component mixture under consideration results in that the optimum etching duration is estimated to be ~30 min. The results of the study can also be of use in the search for conditions minimizing the reflection of incident light by a chip, e.g., for photodetectors.

31 GHz power characteristics of GaN HEMTs with slightly etched AlGaN layer at ohmic contact

AbstractSlight etching of an AlGaN layer at ohmic contact was investigated to reduce contact resistance in AlGaN/GaN HEMTs in Ka‐band operation. In the etching process, etched depth was precisely controlled by ICP‐RIE system with a mixture of BCl3 and Cl2 gases. The relation between ohmic contact resistance and etched depth was examined to determine the optimum depth. It was found that a resistance at an etched depth of 5 nm was reduced to 44% of that in the case of the conventional process. This process was applied to fabrication of GaN HEMTs with a gate length of 0.2 μm, and Ka‐band power characteristics were measured. The linear gain of the device was 11.4 dB, the maximum power‐added efficiency was 45%, and the output power density was 5.1 W/mm, under the conditions of a frequency of 31 GHz, a drain bias of 24 V, and a class‐AB operation. The values are higher than those in the case of the conventional process by 0.5 dB for the linear gain, 2 points for the power‐added efficiency, and 11% for the output power. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Diamond-on-SOI Field Emission Device Patterning

Nanocrystalline diamond films deposited on SOI and electron beam patterning techniques are used to fabricate a field emission device with sub-micron cathode-anode separation. The subsequent aluminum evaporation and dry etch creates a mask for the electrode features, demonstrating that the nanodiamond (ND) roughness does not compromise the device delineation when proper EBL write parameters are used. A mixture of BCl3 and Cl2 were used to dry etch the aluminum, oxygen O2 plasma was used to etch the nanodiamond, and SF6 gas was used to etch the active layer of silicon followed by KOH:DIH2O wet etching.

Creating micro-scale surface topology to achieve anisotropic wettability on an aluminum surface

A technique for fabricating micropatterned aluminum surfaces with parallel grooves 30 µm wide and tens of microns in depth is described. Standard photolithographic techniques are used to obtain this precise surface-feature patterning. Positive photoresists, S1813 and AZ4620, are selected to mask the surface, and a mixture of BCl3 and Cl2 gases is used to perform the etching. Experimental data show that a droplet placed on the micro-grooved aluminum surface using a micro-syringe exhibits an increased apparent contact angle, and for droplets condensed on these etched surfaces, more than a 50% reduction in the volume needed for the onset of droplet sliding is manifest. No chemical surface treatment is necessary to achieve this water repellency; it is accomplished solely by an anisotropic surface morphology that manipulates droplet geometry and creates and exploits discontinuities in the three-phase contact line. These micro-structured surfaces are proposed for use in a broad range of air-cooling applications, where the management of condensate and defrost liquid on the heat transfer surface is essential to the energy-efficient operation of the machine.

Mechanism And Characterization Studies on Boron Carbides Deposited by Chemical Vapor Deposition Technique

ABSTRACTBoron carbide was produced in an impinging jet CVD reactor from a gas mixture of BCl3, CH4 and H2. The mass transfer limitations on the reaction kinetics were minimised by the jet impingement on the substrate surface. XPS characterization of the produced deposits revealed a nearly pure boron carbide phase containing small amounts of oxy-boron and oxy-carbon species. After a detailed kinetic study, a reaction model was proposed to predict the rates of boron carbide and dichloroborane formation reactions. In this model, boron trichloride is adsorbed on the surface non-dissociatively, whereas hydrogen and methane are adsorbed dissociatively. BC is formed on the solid surface through the reaction of adsorbed boron trichloride with adsorbed methane in the form of CH3(s) (adsorbed CH3 on the surface). Produced BC is reacted in successive series reactions including adsorbed boron trichloride and adsorbed hydrogen. In the proposed mechanism, dichloroborane is produced only through the gas phase reaction between boron trichloride and hydrogen. The simultaneous fit of the experimental data to the model expression gave good fits for the boron carbide and dichloroborane formation reactions with the high correlation coefficient values.

Persistence rewarded: successful observation of the B 2Sigmau+-X 2Pig electronic transition of jet-cooled BS2.

The B-X electronic transition of jet-cooled BS2 has been observed using laser-induced fluorescence techniques. The boron disulfide radical was produced in a pulsed electric discharge jet using a mixture of BCl3 and CS2 in high-pressure argon as the precursor. The spectrum consists of a strong 0(0)(0) band with the 2Sigma-2Pi(3/2) component at 24,393.2 cm(-1) and short progressions in the symmetric stretching (nu1' = 506.7 cm(-1)) and bending (nu2' = 303.2 cm(-1)) modes. A rotational analysis of both spin-orbit components of the 0(0)(0) band gave an upper state B value of 0.0932779(19) cm(-1) and a ground-state spin-orbit coupling constant of A = -405.163(4) cm(-1). The ground-state bond length of 1.66492 angstroms increases to 1.6812(1) angstroms on sigmau --> pig electronic excitation. The B-X data have been used to further refine the Renner-Teller analysis, which is in good agreement with our previous work [J. Chem. Phys. 119, 2047 (2003)].

Selective etching of Al/AlN structures for metallization of surface acoustic wave devices

Metallization is a critical step in the fabrication of high frequency AlN thin film based surface acoustic wave devices. Both state-of-the-art lithography as well as high selectivity and anisotropy during etching of Al with respect to AlN are required for low loss and high performance devices. In this work, the etch rates of reactively sputtered AlN, sputtered Al, thermal SiO2, and Shipley 1813 photoresist as well as the selectivity among Al/AlN, Al/SiO2, and resist/Al have been systematically studied during inductively coupled plasma (ICP) etching. Emphasis is focused on obtaining high Al etch rates, while at the same time keeping the etch rate of AlN and that of the resist sufficiently low. High anisotropy is obtained by passivating the sidewalls by the addition of oxygen. The recipe developed is based on a modified Al etch using a mixture of BCl3, Cl2, O2. The parameters varied were gas composition, and substrate bias. Generally it is found that the Al etch rate exhibits a maximum with the O2 flow, while the AlN etch rate decreases monotonically. Substrate bias is found also to be an important parameter with respect to both etch rate and selectivity. At optimized conditions with respect to process selectivity (500 W ICP power, 83 V bias, 50 sccm BCl3, 25 sccm Cl2, 10 sccm O2, pressure 10 mTorr) the Al etch rate is 1000 nm/min with a selectivity of 1000 toward AlN and 9 toward the resist. The same recipe, slightly modified, has also shown similar Al etch rates when etching Al over SiO2 with a selectivity of up to 200. High anisotropy of the Al etch rate is observed with increasing O2 flow. The former has been determined from cross-sectional scanning electron microscope observations.

Influence of surface material on the boron chloride density in inductively coupled discharges

The relative density of BCl radicals has been measured in a modified Applied Materials decoupled plasma source commercial metal etch chamber using laser-induced fluorescence. In plasmas containing mixtures of BCl3 with Cl2, Ar, and/or N2, the relative BCl density was measured as a function of source and bias power, pressure, flow rate, BCl3/Cl2 ratio, and argon addition. To determine the influence of surface materials on the bulk plasma properties, the relative BCl density was measured using four different substrate types; aluminum, alumina, photoresist, and photoresist-patterned aluminum. In most cases, the relative BCl density was highest above photoresist-coated wafers and lowest above blanket aluminum wafers. The BCl density increased with increasing source power and the ratio of BCl3 to Cl2, while the addition of N2 to a BCl3/Cl2 plasma resulted in a decrease in BCl density. The BCl density was relatively insensitive to changes in the other plasma parameters.

Infrared and Microwave Spectra and Force Field of DBO: The Coriolis Interaction between the ν1and ν2+ ν3States

The ν1and ν3bands of D11BO and the ν1band of D10BO were observed by using an infrared diode laser spectrometer. The DBO molecule was generated by an ac discharge in a mixture of BCl3, D2, O2, and He. As inferred previously, a strong Coriolis interaction was in fact found to take place between the ν1and ν2+ ν3states, and an analysis of the observed ν1spectra, which explicitly took into account this Coriolis interaction, predicted the pure rotational transition frequencies of DBO in the ν1state. Pure rotational lines were then detected by microwave spectroscopy, confirming the validity of the infrared assignment. In the microwave experiment DBO molecules were generated by a discharge in a mixture of B2D6and O2. The three fundamental bands and a hot band of D11BO, as well as the ν1and ν3bands of D10BO, were subsequently recorded in emission with a Fourier transform infrared spectrometer. DBO molecules were generated by the reaction of D2with HBO at temperatures above 800°C in a ceramic tube furnace. All of the observed spectra were simultaneously subjected to a least-squares analysis to obtain molecular parameters in the ground, ν1, ν2, ν3, and ν2+ ν3states. The results thus obtained improved the force field and molecular structure of the HBO/DBO molecules reported in a previous study (Y. Kawashima, Y. Endo, and E. Hirota, 1989,J. Mol. Spectrosc.133, 116–127).

Metastable chlorine ion kinetics in inductively coupled plasmas

Laser induced fluorescence has been used to measure the temperature, radial drift velocity, and relative number density of metastable chlorine ions, Cl+*, in inductively coupled discharges containing mixtures of BCl3, Cl2, N2, and Ar. In the center of the plasma, the Cl+* temperature varied between 2000 and 3000 K for most conditions investigated. The addition of BCl3 to a Cl2 plasma significantly decreased the density of metastable chlorine ions without changing their temperature. Addition of nitrogen to a BCl3 plasma resulted in a factor of 3 increase in the Cl+* density. Spatially resolved measurements of the Cl+* density are compared with Langmuir probe measurements of the spatially resolved electron density and ion saturation current. In general, the normalized Cl+* density was a factor of 2–3 lower than the electron density at the edge of the plasma. Spatially resolved measurements of the ion temperature indicated that the ion temperature increased to between 4500 and 5500 K at the edge of the discharge and increased approximately 600–1400 K moving from the rf source towards the lower electrode. Ion drift velocity in the radial direction was between 5×104 and 8×104 cm/s at the edge of the plasma. Measurements within one millimeter of the biased lower electrode surface showed the ion energy parallel to the biased electrode was independent of rf bias voltage while the density decreased with increased bias voltage. Implications of these measurements on the plasma chemistry and the energy transport in the plasma are discussed.

Low-energy electron attachment to BCl3

The rate constants of low-energy electron attachment to BCl3 diluted in N2 are measured as a function of E/N at 1–11 Td, corresponding to mean electron energies at 0.4–1.0 eV. The negative ions produced by hollow-cathode discharges of either pure BCl3 or mixtures of BCl3 in N2 are mass analyzed to identify the products of electron attachment to BCl3. Only Cl− ion is found in the discharge media, although BCl−3 is observed at the applied voltage significantly lower than the breakdown voltage. The electron attachment processes of BCl3 are discussed.

Energy efficiency of laser-induced plasma reaction of BCl3-H2 system.

Ultrafine particles of boron were prepared from a mixture of BCl3 and H2 by laser-induced plasma CVD using a TEA-CO2 laser.Energy efficiency in this case was measured and the highest value was nearly 100 %. The efficiency of this method is defined as the ratio of energy required to induce chemical reaction to that absorbed by the plasma from the laser beam.

Properties and characterization of codeposited boron nitride and carbon materials

The physical properties of carbon-boron nitride (C-BN) prepared from mixtures of BCl3, NH3, and selected hydrocarbons by codeposition methods have been investigated using x-ray diffraction, electron diffraction, transmission electron spectroscopy, x-ray photoelectron spectroscopy, Raman scattering, optical reflectivity, thermal conductivity, thermopower, and electrical resistivity. Taken collectively, the results of these experiments indicate that the compression-annealed C-BN materials studied here consist of separated domains of pyrolytic boronated graphite and pyrolytic boron nitride, while as-deposited samples may possibly be a single-phase mixture of C, B, and N. As-deposited materials containing more than 20% carbon were found to be more highly oriented than unannealed pyrolytic graphite, and the crystallinity of these materials was greatly enhanced by uniaxial compression annealing. Results of the thermal conductivity, thermopower, and electrical resistivity measurements are consistent with a network of turbostratic graphite BN domains with some conduction paths for charge carrier transport between the domains. Increasing the carbon concentration from 20% to 60% leads to an increased linkage between the conducting domains and a percolation conducting network is established.

Removal of phosgene impurity from boron trichloride by laser radiation

The removal of the COCl2 impurity in BCl3 can be accomplished by using CO2 laser radiation. Mixtures of BCl3 and COCl2, and C2H4 and COCl2, were irradiated by a cw CO2 laser. The COCl2 was dissociated with no detectable BCl3 dissociation. The BCl3 acts as an infrared sensitizer.

Isotope separation by laser-induced photo-migration

Pairs of mass peaks 10B and 11B of the sublimated gas from the sample were measured successively at a rate of two pairs per minute throughout each experiment. The sample prepared by solidifying gas mixture of BCl3 and Xe on a cold plate was irradiated for 20 minutes with a 3 W, 10.6 μm cw CO2 laser to excite 11BCl3 ν3 vibration. After the irradiation, the sample was heated to promote the sublimation of gas from the sample surface. The out gas from the sample during laser irradiation is depleted in 11B, on the other hand the gas released by heating is enriched in 11B. This released gas is composed of two parts: the volatile with small separation factor 1.3 and the less volatile with large separation factor 15. The amount of these two parts of the product are estimated to be 0.21 and 0.14 mg respectively, which correspond to 7 and 5 percent of BCl3 fed on the cold plate. This result obtained with a mass spectrometer is likely to support the previous conclusion from infrared spectral analysis: Selectively excited 11BCl3 molecules migrate through Xe matrix to form crystalline 11BCl3 0n the cold plate surface.

The Band Spectrum of Boron Monoxide

IN two recent letters to NATURE (May 24 and 31) Mr. W. Jevons has questioned the adequacy of my evidence as to the oxide origin of a band spectrum which he had previously ascribed to boron nitride.1 In his second letter he reports that these bands are absent from the spectrum of the discharge through a mixture of BCl3 and O2, although the ordinary boric oxide bands are present. This he considers convincing evidence against BO as the emitter of the bands in question. In view, however, of evidence outlined below, a full account of which will appear probably in the Physical Review, there seems little room for doubt that the bands are really due to BO and not to BN. The other oxide bands may then be ascribed, as in the past, and in accordance with their complex character, to B2O3.