B2H6 Gas Research Articles

Preparation and pressureless sintering of chemical vapour deposited SiC-B composite powder

SiC-B composite powder was prepared by chemical vapour deposition (CVD) using (CH3)2SiCl2+B2H6+H2 as source gases at 1673 K. The powder was β-type polycrystalline silicon carbide containing several per cents of boron and carbon. The boron content increased from 0 to 7.7 mass % as the B2H6 gas concentration increased from 0 to 0.7 mol %. Boron and carbon in amorphous form dispersed homogeneously in the β-SiC polycrystalline particles. The particles were spherical, non-agglomerated and uniform in size with an average particle size of about 50 nm. Sintering tests were performed with the resulting composite powder without applying pressure. Powder containing 1 mass % boron and 2 mass % carbon was sintered to a density of 3.16×103kgm−3 at 2273 K, and the Vickers hardness of the sintered body was 30 GPa. When the sintering temperature was higher than 2323 K, significant grain growth due to the phase transformation from β to α form occurred, which decreased bulk density and Vickers hardness.

Cold-wall ultrahigh vacuum chemical vapor deposition of doped and undoped Si and Si1−xGex epitaxial films using SiH4 and Si2H6

Doped and undoped silicon homoepitaxy and Si1−xGex-on-Si heteroepitaxy have been achieved by cold-wall ultrahigh vacuum chemical vapor deposition using disilane (Si2H6), silane (SiH4), digermane (Ge2H6), and germane (GeH4) as the reactant gases. Boron and phosphorus doping were achieved by flowing B2H6 and PH3 dopant gases, respectively, into the reactor. The growth mechanism and film quality of intrinsic Si, B/P-doped films, and Si1−xGex alloys using SiH4 and Si2H6 are comparatively studied in this article. The crystallinity of the films was examined by Nomarski microscopy after Schimmel etching, transmission electron microscopy (TEM), and in situ reflection high energy electron diffraction (RHEED). The defect density of the intrinsic Si films grown by Si2H6 and SiH4 was found to be below the TEM detection limit (105/cm2). B-doped and P-doped single-crystal Si were deposited using Si2H6 or SiH4 with a partial pressure of 10 mTorr at substrate temperatures from 550 to 600 °C. The B- and P-doping concentrations were determined by secondary ion mass spectroscopy (SIMS). From plan-view TEM analysis, it was found that the defect density of the B- and P-doped Si films grown using Si2H6 is lower than that grown using SiH4 at even lower substrate temperatures. It was also found that the phosphine (PH3) ‘‘poisoning effect’’ for growth rate reduction and crystallinity degradation in Si2H6 chemical vapor deposition (CVD) is not as serious as in SiH4 CVD. A model for the PH3 poisoning effect was developed to explain the growth rate reduction in SiH4 CVD with high PH3 flux. The morphology of both P-doped and B-doped Si films using Si2H6 was found to be smoother than for those using SiH4, as indicated by plan-view TEM and by RHEED analysis. Si1−xGex alloys were deposited by using various reactant gases. The thickness of the Si1−xGex alloy films and the Ge mole fraction were measured by SIMS. A 50-period Si1−xGex–Si superlattice was grown using Si2H6 and GeH4. The transition layers were found to be extremely sharp and layer thickness control using Si2H6 was found to be excellent by cross-sectional TEM analysis. In this study, Si2H6 was found to be a better Si precursor compared to SiH4 under our growth conditions. From the growth rate study, the activation energies for the Si growth rate were found to be 1.47 and 1.60 eV for Si2H6 and SiH4, respectively. The activation energies for the Ge growth rate are 0.93 and 1.0 eV using Ge2H6 and GeH4, respectively. A growth kinetic model was developed to predict the growth rate of undoped Si for various reactant gas partial pressures and substrate temperatures. The adsorption rate preexponential constant for SiH4 was found to be about twice that of Si2H6. The model can also predict the Ge mole fraction in Si1−xGex alloys and B/P doping concentrations in the Si films.

Influence of boron doping and hydrogen dilution on p-type microcrystalline silicon carbide thin films prepared by photochemical vapor deposition

Boron doped μc-SiC:H films have been prepared by low power (10 mW/cm2) photochemical vapor decomposition of SiH4, C2H2, and B2H6 gases diluted with hydrogen. The effect of boron doping and hydrogen dilution on structural and opto-electronic properties have been studied. The microstructure consists of Si crystallites while carbon remains at the grain boundaries and amorphous parts. Diborane doping beyond an optimum value has been observed to deteriorate the formation of microcrystallites. By optimizing the process parameters, p-type μc-SiC:H having σd∼3.0×10−3 S cm−1 with an E04 of 2.34 eV has been obtained. This film exhibits high optical transmittivity compared to its amorphous counterpart.

Effect of BeO on the Sintering and Properties of Boron-Doped High-Purity SiC Ceramics

In order to obtain pressureless-sintered SiC ceramics with high thermal conductivity, effect of BeO addition on sintering properties boron-doped β-SiC powder was investigated. The β-SiC powder was produced by the plasma arc method from SiH4, B2H6 and CH4 gases. Pressureless-sintered boron-doped β-SiC ceramics showed high thermal conductivity of 180 W·m-1·K-1 and electrical resistivity of 1100Ω·m (10mV). On the other hand, pressureless-sintered boron-doped β-SiC ceramics containing BeO showed varistor characteristics with electrical resistivity of 1011Ω·m at 10V, and thermal conductivity of 230 W·m-1·K-1. These ceramics consisted of net-like elongated β-SiC grains. Thus, addition of BeO increased the thermal conductivity and electrical resistivity.

Ultrashallow p-type layer formation by rapid vapor-phase doping using a lamp annealing apparatus

Ultrashallow p-type layers below 30 nm were formed by a rapid vapor-phase doping involving a lamp annealing system. A new one-wafer-type apparatus with tungsten lamps has been developed for use in this process. Temperatures at five different points on a 4-in. wafer are in situ monitored by infrared radiative thermometers with optical fibers to maintain a uniform temperature profile across the wafer. By using hydrogen and B2H6 gas, an ultrashallow boron-doped layer of below 30 nm with the surface boron concentration of 5.8×1019 cm−3 was formed after 10 s of 900 °C annealing with a B2H6 flow rate of 100 ml/min.

Simple and quick rotational temperature determination in N2-containing discharge plasma

A quick spectroscopic method of rotational temperature determination based on the low-resolution emission spectrum of the N2 (v′=2→v″=()) vibronic band profile of the second positive system iras developed. The new method of molecular gas temperature determination was used in an rf glow discharge excited in N2 and N2 + Ar + B2 H6 gas mixture at u pressure range 500–13011 Pa. This method of molecular gas temperature measurement is applicable to nonisothermic plasmas used in plasma-chemical reactors.

Preparation of SiB4±x and SiB6 plates by chemical vapour deposition of SiCl4 + B2H6 system

SiB4±x and SiB6 plates were prepared by chemical vapour deposition (CVD) using SiCl4, B2H6 and H2 gases under the conditions of deposition temperatures (Tdep) from 1323–1773 K, total gas pressures (Ptot) from 4–40 kPa and B/Si source gas ratio (mB/Si=2B2H6/SiCl4) from 0.2–2.8. The effects of CVD conditions on the morphology, structure and composition of the deposits were examined. High-purity and high-density SiB4±x and SiB6 plates about 1 mm thick were obtained at the deposition rates of 71 and 47 nm s−1, respectively. The lattice parameter, composition and density of CVD SiB4±x plates were dependent on their non-stoichiometry. The lattice parameter,a, was 0.6325 nm, butc ranged from 1.262–1.271 nm.The B/Si atomic ratio ranged from 3.1–5.0, and the density ranged from 2.39–2.45×103 kg m−3. The CVD SiB6 plates showed constant values of lattice parameters (a=1.444 nm,b=1.828 nm,c=0.9915 nm), composition (B/Si=6.0) and density (2.42×103 kg m−3), independent of CVD conditions.

Electrical and optical properties of boron-doped ZnO thin films for solar cells grown by metalorganic chemical vapor deposition

The highly conductive and textured ZnO films have been grown by metalorganic chemical vapor deposition using diethylzinc and H2O as reactant gases. The B2H6 gas has also been successfully used as an n-type dopant gas to obtain highly conductive ZnO with a sheet resistivity for 2-μm-thick film as low as 10 Ω/⧠ at the very low temperature of 150 °C. It was found that the crystal orientation and grain structure change with B2H6 flow rate. The decreasing of the film transmittance due to the free-carrier absorption in the wavelength region above 1000 nm was observed and it seems that the impurity scattering was the dominant interaction during this process. The shift of the absorption edge due to band filling was also observed as the B2H6 flow rate was increased.

P-Type a-SiC:H Films Using Triethylboron and Its Application to Solar Cells

We propose a new p-type doping gas, B(C2H5)3, instead of the conventional B2H6 gas, which has no B-B bond and B-H bond. The photo- and dark conductivities of 6.0×10-6 Scm-1 and 1.4×10-6 Scm-1 were obtained at the optical band gap of 1.98 eV using B(C2H5)3 and these values are comparable to those of films using B2H6. The conversion efficiency of 11.3% was obtained by applying the p-type a-SiC:H films using B(C2H5)3.

Growth and characterization of undoped and in situ doped Si1−xGex on patterned oxide Si substrates by very low pressure chemical vapor deposition at 700 and 625 °C

Results of strained layer Si1−xGex heteroepitaxy on patterned oxide silicon substrates using a very low pressure chemical vapor deposition reactor are presented. Patterned oxide wafers were in situ cleaned at 700 °C using an Ar/H2 plasma. Undoped Si1−xGex strained layers at 625 and 700 °C along with in situ doped p and n-type Si1−xGex strained layers at 625 °C were deposited using SiH4, GeH4, B2H6, and AsH3 with H2 as a carrier gas. Alternating layers of Si1−xGex and Si were formed by switching the inlet gases. Scanning electron microscope showed a smooth surface morphology for Si1−xGex strained layers deposited with GeH4/SiH4 gas ratios <7.5%. Cross-sectional transmission electron microscope revealed a sharp transition between the Si1−xGex and Si layers with dislocation densities below the detection limit of 105 cm−2. Defect etching confirmed the low defect density at the surface. For epitaxial windows smaller than 50×50 μm, no defects were observed. Germanium solid mole fraction, boron and arsenic chemical dopant concentrations, and interfacial carbon and oxygen contamination were measured by secondary ion mass spectrometry. Undoped, B2H6, and AsH3 in situ doped Si1−xGex strain layers with germanium content up to 23% were demonstrated. The Ge incorporation was controlled by the GeH4/SiH4 gas ratio and the Si1−xGex growth rate decreased with increasing Ge solid mole fraction. The addition of B2H6 did not affect the Si1−xGex growth rate and modulation of the boron chemical incorporation was possible by controlling the B2H6 gas concentration. On the other hand, AsH3 severely degraded the Si1−xGex growth rate and varying the AsH3 gas concentration did not change the arsenic chemical incorporation. Lastly, selective AsH3 doped Si1−xGex heteroepi

B doping using B2H6 in gas source Si molecular beam epitaxy

A new gas mixing system was devised for the control of a gaseous dopant during gas source Si molecular beam epitaxy. The performance of this gas mixing system was demonstrated using B2H6 gas dopant for B doping. B doping level control over five decades was successfully achieved. The B-doping concentration was found to be proportional to the B2H6/Si2H6 flow rate ratio. This relationship holds in both the supply-controlled and the reaction-controlled growth regions. This result indicates that B2H6 is incorporated into epitaxial layers by a similar dissociative adsorption mechanism on Si2H6.

Gas source molecular-beam epitaxy of Si and SiGe using Si2H6 and GeH4

Gas source molecular-beam epitaxy (MBE) has been studied as a low-temperature Si and SiGe epitaxial method. Specular single-crystalline silicon films were successfully grown by the gas source Si MBE technique at a substrate temperature of about 650 °C. N-type doping was carried out using PH3 gas as a dopant and the maximum electron concentration of 2.9x1019cm−3 was obtained. Furthermore, p-type doping using B2H6 gas was carried out for the first time and the maximum hole concentration of 9.5×1017cm−3 was successfully achieved. The SiGe alloy layer was also grown by the gas source MBE technique using GeH4 as a Ge source gas. The Ge concentration of the sample could be precisely controlled by the molar fraction of Ge in supply and it was increased up to 0.30 with increasing the gas ratio of GeH4 to Si2H6.

Gas Source Silicon Molecular Beam Epitaxy

ABSTRACTGas source silicon molecular beam epitaxial (Si-MBE) growth is microscopically governed by a disociative adsorption of silicon hydrides, such as Si2H6 source gas molecules on Si surface. The dissociative adsorption generates SiH species on the surface. From this hydride phase, hydrogen desorbs thermaly. The temperature dependence of the growth rate indicated that the hydrogen desorption from the SiH is the rate limiting step. In HBO2 Knudsen cell doping, B adsorbates block the surface migration. Such a blocking effect can be avoided by B2H6 gas dopant, because of the similar incorpration mechanism of B2H6 to that of Si2H6. However, in PH3 gas doping, a crystal quality degradation was observed at a high doping range due to the preferentially high sticking coefficient of PH3 and the resulting surface dangling bond termination. The selective epitaxial growth of a B doped layer using Si2H6 and B2H6 was applied to a novel structured base fabrication for super self-aligned selectively grown base transistor (SSSBT). A successful achievement of the SSSBT fabrication indicates the high potentiality of gas source Si-MBE to the sub-micron size ultra-high speed bipolar large scale integrated (LSI) circuits.

Ultrashallow, high doping of boron using molecular layer doping

A new doping method named molecular layer doping (MLD) is proposed. MLD is based on surface chemical adsorption of dissolvements from induced dopant gas molecules. Ultrashallow boron-doped layers are successfully achieved by MLD using B2 H6 gas. The p+ n junction formed by MLD exhibits excellent characteristics, with a reverse bias leakage current of less than 2.5×10−16 A/μm2 at 5 V. MLD is attractive in that it offers high-density, shallow-junction, damage-free, selective doping in a short time.

反応性イオンプレーティング法によるＺｒＢ２薄膜の合成

Zirconium boride (ZrB2) thin film has been synthesized on an aluminum substrate by reactive ion plating methods. The following four processes were applied to the synthesis of ZrB2 thin film. (1) Metallic zirconium and BCl3 gas were vaporized on an aluminum substrate by reactive ion plating. (2) A mixture of metallic zirconium and elemental boron was simultaneously deposited on an aluminum plate by ion plating. (3) ZrB2 thin film was prepared with a heating treatment of the multi-layer product after an alternating vaporization using metallic zirconium and elemental boron. (4) Metallic zirconium and B2H6 gas were vaporized on an aluminum plate by reactive ion plating.In these processes, it was found to be difficult to synthesize ZrB2 thin film in terms of the processes from (1) to (3). The process (4) using metallic zirconium and B2H6 gas as a source of boron was found to be more effective for the preparation of ZrB2 thin film when the synthesis was carried out under optimum conditions of a substrate temperature of 410K and a bell-jar pressure of 0.3Pa.

Selective Surface Modification of a Fluorocarbon Resin Into Hydrophilic Material Using an Excimer Laser

AbstractSelective surface modification of fluorocarbon resin has been demonstrated by using an ArF excimer laser beam and an ammonia complex which was made from NH3 and B2H6 gases. The fluorocarbon resin was set in the atmosphere of NH3 gas. NH3 molecules which were adsorbed on the surface reacted quickly with the B2H6 molecules, and an ammonia complex was produced. As a result, the complex was adsorbed on the surface. The resin surface was selectively irradiated by ArF laser beam. The complex and C-F bonds of this resin were excited by the laser beam, and the surface was selectively modified to be hydrophilic property. The modified samples were evaluated by XPS analysis, measuring the contact angles of the water and the SEM image on the surface.

Gas Source Si-Mbe

ABSTRACTGas source Si molecular beam epitaxy (Si-MBE) apparatus has been devised. The growth mechanism was studied using reflection high energy electron diffraction (RHEED) intensity oscillation. Si epitaxial layers grew through a dissociative adsorption of Si2H6 molecules on Si surfaces. This dissociative adsorption enables a selective epitaxial growth on SiO2 patterned Si wafers. At low temperatures, the growth rate was limited by a desorption of hydrogen which terminates surface dangling bonds. Doping with B, Sb and P were also studied. B doping was achieved using HBO2 Knudsen cell or B2H6 gas dopant. Sb doping used an ionized doping cell. P doping was achieved using PH3 gas dopant. The effect of B doping on the growth was studied using RHEED oscillation. A doped layer's selective epiataxial growth was possible by selective epitaxial growth under doping. This technique was applied to bipolar transistor fabrication. Moreover, using GeH4, Si1−xGex compound growth and its selective epitaxial growth was achieved. Using this Si1−xGex selectively grown layer, a Si1−xGex base heterobipolar transistor (HBT) was also fabricated. An electron cyclotron resonance (ECR) gas source Si-MBE cell was used for a low temperature surface cleaning and a surface termination by atomic hydrogen.

Bonding and electrical properties of boron-doped microcrystalline SiNx:H films

Microcrystalline (μc-) SiNx:H films have been prepared by rf glow discharge of SiH4-B2H6-N2-H2 mixtures as a function of the substrate temperature Ts, N2 gas ratio RN, and B2H6 gas ratio RB. The bonding, electrical, and optical properties have been investigated. Crystallization is observed at Ts below 350 °C and above 700 °C, at RN below 0.04, and at RB below 5×10−3. The ratio of the volume fraction ρ of the crystalline phase to the crystallite size δ is roughly constant. The Si-N bond density agrees well with the Si-H bond density, indicating enhanced formation of N-SiH bonds. For the films with larger ρ or δ, N and H atoms are segregated in a part of the amorphouslike boundary region between crystallites, but those for the films with lower ρ or δ are uniformly distributed in the boundary region. The optical gap is mainly characterized by the N and H contents. As the film is deposited at a preparation condition giving transformation from μc to amorphous structure, the dark conductivity and photoconductivity abruptly decrease, and the slope K in the Tauc equation for optical absorption is a maximum. Furthermore, at this condition, we obtained B-doped μc-SiNx:H films with both wide gap (∼1.9 eV) and high conductivity (10−1–10−2 Ω−1 cm−1).

Fabrication of polycrystalline silicon thin‐film transistors by ion shower doping technique

AbstractIn the fabrications of polycrystalline silicon thin‐film transistors (TFTs), doping of impurities is often carried out by ion implantation. In this study, dopings of phosphorus and boron were carried out by an ion shower doping technique, where the rf plasma of H2‐diluted PH3 or H2‐diluted B2H6 gas with a magnetic field was used for the ion source. To form the source‐drain regions using this technique, the doping characteristics such as sheet resistivity and impurity profiles in polycrystalline Si were investigated. Using the conditions obtained experimentally, n and p channel Si gate polycrystalline Si TFTs were fabricated on a fused silica substrate by using a CMOS process. It was also confirmed that the conventional photoresist can be used for this process. For the n‐channel transistor, field‐effect mobility μ = 3 cm2/V·s, threshold voltage Vth = 5 V, and on‐off current ratio ION (VD = 6 V, VG = 10 V)/IOFF (VD = 6 V, VG = 0 V) ≌ 106 were obtained for W/L = 12 μm/6 μm. In the p‐channel transistor, the characteristics were similar to those obtained by ion implantation. The ion shower doping technique made it possible to fabricate polycrystalline Si TFTs with a CMOS structure, using a simple apparatus. By using this technique, a large area process will be possible.

Laser-induced vapour-phase syntheses of boron and titanium diboride powders

Small diameter boron and titanium diboride powders were synthesized from vapour phase reactants heated with infrared radiation from a CO2 laser. Boron powders were synthesized from BCI3 + H2 gas mixtures undfrom B2H6. TiCl4 + B2H6 gas mixtures yielded TiB2 powder. BCI3 + H2 + TiCl4 gas mixtures yielded TiCl2 powder but no TiB2. Novel equipment designed to vapourize TiCI4 liquid is described, Detailed characterizations of the product powders are presented.