Thermal Decomposition Of Disilane Research Articles

Thermal Decomposition Mechanism of Disilane

Thermal decomposition of disilane was investigated using time-of-flight (TOF) mass spectrometry coupled with vacuum ultraviolet single-photon ionization (VUV-SPI) at a temperature range of 675-740 K and total pressure of 20-40 Torr. Si(n)H(m) species were photoionized by VUV radiation at 10.5 eV (118 nm). Concentrations of disilane and trisilane during thermal decomposition of disilane were quantitatively measured using the VUV-SPI method. Formation of Si(2)H(4) species was also examined. On the basis of pressure-dependent rate constants of disilane dissociation reported by Matsumoto et al. [J. Phys. Chem. A 2005, 109, 4911], kinetic simulation including gas-phase and surface reactions was performed to analyze thermal decomposition mechanisms of disilane. The branching ratio for (R1) Si(2)H(6) --> SiH(4) + SiH(2)/(R2) Si(2)H(6) --> H(2) + H(3)SiSiH was derived by the pressure-dependent rate constants. Temperature and reaction time dependences of disilane loss and formation of trisilane were well represented by the kinetic simulation. Comparison between the experimental results and the kinetic simulation results suggested that about 70% of consumed disilane was converted to trisilane, which was observed as one of the main reaction products under the present experimental conditions.

Formation Mechanism of Hydrogenated Silicon Clusters during Thermal Decomposition of Disilane

Hydrogenated silicon clusters (SinHm) were detected during the thermal decomposition of disilane in a flow reactor by using time-of-flight (TOF) mass spectrometry coupled with vacuum ultraviolet (VUV) photoionization at a temperature range of 680−860 K and total pressures of 20−40 Torr. SinHm clusters were photoionized by the VUV radiation at 10.2 eV (121.6 nm). The SinH2n+2 (n ≥ 2), SinH2n (n ≥ 2), SinH2n-2 (n ≥ 5), and SinH2n-4 (n ≥ 5) containing up to 10 silicon atoms were observed as gas-phase products during the disilane pyrolysis, while no ion signal due to Si1 species such as Si, SiH, SiH2, and SiH3 was detected. Energetics for the disilane unimolecular decomposition has been calculated at the Gaussian-3 (G3)//B3LYP level of theory. On the basis of a kinetic model proposed by Swihart and Girshick [J. Phys. Chem. B 1999, 103, 64], the gas-phase kinetic simulation has been performed to analyze the formation mechanism of hydrogenated silicon clusters in the thermal decomposition of disilane. Temperature and time dependences of disilane loss and hydrogenated silicon cluster formation were compared with the results of kinetic simulation. The formation processes of Si2nH2n and SinH2n-2, which have linear or cyclic and polycyclic structures, were suggested to be the key steps for the large cluster growth.

Infrared study of adsorption and thermal decomposition of Si2H6 on Si(100)

Sumario We have investigated the adsorption and thermal decomposition of disilane on Si(100) (2×1) using infrared absorption spectroscopy. We demonstrate that at room temperature, disilane dissociatively adsorbs onto the surface with the dimer bond unbroken, to produce mono-, di-, and tri-hydride species. At low coverages, the disilane molecule adsorbs on the surface without breaking the Si–Si bond of the molecule. Thermal annealing following room-temperature adsorption of disilane produces a hydrogen-terminated adatom dimer (HSi–SiH) and an isolated monohydride species. We suggest that these hydride species are generated through the rupture of the substrate dimer bonds. Hydrogen desorption from the isolated monohydride occurs at much lower temperature than that from the adatom dimer.

Diagnostics of the gas-phase thermal decomposition of Si 2H 6 using vacuum ultraviolet photoionization

Vacuum ultraviolet (VUV) photoionization at 10.2 eV was employed for the detection of gas-phase molecules formed after thermal decomposition of disilane at a total pressure of 30 Torr and in the temperature range of 298–740 K. The Si n H 2( n+1) ( n=3–5) and Si n H 2 n ( n=2–5) species resulting from disilane pyrolysis in a flow reactor were directly observed using time-of-flight mass spectrometry. Unlike multiphoton ionization at 6.4 eV photons, no fragmentation was observed by the VUV single-photon ionization at 10.2 eV.

High-performance thin-film transistors in large grain size polysilicon deposited by thermal decomposition of disilane

The characteristics of polycrystalline silicon thin-film transistors (TFTs), fabricated on films deposited in an LPCVD system using disilane, were investigated as a function of grain size. The grain size and its statistical distribution were correlated with processing conditions; optimum conditions to maximize grain size for device applications were determined. The dependence of the ON current and the OFF (leakage) current of polysilicon TFTs, as well as of their statistical distributions, on the grain size, the gate dielectric processing temperature, the channel length, and the device structure are reported and discussed. Larger grain size polycrystalline silicon films were found to yield devices with higher mobilities and lower leakage currents. TFTs, fabricated in polysilicon films with average grain sizes of 1.8 /spl mu/m with thermally grown silicon dioxide as gate dielectric, had ON/OFF current ratio well above 10/sup 8/, average effective mobility value of 170 cm/sup 2//V.s and subthreshold slope of 0.3 V/dec.

Hydrogen desorption from Si: How does this relate to film growth?

The desorption of hydrogen from the Si(100) surface is investigated. The hydrogen coverage is generated by the adsorption of atomic hydrogen, by the thermal decomposition of disilane, or during silicon epitaxy using silane in a rapid thermal chemical vapor deposition reactor. Temperature programmed desorption studies are then used to help yield information about the hydrogen surface coverage and the desorption kinetics of hydrogen. The desorption order of hydrogen is first order, consistent with previously reported single crystal studies. However, the activation energy for desorption of hydrogen from surfaces generated during Si epitaxy with SiH4 is considerably different. The activation energy for hydrogen desorption from these epitaxially grown layers is 49±3 kcal/mol. The presence of monatomic steps on the surface, which are created during the temperature quench, is believed to play a role in this difference of activation energies. Single crystal, ultra-high vacuum based studies using atomic hydrogen and disilane adsorption and desorption are used to gain further insight into this phenomena.

A quantitative ring dye laser absorption diagnostic for free SiH 2 ( X̃ 1A1) radicals at high temperatures

The silylene radical (SiH 2) was detected in reacting high temperature mixtures of disilane (Si 2H 6) highly diluted in argon by time-resolved ring dye laser absorption measurements at λ = 579.35 nm. The measured absorption was caused by a single line transition in the Ã− X̃(0,2,0)−(0,0,0) band of SiH 2 which was exclusively initiated by the narrow bandwidth laser source. The absorption profiles were measured in the reaction zone behind reflected shock waves at temperatures between 1000 and 1900 K, and at pressures 0.2 bar⩽ p⩽1.3 bar. Several calibration experiments were performed at temperatures above 1500 K and low initial Si 2H 6 concentrations. To establish the connection between measured absorption and the SiH 2 concentrations, numerical simulations on disilane pyrolysis were performed based on a reaction kinetic model. From both the measured absorption and the calculated SiH 2 concentrations the silylene absorption cross section was determined to be σ SiH 2 = 1.3 × 10 -17cm 2, at the reference conditions ν 0 = 17260.82 cm -1, T 0 =1757 K and p 0 = 0.3 bar. A spectroscopic model was introduced to describe the temperature and pressure dependence of the SiH 2 absorption cross section at the given wavelength. All measured concentration time-histories of SiH 2 radicals formed during the thermal decomposition of disilane in the given experimental range could be verified. The detection limit was about 1×10 13cm -3 for an absorption path length of 8 cm and the laser diagnostic was proved well suited for kinetic studies of elementary reactions involving silylene.

Resonance enhanced multiphonon ionization of silicon produced during disilane pyrolysis

Gas phase species generated by thermal decomposition of disilane were studied using resonance enhanced multiphoton ionization at disilane pressures ranging from 1–10 Torr and temperatures ranging from 300–1000 K. Atomic Si, mass 28, was observed at 487.9, 417.7, and 416.2 nm. A mass-30 signal was not observed between 494–515 nm. Masses 2, 32, and 60 were observed using multiphonon ionization and were photoionization fragments from higher silanes and silenes. Thermal decomposition reactions were the main source of atomic Si for the mass-28 signal, although ionization of SiH2 and higher silanes followed by fragmentation may have contributed some of the mass-28 signal.

Deposition and Crystallization of a‐Si Low Pressure Chemically Vapor Deposited Films Obtained by Low‐Temperature Pyrolysis of Disilane

In this work we have studied the deposition and crystallization of silicon films initially deposited in the amorphous phase by thermal decomposition of disilane and subsequently crystallized upon a low temperature thermal anneal. Experiments were performed over a wide range of deposition conditions. The grain size of the crystallized films was found to depend upon the deposition conditions; particularly it was found to increase monotonically with increasing deposition rate, while a nonmonotonic behavior was observed with respect to the deposition temperature. For films deposited with similar deposition rates, in the temperature range of 450 to 550°C, a maximum in the grain size was observed at 470°C. This maximum is attributed to the minimization of the nucleation rate, observed at 470°C, combined with the faster crystallite growth rate at low deposition temperatures. The minimum in the nucleation rate is explained by the combination of two mechanisms which, we propose, contribute to the nucleation process. One mechanism is attributed to nucleation induced by the high free energy associated with a highly disordered silicon matrix. The other mechanism is attributed to nucleation occurring on pre‐existing subnuclei formations, in a less disordered structure.

Nucleation and Grain Growth in Silicon Films Deposited by Thermal Decomposition of Disilane

Nucleation and Grain Growth in Silicon Films Deposited by Thermal Decomposition of Disilane

Interfacial reaction between disilane and a Ge(111)c(2 × 8) surface

We present photoemission results on the thermal and catalytic decomposition of disilane (Si2H6) on a monocrystalline Ge(111)c(2×8) surface. Catalytic decomposition of disilane is obtained at a hot tungsten filament. Germanium substrates were heated by the Joule effect in the 20–600 °C temperature range and exposed to low pressure (10−5 Torr) Si2H6 doses. The thicknesses of the Si layers deposited by both methods were estimated from X-ray photoemission spectroscopy (XPS) measurements. Valence band ultraviolet photoemission spectroscopy (UPS) is used to characterize the crystalline quality of the deposited films. The growth rate of the Si film is found to be 10 times higher when obtained after catalytic decomposition rather than by thermal decomposition of disilane. For substrate temperatures above 400 °C, we observe a silicon-germanium intermixing.

Reduced photoinduced degradation in chemical vapor deposited hydrogenated amorphous silicon films

Hydrogenated amorphous silicon (a-Si:H) films prepared by the thermal decomposition of disilane in a He atmosphere [chemical vapor deposition (CVD)] contain 3–4% hydrogen, considerably less than the hydrogen content in a-Si:H films prepared by glow discharge (GD). The CVD a-Si:H films have been irradiated for up to 175 h at 500 and 600 mW/cm2 using a quartz-halogen lamp. The defect density in CVD a-Si:H films is estimated to approach saturation at mid 1016 cm−3 from an initial defect density of less than 6×1015 cm−3, whereas the typical defect density at saturation is greater than 1018 cm−3 for GD a-Si:H films. The significantly reduced Staebler–Wronski effect in CVD a-Si:H films is attributed to the lower concentration of clustered hydrogen atoms or silicon–hydrogen bonds.

Hydrogenated amorphous silicon films deposited in a helium atmosphere

Hydrogenated amorphous silicon (a-Si:H) films have been deposited on Corning 7059 glass and other substrates by the thermal decomposition of disilane in a helium flow. The deposition rate of a-Si:H films in a He atmosphere has been found to be significantly higher than that deposited in a hydrogen atmosphere under the same conditions. The a-Si:H films deposited in a He atmosphere showed improved structural properties as compared with those deposited in a hydrogen atmosphere. The properties of a-Si:H films deposited in a helium atmosphere such as density, photoconductivity, minority-carrier diffusion length, gap-state density, etc., have been determined. These films appear to have better electronic properties than the chemical-vapor-deposited a-Si:H films heretofore reported.

Deposition and photoconductivity of hydrogenated amorphous silicon films by the pyrolysis of disilane

The thermal decomposition of disilane (Si2H6) in a hydrogen or helium flow has been used for the deposition of hydrogenated amorphous-silicon (a-Si:H) films on the surface of Corning 7059 glass substrates at 450–500 °C. The reaction product consists of monosilane and trisilane in addition to the unreacted disilane and ethylsilane (the major impurity in commercial disilane). The concentration of Si2H6 in the reaction mixture has been found to strongly affect the deposition rate and the photoconductivity of a-Si:H films. At a given Si2H6 concentration, the deposition rate of a-Si:H films increases exponentially with temperature. At a given substrate temperature, the AM1 conductivity of a-Si:H films increases with increasing Si2H6 concentration and approaches 10−5 Ω cm−1 at Si2H6 concentrations higher than about 4%, and the conductivity ratio in better films is about 105. The conductivities of CVD a-Si:H films have been found to show negligible change under illumination over a period of several days. The optical band gap of a-Si:H films has been determined to be 1.65–1.68 eV. The doping of a-Si:H films with arsenic and boron has been carried out, and their activation energies determined.

Properties of Amorphous Silicon Films Deposited at Rates Higher Than 1 μM/MIN.

ABSTRACTThe thermal decomposition of disilane in a helium flow has been used for the deposition of hydrogenated amorphous sil icon (a-Si:H) films on various substrates at rates higher than 1 μm/min, and a-SI:H films with thickness up to 20 μm have been deposited in this manner. Their optical properties, photoconductivity, minority carrier diffusion length, gap state density, etc., have been measured. The electronic properties of these films are superior to those of chemical vapor deposited a-Si:H films heretofore reported, indicating that the thermal decomposition of disilane in a hel ium atmosphere is a promising technique for the deposition of a-SI:H films.

Hydrogenated Amorphous Silicon Films by the Pyrolysis of Disilane(1)

AbstractThe thermal decomposition of disilane in a hydrogen or helium flow has been used for the deposition of hydrogenated amorphous silicon (a-Si:H) films on the surface of several substrates at 450°-500°C. The concentration of disilane in the reaction mixture has been found to affect strongly the deposition rate and the photoconductivity of a-Si:H films. The AMI conductivity of a-Si:H films increases with increasing disilane concentration and approaches lO−5(ohm-cm)−l at disilane concentrations higher than about 4%, and the conductivity ratio is about lO5. The density of gap states in CVD a-Si:H films have been determined by the photothermal deflection spectroscopy, capacitancetemperature, capacitance-frequency, and space-charged-limited current measurements with similar results.