SiH4 Pressure Research Articles

Measurement of SiH2 Densities in an RF-Discharge Silane Plasma Used in the Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Film

Silylene (SiH2) radicals have been detected by intracavity laser absorption spectroscopy in a parallel plate RF-discharge system used in the chemical vapor deposition of hydrogenated amorphous silicon. By the use of two different calibration methods, an absolute density ranging from 2×108 to 6×109 cm-3 has been obtained as a function of the input RF power and of the partial pressure of SiH4. The flux of SiH2 onto the substrate electrode estimated from the gradient of the spatial distribution is less than 1013 cm-2 s-1. This suggests that its direct contribution to the film deposition is small, although it plays an important role in gas phase reactions.

Plasma and surface reactions during a-Si:H film growth

The mechanisms of a-Si:H film deposition from SiH4 glow discharges are analyzed. Recent progress in modeling and diagnostics of electrical power dissipation in DC and RF discharges revealed the importance of electron attachment and powder formation from negative ions. In conventional deposition conditions of optoelectronic-grade a-Si:H, the plasma chemistry favors SiH3 radicals which combine a low sticking probability and a high surface mobility on the H-covered film surface. Low SiH4 pressure discharges involves a large fraction of non mobile species such as SiHm≤2 radicals, but also a high flux of positive ions which can enhance surface mobility and structural rearrangement by momentum transfer (ion kinetic energy). Surface reactions can be also controlled by electronic energy transfer (neutralization of ions, deexcitation of metastables, photon irradiation, radical recombination). H atoms induce microcristalline silicon growth by combining the effects of chemical etching and annealing of the growth zone and H-coverage of the surface.

Chemical processes promoted by CO2 laser-assisted decomposition of silane on silica substrates

Microstructures were produced on silica substrates by localized deposition or etching via cw CO2 laser-induced decomposition of silane. Silicon dots having a Gaussian profile were deposited at SiH4 pressures above 1 Torr for laser-induced surface temperature at the center of the irradiated zone above 850 °C. With SiH4 pressures below 1 Torr, ring-shaped Si microstructures were produced while the temperature at the center of the irradiated zone was varied from 950 to 1050 °C. The absence of deposition in the center of the hot spot may be attributed to a decrease in nucleus density of Si clusters. At temperatures above 1050 °C, silica substrates were attacked since the interaction between SiO2 and Si atoms produced by decomposition of silane led to the formation of volatile SiO. The etching kinetics was governed by the decomposition kinetics of SiH4 molecules in the hot zone irradiated with the cw CO2 laser beam.

PYROLYTIC DECOMPOSITION OF SILANE ON LASER-IRRADIATED SILICA SUBSTRATES

Microstructures were produced on Si-coated or uncoated silica substrates via cw CO2 laser-induced decomposition of silane. The deposition rate of Si dots having a Gaussian profile was found to be proportional to the SiH4 pressure and linearly dependent on the laser power or laser-induced surface temperature. At low SiH4 pressures (below 1 Torr) and above 1050°C, ring-shaped Si dots were deposited on silica substrates and SiO2 was etched at the center of the laser spot. The reaction mechanisms of the deposition of silicon and etching of silica are discussed in this paper.

A-Si:H Deposition from SiH4 and Si2H6 rf-Discharges: Pressure and Temperature Dependence of Film Growth in Relation to α-γ Discharge Transition

We present an interpretation of the pressure and temperature dependence of the growth kinetics of hydrogenated amorphous silicon (a-Si:H) in SiH4 and Si2H6 rf-glow discharges. At constant rf power, the a-Si:H deposition rate increases drastically at a given pressure depending on the nature of the gas and on the wall temperature. The threshold nature of this transition is attributed to the onset of an electron avalanche due to ion-induced secondary electron emission and ionization in the plasma sheaths close to the electrodes. We analyze the effect of various plasma parameters governing this α-γ discharge transition in terms of equivalent circuit of the discharge and power dissipation mechanisms. The ratio of a-Si:H deposition rates from SiH4 and Si2H6 rf discharges at the same rf power and flow rate is strongly dependent on the pressure because the α-γ transition occurs at a lower pressure for Si2H6 than for SiH4. The transition is shifted to higher pressures as the temperature increases primarily because of the reduction of gas density, which explains contradicting results in the literature on the influence of temperature on a-Si:H deposition rate. At a given rf power and substrate temperature, the optical, structural and electrical film properties are correlated with the variation of deposition rate as a function of SiH4 or Si2H6 pressure.

New approach to the kinetics of silicon vapor phase epitaxy at reduced temperature

The rate of silicon homoepitaxy from SiH4/H2 mixtures has been studied between 750 and 850 °C using a new ultrahigh-vacuum-compatible low pressure reactor. The analysis of the experimental data is novel in including the effects of both nonepitaxial deposition within the reactor and of gas pumping speed. Epitaxy by pyrolysis of SiH4/H2 mixtures on clean Si substrates between 800 and 850 °C is first order in SiH4 pressure but zero order in H2 pressure at least to 1 mm Hg. The results do not support models of growth mechanism derived from previous studies.

Laser-induced chemical vapor deposition of silicon nitride films: Film and process characterizations

We have deposited hydrogenated amorphous silicon-nitride (a-SixN1−x:H) films from NH3-SiH4-Ar gas mixtures, heated by gas-phase absorption of CO2 laser radiation. For the first time, stoichiometric (Si/N=0.75) a-Si3N4:H films were obtained for NH3/SiH4 flow ratios of the order of 1000 and substrate temperatures Ts of about 500 °C. Growth rates as high as 13 Å/min were observed, depending on the partial pressure of SiH4, P(SiH4), the gas temperature Tg and Ts. Tg was calculated from a derived energy-balance equation, which depends sensitively on process parameters. To model the deposition process, the experimental film growth rate is separated into the Si growth rate G(Si) and the N growth rate G(N). Film stoichiometry is interpreted as the ratio G(Si)/G(N). The rate-limiting steps for Si growth are the gas-phase decomposition of SiH4 for Tg below about 750 °C and the SiH4 flow rate at higher Tg. G(N) is affected by both Ts and Tg. The NH3/SiH4 flow ratio must be kept large to ensure a sufficient concentration of N to attain stoichiometry. The reactions are likely to occur both in the gas phase and on the film surface.

Low-Temperature Silicon Epitaxial Growth by CO2 Laser CVD Using SiH4 Gas

Silicon epitaxial growth at a low substrate temperature by CO2 laser chemical vapor deposition using SiH4 has been investigated. Single-crystalline Si was grown at a deposition rate of 15 A/s at 650°C under an SiH4 pressure of 0.05 Torr and a CO2 laser power of 6 W/cm2 on an Si substrate. The crystalline quality of deposited Si films was examined by reflection high-energy electron diffraction, and it was found that the deposition rate depends on the incident angle and the polarization of the CO2 laser beam. This is the first report on low-temperature Si epitaxial growth by CO2 laser CVD.

A comparison of AES and RBS analysis of the composition of reactively sputtered TiSix films

By reactive sputtering of Ti in a gas mixture of Ar/SiH4 it is possible to form TiSi2. The influence of rf bias to the target on film composition is investigated. The dependence of partial pressure of SiH4 on film composition TiSix is also demonstrated. A phenomenological description of the physical processes mainly responsible for film composition is outlined. Analysis of the film composition of the TiSix films have been performed by using both Rutherford back scattering (RBS) and quantitative Auger electron spectroscopy (AES). The results obtained from a wide range of stoichiometries show that the composition data obtained from AES analysis deviate from the bulk stoichiometry obtained by RBS analysis. The conclusion is that the surface modification, caused by precleaning the TiSix films prior to AES analysis changes the surface composition significantly. There are, however, other effects which make quantitative AES analyses of the films difficult, i.e., the difference in escape depths for Auger electrons originating from silicon and titanium. There may also be a matrix effect in the sensitivity factors Prel(Si,Ti).

Doping of GaAs From Silane Decomposition Under Pulsed Laser Irradiation

ABSTRACTWe have studied silicon incorporation in GaAs subsequent to Nd-YAG laser irradiation through high pressure silane atmospheres. The process involves SiH4 pyrolysis at contact with a laser-melted GaAs surface, and incorporation of the released Si atoms in the melt. SIMS analyses have allowed us to study silicon incorporation as a function of SiH4 pressure, laser energy density and number of laser shots. The high sheet resistance of the doped layers indicates that the silicon atoms are poorly electrically activated. A compensation mechanism is discussed based on oxygen penetration from native GaAs oxide layers.

Vibrational excitation effects on silane reactivity in its reaction with bromine atoms

A rate increase of SiH3Br formation in SiH4 photobromination under irradiation by a cw CO2 laser is reported. At low SiH4 pressures (∼1–2 Pa) the radiation effect is shown to be isotope-selective.

Characteristics of Whisker Growth in Amorphous Silicon

The growth of amorphous silicon whiskers grown by thermal decomposition of silane (SiH4) in the temperature range between 500 and 800°C in an argon atmosphere has been investigated in detail. A thin gold film (about 200 Å) on the substrate seems to act as the most effective catalyzer for the whisker growth. The time rate of axial growth at the beginning of each growth curve seems to be proportional to the partial pressure of SiH4. Radial growth proceeds at a constant rate and remains constant even after termination of the extension in length. The two mechanisms of elongation and thickening are controlled by independent activation processes whose activation energies are 0.73 eV and 2.1 eV respectively.

Low-pressure, high-temperature siliconizing of tungsten-I

The study of surface siliconizing of tungsten ribbons by low pressure (10−3 to 10−6 Torr) and high temperature (800 to 1200°C) heterogeneous decomposition of SiH4 shows a competition between silicon deposition on the surface and its diffusion in the metal Coatings of W5Si3 and WSi2 are formed which grow parabolically or linearly depending on deposition and temperature conditions; their thickness has been determined without destroying the ribbon by measuring the variations of the electrical conductivity with the quantity of silicon introduced. The activation energy of the inter diffusion coefficients, the composition and resistivity of the phases, and the surface parameters corresponding to the surface evolution (monochromatic and total emissive powers) have been determined for the different compounds. The decomposition kinetics of SiH4 were also determined.