Silicon Source Gas Research Articles

Quasi-monolayer deposition of silicon dioxide

SiO 2 films were deposited layer by layer from a new silicon source gas, i.e. tetra-iso-cyanate-silane (Si(NCO) 4). An average growth rate of about 0.17 nm per cycle was achieved by a cyclic process of alternating reaction of the substrate surface with Si(NCO) 4 and H 2O respectively. The detailed deposition characteristics together with chemical and physical properties of the deposited film were evaluated with ellipsometry, Fourier transform IR spectroscopy, X-ray photoelectron spectroscopy and Auger electron spectroscopy.

Carbon content of silicon oxide films deposited by room temperature plasma enhanced chemical vapor deposition of hexamethyldisiloxane and oxygen

Hexamethyldisiloxane is used as a silicon-source gas for plasma enhanced chemical vapor deposition (PECVD) growth of silicon oxide films for passivation layers in microelectronics. In order to produce low permeability films, it is necessary to minimize the carbon content. Films were deposited by a room temperature PECVD process in a parallel plate reactor, and were characterized by infrared spectroscopy, ellipsometry, microbalance, and elastic recoil detection (ERD). The infrared-active carbon groups appear in Si–CH3, CHx, C=O, and SiC bands. A double band at 2343 cm−1 has also been seen to track these bands. Deposition rate data shows linear behavior as a function of the Hexamethyldisiloxane (HMDSO) concentration in the reactor. The carbon within the films ranges from 36% to <1% of the amount of carbon assisted with HMDSO required to grow the films, depending upon the oxygen flow rate. By comparing the ERD composition data to the infrared spectral data, a carbon content correlation value has been found, and a detailed study of the data reveals evidence of C–C bond existence within films having the greatest total carbon content. Finally, it appears that the 2343 cm−1 band corresponds to CO2 rotational bands, in which the distribution of rotational states is evidence of hindered molecular motion.

Surface Hydrogen Effects on Ge Surface Segregation during Silicon Gas Source Molecular Beam Epitaxy

Using reflection-high-energy-electron diffraction (RHEED), the temperature dependence of Ge surface segregation during silicon gas source molecular beam epitaxy (Si-GSMBE) from hydride sources was studied, and it was found that surface hydrogen, which is produced by the dissociation of Si2H6 and GeH4 on the growing surface, may act as a growth-controlling surfactant. Comparison with results from solid source growth results suggests that hydrogen significantly suppresses the Ge segregation. Segregation kinetics were examined through simulation studies and the results indicate that the addition of surface hydrogen to the system inhibits segregation due to a lowering of the Gibbs heat of segregation.

Study of growth kinetics in silicon gas source molecular beam epitaxy with disilane using RHEED intensity oscillations

We have studied reflection high energy electron diffraction (RHEED) intensity oscillations during silicon deposition from disilane on Si(100) in a gas source molecular beam epitaxy (GSMBE) system. The intensity oscillations were used to determine the growth rate over a wide range of substrate temperatures, disilane mass flows, azimuths and angles of incidence. It was found that the oscillation frequency does not depend on azimuth (with the exception of the 〈110〉 azimuths) or angle of incidence of the electron beam. Oscillations were observed for substrate temperatures ranging from 400 °C to 650 °C. There is no lower temperature limit for the occurrence of oscillations. However, below 400 °C the frequency becomes so low that experiments are impractical. Above about 600 °C, the growth rate is no longer limited by the desorption of surface hydrogen; other reaction steps such as adsorption and dissociation of disilane become rate limiting. Remarkably, even at lower temperatures the growth rate never saturates owing to the complete termination of all surface bonds by hydrogen but keeps increasing slightly with increasing flux. Comparison with RHEED oscillations observed in silicon solid source MBE indicates that the surface adsorbates in GSMBE are much less mobile, probably because of their different nature. Differences and similarities between the deposition processes of the two techniques are discussed.

Chemically deposited epitaxial Si1−xGex thin film growth at atmospheric pressure

A so-called ‘‘three-partial-rates’’ model of Si1−x Gex chemical vapor deposition that describes total growth rate as well as layer composition is applied to experimental data obtained at atmospheric pressure in hydrogen along with germane. The kind of silicon source gas was varied in that investigation using silane, dichlorosilane, and disilane, whereas all the other deposition conditions were maintained constant. Theoretical expectations drawn on the background of the above model agree fairly well with the experimental findings. All the experimental results this letter is related to were independently obtained and published [T. I. Kamins and D. J. Meyer, Appl. Phys. Lett. 61, 190 (1992)].

RHEED investigation of Ge surface segregation during gas source MBE of [formula omitted] heterostructures

Ge segregation during silicon gas source molecular beam epitaxy (Si-GSMBE) has been studied by in situ growth rate measurements using reflection-high-energy-electron diffraction (RHEED) intensity oscillations. Growth rate of Si on Si 1 − x Ge x gradually decreases to the Si homoepitaxial growth rate, which is attributed to Ge surface segregation at the growth interface. This segregation has been modelled using a mass balance equation and it has been found that the observed growth rate enhancement can be used as a direct measure of the Ge segregation. Using this novel in situ technique, concentration dependence of Ge segregation was studied, and it was found that the segregation decay curve is nonlinear, resulting in two segregation regimes dependent upon the Ge concentration, consistent with previous studies. Temperature dependence studies reveal that surface hydrogen, which is produced by the dissociation of Si 2H 6 and GeH 4 on the surface during growth, may act as a growth controlling surfactant, and comparison with solid source growth results suggests that it significantly suppresses the Ge segregation, leading to a more precise control of the interface. Finally, the thermal stability of the segregated surfaces was examined. Growth interruption and annealing during Si overlayer growth on Si 1 − x Ge x resulted in a small increase in the surface Ge concentration, which may be ascribed to the outdiffusion effect of Ge from the near surface region.

Investigation of surface reconstruction domain behaviour during Si-GSMBE

Bilayer reflection-high-energy-electron diffraction (RHEED) intensity oscillations were observed during growth on a double-domain Si(001) (2×1)+(1×2) substrate during silicon gas source molecular beam epitaxy (Si-GSMBE) using disilane. A transition from monolayer to bilayer-mode oscillation behaviour was observed in the [110] azimuth during growth. Simultaneous measurement of RHEED intensity oscillations of the specular beam and (1×2) and (2×1) reconstruction related beams in the [010] azimuth showed that the bilayer oscillations resulted from alternating surface reconstructions. The emergence of these bilayer oscillations is discussed on the basis of the anisotropic growth kinetics on Si(001) surfaces. RHEED measurements on vicinal substrate were made and reveal that a preferential growth of type-B steps results in type-B domain predominance at expense of type-A domains. Temperature studies show that at substrate temperatures above 600°C this anistropy disappears and RHEED intensity variations resume “normal” monolayer-mode growth behavior.

Si<SUB>2</SUB>Cl<SUB>6</SUB>からのシリコン析出の速度および形態

Silicon precipitation reaction was conducted on non-crystalline quartz glass substrate from the hydrogen reduction of Si2Cl6 at temperatures from 873∼1273 K using a horizontal cold wall reactor. The precipitation rate was measured under various experimental conditions and precipitation morphology was observed by X-ray diffraction analysis and SEM. The precipitation rate is one order of magnitude larger than those of other silicon source gases. In the condition when the reaction is controlled by a surface reaction (873∼1073 K), the rate dependence on Si2Cl6 and H2 are proportional to 1/2 order of the former and to the first order of the latter, respectively. From XRD and SEM results, Si precipitated at 1073 K has a preferred crystal orientation in the 〈110〉 direction.

Temperature-dependent growth anisotropy observed on Si(001) surfaces during silicon gas source molecular beam epitaxy using disilane

Bilayer reflection high energy electron diffraction (RHEED) intensity oscillations were observed during growth on double-domain Si(001) (2 × 1) + (1 × 2) substrates during silicon gas source molecular beam expitaxy using disilane. A transition from monolayer to bilayer mode oscillation behaviour was observed in the < 110 > azimuths during growth. Oscillations began with an asymmetric monolayer waveform which transformed into an apparent bilayer mode following several oscillation periods. Simultaneous measurement of RHEED intensity oscillations of the specular beam and (1 × 2)- and (2 × 1)- reconstruction-related beams in the [010] azimuth showed that the bilayer oscillations resulted from alternating surface reconstructions. The emergence of these bilayer oscillations during growth is discussed on the basis of the anisotropic growth kinetics on Si(001) surfaces which results in a preference of type B domains. Temperature studies reveal that, at substrate temperatures above 600 °C, this anisotropy disappears and RHEED intensity variations resume “normal” monolayer mode growth behaviour.

Growth anisotropy observed on Si(001) surfaces during Si-GSMBE using disilane

Bilayer reflection high energy electron diffraction (RHEED) intensity oscillations were observed during growth on double-do-main Si(001)(2 × 1) + (1 × 2) substrates during silicon gas source molecular beam epitaxy (Si-GSMBE) using disilane. A transition from monolayer to bilayer mode oscillation behaviour was observed in the 〈110〉 azimuths during growth. Oscillations began with an asymmetric monolayer waveform which transformed into an apparent bilayer mode following several oscillation periods. Simultaneous measurement of RHEED intensity oscillations of the specular beam and (1 × 2) and (2 × 1) reconstruction related beams in the [010] azimuth showed that bilayer oscillations resulted from alternating surface reconstructions. The emergence of these bilayer oscillations during growth is discussed on the basis of the anisotropic growth kinetics on Si(001) surfaces which results in a preference of type-B domains. RHEED measurements made following growth on vicinal substrates reveal that diffraction features arising from type-B terraces show a marked increase in intensity, while type-A domain features decrease, confirming that the anisotropy results in a preferred growth on type-B terraces. Temperature studies reveal that at substrate temperatures above 600°C, this anisotropy disappears and RHEED intensity variations resume “normal” monolayer-mode growth behaviour.

Effect of silicon source gas on silicon-germanium chemical vapor deposition kinetics at atmospheric pressure

Epitaxial Si1−xGex alloy layers have been deposited in an atmospheric-pressure, chemical-vapor-deposition reactor using dichlorosilane, silane, and disilane, along with germane. The deposition rate increases and the Ge content decreases with increasing reactivity of the silicon-containing gas. The rate increases monotonically with increasing Ge content in the layer for all three gases, in contrast to the behavior seen in systems operating at substantially lower total deposition pressures, suggesting that the differences in previously reported behavior are dominated by the different operating-pressure regimes, rather than the different silicon source gases.

A First Approach to CVD Si1–xGex Layer Growth by Means of Chemical Reaction Kinetics

AbstractA reaction mechanism will be suggested for interpreting Si1–xGex CVD layer deposition from a silicon source and germane reaction gas mixtures in order to explain the observed silicon layer growth increase in consequence of the presence of germane. A successive substitution of the hydrogen atoms available in germane molecules by silyl groups forming a silicon containing intermediate of germane will be assumed. It will further be supposed that both the original silicon source and the germane intermediates will independently be decomposed by chemical reactions leading to Si1–xGex CVD layer deposition from dichlorosilane‐germane‐hydrogen reaction gas mixtures at temperatures in the range of 600 ≦ T(°C) ≦ 900 as recently published by KAMINS and MEYER.

Properties of in Situ Doped Polycrystalline Silicon Films Deposited from Phosphine and Disilane

AbstractThe deposition of in situ phosphorus doped silicon films was performed using disilane (Si2H6) instead of monosilane (SiH4) as the silicon source gas. The negative aspects of in situ doping with phosphine, namely low deposition rates and poor across wafer uniformity, were to a large extent eliminated. Haze-free polycrystalline films were deposited at ∼60 Å-min1 with less than 5% radial thickness variation over a 100 mm wafer. However, the temperature suitable for depositing films using Si2H6 was shifted downward from that used for SiH4 and similarly, the conditions for good quality (haze-free)films were adjusted. Within specific temperature ranges, varying the gas pressure, flow,and Si2H6 to PH3 ratio resulted in the formation of oneof three types of haze. The films produced had unusually low resistivities of ∼770 μohm-cm after furnace annealing at 850ºC for 1800s. A 20 nm thick surface layer of amorphous silicon oxide was revealed during transmission electron microscopy (TEM) examination of annealed films. Although this oxide layer was undoped, the phosphorus gradient, measured by energy dispersive x-ray analysis (EDX) and secondary ion mass spectroscopy (SIMS), increased towards the surface of the polycrystalline film, suggesting that dopant was diffusing to the surface. A matrix involving different annealing and capping layers was conducted to investigate this phenomenon further. Extremely large grains resulted when a capping layer of SiO2 was deposited prior to rapid thermalannealing (RTA). An autodoping effect was observed when another capping layer, such as undoped polycrystalline silicon, was used.

Rapid Thermal Chemical Vapor Deposition of Polycrystalline Silicon From Dichlorosilane

AbstractRapid Thermal Chemical Vapor Deposition (RTCVD) of undoped and insitu doped polycrystalline silicon films has been accomplished in a cold-wall reactor. Dichlorosilane was used for the silicon source and AsH3 gas was used as the dopant source. Thedeposition kinetics of poly-silicon films on silicon dioxide over a range of deposition temperatures, pressures and carrier gas chemistries was studied. Both blanket and selective deposition modes were examined. The poly-silicon films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for morphology and grain size analysis. Using X-ray diffraction technique, preferred grain orientation dependency of poly-silicon films on growth conditions was investigated. Dopant incorporation, dopant activation and oxygen content of polysilicon films were measured by secondary ion mass spectrometry (SIMS), four point probe, and spreading resistance profiling (SRP) techniques.This paper is to report the results of material characterization of polysilicon films deposited by RTCVD, and to address the applications and advantages of ‘Integrated Processing’ technology involving deposition of polysilicon.

Silicon doping of GaAs and Al xGa 1− xAs using disilane in metalorganic chemical vapor deposition

Disilane is presented as a new Si source gas in the metalorganic chemical vapor deposition of both GaAs and Al x Ga 1- x As. The doping characteristics of disilane were studied over a wide range of growth conditions: temperature, gas phase stoichiometry, and disilane concentration in the growth ambient. Disilane exhibits several features as a doping gas which prove it superior in this application to silane, the conventional silicon source gas. Doping by means of disilane shows no dependence on growth temperature in sharp contrast to the strong temperature dependence found using silane. The decomposition reaction of disilane is very efficient, reducing the amount of dopant gas required by about two orders of magnitude at the lower growth temperatures. The doping efficiency of disilane is also independent of the aluminum content of the Al x Ga 1− x As alloy layers. These results indicate that disilane may be the preferred silicon doping gas for GaAs and Al x Ga 1− x As.

High Pressure Plasma (HPP) Deposition of Polycrystalline Silicon Ribbons

A high pressure plasma (HPP) deposition process has been characterized for its potential in producing polycrystalline silicon films (ribbons) at low cost. Gas Chromatographic (GC) analysis of HPP deposition reactor effluent gases has been used for characterizing the deposition process. Silicon tetrachloride, trichlorosilane, dichlorosilane, and silane have been evaluated as possible silicon source gases for silicon deposition by HPP. Deposition efficiencies have been determined under various experimental conditions such as rf power of HPP, concentration and flow rate of reactant gases, and substrate temperature. These efficiencies were found to be higher than those obtained by a conventional chemical vapor deposition (CVD) process under all conditions of practical interest. The observed improvements in HPP silicon deposition may be explained using thermodynamics, operative kinetic processes, and deposition mechanisms. Economic potential of the HPP deposition process for producing silicon films appears favorable.

In-process monitoring and control of doping gas concentration during vapor phase silicon epitaxial growth by using a flame photometric detector

An in-process monitoring and control method of the doping gas concentration during epitaxial growth of Si was developed. A flame photometric detector (FPD) can be used as a monitor for the PH 3 and B 2H 6 dopant concentrations in the injected doping gases. A combination of this dopant monitor with an automatic control system of the silicon source (SiHCl 3) gas concentration using an infrared spectrophotometer as a monitor, makes possible an automatic in-process control of the concentrations of dopant and of silicon source gas supplied to the reactor. The present system provides an accurate and reproducible control of impurity concentrations in Si epitaxial layers. Good correlation between the monitored signal (or the doping gas concentration) and the impurity concentration incorporated into the growth layers was confirmed for PH 3 (n-type) and B 2H 6 (p-type) doping. For the B 2H 6 doping, a divergence from the linear relationship between the doping gas concentration and the impurity concentration in the layers was observed in the level of acceptor concentration below about 10 15 atoms/cm 3. The transient response of the present system was measured by growing epitaxial layers with increasing and decreasing step-changes in the dopant gas flow during continuous deposition of the layers. Some interesting, but complicated, transient responses of impurity concentration in the growth layer were observed. The responses are different between the PH 3 doping and the B 2H 6 doping, and also different between increasing and decreasing steps especially for the B 2H 6 doping.