Epitaxial Silicon Films Research Articles

Low-temperature silicon homoepitaxy by hot-wire chemical vapor deposition with a Ta filament

Growth of 400 nm epitaxial silicon films on (1 0 0) silicon wafers at temperatures as low as 280 °C is demonstrated by use of a tantalum filament in hot-wire chemical vapor deposition. Systematic studies on the effects of substrate temperature and filament current show that the thickest epitaxial layers (450 nm) are grown at temperatures of ∼380 °C and that the epitaxial thickness before breakdown ( h epi) decreases when the filament current (and growth rate) is increased. Higher substrate temperatures reduce the strain in the epitaxial layer. There are significant differences in film quality when films are grown with tantalum versus tungsten filaments, suggesting that growth chemistry is sensitive to the filament material.

Roughness, impurities and strain in low-temperature epitaxial silicon films grown by tantalum filament hot-wire chemical vapor deposition

AbstractWe grow epitaxial silicon films onto (100) silicon wafers from pure silane by hot-wire chemical vapor deposition (HWCVD). The films grow epitaxially for a thickness hepi before a Si:H cones nucleate and expand. We study the dependence of hepi on growth rate and the differences between Ta and W filaments. The surface morphology of thin but completely epitaxial films are studied in order to correlate the surface roughness during growth with the eventual epitaxial breakdown thickness. Surface roughness, strain and H at the wafer/film interface are not likely to cause the observed breakdown.

Five-nanometer thick silicon on insulator layer

Silicon on insulator (SOI) has been achieved using epitaxially grown Si∕Y2O3∕Si structure. Silicon film as thin as 5nm was achieved. Pulsed laser deposition technique was used for the epitaxial deposition of both the Y2O3 and silicon. The growth conditions were adjusted to achieve two-dimensional growths of single crystal silicon films on Y2O3. No dislocations were observed in these silicon epitaxial films. This approach will allow the independent thickness control of both silicon and the oxide in the nanometer range. Si∕CeO2∕Si SOI structure was not as successful due to the formation of an amorphous oxide film at the interfaces.

Defects Induced by Carbon Contamination in Low-Temperature Epitaxial Silicon Films Grown with Monosilane

The structures of the defects induced by carbon contamination in epitaxial silicon films grown with monosilane (SiH4) on silicon substrates were investigated. A new formation mechanism of defects associated with carbon in silicon epitaxial growth processes is proposed. The carbon contaminants were introduced prior to the growth by chemical vapor deposition (CVD), where the growth chamber was intentionally contaminated with organic materials. The carbon contaminant concentration was changed by adjusting the annealing conditions at temperatures ranging from 900°C to 1100°C. Silicon epitaxial films were grown by CVD at a temperature of 700°C. In this experiment, we found that pits were formed as dominant surface defects under the condition of a relatively low carbon concentration of less than 4.5×1013 cm-2, while mound defects were formed at a carbon concentration of more than 4.5×1013 cm-2. These defects can be explained by the formation of silicon carbide (SiC) islands resulting from the carbon contamination.

Polarization-dependent Raman spectra of thin crystalline silicon films

Polarization-dependent Raman spectra are presented to analyze the structural properties of epitaxial, quasiepitaxial, and microcrystalline silicon films deposited on (100) single-crystal silicon substrates by electron cyclotron resonance plasma-enhanced chemical-vapor deposition. We rotate the sample with respect to the polarization direction of the incident laser light and observe the changes in Raman scattering. The measurements are very effective in differentiating between films with a preferred orientation and those that are randomly oriented or amorphous. An interesting anisotropy has been observed for quasiepitaxial films for which the spectra resemble those of single-crystal wafers under normal measurement conditions. However, at sample orientations where the scattering intensity is minimized, additional structure on the low-energy side of the main silicon TO-phonon peak becomes visible. This is tentatively attributed to scattering from crystalline and amorphouslike grain-boundary regions. Polarization-dependent Raman spectra are able to provide useful information on the structure of these films which would normally be masked by the main silicon optical-phonon peak.

Formation mechanism of local thickness profile of silicon epitaxial film

From the viewpoint to obtain a very flat semiconductor silicon epitaxial film, the influence of an epitaxial reactor design on a local thickness profile of a silicon epitaxial film is studied. The characteristic thickness valleys formed in a trichlorosilane–hydrogen system using a horizontal cold wall single-wafer epitaxial reactor at atmospheric pressure are concluded to have a quantitative relationship with the local decrease in the transport rate of trichlorosilane induced by the increase in the velocity, the increase in the temperature and the decrease in the trichlorosilane concentration in the gas phase, which are induced by the gas inlet design.

Epitaxial silicon films deposited at high rates by gas-jet electron beam plasma CVD

We discuss a new method for low temperature epitaxial growth of silicon films by gas-jet electron beam plasma chemical vapor deposition in SiH 4–Ar mixture. The growth rate up to 0.8 μm/min becomes possible at the substrate temperature below 650 °C, without using ultra-high vacuum chamber. Epitaxial Si films were deposited with the thickness up to 2–10 μm. The structure of the films has been studied after deposition by transmission electron microscopy, transmission high energy electron diffraction and reflection high energy electron diffraction. All films were of epitaxial types, but they were characterized by a high density of threading dislocations (≈10 7 cm −2).

Phosphorus and boron diffusion in silicon under equilibrium conditions

The intrinsic diffusion of phosphorus and boron in high-purity epitaxial silicon films has been studied. Phosphorus diffusion in a wide temperature range (810 to 1100 °C) revealed diffusion coefficients with an Arrhenius behavior exhibiting an activation energy of 2.74±0.07 eV and a pre-exponential factor of (8±5)×10−4 cm2/s. In the temperature range of 810 to 1050 °C, boron was found to diffuse with an activation energy of 3.12±0.04 eV and a pre-exponential factor of 0.06±0.02 cm2/s. These results differ from those of many previous studies, but this deviation may to a large extent be attributed to slow transients before equilibrium concentrations of point defects are established at temperatures below ∼1000 °C. Despite a similar diffusion mechanism mediated by Si self-interstitials, P exhibits a lower activation energy than B because of stronger bonding to the Si self-interstitial.

Modeling the influence of arsenic autodoping on the sheet resistance of epitaxial silicon films and its application to statistical process control (SPC)

An epitaxial layer sheet resistance monitoring procedure has been developed to overcome the convolution between intentional epilayer doping and arsenic autodoping for multiwafer reactors. The procedure models the epilayer as an intentionally phosphorous-doped region plus an arsenic autodoped region by approximating the epilayer as two resistors in parallel. The resulting sheet resistance SPC monitoring procedure is sensitive to shifts in epilayer carrier concentration as well as arsenic autodoping induced by product lots.

Flatness Deterioration of Silicon Epitaxial Film Formed in a Horizontal Single-Wafer Epitaxial Reactor II

The thickness profile of a silicon epitaxial film formed using a horizontal single-wafer epitaxial reactor in a trichlorosilane–hydrogen system is evaluated using numerical calculations, taking into account the details of the entire gas inlet geometry for the first time. The characteristic thickness profile is mainly due to the nonuniform temperature distribution above the silicon substrate formed by the gas inlet, consisting of inlet plates, a step and three adjustable inlet sections. The authors conclude that the gas inlet is responsible for the nonuniform thickness profile of the silicon epitaxial film.

Cone Structure Formation by Preferred Growth of Random Nuclei in Chemical Vapor Deposited Epitaxial Silicon Films

Systematic creation of abnormal structures in silicon epitaxial growth is studied. The abnormalities are induced by randomly dispersing 2–4 μm sized diamond particles onto silicon substrates. When the epitaxial plane is not the fastest growing one, elongated crystallites form a radial pattern from the particles enveloped in the epitaxial film, resulting in cone structures much larger than the seed particles (see Figure).

Low temperature epitaxial silicon films deposited by ion-assisted deposition

Ion-assisted deposition (IAD) is an advanced molecular beam epitaxy method that provides additional growth energy due to the use of a small fraction of accelerated Si-ions in the Si beam. At low deposition temperatures T dep≤650 °C, the energetic contribution of ions with an energy of 20 eV improves the electronic quality of (100)-oriented epitaxial Si films as shown by an increase of the minority carrier diffusion length L. However, L of (111)-, (110)-, and (113)-oriented films decreases when using hyperthermal Si-ions. The density of extended defects in IAD films is found to be below 1×10 3 cm −2 on (100)-oriented films, independent of substrate temperature and deposition rate. At T dep=460 °C, L displays a maximum at a high deposition rate of r dep=0.3 μm min −1, which correlates with a minimum in the density of point defects at the same rate.

Mechanism of Locally Formed Profile of Silicon Epitaxial Film Thickness

Mechanism of Locally Formed Profile of Silicon Epitaxial Film Thickness

Morphology of Silicon Oxide Film on Silicon Wafer Surface during Its Removal Process in a Hydrogen Ambient

In order to develop the low-temperature silicon epitaxial growth process, the change in the surface morphology of the silicon dioxide film and the silicon surface is studied in a transient state, for the first time, at 1223 K at a pressure of 40–101 kPa in a hydrogen ambient. A very smooth and clear silicon substrate surface is achieved using a uniform silicon dioxide film formed using ozonated ultrapure water and a very low flow rate of hydrogen gas. The surface morphology of the silicon substrate finally becomes smooth and the pit formation is suppressed, although the surface shows a nonuniform island appearance during the removal of the silicon dioxide film. The microroughness of the silicon substrate surface is improved by heating in a hydrogen ambient and by the silicon epitaxial film growth after complete removal of the ozone oxide film.

Resonant scattering in delta-doped heterostructures

We demonstrate the utility of resonant x-ray scattering in probing the structure of doping layers at a heterostructure interface. The positions of germanium layers inserted at the interface of a silicon epitaxial film assert a strong influence of the phase of the scattered intensity along the crystal truncation rods. The phase of the scattering, and hence the internal structure of the layers, can be determined conveniently by analyzing its energy dependence in the vicinity of the Germanium absorption edge at 11.103 keV.

Flatness Deterioration of Silicon Epitaxial Film Formed Using Horizontal Single-Wafer Epitaxial Reactor

This study theoretically clarifies, for the first time, the mechanism of the flatness deterioration of a silicon epitaxial film which is formed on a rotating silicon substrate in a SiHCl3–H2 system at atmospheric pressure using an industrially used horizontal single-wafer epitaxial reactor. The plate of the multi-inlet in the reactor generates the narrow region having a small SiHCl3 gas concentration, because this plate locally weakens the cold finger effect due to various changes in transport phenomena in the reactor. This nonuniform distribution of SiHCl3 gas concentration generated above the silicon substrate results in a nonuniform epitaxial growth rate distribution on the silicon substrate. The substrate rotation then results in a silicon epitaxial film having a concentrically reduced thickness profile, the radius of which corresponds to the position of the plate of the multi-inlet. Due to this mechanism, the multi-inlet design leads to the flatness deterioration of the silicon epitaxial wafer.

Hot-wall and cold-wall environments for silicon epitaxial film growth

From the viewpoint of a systematic designing method for a chemical vapor deposition (CVD) reactor, double-wafer hot-wall and single-wafer cold-wall environments for silicon epitaxial film growth are studied, for the first time, by means of numerical calculations using the transport and epitaxy model which is effective for the SiHCl 3–H 2 system at atmospheric pressure. The distribution of the silicon epitaxial film growth rate and the profile of the silicon epitaxial film thickness are discussed in relation to the temperature and the gas velocity in the gas phase. The difference in the distribution of the epitaxial growth rate between the two types of reactors is discussed based on the transport phenomena of SiHCl 3 gas in the gas phase. Furthermore, in order to design future operations, the effect of the rotation direction of each substrate on the distribution of the silicon epitaxial growth rate is additionally discussed using the horizontal double-wafer hot-wall reactor.

Model of boron incorporation into silicon epitaxial film in a B 2H 6–SiHCl 3–H 2 system

A model of boron incorporation into a silicon epitaxial film is experimentally and theoretically studied in a B 2H 6–SiHCl 3–H 2 system at atmospheric pressure. The boron concentration in the silicon epitaxial film is evaluated using the ratio of the boron deposition rate to the total deposition rate of boron and silicon, both of which are calculated accounting for the entire transport phenomena in the horizontal cold-wall single-wafer epitaxial reactor having a rotating susceptor and substrate. The overall rate constant for the surface reaction of B 2H 6 gas is found to be a function of the surface coverage of the silicon substrate surface due to the chemisorption of SiHCl 3 gas. The practical application for adjusting the carrier concentration profile using the combination of the substrate rotation and the inlet of the reactor is also discussed.

Orientation-Dependence of Low Temperature Epitaxial Silicon Growth

ABSTRACTElectronic properties of thin epitaxial silicon films deposited at temperatures below 650°C by means of ion-assisted deposition strongly depend on substrate orientation as well as on deposition temperature: In (100)-oriented epitaxial films we find a low density of structural defects, and the minority carrier diffusion length is only limited by the presence of point defects or point defect complexes. These investigations also show an improvement of the electronic quality with increasing deposition temperature. Epitaxy on non-(100)-oriented substrates results in a significantly higher density of structural defects. The electronic properties of films deposited on stable flat surfaces, such as (111)- and (113)-oriented substrates are inferior as compared to (100)-oriented films, but are still superior to those of films deposited on faceted surfaces, as shown by light beam induced current and electron back-scattering diffraction measurements of polycrystalline thin films.

Chemical vapor deposition of undoped and in-situ boron- and arsenic-doped epitaxial and polycrystalline silicon films grown using silane at reduced pressure

A nonselective epitaxial growth process for heterojunction bipolar transistors has been studied. The difference in growth rates for epitaxial and polycrystalline films could be used to monitor the thickness of the intrinsic and extrinsic base layers. The films were grown using chemical vapor deposition on Si 〈100〉 (epitaxy) and on silicon dioxide (polycrystalline) at reduced pressure (20–80 Torr) for undoped and in situ B or As doping. The depositions were carried out using silane diluted in hydrogen. Diborane and arsine were used as the source gas for dopants. For the undoped Si films, the deposition of polycrystalline films had a substantially higher rate than that of epitaxial ones. The growth rate of both epitaxial and polycrystalline depositions decreased with increasing total pressure. It was, however, linearly proportional to the silane partial pressure, pSiH4. The dependence of the growth rate on the hydrogen partial pressure was proportional to pH2−0.82 for epitaxial and to pH2−0.60 for polycrystalline depositions. The apparent activation energy was 2.1 and 1.6 eV for the epitaxial and polycrystalline depositions, respectively. A growth mechanism assuming the dissociative adsorption of silane on the Si surface, in combination with first-order hydrogen desorption kinetics, was employed to describe the experimental observations, including the differences in deposition rates, dependency on the hydrogen partial pressure as well as apparent activation energy. In situ B doping influenced neither the epitaxial nor polycrystalline depositions. In situ As doping, on the other hand, largely reduced the growth rate compared to the undoped films to such an extent that there was no appreciable difference in growth rate between the epitaxial and polycrystalline Si. The doping concentration in the epitaxial B and As films were of the order of 1018 cm−3, identical deposition conditions yielded a 5 and 20 times larger dopant incorporation in the B and As doped polycrystalline films, respectively.