Growth Of Silicon Films Research Articles

A Reflection High Energy Electron Diffraction–Reflectance Anisotropy Spectroscopy Study of Silicon Growth Dynamics During Gas Source Molecular Beam Epitaxy from Silanes

Molecular beam epitaxy (MBE) provides an ideal experimental vehicle for the in situ study of thin film growth dynamics. By using a combination of reflection high energy electron diffraction (RHEED) and reflectance anisotropy (difference) spectroscopy [RA(D)S], it is possible to separate morphological (long range order) and local electronic structure effects, which we demonstrate with the growth of silicon films from disilane ( Si 2 H 6) on Si(001) (2 × 1)+(1 × 2) reconstructed surfaces. The rate-limiting step in Si growth from both monosilane ( SiH 4) and disilane is the desorption of molecular hydrogen and we have found using RAS that, over a significant range of temperature and coverage, hydrogen desorption follows zeroth order kinetics as the result of a step-mediated process. Finally, we show how this influences the growth rate on substrates of differing degrees of vicinality.

Molecular-dynamics simulation of silicon film growth from cluster beams

Silicon thin film growth from cluster beams has been investigated with molecular-dynamics simulations utilizing the Stillinger–Weber two- and three-body interaction potential. The spreading of Si-atom clusters and the structure of grown films have been studied as a function of incident cluster velocity. Higher surface diffusion and spreading of the deposited clusters was achieved with increasing cluster velocity. Epitaxial Si (1 1 1) growth was obtained under a moderate cluster velocity.

Ion assisted growth and characterization of polycrystalline silicon and silicon-germanium films

Polysilicon films have been deposited at a low temperature by single and dual ion beam sputtering. The structural and electrical properties of as-deposited and annealed films have been characterized by x-ray diffraction, secondary ion mass spectroscopy, atomic force microscopy, and Hall mobility measurements. The films are microcrystalline with average grain size ranging from 200 to 400 Å. The films exposed to a low-energy secondary ion beam during sputtering from a silicon target have exhibited smoother surface topography and different electrical behavior than the films deposited without any secondary ion bombardment. Some preliminary studies on ion beam sputtered SiGe films using a compound target are also presented.

Nucleation and Growth of Crystalline Silicon Films on Glass for Solar Cells

Nucleation and Growth of Crystalline Silicon Films on Glass for Solar Cells

Nucleation and Growth of Crystalline Silicon Films on Glass for Solar Cells

Understanding nucleation and growth of crystalline Si films on glass is of prime importance in order to tailor and optimize semiconductor properties for electronic devices such as solar cells. Commercial glass limits the maximum processing temperature of Si films to 600 C. Solid phase and laser crystallization, or a combination of both techniques, are thus primarily used to crystallize Si films on glass. While random nucleation and growth processes always result in the formation of a log± normal size distribution, control of nucleation sites allows one to determine the location of grain growth or even the crystallographic orientation of grains. Via sequential lateral solidification using a copper vapor laser, we obtain Si crystallites on glass of several tens of mm in length.

Characterization of Hydrogen in Epitaxial Silicon Films Grown at Very Low Temperatures

Experimental and theoretical analyses of hydrogen atoms incorporated in epitaxial silicon films grown at very low temperatures were investigated using a high resolution X-ray diffractometer (HRXRD) and an ab-initio total energy calculation. We found that the lattice constant of the epitaxial films was expanded by the H atoms and this lattice expansion occurred only in a direction normal to the surface. We proposed the Si–H–Si configuration as a model to explain the lattice expansion phenomenon. The results of the calculation supported this model and also suggested that the microscopic stress was introduced by the H atom in the configuration. In B-doped epitaxial Si films, the B atoms were 100% neutralized by the H atoms and activated by thermal annealing. We increased the growth temperature to overcome these H related problems and succeeded in controlling the H incorporation. The B-doped Si film with a hole concentration of 1.7×1019 cm-3 was obtained at a growth temperature of 240°C.

In situ ellipsometry for monitoring nucleation and growth of silicon on silicon dioxide

The nucleation and growth of silicon (Si) films on silicon dioxide (SiO 2) surfaces has implications for both selective Si deposition in microelectronics manufacturing and thin film transistor performance in liquid crystal displays. We report the evolution of Si nuclei on a SiO 2 surface as observed by in situ single wavelength ellipsometry and the modeling of the Si films by spectroscopic ellipsometry. The Si is deposited on thermally grown SiO 2 films by rapid thermal chemical vapor deposition (650°C and 20 millitorr) with a disilane (5% in He) source gas. Single wavelength ellipsometry measurements are made at 3.65 eV (for temperature stability reasons) and spectroscopic measurements are made in the range of 2.5–5.0 eV. Modeling of the ellipsometric results indicate that the H 2 pretreatments passivate the Si sites on the oxide surface leading to sparse nuclei, hence larger grained and rougher films. Ion beam pretreatments shorten the incubation time and yield small grained, smooth films. In the range investigated, ion dose is more influential than ion energy on incubation time. Creation of nucleation sites by ion pretreatments appears to be from a physical, rather than chemical mechanism. High temperature pretreatments damage the surface less than room temperature treatments.

Ion bombardment of amorphous silicon films during plasma-enhanced chemical vapor deposition in an rf discharge

The characteristics of ion and electron fluxes to the surface of a growing silicon film are investigated in various rf discharge regimes in silane at frequencies of 13.56 MHz and 58 MHz in plasma-enhanced chemical vapor-deposition (PECVD) apparatus. The energy spectra of the ions and electrons bombarding the growing film are measured. The electronic properties of films grown under various degrees of ion bombardment are studied. The correlation of these properties with the ion parameters in the rf discharge plasma during film growth is discussed.

In-Situ Boron-Doped Epitaxial Silicon Films Grown by UHVRTCVD: Applications in Channel Engineering & Ultra-Shallow Junction Formation

ABSTRACTA low-thermal budget, in-situ boron doped silicon epitaxy process for channel engineering and ultra shallow junction formation is presented. Ultra-thin silicon films (100–500 Å) have been deposited in a single-wafer Ultra High Vacuum Rapid Thermal Vapor Deposition (UHV-RTCVD) reactor using disilane (Si2H6), diborane (B2H6), and chlorine (Cl2) at temperatures between 750- 800°C. Boron doping can be varied five orders of magnitude (1016 cm-3 1021 cm3) with very abrupt doping transitions (∼50–70 Å/decade). Short channel (Leff =0.12 /μm) lightly-doped nchannel MOSFETs have been successfully realized free of ion-implantation in the channel region. As another application, ultra-shallow, defect-free, abrupt junctions (<500 Å) through diffusion from selectively-deposited in-situ boron doped films have been demonstrated.

Second-harmonic spectroscopy of a Si(001) surface during calibrated variations in temperature and hydrogen coverage

The epitaxial growth of silicon films by chemical vapor deposition (CVD) is strongly affected by temperature and hydrogen (H) termination. We report measurements of $p$-polarized optical second-harmonic (SH) spectra generated in reflection from clean $2\ifmmode\times\else\texttimes\fi{}1$-reconstructed and H-terminated epitaxial Si(001) surfaces with no intentional doping by Ti:sapphire femtosecond laser pulses for SH photon energies $3.0l~2\ensuremath{\Elzxh}\ensuremath{\omega}l~3.5\mathrm{eV}$ near the bulk ${E}_{1}$ resonance. Temperatures were varied from 200 to 900 K and H coverages from 0 to 1.5 monolayers (ML). Increases in temperature at fixed H-coverage redshift and broaden the ${E}_{1}$ resonance, as observed in linear bulk spectroscopy. Increases in H coverage from 0 to 1 ML at fixed temperature strongly quench, redshift, and distort the lineshape of the ${E}_{1}$ resonance even though reflection high-energy electron diffraction shows that the surface maintains the dimerized $2\ifmmode\times\else\texttimes\fi{}1$ reconstruction. The latter spectroscopic variations cannot be explained by vertical strain relaxation in the selvedge region, nor by bulk electric-field-induced SH (EFISH) effects. We instead attribute these variations to a monohydride-induced surface chemical modification, which we parametrize as a surface EFISH effect because submonolayer H strongly alters surface electric fields by redistributing charge from surface dimers into the bulk. The effects of vertical strain relaxation are weakly evident as a blueshift of the ${E}_{1}$ resonance accompanying dihydride termination (1.0--1.5 ML), which breaks the surface dimer bond. This modification is parametrized as a separate field-independent alteration to the surface dipole susceptibility ${\ensuremath{\chi}}_{\mathrm{surface}}^{(2)}.$ Finally, guided by these SH spectroscopic studies, we demonstrate dynamic real-time (100-ms resolution) SH monitoring of H coverage (5% accuracy) during temperature programmed hydrogen desorption and CVD epitaxial growth of silicon from disilane.

Characterization of In Situ Phosphorus‐Doped Polycrystalline Silicon Films Grown by Disilane‐Based Low‐Pressure Chemical Vapor Deposition

Low‐pressure chemical vapor deposition of in situ phosphorus‐doped silicon films using disilane and phosphine has been investigated in the growth temperature range of 415 to 560°C and for doping levels between 1019 and . Regarding the film deposition, no significant difference in apparent activation energy was observed between the undoped and heavily doped deposition process. The electrical and structural properties of the films grown at 480°C have been studied as a function of doping level and post‐heat‐treatment including furnace and rapid thermal annealings. The observed changes in film resistivity after isochronal annealings for doping levels above are interpreted in terms of dopant segregation and supersaturation of carriers. The impact on resulting film properties when replacing disilane with silane in the deposition process has been investigated. The films were grown under identical conditions except for the deposition temperature which was 80°C higher for the silane than for the disilane case. There is no indication of different phosphorus incorporation when comparing electrical properties of crystallized silane‐ and disilane‐based films. However, the disilane layers exhibit larger crystallite grains and lower specific resistivities than the silane layers. In addition, the disilane films demonstrate a strongly preferred 〈111〉 texture after crystallization which is absent for the silane films. The observations are attributed to the higher degree of disorder of the as‐deposited disilane films compared to the silane films resulting from the difference in deposition temperature.

Low Temperature Growth of Amorphous and Polycrystalline Silicon Films from a Modified Inductively Coupled Plasma

A conventional inductive rf discharge is modified by inserting a discharge antenna in a plasma vessel with magnetic multipole confinement, which gives a high-density (∼1011 cm-3) silane plasma at very low pressures (∼1 mTorr). This new type of inductively coupled plasma (ICP) enables high-rate deposition (∼1 nm/s) of a-Si:H films at low substrate temperatures of ∼100°C, which have the photoconductivity of 10-5–10-4 S/cm and the dark conductivity of 10-10–10-9 S/cm. Moreover, microcrystalline or polycrystalline silicon films are formed on glass substrates at moderate temperatures of 200–300°C where the dark conductivity becomes comparable to the photoconductivity and the X-ray diffraction pattern shows sharp peaks corresponding to the silicon crystalline surfaces. Mass spectrometric measurements of the highly dissociated silane plasma show unique radical compositions; ∼90% of ions are hydrogen species (H3+, H2+, H+) while the density of neutral radicals (SiH3, SiH2, SiH) is lower than that of ionic radicals (SiH3+, SiH2+, SiH+, Si+). Thus, the main precursor of film growth from high-density plasmas may be ionic radicals rather than neutral radicals.

Deposition and characterisation of silicon grown in a SiF 4/SiH 4/H 2 mixture for TFT applications

The growth of polycrystalline silicon (polysilicon) films from SiF 4/SiH 4/H 2 gas mixtures is reported. These silicon films have been deposited on Corning 1737 glass substrates by adding SiF 4 to an existing LPCVD polysilicon process in a Multi Process reactor. In addition, polysilicon films have been deposited in the same reactor by a PECVD process. The fluorine concentration was measured by SIMS. Grain size was determined by atomic force microscopy and showed a marked increase with fluorine incorporation.

Early stages of microcrystalline silicon film growth on amorphous substrate with SiH 4 gas heating

The effect of SiH 4 gas heating has been investigated for the growth of microcrystalline silicon (μc-Si) thin film by plasma-enhanced chemical vapor deposition (PECVD) and low pressure CVD to improve the crystallinity and inhomogenities at the early stage of growth on amorphous substrate such as SiO 2. By using the cathode heating technique, T c=550°C, the crystallinity was enhanced from the early stage of growth in the PECVD of SiH 4 highly diluted in H 2 at substrate temperature, T s=200°C.

Growth of polycrystalline silicon films on glass by high-temperature chemical vapour deposition

Covering glass substrates with polycrystalline Si films for electronic devices such as solar cells still presents a great challenge. In a two-step process, we first coat a novel high-temperature resistant glass substrate with a thin film of amorphous Si, which is then solid-phase crystallized at . In the second step, atmospheric pressure chemical vapour deposition at serves to deposit a several micron thick light-absorbing film. The minority carrier diffusion length in our films correlates with the area weighted grain size determined by transmission electron microscopy. We obtain a hole mobility of after hydrogen passivation and an electron diffusion length of .

Low-temperature growth of microcrystalline silicon using 100% by rf glow discharge method

The growth of microcrystalline silicon () films by plasma enhanced chemical vapour deposition (PECVD) of silane in the temperature range 200 - has been investigated. The growth system was a capacitively coupled parallel plate radio frequency (rf) glow discharge reactor in which the substrates were mounted on the cathode (powered electrode). It was found that films could be grown using 100% at a substrate temperature above with a high deposition rate and high degree or crystallinity. The main effect of mesh attachment was found to be the reduction of ionic bombardment to the film growth zone which prevents the degradation of surface crystallinity. It was also found that both P- and B-doped films with good optoelectronic properties could be grown using 100% .

Limits to the efficiency of silicon multilayer thin film solar cells

Thin film crystalline silicon solar cells can only achieve high efficiencies if light trapping can be used to give a long optical path length, while simultaneously achieving near unity collection probabilities for all generated carriers. This necessitates a supporting substrate of a foreign material, with refractive index compatible with light trapping schemes for the silicon. The resulting inability to nucleate growth of crystalline silicon films of good crystallographic quality on such foreign substrates, at present, prevents the achievement of high efficiency devices using conventional single junction solar cell structures. The parallel multijunction solar cell provides a new approach for achieving high efficiencies from very poor quality material, with near unity collection probabilities for all generated carriers achieved through appropriate junction spacing. Heavy doping is used to minimise the dark saturation current contribution from the layers, therefore allowing respectable voltages. The design strategy, corresponding advantages, theoretical predictions and experimental results are presented.

Molecular dynamics simulation of the thin film fabrication process

There is an increased demand of the explanation of the thin film fabrication mechanism, especially for thickness uniformity, film quality and product yield. Any modeling of the mechanism requires a sufficient knowledge of the basic mechanism of interaction and reaction of the particles with the substrate. As a first step, here, the model of silicon thin film formation under low-pressure CVD is considered. Silicon film formation and growth on a clean solid substrate is simulated applying the molecular dynamics and chemical reaction principles. The analyzed domain is enclosed in a hexagonal box which has periodic boundary conditions and a different flow energy of the particle. The atom surface adsorption and inelastic collision are discussed considering the exchange energy between the particles and the surface. In order to provide a well visualized description, a graphics program is made to show the particle movement and the film fabricating process in three dimensions. The present simulation is advantageous to the macro-understanding of the thin film formation mechanism and to fabricating the machine design with optimum control.

Pulsed supersonic jet epitaxy: A nonthermal approach to silicon growth

In this letter, we demonstrate a unique approach for low temperature epitaxial growth of single crystal silicon films on Si(100). Pulsed supersonic jet epitaxy (PSJE), employs high kinetic energy jets of a disilane-hydrogen mixture incident on the surface leading to layer by layer growth. Precise control of film thickness and significantly higher sticking coefficients are demonstrated. Growth rate dependence of pulse frequency and its implications are discussed. We have been able to reproducibly deposit good quality single crystalline films at temperatures as low as 400 °C with this technique, without the use of any external activation.

Silicon thin films obtained by rapid thermal atmospheric pressure chemical vapour deposition

Epitaxial growth of silicon films over the temperature range from 900 to 1300 °C was investigated in a rapid thermal chemical vapour deposition reactor working at atmospheric pressure. The growth of boron doped Si was performed from trichlorosilane and trichloroborine diluted in hydrogen. The epilayers were analysed by Rutherford backscattering spectroscopy, specular reflectance, scanning electron microscopy and Nomarski microscopy. Mechanisms for the observed growth rate are examined, and are tied closely to the degree of surface coverage by Cl. The electrical properties of the deposited films were also checked using the spreading resistance and the four point probe techniques.