Growth Of Silicon Films Research Articles

Improved electrical properties of non-hydrogenated a-Si densified by IBAD

Some effects of ion bombardment on the growth of non-hydrogenated amorphous silicon films were studied using samples prepared with low-energy ion-beam-assisted deposition (IBAD). Inert gas ions were used to determine the effects of the ion beam on pure amorphous silicon without the complication of simultaneous chemical effects. The ion bombardment was found to increase the film density, improve film stability, increase the effective conductivity activation energies and to move the position of the infrared absorption peak assigned to silicon-carbon bonds to larger wavenumbers. The largest effective conductivity activation energies and the lowest conductivities were obtained from films made with Ar+ ions and bombarding energies around 100 eV. However, these 'best' films still do not have a sufficiently low defect density to be useful semiconductors. The improvements are consistent with the thesis that densification of the growing film is the primary effect of the beam. However, for the conditions used, the densification appears to saturate, leaving a relatively large number of dangling bonds in the films. These may result from the presence of Ar known to be in the films, although the results are consistent with the topological model which suggests that the best conditions for forming covalently bonded solids are obtained when the number of bonding constraints is equal to the number of degrees of freedom.

Synchrotron Radiation-Assisted Silicon Film Growth by Irradiation Parallel to the Substrate

Growth of silicon films by synchrotron radiation (SR) photolysis of Si2H6 is studied for temperatures below 500°C. SR is irradiated parallel to the substrate to grow silicon film over a large area and to avoid substrate heating and gas dissociation by photoelectrons. The thickness uniformity in a 2-inch wafer is over 50% while an SR cross section is about 1×10 mm. At substrate temperatures above 300°C, the hydrogen content of the film is low enough that epitaxial silicon film is successfully grown.

State-specific study of hydrogen desorption from Si(100)-(2×1): Comparison of disilane and hydrogen adsorption

The desorption of hydrogen from the monohydride species on Si(100) has been studied state specifically using (2+1) resonance-enhanced multiphoton ionization. The monohydride phase was prepared by dosing the surface with either disilane (Si2H6) or atomic hydrogen. Adsorption of disilane with subsequent desorption of H2 leads to the growth of an epitaxial silicon film, based on evidence obtained with scanning electron microscopy and low energy electron diffraction. We report that the rovibrational-state distribution for hydrogen desorbed from Si(100) is the same after both disilane and atomic-H adsorption. Hydrogen desorbs with low average rotational energy but with a population in the v=1 state enhanced by roughly 20 times over a thermal distribution at the temperature of the surface. The agreement between internal-state distributions for both adsorption schemes indicates that the desorption of hydrogen during epitaxial growth of Si after Si2H6 adsorption proceeds in the same manner as that for a hydrogen-prepared Si(100)-(2×1):H surface.

A real time study of the growth of microcrystalline silicon on transparent conducting oxide substrates

A detailed real time ellipsometry study of the growth of microcrystalline silicon (μc-Si) films on transparent conducting oxide (TCO) substrates is presented. Indium tin oxide and ZnO substrates are compared. μc-Si films prepared either from a high power (SiH4,H2) plasma or by alternating the SiH4 and H2 plasmas (layer-by-layer technique) are considered. Insights into the mechanisms of the TCO/μc-Si interface formation are obtained. A strong chemical reduction of the TCO substrate is observed during the early stage of exposure to the (SiH4,H2) plasma. Then the ellipsometric measurements reveal an induction period of about 1 min before the nucleation of microcrystallites. μc-Si films deposited by the layer-by-layer technique display a different behavior, in particular the chemical interaction at the ZnO/μ-Si interface is not observed in this case.

Bond Selectivity in Silicon Film Growth

Hydrogen atoms can selectively eliminate strained bonds that form during the growth of amorphous silicon films. By periodically interrupting the growth and exposing the grown material to hydrogen, the film composition can be varied continuously from a non-equilibrium amorphous structure to that of a crystalline solid. Furthermore, by tuning the hydrogen exposure it is possible to discriminate between Si-Si bonds formed on different substrates, thereby allowing substrate-selective growth. The evolution of the film structure during hydrogen exposure is directly observed by scanning tunneling microscopy, and a model describing the role of hydrogen is presented.

Phosphorous doping in low temperature silicon molecular beam epitaxy

Phosphorus doping with silicon molecular beam epitaxy was studied using a novel design of a solid doping source based on evaporation of highly doped silicon. Doping concentrations up to the level of the source material are possible. Bulklike Hall mobilities can be achieved. No memory effect was detectable in the course of this work. Phosphorus incorporation in the growing silicon film was investigated with secondary ion mass spectrometry. A drastic increase of segregation with growth temperature was found between 320 and 540 °C. This temperature range represents a kinetically limited regime, which also explains the observed enhancement of segregation with reduced growth rate.

Growth and Surface Morphology of Thin Silicon Films Using an Atomic Force Microscope

ABSTRACTThe growth and surface morphology of thin LPCVD silicon films were investigated with an atomic force microscope (AFM). Silicon films of 30 nm thicknesses were deposited on SiO2 using SiH4 at four different temperatures between 550 °C and 625 °C. These AFM results permitted visualization of silicon surface granularity, roughness, and the transition with temperature from amorphous to crystalline structure between 550 °C and 580 °C. The surface of the amorphous film deposited at 550 °C is very smooth and the film is continuous physically, while the film formed at 580 °C appears crystalline, rough and porous. At 600 °C and 625 °C the films are fully crystalline. For these higher temperature films surface roughness and the average grain size decreased significantly compared to 580 °C film. Crystallinity and film continuity were further examined by x-ray diffraction (XRD) and cross-sectional TEM measurements.

Growth and Surface Morphology of Thin Silicon Films Using an atomic Force Microscope

AbstractThe growth and surface morphology of thin LPCVD silicon films were investigated with an atomic force microscope (AFM). Silicon films of 30 nm thicknesses were deposited on SiO2 using SiH4 at four different temperatures between 550 °C and 625 °C. These AFM results permitted visualization of silicon surface granularity, roughness, and the transition with temperature from amorphous to crystalline structure between 550 °C and 580 °C. The surface of the amorphous film deposited at 550 °C is very smooth and the film is continuous physically, while the film formed at 580 °C appears crystalline, rough and porous. At 600 °C and 625 °C the films are fully crystalline. For these higher temperature films surface roughness and the average grain size decreased significantly compared to 580 °C film. Crystallinity and film continuity were further examined by x-ray diffraction (XRD) and cross-sectional TEM measurements.

Simulation of silicon film growth by silane decomposition at low pressures and temperatures

Silicon film deposition by silane decomposition in LPCVD (Low Pressure Chemical Vapor Deposition) process has been simulated by numerical computation of the governing transport and reaction equations, assuming that the rate of silane decomposition in the gas phase controls the overall film growth rate. The film growth rate and the film uniformity increase with the reactant flow rate when the flow rate is relatively low, but they decrease at higher flow rates due to the negative effect of the reduced reaction time in the reactor. Accordingly, the film deposition process is optimized by controlling the reactant flow rate so that the position of the maximum SiH4-decomposition rate in the gas phase is located above the substrate region. With a larger degree of the substrate tilting, the growth rate decreases but the film uniformity is improved. The film uniformity is also improved when the pressure is low.

Simulation of silicon film growth by silane decomposition in a mercury-sensitized photo-CVD process

Deposition of silicon film by a mercury-sensitized photo-CVD process has been simulated by numerical solution of governing equations with proper boundary conditions. The results indicate that the film deposition rate is controlled by homogeneous decomposition of the reactant, silane, in the gas phase. The growth rate increases but the film uniformity decreases with the increase of reactant inlet concentration. Increase in the reactant flow rate decreases the deposition rate but gives no effect on the film uniformity. Among process variables, the light intensity and the mercurysaturator temperature are important parameters.

Elementary processes of surface reaction in amorphous silicon film growth

Surface reactions contributing to a-Si:H film growth both in thermal and in plasma chemical vapor deposition (CVD) were investigated by ab initio molecular orbital calculations. The conclusions obtained are as follows: (i) The primary activation process of a-Si:H growing surface is the silylene structure formation by hydrogen elimination. (ii) At low temperature, the subsequent reaction on the growing surface is the hydrogen migration from the adjacent SiH 2 group to the silylene structure and then the disilene structure is produced. Silyl radicals prepared in plasma reactors stick themselves to the disilene structures and contribute to a-Si:H film growth. (iii) At high temperature, rows of silylene radicals are produced on the growing surface. The silylene structures in the rows have a life time long enough to react with silane molecules in the CVD reactor. This reaction contributes to a-Si:H film growth in the thermal CVD. (iv) The conclusions (ii) and (iii) are the reason that higher surface temperature is required for a-Si:H film growth in the thermal CVD than in the plasma CVD.

Monte Carlo simulations of magnetron sputtering particle transport

Monte Carlo simulations of the particle transport process during dc magnetron sputter deposition were performed to determine the energy and angular distributions of the energetic deposition species. The model itself is quite general, and here we present the specific example of hydrogenated amorphous silicon film growth. This process involves the sputtering of a silicon target in an argon-plus-hydrogen plasma. The three-dimensional model incorporates fractal trim data for the distribution of Si energies and emission angles sputtered from the target surface. Modified ‘‘universal’’ interatomic potentials are used to determine the scattering processes during gas phase transport. Energy and angular distributions of the deposition flux reaching the substrate are calculated as a function of pressure from 0.01 to 5.5 mTorr. As the pressure increases we find that the average energy per deposited atom remains essentially constant, but the energy and angular distributions of the arrival flux change dramatically.

Growth of microcrystal silicon by remote plasma chemical vapor deposition

We have studied the growth of microcrystal silicon films by remote plasma chemical vapor deposition as growth parameters of substrate temperature and rf power. With increasing substrate temperature, the growth rate increases because of the decrease of the etch rate. The rf power dependence shows that the growth rate decreases with increasing rf power at high power levels. The results indicate that the chemical equilibrium between the deposition and etching of Si on the growing surface gives rise to the growth of microcrystal Si, resulting in the optimum rf power and substrate temperature for the growth of microcrystalline silicon.

Experimental and Model Studies of Dopant Segregation During Growth of Silicon Films by Molecular Beam Epitaxy

ABSTRACTDopant incorporation and surface segregation are studied for thermal Sb and Al cases. The values of the incorporation probability and the segregation ratio have been mainly determine by SIMS measurements. The doping kinetics is discussed using a multi-site model including high dopant surface coverage effects. The calculated results were in good agreement with experimental data.

Modeling and optimization of the growth of polycrystalline silicon films by thermal decomposition of silane

A mathematical model for deposition of polysilicon films on silicon wafers in a horizontal tube reactor by thermal decomposition of silane at low pressure is proposed. The influence of temperature, pressure and gas flow rate on the film thickness uniformity is studied experimentally and by the model. An optimization criterion accounting for the energy and material consumption is defined. The limits of the technological factor variations allowed are discussed and the optimization criterion values within these limits are calculated. The analysis presented, demonstrating the significance of the chosen factors for the production cost-price is of great practical importance.

Growth of silicon and germanium on Cu(111) studied by angle-resolved direct and inverse photoemission.

The growth of evaporated silicon and germanium on Cu(111) has been studied by angle-resolved direct and inverse photoemission. At room temperature both semiconductors form a reacted interface a few angstroms thick. For overlayers of more than 20-\AA{} thickness the surface-sensitive photoemission techniques demonstrate the growth of pure silicon or germanium films. Annealing of thin films (5 \AA{}) of Si on Cu(111) results in a uniformly reacted interface with a (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} low-energy electron diffraction (LEED) pattern, while annealing of Ge films results in a 1\ifmmode\times\else\texttimes\fi{}1 LEED pattern. The dispersion of two unoccupied surface states of the annealed Ge film is determined by angle-resolved inverse photoemission. Based on our photoemission results, a description of the chemical reaction in the semiconductor-on-metal interface is presented.

A Monte Carlo study of the silicon film growth from molecular beams

The Monte Carlo simulation has been used for silicon film growth from molecular beams at high supersaturations. The account of atom displacements (deformations) taken in the simulation of growth by attachments has shown the mechanism of dislocation formation and of their density variation with growth temperature. The calculation of their attachment probabilities to the growth surface of differently oriented (to (100) and (110) from (111)) complexes has allowed us to study the mechanism of the film grain structure development. The conditions for epitaxial growth on substrates with (111) and (110) orientations have been analysed.

Dopant incorporation kinetics and abrupt profiles during silicon molecular beam epitaxy

Controlled dopant incorporation behavior during the growth of single crystal silicon films by molecular beam epitaxy (MBE) is crucial for most device applications. However, since all dopants except boron exhibit low incorporation probabilities and/or a high degree of surface segregation, achievement of sharp doping layers with well defined concentration levels is not straightforward. In order to overcome these problems, techniques involving either the use of accelerated low-energy ions (secondary and direct implantation) or solid-phase epitaxy regrowth have been developed. Recent results on dopant incorporation using low-energy secondary and direct implantation are presented in this paper. Using indium as a model dopant, it is shown that the incorporation probability during secondary implantation, as measured by secondary-ion mass spectroscopy, exhibits a complicated dependence on the film growth temperature and the indium flux. From a detailed investigation of the adsorption/desorption behavior of indium on Si(100) surfaces, it was found that the incorporation behavior was directly correlated to corresponding changes in the segregated indium surface overlayer. Physical models describing dopant incorporation during silicon MBE are discussed and particular emphasis is placed on a newly developed multi-site model. This model is based on an exchange process for dopant atoms moving between potential wells corresponding to different lattice sites in the near-surface region. Five different dopant sites, including surface, bulk and three intermediate sites were used and surface segregation, incorporation, and bulk diffusion were accounted for by solving simultaneous rate equations. The model is demonstrated in the case of both thermal and accelerated antimony doping, to fit experimental incorporation data both as a function of growth temperature and growth rate very well. Finally, results on δ-doped structures are also presented.

Control of preferential orientation by i n s i t u plasma supply during growth of polycrystalline silicon films

Polycrystalline silicon (poly-Si) films were prepared on a fused quartz substrate at 700 °C by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced CVD (PECVD) using the same fabrication system. Poly-Si films with a strong 〈100〉 and 〈110〉 preferential orientation (P.O.) are obtained by changing the rf power for generating the plasma under the same preparation condition. The surface of the PECVD films with dominant 〈100〉 and 〈110〉 textures is very smooth in contrast with that of LPCVD films. These textures are maintained after thermal oxidation at 1000 °C, and the degree of P.O. and the grain size increase.

Crystal structure analysis of epitaxial silicon films formed by a low kinetic energy particle process

Formation of high quality epitaxial silicon films at 350 °C by a low kinetic energy particle process has been verified by a series of crystal structure analyses performed on these films. It was found that the crystallinity of a grown film is drastically changed by the energy of Ar ions concurrently bombarding the growing silicon film surface. The epitaxially grown film with an optimum ion bombardment energy is defect-free both at the interface and in the bulk of the film as revealed by high-resolution transmission electron microscopy.