Silane Flow Rate Research Articles

Silicon and germanium nanoparticle formation in an inductively coupled plasma reactor

We have studied the formation of Si nanoparticles in a SiH4–Ar plasma discharge generated in a helical resonator type inductively coupled plasma reactor. It is observed that Si particles vary in sizes from 5 to 15 nm under different conditions. The particles were mostly spherical and made up of a crystalline core with a 1–2 nm thick amorphous shell. The size distribution was narrow for particles formed at a pressure of 200 mTorr, plasma power of 400 W and silane flow rate of 20 sccm (+980 sccm Ar). The effect of a dc bias applied to the particle collecting grids has also been studied. It is found that a negative bias (−25 to −100 V) applied to the grids used for particle collection results in a large increase in the number of Si nanoparticles collected, while a positive bias does not change the collection efficiency considerably, suggesting that the particles are positively charged. Under very low flow rates and under high plasma powers, the Si particle density decreases considerably and a film like deposition occurs on transmission electron microscopy grids placed in the reactor for collecting the particles. We have also studied the formation of Ge particles (50–200 nm) in a GeH4–Ar plasma generated in the same reactor. These particles are crystalline with a spherical morphology.

Evolution of Texture and Microstructure in Rough Polycrystalline Silicon for Advanced Dram Applications

ABSTRACTThis study investigates the morphology, roughness and electrical performance of rough polysilicon films deposited by LPCVD process. The deposition duration was varied over a broad range to study the evolution of microstructural texture in terms of nuclei formation, growth and grain coalescence. The area enhancement factor (AEF) of rough polysilicon film, expressed as the ratio of cell capacitance incorporating textured film to that of a smooth polysilicon film is observed to range from 1.4 to 2.4 for the above conditions. It is observed that the AEF shows a strong dependence on the microstructural texture and correlates with the surface roughness. A model for electrical AEF based on grain morphology attributes from AFM is included. The dependence of rough polysilicon nucleus cluster density on silane flow rate and deposition temperature is also presented.

Modeling the growth of PECVD silicon nitride films for solar cell applications using neural networks

Silicon nitride films grown by plasma-enhanced chemical vapor deposition (PECVD) are useful for a variety of applications, including anti-reflection coatings in solar cells, passivation layers, dielectric layers in metal/insulator structures, and diffusion masks, PECVD nitride films are known to contain hydrogen, and defect passivation by hydrogenation enhances efficiency in polycrystalline silicon solar cells. PECVD systems are controlled by many operating variables, including RF power, pressure, gas flow rate, reactant composition, and substrate temperature. The wide variety of processing conditions, as well as the complex nature of particle dynamics within a plasma, makes tailoring Si/sub 3/N/sub 4/ film properties very challenging, since it is difficult to determine the exact relationship between desired film properties and controllable deposition conditions. In this study, silicon nitride PECVD modeling using neural networks has been investigated. The deposition of Si/sub 3/N/sub 4/ was characterized via a central composite experimental design, and data from this experiment was used to train optimized feed-forward neural networks using the back-propagation algorithm. From these neural process models, the effect of deposition conditions on film properties has been studied. It was found that the process parameters critical to increasing hydrogenation and therefore enhancing carrier lifetime in polysilicon solar cells are temperature, silane, and ammonia flow rate. The deposition experiments were carried out in a Plasma Therm 700 series PECVD system.

Chemical bonds and microstructure in nearly stoichiometric PECVD aSi xN yH z

Silicon nitride thin films were prepared by low frequency plasma enhanced chemical vapour deposition in silane, nitrogen and helium mixtures. With different silane flow rates, various thin films with nearly stoichiometric composition but different chemical bonds were prepared with hydrogen content lower than 12%. The films were annealed up to 1100 °C and the hydrogen content was measured by elastic recoil detection analysis and compared to the infrared vibration of hydrogenated modes of silicon and nitrogen atoms. Two kinds of behaviour were observed in the chemical bonding with the annealing temperature: either NH and SiH bonds show a decrease, as is generally reported in the literature, or a strong increase of the SiH one is observed. There is also a dramatic discrepancy between the hydrogen content measured by nuclear technique and by infrared spectroscopy if constant oscillator strengths of the stretching modes of hydrogenated sites are used. As in amorphous silicon, these results confirm the difficulty of deducing the concentration of hydrogen bonded to the silicon atoms in silicon nitride. We suggest that these effects are closely correlated to the local microstructure of the films and specific arrangements around SiH dipoles.

Properties of Gate-Quality SiO2 Films Prepared by Electron Cyclotron Resonance Chemical Vapour Deposition in an Ultrahigh Vacuum Processing System

ABSTRACTWe have prepared thin SiO2 layers on Si(100) wafers by electron cyclotron resonance chemical vapour deposition (ECR-CVD) in a multi-chamber ultra-high vacuum (UHV) processing system. The oxides were characterized in-situ by single wavelength ellipsometry (SWE) and x-ray photoelectron spectroscopy (XPS) and ex-situ by Fourier transform infra-red spectroscopy (FTIR), spectroscopic ellipsometry (SE) and capacitance-voltage (CV) electrical measurements. Films deposited at higher pressures, low powers and low silane flow rates had excellent physical and electrical properties. Films deposited at 400 °C had better physical properties than those of thermal oxides grown in dry oxygen at 700 °C. A 1 minute anneal at 950 °C reduced the fast interface state density from 1.2×1011 to 7×1010 eV−1cm−2

PECVD deposition of device-quality intrinsic amorphous silicon at high growth rate

Abstract The combined influence of RF-power density (RFP) and silane flow-rate (Φ) on the deposition rate of plasma-enhanced chemical vapour deposition (PECVD) intrinsic amorphous silicon has been investigated. The correlation of the results obtained from the characterisation of the material with the silane deposition efficiency, as deduced from mass spectrometry, has led to an interpretation allowing to deposit intrinsic amorphous-silicon films having an optical gap of 1.87 eV and a photoconductive ratio (ratio of ambient-temperature conductivities under 1 sun AM1 and in dark) of 6 orders of magnitude at growth rates up to 10 A/s, without any structural modification of the PECVD system used. Such results are considered of high relevance regarding industrial competitiveness.

Hydrogenated microcrystalline silicon films produced at low temperature by the hot wire deposition method

In this letter we report the synthesis of hydrogenated microcrystalline silicon at low temperature and without hydrogen dilution of the silane gas by the hot wire method. These films are characterized by higher dark conductivity and larger band gap compared to hydrogenated amorphous silicon. Microcrystallinity in these films is clearly established from the sharp crystalline TO-like peak in the first-order Raman spectra. The crystallite size and its volume fraction show a critical dependence on the silane flow rate.

Low temperature (313 °C) silicon epitaxial growth by plasma-enhanced chemical vapor deposition with stainless steel mesh

This letter presents the low temperature silicon epitaxial growth on p-type, 〈100〉 Si wafers by plasma-enhanced chemical vapor deposition with a stainless steel mesh. Following a modified ex situ spin-etch cleaning and an in situ H2 baking step, the epitaxial layer was grown at 313 °C using SiH4 (30 sccm)/H2 (22 sccm) with a pressure of 61 mTorr and a rf power of 10 W. Epitaxial layers were also grown at 323 °C with different silane flow rates. The epitaxial film contains higher defect density when the silane flow rate is low.

Effect of pressure on the growth of crystallites of low-pressure chemical-vapor-deposited polycrystalline silicon films and the effective electron mobility under high normal field in thin-film transistors

The morphology of polycrystalline films grown by low-pressure chemical-vapor deposition (LPCVD) is investigated by transmission electron microscopy (TEM) as a function of the film thickness, the deposition pressure, and the level of contamination. An orientation filtering mechanism, due to the growth-velocity competition in the early stage of growth, is responsible for the preferred orientation of the films. The size of the crystallites, the surface roughness, and the type of the structural defects are investigated by combined cross-sectional and plane-view TEM analysis. In polycrystalline silicon thin-film transistors (TFTs), the influence of surface roughness scattering on the mobility is investigated by measuring the effective electron mobility under high effective normal field at 295 and 77 K. Although the surface curvature is increased when the deposition pressure is decreased, the surface roughness scattering is constant in the deposition pressure range from 40 to 0.5 mTorr. By decreasing the deposition pressure from 40 to 10 mTorr, although the grain size increases, the TFT performance degrades due to the following factors: (a) the increase of the grain-boundary trap density which is related to the change of the mode of growth at 10 mTorr; and (b) the increase of impurity contamination in the environment of the LPCVD system with constant silane flow rate at all pressures. At a deposition pressure of 0.5 mTorr the TFT performance is improved indicating that the grain size is the prevailing key factor.

Deposition of amorphous silicon using a tubular reactor with concentric-electrode confinement

High-quality, hydrogenated amorphous silicon (a-Si:H) is deposited at room temperature by rf glow discharge at a high deposition rate using a tubular reactor with cylindrical symmetry (concentric-electrode plasma-enhanced chemical vapor deposition, CE-PECVD). Using the novel CE-PECVD design, room-temperature deposition of a-Si:H with growth rates up to 14 Å s−1, low hydrogen concentration (≲10%), and the bonded hydrogen in the Si-H monohydride configuration, is achieved for the first time using an rf glow-discharge technique. The influence of the deposition parameters (silane flow rate, pressure, and power density) on the growth rate, optical band gap, and silicon-hydrogen bonding configuration, is quantitatively predicted using a deposition mechanism based on the additive contribution of three growth precursors, SiH2, SiH3, and Si2H6, with decreasing sticking coefficients of 0.7, 0.1, and 0.001, respectively. The low hydrogen concentration is due to the enhanced ion bombardment resulting from the concentric electrode design.

The Low Temperature Catalyzed Chemical Vapor Deposition and Characterization of Silicon Nitride Thin Films

Silicon nitride thin films have been grown via low pressure chemical vapor deposition at substrate temperatures ranging from 662 to 904 K by the catalytic action of a heated tungsten filament. A tungsten filament heated to 2020 K was used to decompose ammonia, which reacted with silane introduced downstream of the filament to form silicon nitride films at deposition rates between 50 and 250 nm/min. The resultant films were characterized by Fourier‐transform infrared spectroscopy, x‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and spectroscopic ellipsometry (SE). Infrared spectroscopy indicated that, under appropriate deposition conditions, the amount of bonded hydrogen in the films could be reduced to less than 3%. XPS sputter depth profiles showed that the level of oxygen in the films decreased as the silane flow rate was increased. Oxygen free silicon nitride films were obtained at high silane flow rates. XPS and SE were used to profile the films and to establish the thickness and composition of the bulk, surface, and interfacial layers. SEM confirmed the specular nature of the deposited silicon nitride films.

Influence of silicon on the physical properties of diamond-like films

The effect of the inclusion of silicon atoms in the network of diamond-like carbon (amorphous carbon and hydrogenated amorphous carbon) is studied. Samples of amorphous hydrogenated CSi are deposited by means of a sputter-assisted plasma chemical vapour deposition system in which a carbon target is sputtered in an atmosphere composed of silane-diluted argon, where the silane flow rate is varied. It is shown that initially the effect of silicon inclusion is to reduce the size of the graphitic-like islands. When the amount of silicon is increased over a critical value, the network assumes the characteristic of the semiconductor-type amorphous hydrogenated SiC, where the properties of silicon are predominant.

Electron cyclotron resonance plasma chemical vapor deposition of large area uniform silicon nitride films

Electron cyclotron resonance plasma (f=2.45 GHz, microwave power P=200–800 W) generated in a radially uniform magnetic field (B=875–1000 G) was used to produce a large area (15–20 cm diam) uniform plasma stream at 20–30 cm from the source output. Low temperature (70–300 °C) silicon nitride films with a thickness of 800–3000 Å were deposited on 5–20 cm diameter wafers with deposition rates of 100–350 Å/min. Film thickness uniformity was ±1% for 7.6–10.0 cm diam wafers, ±3% for 15 cm diam wafers, and ±9% for 20.0 cm diam wafers. It was found that the film deposition rate Wg increased linearly with the silane flow rate, while Wg increased slower than power 1/2 with the nitrogen flow rate. The film refractive index was 1.9–2.0 at a silane/nitrogen flow rate ratio of 0.40–0.6. The effects of plasma density and its profile on the film growth rate and uniformity are discussed.

Low hydrogen content stoichiometric silicon nitride films deposited by plasma-enhanced chemical vapor deposition

We have deposited silicon nitride films by plasma-enhanced chemical vapor deposition (PECVD) at 250 °C with properties similar to films prepared at 700 °C by low-pressure chemical vapor deposition (LPCVD). Films are prepared using silane and nitrogen source gases with helium dilution. The film properties, including N/Si ratio, hydrogen content and electrical quality are most sensitive to changes in the silane flow rate during deposition. For films deposited under optimized conditions at a substrate temperature of 250 °C, current versus voltage measurements in metal-insulator-semiconductor structures show the onset of carrier injection at 3–4 MV/cm, slightly lower than LPCVD films. When bias-stressed to 2 MV/cm, capacitance versus voltage measurements show some hysteretic behavior and evidence for positive fixed charge, similar to LPCVD films. For the optimized films: N/Si=1.33±.02; refractive index (λ=6328 Å)=1.980±0.01; dielectric constant (1 MHz) ∼7.5; density=2.7±0.1; and the etch rate in 10% buffered HF ranges from 32 to 70 Å/min. In addition, the hydrogen is distributed equally in Si-H and N-H groups, with a total hydrogen content <10 at.%. These films have a significantly lower hydrogen content than observed in other PECVD silicon nitride films deposited at this temperature. When the substrate temperature is increased to 350 °C, the films have the same Si/N ratio, and similar electrical properties; the hydrogen content is reduced to <6×1021 cm−3, and the etch rate is 17 Å/s in 10% buffered HF solution.

Statistical approach to parameter study of stress in multilayer films of phosphosilicate glass and silicon nitride

Mechanical stress in chemical vapor deposited phosphosilicate (APCVD-PSG), plasma deposited PSG (P-PSG), plasma deposited SiN (P-SiN) and a combination of APCVD-PSG and P-SiN films has been characterized through the use of screening and modeling experimental designs. Total stress in these films was determined by measuring the changes in the radius of curvature of silicon substrate. As deposited APCVD-PSG exhibits tensile stress at room temperature. This stress decreases with increase in phosphorus content. The total stress in P-PSG films was compressive. Of the seven process factors studied in the screening experiment, only three factors (phosphorus content, silane and argon flow rates) had statistical significant effect on stress. Over the process domain covered, no factor–factor interactions were observed. P-SiN films showed high compressive stress levels. Modeling study resulted in a parametric model relating room temperature stress to deposition temperature and ammonia flow rate. For dual films, APCVD-PSG and P-SiN, the total stress was a function of nitride film thickness and phosphorus content in PSG. Parametric models were developed for stress after deposition, sinter and aging. In all cases studied, the total stress changed from tensile to compressive with additional processing. The general trend tends to support the direction observed in previous single factor studies for single dielectric films. The current experiments extend these studies for single films and their combinations, by quantifying the various process factor interactions.

Remote plasma-enhanced CVD of silicon: Reaction kinetics as a function of growth parameters

The reaction kinetics in Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) have been studied for a chamber pressure of 200 mTorr, rf powers between 4 and 8 W, diluted silane flow rates between 5 and 40 sccm, and temperatures between 190 and 480° C. The observed temperature dependence of growth rate reveals a change in activation energy at 300–325° C, suggesting that hydrogen desorption is the rate limiting step in the deposition reaction. A strong dependence of growth rate on rf power has been attributed in part to the extension of the glow discharge region closer to the substrate at higher rf powers. Growth rate has been shown to increase when the sample is positioned closer to the glow, indicating that the reaction precursor is a short-lived species, probably SiH2 or SiH3. Growth rate has been shown to exhibit a sublinear dependence on silane partial pressure. Oxygen incorporation in the deposited films has been studied using Secondary Ion Mass Spectroscopy (SIMS), and it has been found that the main source of oxygen contamination is the process gases. However, it has also been found that “point of use” purification of the process gases reduces water and oxygen contamination significantly, reducing the oxygen incorporation in the films by an order of magnitude.

Defect microstructure in low temperature epitaxial silicon grown by RPCVD

Defect characterization of epitaxial silicon films grown by low temperature remote plasmaenhanced chemical vapor deposition (RPCVD) under various conditions is discussed. The film morphology and crystallinity have been examined by defect etching/Nomarski optical microscopy and transmission electron microscopy. Prior to epitaxial growth, anex situ wet chemical clean and anin situ remote hydrogen plasma clean were performed to remove the native oxide as well as other surface contaminants such as carbon. A damage-free (100) Si surface with extremely low concentrations of carbon and oxygen as confirmed byin situ Auger electron spectroscopy can be achieved using this cleaning technique at temperatures as low as 250°. Low temperature Si homoepitaxy was achieved by RPCVD on lightly doped (100) Si substrates. Growth parameters such as silane flow rate (partial pressure), chamber pressure, and substrate temperature were varied during epitaxial growth to investigate the dependence of film quality on these parameters. For comparison,in situ remote hydrogen plasma and epitaxial growth were also performed on heavily dopedp-type (100) Si substrates. Finally, the results of epitaxial growth at temperatures as low as 150° are presented.

Reaction Kinetics of Epitaxial Silicon Deposition at 220-400°C Using Remote Plasma-Enhanced Chemical Vapor Deposition

AbstractIn this paper the reaction kinetics of Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) are investigated. Growth rate characterization has been performed for substrate temperatures of 220 – 400°C, r-f powers from 4 – 8 W, and silane flow rates of 10 – 30 sccm. Growth rate has been found to increase exponentially with r-f power, which is, as yet, unexplained. An approximate square root dependence of growth rate on silane partial pressure agrees with the theory of Claasen et. Al for Chemical Vapor Deposition (CVD) of silicon from silane with an inert carrier gas. From an Arrhenius plot of the temperature dependence of growth rate, we note a change of slope at ∼300°C which we have attributed to the behavior of hydrogen at the silicon surface.

Characterization of Oxygen‐Doped, Plasma‐Deposited Silicon Nitride

The physical properties of amorphous plasma‐deposited silicon nitride and silicon oxynitride films deposited in a load‐locked parallel plate reactor operating at 380 kHz were determined. Nitrous oxide was added to a mixture of 2% silane in nitrogen to produce the oxynitride films deposited from 200° to 350°C. The hydrogen content of these films is about half that of films deposited with ammonia as the source of nitrogen. The refractive index of the undoped silicon nitride is proportional to the Si‒H/N‒H ratio of the film while the refractive index of all films is proportional to Si‒H content. Increasing the nitrous oxide flow at constant silane and nitrogen flow rates: (i) improves the thickness uniformity across a wafer, (ii) increases the deposition rate; (iii) increases the oxygen content and decreases the silicon content; (iv) decreases the total H content; (v) reduces the compressive stress; and (vi) increases the buffered etch rate of the film. Our results suggest that discrepancies in the literature about the properties of plasma nitride are because of unwanted oxygen in the films.

The counterflow diffusion flame burner: A new tool for the study of the nucleation of refractory compounds

This paper describes the development of the counterflow diffusion flame burner into a tool which provides great promise as a technique for the study of the nucleation from the vapor phase of refractory compounds such as SiO 2, Al 2O 3, and other metal oxides. This burner produces a flame which is flat, stable, and rectangular in shape, with temperature and species-concentration distributions which are uniform in the horizontal plane. Thus, concentrations and temperatures can be measured spectroscopically. Hydrogen (diluted in argon) and oxygen (diluted in argon) have been used as the primary fuels and oxidants. Small amounts of appropriate gases, e.g., silane, are added to the fuel stream. Light scattering measurements indicate that an avalanche of nucleation occurs when the silane flow rate is increased beyond a critical value (e.g., 2.3 cm 3/min). The temperatures and the partial pressures of SiO and O 2 were measured. Assuming chemical equilibrium in the vapor phase, the SiO 2 partial pressure and the SiO 2 supersaturation were calculated. The H 2 O 2 flame changes color from pale-blue to a whitish pale-yellow when small amounts of silane are introduced into the flame. Increasing the silane flow rates makes this flame brighter and brighter. When the silane flow rate is increased sufficiently (e.g., to 9.3 cm 3/min), a second flame, thin and orange in color, appears on the H 2-side of the H 2 O 2 flame zone. Between the two flames there is always a dark space. The peak in light scattering intensity always occurs in the middle of this dark space.