SiH4 Flow Research Articles

High rate synthesis of crystalline silicon films from SiH4+He using high density microwave plasma

By using a high density microwave-induced plasma source, depositions of crystalline silicon films from SiH4+He mixture are investigated systematically. Microwave power and SiH4 flow rate are used as the variable deposition parameters. Results demonstrate that film deposition rate increases with increasing both the microwave power and the SiH4 flow rate. While film crystallinity promotes with increasing the microwave power but degrades with increasing the SiH4 flow rate. After optimizing the film deposition conditions, highly crystallized Si films are deposited at a rate higher than 1000 nm/s. Promotion of the dissociation efficiency of source gases and enhancement in the diffusion length of film precursors on growing surface are suggested to be main factors responsible for the simultaneous achievements of the high deposition rate and the high film crystallinity. Mechanisms under these phenomena are discussed in detail.

Control of the Surface Morphology on Low Off Angled 4H-SiC Homoepitaxal Growth

We have carried out detailed investigations on the influence of the growth conditions and the wafer off angle on the surface morphology of low off angle homoepitaxial growth. We found triangular features to be also serious problems on a 4 degree off 4H-SiC Si-face epitaxial layer surface. The control of the C/Si ratio by controlling the SiH4 flow rate is effective in suppressing the triangular features on 4 degree off Si-face homoepitaxial layer. As regards epitaxial growth on a vicinal off-axis substrate, the small off angle difference of a tenth part of a degree has an influence on the surface morphology of the epitaxial layer. This tendency depends on the face polarity and a C-face can be obtained that has a specular surface with a lower vicinal off angle than a Si-face. By controlling this off angle, a specular surface morphology without a bunched step structure could be obtained on a vicinal off angle 4H-SiC Si-face.

Ammonia-free deposition of silicon nitride films using pulsed-plasma chemical vapor deposition under near atmospheric pressure

Ammonia-free deposition of silicon nitride (SiNX) films have been achieved on Si(100) substrate at low temperature (200°C) by using plasma enhanced chemical vapor deposition operated at near atmospheric pressure. A pulsed power supply enables a stable discharge of a SiH4–H2–N2 system at near atmospheric pressures without using any inert gases such as He. Characterization by x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy indicates that the grown film is a SiNx film with its N∕Si ratio varying for 0.85–0.90, depending on the N2∕SiH4 flow ratio (1000–4000). Despite the use of N2 instead of NH3, a high rate growth (10–70nm∕min) is enabled, which would be beneficial in forming protection/passivation layers in solar cells. The breakdown field of 7.4MV∕cm seems also promising for its use as a gate insulator in amorphous-silicon-based thin film transistors (TFTs).

Comparison of Si Doping Effect on GaN Nanowires and Films Synthesized by Metal-Organic Chemical Vapor Deposition

We investigated Si doping effect on GaN nanowires and GaN films grown by metal-organic chemical vapor deposition (MOCVD). Si as n-type dopant is incorporated to GaN nanowires and GaN films controlled by SiH4 flow rate (0, 1, 5, 8, and 10 sccm). The charge concentration and mobility of GaN films increased and decreased, respectively, as increasing the SiH4 flow rate, whereas those for GaN nanowires were not influenced by the SiH4 flow rate. Significant vacancies and impurities resulted in the intense yellow band in GaN nanowires as compared with GaN films, which leads to the large device-to-device variation and negligible dependence of Si doping and the SiH4 flux rate on the electrical properties of GaN nanowires.

Enhancement of film-forming reactions for microcrystalline Si growth in atmospheric-pressure plasma using porous carbon electrode

We have investigated the structural and electrical properties of microcrystalline silicon (μc-Si:H) films deposited with high rates (≥5 nm/s) at 220 °C in atmospheric-pressure He/H2/SiH4 plasma excited by a 150 MHz, very high-frequency (VHF) power. For this purpose, Si films are prepared varying the deposition parameters, such as H2 and SiH4 flow rates (H2 and SiH4 concentrations) and VHF power density, using two types of electrode (porous carbon and cylindrical rotary electrodes). In the case of using the porous carbon electrode, a μc-Si:H film having a crystalline volume fraction of 71.9% is obtained even when hydrogen is not added to the process gas mixture (H2/SiH4=0). In addition, the films exhibit considerably low defect densities of (3–5)×1016 cm–3 despite the high deposition rates. Such high-rate depositions of good-quality films are realized primarily due to the chemical and physical excitations of the film-growing surface by the atmospheric-pressure plasma while suppressing ion damage and excessive heating of the surface. On the other hand, when using the cylindrical rotary electrode, the phase transition from amorphous to microcrystalline occurs at around H2/SiH4=70. The enhancement of the film-forming reactions by the porous carbon electrode are discussed from the viewpoint of the gas residence time in the plasma.

Temperature effect on charge density of silicon nitride films deposited in SiH4–NH3–N2 plasma

Improved surface passivation of silicon nitride films requires a high positive charge density. A neural network model of SiN charge density was used to investigate temperature effects on charge density. For a systematic modeling, the deposition process was characterized by means of a face-centered Box Wilson experiment. Prediction performance of neural network model was optimized by using genetic algorithm. Interestingly, charge density was varied little with the substrate temperature regardless of SiH4 flow rates. Charge density variation was not sensitive to [Si–H] variation. A pronounced temperature effect at higher NH3 flow rate or lower radio frequency (rf) power was attributed to a relatively large [N–H]. For NH3 or rf power variation, charge density was strongly correlated to [N–H]/[Si–H].

Effect of film chemistry on refractive index of plasma-enhanced chemical vapor deposited silicon oxynitride films: A correlative study

Thick SiOxNy films were deposited by radiofrequency (rf) plasma chemical vapor deposition using silane (SiH4) and nitrous oxide (N2O) source gases. The influence of deposition conditions of gas flow ratio, rf plasma mixed-frequency ratio (100 kHz, 13.56 MHz), and rf power on the refractive index were examined. It was observed that the refractive index of the SiOxNy films increased with N and Si concentration as measured via x-ray photoelectron spectroscopy. Interestingly, a variation of refractive index with N2O:SiH4 flow ratio for the two drive frequencies was observed, suggesting that oxynitride bonding plays an important role in determining the optical properties. The two drive frequencies also led to differences in hydrogen concentration that were found to be correlated with refractive index. Hydrogen concentration has been linked to significant optical absorption losses above index values of ∼1.6, which we identified as a saturation level in our films.

Measured Gas Concentrations and Flow Properties in SiH4–H2 Mixtures

Each gas concentration in silane–hydrogen (SiH4–H2) gas mixtures was measured using a diaphragm gauge and a quartz friction pressure gauge (D- and Q-gauges). At constant pressures of 0.13–1.3 kPa, the Q-gauge pressure readings depended on the densities of SiH4 and H2. Therefore, the dependence of the Q-gauge pressure readings on the partial pressures of SiH4 could be used to measure the concentrations of these gases in the gas mixtures. The relative SiH4 density in the flow of gas mixtures was higher than the SiH4 flow rate ratio, indicating that the flow of the mixtures was intermediate between molecular and viscous. The viscosities of the gas mixtures estimated from the pressure-normalized Q-gauge pressures were compared with the calculations by Wilke's equation, with the finding that the viscosity of the gas mixture can be derived using the present measurement.

Highly Reliable Cu Interconnect Using Low-Hydrogen Silicon Nitride Film Deposited at Low Temperature as Cu-Diffusion Barrier

We demonstrated highly reliable Cu interconnects using a high-quality silicon nitride film grown at temperatures below 300 °C. The low-temperature silicon nitride (LT-SiN) film, which was used as a Cu-diffusion barrier layer and a final passivation layer, was deposited at 275 °C by plasma-enhanced chemical vapor deposition at a low SiH4 flow ratio. The low SiH4 flow ratio was due to the use of a highly dilute nitrogen flow, leading to the generation of many nitrogen radicals or ions in the plasma. These radicals or ions might reduce the hydrogen concentration and defect density of the film. As a result, a stoichiometric silicon nitride (Si3N4) film with a low hydrogen concentration was successfully obtained. By applying this LT-SiN film in 130-nm-node Cu interconnects for magnetoresistive random access memory, highly reliable via-hole electromigration (Via-EM) and line-to-line time-dependent dielectric breakdown (TDDB) characteristics were obtained.

Deposition of microcrystalline silicon films at ultrafast rate by using a new microwave induced plasma source

Synthesis of microcrystalline silicon (μc-Si) film at an ultrafast deposition rate over 100nm/s is achieved from SiH4+He by using a high density microwave plasma source even without employing H2 dilution and substrate heating techniques. Systematic deposition studies show that high SiH4 flow rate and working pressure increase film deposition rate while high He flow rate decreases the rate. On the other hand, crystallinity of deposited Si film decreases with increasing SiH4 or He flow rate and working pressure. Enhancements of gas phase and surface reactions during film deposition process are responsible for the achievement of high deposition rate and high film crystallinity.

Nano-structured GeySi1-y:H Films Deposited by Low Frequency Plasma for Photovoltaic Application

ABSTRACTIn this work we present the study of fabrication, Ge incorporation, structure and electronic properties of nano-structured GeySi1-y:H films with y>0.5 prepared by low frequency (LF) PECVD. GeySi1-y:H films were deposited by LF PECVD at a frequency f= 110 kHz from SiH4+GeH4+H2 gas mixture. SiH4 and GeH4 flows were varied to fabricate the films in wide range of 0<y<l. Hydrogen dilution was varied in the range of RH =20 to 80. Structure of the films was studied by AFM and SEM with consequent image processing to extract statistical parameters such as grain distribution and mean values. Composition of the films was characterized by SIMS and EDX. Electronic properties were characterized by temperature dependence of conductivity, spectral dependence of optical absorption. Sub-gap absorption was characterized by Urbach energy, EU; and defect absorption, αD. We observed grain like nano-structure with Gauss distribution of grain diameters by both AFM and SEM measurements. The most interesting films had mean grain diameter<D> = 24.0±0.7 nm, dispersion D=11.0±0.2 nm and fill factor FF=0.313, Ge content y=0.96-0.97(by SIMS and EDS). These films showed also the lowest values of Urbach energy EU = 0.030 eV and low defect absorption αD = 5×102 cm −1 (at photon energy hv = 1.04 eV) indicating on low density of localized states in mobility gap. Doped films have been also fabricated and studied. Finally we shall discuss application of the above films in photovoltaic devices.

Use of a neural network to characterize the charge density of PECVD-silicon nitride films

Silicon nitride (SiN) films were deposited using a plasma-enhanced chemical vapor deposition system (PECVD). The charge density of the SiN films was modeled using a generalized regression neural network (GRNN). The PECVD process was characterized by means of a face-centered Box Wilson experiment. The prediction performance of the GRNN model was optimized using a genetic algorithm (GA). The GA-GRNN model significantly improved the GRNN prediction performance by more than 55%. The optimized GA-GRNN model was used to investigate the effects of various parameters on the charge density. A higher charge density was obtained at higher temperatures (i.e. a lower H concentration). Increasing the pressure increased the charge density at all temperatures levels with a much stronger impact at a lower H concentration. The effects of the SiH4 and N2 (or NH3) flow rates on the charge density were similar in that a higher charge density was achieved at a lower Si−N ratio (N-rich films). A considerable increase in the charge density with a radio frequency power at a lower NH3 flow rate was attributed to the generation of more Si−H than N−H bonds.

Impurity-Free Vacancy Diffusion of InGaAsP/InGaAsP Multiple Quantum Well Structures Using SiH4-Dependent Dielectric Cappings

We report the impurity-free vacancy diffusion (IFVD) behaviors of In0.86Ga0.14As0.64P0.36/In0.88Ga0.12As0.25P0.75 multiple quantum well (MQW) structures using dielectric films as a capping layer. The effects of SiOx and SiNx films deposited using different SiH4 flow rates on the IFVD are investigated by photoluminescence measurements and ellipsometry analysis. The properties of dielectric capping layer play a key role in the intermixing of this MQW structure, indicating that the increased porosity of SiOx and SiNx layers enhances the bandgap energy shift of MQWs. A significant blue shift of 173 nm (i.e., 106 meV) for the sample capped with a relatively more porous SiNx, which was deposited using 20 sccm SiH4, was obtained after a thermal annealing of 850 °C for 30 s. The mechanism was analyzed by using transmission electron microscopy and energy dispersive X-ray spectroscopy. It is believed that the enhanced blue shift is ascribed to the dominant interdiffusion of group V atoms because the compositions of group III atoms are kept almost identical in the wells/barriers.

Effect of the property of dielectric capping layers on impurity-free vacancy diffusion in InGaAs/InGaAsP MQW structures

A dependence of the interdiffusion in InGaAs/InGaAsP multiple quantum well (MQW) structures on the stoichiometry of SiOx and SiNx capping layers, which were deposited with different SiH4 flow rates by plasma enhanced chemical vapor deposition (PECVD), has been studied. Decreasing the SiH4 flow rate during PECVD deposition produces relatively more voids inside SiOx or SiNx film. For both SiOx and SiNx capping layers, the blue shift of intermixed samples after rapid thermal annealing (RTA) becomes larger due to the enhancement of the interdiffusion of well/barrier caused by the increased porosity of dielectric capping layers as SiH4 flow rate decreases from 300 sccm to 20 sccm. Using SiOx (SiNx) deposited with different SiH4 flow rates, the magnitude of blue shift is varied by about 98 nm (75 nm) for the samples annealed at 850 °C for 30 s. The blue shifts of 138 nm and 98 nm of photoluminescence peak wavelength for the SiOx (deposited with 20 sccm SiH4) capped MQWs without and with an InGaAs cap layer, respectively, are observed after RTA of 850 °C for 30 s. A possible mechanism is discussed for these phenomena.

Study of SiOxNy as a bottom antireflective coating and its pattern transferring capability

To meet such challenges for the controlling of critical feature dimension at sub-50–100‐nm, it has been a general industrial trend to employ shorter wavelength (193nm, for example) lithography for better resolution and to use bottom antireflective coating (BARC) for a reduced standing wave formation and thus, a better critical dimensional control. Matching the optical constants (n,k) between the BARC, photoresist, and the underlayer to be patterned is critical for the elimination of such standing waves. SiOxNy and SiOxCy are two attractive inorganic BARC candidates in view of their easily adjustable optical constants by varying the deposition parameters and their etching compatibility with standard semiconductor plasma processes. In this article, SiOxNy films were prepared by plasma enhanced chemical vapor deposition approach. These films have been further characterized using x-ray photoelectron spectroscopy for chemical composition depth profile, Fourier transform infrared spectroscopy for local chemical bonding, and ellipsometry for optical constants. It has been demonstrated that the refractive indices of SiOxNy can be tuned from 1.6 to 2, while the absorption constants k can be adjusted from 0.1 to 0.9 by changing the process parameters, such as SiH4 flow rate, NH3 flow rate, and SiH4∕N2O ratio. To integrate the SiOxNy BARC film into the storage device manufacturing, the pattern transferring capability of SiOxNy has been discussed. A film stack structure of photoresist∕SiOxNy∕carbon or SiC hard mask∕magnetic device layer has been used to evaluate the performance of the SiOxNy BARC. SiOxNy film was opened via inductively coupled plasma etching with CHF3+O2 chemistry, while carbon and SiC hard masks were opened using He–O2 and SF6–He–O2 chemistries, respectively. SiF emission line at 388nm wavelength was used for end point during the SiOxNy etching, while the 778nm O peak and 685nm F peak have been used for carbon and SiC end pointing. The profiles of the etched SiOxNy and carbon∕SiC were analyzed by cross-section transmission electron microscopy.

Microcrystalline silicon solar cells with an open-circuit voltage above 600mV

Microcrystalline silicon solar cells with an open-circuit voltage surpassing the 600mV barrier were prepared by combining the use of a hot wire deposited p-i interface with that of an i layer deposited by radio-frequency parallel plate plasma deposition using controlled SiH4 flow profiling. The control of the bulk and interface properties facilitated effective charge carrier collection from i layers with a crystalline volume fraction as low as ∼30%. Judging from the absorption in the infrared and the excellent charge carrier transport, the optoelectronic properties of this material were still dominated by the crystalline rather than the amorphous phase.

Radio Frequency Power Effect on Charge Density of PECVD-SiN Thin Films

Charge density is an important film characteristic that determines the quality of film surface passivation. In this study, a prediction model of charge density was constructed by using a neural network and generic algorithm. For a systematic modeling, plasma enhanced chemical vapor deposition process of silicon nitride films was characterized by means of a statistical experimental design. Effects of parameters under various radio frequency (rf) powers were examined under various plasma conditions. An increase in charge density was observed with increasing rf power over the entire range of SiH4 flow rate as well as at lower N2 flow rates or pressures. The effect of SiH4 flow rate on charge density was opposite to that for N2 flow rate given rf powers. For the variations in N2 or SiH4 flow rate, charge density seemed to be strongly correlated to N/Si ratio. Under the variations in pressure or N2 flow rate, maintaining a lower pressure was beneficial in achieving a higher charge density. A pronounced rf power effect at smaller grain size was expected.

N, NH, and NH2 radical densities in a remote Ar–NH3–SiH4 plasma and their role in silicon nitride deposition

The densities of N, NH, and NH2 radicals in a remote Ar–NH3–SiH4 plasma used for high-rate silicon nitride deposition were investigated for different gas mixtures and plasma settings using cavity ringdown absorption spectroscopy and threshold ionization mass spectrometry. For typical deposition conditions, the N, NH, and NH2 radical densities are on the order of 1012cm−3 and the trends with NH3 flow, SiH4 flow, and plasma source current are reported. We present a feasible reaction pathway for the production and loss of the NHx radicals that is consistent with the experimental results. Furthermore, mass spectrometry revealed that the consumption of NH3 was typically 40%, while it was over 80% for SiH4. On the basis of the measured N densities we deduced the recombination and sticking coefficient for N radicals on a silicon nitride film. Using this sticking coefficient and reported surface reaction probabilities of NH and NH2 radicals, we conclude that N and NH2 radicals are mainly responsible for the N incorporation in the silicon nitride film, while Si atoms are most likely brought to the surface in the form of SiHx radicals.

Lower-Temperature Epitaxial Growth of 4H-SiC Using CH<sub>3</sub>Cl Carbon Gas Precursor

The advantages of the CH3Cl carbon precursor were investigated in order to achieve good-quality homoepitaxial layers of the 4H-SiC polytype at temperatures lower than what was considered practical (or even possible) with C3H8-based growth. It was observed that the process window for good epilayer morphology becomes narrower when the growth temperature is decreased. Successful growth experiments have been conducted in this work down to a temperature of 1290-13000C, with the growth rate in excess of 2 +m/hr and a mirror-like defect-free epilayer surface morphology. Growth on a 2” substrate produced promising growth rate homogeneity. The dependence of the growth rate on SiH4 flow followed a clear exponential dependence. This trend is tentatively attributed to Si vapor condensation. Photoluminescence results suggest that the crystalline quality of the epilayers grown at 13000C is comparable to that of 17000C growth.

New insights in microcrystalline silicon deposition with expanding thermal plasma chemical vapor deposition

We report on further insights in the microcrystalline silicon (μc-Si:H) deposition using expanding thermal plasma chemical vapor deposition. We have shown before that the refractive index at 2eV of μc-Si:H layers increased if the silane (SiH4) was injected close to the substrate, while the deposition rate remained the same. We argued that at high injection-ring position, the SiH4 travels a long way to the substrate and therefore has a long interaction time with the plasma, in particular atomic hydrogen. In this way, the SiH4 injection position influences the number of hydrogen atoms stripped from the SiH4 as well as the consumption of atomic hydrogen. In this paper, we present an analysis of the growth flux of depositing particles as function of the radical production rate. The data suggest that there is no dependence on the SiH4 injection position, implying that the mix of depositing radicals is not changed. However, the data also show the microcrystalline-to-amorphous transition shifts to higher SiH4 flows for lower injection positions. We therefore now think that it is not the interaction time between the SiH4 and the arc plasma determining the material properties, but the interaction of excess atomic hydrogen with the μc-Si:H growth surface.