Plasma-enhanced Chemical Vapor Deposition Conditions Research Articles

Amine plasma polymers deposited on porous hydroxyapatite artificial bone with bipolar pulsed discharges

A recent in vivo study [Kodama et al., Sci. Rep. 11, 1 (2021)] showed that porous artificial bones coated with amine-containing polymers deposited by plasma-enhanced chemical vapor deposition (PECVD) significantly enhanced bone regeneration. This article reports the chemical and physical properties of amine plasma polymers (PPs) formed under the same deposition conditions, including the film stability for up to two months, the effects of sterilization on the chemical compositions of the films, and the penetration of amine PPs into the inner surfaces of interconnected microscopic pores of the amine PP-coated porous artificial bone. It was found that, immediately after the plasma polymerization process, approximately 20% of nitrogen atoms on the surface of the deposited amine PP formed primary amines. However, the value decreased to approximately 5% over one month if the sample was exposed to ambient air. The relative concentration of primary amines also decreased to a similar value after the sample was sterilized by autoclaving or ethylene oxide gas. Molecular dynamics simulations were used to examine possible formation mechanisms of nitriles in deposit films under the PECVD conditions and found that ion impact can significantly reduce the nitrile content.

Photovoltaics literature survey (no. 149)

Photovoltaics literature survey (no. 149)

Optimization of N-doped TiO2 multifunctional thin layers by low frequency PECVD process

A one-step low-frequency Plasma Enhanced Chemical Vapor Deposition (PECVD) process, operating at temperature as low as 350°C, has been implemented to prepare single-oriented pure and N-doped anatase films. The layers have been synthesized using titanium isopropoxide as a precursor, and NH3 as a doping agent. Optimized PECVD conditions have enabled to obtain homogeneous micro-columnar porous thin films with thicknesses close to 500nm. Depth profiling XPS analyses have proved the nitrogen incorporation into TiO2 lattice after ammonia introduction in the deposition chamber. As another proof of N-doping, Raman and XRD peaks shifting have been observed. Such thin films have been demonstrated as efficient photocatalytic materials which activity region can be tailored from UV to visible region by adjusting the proportion of doping agent in the plasma phase. Due to their microstructural and photocatalytic properties, the prepared thin layers should have an interest as anode materials in solar water splitting cells.

Nanocrystalline TiO2 thin film prepared by low-temperature plasma-enhanced chemical vapor deposition for photocatalytic applications

A PECVD (Plasma-enhanced Chemical Vapor Deposition) process operating at 150°C has been implemented to prepare micro-columnar porous TiO2 anatase thin films, performing post-annealing at 300°C for 5h. Optimized PECVD conditions have enabled us to obtain homogeneous films with thickness equal to 1–2μm±0.2μm. An anatase seeding interface deposited prior to the PECVD process has enabled us to reduce crystallization time down to 1.5h. The size of nano-crystals in prepared anatase thin films has been estimated to be 20nm by applying the Scherrer equation. Besides, the band-gap energy (Eg) of synthesized anatase thin films on quartz was found to be 3.30eV.

Comparison of amorphous silicon absorber materials: Light-induced degradation and solar cell efficiency

Several amorphous silicon (a-Si:H) deposition conditions have been reported to produce films that degrade least under light soaking when incorporated into a-Si:H solar cells. However, a systematic comparison of these a-Si:H materials has never been presented. In the present study, different plasma-enhanced chemical vapor deposition conditions, yielding standard low-pressure VHF a-Si:H, protocrystalline, polymorphous, and high-pressure RF a-Si:H materials, are compared with respect to their optical properties and their behavior when incorporated into single-junction solar cells. A wide deposition parameter space has been explored in the same deposition system varying hydrogen dilution, deposition pressure, temperature, frequency, and power. From the physics of layer growth, to layer properties, to solar cell performance and light-induced degradation, a consistent picture of a-Si:H materials that are currently used for a-Si:H solar cells emerges. The applications of these materials in single-junction, tandem, and triple-junction solar cells are discussed, as well as their deposition compatibility with rough substrates, taking into account aspects of voltage, current, and charge collection. In sum, this contributes to answering the question, “Which material is best for which type of solar cell?”

Structural origins of intrinsic stress in amorphous silicon thin films

Hydrogenated amorphous silicon (a-Si:H) refers to a broad class of atomic configurations, sharing a lack of long-range order, but varying significantly in material properties, including optical constants, porosity, hydrogen content, and intrinsic stress. It has long been known that deposition conditions affect microstructure, but much work remains to uncover the correlation between these parameters and their influence on electrical, mechanical, and optical properties critical for high-performance a-Si:H photovoltaic devices. We synthesize and augment several previous models of deposition phenomena and ion bombardment, developing a refined model correlating plasma-enhanced chemical vapor deposition conditions (pressure and discharge power and frequency) to the development of intrinsic stress in thin films. As predicted by the model presented herein, we observe that film compressive stress varies nearly linearly with bombarding ion momentum and with a (\ensuremath{-}1/4) power dependence on deposition pressure, that tensile stress is proportional to a reduction in film porosity, and the net film intrinsic stress results from a balance between these two forces. We observe the hydrogen-bonding configuration to evolve with increasing ion momentum, shifting from a void-dominated configuration to a silicon-monohydride configuration. Through this enhanced understanding of the structure-property-process relation of a-Si:H films, improved tunability of optical, mechanical, structural, and electronic properties should be achievable.

Effect of Deposition Gas Ratio, RF Power, and Substrate Temperature on the Charging/Discharging Processes in PECVD Silicon Nitride Films for Electrostatic NEMS/MEMS Reliability Using Atomic Force Microscopy

The dependence of the electrical properties of silicon nitride, which is a commonly used dielectric in nano- and micro-electromechanical systems (NEMS and MEMS), on the deposition conditions used to prepare it and, consequently, on material stoichiometry has not been fully understood. In this paper, the influence of plasma-enhanced chemical vapor deposition conditions on the dielectric charging of films is investigated. The work targets mainly the dielectric-charging phenomenon which constitutes a major failure mechanism in electrostatically driven NEMS/MEMS devices and particularly in capacitive MEMS switches. The charging/discharging processes are studied using two nanoscale characterization techniques: Kelvin probe force microscopy (KPFM) and, for the first time, force-distance curve (FDC) measurements. KPFM is used to investigate dielectric charging at the level of a single asperity, while FDC is employed to measure the multiphysics coupling between the charging phenomenon and tribological issues, mainly meniscus force. The electrical properties of the films obtained from both techniques show a very good correlation. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy material characterization techniques are also used to determine the compositions and chemical bonds, respectively, of the films. An attempt to correlate between the chemical and electrical properties of films is made.

Optimization of silicon oxynitrides by plasma-enhanced chemical vapor deposition for an interferometric biosensor

In this paper, silicon oxynitride layers deposited with different plasma-enhanced chemical vapor deposition (PECVD) conditions were fabricated and optimized, in order to make an interferometric sensor for detecting biochemical reactions. For the optimization of PECVD silicon oxynitride layers, the influence of the N2O/SiH4 gas flow ratio was investigated. RF power in the PEVCD process was also adjusted under the optimized N2O/SiH4 gas flow ratio. The optimized silicon oxynitride layer was deposited with 15 W in chamber under 25/150 sccm of N2O/SiH4 gas flow rates. The clad layer was deposited with 20 W in chamber under 400/150 sccm of N2O/SiH4 gas flow condition. An integrated Mach–Zehnder interferometric biosensor based on optical waveguide technology was fabricated under the optimized PECVD conditions. The adsorption reaction between bovine serum albumin (BSA) and the silicon oxynitride surface was performed and verified with this device.

Properties of a Permeation Barrier Material Deposited from Hexamethyl Disiloxane and Oxygen

We characterize a recently discovered material that forms an ultra-hermetic environmental barrier layer for the protection of organic light-emitting displays. The layer is deposited by plasma-enhanced chemical vapor deposition (PE-CVD) from the nontoxic precursor gases, hexamethyl disiloxane and oxygen. We measured the PE-CVD deposition rate, wet and dry etch rates, IR absorption spectrum, wetting contact angle with water, surface roughness and phase shift from atomic force microscopy, coefficient of thermal expansion, elastic modulus, critical tensile strain, indentation hardness, optical absorption spectrum, refractive index, relative dielectric constant, and electrical conduction, many over a range of PE-CVD conditions. The properties reflect a continuous transition from those of plasma-polymerized silicon to those of silicon dioxide prepared by thermal oxidation of silicon. In addition to low permeability, the critical strain, fracture toughness, thermal expansion coefficient, optical transmittance, and refractive index have values that are desirable in a hermetic encapsulant for organic light-emitting displays.

Plasma-chemical processes in microwave plasma-enhanced chemical vapor deposition reactors operating with C/H/Ar gas mixtures

Microwave (MW) plasma-enhanced chemical vapor deposition (PECVD) reactors are widely used for growing diamond films with grain sizes spanning the range from nanometers through microns to millimeters. This paper presents a detailed description of a two-dimensional model of the plasma-chemical activation, transport, and deposition processes occurring in MW activated H/C/Ar mixtures, focusing particularly on the following base conditions: 4.4%CH4/7%Ar/balance H2, pressure p=150 Torr, and input power P=1.5 kW. The model results are verified and compared with a range of complementary experimental data in the companion papers. These comparators include measured (by cavity ring down spectroscopy) C2(a), CH(X), and H(n=2) column densities and C2(a) rotational temperatures, and infrared (quantum cascade laser) measurements of C2H2 and CH4 column densities under a wide range of process conditions. The model allows identification of spatially distinct regions within the reactor that support net CH4→C2H2 and C2H2→CH4 conversions, and provide a detailed mechanistic picture of the plasma-chemical transformations occurring both in the hot plasma and in the outer regions. Semianalytical expressions for estimating relative concentrations of the various C1Hx species under typical MW PECVD conditions are presented, which support the consensus view regarding the dominant role of CH3 radicals in diamond growth under such conditions.

Optimizing the dielectric performance of TiO2 thin films through control of plasma-enhanced chemical vapor deposition process conditions

The influence of plasma-enhanced chemical vapor deposition conditions on the dielectric performance of as-deposited TiO2 films was studied. It was found that the leakage current density was strongly correlated to the flatband voltage shift (ΔVFB). The value of ΔVFB increased linearly with the oxygen density, while an optimum was observed with respect to plasma power. By appropriate control of these two variables the electrical performance of as-deposited films approached those of annealed samples.

Formation of amine groups by plasma enhanced chemical vapor deposition and its application to DNA array technology

A plasma enhanced chemical vapor deposition (PECVD) method using plasma polymerized ethylenediamine (PPEDA) was employed to coat glass slides with amine functional groups. Fluorescein isothiocyanate (FITC) labeling indicated that the density of amine functional groups on these coated slides was affected by PECVD conditions, particularly deposition time. The PPEDA-coated slides were used for the development of DNA arrays. 5′-Amino-modified oligodeoxyribonucleotides (ODNs) and cDNA strands were immobilized onto PPEDA-coated slides and used for hybridization to labeled target strands. In addition, patterning of amine groups, which is a very useful technique for preparing high-density DNA arrays, was achieved by selectively depositing PPEDA films on specific areas of a glass surface. These results demonstrate that the formation of amine groups on glass slides by PECVD is an excellent tool for DNA array technology.

Development of Deposition Phase Diagrams for Thin Film Si:H and Si1-xGex:H Using Real Time Spectroscopic Ellipsometry

AbstractThe growth of hydrogenated silicon (Si:H) and silicon-germanium alloys (Si1-xGex:H) by plasma-enhanced chemical vapor deposition (PECVD) on crystalline silicon (c-Si) substrates has been studied by real time spectroscopic ellipsometry (RTSE). The motivation is to develop deposition phase diagrams that can provide greater insight into the optimization of amorphous Si1-xGex:H (a-Si1-xGex:H) for multijunction photovoltaics. In initial studies, the phase diagram for bottom cell a-Si1-xGex:H (Eg ˜ 1.4 eV) is found to exhibit fundamental similarities to that for Si:H when both materials are prepared under standard PECVD conditions that optimize pure a-Si:H. These similarities suggest directions for optimizing a-Si1-xGex:H by identifying conditions under which a smooth, stable surface is obtained to the largest possible bulk layer thickness. In phase diagram development for PECVD Si1-xGex:H on c-Si, it has been found that the highest surface stability and smoothest surfaces are obtained using cathodic deposition (self bias: ˜-20 V) with a H2-dilution level just below that of the amorphous-to-(mixed-phase microcrystalline) [→(a+μc)] transition for a thick layer. Due to the promising nature of these results, full phase diagrams are compared for cathodic and anodic Si1-xGex:H as well as for cathodic and anodic Si:H, all on c-Si substrates. The cathodic phase diagram for Si1-xGex:H reveals a narrow range of significant improvement in surface structural evolution near the →(a+μc) transition, and for a-Si:H reveals an extension of the ultrasmooth protocrystalline regime to a much wider range of thickness.

Copper blocking ability of nitrogen-incorporated silicon oxide film

Silicon oxynitride films were deposited by plasma-enhanced chemical vapor deposition (PECVD) using nitrous oxide (N2O) and monosilane (SiH4) chemistry. A wide range of nitrogen concentrations (from 0 to 8 at. %) in silicon oxynitride film was successfully obtained by controlling PECVD deposition conditions (rf power and SiH4/N2O flow ratio). The dependence of time-dependent dielectric-breakdown (TDDB) lifetime of such films with a copper anode on these PECVD conditions can be basically explained as the nitrogen-concentration dependence of the dielectric-breakdown lifetime. Increasing the nitrogen content from zero to 6 at. % improved the TDDB lifetime of the film by about seven orders of magnitude at a TDDB test temperature of 140 °C. However, increasing the nitrogen concentration to over 6 at. % did not improve the TDDB lifetime; in fact, doing so degraded it.

Molecular dynamics simulation of ion bombardment on hydrogen terminated Si(001)2×1 surface

Molecular dynamics simulations were performed to investigate H2+ and SiH3+ ion bombardment of hydrogen terminated Si(001)2×1 surfaces. Normal incidence ion bombardment effects on dangling bond generation, adatom diffusion, and nucleation were studied as a function of incident energy between 10 and 40 eV. The dangling bond generation rate due to H2+ impacts at 20 and 40 eV was about twice that of SiH3+. However these effects appeared to be insignificant compared to probable neutral radical effects under typical plasma-enhanced chemical vapor deposition conditions. The enhanced diffusion of Si adatoms due to ion bombardment was observed to be minor in comparison with thermal diffusion and the disruption of ledge sites due to SiH3+ ion bombardment is not significant, with ion incident energies up to 40 eV. Ion bombardment in the incident energy range between 10 and 20 eV can contribute the modification of surface kinetics without bulk damage.

Phase diagrams for Si:H film growth by plasma-enhanced chemical vapor deposition

Phase diagrams for plasma-enhanced chemical vapor deposition (PECVD) of thin film silicon (Si:H) describe the thicknesses and deposition-parameter values at which different microstructural and phase transitions are detected during film growth, using real time spectroscopic ellipsometry (RTSE) as a probe. In such diagrams, the positions of the transitions are plotted in the plane defined by the Si:H bulk layer thickness ( d b) and by the value of a key deposition parameter, usually the hydrogen-to-silane dilution ratio R=[H 2]/[SiH 4]. In this study, phase diagrams of d b vs. R are presented for Si:H films prepared under different rf PECVD conditions on crystalline silicon substrates. The variable parameters explored here include the rf plasma power, substrate temperature, and total gas pressure. The presented diagrams provide insights into the film growth processes that yield optimum electronic quality amorphous and microcrystalline Si:H at elevated deposition rates (>0.3 nm/s).

Phase Diagrams for the Optimization of rf Plasma Enhanced Chemical Vapor Deposition of a-Si:H: Variations in Plasma Power and Substrate Temperature

ABSTRACTReal time spectroscopic ellipsometry (RTSE) has been applied to characterize surface roughening transitions during the growth of undoped hydrogenated silicon (Si:H) thin films by rf plasma-enhanced chemical vapor deposition (PECVD). In particular, the amorphous–to–amorphous surface roughening transition [→] and the amorphous–to–(mixed-phase-microcrystalline) roughening transition [a→(a+µc)] observed during Si:H growth have been studied under different PECVD conditions of hydrogen dilution ratio R=[H2]/[SiH4], rf plasma power P, and substrate temperature T. For Si:H growth on crystalline Si substrates under the different conditions, phase diagrams have been constructed by plotting the bulk film thicknesses at which these transitions occur as a function of R. The effects of the substrate (c-Si wafers versus amorphous Si:H films) on the a→(a+µc) transition of the phase diagram are also explored. The results provide deeper insights into recent attempts to improve the material properties and solar cell performance for a-Si:H i-layers prepared by rf PECVD at higher rates.

Performance of heterojunction p+ microcrystalline silicon n crystalline silicon solar cells

We have studied by Raman spectroscopy and electro-optical characterization the properties of thin boron doped microcrystalline silicon layers deposited by plasma enhanced chemical vapor deposition (PECVD) on crystalline silicon wafers and on amorphous silicon buffer layers. Thin 20–30 nm p+ μc-Si:H layers with a considerably large crystalline volume fraction (∼22%) and good window properties were deposited on crystalline silicon under moderate PECVD conditions. The performance of heterojunction solar cells incorporating such window layers were critically dependent on the interface quality and the type of buffer layer used. A large improvement of open circuit voltage is observed in these solar cells when a thin 2–3 nm wide band-gap buffer layer of intrinsic a-Si:H deposited at low temperature (∼100 °C) is inserted between the microcrystalline and crystalline silicon [complete solar cell configuration: Al/(n)c-Si/buffer/p+μc-Si:H/ITO/Ag)]. Detailed modeling studies showed that the wide band-gap a-Si:H buffer layer is able to prevent electron backdiffusion into the p+ μc-Si:H layer due to the discontinuity in the conduction band at the amorphous-crystalline silicon interface, thereby reducing the high recombination losses in the microcrystalline layer. At the same time, the discontinuity in the valence band is not limiting the hole exit to the front contact and does not deteriorate the solar cell performance. The defect density inside the crystalline silicon close to the amorphous-crystalline interface has a strong effect on the operation of the cell. An extra atomic hydrogen passivation treatment prior to buffer layer deposition, in order to reduce the number of these defects, did further enhance the values of Voc and fill factor, resulting in an efficiency of 12.2% for a cell without a back surface field and texturization.

A versatile substrate heater for thermal and plasma-enhanced chemical-vapor deposition

A simple and inexpensive substrate heater that can be used in both thermal- and plasma-enhanced chemical-vapor deposition (PECVD) systems has been constructed. This heater design can be used to achieve and sustain substrate temperatures as high as 650 °C with a minimal amount of outgassing under both CVD and PECVD conditions. Substrates are heated very quickly with all but the highest temperatures achieved within 30 min. The heater is also very robust, with a lifetime of more than 30 h of continuous use under vacuum with several heating and cooling cycles. We have used this heater design to thermally deposit TiS2 from 1-methyl-1-propanethiol and TiCl4 in the temperature range of 200–500 °C. In addition, amorphous hydrogenated silicon carbide (a-Si1−xCx:H) was deposited in the temperature range of 30–570 °C using a 13.56 MHz rf plasma reactor and a modified version of the same heater.

Thin thermal SiO 2 after NH 3 or N 2O plasma action under plasma-enhanced chemical vapor deposition conditions

The effect of two kinds of plasma (NH 3 and N 2O) nitridation under plasma-enhanced chemical vapor deposition conditions on the properties of 10 nm and 20 nm thermally grown oxides was studied. It was established that both kinds of plasma induce radiation defects in the Si-SiO 2 structures in the form of a fixed oxide charge and negatively charged interface states, without transformation of the oxide into an oxynitride. It has been suggested that this is due to the relatively low process temperature (643 K) as well as to the short plasma nitridation times (5–20 min). These conditions do not allow incorporation of N in the depth of the oxide. The plasma induced charges lead to degradation of the mobility and influence strongly the scattering mechanisms in the inversion channel. The interface and dielectric properties of the plasma treated Si-SiO 2 structures depend on the initial oxide thickness and on the duration of the nitridation process. Degradation of the properties is stronger for thinner oxides and longer nitridation times. The N 2O plasma treated oxides display a lower plasma sensitivity. The nature of plasma induced charges is connected mainly to the influence of plasma chemistry.