Plasma-enhanced Chemical Vapor Deposition Process Research Articles

Effect of C2H2 flow rate and a Ti/TiN/TiCN interlayer on the structure, mechanical and tribological properties of a-C:H films deposited using a hybrid PVD/PECVD process with an anode-layer ion source

Diamond-like carbon (DLC) films were deposited onto 316L stainless steel using the hybrid physical vapor deposition (PVD)/plasma-enhanced chemical vapor deposition (PECVD) process with an auxiliary anode-layer ion source at C2H2 flow rates of 40–100 sccm to enhance mechanical and tribological properties of a-C:H films. The films were characterized using transmission electron microscope (TEM), field emission scanning electron microscopy (FESEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation and ball-on-disk rubbing tribometry. The hardness, tribological properties and interfacial bonding were significantly improved in the presence of the Ti/TiN/TiCN interlayer deposited by high-power impulse magnetron sputtering (HiPIMS). Results showed that a-C:H films were uniform and dense, the sp3 C content increased with an increase in the C2H2 flow rate from 40 to 80 sccm, and decreased when it was further increased to 100 sccm. The a-C:H film with the interlayer prepared at 80 sccm C2H2 exhibited the highest hardness (27.2 ± 0.5 GPa), H/E (0.137), and H3/E2 (0.510). Moreover, friction-wear tests demonstrated that the incorporation of the Ti/TiN/TiCN layer increased the wear resistance of the a-C:H film, achieving the lowest coefficient of friction (CoF, 0.148), wear rate (1.08 × 10−9 mm3 N−1 mm−1) and width of the wear track (177 μm) at 80 sccm C2H2.

Beam Trajectory Analysis of Vertically Aligned Carbon Nanotube Emitters with a Microchannel Plate

Vertically aligned carbon nanotubes (CNTs) are essential to studying high current density, low dispersion, and high brightness. Vertically aligned 14 × 14 CNT emitters are fabricated as an island by sputter coating, photolithography, and the plasma-enhanced chemical vapor deposition process. Scanning electron microscopy is used to analyze the morphology structures with an average height of 40 µm. The field emission microscopy image is captured on the microchannel plate (MCP). The role of the microchannel plate is to determine how the high-density electron beam spot is measured under the variation of voltage and exposure time. The MCP enhances the field emission current near the threshold voltage and protects the CNT from irreversible damage during the vacuum arc. The high-density electron beam spot is measured with an FWHM of 2.71 mm under the variation of the applied voltage and the exposure time, respectively, which corresponds to the real beam spot. This configuration produces the beam trajectory with low dispersion under the proper field emission, which could be applicable to high-resolution multi-beam electron microscopy and high-resolution X-ray imaging technology.

Conversion of vertical-to-planar graphene by morphing of copper nanostructure during a moderate temperature plasma process

The plasma-enhanced chemical vapor deposition process enables the growth of graphene at a moderate temperature, but it is vertical graphene (VG) with a large number of defects. In this letter, we report a successful method to obtain planar graphene by morphing of Cu nanostructure during a modified Ar/CH4 plasma process at 600 °C. The insertion of meshed metal shields within the plasma region reduces the magnitude of ions bombardment on the substrate. In this circumstance, the evaporated Cu with a thickness of 200 nm on a black Si template is permitted to diffuse and form a planar film. The reduced plasma etching allows the growth of VG leaves and they are converted into planar multilayer graphene during the Cu morphing process. The crystal defect on planar graphene is minimum, where the values of Raman ID/IG and ID’/IG are 1.91 ± 0.06 and 0.20 ± 0.02, respectively.

Plasma–induced damage in magnetic tunneling junctions

Plasma–induced damage (PID) in the fabrication of magnetic tunnel junction (MTJ) based magnetic random access memory (MRAM) is studied after the formation of MTJ devices, which excludes process effect directly from the ion beam etching and protection layer deposition. Large degradation in coercivity (Hc) of MTJs is found in comparison with that measured just after the top metal （TM） was formed, which heavily deteriorates MRAM performances. This Hc degradation is found to be mainly introduced in plasma-enhanced chemical vapor deposition (PECVD) for passivation (PA) film after TM formation. The amplitude of the degradation depends on plasma power, but independent of the composition of the PA film. Hc reduction is observed once the plasma is turned on even though no PA deposition is performed. These results suggest that the observed Hc degradation is from PID effect most likely due to the plasma charge damage (PCD) induced in the PECVD process as no direct plasma contact with MTJ devices is involved in the process. It is argued that this PCD effect is due to the charge accumulations at the interface between the free layer and MgO barrier based on electric field–modulated magnetic anisotropy effect. This is further confirmed by an experiment in which Hc degradation is largely cured through partially removing the trapped charges by an annealing process.

Evolution of Nanocrystalline Graphite’s Physical Properties during Film Formation

Nanocrystalline graphite (NCG) layers represent a good alternative to graphene for the development of various applications, using large area, complementary metal-oxide semiconductor (CMOS) compatible technologies. A comprehensive analysis of the physical properties of NCG layers—grown for different time periods via plasma-enhanced chemical vapour deposition (PECVD)—was conducted. The correlation between measured properties (thickness, optical constants, Raman response, electrical performance, and surface morphology) and growth time was established to further develop various functional structures. All thin films show an increased grain size and improved crystalline structure, with better electrical properties, as the plasma growth time is increased. Moreover, the spectroscopic ellipsometry investigations of their thickness and optical constants, together with the surface roughness extracted from the atomic force microscopy examinations and the electrical properties resulting from Hall measurements, point out the transition from nucleation to three-dimensional growth in the PECVD process around the five-minute mark.

Tailoring the nanostructure of plasma-deposited CoOX-based thin films for catalytic applications – A step forward in designing nanocatalysts

Among the heterogeneous catalysts based on non-noble metals, cobalt oxides, mainly in the Co3O4 form, are particularly promising materials. Herein, we developed a facile bottom-up approach to synthesize a novel and sophisticated Co3O4-based thin-film material with a tailored nanostructure that is crucial for catalytic properties. The films were produced using a low-pressure plasma-enhanced chemical vapor deposition (PECVD) process that was thoroughly analyzed. The as-deposited films, in the amorphous form composed of Co, O, C, and H atoms (called CoOX-based films), were thermally treated (calcined), transforming them into films containing Co3O4 nanocrystallites. For a fundamental understanding of the transformation process, the calcination was performed in a controlled manner by Raman spectroscopy using the Raman laser as a heat source. An original model to describe the formation of Co3O4 nanocrystallites was proposed. We have shown that the concentration of Co3O4 and also the number and size of its nanocrystallites in the films can be rationally tailored to the specific needs by selecting the parameters of the PECVD and calcination processes. Our research provides a practical strategy for the molecular design of nanostructured thin-film catalysts in a controllable way using the PECVD process.

Fastly PECVD-Grown vertical carbon nanosheets for a composite SiOx-C anode material

SiOx has been regarded as the most promising anode material for high energy density lithium-ion batteries (LIBs). However, SiOx materials suffer from intrinsic defects such as poor electrical conductivity, large volume expansion effects, and low initial Coulomb efficiency. In order to solve these problems, vertically arrayed carbon nanosheet encapsulated disproportionated-SiOx (d-SiOx@CNs) composites was fabricated by using a fast plasma-enhanced chemical vapor deposition (PECVD) processing. The PECVD produced vertically arrayed carbon nanosheets provided good interfacial contacts and significantly improved the electronic conductivity and Li+ diffusivity of the SiOx material. As LIBs anode, the d-SiOx@CNs composite displays a high reversible capacity (first charge/discharge capacity of 1456.7 and 1794.4 mAhg−1, respectively) and excellent cycling stability (capacity retention of 87.2 % after 200 cycles at a current density of 0.4 Ag−1). The full cell (d-SiOx@CNs15/G‖NCM811) assembled with the commercial NCM811cathode material also showed an excellent electrochemical performance (capacity retention rate of 76.3 % after 200 cycles at 1C current density) and provided a high energy density of 424.2 Wh kg−1. The fast-growth mechanism of the vertically oriented carbon nanosheet by PECVD was also analyzed in terms of the plasma characteristic.

PECVD-derived graphene saturable absorber mirror for 2.8 μm pulsed Er:ZBLAN fiber laser

Graphene has been emerging as an ideal mid-infrared saturable absorber (SA) due to its broadband absorption, ultrafast nonlinear optical response, high stability and thermal tolerance. However, the current routes (e.g. chemical vapor deposition and spin coating) for constructing graphene SAs are suffering from the limited flexibility in substrate choice and the introduction of impurities during the transfer process, resulting in poor film quality and unstable laser modulation. Here, we demonstrate a high-quality graphene SA mirror (GSAM) grown directly on calcium fluoride (CaF2) substrate by a low-temperature plasma enhanced chemical vapor deposition (PECVD) method for mid-infrared pulse modulation. The controllable growth of high-quality graphene film on the nickel-modified CaF2 substrate is realized by adjusting the growth time and hydrocarbon ratio during PECVD process. Consequently, the GSAM shows excellent nonlinear optical absorption with the modulation depth of 11.2%. By inserting the GSAM into the Er:ZBLAN fiber laser, a stable passive Q-switched (QS) operation can be achieved with an average output power of 142 mW and a pulse width of 300.2 ns. The slope efficiency of QS laser is up to 17.4% and the peak power is 7.76 W. Our strategy paves the way for developing high quality and modulation stability GSAM towards industrial applications of pulsed mid-infrared lasers.

Effect of precursor gas inlet position relative to hot wire cells in HWC-IP-PECVD systems for low-temperature graphene growth

ABSTRACT Graphene growth at low temperatures was investigated by integrating a hot wire cell made from coil-shaped tungsten into a plasma-enhanced chemical vapour deposition (PECVD) system. It was found that the suitable position of the hot wire was such that the precursor gas comes out of the end of the gas pipeline and directly flows into the hot wire along its axis. This position puts the gas pipeline outside of plasma area, yielding uninterrupted plasma. The obtained films, which were grown at a low temperature between 290 °C to 300 °C, showed the presence of sharp G band in Raman spectra, indicating the presence of graphitic carbon structure and was confirmed by X-Ray Diffraction data. Also, sharp D band was detected in Raman spectra, which indicated that the film contains many defects. In addition to the nature of ion bombardment in the PECVD process, the defects were due to the addition of O-H functional groups and the formation of sp3 C-H in the samples, as shown in the FTIR spectra. Due to these defects, the Raman spectra obtained of the films showed very weak 2D bands, suggesting that our samples were in the form of graphene oxide.

Roll-to-roll fabrication of large-scale polyorgansiloxane thin film with high flexibility and ultra-efficient atomic oxygen resistance

One of the most widely used and well-established atomic oxygen (AO) protection solutions for low Earth orbit (LEO) satellites is the deposition of protective coatings on polymeric materials. However, manufacturing extensive expanses of these coating materials with good transparency, flexibility, smoothness, ultra-thinness, and exceptional AO resistance remains a critical issue. Herein, we successfully deposited a 400 nm thick polyorgansiloxane (SiO x C y H z ) coating with high optical transparency and uniform good adherence on to a 1.2 m wide polyimide surface, by optimizing the distribution of hexamethyldisiloxane and oxygen as precursors in the roll-to-roll compatible plasma-enhanced chemical vapor deposition process. After AO irradiation with the fluence of 7.9 × 1020 atoms·cm–2, the erosion yield of the SiO x C y H z -coated Kapton was less than 2.30 × 10–26 cm3·atom–1, which was less than 0.77% of that of the Kapton. It indicates that the SiO x C y H z coating can well prevent the erosion of Kapton by AO. In addition, it was also clarified that a SiO2 passivation layer was formed on the surface of the SiO x C y H z coating during AO irradiation, which exhibited a ‘self-reinforcing’ defense mechanism. The entire preparation process of the SiO x C y H z coating was highly efficient and low-cost, and it has shown great potential for applications in LEO.

Synthesis and Characterization of Boron Thin Films Using Chemical and Physical Vapor Depositions

Boron as thin film material is of relevance for use in modern micro- and nano-fabrication technology. In this research boron thin films are realized by a number of physical and chemical deposition methods, including magnetron sputtering, electron-beam evaporation, plasma enhanced chemical vapor deposition (CVD), thermal/non-plasma CVD, remote plasma CVD and atmospheric pressure CVD. Various physical, mechanical and chemical characteristics of these boron thin films are investigated, i.e., deposition rate, uniformity, roughness, stress, composition, defectivity and chemical resistance. Boron films realized by plasma enhanced chemical vapor deposition (PECVD) are found to be inert for conventional wet chemical etchants and have the lowest amount of defects, which makes this the best candidate to be integrated into the micro-fabrication processes. By varying the deposition parameters in the PECVD process, the influences of plasma power, pressure and precursor inflow on the deposition rate and intrinsic stress are further explored. Utilization of PECVD boron films as hard mask for wet etching is demonstrated by means of patterning followed by selective structuring of the silicon substrate, which shows that PECVD boron thin films can be successfully applied for micro-fabrication.

Lead-based chalcogenide thin films for mid-IR photoreceivers: plasma synthesis, semiconductor, and optical properties

Complex chalcogenide systems like PbS1-xSex seem to be promising semiconductors with a great potential for highly sensitive photodetectors of the mid-IR range and thermoelectric working at room temperature. The first group of problems that scientists face is how to synthesize materials with a homogeneous chemical and phase composition and a well-defined stoichiometry. The second is how to avoid contamination of such sensitive materials with residues of unreacted precursors and installation materials. In addition, the technological approach should allow the potential scale-up of the process for commercial applications of the above materials. In this work, we report the applicability of the plasma-enhanced chemical vapor deposition (PECVD) in preparation of PbS1-xSex complex inorganic chalcogenide materials of various stoichiometry and phase composition in function of plasma process conditions. Elemental high-pure lead, sulfur, and selenium were the initial substances. RF (40.68 MHz) non-equilibrium plasma discharge at low pressure (0.01 Torr) was used for the initiation of interactions between the starting materials. The PECVD process was studied by optical emission spectroscopy (OES). Various analytical methods were utilized to characterize the obtained materials.

Polycrystalline Silicon Membranes for Solar Cells Fabricated Using Water-soluble Sacrificial Layers

During the fabrication of crystalline silicon solar cells, kerf-loss caused by the wire-sawing of silicon ingots to produce thin wafers inevitably limits the reduction of electricity production cost. To avoid the kerf-loss, direct growth of crystalline silicon wafers of 50-150 μm with a porous separation layer that can be mechanically broken during the exfoliation process, has been widely investigated. However, several issues including flattening of the surface after the exfoliation remain unsolved. In this work an alternative method that utilizes a water-soluble Sr3Al2O6 (SAO) sacrificial layer inserted between the mother substrate and the grown crystalline silicon layers is introduced. Polycrystalline silicon layers were grown on SAO/Si by plasma-enhanced CVD process and silicon membranes could be successfully obtained after the dissolution of SAO in the water. Same process could be applied to obtain flexible amorphous silicon membranes. Further research is being conducted to increase the size of the exfoliated wafer, which expects to reduce the production cost of crystalline silicon solar cells effectively.

Evaluation of the membrane performance of ultra-smooth silicon organic coatings depending on the process energy density

Plasma-enhanced chemical vapor deposition (PECVD) can be used to apply thin layers to plastics with a wide range of customizable functionality. The selective permeation properties of the layers are particularly interesting for the application field of membrane gas separation processes. In order to be able to produce plasma polymerized membranes in an application specific manner, it is necessary to be able to correlate the plasma process parameters, such as the energy density introduced into the system, with the coating and thus separation properties. Within the scope of this work, different layers produced in a Plasma-enhanced chemical vapor deposition process were investigated with respect to their growth behavior, topographic and chemical properties as well as permeability to evaluate their performance as separation layers of a membrane. The results of the investigations show a strong dependence of the layer and separation properties on the pulsed microwave (MW) power coupled into the process. Energy input was varied over the MW power level as well as the MW pulse duration. Analysis shows the highest permeation and separation performance of the produced layers in the low energy density range of the process.

Ultrathin Ge epilayers on Si produced by low-temperature PECVD acting as virtual substrates for III-V / c-Si tandem solar cells

Ultrathin (20 nm) epitaxial films of germanium are deposited on crystalline silicon wafers, to act as virtual substrates for the growth of III-V materials, opening a low-cost approach to tandem solar cells. Such ultrathin layers allow for material cost reduction, along with the possibility of using the silicon wafer as the bottom cell in tandem devices. A simple plasma-enhanced chemical vapor deposition (PECVD) process at 175 °C has been optimized to deposit these heteroepitaxial germanium films, which grow directly on the silicon wafers without any intermediate silicon-germanium alloy. Thanks to an in-situ plasma cleaning step prior to Ge epitaxy, the films can sustain high-temperature annealing in vacuum (up to 800 °C) without any delamination. The suitability of the germanium heteroepitaxial films as virtual substrates is analyzed by depositing III-V layers on them by conventional growth methods like chemical beam epitaxy (CBE) and metalorganic chemical vapor deposition (MOCVD). The properties of the GaAs films deposited on the virtual substrates are comparable in terms of roughness, microstructure, and crystallinity to these of the III-V layers co-deposited on c-Ge wafers, pointing at the effectiveness of the ultrathin c-Ge epitaxial layers to act as virtual substrates for III-V epitaxial growth. Moreover, growing the c-Ge layers on c-Si substrates with 5° miscut avoids the formation of antiphase domains. These substrates are finally used to demonstrate proof of concept tandem solar cells, proving the suitability of our low temperature and ultrathin virtual substrate approach.

Synergistic Effect of Au Interband Transition on Graphene Oxide/ZnO Heterostructure: Experimental Analysis with FDTD Simulation.

We furnish a comprehensive study on light-induced carrier generation due to the synergistic contribution of Au interband transition and graphene oxide (GO)/ZnO heterostructure. Plasmonic gold nanoparticles (Au_nps) are incorporated as a substructure sandwiched between GO and ZnO, assisting in additional photo-induced charge carrier generation. GO is prepared by a single-step plasma-enhanced chemical vapor deposition process. The GO/ZnO heterostructure having an active working area of 0.25 cm2 is created to unleash the pyroelectric property of ZnO, and subsequently, Au_np is introduced at the interface of GO/ZnO. Here, the interband transition of Au_np and its capability for charge carrier generation combined with the excitonic charge carrier generation of the highly crystalline non-centrosymmetric hexagonal wurtzite ZnO enhances the photoresponse. Furthermore, the interaction of Au_np with ZnO and its spatial electric field intensity distribution is demonstrated by finite difference time domain simulation which indicate toward an efficient carrier generation at the interface of Au_np and ZnO. The fabricated heterostructure has an active working wavelength in the UV-A region with the highest responsivity at 375 nm of the electromagnetic spectrum. The ultrafast response time (∼29 μs) of the device is due to the pyro-phototronic effect of the GO/ZnO heterostructure enhanced by the interband transition of Au. In the comparative study of the Au_np-enriched GO/ZnO heterostructure device with a GO/ZnO device, the former shows better performance. Both the devices work in the self-powered mode as well as the photoconductive mode, but with a higher on–off current ratio in the photoconductive mode. Hence, this work helps in properly understanding photo-induced charge generation in a Au interband transition enriched GO/ZnO heterostructure.

Prediction of Surface Roughness as a Function of Temperature for SiO2 Thin-Film in PECVD Process.

An analytical model to predict the surface roughness for the plasma-enhanced chemical vapor deposition (PECVD) process over a large range of temperature values is still nonexistent. By using an existing prediction model, the surface roughness can directly be calculated instead of repeating the experimental processes, which can largely save time and resources. This research work focuses on the investigation and analytical modeling of surface roughness of SiO2 deposition using the PECVD process for almost the whole range of operating temperatures, i.e., 80 to 450 °C. The proposed model is based on experimental data of surface roughness against different temperature conditions in the PECVD process measured using atomic force microscopy (AFM). The quality of these SiO2 layers was studied against an isolation layer in a microelectromechanical system (MEMS) for light steering applications. The analytical model employs different mathematical approaches such as linear and cubic regressions over the measured values to develop a prediction model for the whole operating temperature range of the PECVD process. The proposed prediction model is validated by calculating the percent match of the analytical model with experimental data for different temperature ranges, counting the correlations and error bars.

Estimated approach development and experimental validation of residual stress-induced warpage under the SiNx PECVD coating process

Depositing silicon nitride (SiNx) coating by utilizing the plasma-enhanced chemical vapor deposition (PECVD) procedure is currently an important approach in the semiconductor industry because SiNx coating has several excellent application functions, such as passivation layer and oxygen/vapor barrier. However, residual stress occurs in the thin film resulted from the coefficient of thermal expansion (CTE) mismatch, lattice mismatch, defects, and impurities during the PECVD process. The SiNx-coated wafer would induce harsh warpage generated by coating film's residual stress. Aforementioned issue might generate the defects in the products, thus resulting in disrupted process and reliability problems. Such warpage is also unfavorable to the high flatness requirement for subsequent fabrication with the continuous scaling of advanced-technology devices. Accordingly, this study presents a novel process-oriented simulation methodology integrated with fluid dynamics-mechanical coupling responses to estimate its induced warpage magnitude affected by the pressure and temperature distributions during PECVD process and the initial intrinsic stress of SiNx coating. Under the consideration of the abovementioned loadings, the resultant stress and warpage after force balance for depositing SiNx coatings are obtained through process-oriented layer-by-layer simulation. On the basis of the simulated results and the data of experimental measurements, an intrinsic stress surface for SiNx is established by the radio frequency power, ammonia, and silane gas flow rate. Accordingly, the warpage magnitude and intrinsic stress of PECVD SiNx thin coating prior to actual processing can be immediately and accurately judged by the simulation methodology and SiNx intrinsic stress surface presented in this investigation.

Effect of 2 MHz frequency power applied to the substrate for low-temperature silicon nitride thin film deposition

Silicon nitride (SiNx) thin films were deposited at a low temperature of 80 °C using a dual-frequency plasma-enhanced chemical vapor deposition (PECVD) equipment. The density of the thin film was increased by 17% by increasing the low-frequency (LF) power of 2 MHz applied to the lower electrode to 100 W separately from the plasma generated by the 180 W power of 13.56 MHz applied to the upper electrode. The advantage of this dual-frequency PECVD process is that even if it is deposited at a low temperature, it shows similar effects to high-temperature deposition or post-deposition annealing process. Due to the LF power applied to the substrate, the hydrogen concentration in the deposited SiNx thin film decreases, which in turn leads to an increase in the film density. The increase in SiNx thin film density eventually results in a 21% increase in dielectric constant. It was shown that the use of SiNx thin films with improved properties as a dielectric layer of a thin film transistor can increase mobility and on-off ratio and reduce leakage current and subthreshold swing of the transistor.

Reactive force-field molecular dynamics simulation for the surface reaction of SiHx (x = 2–4) species on Si(1 0 0)-(2 × 1):H surfaces in chemical vapor deposition processes

Reactive force-field molecular dynamics simulation of Si thin film deposition in order to prove the availability of the simulation model including both chemical reactions and physical dynamics for a plasma-enhanced chemical vapor deposition process was performed. We simulated surface reactions of SiHx (x = 2–4) formed in the plasma on a Si(100)-(2 × 1) surface covered with H atoms and evaluated the surface reactions with different substrate temperature and H coverage. The existing potential parameter set was modified to fit the dissociation energies in the gaseous species. The gaseous species collided with the surface one by one, and then the surface reactions were classified into four events: reflection, desorption, chemisorption, and physisorption. Our results show that an increase in substrate temperature affects both the bond dissociation in the gaseous species and the desorption of gaseous species on the surface. The H atoms inhibit the chemisorption by terminating dangling bonds on the surface and promote reflection and desorption by thermal movement. This method should facilitate the simulation of much more complex systems such as SiC and SiGe.