Low-temperature Plasma-enhanced Chemical Vapor Deposition Research Articles

Electrical Characterization of Low Temperature PECVD Oxides for TSV Applications

Abstract In the present work we investigate the quality of low temperature Plasma Enhanced Chemical Vapor Deposition (PECVD) and plasma treated Tetraethyl orthosilicate (TEOS)-based TSV-liner films. Different designs of Trough Silicon Via (TSV) Test structures with 10μm and 20μm width and a depth of 100μm have been fabricated. Two differently doped silicon substrates have been used – highly p-doped and moderately doped. The results for break-through, resistivity and capacitance for the 20μm structures show a better performance compared to the 10μm structures. This is mainly due to increased liner thickness in the reduced aspect ratio case. Lower interface traps and oxide charge densities have been observed in the C-V measurements results for the 10μm structures.

Athermal 4-channel (de-)multiplexer in silicon nitride fabricated at low temperature

We have designed and realized an athermal 4-channel wavelength (de-)multiplexer in silicon nitride (SiN). Minimized thermal sensitivity is achieved in a wide wavelength range by using wide and narrow waveguides with low and different thermal-optic coefficients in the two arms of Mach–Zehnder interferometers (MZIs). The SiN core layer and SiO2 cladding layers are deposited by a low-temperature plasma-enhanced chemical vapor deposition process. The fabricated MZI filter exhibits a thermal sensitivity within ±2.0 pm/°C in a wavelength range of 55 nm to near 1300 nm. Then, an athermal (de-)multiplexer based on cascaded MZIs has been demonstrated with a crosstalk ≤−22 dB and a thermal sensitivity <4.8 pm/°C for all four channels, reduced by 77% compared to a conventional SiN (de-)multiplexer. Owing to the passive operation and compatibility with the CMOS backend process, our devices have potential applications in 3D integration of photonics and electronics.

Amorphous gallium oxide grown by low-temperature PECVD

Owing to the wide application of metal oxides in energy conversion devices, the fabrication of these oxides using conventional, damage-free, and upscalable techniques is of critical importance in the optoelectronics community. Here, the authors demonstrate the growth of hydrogenated amorphous gallium oxide (a-GaOx:H) thin-films by plasma-enhanced chemical vapor deposition (PECVD) at temperatures below 200 °C. In this way, conformal films are deposited at high deposition rates, achieving high broadband transparency, wide band gap (3.5–4 eV), and low refractive index (1.6 at 500 nm). The authors link this low refractive index to the presence of nanoscale voids enclosing H2, as indicated by electron energy-loss spectroscopy. This work opens the path for further metal-oxide developments by low-temperature, scalable and damage-free PECVD processes.

A novel approach for the fabrication of low-stress bimorph RF-MEMS switches

PurposeThe purpose of this paper is to design a low-cost stress bimorph RF-MEMS switch which is the desired transmission area application.Design/methodology/approachThe bimorph structure of the low-temperature plasma-enhanced chemical vapor deposition (PECVD) of thermal oxide and gold are utilized to create the vibrating membrane. The effects of process conditions of low-temperature oxide deposited using the PECVD technique enable stress-free deposition of the key structural layer.FindingsScanning electron microscope images of the RF micro-switch confirms negligible stress in the released structure. The RF performances of this device exhibit isolation around 43 dB of up to 50 GHz in the OFF-state position and an insertion loss of less than 0.18 dB in the ON-state.Originality/valueThe finite element method results show good isolation of 43 dB and less insertion loss of 0.18 dB.

Electron microscopy studies of crystallites in carbon nanopillars grown by low-temperature plasma-enhanced chemical-vapor deposition

Carbon crystallites in separate vertically oriented nanopillars grown on the surface of a substrate by low-temperature plasma-enhanced chemical-vapor deposition (LTPECVD) without a catalyst are studied by transmission electron microscopy (TEM) and electron diffraction. Thin planar lamellae are manufactured from the half-height section of an array of nanopillars using a focused ion beam. It is established that the crystallites in an amorphous environment are constructed from fragments of basal planes (002), have no well-distinguished boundaries, and their size is generally 1–2 nm. It is shown that the fraction of crystallites in the total volume of the material of nanopillars gradually grows, and the average distance between the basal planes decreases after annealing at temperatures of 250 and 700°C.

Optical Modeling of Microcrystalline Silicon Deposited by Plasma-Enhanced Chemical Vapor Deposition on Low-Cost Iron-Nickel Substrates for Photovoltaic Applications

This paper deals with the optical modeling of thin hydrogenated microcrystalline silicon films grown on flexible low-cost iron-nickel alloy substrates by low-temperature (175°C) plasma-enhanced chemical vapor deposition. This material serves as the absorber in solar cells and hence it has direct impact on the resulting solar cell performance. Since the crystallinity and the material quality of hydrogenated microcrystalline silicon films evolve during the growth, the deposited film is inhomogeneous, with a rather complex structure. Real-time spectroscopic ellipsometry has been used to trace the changing composition of the films. In-situ ellipsometric data taken for photon energies from 2.8 to 4.5eV every 50seconds enabled us to study the evolution of the monocrystalline silicon fraction of the hydrogenated microcrystalline silicon films.

10-Gb/s Direct Modulation of Widely Tunable 1550-nm MEMS VCSEL

We demonstrate direct modulation of a widely tunable microelectromechanical system (MEMS) vertical-cavity surface-emitting laser (VCSEL). The wavelength tuning is realized with electrothermal actuation of a SiO $_x$ /SiN $_y$ -based MEMS distributed Bragg reflector (DBR). The DBR is deposited in a low-temperature plasma-enhanced chemical vapor deposition chamber on a InP-based half-VCSEL by means of surface micromachining. More than 60 nm of mode-hop free continuous tuning with a center wavelength of 1554 nm is achieved. A maximum 3-dB small-signal modulation response ( $S_{21}$ ) bandwidth of 7.05 GHz is reported. Quasi-error-free operation of a back-to-back link is demonstrated at 10 Gb/s for a record 47-nm tuning range, showing the compatibility of the MEMS tunable VCSEL as a cost-effective optical source in access networks and interconnects.

Direct low-temperature synthesis of graphene on various glasses by plasma-enhanced chemical vapor deposition for versatile, cost-effective electrodes

Catalyst-free and scalable synthesis of graphene on various glass substrates at low temperatures is of paramount significance to numerous applications such as low-cost transparent electronics and state-of-the-art displays. However, systematic study within this promising research field has remained scarce thus far. Herein, we report the direct growth of graphene on various glasses using a low-temperature plasma-enhanced chemical vapor deposition method. Such a facile and scalable approach guarantees the growth of uniform, transfer-free graphene films on various glass substrates at a growth temperature range of 400–600 °C. The morphological, surface wetting, optical, and electrical properties of the obtained graphene can be tailored by controlling the growth parameters. Our uniform and high-quality graphene films directly integrated with low-cost, commonly used glasses show great potential in the fabrication of multi-functional electrodes for versatile applications in solar cells, transparent electronics, and smart windows.

Copper-Assisted Direct Growth of Vertical Graphene Nanosheets on Glass Substrates by Low-Temperature Plasma-Enhanced Chemical Vapour Deposition Process.

Vertical graphene (VG) nanosheets are directly grown below 500 °C on glass substrates by a one-step copper-assisted plasma-enhanced chemical vapour deposition (PECVD) process. A piece of copper foil is located around a glass substrate as a catalyst in the process. The effect of the copper catalyst on the vertical graphene is evaluated in terms of film morphology, growth rate, carbon density in the plasma and film resistance. The growth rate of the vertical graphene is enhanced by a factor of 5.6 with the copper catalyst with denser vertical graphene. The analysis of optical emission spectra suggests that the carbon radical density is increased with the copper catalyst. Highly conductive VG films having 800 Ω/□ are grown on glass substrates with Cu catalyst at a relatively low temperature.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-1019-8) contains supplementary material, which is available to authorized users.

Ge-on-Si Plasma-Enhanced Chemical Vapor Deposition for Low-Cost Photodetectors

The development of low-thermal-budget Ge-on-Si epitaxial growth for the fabrication of low-cost Ge-on-Si devices is highly desirable for the field of silicon photonics. At present, most Ge-on-Si growth techniques require high growth temperatures, followed by cyclic annealing at temperatures > 800°C, often for a period of several hours. Here, we present a low-temperature (400°C) low-cost plasma-enhanced chemical vapor deposition (PECVD) Ge-on-Si growth study and, subsequently, fabricate a high-speed zero-bias 12.5-Gb/s waveguide integrated photodetector with a responsivity of 0.1 A/W at a wavelength of 1550 nm. This low-energy device demonstrates the feasibility of the PECVD method for the fabrication of low-cost low-thermal-budget Ge-on-Si devices.

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.

Effect of RF power and gas flow ratio on the growth and morphology of the PECVD SiC thin film s for MEMS applications

Low temperature PECVD (Plasma Enhanced Chemical Vapour Deposition) deposited SiC thin films are promising materials for development of high temperature working MEMS (Microelectromechanical System) due to their excellent mechanical properties, non-corrosive nature and ability to withstand high temperature. However, the surface roughness of such thin films is the main obstacle to achieve thicker thin films for MEMS applications as the surface more rougher by increasing the thickness of PECVD SiC thin films. Therefore, in this present study, thicker SiC thin films were deposited by PECVD process by using the CH4 and SiH4 as the precursor gases in presence of Ar as the carrier gas and two process parameters i.e. RF (Radio Frequency) power with mixed frequency condition and flow ratio of silane to methane were varied by keeping the temperature and pressure constant to investigate the influence of these parameters on the growth rate, surface roughness and morphology of SiC thin films. It was observed that both the RF power (with the mixed frequency condition) and flow ratio of SiH4/CH4 can control the growth rate, surface roughness and morphology of the PECVD SiC thin films. Higher the carbon content in the thin films the surface became more smoother whereas the surface became for rougher by increasing the RF power.

Low-temperature plasma-enhanced chemical vapour deposition of transfer-free graphene thin films

Large area transfer free graphene films were deposited at low substrate temperature of 380°C by plasma-enhanced chemical vapour deposition (PECVD) using a nickel buffer layer. The Raman spectrum indicated a structure of highly disordered sp2-C. The current–voltage characteristics of the films showed ohmic behaviour with sheet resistance of ~10.1kΩ/sq and transmittance of 70% at wavelength of 550nm. This transfer-free graphene growth technique is reproducible and is promising for applications in devices.

Comparison of graphene growth on arbitrary non-catalytic substrates using low-temperature PECVD

Conventional Chemical Vapor Deposition (CVD) techniques require the use of a catalyst surface and high temperature of growth (∼1000°C) to grow graphene, which renders the process incompatible with arbitrary substrates. While post-synthesis transfer of graphene onto required substrates is widely used, it causes undesirable effects such as wrinkles/folds/cracks and unintentional doping. Here, we report low-temperature growth of graphene at 650°C on non-catalytic SiO2 and quartz substrates using a one-step, rapid Plasma Enhanced Chemical Vapor Deposition (PECVD) process. We simultaneously study PECVD graphene growth on a traditional catalytic material such as copper and show that the growth substrate does not play any role in the dissociation of hydrocarbon precursor during PECVD, thus eliminating the possibility of a catalytic effect. Using several characterization techniques, we observe an increasing rate of growth from SiO2 to quartz to copper, which can be attributed to different adsorption and diffusion energies of plasma radicals on these substrates. As opposed to thermal CVD growth on copper, which is self-limiting, the PECVD method developed here is scalable in terms of number of layers, allowing its adept integration in commercial devices.

Copper nanowire-graphene core-shell nanostructure for highly stable transparent conducting electrodes.

A copper nanowire-graphene (CuNW-G) core-shell nanostructure was successfully synthesized using a low-temperature plasma-enhanced chemical vapor deposition process at temperatures as low as 400 °C for the first time. The CuNW-G core-shell nanostructure was systematically characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman, and X-ray photoelectron spectroscopy measurements. A transparent conducting electrode (TCE) based on the CuNW-G core-shell nanostructure exhibited excellent optical and electrical properties compared to a conventional indium tin oxide TCE. Moreover, it showed remarkable thermal oxidation and chemical stability because of the tight encapsulation of the CuNW with gas-impermeable graphene shells. The potential suitability of CuNW-G TCE was demonstrated by fabricating bulk heterojunction polymer solar cells. We anticipate that the CuNW-G core-shell nanostructure can be used as an alternative to conventional TCE materials for emerging optoelectronic devices such as flexible solar cells, displays, and touch panels.

An old workhorse for new applications: Fe(dpm)3 as a precursor for low-temperature PECVD of iron(III) oxide.

An iron(III) β-diketonate complex, Fe(dpm)3 (Hdpm = 2,2,6,6-tetramethyl-3,5-heptanedione), has been investigated as a potential precursor for plasma enhanced chemical vapor deposition (PECVD) of iron(III) oxide nanomaterials. Thanks to the combined experimental-theoretical approach, spectroscopic properties, spin state, thermal behavior and fragmentation pathways of Fe(dpm)3 have been carefully analysed, obtaining an excellent agreement between simulation and experiment. Preliminary PECVD tests evidenced the possibility of obtaining pure and homogeneous Fe2O3 deposits with controlled nano-organization at temperatures as low as 100 °C, even on flexible plastic substrates. The present results open up intriguing perspectives for the exploitation of Fe(dpm)3 as an efficient molecular source for the preparation of nanostructured iron(III) oxides to be used in energetics and gas sensing applications.

High Performance p-type SnO thin-film Transistor with SiOxGate Insulator Deposited by Low-Temperature PECVD Method

We have investigated the gate insulator effects on the electrical performance of p-type tin monoxide (SnO) thin-film transistors (TFTs). Various SnO TFTs are fabricated with different gate insulators of a thermal SiO₂, a plasma-enhanced chemical vapor deposition (PECVD) SiNx, a 150 ℃-deposited PEVCD SiO<SUB>x</SUB>, and a 300 ℃-deposited PECVD SiO<SUB>x</SUB>. Among the devices, the one with the 150℃-deposited PEVCD SiO<SUB>x</SUB> exhibits the best electrical performance including a high field-effect mobility (=4.86 cm²/Vs), a small subthreshold swing (=0.7 V/decade), and a turn-on voltage around 0 (V). Based on the X-ray diffraction data and the localizedtrap-states model, the reduced carrier concentration and the increased carrier mobility due to the small grain size of the SnO thin-film are considered as possible mechanisms, resulting in its high electrical performance.

Nano-Crystalline Silicon-Based Bottom Gate Thin-Film Transistor Grown by LTPECVD With Hydrogen-Free He Diluted ${\hbox{SiH}} _{4}$

The bottom-gate nc-Si based thin-film-transistors (TFTs) grown by using the low-temperature plasma-enhanced chemical vapor deposition (LT-PECVD) system with He diluted SiH are demonstrated. With the RF plasma power increasing from 20 to 100 W, the crystalline volume ratio of the nc-Si inside the a-Si:H film significantly increases from 12.5% to 32%, and its deposition rate is also enhanced from 9.5 to 14.5 nm/min. The faster deposition at higher plasma greatly suppresses the residual oxygen content in nc-Si film to 4% or less, which reduces the flat-band shifted voltage of the MOS diode by 2 volts. The increased crystalline volume with suppressed oxide in nc-Si films contribute to the enhanced Hall mobility and conductivity. The nc:Si TFT decreases its threshold voltage from 3.3 V to 2.7 V, and enlarges its field mobility from 0.3 to 1.3 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V-s. The defect density in the nc-Si TFTs further decrease by one order of magnitude to 7.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> eV, which causes a shrinkage on the sub-threshold operation range to make easier the operation of the nc-Si TFTs entering into the above-threshold regime at lower voltage. The hydrogen-free He diluted SiH growth has shown its compatibility with the conventional recipe for the high-mobility nc-Si TFT fabrication.

Use of Amorphous Silicon for Active Photonic Devices

Silicon photonics is a new emerging and disruptive technology aimed at using cost-effective silicon-based materials for the generation, control, and detection of modulated light signals for optical communication. Hydrogenated amorphous silicon (a-Si:H) is a particularly promising platform for enabling the desired matching between electronics and on-chip photonics. Thin a-Si:H layers can be in fact deposited using the CMOS-compatible low-temperature plasma-enhanced chemical vapor deposition technique, with no impact at all on the microelectronic layers. This paper provides an overview of the progress and the state of the art of a-Si:H-based active photonic devices, focusing, in particular, on the low technological complexity required for an easy integration within a single photonic microchip. This paper consists of three main sections, in each of which the exploitable optoelectronic effects present in a-Si:H are presented. A comparison between some experimental a-Si:H and crystalline-Si photonic components available in the literature is presented.

Characteristics of Low-Temperature(≤200 °) PECVD Silicon Nitride for Gate Dielectric of TFTs by Using N2 Highly Diluted SiH4

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