Low-pressure Thermal Chemical Vapor Deposition Research Articles

Synthesis of organic functional thin films and their application tests of graphene based FET

This study investigated on the effects of gate dielectrics for field effect transistors (FETs). The gate dielectrics with organic and inorganic layers were deposited on Si (100) substrates using cyclohexane and tetraethyl orthosilicate (TEOS) by plasma enhanced chemical vapor deposition (PECVD) method. After the Si (100) substrates were dry-cleaned by in situ Ar plasma bombardment with 60 W for 15 min., the gate dielectric plasma polymer thin films deposited under plasma power between 20 W and 60 W with different precursor flow ratio. Also, the active graphene layer was grown on a Ni substrate using CH4 by low-pressure thermal chemical vapor deposition (CVD) method, and the Ni substrate was then etched away. In order to fabricate a back-gate graphene-based FET, the graphene layer was adsorbed onto the plasma-polymer gate dielectric film, then 80 nm thick Au electrodes were finally evaporated onto the graphene using a mask with a gap of 370 nm, and a probe-station system was utilized to characterize the devices. As the plasma power and flow rate of TEOS increases, the gate voltage moves at a positive voltage, indicting p-doping by high fragmented Si and O elements under high plasma power and TEOS flow rate.

Silicon–Carbon Core–Shell Hollow Nanotubular Configuration High-Performance Lithium-Ion Anodes

Silicon anode systems, due to their intrinsic high theoretical specific capacity, show tremendous potential in lithium ion batteries (LIBs). Unfortunately, commercial application still remains elusive due to the cycling-related colossal volume expansion issues following Li alloying and dealloying. Herein, core–shell C@Si@C hollow nanotubes with optimal Si thickness (∼60 nm) showing no microstructural damage during lithiation and delithiation processes, have been developed as a stable anode for LIBs with low first-cycle irreversible loss (FIR) of ∼13% and high areal capacity (∼3 mAhcm–2) for the first time. The hollow Si nanotubes (h-SiNTs) have been generated via our previously reported high-throughput and recyclable, sacrificial MgO wire template fabrication approach. Generation of Si films of varying thickness by low-pressure thermal chemical vapor deposition (LPCVD) with subsequent etching yields h-SiNTs. Modification/optimization of the h-SiNT physical characteristics exhibit improved performance in L...

Growth of Vertically Aligned Carbon Nanotube Arrays on Al Substrates through Controlled Diffusion of Catalyst

Atomic diffusion-induced catalyst evolution affects the iron catalyst lifetime and the collective termination of VACNT growth on a metal substrate. We demonstrated that controlled catalyst diffusion in the pretreatment stage is capable of extending the iron catalyst lifetime on an aluminum thin-film substrate to allow enhanced vertically aligned carbon nanotube (VACNT) growth by a conventional low-pressure thermal chemical vapor deposition. In adopting a fast-heating pretreatment to control the catalyst loss from diffusion, catalyst lifetime was extended, leading to the VACNT growth with heights up to 65% taller than those without the diffusion control strategy. Atomic diffusion of iron catalyst along the grain boundaries of aluminum thin films was found to play a critical role in the catalyst loss mechanism. This work provides the basic understanding of catalyst diffusion control to facilitate the growth of VACNT arrays on metallic substrates for various applications such as through silicon via interconn...

Dielectric/Si Interface Quality Characterization Using Room Temperature Photoluminescence

Advanced metal-oxide-semiconductor (MOS) and metal-insulator-semiconductor (MIS) devices employ ultra thin dielectric gate layers. The physical dimensions are in the range of single digit to double digit nanometers. The effective oxide thickness (EOT) is significantly less than 10 nm. Pure SiO2 or combinations of SiO2and SiN layers are typically used as gate dielectrics. High dielectric constant materials (high-k dielectrics) and metal gates are also frequently used, depending on chip design.Physical dimensions of dielectric layer(s) are typically measured using ellipsometry and high resolution cross-section transmission microscopy (HRXTEM). Electrical characteristics are typically characterized using either contact or non-contact C-V and I-V measurements tools. Non-contact characterization techniques are generally preferred for in-line monitoring applications. However, spatial resolution of non-contact C-V and I-V measurement techniques is in the range of a few millimeters, which are 3 orders of magnitude larger than typical dimensions of actual devices. High spatial resolution, non-contact dielectric/Si interface quality characterization techniques must be developed.In this paper, ultra thin (~7 nm) SiO2/Si and ultra thin SiN/SiO2/Si wafers were prepared by low pressure thermal chemical vapor deposition (CVD) and thermal oxidation. Dielectric/Si interface quality was characterized by room temperature spectroscopic photoluminescence (PL) measurements. The PL intensity and spectra from Si were measured under different excitation wavelengths which have different probing depths. PL is an optical characterization technique which does not require any sample preparation and physical contact. Typical spatial resolution is in the range of a few microns. Small variations in dielectric/Si interface quality modulates electronic carrier behaviors significantly which results in large variations in PL intensity and spectra. Significant variations in PL intensity and spectra were measured from ultra thin (~7 nm) SiO2/Si wafers prepared by and low pressure thermal CVD and thermal oxidation. Si wafers with thermal oxide films generally showed significantly stronger PL intensity than Si wafers with thermal CVD grown oxide films (Fig. 1). Trends in PL intensity and spectra indicate the SiO2/Si interface quality of the thermally oxidized SiO2/Si is superior to that of the thermal CVD grown SiO2/Si (Fig. 2). PL characterization is found to be very sensitive to the integrity of dielectric/Si interface and thus, is promising as an in-line, non-contact interface quality monitoring technique.The excitation wavelength dependence of PL intensity and spectra of SiO2/Si and SiN/SiO2/Si will be discussed along with conventional physical and electrical characterization results.

Production of a 100-m-long high-quality graphene transparent conductive film by roll-to-roll chemical vapor deposition and transfer process

A high-quality graphene transparent conductive film was fabricated by roll-to-roll chemical vapor deposition (CVD) synthesis on a suspended copper foil and subsequent transfer. While the high temperature required for the CVD synthesis of high-quality graphene has prevented efficient roll-to-roll production thus far, we used selective Joule heating of the copper foil to achieve this. Low pressure thermal CVD synthesis and a direct roll-to-roll transfer process using photocurable epoxy resin allowed us to fabricate a 100-m-long graphene transparent conductive film with a sheet resistance as low as 150 Ω/sq, which is comparable to that of state-of-the-art CVD-grown graphene films.

X-Ray Photoelectron Spectroscopy Study of SnO<SUB>2</SUB> and SnO<SUB>2+<I>x</I></SUB> Thin Films

SnO2 thin films were fabricated using low-pressure thermal chemical vapor deposition. The results of X-ray photoelectron spectroscopy revealed that the SiO2 layer with an O1S-binding energy of 531.2 eV was formed before the SnO2 layer with an O1S-binding energy of 530.5 eV was formed. In the beginning, the SnO2 thin film showed Sn3d5-binding energy peaks of 485 eV and 486.5 eV. Subsequently, it grew in the direction of 486.5 eV. The Sn3d5-binding strength of the SnO2+x thin film that was annealed in oxygen atmosphere was weaker than that of the SnO2 thin film. Additionally, the Sn3d5-binding strength decreased linearly as the depth of the thin film increased. The surface O1S-binding strength of the SnO2+x thin film annealed in oxygen atmosphere was stronger than that of the SnO2 thin film; however, this strength became weaker than that that of the SnO2 thin film when the depth of the thin film was 2500A or higher.

Effects of Laser Ablation on Growth of ZnO/ZnS/ZnO Multilayer Structured Nanorods by Chemical Vapor Deposition

ABSTRACTZnO is an attractive II-VI compound semiconductor material for various optoelectronic devices. Recently, growth of various nanostructures of ZnO such as nanorod, nanobelt, nanowall, etc. has been reported, and ZnO has been considered as a promising material for nanodevices. We have studied on fabrication of aligned ZnO nanorods by a low-pressure thermal chemical vapor deposition (CVD) method cooperated with laser ablation of Mn pellet. In this paper, we report on fabrication of ZnO/ZnS/ZnO multilayer structured nanorods and particularly on effects of laser ablation on the morphology of the nanorods intending to develop a new electroluminescent device including ZnO nanorods. The fabrication method of ZnO/ZnS/ZnO multilayer structured nanorods is almost same method used in our previous study. Metal Zn vapor and O2 gas or H2S are used as precursors to synthesize ZnO or ZnS, and N2 is used as carrier gas. A Mn pellet is placed near a Si(111) substrate in a deposition chamber and ablated by a pulsed Nd:YAG laser beam (wavelength =1.064 mm, pulse width = 8 ns, repetition frequency = 10 shots/sec). The pressure is 13.3 Pa and the temperature is 550 C. When ZnO is grown, O2 of 0.88 SCCM mass flow rate is used as a precursor. When ZnS is grown, on the other hand, H2S of 2.0 SCCM mass flow rate is used as a precursor. The growth time is 15 min for each layer. Firstly, ZnO nanorods are grown. Laser ablation of Mn is executed for initial 3 min and only CVD is performed for remaining 12 min. The vertically aligned ZnO nanorods with 100 nm diameter and 1500 nm height are grown. Secondly, ZnS nanorod is grown on the top surface of the first ZnO nanorods. In this process, the morphology is not so dependent on execution of laser ablation of Mn for initial 3 min in this growth process. Finally, ZnO layer is again grown on ZnS/ZnO nanorods described above. When the laser ablation of Mn for initial 3 min is not executed, many fine ZnO whiskers with long length are grown with random directions on the top surface and on the side surfaces of ZnS/ZnO nanorods. When the laser ablation of Mn for initial 3 min is executed, on the other side, a thick whisker is grown on top surface of ZnS/ZnO nanorods. The shape is not nanorod. The diameter is abruptly decreased and the tip is very sharp. The growth of ZnO whisker on the side surface of ZnS/ZnO nanorods is not almost observed. It is found that the laser ablation of Mn for initial 3 min in the third ZnO growth strongly influences the morphology of the third ZnO layer. We estimate that the Mn species that are ablated from a Mn pellet and reaches the surface of ZnS/ZnO nanorods change any quality of the surface of ZnS/ZnO nanorods. We are now studying of finding the growth conditions of the third ZnO layer with morphology of nanorod on ZnS/ZnO nanorods that is considered to be suitable for electroluminescent devices.

Novel Inorganic DC Lateral Thin Film Electroluminescent Devices Composed of ZnO Nanorods and ZnS Phosphor

ABSTRACTA novel inorganic thin-film electroluminescence (TFEL) device exhibiting bright EL emission when driven by a low DC voltage is demonstrated. The DC-TFEL device is based on a composite layer in which aluminum-doped ZnO nanorods are vertically embedded in ZnS:Mn as an EL phosphor. The DC driving voltage is then applied laterally to the composite layer via two side electrodes set 3.5 mm apart. The aluminum-doped ZnO nanorods were synthesized on a glass substrate by low-pressure thermal chemical vapor deposition combined with laser ablation, and the composite layer was formed by electron-beam deposition of ZnS:Mn onto the ZnO nanorods. The thickness of the composite layer was about 160 nm. After electrical modification to breakdown a basal conduction ZnO path, the lateral DC-TFEL device exhibited bright EL emission without avalanche breakdown, achieving a luminance of 747 cd/m2 at 4200 V with a luminous efficiency of 9.2×10−3 lm/W.

Vapor−Solid−Solid Synthesis of Ge Nanowires from Vapor-Phase-Deposited Manganese Germanide Seeds

We report the sequential synthesis of solid-phase manganese germanide seed particles and crystalline Ge nanowires using low-pressure thermal chemical vapor deposition. Mn was deposited on inert substrates from a gas-phase precursor. Mn particles were converted to solid manganese germanide particles upon exposure to germane gas, and these seed particles directed the one-dimensional growth of Ge nanowires. Growth rates for this vapor−solid−solid process approached 200 nm per minute, and the diameter distribution was tightly clustered around 18 nm. This approach to Ge nanowire growth has at least three attractive features: (1) the seed particle is not Au, avoiding the potentially negative influence of Au impurities on electrical properties; (2) the vapor-phase deposition and self-assembly of the seed greatly simplifies the nanowire synthesis process; and (3) the self-assembled seed naturally produces a narrow distribution of nanowire diameters.

Control of diameter of ZnO nanorods grown by chemical vapor deposition with laser ablation of ZnO

Abstract We made a study of controlling diameters of well-aligned ZnO nanorods grown by low-pressure thermal chemical vapor deposition combined with laser ablation of a sintered ZnO target, which was developed by us. Until now, it has been impossible to control diameters of ZnO nanorods, while the growth orientation was maintained well-aligned. In this study we developed a multi-step growth method to fabricate well-aligned nanorods whose diameters could be controlled. Metal Zn vapor and O2 are used as precursors to grow ZnO nanorods. N2 is used as a carrier gas for the precursors. A substrate is an n -Si (111) wafer. A sintered ZnO target is placed near the substrate and ablated by a Nd–YAG pulsed laser during ZnO nanorod growth. The growth temperature is 530 ∘C and the pressure is 66.5 Pa. A vertical growth orientation of ZnO nanorods to the substrate is realized in the first-step growth although the diameter cannot be controlled in this step. When an O2 flow rate is 1.5 sccm, well-aligned nanorods with 100 nm diameter are grown. Next, the second-step nanorods are grown on only the flat tip of the first-step nanorods. The diameters of the second-step nanorods can be controlled by adjusting the O2 flow rate, and the growth direction is kept the same as that of the first-step nanorods. When the O2 flow rate in second-step growth is smaller than 0.6 sccm, the diameter of the second-step nanorods is 30–50 nm. When the O2 flow rate is between 0.75 and 3.0 sccm, the diameter is almost same as that of the first-step nanorods. When the O2 flow rate is larger than 4.5 sccm, the diameter is increased with increasing O2 flow rate. Further, the third-step ZnO nanorods with gradually increased diameters can be grown on the second-step nanorods with 1.5 sccm O2 flow rate and without laser ablation.

Synthesis of Crystalline Carbon Nanotube Arrays on Anodic Aluminum Oxide Using Catalyst Reduction with Low Pressure Thermal Chemical Vapor Deposition

Well-aligned crystalline carbon nanotubes (CNTs) were synthesized on anodic aluminum oxide (AAO) template using low-pressure thermal chemical vapor deposition (TCVD). The AAO templates were fabricated using an anodization process, and Fe as a catalyst was electrochemically deposited inside the bottom of the pores on the AAO template. For promotion of catalytic reaction of Fe, pore widening and catalyst reduction were performed. The enhancement of the catalytic reaction between C2H2 and the Fe catalyst particles results in CNTs with good crystallinity and a high packing density without the deposition of amorphous carbon on the pore surface of the AAO templates. The diameter and density of the CNTs were approximately 50 nm and 7×109 CNTs/cm2 (70% of pore density), respectively. When the threshold voltage of the electron emission was measured with a gap of 300 µm, it showed a very low turn-on field of 0.87 V/µm and the field enhancement factor was greater than 5600.

Effects of laser ablation in fabrication of ZnO nanorods by chemical vapor deposition

We studied the effects of laser ablation on morphology of ZnO nanorods fabricated by low-pressure thermal chemical vapor deposition combined with laser ablation of Mn. In this paper, we studied the effects of laser-ablation time period at an initial stage of ZnO nanorods’ growth. Both laser ablation and chemical vapor deposition are started simultaneously and only laser ablation is stopped on the way to ZnO nanorods’ growth. It is concluded from the experimental results that a laser ablation less than about 3 min after ZnO growth initiated shows remarkable effects on diameter, length, number-density and growth direction of ZnO nanorods, and that a laser ablation more than about 5 min has little effect on morphology of ZnO nanorods. Further, it is especially recognized that even if the laser-ablation time period is only 5 s the laser ablation has an outstanding effect on nanorod growth.

Effects of laser-ablated impurity on aligned ZnO nanorods grown by chemical vapor deposition

Highly oriented ZnO nanorod arrays are fabricated on a p −-Si (111) wafer by low-pressure thermal Chemical Vapor Deposition (CVD) at low temperature using metal Zn vapor and O 2 as precursors. A laser ablation in combination with the CVD is used to vaporize an impurity and to dope it into a growing ZnO. The impurity sources are W, Co, Mn, Er, Al metals and sintered ZnO. It is concluded that the type of impurity remarkably influences the shape, size, growth orientation and photoluminescence spectrum of ZnO nanostructures. When the impurity is Er or Mn, the ZnO nanorods oriented vertically to a wafer are fabricated.

Roles of Laser-Ablation of Mn in Initial Stage of Growth of ZnO Nanorods by Chemical Vapor Deposition

ABSTRACTWe studied on effects of laser ablation on morphology of ZnO nanorods fabricated by low-pressure thermal chemical vapor deposition combined with laser ablation of Mn. In this paper, we studied on the effects of laser-ablation time period and energy density of laser beam at an initial stage of growth of ZnO nanorods. Both of laser ablation and chemical vapor deposition are started simultaneously and the laser ablation is stopped on the way of growth of ZnO nanorods. After the laser ablation is stopped, only chemical vapor deposition is continued. It is concluded from the experimental results that even if laser-ablation time period is only 30 sec and energy density of laser is only 0.023 Joule/cm2/pulse, the laser ablation shows remarkable effects on growth of ZnO nanorods.

Selective Growth of Straight Carbon Nanotubes by Low-Pressure Thermal Chemical Vapor Deposition

Carbon nanotubes (CNTs) were grown by low-pressure thermal chemical vapor deposition using pure ethylene. It was found that straight CNTs, which were composed of bundled single- or double-wall CNTs and multiwall CNTs, were preferentially bridged between Fe nanoparticles under a low pressure of 100 Pa. Moreover, utilizing this method, we attempted to grow CNT bridges between patterned Ta electrodes. By nitriding the surface of the Ta electrodes, Fe nanoparticles with a moderate size were effectively formed, resulting in bridging CNTs between the electrodes.

New Electroluminescence Spectrum from Co-doped ZnS:(Mn, Si) Films Prepared by Chemical Vapor Deposition with Laser Ablation

ABSTRACTCo-doped ZnS:(Mn, Si) films were fabricated. The ZnS was synthesized by a low-pressure thermal chemical vapor deposition. Metal Zn vapor and H2S gas were used as the CVD-precursors. Mn and Si were doped using a laser ablation technique during the ZnS growth. A solid MnSi alloy (Mn:Si = 1:1) was used as the laser ablation target. The films were deposited at the range from 650°C to 750°C. At the deposition temperature of 650°C, only a EL emission peak at 585 nm same as conventional ZnS:Mn films appeared, i.e., the Si co-doping had no effects on the EL spectrum. At the deposition temperature of 700°C, the Si co-doping to ZnS:Mn film caused the shift of the EL emission peak at 585 nm to shorter wavelength by 15 nm and provided new EL emission at 760 nm. The film deposited at 750°C exhibited new UV and blue EL emissions at 390 nm and 450 nm, respectively, although the host material of the film differed from usual ZnS.

Micro-scratch test study of TiN films grown on silicon by chemical vapor deposition

TiN thin films (0.095 μm) were deposited on silicon wafers at 800°C by rapid thermal low-pressure chemical vapor deposition from a TiCl 4+NH 3+H 2 gaseous mixture. Micro-scratches were performed using a system equipped with an optical microscope, an acoustic emission sensor and a friction force sensor. Critical loads were determined to evaluate the adhesion of TiN to the substrate. The influence of the indenter state on the critical load was studied. Scanning electron micrographs, electron probe microanalyses and chemical etching of the film were performed to identify and interpret the damage mechanisms. Experimental results were analyzed using the Weibull statistic. It was shown that small particles of TiN were chipped off and formed a third body, which modified the indenter–film contact and contributed to an increase in the range of the critical load. Models previously proposed in the literature, which allow calculation of the work of adhesion from a critical load, are discussed with respect to the damage mechanisms observed.

Growth of high quality silicon carbide films on Si by triode plasma CVD using monomethylsilane

Cubic-silicon carbide (3C-SiC) epitaxial films were grown on Si substrates by the triode plasma chemical vapor deposition (CVD) method using monomethylsilane (MMS) diluted with hydrogen as a source gas. Under negative grid bias condition, the single crystal films with high quality were grown at temperatures higher than 900°C. The growth rate by triode plasma CVD appreciably increased at temperatures lower than 1100°C, compared to that grown by low-pressure thermal CVD (LPCVD). Activation energy of the growth rate decreased about 30kcalmol−1 by using the triode plasma CVD method.

Optimization of Titanium Nitride Rapid Thermal CVD Process

Anomalous behavior during TiN growth through rapid thermal low-pressure chemical vapor deposition (RTLPCVD) from gas phase TiCl 4 -NH 3 -H 2 has been observed. Two deposition temperatures are used (500 °C and 800 °C) and two types of deposition process are defined (a long one-step process, and a multiple-step process). Resistivity, structure, composition, and growth behavior are examined and discussed in terms of oxygen contamination and classical nucleation theory. The long one-step process is better for mechanical applications, whereas the multiple-step process is more suitable for microelectronics.

Dépôt chimique en phase vapeur et à basse pression de couches minces à base de silicium dans un réacteur à lampes halogène

Low-pressure chemical vapor deposition (LPCVD) in halogen lamp-heated reactor (RTLPCVD: rapid thermal LPCVD) is a promising technique for silicon-based thin films deposition. Indeed, overall process time and gas consumption reduction in RTP reactors allows to project new device fabrication technologies (microsensors, solar cells) in order to reach a higher environmental safety with respect to classical technologies.Various gases available on our RTP installation (SiH4, NH3, N2O, O2, PH3, B2H6) enable several silicon-based thin films RTLPCVD deposition: intrinsic polycrystalline silicon (poly-Si) films or in situ doped poly-Si, silicon nitride (Si-N) and oxynitride (Si-O-N). In this paper, we discuss our results on deposition kinetics and physical properties of these thin films. It appeared that RTLPCVD silicon-based thin films with interesting structural, electrical, and optical properties can be synthesized in our lamp-heated reactor with a tight control of process parameters such as temperature, pressure, and gas flow ratios.