Low-pressure Chemical Vapor Deposition Growth Research Articles

Impact of alternating precursor supply and gas flow on the LPCVD growth behavior of polycrystalline 3C-SiC thin films on Si

In this paper, we will provide information on the growth mechanism of 3C-SiC using alternating supply deposition (ASD). SiH4 and C3H8 were introduced successively in a low-pressure chemical vapor deposition (LPCVD) system at 1000 °C, forming a stoichiometric polycrystalline 3C-SiC thin film on Si substrates. We demonstrate the influence of different gas flow rates on thin film properties. In detail, altering the flow rates of the precursors and the carrier gas resulted in changes of the growth rate, the surface roughness, the crystal growth mechanisms as well as the crystal quality. Hydrogen inhibition and passivation are proposed to be the main effects influencing the growth behavior of ASD thin films. Applying ASD to grow 3C-SiC thin films with precursors from low to high flow rates resulted in a transition of different growth mechanisms influencing the surface roughness and grain size. Furthermore, we could prove that ASD is a cyclic step-by-step carbon-assisted redistribution of a prior deposited silicon film. This is shown by contact angle measurements of three differently terminated surfaces during the specific phases of one ASD cycle. High resolution transmission electron microscopy (HRTEM) analysis showed a continuous and homogenous thin film and confirmed the absence of silicon- or carbon-rich layers. ASD enables 3C-SiC thin films with customized properties for tailored micro electromechanical system (MEMS) applications.

Kinetics of Catalyst-Free and Position-Controlled Low-Pressure Chemical Vapor Deposition Growth of VO2 Nanowire Arrays on Nanoimprinted Si Substrates.

In the present article, the position-controlled and catalytic-free synthesis of vanadium dioxide (VO2) nanowires (NWs) grown by the chemical vapor deposition (CVD) on nanoimprinted silicon substrates in the form of nanopillar arrays was analyzed. The NW growth on silicon nanopillars with different cross-sectional areas was studied, and it has been shown that the NWs' height decreases with an increase in their cross-sectional area. The X-ray diffraction technique, scanning electron microscopy, and X-ray photoelectron spectroscopy showed the high quality of the grown VO2 NWs. A qualitative description of the growth rate of vertical NWs based on the material balance equation is given. The dependence of the growth rate of vertical and horizontal NWs on the precursor concentration in the gas phase and on the growth time was investigated. It was found that the height of vertical VO2 NWs along the [100] direction exhibited a linear dependence on time and increased with an increase in the precursor concentration. For horizontal VO2 NWs, the height along the direction [011] varied little with the growth time and precursor concentration. These results suggest that the high-aspect ratio vertical VO2 NWs formed due to different growth modes of their crystal faces forming the top of the growing VO2 crystals and their lateral crystal faces related to the difference between the free energies of these crystal faces and implemented experimental conditions. The results obtained permit a better insight into the growth of high-aspect ratio VO2 NWs and into the formation of large VO2 NW arrays with a controlled composition and properties.

Low pressure CVD growth of 2D PdSe2 thin film and its application in PdSe2-MoSe2 vertical heterostructure

Palladium diselenide (PdSe2) is a novel member of the transition metal dichalcogenide family with layer dependent bandgap in the infrared regime with potential applications in many electronic and optoelectronic devices. Low pressure chemical vapor deposition (LPCVD) could be an effective way to synthesize large area 2D PdSe2 materials at low growth temperatures creating new opportunities for the widescale applications of PdSe2. Here, we report LPCVD growth of PdSe2 for the first time at a growth temperature down to 250 °C, which is significantly lower than what was previously reported. The 2 nm Pd films became 8 nm PdSe2 after selenization in the temperature range of 250 °C–375 °C and no thickness variation with growth temperature was observed in our atomic force microscopy study. Raman study showed narrowing of PdSe2 related peaks with increasing growth temperature suggesting improved structural quality of the films. X-ray photoelectron spectroscopy study confirmed complete selenization of the thin films to the lowest growth temperature of 250 °C. Electrical transport properties study showed resistance of the devices decrease with increasing growth temperature possibly due to the improvement of crystallinity. We also found that the devices show p-type behavior with mobilities up to 1 cm2 V−1 s−1. The good electrical quality of the film was further confirmed by demonstrating its application in fabricating PdSe2/MoSe2 vertical heterojunction which showed rectification behavior with a rectification ratio of up to 232. Kelvin probe force microscopy confirmed that the rectification behavior was originated from the work function difference of 0.76 eV between MoSe2 and PdSe2.

Close oxygen coupled low-pressure chemical vapor deposition growth of high quality [formula omitted] on sapphire

We report on the close oxygen coupled low-pressure chemical vapor deposition (COC-LPCVD) hetero-epitaxial growth of atomically smooth (−201) oriented β−Ga2O3 on c-plane sapphire. Utilizing a dedicated line within the main tube, O2 could be delivered to the substrate surface which enables effective control of growth regime. Under optimized conditions (Ga-rich and near stoichiometric feed rate), step flow growth was obtained with X-ray rocking curve full-width at half maximum of 0.09° and 0.20° at a growth rate of 0.49 μm/h and 3.42 μm/h, respectively. On the other hand, oxygen-rich growth at high growth rates produced in-plane rotational domains. In addition, the alignment of single crystal (−201) β−Ga2O3 with respect to the sapphire offcut direction was revealed such that [-20-1] β−Ga2O3 is along [11–20] (offcut direction) sapphire. This study demonstrates the potential of the versatile COC-LPCVD system on the thin film growth of high quality β−Ga2O3.

Impact of the precursor gas ratio on dispersion engineering of broadband silicon nitride microresonator frequency combs

Microresonator frequency combs, or microcombs, have gained wide appeal for their rich nonlinear physics and wide range of applications. Stoichiometric silicon nitride films grown via low-pressure chemical vapor deposition (LPCVD), in particular, are widely used in chip-integrated Kerr microcombs. Critical to such devices is the ability to control the microresonator dispersion, which has contributions from both material refractive index dispersion and geometric confinement. Here, we show that modifications to the ratio of the gaseous precursors in LPCVD growth have a significant impact on material dispersion and hence the overall microresonator dispersion. In contrast to the many efforts focused on comparisons between Si-rich films and stoichiometric (Si3N4) films, here, we focus on films whose precursor gas ratios should nominally place them in the stoichiometric regime. We further show that microresonator geometric dispersion can be tuned to compensate for changes in the material dispersion.

Ultrafast growth rate and high mobility In2O3 films grown on c-sapphire via low pressure chemical vapor deposition

In this study, the growth of unintentionally doped semiconductor indium oxide with ultrafast growth rates on c-plane sapphire by low pressure chemical vapor deposition (LPCVD) was demonstrated. The effect of key growth parameters, such as oxygen flow rate and distance between the substrate to the indium source, on the growth rate, crystalline quality, surface morphology, as well as carrier transport properties were studied. The growth rate is highly dependent on the oxygen flow rate and the distance between the indium source and the substrate: (i) the growth rate reaches 113 μm/h with an oxygen flow rate of 75 sccm under the investigated growth condition; and (ii) it decreases exponentially with the increase of distance between the indium source and the substrate. X-ray diffraction characterization of the as-grown films indicates that the increase of oxygen flow rate leads to the suppression of (100) facet formation, significantly influencing the film morphology. The LPCVD growth conditions also determine the background doping and carrier mobility. With an oxygen flow rate of 75 sccm, a high electron mobility of 126 cm2 V−1 s−1 with a bulk concentration of 3.9 × 1017 cm−3 was obtained. Results from this work provide guidance on LPCVD growth of In2O3 with targeted growth rate, surface morphology, carrier concentration, and mobility.

Low pressure chemical vapor deposition of β-Ga2O3 thin films: Dependence on growth parameters

Low pressure chemical vapor deposition (LPCVD) has been used to produce high quality β-Ga2O3 materials with controllable n-type doping. In this work, we focus on the studies of key LPCVD growth parameters for β-Ga2O3 thin films, including oxygen/carrier gas flow rates, growth temperature, pressure, and the substrate to Ga crucible distance. These growth parameters play important roles during the LPCVD β-Ga2O3 growth and determine the thin film growth rate, n-type dopant incorporation, and electron mobilities. The dependence of the growth parameters on LPCVD of β-Ga2O3 was carried out on both conventional c-plane sapphire and 6 degree off-axis (toward ⟨11-20⟩ direction) sapphire substrates. To better understand the precursor transport and gas phase reaction process during the LPCVD growth, a numerical model for evaluating the growth rate was developed by using a finite element method and taking into account the gas flow rate, chamber pressure, and chamber geometry. The results from this work can provide guidance for the optimization of the LPCVD growth of β-Ga2O3 with targeted growth rate, surface morphology, doping concentration, and mobility. In addition, β-Ga2O3 grown on off-axis c-sapphire substrates features with faster growth rates with higher electron mobilities within a wide growth window.

Selective LPCVD growth of graphene on patterned copper and its growth mechanism

Copper-catalyzed graphene low-pressure chemical-vapor deposition (LPCVD) growth has been regarded as a viable solution towards its integration to CMOS technology, and the wafer-bonding method provides a reliable alternative for transferring the selective graphene grown on a patterned metal film for IC manufacturing. In this paper, selective LPCVD graphene growth using patterned copper dots has been studied. The Raman spectra of grown films have demonstrated large dependence on the growth conditions. To explain the results, the growth mechanisms based on surface adsorption and copper-vapor-assisted growth are investigated by the comparison between the blanket copper films with/without the additional copper source. The copper vapor density is found to be critical for high-quality graphene growth. In addition, the copper-vapor-assisted growth is also evidenced by the carbon deposition on the SiO2 substrate of the patterned-copper-dot sample and chamber wall during graphene growth. This growth mechanism explains the correlation between the growth condition and Raman spectrum for films on copper dots. The study on the copper-catalyzed selective graphene growth on the hard substrate paves the way for the synthesis and integration of the 2D material in VLSI.

Increased monolayer domain size and patterned growth of tungsten disulfide through controlling surface energy of substrates

We report a surface energy-controlled low-pressure chemical vapor deposition growth of WS2 monolayers on SiO2 using pre-growth oxygen plasma treatment of substrates, facilitating increased monolayer surface coverage and patterned growth without lithography. Oxygen plasma treatment of the substrate caused an increase in the average domain size of WS2 monolayers by 78% ± 2% while having a slight reduction in nucleation density, which translates to increased monolayer surface coverage. This substrate effect on growth was exploited to grow patterned WS2 monolayers by patterned plasma treatment on patterned substrates and by patterned source material with resolutions less than 10 µm. Contact angle-based surface energy measurements revealed a dramatic increase in polar surface energy. A growth model was proposed with lowered activation energies for growth and increased surface diffusion length consistent with the range of results observed. WS2 samples grown with and without oxygen plasma were similar high quality monolayers verified through transmission electron microscopy, selected area electron diffraction, atomic force microscopy, Raman, and photoluminescence measurements. This technique enables the production of large-grain size, patterned WS2 without a post-growth lithography process, thereby providing clean surfaces for device applications.

Epitaxial growth and electrochemical transfer of graphene on Ir(111)/α-Al2O3(0001) substrates

Low-pressure chemical vapor deposition growth of graphene on Iridium (Ir) layers epitaxially deposited on α-Al2O3 (0001) substrates was investigated. The X-ray diffraction, Raman and reflection high energy electron diffraction characterizations revealed that graphene films were epitaxially grown on Ir(111) layers, and the in-plane epitaxial relationship between graphene, Ir(111), and α-Al2O3(0001) was graphene ⟨11¯00⟩//Ir⟨112¯⟩//α-Al2O3⟨112¯0⟩. The graphene on Ir(111) was electrochemically transferred onto SiO2/Si substrates. We also demonstrated the reuse of the Ir(111)/α-Al2O3(0001) substrates in multiple growth and transfer cycles.

Studying the morphology of hemispherical-grain polycrystalline silicon films

The effect of the deposition temperature on the morphology of hemispherical-grain polycrystalline silicon (HSG-Si) films obtained by low-pressure chemical vapor deposition (LPCVD) has been studied using atomic force microscopy. The dependences of the relative surface area increment, density of grains, average height and lateral size of grains, mean square roughness, and correlation length on the deposition temperature have been determined in an interval used for the LPCVD growth of HSG-Si films.

The Stress and Microstructure analysis of Polycrystalline Silicon Films Deposited by LPCVD

ABSTRACTAmorphous (a-Si) and polycrystalline silicon(c-Si) films have been obtained by low pressure chemical vapor deposition (LPCVD) in fixed silane flow at low pressure (200 mtorr) with variable growth temperature. Measurement of residual stress of polysilicon films growth between 570°C to 620°C was reported. Residual stress of polycrystalline silicon depends on film microstructure. The poly-silicon microstructure is a strong function of LPCVD growth temperature and pressure. In this work, Raman Scattering and X-ray diffraction (XRD) were used to study the film structure and composition. The multilayer optical model of Spectroscopic ellipsometry (SE) was used to crosscheck the crystallinity fraction. The surface roughness was identified by Atomic force microscopy (AFM) and SE. The residual stress changed from compressive to tensile and back to compressive for deposition temperature between 570°C and 620°C. Film’s c-Si fraction increased as a function of deposition temperature. The roughness surface was found at deposition temperature of 580°C. For deposition temperature larger then 580°C, all films shown (200) texture. The (220) grain size increased from 18.6 nm to 25 nm when deposition temperature increased from 580°C to 620°C. The film residual stress change can be explained by grain structure, surface stress and volume stress. At deposition temperature from 580°C to 587°C, grain is equi-axes type and volume stress dominate which cause the tensile stress. For temperature higher then 587°C inverse conical grain formed from oxide interface to surface and surface stress dominate cause the stress back to compressive. The columnar structure formed when deposition temperature > 600°C, grain growth push the compressive stress decrease again.

Ink jet printing of ferritin as method for selective catalyst patterning and growth of multiwalled carbon nanotubes

Ferritin, an iron containing protein was used as catalyst precursor for nanoscopic iron particles from which an iron/iron oxide mixed catalyst can be generated. Multiwall carbon nanotubes can be grown by chemical vapor deposition (CVD) therefrom. When printing the ferritin catalyst precursor via ink jet printing the distribution of the catalyst particles generated from the ferritin precursor on the substrate surface was found to be dependent on the surface wetting of the aqueous ferritin solution. Ink jet printing of the aqueous ferritin solution with a non-ionic sugar based tenside which incorporates the ferritin molecules in a micellar structure allows to form a homogeneous precursor distribution due to a good wetting behaviour on the substrate. Conversion of the ink jet printed solution of the ferritin precursor molecules into the active iron/iron oxide catalyst particles by thermal treatment was followed by a water assisted low pressure CVD growth with ethylene. Multiwall carbon nanotubes in prepatterned areas, e.g. in line or dot shaped morphology on the substrate were obtained.

Field emission from silicon nanowires: Conditioning and stability

We report the low-pressure chemical vapor deposition growth and field emission characterization of silicon nanowires (SiNWs). Our field emission results show the importance of the so called conditioning process on the reproducibility of the emission performance itself; this effect has proven to be reversible for the investigated current regime. We explained this behavior by invoking a current-driven desorption of residual adsorbed gases. A highly reproducible turn-on electric field of 27 V∕μm is found for a diode-connected SiNW planar sample. Furthermore, stability analysis is performed showing the technologically promising field emission behavior of the samples.

Si(111)-(7 × 7) Under Silane UHV-LPCVD: A STM Study

In this work, we present a scanning tunneling microscopy (STM) study of the LPCVD (low pressure chemical vapor deposition) growth of Si on Si(111)-(7 × 7) using silane ( SiH 4) decomposition. Surface reactivities have been studied at room and high temperature (700 < T < 800 K ), and the major chemical mechanisms have been identified at an atomic scale on the basis of room temperature STM images of the reacted surfaces. The study provides a better understanding of nucleation and initial stages of growth. More particularly, we show that the growth kinetics and the final structure of the film are different from what is observed by molecular beam epitaxial (MBE) growth.