Remote Plasma-enhanced Chemical Vapor Deposition Research Articles

Exfoliated, thin, flexible germanium heterojunction solar cell with record FF=58.1%

A thin, flexible monocrystalline germanium (c-Ge) heterojunction solar cell has been developed based on a novel kerfless exfoliation process and remote plasma-enhanced chemical vapor deposition (RPCVD) of hydrogenated amorphous silicon (a-Si:H). The performance of the exfoliated 50μm thick and bulk 500μm Ge heterojunction cells is compared in this paper. A superior conversion efficiency of 5.28% was achieved with the 50μm exfoliated Ge cell versus 1.78% for the bulk Ge cell, in agreement with simulation results. A record fill factor of 58.1% for an a-Si:H/c-Ge heterojunction cell was obtained with the exfoliated cell. Moreover, the conversion efficiency achieved with the 50μm exfoliated cell (without intrinsic a-Si:H passivation) is comparable to the best reported in literature with bulk Ge heterojunction cells and intrinsic a-S:H passivation.

Spectroscopic Detection of Medium Range Order in Hydrogenated Amorphous Silicon, a-Si(H): Applications in Photovolatics, Thin Film Transistors and Si-based Microelectronics

Abstract Hydrogenated amorphous silicon, a-Si1-xHx, with ~ at.10% or x ~0.1±0.02, is used in photovoltaics (PV), and thin film transistors (TFT's). Amorphous Si (a-Si) thin films, thought to be free of H, are used as precursors for polycrystalline gate electrodes in microelectronics. PV and TFT alloys has been deposited by the glow discharge method (GD), remote plasma-enhanced chemical vapor deposition (RPECVD, and reactive magnetron sputtering (RMS) with bonded-H determined by deposition precursors and substrate temperatures. Two conditions are required for low Si dangling bond densities ~0.5 to 1x1016 cm−3: (i) a bonded monohydride, Si-H, concentration of ~10 at. % H, and (ii) a deposition, and/or a post-deposition anneal at ~240 °C to 300 °C. These reduce strain by introducing medium range order (MRO) as nano-meter scale aperiodically-assembled clusters. Si L2,3 X-ray absorption spectroscopy (XAS) has been used to confirm MRO extending beyond short-range order (SRO) of continuous random networks (CRN) through observation of ligand-field split d-state features. These are associated with symmetry-adapted linear combinations (SALCs) of atomic states forming molecular orbital valence bands. XAS and photoelectron spectroscopy (PES) studies have confirmed that a-Si used for microelectronic applications also has MRO as well. This is associated with a H-transfer reaction from an Si-H bond of the cluster into a Si-H-Si bonding arrangement on near-neighbor sites. MRO has also identified by other spectroscopic techniques: spectroscopic ellipsomentry (SE), and ultra-violet or X-ray photoemission spectroscopy (UPS or XPS). The same H-atom motion induced by absorption of sun-light is responsible for the Staebler-Wronski Effect (SWE); the generation of Si-atom dangling bonds that degrade PV performance.

High quality amorphous–crystalline silicon heterostructure prepared by grid-biased remote radio-frequency plasma enhanced chemical vapor deposition

Very high effective minority carrier lifetime (6.3ms) and very low surface recombination velocity (2.6cm/s) have been demonstrated on float-zone 1–2Ωcm crystalline silicon (c-Si) wafers by depositing a-Si:H films using grid-biased remote radio-frequency plasma enhanced chemical vapor deposition (RF PECVD). This method employs a semi-transparent DC biased-grid within the conventional RF PECVD configuration. The DC-biased grid is positioned between the RF electrodes in order to develop a remote plasma and thus allow control of the flux and type of precursors involved in the growth of hydrogenated amorphous silicon (a-Si:H) film. It is shown that compared to conventional RF diode, the grid-biased remote RF PECVD method produces a-Si:H films with superior passivating properties as well as significantly lower concentrations of void and SiH2 bonding and a lower overall hydrogen content, all of which contribute to a higher quality a-Si:H–c-Si heterostructure.

Systems and control challenges in photovoltaic manufacturing processes: A modeling strategy for passivation and antireflection films

A view of contemporary systems and control challenges in photovoltaic cell manufacturing is given in this paper, with emphasis on developing a modeling strategy for the optimization of silicon nitride SiNx:H films used for passivation and antireflection coatings in single and multicrystalline silicon solar cells. The overall framework integrates three modeling modules: a remote plasma-enhanced chemical vapor deposition reactor process model that predicts film composition and thickness based on process input parameters, a solar-optical module that relates antireflection film physical and chemical properties to the degree to which the spectral irradiance distribution is attenuated, and a solar cell device model that predicts cell power output and efficiency from the film properties and irradiance. Because the model couples process inputs to both photovoltaic cell performance and manufacturing process efficiency, the modeling approach can be used for the simultaneous optimization of process and product performance.

Vapour-phase graphene epitaxy at low temperatures

We report an epitaxial growth of graphene, including homo- and hetero-epitaxy on graphite and SiC substrates, at a temperature as low as ∼540 °C. This vapour-phase epitaxial growth, carried out in a remote plasma-enhanced chemical vapor deposition (RPECVD) system using methane as the carbon source, can yield large-area high-quality graphene with the desired number of layers over the entire substrate surfaces following an AB-stacking layer-by-layer growth model. We also developed a facile transfer method to transfer a typical continuous one layer epitaxial graphene with second layer graphene islands on top of the first layer with the coverage of the second layer graphene islands being 20% (1.2 layer epitaxial graphene) from a SiC substrate onto SiO2 and measured the resistivity, carrier density and mobility. Our work provides a new strategy toward the growth of graphene and broadens its prospects of application in future electronics. Open image in new window

Growth, Characterization, and Properties of Nanographene

A systematic study on nanographene grown directly on silicon dioxide substrates is reported. The growth is carried out in a remote plasma-enhanced chemical vapor deposition system at a low temperature of around 550 °C with methane gas as the carbon source. Atomic force microscopy is used to characterize the nanographene morphology, and Raman spectroscopy, X-ray photoelectron spectroscopy, and scanning tunneling microscopy are exploited to identify the in-plane sp(2) bonding structures of nanographene samples. Electrical transport properties are measured at various temperatures down to 4 K. Tunneling effects, minimal conductance at the charge-neutral point, sheet resistances, and Dirac point position at different channel lengths are investigated. In addition, nanographene film possesses high transmittance properties, as indicated by transmittance spectra. Nanographene devices are fabricated from rippled structures, and show great promise for strain-gauge sensor applications.

Modulation of the propagation speed of mechanical waves in silicon quantum dots embedded in a silicon-nitride film

Using a vectorial picosecond self-diffraction method, we evaluate the modification of the speed of the sound in a silicon-nitride film containing silicon quantum dots prepared by remote plasma-enhanced chemical vapor deposition. Our non-contact technique is based on the stimulation of the electrostriction contribution to the nonlinearity of index exhibited by the sample in a multiwave mixing laser experiment. We identified the electronic birefringence using two of the incident beams to generate a self-diffraction signal, then, we modified the third order nonlinear response by means of the optical Kerr effect given by a phase-mismatched third beam which induced electrostriction. Our results indicated that the speed of the sound in a silicon-nitride film can be simultaneously tailored by an electronic nonlinear refractive index, and by an electrostriction effect, both resulting from silicon quantum dots doping.

Low-temperature graphene growth using epochal catalyst of PdCo alloy

Palladium-Cobalt alloy as a catalyst was introduced to realize low temperature graphene growth on glass substrate by using remote RF plasma-enhanced chemical vapor deposition. Few layer graphene films were easily formed with high transmittance of 88.8% at temperature as low as 400 °C, in good contrast with Ni catalyst in which no graphitic layer was formed at all at the same conditions. High decomposition rate of hydrocarbon gases and formation of nanosize aggregates giving rise to enhancement of carbon incorporation into PdCo alloy and consequently formation of graphene layers at such low temperatures are further discussed with observed Raman spectroscopy and x-ray diffraction.

Remote Plasma Processing of Sapphire Substrates for Deposition of TiN and TiO<SUB>2</SUB>

The paper uses remote plasma assisted deposition, oxidation and nitridation processes for depositing thin films of metallic TiN on crystalline sapphire (0001) substrates. These films on sapphire substrates are being studied as window materials for high power radio frequency (RF) power tubes. A sequence of four process steps has been performed in a reactor chamber that isolates the deposition and surface-processing chamber from the plasma generation region. The chamber is part of an ultra-high-vacuum (UHV) compatible multi-chamber cluster in which the sequence of four process steps can be interrupted after each step, and surface chemistry changes can be identified by in-line Auger electron spectroscopy (AES). The four process steps, performed after an ex-situ chemical clean and blow-dry in nitrogen gas, are (i) a remote plasma-assisted oxidation (RPAO) in which surface contaminants including adventitious carbon are removed; (ii) a remote plasma-assisted nitridation (RPAN) process which forms a superficial layer of generic AION used to increase surface adhesion of the TiN films; (iii) a remote plasma-enhanced chemical-vapor deposition (RPECVD) process for deposition of 2 to 5 nm thick TiN films, and finally (iv) a second RPAN step that increases the ratio of Ti-N bonding in the TiN films with respect to adventitious O-atom incorporation from the Ti precursor, Ti tetra-butoxide.

Indium-Doped MgxZn1-xO Films for ZnO-Based Heterojunction Diodes

Indium-doped MgxZn1-xO (MgxZn1-xO:In) thin film and ZnO:In thin films were successfully grown by remote plasma-enhanced metalorganic chemical vapor deposition (RPE-MOCVD). The In supply source used is trimethylindium (TMIn). The surface morphology, structural changes, and optical band gap energy in MgxZn1-xO:In were investigated by varying the amount of the supplied TMIn and were compared with ZnO:In systems. Our main achievement point is that we have markedly improved the surface morphology of Mg0.05Zn0.95O:In films from being pillar like to being film like with an increase in the amount of indium. The improved green electoluminescence emission (EL) characteristic the ZnO-based DH system was employing the Mg0.05Zn0.95O:In film here and in conclusions.

Analysis of mass transport in an atmospheric pressure remote plasma-enhanced chemical vapor deposition process

In remote microwave plasma enhanced chemical vapor deposition processes operated at atmospheric pressure, high deposition rates are associated with the localization of precursors on the treated surface. We show that mass transport can be advantageously ensured by convection for the heavier precursor, the lighter being driven by turbulent diffusion toward the surface. Transport by laminar diffusion is negligible. The use of high flow rates is mandatory to have a good mixing of species. The use of an injection nozzle with micrometer-sized hole enables us to define accurately the reaction area between the reactive species. The localization of the flow leads to high deposition rates by confining the reactive species over a small area, the deposition yield being therefore very high. Increasing the temperature modifies nonlinearly the deposition rates and the coating properties.

? The Study of dielectric constant change of a-SiC:H films deposited by remote PECVD with low deposition temperatures

a-SiOC:H films were deposited by using a remote Plasma Enhanced Chemical Vapor Deposition (PECVD) system with HMDS (Hexamethyldisilane) as a precursor. The H2 gas and the C2H2 gas were used as carrier gas and dilution gas, respectively. The flow rate of C2H2 gas was fixed at 3 sccm. The deposition temperature was varied between 100 to 200 to study the eect of temperature on the film stoichiometry and bonding properties, which can aect changes in the dielectric constant of the deposited films. A Rapid Thermal Annealing (RTA) treatment was conducted to determine the thermal stability and any changes in the dielectric constant. A change in carbon hybridization bonds caused by dierent deposition temperatures played an important role in the changes in the dielectric constant.

Preparation of Native Oxide and Carbon-Minimized Ge Surface by NH4OH -Based Cleaning for High-k ∕ Ge MOS Gate Stacks

The native oxide and carbon-contaminant-minimized Ge surface with ammonium hydroxide -based cleaning for high- metal-oxide-semiconductor (MOS) gate stack application is reported. Furthermore, the carbon-free interfacial Ge-oxide layer preparation on the cleaned Ge surfaces was also studied. The thickness of on Ge surface before, during, and after different cleaning processes was evaluated by the spectroscopic ellipsometry measurements. The HF rinsing step in the cyclic HF∕deionized water cleaning was not effective for a removal of native because it cannot form the soluble species by a chemical reaction in the low pH HF solution. A cyclic -based cleaning results in a minimum residual at 3 and on Ge(111) and (100), respectively. The fast regrowth of on cleaned Ge surfaces under air exposure was observed, regardless of the cleaning methods. However, Auger electron spectroscopy spectra showed less amount of carbon on Ge surfaces with -based cleaning than HF-based cleaning. The small amount of residual carbon after -based wet cleaning was completely removed by plasma for a very thin surface oxidation in the remote plasma-enhanced chemical vapor deposition chamber.

Low-Temperature Growth of Multiwalled Carbon Nanotubes by Surface-Wave Plasma-Enhanced Chemical Vapor Deposition Using Catalyst Nanoparticles

Carbon nanotubes (CNTs) have been grown by surface-wave plasma-enhanced chemical vapor deposition (CVD) using size-classified Co nanoparticles at low temperatures. A mesh grid is used in the remote plasma-enhanced CVD system for the suppression of ion bombardment damage from plasma. The control of the electric field distribution using a mesh grid with a narrower opening is effective for the CNT growth. Multiwalled CNTs are obtained at a low temperature of 400 °C under low ion-density conditions. No significant difference in the microscopic structure of the CNTs grown at temperatures between 400 and 500 °C is observed.

Modification of the nonlinear optical absorption and optical Kerr response exhibited by nc-Si embedded in a silicon-nitride film

We studied the absorptive and refractive nonlinearities at 532 nm and 26 ps pulses for silicon-nitride films containing silicon nanoclusters (nc-Si) prepared by remote plasma-enhanced chemical vapor deposition (RPECVD). Using a self-diffraction technique, we measured for the as-grown sample beta=7.7x10(-9)m/W, n(2)=1.8x10(-16)m(2)/W, and /chi(3)1111/ = 4.6x10(-10)esu; meanwhile, when the sample was exposed to an annealing process at 1000 degrees C during one hour in a nitrogen atmosphere, we obtained beta=-5x10(-10)m/W, n2=9x10(-17)m(2)/W, and /chi(3)1111/=1.1x10(-10)esu. A pure electronic nonlinear refraction was identified and a large threshold ablation of 41 J/cm(-2) was found for our films. By fitting nonlinear optical transmittance measurements, we were able to estimate that the annealed sample exhibits a response time close to 1 fs. We report an enhancement in the photoluminescence (PL) signal after the annealing process, as well as a red-shift due to an increment in size of the nc-Si during the thermal process.

Chemical characterization of SiC xN y nanolayers by FTIR-and Raman spectroscopy, XPS and TXRF-NEXAFS

SiC x N y nanolayers were synthesized by a remote plasma enhanced chemical vapour deposition (RPECVD) method and chemically characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure investigations in total reflection X-ray fluorescence geometry (TXRF-NEXAFS). The results are compared with those obtained for standard samples SiC and Si 3N 4 (and with spectra from the literature). As a first result, two or more compounds containing Si–N bonds (not Si 3N 4), one compound with a Si–C bond (not SiC), and graphitic carbon were identified.

Formation of Isotopically Enriched Silicon Film from Fluorosilane Produced by Isotopically Selective Infrared Multiphoton Dissociation

Fabrication of isotopically enriched silicon thin film by plasma-enhanced chemical vapor deposition (PE-CVD) has been performed with source gas mixtures of SiF4, H2 and Ar. Enriched SiF4 gases with 30Si exceeding 25% were obtained from isotopically selective infrared multiphoton dissociation of hexafluorodisilane. The crystalline silicon films were successfully grown by a remote type microwave PE-CVD system on a quartz glass and Si wafers at substrate temperature of 623-1023 K. Secondary ion mass spectroscopy and energy-dispersive X-ray spectroscopy analyses indicated that the films had small impurity contents. The isotopic fraction of the grown Si film almost coincided with that of source gas.

Characterization of SiC:H films deposited using HMDS precursor with C2H2 dilution gas by remote PECVD system

Amorphous SiC:H films were deposited on (100) silicon wafer by remote-Plasma Enhanced Chemical Vapor Deposition system in the temperature range of 400°C-450°C. Hexamethyldisilane (HMDS) and C2H2 gas were used as a precursor and a dilution gas, respectively. The lower deposition temperature and lower sp3/sp2 carbon bonding ratio made lower dielectric constant.

Thermo-optic effect and optical third order nonlinearity in nc-Si embedded in a silicon-nitride film

Using a self-diffraction experiment with 7ns pulses at 532nm we studied a silicon nitride film containing silicon nanoclusters (nc-Si) of 3.1+/-0.37 nm mean size. The sample was prepared by remote plasma-enhanced chemical vapor deposition (RPECVD), and we found that its nonlinearity consists of a combination of electronic and thermal contributions. By varying the repetition rate of the laser, we discriminated the responsible mechanisms for the nonlinear response. Using this procedure we determined a total /chi((3))1111/ = 3.3x10(-10)esu, n2 = 2.7x10(-16) m(2)/W, beta = 1x10(-9) m/W and dn/dT =1x10(-4) degrees C(-1) for our sample. We also show results for the optical Kerr effect using 80 fs pulses at 820 nm. The purely electronic nonlinearity measured is characterized by /chi((3))1111/=9.5 x10(-11) esu.

On the mechanism of remote plasma-enhanced chemical vapor deposition of films

332 As we showed earlier [1], the remote plasmaenhanced chemical vapor deposition (RPE-CVD) process used for film fabrication makes it possible to preserve intact fragments of a precursor molecule that are required to synthesize the desired material. Despite close attention given by researchers to such processes, most works in this field deal with the study of the dependence of the properties of the film material on the synthesis conditions, while the mechanism of plasmaassisted activation of precursor molecules remains beyond the area of experimental interest [2–4].