Remote Plasma Enhanced Chemical Vapor Deposition Process Research Articles

Epitaxial twin coupled microstructure in GeSn films prepared by remote plasma enhanced chemical vapor deposition

Growth of GeSn films directly on Si substrates is desirable for integrated photonics applications since the absence of an intervening buffer layer simplifies device fabrication. Here, we analyze the microstructure of two GeSn films grown directly on (001) Si by remote plasma-enhanced chemical vapor deposition (RPECVD): a 1000 nm thick film containing 3% Sn and a 600 nm thick, 10% Sn film. Both samples consist of an epitaxial layer with nano twins below a composite layer containing nanocrystalline and amorphous. The epilayer has uniform composition, while the nanocrystalline material has higher levels of Sn than the surrounding amorphous matrix. These two layers are separated by an interface with a distinct, hilly morphology. The transition between the two layers is facilitated by formation of densely populated (111)-coupled nano twins. The 10% Sn sample exhibits a significantly thinner epilayer than the one with 3% Sn. The in-plane lattice mismatch between GeSn and Si induces a quasi-periodic misfit dislocation network along the interface. Film growth initiates at the interface through formation of an atomic-scale interlayer with reduced Sn content, followed by the higher Sn content epitaxial layer. A corrugated surface containing a high density of twins with elevated levels of Sn at the peaks begins forming at a critical thickness. Subsequent epitaxial breakdown at the peaks produces a composite containing high levels of Sn nanocrystalline embedded in lower level of Sn amorphous. The observed microstructure and film evolution provide valuable insight into the growth mechanism that can be used to tune the RPECVD process for improved film quality.

FORMATION OF NANO STRUCTURES IN RESULT OF HOMOGENOUS NUCLEATION OF CARBON OBTAINED IN THERMAL PLASMA UNDER ATMOSPHERIC PRESSURE

Thermal plasma processing of carbon sources using a plasma jet with high heat capacity is one of the most promising methods for the synthesis of new materials. This paper describes the low-temperature deposition of carbon nanomaterials by remote plasma-enhanced chemical vapor deposition (PECVD) in the absence of catalysts. The remote PECVD process differs from conventional and direct PECVD process in two ways: (a) only a subset of the process reactants and/or diluents are directly plasma excited; and (b) thin film deposition takes place on a substrate that is outside of the plasma glow region. In conventional CVD methods, carbon is produced from the decomposition of carbon sources such as hydrocarbons, carbon monoxide, alcohols, and so on, over a metal catalyst. The unavoidable metal species remaining in carbon nanomaterials would lead to obvious disadvantages for property characterization and application exploration. Despite sustained efforts, it is still an intractable problem to remove metal catalysts completely from carbon nanomaterials samples without introducing defects and contaminations. Good reactor design allowed to overcome problems of chemical and structural purity, and poor process robustness in terms of phase composition of product from run to run. For the synthesis of graphene materials, carbon black, carbon nanotubes, nanowires we used the thermal plasma generator which is a high current divergent anode-channel DC plasma torch. The experiment involved a simultaneous input of hydrocarbons (methane, propane, butane, acetylene) with the plasma forming gas (helium, argon, nitrogen) into the plasma torch, wherein heating and decompositions occurred in the plasma jet and in the region of the arc discharge, followed by condensation of the synthesis product on metallic surfaces. The deposition rate was varied with distance from the plasma. Consumption of carbon source, plasma forming gas and plasma torch power were changed independently from each other. For the experimental conditions the electric power of plasma torch was set up to 40 kW. Regularities of formation of carbon thread-like nanostructures and graphene in the course of hydrocarbons pyrolysis in thermal plasma without participation of catalytic particles were studied by means of electron microscopy, X-ray diffraction, IR-spectrometry and thermogravimetry. Depending on the pyrolytic synthesis parameters, different proportions of crystal carbon and soot may be obtained. It has been demonstrated that the phase composition is varied by hydrocarbons flow rate, plasma forming gas pressure and dc plasma torch power. It has been established through the experiments that carbon nucleation is volumetric and proceeds according to the model of explosive soot formation.

Device-quality GaN–dielectric interfaces by 300 °C remote plasma processing

In previous studies, device-quality Si–SiO 2 interfaces and dielectric bulk films (SiO 2) were prepared using a two-step process; (i) remote plasma-assisted oxidation (RPAO) to form a superficially interfacial oxide (∼0.6 nm) and (ii) remote plasma enhanced chemical vapor deposition (RPECVD) to deposit the oxide film. The same approach has been applied to GaN–SiO 2 system. Low-temperature (300 °C) remote N 2/He plasma cleaning of the GaN surface, and the kinetics of GaN oxidation using RPAO process and subcutaneous oxidation during the SiO 2 deposition using an RPECVD process have been investigated from analysis of on-line Auger electron spectroscopy (AES) features associated N and O. Compared to single-step SiO 2 deposition, significantly reduced defect state densities are obtained at the GaN–dielectric interfaces by independent control of GaN–GaO x ( x∼1.5) interface formation by RPAO, and SiO 2 deposition by RPECVD.

Formation mechanism for TiO x thin film obtained by remote plasma enhanced chemical vapor deposition in H 2–O 2 mixture gas plasma

TiO x thin film formation mechanism from titanium tetraisopropoxide [Ti-(O- i-C 3H 7) 4, TTIP] by remote plasma enhanced chemical vapor deposition (RPE-CVD) was investigated. Plasma was generated by a microwave discharge in single H 2, O 2, or H 2–O 2 mixture gases. Emission spectra measurements suggested that H radical atoms dissociated TTIP molecules. By addition of O 2 to H 2 gas, the H radical density and film deposition rate drastically increased. Moreover, it was proved that the deposition rate was decreased by OH radical molecules formed in H 2–O 2 mixture gas plasma. OH radical molecules caused deactivation of precursors and hence suppressed TiOTi bond formation in the gas phase. The highest deposition rate of 11 nm/min, which was two orders higher than that for the case of single gas plasma, was obtained in the case of mixture gas ratio of 80% H 2 and 20% O 2. The substrate temperature had not affected the deposition rate, but significantly changed the film structure. It is concluded that the use of H 2–O 2 mixture gas is effective for obtaining a high deposition rate for the RPE-CVD process, and the deposition rate strongly depends on H radical density and ratio of H and OH radical densities.

Remote Plasma Enhanced Chemical Vapor Deposition of TiOx Films from Titanium Tetraisopropoxide

ABSTRACTTiOx thin films were prepared from titanium tetraisopropoxide (Ti-(O-i-C3H7)4, TTIP) in a remote plasma enhanced chemical vapor deposition (RPE-CVD) using a mixture of hydrogen/oxygen plasma gas. Emission spectra suggested that H-radicals dissociated TTIP molecules in gas phase. By mixing with oxygen, H-radical density was increased with the correlation effect to result in enhancement of deposition rate. Deposition rate was also influenced by OH-radicals. OH-radicals caused deactivation of precursors and hence suppressed Ti-O-Ti bond formation in gas phase. The highest deposition rate of 11 nm/min, which was two orders higher than that for the case of single gas plasma, was achieved in the case of mixture gas ratio of 20% oxygen and 80% hydrogen. Surface reaction due to the heated substrate did not affect the deposition rate though the film structure was remarkably changed. It was demonstrated that for RPE-CVD process, oxygen/hydrogen mixture gas plasma was effective for obtaining high deposition rate, and also H-to-OH radical density ratio was an important factor to control the deposition rate.

Low-temperature (<450 °C), plasma-assisted deposition of poly-Si thin films on SiO2 and glass through interface engineering

A low-temperature, two-stage process that employs interface engineering is investigated for deposition of poly-Si thin films on SiO2 and glass. In this two-stage process, film growth is separated into two regimes: (i) interface formation and (ii) bulk film growth. Interface formation (stage 1) was optimized for remote plasma enhanced chemical-vapor deposition (PECVD) of ultra thin (<100 Å) μc-Si films on the oxide. This layer acts as a seed template, providing ordered growth sites for the next stage of film growth. Bulk Si film deposition (stage 2) was then initiated on the seed template using remote PECVD process conditions shown to produce low-temperature (<450 °C), epitaxial-Si films on crystalline silicon substrates, so as to drive a transition to larger grain growth off of the seed crystals. Results showed that the seed layer had a dramatic impact on bulk film crystallinity. Films deposited without a μc-Si seed layer were amorphous, whereas films deposited using a seed layer, in conjunction with the appropriate second stage conditions, were highly oriented (220) poly-Si.

Effects of NH3 and N2 source gases and plasma excitation frequencies on the reaction chemistry for Si3N4 thin-film growth by remote plasma-enhanced chemical-vapor deposition

NH3/He and N2/He discharges can produce qualitatively different silicon nitride films when they are used as N-atom sources in the remote plasma-enhanced chemical-vapor deposition process. Radio frequency and microwave excitation at frequencies, 13.56 MHz and 2.54 GHz, respectively, were used to produce significantly different electron temperatures Te, electron energy distribution functions, and electron densities ne. Differences in these plasma parameters were then correlated with important aspects of the silicon nitride reaction chemistry, including the incorporation of hydrogen in SiH and/or Si–NH bonding arrangements.

Advances in remote plasma-enhanced chemical vapor deposition for low temperature In situ hydrogen plasma clean and Si and Si1-xGex epitaxy

Remote plasma-enhanced chemical vapor deposition (RPCVD) is a low temperature growth technique which has been successfully employed inin situ remote hydrogen plasma clean of Si(100) surfaces, silicon homoepitaxy and Si1- xGex heteroepitaxy in the temperature range of 150–450° C. The epitaxial process employs anex situ wet chemical clean, anin situ remote hydrogen plasma clean, followed by a remote argon plasma dissociation of silane and germane to generate the precursors for epitaxial growth. Boron doping concentrations as high as 1021 cm−3 have been achieved in the low temperature epitaxial films by introducing B2H6/He during the growth. The growth rate of epitaxial Si can be varied from 0.4A/min to 50A/min by controlling therf power. The wide range of controllable growth rates makes RPCVD an excellent tool for applications ranging from superlattice structures to more conventional Si epitaxy. Auger electron spectroscopy analysis has been employed to confirm the efficacy of this remote hydrogen plasma clean in terms of removing surface contaminants. Reflection high energy electron diffraction and transmission electron microscopy have been utilized to investigate the surface structure in terms of crystallinity and defect generation. Epitaxial Si and Si1-xGex films have been grown by RPCVD with defect densities below the detection limits of TEM (~105 cm-2 or less). The RPCVD process also exploits the hydrogen passivation effect at temperatures below 500° C to minimize the adsorption of C and 0 during growth. Epitaxial Si and Si1-xGex films with low oxygen content (~3 × 1018 cm-3) have been achieved by RPCVD. Silicon and Si/Si1-xGex mesa diodes with boron concentrations ranging from 1017 to 1019 cm-3 in the epitaxial films grown by RPCVD show reasonably good current-voltage characteristics with ideality factors of 1.2-1.3. A Si/Si1-xGex superlattice structure with sharp Ge transitions has been demonstrated by exploiting the low temperature capability of RPCVD.In situ plasma diagnostics using single and double Langmuir probes has been performed to reveal the nature of the RPCVD process.

REMOTE PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITION (RPCVD) PROCESS FOR LOW TEMPERATURE (≤450°C) EPITAXY OF Si AND Si1−x, Gex

ABSTRACT Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD) is a low temperature growth technique which has: been successfully employed tor in situ remote hydrogen plasma cleaning, dielectric deposition, silicon homoepitaxy and Si1−x, Gex heteroepitaxy in the temperature range of 150°C-450°C. The growth rate of epitaxial Si in the RPCVD process can be varied from 0.4A/min to 50A/min by controlling the r-f power. The wide range of controllable growth rates makes RPCVD a excellent tool for applications ranging from quantum-well type structures to more conventional Si epitaxy. Epitaxial Si and Si1−x, Gex films with defect densities below the detectable limits of TEM (∼105 cm− 2 or less) and low oxygen content (∼3×101B cm− 3) have been achieved by RPCVD. The in situ boron-doped Si films have been grown on n-typo, phosphorus-doped substrates to form p-n junctions for mesa diode fabrication. The mesa diodes with different boron doping concentrations (1017-1019 cm− 3) show good current-voltage characterist...

Deposition and characterization of amorphous and micro-crystalline Si,C alloy thin films by a remote plasma-enhanced chemical-vapor deposition process - RPECVD

The RPECVD process has been extended to deposit a-Si,C:H and μ c-Si,C:H. The degree of crystallinity in the μc-Si,C:H alloys is lower than in μc-Si:H films deposited under comparable conditions. Attempts to dope μc-Si,C:H alloys indicate that high levels of both B and P doping can promote a transition from μc-Si,C:H to a-Si,C:H. Raman spectra indicate that crystallites in the μc-Si,C:H alloys are Si, while IR measurements show that the amorphous component is an a-Si,C:H alloy.

Deposition of Amorphous and Microcrystalline Si,C Alloy Thin Films by a Remote Plasma-Enhanced Chemical-Vapor Deposition Process

ABSTRACTWe have extended the remote PECVD process to the deposition of intrinsic and doped, amorphous and microcrystalline silicon, carbon alloy films, a-Si,C:H and μc-Si,C, respectively. The electrical and optical properties of a-Si,C:H deposited by remote PECVD are comparable to those of films deposited by the glow discharge or GD process. The degree of crystallinity in the μc-Si,C alloys, as determined from the relative intensities of crystalline and amorphous features in the Raman spectra, is lower than that of μc-Si films deposited under comparable deposition conditions. The Raman spectra indicate that the crystallites in the μc-Si,C alloys are Si, while the infrared measurements establish that the intervening amorphous component is an a-Si,C:H alloy.

Properties of intrinsic and doped a-Si:H deposited by remote plasma enhanced chemical vapor deposition

We have grown films of a-Si:H by remote plasma enhanced chemical vapor deposition (RPECVD) with substrate temperatures Ts between 38 and 400 °C and studied the infrared and optical absorbance (including sub-band-gap absorbance), and other photoelectronic properties. The RPECVD films differ from glow discharge (GD) and sputtered films, most notably in the Ts dependence of the hydrogen bonding environments (SiH, SiH2, etc.) and the photoconductivity. RPECVD films produced with Ts=235 °C are similar to ‘‘device grade’’ GD films. Based on the differences between these films, we construct a model for the RPECVD deposition process that includes SiH3 species as precursors to the growth of high-quality films. We also present experimental evidence of the selectability of precursor formation in the RPECVD process.