Photo-enhanced Chemical Vapor Deposition Research Articles

Characterization of low temperature synthesized hexagonal diamond thin films

Characterization of hexagonal diamond thin films synthesized by photo-enhanced chemical vapor deposition method at 450 °C on Al/Ni coated thermally oxidized Si wafer substrates is reported here. Measurements of optical, electrical and mechanical properties of synthesized hexagonal diamond films are reported for the first time. Optical band gap of the hexagonal diamond film is approximately 1.0 eV as obtained from the Tauc plot utilizing UV---Visible spectroscopy. Nanoindenter is utilized for I---V and reduced modulus measurements on the hexagonal diamond films.

Low temperature carbon nanotube and hexagonal diamond deposition with photo-enhanced chemical vapor deposition

Deposition of carbon nanotube and hexagonal diamond thin films at low substrate temperature with photo-enhanced chemical vapor deposition is described here. Extensive experimentation is conducted to optimize the catalyst layer utilized for deposition by varying Al/Ni/Al metal layer thicknesses on SiO2 coated Si substrates. The coated substrates are annealed to transform the thin metal layers into nanoparticles. Suitable catalyst layer thicknesses obtained are 3/2/3, 5/1/5 and 5/3/5 nm for Al/Ni/Al sandwich metal layers. Suitable annealing conditions are in the range of 350---450 °C for substrate temperature and from 0.22 to 10 Torr for chamber pressure in ammonia ambient for 25 min. Carbon tetrachloride (CCl4) is used as a carbon precursor in this work. Argon to CCl4 flow ratio is varied in 1.5---19 range, chamber pressure is varied in 3---10 Torr range, and the substrate temperature is varied in 350---450 °C range. Carbon nanotubes (CNT) growth is observed at lower chamber pressure, lower partial pressure of CCl4, lower substrate temperature and for thin Ni catalyst layer. The optimal CNT deposition condition observed is 5 Torr total chamber pressure, 9:1 partial pressure ratio of Ar to CCl4, 400 °C substrate temperature and 5/1/5 nm thick Al/Ni/Al catalyst layers. The hexagonal diamond deposition is observed at a higher chamber pressure, higher partial pressure of CCl4, higher substrate temperature and for a thicker Ni catalyst layer. The optimal condition for hexagonal diamond deposition observed is 10 Torr total chamber pressure, 7:3 partial pressure ratio of Ar to CCl4, 450 °C substrate temperature and 5/3/5 nm thick Al/Ni/Al catalyst sandwich layers.

Study on low temperature growth and formation mechanism of hexagonal diamond

Synthesis of hexagonal diamond on Al/Ni coated thermally oxidized SiO2 covered Si wafer substrate with photo-enhanced chemical vapor deposition (CVD) method at 450°C is reported here. The Raman spectroscopy on grown samples shows a 1322cm−1 peak with 75.4cm−1 full width at half maximum (FWHM). The X-ray diffraction (XRD) data shows hexagonal diamond peaks. Various stages of hexagonal diamond formation are observed in the scanning electron microscope (SEM) images. Based on these images, a mechanism of hexagonal diamond nucleation and growth is proposed.

Increased spatial homogeneity in a light-emitting InGaN thin film using optical near-field desorption

We report a self-assembly method that produces greater spatial uniformity in InGaN thin films using optical near-field desorption. Spatial homogeneity in the In fraction was reduced by introducing additional light during the photo-enhanced chemical vapor deposition of InGaN. Near-field desorption of InGaN nanoparticles, upon addition depended on the In content of the film, and the photon energy of the illumination source determined the energy of the emitted photons. Since this deposition method is based on a photo-desorption reaction, it can easily be applied to other deposition techniques and used with other semiconductor systems.

RESULTS ON PASSIVATION OF InP BY PHOTO-CVD SiO2 AND SiNx OBTAINED BY USING THE LOW-FREQUENCY NOISE MEASUREMENT TECHNIQUE

Photo enhanced chemical vapour deposition (PVD) of SiO 2 and Si 3 N 4 has been applied for surface passivation of specially designed n-type InP planar test resistors prepared by mesa etching on a semiinsulating InP substrate. The deposition temperatures were 150, 200 and 300 °C. The low-frequency noise (LFN) measurement technique was used for the characterisation. It was stated that the commercial PVD technology using Hg sensitization results in a low-damage passivation of InP, if a SiO 2 layer is deposited at a temperature around 300 °C. Low 1/f noise and low generation-recombination noise are generated in the test resistors passivated by this technology, and no surface conduction has been caused on the high-resistivity substrate-material holding the resistor patterns. Otherwise, for the PVD deposited Si 3 N 4 layer a significantly higher noise level has been measured, and surface conduction has also appeared.

Laser-enhanced epitaxy of Si and Si-Ge: Microelectronics Research Center, University of Texas at Austin, Austin 78712, TX, USA

This paper discusses low temperature Si homoepitaxy on Si (100) substrates by the photolytic decomposition of Si 2H 6 by the 193 nm emission of an ArF excimer laser in a photo-enhanced chemical vapor deposition (PCVD) system. The growth involves photolytic decomposition of Si 2H 6 and the generation and adsorption of SiHSiH 3 precursors on the hydrogenated Si surface. PCVD of Si was achieved in two ways: with the laser passing parallel to the substrate or directly incident on it. For parallel laser incidence, controllable deposition rates of 0.5–4 A min −1 were achieved. Epitaxial films were achieved at temperatures as low as 250 °C using photon flux densities of 10 16 photons pulse −1 cm −2, and Si 2H 6 partial pressures of 20 mTorr. For parallel incidence, very low defect density films in terms of stacking faults and dislocation loops (less than 10 5 cm −2), and excellent crystallinity have been grown at 250 °C and low laser power, as confirmed by Schimmel etching and Nomarski microscopy, transmission electron microscopy (TEM), electron diffraction and in situ reflection high energy electron diffraction (RHEED). The growth rates were observed to be linearly dependent on laser power. For direct laser incidence, very high growth rates (20–80 A min −1) were obtained. Single crystal films with a growth rate of ~ 20 A min −1 were obtained at a photon flux density of 7 × 10 14 photons pulse −1 cm −2 at 300 °C and 20 mTorr Si 2H 6 partial pressure. Boron doping with abrupt doping transitions has been achieved in the low temperature epitaxial films by introducing B 2H 6 during the process. Phosphorus doping has been achieved using PH 3. Epitaxial Si 1− x Ge x films using Si 2H 6 and Ge 2H 6 have been achieved. Si/Si 1− x Ge x heterostructures with sharp Ge transitions have been grown by exploiting the low temperature capability of the PCVD process.

An InSb integrated photo-MOSFET fabricated by photo-enhanced chemical vapour deposition

A new output-controllable InSb infrared (i.r.) detector is proposed. The detector is fabricated by monolithically integrating an InSb p-n junction with an InSb p-channel enhancement mode metal oxide semiconductor field effect transistor (MOSFET). During operation, a photocurrent generated near the source junction is controllably switched to the drain terminal by a gate of the integrated MOSFET. The observed internal quantum efficiency in the ‘on’ state is as high as 85%. Photocurrent on-off ratios are between 260 and 730, improving with increasing channel length. For longchannel devices, the photocurrent in the ‘off’ state is limited by undesired leakage paths. The new structure can be used as an output-controllable i.r. detector.

Photo-enhanced chemical vapour deposition of hydrogenated amorphous silicon carbon using an internal discharge lamp

Hydrogenated amorphous silicon carbon (a-Si 1− x C x :H) is becoming an increasingly important technological materials with a wide and controllable bandgap. Using an internal hydrogen lamp, a-Si 1− x C x :H was produced from a mixture of monosilane and methane or acetylene. Raman and TEM measurements showed that these films are highly amorphous with occasional small microcrystals. When using acetylene as the gaseous source of carbon, the refractive index decreases from 3.8 to 2.2 and the bandgap increases from 1.7 to 2.4 eV as the gas ratio ( C 2 H 2 SiH 4 increases from 0.25 to 2.7. When using methane, a CH 4 SiH 4 gas ratio of the order of 10 is necessary to produce a film with a refractive index of 3.0 and the increase in the optical bandgap is limited to 0.3 eV. The photoluminescence peak energy corresponds well to the optical bandgap and the difference between the peak energy and the bandgap remains within 0.3 eV at most. The reaction mechanism of the deposition is discussed.

Low temperature heteroepitaxial growth of Si1−xGexon-Si by photo-enhanced ultra high vacuum chemical vapor deposition using Si2H6 and Ge2H6

Strained-layer Si1×Gex-on-Si heteroepitaxy has been achieved by photolytic decomposition of disilane (Si2H6) and digermane (G e2H6) in an ultra high vacuum (UHV) chamber at substrate temperatures as low as 275°C. An ArF excimer laser (193 nm) shining parallel to the Si substrate was used as the UV light source to avoid surface damage and substrate heating. The partial pressures of the source gases in the reactor were chosen to vary the Ge mole fraction x from 0.06 to 0.5 in the alloy. The Si2H6 partial pressure was kept at 10 mTorr and the Ge2H6 partial pressure was varied from 0.13 to 2 mTorr with the laser intensity fixed at 2.75 × 1015 photons/cm2·pulse. To fit the Si1−xGex growth rate and Ge mole fraction data, the absorption cross section of Ge2H6 at 193 nm was set to 1 × 10−16 cm2, which is 30 times larger than that of Si2H6 (3.4 × 10−18 cm2). For Si1−xGex alloy growth, the deposition rate of Si increases with Ge mole fraction, resulting in increased Si1−xGex alloy growth rates for higher Ge content. The increase of the Si growth rate was attributed to the enhanced adsorption rate of Si2H6 pyrolytically in the presence of Ge, rather than due to photolytic decomposition reaction. The Ge mole fraction in Si1−xGex alloys can be predicted by a new model for Si and Ge pyrolytic and photolytic growth. The model describes the increased growth rate of Si1−xGex alloys due to a Ge2H6 catalytic effect during photo-enhanced chemical vapor deposition.

Silicon interlayer based surface passivation of near-surface quantum wells

In view of the urgent necessity to establish a suitable passivation technology applicable to compound semiconductor quantum structure surfaces, the latest version of the silicon interlayer based passivation process was applied to passivation of Al0.3Ga0.7As/GaAs/Al0.3Ga0.7As near-surface quantum wells (QWs). The process utilizes an ultrathin molecular beam epitaxy silicon/ultrathin photo-enhanced chemical vapor deposition (photo-CVD) silicon nitride double layer as the interface control layer together with a main passivation dielectric of thick photo-CVD SiO2 layer. The effectiveness of passivation was studied by comparing the photoluminescence (PL) intensities of passivated samples with those of unpassivated QWs that showed exponential decrease with reduction of surface-to-well distance. A complete recovery of PL intensity was achieved by passivation with a maximum recovery factor larger than 103, consistent with reduced interface state densities in low 1010 cm−2 eV−1 range recently realized on In0.53Ga0.47As metal–insulator–semiconductor capacitors using the same technique.

Detailed investigation of InSb p-channel metal-oxide-semiconductor field effect transistor prepared by photo-enhanced chemical vapor deposition

An InSb metal-oxide-semiconductor field effect transistor (MOSFET) with three different channel lengths 5, 15 and 30 /spl mu/m was fabricated successfully. The SiO/sub 2/ prepared by photo-enhanced chemical vapor deposition was used both as the gate insulator and the source/drain passivation layer to reduce the source/drain pn junction surface leakage current. The common-source current-voltage characteristics show breakdown voltage exceeding 2 V indicating excellent pn junction reverse characteristics. The capacitance-voltage and the transferred current versus gate voltage characteristics are discussed in detail to explain the geometry effect on the device performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Compositional and electrical properties of Si metal–oxide–semiconductor structure prepared by direct photoenhanced chemical vapor deposition using a deuterium lamp

High quality SiO2 layers have been grown on (111) Si substrates by direct photoenhanced chemical vapor deposition using monosilane (SiH4) and oxygen (O2) as gas sources under irradiation of a deuterium lamp. The refractive index of the deposited oxide is 1.462 at 250 °C when the gas ratio (O2/SiH4) is 5. The measurements of the Fourier transform infrared spectrum, x-ray photoelectron spectroscopy, and Auger electron spectroscopy show that the dominant components of the oxide are silicon and oxygen and the film is SiO2. Hysteresis free capacitance–voltage characteristics of the metal–oxide–semiconductor diode was observed. After low temperature postoxidation annealing, the minimum interface trap density is 1.5×1011 cm−2 eV−1, which is comparable to that of thermal oxidation.

SiO2/InP Structure Prepared by Direct Photo-Chemical Vapor Deposition Using Deuterium Lamp and Its Applications to Metal-Oxide-Semiconductor Field-Effect Transistor

Silicon dioxide ( SiO2) films have been successfully deposited on indium phosphide (InP) substrate at low temperature and low pressure by direct photo-enhanced chemical vapor deposition (photo-CVD) under irradiation by a deuterium lamp. Silane ( SiH4) and oxygen ( O2) are used as reactant sources. The measurements of Fourier transform infrared (FTIR), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) show that the dominant components of the oxide are silicon and oxygen and the film is SiO2. Metal-oxide-semiconductor (MOS) capacitors show sharp interfaces with densities of states in the range of 1.2×1011 cm-2 eV-1. N-channel depletion-mode InP metal-oxide-semiconductor field-effect transistors (MOSFETs) have been fabricated with a transconductance of 63 mS/mm for 2 µ m gate length and an effective channel mobility as high as 1140 cm2 V-1 s-1. High-frequency S-parameter measurements of microwave characteristics for the devices indicate a current-gain cutoff frequency f t=6.3 GHz.

The role of the substrate in photoenhanced metalorganic chemical vapor deposition

A GaAs laser diode has been used as the light source for the selective epitaxial growth of GaAs by photoenhanced metalorganic chemical vapor deposition (PE-MOCVD). The use of GaAs/InGaP layered structures as substrates for these experiments permitted to accurately control the availability of photoexcited carriers reaching the GaAs growth surface. The experimental results obtained rule out pure pyrolysis and photolysis as possible mechanisms responsible for the PE growth rate, and indicate that photoexcited carriers are directly involved in the PE process. The experimental data are consistent with a kinetic model that invokes surface recombination as the main physical mechanism for the PE growth rate effect.

Total Pressure Effects on the Properties of Silicon Nitride Films Fabricated by Photoenhanced Chemical Vapor Deposition

Silicon nitride ( SiNx ) films were deposited on (100)Si substrates using silane and ammonia gases by the direct-photolysis photoenhanced chemical vapor deposition method at 280° C. The depositions were performed with emphasis on the total pressures, which ranged from 0.51 Torr to 4.04 Torr. As the total pressure increased, the film resistivity decreased from 3.7×1015 Ω· cm to 4.8×109 Ω· cm. The effective trapped carrier density at the SiNx /(100)Si interface reached a minimum value (2.1×1010 cm-2) at 1.52 Torr. The film included silicon bonded with silicon (Si–Si) components as well as nitrified silicon (Si–N) components. The Si–Si components increased and the Si–N components decreased in number as the total pressure increased. Based on these results and gas analysis findings, two important reactions to characterize the film properties were discussed.

Effects of O3 on Growth and Electrical Properties of Pb(Zr, Ti)O3 Thin Films by Photoenhanced Metalorganic Chemical Vapor Deposition

Effects of O3 on the growth and electrical properties of Pb(Zr, Ti)O3 (PZT) thin films grown by photoenhanced metalorganic chemical vapor deposition (MOCVD) were investigated. Ferroelectric PZT films were obtained by both MOCVD and photoenhanced MOCVD using O3 at substrate temperatures ranging from 560° C to 625° C. The crystalline orientation, growth rate and growth temperature were not appreciably influenced by the use of O3 and photoirradiation. However, in the leakage current characteristics, an improvement in breakdown voltage by the use of O3 and photoirradiation was observed. From scanning electron microscope (SEM) observations, it was found that this improvement may be caused by the microscopic change in film structure.

Selective growth of GaAs/InGaP heterostrusctures by photo-enhanced organomettalic chemical vapor deposition

Selective epitaxial growth of GaAs on GaAs and In 0.49Ga 0.51P surfaces, using photo-enhanced organomettalic chemical vapor deposition, was investigated. The growth rate dependence on illumination intensity, trimethylgallium partial pressure, and temperature is reported. In-situ patterning and three-dimensional shaping during growth of GaAs/InGaP burried heterostructures, are demonstrated. The experimental results are in good agreement with a simple model, in which the decomposition of absorbed trimethylgallium is assisted by surface recombination of photo-exicited free carriers.

InSb p-channel metal-oxide-semiconductor field-effect transistor prepared by photoenhanced chemical vapor deposition

The InSb metal-oxide-semiconductor field-effect transistor (MOSFET) was fabricated successfully. The SiO2 prepared by photoenhanced chemical vapor deposition was used both as the gate insulator and the source/drain passivation layer to reduce the source/drain pn junction surface leakage current. The common-source current-voltage (I-V) characteristics show a breakdown voltage exceeding 2 V indicating excellent pn junction reverse characteristics. The achieved field-effect mobility for a hole in the linear region is 230 cm2/V s. An anomalous kink effect is observed in the common-source I-V characteristics when the substrate is floating.

Photo-enhanced chemical vapor deposition: System design considerations

ArF excimer laser-enhanced photochemical vapor deposition of Si from Si2H6 in an UHV deposition chamber has been used to achieve Si epitaxy at temperatures as low as 250 °C. The system design criteria are discussed. Modified Schimmel etching/Nomarski microscopy, transmission electron microscopy, and reflection high energy electron diffraction have been used to study the microstructure of Si films as a function of laser power, substrate temperature and disilane partial pressure. The growth rates were observed to be linearly dependent on laser intensity and Si2H6 partial pressure. The morphology of the films is excellent and defects such as dislocation loops and stacking faults are not seen.

Thin Film Growth of Pb(Zr, Ti)O3 by Photoenhanced Metalorganic Chemical Vapor Deposition Using NO2

Ferroelectric Pb(Zr, Ti)O3 thin films were successfully grown by photoenhanced metalorganic chemical vapor deposition (photo-MOCVD), using Pb(C2H5)4, Zr(O-t-C4H9)4, Ti(O-i-C3H7)4 and NO2. Both tetragonal and rhombohedral Pb(Zr, Ti)O3 thin films were obtained at substrate temperatures higher than 535°C. Significant effects of photoirradiation on the growth behavior were observed. The observed effects included an increase in the growth rate and film compositional ratio of Zr/(Zr+Ti), and a change in the electrical properties. A decrease in the growth temperature of the Pb(Zr, Ti)O3 films caused by photoirradiation was observed only when the films were grown at low gas supply ratios of [Zr]/([Zr]+[Ti]). The photodeposited Pb(Zr, Ti)O3 films obtained showed good ferroelectric properties, good leakage characteristic and good step coverage.