Plasma-enhanced Chemical Vapor Deposition Method Research Articles

高周波およびマイクロ波プラズマ励起MOCVD法によるYBaCuO超電導薄膜の作製

Plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) method is developed for preparation of YBaCuO superconducting thin films. The discharge plasmas generated by using rf and microwaves are used to enhance decomposition of source materials of Y(dgm)3, Ba(dpm)2 and Cu(dpm)2. The films are deposited under the conditions; total pressures of 0.6-5 Torr, O2 contents of 0-30% and substrate temperatures of 500-650°C. Most of as-grown films prepared by the two techniques were porous and consisted of crystalline grains. After annealing at high temperatures, the films had c-axis orientations perpendicular to the substrate surface. The post-annealed films deposited by rf PE-MOCVD showed superconducting transition with zero-resistivity temperatures of 85-89K. The excitation temperatures estimated from the spectral line intensity ratios showed weak dependence on process conditions of the PE-MOCVD. However, numbers and intensities of plasma emission spectral lines depended on the oxygen partial pressures and the plasma production technique such as rf and microwave discharge. The results indicate that the as-grown YBaCuO films prepared by the microwave PE-MOCVD method have smooth surface and superconducting property with c-axis orientations.

Visible photoluminescence in crystallized amorphous Si:H/SiNx:H multiquantum-well structures

Visible photoluminescence has been observed in crystallized a-Si:H/a-SiNx:H multiquantum-well structures at room temperature. The MQW heterostructures consisting of 72 layers were formed by computer controlled plasma-enhanced chemical-vapor deposition method and then crystallized by Ar+ laser annealing technique. The crystallinity and average grain size of the silicon microcrystals were determined by means of Raman and x-ray diffraction spectroscopy. The crystallized samples with well-layer thickness Ls=40 Å showed an intense photoluminescence which is peaked at 2.1 eV with a full width at half-maximum of 0.25 eV. This is consistent with calculations based on the quantum confinement model.

Low-temperature silicon nitride: a promising dielectric in semiconductor technology

We obtained thin dielectric solid films of SiN x :H on Si(100). The deposition was carried out from a gas mixture of SiH 4NH 3N 2 using an r.f. plasma discharge (450 kHz) at 293 < T < 400 K, where T is the substrate temperature. We studied the properties of the films by means of scanning electron microscopy, IR spectrocopy, Auger electron spectroscopy, electron energy-loss spectroscopy, and X-ray photoelectron spectroscopy. We also measured the porosity, capacitance-voltage curves and breakdown strength of the metal-nitride-silicon capacitor. We show that for low-temperature films (297 K), x changes within the limits 0.65–0.90. The mechanical strength and dielectric properties of the low-temperature films are comparable with those of silicon nitride films deposited by the conventional plasma-enhanced chemical vapour deposition method at 475–613 K.

Relationship between electrical properties and structure in uniaxially oriented polycrystalline silicon films

Undoped polycrystalline Si (poly-Si) films were prepared on a fused quartz substrate as a function of the rf power (0–30 W) and deposition temperature (620–770 °C) by a plasma-enhanced chemical vapor deposition method. The preferential orientation to a random, 〈100〉 or 〈110〉 crystal axis can be selected by changing some of these preparation conditions. Electron spin resonance (ESR) and the dependence of the dark conductivity σd on the measurement temperature T have been investigated to examine how the structure of the grain boundary depends on the preferential orientation (P.O.) and affects the electrical properties. An enhancement in the degree of P.O. is found to lead to a reduction in the local ESR spin density within the boundary region and g factor. Also, for the films with a random or weak P.O., σd as a function of 1/T exhibits a kink around room temperature, and the conduction in a low-T range is interpreted in terms of the model of variable range hopping within the boundary region. These results and the characteristics of thin-film transistors fabricated on the poly-Si films are discussed in terms of the structural change of the boundary region.

A-Si:H position-sensitive detector with striped metal electrodes

A novel dual-axis tetralateral position-sensitive detector (PSD) has been fabricated with a hydrogenated amorphous silicon (a-Si:H) p-i-n structure. The a-Si:H film for a photocurrent generator is formed by a plasma-enhanced chemical vapour deposition (PECVD) method. The PSD has striped metal electrodes formed by a chromium resistive layer on its photosensitive surface. It is confirmed from the experimental data that the PSD has very good linearity with the detected positions for both axes and that it can determine the positions of two or more incident light spots simultaneously if they illuminate different electrode stripes.

Structure and Properties of Silicon Titanium Oxide Films Prepared by Plasma-Enhanced Chemical Vapor Deposition Method

We have developed a novel material of silicon titanium oxide with high dielectric constant and low leakage current. The silicon titanium oxide films were prepared by plasma-enhanced chemical vapor deposition (plasma CVD) with the gas mixture of TiCl4-SiH4-N2O. It was found that these films have intermediate properties of silicon dioxide and titanium dioxide by varying the ratio of SiH4/(SiH4+TiCl4). The properties of silicon titanium oxide nearly corresponded to those of Ta2O5 when the gas mixture ratio was 0.075, with a dielectric constant of 18 and a leakage current density of 2.5×10-8 A/cm2 at 1 MV/cm.

New method to suppress encroachment by plasma-deposited β-phase tungsten nitride thin films

&amp;lt;m1;40p&amp;gt;Tungsten nitride thin films are prepared with the WF6-NH3-H2 system by the plasma-enhanced chemical vapor deposition method. X-ray diffraction and Auger spectroscopy show that the crystal structure and the composition of tungsten nitride thin films grown at the WF6/NH3 ratio of 1 are β-phase W2N. The resistivity of W2N is about 190–210 μΩ cm and it is demonstrated that severe encroachment and SiO2 etching during the low-pressure chemical vapor deposition of tungsten is remarkably suppressed by the predeposition of W2N.

Development of the quadrupole plasma chemical vapour deposition method for low temperature, high speed coating on an optical fibre

For the purpose of low temperature, high speed coating fine wire such as a heavy metal fluoride optical fibre, we have developed a new plasma-enhanced chemical vapour deposition method using quadrupole electrodes. We have investigated fundamental discharge characteristics in a 10% CH 4H 2 gas and measured the substrate temperature using the temperature dependence of the electrical resistance to verify the low temperature process. The substrate temperature could be kept below the glass transformation temperature of about 300 °C by cooling the electrodes. A magnetic field was applied perpendicular to the discharge electric field to increase the neutral radical species which were generated by collision with electrons (the magnetron effect). Then the CH ∗ optical emission intensity from the centre of the quadrupole electrodes has a maximum value for some value of the magnetic flux density. The trial preparation of an amorphous carbon thin film on an optical fibre was successfully performed. The above results are very useful to obtain low temperature, high speed coating on fibre materials.

Averaging effect of radical particle profile by the scanning plasma method in SiH 4Ar plasmas

A new plasma-enhanced chemical vapour deposition (PECVD) method has been developed for preparation of large-area uniform hydrogenated amorphous silicon (aSi:H) thin films. Detailed two-dimensional profiles of both charged particles and radical particles have been measured in magnetized multielectrode glow discharge plasmas in 10% SiH 4Ar gas. The detailed profiles of SiH ∗ and Ar I emissions had two peaks in the negative glow and cathode sheath regions but, for Hα emission, only one peak was observed in the cathode sheath region. It was verified that large-area uniform profiles of not only plasmas but also SiH ∗ emission could be realized in the presence of modulated crossed magnetic and electric fields. By using this scanning plasma method (SPM), inhomogeneities for both profiles of plasma and SiH ∗ (413.5 nm) emission intensity have improved to less than 2.5% near the substrate outside the discharge region. The thickness profile of prepared a-Si:H thin film has also been unified to less than 4.8% by SPM.

Plasma impulse chemical vapour deposition—a novel technique for the production of high power laser mirrors

Chemical vapour deposition (CVD) methods are known to be most advantageous for the production of very high quality optical materials ( i.e. performs for low loss fibres or high damage threshold, and reflection coatings on thin fibres). It is also well known that plasma-enhanced CVD methods show improved deposition efficiencies. Pulsed microwave plasmas (2.45 GHz) are used to realize interference filters with very high laser damage threshold as well as high reflection. The impact of the coating temperature on the layer quality is discussed. The high deposition rate together with the almost monolayer-by-monolayer growth control in the pulsed plasma mode is suitable for producing extreme small-band, high reflection coatings, which have no harmonics. By almost individual shaping of the refractive index distribution within one λ/4 layer a new degree of freedom in the design of these coatings has been accomplished. The theoretical background as well as experimental results are discussed.

Optical channel waveguide fabrication based on electron beam irradiation of silica

The bombardment of silica by low-energy electrons induces compaction and an increase in refractive index. We have used this phenomenon, combined with photolithographic processing, to make channel waveguides in silica, most of which are monomode, with a depth of 2–7 μm, and peak index variation between 10−3 and 10−2. Channel waveguide widths down to 2 μm have been fabricated on fused silica plates and on silica layers grown on silicon by plasma-enhanced chemical vapor deposition (PECVD) methods. The lowest measured linear losses at 633 nm were 0.3 db/cm in PECVD silica and 1.9 db/cm in the fused silica plates, although much lower losses are anticipated in the latter material. Using this method we have fabricated 3 dB directional couplers in both materials.

High-temperature Schottky diodes with thin-film diamond base

High-temperature (500-580 degrees C) current-voltage (I-V) characteristics of gold contacts to boron-doped homoepitaxial diamond films prepared using a plasma-enhanced chemical vapor deposition (CVD) method are described. Schottky diodes were formed using gold contacts to chemically cleaned boron-doped homoepitaxial diamond films. These devices incorporate ohmic contacts formed by annealing Au(70 nm)/Ti(10 nm) layers in air at 580 degrees C. The experiments with homoepitaxial diamond films show that the leakage current density increases with the contact area. This implies that a nonuniform current distribution exists across the diode, presumably due to crystallographic defects in the diamond film. As a result, Au contacts with an area >1 mm/sup 2/ are essentially ohmic and can be used to form back contacts to Schottky diodes. Schottky diodes fabricated in this matter also show rectifying I-V characteristics in the 25-580 degrees C temperature range. >

The Effect of Amorphous Silicon Layer in Pe-Cvd Titanium Polycide Gate Dielectrics

ABSTRACTTitanium silicide (TiSix), used as polycide gate consists of TiSi1.1 and amorphous silicon (a-Si), was deposited by Plasma Enhanced Chemical Vapor Deposition method (PE-CVD). The effect of a-Si layer in PE-CVD Ti polycide gate dielectrics has been studied. In order to evaluate the a-Si layer effect, three types of samples were prepared on gate SiO2 film with following structures : a) a-Si / TiSi-1.1 / a-Si / phosphorus (P) doped poly-Si, b) a-Si / TiSi-1.1 / non-doped poly-Si / P doped poly-Si and c) a-Si / TiSi1.1 / P doped poly-Si, respectively. Furthermore, in order to avoid the influence of native oxide existence at the interface, the pre-cleaning treatment was performed in-situ on the poly-Si film surface before TiSi1.1 film deposition. The gate dielectric strengths of these samples indicate that the gate dielectric degradation in PE-CVD Ti polycide gate is greatly dependent on Si under layer crystallization. It is effective using a-Si film as the under layer in decreasing the gate dielectric degradation . This is due to the Ti oxide interlayer, formed at the interface of TiSi2.0 and poly-Si films, which restrains the TiSix local penetration.

On epitaxial growth of diamond films on (100) silicon substrates

We have investigated characteristics of polycrystalline diamond thin films formed by plasma-enhanced chemical vapor deposition method on silicon substrates using Raman spectroscopy, analytical and high-resolution transmission electron microscopy techniques. Grains with average size 1 μm in diameter were observed in these films. The Raman spectra from these films contain the strongest peak at 1335 cm−1, providing the characteristic signature for sp3 (diamond) bonding. The broad peak centered around 1550 cm−1 is believed to be due to some graphitic bonding. From detailed high-resolution images and microdiffraction, films were characterized to be cubic diamond with a lattice parameter of 3.56 Å. Diamond crystallites with fivefold external morphologies were also observed. The large crystallites in the films exhibited preferential texture in 〈011〉 type orientations. These crystallites were found to be twinned in {111} planes. The large 〈011〉 crystallites exhibited matching in {111} or {200} lattice planes of diamond with {022} planes of silicon. This is in agreement with our previous work on the growth of Ni on MgO, which showed that textured growth can occur by matching a set of lattice planes in the absence of matching of lattice constants.

Characterization of silicon nitride films formed in an RF glow discharge

Silicon nitride (SiN) thin films have been deposited using radio frequency (RF) sputtering and plasma enhanced chemical vapor deposition (PECVD) methods. The RF sputtering is carried out in a mixture of Ar and N 2 gases with a Si 3N 4 target. In the PECVD method, a mixture of SiH 4 and NH 3 gases is decomposed by a glow discharge (GD). The relations between the deposition parameters and the properties of the SiN films are investigated for both methods. The formed films are characterized by measurements of refractive index, optical band gap and infrared absorption. The results indicate that the refractive index of RF sputtered films changes from that of pure Si to that of Si 3N 4 formed by a thermal decomposition method as the flow rate of N 2 gas increases, while the optical band gap does not expand. On the other hand, the refractive index of PECVD films is nearly constant under various conditions and is less than that of Si 3N 4, and the optical band gap increases with an increase in the flow ratio of NH 3 to SiH 4. Moreover, the infrared absorption spectra show several bonding modes in the films such as Si-N, Si-H, N-H stretching and N-H, N-H 2 bending modes, and the peak intensities change depending on the deposition conditions. It is suggested from the results that the PECVD films correspond to Si(NH) 2 rather than Si 3N 4. The results obtained by Auger electron spectroscopy and Raman spectroscopy are also used for the discussion.

A comparison of different deposition techniques for fabricating polysilicon contacted emitter bipolar transistors

Four methods for fabricating polysilicon contacted bipolar junction transistors (BJT’s) have been investigated. In the first method polysilicon was deposited using low-pressure chemical vapor deposition (LPCVD) at 620 °C. In the remaining three methods a-Si was first deposited and then recrystallized to form polysilicon. In the second method a-Si was deposited using LPCVD at 580 °C. The third method used plasma-enhanced chemical vapor deposition (PECVD) to deposit a-Si:H. The fourth method involved a plasma etch with argon or hydrogen prior to deposition of a-Si:H using PECVD. The results indicated that using the PECVD method for depositing a-Si:H without any prior plasma-etch step and recrystallizing it to form polysilicon resulted in the highest current gain (β) enhancement of 3.5 and also allowed the reduction of the polysilicon anneal temperature down to 800 or 900 °C from 1000 °C. The compactness in the spread of the peak β values for the devices fabricated using this technique also reflects its ability for reproducible fabrication of polysilicon contacted shallow emitter BJT’s.

Direct-current hollow-cathode glow-discharge plasma-enhanced-chemical-vapour-deposition technique for a-Si:H thin-film production

The direct-current hollow-cathode glow-discharge plasma-enhanced-chemical-vapour-deposition (PCVD) technique has been developed for the production of a-Si:H thin films. The electric conductivity, deposition rate, and optical characteristics of films produced by this method are similar to those of films produced by the conventional RF-discharge PCVD method. However, the properties of the former can be easily controlled by the discharge current without external substrate heating. The power consumption per deposition rate is much smaller than the microwave methods; but similar to that which is characteristic of RF-discharge methods.

Sputtering and chemical vapour deposition of piezoelectric ZnO, AlN and K 3Li 2Nb 5O 15 films for optical waveguides and surface acoustic wave devices

Epitaxial and c-axis-oriented ZnO thin films with surface flatness were successfully grown on various kinds of substrate by r.f. planar magnetron sputtering, ZnOH 2H 2OO 2 isothermal chemical vapour deposition (CVD) and plasma-enhanced organometallic CVD methods. c-axis-oriented AlN films were also prepared on glass and silicon substrates at substrate temperatures as low as 20–460°C by reactive r.f. planar magnetron sputtering. Furthermore, ferroelectric K 3Li 2Nb 5O 15(KLN) crystal films were grown with good epitaxy on K 2BiNb 5O 15 or sapphire substrates by sputtering. The quality of the ZnO, AlN and KLN films was evaluated from X-ray diffraction, scanning electron microscopy and reflection electron diffraction measurements. These films are excellently transparent and are of extremely good quality. The epitaxial CVD and c-axis-oriented sputtered ZnO films have guided optical wave losses as low as 0.7 dB cm −1 and 2.1 dB cm −1 respectively. All the films are piezoelectrically active and show surface acoustic wave response.