Chemical Vapor Deposited SiO2 Films Research Articles

Enhancement of reliability and stability for transparent amorphous indium-zinc-tin-oxide thin film transistors

The influence of a backchannel passivation layer on the ambient stability of amorphous indium-zinc-tin-oxide thin-film transistors was studied. The ALD Al2O3 films and plasma-enhanced chemical vapor deposited SiO2 films were separately used as channel passivation layers.

Variation of Chemical Vapor Deposited SiO2 Density Due to Generation and Shrinkage of Open Space During Thermal Annealing

Chemical vapor deposited (CVD) SiO2 using tetraethoxysilane has a low density compared with thermally grown SiO2, and the as-deposited film contains impurities. In addition, compressive stress exists in the Si–O–Si network. In this work, CVD SiO2 films annealed with various thermal budgets were evaluated using ellipsometry. Positron annihilation spectroscopy indicated that the desorption of residual impurities by thermal annealing generates open spaces in the films. Subsequent annealing shrinks the open spaces and relaxes the compressive stress with reconstruction of the Si–O–Si network. Consequently, the refractive index of CVD SiO2 shows turn-around characteristics with increasing annealing temperature.

Improvement in Chemical-Vapor-Deposited-SiO2 Film Properties by Annealing with UV-Light-Excited Ozone

Ultraviolet-enhanced, highly concentrated (>90 vol %) ozone gas annealing was carried out at 200 °C to fabricate as-deposited tetraethoxysilane chemical vapor deposited SiO2 film (TEOS-CVD films) applicable as a gate dielectric material for thin-film transistors. As a result of this annealing, the leakage current density, fixed charge density, and dielectric constant of the films decreased to those of thermally grown silicon oxide. The relative dielectric constant, for example, was reduced from 5.4 to 4.0. The films' resistance to wet-etching solution was also improved, particularly within the region located 3–5 nm from the films' surface. In the region, the reduction in the amount of the excess positive charges of Si and the increase in the density of an ideal Si–O bonding network were confirmed from X-ray photoelectron spectroscopy measurements. These results suggest that oxygen atoms are incorporated into the film, while impurities contained in the film such as OH are out gassed by the diffusion of oxygen atoms generated from the photo dissociation of ozone in the gas phase. The annealing effects with and without oxygen atom supply were compared and the mechanism of the annealing is discussed.

The Effect of Stress on Solid-Phase Epitaxial Regrowth in As+-Implanted Two-Dimensional Amorphized Si

The effect of stress induced by a chemical-vapor-deposited (CVD) SiO2 film on the solid-phase epitaxial (SPE) regrowth in As+-implanted, two-dimensional amorphized Si has been studied. Trench structures were used to form the two-dimensional amorphous layer and to induce the stress in the Si substrate. As+ implantation at an energy of 80 keV with a dose of 3×1015/cm2 amorphized the silicon surface and produced a curved amorphous/crystalline (a/c) interface under the bottom corner of the trenches. At the trenches filled with the high-tensile-stress CVD SiO2 film, the regrowth of the amorphous Si layers was retarded and a notch remained in the a/c interface immediately under the bottom corner of the trench after annealing at 500°C for 4 h. The regrowth retardation and the remaining notch were explained by the effect of the stress induced by the CVD SiO2 film on the activation barrier of the SPE regrowth.

High-Quality CVD/Thermal Stacked Gate Oxide Films with Hydrogen-Free CVD SiO2 Formed in a SiCl4–N2O System

We have developed and evaluated chemical vapor deposition (CVD) SiO2 films formed in a hydrogen-free system in which tetrachlorosilane ( SiCl4; TCS) and nitrous oxide ( N2O) are used as low pressure CVD source gases. It has been found that the hot-carrier degradation, the constant current time-dependent dielectric breakdown (TDDB) and the charge-trapping characteristics are superior to those of conventional CVD SiO2 films formed from dichlorosilane ( SiH2Cl2; DCS) and N2O. We have concluded that TCS–SiO2 is appropriate for CVD stacked gate oxide films due to its low electron trap density and high reliability.

Characterization of Charged Traps near Si–SiO2 Interface in Photo-Induced Chemical Vapor Deposited SiO2 Film

Charged traps near the Si–SiO2 interface in a SiO2 film deposited by photo-induced chemical vapor deposition (photo-CVD) have been analyzed by the photo I–V method. In the as-deposited film, positively charged traps distribute in the region between 2 nm and 10 nm from the Si–SiO2 interface, and their density decreases monotonically with increasing depth. The density of traps in the region between 2 nm and 4 nm is decreased by annealing in N2 or O2, and that of traps in the region between 4 nm and 10 nm is decreased only by annealing in O2. Furthermore, the results of electron spin resonance (ESR) analysis suggest the possibility that the positively charged traps in the 2–4 nm region are related to the defects observed in ESR.

Structural properties of low temperature plasma enhanced chemical vapor deposited silicon oxide films using disilane and nitrous oxide

The structural properties of low temperature plasma enhanced chemical vapor deposited SiO2 films using Si2H6 and N 2O have been studied. It is observed that the degree of compaction of as-deposited SiO2 films, upon subsequent annealing, increases up to 4%. The shift of Si-O-Si stretching peak wave number of the as-deposited SiO 2 films (Δω=−20 cm−1) compared to the undensified SiO 2 films is attributed to 9.4% increase in the film density, resulting in smaller Si-O-Si bridging bond angle of 138°. It is also believed that the high temperature annealing results in the reduction of hydroxyl containing species in the film and in turn drives the dielectric constant towards that of thermal SiO2 films.

Process-Induced Defects in InP Caused by Chemical Vapor Deposition of Surface Passivation Dielectrics

Near-surface defects of InP produced during three different chemical vapor deposition (CVD) processes were systematically characterized by capacitance-voltage ( C-V ) and deep level transient spectroscopy (DLTS) techniques. Deposition of plasma-enhanced CVD (PECVD) phosphosilicate glass (PSG) and SiO2 films produced the same bulk level, lying at 0.35 eV below the conduction band edge, near the surface region of InP. Such a level was absent in the samples prepared by the photo CVD process. In addition, the photo CVD process gave a lower density of interface states than the PECVD process. The origin of the bulk trap and the energy- and space-distributed nature of interface states are discussed.

Characterization of Water as an Impurity in SiO2 Films Deposited on Si by Chemical Vapor Deposition Using Si(OC2H5)4.

SiO2 films (thickness : 500 nm) deposited on Si(100) by plasma- and thermal-assisted chemical vapor deposition (CVD) using tetraethylorthosilicate (TEOS) were studied by Fourier transform infrared spectroscopy (FTIR), etch rate, and variable-energy positron annihilation spectroscopy. As the substrate temperature at deposition was raised, the density of the SiO2 films increased and the Si-OH impurity content decreased. On the other hand, Si-OH impurities in the SiO2 films could not be removed even at a substrate temperature of 440°C The Si-OH content in plasma-assisted CVD SiO2 films was much lower than that in thermal-assisted CVD SiO2 films at the same substrate temperature. It was found from FTIR and the positron study that the water tended to exist as Si-OH clusters, whose surroundings had more open space than those of normally bonded O3≡Si-O-Si≡O3.

An all refractory NbN Josephson junction medium scale integrated circuit process

The fabrication and electrical performance of an all refractory, eight mask step, NbN medium scale integrated circuit process are discussed. In situ rf sputter deposited trilayers of NbN/MgO/NbN are plasma etched to fabricate Josephson junctions. A novel low temperature, plasma enhanced chemical vapor deposited SiO2 film is used for wiring and resistor insulation. Sputter deposited molybdenum films are used for resistors. Tunnel junctions fabricated with this process have Vm=61 mV at jc=1100 A/cm2, and Vg = 5.1–5.2 mV at 4.2 K. Critical currents are uniform to within ±3% for 101 junction strings and are within ±25% over all die on 3 in. wafers. This process has been used to fabricate 8-bit single flux quantum counter circuits, squid magnetometer circuits, 870 junction strings, and arrays of 256 squids. Preliminary circuit testing indicates operation at temperatures within the range of small closed-cycle refrigerators.

E′ centers and nitrogen-related defects in SiO2 films

We have observed an electron paramagnetic resonance signal corresponding to a neutral fourfold coordinated nitrogen in plasma-enhanced chemical vapor deposited SiO2 films fabricated under certain conditions. The same films contain E′ centers (positive oxygen vacancies) in an equal quantity. Our data support a model in which these two paramagnetic centers are created simultaneously by an electron transfer, starting from a positive fourfold nitrogen and a neutral oxygen vacancy. This model allows an earlier observation of an apparently neutral E′ variant to be interpreted as a normal positive E′ plus a nitrogen center to conserve charge.

Trapped positive charge in plasma-enhanced chemical vapor deposited silicon dioxide films

We report an investigation of trapped positive charge in as-fabricated plasma-enhanced chemical vapor deposited SiO2 films using electrical and spin resonance techniques. We show that the positive charge results from donor-like ‘‘slow’’ interface states (‘‘anomalous positive charge’’) rather than trapped holes, and that most (∼95%) of the positive charge is not related to E′ centers. The positive charge is similar to that seen in electron-injected thermally grown SiO2, and unlike radiation-induced trapped holes.

Soft x-ray photoemission study of downstream plasma enhanced chemical vapor deposited SiO2

The distribution of Si oxidation states in 1.7-, 2.0-, and 3.0-nm-thick downstream plasma enhanced chemical vapor deposited SiO2 film upon Si has been studied by soft x-ray photoemission, using synchrotron radiation. The spectra from the as-deposited 3.0-nm-thick oxide show two prominent Si oxidation states, the Si4+ and the Si3+, with the Si3+ oxidation state preferentially located at the oxide vacuum interface. The Si3+ state is considerably larger than that observed in thermal SiO2 and is radiation and thermally sensitive, partially converting to the Si4+ state during annealing and extended irradiation. The analysis of the photoinduced conversion from the Si3+ to the Si4+ oxidation state suggests that the paramagnetic component of the Si3+ structure matrix can be correlated with the structure of the E′ defect center, as measured by electron spin resonance. A model is proposed for the SiO2 deposition mechanism whereby a temperature activated surface oxidation of the Si3+ structure is taking place.

An investigation of hydrogen concentration profiles in as-deposited and annealed chemical vapor deposited SiO2 films

Hydrogen concentration depth profiles in as-deposited and annealed chemical vapor deposited silicon oxide [2% P glass, 8% P glass, tetraethylorthosilicate (TEOS), phosphorous-doped TEOS and plasma oxide] films were measured using the nuclear reaction profiling technique with a 6.4 MeV 15N ion beam. The H2/Ar annealing of 450 °C for 60 min in furnace and the rapid thermal annealing at 1000 °C for 60 s in O2 or H2/Ar were carried out. It is found that hydrogen concentration is in the range 1021–1022 per cm3 in as-deposited films. Annealing at high temperatures, even in hydrogen containing medium, lowers the hydrogen concentration in all films. The hydrogen concentration gradually increased with time when the films were left in the room environment. The electrical properties of the oxide are found to be related to the presence of hydrogen. The observed correlation between the flatband voltage and the hydrogen concentration is presented and discussed.

Electron-beam evaporated phosphosilicate glass encapsulant for post-implant annealing of GaAs

Electron-beam deposited films of phosphosilicate (PSG) have been investigated as dielectrics for the encapsulation of Si-implanted GaAs for the purpose of post-implant annealing. The processing parameters that were optimized included the thickness of PSG film, the substrate temperature, and the annealing time and temperature. PSG films deposited at temperatures ≥300 °C showed no signs of deterioration up to temperatures in excess of 900 °C for 30-min anneals carried out in a forming gas and/or nitrogen ambient. Depth profiles in excellent agreement with the Lindhard–Scharff–Schiott curves were obtained with 1000-Å-thick films when annealed at 850 °C for 30 min. The diffusion coefficient of implanted silicon was found to be an order of magnitude smaller for the PSG films than that for the conventional plasma assisted chemical vapor deposited SiO2 films at 850 °C.

Silicon-ion implantation in InP and annealing with CVD SiO2 encapsulation

Silicon-ion implantation in semi-insulating Fe-doped InP has been investigated. Chemical vapor deposited (CVD) SiO2 encapsulation film for annealing of the Si-implanted layer has been investigated by Auger electron analysis. It indicated that by selecting deposition condition, CVD SiO2 films can be used effectively as an annealing encapsulant of InP. The electrical activation of 80% was realized at 750 °C annealing for doses ranging from 6×1012 to 3×1014 cm−2 at 350 keV. Depth profiles after annealing were found to be close to the Lindhard-Scharff-Schiott (LSS) theory, with no redistribution of implanted Si by the annealing process. Anomalous behavior in activation efficiency was found at relatively low doses of the order of 1012 cm−2, and it is considered to be due to compensation by Fe in the substrate.

Electromigration in Aluminum Film Stripes Coated with Anodic Aluminum Oxide Films

The effect of an anodic-Al2O3-coating on the electromigration lifetime of Al stripes is investigated. Experiments show that the mean time to failure (MTF) of Al stripes is significantly increased by the presence of the anodic Al2O3 on stripe-surfaces. In particular the most effective structure of anodic oxide film for MTF is constructed by double layers of porous and composite oxides. It is also observed that coating with the double layers of alumina films has an effect greater than that with chemical-vapor deposited SiO2 films, and that the Al stripes coated with either alumina or SiO2 films have the same activation energy as Al stripes without coating. The observed difference in MTF-improvement can be explained by the difference of mechanical characteristics of the coating films.