Vapour-deposited silicon dioxide for device applications

Silicon dioxide layers deposited from the vapour phase at low temperatures are extensively applied in integrated circuit technology. Applications include doped oxide diffusion sources, protective layers and cross-over insulators in multilevel metallization systems.In this paper we show the feasibility of obtaining a SiO₂Si interface whose electrical characteristics closely approach those of thermally grown SiO₂Si sandwich structures. Interface state densities lying in the low 10¹⁰ cm^?2 eV^?1 range have been determined from quasi-static C(V) measurements. The results of excess noise measurements made on deposited gate oxide and thermally grown gate oxide MOSFETs are in reasonable agreement with the interface state density measurements. C(V) dispersion and C(V) hysteresis measurements prior to and after exposure to 10⁷ rad of ⁶⁰Co γ radiation are also presented. Potential applications of low temperature vapour-deposited oxides include the silicon on insulating substrate (SOS) technology where it is generally desirable to minimize high temperature processing steps. Other applications are in the field of impurity profile determinations using the MOS capacitor method. In these applications one desires to measure the original profile without having to deal with the additional complication of the diffusion and redistribution phenomena that occur unavoidably during high temperature thermal oxide growth.     

Direct measurement of the direction of interface motion in the oxidation of metals and covalent solids—Al(111) and Si(100) oxidation with O2 at 300 K

Four point probe measurements of the surface electrical resistance at an oxide film-metal interface and at an oxide-film semiconductor interface have shown with Å sensitivity that the direction of the buried interface motion during oxide film growth is opposite in the two cases in accordance with the Mott-Cabrera theory. During the formation of amorphous Al₂O₃ layers on Al(111) at 300 K, outward film growth occurs due to Al³⁺ ion transport from the metal into the growing oxide film. For the formation of amorphous SiO₂ layers on Si(100) at 300 K, oxygen transport occurs inwardly into the Si lattice as the oxide film forms.     

Interface states in MNOS systems

The quasistatic C-V technique can be used under certain conditions to obtain the energy distribution of the interface states located in the silicon band gap of an MNOS system. An increase of the SiO₂ thickness leads to a considerable decrease in the interface state density around the mid-gap. It is shown that, for the thin oxide MNOS capacitors we measured, the Si₃N₄SiO₂ interface dominates over the SiSiO₂ interface in producing interface states with a high density.     

Depth redistribution of components of SiOx layers prepared by magnetron sputtering in the process of their decomposition

The process of thermal decomposition of SiO_x layers prepared by magnetron co-sputtering of Si and SiO₂ on Si and quartz substrates is studied by Auger and secondary ion mass spectroscopies. It is found that high temperature annealing of the layers causes a Si-depleted region near the layer/substrate interface. It is shown that the formation of this region does not depend on the type of substrate but depends on the content of excess Si and is observed at high content of excess Si. When the excess Si content decreases, the Si-depleted region at first smears and then disappears. The mechanism of SiO_x decomposition and possible reasons for the appearance of the Si-depleted region are discussed.     

Tunable SiO<Subscript>2</Subscript>/Si-based nanostructures

We model the formation of a nanoscale potential well with quantum wires on the semiconductor surface near the SiO₂/Si interface owing to a special charge distribution in the oxide. We consider an SiO₂/Si structure in the form of a cylindrical substrate covered with a coaxial oxide layer. The charge distribution in the oxide is taken to have the form of charged circular rings of finite thickness, coaxial with the cylindrical substrate. The parameters of the quantum wires are analyzed in relation to the charge distribution and density. Reducing the separation between two charged rings decreases the width of the quantum wires produced on the semiconductor surface and increases their depth.     

Glass coatings in fission and fusion reactor environments

Secondary ion mass spectrometry measurements on silicon substrates oxidized in trichloroethylene-oxygen showed a narrow chlorine distribution (halfwidth 14±1 nm) in the SiO₂ near the SiSiO₂ interface. The total amount of chlorine correlated with the passivation against sodium ions but not with surface state and fixed oxide charge densities. Measurements on carbon tetrachloride-oxygen oxides were made for comparison.     

Line-shape extraction analysis of silicon oxide layers on silicon by channelling effect measurements

A technique of line-shape extraction has been developed and applied to find the number of Si atoms and O atoms per square centimeter of anodically grown and thermally oxidized silicon oxide layers. Back-scattering and channelling effect measurements with 0.3-2.0 MeV ⁴He⁺ ions were used. The thicknesses of the silicon oxide investigated ranged from native oxide thickness to 1500 Å. For all thicknesses the composition was found to be silicon-rich, with the number of Si atoms per square centimeter equal to one-half the number of oxygen atoms per square centimeter plus (0.8-1) × 10¹⁶ Si/cm². We propose that the oxide layer is stoichiometric SiO₂ with a silicon-rich transition region between the oxide layer and the crystal substrate. The presence of such a transition region at the interface should be considered when evaluating the composition of dielectric layers on semiconductors.     

Measurement of the interlayer between aluminum and silicon dioxide using ellipsometric,capacitance-voltage and auger electron spectroscopy techniques

Ellipsometric and capacitance-voltage measurements were combined to detect both the AlSiO₂ interlayer and the SiSiO₂ interlayer for the Si/SiO₂/Al system. The AlSiO₂ interlayer was characterized by Auger electron spectroscopy (AES), combined with argon ion sputter profiling, of the Al/SiO₂/Si structure and also of the remaining SiO₂/Si structure after the aluminum had been chemically removed. An effective interlayer thickness is defined as the product of the interlayer thickness and the fractional change in the dielectric SiO₂ constant. The results of these experiments indicate that the Alz.sbnd;SiO₂ effective interlayer thickness has a range of 0.1–0.5 nm. The AES data can be readily interpreted if it is assumed that collision cascade mixing and recoil implantation occur as a consequence of sputter depth profiling through the aluminum.     

Gold catalysts for the abatement of environmentally harmful materials: Modeling the structure dependency

FeO_x, TiO₂ and CeO_x layers were deposited by pulsed laser deposition (PLD) technique onto Au films or Au nanoparticles supported on SiO₂/Si(100). The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and their reactivity was studied in catalytic CO oxidation. Comparison was made with reference samples of FeO_x/SiO₂/Si(100), TiO₂/SiO₂/Si(100), CeO_x/SiO₂/Si(100) and Au/SiO₂/Si(100) layers. The catalytic activity of the metal-oxide/Au/SiO₂/Si(100) samples must be attributed to active sites located on the metal-oxides overlayer modified by gold underneath, since no Au was exposed to the surface according to the XPS and SIMS. We found a promoting effect of gold on the catalytic activity of the FeO_x overlayer and an inhibiting effect of gold on the TiO₂ and CeO_x overlayers. These findings are discussed in terms of electronic interactions at the Au/metal oxide interface.     

Electrical and photovoltaic properties of tin oxide-silicon heterojunctions

SnO₂-Si heterojunctions, using n-type and p-type single crystals of silicon, were fabricated by depositing tin oxide using a chemical vapour deposition technique. The electrical and photovoltaic characteristics of these heterojunctions were investigated. The polarity observed in V_oc and I_sc is consistent with the band bending of a simple SnO₂Si heterojunction energy band diagram, neglecting interface states. The results also show that the (n?n) SnO₂Si heterojunction has better electrical and photovoltaic characteristics than the (n?p) SnO₂Si heterojunction. Typical values of V_oc and J_sc (under Air Mass 1 conditions) for an (n?n) SnO₂Si heterojunction are 0.485 V and 16.0 mA cm^-2 respectively, resulting in an efficiency of nearly 5%.     

Electrical properties of bulk silicon dioxide and SiO2/Si interface formed by tetraethylorthosilicate (TEOS)-oxygen plasma enhanced chemical vapor deposition

The electrical properties of bulk silicon dioxide and the SiO₂/Si interface formed by TEOS/O₂ PECVD were investigated. Additionally, the gas phase in the glow discharge was investigated using OES analysis under various experimental conditions. Changes of TEOS/O₂ ratio and the deposition temperature influenced the electrical properties of silicon oxide films. With decreasing TEOS/O₂, ratio, the electrical properties of bulk silicon dioxide and the SiO₂/Si interface were improved. This is thought to be due to the decrease of carbon impurity in the growing oxide film. At higher deposition temperatures, the oxide films had good electrical properties, which is thought to be due to the change of structure in the oxide film. From C–V analysis for all experimental conditions, the P_b center defects were observed near E_v+0.25eV and E_v+0.73eV in the Si band gap. The magnitude was influenced by process parameters such as the TEOS/O₂ ratio and the deposition temperature. From OES analysis, the main emission peaks observed in the glow discharge were from CO, CO ₂ ⁺ , CH, and C. With decreasing TEOS/O₂ ratio, the emission intensity of CH decreased and that of CO increased.     

Structural, optical and electrical properties of high-k ZrO2 dielectrics on Si prepared by plasma assisted pulsed laser deposition

ZrO₂ films were grown on p-type Si(100) using plasma assisted pulsed laser deposition and the electrical characteristics of the ZrO₂ dielectrics incorporated in metal oxide silicon (MOS) capacitors were studied in combination with their structural and optical properties. The ZrO₂ dielectric layers are of polycrystalline structure with a monoclinic phase and show good interfacial properties without obvious SiO_x interface. The electrical performance of the capacitors exhibits typical MOS-type capacitance-voltage (C-V) and leakage current density-voltage (J-V) characteristics. Thermal annealing of the ZrO₂ dielectrics results in an improvement in C-V and J-V characteristics and a reduction in C-V hysteresis without obvious introduction of leakage paths for the fabricated MOS capacitors. The dielectric constant was calculated to be 15.4 and the leakage current density was measured to be 6.7 × 10^− 6 A/cm² at a gate voltage of + 1.0 V for 900 °C annealed ZrO₂ dielectric layers with an equivalent oxide thickness of 5.2 nm.     

Enhanced oxygen exchange near the oxide/silicon interface during silicon thermal oxidation

The effect of the SiO₂/Si interface on oxygen exchange diffusion during oxidation was investigated using oxygen isotopes. A 40-nm thick Si¹⁸O₂ layer was first grown in ¹⁸O₂ and then the sample was reoxidized in ¹⁶O₂ at 1100 °C. The ¹⁸O diffusion in Si¹⁶O₂ during the ¹⁶O₂ oxidation was investigated by secondary ion mass spectrometry measurements. A significant broadening of the ¹⁸O profile toward the newly grown Si¹⁶O₂ was observed. The average oxygen diffusivity was initially about one order of magnitude larger than the reported thermal diffusivity in the SiO₂ network. In addition, the ¹⁸O diffusion became slower with oxidation time and hence with increasing distance between ¹⁸O diffusion region and the interface. This distance-dependent ¹⁸O self-diffusion was simulated taking into account the effect of Si¹⁶O molecules generated at the interface upon oxidation and diffusing into SiO₂ to enhance the oxygen exchange. The simulation fits the SIMS profiles and shows that the SiO diffusion is greatly retarded by the oxidation with O₂ from the oxygen-containing atmosphere. Therefore, the Si¹⁶O concentration becomes smaller as the interface leaves the ¹⁸O region and the oxygen exchange becomes slower with time.     

Interface reactions between SiO2-PbO glass and Ni-Zn ferrite

The interface reactions between SiO₂-PbO melt and Ni-Zn ferrite were studied using electron probe microanalysis and X-ray diffraction. The mechanisms of interface reaction were investigated in relation to the glass-forming region. No intermediate layers were produced at the interface between SiO₂-PbO glass and Ni-Zn ferrite because of the small amount of dissolution of Ni²⁺ ion from the ferrite. A model of the interface reaction mechanism between SiO₂-PbO melt and Ni-Zn ferrite is proposed.     

The effect of He or Ar/O2 plasma treatment on Si surface prior to chemical vapor deposition of SiO2

The effect of O₂ plasma pretreatment on the SiO₂/Si interface property was studied using direct plasma varying the plasma power, He or Ar/O₂ ratio and the pretreatment time. The decrease of the pretreatment plasma power decreased the plasma damage and improved the interface property. The addition of He in O₂ glow discharge improved the electrical and the interface properties and there was an optimum He/O₂ ratio. The improvement of the interface property by Ar/O₂-plasma pretreatment was better than that by He/O₂, which is believed to be due to the lower oxidation rate of the Si surface. C–V analysis showed that the P_b center defect density was influenced by plasma pretreatment process parameters. To investigate the oxidation states near to and at the SiO₂/Si interface, X-ray photoelectron spectroscopy depth analysis was used and the gas phase in the glow discharge was investigated using optical emission spectroscopy analysis at various experimental conditions.     

Depth profiles and concentration percentages of SiO2 and SiO x induced by ion bombardment of a silicon (100) target

Very thin-film of silicone oxide is of importance in many microelectronics device fabrication. A 9 keV Ar⁺ beam was applied to bombard a silicon (100) target ambient oxygen gas. The measurement was performed with a fixed time of bombardment but different oxygen pressure, beam intensity and temperature. An X-ray Photoelectron Spectroscopy (XPS) was employed to analyze the depth profiles and the concentration percentages of SiO₂ and SiO _x within the bombarded Si (100) samples. The percentage of SiO₂ in different depth of the sample is found to be proportional to the oxygen pressure. The thickness of SiO₂ film formed at room temperature is larger than the thickness at temperature 650 °C. The net percentages of SiO _x , except at the top layer of the surface, are varied in a small difference among different ion-bombardment conditions as the depth below 2 nm.     

Effect of postdeposition annealing on the structural and electrical properties of thin Dy2TiO5 dielectrics

This paper describes the effect of postdeposition annealing on the structural and electrical characteristics of high-k Dy₂TiO₅ dielectric films deposited on Si (100) through reactive cosputtering. We used X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and atomic force microscopy to investigate the structural and morphological features of these films after they had been subjected to annealing at different temperatures. The Dy₂TiO₅ dielectrics annealed at 800 °C exhibited excellent electrical properties such as high capacitance value, small density of interface state, almost no hysteresis voltage, and low leakage current. This phenomenon is attributed to a rather well-crystallized Dy₂TiO₅ structure and the reduction of the interfacial layer at oxide/Si interface. This film also shows almost negligible charge trapping under high constant voltage stress.     

Investigations of gold surface state energy levels at the silicon-silicon dioxide interface by the MOS capacitance-voltage measurement technique

The influence of gold in the Si/SiO₂ system has been studied both theoretically and experimentally. The gold is found to introduce two regions of shallow acceptor surface state energy levels in the silicon band gap at the SiSiO₂ interface: one at 0.09 eV from the valence band edge and the other at 0.13 eV from the conduction band edge. It is tentatively postulated that both the surface state energy levels are due to gold atoms in substitutional sites.The two deep normal bulk gold energy levels in silicon do not seem to occur at the SiSiO₂ interface.Finally a model of gold diffusion is suggested, and gold is found to diffuse through the bulk silicon by a complex interstitial and substitutional mechanism.     

Formation of silicon dioxide layers at low temperatures (150-400 °C) by atmospheric pressure plasma oxidation of silicon

The formation of silicon dioxide (SiO₂) layers at low temperatures (150-400 °C) by atmospheric pressure plasma oxidation of Si(0 0 1) wafers have been studied using a gas mixture containing He and O₂. A 150 MHz very high frequency (VHF) power supply was used to generate high-density atomic oxygen in the atmospheric pressure plasma. Oxidation rate, structure, and thickness and refractive index profiles of the oxidized layers were investigated by ellipsometry and infrared absorption spectroscopy. Atomic force microscopy was also employed to observe atomic-scale morphologies of the layer surface and wafer Si surface, after chemical removal of the oxidized layers. It was found that stoichiometric SiO₂ layers were obtained at higher oxidation rates than conventional dry O₂ thermal oxidation and radical oxidation processes, even at a very low substrate temperature of 150 °C. Although thickness variations were observed in the plasma region, the refractive index was independent of both substrate temperature and VHF power. In addition, the SiO₂ surface and SiO₂/Si interface roughnesses were comparable to those obtained in conventional dry oxidation at high temperatures.     

Atomic-layer-deposited (ALD) Al_2O_3passivation dependent interface chemistry,band alignment and electrical properties of HfYO/Si gate stacks

In this work, the effects of atomic-layer-deposited(ALD) Al_2O_3 passivation layers with different thicknesses on the interface chemistry and electrical properties of sputtering-derived HfYO gate dielectrics on Si substrates have been investigated. The results of electrical measurements and X-ray photoelectron sepectroscopy(XPS) showed that 1-nm-thick Al_2O_3 passivation layer is optimized to obtain excellent electrical and interfacial properties for HfYO/Si gate stack. Then, the metal-oxide-semiconductor capacitors with HfYO/1-nm Al_2O_3/Si/Al gate stack were fabricated and annealed at different temperatures in forming gas(95% N_2+5% H_2). Capacitance-voltage(C-V) and current density-voltage(J-V) characteristics showed that the 250℃-annealed HYO high-k gate dielectric thin film demonstrated the lowest border trapped oxide charge density(-3.3 × 10~(10) cm~(-2)), smallest gate-leakage current(2.45 × 10~(-6) A/cm~2 at 2 V)compared with other samples. Moreover, the annealing temperature dependent leakage current conduction mechanism for Al/HfYO/Al_2O_3/Si/Al MOS capacitor has been investigated systematically. Detailed electrical measurements reveal that Poole-Frenkle emission is the main dominant emission in the region of low and medium electric fields while direct tunneling is dominant conduction mechanism at high electric fields.