Electrical characterization of AlN MIS and MIM structures

Aluminum nitride (AlN) thin films have been deposited on p-Si[100] and Mo-Si[100] substrates. The sputter deposited Mo was polycrystalline, predominantly showing a [110] orientation. Thin AlN films were grown under different process conditions in a physical vapor deposition (PVD) system to attain highly textured polycrystalline films as well as close to amorphous films. MIS and MIM structures were fabricated and electrical properties such as the dielectric constant, leakage current, and high-frequency behavior were investigated. It is found that the dielectric constant is 10 and does not change with the crystallinity of the films. High-frequency measurements up to 10 GHz show no frequency dispersion of the capacitance. The leakage current stays relatively constant between films and is believed to be Poole-Frenkel controlled. Capacitance-voltage (C-V) measurements for MIS structures revealed the presence of charges in the interface layer between the substrate and the dielectric film. The temperature dependence of the capacitance has also been studied.     

Characteristics of RF sputtered barium titanate thin films

Results of a study on the deposition of thin-film barium titanate (BaTiO3) by RF sputtering are discussed. BaTiO3was deposited onto Pt foil and onto thin-film electrodes on various substrates, and counterelectroded to form metal-dielectrio-metal structures. Dielectrics were deposited at substrate temperatures from 23° to 1000°C, some of the dielectrics fired in air at temperatures up to 1400°C after deposition. On bulk Pt, the BaTiO3film matrix indicated an average grain size of 2000 Å after heat treatment Constant Ba/Ti ratios were measured for the films deposited over the entire substrate temperature range. Dielectric constants ranged from 16- 1900, the tan δ of the capacitors varying from 0.005 for amorphous films to 0.065 for polycrystalline films with highest dielectric constants. Effects of temperature and frequency on the capacitors and the charge-voltage and field dependence of the dielectric constant are described. Current-voltage relationships, breakdown strengths, and processing conditions indicate the potential of the capacitor structures for practical applications.     

Integration of high dielectric Ba0.5Sr0.5TiO3 films into amorphous TaSiN barrier layer structures

The high-k dielectric material (Ba,Sr)TiO₃ has been intensively investigated for possible applications in dynamic random access memory circuits. During the BST deposition process in O₂ ambient, typically at 650°C, the diffusion of oxygen through the bottom electrode into the poly Si plug must be prevented. Amorphous TaSiN films are excellent candidates as oxygen barrier layers. Ba_0.5Sr_0.5TiO₃ (BST) films with thickness of 100 nm were deposited on the electrode structure SiO₂/TaSiN/Pt. The sol–gel method was used to grow the BST films. The barrier effect for oxygen diffusion is studied in TaSiN layers with thickness of 50 nm, which were deposited by a reactive sputter process. X-ray photoemission spectroscopy results confirm that this amorphous material is a suitable barrier against oxygen diffusion at 650°C. The BST films, deposited at 650°C and post-annealed at 650°C show a dielectric constant of 100 at 100 kHz and a dissipation factor of less than 5%.     

Thin films of ZrO2 metal organic chemical vapor deposition

ZrO₂ layers were deposited for the purpose of obtaining high dielectric constant insulating layers for capacitance applications. Trifluoroacety lacetonate of zirconium was used as the source material in our open MOCVD system. Layer thickness was in the range 300–1500 Å, the substrate being degenerate n-type silicon wafers. Under optimum conditions layers with good adhesion and uniformity were obtained. The layers were polycrystalline with characteristic linear dimensions of 400 Å. Electrical measurements were used for characterization and the relative dielectric constants obtained were 30 ± 1.     

Thermo-Sensitive Ba0.64Sr0.36TiO3 Thin Film Capacitors for Dielectric Type Uncooled Infrared Sensors

Ba_0.64Sr_0.36TiO₃ (BST) thin films are prepared on Pt/Ti/SiO₂/Si₃N₄/SiO₂/Si substrates by a sol-gel method. Thermo-sensitive BST thin film capacitors with a Metal-Ferroelectrics-Metal (M-F(BST)-M) structure are fabricated as the active elements of dielectric type uncooled infrared sensors. XRD are employed to analyze the crystallographic structures of the films. AFM observations reveal a smooth and dense surface of the films with an average grain size of about 35 nm. Rapid temperature annealing (RTA) process is a very efficient way to improve crystallization quality. The preferable annealing temperature is 800°C for 1 min. The butterfly shaped C-V curves of the capacitors indicate the films have a ferroelectric nature. The dielectric constant and dielectric loss of the films at 100 kHz are 450 and 0.038, respectively. At 25°C, where the thermo-sensitive capacitors work, the temperature coefficient of dielectric constant (TCD) is about 5.9 %/°C. These results indicate that the capacitors with sol-gel derived BST thin films are promising to develop dielectric type uncooled infrared sensors.     

Properties of the GaSb:Mn layers deposited from laser plasma

The X-ray diffraction and electrical and magnetic properties of GaSb:Mn layers deposited on GaAs (100) substrates from a laser plasma in free space are studied. It is shown that the films deposited at 200–440°C are epitaxial mosaic single crystals. Manganese-doped layers (up to ～4 at % Mn) had a hole concentration higher than 1 × 10¹⁹ cm^?3. Structures with the GaSb:Mn layers grown at 200°C had an anomalous Hall effect. A normal Hall effect was observed for the GaSb:Mn layers grown at 440°C. The exposure of these layers to a laser pulse (wavelength λ = 0.68 μm, duration 25 ns) caused an increase in the hole concentration and the emergence of the anomalous Hall effect at room temperature. Magnetic ultrahigh-frequency measurements confirmed that the films were ferromagnetic up to 293 K and revealed a magnetism anisotropy.     

Low Leakage Current Transport and High Breakdown Strength of Pulsed Laser Deposited HfO<Subscript>2</Subscript>/SiC Metal-Insulator-Semiconductor Device Structures

Hafnium oxide (HfO₂) thin films were deposited by the pulsed laser deposition (PLD) method on SiC substrates. The bandgap of HfO₂ thin films was observed to be 5.8 eV. The chemical nature and stoichiometry of the films were analyzed by x-ray photoelectron spectroscopy (XPS). Metal-insulator-semiconductor (MIS) structures with Ni as a top electrode and TiN as a bottom electrode were fabricated to study the leakage current properties. The devices exhibited leakage current density of 50 nA/cm². The dielectric constant of these films is estimated to be in the range 17–24 from capacitance-voltage (C-V) measurements. The frequency dependence of the interface trapped charges is studied.     

SiOF and SiO2 deposition in a HDP reactor: tool characterization and film analysis

A high density plasma chemical vapour deposition (HDP CVD) system based on electron cyclotron resonance (ECR) plasma excitation for deposition of inter metal dielectric (IMD) is presented. With the system deposition of SiO₂ and SiOF has been performed. The influence of pressure, Ar content in the flow, total flow, bias voltage, microwave power on gap fill capability and growth rate has been investigated. A figure of merit, the product of gap filling capability and growth rate is defined. In addition measurements of the uniformity of the composition over the wafer of the deposited SiO₂ and SiOF layers were performed. The dielectric constant of the layers was measured on SiOF films with different composition. The stability of these SiOF films was also analysed. This was done by treating the films with moisture and measuring composition before and after this treatment.     

High performance sol–gel spin-coated titanium dioxide dielectric based MOS structures

High-κ TiO₂ thin films have been fabricated using cost effective sol–gel and spin-coating technique on p-Si (100) wafer. Plasma activation process was used for better adhesion between TiO₂ films and Si. The influence of annealing temperature on the structure-electrical properties of titania films were investigated in detail. Both XRD and Raman studies indicate that the anatase phase crystallizes at 400 °C, retaining its structural integrity up to 1000 °C. The thickness of the deposited films did not vary significantly with the annealing temperature, although the refractive index and the RMS roughness enhanced considerably, accompanied by a decrease in porosity. For electrical measurements, the films were integrated in metal-oxide-semiconductor (MOS) structure. The electrical measurements evoke a temperature dependent dielectric constant with low leakage current density. The Capacitance–voltage (C–V) characteristics of the films annealed at 400 °C exhibited a high value of dielectric constant (~34). Further, frequency dependent C–V measurements showed a huge dispersion in accumulation capacitance due to the presence of TiO₂/Si interface states and dielectric polarization, was found to follow power law dependence on frequency (with exponent ‘s’=0.85). A low leakage current density of 3.6×10⁻⁷ A/cm² at 1 V was observed for the films annealed at 600 °C. The results of structure-electrical properties suggest that the deposition of titania by wet chemical method is more attractive and cost-effective for production of high-κ materials compared to other advanced deposition techniques such as sputtering, MBE, MOCVD and ALD. The results also suggest that the high value of dielectric constant ‘κ‘ obtained at low processing temperature expands its scope as a potential dielectric layer in MOS device technology.     

p-Si TFT栅绝缘层用SiN薄膜的研究

以NH3和SiH4为反应源气体,采用射频等离子体增强化学气相沉积(RF-PECVD)法在多晶硅(p-Si)衬底上沉积了一系列SiN薄膜,并利用椭圆偏振测厚仪、超高电阻-微电流计、C-V测试仪对所沉积的薄膜作了相关性能测试.系统分析了沉积温度和射频功率对SiN薄膜的相对介电常数、电学性能及界面特性的影响.分析表明,沉积温度和射频功率主要是通过影响SiN薄膜中的Si/N比影响薄膜的性能,在制备高质量的p-Si TFT栅绝缘层用SiN薄膜方面具有重要的参考价值.     

Low-Temperature deposition of dielectric films by microwave plasma enhanced decomposition of hexamethyldisilazane

Hexamethyldisilazane (HMDS) has been used as an organosilicon source for the deposition of dielectric films at low temperatures (200-250° C) by microwave plasma enhanced CVD technique. Hydrogenated films of variable composition of silicon carbonitride, silicon oxynitride and silicon dioxide have been deposited by decomposition of HMDS in the presence of additive gases like NH₃, O₂ and H₂ under different process conditions. Deposited films have been characterized by the measurement of refractive index and buffered HF etch rate, and by the analysis of XPS and infrared transmission spectra. An increase in HMDS partial pressure generally results in the decrease of refractive index. The films show stable C-V characteristics of metal-insulator-semicon-ductor (MIS) capacitors with positive insulator charge density.     

The effect of post-deposition thermal processing on MOS gate oxides formed by remote PECVD

The effects of post-deposition thermal exposure, at temperatures typical of MOS fabrication processes, on gate oxides formed by remote plasma enhanced chemical vapor deposition (RPECVD) is discussed. SiO₂ films were prepared by (1) thermal oxidation of silicon at temperatures from 700 to 1150° C, and (2) by RPECVD at a substrate temperature of 350° C. Post deposition thermal processing was achieved by rapid thermal annealing for 100 sec from 850–1200° C. Film properties were studied by infrared spectroscopy (IR), ellipsometry, and by measurements of stress, capacitance voltage characteristics, and dielectric breakdown. Post-formation, thermal processing in the range of 850–1200° C was shown to modify both thermally grown and deposited oxides, but it has been shown that RPECVD films could be stabilized against post-deposition changes by rapid thermal annealing at temperatures of about 900° C for periods of at least 100 sec.     

Preparation and Dielectric Characteristics of Semitransparent CoFe2O4–P(VDF-TrFE) Nanocomposite Films

Polymer–ceramic nanocomposites play an important role in embedded capacitors. However, polymer–ceramic dielectrics are limited for commercial applications due to their low transmittance, poor adhesion, and poor thermal stress reliability at high filler loadings. Thus, materials design and processing is critical to prepare films with improved dielectric properties and low filler loading. In this work, we use a spin coating-assisted method to fabricate poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)]–CoFe₂O₄ (CFO) nanocomposite films. Magnetic CFO nanoparticles in the size range of 10 nm to 40 nm were successfully synthesized using a hydrothermal process. The dispersion of the nanoparticles, the dielectric properties, and the transmittance of the nanocomposite films were studied. The dielectric constant of the nanocomposite films increased by about 45% over the frequency range of 100 Hz to 1 MHz, compared with that of pristine P(VDF-TrFE) film. Optical measurements indicated that the transmittance of the films remains above 60% in the visible range, indicating a relatively low content of CFO in the polymer matrix. Our experimental results suggest that spin coating-assisted dispersion may be a promising route to fabricate dielectric polymer–ceramic nanocomposite films of controllable thickness.     

Characteristics of the NO dielectric film with low pressure chemical vapor deposition in-situ nitridation

We investigated the formation of the thin NO dielectric films by in-situ nitridation of native oxide, and subsequent deposition of silicon nitride in the low pressure chemical vapor deposition systems for the application to the capacitors in high density dynamic random access memory. The native oxide was nitrided at elevated temperatures of 690 or 780°C in the flowing ammonia gas atmosphere, and nitride was deposited by flowing silane gas additionally immediately after the nitridation process. By in-situ nitridation process, we could obtaine 5 and 4.5 nm thick (equivalent oxide thickness) nitride/oxide (NO) dielectric films. These films were characterized to be electrically more reliable than the conventional oxide/nitride/oxide (ONO) films of the same equivalent oxide thickness. The nitrided NO films also showed lower leakage current and higher breakdown voltage than conventional ONO films. We obtained electrically most reliable NO films by loading the wafer at 400°C and nitriding the native oxide at 780°C.     

ITO玻璃衬底上PLZT铁电薄膜的制备与电性能

用sol-gel法在掺Sn的In2O3导电透明膜(ITO)衬底上,制备了La掺杂的PbZr0.5Ti0.5O3(PLZT)铁电薄膜。研究了La掺杂量对薄膜的铁电、介电和漏电性质的影响。结果表明,x(La)为5%的PLZT薄膜经650℃退火,有优良的铁电特性,外加15V电压下,剩余极化强度为35.4×10–6C/cm2,矫顽场强为111×103V/cm。100kHz时的εr和tgδ分别为984和0.13。在外加电场小于9V时,薄膜的漏电流密度不超过10–8A/cm2。     

Structural and electrical properties of polycrystalline silicon films deposited by low pressure chemical vapor deposition with and without plasma enhancement

Silicon thin films prepared by chemical vapor deposition of silane at very low pressures (4 mTorr) in an experimental reactor that allows deposition with and without plasma enhancement have been characterized. The temperature range of the substrates on which the films were deposited was varied from 500 to 800° C for plasma-enhanced depositions and 600 to 800° C for nonplasma depositions. Conductivity measurements as a function of temperature as well as average grain size and crystallographic texture measurements were performed. The results indicate that the films deposited with the assistance of a plasma were amorphous at deposition temperatures of 650° C and below and polycrystalline at deposition temperatures of 700° C and above. In the temperature regime investigated, this amorphous-to-crystalline transition was not observed in films deposited without the assistance of a plasma. Furthermore, all the films deposited at temperatures of 650° C and below have been found to have significantly different properties from the similarly prepared films deposited at higher temperatures.     

Transport Properties of CuInTe<Subscript>2</Subscript> Thin Films Obtained by the Electrochemical Route

CuInTe₂ (CIT) thin films were potentiostatically electrodeposited onto cadmium sulfide thin films coated on fluorine doped tin oxide (FTO) glass in an aqueous bath at 75°C by the standard three-electrode system at ??0.7 V and ??0.8 V, with respect to an Ag/AgCl reference electrode. The electrodeposited layers were heat treated at?～?80°C in air ambient for 60 min. X-ray diffraction pattern and Raman analysis confirmed the formation of chalcopyrite CIT thin films upon heat treatment. The optical band gap of heat treated CIT films was found to be?～?1.0 eV and 0.95 eV deposited at ??0.7 V and ??0.8 V, respectively. Compact and good adhesive growth of CIT layers onto CdS coated FTO substrates is confirmed by field emission scanning electron microscopy. The current density–voltage (J–V) and capacitance–voltage (C–V) measurement was studied to understand the electronic quality of material for development of CIT layers for solar cell applications. The current density was found to be increased by two orders of magnitude upon low-temperature heat treatment. The capacitance–voltage measurement showed sharp depletion and accumulation region. The built in potential was found to be ～?60 mV and 145 mV in the as-deposited samples, deposited at ??0.7 V and ??0.8 V, respectively, whereas upon heat treatment it shifted to 159 mV and 210 mV. The capacitance of the CIT films was found to be a function of applied bias and increased with increasing the bias voltage. The depletion width of the heat treated sample was found to be?～?20 nm and 200 nm for the sample deposited at ??0.7 V and ??0.8 V, respectively. Thus, the sample deposited at ??0.8 V shows optimum electronic properties and is found to be suitable for opto-electronic applications.     

Properties of ZrO2 thin films prepared by laser ablation

ZrO₂ thin films have been prepared by laser ablation of Zr or ZrO₂ targets in oxygen reactive atmosphere. The influence of the deposition parameters as oxygen pressure and target composition on the structure and morphology of the deposited layers has been studied. Scanning electron microscopy, secondary ion mass spectroscopy and dielectric constant measurements have been performed to characterize the deposited layers. Dielectric constant values in the range 15–20 and low losses were evidenced for samples prepared in a narrow range of experimental conditions.     

ZnO films deposited on GaAs substrates with a SiO2 thin buffer layer

Sputter deposition of ZnO films on GaAs substrates has been investigated. ZnO films were radio frequency (rf)-magnetron sputter deposited on GaAs substrates with or without SiO₂ thin buffer layers. Deposition parameters such as rf power, substrate-target distance, and gas composition/pressure were optimized to obtain highly c-axis oriented and highly resistive films. Deposited films were characterized by x-ray diffraction, scanning electron microscopy (SEM), capacitance, and resistivity measurements. Thermal stability of sputter-deposited ZnO films (0.5–2.0 μm thick) was tested with a post-deposition heat treatment at 430°C for 10 min, which is similar to a standard ohmic contact alloying condition for GaAs. The ZnO/SiO₂/GaAs films tolerated the heat treatment well while the ZnO/GaAs films disintegrated. The resistivity (10¹¹ Ω-cm) of the ZnO films on SiO₂-buffered GaAs substrates remained high during the heat treatment. The post-deposition anneal treatment also enhances c-axis orientation of the ZnO films dramatically and relieves intrinsic stress almost completely. These improvements are attributed to a reduction of grain boundaries and voids with the anneal treatment as supported by SEM and x-ray diffraction measurement results.     

Plasma deposition of aluminum oxide films

A plasma deposition technique for amorphous aluminum oxide films is discussed. A 450 kHz or 13.56 MHz power supply was used to generate the plasma and the deposition of the film was achieved at low plasma power using trimethyl-aluminum and carbon dioxide reactant sources. It has been found that for the low frequency plasma the growth is strongly dependent upon TMA concentration, indicating that the growth process is mass transport limited. On the other hand using the 13.56 MHz discharge results in a surface controlled growth rate. An increase in the deposition temperature up to 300° C makes the films more dense and lowers their etching rate. FTIR and ESCA measurements showed that oxidation is only completed with high CO₂ concentrations and a deposition temperature above 250° C. The dielectric films were found to have a dielectric constant in the range 7.3=2-9 and a refractive index between 1.5–1.8 depending upon deposition conditions.