High Frequency Capacitance-voltage Measurements Research Articles

SiO2 films deposited on silicon at low temperature by plasma-enhanced decomposition of hexamethyldisilazane: Defect characterization

Silicon dioxide films have been deposited by plasma-enhanced chemical vapor deposition at low substrate temperature (50 °C) in a parallel-plate reactor using hexamethyldisilazane (HMDS), diluted in He, and O2 as Si and O precursors. The effect of the O2/(HMDS+He) flow rate ratio on the oxide properties has been investigated in the range of 0.05–1.25 by means of deposition rate, wet etching rate, secondary ion mass spectrometry, thermally stimulated luminescence, and high frequency capacitance–voltage measurements. Both the deposition rate and the etching rate increase by increasing the O2/(HMDS+He) flow rate ratio and reach a constant value at flow rate ratios higher than 0.6. The strong increase and saturation in the deposition rate can be attributed to the impinging oxide atoms flux and to the consumption of silyl radicals at the deposition surface, respectively. The Si/SiO2 interface state density and the positive fixed charge density are in the range 1×1011–1×1012eV−1 cm−2 and 6×1011–1.5×1012C cm−2, respectively. These concentrations are comparable with literature data concerning SiO2 films obtained by plasma enhanced chemical vapor deposition at temperatures higher than 200 °C using other Si precursors. Moreover, the interface state density decreases while the fixed oxide charge increases by increasing the O2/(HMDS+He) flow rate ratio. A correlation has been found between defects monitored by thermally stimulated luminescence and fixed oxide charges. From a comparison with secondary ion mass spectrometry results, the fixed oxide charges can be preliminarily attributed to intrinsic defects.

Crystal-orientation controlled epitaxial CeO 2 dielectric thin films on Si(100) substrates using pulsed laser deposition

Cerium oxide (CeO 2) is the potential dielectric candidate for the Si-based devices due to its stable chemical properties, high dielectric constant and good lattice match with silicon. In this paper, the impacts of process conditions on the structural and electrical characteristics of CeO 2 thin films deposited on Si(100) substrates have been studied. Epitaxial CeO 2 thin films with different crystal orientations on Si(100) substrates have been grown by pulsed laser deposition (PLD). The structural and electrical characteristics of CeO 2 thin films have been characterized by x-ray diffraction (XRD), atomic force microscopy (AFM), and high frequency capacitance–voltage measurements (C–V).

Oxynitridation of silicon with nitrogen plasma for flash memory applications characterized by high frequency capacitance–voltage measurements

Si(100) wafers were oxynitrided by nitrogen plasma exposure under different conditions and thermally oxidized in dry O2 without the use of toxic or global warming gases. The atomic concentration ratio of N/Si was 0.075 at a plasma discharge power of 0.5 kW and an exposure time of 1 min and 0.176 at a plasma power of 2.0 kW and an exposure time of 3 min, as determined from X-ray photoelectron spectroscopy measurements. A progressive reduction in the oxidation rate with increasing N concentration, corresponding to an increase in N plasma power, was observed. The uniformity of film thickness over a 4-inch wafer was improved after nitrogen plasma exposure and rapid thermal oxidation, with a thickness variation of less than 2.6% compared with 13.2% for the N2O thermal oxidation process. The advantages of exposing Si to N plasma for application in silicon devices was investigated by high-frequency capacitance–voltage measurements. A distortion in the capacitance–voltage curve was observed for samples that did not undergo nitridation, a distortion that was not observed in the nitrided samples. Capacitance–voltage curve distortion was found to be significantly reduced by Si nitridation under low plasma power.

Electrical characteristics of metal–ferroelectric (PbZrxTi1−xO3)–insulator(Ta2O5)–silicon structure for nonvolatile memory applications

A metal–ferroelectric–insulator–silicon (MFIS) structure using lead–zirconate–titanate (PZT) as the ferroelectric layer and Ta2O5 as the insulator layer is fabricated. This structure is studied for the potential application of nonvolatile memory devices. The Ta2O5 layer is used as a buffer layer to minimize the out diffusion of silicon atoms during heat treatment processes. High frequency capacitance–voltage measurements show a flat band voltage shift of 13 V under a ±15 V writing pulse. The interface-trap density Dit is measured by the conductance method. The MFIS capacitors are shown to have a fatigue lifetime of 1×1011 cycles and 5×107 cycles for 11.4 and 15 V writing pulses, respectively.

Fabrication of Enhancement-Mode GaN-Based Metal–Insulator-Semiconductor Field Effect Transistor

ABSTRACTAn enhancement-mode GaN metal-insulator-semiconductor field-effect transistor was successfully fabricated on a GaN/AlGaN/GaN double heterojunction structure with SiO2 as insulator layer. The enhancement mode DC characteristics have been achieved in the device with a gate length of 6 μm and a gate width of 100 μm. The device exhibited a DC transconductance of 0.6 mS/mm and a maximum drain-source current of 5 mA/mm. The gate leakage current is lower than 10−6 A at a bias of -10 V and the gate breakdown voltage is higher than 20 V. The channel stands a good chance of forming by hole accumulation between the top GaN layer and the AlGaN layer. The p-channel can be attributed to the presence of a piezoelectric field in the heterojunction, and the strongly asymmetric band bending and carriers distribution induced by the piezoelectric field. High-frequency capacitance-voltage measurement also gives a circumstantial evidence of the presence of a p-channel in the device structure.

Thick Oxide Layers on N and P SiC Wafers by a Depo-Conversion Technique

ABSTRACTThe electrical properties of thick oxide layers on n and p-type 6H-SiC obtained by a depoconversion technique are presented. High frequency capacitance-voltage measurements on MOS capacitors with a ∼ 3000 Å thick oxide indicates an effective charge density comparable to that of MOS capacitors with thermal oxide. The breakdown field of the depo-converted oxide obtained using a ramp response technique indicates a good quality oxide with average values in excess of 6 MV/cm on p-type SiC and 9 MV/cm on n-type SiC. The oxide breakdown field was observed to decrease with increase in MOS capacitor diameter.

Ultrathin Gate Oxides with Shallow Nitrogen Implants as Effective Barriers to Boron Diffusion

ABSTRACTPlasma immersion ion implantation (PIII) has been employed to controllably place nitrogen ions from an inductively coupled plasma into a thin furnace grown gate oxide 2.0nm thick with implant voltages from 25 to 500V. Control of the implant energy enables shallow implantation confining the nitrogen mainly within the oxide. Rapid thermal annealing is essential in repairing any damage to the implanted silicon dioxide and silicon while consolidating the bonding of nitrogen into the oxide film prior to gate polysilicon deposition. High frequency capacitance-voltage measurements of capacitors made with BF2+ implanted gates throughout a series of furnace anneals demonstrates the efficiency for blocking boron compared to non-nitrided oxides of similar thickness. Tddb measurements verify excellent reliability compared to a non-implanted oxide for both stress polarities.

Properties of low dielectric constant fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition

The chemical and electrical properties of fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition at 180°C were studied. The deposition of these films was made by incorporating CF4 as the fluorine source into the deposition process of SiO2 films using Si2H6 and N2O. With increasing CF4 flow, the deposition rate of these films decreased; meanwhile, the P-etch rate increased. With post-deposition anneal, the thickness of the films without CF4 slightly decreased; meanwhile, the thickness slightly increased with the incorporation of CF4. The Fourier transform infrared (FTIR) spectroscopy showed that the characteristic peak around 940 cm−1 due to the Si–F stretching bonds increased with increasing CF4 flow, also the Si–O stretching wave number increased but its full width at half maximum decreased with increasing CF4 flow. The dielectric constant evaluated by high frequency capacitance-voltage measurements decreased from 4.13 to 3.52 as the CF4 flow increased. In addition, the effective oxide charge density and interface trap density also decreased with increasing CF4 flow. The ramp current-voltage measurements showed that the leakage current density of the films decreased with increasing CF4 flow. However, high average breakdown field strength with low early failures was observed for medium flow of CF4.

Investigations of SiO2/n-GaN and Si3N4/n-GaN insulator–semiconductor interfaces with low interface state density

The electrical properties of electron beam (EB) evaporated silicon dioxide (SiO2)/n-GaN, plasma enhanced chemical vapor deposited (PECVD) SiO2/n-GaN, and PECVD silicon nitride (Si3N4)/n-GaN interfaces were investigated using high frequency capacitance–voltage measurements. Compositions of the deposited insulating layers (SiO2 and Si3N4) were analyzed using x-ray photoelectron spectroscopy. Metal-insulator-semiconductor structures were fabricated on the metalorganic chemical vapor deposition grown n-type GaN layers using EB, PECVD grown SiO2 and PECVD grown Si3N4 layers. Minimum interface state density (2.5×1011 eV−1 cm−2) has been observed in the PECVD grown SiO2/n-GaN interface when it was compared with EB evaporated SiO2/n-GaN interface (5.3×1011 eV−1 cm−2) and PECVD Si3N4/n-GaN interface (6.5×1011 eV−1 cm−2). The interface state density (Nf) depends on the composition of deposited insulating layers.

Characterization of low dielectric constant plasma enhanced chemical vapor deposition fluorinated silicon oxide films as intermetal dielectric materials

The characteristics of fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition are discussed. The deposition of these films was carried out in the temperature range of 80–220 °C in a conventional parallel plate plasma reactor with <±3% uniformity across 4 in. wafer by flowing 2 sccm of disilane, 100 sccm of nitrous oxide and 20 sccm of tetrafluoromethane. As the deposition temperature increased from 80 to 220 °C, the deposition rate of the films increased from 16.7 to 18.4 nm/min; meanwhile, the etch rate decreased from 2.69 to 1.48 nm/s. The refractive index was 1.46 regardless of the deposition temperature. The Fourier transform infrared spectra of the films showed a decreasing Si–O stretching wave number with an increasing full width at half maximum as the deposition temperature increased. The high frequency capacitance–voltage measurements of the metal–oxide–semiconductor (MOS) capacitors fabricated using the films showed increasing effective oxide charge density and decreasing dielectric constant with increasing deposition temperature. A deposition temperature of 180 °C resulted in films with the smallest dielectric constant of 3.75. These films showed an average breakdown strength of 9.14 MV/cm with 77.5% of the MOS capacitors having breakdown field strengths ⩾9.5 MV/cm.

Comparison of SiO<sub>2</sub> and AIN as Gate Dielectric for SiC MOS Structures

The electrical properties of silicon dioxide (thermal oxidation) and aluminum nitride (metal organic chemical vapor deposition) have been compared for use as gate dielectric for silicon carbide metal insulator semiconductor structures. High frequency capacitance voltage measurements at room temperature were used to investigate fixed charge and deep interface states. The deep interface states could be passivated with hydrogen if introduced during growth of silicon dioxide. Although results are promising for aluminum nitride, the morphology of the films grown so far do not allow a fair comparison with silicon dioxide.

Investigation of aluminum nitride grown by metal–organic chemical-vapor deposition on silicon carbide

Undoped single crystalline aluminum nitride films were grown on 4H and 6H SiC substrates using metal–organic chemical-vapor deposition at 1200 °C. From in situ reflection high-energy electron diffraction, x-ray diffraction rocking curves, and cathodoluminescence spectra, the crystallinity of the films was confirmed. Atomic force microscopy showed that some films were substantially dominated by island growth, rather than step flow growth. Aluminum was evaporated to form metal–insulator–semiconductor (MIS) capacitors for high-frequency capacitance voltage measurements carried out at room temperature. Low leakage made it possible to measure the structures and characterize accumulation, depletion, deep depletion, and, in some cases, inversion. From independent optical thickness measurements, the relative dielectric constant of aluminum nitride was confirmed at 8.4. The flatband voltage of the AlN MIS capacitors on p-type SiC was close to the theoretical value expected. The films were stressed up to 60 V (3 MV/cm) without breakdown, but excessive leakage currents (>0.1 A/cm2), probably dominated by grain-boundary conduction, shifted the flatband voltage of the capacitors. These results indicate the possibility of replacing silicon dioxide with aluminum nitride in SiC field effect transistors using insulated gates.

Amorphous silicon/p-type crystalline silicon heterojunction solar cells

We have investigated the photovoltaic (PV) characteristics of both glow discharge deposited hydrogenated amorphous silicon (a-Si:H) on crystalline silicon (c-Si) in a n + a-Si:H/undoped a-Si:H/p c-Si type structure, and DC magnetron sputtered a-Si:H in a n-type a-Si:H/p c-Si type solar cell structure. It was found that the PV properties of the solar cells were influenced very strongly by the a-Si/c-Si interface. Properties of strongly interface limited devices were found to be independent of a-Si thickness and c-Si resistivity. A hydrofluoric acid passivation prior to RF glow discharge deposition of a-Si:H increases the short circuit current density from 2.57 to 25.00 mA/cm 2 under 1 sun conditions. DC magnetron sputtering of a-Si:H in a Ar H 2 ambient was found to be a controlled way of depositing n type a-Si:H layers on c-Si for solar cells and also a tool to study the PV response with a-Si/c-Si interface variations. 300 Å a-Si sputtered onto 1–10 ω cm p-type c-Si resulted in 10.6% efficient solar cells, without an A/R coating, with an open circuit voltage of 0.55 V and a short circuit current density of 30 mA/cm 2 over a 0.3 cm 2 area. High frequency capacitance-voltage measurements indicate good junction characteristics with zero bias depletion width in c-Si of 0.65 μm. The properties of the devices have been investigated over a wide range of variables like substrate resistivity, a-Si thickness, and sputtering power. The processing has focused on identifying and studying the conditions that result in an improved a-Si/c-Si interface that leads to better PV properties.

Influence of growth conditions on electrical characteristics of AlN on SiC

Undoped aluminum nitride films were grown on 4H or 6H silicon carbide substrates, using metal–organic chemical-vapor deposition at 1150 °C. Different growth conditions were used, and two different V/III ratios were tested. Metal–insulator–semiconductor capacitors were made for high-frequency capacitance–voltage measurements at room temperature, from which the film thickness was determined. Accumulation, depletion, deep depletion, and inversion were seen for the best films, which also displayed peaks in x-ray diffraction rocking curves. Although large flatband voltage shifts occurred, indicating a fixed charge and interface trap problem, low conductance was observed. A flow of ammonia during ramp-up was found to improve the AlN films.

ELECTRICAL CHARACTERIZATION OF SOLID C60/Si HETEROJUNCTIONS——RECTIFYING PROPERTIES, ENERGY-BAND MODELS, AND BIAS-TEMPERATURE EFFECT

This work investigates electrical properties of contacts between undoped solid C60 and n-or p-type Si. Current-voltage measurements show that the two contacts result in strong rectification with opposite conduction directions, indicating two different kinds of barriers for carrier transportation at the interface of the two contacts. Current-temperature measurements show that the current is an exponential function of reciprocal temperature, from which we estimate the effective barrier height to be 0.30 and 0.48 eV for C60/n-Si and C60/p-Si, respectively. Within energy-band models we interpret successfully the above experimental results. Based on the energy-band model and experimental data we derived the electron affinity of solid C60 film to be 3.92 eV and its energy gap to be below 1.72 eV. Highfrequency capacitance-voltage measurements show that biastemperature treatments have considerable effect on the C-V characteristics of the heterojunction. Assuming the existence of mobile negative charges in the solid C60 film we explain the effect successfully and estimate the density of the negative charges to be 3.1×1012cm-2. By use of the C-V results we determine the dielectric constant of the solid C60 film to be 3.7±0.1 in the temperature range of 300-370 K.

Growth and characterization of yttrium oxide thin layers on silicon deposited by yttrium evaporation in atomic oxygen

Polycrystalline yttrium oxide films have been grown under high vacuum conditions by evaporation of yttrium in an atomic oxygen plasma. Well-oxidized uniform layers in the thickness interval 30–170 nm were deposited on silicon over a large temperature range (80–800 °C), Film surfaces were very smooth with average surface roughness 1.6 nm for 70 nm films grown at 350 °C. No impurity phases were found by X-ray diffraction even for the highest growth temperatures. The layers exhibited a strong (111) texture for growth temperatures ⩾ 300 °C irrespective of the substrate orientation. High frequency capacitance-voltage measurements on aluminium/yttrium oxide/silicon capacitors showed metal-insulator-semiconductor operation with large hysteresis effects in the depletion region. The calculated values of the relative dielectric constant for the capacitor structures were 14 and 11 for 100 nm thick yttrium oxide films grown at 350 °C and 750 °C, respectively. The breakdown strength of the capacitors was found to be 3.8 MV cm −1.

Electrical properties of hydrogen-rich [formula omitted] structures

The electrical properties of Si SiO 2 interfaces grown by oxidation of a-Si:H films are studied using quasistatic and high frequency capacitance-voltage measurements. The results obtained point out that the presence of hydrogen in the ambient and in the oxidizing film leads to an increase in the density of the interface states. This effect is suggested to be similar to postoxidation hydrogenation.

Capacitance-Voltage Characteristics of p-Si/SiGeC Mos Capacitors

ABSTRACTThe first measurements of Si/SiGeC valence band offsets have been performed using heterostructure p-type MOS capacitors. Single crystalline epitaxial layers of SiGeC and Si were grown by the rapid thermal CVD technique, limited reaction processing, using ethylene as the carbon source. Films with carbon contents of up to ∼1.2% were studied. X-ray diffraction analysis shows the strain compensating effect of carbon in SiGeC. Substitutionality of carbon in SiGe was also confirmed by Fourier transform infrared spectroscopy measurements. MOS capacitors were fabricated by thermal oxidation (750°C) of the epitaxial Si cap on top of the SiGeC layer. Quasi-static and high frequency capacitance-voltage measurements show wellbehaved characteristics for the samples with carbon contents up to approximately 1%. Onedimensional Poisson simulations of the C-V curves were used to extract the valence band offset between Si and SiGeC. For a fixed germanium fraction, the offset decreases with increasing carbon content. However, for a given lattice mismatch, the offset for Si/Si1−x−yGexCy is larger than the measured value for Si/Si1−zGez.

Si/Ge/S multilayer passivation of GaAs(100) for metal-insulator-semiconductor capacitors

We describe a new multilayer passivation method on GaAs(100), an ex situ method that doesn’t require GaAs epitaxy. Thin 20 Å Si films or thin films consisting of 15 Å Si and 5 Å Ge were grown on (NH4)2S cleaned and S passivated GaAs(100) wafers. High-energy resolution x-ray photoelectron spectroscopy has been used to study the chemical structure of the buried GaAs surfaces. As and Ga 3d core level studies show that the surface is free of gallium and arsenic oxides as well as elementary As. The Ga-S-Ga bridge bond termination is found preserved on the buried GaAs surface. SiNx/Si/Ge/S/GaAs and SiNx/Si/S/GaAs capacitors have been made and analyzed using quasistatic and high frequency capacitance-voltage measurements. Using the high-low method, an interface state density of about 1012 cm−2 eV−1 is obtained. The modulation of the surface potential is the highest reported for a method not requiring GaAs epitaxy.

Developing biosensors with pH-ISFET transducers utilizing lipid bilayer membranes with transport proteins

We present a biosensor based on the transport protein lactose permease (LP) which is imbedded in a supported planar lipid bilayer (SPB) membrane, and which allows the potentiometric detection of lactose via pH measurement. Different experimental setups were used to study systematically the electric properties of the different biosensor components. In a first step the preparation of the SPB is investigated by means of high-frequency capacitance—voltage measurements. The sensor consists of an ion-sensitive field-effect transistor (ISFET) coated with the SPB membrane, the latter containing the lactose/H + cotransporter LP from Escherichia coli ( E. coli). The sensor effect consists of a rise in the proton concentration in the small volume between the lipid membrane and the gate area upon addition of lactose to the external medium. This effect is monitored directly by the pH-sensitive ISFET.