Determination of the semiconductor doping profile right up to its surface using the MIS capacitor

A new method has been developed by which the doping profile of the semiconductor can be obtained right up to its surface. Contrary to the well known dC/dV-method, which is valid only in the depletion range, we have considered the majority carriers in deriving relations for doping density as well as distance from the semiconductor surface, in terms of the space charge capacitance and its derivative with respect to the surface potential. This method can be realized experimentally on any MIS structure. Measurements on MOS capacitors with steam grown oxides showed a drooping profile towards the SiSiO₂ interface for boron doped and a rising one for phosphorus doped silicon. Post-oxidation annealing in dry nitrogen at 1200°C produced a uniform profile for phosphorus doped silicon.     

Frequency and temperature tests for lateral nonuniformities in MIS capacitors

Interface states and lateral nonuniformities produce very similar abnormalities in theC-Vcurves of MIS capacitors. TwoC-Vtechniques are presented here to aid in distinguishing between them. The first technique is based on the frequency dependence of the interface-state capacitance and utilizes the resulting frequency dispersion of the "high-frequency" capacitance in the depletion regime, which occurs in a frequency range typically between a few hundred Hz and 1 MHz. The second method utilizes a freeze-in of carriers in the interface states at liquid nitrogen temperature. A sweep of bias from accumulation into deep depletion at low temperature produces aC-Vcharacteristic which, when compared with the corresponding ideal characteristic for the same semiconductor doping profile, reveals the presence of lateral nonuniformities. A complementary test is provided by temporary illumination of the deep-depleted structure followed by a sweep of bias from inversion into accumulation. A ledge in theC-Vcharacteristic reveals the presence of interface states in the central half of the bandgap.     

Improved MOS capacitor measurements using the Q-C method

We describe a method for determining band bending vs gate bias, doping profile and oxide charge density by simultaneous measurement of charge and high frequency MOS capacitance as a function of applied voltage. This charge-capacitance or Q-C method is compared with the usual MOS measurements for the same properties. We find the Q-C method is more accurate and more routine than methods presently in use.In addition, accurate and systematic procedures are introduced for (1) finding the additive constant in the band bending vs gate bias relation, (2) eliminating interface trap error in the doping profile, (3) extrapolation of the doping profile to the interface in the region inaccessible to measurement, (4) correction of oxide charge and work-function determination for interface trap errors and effects of nonuniform doping profiles.     

非均匀掺杂衬底MOS结构少子产生寿命的测量

本文分析了非均匀掺杂衬底MOS电容对线性扫描电压的瞬态响应,提出了三角波C-V技术测量非均匀掺杂MOs电容少子产生寿命的方法.该方法简单、且不需知道衬底的掺杂分布.     

Hybrid-mode analysis of homogeneously and inhomogeneously dopedlow-loss slow-wave coplanar transmission lines

A hybrid-mode analysis is presented to characterize the propagation properties of uniplanar slow-wave MIS (metal-insulator-semiconductor) coplanar transmission lines. The effect of homogeneous versus gradually inhomogeneous doping profile is investigated as well as the influence of the metal conductor losses and finite metallization thickness on the slow-wave factor and the overall losses. Numerical results indicate that thick-film MIS CPWs can support a slow-wave mode with moderate loss up to 40 GHz when the line dimensions are kept in the micrometer range. Furthermore, it is found that an inhomogeneous doping profile can reduce the overall losses and that the effect of metal conductor losses in heavily doped MIS structures is only marginal. On the other hand, in weakly doped or insulating GaAs material a lossy metal conductor leads to a higher propagation constant, exhibiting a negative slope with increasing frequency     

离子注入层少子寿命空间分布的测量

本文分析了非均匀掺杂衬底MOS电容对线性扫描电压的瞬态响应,提出了饱和电容法测量非均匀掺杂MOS电容少子产生寿命空间分布的方法.该方法的优点是测量与计算简单.     

Propagation characteristics of MIS transmission lines withinhomogeneous doping profile

The authors present a hybrid-mode analysis of slow-wave MIS (metal-insulator-semiconductor) transmission lines with a gradually inhomogeneous doping profile. In general it was found that, in comparison with homogeneously doped semiconductor layers, a Gaussian-type doping distribution results in lower losses for the slow-wave mode in both thin- and thick-film MIS CPWs. While the effect of the doping profile is more pronounced in thin-film structures which support a slow-wave mode only up to 3 GHz, it is less significant in thick-film structures. On the other hand, numerical analysis indicates that thick-film structures can support a slow-wave mode at moderate loss up to 40 GHz. The behavior of MIS microstrip lines is similar to that of MIS CPWs, except that for thick-film transmission lines an increase in losses can be observed when the doping profile becomes inhomogeneous. The numerical investigation was carried out using the method of lines. Several transmission lines have been investigated, and results are presented for microstrip, coupled microstrips, and coplanar lines     

Effects of diffused nickel on the silicon-silicon dioxide interface

The effects of diffused nickel on the interface of silicon and a thermally grown oxide are examined. Information regarding effective fixed charge at the interface, surface state distribution and surface state type, is derived from capacitance-voltage characteristics of metal-oxide-semiconductor capacitors made with nickel doped and non-nickel doped silicon. Nickel doping is shown to reduce the density of effective surface states with energies more than 0·15 eV below E_i, and to remove effective charge at the interface of the order of 0·1 μC/cm².     

Interface state analysis using integrated room temperature gated photoluminescence

A gated room temperature integrated photoluminescence (PL) technique for estimating interface state densities in III-V metal-insultaor-semiconductor (MIS) structures is described. The use of gated low temperature spectral PL has already been demonstrated to be more sensitive than conventional 1 MHz capacitance-voltage (C-V) measurements. Room temperature integrated PL was measured on InP MIS structures and interface state densities of approximately 10/sup 12/ (cm/sup 2/ eV)/sup -1/ were calculated, similar to those reported earlier. Furthermore, the elimination of spectroscopic and cryogenic equipment makes this technique simpler and more cost effective than the spectral method, more comparable to C-V measurements.<>     

Measurement of carrier lifetime profiles in diffused layers of semiconductors

This paper describes a method for the measurement of carrier generation lifetime profiles within diffused layers in semiconductors. Knowledge of the lifetime distribution is the key to being able to accurately predict terminal electrical properties as well as understanding the physical processes operating in devices. In addition, the lifetime profile should be a sensitive measure of the quality of the device processing. Although many methods have been developed and applied to the measurement of lifetime in uniformly doped semiconductor regions, this is the first time that lifetime profile measurements have been achieved within diffused layers. In this paper, the lifetime measurements were done by the ZERBST technique using an MOS capacitor created by anodization of the wafer surface. The use of ZERBST plots allows the easy separation of surface recombination from the bulk lifetime eliminating one major source of error during lifetime measurements. In addition, the MOS capacitor used for the lifetime measurement can also be used for the measurement of the carrier concentration allowing excellent correlation between the lifetime and the doping concentration. The anodization techniques used for these measurements allow the stripping of small sections of even shallow diffused layers providing good depth resolution during the profiling. Using this method of lifetime profiling, lifetime measurements have been made up to concentrations of 10¹⁸atoms/cm³in both n- and p-type diffused layers in silicon.     

A single-frequency approximation for interface-state density determination

Fast interface state densities in the SiSi₂ system can be determined by measurements of the MIS capacitor admittance. Traditional detailed analysis require elaborate frequency dependent techniques. The more commonly used approximation techniques are difficult to interpret for interface state densities less than 1 × 10¹¹ eV^?1 cm^?2. We present here a new single frequency technique as an approximation method which provides quantitative criteria on the quality of such interfaces. The data required are a single high frequency capacitance vs voltage measurement and a corresponding conductance vs voltage measurement. The validity of this technique is best demonstrated in a three-dimensional plot of conductance, frequency and voltage. This also gives added insight into the relationship between the temporal and thermodynamic properties of interface electronic states. Comparison of results using this approximation to more detailed treatments demonstrates the validity of this new method for low surface state density determination in a range from 7 × 10⁹ eV^?1 cm^?2 to 8 × 10¹¹ eV^?1 cm^?2.     

I(t) technique for generation rate determination in implanted MOSstructures

A technique for evaluating the generation rare profile of MOS structures based on the measurement of gate current transients at two different gate voltage waveforms in non-equilibrium nonsteady-state is presented. The method allows the evaluation of the generation rate profile in the bulk of inhomogeneously doped MOS structures without requiring knowledge of the doping profile and provides, in contrast to high frequency methods, reliable results in such cases where MOS structures with high series resistances are to be investigated     

Modeling MOS capacitors to extract Si—SiO2interface trap densities in the presence of arbitrary doping profiles

A conventional Poisson solver has been used to calculate the quasi-static capacitance of an MOS capacitor. The effects of an energy dependent Si-SiO2interface trap density and of an arbitrary silicon substrate doping profile have been included. This model has been used to calculate the quasi-staticC-Vcharacteristics and to compare them with those measured using Kuhn's technique for as-received and for gamma-irradiated p-type and n-type silicon MOS capacitors. The substrate doping profiles were obtained from high-frequencyC-Vcurves. Experimental and theoreticalC-Vcurves were made to agree by varying the voltage offset due to fixed oxide charge and both the magnitude and the energy distribution of interface trapped charge. The distributions of interface traps that gave the best fits between experiment and theory are donor-like with a peak 0.1 eV below midgap for the p-type and 0.1 eV above midgap for the n-type silicon MOS capacitors. The predictedC-Vcurves are insensitive to increases in the density of interface traps near the band edge.     

Determination of interface state density in small-geometry MOSFETsby high-low-frequency transconductance method

A method for determining the interface state profile in small-geometry MOSFETs operating in the linear region is described. By comparing the measured high- and low-frequency transconductance of the MOSFET, the interface state density is determined. In addition, using a static drain current measurement, the surface potential can be related to the gate bias without knowledge of the doping profile in the channel     

Analytical investigation of surface potential and related properties of metal/insulator/III–V semiconductor capacitors

An analytical study of the effect of an applied gate bias on the potential and electron density in the semiconductor of metal/insulator/III–V semiconductor (III–V MIS) capacitors is carried out. For this, Poisson's equation is rewritten to a form amenable to analytical study. Si₃N₄ is used as an insulator layer for the MIS capacitors. In order to highlight the advantages of III–V MIS capacitors over metal-SiO₂---Si (MOS) capacitors, the ideal case free from interface traps is considered and theoretical results are obtained also for MOS capacitors. The calculated results strongly demonstrate the superiority of InGaAs MIS and GaAs MIS capacitors to Si MOS capacitors and pinpoint the situation in which the interface states are present.     

Temperature and frequency characterization of InAs nanowire and HfO2 interface using capacitance-voltage method

InAs/HfO₂ nanowire capacitors using capacitance-voltage (CV) measurements are investigated in the range of 10 kHz to 10 MHz. The capacitors are based on vertical nanowire arrays that are coated with an 8 nm-thick HfO₂ layer by atomic layer deposition. CV characteristics are measured at temperatures in the range between −140 and 40 °C and the CV characteristics for nanowires with different Sn and Se n-type doping levels are compared. The comparison of the data at various doping levels points towards large number of traps for highly doped samples, caused by the preferential dopant precursor incorporation at the nanowire surface. We also evaluate the frequency dispersion of the accumulation capacitance and determine values below 2% with weak temperature dependence, indicating the existence of border traps in these nanowire capacitors.     

Surface states at the nGaAsSiO2 interface from conductance and capacitance measurements

Conductance and capacitance measurements have been used to investigate the interface properties of MOS capacitors formed by depositing an insulating layer of SiO₂ on n-type GaAs. The surface potential as a function of applied bias is evaluated using results of high and low frequency capacitance measurements and the two methods are found to yield roughly similar results. The interface state density evaluated from the conductance and capacitance measurements is found to peak near the center of the band gap and also near the conduction band edge. Plots of conductance vs frequency indicate the presence of both fast and slow interface states in these materials.     

Practical quantitative scanning microwave impedance microscopy

Scanning microwave impedance microscopy (sMIM) is an emerging technique that has the potential to displace conventional scanning capacitance microscopy (SCM), and other electrical scanning probe microscopy (SPM) techniques, for the profiling of dopants in semiconductor samples with sub-micron spatial resolution. In this work, we consider the practical application of sMIM for quantitative measurement of the dopant concentration profile in production semiconductor devices. We calibrate the sMIM using a doped calibration sample prior to performing the measurements on an “unknown” production device. We utilize nanoscale C-V curves to establish a calibration curve for both n- and p-type carriers in a single reference and apply the calibration curve to an “unknown” device presenting the measurements in units of doping concentration. The calibrated results are compared to SRP measurements on the same area of the device.     

The relative contributions of recombination and tunnelling at interface states to the a.c. conductance of metal-insulator-semiconductor diodes

The effect on the a.c. conductivity of MIS structures of localized states at the interface between the insulator and semiconductor has been described previously by either Shockley-Read recombination or tunnelling effects. Both of these models are examined here using MIS diodes fabricated from films of semi-insulating silicon doped with oxygen (SIPOS) on p-type Si. The tunnelling model as presently understood does not explain the frequency dispersion seen in the conductance but the inclusion of an extra Shockley-Read term corrects this. Nevertheless we conclude that, although the “extended” tunnelling model provides a better physical understanding of the a.c. conductance, it is more convenient for computational purposes to use the statistical model.     

Determination of a microwave transistor model based on an experimental study of its internal structure

Based on an analysis of the physical structure of a bipolar interdigitated microwave transistor, a simple model is developed which accurately describes the high frequency small signal operation. The transistor model contains 15 elements. The values for ten of these parameters are determined by technological measurements using a special test pattern mask. The values of four of the parameters are determined through measurements made on the transistor, and one parameter is adjusted using the microwave S parameters measurements.A circuit model for the transistor package is also developed. The emitters are all arsenic doped, and the transistor structure does not exhibit a push effect. However, our measurements indicate that the emitter depth varies significantly with the width of the emitter window. This result shows that doping profiles measured on a uniformly doped test wafer may be quite different from the doping profile in the active base of a fine geometry microwave transistor. This implies that much recent work on microscopic models treating charge carrier transport may be invalid, since calculations are based on inaccurate doping profiles. The model in its present form neglects the physical mechanisms related to high current injection, but it describes accurately the transistor characteristics at normal operating currents and provides a valuable guide in optimizing the fabrication technology.