Oxidation-induced defect generation in advanced DRAM structures

Structures containing deep-trenched storage capacitors and shallow-trench isolation were examined in patterns suitable for future generation dynamic RAMs (DRAMs). These same effects were also examined in similar structures which included only the shallow isolation trenches. Observed was a strong interaction between the deep and shallow trenches, which makes structures which incorporate both types much more susceptible to oxidation-induced defect generation than those without deep trenches. It was observed that at higher oxidation temperatures, more oxide can be grown before defects are generated. This is interpreted as a combination of more-efficient visco-elastic relaxation in the oxide and a lower differential oxidation rate between the {110} trench sidewalls and the {100} planar surface at higher temperatures. It was also observed that substantial defect immunity can be obtained by incorporating an oxidation barrier in the trench structures. An overall processing strategy to eliminate defect generation in these advanced structures is suggested     

Bulk growth of single crystal silicon carbide

Silicon carbide (SiC) is a promising wide bandgap semiconductor material particularly suitable for future high power devices operable at high temperatures (>200 °C), at high frequencies, and in harsh environments (chemical and radiation) due to its unique physical and crystallographic properties. The absence of SiC liquid phase, under easily achievable growth conditions of pressure and temperature has created unique challenges for crystal growers.This paper reviews the basics of bulk growth processes, including source sublimation, mass transport of the Si and C species to the growing seed and crystallization. The growth process is shown to be a self-congruent phenomenon where the mass transport of the vapor species and the heat dissipation at the surface of phase transformation are interrelated. This process results in reduction of the growth velocity as a function of crystal thickness. Major mechanisms of defect generation in the grown crystal are discussed.     

Electron bombardment induced defect states in p-InP

A deep level transient spectroscopy (DLTS) study has been made of 1 MeV electron bombardment induced defect states in the lower half band gap of LEC grown Zn doped p-InP. One state was observed in the unirradiated material with a hole emission activation energy H of 0.15 eV. Irradiation resulted in two new states with H of 0.34 and 0.58 eV, and introduction rates dN_t/d? of 1 and 0.04 cm^?1, respectively. Annealing experiments revealed the appearance of an additional state with H(0.52 eV), and recovery of the 0.34 eV defect state above 150°C. The 0.52 eV and 0.58 eV states were found at the highest concentration near the metal-semiconductor interface. The implications of the large introduction rate of the 0.34 eV state are discussed.     

High temperature Hall effect measurements of semi-insulating 4H–SiC substrates

High temperature Hall effect and resistivity measurements have been made on semi-insulating 4H–SiC samples. Both vanadium doped and undoped materials have been studied. Resistivity measurements before and after annealing up to 1800 °C are also reported. The thermal activation energy of the resistivity in vanadium doped samples has one of two values, 1.5 and 1.1 eV, due, respectively, to the vanadium donor level and an as yet unidentified defect. The activation energies for high purity semi-insulating material (HPSI) varied from 0.9 to 1.5 eV. Hall effect measurements were made on several HPSI and 1.1 eV V-doped samples. In all cases the material was found to be n-type. Mixed conduction analysis of the data suggests that the hole concentration is negligible in all samples studied. This suggests that the defects responsible for the semi-insulating properties have deep levels located in the upper half of the bandgap. The resistivity of V-doped samples were unaffected by anneals up to 1800 °C. The annealing results for HPSI samples were mixed.     

Improvement of hardness of MOS capacitors to electron-beamirradiation and hot-electron injection by ultradry oxidation of silicon

The sensitivity to electron-beam-induced damage and to hot-electron-induced damage of metal/SiO₂/Si capacitors has been improved by using ultradry oxide. The ultradry oxide was grown in a double-walled quartz furnace in which water concentration was reduced to less than 1 p.p.m. The interface trap generation in ultradry MOS capacitors due to electron beams is nearly one order of magnitude smaller than that in conventional dry MOS capacitors. Interface trap generation in ultradry MOS capacitors caused by hot electrons is half of that in dry MOS capacitors     

MOS interface-state density measurements using transient capacitance spectroscopy

The use of a deep-level transient capacitance technique for characterizing the interface properties of an MOS transistor (MOSFET) is discussed. A formulation to calculate interface-state densities is extended from the previous work. Experimental results done with both MOSFET's and MOS capacitors are shown to illustrate the advantages of using a transistor-type structure. The use of MOSFET's provides not only the capability of probing the interface-state densities throughout the bandgap but also eliminates the effects of minority-carrier generation at the interface. The interface-state densities for variously processed MOS structures were investigated. For hydrogen-annealed MOSFET's and MOS capacitors on and orientations of n-type substrates, the interface-state densities were shown to peak near the energies close to the band edges, these corresponding to the measurement temperature where the freeze-out of bull majority carriers occurs. The ability to measure mobile-ion-induced interface states was discussed. The present technique, being a direct differential measurement, has several advantages over the conventionalC(V)technique. It may provide a higher sensitivity and more reliable data on the densities of states. Moreover, the measurement of the densities of states does not necessarily require a determination of surface potential.     

Characteristics of inversion-channel and buried-channel MOS devicesin 6H-SiC

Inversion-channel and buried-channel gate-controlled diodes and MOSFET's are investigated in the wide bandgap semiconductor 6H-SiC. These devices are fabricated using thermal oxidation and ion implantation. The gate-controlled diodes allow room temperature measurement of surface states, which is difficult with MOS capacitors due to the 3 eV bandgap of 6H-SiC. An effective electron mobility of 20 cm²/Vs is measured for the inversion-channel devices and a bulk electron mobility of 180 cm²/Vs is found in the channel of the buried-channel MOSFET. The buried-channel transistor is the first ion-implanted channel device in SIC and the first buried-channel MOSFET in the 6H-SiC polytype     

Design of Novel Compact Electromagnetic Bandgap Structures with Enhanced Bandwidth

Two kinds of compact electromagnetic band gap （EBG） structures are designed. A two layer compact EBG structure configured with cross spiral shape line inductors and interdigital capacitors is first presented. Because of its significantly enlarged equivalent inductor and capacitance, the period of the lattice is approximately 4.5% of the free space wavelength. By insetting several narrow slits in the ground plane, the bandwidth of the main bandgap is enhanced by nearly 19%. Further effort has been made for designing a three layer compact EBG structure. Simulation results show that its period is reduced by about 26% compared to that of proposed two layer EBG structure, and the bandwidth of the main bandgap is about 3 times as that of the proposed two layer EBG structure. The detailed designs including a two layer compact 3×7 EBG array with and without defect ground plane and the three layer EBG array are given and simulation results are presented.     

Electrical stimulation of the auditory nerve: direct current measurement in vivo

Neural prostheses use charge recovery mechanisms to ensure the electrical stimulus is charge balanced. Nucleus cochlear implants short all stimulating electrodes between pulses in order to achieve charge balance, resulting in a small residual direct current (DC). In the present study we sought to characterize the variation of this residual DC with different charge recovery mechanisms, stimulation modes, and stimulation parameters, and by modeling, to gain insight into the underlying mechanisms. In an acute study with anaesthetised guinea pigs, DC was measured in four platinum intracochlear electrodes stimulated using a Nucleus C124M cochlear implant at moderate to high pulse rates (1200-14,500 pulses/s) and stimulus intensities (0.2-1.75 mA at 26-200 microseconds/phase). Both monopolar and bipolar stimulation modes were used, and the effects of shorting or combining a capacitor with shorting for charge recovery were investigated. Residual DC increased as a function of stimulus rate, stimulus intensity, and pulse width. DC was lower for monopolar than bipolar stimulation, and lower still with capacitively coupled monopolar stimulation. Our model suggests that residual DC is a consequence of Faradaic reactions which allow charge to leak through the electrode tissue interface. Such reactions and charge leakage are still present when capacitors are used to achieve charge recovery, but anodic and cathodic reactions are balanced in such a way that the net charge leakage is zero.     

Modeling of the silicon (100) thermal oxidation: from quantum to macroscopic formulation

In this paper, we investigate the modeling of dry silicon thermal oxidation in the light of the model capabilities and the trends in microelectronics. We show how a combined use of different models can be made in a way to generate process simulations that are strongly related to microscopic physical phenomena. In conjunction with experimental literature data, first principle calculations have been carried out with the objective of isolating some elementary oxidation mechanisms, i.e. basic atomic movements and their corresponding activation energies. This preliminary list of mechanisms is discussed in detail. A growth mechanism allowing the oxide defect generation is proposed. We then present Monte Carlo calculations with the implemented mechanisms where at least three silicon layers are oxidized. Finally, we introduce a macroscopic formulation of these mechanisms via the Chemical Rate Theory.     

Ultra-thin silicon-dioxide breakdown characteristics of MOS devices with n+and p+polysilicon gates

In this work we investigate the effect of the gate material on the breakdown characteristics of ultra-thin silicon dioxide films at low voltages (<6 V). When MOS capacitors are stressed with a positive gate voltage, the charge to breakdown and time to breakdown at a fixed oxide-voltage drop are significantly smaller in p+ polysilicon-gate capacitors than in n+ polysilicon-gate capacitors. The results are interpreted in terms of a simple model of hole tunneling resulting from hot-hole generation in the anode by hot electrons entering from the silicon dioxide. Extrapolation of high-voltage-breakdown lifetime measurements for relatively thick-oxide devices to low voltages may be complicated by this mechanism.     

Proposal for All-Solid Photonic Bandgap Fiber With Improved Dispersion Characteristics

We propose a novel design of all-solid photonic bandgap fiber (AS-PBGF). It is designed by introducing a new defect, several bigger high-index rods, in the cladding of a conventional AS-PBGF. Using the plane-wave expansion method and the full-vector finite-element method, we study the effect of introducing such bigger high-index rods. The numerical results show that both large normal and anomalous dispersion are induced within bandgap rather than near the edge of bandgap as conventional PBGF does. More importantly, the confinement loss of the LP₀₁ modes around the wavelengths, where large normal and anomalous dispersion are induced, could be decreased by increasing the rings of high-index rods for the fact that these wavelengths are within the bandgap.     

MOS capacitor on 4H-SiC as a nonvolatile memory element

Nonvolatile memory characteristics of MOS capacitors are presented in this letter. The MOS capacitors have been fabricated on N-type 4H SiC substrate with nitrided oxide-semiconductor interface. The charge-retention time is in the order of 4.6×10⁹ years, as determined by thermally activated (275-355°C) capacitance-transient measurements and extrapolation to room temperature. The estimated activation energy of the charge-generation processes is 1.6 eV. The results and the analysis presented in this letter demonstrate that 4H SiC MOS capacitors can be used as a memory element in nonvolatile RAMs     

Surface Plasmon Bragg Gratings Formed in Metal-Insulator-Metal Waveguides

We propose and numerically analyze surface plasmon Bragg gratings formed by a periodic variation of the width of the insulator in a metal-insulator-metal waveguide. The results indicate that very good filtering characteristics can be achieved in these plasmonic Bragg gratings. To suppress the sidelobes in the transmission spectrum, we further propose S-shaped Bragg cells and find better performance. By introducing a defect into the grating, a defect state with high Q-value is introduced into the bandgap and a Fabry-Peacuterot-like structure is formed     

Electrical characterization of a JFET-accessed GaAs dynamic RAMcell

A complete one-transistor dynamic RAM cell in GaAs is discussed. Read and write operations is monitored by observing the capacitance of the storage node. Storage times on the order of a few seconds are obtained at room temperature with an activation energy slightly less than half the zero-temperature bandgap     

Refinements in the measurement of depleted generation lifetime

Constant capacitance measurement of bulk generation lifetime using MOS capacitors with a typical desktop computer controlled interface bus measurement system is shown to be practical for medium-and high-lifetime silicon. Refinements to the basic technique are developed to deal with surface generation, diffusion from the neutral bulk, and generation in the lateral surface depletion region.     

Comphy — A compact-physics framework for unified modeling of BTI

Metal-oxide-semiconductor (MOS) devices are affected by generation, transformation, and charging of oxide and interface defects. Despite 50 years of research, the defect structures and the generation mechanisms are not fully understood. Most light has been shed onto the charging mechanisms of pre-existing oxide defects by using the non-radiative multi-phonon theory. In this work we present how the gist of physical models for pre-existing oxide defects can be efficiently abstracted at a minimal loss of physical foundation and accuracy. Together with a semi-empirical model for the generation and transformation of defects we establish a reaction-limited framework for unified simulation of bias temperature instabilities (BTI). The applications of the framework we present here cover simulation of BTI for negative (NBTI) and positive (PBTI) gate voltages, life time extrapolation, AC stress with arbitrary signals and duty cycles, and gate stack engineering.     

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.     

Influence of different deposition conditions of top and bottom electrode on the reliability of Sr0.8Bi2.2Ta2O9 ferroelectric capacitors

In this study, the reliability (fatigue, imprint, and retention) of Pt/SBT/Pt capacitors was investigated. For non-integrated test capacitors, using a different process for top and bottom electrode formation, fatigue degradation is larger than for integrated capacitors using symmetric top and bottom electrode deposition process. Also, for the non-integrated capacitors, imprint behavior and retention loss were observed to depend on the voltage polarity. From hysteresis as well as leakage characteristics, these effects were attributed to the presence of a built-in field favoring the polarization of SBT from the bottom to the top electrode in non-integrated capacitors. The built-in field was attributed to defect generation during the top electrode sputtering at room temperature. For the integrated capacitors, whereby the top electrode is deposited using the same high temperature process (>150 °C) as the bottom electrode, neither imprint degradation nor retention loss was observed under the applied conditions, showing excellent reliability of integrated SBT capacitors.     

Electron-beam-induced-current investigations on MOS and MNOS devices

The transient behavior of the electron beam induced current (EBIC) in MOS and MNOS capacitors was studied for various Si-oxide and Si-nitride preparation and annealing conditions and interpretations of the corresponding SEM-EBIC micrographs are given. Due to the higher radiation hardness of MNOS structures as revealed by HF and quasistatic CV data, appropriate defect imaging without beam artifacts is far more easily achieved in MNOS than in MOS devices, particularly at higher magnifications. The useful application of MNOS structures for defect characterization by EBIC imaging and generation lifetime is demonstrated.