Metal Oxide Silicon Capacitors Research Articles

Bidirectional stress on a p-metal–oxide–silicon capacitor

Tunneling Fowler–Nordheim bidirectional electron injections were performed on a metal–oxide–silicon capacitor under constant voltage, and the study of generated defects behavior was investigated. It was found that defects generated within the oxide are of the same physical nature and are mainly composed of neutral traps. The charge and discharge of these traps depend on the oxide field polarity. At the oxide–silicon interface, the saturation of interface state generation is maintained by the alternate change of the stress field polarity. This saturation is linked to the Si−δ–H+δ or other Si−δ–A+δ polar bonds at the silicon/oxide interface.

Bias Dependent Contrast Mechanisms in EBIC Images of MOS Capacitors

Defects and inhomogeneities in the electrical properties of metal oxide silicon capacitors are analyzed by scanning electron microscopy, using the electron beam induced current technique (MOS/EBIC). All capacitors were analyzed in their as‐fabricated or prebreakdown condition. The collected signals and image contrast are found to be highly dependent on the gate‐to‐substrate bias applied during MOS/EBIC examination, and this bias‐dependence is shown to be correlated with the nature and physical location of the defect. Specific MOS defects were selected for this study according to their position in the substrate, in the oxide, or at the interface. Substrate defects examined were misfit dislocations in epitaxial Si(Ge) on Si. Interfacial inhomogeneities included thermally oxidized, reactive ion etched (RIE) Si surfaces, and precipitates or “D‐defects” which extend to meet the Si surface. Oxide layer inhomogeneities were also detectable which exhibited a strong contrast dependence on the oxide electric field strength. © 1999 The Electrochemical Society. All rights reserved.

Suppressing Plasma Induced Degradation of Gate Oxide Using Silicon-on-Insulator Structures

Plasma-process induced degradation of gate oxide of metal/oxide/silicon (MOS) devices on silicon-on-insulator (SOI) structures and bulk wafers was investigated. In order to evaluate the degradation of the gate oxide, the charge-to-breakdown Qbd of the MOS capacitors was measured under a constant current condition. It was found that the degradation of the gate oxide could be drastically suppressed using SOI. A thicker buried oxide layer showed greater suppression of the gate oxide degradation. A smaller device island size showed lower gate oxide degradation, although the dependence was rather weak. An electrical model is discussed, to account for the effect of SOI, in which the capacitance of the buried oxide played a key role in suppressing the degradation.

Influence of Crystal-Originated “Particle” Microstructure on Silicon Wafers on Gate Oxide Integrity

To clarify the influence of crystal-originated “particles” (COPs) on gate oxide integrity (GOI), a new GOI evaluation method has been developed. This method compares the GOI of a metal oxide silicon (MOS) capacitor which includes a COP with a MOS capacitor that is COP-free by measuring the capacitors' I–V characteristics. Furthermore, to study the relationship between the shape of COP and GOI, the COP microstructure on the wafers was observed by atomic force microscopy (AFM) in the as-received state, after NH4OH/H2O2/H2O (SC-1) cleaning, high temperature annealing and repolishing. It was found that the presence of COP was the main cause of GOI failure and also that the shape of COP was closely related to the GOI yield. The microstructure of the original COP in a crystal is concluded to be an octahedral void and the same as an IR scattering defect.

Thermally oxidized AlN thin films for device insulators

The structural, optical, and electronic properties of an insulating material prepared by the thermal oxidation of AlN thin films on Si have been studied by a number of different experimental techniques. The thermal oxidation at 1100 °C of reactively sputtered AlN films on Si wafers was found to result in the formation of an oxide with a relative Al to O concentration near Al2O3 with small amounts of incorporated N. The structure of the AlO:N oxide could be varied between amorphous and polycrystalline, depending on the preparation conditions, and the oxide surface was found to be approximately three time smoother than the as-sputtered AlN films. Metal–oxide–silicon capacitors had an oxide charge density of about 1011 cm−2, capacitance–voltage characteristics similar to pure SiO2, and a dielectric constant of 12.4. Infrared measurements yielded a refractive index of 3.9. These results indicate that thermally oxidized AlN films show promise as insulating structures for many integrated circuit applications, particularly for the case of III–V and group III–nitride based semiconductors.

Analysis of positive charge trapping in silicon dioxide of MOS capacitors during Fowler-Nordheim stress

Metal-oxide-silicon (MOS) device degradation due to trapped holes in thermally grown thin (22–33 nm) SiO 2 gate oxides under Fowler-Nordheim (FN) stress at low injected electron fluence has been analyzed theoretically. A comparative study of degradation under various modes of FN stressing (constant current and constant voltage) from the accumulated layer of 〈100〉 n-Si of n-PolySi gate MOS capacitors is presented. The present analysis is based on tunneling electron initiated band-to-band impact ionization in SiO 2 as the possible source of generated holes. The theoretical analysis is extended with Gaussian and uniform distribution of trapped holes in the oxide. The theoretical results obtained from the model are in good agreement with the experimental results of FN threshold voltage shift as a function of electron fluence obtained by Fazan et al.

Capacitance–voltage curve recovery of MOS capacitors passivated with BaF2–BeF2–SiO2 –B2O3–P2O5 glasses

K. Kobayashi, J. Mater. Chem., 1997, 7, 127 DOI: 10.1039/A602563C

Mechanism of nitrogen coimplant for suppressing boron penetration in p+-polycrystalline silicon gate of p metal–oxide semiconductor field effect transistor

The mechanism of the nitrogen co-implant to suppress the boron penetration in p+-polycrystalline silicon gate has been investigated. The nitrogen coimplant with the BF+2 combines with the boron to form a B–N complex which results in a retardation of boron diffusion. It is found that metal–oxide–silicon capacitors with nitrogen implantation show improved electrical properties.

Hysteresis Curve Variations of MOS Capacitors Passivated by Ba(PO3)2-Al(PO3)3-B2O3 Glasses

Abstract The purpose of this work is to clarify the relationship between some of the properties of MOS (metal, oxide, silicon) capacitors passivated by Ba(PO3)2-Al(PO3)3-B2O3 glasses and the hydroxyl contents of the glasses. When substitution of Al(PO3)3 for Ba(PO3)2 progressively decreased the OH− absorption intensity, the C-V (capacitance-voltage) curve shift, ΔVG in the MOS capacitors decreased.

Reflow of BeF 2-B 2O 3-GeO 2-SiO 2 glasses and application of their membranes to metal-oxide-silicon (MOS) capacitors

The capacitance-voltage ( C-V) characteristics of metal-oxide-silicon (MOS) capacitors passivated by BeF 2-B 2O 3-GeO 2-SiO 2 glasses with various water and fluoride contents were investigated. As the OH − absorption coefficient of the glass increased, adverse effects on the recovery of hysteresis loops of C-V curve shifts were observed. The water content is closely related to the fluoride content in the BeF 2-B 2O 3-GeO 2-SiO 2 glass. The viscous flow point of the glass was lowered with increasing degree of ionic character obtained from Hannay's equation. The normal C-V curve shift was observed for the MOS capacitors passivated with the glass with 25% BeF 2.

Effects of carbon implantation on generation lifetime in silicon

In this study, we present characterization of metal–oxide–silicon (MOS) capacitors fabricated on carbon (C12) implanted Si substrates. Carbon was implanted at an energy of 50 keV with doses ranging from 1×1012 cm−2 to 4.1×1015 cm−2. Metal–oxide silicon capacitors were fabricated and used to determine the MOS capacitance–voltage (C–V) and capacitance–time (C–t) behavior. These measurements revealed a strong correlation between carrier lifetime and the C dose. Degradation in lifetime was observed for C dose levels as low as 4×1012 cm−2. At C doses equal to and above 6.4×1013 cm−2, extremely low generation lifetimes were obtained (∼10−7 s). On the other hand, for C dose levels higher than 2.7×1014 cm−2, a low accumulation capacitance was observed at high frequencies and attributed to hole traps. Below this dose, both flatband voltage and interface trap density of the C implanted samples were comparable to those of the monitors.

SiO2 hole traps with small cross section

SiO2 hole traps with small cross section (σ≤10−15 cm2) in Al gated metal–oxide–silicon capacitors have been studied using vacuum ultraviolet hole injection in combination with capacitance voltage measurements. The data show that small σ hole traps are related to H/hole pairs or protons trapped in the oxide. Since accumulated positive charge and H vanish simultaneously from the oxide in times of the order of 102 s, it is proposed that they migrate together through the oxide as a proton. The small σ hole traps are not associated with defects in the as-grown oxide; they are generated by radiation induced release of atomic H. Their number is governed by the rates of release and of removal (dimerization) of atomic H.

Ion beam mixing for enhanced electron tunneling in metal-oxide-silicon structures

Metal-oxide-silicon (MOS) structures were fabricated to investigate enhanced Fowler–Nordheim tunneling in thin oxides due to ion beam mixing. Ions of germanium were implanted into a 100 nm polycrystalline silicon layer deposited on 10 nm thermal silicon dioxide such that the tail of the implant profile contains the thin oxide. Besides simple MOS capacitors and transistors, flash electrically erasable programmable read only memory (flash EEPROM) cells were fabricated for the first time using this technique. Using 1×1015 cm−2 at 80 keV the Fowler–Nordheim tunneling barrier reduced by about 0.9 eV at the polycrystalline gate/oxide interface and by 1.3 eV at the oxide/substrate interface. The consequently lower program/erase voltages in the flash EEPROM were measured. Flash EEPROM charge retention measurements show that the discharge process is logarithmic in time. This leads to the possibility of flash EEPROMs being programmed and erased at low voltages and having sufficient charge retention for several years operation.

New methods for using the Q-V technique to evaluate Si-SiO2 interface states

The Q-V technique applied to metaloxide silicon capacitors makes it possible to measure the silicon-oxide interface potential directly with only a few simple assumptions. From these data of interface potential versus gate voltage it is possible to calculate the interface state distribution. The Q-V technique can be used over the entire band gap range and separate n- and p-type samples are not required. New simplified techniques for doing this are presented. The measurements can also be used to determine the band gap of the semiconductor which should have application for the study of silicon-germanium alloys.

Compensating effects in time-dependent dielectric breakdown (MOS capacitors)

Current and cathode electric field data have been measured in a constant-voltage accelerated test of metal-oxide-silicon (MOS) capacitors. The data show that the coefficients in the Fowler-Nordheim equation are: (1) random variables (varying across the MOS capacitors), and (2) have a correlation coefficient of 0.88. The analysis suggests that for typical electric fields used in accelerated testing of MOS capacitors, the standard deviation of log (failure time) increases with decreasing electrical stress. >

Ion-induced electrical breakdown in metal-oxide-silicon capacitors

Metal-oxide-silicon (MOS) capacitors used in the breakdown mode were constructed to detect 252Cf fission fragments. The physical effects related to radiation-induced breakdown were studied and found to have a relationship to intrinsic dielectric breakdown. Physical studies were made of the effect of oxide annealing temperature between 100 and 400 K, oxide thickness, differing metal electrodes, and the materials interaction due to the spark discharge breakdown. By means of both silicon-ion and cesium-ion implants near the metal-SiO2 interface of the MOS capacitor, the current emission into the SiO2 was found to be significantly enhanced; however, the enhanced emission was found to have no effect on increasing the sensitivity to lower specific ionization radiation as seen by fission-fragment detection. The results indicate that the radiation-induced breakdown mechanism occurs within the bulk, or body, of the SiO2 film and is not influenced by conditions at the dielectric interfaces. It was found that thin films of the refractory metals HfO2 or ZrO2 between the oxide film and a top aluminum electrode prevented Al-SiO2 interaction during discharge and allowed operation of the MOS capacitor at higher electric fields. Obtaining higher operating fields significantly improved the minimum specific ionization detectability to 14 MeV cm2/mg from a prior value of 22 MeV cm2/ mg.

Construction of a prototype MOS electrometer

A parametric metal-oxide-silicon (MOS) electrometer, which offers the possibility of an electrometer with an input bias current lower, and an input resistance higher than any presently available has been constructed. The design of the electrometer permits the use of thicker silicon dioxide gate insulation than is possible with MOS field-effect-transistors (MOSFET) electrometers; thus reducing gate leakage currents. It also has a unique feedback configuration which eliminates any leakage current through the feedback loop. The electrometer is a solid-state analog of the vibrating-capacitor electrometer with MOS capacitors replacing the vibrating capacitor. The design and construction of a prototype which demonstrates the feasibility of the MOS electrometer is described.

Polarizable capacitance versus voltage characteristics for metal, oxide, and silicon capacitors passivated by various oxide glasses

It was found experimentally that polarizable capacitance versus voltage (C-V) characteristics for metal-oxide-silicon (MOS) capacitors, passivated by various oxide glasses, depend on molar polarizability for passivation glasses. Experimental data showed C-V curve shifts toward higher voltage were evidently caused by polarizable ions in glasses. The possibility for making a material choice in semiconductor device passivation was discussed, using the Poisson equation for the glass-passivated MOS capacitors.

TIME PERTURBATION ANALYSIS FOR THE MOS SYSTEM

The development of a numerical implementation of the small signal response of the MOS (Metal‐Oxide‐Silicon) capacitor using time perturbation analysis is discussed. The effects of nonconstant doping profiles and interface and bulk traps are included. The model uses Fermi‐Dirac statistics to describe the occupancy of the interface and bulk traps. The oxide region is considered to have no mobile carriers and any fixed oxide charge distribution is modeled as a charge sheet at the Si‐SiO2 interface. This technique can be used to find the small signal response of the device from the static solution.

Hydrogenation and annealing kinetics of group-III acceptors in oxidized silicon

Acceptor (B, Al, Ga, and In) density versus time curves during avalanche electron injection (AEI) and constant-temperature thermal annealing experiments obtained from metal-oxide-silicon capacitors (MOSCs) show two distinguishable phases. The time dependence of the acceptor density during AEI shows an initial delay due to electron-impact release of hydrogen trapped in the gate conductor and oxide layers and a long-time decay due to the thermal capture and electron-impact emission of the atomic hydrogen at the group-III acceptor centers in the silicon surface layer. Thermal anneal of hydrogenated acceptor begins at 50 °C for boron and 100 °C for Al, Ga, and In. The initial phase during thermal annealing of AEIed MOSCs follows a first order kinetics at higher annealing temperatures, reaching a steady-state acceptor density before the second phase begins. The long-time anneal follows strictly a second-order kinetics which is rate limited by the recombination of two hydrogen atoms to form a molecule. Incomplete anneal is observed at higher temperatures when the dissociation rate of the hydrogen molecule becomes comparable with the recombination rate of two hydrogen atoms. Analytical solutions are obtained which account for all the details of the observed hydrogenation and annealing curves. These solutions are used to evaluate the thermal capture and emission rates and electron-impact emission rates of hydrogen or proton at the group-III impurity centers and the bimolecular generation and recombination rates of hydrogen. A new concept of hydrogen or proton traps in analogy to the electronic hole or electron traps is introduced to analyze the kinetics and account for the observed chemical trends between thermal capture and emission rates, thermal activation energy and bond strength. Chemical trends are noted which are consistent with the trapped proton activation energy and hydrogen bond strength trend, B<Al<Ga<In.