Silicon Dangling Bond Defects Research Articles

A spin-dependent recombination study of radiation-induced P/sub b1/ centers at the [001] Si/SiO/sub 2/ interface

The generation of interface defects at the Si/SiO/sub 2/ boundary is an important aspect of radiation damage in MOS devices. The observations of several independent groups over the last twenty years have demonstrated that Si/SiO/sub 2/ interface silicon dangling bond defects called P/sub b/ centers dominate the interface trap generation process. In the technologically important [001] Si/SiO/sub 2/ system, two P/sub b/ variants may appear. One variant, the P/sub b0/ center, generally dominates radiation and hot carrier damage; however, a less well studied variant, called P/sub b1/, may play a significant secondary role. The electronic properties of the P/sub b1/ centers are quite controversial. Early work by Gerardi et al. indicated quite strongly that the P/sub b1/ centers, like the other P/sub b/ family members, have two levels in the Si bandgap. Several recent publications by Stesmans and Afanas'ev argue that P/sub b1/ centers do not have any levels in the Si bandgap. We present spin-dependent recombination (SDR) measurements which demonstrate that P/sub b1/ centers have levels around the middle of the Si bandgap. Our SDR results strongly suggest that the P/sub b1/ center electron correlation energy is significantly smaller than that of P/sub b0/. Our results may help explain some apparently contradictory studies involving the energy distribution of radiation induced interface states. We also discuss possible relevance of these results to the precision of oxide charge measurements based on the shifts in capacitance versus voltage curves for the Fermi energy at midgap.

Leakage currents and silicon dangling bonds in amorphous silicon dioxide thin films

We use electron spin resonance and current density versus electric field measurements to link silicon dangling bond defects, called E′ centers, to leakage currents in thin films of SiO 2 on silicon.

Hydrogen Cracking in SiO2: Kinetics for H2 Dissociation at Silicon Dangling Bonds

The passivation of silicon dangling bond defects by H2 is an important reaction in Si/SiO2 devices. The dangling bonds studied in this work are those in the a-SiO2 layers, prototype E‘ centers. Experimental estimates of the activation energy of this process are 0.3−0.4 eV, but theoretical calculations give energy barriers that are much larger, around 0.7−0.8 eV. It was suggested that the lack of tunneling in the energy barrier calculations is responsible for the overestimation. This paper is a systematic examination of this reaction, which includes tunneling corrections using the direct dynamics variational transition state theory. The inclusion of this effect is shown to provide an Arrhenius activation energy in good accord with the experimental values.

Two types of traps at the [formula omitted] interface characterized by their cross sections

The dispersion behavior of traps at the Si SiO 2 interface has been investigated applying the modulation capacitance voltage method. N-type MOS samples of different material parameters and preparation conditions were used to vary the state density distribution. Two dispersion regions have been resolved in the upper half of the gap which can be described by two Gaussian broadened time constants. The evaluated capture cross sections can be classified in two groups independent of the specific properties of the samples. The cross sections were assigned to two types of silicon dangling bond defects with different back bond configurations.

Carrier recombination at silicon–silicon nitride interfaces fabricated by plasma-enhanced chemical vapor deposition

Using the light-biased microwave-detected photoconductance decay method, injection level dependent measurements of the effective surface recombination velocity Seff at silicon surfaces passivated by plasma-enhanced chemical vapor deposited (PECVD) silicon nitride (SiNx) films are performed on monocrystalline silicon wafers of different resistivities and doping types. In order to theoretically simulate the measured dependences of Seff on the bulk injection level Δn, the extended Shockley-Read-Hall formalism is used. Simulation input parameters are the energy dependent interface state densities and capture cross sections of the involved interface defects as well as the positive insulator charge density Qf. The energy dependent properties of the interface defects are experimentally determined by means of small-pulse deep-level transient spectroscopy. These measurements reveal the existence of three “deep” silicon dangling bond defects at the Si-SiNx interface with similar interface state densities but very different capture cross sections and hence recombination rates. Another defect is found very close (⩽0.1 eV) to the edge of the silicon conduction band. This defect is identified with the K+ center which is responsible for the large positive Qf values (∼1012 cm−2) at Si-SiNx interfaces obtained from standard dark capacitance-voltage measurements. In order to get a good agreement between measured and calculated Seff(Δn) dependences, a reduction of Qf by one order of magnitude is found to be necessary. The explanation for this reduction is the capture of electrons from the silicon conduction band into the K+ centers. The comparison of Si-SiNx interfaces fabricated by different PECVD techniques shows that the dominant interface defect is produced by the ion bombardment during the SiNx deposition. Thus, avoidance of the ion bombardment leads to a strongly reduced interface recombination and hence a better surface passivation quality.

A physically based predictive model of Si/SiO2 interface trap generation resulting from the presence of holes in the SiO2

A physically based model is developed which explains apparently unrelated aspects of the Si/SiO2 interface trap generation process; the predictions of the model are in at least semiquantitative agreement with observations previously reported in the literature. The model involves interactions between molecular hydrogen and trivalent silicon dangling bond defects in the oxide (E′ centers) and at the Si/SiO2 interface (Pb centers). Our model is primarily directed at interface trap generation caused by ionizing radiation and by hot hole injection phenomena observed in short channel transistors.

Dissociation kinetics of hydrogen-passivated (100) Si/SiO2 interface defects

The activation energy for thermal dissociation of hydrogen from silicon dangling-bond defects (Pb centers) has been measured using both (111)- and (100)-oriented samples. The behavior of each of the three Pb varieties [P111b at the (111) interface, P100b0 and P100b1 at the (100) interface] is compared. For P111b, excellent agreement with previous results by Brower [Phys. Rev. B 42, 3444 (1990)] is obtained. The activation energies of the (100)-interface Pb centers are slightly higher, assuming the same vibrational frequency, and, unlike that of P111b, are affected by a postoxidation anneal.

Room temperature reactions involving silicon dangling bond centers and molecular hydrogen in amorphous SiO2 thin films on silicon

Exposing thin films of amorphous SiO2 to molecular hydrogen at room temperature converts some silicon dangling bond defects, E′ centers, into two hydrogen coupled complexes. These reactions may play important roles in radiation and hot carrier instabilities in metal/oxide/silicon devices.

Room temperature reactions involving silicon dangling bond centers and molecular hydrogen in amorphous SiO/sub 2/ thin films on silicon

Exposing thin films of amorphous SiO/sub 2/ to molecular hydrogen at room temperature converts some silicon dangling bond defects, E' centers, into two hydrogen coupled complexes. It is argued that these reactions may play important roles in radiation and hot carrier instabilities in metal/oxide/silicon devices. The results suggest that an extension of the recent model of M.R. Shaneyfelt et al. (1990) to include molecular hydrogen/E' reactions may provide the most reasonable current explanation for the generation of interface traps at the Si/SiO/sub 2/ boundary. This extension of the Shaneyfelt model would link the idea of molecular hydrogen/oxide defect reactions proposed by D.L. Griscom (1985) with original proton drift ideas of F.B. McLean (1980) and the Shaneyfelt et al. contribution that the proton liberation process is initiated at oxide hole trap sites. >

Direct observation of interfacial point defects generated by channel hot hole injection in n-channel metal oxide silicon field effect transistors

Using a modified electron spin resonance technique known as spin-dependent recombination, we have found that channel hot hole injection in n channel metal oxide silicon (MOS) transistors creates the trivalent silicon dangling bond defect known as the Pbo center. This letter reports the first direct identification of the atomic structure of interfacial point defects created by channel hot carrier stressing in MOS transistors.

Low-temperature electron spin resonance investigations of silicon paramagnetic defects in silicon nitride

We have reproduced and extended some recently reported electron spin resonance (ESR) measurements related to the nature of the dominant charge traps in silicon nitride. We detected defect centers at low temperatures using ESR, in both as-deposited and ultraviolet-irradiated silicon nitride powders and films prepared by low-pressure chemical vapor deposition (LPCVD). Only two silicon dangling bond defects were observed in the silicon nitride, one at g=2.003 (⋅Si≡N3), and the other at g=2.005 (⋅Si≡Si3). The signal intensity at g=2.003 is by far the dominant signal in the LPCVD films and powders subjected to UV illumination; the signal at g=2.005 is only about 3% of its intensity. These results support the idea that there is just one dominant silicon paramagnetic center (⋅Si≡N3), which is responsible for charge trapping in silicon nitride.

Defects in a-SiO2 deposited from a tetraethoxysilane-oxygen plasma

We have studied intrinsic and extrinsic paramagnetic defects in as-deposited and annealed samples of amorphous SiO2 produced by plasma enhanced chemical vapor deposition using tetraethoxysilane and O2. In as-deposited samples the total paramagnetic defect density is 1.7×1018 cm−3 decreasing to 3× 1016 cm−3 after annealing for 10 min in N2 at 800 °C. We identify silicon dangling bond defects (O3 ≡Si•) and, tentatively, nonbridging oxygen-hole centers (O3 ≡SiO•), O−2 ions, C2H•5 radicals, and CO−2 radicals. We observe a defect having a g factor of 2.0040 which we cannot identify.

Identification of silicon nitride/InGaAs interface states

Electrical characterization of the SiNx/InGaAs and SiNx/Si interfaces was carried out by high-frequency capacitance-voltage (C-V) measurements (1 MHz). Two impurity levels, regardless of substrate nature, have been identified and attributed to silicon dangling bond defects, such as 3/4 Si0 and 3/4 Si−. Electron spin resonance measurements, carried out both at room temperature and at 77 K, confirmed the presence of defects such as 3/4 Si0 surrounded by Si bonds.

Characteristics of electron spin resonance in hydrogenated amorphous silicon-carbon/hydrogenated amorphous silicon heterojunctions

The characteristics of light soaking and equilibrium electron spin resonance (ESR) in p-hydrogenated amorphous silicon-carbon/i-hydrogenated amorphous silicon heterojunction are investigated. The influence of the carbon content in the p layer on ESR is also studied in this letter. We find that the light-induced silicon dangling bond defects mainly originate from the i layer and the increased spin density can be decayed by annealing at a low temperature (160 °C). Possible microscopic mechanisms of the light-induced defects observed in the p/i heterojunction are discussed as well.

Optical absorption and defects in amorphous SiNx and SiOx

Abstract Photothermal deflection spectroscopy has been used to measure optical absorption for two series of amorphous silicon-based alloys prepared by the decomposition of silane/ammonia or silane/nitrous oxide mixtures to produce a-SiNx or a-SiOx respectively. Measurements have been made in the energy range 1 to 5 e V. Each sample shows a well-defined exponential edge and a low-absorption region. The inverse slope of the exponential edge increases monotonically with nitrogen or oxygen content. The low-absorption region is analysed and discussed in terms of the defect-state density. For the silicon nitride samples the results can be interpreted in terms of silicon dangling-bond defect states. On the incorporation of some nitrogen the density of defect states increases, but the defect remains at a certain energy above the valence band edge. As stoichiometry is approached the number of such states decreases. For the silicon oxide samples, oxygen incorporation results in a decrease in the density of silicon ...

Energy placement of the D − dangling-bond transition in a-Si:H from photocapacitance and photocurrent spectroscopies

The characteristic gap — state distribution in a-Si:H was measured by photocapacitance transient spectroscopy and steady-state photoconductivity on p- n junction diodes. The results yield a peak placement of 0.8–0.9 eV for the D − transition of the silicon dangling-bond defect and a value of ∼30 A ̊ 2 for the square of the average optical matrix element for this transition.

Identification of deep-gap states in a-Si:H by photo- depopulation-induced electron-spin resonance.

A new technique is described for the microscopic identification of electronic deep levels in semiconductors. Photodepopulation of deep levels is monitored simultaneously with electrical and electron-spin-resonance (ESR) techniques to obtain the distribution of deep levels corresponding to a preselected paramagnetic defect. The technique is demonstrated with combined photodepopulation-induced ESR and photocapacitance measurements on hydrogenated amorphous silicon. The results identify the characteristic Gaussian distribution of midgap states with the distribtuion of the transition between double and single occupancy of the silicon dangling-bond defect.

Effects of dopants and defects on light-induced metastable states in a-Si:H.

Using photothermal deflection spectroscopy we measure the gap-state optical absorption of light-induced metastable defects in undoped, singly-doped, and compensated a-Si:H. We observe an enhancement in the gap-state absorption after illumination which is shown to be due to the creation of new silicon dangling-bond defects and not to a shift in the Fermi level. For singly-doped material, the number of light-induced defects scales with dopant concentration, while full compensation (counter doping) drastically minimizes the density of these defects. The results provide evidence that the doping level influences the light-induced defect formation mechanism, and imply that simply breaking Si--Si bonds may not be the primary mechanism.

Comparison of the Optical Cross Section for the Si Dangling Bond in a- Si:H and At the c - Si/SiO2 Interface

AbstractThe optical properties of the trivalent silicon dangling bond defect in hydrogenated amorphous silicon and at the Si/SiO2 interface are compared. While both defects give rise to ambipolar deep levels within the gap, significant differences in the optical properties between the two systems are found. The absorption in a-Si:H is significantly stronger and is dominated by a transition from the defect to the conduction band while the absorption at the interface is dominated by hole emission. The average dipole matrix element squared is roughly independent of energy in both systems with a magnitude of ∼30Å2. Implications of these results for optical measurements in other silicon systems are discussed.

Material Properties Controlling the Performance of Amorphous Silicon Thin Film Transistors

ABSTRACTAmorphous silicon thin film transistors have been fabricated with a number of different structures and materials. To date, the best performance is obtained with amorphous silicon - silicon nitride thin film transistors in the inverted staggered electrode structure, where the gate insulator and semiconductor are deposited sequentially by plasma enhanced chemical vapour deposition in the same growth apparatus.Localised electron states in the amorphous silicon are crucial in determining transistor performance. Conduction band states (Si-Si antibonding σ*) are broadened and localised in the amorphous network, and their energy distribution determines the field effect mobility. The silicon dangling bond defect is the most important deep localised state and their density determines the prethreshold current and hence the threshold voltage. The density of states is influenced by the gate insulator interface and there is probably a decreasing density of states away from this interface. The silicon dangling bond defect in the bulk amorphous silicon nitride also leads to a localised gap state, which is responsible for the observed threshold voltage instability.Other key material properties include the fixed charge densities associated with primary passivating layers placed on top of the amorphous silicon. The low value of the bulk density of states in the amorphous silicon layer increases the sensitivity of device characteristics to charge at the top interface.