Quantitative TEM of point defects in Si

We review the use of transmission electron microscopy (TEM) to provide a quantitative measurement of both vacancy and interstitial clusters in ion-implanted silicon. Interstitials agglomerate into rod-like defects on 131I) planes, and the evaporation of these defects can be directly correlated to the diffusion enhancements observed during annealing of ion-damaged silicon. Vacancy clusters are easily detected in TEM once they have been labelled using a Au-diffusion technique. The combination of the two approaches provides a quantitative test for models of implantation and annealing in silicon. Detailed models for point defect behaviour, which include Ostwald-ripening and the surface recombination velocity, reproduce all of the crucial features of the observed defect annealing.     

Isochronal annealing study of hydrogen interaction with implantation-induced point defects in p-type silicon

Isochronal annealing with zero and reverse bias applied to Schottky diodes was used to monitor the evolution of hydrogen interaction with point defects observed in hydrogen-implanted p-type silicon, i.e., divacancy (VV), carbon–oxygen interstitial pair (C_iO_i) and two levels at E_v+0.28 and E_v+0.50 eV. The VV and C_iO_i are passivated by hydrogen liberated from hydrogen-containing defects during annealing in the temperature range 90–150°C and reappear upon annealing above 180°C under reverse bias due to hydrogen liberation and its field drift. Two levels at E_v+0.50 and E_v+0.28 eV are ascribed to irradiation-induced and hydrogen-related defects, respectively.     

The influence of sinks of intrinsic point defects on phosphorus diffusion in Si

The influence of sinks associated with structural defects is analyzed qualitatively based on the model of P diffusion in Si by the dual pair mechanism. It is demonstrated that the allowance made for sinks of self-interstitials leads to the retardation of the enhanced P diffusion for the low-content region in the tail of the concentration profile. The influence of sinks is most pronounced if the position of their peak concentration is in the region of the peak of generation of self-interstitials inside the diffusion layer. From a comparison of the result of calculations with the experimental data, the parameters of the capture of self-interstitials by structural defects, which are introduced by the P diffusion and implantation of electrically inactive Ge and N impurities, are determined.     

Poxvirus virions: their surface ultrastructure and interaction with the surface membrane of host cells

Virions of vaccinia and orf viruses were examined by ultrahigh-resolution scanning electron microscopy using a non-coating method. Intracellular mature particles of vaccinia virus appeared to be covered with a net and ultrastructurally their surface consists of many fine ridges and globules, while the surfaces of orf virus mature particles recovered from infected cells consist of spirally running protrusions. The ridge-like structures of vaccinia virus were presumed to correspond to surface tubules shown by negative staining of this virus, while the spiral protrusions of orf virus were presumed to correspond to spiral threads having a criss-cross appearance by the same staining. Using scanning electron microscopy in which the samples were prepared by the conventional method, we observed: (i) many virions, i.e. one or two hundreds, or occasionally more reaching about one thousand particles, of the IHD strain of vaccinia virus, (ii) many or a moderate number of virions, i.e. about one hundred or fewer particles, of the 58 strain of cowpox virus and (iii) rather few virions, i.e. several tens or fewer particles, of the Iwate strain of orf virus on the free surface of each cell infected with these viruses. It must be noted that the number of virions detected considerably differed in respective cells examined. Virus budding was frequently observed at the cell surface of monolayer cells infected with vaccinia virus but it was never detected with cowpox or orf virus, indicating a difference in the mechanism of virus release between vaccinia and the other two viruses. When whole cells infected with vaccinia virus were examined by a combination of high-voltage and scanning electron microscopies, virions on the cell surface and those inside the cells were clearly differentiated. All virions on the cell surface had an envelope, and some of the envelopes had a slack and/or one or more bulges.     

Formation of defects in GaAs and Si as a result of Pd deposition onto the surface

Photoelectric spectroscopy applied to the barriers between a semiconductor on a metal and an electrolyte is used to study the formation of defects in the near-contact region of GaAs and Si as a result of Pd deposition onto the surface. It is shown that a layer that arises as a result of the chemical interaction between Pd and a semiconductor at 100°C, containing defects with deep levels, extends to ～0.4 μm deep in GaAs and ～1 μm in Si. If one or several strained layers of InGaAs quantum wells are incorporated into the near-contact GaAs region, the defects do virtually not penetrate deeper than the first quantum well. This circumstance makes it possible to reduce the depth of the defect-containing layer; however, the volume concentration of the defects in this layer increases appreciably in this case.     

Hydrogen interaction with defects and impurities in 6H-SiC

The dynamics of hydrogen capture and release from trapping centers in 6H-SiC after plasma hydrogenation and annealing was investigated by low-temperature photoluminescence (PL). Indications of competing processes of hydrogen capture by different trapping centers were observed. Passivation of Al acceptors with hydrogen is the dominating process during plasma hydrogenation or plasma etching. Irreversible release of hydrogen from Al-trapping centers and additional trapping of hydrogen by Si vacancy (V_Si) to form a V_Si+H complex occurred during annealing at temperatures above 300°C. It is suggested that the V_Si+H complex may be playing an important role in keeping hydrogen in SiC after higher temperature treatment.     

Localized electron irradiation methods and their application to detection of flow-field of point defects

We propose new techniques of electron irradiation for studying the kinetics of simple point defects and their agglomeration, by making the most use of the intrinsic function of an ultrahigh-voltage scanning transmission electron microscope. The methods enable us to realize a very high defect production rate at a localized area and create a spot or band-shape source of point defects. The present methods were applied to an attempt to detect the point defects flowing out of a very localized area, examining the growth and shrinkage of pre-introduced interstitial clusters. At low temperatures where vacancies are immobile, outflow of the interstitials was observed. In contrast, at an elevated temperature where vacancies are mobile, outflow of the vacancies seemed to play a dominant role in the apparent secondary defect reactions. A possible explanation to aid understanding of the present results is proposed.     

Interaction of mechanical stress with residual defects in implanted Si

After drive-in of arsenic-implanted emitter structures dislocations are found at the edge of the masking window and in the unimplanted surrounding regions while the implanted areas are defect-free. These dislocations originate from a defect structure which exists temporarily in the emitters during drive-in heat treatment. The dislocations are attracted to the window edge and are pushed into the surrounding region by mechanical stresses which have their origin in the intrinsic stress of the masking layer. No penetration of dislocations outside the implanted area is observed when the implantation is done through a thin oxide film. A mechanical stress analysis of film edge induced stresses can account for the observed defect patterns.     

Temperature anomalies of the work function and relaxation of the surface conductivity of n-type Si in the presence of structural defects

The temperature behavior of the high-frequency conductivity of surface electron channels in Schottky diodes based on high-resistivity p-type Si containing near-surface, oxidation-induced stacking faults is studied. It is shown that the reversible temperature-induced changes in the surface band bending and the work function of Si have a stepwise character in the temperature range 80–300 K. It is concluded that the surface concentration of free electrons increases during cooling from 180 to 80 K at temperatures which are characteristic of the ordering of water dipoles. These effects are associated with structuring of the water adsorbed on the Si-SiO₂ interface and with the ordered orientation of the water dipoles on the surface in response to the loss of their rotational mobility. Fiz. Tekh. Poluprovodn. 32, 82–88 (January 1998)     

Stationary Intensity Profiles of Recombination Waves in Si:Zn

For slow recombination waves in Si:Zn, stationary intensity profiles along the specimen are measured with an SEM operated in the voltage-contrast mode. The main findings are as follows: (i) The intensity falls from a maximum with increasing distance from the cathode, where a stationary high-field domain is located, and almost vanishes far short of the anode. (ii) The intensity grows with specimen voltage. (iii) The voltage-contrast image for the highest specimen voltage displays oscillatory potential variation over the stationary high-field domain, indicating the stratification of electric field.     

In situ study of the interaction of oxygen with the Si(111) surface by ultrahigh-vacuum reflection electron microscopy

Reactions of gases with an atomically clean silicon surface were examined by ultrahigh-vacuum reflection electron microscopy. The initial stages of interaction of oxygen with the Si(111) surface were studied in the temperature range from 500 to 900°C. Motion of monatomic steps to the upper terraces during etching by oxygen at high temperatures was visualized. The conditions for the formation of surface vacancies were determined. The dependence of the step velocity on the width of adjacent terraces was measured. Oscillations of the intensity of the electron beam reflected specularly from the Si surface were observed during the etching of silicon by molecular oxygen, which proceeded by a two-dimensional-island mechanism. The activation energy for the diffusion of surface vacancies, which are formed owing to the interaction of oxygen with silicon, was estimated to be 1.35±0.15 eV.     

The nature of point defects in CdTe

High temperature in-situ Hall effect measurements in CdTe single crystals grown by different techniques at 500–1,200 K under well-defined Cd and Te vapor pressure were made. It was established that native point defects (PD) Cd _i ²⁺ and V _Te ²⁺ are dominant at T>770 K in Cd-rich CdTe. Their formation enthalpies were determined (ΔH _VTe ²⁺ =1.3 eV; ΔH _Cdi ²⁺ =2.5 eV). It was shown that V _Te ²⁺ dominate at low temperatures and Cd _i ²⁺ begin to prevail at T>930 K. In Te-saturated CdTe at heating up to ～800 K, the hole density was Te vapor pressure independent. At higher temperatures (HT), the conductivity changed to intrinsic type, turning then into n-type. The results were explained in the framework of Kröger’s quasichemical formalism assuming the presence of an electrically active foreign point defect, the oxygen acceptor. The PD structure modeling demonstrated satisfactory agreement with experimental results both for temperature and component vapor pressure dependencies.     

TFT LCD常见点缺陷的检测与修复

TFT—LCD在制程中会产生亮点、暗点、闪点、碎亮点等常见点缺陷。说明了检测点缺陷的装置、方法和过程。采用ITO隔离、激光炸射等方法对点缺陷进行修复或者淡化,其中ITO隔离法修复或淡化效果显著。修复成功率从45％提升到80％。     

Stationary High-Field Domain in Si : Zn at the Excitation Threshold of Recombination Waves

The generation and voltage dependence of a stationary high-field domain in Si : Zn about the excitation threshold of slow recombination waves are investigated by scanning electron microscopy. It is found that the domain arises at the cathode when the electric field in the specimen is about 10 V/cm. The field inside the domain and at its boundary (10³ V/cm) considerably exceeds the average specimen field. The field in the domain linearly increases with dc specimen voltage but stays within the same order of magnitude. The domain linearly grows to approximately 100 m with increasing dc specimen voltage. Domain generation is found to occur in passing from a linear to a sublinear portion of the specimen current–voltage characteristic.     

Equilibrium of native point defects in tin dioxide

A model of electrically active and neutral native point defects in SnO₂ is developed. Thermodynamic analysis of the equilibrium of the native point defects makes it possible to construct the phase diagram of lead dioxide. The contradiction between n-type monopolar conductivity and the two-sided homogeneity region of the SnO₂ phase is resolved. Fiz. Tekh. Poluprovodn. 32, 1158–1160 (October 1998)     

Ripple structures associated with ordered surface defects in dielectrics

Laser-induced ripple structures on material surfaces have been observed by a number of workers for various materials including metals, semiconductors, and dielectrics. A model has been proposed [1] which correctly accounts for the spacing and polarization dependence of the ripples, and the association of the ripples with material defects. In this letter, experimental results which unambiguously show the association of these features with defects are presented. Quantitative measurements of laser-induced damage thresholds show a reduction of damage thresholds for surfaces with controlled linear defects aligned orthogonal to the incident laser field (as predicted in [1]).     

On the interaction of hydrogen RF plasma with implantation-induced defects in MOS structures

The interaction of atomic hydrogen with defects in boron-implanted MOS structures under the influence of RF plasma is studied using the method of thermally stimulated charge release. The observed variation of defect parameters suggests that plasma radiation and hydrogen-defect reaction, supported by enhanced wafer temperature, cause the reconstruction of defect structure. It is found that when atomic hydrogen reacts with a defect of the proper structure the temperature of the passivation process can be decreased.     

Electrical effects of clustered defects in heteroepitaxial Si films

Our work indicates that the behavior of injected majority and minority carriers in representative Si/spinel samples is dominated by deep-level defects that are agglomerated into defect clusters rather than being uniformly distributed in the volume of the Si layer. Since these defect clusters will be surrounded by space-charge regions, the resulting trap occupancy-dependent potential barriers result in slow, nonexponential majority carrier trapping effects but subnanosecond minority carrier lifetimes. Accurate numerical calculations of the electrical properties of a sheet of clustered defects are shown to agree with detailed measurements at 90 and 300°K of the transient conductance decay in P- and N-type films following pulsed carrier injection from electron bombardment. A significant conclusion of the theoretical calculations is that the electrical behavior of a defect cluster is insensitive to any of the model parameters chosen as long as there are a sufficient number of defects to completely deplete the material in the vicinity of the defect plane. Our results show that the observed short minority carrier lifetimes, long-term majority carrier trapping effects and mobility temperature dependences can all be explained by the same cluster defect model and cannot be explained by uniformly distributed point defects. Our calculations also imply that minority carrier lifetime in these films should be strongly injection level dependent. Thus, lifetime measured by the MOS transient capacitance technique will not be the lifetime needed to evaluate the material for bipolar device applications.     

Role of point defects on B diffusion in Ge

The key role of Ge in microelectronics is well established. Despite this, the behavior of dopants in Ge is not definitively clear. This paper aims at reviewing our experimental studies on B diffusion in Ge. In particular, B diffusion was investigated both in equilibrium and non-equilibrium conditions (i.e. during and after passing proton irradiation or during the dissolution of end of range defects produced by amorphization) in order to shed light on its microscopic mechanism as well as on the activation energies involved. The obtained results demonstrate that B diffusion in Ge is interstitials driven and that the found diffusion mechanism in Ge is still the same in equilibrium and non-equilibrium condition. Indeed, the mechanism that makes the B mobile species to return substitutional has an exponential behavior in which the diffusion length of the mobile species increases by decreasing the temperature, with an activation energy of −0.64 eV. On the basis of these results, B diffusion can be exploited to indirectly monitor the interstitial concentration in Ge. This is very important when a point defect engineering wants to be achieved. For instance, we demonstrates that O implantation and subsequent annealing leads to the formation of GeO₂ nanoclusters, that induces a high injection of interstitials, as monitored by the diffusion of B layers, with clear potentiality to control the diffusion of dopants that diffuse through a vacancy mediated mechanism.     

The influence of defects on device performance of MBE-grown Si homojunction and strained Si1-xGex/Si heterostructures

Different Si homojunction and strained Si_1-xGe_x/Si heterojunction diodes and bipolar transistors have been fabricated by Si-MBE. The effect of annealing on Si homojunction diodes and transistors are studied. It is found that annealing generally improves the Si device performance, such as the ideality factor and breakdown characteristics. The influence of⁶⁰Co γ irradiation on the Si_1-xGe_x/Si diode performances are investigated by studying the temperature dependence of their electrical characteristics, and the results are correlated with the quality of the MBE-films. γ irradiation causes a drop in material conductivity due to the generation of atom-displacement defects in the whole volume of the wafers and increases the defect density at hetero-interfaces. The forward I-V curves of Si_1-xGe_x/Si devices may shift towards lower or higher voltages, depending on the film quality and the irradiation dose. The increase of defect density in strained Si_1-xGe_x/Si films appears to occur easier for the films with lower quality. Electrical measurements and calculations show that the defect-associated tunneling process is important in current transport for these MBE grown Si homojunction and strained Si_1-xGe_x/Si heterojunction devices, which have initially medium film quality or have been treated by irradiation.