Defects In Epitaxial Layers Research Articles

The Influence of Extended Defects in 4H-SiC Epitaxial Layers on Gate Oxide Performance and Reliability

For the ongoing commercialization of power devices based on 4H-SiC, increasing the yield and improving the reliability of these devices is becoming more and more important. In this investigation, gate oxide on 4H-SiC was examined by time-zero dielectric breakdown (TZDB) and constant current stress (CCS) time-dependent dielectric breakdown (TDDB) method in order to get insights into the influence of the epitaxial defects on the gate oxide performance and reliability. For that purpose, MOS capacitors with different gate oxides have been fabricated. Crystal defects in the epitaxial layers have been detected and mapped by ultraviolet photoluminescence (UVPL) and interference contrast (DIC) imaging. The results of the comparison of electrical data and surface mapping data indicate a negative influence on the leakage current behavior for some extended epitaxial defects. Results from TDDB measurement indicated numerous extrinsic defects, which can be traced back to gate oxide processing conditions and defect densities.

Correlation between Thermal Oxide Breakdown and Defects in n-Type 4<i>H</i>-SiC Epitaxial Wafers

In this work, the correlation between thermal oxide breakdown and dislocations in n-type 4H-SiC epitaxial wafers has been investigated. Thermal oxide was grown by oxidation in N2O at 1250°C followed by annealing in NO atmosphere. The electron beam induced current (EBIC) technique was employed to find correlations between the electrically active defects in epitaxial layers and regions where the oxide breakdowns occurred. The test measurements of leakage currents in MOS devices were performed in order to correlate the leakage currents with number of defects in the epi-layer detected by EBIC technique.

The relation between green-band luminescence of 4H-SiC homoepitaxial layer and defects

The Green-band luminescence (GL) from an Al-doped 4H-SiC Homoepitaxial layer prepared by using chemical vapur deposition (CVD) has been observed and studied. The deep pattern obtained by SEM and the buffer layer can be found in the interface between SiC substrate and epilayer. The deep profiles of Si atom in 4H-SiC epilayers obtained by using the secondary ion mass spectrometry (SIMS) and the X-ray photoelectron spectroscopy (XPS) show the relative distribution of Si and C. The results strongly suggest that the vacancy of C and the extended defects (point defects, threading dislocations, et al) from buffer layer are responsible for the GL emission. The full width at half maximum (FWHW) of GL indicates the distributions of VC and its complex defects. The quality of crystals and the distribution of defects in epitaxial layers can be characterized by the intensity and the wavelength of GL obtained from samples at room temperature.

Effect of the sign of misfit strain on the formation of a dislocation structure in SiGe epitaxial layers grown on Si and Ge substrates

Comparative analysis of the specific features of the formation of a dislocation structure in the single-layer epitaxial heterostructures Si1−x Gex/Si and Ge1−y Siy/Ge is performed. It is ascertained that, at a relatively low lattice mismatch between an epitaxial layer and a substrate, the sign of misfit strain at the interface significantly affects the processes of defect formation. The most probable reasons for the observed phenomena are analyzed with allowance for the specific features of the state of the ensemble of intrinsic point defects in epitaxial layers subjected to elastic strains of a different sign.

Crystal Defects in Epitaxial Layer on Nitrogen-doped Czochralski-grown Silicon Substrate (I) –Investigation of the Crystallographic Structure–

We have investigated crystal defects in the epitaxial layer on nitrogen-doped Czochralski-grown silicon (CZ-Si) substrate. It was found that two types of crystal defects are generated in the epitaxial layer on the nitrogen-doped CZ-Si substrate. One is revealed to be a stacking fault and the other is a perfect dislocation pair. The origin of these defects is a rod like void and a dislocation loop in the nitrogen-doped CZ-Si substrate. We discuss the formation mechanism of the crystal defect in the epitaxial layer caused by the grown-in defect.

Crystal Defects in Epitaxial Layer on Nitrogen-doped Czochralski-grown Silicon Substrate (II) –Suppression of the Crystal Defects in Epitaxial Layer by the Control of Crystal Growth Condition and Carbon Co-doping–

Two types of crystal defects, stacking fault induced by a nitrogen-doped substrate (N-SF) and elliptical pit (E-pit), are generated in the epitaxial layer due to grown-in defects in a nitrogen-doped Czochralski-grown silicon (CZ-Si) substrate. We investigate the dependence of N-SF and E-pit formation on the quality of nitrogen-doped substrates. It was revealed that the control of both nitrogen concentration and crystal growth parameter of the CZ-Si ingot is effective for suppressing N-SF and E-pit formation. We also examined crystal defect in the epitaxial layer on a nitrogen and carbon co-doped substrate, which is the other candidate for realizing the epitaxial wafer having a high intrinsic gettering ability. It was clarified that carbon co-doping in addition to nitrogen doping suppresses N-SF and E-pit generation.

Investigation of Crystal Defects in Epitaxial Layers on Nitrogen-Doped Substrates and a Method for their Suppression

Investigation of Crystal Defects in Epitaxial Layers on Nitrogen-Doped Substrates and a Method for their Suppression

Proceedings of the 6th International Workshop on Expert Evaluation and Control of Compound Semiconductor Materials and Technology (EXMATEC'02)

The scientific scope of EXMATEC encompasses a broad range of compound semiconductor device-related issues as well as materials related problems, in both cases emphasizing fabrication, processing and characterization. The conference presentations were grouped into eight sections: – Growth: Process monitoring, improving of individual steps – Gallium nitride and related compounds: materials and devices – Characterization, identification and reduction of defects in epitaxial layers – High frequency and high power devices: material related issues – Optoelectronic materials and devices, reliability issues – Quantum dots, nanostructures, low-dimensional systems – Characterization techniques – New frontiers: materials, technologies, structures, devices

Ion-Assisted Deposition of Silicon Epitaxial Films with High Deposition Rate Using Low Energy Silicon Ions

ABSTRACTIon-assisted deposition (IAD) enables low temperature (≥ 435°C), high-rate (≤ 0.5 μm/min) epitaxial growth of silicon films. Therefore, IAD is an interesting deposition technique for microelectronic devices and thin film solar cells. The Hall-mobility of monocrystalline epitaxial layers increases with deposition temperature Tdep and reaches values comparable to those of bulk Si at Tdep ≥ 540°C. Polycrystalline epitaxial layers exhibit inhomogeneous electrical properties, as shown by Light Beam Induced Current measurements. Recombination within the grains dominates over recombination at grain boundaries. Secco etching identifies an inhomogeneous density of extended structural defects in the polycrystalline epitaxial layers and in the substrate. A major part of the extended defects in the epitaxial layers originates from defects in the substrate.

Defects in semiconductors and their effects on devices

The classification of defects in semiconductors and their electronic properties are discussed. The sources of dislocations in bulk crystals and defects in epitaxial layers have been identified. Some of the approaches used to lower the density of dislocations in crystals and layers are presented. Effects of defects on devices are also considered.

Critical thickness and relaxation of (111) oriented strained epitaxial layers

Growth on the <111> orientation brings with it new possibilities for nucleation and multiplication mechanisms for misfit relieving defects in epitaxial layers. Yet, despite these changes, the macroscopic relaxation behaviour of good quality In x Ga 1− x As layers on <111> GaAs is remarkably similar to the relaxation behaviour of 〈001〉 oriented layers. Using high resolution X-ray diffraction, we present the full analysis of <111> oriented strained In x Ga 1− x As layers showing the optimum data handling to derive strain and misfit. Data from partially relaxed layers are presented and compared with theoretical equilibrium critical thickness for the <111> orientation. We find that there is excellent agreement between the experimental data and the theory.

Development of non-destructive bulk micro-defect analyzer for Si wafers

A non-destructive and non-contact observation method was developed to detect defects in Si crystals. By this method, cross-sectional images of the defects in a crystal are obtained. There are functions for both horizontal and vertical cross sections. It is found that this method is effective for revealing near-surface defects, precipitates within the denuded zone of intrinsic gettering-treated wafers, twins or slip plane defects in epitaxial layers, and defects on the layer boundaries in SOI (SIMOX, etc.) wafers. The observed results were compared with results detected by conventional laser scattering tomography and in some cases inconsistencies were noticed.

The consequences of dislocations and thermal degradation on the quality of InGaAsP/InP epitaxial layers

Thermal degradation is identified as the origin for a variety of defects in epitaxial layers. The consequences of these defects are more critical than those of dislocations. It turns out that thermal degradation affects the layer quality more than dislocations.

Material Characterization of Low-Temperature Silicon Epitaxial Growth on Patterned Oxidized Wafers by ULPCVD From SiH4/SiF4/H2

ABSTRACTLow temperature silicon selective epitaxial growth on patterned oxidized wafers is becoming crucial to ultra large scale integration (ULSI) technologies. Low temperature processes can reduce dopant redistribution via solid state diffusion so that a sharp transition region can be obtained. This paper presents material characterization of epitaxial films grown on patterned oxidized wafers by ultralow pressure chemical vapor deposition (ULPCVD) from SiH4/SiF4/H2 (≤ 10 mTorr), in which SiF4 was used to explore its capability for selective epitaxial growth. The deposition temperature is 800°C. The effects of the SiF4 addition to SiH4/H2 are discussed. Defects in epitaxial layers resulting from a high composition of the SiF4 during deposition were characterized. Results of in–situ surface cleaning using a SiF4/H2 plasma are also presented.

Nature and parameters of radiation defects in epitaxial layers of silicon

Abstract The peculiarities of the radiation defects accumulation processes during irradiation by60Co γ-quanta and rearrangement of these defects at further isochronal annealing are studied for n-type silicon epitaxial layers of 1.2 and 5 μm thickness and ρ = lΩ.cm. The experimental results are based an analysis of the Hall coefficient temperature dependencies obtained at various stages of irradiation or annealing. It is established that, as compared to bulk crystals, the epitaxial silicon layers demonstrate a number of salient features during radiation defect formation and annealing. Among them are the lower rate of vacancy defects introduction, lower annealing temperature for certain defects etc. It is demonstrated that these features are caused by interaction of irradiation-generated mobile-at-annealing defects with the surface and atoms of impurities. The vacancies generated by γ-quanta efficiently migrate to the surface. This process decreases the rate of vacancy defects formation in thin layers. The ...

InP and InGaAsP Semiconducting Materials for Optical Communications

A brief overview is presented of materials aspects of InP and InGaAsP compound semiconductors that are being used in state-of-the-art lightwave communication systems. It is feasible to grow high-quality InP single crystals from which suitable substrates can be cut for device growth. Lattice-matched InGaAsP layers of different compositions can be grown on these substrates by liquid phase epitaxy. Dislocations in the underlying substrates constitute a major source of defects in epitaxial layers. Also, macroscopic defects in epi layers can be caused by melt carryover during the layer formation process. Finally, another problem, dark spot defects, can result from electromigration of gold.

Microstructural defects in laser recrystallized, graphite strip heater recrystallized and buried oxide silicon-on-insulator systems: A status report

Laser recrystallized silicon-on-oxide, graphite strip heater recrystallized silicon-on-oxide and buried oxide by high dose oxygen ion implantation are three of the silicon-on-insulator technologies that are currently being evaluated for VLSI and VHSIC applications. This status report compares the microstructure of these materials. The main defects in both the laser and graphite strip heater recrystallized material are subgrain boundaries. The misorientations across the boundaries are normally less than one degree. The boundaries are formed by dislocation coalescence. The dislocations are generated by the stresses caused by the volume expansion during solidification of silicon droplets trapped in the solid silicon matrix. The droplets are caused by constitutional supercooling. Buried oxide SOI formed by high dose oxygen ion implantation has fewer crystallographic defects than the other two materials. The entire ion implanted area is a single crystal after high temperature annealing. The primary defects in epitaxial layers grown on implanted substrates are dislocations. The oxide/silicon interfaces are abrupt if the dose is large enough. The sharp interfaces are formed by an internal oxidation mechanism. The minimum MeV He ion channeling yield from epitaxial silicon layers grown on buried oxide is about 2.5%, the lowest of any SOI material.

Electrical characteristics of GaAs LPE schottky diodes

AbstractStructural and electrical properties of IMPATT diodes prepared from homoepitaxial GaAs films grown by liquid phase epitaxy have been investigated with the help of metallography and reverse I–V characteristic derivatives. The structural defects in epitaxial layers have been shown lead to the localization of current in separate regions (microplasmas) which brings up a soft breakdown. A method as been proposed for the observation of microplasmas at large currents.

Defects in epitaxial layers of silicon-germanium grown on silicon substrates

Crystal defects of various kinds found in epitaxially grown Si/Ge alloy layers on Si substrate, may be either inherent to the material and originating from atomic radii misfit, or can be traced to the growth process and controlled or eliminated by varying its parameters. A network of slip lines, becoming more pronounced with increased Ge content, indicates plastic deformation resulting from partial relief of stresses during the high temperature growth process. Electron microprobe and X-ray diffraction analysis indicate some Ge segregation in the fault vicinity, and a slight anisotropy in the lattice constant expansion due to the Ge.

Crystallographic defects in epitaxial layers of cadmium sulphide

Thin epitaxial films of CdS deposited in high vacuum on ionic single crystal substrates have been studied by transmission electron microscopy. The (100), (110) and (111) faces of NaCl and the (111) face of BaF 2 were used as substrate surfaces. Both cubic sphalerite and hexagonal wurtzite structure films have been produced. The orientations of the sphalerite structure films were (100) and (110) and were produced on substrate faces having the same two orientations. The wurtzite structure films were in (0001) orientation and grew on (111) oriented substrate faces. For a fixed rate of deposition both the number and type of defects found in the films appear to be dependent upon the growth temperature and the crystal structure. Annealing the films at a high temperature has been tested as a means for reducing their defect content and the effect is very different for the two crystal structures. A reduction in the defect content of the wurtzite structure films is induced but no change in the crystal structure occurs. In contrast to this, the sphalerite structure films undergo a progressive phase transformation to the wurtzite stucture while at the same time losing a high proportion of their defects.